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2. Tool steels

2.2 High speed steels

3. Hard alloys

3.1 Tungsten-cobalt alloys (VK group)

3.2 Titanium-tungsten-cobalt alloys (TC group)

3.3 Titanium-tantalum-tungsten-cobalt alloys (TTK group)

4. Cutting ceramic

5.2 Characteristics of the main properties and scope of synthetic diamond polycrystals (PCD)

5.3 Characteristics of the main properties and scope of PSTM based on dense modifications of boron nitride BN

6. Tool materials with wear-resistant coating

1. Requirements for tool materials

When cutting, the contact pads of the tool are subjected to intensive action of high force loads and temperatures, the values ​​of which are of a variable nature, and the interaction with the material being processed and reagents from the environment leads to intense physical and chemical processes: adhesion, diffusion, oxidation, corrosion, etc.

Taking into account the need for resistance of the contact pads of the cutting tool to micro- and macro-destruction in specified conditions, a number of special requirements are imposed on the properties of tool materials, the fulfillment of which determines the place of their effective use for cutting tools. The main requirements for tool materials are as follows:

1. The tool 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 tool 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., maintaining hardness when heated to the temperatures at which 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 2.1).

Table 2.1 - Heat resistance and allowable cutting speed of tool materials

3. An important requirement is a sufficiently high strength of the 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. 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. The tool material must have high wear resistance at elevated temperatures, i.e. have good abrasion resistance of the workpiece material, which is manifested in the resistance of the material to contact fatigue.

5. Necessary condition to achieve high cutting properties of the tool is the low physical and chemical activity of the tool material in relation to the workpiece. 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. The tool material must have technological properties that provide 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.

On fig. 2.1 shows the location of the main groups of tool materials according to their properties. It can be seen from the figure that the hardness and strength of tool materials are antagonistic properties, i.e. the higher the hardness of the material, the lower its strength. Therefore, the set of basic properties determines the area and condition rational use tool material in the cutting tool.

For example, a tool made of superhard tool materials based on diamond and cubic boron nitride (CTM) or cutting ceramics (RC) is used exclusively for superfinishing workpieces at high and over high speeds cutting, but with very limited cut sections.

When machining structural steels at low and medium cutting speeds, in combination with medium and large shear sections, high-speed steel tools are of great advantage.

Tool materials are divided into five main groups: tool steels (carbon, alloy and high-speed); metal-ceramic hard alloys (VK, TK and TTK groups); cutting ceramics (oxide, oxycarbide and nitride); abrasive materials (see abrasive processing) and superhard STM materials (based on diamond and cubic boron nitride (CBN)).

1 - Fundamental dependence of the main properties of tool materials (hardness - strength)

Figure 2.1 - Classification of tool materials according to their properties

The most common of these groups is high-speed steel, from which about 60% of the tool is made, from metal-ceramic hard alloys - about 30%, from other groups of materials - only about 10% of the blade tool.

An analysis of the main directions for improving tool materials (see Fig. 2.1) allows us to note that they are associated with an increase in hardness, heat resistance, wear resistance with a decrease in strength characteristics, toughness and crack resistance. These trends do not correspond to the idea of ​​creating an ideal tool material with an optimal combination of properties in terms of hardness, heat resistance, impact strength, crack resistance, and strength.

Obviously, the solution to this problem should be associated with the development of a composite tool material, in which high values ​​of surface hardness, heat resistance, physicochemical inertness would be combined with sufficient values ​​of bulk strength in bending, impact strength, and endurance limit.

In world practice, these methods for improving tool materials are increasingly being used, especially in the production of replaceable polyhedral inserts (SMP) for mechanical fastening on a cutting tool.

2. Tool steels

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 than other materials for the manufacture of cutting tools, carbon tool steel grades U7, U7A ... U13, U13A began to be used. 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 ... 250C) their hardness decreases sharply.

Alloyed tool steels, in their chemical composition, differ from carbon steels by an increased content of silicon or manganese, or by the presence of one or more alloying elements: chromium, nickel, tungsten, vanadium, cobalt, molybdenum. For cutting tools, low-alloy steel grades 9ХФ, 11ХФ, 13Х, В2Ф, ХВ4, ХВСГ, ХВГ, 9ХС, etc. are used. These steels have higher technological properties - better hardenability and hardenability, less tendency to warp, but their heat resistance is 350 ... 400C 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 carbide, ceramic and STM tools provide higher machining performance.

The widespread use of high-speed steels for the manufacture of complex tools is determined by a combination of high hardness (up to HRC68) and heat resistance (600-650C) 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 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.

Steels of normal heat resistance include tungsten R18 and tungsten-molybdenum R6M5 steels (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…620C. 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 are characterized by a high content of carbon, vanadium and cobalt.

Among vanadium steels, the R6M5F3 grade has received the greatest use.

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 grains of an 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 2.2 Chemical composition of high speed steels

According to the grindability, high-speed steels can be divided into 4 groups:

Powder high speed steels, regardless of the vanadium content, belong to groups 1 and 2 i.e. have good sandability.

Steels with reduced grindability are prone to burns, i.e. to a change in the structure of the near-surface layers of steel after grinding or sharpening, the appearance of secondary hardening or secondary tempering zones with reduced hardness.

The consequence of burns can be a significant reduction in tool life.

