Federal state budget educational institution higher education
"Volzhsky state university water transport"
PERM BRANCH
E.A . Sazonova
MATERIALS SCIENCE
COLLECTION OF PRACTICAL AND LABORATORY WORKS
26.02.06 “Operation of ship electrical equipment and automation equipment”
23.02.01 “Organization of transportation and management in transport” (by type)
PERMIAN
2016
Introduction
Methodical recommendations to perform laboratory and practical work in the academic discipline “Materials Science” are intended for students of secondary vocational education in the specialty 26.02.06 “Operation of ship electrical equipment and automation equipment”
This methodological manual provides instructions for performing practical and laboratory work on the topics of the discipline, indicates the topics and content of laboratory and practical work, forms of control for each topic and recommended literature.
As a result of mastering this academic discipline, the student should be able to:
˗ perform mechanical tests of material samples;
˗ use physical and chemical methods for studying metals;
˗ use reference tables to determine the properties of materials;
˗ choose materials for professional activities.
As a result of mastering this academic discipline, the student should know:
˗ basic properties and classification of materials used in professional activities;
˗ name, marking, properties of the material being processed;
˗ rules for the use of lubricants and cooling materials;
˗ basic information about metals and alloys;
˗ basic information about non-metallic, gasket,
Sealing and electrical materials, steel, their classification.
Laboratory and practical work will allow you to develop practical work skills and professional competencies. They are included in the structure of studying the academic discipline “Materials Science”, after studying the topic: 1.1. “Basic information about metals and alloys”, 1.2 “Iron-carbon alloys”, 1.3 “Non-ferrous metals and alloys”.
Laboratory and practical work constitute an element of the academic discipline and are assessed according to the criteria presented below:
A grade of “5” is given to a student if:
˗ the topic of the work corresponds to the given one, the student demonstrates systematic and complete knowledge and skills on this issue;
˗ the work is designed in accordance with the teacher’s recommendations;
˗ the amount of work corresponds to the specified one;
˗ the work was completed exactly within the time frame specified by the teacher.
A grade of “4” is given to a student if:
˗ the topic of the work corresponds to the given one, the student makes minor inaccuracies or some mistakes in this matter;
˗ the work is designed with inaccuracies in design;
˗ the amount of work corresponds to the specified or slightly less;
˗ the work was submitted on time specified by the teacher, or later, but no more than 1-2 days.
A grade of “3” is given to a student if:
˗ the topic of the work corresponds to the given one, but the work lacks significant elements in the content of the work or the topic is presented illogically, the main content of the issue is not clearly presented;
˗ the work was prepared with errors in design;
˗ the amount of work is significantly less than specified;
˗ the work was submitted 5-6 days late.
A grade of “2” is given to a student if:
˗ the main topic of the work is not disclosed;
˗ the work is not designed in accordance with the requirements of the teacher;
˗ the amount of work does not correspond to what was specified;
˗ the work was submitted more than 7 days late.
Laboratory and practical work have a certain structure in their content, we suggest you consider it: the progress of work is given at the beginning of each practical and laboratory work; when performing practical work, students complete the task indicated at the end of the work (item “Task for students”); When performing laboratory work, a report on its implementation is drawn up, the contents of the report are indicated at the end of the laboratory work (item “Contents of the report”).
When performing laboratory and practical work, students follow certain rules, consider them below: laboratory and practical work are performed during classes; final registration of laboratory and practical work at home is allowed; the use of additional literature is permitted when performing laboratory and practical work; Before performing laboratory and practical work, it is necessary to study the basic theoretical principles on the issue under consideration.
Practical work No. 1
“Physical properties of metals and methods for their study”
Purpose of the work : study the physical properties of metals, methods for their determination.
Work progress:
Theoretical part
Physical properties include: density, melting point (melting point), thermal conductivity, thermal expansion.
Density is the amount of substance contained in a unit volume. This is one of the most important characteristics metals and alloys. Based on their density, metals are divided into the following groups:lungs (density no more than 5 g/cm 3 ) - magnesium, aluminum, titanium, etc.;heavy - (density from 5 to 10 g/cm 3 ) - iron, nickel, copper, zinc, tin, etc. (this is the most extensive group);very heavy (density more than 10 g/cm 3 ) - molybdenum, tungsten, gold, lead, etc. Table 1 shows the density values of metals.
Table 1
Density of metals
Melting point is the temperature at which a metal changes from a crystalline (solid) state to a liquid state with the absorption of heat.
The melting points of metals range from −39 °C (mercury) to 3410 °C (tungsten). Most metals (except alkalis) have a high melting point, but some "normal" metals, such as tin and lead, can be melted on a regular electric or gas stove.
Depending on the melting point, the metal is divided into the following groups:fusible (melting point does not exceed 600 o C) - zinc, tin, lead, bismuth, etc.;medium-melting (from 600 o From to 1600 o C) - these include almost half of the metals, including magnesium, aluminum, iron, nickel, copper, gold;refractory (more than 1600 o C) - tungsten, molybdenum, titanium, chromium, etc. When additives are introduced into the metal, the melting point, as a rule, decreases.
Table 2
Melting and boiling points of metals
Thermal conductivity is the ability of a metal to conduct heat at one rate or another when heated.
Electrical conductivity is the ability of a metal to conduct electric current.
Thermal expansion is the ability of a metal to increase its volume when heated.
The smooth surface of metals reflects a large percentage of light, a phenomenon called metallic luster. However, when in powder form, most metals lose their luster; aluminum and magnesium, however, retain their shine even in powder. Aluminum, silver and palladium reflect light most well - mirrors are made from these metals. Rhodium is sometimes used to make mirrors, despite its extremely high price: due to its much greater hardness and chemical resistance than silver or even palladium, the rhodium layer can be much thinner than the silver one.
Research methods in materials science
The main research methods in metallurgy and materials science are: fracture, macrostructure, microstructure, electron microscopy, x-ray research methods. Consider their features in more detail.
1. Fracture is the simplest and most accessible way to assess the internal structure of metals. The fracture assessment method, despite its apparent roughness in assessing the quality of the material, is used quite widely in various industries production and scientific research. Fracture assessment can in many cases characterize the quality of the material.
The fracture can be crystalline or amorphous. Amorphous fracture is characteristic of materials that do not have a crystalline structure, such as glass, rosin, and glassy slag.
Metal alloys, including steel, cast iron, aluminum, magnesium alloys, zinc and its alloys produce granular, crystalline fracture.
Each face of a crystalline fracture is a plane of cleavage of an individual grain. Therefore, the fracture shows us the grain size of the metal. Studying the fracture of steel, one can see that the grain size can vary within very wide limits: from a few centimeters in cast, slowly cooled steel to thousandths of a millimeter in properly forged and hardened steel. Depending on the grain size, the fracture can be coarse-crystalline or fine-crystalline. Typically, a fine-crystalline fracture corresponds to a higher quality metal alloy.
If the destruction of the sample under study occurs with previous plastic deformation, the grains in the fracture plane are deformed, and the fracture no longer reflects the internal crystalline structure of the metal; in this case the fracture is called fibrous. Often in one sample, depending on the level of its ductility, there may be fibrous and crystalline areas in the fracture. Often, the quality of the metal is assessed by the ratio of the fracture area occupied by the crystalline areas under given test conditions.
A brittle crystalline fracture can occur when fracture occurs along grain boundaries or along slip planes intersecting grains. In the first case, the fracture is called intergranular, in the second, transgranular. Sometimes, especially with very fine grains, it is difficult to determine the nature of the fracture. In this case, the fracture is examined using a magnifying glass or binocular microscope.
Recently, the branch of metallurgy has been developing in the fractographic study of fractures on metallographic and electron microscopes. At the same time, new advantages are found in the old method of research in metallurgy - fracture research, applying the concepts of fractal dimensions to such research.
2. Macrostructure is the next method for studying metals. Macrostructural research consists of studying the cross-sectional plane of a product or sample in longitudinal, transverse or any other directions after etching, without the use of magnifying devices or using a magnifying glass. The advantage of macrostructural research is the fact that using this method it is possible to study the structure of an entire casting or ingot, forging, stamping, etc. directly. Using this research method, you can detect internal metal defects: bubbles, voids, cracks, slag inclusions, study the crystal structure of the casting, study the heterogeneity of the crystallization of the ingot and its chemical heterogeneity (liquation).
Using sulfur prints of macrosections on photographic paper according to Bauman, the uneven distribution of sulfur over the cross section of the ingots is determined. This research method is of great importance when examining forged or stamped workpieces to determine the correct direction of the fibers in the metal.
3. Microstructure - one of the main methods in metal science is the study of the microstructure of metal using metallographic and electron microscopes.
This method allows you to study the microstructure of metal objects with high magnifications: from 50 to 2000 times on an optical metallographic microscope and from 2 to 200 thousand times on an electron microscope. The microstructure is studied on polished sections. Using unetched sections, the presence of non-metallic inclusions, such as oxides, sulfides, small slag inclusions and other inclusions that differ sharply from the nature of the base metal, is studied.
The microstructure of metals and alloys is studied using etched sections. Etching is usually done with weak acids, alkalis or other solutions, depending on the nature of the metal of the section. The effect of etching is that it dissolves different structural components in different ways, coloring them in different tones or colors. Grain boundaries that differ from the base solution have an etchability that is usually different from the base and stands out on the thin section in the form of dark or light lines.
The polyhedra of grains visible under a microscope are cross-sections of grains by the surface of a polished section. Since this section is random and can pass at different distances from the center of each individual grain, the difference in the sizes of the polyhedra does not correspond to the actual differences in the grain sizes. The closest value to the actual grain size is the largest grains.
When etching a sample consisting of homogeneous crystalline grains, for example, pure metal, a homogeneous solid solution, etc., the surfaces of different grains are often etched differently.
This phenomenon is explained by the fact that grains with different crystallographic orientation appear on the surface of the polished section, as a result of which the degree of acid action on these grains is different. Some grains look shiny, others are heavily etched and darken. This darkening is due to the formation of different etching patterns that reflect light rays differently. In the case of alloys, individual structural components form a microrelief on the surface of the polished section, which has areas with different inclinations of individual surfaces.
Normally located areas reflect the greatest amount of light and are the lightest. Other areas are darker. Often the contrast in the image of the grain structure is associated not with the structure of the surface of the grains, but with the relief at the grain boundaries. In addition, different shades of structural components may be the result of the formation of films formed during the interaction of the etchant with the structural components.
With the help of metallographic research, it is possible to carry out a qualitative identification of the structural components of alloys and a quantitative study of the microstructures of metals and alloys, firstly, by comparison with known studied microcomponents of structures and, secondly, by special methods of quantitative metallography.
The grain size is determined. The method of visual assessment, which consists in the fact that the microstructure in question is approximately assessed by points of standard scales according to GOST 5639-68, GOST 5640-68. According to the corresponding tables, for each point the area of one grain and the number of grains per 1 mm are determined 2 and 1 mm 3 .
The method of calculating the number of grains per unit surface of a polished section using the appropriate formulas. If S is the area on which the number of grains n is counted, and M is the microscope magnification, then the average grain size in the section of the polished surface
Determination of phase composition. The phase composition of an alloy is often assessed by eye or by comparing the structure with standard scales.
An approximate method for quantitatively determining the phase composition can be carried out using the secant method by calculating the length of segments occupied by different structural components. The ratio of these segments corresponds to the volumetric content of the individual components.
Point method A.A. Glagoleva. This method is carried out by estimating the number of points (intersection points of the microscope eyepiece grid) falling on the surfaces of each structural component. In addition, the method of quantitative metallography produces: determination of the size of the interface between phases and grains; determination of the number of particles in a volume; determination of grain orientation in polycrystalline samples.
4. Electron microscopy. The electron microscope has recently found great importance in metallographic research. Undoubtedly, he has a great future. If the resolution of an optical microscope reaches 0.00015 mm = 1500 A, then the resolution of electron microscopes reaches 5-10 A, i.e. several hundred times more than optical.
An electron microscope is used to study thin films (replicas) taken from the surface of a polished section or to directly study thin metal films obtained by thinning a massive sample.
The greatest need for the use of electron microscopy is to study processes associated with the release of excess phases, for example, the decomposition of supersaturated solid solutions during thermal or strain aging.
5. X-ray research methods. One of the most important methods in establishing the crystallographic structure of various metals and alloys is X-ray diffraction analysis. This research method makes it possible to determine the nature of the relative arrangement of atoms in crystalline bodies, i.e. solve a problem that is inaccessible to either a conventional or an electron microscope.
The basis of X-ray diffraction analysis is the interaction between X-rays and the atoms of the body under study lying in their path, thanks to which the latter become, as it were, new sources of X-rays, being the centers of their scattering.
The scattering of rays by atoms can be likened to the reflection of these rays from the atomic planes of a crystal according to the laws of geometric optics.
X-rays are reflected not only from planes lying on the surface, but also from deep ones. Reflecting from several equally oriented planes, the reflected beam is intensified. Each plane of the crystal lattice produces its own beam of reflected waves. Having received a certain alternation of reflected X-ray beams at certain angles, the interplanar distance, crystallographic indices of the reflecting planes, and ultimately the shape and dimensions of the crystal lattice are calculated.
Practical part
Contents of the report.
1. The report must indicate the title and purpose of the work.
2. List the basic physical properties of metals (with definitions).
3. Record tables 1-2 in your notebook. Draw conclusions from the tables.
4. Fill out the table: “Basic research methods in materials science.”
X-rayresearch methods
Practical work No. 2
Topic: "Studying state diagrams"
Purpose of the work: familiarizing students with the main types of state diagrams, their main lines, points, and their meaning.
Work progress:
1.Study the theoretical part.
Theoretical part
The state diagram represents graphic image state of any alloy of the system under study depending on concentration and temperature (see Fig. 1)
Fig.1 State diagram
State diagrams show stable states, i.e. states that, under given conditions, have a minimum free energy, and therefore it is also called an equilibrium diagram, since it shows which equilibrium phases exist under given conditions.
The construction of phase diagrams is most often carried out using thermal analysis. As a result, a series of cooling curves is obtained, in which inflection points and temperature stops are observed at phase transformation temperatures.
Temperatures corresponding to phase transformations are called critical points. Some critical points have names, for example, the points corresponding to the beginning of crystallization are called liquidus points, and the end of crystallization are called solidus points.
Based on the cooling curves, a composition diagram is constructed in coordinates: along the abscissa axis - the concentration of components, and along the ordinate axis - temperature. The concentration scale shows the content of component B. The main lines are the liquidus (1) and solidus lines (2), as well as the lines corresponding to phase transformations in the solid state (3, 4).
From the phase diagram, one can determine the temperatures of phase transformations, changes in phase composition, approximately, the properties of the alloy, and the types of processing that can be used for the alloy.
Below are the different types of state diagrams:
Fig.2. Phase diagram of alloys with unlimited solubility
components in the solid state (a); typical cooling curves
alloys (b)
Analysis of the resulting diagram (Fig. 2).
1. Number of components: K = 2 (components A and B).
2. Number of phases: f = 2 (liquid phase L, solid solution crystals)
3. Main lines of the diagram:
acb – liquidus line, above this line the alloys are in a liquid state;
adb is the solidus line; below this line the alloys are in the solid state.
Fig.3. State diagram of alloys with no solubility of components in the solid state (a) and cooling curves of alloys (b)
State diagram analysis (Fig. 3).
1. Number of components: K = 2(components A and B);
2. Number of phases: f = 3(crystals of component A, crystals of component B, liquid phase).
3. Main lines of the diagram:
the solidus line ecf, parallel to the concentration axis, tends to the axes of the components, but does not reach them;
Rice. 4. State diagram of alloys with limited solubility of components in the solid state (a) and cooling curves of typical alloys (b)
Analysis of the state diagram (Fig. 4).
1. Number of components: K = 2 (components A and B);
2. Number of phases: f = 3 (liquid phase and crystals of solid solutions (solution of component B in component A) and (solution of component A in component B));
3. Main lines of the diagram:
the liquidus line acb consists of two branches converging at one point;
solidus line adcfb, consists of three sections;
dm – line of the maximum concentration of component B in component A;
fn is the line of the maximum concentration of component A in component B.
