Grades and types of tool steel: description of carbon, alloy and high-speed

Tool steel is a material that consists of more than 0.7% carbon. Its key characteristics are hardness and strength, their maximum performance is achieved during heat treatment of steel. It is mainly used in the manufacture of various instruments.

This is the name given to steel containing more than 0.7% carbon. Its main characteristics are strength and hardness, which reach maximum values ​​after heat treatment. The main use of this steel material is in the manufacture of tools.

Tool steels and their characteristics

Man, having learned to combine iron and carbon, obtained a new material that opened up new possibilities and obtained previously unknown properties inherent in solid material. The instrumental form of steel has undergone significant changes, giving people the opportunity to use its new characteristics. Thus, components and parts of mechanisms subject to high mechanical loads must be highly wear-resistant and durable. This implies the use of steels other than structural-tool steels.

Application of tool steels

Steels of this type are characterized by the presence of carbon in their composition. Its critical content is usually about 0.7%. According to their structure, they can be of the following types: hypoeutectoid, ledeberite, hypereutectoid.

The composition also contains secondary carbides that affect the internal structure. This does not apply to alloys with a hypoeutecloid structure. However, in other types it is mandatory. They are a product of martensite splitting or arise during eutectoid changes.

Tool steels are widely used in the national economy. They are used when releasing:

• surfaces of stamps to change the shape of parts at contrasting temperatures;
• cutting devices;
• measuring instruments;
• Pressure foundry equipment.

For tool steels, depending on the area of ​​their use, certain requirements are established. Each of them is taken into account during production, but there are also those that are common. Their list includes the following types of indicators:

• high percentage of viscosity. This is especially important for products that will subsequently be subject to significant mechanical stress during operation;
• strength indicator;
• long service life;
• high hardness coefficient.

Each of the existing grades of steel used during deformation at low temperatures must have the following distinctive characteristics: a smooth, rough-free main part related to the working surface, the ability to maintain a stable shape, and no deformation. Fluidity, elasticity, and reaching a certain limit are also important.

The type of steel that is used in the process of changing shapes using the technology of increasing temperature (thermal deformation) must have the following properties: an increased level of thermal conductivity, immunity to tempering, resistance to extreme temperature changes. Requirements also exist for those grades of steel that are manufactured specifically for the production of cutting devices.

Material requirements

Requirements for these materials depend on how exactly they will be used. But there are general requirements for them, regardless of brand:

• high level of hardness;
• high level of strength;
• wear resistance;
• good viscosity, which is especially important in the manufacture of parts that will be subject to shock during use;
• low level of sensitivity to overheating, adhesion and welding processes to parts that are subject to processing;
• good level of processing through metal cutting;
• resistance to cracks;
• susceptibility to calcination;
• hot plasticity;
• possibility of grinding;
• the ability to resist decarbonization.

Naturally, these are not all the requirements. Thus, grades that are intended for use in cold deformation conditions must additionally have a smooth working surface, retain their shape and size, and have a yield and elasticity limit. And those materials that must be used under conditions of hot deformation must have high thermal conductivity, prevent tempering and be resistant to temperature fluctuations.

Technical requirements

Carbon tool steels must meet the following conditions:

• Easy to process with metal-cutting equipment.
• Do not react to elevated temperatures.
• Maintain stability when attached and glued to other parts during processing.
• Good workability when sanding.
• Positively amenable to calcination.
• Maintain plasticity when heated.
• Maintain carbon in the composition and minimize its release.
• Do not cause cracks in the final product.

Types of tool steels

Manufacturers of tool steels offer five types of such material for the production sector related to the manufacture of tools.

Heat-resistant and tough tool steels

These include hypereutectoid and hypoeutectoid steels. In their composition, the carbon index should be between minimum and average values. The presence of molybdenum, tungsten and chromium atoms in such alloy steels is mandatory.

Particularly hard, tough, non-heat-resistant steels

A distinctive feature of tool grade steels is a small amount of alloyed substances and a significantly larger amount of carbon. Hence the resistance to calcination.

Particularly hard, heat-resistant, wear-resistant tool steels

This type includes fast cutting steels. They contain the maximum amount of alloying elements, in addition, there are alloys with a ledeburite composition (carbon content of three percent).

Wear-resistant, particularly hard, medium-heat-resistant alloys

These are steels with a hypereutecloid and ledeburite composition. Components 2 – 3% carbon. Limits for chromium from 5 – 12%.

