The rational area of ​​application of a particular tool material is determined by the totality of its operational and technological properties (depending in turn on the physical, mechanical and chemical properties), as well as economic factors.

Tool materials work in difficult conditions - at high loads and temperatures. Therefore, all properties of tool materials can be divided into mechanical and thermal.

The most important operational properties of tool materials include: hardness, strength, wear resistance, heat resistance, thermal conductivity.

HardnessH and contact surfaces of the tool must be higher than the hardness H m of processed material. This is one of the main requirements for the tool material. But with increasing hardness of the tool material, as a rule, its resistance to brittle fracture decreases. Therefore, for each pair of processed and tool materials, there is an optimal value of the ratio H and / H m, at which the wear rate of the tool material will be minimal.

From point of view strength tool, it is important that the tool material combines high hardness at elevated temperatures of the cutting zone with good resistance to compression and bending, and also has high values ​​of endurance limit and impact strength.

wear resistance is measured by the ratio of the work expended on the removal of a certain mass of material to the value of this mass. Wear observed in cutting as a total loss of tool material mass is caused by various mechanisms: adhesion-fatigue, abrasive, chemical-abrasive, diffusion, etc. The wear resistance of the tool material during adhesive wear depends on the microstrength of the surface layers and the intensity of adhesion with the material being processed. With brittle adhesive wear, the wear resistance of the tool material is correlated with its endurance limit and strength, with plastic wear, with the yield strength and hardness. As a measure of wear resistance of a tool material during abrasive wear, its hardness is approximately taken. Diffusion wear of the cutting tool occurs due to the mutual dissolution of the components of the cutting and processed materials, followed by the destruction of the surface layers of the cutting material, softened due to diffusion processes. A characteristic of resistance to diffusion wear is the degree of inertness of tool materials in relation to the processed ones.

The hardness of the contact surfaces of the tool in the cold state, i.e. measured at room temperature does not fully characterize its cutting ability. To characterize the cutting properties of tool materials at elevated temperatures, such concepts as "hot" hardness, red hardness and heat resistance are used.

Under red hardness is understood as the temperature that causes a decrease in the hardness of the tool material not below the specified value. According to GOST 19265-73, the red hardness of high-speed steel of normal productivity should be 620°C, and of high-performance steel - 640°C. Red hardness is determined by measuring the hardness of samples at room temperature after heating to temperatures of 620°-640°C with exposure for 4 hours and subsequent cooling. For the control rate of softening of steel after the specified heating, the hardness HRC 58 was taken.

Under heat resistance tool material is understood as the ability of the material to maintain, when heated, hardness sufficient for the cutting process. Heat resistance is characterized by the so-called critical temperature. The critical temperature is the temperature established during the cutting process at which the tool material does not yet lose its cutting properties, and the tool from which it is made is able to cut.

The dependence of the tool performance on the temperature conditions of its operation is also expressed by such a characteristic of the tool material as thermal shock resistance. This characteristic determines the maximum temperature difference at which the material retains its integrity and reflects the possibility of brittle fracture of the tool as a result of thermal stresses. Knowledge of thermal shock resistance is especially important when using relatively brittle tool materials in interrupted cut conditions. The magnitude of thermal stresses depends on thermal conductivity, coefficient of linear expansion, modulus of elasticity, Poisson's ratio and other properties of the tool material.

Thermal conductivity- one of the most important physical properties of tool materials. The lower the thermal conductivity, the higher the temperature of the contact surfaces of the tool and, consequently, the lower the permissible cutting speeds.

Among the technological properties of tool materials, the most importance has them machinability in hot (forging, casting, stamping, welding, etc.) and cold (cutting, grinding) states. For tool materials subjected to heat treatment, the conditions of their heat treatment are of no less importance: the range of hardening temperatures, the amount of residual austenite, the ability of residual austenite to transform, deformation during heat treatment, sensitivity to overheating and decarburization, etc. Machinability of tool materials by cutting depends on many factors, the main of which are: chemical composition, hardness, mechanical properties (strength, toughness, plasticity), microstructure and grain size, thermal conductivity. Machinability should not be considered in terms of the possibility of using high cutting speeds in tool making, but also in terms of the quality of the resulting surfaces. Tool material, during the processing of which scuffs, high roughness, burns and other defects are obtained, is difficult to use for the manufacture of cutting tools.

Price tool material, refers to economic factors. Tool material should be as cheap as possible. But this requirement is conditional, since more expensive material can provide cheaper processing. In addition, the ratio between the cost of individual materials is constantly changing. It is important that instrumental material is not in short supply.

It is impossible to create an ideal tool material that is equally suitable for the whole variety of machining conditions. Therefore, a large range of tool materials is used in industry, united in the following main groups: carbon and alloy steels; high speed steels; hard alloys; cutting ceramics; superhard materials; coated tool.

Cutting tool materials 5.00 /5 (100.00%) voted 5

Materials for cutting tools.

The cutting ability of a turning tool is determined by the physical and mechanical properties of the material from which it is made. The main properties that determine the performance of the tool include hardness, heat resistance, wear resistance, thermal conductivity and adhesive ability.

The hardness of the material from which the tool is made must exceed the hardness of the material being machined. Due to the fact that significant cutting forces act on the working part of the tool, creating bending deformations, the tool material must have strength. The hardness and strength of the tool material is significantly affected by the ratio of alloying components and carbon included in their composition in the form of carbides. With an increase in the amount of carbides and a decrease in their grain size, the hardness and wear resistance of the tool increases, and the strength decreases.

The heat resistance of the tool is determined temperature above which hardness decreases and wear increases.

Tool wear resistance is characterized by the resistance of the tool to abrasion under the action of friction forces arising in cutting processes.

Tool thermal conductivity is determined by its ability to remove the heat generated in the cutting process from the cutting edges of the tool. The higher the thermal conductivity, the better the heat is removed from the cutting edges, thereby increasing tool life.

Adhesion The temperature of the tool and workpiece material is characterized by the temperature at which the workpiece material sticks to the cutting edges of the tool. It depends on the molecular forces that develop at high temperatures and pressures at the points of contact of the cutting tool with the surface to be machined. The higher the sticking temperature of the processed material on the tool, the better the material from which the tool is made should be.