Practical part
Assignment for students:
1. Write down the title of the job and its purpose.
2. Write down what a state diagram is.
Answer the questions:
1. How is a state diagram constructed?
2. What can be determined from a state diagram?
3. What are the names of the main points of the diagram?
4. What is indicated on the diagram along the x-axis? Y-axis?
5. What are the main lines of the diagram called?
Assignment by options:
Students answer the same questions, but the pictures they need to answer are different. Option 1 gives answers according to Figure 2, option 2 gives answers according to Figure 3, option 3 gives answers according to Figure 4. The figure must be recorded in a notebook.
1. What is the name of the diagram?
2. Name how many components are involved in the formation of the alloy?
3. What letters indicate the main lines of the diagram?
Practical work No. 3
Topic: “Study of cast irons”
Purpose of the work: familiarizing students with the markings and scope of application of cast iron; developing the ability to decipher cast iron grades.
Work progress:
Theoretical part
Cast iron differs from steel: in composition - a higher content of carbon and impurities; in terms of technological properties - higher casting properties, low ability to plastic deformation, almost not used in welded structures.
Depending on the state of carbon in cast iron, they are distinguished: white cast iron - carbon in a bound state in the form of cementite, in a fracture it has white and metallic luster; gray cast iron - all or most of the carbon is in a free state in the form of graphite, and no more than 0.8% of carbon is in a bound state. Due to the large amount of graphite, its fracture has gray; half - part of the carbon is in a free state in the form of graphite, but at least 2% of the carbon is in the form of cementite. Little used in technology.
Depending on the form of graphite and the conditions of its formation, the following groups of cast iron are distinguished: gray - with lamellar graphite; high-strength - with spherical graphite; malleable - with flake graphite.
Graphite inclusions can be considered as a corresponding form of void in the structure of cast iron. Near such defects, during loading, stresses are concentrated, the greater the value of which, the sharper the defect. It follows that plate-shaped graphite inclusions soften the metal to the maximum extent. The flake-like form is more favorable, and the spherical form of graphite is optimal. Plasticity depends on shape in the same way. The presence of graphite most dramatically reduces resistance under severe loading methods: impact; gap The compression resistance decreases little.
Gray cast iron
Gray cast iron is widely used in mechanical engineering, as it is easy to process and has good properties. Depending on the strength, gray cast iron is divided into 10 grades (GOST 1412).
Gray cast irons, with low tensile strength, have fairly high compressive strength. The structure of the metal base depends on the amount of carbon and silicon.
Given the low resistance of gray cast iron castings to tensile and impact loads, this material should be used for parts that are subject to compressive or bending loads. In the machine tool industry these are basic, body parts, brackets, gears, guides; in the automotive industry - cylinder blocks, piston rings, camshafts, clutch discs. Gray cast iron castings are also used in electrical engineering and for the manufacture of consumer goods.
Marking of gray cast iron: indicated by the index SCh (gray cast iron) and a number that shows the value of the tensile strength multiplied by 10 -1 .
For example: SCh 10 – gray cast iron, tensile strength 100 MPa.
Malleable iron
Good properties of castings are ensured if graphitization does not occur during the process of crystallization and cooling of the castings in the mold. To prevent graphitization, cast irons must have a reduced carbon and silicon content.
There are 7 grades of malleable cast iron: three with a ferritic (CN 30 - 6) and four with a pearlitic (CN 65 - 3) base (GOST 1215).
In terms of mechanical and technological properties, malleable cast iron occupies an intermediate position between gray cast iron and steel. The disadvantage of malleable cast iron compared to high-strength cast iron is the limited wall thickness for casting and the need for annealing.
Ductile iron castings are used for parts operating under shock and vibration loads.
Gearbox housings, hubs, hooks, brackets, clamps, couplings, and flanges are made from ferritic cast iron.
Pearlitic cast iron, characterized by high strength and sufficient ductility, is used to make driveshaft forks, links and rollers of conveyor chains, and brake pads.
Marking of malleable cast iron: indicated by the index KCH (malleable cast iron) and numbers. The first number corresponds to the tensile strength multiplied by 10 -1 , the second number is the relative elongation.
For example: KCh 30-6 – malleable cast iron, tensile strength 300 MPa, relative elongation 6%.
Ductile iron
These cast irons are obtained from gray cast irons as a result of modification with magnesium or cerium. Compared to gray cast irons, the mechanical properties are increased, this is caused by the lack of unevenness in stress distribution due to the spherical shape of graphite.
These cast irons have high fluidity, linear shrinkage is about 1%. Casting stresses in castings are slightly higher than for gray cast iron. Due to the high modulus of elasticity, the machinability is quite high. They have satisfactory weldability.
High-strength cast iron is used to make thin-walled castings (piston rings), forging hammers, beds and frames of presses and rolling mills, molds, tool holders, and faceplates.
Casting crankshafts weighing up to 2..3 tons, instead of forged steel shafts, have higher cyclic toughness, are insensitive to external stress concentrators, have better anti-friction properties and are much cheaper.
Marking of ductile cast iron: indicated by the index HF (ductile cast iron) and a number that shows the tensile strength value multiplied by 10 -1 .
For example: HF 50 – high-strength cast iron with a tensile strength of 500 MPa.
Practical part
Assignment for students:
1. Write down the name of the work and its purpose.
2. Describe the production of pig iron.
3.Fill out the table:
3.High strengthcast iron
Practical work No. 4
Topic: “Study of carbon and alloy structural steels”
Purpose of the work:
Work progress:
1.Familiarize yourself with the theoretical part.
2. Complete the tasks of the practical part.
Theoretical part
Steel is an alloy of iron and carbon, which contains carbon in an amount of 0 -2.14%. Steels are the most common materials. They have good technological properties. Products are obtained as a result of pressure and cutting processing.
Quality, depending on the content of harmful impurities: sulfur and phosphorus, steel is divided into steel:
˗ Ordinary quality, content up to 0.06% sulfur and up to 0.07% phosphorus.
˗ High-quality - up to 0.035% of sulfur and phosphorus each separately.
˗ High quality - up to 0.025% sulfur and phosphorus.
˗ Particularly high quality, up to 0.025% phosphorus and up to 0.015% sulfur.
Deoxidation is the process of removing oxygen from steel, i.e., according to the degree of its deoxidation, there are: calm steels, i.e., completely deoxidized; such steels are designated by the letters “sp” at the end of the grade (sometimes the letters are omitted); boiling steels – slightly deoxidized; are marked with the letters "kp"; semi-quiet steels, occupying an intermediate position between the previous two; are designated by the letters "ps".
Ordinary quality steel is also divided into 3 groups based on supplies: group A steel is supplied to consumers based on mechanical properties (such steel may have a high sulfur or phosphorus content); steel group B – by chemical composition; Group B steel – with guaranteed mechanical properties and chemical composition.
Structural steels are intended for the manufacture of structures, machine parts and devices.
Thus, in Russia and in the CIS countries (Ukraine, Kazakhstan, Belarus, etc.), an alphanumeric system for designating steel grades and alloys, developed early in the USSR, has been adopted, where, according to GOST, letters conventionally indicate the names of elements and methods of steel smelting, and numbers indicate the content elements. To date, international standardization organizations have not developed a unified steel marking system.
Marking of structural carbon steels
ordinary quality
˗ Designated according to GOST 380-94 with the letters “St” and a conventional brand number (from 0 to 6) depending on chemical composition and mechanical properties.
˗ The higher the carbon content and strength properties of the steel, the higher its number.
˗ The letter “G” after the brand number indicates a high manganese content in the steel.
˗ The steel group is indicated before the grade, and group “A” is not included in the designation of the steel grade.
˗ To indicate the steel category, the number corresponding to the category is added to the brand designation at the end; the first category is usually not indicated.
For example:
˗ St1kp2 - carbon steel of ordinary quality, boiling, grade No. 1, second category, supplied to consumers based on mechanical properties (group A);
˗ VSt5G - carbon steel of ordinary quality with a high manganese content, calm, grade No. 5, first category with guaranteed mechanical properties and chemical composition (group B);
˗ VSt0 - carbon steel of ordinary quality, grade number 0, group B, first category (steel grades St0 and Bst0 are not separated by degree of deoxidation).
Marking of structural carbon quality steels
˗ In accordance with GOST 1050-88, these steels are marked with two-digit numbers showing the average carbon content in hundredths of a percent: 05; 08 ; 10 ; 25; 40, 45, etc.
˗ For mild steels, letters are not added at the end of their names.
For example, 08kp, 10ps, 15, 18kp, 20, etc.
˗ The letter G in the steel grade indicates a high manganese content.
For example: 14G, 18G, etc.
˗ The most common group for the manufacture of machine parts (shafts, axles, bushings, gears, etc.)
For example:
˗ 10 – structural high-quality carbon steel, with a carbon content of about 0.1%, quiet
˗ 45 – structural high-quality carbon steel, with a carbon content of about 0.45%, quiet
˗ 18 kp – structural high-quality carbon steel with a carbon content of about 0.18%, boiling
˗ 14G – structural high-quality carbon steel with a carbon content of about 0.14%, calm, with a high manganese content.
Marking of alloyed structural steels
˗ In accordance with GOST 4543-71, the names of such steels consist of numbers and letters.
˗ The first digits of the brand indicate the average carbon content in steel in hundredths of a percent.
˗ Letters indicate the main alloying elements included in the steel.
˗ The numbers after each letter indicate the approximate percentage content of the corresponding element, rounded to the nearest whole number; if the content of the alloying element is up to 1.5%, the number after the corresponding letter is not indicated.
˗ The letter A at the end of the brand indicates that the steel is high quality (with low sulfur and phosphorus content)
˗ N – nickel, X – chromium, K – cobalt, M – molybdenum, B – tungsten, T – titanium, D – copper, G – manganese, C – silicon.
For example:
˗ 12Х2Н4А – structural alloy steel, high quality, with a carbon content of about 0.12%, chromium about 2%, nickel about 4%
˗ 40ХН – structural alloy steel, with a carbon content of about 0.4%, chromium and nickel up to 1.5%
Marking of other groups of structural steels
Spring steels.
basic hallmark these steels - the carbon content in them should be about 0.8% (in this case, elastic properties appear in the steels)
˗ Springs and springs are made from carbon (65,70,75,80) and alloy (65S2, 50KhGS, 60S2KhFA, 55KhGR) structural steels
˗ These steels are alloyed with elements that increase the elastic limit - silicon, manganese, chromium, tungsten, vanadium, boron
For example: 60C2 - structural carbon spring-spring steel with a carbon content of about 0.65%, silicon about 2%.
Ball bearing steels
˗ GOST 801-78 is marked with the letters “ШХ”, after which the chromium content is indicated in tenths of a percent.
˗ For steels subjected to electroslag remelting, the letter Ш is also added at the end of their names separated by a dash.
For example: ShKh15, ShKh20SG, ShKh4-Sh.
˗ They are used to make parts for bearings, and they are also used to make parts operating under high loads.
For example: ШХ15 – structural ball bearing steel with a carbon content of 1%, chromium 1.5%
Automatic steels
˗ GOST 1414-75 begin with the letter A (automatic).
˗ If the steel is alloyed with lead, then its name begins with the letters AC.
˗ To reflect the content of other elements in steels, the same rules are used as for alloyed structural steels. For example: A20, A40G, AS14, AS38HGM
For example: AC40 - automatic structural steel, with a carbon content of 0.4%, lead 0.15-0.3% (not indicated in the grade)
Practical part
Assignment for students:
2. Write down the main characteristics of marking all groups of structural steels (ordinary quality, high-quality steels, alloy structural steels, spring steels, ball bearing steels, automatic steels), with examples.
Assignment by options:
Decipher the steel grades and write down the scope of application of a particular grade (i.e., what it is intended for manufacturing)
Practical work No. 5
Topic: “Study of carbon and alloy tool steels”
Purpose of the work: familiarizing students with the markings and scope of application of structural steels; developing the ability to decipher the markings of structural steels.
Work progress:
1.Familiarize yourself with the theoretical part.
2. Complete the practical part.
Theoretical part
Steel is an alloy of iron and carbon, which contains 0-2.14% carbon.
Steels are the most common materials. They have good technological properties. Products are obtained as a result of pressure and cutting processing.
The advantage is the ability to obtain the desired set of properties by changing the composition and type of processing.
Depending on their purpose, steels are divided into 3 groups: structural, tool and special-purpose steels.
Quality, depending on the content of harmful impurities: sulfur and phosphorus, steel is divided into: steel of ordinary quality, content up to 0.06% sulfur and up to 0.07% phosphorus; high-quality - up to 0.035% of sulfur and phosphorus each separately; high quality - up to 0.025% sulfur and phosphorus; especially high quality, up to 0.025% phosphorus and up to 0.015% sulfur.
Tool steels are intended for the manufacture of various tools, both for manual and mechanical processing.
The presence of a wide range of steels and alloys produced in different countries has necessitated their identification, but to date there is no unified system for marking steels and alloys, which creates certain difficulties for the metal trade.
Marking of carbon tool steels
˗ These steels, in accordance with GOST 1435-90, are divided into high-quality and high-quality.
˗ High-quality steels are designated by the letter U (carbon) and a number indicating the average carbon content in the steel, in tenths of a percent.
For example: U7, U8, U9, U10. U7 – carbon tool steel with a carbon content of about 0.7%
˗ The letter A is added to the designations of high-quality steels (U8A, U12A, etc.). In addition, the designations of both high-quality and high-quality carbon tool steels may contain the letter G, indicating an increased content of manganese in the steel.
For example: U8G, U8GA. U8A – carbon tool steel with a carbon content of about 0.8%, high quality.
˗ Make tools for self made(chisel, center punch, scriber, etc.), mechanical work at low speeds (drills).
Marking of alloy tool steels
˗ The rules for designating tool alloy steels according to GOST 5950-73 are basically the same as for structural alloy steels.
The difference lies only in the numbers indicating the mass fraction of carbon in the steel.
˗ The percentage of carbon is also indicated at the beginning of the name of the steel, in tenths of a percent, and not in hundredths, as for structural alloy steels.
˗ If the carbon content of tool alloy steel is about 1.0%, then the corresponding figure is usually not indicated at the beginning of its name.
Let's give examples: steel 4Х2В5МФ, ХВГ, ХВЧ.
˗ 9Х5ВФ – alloy tool steel, with a carbon content of about 0.9%, chromium about 5%, vanadium and tungsten up to 1%
Marking of high-alloy (high-speed)
tool steels
˗ Designated by the letter “P”, the number following it indicates the percentage of tungsten in it: Unlike alloy steels, the names of high-speed steels do not indicate the percentage of chromium, because it is about 4% in all steels and carbon (it is proportional to the vanadium content).
˗ The letter F, indicating the presence of vanadium, is indicated only if the vanadium content is more than 2.5%.
For example: R6M5, R18, R6 M5F3.
˗ Typically, high-performance tools are made from these steels: drills, cutters, etc. (to reduce the cost, only the working part)
For example: R6M5K2 - high-speed steel, with a carbon content of about 1%, tungsten about 6%, chromium about 4%, vanadium up to 2.5%, molybdenum about 5%, cobalt about 2%.
Practical part
Assignment for students:
1. Write down the name of the work and its purpose.
2. Write down the basic principles of marking all groups of tool steels (carbon, alloy, high-alloy)
Assignment by options:
1. Decipher the steel grades and write down the scope of application of a specific grade (i.e., what it is intended for manufacturing).
Practical work No. 6
Topic: “Study of copper-based alloys: brass, bronze”
Purpose of the work: familiarizing students with the markings and scope of application of non-ferrous metals - copper and alloys based on it: brass and bronze; developing the ability to decipher the markings of brass and bronze.
Recommendations for students:
Work progress:
1.Familiarize yourself with the theoretical part.
2. Complete the practical part.
Theoretical part
Brass
Brasses can contain up to 45% zinc. Increasing the zinc content to 45% leads to an increase in tensile strength to 450 MPa. Maximum ductility occurs at a zinc content of about 37%.
According to the method of manufacturing products, a distinction is made between wrought and cast brass.
Wrought brasses are marked with the letter L, followed by a number indicating the percentage of copper content, for example, L62 brass contains 62% copper and 38% zinc. If, in addition to copper and zinc, there are other elements, then their initial letters are put (O - tin, C - lead, F - iron, F - phosphorus, Mts - manganese, A - aluminum, C - zinc).
The amount of these elements is indicated by the corresponding numbers after the number indicating the copper content, for example, the LAZh60-1-1 alloy contains 60% copper, 1% aluminum, 1% iron and 38% zinc.