Particularly hard, non-heat-resistant types of tool steels

These types of steels with a hypereutecloid composition contain no alloyed substances or relatively few of them. The degree of strength in this composition is influenced by the carbon content. The more atoms there are in the crystal lattice, the better for the properties of hardness and strength. This type of material is not in demand in the manufacture of tools that are subject to shocks and other significant physical stress during operation. These alloys have minimal viscosity and high fragility, which reduces the service life of the tool.

According to the hardness characteristics, all types of tool steels can be divided into the following types:

• containing carbon in an amount of 0.4 - 0.7% (increased viscosity);
• with the presence of carbon 0.7 - 1.5% (increased wear resistance and hardness).

Steel grades are distinguished by types of calcination level. Therefore, in principle, alloy steels are divided into three types:

• increased hardenability (applicable diameter for hardening from 8 cm to 10 cm);
• normal (diameter 5 – 8 cm);
• reduced (the value is within 1 cm and up to 2.5 cm).

General information

Steel, the percentage of carbon in which is more than 0.7%, is called tool steel. The phase structure is based on martensite and only in some cases ladyburite.

It is used mainly in mechanical engineering as a material for the production of tools for processing ferrous and non-ferrous alloys.

Tool steel has a number of features compared to structural steel. Among them, the most important are:

• Increased hardness, which is 60-65 units on the Rockwell scale.
• Extra strength. The tensile strength should not be lower than 900 MPa.
• Ability to resist abrasive wear.
• High hardenability is the property of steels to be thermally hardened.
• Red resistance, which characterizes a metal in terms of its ability to maintain its strength characteristics with increasing temperature exposure to it.

According to state standards, the following types of tool grades are provided, based on their technological purpose:

• Tool carbon steels GOST 1435-99. Marked with the letter “U” at the beginning of the marking. The number that follows in the designation shows the carbon component: U12, U10, etc. The dimension is taken in hundredths of a percent. The letter “A” may be placed at the end (for example, U10A), which indicates that this tool steel has a reduced number of negative inclusions. In particular, this applies to sulfur and phosphorus, elements responsible for the deterioration of the mechanical properties of the steel alloy.
• Alloyed tool steels GOST 5950-2000. The number at the beginning shows one hundredth of a percent of carbides in steel. If it is absent, the value of this parameter is assumed to be 1%. This is followed by the letter designation of alloying elements with numbers indicating their content in whole fractions of a percent: X, 5ХВГ, 9ХС and so on.
• High-speed tool steels GOST 19265-73. In technical documentation they are marked with the letter “P”. The number behind it indicates the approximate content of tungsten, the basic chemical component for this steel. In addition to it, high-speed cutters can contain cobalt and vanadium. They are also indicated in the marking with the corresponding letters: K and F. The chromium content in all high-speed steels ranges from 3-4%. For this reason, it is not indicated in the labeling.
• Stamped tool steels GOST 1265-74. This type of steel is marked similarly to alloyed steel. Depending on the nature of their application, they can be cold- and hot-formed stamped steels.

Tool steels and alloys

Carbon cutting steel. The first material used for the production of cutting tools was carbon cutting steel; this material has been known for a long time, is well studied and represents the following steel grades: U9A, U10A, U12A and U13A, the number in which indicates tenths of a percent of carbon in its composition. The material is hardened to a hardness of 61 - 63 HRC. The mechanical strength of cutting tools made of this material is quite high, but this material has the shortest service life of all known tool steels and alloys due to its low heat resistance and wear resistance.

Low-alloy tool steels are carbon tool steels with a low content (up to 1%) of alloying additives, such as vanadium, silicon, tungsten, manganese, chromium. This cutting material is marked accordingly, for example: Х6ВФ, 95ХГСВФ, 9ХС, ХВГ. These grades are also the most widely used of this group and are hardened to a hardness of 65 HRC. Increased wear resistance, compared to conventional carbon steels, and equally low heat resistance of 250-350 ° C - does not allow processing hard materials and alloys. These characteristics allow us to produce standard hand and machine tools for non-responsible and low-precision work, for processing materials at low speeds and low loads. The advantage is the low cost of manufacturing cutting material from carbon and low-alloy carbon steels.