Tool steels.

Tool steels are divided into:

• carbonaceous;
• alloyed;
• fast cutting.

Carbon tool steels.

In order to make a cutting tool, carbon steel grades U10A, U11A, U12A and U13A are used. The letter U means that carbon tool steel. The number after the letter indicates approximately how much carbon in tenths of a percent is contained in this steel.

If there is a letter A at the end of the name of the steel grade, then this indicates that the steel belongs to the high-quality group (U10A; U12A).

After quenching and tempering, the tool hardness of these steels is HRC 60-64. However, when heated to a temperature above 220-250°C, the hardness of the tool decreases sharply. Therefore, at present, on lathes, such a tool is used only for work associated with low cutting speeds (some types of taps, countersinks and reamers).

alloyed tool steels.

Alloy tool steels- these are those into which special impurities (alloying elements) are introduced in order to improve the physical and mechanical properties.

With the introduction of chromium, molybdenum, tungsten, vanadium, titanium and manganese, the hardness of steel increases, since they form simple or complex compounds (carbides) with carbon, which have high hardness (especially tungsten and vanadium carbides). At the same time, the steel retains sufficient toughness. Nickel, cobalt, aluminum, copper and silicon, dissolving in iron, harden steel.

With appropriate heat treatment, the tool has a hardness of HRC 62-64 and retains it when heated to a temperature of 250-300°C. Countersinks, reamers, taps, broaches are made of steel grades 9XC, KhVG and KhV5.

High-speed tool steels.

High speed tool steels- these are alloy steels with a significant content of tungsten, cobalt, vanadium and molybdenum. They retain the hardness HRC 62 - 64 obtained after heat treatment when heated to a temperature of 600 ° C, and some grades of complex alloyed steels retain their hardness even when heated to a temperature of 700-720 ° C.

These qualities of high-speed steels make it possible to increase the cutting speed during processing by two to three times in comparison with a tool made of carbon and ordinary alloyed tool steel.

All grades of high speed steel are designated by the letter P (P9, P12, P18), the number after the letter P shows the average percentage of tungsten in this steel.

Have a wide application high speed steels containing 3-5% molybdenum (P6M3, P6M5). These steels are superior in strength to P18 steel, although they have somewhat lower heat resistance. They are usually used for tools operating under heavy power conditions.

When processing alloyed, heat-resistant and stainless alloys and steels, it is effective to use high-speed steels of increased productivity, which include vanadium and cobalt (R10KF5, R18K5F2), or complex alloyed steels (grades R18MZK25, R18M7K25 and R10M5K25). In the presence of 10% or more cobalt in steel, its hardness after heat treatment is 67-68 and is maintained up to a heating temperature of 640-720°C.

High-speed tool steels are used for the manufacture of cutters, drills, countersinks, reamers, taps, dies and other tools. .

hard alloys.

Carbide consist of carbides of refractory metals, which are evenly distributed in a cobalt bond. They are made by pressing and sintering. Hard alloys have high density and hardness, which does not decrease even when heated to 800-900°C. According to the composition, hard alloys are divided into three groups:

• tungsten;
• titanium-tungsten;
• titanium-tantalum-tungsten.

The main grades of hard alloy of the tungsten group used for the manufacture of cutting tools are VKZ, VKZM, VK4, VK4M, VK6 VK6M VK6V, VK8, VK8V, VK10. In the designation of the brand of hard alloy of this group, the letter B indicates the group, the letter K and the number following it - the percentage of cobalt, which is a binding metal. The letter M indicates that the structure of the alloy is fine-grained, and the letter B indicates that it is coarse-grained.

Hard alloys of the titanium-tungsten group.

Hard alloys of the titanium-tungsten group consist of grains of a solid solution of tungsten carbide in titanium carbide, excess grains of tungsten carbide and cobalt, which is a binder. The main alloy grades of this group are T5K10, T5K12, T14K8, T15K6. In the designation of alloys of this group, the number after the letter T indicates the percentage of titanium carbide, and the number after the letter K indicates the percentage of cobalt. The rest of the alloy is tungsten carbides.

Hard alloys of the titanium-tantalum-tungsten group.

Hard alloys of the titanium-tantalum-tungsten group consist of grains of titanium, tantalum, tungsten carbides and a binder, which is also used as cobalt. The brands of this group of alloys are TT7K12, TT8K6, TT10K8B and TT20K9. In the designation of this group of alloys, the number after the letters TT indicates the content of titanium and tantalum carbides, and the number after the letter K indicates the percentage of cobalt.

Depending on the content of tungsten carbide, titanium carbide, tantalum carbide and cobalt, hard alloys have different properties. The more cobalt, the more viscous the alloy and the better it resists shock loading. Therefore, alloys with a high content of cobalt are used for the manufacture of tools that perform peeling work. When machining steel, hard alloys containing titanium carbide are used, since steel chips stick less to a tool made of these alloys.

Tungsten-cobalt hard alloys.

According to GOST 3882 - 74 hard alloys of the VK group (tungsten-cobalt) are recommended for processing brittle materials (cast iron, bronze). Alloys of the TK group (titanium-tungsten-cobalt) are recommended for processing viscous materials(steel, brass). Alloys of the titanotantalum-tungsten group are used under unfavorable working conditions of the tool with shock loads, in the processing of steel castings and forgings.

Mineral ceramic materials.

Mineral-ceramic materials for cutting tools are made in the form of plates of aluminum oxide Al 2 O 3 (alumina) by pressing under high pressure followed by sintering. They have high hardness, temperature resistance (up to 1200°C), wear resistance and sufficient compressive strength. The disadvantages of these materials include high brittleness and low impact strength. Tools equipped with mineral ceramics are usually used for finishing in turning with a constant load and in the absence of vibration.

Synthetic materials.

synthetic diamond characterized by high hardness and wear resistance, chemically little active. It has a low coefficient of friction and a slight tendency to sticking chips of the material being processed. The disadvantages of diamond are its brittleness and relatively low temperature resistance (750-850°). Diamond cutters are used for finishing non-ferrous metals, alloys and non-metallic materials.