Brasses have good corrosion resistance, which can be further increased by adding tin. Brass LO70-1 is resistant to corrosion in sea water and is called “marine brass”. The addition of nickel and iron increases mechanical strength up to 550 MPa.
Cast brasses are also marked with the letter L. After the letter designation of the main alloying element (zinc) and each subsequent one, a number is placed indicating its average content in the alloy. For example, brass LTs23A6Zh3Mts2 contains 23% zinc, 6% aluminum, 3% iron, 2% manganese. Brass grade LTs16K4 has the best fluidity. Cast brasses include brasses of the LS, LK, LA, LAZH, LAZHMts types. Casting brass is not prone to segregation, has concentrated shrinkage, and castings are obtained with high density.
Brasses are a good material for structures operating at subzero temperatures.
Bronze
Alloys of copper with elements other than zinc are called bronzes. Bronzes are divided into wrought and cast bronzes.
When marking deformable bronzes, the letters Br are placed first, then letters indicating which elements, other than copper, are included in the alloy. After the letters there are numbers showing the content of alloy components. For example, the BrOF10-1 brand means that bronze contains 10% tin, 1% phosphorus, and the rest is copper.
The marking of cast bronzes also begins with the letters Br, then the letter designations of the alloying elements are indicated and a number is placed indicating its average content in the alloy. For example, BrO3Ts12S5 bronze contains 3% tin, 12% zinc, 5% lead, and the rest is copper.
Tin bronzes When copper is fused with tin, solid solutions are formed. These alloys are very prone to segregation due to the wide temperature range of crystallization. Thanks to segregation, alloys with a tin content above 5% are favorable for parts such as sliding bearings: the soft phase provides good run-in, hard particles create wear resistance. Therefore, tin bronzes are good anti-friction materials.
Tin bronzes have low volumetric shrinkage (about 0.8%), therefore they are used in artistic casting. The presence of phosphorus ensures good fluidity. Tin bronzes are divided into wrought and cast bronzes.
In deformable bronzes, the tin content should not exceed 6% to ensure the necessary ductility, BrOF6.5-0.15. Depending on the composition, deformable bronzes are distinguished by high mechanical, anti-corrosion, anti-friction and elastic properties, and are used in various industries. Rods, pipes, tape, and wire are made from these alloys.
Practical part
Assignment for students:
1. Write down the title and purpose of the work.
2.Fill out the table:
Namealloy, it
definition
Basic
properties
alloy
Example
markings
Decoding
stamps
Region
applications
Practical work No. 7
Topic: “Study of aluminum alloys”
Purpose of the work: familiarizing students with the markings and scope of application of non-ferrous metals - aluminum and alloys based on it; studying the features of the use of aluminum alloys depending on their composition.
Recommendations for students: Before you begin the practical part of the assignment, carefully read the theoretical provisions, as well as the lectures in your workbook on this topic.
Work progress:
1.Familiarize yourself with the theoretical part.
2. Complete the practical part.
Theoretical part
The principle of marking aluminum alloys. At the beginning, the type of alloy is indicated: D - alloys of the duralumin type; A - technical aluminum; AK - malleable aluminum alloys; B - high-strength alloys; AL - casting alloys.
The following is the reference number of the alloy. The conventional number is followed by a designation characterizing the state of the alloy: M - soft (annealed); T - heat treated (hardening plus aging); N - hard-worked; P – semi-hardened.
According to their technological properties, alloys are divided into three groups: deformable alloys, non-hardening alloys heat treatment; wrought alloys, strengthened by heat treatment; casting alloys. Sintered aluminum alloys (SAS) and sintered aluminum powder alloys (SAP) are produced using powder metallurgy methods.
Wrought casting alloys that cannot be strengthened by heat treatment.
The strength of aluminum can be increased by alloying. Manganese or magnesium is introduced into alloys that cannot be strengthened by heat treatment. The atoms of these elements significantly increase its strength, reducing ductility. Alloys are designated: with manganese - AMts, with magnesium - AMg; After the designation of an element, its content is indicated (AMg3).
Magnesium acts only as a hardener, manganese strengthens and increases corrosion resistance. The strength of alloys increases only as a result of cold deformation. The greater the degree of deformation, the more significantly strength increases and ductility decreases. Depending on the degree of hardening, cold-worked and semi-work-worked alloys (AMg3P) are distinguished.
These alloys are used for the manufacture of various welded containers for fuel, nitric and other acids, light and medium loaded structures. Deformable alloys, strengthened by heat treatment.
Such alloys include duralumin (complex alloys of the aluminum - copper - magnesium or aluminum - copper - magnesium - zinc systems). They have reduced corrosion resistance, to increase which manganese is introduced. Duralumins are usually hardened at a temperature of 500 O C and natural aging, which is preceded by a two- to three-hour incubation period. Maximum strength is achieved after 4.5 days. Duralumin is widely used in aircraft, automotive, and construction.
High-strength aging alloys are alloys that contain zinc in addition to copper and magnesium. Alloys V95, V96 have a tensile strength of about 650 MPa. The main consumer is the aircraft industry (skin, stringers, spars).
Forging aluminum alloys AK, AK8 are used for the manufacture of forgings. Forgings are manufactured at a temperature of 380-450 O C, subjected to hardening at a temperature of 500-560 O C and aging at 150-165 O C for 6 hours.
Nickel, iron, and titanium are additionally introduced into the composition of aluminum alloys, which increase the recrystallization temperature and heat resistance to 300 O WITH.
They manufacture pistons, blades and discs of axial compressors and turbojet engines.
Casting alloys
Casting alloys include alloys of the aluminum-silicon system (silumins), containing 10-13% silicon. An additive to silumins of magnesium and copper promotes the effect of hardening of cast alloys during aging. Titanium and zirconium grind the grain. Manganese increases anti-corrosion properties. Nickel and iron increase heat resistance.
Casting alloys are marked from AL2 to AL20. Silumins are widely used for the manufacture of cast parts for devices and other medium- and lightly loaded parts, including thin-walled castings of complex shapes.
Practical part
Assignment for students:
1. Write down the title and purpose of the work.
2. Fill out the table:
Namealloy, it
definition
Basic
properties
alloy
Example
markings
Decoding
stamps
Region
applications
Laboratory work No. 1
Topic: “Mechanical properties of metals and methods of studying them (hardness)”
Purpose of the work:
Work progress:
1. Familiarize yourself with the theoretical principles.
2.Complete the teacher’s assignment.
3.Make a report according to the assignment.
Theoretical part
Hardness is the ability of a material to resist the penetration of another body into it. When testing for hardness, the body introduced into the material and called an indenter must be harder, have a certain size and shape, and must not receive residual deformation. Hardness tests can be static or dynamic. The first type includes tests by the indentation method, the second - the impact indentation method. In addition, there is a method for determining hardness by scratching - sclerometry.
Based on the hardness of a metal, you can get an idea of the level of its properties. For example, the higher the hardness, determined by the pressure of the tip, the lower the ductility of the metal, and vice versa.
Hardness tests using the indentation method consist of pressing an indenter (diamond, hardened steel, hard alloy) into the sample under the influence of a load, in the shape of a ball, cone or pyramid. After removing the load, an imprint remains on the sample, by measuring the size of which (diameter, depth or diagonal) and comparing it with the dimensions of the indenter and the magnitude of the load, one can judge the hardness of the metal.
Hardness is determined using special devices - hardness testers. Most often, hardness is determined by the Brinell (GOST 9012-59) and Rockwell (GOST 9013-59) methods.
There are general requirements to prepare samples and conduct tests using these methods:
1. The surface of the sample must be clean and free of defects.
2. Samples must be of a certain thickness. After receiving the print, there should be no signs of deformation on the back of the sample.
3. The sample should lie rigidly and stable on the table.
4. The load must act perpendicular to the surface of the sample.
Determination of Brinell hardness
The Brinell hardness of the metal is determined by pressing a hardened steel ball (Fig. 1) with a diameter of 10 into the sample; 5 or 2.5 mm and is expressed by the hardness number HB, obtained by dividing the applied load P in N or kgf (1H = 0.1 kgf) by the surface area of the imprint formed on the sample F in mm
Brinell hardness number HB expressed by the ratio of the applied loadFto the squareSspherical surface of the imprint (hole) on the measured surface.
HB = , (Mpa),
Where
S– area of the spherical surface of the print, mm 2 (expressed throughDAndd);
D– ball diameter, mm;
d– imprint diameter, mm;
Load sizeF, ball diameterDand the duration of exposure under load τ are selected according to Table 1.
Figure 1. Scheme of hardness measurement using the Brinell method.
a) Scheme of pressing the ball into the test metal
FD– ball diameter,d otp – imprint diameter;
b) Measuring the diameter of the print with a magnifying glass (in the figured=4.2 mm).
Table 1.
Selection of ball diameter, load and load holding time depending on
on the hardness and thickness of the sample
more than 66…3
less than 3
29430 (3000)
7355 (750)
1840 (187,5)
Less than 1400
more than 6
6…3
less than 3
9800 (1000)
2450 (750)
613 (62,5)
Non-ferrous metals and alloys (copper, brass, bronze, magnesium alloys, etc.)
350-1300
more than 6
6…3
less than 3
9800 (1000)
2450 (750)
613 (62,5)
30
Non-ferrous metals (aluminum, bearing alloys, etc.)
80-350
more than 6
6…3
less than 3
10
5
2,5
2450 (250)
613 (62,5)
153,2 (15,6)
60
Figure 2 shows the diagram lever device. The sample is placed on the object stage 4. By rotating the flywheel 3, screw 2 lifts the sample until it comes into contact with the ball 5 and then until the spring 7, put on the spindle 6, is completely compressed. The spring creates a preliminary load on the ball equal to 1 kN (100 kgf), which ensures a stable position of the sample during loading. After this, the electric motor 13 is turned on and through the worm gear of the gearbox 12, the connecting rod 11 and the system of levers 8,9 located in the hardness tester housing 1 with weights 10 creates a given full load on the ball. A spherical imprint is obtained on the test sample. After unloading the device, the sample is removed and the diameter of the indentation is determined with a special magnifying glass. The calculated diameter of the print is taken as the arithmetic mean of measurements in two mutually perpendicular directions.
Figure 2. Diagram of the Brinell device
Using the above formula, using the measured diameter of the indentation, the hardness number HB is calculated. The hardness number depending on the diameter of the resulting print can also be found in tables (see table of hardness numbers).
When measuring hardness with a ball with a diameter of D = 10.0 mm under a load F = 29430 N (3000 kgf), with a holding time of τ = 10 s, the hardness number is written as follows:HB2335 MPa or according to the old designation НВ 238 (in kgf/mm 2 )
When measuring Brinell hardness, remember the following:
It is possible to test materials with a hardness of no more than HB 4500 MPa, since with a higher hardness of the sample, unacceptable deformation of the ball itself occurs;
To avoid punching, the minimum thickness of the sample must be at least ten times the depth of the indentation;
The distance between the centers of two adjacent prints must be at least four print diameters;
The distance from the center of the print to the side surface of the sample must be at least 2.5d.
Rockwell hardness determination
According to the Rockwell method, the hardness of metals is determined by pressing a hardened steel ball with a diameter of 1.588 mm or a diamond cone with an apex angle of 120 into the test sample. O under the influence of two sequentially applied loads: preliminary P0 = 10 kgf and total P, equal to the sum of the preliminary P0 and main P1 loads (Fig. 3).
Rockwell hardness numberHRmeasured in conventional dimensionless units and determined by the formulas:
HR c = – when pressing the diamond cone
HR V = – when pressing a steel ball,
where 100– the number of divisions of the black scale C, 130 – the number of divisions of the red scale B of the indicator dial that measures the depth of indentation;
h 0 – depth of indentation of a diamond cone or ball under the influence of preload. Mm
h– depth of indentation of a diamond cone or ball under the action of a total load, mm
0.002 – scale division value of the indicator dial (moving the diamond cone when measuring hardness by 0.002 mm corresponds to moving the indicator needle by one division), mm
The type of tip and load value are selected according to Table 2, depending on the hardness and thickness of the test sample. .
Rockwell hardness number (HR) is a measure of the depth of indentation of the indenter and is expressed in conventional units. The unit of hardness is taken to be a dimensionless value corresponding to an axial displacement of 0.002 mm. The Rockwell hardness number is indicated directly by the arrow on the C or B scale of the indicator after automatic removal of the main load. The hardness of the same metal, determined by different methods, is expressed by different units of hardness.
For example,HB 2070, HR c 18 orHR V 95.
Figure 3. Rockwell hardness measurement scheme
Table 2
IN
HR IN
steel ball
981 (100)
0,7
25…100
on scale B
from 2000 to 7000 (hardened steels)
WITH
HR WITH
Diamond cone
1471 (150)
0,7
20…67
on a C scale
From 4000 to 9000 (parts subjected to carburization or nitriding, hard alloys, etc.)
A
HR A
Diamond cone
588 (60)
0,4
70…85
on scale B
The Rockwell method is characterized by simplicity and high productivity, ensures the preservation of a high-quality surface after testing, and allows testing metals and alloys of both low and high hardness. This method is not recommended for alloys with a heterogeneous structure (gray cast iron, malleable and high-strength cast iron, antifriction bearing alloys, etc.).
Practical part
Contents of the report.
Indicate the title of the work and its purpose.
Answer the questions:
1. What is hardness called?
2. What is the essence of the definition of hardness?
3. What 2 methods for determining hardness do you know? What is their difference?
4. How should a sample be prepared for testing?
5. How to explain the lack of a universal method for determining hardness?
6. Why is hardness most often determined among the many mechanical characteristics of materials?
7. Record in your notebook the scheme for determining hardness according to Brinell and Rockwell.
Laboratory work No. 2
Topic: “Mechanical properties of metals and methods of studying them (strength, elasticity)”
Purpose of the work: study the mechanical properties of metals, methods for studying them.
Work progress:
1. Familiarize yourself with the theoretical principles.
2.Complete the teacher’s assignment.
3.Make a report according to the assignment.
Theoretical part
The main mechanical properties are strength, elasticity, viscosity, hardness. Knowing the mechanical properties, the designer reasonably selects the appropriate material that ensures the reliability and durability of structures with minimal weight.
Mechanical properties determine the behavior of a material during deformation and destruction under external loads. Depending on the loading conditions, mechanical properties can be determined by:
1. Static loading - the load on the sample increases slowly and smoothly.
2. Dynamic loading - the load increases at high speed and has an impact character.
3. Repeatedly variable or cyclic loading - the load during the test changes many times in magnitude or in magnitude and direction.
To obtain comparable results, samples and methods for conducting mechanical tests are regulated by GOSTs. In a static tensile test: GOST 1497, strength and ductility characteristics are obtained.
Strength is the ability of a material to resist deformation and destruction.
Plasticity is the ability of a material to change its size and shape under the influence of external forces; a measure of plasticity is the amount of residual deformation.
The device that determines strength and ductility is a tensile testing machine that records a tensile diagram (see Fig. 4), expressing the relationship between the elongation of the sample and the applied load.
Rice. 4. Tension diagram: a – absolute, b – relative.
Section oa in the diagram corresponds to the elastic deformation of the material when Hooke’s law is observed. The stress corresponding to the elastic limiting deformation at point a is called the limit of proportionality.
The limit of proportionality is the maximum voltage up to which Hooke's law is valid.
At stresses above the proportionality limit, uniform plastic deformation occurs (elongation or narrowing of the cross-section).
Point b is the elastic limit - the highest stress, until which residual deformation does not occur in the sample.
Area cd is the yield area; it corresponds to the yield strength - this is the stress at which an increase in deformation occurs in the sample without an increase in load (the material “flows”).
Many grades of steel and non-ferrous metals do not have a clearly defined yield point, so a conditional yield limit is established for them. The conditional yield strength is a stress that corresponds to a residual deformation equal to 0.2% of the original length of the sample (alloy steel, bronze, duralumin and other materials).
Point B corresponds to the ultimate strength (a local thinning appears on the sample - a neck; the formation of thinning is characteristic of plastic materials).
Tensile strength is the maximum stress that a sample can withstand before resolution (temporary tensile strength).
Beyond point B, the load drops (due to neck elongation) and failure occurs at point K.
Practical part.
Contents of the report.
1. Indicate the title of the work and its purpose.
2. What mechanical properties do you know? What methods are used to determine the mechanical properties of materials?
3. Write down the definition of the concepts of strength and ductility. By what methods are they determined? What is the name of the device that determines these properties? How are properties determined?