High-alloy tool steel - made on the basis of high-carbon high-speed steel with a carbon content (C) of 0.7-1.4% with a significant content of carbides (chromium carbide, molybdenum carbide, vanadium carbide, tungsten carbide) - this significantly increases the heat resistance of the material (up to 670 °C), increases tool strength and wear resistance. These characteristics make it possible to increase the processing speed by 2-4 times compared to previous materials in this group (US and NLIS). Below we provide a grouped list of high-alloy tool steels in chronological order that appeared in the tool industry with a description of their characteristics:

• P9 and P18 are grades of high-speed tool steel that first appeared in production. The chemical composition of high-speed steel P9 is 0.8% carbon, 4% chromium, 9% tungsten, 2% vanadium. The chemical composition of high-speed steel P18 is 0.8% carbon, 4% chromium, 18% tungsten, 1% vanadium. They have equally high heat resistance. Increased wear resistance of high-speed steel P18 by 2 times compared to P9 due to the higher content of free carbides (about 3 times). P18 sands much better than P9 and burns less*. In view of all these advantages and positive qualities, it has long been accepted to consider P18 high-speed steel as a standard, in comparison with which other grades of cutting material in this group are evaluated.
• In an attempt to reduce the consumption of expensive tungsten and increase the cutting properties of cutting tools, scientists and engineers at domestic research institutes have developed many grades of molybdenum cutting steels: R9M4, R6M5, R6M3; cobalt cutting steels: R9K10, R9K5; vanadium cutting steels: R18F2, R14F4, R12F3, R9F5; and high-speed steels with a combination of alloying additives: R18F2K5, R12F2M3K8, R12F4K5, R6M5K5. These grades of high-speed steels, there are more than 40 types in total, are divided according to performance and heat resistance into groups: normal, increased and high: Cutting steel with normal heat resistance is tool steel containing tungsten P9, P12 and P18, as well as their modern analogues - P6M5 (imported analogue - HSS), Р6М3.
• Cutting steel with increased heat resistance is a tool steel containing 2% molybdenum, 2% to 4% tungsten with 6% - 8% vanadium, or 9% - 10% tungsten with 4% - 5% vanadium. This group also includes steels with alloying additives in the form of 5% cobalt, 3.5% - 4% vanadium and ≤ 12% tungsten. And also steels with 6% - 8% cobalt, 1.5% - 2% vanadium and ≤ 10% tungsten. Examples - R6M5K5 (HSS Co), R6M5K8, R9K5.
• High heat resistant cutting steel is a high alloy carbon steel containing ≥ 12% cobalt, ≤ 18% tungsten and ≤ 3.5% vanadium. In some brands, the share of tungsten is reduced to ≤ 14% by introducing an additional amount of molybdenum.

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All tools for working on machine tools are mainly made of high-speed steels. Technologists and managers of metalworking organizations are required to understand the grades of high-speed steel, their characteristics and the properties of alloying additives, since this data will allow them to reasonably approach the choice of a grade of high-speed steel that will be optimal for specific operating conditions and the material being processed. This choice can be made only on the basis of the technological and operational properties determined by the alloying additives included in the composition of high-speed steels.

The influence of alloying additives of cobalt, vanadium, molybdenum and tungsten on the properties of high-speed steel

• Tungsten is an alloying additive that gives high-speed steel heat resistance, increases wear resistance and significantly increases hardness. High-speed steel P18, which contains 18% tungsten in free form and is taken as the standard, is perfectly hardened and ground. High heat resistance (≤620°C) in relation to carbon and low-alloy carbon steels is due to the high tungsten content. Tungsten slightly reduces strength and thermal conductivity. Steel P18 is less ductile than P9 and P12. High carbide heterogeneity (it has slightly larger carbide segregations), therefore it is less plastic than the same P9 and P12 and is more difficult to process under pressure in a heated state.
• Molybdenum is an alloying additive for high-speed steel with more pronounced characteristics than tungsten. The molybdenum content in steel is reduced by 1.5 times compared to tungsten, while maintaining the same level of heat resistance. Steel containing molybdenum in the hot state is more ductile than steel containing tungsten, and it is easier to process using pressing and forging equipment. In addition, molybdenum significantly increases thermal conductivity (heat removal from the working area). Increased strength in steels with molybdenum content ≤5%. Carbide heterogeneity in steels with molybdenum is less, and the quenching temperature range increases. The downside is decarburization when heated before hardening.
• Vanadium is an alloying additive for high-speed steel, which gives it increased hardness (≤ 67 HRC) and increases heat resistance (≤ 635 ° C). Somewhat negatively affects such indicators as fragility, strength and thermal conductivity. Vanadium in steel worsens the grindability due to the tendency of these steels to burn*, which depends on the concentration of vanadium carbides, since they have low thermal conductivity and are harder than the base composition of the steel; the more vanadium, the worse in this sense.
• Cobalt - as an alloying additive in high-speed steel, forms finely dispersed intermetallic compounds in its composition, and not carbides as with chromium, molybdenum, vanadium and tungsten, which increases heat resistance to 670 ° C and hardness to 65 HRC. Cobalt significantly increases thermal conductivity, surpassing molybdenum in this indicator. High-speed steel with cobalt, for example R6M5K5 (imported analogue - HSS-Co), grinds better than vanadium steels. Despite these positive characteristics, cobalt reduces strength and increases fragility, high carbide-intermetallic heterogeneity. In addition, cobalt drills are almost 100% more expensive than P18 drills.