Cubic boron nitride (CBN) is a synthetic superhard material (elbor, cubanite, hexanite) consisting of boron and nitrogen compounds. Its hardness is somewhat lower than the hardness of diamond, but the temperature resistance is much higher (1200 - 1300°C). It is chemically inert to materials containing carbon, therefore, when machining steels and cast irons, its wear resistance is much higher than that of diamonds. CBN inserts are used on turning tools for hardened steel and ductile iron.

For the manufacture of the working part of cutting tools, five groups of tool materials are used: tool carbon and alloy steels, high-speed steels, hard alloys, mineral ceramics and superhard materials.

In the process of cutting, tools experience high specific forces, are exposed to heat and wear, therefore, tool materials must have certain physical, mechanical and technological properties, of which the main ones are: hardness, strength and ductility, heat resistance and thermal conductivity, resistance to seizure with the workpiece material, wear resistance, as well as hardenability and hardenability (for tool steels), resistance to overheating and oxidation, weldability or solderability, susceptibility to solder cracking, and grindability.

Such important technological indicators as cutting performance, durability, tool reliability, etc. depend on the specified properties of these materials.

There are practically no materials that would simultaneously have high hardness, strength, thermal characteristics, etc.

In order to choose the right tool material for specific machining conditions, or to use the available material correctly when such a choice is not possible, it is necessary to know the influence of its properties on the cutting process.

Hardness. The implementation of the cutting process is possible if the hardness of the cutting tool is much higher than the hardness of the material being processed. The higher the hardness of the tool, the higher its tool life and cutting speed. With an increase in hardness, the resistance of the tool to mechanical wear increases and more long time sharpness remains cutting edge.

However, not for all tools and processing conditions it is advisable to choose a tool material with the highest hardness, since with its increase, brittleness and a tendency to form cracks during soldering and sharpening increase, and grindability deteriorates. Therefore, when choosing a tool material, it is necessary to take into account not only hardness, but also its other properties.

Strength. During the cutting process, forces act on the tool that subject it to compression, bending, twisting and other types of deformation. The ability of a tool to resist deformation is a very important property and is characterized by tensile strength. The concept of tool strength has a dual meaning: the strength of the cutting elements located in the cutting zone and exposed to the descending chips and the resulting heat, and the strength of the non-cutting tool elements. In the first case, strength characterizes such cutting properties of the tool as resistance to brittle and plastic fracture of the cutting part; in the second - the rigidity, vibration resistance and reliability of the tool as a whole.

Heat resistance. The mechanical properties of the tool material change under the influence of the cutting temperature. With an increase in temperature above a certain value, the hardness and strength of the material decrease and reach such values ​​when the tool begins to quickly soften, wear out and lose its cutting ability.

The temperature up to which the tool material retains its cutting ability is called heat resistance (in state standards on tool and high-speed steels, the term "red hardness" is used, which is identical with the term "heat resistance").

For high speed steels and carbide, this is the temperature at which the hardness drops to HRA 58…60.

Considering that the temperature of the cutting blade is highly dependent on the cutting speed (increases with increasing speed), materials with greater heat resistance, even with equal hardness, can work at higher cutting speeds and machine harder materials.

Thermal conductivity- this property that affects the temperature of the cutting blade during processing. The higher the thermal conductivity, the better the heat is removed from the zone of contact of the tool with the workpiece material and the lower the cutting temperature. In addition, materials with higher thermal conductivity are less prone to cracking during sharpening and soldering.

Adhesion resistance is resistance against seizure. The low adhesive resistance of the tool material leads to an increase in tool wear, especially at high temperatures and pressures in the cutting zone.

wear resistance- this is the property of the tool material to resist the mechanical, thermal and chemical effects of the material being processed during the cutting process. The most important factors affecting wear resistance are the properties discussed above - hardness, heat resistance, thermal conductivity, adhesive resistance.

When choosing a tool material, it is necessary to strive for the optimal value of its wear resistance, taking into account chemical composition and strength, the material being processed, the nature of the operation and the design of the tool, the rigidity of the equipment, the possibility of using coolant, etc.

1.2. Tool steels

According to the chemical composition, the degree of alloying, tool steels are divided into tool carbon, tool alloyed and high-speed steels. The physical and mechanical properties of these steels at normal temperature are quite close, they differ in heat resistance and hardenability during quenching.

Disintegration of martensite during heating (during cutting) hardened carbon steels takes place at 200°C. In alloyed and high-speed steels, the softening of martensite is restrained by the presence of alloying elements. In alloyed tool steels, the mass content of alloying elements is not enough to bind all carbon into carbides, therefore, the heat resistance of steels of this group is only 50 ... 100 ° C higher than the heat resistance of tool carbon steels. In high-speed steels, they strive to bind all the carbon into alloying element carbides, while eliminating the possibility of the formation of iron carbides. Due to this, the softening of high-speed steels occurs at higher temperatures.

MINISTRY OF EDUCATION AND SCIENCE

RUSSIAN FEDERATION

NOVOSIBIRSK STATE TECHNICAL UNIVERSITY

TEST

in engineering technology

Subject: " Tool materials »

Performed:

Student of the OTZ-873 group

Vasilyeva Olga Mikhailovna

Checked:

Martynov Eduard Zakharovich

Tatarsk 2010

Introduction…………………………………………………………………………………………...……3

1. Basic requirements for tool materials………………………………….…..4

2. Types of tool materials……………………………………………………….…..6

2.1. Carbon and Alloy Tool Steels………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….6

2.2. High speed steels………………………………………………………….………....7

3. Hard alloys…………………………………………………………………………….……8

3.1.Mineral-ceramic materials………………………………………………………....10

3.2. Metal-ceramic materials………………………………………………………..11

3.3. Abrasive materials………………………………………………………………..…..12

4. Features of obtaining tool materials based on diamond and cubic boron nitride……………………………………………………………………………………………..14

5. Steels for the manufacture of element cases………………………………………….…..16 Conclusion………………………………………………………… ……………………………….…...17 List of references………………………………………………………………..….18

Introduction

The history of the development of metal processing shows that one of the effective ways increasing labor productivity in mechanical engineering is the use of new tool materials. For example, the use of high-speed steel instead of carbon tool steel made it possible to increase the cutting speed by 2...3 times. This required a significant improvement in the design of metal-cutting machines, primarily to increase their speed and power. A similar phenomenon has been observed

also when used as a tool material of hard alloys.