4. Record the absolute tension diagram of the plastic material.
5. After the diagram, indicate the names of all points and sections of the diagram.
6. What limit is the main characteristic when choosing a material for the manufacture of any product? Justify your answer.
7. Which materials are more reliable, brittle or ductile? Justify your answer.
References
Main:
Adaskin A.M., Zuev V.M. Materials science (metalworking). – M.: JIC “Academy”, 2009 – 240 p.
Adaskin A.M., Zuev V.M. Materials science and technology of materials. – M.: FORUM, 2010 – 336 p.
Chumachenko Yu.T. Materials science and plumbing (NPO and SPO). – Rostov n/d.: Phoenix, 2013 – 395 p.
Additional:
Zhukovets I.I. Mechanical testing of metals. – M.: Higher school, 1986. – 199 p.
Lakhtin Yu.M. Fundamentals of materials science. – M.: Metallurgy, 1988.
Lakhtin Yu.M., Leontyeva V.P. Materials Science. – M.: Mechanical Engineering, 1990.
Electronic resources:
1. Journal “Materials Science”. (Electronic resource) – access form http://www.nait.ru/journals/index.php?p_journal_id=2.
2. Materials science: educational resource, access form http:// www.supermetalloved/narod.ru.
3. Steel brand. (Electronic resource) – access form www.splav.kharkov.com.
4. Federal Center for Information and Educational Resources. (Electronic resource) – access form www.fcior.ru.
Laboratory work for the course “Materials Science”
1st semester
1. “Analysis of the crystal structure of metals and alloys” (No. 1, workshop 2). 2 z.
2. “Testing materials for hardness” (No. 10, workshop 2). 1 z.
3. “Tensile testing of samples” (No. 11, workshop 2; or “Mechanical properties of structural materials”, separate file). 2 z.
4. “Determination of impact strength of a material” (No. 12, workshop 2). 1 z.
5. “Fractographic analysis of the destruction of metallic materials” (No. 9, workshop 2). 1 z.
6. “The influence of cold plastic deformation and recrystallization temperature on the structure and properties of metals” (No. 4, workshop 1). 2 z.
7. “Thermal analysis of alloys” (No. 1, workshop 1). Part 1 – constructing a state diagram of the “zinc-tin” system using the thermal method. Part 2 – analysis of state diagrams of binary alloys: perform an individual task according to point 5 in “Report Contents”. 2 z.
8. “Macroscopic analysis (macroanalysis) of the structure of metallic materials” (No. 2, workshop 2). 1 z.
9. “Microscopic analysis (microanalysis) of the structure of metallic materials” (No. 3, workshop 2). 1 z.
1st semester
1 (10). “Microscopic analysis of metals and alloys. Structure of carbon steel" (No. 2, workshop 1) or similar work No. 7 "Study of the structure of carbon steels in an equilibrium state by microanalysis method", workshop 2). Practical part: students look at the structures of four iron-carbon alloys on a MIM-7 microscope: technical iron, hypoeutectoid, eutectoid and hypereutectoid alloys. They make schematic sketches, label the structural components, give an example of a steel grade, and for a hypoeutectoid alloy, calculate the carbon content using the formula. 1 z. + t.
2 (11). “Iron-carbon phase diagram. Structure, properties and application of cast irons" No. 3 from workshop 1) or similar work No. 8 "Study of the structure of carbon cast irons by microanalysis" from workshop 2). Practical part: students look at the structures of three cast irons using a MIM-7 microscope: gray cast iron with fine-lamellar graphite on a pearlite base, high-strength cast iron on a ferrite-pearlite base, and hypoeutectic white cast iron. Unfortunately, not anymore. They also make sketches and write the names of cast irons and structural components. 1 z. + t.
3 (12). “The influence of cooling rate on the hardness of carbon steel” No. 20 from workshop 2). Practical part: four samples made of U8 steel. One is subjected to annealing, the second is normalized, the third is quenched in oil, the fourth is quenched in water. The hardness is measured and a graph of hardness versus cooling rate is plotted. The cooling rate values are taken from the table in the laboratory work. 2 z.
4 (13). “Hardening of carbon steels” No. 5 from workshop 1). Practical part: three samples from steels 20, 45, U9 are quenched in water, one sample from steel 45 is quenched in oil. Hardness is measured before (HRB) and after (HRC) hardening. Using the conversion table, hardness is determined in HB units. Based on the results, two graphs are constructed: HB=f(%C) and HRC=f(Vcool). 2 z. + t.
5 (14). “Tempering steel” No. 6 from workshop 1) or similar work No. 18 “Tempering carbon steel” from workshop 2). Practical part: according to the workshop 1) conduct low (200ºС), medium (400ºС) and high (600ºС) tempering of hardened samples from steel 45 and low tempering (200ºС) of a hardened sample from U9 steel. Hardness is measured. Build a graph HRC=f(Tref.). According to workshop 2), low, medium and high tempering of hardened samples from U8 steel is carried out. 2 z. + t.
6 (15). “Annealing and normalization of steel” No. 7 from workshop 1). Practical part: two samples made of steel 45. One is subjected to isothermal annealing, and the second is subjected to normalization. 2 z. + t.
7 (16). “Chemical-thermal treatment of steel” No. 8 from workshop 1. 1 z.
8 (17). “The influence of alloying elements on the hardenability of steel, determined by the end-hardening method” No. 21 from workshop 2. 2 z.
9 (18). "Classification, labeling and use of structural materials." Practical part: students receive a card with five stamps on it and write each one in detail. 1 z.
Laboratory work No. 1
ANALYSIS OF CRYSTAL STRUCTURE
METALS AND ALLOYS
Purpose of the work:
Familiarize yourself with the types of crystal lattices of metals and alloys, defects in the crystal structure and types of solid solutions.
Devices, materials and tools
Models of the main types of crystal lattices of metals and solid solutions.
Brief theoretical information
Atomic crystal structure of metals. Metals at normal conditions have a crystalline structure, distinctive feature which is a certain mutual periodic arrangement of atoms, extending over arbitrarily large distances. This arrangement of atoms is usually called long-range order. Thus, the atomic-crystal structure is understood as the relative arrangement of atoms (ions) that exists in a real crystal. To describe the atomic-crystalline structure, the concept of a spatial or crystal lattice is used. The crystal lattice of a metal is an imaginary spatial grid, at the nodes of which atoms (ions) are located, between which free electrons move. The electrostatic forces of attraction between ions and electrons balance the repulsive forces between ions. Thus, the positions of the atoms are such that the minimum energy of interaction between them is ensured, and, consequently, the stability of the entire aggregate.
The minimum volume of a crystal, which gives an idea of the atomic structure of the metal in its entire volume, is called unit crystal cell. Pure metals have one of the following types of crystal lattices: body-centered (bcc), face-centered (fcc) and hexagonal close-packed (hcp) (Fig. 1).
For example, a-iron, lithium, vanadium, tungsten, molybdenum, chromium, tantalum have a bcc lattice; FCC lattice - aluminum, g-iron, copper, gold, nickel, platinum, lead, silver. HCP lattice has magnesium, zinc, beryllium, cadmium, cobalt, a-titanium.
Coordinate directions (crystallographic axes). In a system of crystallographic axes, the shape of a unit cell of a spatial lattice can be described using three coordinate angles a, b and g between the crystallographic axes and three lattice parameters a, b, c.
Elementary cells of cubic lattices of bcc (Fig. 1a) and fcc (Fig. 1b) are characterized by equality of angles a = b = g = 90° and equality of lattice parameters a = b = c. The hcp lattice (Fig. 1c) is characterized by the angles a = b = 90° and g = 120° and the equality of two lattice parameters a = b c.
Crystallographic symbols are used to describe atomic planes and directions in a crystal. To determine the symbols of planes, use the method of indicating a plane by segments. To do this, choose a coordinate system in such a way that the coordinate axes I, II, III are parallel to the three intersecting edges of the crystal (Fig. 2). As a rule, the first crystallographic axis is directed towards the observer, the second is horizontal, and the third is oriented upward. The plane A 1 B 1 C 1 cuts off on the coordinate axes segments equal in magnitude to the lattice parameters OA 1 = a, OB 1 = b, OS 1 = c. The plane A 1 B 1 C 1 is called unit. The lattice parameters a, b, c are taken as axial units.
To determine the crystallographic indices of the A 2 B 2 C 2 plane, it is necessary:
Find options given plane, i.e. segments in axial units, cut off by a given plane on the coordinate axes;
Write down the ratio of three fractions, the numerators of which are the parameters of the unit plane A 1 B 1 C 1, and the denominators are the parameters of the given plane A 2 B 2 C 2, i.e. 1/OA 2: 1/OB 2: 1/OS 2;
Reduce the resulting ratio to the ratio of three integer coprime numbers, that is, reduce the fractions to a common denominator, reduce, if possible, by a common factor, and discard the denominator.
The resulting three integers and coprime numbers, denoted h, k, l, are called atomic plane indices. The set of indices is called the atomic plane symbol, which is usually enclosed in parentheses and written (hkl). If the plane intersects the coordinate axes in the negative quarter, then a “-” sign is placed above the index. If the plane under consideration is parallel to one of the crystallographic axes, then the index corresponding to this axis is equal to zero. Figure 3 shows examples of indexing planes in a Bravais cubic unit cell.
The symbols should be read numerically, for example, (100) as 1, 0, 0. The symbols for parallel planes are the same. Therefore, the plane symbol describes an infinitely large family of parallel atomic planes that are structurally equivalent. Atomic planes of the same family are located from each other at an equal interplanar distance d.
Atomic planes of different families may not be parallel, but identical in arrangement of atoms and interplanar distance d. Such planes are combined and designated by the symbol (hkl). Thus, in cubic crystals, one set includes families of planes, the indices of which differ only in sign and location in the symbol. For example, the set of atomic planes (100) includes six families: (100), (͞100), (010), (0͞10), (001), (00͞1).
The symbol of the crystallographic direction is determined using three relatively prime numbers (indices) u, v, w, which are proportional to the coordinates of the radius vector R connecting the origin (initial node) with the nearest node of the crystal lattice in a given direction. Subscripts are enclosed in square brackets and written . If the direction does not pass through the origin (start node), then you need to mentally move it parallel to itself or move the origin and coordinate axes so that the direction passes through the origin.
Figure 4 shows examples of indicating crystallographic directions in a cubic crystal.
Let's place the origin of coordinates at the point O. Then, for example, point With has coordinates 0, 0, 1; direction symbol OS– . It is read separately – “direction zero – zero – one.” Dot e has coordinates ½; ½; 1; direction symbol oh– . To define a direction symbol aw, mentally transfer it parallel to itself to the point O; then the coordinates of the point V– ͡͞1, 1, 0; direction symbol is [͞110]. When the direction is reversed, the signs of the indices change to the opposite, for example, and (see Figure 1.5). Parallel directions have the same symbols and are combined into families. Families of identical but non-parallel directions form a set, which is designated
In hexagonal crystals, a four-axis coordinate system is mainly used to indicate planes. Examples of indexing planes in a hexagonal crystal are shown in Figure 5.
The fourth coordinate axis OU lies in the horizontal plane and is located along the bisector between the negative semi-axes (-OX) and (-OY). The plane symbol consists of four indices and is written (hkil). Three of them (h, k and l) are calculated from the reciprocal values of the segments cut off by the plane under consideration on three crystallographic axes (OX), (OY), (OZ), and the fourth index i calculated by the ratio:
h + k + i =0 (1)
For example, if h =1; k =1, l = 0, then using relation (1), you can find the fourth index: i = -(h + k) = -(1 +1) = -2. The plane symbol is written as (11͞20). This is the plane closest to us in Figure 6. The fourth index i is used when it is necessary to designate identical planes, and is not used when calculating interplanar distances, angles between planes and directions. Therefore, instead of writing the full plane symbol, for example, (11͞20), sometimes they use (11.0), i.e. Instead of the index i, put a dot. Families and sets of identical planes are defined similarly to families and sets in cubic crystals.
Both triaxial and tetraaxial symbols are used to describe crystallographic directions in hexagonal crystals. Triaxial symbols are determined by the coordinates of a given radius vector (as in cubic crystals).
There is a relationship between four-axis direction indices:
r 1 + r 2 + r 3 = 0 (2)
To transition from three-axis symbols to four-axis symbols, the following relations are used:
r 1 = 2u –v; r 2 = 2v – u; r 3 = -u – v; r 4 = 3w (3)
Examples of indicating crystallographic directions in a hexagonal crystal are shown in Figure 6.
In addition to the geometric characteristics of a crystal, in physical materials science the following concepts are used: the number of atoms per cell n i, coordination number (CN) and filling factor η.
The number of atoms per cell ni is understood as the number of atomic volumes per Bravais unit cell. Let's take the volume of one atom as one. For example, consider a body-centered cell, which is formed by 9 atoms, 8 of which are located at the vertices of the cube, and 1 at the center of the cube. Each atom at a vertex belongs simultaneously to eight neighboring cells, therefore, one cell owns 1/8 of each of the 8 atoms: 1/8. 8 = 1; the atom in the center of the cube belongs entirely to the cell. Thus, a body-centered cell is formed by two atomic volumes, i.e., there are two atoms per cell.
The coordination number (CN) is the number of atoms located at an equal and shortest distance from a given atom. The higher the coordination number, the greater the atomic packing density. Thus, in a body-centered cubic lattice, CN = 8; in face-centered and hexagonal lattices, CN = 12.
The filling factor η is the percentage ratio of the volume V a occupied by atoms in a cell to the volume of the entire cell V i:
η = (V a /V i) ∙ 100% (4)
The coordination number (CN) and filling factor η characterize the packing density of atoms in the unit cell of a metal crystal. The densest packing of atoms is realized in face-centered and hexagonal Bravais cells.
Defects in crystal structure . A real crystal differs from an ideal one in the presence of defects in the crystal structure, which have an influence, often decisive, on the macroscopic properties of crystalline bodies. Based on geometric characteristics, defects are divided into three groups:
Point (zero-dimensional);
Linear (one-dimensional);
Surface (two-dimensional).
Point defects have dimensions in all directions from one to four atomic diameters. They are divided into intrinsic and impurity.
Intrinsic point defects include: vacancies formed when an atom (ion) is removed from its normal position in a site of the crystal lattice, and interstitial atoms - atoms of the base metal located in the interstices of the crystal lattice. Impurities include atoms of another (or other) elements dissolved in the main lattice according to the principle of substitution or insertion.
Figure 7 shows vacancies, an intrinsic interstitial atom, and substitutional and interstitial impurity atoms in a two-dimensional crystal model.
The most common are vacancies. Two mechanisms for the occurrence of vacancies are known: the Schottky mechanism - when an atom emerges on the outer surface or the surface of a pore or crack inside a crystal under the influence of thermal fluctuations, and the Frenkel mechanism - when a pair “own interstitial atom - vacancy” is formed inside the crystal lattice during deformation, irradiation of metals with ionizing agents radiation: fast electrons, γ - rays. In real crystals, vacancies are constantly formed and disappear under the influence of thermal fluctuations. The activation energy for the formation of a vacancy is approximately 1 eV, and that of an interstitial atom is from 3 to 10 eV.
With increasing temperature, the equilibrium concentration of point defects in the crystal increases. During plastic deformation, irradiation, and hardening, the number of point defects increases sharply, which leads to their disruption equilibrium concentration by several orders of magnitude.
Substitutional impurity atoms migrate in the same way as main atoms - according to the vacancy mechanism. Interstitial impurity atoms are small in size and therefore, unlike large intrinsic interstitial atoms, can migrate through the voids between the atoms of the crystal lattice.
Point defects have a great influence on the mechanism and kinetics of the processes of creep, long-term destruction, the formation of diffusion porosity, decarburization, graphitization and other processes associated with the transfer of atoms in the volume of a substance, as well as on physical properties: electrical resistance, density.
Linear defects small (several atomic diameters) in two directions and have a large extent, comparable to the length of the crystal, in the third. Linear defects include dislocations, chains of vacancies and interstitial atoms.
Dislocations are divided into two main types: edge and screw.
An edge dislocation can be imagined if you mentally partially split a perfect crystal vertically, say with a primitive cubic lattice, and insert into it an extra short atomic layer called an extraplane. An extraplane can also be obtained by shifting one part of the crystal relative to another. The extraplane, acting like a wedge, bends the lattice around its lower edge inside the crystal (Fig. 8).