The use of cutting tools made from steels with increased and high heat resistance is rational only when working at high speeds and processing difficult-to-cut materials, since only in this case can one gain an advantage due to a faster processing speed (3-4 times faster) than with tools made from high-speed steels. steels of normal heat resistance. Steels of normal heat resistance have a number of advantages - low price, higher strength, easier to process. It is very important to take into account the professionalism and equipment of the production site with all the necessary tools to perform the work and sharpen. If the recommendations for hardening, tempering, sharpening and grinding are violated, the advantages of such steels will not be realized, in addition, the tool will be damaged (the characteristics of the tool will become worse than those of a tool made of cutting steel with normal thermal conductivity) and costs will increase.

Additionally, the cutting properties of steel can be increased by adding nitrogen to their composition in an amount of 0.06% - 0.09%. It is marked very simply, with the letter A, for example: P6M5 - P6AM5 (AP6M5), AP18, AP12. The introduction of nitrogen into the composition of high-speed steel increases the hardness by 1-2 HRC and increases the cutting properties by 20% - 30%.

The use of powder metallurgy technology in the production of cutting tools significantly increases the properties of high-speed steels. The process consists of pressing from powder, rolling and at the end of the process - forging the workpiece (hardening and shaping). This technology makes it possible to obtain cutting steel that is more homogeneous in its structure, reduce deformation during heat treatment and improve the wear resistance of the tool by up to 2 times.

Since tungsten has limited reserves on Earth and the process of obtaining tungsten is quite expensive, the world, as well as our country, began to develop tungsten-free grades of cutting steel, such as: EK-42, EK-41, 11M5F, etc. These grades of cutting steel are similar in their characteristics to grade R6M5.

Relatively recently, carbon-free highly alloyed alloys (dispersion-hardening DTS) with a carbon content of up to 0.06% have appeared, for example: V16M4K16Kh4N2, ZV20K20Kh4, R10M5K25, R18M7K25, R18MZK25. Dispersion hardening of these alloys during quenching and tempering leads to an increase in hardness to 69 HRC and heat resistance ≤ 720 °C. Having high strength ≤2000 N/mm2, cutting tools made from this material are used to work with difficult-to-cut materials, and the cutting speed increases by 1.5-2 times in comparison with P18 high-speed steel. It is economically inexpedient to process carbon and moderately alloyed structural materials with tools made from DTS, since they have a high cost and when processing ordinary materials, their properties appear at the level of R18F2 and R9K5, no more.

High speed tool steel

High-speed tool steels are distinguished from all the types of tool steel alloys presented above by their higher red resistance. These alloys do not change their mechanical characteristics at temperatures up to 650 ºС. As a result, cutting speed increases by 5 times, and tool life increases by 32 times.

This became possible due to the inclusion of tungsten or its analogue of molybdenum in their chemical composition. Also, the addition of metals such as cobalt, vanadium and chromium to steel has a positive effect on heat resistance. The most popular brands in the mechanical and machine tool industry are R18, R12, R6M4 and R10K5F5. Of this group of tool steels, it is worth noting P12, because it has better manufacturability: it is more amenable to pressure treatment.

Thermal treatment of these steel alloys includes hardening at 1250 ºС and repeated low tempering at 350 ºС. Exceeding the specified temperatures is extremely undesirable, because this leads to a sharp decrease in mechanical characteristics, in particular the formation of brittleness. Sometimes, to improve the corrosion-resistant properties, high-speed cutters are additionally treated with steam.

Stamped steel

Stamped tool steel is used in the production of dies and punches. As mentioned earlier, it is divided into cold and hot deformed steel.