The tool material must have high hardness in order to shear chips for a long time. A significant excess of the hardness of the tool material compared to the hardness of the workpiece must be maintained even when the tool is heated during the cutting process. The ability of the tool material to maintain its hardness at high heating temperatures determines its red hardness (heat resistance). The cutting part of the tool must have a large

wear resistance under conditions of high pressures and temperatures.

An important requirement is also a sufficiently high strength of the tool material, since insufficient strength results in chipping of the cutting edges or breakage of the tool, especially with their small sizes.

Tool materials must have good processing properties, i.e. easy to process in the process of tool manufacturing and regrinding, and also be relatively cheap. At present, tool steels (carbon, alloy and high-speed), hard alloys, mineral-ceramic materials, diamonds and other superhard and abrasive materials are used for the manufacture of cutting elements of tools.

1. Basic requirements for tool materials.

The main requirements for tool materials are as follows:

1. Tooling material must have high hardness.

The hardness of the tool material must be at least 1.4 - 1.7 times higher than the hardness of the material being processed.

2. When cutting metals, a significant amount of heat is released and the cutting part of the tool heats up. Therefore, the instrumental material must have high heat resistance . The ability of a material to maintain high hardness at cutting temperatures is called heat resistance .. For high-speed steel - heat resistance is also called red hardness (i.e., the preservation of hardness when heated to the temperatures at which the steel begins to glow)

An increase in the level of heat resistance of the tool material allows it to work at high cutting speeds (Table 1).

Table 1 - Heat resistance and allowable cutting speed of tool materials.

3. An important requirement is enough high strength tool material. If the high hardness of the material of the working part of the tool is not provided with the necessary strength, then this leads to tool breakage and chipping of the cutting edges.

Thus, the tool material must have a sufficient level of toughness and resist the appearance of cracks (ie, have a high fracture toughness).

4. Tooling material must have high wear resistance at elevated temperature, i.e. have good resistance to abrasion by the workpiece material, which manifests itself in the resistance of the material to contact fatigue.

5. Necessary condition achieving high cutting properties of the tool is low physical and chemical activity of the tool material in relation to the processed . Therefore, the crystal-chemical properties of the tool material must differ significantly from the corresponding properties of the material being processed. The degree of such a difference strongly affects the intensity of physical and chemical processes (adhesion-fatigue, corrosion-oxidation and diffusion processes) and wear of the contact pads of the tool.

6. Tool material must have technological properties , providing optimal conditions for the manufacture of tools from it. For tool steels, these are good machinability by cutting and pressure; favorable features of heat treatment (low sensitivity to overheating and decarburization, good hardenability and hardenability, minimal deformation and cracking during hardening, etc.); good sandability after heat treatment.

2. TYPES OF TOOL MATERIALS

For cutting tools, high-speed steels are used, as well as, in small quantities, hypereutectoid carbon steels with a carbon content of 0.7-1.3% and a total content of alloying elements (silicon, manganese, chromium and tungsten) from 1.0 to 3.0 %.

2.1. Carbon and alloy tool steels.

Earlier, other materials for the manufacture of cutting tools began to be used carbon tool steels grades U7, U7A…U13, U13A. In addition to iron and carbon, these steels contain 0.2 ... 0.4% manganese. Tools made of carbon steels have sufficient hardness at room temperature, but their heat resistance is low, since at relatively low temperatures (200 ... 250 ° C) their hardness decreases sharply.

alloyed tool steels, in their chemical composition, they differ from carbon ones in an increased content of silicon or manganese, or in the presence of one or more alloying elements: chromium, nickel, tungsten, vanadium, cobalt, molybdenum. For cutting tools, low-alloy steel grades 9HF, 11HF, 13X, V2F, XV4, KhVSG, KhVG, 9XS, etc. are used. These steels have higher technological properties - better hardenability and hardenability, less tendency to warp, but their heat resistance is 350 ... 400 °C and therefore they are used for the manufacture of hand tools (reamers) or tools intended for processing on machines with low cutting speeds (small drills, taps).

It should be noted that over the past 15-20 years there have been no significant changes in these grades, however, there is a steady downward trend in their share in the total volume of tool materials used.

2.2. High speed steels.

Currently, high speed steels are the main material for the manufacture of cutting tools, despite the fact that tools made of carbide, ceramic and STM provide higher machining performance.

The widespread use of high-speed steels for the manufacture of complex-shaped tools is determined by a combination of high hardness values ​​(up to [email protected]) and heat resistance (600-650°C) with a high level of brittle strength and toughness, significantly exceeding the corresponding values ​​for hard alloys. In addition, high-speed steels have a fairly high manufacturability, as they are well processed by pressure and cutting in the annealed state.

In the designation of high-speed steel, the letter P means that the steel is high-speed, and the number following the letter indicates the content of the average mass fraction of tungsten in%. The following letters denote: M - molybdenum, F - vanadium, K - cobalt, A - nitrogen. The numbers following the letters indicate their average mass fraction in%. The content of mass fraction of nitrogen is 0.05-0.1%.

Modern high-speed steels can be divided into three groups: normal, high and high heat resistance.

To the steels normal heat resistance include tungsten R18 and tungsten-molybdenum R6M5 steel (Table 2.2). These steels have hardness in the quenched state of 63…64 HRC, flexural strength of 2900…3400 MPa, impact strength of 2.7…4.8 J/m 2 and heat resistance of 600…620°C. These steel grades are most widely used in the manufacture of cutting tools. The volume of production of R6M5 steel reaches 80% of the total output of high-speed steel. It is used in the processing of structural steels, cast irons, non-ferrous metals, plastics.

Steels of increased heat resistance characterized by a high content of carbon, vanadium and cobalt.

Among vanadium steels the most widely used brand R6M5F3.

Along with high wear resistance, vanadium steels

have poor grindability due to the presence of vanadium carbides (VC), since the hardness of the latter is not inferior to the hardness of the grains of the electrocorundum grinding wheel (Al 2 O 3). Machinability during grinding - "grindability" - is the most important technological property, which determines not only the features in the manufacture of tools, but also during its operation (regrinding).