The area of imperfection around the edge of the extraplane is called an edge dislocation. Strong distortions of the crystal lattice are contained, as it were, inside a “pipe” with a diameter of two to ten atomic diameters, the axis of which is the edge of the extraplane. Along the extraplane line, the imperfections are macroscopic in nature, but in the other two directions (along the diameter of the “pipe”) they are very small. If the extraplane is located in the upper part of the crystal, then the dislocation associated with it is called positive and is designated (┴); if the extraplane is located in the lower part, then the dislocation is called negative and is designated (┬).
Under the action of an externally applied voltage, an edge dislocation can move by sliding along certain crystallographic planes and directions. Predominant sliding occurs along closely packed planes. The combination of the sliding plane and sliding direction is called the sliding system. Each type of crystal lattice is characterized by its own slip systems. Thus, in crystals with a face-centered cubic lattice, these are the planes of the aggregate (111) and the directions of the aggregate<110>(Cu, Al, Ni), with a body-centered cubic lattice – (110) (α-Fe, Mo, Nb), (211) (Ta,W, α-Fe), (321) (Cr, α-Fe) and<111>, with hexagonal close-packed – (0001),<11͞20>(Zn, Mg, Be), (1͞100), (10͞11),<11͞20>(Ti), (11͞22),<1͞213>(Ti). The stress required for shear is called critical shear or shear stress. Moreover, at each moment of time, only a small group of atoms participates in the displacement on both sides of the slip plane. Figure 9 shows a diagram of the sliding of an edge dislocation through a crystal.
The final stage of sliding is the emergence of an edge dislocation (extraplane) onto the crystal surface. In this case, the upper part of the crystal shifts relative to the lower one by one interatomic distance in the direction of the shift. Such movement is an elementary act of plastic deformation. Sliding is a conservative movement not associated with the transfer of mass of matter. The direction and magnitude of the shift during the movement of an edge dislocation are characterized by the Burgers vector b and its power, respectively. The direction of movement of the edge dislocation is parallel to the Burgers vector.
In addition to sliding, an edge dislocation can move by creep, which occurs by diffusion and is a thermally activated process. Positive creep occurs when a chain of atoms from the edge of the extraplane moves to adjacent vacancies or interstices, i.e. the extraplane is shortened by one interatomic distance and the edge dislocation passes into the upper slip plane parallel to the first. Negative creep occurs when the edge of the extraplane is completed by an atomic row due to the addition of interstitial or neighboring atoms, and the edge dislocation moves to the lower slip plane. Crawling is a non-conservative movement, i.e. occurs with mass transfer. The rate of crawling depends on both temperature and the concentration of point defects.
A screw dislocation, like an edge dislocation, can be created using shear. Let's imagine a crystal in the form of a stack of horizontal parallel atomic planes. Let's mentally make a non-through cut in the crystal (Fig. 10a) and move, for example, the right side down (along the ABCD plane) by one interplanar distance (Fig. 10b).
A screw dislocation is divided into right-handed (Fig. 10b), when when moving from the upper plane to the lower plane the dislocation line must be bypassed clockwise, and left-handed, when when moving from the upper plane to the lower plane the dislocation line must be bypassed counterclockwise (if relative to the ABCD plane move down the left side of the crystal). The screw dislocation line is always parallel to the Burgers vector (Fig. 11).
A screw dislocation, unlike an edge dislocation, is not associated with a specific shear plane; therefore, it can move by sliding in any crystallographic plane containing a dislocation line and a shear vector (Fig. 12). The direction of movement of a screw dislocation is always perpendicular to the Burgers vector. As a result of the sliding of both edge and screw dislocations, a step is formed on the surface of the crystal with a height equal in magnitude to the Burgers vector b(Fig. 12).
Dislocations are present in all crystals. Thus, in undeformed metals, the dislocation density is 10 6 -10 8 cm -2; in homeopolar crystals – 10 4 cm -2. At an external stress equal to the critical shear stress τ cr = 10 -5 G, where G is the elastic modulus of the material, the dislocations begin to move, i.e., plastic deformation begins. During plastic deformation, the dislocation density increases. For example, in deformed metals the dislocation density is 10 10 –10 12 cm -2; in homeopolar crystals up to 10 8 cm -2. Various types of barriers (second phase particles, point defects, grain boundaries, etc.) serve as obstacles to moving dislocations. In addition, as the number of dislocations increases, they begin to accumulate, become entangled in balls and interfere with other moving dislocations. As the degree of deformation increases, τ cr increases, i.e., to continue the deformation process, an increase in external stress is required, which to a certain extent determines the strengthening of the material.
Surface defects. Surface defects include grain boundaries (subgrains) (Fig. 13). Surface defects are two-dimensional, that is, they have macroscopic dimensions in two directions and atomic dimensions in the third direction. Boundaries are called low-angle if the misorientation of the crystal lattices of neighboring grains does not exceed 10°, and high-angle (high-angle) if the misorientation is greater.
Low-angle boundaries can be formed by systems of both edge and screw dislocations of different orientations and with different Burgers vectors. Low-angle boundaries arise during the growth of crystals from a melt, during plastic deformation, etc. Dislocations of a low-angle boundary attract point defects due to elastic interaction with them. Migration of a low-angle boundary occurs only by diffusion. Therefore, point defects concentrated in the border zone at several interatomic distances inhibit this process and stabilize the substructure.
High-angle boundaries were discovered much earlier than low-angle boundaries and are the “oldest” type of defects in the crystal structure. It is believed that the high-angle boundary is a layer 2-3 atomic diameters thick, in which the atoms occupy some intermediate positions with respect to the correct positions of the lattice sites of neighboring grains. This position of the atoms provides minimal potential energy in the boundary layer and is therefore quite stable.
The nature and behavior of both low-angle and high-angle boundaries under force and temperature influence the mechanical properties of the material.
Exercise
1. A plane in a cubic crystal cuts off segments equal to a on the coordinate axes; 2c; With. Determine the crystallographic indices of the plane (hkl).
2. Construct a spatial image of planes (using the example of a cube) having crystallographic indices (110); (111); (112); (321); (1͞10); (͞111); (͞1͞1͞1).
3. Define the symbol for the direction passing through the points (0, in/3, s/3).
4. Construct a spatial image of the following directions in the cube; ; ; [͞100]; ; ; ; ; ; ; [͞111]; ; ; [͞1͞11]; [͞111]; ; [͞1͞1͞1]; ; .
5. Calculate the number of atoms in a cell and the coordination number for bcc and fcc and hcp lattices.
1. How many types of Bravais unit cells are known today? Which of them are most characteristic of metals?
2. What are crystallographic symbols? Describe the scheme for determining the atomic plane symbol in a crystal.
3. What types of point defects exist in crystals? Over what distances does the distortion caused by a point defect extend?
4. How does the concentration of vacancies change with increasing temperature?
5. Why are dislocations called linear defects?
6. On what basis are dislocations divided into edge and screw?
7. What is the Burgers vector? What is the power of the Burgers vector?
8. What is the direction of the Burgers vector relative to the edge and screw dislocation line?
9. What are surface defects?
10. What physical properties of crystalline solids are affected by defects in the crystal structure?
Laboratory work No. 2
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FEDERAL STATE BUDGET EDUCATIONAL
HIGHER EDUCATION INSTITUTION
"VOLGA STATE UNIVERSITY OF WATER TRANSPORT"
PERM BRANCH
E.A. Sazonova
MATERIALS SCIENCE
COLLECTION OF PRACTICAL AND LABORATORY WORKS
methodological recommendations for performing laboratory and practical
works for students of secondary vocational education specialty
02/26/06 “Operation of ship electrical equipment and automation equipment”
02.23.01 “Organization of transportation and management in transport” (by type)
PERMIAN
2016
Introduction
Methodological recommendations for performing laboratory and practical work
in the academic discipline "Materials Science" are intended for students of secondary
professional education in specialty
02/26/06 “Operation of a ship
electrical equipment and automation equipment"
This manual provides instructions for performing
practical and laboratory work on the topics of the discipline, topics and content are indicated
laboratory and practical work, forms of control for each topic and recommended
literature.
These recommendations contribute to the development of general and professional
competencies, gradual and targeted development of cognitive abilities.
As a result of mastering this academic discipline, the student should be able to:
˗
perform mechanical tests of material samples;
˗
use physical-chemical methods for studying metals;
˗
use lookup tables to determine material properties;
˗
choose materials for professional activities.
As a result of mastering this academic discipline, the student should know:
˗
basic properties and classification of materials used in
professional activities;
˗
name, marking, properties of the material being processed;
˗
rules for the use of lubricants and cooling materials;
˗
basic information about metals and alloys;
˗
basic information about non-metallic, gasket,
sealing and electrical materials, steel, their classification.
Laboratory and practical work will allow you to develop practical skills
work, professional competencies. They are included in the structure of the study of educational
discipline "Materials Science", after studying the topic: 1.1. "Basic information about
metals and alloys", 1.2 "Iron-carbon alloys", 1.3 "Non-ferrous metals and alloys".
Laboratory and practical work are an element of educational
disciplines and are assessed according to the criteria presented below:
A grade of “5” is given to a student if:
˗
the topic of the work corresponds to the given one, the student shows systemic and complete
knowledge and skills on this issue;
˗
the work is designed in accordance with the teacher’s recommendations;
˗
the amount of work corresponds to the given one;
˗
The work was completed exactly within the time frame specified by the teacher.
A grade of “4” is given to a student if:
˗
the topic of the work corresponds to the given one, the student allows small
inaccuracies or some errors in this matter;
˗
the work is framed with inaccuracies in design;
˗
the amount of work corresponds to the specified or slightly less;
˗
the work was submitted on time specified by the teacher, or later, but no more than 12
day.
A grade of “3” is given to a student if:
2
the topic of the work corresponds to the given one, but the work lacks significant
elements of the work content or topic are presented illogically, not clearly presented
the main content of the question;
˗
the work was prepared with errors in design;
˗
the amount of work is significantly less than specified;
˗
The work was submitted 56 days late.
A grade of “2” is given to a student if:
˗
the main topic of the work is not disclosed;
˗
the work is not designed in accordance with the requirements of the teacher;
˗
the amount of work does not correspond to what was specified;
˗
The work was submitted more than 7 days late.
Laboratory and practical work have a certain content in their content.
structure, we suggest you consider it: the progress of the work is given at the beginning of each practical
and laboratory work; when performing practical work, students perform
the task that is indicated at the end of the work (item “Task for students”); at
carrying out laboratory work, a report on its implementation is drawn up, the contents of the report
indicated at the end of the laboratory work (item “Contents of the report”).
˗
When performing laboratory and practical work, students perform
certain rules, consider them below: laboratory and practical work
performed during training sessions; finalization is allowed
laboratory and practical work at home; permitted use
additional literature when performing laboratory and practical work; before
By performing laboratory and practical work, it is necessary to study the basic
theoretical provisions on the issue under consideration.
3
Practical work No. 1
“Physical properties of metals and methods for their study”
Purpose of the work: to study the physical properties of metals and methods for their determination.
Work progress:
Theoretical part
Physical properties include: density, melting point (melting point),
thermal conductivity, thermal expansion.
Density is the amount of substance contained in a unit volume. This is one of
the most important characteristics of metals and alloys. Based on their density, metals are divided into
the following groups: light (density no more than 5 g/cm3) magnesium, aluminum, titanium, etc.;
heavy (density from 5 to 10 g/cm3) iron, nickel, copper, zinc, tin, etc. (this
the most extensive group); very heavy (density more than 10 g/cm3) molybdenum,
tungsten, gold, lead, etc. Table 1 shows the density values of metals.
Table 1
metal
Magnesium
Aluminum
Titanium
Zinc
Tin
density g/cm3
Density of metals
metal
1,74
2,70
4,50
7,14
7,29
Iron
Copper
Silver
Lead
Gold
density g/cm3
7,87
8,94
10,50
11,34
19,32
Melting point is the temperature at which a metal goes from
crystalline (solid) state into liquid with heat absorption.
Melting points of metals range from −39 °C (mercury) to 3410 °C
(tungsten). Melting point of most metals (except alkali)
high, but some “normal” metals, such as tin and lead, can be
melt on a regular electric or gas stove.
Depending on the melting point, the metal is divided into the following
groups: low-melting (melting point does not exceed 600 oC) zinc, tin,
lead, bismuth, etc.; medium-melting (from 600 oC to 1600 oC) these include almost
4
half of the metals, including magnesium, aluminum, iron, nickel, copper, gold;
refractory (more than 1600 oC) tungsten, molybdenum, titanium, chromium, etc. When introduced into
metal additives melting point tends to decrease.
Table 2
metal
Tin
Iron
Copper
Gold
Titanium
Melting and boiling points of metals
Temperature oС
melting
boiling
232
1539
1083
1063
1680
2600
2900
2580
2660
3300
metal
Silver
Magnesium
Zinc
Lead
Aluminum
Temperature oС
melting
boiling
960
650
420
327
660
2180
1100
907
1750
2400
Thermal conductivity is the ability of a metal to conduct
heat when heated.
heating.
Electrical conductivity is the ability of a metal to conduct electric current.
Thermal expansion is the ability of a metal to increase its volume when
The smooth surface of metals reflects a large percentage of light - this phenomenon
called metallic luster. However, in powder form, most
metals lose their shine; aluminum and magnesium, however, retain their shine
and in powder. Of these, aluminum, silver and palladium reflect light most well.
metals are used to make mirrors. Rhodium is sometimes used to make mirrors.
despite its exceptionally high price: thanks to its significantly higher
silver or even palladium, hardness and chemical resistance, the rhodium layer can
be significantly thinner than silver.
Research methods in materials science
The main research methods in metallurgy and materials science
microstructure, electron microscopy,
are:
X-ray research methods. Consider their features in more detail.
kink,
macrostructure,
1. Fracture is the simplest and most accessible way to assess the internal structure
metals A method for assessing fractures, despite its apparent roughness of assessment
quality of the material, is used quite widely in various industries and
scientific research. Fracture assessment in many cases can characterize the quality
material.
The fracture can be crystalline or amorphous. Amorphous fracture is characteristic
for materials that do not have a crystalline structure, such as glass, rosin,
glassy slags.
Metal alloys, including steel, cast iron, aluminum, magnesium
alloys, zinc and its alloys give granular, crystalline fracture.
Each face of a crystalline fracture is a cleavage plane
individual grain. Therefore, the fracture shows us the grain size of the metal. Exploring the kink
steel, it can be seen that the grain size can vary within very wide limits: from
several centimeters in cast, slowly cooled steel to thousandths
millimeters in properly forged and hardened steel. Depending on size
grains, the fracture can be coarse-crystalline and fine-crystalline. Usually
fine-crystalline fracture corresponds to a higher quality metal
alloy
5
If the destruction of the test sample occurs with a previous
plastic deformation, the grains in the fracture plane are deformed, and the fracture no longer
reflects the internal crystalline structure of the metal; in this case a break
called fibrous. Often in one sample, depending on its level
plasticity, the fracture may contain fibrous and crystalline areas. Often by
the ratio of the fracture area occupied by crystalline areas for given
testing conditions evaluate the quality of the metal.
A brittle crystalline fracture can occur when fractured along grain boundaries.
or along slip planes intersecting grains. In the first case, the break is called
intergranular, in the second transgranular. Sometimes, especially with very small
grain, it is difficult to determine the nature of the fracture. In this case, the fracture is examined using a magnifying glass or
binocular microscope.
Recently, the branch of metallurgy has been developing based on fractographic
studying fractures on metallographic and electron microscopes. At the same time
find new advantages of the old research method in metallurgy
research
to such studies of the concept of fractal
dimensions.
applying
break,
2. Macrostructure is the next method for studying metals.
Macrostructural research consists of studying the cross-sectional plane of a product or
sample in longitudinal, transverse or any other directions after etching, without
use of magnifying devices
Dignity
macrostructural study is the fact that with the help of this
method, you can directly study the structure of an entire casting or ingot, forging,
stamping, etc. Using this research method, you can detect internal
metal defects: bubbles, voids, cracks, slag inclusions, investigate
crystal structure of the casting, study the heterogeneity of crystallization of the ingot and its
chemical heterogeneity (liquation).
help
magnifying glasses.
at
or
Using sulfur prints of macrosections on photographic paper, according to Bauman, it is determined
uneven distribution of sulfur over the cross section of the ingots. This method is of great importance
research has in the study of forged or stamped blanks for
determining the correct direction of fibers in the metal.