Cold-formed tool steel operates at a temperature of 250-300 ºС. These include X12M and X12F1, which are based on the ladyburite phase structure. Their difference is the high value of hardenability, red-hardness and hardness (64 HRC). They are used to make massive dies of complex shapes, rollers for thread rolling, etc.

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Hot stamped steels work with hotter metal, the temperature of which can reach up to 550 ºC. Therefore, among other things, they must have heat resistance - the ability to withstand repeated overheating without cracking. The most popular brands here are 5ХНМ and ХГМ.

Tool steels at one time made a technological breakthrough in the field of metal processing. Their use made it possible to increase the cutting speed by almost 5 times. But progress does not stand still. Now they are becoming less and less relevant. Especially against the backdrop of news about the improvement of ceramic alloys.

Marking of tool steels

The concept of marking is necessary to establish the grade of tool steel. In its name, every letter and number has a meaning.

The system is simple. The key symbol in the signs is the letter “U”. This is a sign of carbon content.

It may be insignificant, tenths of a percent. The numbers that are written after the letter designation indicate its quantity. Maybe the letter "A". Its presence indicates a high level of quality. Writing the letter “P” is mandatory for high-speed alloys. Tungsten is the leading substance. Its content and quantity are indicated by the numbers after the letter “P”. The amount of other constituent substances in high-speed steels (molybdenum, vanadium, cobalt) is indicated by the values ​​​​behind their initial letters in the marking. In addition, the composition also contains chromium. Its amount is much lower, but mandatory (no more than 4%).

The presence of carbon in the composition is indicated by a number, which is almost always found in the marking before the letters X, XC. This is what they write if there is little carbon, no more than a percent; if the value is less, there may be no designation at all. In the marking, after the letters naming the alloying element, there are numbers indicating the presence of other elements, indicated by whole fractions.

Stamped steel

Stamped tool steel is used in the production of dies and punches. As mentioned earlier, it is divided into cold and hot deformed steel.

Cold-formed tool steel operates at a temperature of 250-300 ºС. These include X12M and X12F1, which are based on the ladyburite phase structure. Their difference is the high value of hardenability, red-hardness and hardness (64 HRC). They are used to make massive dies of complex shapes, rollers for thread rolling, etc.

Hot stamped steels work with hotter metal, the temperature of which can reach up to 550 ºC. Therefore, among other things, they must have heat resistance - the ability to withstand repeated overheating without cracking. The most popular brands here are 5ХНМ and ХГМ.

Tool steels at one time made a technological breakthrough in the field of metal processing. Their use made it possible to increase the cutting speed by almost 5 times. But progress does not stand still. Now they are becoming less and less relevant. Especially against the backdrop of news about the improvement of ceramic alloys.

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Hardening and tempering of alloys for tool steels

The percentage of substances in tool steels, the main parameters are specified in GOST 1435. According to the grade of tool steel, the percentage of carbon is within 0.65 - 1.35%

To make a tool, it is necessary to improve the properties of tool steel (increase the strength index). This is achieved by the annealing process. Spherodizing annealing is used only for alloys with a hypereutectoid constitution. This type of thermal process contributes to the formation of cementite with a granular structure.

The required volume of grains is achieved by cooling technology. This is achieved quickly and the process can be adjusted.

By performing the process at 290 degrees, a better degree of hardness can be achieved (56 - 58 HRC). Hardness indicators are also needed for tool steel in the production of tools. Made from such material, it can be subject to significant loads and withstand them while in use for a long time. In the manufacture of such types of tools as dies, engraving tools, files, the indicators are overestimated by about 63 according to the requirements of the HRC scale.

During the tempering process, temperature limits are maintained within 150 to 200 degrees Celsius. The hardening process increases the strength of carbon steels. In addition, it becomes possible to achieve the best combination of iron and carbon. The types of such connections can be as follows:

• carbides with martensite;
• martensite

Tool carbon steel

This class in mechanical engineering is used as a material for the production of cutting tools with a minimum overall size of no more than 13 mm. The reason for this limitation lies in their limited hardenability. Larger overall dimensions are only possible if most of the cutting edge is on the surface (short drills, countersinks, etc.).

For most cutting tools - countersinks, hacksaws and cutters - U13, U11 and U10 steels are used. If the steel alloy operates under conditions of strong impact, it is recommended to use grades of type and U7. They have a high impact strength coefficient and, accordingly, are able to withstand large dynamic loads.