Table 2. Chemical composition of high speed steels

3.3. Abrasives A large place in the modern production of machine parts is occupied by grinding processes, in which various abrasive tools are used. The cutting elements of these tools are hard and heat-resistant grains of abrasive material with sharp edges. Abrasive materials are divided into natural and artificial. Natural abrasive materials include minerals such as quartz, emery, corundum, etc. Natural abrasive materials are highly heterogeneous and contain foreign impurities. Therefore, in terms of the quality of abrasive properties, they do not meet the growing needs of the industry. Currently, the processing of artificial abrasive materials occupies a leading place in mechanical engineering. The most common artificial abrasive materials are electrocorundum, silicon and boron carbides. Artificial abrasive materials also include polishing and finishing powders - oxides of chromium and iron. A special group of artificial abrasive materials are synthetic diamonds and cubic boron nitride. Electrocorundum is obtained by electric melting of materials rich in aluminum oxide, for example, from bauxite or alumina, mixed with a reducing agent (anthracite or coke). Electrocorundum is produced in the following varieties: normal, white, chromium, titanium, zirconium, monocorundum and spherocorundum. Normal electrocorundum contains 92-95% aluminum oxide and is divided into several grades: 12A, 13A, 14A, 15A, 16A. Grains of normal electrocorundum, along with high hardness and mechanical strength, have a significant viscosity, which is necessary when performing work with variable loads at high pressures. Therefore, normal electrocorundum is used for processing various materials of increased strength: carbon and alloy steels, malleable and high-strength cast iron, nickel and aluminum alloys. White electrocorundum grades 22A, 23A, 24A, 25A are distinguished by a high content of aluminum oxide (98-99%). Compared to normal electrocorundum, it is harder, has increased abrasive ability and brittleness. White electrocorundum can be used for processing the same materials as normal electrocorundum. However, due to its higher cost, it is used in more demanding jobs for final and profile grinding, thread grinding, and sharpening of cutting tools. Chromium electrocorundum grades 32A, ZZA, 34A, along with aluminum oxide A12O3, contains up to 2% chromium oxide Cr2O3. The addition of chromium oxide changes its microstructure and structure. In terms of strength, chromium electrocorundum approaches normal electrocorundum, and in terms of cutting properties - to white electrocorundum. It is recommended to use chromium electrocorundum for cylindrical grinding of products made of structural and carbon steels under intensive conditions, where it provides a 20-30% increase in productivity compared to white electrocorundum. Titanium electrocorundum grade 37A along with aluminum oxide contains TiO2 titanium oxide. It differs from normal electrocorundum in greater constancy of properties and increased viscosity. This allows it to be used in conditions of heavy and uneven loads. Titanium electrocorundum is used in preliminary grinding operations with increased metal removal. Electrocorundum zirconium grade ZZA along with aluminum oxide contains zirconium oxide. It has high strength and is mainly used for peeling operations with high specific cutting pressures. Monocorundum grades 43A, 44A, 45A is obtained in the form of a grain with increased strength, sharp edges and peaks with a more pronounced self-sharpening property compared to electrocorundum. This provides him with increased cutting properties. Monocorundum is preferred for grinding hard-to-cut steels and alloys, for precision grinding of complex profiles and for dry grinding of cutting tools, Spherocorundum contains more than 99% A1203 and is obtained in the form of hollow spheres. In the process of grinding, the spheres are destroyed with the formation of sharp edges. Spherocorundum is advisable to use when processing such materials as rubber, plastics, non-ferrous metals. Silicon carbide is obtained by reacting silica and carbon in electric furnaces and then crushing into grains. It consists of silicon carbide and a small amount of impurities. Silicon carbide has a high hardness, superior to the hardness of electrocorundum, high mechanical strength and cutting ability. Black silicon carbide grades 53C, 54C, 55C are used for processing hard, brittle and very tough materials; hard alloys, cast iron, glass, non-ferrous metals, plastics. Silicon carbide green grades 63C, 64C is used for sharpening carbide tools, grinding ceramics. Boron carbide B4C has high hardness, high wear resistance and abrasive ability. At the same time, boron carbide is very brittle, which determines its use in industry in the form of powders and pastes for finishing hard-alloy cutting tools. Abrasive materials are characterized by such basic properties as the shape of abrasive grains, granularity, hardness, mechanical strength, abrasive ability of grains. The hardness of abrasive materials is characterized by the resistance of grains to surface grinding, local impact of applied forces. It must be higher than the hardness of the material being processed. The hardness of abrasive materials is determined by scratching the tip of one body on the surface of another or by pressing a diamond pyramid under a small load into the abrasive grain. Mechanical strength is characterized by the crushability of grains under the influence of external forces. Strength is assessed by crushing a sample of abrasive grains in a steel mold under a press using a certain static load. Roughing conditions with high metal removal require strong abrasives, while fine grinding and machining of difficult-to-cut materials prefer abrasives with greater brittleness and the ability to self-sharpen.

4. Features of Obtaining Tool Materials Based on Diamond and Cubic Boron Nitride

Diamond as a tool material has been widely used in mechanical engineering in recent years. Currently released a large number of a variety of tools using diamonds: grinding wheels, tools for dressing grinding wheels made of electrocorundum and silicon carbide, pastes and powders for finishing and lapping operations. Diamond crystals of considerable size are used for the manufacture of diamond cutters, milling cutters, drills and other cutting tools. The scope of the diamond tool is expanding every year. Diamond is one of the modifications of carbon crystal structure. Diamond is the hardest mineral known in nature. The high hardness of diamond is explained by the peculiarity of its crystal structure, the strength of the bonds of carbon atoms in the crystal lattice, located at equal and very small distances from each other. The thermal conductivity coefficient of diamond is two or more times higher than that of the VK8 alloy, so heat is removed from the cutting zone relatively quickly. The increased demand for diamond tools cannot be fully met by natural diamonds. Currently mastered industrial production synthetic diamonds from graphite at high pressures and high temperatures. Synthetic diamonds can be of various grades, which differ in strength, brittleness, specific surface area and grain shape. In order of increasing strength, decreasing brittleness and specific surface, grades of grinding powders made of synthetic diamonds are arranged as follows: AC2, AC4, AC6, AC15, AC32. Among the new types of tool materials are superhard polycrystals based on diamond and cubic boron nitride.