3. Microstructure is one of the main methods in metallurgy.
study of metal microstructure using metallographic and electronic
microscopes.
This method makes it possible to study the microstructure of metal objects with large
magnifications: from 50 to 2000 times on an optical metallographic microscope and from
2 to 200 thousand times on an electron microscope. Microstructure Study
produced on polished sections. On unetched sections, the presence of
non-metallic inclusions, such as oxides, sulfides, small slag inclusions
and other inclusions that differ sharply from the nature of the base metal.
The microstructure of metals and alloys is studied using etched sections. Etching
usually produced with weak acids, alkalis or other solutions, depending
from the nature of the metal section. The effect of etching is that it varies
dissolves various structural components, coloring them in different tones or
colors. Grain boundaries that differ from the main solution usually have etchability
different from the base and stands out on the thin section in the form of dark or light lines.
Grain polyhedra visible under a microscope are cross sections of grains
grinding surface. Since this section is random and can take place at different
distances from the center of each individual grain, then the difference in the sizes of the polyhedra is not
corresponds to actual differences in grain sizes. The closest value to
6
The actual grain size is the largest grain.
When etching a sample consisting of homogeneous crystalline grains,
for example, pure metal, homogeneous solid solution, etc. is often observed
Differently etched surfaces of different grains.
This phenomenon is explained by the fact that grains with
different crystallographic orientation, resulting in the degree of impact
acids on these grains turn out to be different. Some grains look shiny, others
strongly etched and darkened. This darkening is associated with the formation of various
etched figures that reflect light rays differently. In the case of alloys, individual
structural components form a microrelief on the surface of the thin section, which has
areas with different inclinations of individual surfaces.
Normally located areas reflect the greatest amount of light and
appear to be the brightest. Other areas are darker. Often the contrast in
image of the grain structure is associated not with the structure of the grain surface, but with
relief at grain boundaries. In addition, different shades of structural components
may be the result of the formation of films formed during the interaction
etchant with structural components.
With the help of metallographic examination it is possible to carry out qualitative
identification of structural components of alloys and quantitative study of microstructures
metals
studied
microcomponents of structures and, secondly, special methods of quantitative
metallography.
firstly, by comparison
with famous
alloys,
And
The grain size is determined. By visual assessment method, which consists in the fact that
the microstructure under consideration is approximately assessed by points of standard scales
according to GOST 563968, GOST 564068. According to the corresponding tables, for each point
The area of one grain and the number of grains per 1 mm2 and 1 mm3 are determined.
The method of counting the number of grains per unit surface of a polished section according to
corresponding formulas. If S is the area on which the quantity is counted
grains n, and M is the magnification of the microscope, then the average grain size in the cross-section of the surface
polished section
Determination of phase composition. The phase composition of the alloy is more often assessed by eye or
by comparing the structure with standard scales.
An approximate method for quantifying phase composition can be
carried out using the secant method with calculation of the length of segments occupied by different
structural components. The ratio of these segments corresponds to the volumetric
content of individual components.
Point method A.A. Glagoleva. This method is carried out by assessing
number of points (points of intersection of the microscope eyepiece grid) falling on
surfaces of each structural component. In addition, using the method of quantitative
metallography produces: determination of the size of the interface between phases and grains;
determination of the number of particles in a volume; determination of grain orientation in polycrystalline
samples.
4. Electronic
microscopy. Big
in metallographic
Research has recently been carried out using an electron microscope. Undoubtedly he
has a great future. If the resolution of an optical microscope
reaches values of 0.00015 mm = 1500 A, then the resolution of electronic
microscopes reaches 510 A, i.e. several hundred times more than optical.
meaning
An electron microscope is used to study thin films (replicas),
taken from the surface of a thin section or direct examination of thin metal
films obtained by thinning a massive sample.
7
Most in need of electron microscopy
studies of processes associated with the release of excess phases, for example, decomposition
supersaturated solid solutions during thermal or strain aging.
5. X-ray research methods. One of the most important methods in
establishing the crystallographic structure of various metals and alloys is
X-ray diffraction analysis. This research method makes it possible to determine
the nature of the relative arrangement of atoms in crystalline bodies, i.e. solve the problem
inaccessible to either a conventional or an electron microscope.
X-ray diffraction analysis is based on the interaction between
x-rays and the atoms of the body under study lying in their path, thanks to
to which the latter become, as it were, new sources of X-rays,
being the centers of their dispersion.
The scattering of rays by atoms can be likened to the reflection of these rays from atomic
crystal planes according to the laws of geometric optics.
X-rays are reflected not only from planes lying on
surface, but also from the deep. Reflecting from several equally oriented
planes, the reflected beam is intensified. Each plane of the crystal lattice
gives its own beam of reflected waves. Having received a certain alternation of reflected
X-ray beams at certain angles, the interplanar
distance, crystallographic indices of reflecting planes, ultimately
shape and dimensions of the crystal lattice.
Practical part
Contents of the report.
1. The report must indicate the title and purpose of the work.
2. List the basic physical properties of metals (with definitions).
3. Record Table 12 in your notebook. Draw conclusions from the tables.
4. Fill out the table: “Basic research methods in materials science.”
Method name
What is being studied
The essence of the method
Devices,
for research
necessary
Kink
Macrostructure
Microstructure
Electronic
microscopy
X-ray
research methods
8
Practical work No. 2
Topic: "Studying state diagrams"
Purpose of the work: to familiarize students with the main types of state diagrams,
their main lines, points, their meaning.
Work progress:
1.Study the theoretical part.
Theoretical part
A state diagram is a graphical representation of a state
any alloy of the system under study depending on concentration and temperature (see Fig.
1)
9
Fig.1 State diagram
State diagrams show stable states, i.e. states that
under given conditions they have a minimum free energy, and therefore it is also
is called an equilibrium diagram, since it shows what, under given conditions,
there are equilibrium phases.
The construction of state diagrams is most often carried out using
thermal analysis. As a result, a series of cooling curves are obtained, in which, at
temperatures of phase transformations, inflection points and temperature
stops.
Temperatures corresponding to phase transformations are called critical
dots. Some critical points have names, for example, points responsible
the beginning of crystallization is called liquidus points, and the end of crystallization is called liquidus points
solidus.
Based on the cooling curves, a composition diagram is constructed in coordinates: along the abscissa axis
concentration of components, temperature on the ordinate. The concentration scale shows
content of component B. The main lines are the liquidus (1) and solidus lines
(2), as well as lines corresponding to phase transformations in the solid state (3, 4).
From the phase diagram one can determine the temperatures of phase transformations,
change in phase composition, approximately, properties of the alloy, types of processing that
can be used for alloying.
Below are the different types of state diagrams:
10
Fig.2. Phase diagram of alloys with unlimited solubility
components in the solid state (a); typical cooling curves
alloys (b)
Analysis of the resulting diagram (Fig. 2).
1. Number of components: K = 2 (components A and B).
2. Number of phases: f = 2 (liquid phase L, solid solution crystals
3. Main lines of the diagram:
acb – liquidus line, above this line the alloys are in a liquid state;
adb is the solidus line; below this line the alloys are in the solid state.
Fig.3. State diagram of alloys with no solubility of components in
solid state (a) and cooling curves of alloys (b)
State diagram analysis (Fig. 3).
2. Number of phases: f = 3 (crystals of component A, crystals of component B, liquid phase).
3. Main lines of the diagram:
11
the solidus line ecf, parallel to the concentration axis, tends to the axes of the components, but
does not reach them;
Rice. 4. State diagram of alloys with limited solubility of components in
solid state (a) and cooling curves of typical alloys (b)
Analysis of the state diagram (Fig. 4).
1. Number of components: K = 2 (components A and B);
2. Number of phases: f = 3 (liquid phase and crystals of solid solutions
B in component A) and
(solution of component A in component B));
(component solution
3. Main lines of the diagram:
the liquidus line acb consists of two branches converging at one point;
solidus line adcfb, consists of three sections;
dm – line of the maximum concentration of component B in component A;
fn is the line of the maximum concentration of component A in component B.
Practical part
Assignment for students:
1. Write down the title of the job and its purpose.
2. Write down what a state diagram is.
Answer the questions:
1. How is a state diagram constructed?
2. What can be determined from a state diagram?
3. What are the names of the main points of the diagram?
4. What is indicated on the diagram along the x-axis? Y-axis?
5. What are the main lines of the diagram called?
Assignment by options:
Students answer the same questions, the drawings are different, according to
which need to be answered. Option 1 gives answers according to Figure 2, option 2 gives answers according to
Figure 3, option 3 gives answers according to Figure 4. The drawing must be recorded in a notebook.
1. What is the name of the diagram?
2. Name how many components are involved in the formation of the alloy?
12
3. What letters indicate the main lines of the diagram?
Practical work No. 3
Topic: “Study of cast irons”
cast iron; developing the ability to decipher cast iron grades.
Work progress:
Theoretical part
Cast iron differs from steel: its composition has a higher carbon content and
impurities; in terms of technological properties, higher casting properties, low
ability to undergo plastic deformation, almost never used in welded structures.
Depending on the state of carbon in cast iron, they are divided into: white cast iron -
carbon in a bound state in the form of cementite, when fractured it is white and
metallic shine; gray cast iron - all or most of the carbon is in
free state in the form of graphite, and in a bound state there is no more than 0.8
% carbon. Due to the large amount of graphite, its fracture has a gray color;
half - part of the carbon is in a free state in the form of graphite, but
at least 2% of the carbon is in the form of cementite. Little used in technology.
Depending on the form of graphite and the conditions of its formation, the following are distinguished:
cast iron groups: gray with lamellar graphite; high-strength with spherical
graphite; malleable with flake graphite.
Graphite inclusions can be considered as a corresponding form of void
in the structure of cast iron. Stresses are concentrated near such defects during loading,
the more acute the defect, the greater the value. It follows that graphite
plate-shaped inclusions soften the metal to the maximum extent. More
The flake shape is favorable, and the spherical shape of graphite is optimal.
Plasticity depends on shape in the same way. The presence of graphite is most pronounced
reduces resistance under severe loading methods: impact; gap Resistance
compression decreases little.
Gray cast iron
Gray cast iron is widely used in mechanical engineering because it is easy
processed and has good properties. Depending on strength gray
Cast iron is divided into 10 grades (GOST 1412).
Gray cast irons, with low tensile strength, have a fairly high
compression resistance. The structure of the metal base depends on the amount of carbon and
silicon
Considering the low tensile and tensile strength of gray cast iron castings
impact loads, this material should be used for parts that
are subject to compressive or bending loads. In machine tool building these are basic,
case parts, brackets, gears, guides; blocks in the automotive industry
cylinders, piston rings, camshafts, clutch discs. Castings from
gray cast iron is also used in electrical engineering, for the manufacture of goods
public consumption.
Marking of gray cast iron: indicated by the index SCh (gray cast iron) and the number
which shows the tensile strength value multiplied by 101.
13
For example: SCh 10 – gray cast iron, tensile strength 100 MPa.
Malleable iron
Good properties of castings are ensured if, during crystallization and
When the castings are cooled in the mold, the process of graphitization does not occur. To
to prevent graphitization, cast irons must have a low carbon content and
silicon
There are 7 grades of malleable cast iron: three with ferritic cast iron (CC 30 6) and four with
pearlite (CC 65 3) base (GOST 1215).
In terms of mechanical and technological properties, malleable cast iron ranks
intermediate position between gray cast iron and steel. Disadvantage of malleable cast iron
compared to high-strength is the limitation of the wall thickness for casting and
need for annealing.
Ductile iron castings are used for parts operating under impact and
vibration loads.
Gearbox housings, hubs, hooks, brackets,
clamps, couplings, flanges.
Made from pearlitic cast iron, characterized by high strength, sufficient
plasticity, they produce cardan shaft forks, links and rollers of conveyor chains,
brake pads.
Marking of malleable cast iron: indicated by the index KCH (malleable cast iron) and
numbers. The first number corresponds to the tensile strength multiplied by
101, the second number is the relative elongation.
For example: KCh 306 – malleable cast iron, tensile strength 300 MPa,
relative elongation 6%.
Ductile iron
These cast irons are obtained from gray cast irons as a result of modification with magnesium or
cerium Compared to gray cast iron, the mechanical properties are increased, this
caused by the lack of unevenness in stress distribution due to the spherical
forms of graphite.
These cast irons have high fluidity, linear shrinkage is about 1%.
Casting stresses in castings are slightly higher than for gray cast iron. Izza
high modulus of elasticity; sufficiently high machinability. Possess
satisfactory weldability.
Thin-walled castings (piston rings) are made from high-strength cast iron.
forging hammers, beds and frames of presses and rolling mills, molds,
tool holders, faceplates.
Castings of crankshafts weighing up to 2..3 tons, instead of forged steel shafts,
have a higher cyclic viscosity and are insensitive to
external
stress concentrators, have better anti-friction properties and
much cheaper.
Marking of high-strength cast iron: indicated by the HF index (high-strength
cast iron) and a number that shows the tensile strength value multiplied by 101.
For example: HF 50 – high-strength cast iron with tensile strength
500 MPa.
Assignment for students:
1. Write down the name of the work and its purpose.
Practical part
14
2. Describe the production of pig iron.
3.Fill out the table:
Properties of cast iron
Cast iron marking
Application of cast iron
Name of cast iron
1. Gray cast iron
2. Malleable cast irons
3.High strength
cast iron
Topic: “Study of carbon and alloy structural steels”
Practical work No. 4
Purpose of the work: to familiarize students with labeling and scope of application
decoding of markings
formation
skills
steels;
structural
structural steels.
Work progress:
1.Familiarize yourself with the theoretical part.
2. Complete the tasks of the practical part.
Theoretical part
Steel is an alloy of iron and carbon, which contains 0 carbon
2.14%. Steels are the most common materials. have good
cutting.
composition and type of processing.
divided into steels:
˗
Ordinary quality, content up to 0.06% sulfur and up to 0.07% phosphorus.
˗
Qualitative up to 0.035% sulfur and phosphorus each separately.
˗
High quality up to 0.025% sulfur and phosphorus.
˗
Particularly high quality, up to 0.025% phosphorus and up to 0.015% sulfur.
Deoxidation is the process of removing oxygen from steel, i.e. according to its degree
deoxidation, there are: calm steels, i.e., completely deoxidized; they became like that
are indicated by the letters "sp" at the end of the mark (sometimes the letters are omitted); boiling steel -
slightly deoxidized; are marked with the letters "kp"; semi-quiet steels occupying
intermediate position between the previous two; are designated by the letters "ps".
Ordinary quality steel is also divided according to supplies into 3 groups: steel
group A is supplied to consumers based on mechanical properties (such steel can
have a high content of sulfur or phosphorus); steel group B – according to chemical
composition; Group B steel – with guaranteed mechanical properties and chemical properties
composition.
Structural steels are intended for the manufacture of structures and machine parts
and instruments.
So in Russia and in the CIS countries (Ukraine, Kazakhstan, Belarus, etc.)
an alphanumeric system for designating steel grades and
15
˗
number.
˗
steel.
˗
steel is not installed.
˗
˗
˗
˗
˗
˗
˗
alloys, where, according to GOST, letters conventionally indicate the names of elements and methods
steel smelting, and in numbers
- content of elements. Until now
international standardization organizations have not developed a unified labeling system
steels
Marking of structural carbon steels
ordinary quality
Designated according to GOST 38094 with the letters “St” and a conventional brand number (from 0 to 6) in
depending on the chemical composition and mechanical properties.
The higher the carbon content and strength properties of steel, the more
The letter "G" after the brand number indicates a high content of manganese in
The steel group is indicated before the grade, with group “A” in the grade designation
To indicate the steel category, add a number at the end to the brand designation
corresponding to the category, the first category is usually not indicated.
For example:
˗
St1kp2 carbon steel of ordinary quality, boiling, grade No. 1,
the second category, supplied to consumers based on mechanical properties (group A);
VSt5G carbon steel of ordinary quality with increased
manganese content, calm, grade No. 5, first category with guaranteed
mechanical properties and chemical composition (group B);
VSt0 carbon steel of ordinary quality, grade number 0, group B,
first category (steel grades St0 and Bst0 are not separated by degree of deoxidation).
Marking of structural carbon quality steels
In accordance with GOST 105088, these steels are marked with two-digit numbers,
showing the average carbon content in hundredths of a percent: 05; 08 ; 10 ; 25;
40, 45, etc.