The advantages of tool steels of this class are low price, acceptable cutability in the annealed state and moderate hardness. To improve their mechanical properties, various types of heat treatment are used. First of all, this is quenching in a saline solution or water at 820 ºС plus low tempering, the main purpose of which is to relieve internal stresses.

The main disadvantage of carbon tool steel is the narrow range of hardening temperatures, which increases the internal deformation of the steel during heat treatment. For this reason, the use of these alloys is limited to tools operating at low cutting speeds and heating temperatures up to 220 ºС.

Tool stamping steel

Processing of metal products manufactured by physical change of shape (deformation) occurs in heated or cold form. Therefore, dies for such production processes are classified into cold and hot deformed. It is clear that in the manufacture of various types of dies, tool alloys of various grades are used.

Carbon steels U 10, U 11, U 12 are used for thin cold-formed dies (width up to 25 mm). The hardness of these types of steels ranges from 57 to 59 HRC units, the viscosity criterion is at a high level, and the resistance to plastic physical loads is quite high. The degree of strength allows you to withstand possible force impacts, preventing damage during operation.

For larger devices (volume more than 25 mm), subject to maximum loads during use, alloys with a high chromium composition (X9, X, XGBF) are used.

Alloys used for the manufacture of structural parts, the tools themselves, and assemblies that are subject to significant mechanical stress during operation must be particularly viscous (4ХС4 and 5ХНМ).

To perform such tasks it is necessary to ensure:

• low carbon content in the alloy;
• adding special substances.

A prerequisite is high-temperature processing of all types of tool steels.

The surfaces of dies operating at high temperatures and with high mechanical forces are subject to serious testing. This imposes a number of serious requirements when choosing alloys for the production of these dies:

• resistance to the formation of minor mechanical damage due to temperature changes (cold and heating);
• increased degree of heating and heat conduction;
• resistance to scale.

Various requirements, compliance with the prescribed requirements ensures that only high-quality material is obtained and its further long-term use.

Advantages and range

Tool steel is one of the most popular materials on the market. The alloy has high hardness and low cost. However, the material also has a drawback - its low wear resistance, so it is not used for the production of machine parts and equipment that are subject to constant loads.

The range of this material is as follows:

• hot rolled squares and circles;
• forged strips, circles and squares.

Grades and chemical composition of tool steels according to smelting analysis

STEEL FOR MEASURING TOOLS

Steels for measuring instruments are subject to a set of requirements, the most important of which are: high wear resistance, maintaining constant linear dimensions and shape during operation, high surface cleanliness (high polishability).

Steel, which has high hardness after quenching and low tempering, experiences transformations (aging) over time, as a result of which the volume and original shape of the products change. The absolute value of changes in linear dimensions often does not exceed several microns, which, however, may be unacceptable for measuring instruments of a high accuracy class. Aging causes the following processes, occurring both isothermally and depending on temperature changes within climatic fluctuations:

1) martensitic transformation of some part of the retained austenite;

2) reducing the degree of tetragonality of martensite and the release of fine carbide particles;

3) redistribution in the volume of the tool and reduction of residual stresses due to the partial transition of elastic deformation to plastic (relaxation).

The first process increases the volume, the second reduces it, the third process develops depending on the conditions of stress distribution, the shape and size of the tool and often reduces the dimensions along the longest length.

Cold treatment after hardening is an effective method to reduce subsequent aging.

For steel ШХ-15, quenching is carried out in oil from 840-860°C and tempering at a temperature of 150-170°C, 1-2 hours. Before tempering, to reduce the amount of retained austenite, the tool is cooled to a temperature not higher than 20-25°C. This improves dimensional stability. The structure is tempered fine-acicular martensite with a uniform distribution of excess carbides and some retained austenite (8-15%). Then cold treatment is carried out to eliminate retained austenite, which can transform into martensite during operation and change dimensions.

For measuring instruments, steels X, KhG, KhVG are used after hardening and special low tempering at 120-130°C, followed by cold treatment (up to -70°C) to reduce the amount of retained austenite. In some cases, it is recommended to repeat the cold treatment and tempering six times, and the amount of retained austenite is reduced several times.

To manufacture tools with high hardness and wear resistance, as well as with slight deformation during hardening, steels of the X12F1, 4X13, X18, etc. types are used.