Cubic boron nitride (CBN) is a superhard material that has no natural analogue. For the first time, cubic boron nitride was synthesized in 1956 (by the General Electric Company) at high pressures (over 4.0 GPa) and high temperatures (over 1473 K) from hexagonal boron nitride in the presence of alkaline and alkaline earth metals(lead, antimony, tin, etc.). Cubic boron nitride manufactured by General Electric was named Borazon.

The diameter of blanks made of superhard polycrystals is in the range of 4-8mm, and the height is 3-4mm. Such dimensions of workpieces, as well as a combination of physical and mechanical properties, make it possible to successfully use the considered materials as a material for the manufacture of the cutting part of such tools as cutters, end mills, etc. Superhard diamond-based polycrystals are especially effective in cutting materials such as fiberglass, non-ferrous metals and their alloys, titanium alloys. The significant distribution of the considered composites is explained by a number of unique properties inherent in them - hardness approaching the hardness of diamond, high thermal conductivity, and chemical inertness to iron. However, they have increased brittleness, which makes it impossible to use them under shock loads. Composite 09 and 10 tools are more resistant to impact. They are effective in heavy duty and impact machining of hardened steels and cast irons. The use of superhard synthetic materials has a significant impact on mechanical engineering technology, opening up the prospect of replacing in many cases grinding, turning and milling. perspective view tool material are two-layer plates of round, square, trihedral or hexagonal shapes. The upper layer of the plates consists of polycrystalline diamond, and the lower one is made of a hard alloy or a metal substrate. Therefore, inserts can be used for mechanically held tools in the holder. Silinit-R alloy based on silicon nitride with additions of aluminum oxide and titanium occupies an intermediate position between hard alloys based on carbide and superhard materials based on diamond and boron nitride. Studies have shown that it can be used for fine turning of steels, cast iron, aluminum and titanium alloys. The advantage of this alloy is that silicon nitride will never become scarce. 5. Steels for the manufacture of element cases For prefabricated tools, the bodies and fastening elements are made of structural steel grades: 45, 50, 60, 40X, 45X, U7, U8, 9XS, etc. Steel 45 is most widely used, from which cutter holders, drill shanks, countersinks, reamers, taps, prefabricated cutter bodies, boring bars. For the manufacture of tool cases operating in difficult conditions, use steel 40X. After quenching in oil and tempering, it maintains the accuracy of the grooves into which the knives are inserted. In the case when individual parts of the tool body work for wear, the choice of steel grade is determined by considerations of obtaining high hardness in friction points. Such tools include, for example, carbide drills, countersinks, in which the guide strips come into contact with the surface of the machined hole during operation and wear out quickly. For the body of such tools, carbon tool steel is used, as well as alloy tool steel 9XC. Conclusion

Development new technology dictates the requirements for the development of new materials, which include superhard materials. Traditionally, they are used in metalworking, tool making, stone and glass processing, building materials, ceramics, ferrites, semiconductor and other materials. In recent years, intensive work has been carried out on the use of diamonds in electronics, laser technology, medicine, and other fields of science and technology. In the industrialized countries of the world, much attention is paid to the production of superhard materials and products from them. the Russian Federation in recent years has made significant progress in creating a domestic diamond production. A great contribution to solving this problem is made by the state scientific and technical program "Diamonds", thanks in large part to the support of which over 25% of the republic's needs for diamond products are now met by its own production.

A more complete solution to the problem of import substitution requires further work to improve existing and develop new materials and technologies for producing superhard materials and products based on them, expanding their areas of application. Today, work in the field of superhard materials in Russia is carried out in a wide range of problems, including: the synthesis of powders of diamond and cubic boron nitride, the growth of large single crystals of diamond, the growth of single crystals of precious stones, the production of polycrystals of diamond, cubic boron nitride and compositions based on them, in including the use of nanopowders, the development of new composite diamond-containing materials and technologies for obtaining tools from them, the development of technology and equipment for applying diamond films and coatings, the certification of diamond products, as well as the development of facilities for the production of diamond products.

1. New tool materials and areas of their application. Textbook allowance / V.V. Kolomiets, - K .: UMK VO, 1990. - 64 p.

2. Vasin S.A., Vereshchaka A.S., Kushnir V.S. Cutting metals: Thermomechanical approach to the system of relationships in cutting: Uchebn. for tech. universities. - M .: Publishing house of MSTU im. N.E. Bauman, 2001. - 448 p.

3. Metalworking carbide tool: V.S. Samoilov, E.F. Eichmans, V.A. Falkovsky and others. - M .: Mashinostroenie, 1988. - 368 p.

4. Tools from superhard materials / Ed. N.V. Novikova. - Kyiv: ISM NASU, 2001. - 528 p.

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To ensure the operability of a metal-cutting tool, it is necessary to manufacture its working part from a material that has a complex of certain physical and mechanical properties (high hardness, wear resistance, strength, heat resistance, etc.). Materials that meet the requirements of this complex and are capable of cutting are called tool materials. Let us consider the physical and mechanical properties of tool materials.

To penetrate into the surface layers of the workpiece, the cutting blades of the working part of the tools must be made of materials with high hardness. The hardness of tool materials can be natural (i.e., inherent in the material during its formation) or achieved by special processing. For example, tool steels as delivered with metallurgical plants easily machinable. After machining, heat treatment, grinding and sharpening of steel tools, their strength and hardness increase dramatically.

Hardness is determined using various methods. Rockwell hardness is indicated by numbers characterizing the hardness number, and by the letters HR indicating the hardness scale A, B or C (for example, HRC). The hardness of heat-treated tool steels is measured on the Rockwell C scale and is expressed in conventional HRC units. The most stable mode of operation and the least wear of tool blades made of tool steels and heat treated is achieved with a hardness of HRC 63 ... 64. With a lower hardness, the wear of the tool blades increases, and with a higher hardness, the blades begin to crumble due to excessive fragility.