˗
For mild steels, letters are not added at the end of their names.
For example, 08kp, 10ps, 15, 18kp, 20, etc.
˗
The letter G in the steel grade indicates a high manganese content.
For example: 14G, 18G, etc.
˗
The most common group for the manufacture of machine parts (shafts, axles,
bushings, gears, etc.)
For example:
˗
10 – structural carbon quality steel, containing carbon
about 0.1%, calm
about 0.45%, calm
45 – structural carbon quality steel, containing carbon
18 kp – structural carbon quality steel containing
carbon about 0.18%, boiling
˗
14G – structural carbon quality steel with carbon content
about 0.14%, calm, with a high manganese content.
Marking of alloyed structural steels
˗
In accordance with GOST 454371, the names of such steels consist of numbers and letters.
˗
The first digits of the brand indicate the average carbon content in steel in hundredths
fractions of a percent.
˗
The letters indicate the main alloying elements included in the steel.
˗
The numbers after each letter indicate the approximate percentage
of the corresponding element, rounded to the nearest whole number, with the alloying content
16
˗
˗
˗
˗
˗
˗
Marking of other groups of structural steels
Spring steels.
˗
The main distinguishing feature of these steels is the carbon content in them should be
be about 0.8% (in this case, elastic properties appear in steels)
Springs and springs are made from carbon (65,70,75,80) and alloy
(65S2, 50HGS, 60S2HFA, 55HGR) structural steels
These steels are alloyed with elements that increase the elastic limit - silicon,
manganese, chromium, tungsten, vanadium, boron
For example: 60С2 – carbon spring structural steel with
carbon content about 0.65%, silicon about 2%.
GOST 80178 is marked with the letters “ШХ”, after which the content is indicated
Ball bearing steels
˗
chromium in tenths of a percent.
For steels subjected to electroslag remelting, the letter Ш is added
also at the end of their names with a dash.
For example: ШХ15, ШХ20СГ, ШХ4Ш.
˗
They are used to make parts for bearings, and they are also used to make
parts operating under high loads.
For example: ШХ15 – structural ball bearing steel containing
carbon 1%, chromium 1.5%
˗
GOST 141475 begin with the letter A (automatic).
˗
If the steel is alloyed with lead, then its name begins with the letters
Automatic steels
AC.
element up to 1.5%, the number following the corresponding letter is not indicated.
The letter A at the end of the brand indicates that the steel is high quality (with
reduced sulfur and phosphorus content)
˗
N – nickel, X – chromium, K – cobalt, M – molybdenum, V – tungsten, T – titanium, D
– copper, G – manganese, C – silicon.
For example:
˗
12Х2Н4А – structural alloy steel, high quality, with
carbon content about 0.12%, chromium about 2%, nickel about 4%
40ХН – structural alloy steel, with a carbon content of about 0.4%,
chromium and nickel up to 1.5%
To reflect the content of other elements in steels, the same
rules as for alloyed structural steels. For example: A20, A40G, AC14,
AS38HGM
For example: AC40 – automatic structural steel, containing carbon
0.4%, lead 0.150.3% (not indicated in the brand)
Practical part
Assignment for students:
2. Write down the main marking characteristics of all groups of structural steels
(ordinary quality, quality steels, alloyed structural steels,
spring-spring
steels, ball bearing steels, automatic steels), with
examples.
Assignment by options:
1.
Decipher the steel grades and write down the area of application of a particular
brand (i.e. what it is intended for manufacturing)
17
No. Assignment for option 1
St0
1
BSt3Gps
2
08
3
40
4
18Х2Н4МА
5
30ХГСА
6
70
7
55С2А
8
9
50HFA
10 ШХ4Ш
11
A40
Assignment for option 2
St3
VSt3ps
10
45
12ХН3А
38ХМУА
85
60С2Х2
55С2
ШХ20
A11
Practical work No. 5
Topic: “Study of carbon and alloy tool steels”
Purpose of the work: to familiarize students with labeling and scope of application
decoding of markings
formation
skills
structural
structural steels.
steels;
Work progress:
1.Familiarize yourself with the theoretical part.
2. Complete the practical part.
Steel is an alloy of iron and carbon, which contains 0 carbon
Theoretical part
2,14%.
Steels are the most common materials. have good
technological properties. Products are obtained as a result of pressure treatment and
cutting.
The advantage is the ability to obtain the desired set of properties by changing
composition and type of processing.
Depending on their purpose, steels are divided into 3 groups: structural,
tool and special purpose steels.
Quality depending on the content of harmful impurities: sulfur and phosphorus of steel
divided into: steel of ordinary quality, content up to 0.06% sulfur and up to 0.07%
phosphorus; qualitative up to 0.035% of sulfur and phosphorus each separately;
high quality up to 0.025% sulfur and phosphorus; especially high quality, up to 0.025%
phosphorus and up to 0.015% sulfur.
Tool steels are intended for the manufacture of various tools,
both for manual and mechanical processing.
Availability of a wide range of produced steels and alloys manufactured in
different countries, necessitated their identification, but until now
time there is no unified system for marking steels and alloys, which creates
certain difficulties for the metal trade.
Marking of carbon tool steels
˗
These steels, in accordance with GOST 143590, are divided into high-quality and
high quality.
18
High-quality steels are designated by the letter U (carbon) and a number indicating
average carbon content in steel, in tenths of a percent.
For example: U7, U8, U9, U10. U7 – carbon tool steel with
carbon content about 0.7%
The letter A is added to the designations of high-quality steels (U8A, U12A and
etc.). In addition, in the designations of both quality and high-quality
carbon tool steels may have the letter G indicating
increased manganese content in steel.
For example: U8G, U8GA. U8A – carbon tool steel with
carbon content about 0.8%, high quality.
They make tools for handwork (chisel, punch, scriber, etc.),
mechanical work at low speeds (drills).
Marking of alloy tool steels
Rules for the designation of tool alloy steels according to GOST 595073 in
basically the same as for structural alloys.
The difference lies only in the numbers indicating the mass fraction of carbon in
steel.
˗
˗
˗
˗
˗
˗
The percentage of carbon content is also indicated at the beginning of the name
steel, in tenths of a percent, and not in hundredths, as for structural alloys
steels
˗
If the carbon content in tool alloy steel is
about 1.0%, then the corresponding figure is usually not indicated at the beginning of its name.
Let's give examples: steel 4Х2В5МФ, ХВГ, ХВЧ.
˗
9Х5ВФ – alloyed tool steel, with a carbon content of about
0.9%, chromium about 5%, vanadium and tungsten up to 1%
Marking of high-alloy (high-speed)
tool steels
Designated by the letter “P”, the number following it indicates the percentage
tungsten content in it: Unlike alloy steels in the names
high-speed steels do not indicate the percentage of chromium, because it amounts to
about 4% in all steels, and carbon (it is proportional to the vanadium content).
˗
The letter F, indicating the presence of vanadium, is indicated only if
Vanadium content is more than 2.5%.
For example: R6M5, R18, R6 M5F3.
˗
Typically, high-performance tools are made from these steels: drills,
cutters, etc. (to reduce the cost, only the working part)
For example: R6M5K2 - high-speed steel, with a carbon content of about 1%,
tungsten about 6%, chromium about 4%, vanadium up to 2.5%, molybdenum about 5%, cobalt
about 2%.
Practical part
Assignment for students:
1. Write down the name of the work and its purpose.
2. Write down the basic principles of marking all groups of tool steels
(carbon, alloy, high alloy)
Assignment by options:
1. Decipher the steel grades and write down the scope of application of a particular grade
(i.e. what it is intended for making).
19
No. Assignment for option 1
1
2
3
4
5
6
U8
U13A
X
HVSG
P18
R6M5
Assignment for option 2
U9
U8A
9ХС
CHVG
P6
R6M5F3
Practical work No. 6
Topic: “Study of copper-based alloys: brass, bronze”
Purpose of the work: to familiarize students with labeling and scope of application
non-ferrous metals - copper and alloys based on it: brass and bronze; formation
skills in deciphering the markings of brass and bronze.
Recommendations for students: before starting the practical
parts of the assignment, carefully read the theoretical provisions, as well as lectures
in your workbook on this topic.
Work progress:
1.Familiarize yourself with the theoretical part.
2. Complete the practical part.
Theoretical part
Brass
Brasses can contain up to 45% zinc. Increased content
zinc up to 45% leads to an increase in tensile strength to 450 MPa. Maximum
ductility occurs at a zinc content of about 37%.
According to the method of manufacturing products, a distinction is made between wrought and cast brass.
Deformable brasses are marked with the letter L followed by a number,
showing the copper content as a percentage, for example, L62 brass contains 62% copper
and 38% zinc. If, in addition to copper and zinc, there are other elements, then they are placed
initial letters (O tin, C lead, F iron, F phosphorus, MC manganese, A
aluminum, zinc).
The number of these elements is indicated by the corresponding numbers after the number,
indicating the copper content, for example, the LAZh6011 alloy contains 60% copper, 1%
aluminum, 1% iron and 38% zinc.
Brasses have good corrosion resistance, which can be improved
additionally with a tin additive. Brass LO70 1 resistant against corrosion in sea water
20
and is called “marine brass”. The addition of nickel and iron increases the mechanical
strength up to 550 MPa.
Casting brasses are also marked with the letter L, after the letter designation
the main alloying element (zinc) and each subsequent one is given a number,
indicating its average content in the alloy. For example, brass LTs23A6Zh3Mts2
contains 23% zinc, 6% aluminum, 3% iron, 2% manganese. The best
Brass grade LTs16K4 has fluidity. Cast brasses include brass
type LS, LK, LA, LAZH, LAZHMts. Cast brasses are not prone to segregation and have
concentrated shrinkage, castings are obtained with high density.
Brasses are a good material for structures operating at
negative temperatures.
Alloys of copper with elements other than zinc are called bronzes. Bronze
Bronze
are divided into wrought and cast.
When marking deformable bronzes, the letters Br are placed first, then
letters indicating which elements, other than copper, are included in the alloy. After the letters come
numbers showing the content of components in the alloy. For example, brand BrOF101
means that bronze contains 10% tin, 1% phosphorus, and the rest copper.
Marking of cast bronzes also begins with the letters Br, then indicate
letter designations of alloying elements and a number indicating it
average content in the alloy. For example, bronze BrO3Ts12S5 contains 3% tin, 12
% zinc, 5% lead, the rest copper.
Tin bronzes When copper is fused with tin, solid solutions are formed. These
alloys are very prone to segregation due to the large temperature range
crystallization. Thanks to segregation, alloys with a tin content above 5% are
favorable for parts such as plain bearings: the soft phase ensures
good run-in, hard particles create wear resistance. That's why
Tin bronzes are good anti-friction materials.
Tin bronzes have low volumetric shrinkage (about 0.8%), therefore
used in artistic casting. The presence of phosphorus provides good
fluidity. Tin bronzes are divided into wrought and cast bronzes.
In wrought bronzes, the tin content should not exceed 6%, for
ensuring the necessary plasticity, BrOF6,50,15. Depending on the composition
deformable bronzes are characterized by high mechanical, anti-corrosion,
antifriction and elastic properties, and are used in various industries
industry. Rods, pipes, tape, and wire are made from these alloys.
Practical part
Assignment for students:
1. Write down the title and purpose of the work.
2.Fill out the table:
Name
alloy, it
definition
Basic
properties
alloy
Example
markings
Decoding
stamps
Region
applications
21
Practical work No. 7
Topic: “Study of aluminum alloys”
Purpose of the work: to familiarize students with labeling and scope of application
non-ferrous metals - aluminum and alloys based on it; study of application features
aluminum alloys depending on their composition.
Recommendations for students:
before you start
practical part of the task, carefully read the theoretical provisions, and
also lectures in your workbook on the topic.
Work progress:
1.Familiarize yourself with the theoretical part.
2. Complete the practical part.
Theoretical part
The principle of marking aluminum alloys. The type of alloy is indicated at the beginning: D
alloys such as duralumin; And technical aluminum; AK malleable aluminum
alloys; In high-strength alloys; AL casting alloys.
The following is the reference number of the alloy. The conditional number is followed by
designation characterizing the state of the alloy: M soft (annealed); T
heat treated (hardening plus aging); N cold-hardened; P –
semi-hardened.
According to their technological properties, alloys are divided into three groups: deformable
alloys that cannot be strengthened by heat treatment; wrought alloys, hardenable
heat treatment; casting alloys. Using powder metallurgy methods
produce sintered aluminum alloys (SAS) and sintered aluminum powder
alloys (SAP).
Wrought casting alloys that cannot be strengthened by heat treatment.
The strength of aluminum can be increased by alloying. In alloys that are not hardenable
heat treatment, introducing manganese or magnesium. The atoms of these elements are significantly
increase its strength, reducing ductility. Alloys are designated: with manganese AMts,
with magnesium AMg; After the designation of an element, its content is indicated (AMg3).
Magnesium acts only as a hardener, manganese strengthens and increases
corrosion resistance. The strength of alloys increases only as a result of deformation
in a cold state. The greater the degree of deformation, the more significant the increase
22
strength and reduced ductility. Depending on the degree of hardening, they distinguish
cold-worked and semi-hardened alloys (AMg3P).
These alloys are used for the manufacture of various welded fuel tanks,
nitric and other acids, light and medium loaded structures. Deformable
alloys strengthened by heat treatment.
Such alloys include duralumin (complex alloys of aluminum systems
copper magnesium or aluminum copper magnesium zinc). They have a reduced
corrosion resistance, to increase which manganese is introduced. Duralumins
are usually subjected to hardening at a temperature of 500°C and natural aging, which
preceded by a two to three hour incubation period. Maximum strength
achieved after 4.5 days. Duralumins are widely used in aircraft construction,
automotive industry, construction.
High-strength aging alloys are alloys that, in addition to copper and
magnesium contain zinc. Alloys V95, V96 have a tensile strength of about 650 MPa.
The main consumer is the aircraft industry (skin, stringers, spars).
at
Forging aluminum alloys AK, AK8 are used for the manufacture of forgings.
temperature 380-450oC, subjected to hardening from
Forgings
temperature 500560оС and aging at 150165оС for 6 hours.
are being manufactured
The composition of aluminum alloys additionally includes nickel, iron, titanium, which
increase the recrystallization temperature and heat resistance up to 300°C.
Manufacture of pistons, blades and discs of axial compressors, turbojet
engines.
Casting alloys
Casting alloys include alloys of the aluminum-silicon system (silumin),
containing 1013% silicon. Additive to magnesium and copper silumins promotes the effect
strengthening of cast alloys during aging. Titanium and zirconium grind the grain.
Manganese increases anti-corrosion properties. Nickel and iron increase
heat resistance.
Casting alloys are marked from AL2 to AL20. Silumins are widely used
for the manufacture of cast parts for devices and other medium and lightly loaded
parts, including thin-walled castings of complex shapes.
Practical part
Assignment for students:
1. Write down the title and purpose of the work.
2. Fill out the table:
Name
alloy, it
definition
Basic
properties
alloy
Example
markings
Decoding
stamps
Region
applications
23
Laboratory work No. 1
Topic: “Mechanical properties of metals and methods of studying them (hardness)”
Work progress:
1. Familiarize yourself with the theoretical principles.
2.Complete the teacher’s assignment.
3.Make a report according to the assignment.
Theoretical part
called
material
Hardness
ability
resist
penetration of another body into it. When testing for hardness, the body embedded in
material and called an indenter, must be harder, have certain
size and shape, should not receive residual deformation. Hardness tests
can be static and dynamic. The first type includes tests
by pressing method, to the second by impact pressing method. Besides,
There is a method for determining hardness by scratching - sclerometry.
Based on the hardness of the metal, you can get an idea of its level.
properties. For example, the higher the hardness determined by tip pressure, the
less ductility of the metal, and vice versa.
Hardness tests using the indentation method consist of placing a sample under
the action of the load presses the indenter (diamond, hardened steel, hard
alloy), having the shape of a ball, cone or pyramid. After removing the load on
the sample leaves an imprint, measuring the size of which (diameter, depth or
diagonal) and comparing it with the dimensions of the indenter and the magnitude of the load, one can judge
about the hardness of the metal.
Hardness is determined using special hardness testers. Most often
hardness is determined by the Brinell (GOST 901259) and Rockwell (GOST 901359) methods.