Medium and low carbon steels 50, 55 and 20, due to their better ductility, are well suited to cold stamping (punching) in the manufacture of flat-shaped tools. Tools made from steels 50 and 55 are hardened with high-frequency heating, and steel 20 is subjected to chemical treatment (for example, carburization), and then hardened from 790-810°C in water or aqueous solutions. After hardening, tempering is carried out at 150-170°C for 2-3 hours. Since tools from these steels receive a hardened layer of small thickness, the development of the aging process in it causes only a slight change in size relative to the size of the entire tool. The presence of a viscous core makes it easier to dress the tool.

Questions for self-control

1. What are the requirements for tool materials?

2. What are the principles of alloying, the role of alloying elements in tool steels for various purposes?

3. What are the heat treatment regimes for ledeburite class steels?

4. What are the new trends in the creation of high-speed steels?

5. What is the principle of alloying and heat treatment of cold forming dies?

6. What is the principle of alloying and heat treatment of hot forming dies?

7. What new methods exist for surface hardening of steels for cutting tools?

8. What are the requirements for steels for the production of hot rolling rolls? What hardening coatings are used for rolls and technological equipment of sheet rolling mills?

9. What are the requirements for steels for calibration and measuring instruments? What is the role of alloying elements in the formation of properties, heat treatment technology?

10. What hard and superhard materials exist? What is their composition and properties?

16. CONTROL TASKS FOR CORRESPONDENCE STUDY STUDENTS

Option #1

1. Describe the concept of structural strength. Specify the criteria for its evaluation and ways to improve it.

2. Consider case-hardening steels, the requirements for them, working conditions, principles of their creation, areas of application, new directions in their creation.

3. Provide information about antifriction materials, their properties, and areas of application. What new directions have emerged in their creation.

4. Propose a material for cutting tools with red resistance up to 620°C, sparingly alloyed with tungsten. Consider the role of alloying elements, the principle of heat treatment and modern methods of increasing the performance properties of a tool made from the selected steel.

5. Consider the principles of alloying steels for injection molds. Select a reasonable grade of steel for pressure smelting of aluminum alloy parts. Justify the mode of its heat treatment.

Option No. 2

1. Consider the requirements, principles of alloying, properties of construction steels, areas of their application, new directions in the creation of high-strength steels.

2. Describe the types of wear. Patterns of wear and ways to reduce wear. Choose materials that are resistant to impact and abrasion wear. What is the role of austenite in the abrasive wear resistance of steels? Indicate new directions in increasing abrasive wear resistance.

3. Consider high-nickel spring alloys, their features, heat treatment conditions and applications.

4. Provide information about new hard alloys and superhard materials. Indicate their differences from widely used ones, as well as their advantages over them.

5. Provide data on economically nickel-alloyed steels for hammer dies, the principles of their alloying, the role of alloying elements, the technology of thermal and chemical-thermal treatments (including the use of concentrated energy sources).

Option No. 3

1. Consider the principles of creating two-phase steels for deep drawing, their alloying system, the role of alloying elements, and the technology of their heat treatment. Indicate their advantages over steels of type 08kp and 08Yu used for deep drawing.

2. Suggest a material for liquid nitrogen storage vessels if it requires an impact strength at -196°C KCU ³ 1.0 MJ/m2 and economical nickel alloying.

3. Select a material for a ball bearing ring with a diameter of 2.5 m and a cross-section of 150 mm. Indicate the method of its strengthening treatment.

4. Provide information based on patent and literary data for recent years on steels for pressing tools. Indicate the alloying system, the purpose of alloying elements and what is new in heat treatment technology.

5. Provide information about tungsten-free high-speed steels, as well as methods for increasing their resistance.

Option No. 4

1. Provide information about construction low-alloy steels. Indicate the principles of their alloying, the role of alloying elements, the technology of their heat treatment and the resulting mechanical properties. Consider the advantages of low alloy steels compared to carbon steels. Analyze current trends in their improvement.

2. Consider the role of microalloying with strong carbide-forming elements (vanadium, niobium, zirconium, titanium), as well as modification with calcium and rare earth elements in increasing the properties of structural steels.

3. Analyze literature data and patent materials on nitrogen-alloyed structural steels (composition, structure, properties). Indicate their advantages over steels that do not contain nitrogen.

4. Provide an economical material for injection molding of copper-based alloy workpieces. Justify their choice. Provide data on the chemical composition, structure and properties.

5. Consider the principles of alloying high-speed steels with increased red resistance. Give compositions, structure, properties and applications.