Metals with a hardness of HRC 30 ... 35 are satisfactorily processed with tools made of heat-treated tool steels (HRC 63 ... 64), i.e., with a hardness ratio of approximately two. For processing heat-treated metals (HRC 45...55), it is necessary to use tools made only from hard alloys. Their hardness is measured on the Rockwell A scale and has HRA values ​​of 87...93. The high hardness of synthetic tool materials allows them to be used for machining hardened steels.

In the process of cutting, cutting forces of up to 10 kN or more act on the working part of the tools. Under the action of these forces, large stresses arise in the material of the working part. In order for these stresses not to lead to the destruction of the tool, the tool materials used for its manufacture must have a sufficiently high strength.

Among all instrumental materials the best combination strength characteristics have tool steels. Thereby working part tools made of tool steels successfully withstand the complex nature of loading and can work in compression, torsion, bending and tension.

As a result of the intense release of heat in the process of cutting metals, the blades of the tool are heated, and to the greatest extent - their surfaces. At a heating temperature below the critical one (it has different values ​​for different materials), the structural state and hardness of the tool material do not change. If the heating temperature exceeds the critical one, then structural changes occur in the material and the associated decrease in hardness. The critical temperature is also called the red hardness temperature. The term "red hardness" is based on the physical property of metals to emit dark red light when heated to 600 °C. Red hardness is the ability of a material to maintain high hardness and wear resistance at elevated temperatures. At its core, red hardness means the temperature resistance of tool materials. The temperature resistance of various tool materials varies over a wide range: 220... 1800°C.

An increase in the working capacity of a cutting tool can be achieved not only by increasing the temperature resistance of the tool material, but also by improving the conditions for removing heat released during cutting on the tool blade and causing it to heat up to high temperatures. How large quantity heat is removed from the blade deep into the tool, the lower the temperature on its contact surfaces. The thermal conductivity of tool materials depends on their chemical composition and heating temperature.

For example, the presence in steel of such alloying elements as tungsten and vanadium reduces the heat-conducting properties of tool steels, while alloying them with titanium, cobalt and molybdenum, on the contrary, significantly increases it.

The value of the sliding friction coefficient of the workpiece material over the tool material depends on the chemical composition and physical and mechanical properties of the materials of the contacting pairs, as well as on the contact stresses on the rubbing surfaces and the sliding speed.

The coefficient of friction is functionally related to the friction force and the work of friction forces on the path of mutual sliding of the tool and workpiece, so the value of this coefficient affects the wear resistance of tool materials.

The interaction of the tool with the material being processed proceeds under conditions of constant (moving) contact. In this case, both bodies forming a friction pair mutually wear out.

The material of each of the interacting bodies has:

• the property to abrade the material with which it interacts;
• wear resistance, i.e. the ability of a material to resist the abrasive action of another material.

The wear of the tool blades occurs throughout the entire period of interaction with the material being processed. As a result of this, the tool blades lose some of their cutting properties, the shape of the working surfaces of the tool changes.

Wear resistance is not an invariable property of tool materials, it depends on the cutting conditions.

Modern tool materials meet the requirements discussed above. They are divided into the following groups:

• tool steels;
• hard alloys (cermet);
• mineral ceramics and cermets;
• synthetic compositions of boron nitride;
• synthetic diamonds.

Tool steels are divided into carbon, alloy and high-speed.

Carbon tool steels are used for the manufacture of tools operating at low cutting speeds.

The grades of such steels are denoted by the letter Y (carbon), then by numbers that show the carbon content in steel (in tenths of a percent), the letter A at the end of the grade means that the steel is high-quality (sulfur and phosphorus content is not more than 0.03% of each element) .

The main properties of carbon tool steels are high hardness (HRC 62...65) and low temperature resistance.

Saws are made from steel grades U9 and U10A; from steel grades U11; U11A; U12 - hand taps, etc.

The temperature resistance of steel grades U10A...U13A is 220 °C, therefore it is recommended to use tools made of these steels at a cutting speed of 8...10 m/min.

Alloyed tool steel, depending on the main alloying elements, can be chromium (X), chromium-silicon (XS), tungsten (B), chromium-tungsten-manganese (CVG), etc.

The grades of such steels are indicated by numbers and letters (the first letters of the names of alloying elements). The first digit to the left of the letters shows the carbon content in tenths of a percent (if the carbon content is less than 1%), the numbers to the right of the letters show the average content of the alloying element in percent.

Taps and dies are made from grade X steel, drills, reamers, taps and dies are made from 9XC steel. Steel B1 is recommended for the manufacture of small drills, taps and reamers.

The temperature resistance of alloyed tool steels is 350...400°C, therefore, the allowable cutting speeds for tools made from these steels are 1.2...1.5 times higher than for tools made from carbon tool steels.

High-speed (high-alloy) steels are most often used for the manufacture of drills, countersinks and taps. Grades of high-speed steels are denoted by letters and numbers, for example R6MZ. The letter P means that the steel is high-speed, the numbers after it show the average tungsten content in percent, the remaining letters and numbers indicate the same as in alloy steel grades. The most important components of high speed steels are tungsten, molybdenum, chromium and vanadium.

High-speed steels, depending on the cutting properties, are divided into steels of normal and increased productivity. Steels of normal performance include tungsten steel grades P18; P9; R9F5 and tungsten-molybdenum steel grades R6MZ; R6M5, retaining a hardness of at least HRC 58 up to a temperature of 620 °C. High performance steels include R18F2 grades; R14F4; R6M5K5; R9M4K8; P9K5; P9K10; R10K5F5; R18K5F2, retaining the hardness HRC 64 up to a temperature of 630...640°C.

Steels of normal productivity - hardness HRC 65, temperature resistance 620 ° C, bending strength 3 ... 4 GPa (300 ... 400 kgf / mm 2) - designed for processing carbon and low-alloy steels with bending strength up to 1 GPa (100 kgf / mm 2), gray cast iron and non-ferrous metals. High-speed steels of increased productivity, alloyed with cobalt or vanadium (hardness HRC 70...78, temperature resistance 630...650°С, bending strength 2.5...2.8 GPa, or 250...280 kgf/ mm 2), are designed for processing hard-to-cut steels and alloys, and with a bending strength of more than 1 GPa (100 kgf / mm 2) - for processing titanium alloys.