There are general requirements for sample preparation and testing
by these methods:
1. The surface of the sample must be clean and free of defects.
2. Samples must be of a certain thickness. After receiving the fingerprint
there should be no signs of deformation on the reverse side of the sample.
3. The sample should lie rigidly and stable on the table.
4. The load must act perpendicular to the surface of the sample.
Determination of Brinell hardness
The Brinell hardness of a metal is determined by pressing a hardened material into the sample.
24
steel ball (Fig. 1) with a diameter of 10; 5 or 2.5 mm and expressed by hardness number
NV obtained by dividing the applied load P in N or kgf (1Н = 0.1 kgf) by
surface area of the indentation formed on the sample F in mm
The Brinell hardness number HB is expressed as the ratio of the applied load F
to the area S of the spherical surface of the imprint (hole) on the measured surface.
HB =
, (Mpa),
D−√D2−d2
πD¿
F
S=2F
¿
Where
F – load, N;
S – area of the spherical surface of the print, mm2 (expressed through D and d);
D – ball diameter, mm;
d – imprint diameter, mm;
The magnitude of the load F, the diameter of the ball D and the duration of exposure
load
τ
, selected according to table 1.
Figure 1. Scheme of hardness measurement using the Brinell method.
a) Scheme of pressing the ball into the test metal
F load, D – ball diameter, dot – imprint diameter;
b) Measuring the diameter of the print with a magnifying glass (in the figure d=4.2 mm).
Table 1.
Selection of ball diameter, load and load holding time depending on
on the hardness and thickness of the sample
Diameter
ball D,
mm
Thickness
subject
sample, mm
Material
Ferrous metals
Interval
hardness in
units
Brinell,
MPa
14004500
more than 6
6…3
less than 3
more than 6
6…3
10
5
2,5
10
5
Less than 1400
Excerpt
under
load
With
, τ
10
Load
F, N (kgf)
29430
(3000)
7355 (750)
1840
(187,5)
9800
(1000)
25
Non-ferrous metals
and alloys (copper,
brass, bronze,
magnesium alloys
etc.)
3501300
Non-ferrous metals
(aluminum,
bearing
alloys, etc.)
80350
less than 3
more than 6
6…3
less than 3
more than 6
6…3
less than 3
2,5
10
5
2,5
10
5
2,5
2450 (750)
613 (62,5)
9800
(1000)
2450 (750)
613 (62,5)
2450 (250)
613 (62,5)
153,2
(15,6)
30
60
Figure 2 shows a diagram of a lever device. The sample is mounted on
object stage 4. Rotating the handwheel 3, use screw 2 to raise the sample until it touches
it with ball 5 and further until spring 7, placed on spindle 6, is completely compressed. Spring
creates a preliminary load on the ball equal to 1 kN (100 kgf), which ensures
stable position of the sample during loading. After that turn on
electric motor 13 and through the worm gear of the gearbox 12, connecting rod 11 and lever system
8,9, located in the housing 1 of the hardness tester with weights 10 creates a given full load
on the ball. A spherical imprint is obtained on the test sample. After unloading the device
The sample is removed and the diameter of the print is determined with a special magnifying glass. Per design diameter
fingerprint take the arithmetic mean of measurements in two mutually
perpendicular directions.
Figure 2. Diagram of the Brinell device
According to the above formula, using the measured diameter of the print,
the hardness number HB is calculated. Hardness number depending on the diameter of the resulting
The print can also be found in tables (see table of hardness numbers).
When measuring hardness with a ball with a diameter of D = 10.0 mm under a load F = 29430 N
HB 2335 MPa or according
= 10 s – the hardness number is written as follows:
τ
(3000 kgf), with holding time
old designation NV 238 (in kgf/mm2)
When measuring Brinell hardness, remember the following:
1.
It is possible to test materials with a hardness of no more than HB 4500 MPa, since when
With greater hardness of the sample, unacceptable deformation of the ball itself occurs;
2.
To avoid punching, the minimum thickness of the sample should not be
less than ten times the depth of the print;
26
3.
4.
four print diameters;
not less than 2.5 d.
The distance between the centers of two adjacent prints must be at least
The distance from the center of the print to the side surface of the sample should be
Rockwell hardness determination
According to the Rockwell method, the hardness of metals is determined by pressing into the test piece.
sample of a hardened steel ball with a diameter of 1.588 mm or a diamond cone with an angle at
top
loads:
preliminary Р0 = 10 kgf and total Р, equal to the sum of preliminary Р0 and
main P1 load (Fig. 3).
two in series
attached
action
120o under
The Rockwell hardness number HR is measured in conventional dimensionless units and
HRc = 100−
determined by the formulas:
h−h0
0.002 – when pressing in the diamond cone
h−h0
0.002 – when pressing a steel ball,
HRв = 130−
where 100 is the number of divisions of the black scale C, 130 is the number of divisions of the red scale B
indicator dial measuring the depth of indentation;
h0 – depth of indentation of a diamond cone or ball under the influence of
preload. Mm
h – depth of indentation of a diamond cone or ball under the action of a total load,
mm
0.002 – scale division value of the indicator dial (movement of the diamond cone
when measuring hardness by 0.002 mm corresponds to the movement of the indicator needle by
one division), mm
The type of tip and load value are selected according to Table 2, depending on
hardness and thickness of the test sample. .
The Rockwell hardness number (HR) is a measure of the indentation depth of the indenter and
expressed in conventional units. The unit of hardness is taken to be a dimensionless value,
corresponding to an axial movement of 0.002 mm. Rockwell hardness number
indicated directly by an arrow on the C or B scale of the indicator after automatic
removing the main load. The hardness of the same metal, determined by different
methods is expressed by different units of hardness.
For example, HB 2070, HRc 18 or HRв 95.
Figure 3. Rockwell hardness measurement scheme
27
View
finally
ika
General
load F,
N (kgf)
Minimum
thickness
sample
Designation
hardness according to
Rockwell
scale
Number
firmly
sti
IN
WITH
A
HRВ
Steel
ball
981 (100)
HRС
Almazny
th cone
1471 (150)
HRA
Almazny
th cone
588 (60)
0,7
0,7
0,4
Table 2
Limits
measurements
in units
Rockwell
25…100
on scale B
20…67
on a C scale
70…85
on scale B
Limits
measurements
hardness
sample in
units
Brinell, NV
From 500 to 2300
(unhardened
steel, non-ferrous
metals and their
alloys
from 2000 to 7000
(hardened
steel)
From 4000 to
9000 (details
exposed
cementation or
nitriding,
hard alloys
etc.)
The Rockwell method is simple and highly efficient, providing
maintaining a high-quality surface after testing, allows you to test metals and
alloys, both low and high hardness. This method is not recommended for
alloys with a heterogeneous structure (gray, malleable and high-strength cast irons,
antifriction bearing alloys, etc.).
Practical part
Contents of the report.
Answer the questions:
1. What is hardness called?
2. What is the essence of the definition of hardness?
3. What 2 methods for determining hardness do you know? What is their difference?
4. How should a sample be prepared for testing?
5. How to explain the lack of a universal method for determining hardness?
6. Why, of the many mechanical characteristics of materials, the most common
determine hardness?
7. Record in your notebook the scheme for determining hardness according to Brinell and Rockwell.
28
Laboratory work No. 2
Topic: “Mechanical properties of metals and methods of studying them (strength, elasticity)”
Purpose of the work: to study the mechanical properties of metals, methods for studying them.
Work progress:
1. Familiarize yourself with the theoretical principles.
2.Complete the teacher’s assignment.
3.Make a report according to the assignment.
Theoretical part
The main mechanical properties are strength, elasticity, viscosity,
the designer makes a reasonable choice
hardness.
appropriate material ensuring reliability and durability of structures when
their minimum mass.
Knowing the mechanical properties,
Mechanical properties determine the behavior of a material under deformation and
destruction from external loads. Depending on loading conditions
mechanical properties can be determined by:
1. During static loading, the load on the sample increases slowly and smoothly.
29
2. During dynamic loading, the load increases at high speed, has
shock character.
3. Repeatedly alternating or cyclic loading load in progress
test changes repeatedly in magnitude or in magnitude and direction.
To obtain comparable results, samples and methods
mechanical tests are regulated by GOSTs. When statically tested for
tensile: GOST 1497 obtains the characteristics of strength and ductility.
Strength is the ability of a material to resist deformation and destruction.
Plasticity is the ability of a material to change its size and shape under
influence of external forces; a measure of plasticity is the amount of residual deformation.
A device that determines strength and ductility is a tensile testing machine.
which records a stretch diagram (see Fig. 4), expressing the relationship between
elongation of the sample and the effective load.
Rice. 4. Tension diagram: a – absolute, b – relative.
Section oa in the diagram corresponds to elastic deformation of the material when
Hooke's law is observed. Stress corresponding to elastic limiting strain
at point a is called the limit of proportionality.
The proportional limit is the highest voltage until it reaches
which Hooke's law is valid.
At voltages above the proportionality limit, uniform
plastic deformation (elongation or narrowing of the section).
Point b – elastic limit – the greatest stress, before reaching which in
no residual deformation occurs in the sample.
Area cd is the yield area, it corresponds to the yield point – this is
stress at which an increase in strain occurs in the sample without an increase
load (material “flows”).
Many grades of steel and non-ferrous metals do not have a clearly defined area
fluidity, therefore a conditional yield limit is established for them. Conditional
yield strength is the stress that corresponds to permanent deformation
equal to 0.2% of the original length of the sample (alloy steel, bronze, duralumin and
other materials).
Point B corresponds to the ultimate strength (a local
thinning - neck; the formation of thinning is characteristic of plastic materials).
30
Tensile strength is the maximum stress that the sample can withstand
until resolution (temporary tensile strength).
Beyond point B, the load drops (due to neck elongation) and fracture
occurs at point K.
Practical part.
Contents of the report.
1. Indicate the title of the work and its purpose.
2. What mechanical properties do you know? What methods are used to determine
mechanical properties of materials?
3. Write down the definition of the concepts of strength and ductility. By what methods
are they defined? What is the name of the device that determines these properties? WITH
How are properties determined?
4. Record the absolute tension diagram of the plastic material.
5. After the diagram, indicate the names of all points and sections of the diagram.
6. What limit is the main characteristic when choosing a material for
manufacturing any product? Justify your answer.
7. Which materials are more reliable, brittle or ductile? Answer
justify.
References
Main:
1.
Adaskin A.M., Zuev V.M. Materials science (metalworking). – M.: JIC
"Academy", 2009 - 240 p.
FORUM, 2010 – 336 p.
2.
3.
Adaskin A.M., Zuev V.M. Materials science and technology of materials. – M.:
Chumachenko Yu.T. Materials science and plumbing (NPO and SPO). –
Rostov n/d.: Phoenix, 2013 – 395 p.
Additional:
1.
Zhukovets I.I. Mechanical testing of metals. – M.: Higher school, 1986. –
199 p.
2.
3.
Lakhtin Yu.M. Fundamentals of materials science. – M.: Metallurgy, 1988.
Lakhtin Yu.M., Leontyeva V.P. Materials Science. – M.: Mechanical Engineering, 1990.
31
Electronic resources:
1. Journal “Materials Science”. (Electronic resource) – access form
http://www.nait.ru/journals/index.php?p_journal_id=2.
2. Materials science: educational resource, access form http://
steels
(Electronic
resource)
–
form
access
www.supermetalloved/narod.ru.
3.
Vintage
www.splav.kharkov.com.
4. Federal Center for Information and Educational Resources. (Electronic
resource) – access form www.fcior.ru.
32
Subject:Study of the crystallization process of metals
Purpose of the work: study the mechanism of crystallization of metals, the energy conditions for the crystallization process.
Work order
1. Study theoretical information.
2. Answer test questions in writing in your notebook for practical work.
Theoretical information
A common property of metals and alloys is their crystalline structure, which is characterized by a certain arrangement of atoms in space. To describe the atomic-crystal structure, the concept of a crystal cell is used - the smallest volume, the translation of which in all dimensions can completely reproduce the structure of the crystal. In a real crystal, atoms or ions are brought close to each other to the point of direct contact, but for simplicity they are replaced by diagrams where the centers of attraction of atoms or ions are depicted by dots; The most typical cells for metals are shown in Fig. 1.1.
Fig.1.1. Types of crystal lattices and the arrangement of atoms in them:
a) face-centered (fcc), b) body-centered (bcc), c) hexagonal close-packed (HC)
Any substance can be in three states of aggregation: solid, liquid and gaseous, and the transition from one state to another occurs at a certain temperature and pressure. Most technological processes occur at atmospheric pressure, then phase transitions are characterized by the temperature of crystallization (melting), sublimation and boiling (evaporation).
As the temperature increases solid The mobility of atoms at the nodes of the crystal cell increases, and their vibration amplitude increases. When the melting point is reached, the energy of the atoms becomes sufficient to leave the cell - it collapses to form a liquid phase. Melting point is an important physical constant of materials. Among metals, mercury has the lowest melting point (-38.9 ° C), and tungsten has the highest (3410 ° C).
The opposite picture occurs when the liquid is cooled with its further solidification. Near the melting point, groups of atoms are formed, packed into cells, as in a solid. These groups are centers (nuclei) of crystallization; a layer of crystals then grows on them. When the same melting temperature is reached, the material transforms into a liquid state with the formation of a crystal lattice.
Crystallization is the transition of a metal from a liquid to a solid state at a certain temperature. According to the law of thermodynamics, any system tends to go into a state with a minimum value of free energy - composite internal energy, which can be isothermally converted into work. Therefore, a metal solidifies when there is less free energy in the solid state and melts when there is less free energy in the liquid state.
The crystallization process consists of two elementary processes: the nucleation of crystallization centers and the growth of crystals from these centers. As noted above, at a temperature close to crystallization, the formation of a new structure begins - a crystallization center. As the degree of supercooling increases, the number of such centers around which crystals begin to grow increases. At the same time, new crystallization centers are formed in the liquid phase, so the increase in the solid phase simultaneously occurs both due to the emergence of new centers and due to the growth of existing ones. The total rate of crystallization depends on the progress of both processes, and the rates of nucleation of centers and crystal growth depend on the degree of supercooling ΔT. In Fig. Figure 1.2 schematically shows the crystallization mechanism.
Rice. 1.2. Crystallization mechanism
Real crystals are called crystallites, they have irregular shape, which is explained by their simultaneous growth. Crystallization nuclei can be fluctuations of the base metal, impurities and various solid particles.
The grain sizes depend on the degree of supercooling: at low values of ΔT, the crystal growth rate is high, so a small number of large crystallites are formed. An increase in ΔT leads to an increase in the rate of nucleation formation, the number of crystallites increases significantly, and their sizes decrease. However, the main role in the formation of the metal structure is played by impurities (non-metallic inclusions, oxides, deoxidation products) - the more of them, the smaller sizes grains Sometimes the metal is specially modified - the deliberate introduction of impurities in order to reduce the grain size.
During the formation of a crystalline structure, the direction of heat removal plays an important role, because the crystal grows faster in this direction. The dependence of the growth rate on the direction leads to the formation of branched tree-like crystals - dendrites (Fig. 1.3).
Rice. 1.3 Dendritic crystal
During the transition from a liquid to a solid state, selective crystallization always takes place - the more solidified first pure metal. Therefore, grain boundaries are more enriched in impurities, and the heterogeneity of the chemical composition within the dendrites is called dendritic segregation.
In Fig. 1.4. shows the structure of a steel ingot, in which 3 characteristic zones can be distinguished: fine-grained 1, zone of columnar crystals 2 and zone of equilibrium crystals 3. Zone 1 consists of a large number of crystals not oriented in space, formed under the influence of a significant temperature difference between the liquid metal and the cold walls.
Rice. 1.4. Structure of a steel ingot
After the formation of the outer zone, the conditions for heat removal worsen, overcooling decreases, and fewer crystallization centers appear. From them, crystals begin to grow in the direction of heat removal (perpendicular to the walls of the mold), forming zone 2. In zone 3, there is no clear direction of heat removal, and the crystallization nuclei in it are foreign particles displaced during the crystallization of the previous zones.
Security questions
1. In what states of aggregation can a material exist?
2. What is called a phase transformation of the first kind?
3. What process is called crystallization, what type of phase transformation does it belong to?
4. Describe the mechanism of metal crystallization and the conditions necessary for its initiation.
5. What causes the dendritic shape of crystals?
6. Describe the structure of a metal ingot