Option No. 5

1. Consider the principles of alloying, the role of alloying elements, and methods of strengthening general-purpose spring steels. Indicate modern directions for improving their composition and processing methods.

2. Analyze literature data and patents (copyright certificates) on wear-resistant austenitic steels sparingly alloyed with manganese, their chemical composition, the role of alloying elements, heat treatment technology, properties and areas of application.

3. Consider the principle of alloying ball bearing steels. Give the composition, properties and processing modes, current trends in improving their chemical composition and hardening technology.

4. Provide information about dispersion-hardening steels for hot deformation tools. Indicate their chemical composition, the role of alloying elements, heat treatment technology, advantages and disadvantages.

5. Suggest a material for cutters intended for processing austenitic heat-resistant alloys. Justify your choice. Provide information about the selected material (chemical composition, structure, properties, heat treatment modes).

Option No. 6

1. Provide information about antifriction metal materials. Indicate their chemical composition, principles of alloying, structure, properties, areas of application, modern trends in their improvement, advantages and disadvantages.

2. Conduct an analysis of literature data and patents (copyright certificates) on wear-resistant steels operating under conditions of impact-abrasive wear (such as steel 110G13L) and identify trends in increasing their wear resistance.

3. Consider the principles of alloying free-cut steels, the role of elements such as sulfur, phosphorus, lead, calcium, selenium, tellurium, give the compositions of such steels, their mechanical properties, as well as machinability.

4. Suggest a material for cold-formed punches subjected to intense wear and heating up to 450°C. Justify your choice. Provide information about the selected material (chemical composition, structure, properties, heat treatment modes).

5. Select a material for press inserts that operate at temperatures of 550-600°C and have increased wear resistance.

Option No. 7

1. Provide information about reinforcing steels. Indicate the principles of their alloying and heat treatment, directions for their improvement. Review structure and property data.

2. Propose and justify the choice of material for highly loaded gears and their heat treatment.

3. Select material for springs operating at temperatures up to 500°C. Justify the system of its alloying and the role of alloying elements, as well as the heat treatment technology and the resulting structure.

4. Give the compositions and properties, areas of application of carbide-based hard alloys. Indicate modern trends in improving their compositions in order to save expensive and scarce elements.

5. Provide data on increasing the performance properties of high-speed steels through the use of treatments using concentrated energy sources.

Option No. 8

1. Provide information about the alloying system, the role of alloying elements, the structure and properties of case-hardening steels, areas of their application, and improving their properties by heat treatment.

2. Provide data on the role of nickel in improved structural steels. Indicate the directions for creating sparingly alloyed nickel steels, give the compositions and properties of sparingly alloyed steels in comparison with widely used nickel-containing steels.

3. Based on patent and literary data, identify new directions in the creation of high-speed steels. Indicate their compositions, their heat treatment technology, structure and properties. Compare the latter with widely used high-speed steels (for example, P6M5).

4. Compare the properties of cold work die steels containing 12 and ~6% Cr, their advantages and disadvantages.

5. Consider the use of thermal diffusion surface treatment (chrome plating, nitriding, boriding, etc.) to improve the performance properties of die steels.

Option No. 9

1. Suggest a material for a high-speed motor shaft with a cross-section of 150 mm, which should have: s0.2=900 MPa; sB=1200 MPa; d=12-14%; y=55-60%; KCU=1.0 MJ/m2 and through hardenability.

2. Provide data on deep drawing steels, their composition, processing technology, structure and properties. Indicate ways to create non-aging steels.

3. Conduct an analysis of literature data and patents (copyright certificates) on spring steels. Provide data on processing modes, structure, properties and applications, as well as methods for increasing fatigue strength.

4. Consider the principles of alloying hot deformation dies designed to operate at temperatures of 700-800°C. Give brands, compositions, heat treatment modes, properties.

5. Consider the principles of creating carbide steels, their production technology, structure, properties and applications, advantages over conventional tool steels.

Option No. 10

1. Provide data on nitrided temperable steels (compositions, structure, properties). What are their advantages and disadvantages compared to case-hardened steels.

2. Consider the principles of alloying construction steels of various strength classes. Indicate the areas of their application.

3. Suggest steel for especially deep drawing, justify your choice. Indicate the brand, properties, areas of application.

4. Consider the principles of alloying and heat treatment of steels for measuring instruments.

5. Conduct an analysis of literature data and patents (copyright certificates). Identify current trends in the development of high-speed steels.

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