All tools made from tool steels are subjected to heat treatment. High speed steel tools can operate at more than high speeds cutting than tools made of carbon and alloy tool steels.

Hard alloys are divided into metal-ceramic and mineral-ceramic. The shape of the plates made from these alloys depends on their mechanical properties. Tools equipped with tungsten carbide inserts allow higher cutting speeds than HSS tools.

Metal-ceramic hard alloys are divided into tungsten, tungsten-titanium and titanium-tungsten-tantalum. Tungsten alloys of the VK group consist of tungsten and titanium carbides. The grades of these alloys are designated by letters and numbers, for example VK2; VKZM; BK4; BK6; VK6M; VK8; VK8V. The letter B means tungsten carbide, the letter K means cobalt, and the number shows the percentage of cobalt (the rest is tungsten carbide). The letter M, given at the end of some grades, means that the alloy is fine-grained. A tool made from this alloy has increased wear resistance, but its impact resistance is reduced. Tools made of tungsten hard alloys are used for processing cast iron, non-ferrous metals and their alloys and non-metallic materials (rubber, plastic, fiber, glass, etc.).

Tungsten-titanium alloys of the TK group consist of tungsten, titanium and cobalt carbides. The grades of these alloys are designated by letters and numbers, for example T5K10; T5K12V; T14K8; T15K6; T30K4; T15K12V. The letter T means titanium carbide, the number behind it is the percentage of titanium carbide, the letter K is cobalt carbide, the number behind it is the percentage of cobalt carbide (the rest in this alloy is tungsten carbide). Tools from these alloys are used for processing all types of steels.

Tungsten-titanium-tantalum alloys of the TTK group consist of titanium, tungsten, tantalum and cobalt carbides. For the manufacture of metal-cutting tools, alloys of the TT7K12 and TT10K8B grades are used, containing respectively 7 and 10% titanium and tantalum carbides, 12 and 8% cobalt carbides (the rest is tungsten carbide). Tools made of these alloys are used in particularly difficult machining conditions, when the use of other tool materials is inefficient.

Hard alloys have high temperature resistance. Tungsten hard alloys retain a hardness of HRC 83...90, and tungsten-titanium - HRC 87...92 at a temperature of 800...950 °C, which allows alloy tools to work at high cutting speeds (up to 500 m/min when machining steels). and up to 2700 m/min when machining aluminium).

For processing parts made of corrosion-resistant, heat-resistant and other hard-to-cut steels and alloys, tools made of fine-grained alloys of the OM group are intended: from VK6-OM alloy for finishing, and from VK10-OM and VK15-OM alloys for semi-finishing and roughing. Even more effective for machining hard-to-cut materials is the use of tools made of hard alloys of the BK10-XOM and VK15-HOM grades, in which tantalum carbide is replaced by chromium carbide. Alloying alloys with chromium carbide increases their hardness and strength at high temperatures.

To increase the strength of the hard alloy plates are clad, i.e. covered with protective films. Widely used wear-resistant coatings of titanium carbides, nitrides and carbonides, deposited in a thin layer (5 ... 10 microns thick) on the surface of hard alloy plates. On the surface of these plates, a fine-grained layer of titanium carbide is formed, which has high hardness, wear resistance and chemical resistance at high temperatures. The wear resistance of coated carbide inserts is on average three times higher than the wear resistance of uncoated inserts, which makes it possible to increase the cutting speed by 25...30%.

Under certain conditions, mineral-ceramic materials obtained from aluminum oxide with the addition of tungsten, titanium, tantalum and cobalt are used as tool materials.

For cutting tools, mineral ceramics of the TsM-332 brand are used, which are distinguished by high temperature resistance (hardness HRC 89 ... 95 at a temperature of 1200 ° C) and wear resistance, which makes it possible to process steel, cast iron and non-ferrous alloys at high cutting speeds cast iron at a cutting speed of 3700 mm/min, which is twice the cutting speed when machining with a tool made of hard alloys). The disadvantage of mineral ceramics brand TsM-332 is increased brittleness.

For the manufacture of cutting tools, cutting ceramics (cermet) grades B3 are also used; VOK-60; VOK-63, which is an oxide-carbide compound (aluminum oxide with the addition of 30 ... 40% tungsten and molybdenum carbides). The introduction of metal carbides (and sometimes pure metals - molybdenum, chromium) into the composition of mineral ceramics improves its physical and mechanical properties (in particular, reduces brittleness) and increases the productivity of processing as a result of an increase in cutting speed. Semi-finishing and finishing with a cermet tool of parts made of gray, malleable cast irons, hard-to-cut steels, some non-ferrous metals and alloys is carried out at a cutting speed of 435 ... 1000 m/min without supplying coolant (coolant) to the cutting zone. The cutting ceramic is characterized by high temperature resistance (hardness HRC 90...95 at 950...1100 °C).

To process hardened steels (HRC 40...67), ductile irons (HB 200...600), hard alloys such as VK25 and VK15 and fiberglass, a tool is used, the cutting part of which is made of superhard materials (STM) based on boron nitride and diamonds. When processing parts made of hardened steels and high-strength cast irons, a tool is used made of large polycrystals (3 ... 6 mm in diameter and 4 ... 5 mm long) based on cubic boron nitride (elbor R). The hardness of elbor P approaches that of diamond, and its temperature resistance is twice that of diamond. Elbor R is chemically inert to iron-based materials. The ultimate strength of polycrystals in compression is 4 ... 5 GPa (400 ... 500 kgf / mm 2), in bending - 0.7 GPa (70 kgf / mm 2), temperature resistance 1350 ... 1450 ° C.

Of the other STMs used for cutting, synthetic diamonds balas (ASB brand) and carbonado (ASPK brand) should be noted. Carbonado is chemically more active towards carbon-containing materials, therefore it is used when turning parts made of non-ferrous metals, high-silicon alloys, hard alloys VK10 ... VK30, non-metallic materials. The durability of cutters made of carbonates is 20...50 times higher than the durability of cutters made of hard alloys.