However, the problem of "grindability" of high-vanadium high-speed steels is successfully solved if abrasive wheels with STM grains based on cubic boron nitride (CBN) are used when sharpening and finishing cutting tools.

Vanadium high-speed steels are used for tools of simple shapes under finishing and semi-finishing cutting conditions for processing materials with increased abrasive properties.

Among cobalt steels, grades R6M5K5, R9M4K8, R18K5F2, R9K5, R2AM9K5, etc. have found the greatest use. The introduction of cobalt into the composition of high-speed steel most significantly increases its hardness (up to 66-68 HRC) and heat resistance (up to 640-650C). In addition, the thermal conductivity of steel increases, since cobalt is the only alloying element that leads to this effect.

This makes it possible to use them for processing heat-resistant and stainless steels and alloys, as well as structural steels of increased strength. The service life of tools made of such steels is 3-5 times higher than that of steels R18, R6M5.

Steels of high heat resistance are characterized by a low carbon content, but very large quantity alloying elements - V11M7K23, V14M7K25, 3V20K20Kh4F. They have a hardness of 69...70 HRC and a heat resistance of 700...720C. The most rational area of ​​their use is the cutting of hard-to-cut materials and titanium alloys. In the latter case, the tool life is 60 times higher than that of R18 steel, and 8-15 times higher than that of VK8 hard alloy.

Significant disadvantages of these steels are their low bending strength (not higher than 2400 MPa) and low machinability in the annealed condition (38-40 HRC) in the manufacture of tools.

Due to the ever increasing scarcity of tungsten and molybdenum - the main alloying elements used in the production of high speed steel, sparingly alloyed grades are increasingly used. Among the steels of this type, steel 11R3AM3F2, which is used in the manufacture of tools, has received the greatest use, as it has sufficiently high rates of hardness (HRC 63-64), strength (and -3400 MPa) and heat resistance (up to 620C).

Economically alloyed steels

Steel 11R3AM3F2 is technologically metallurgical production, however, due to the worse grindability, its use is limited to simple-shaped tools that do not require large amounts of abrasive processing (metal saws, cutters, etc.).

Powder high speed steels

The most effective opportunities for improving the quality of high-speed steel, its performance properties, and the creation of new cutting materials appeared when using powder metallurgy.

Powder high-speed steel is characterized by a uniform fine-grained structure, uniform distribution of the carbide phase, reduced deformability during heat treatment, good grindability, higher technological and mechanical properties than steel of similar grades obtained by traditional technology. Technology system the production of powder high-speed steels is as follows: gas atomization of a liquid jet of high-speed steel into powder, filling and degassing of the powder into a cylindrical container, heating and forging (or rolling) containers into bars, final incisal peeling of the remains of the container from the surface of the bars. The main advantage of powder technology is a sharp reduction in the size of carbides formed during the crystallization of the ingot in the mold. Thus, the powder obtained by gas spraying is a micro-ingot in which large carbides are not formed.

The new technology makes it possible to significantly change the alloying scheme in order to purposefully increase certain performance characteristics that determine tool life.

The main examples of the development of new compositions of powder high-speed steel are reduced to the possibility of introducing up to 7% vanadium into the composition and, in connection with this, a significant increase in wear resistance without compromising grindability. As well as the introduction of carbon with a "supersaturation" of up to 1.7%, which makes it possible to obtain a significant amount of vanadium carbides and high secondary hardness after quenching and tempering. A number of powder steel grades are produced in Ukraine: (R7M2F6-MP, R6M5F3-MP, R9M2F6K5-MP, R12MF5-MP, etc. GOST 28369-89).

Powder metallurgy technology is also used to produce carbide steel, which in terms of its properties can be classified as intermediate between high speed steel and hard alloys.

Carbide steel differs from ordinary high-speed steel by a high content of the carbide phase (mainly titanium carbides), which is achieved by mixing high-speed steel powder and fine particles of titanium carbide. The content of TiC in carbide steel is 20%. By plastic deformation of the compressed powder, blanks of a simple shape are obtained. In the annealed state, the hardness of carbide steel is HRC 40-44, and after quenching and tempering, HRC 68-70.

When used as a cutting tool material, carbide steel provides a 1.5-2-fold increase in tool life compared to similar grades of conventional production technology. In some cases, carbide steel is a full-fledged substitute for hard alloys, especially in the manufacture of shaping tools (deforming broaches).

3. Hard alloys

Carbide alloys are the main tool material providing high-performance cutting of materials. Now the total amount of carbide tools used in machining production is up to 30%, and up to 65% of chips are removed with this tool, since the cutting speed used in processing with this tool is 2-5 times higher than that of a high-speed tool. Hard alloys are obtained by powder metallurgy in the form of plates. The main components of such alloys are tungsten carbides WC, titanium TiC, tantalum TaC, and niobium NbC, the smallest particles of which are connected by relatively soft and less refractory bonds of cobalt or nickel mixed with molybdenum. Hard alloys can be divided into four groups according to their composition and applications: tungsten-cobalt (WC-Co), titanium-tungsten-cobalt (WC-TiC-Co), titanium-tantalum-tungsten-cobalt (WC-TiC-TaC-Co), tungsten-free (based on TiC, TiCN with various binders ).

3.1 Tungsten-cobalt alloys (VC)

Tungsten-cobalt alloys (VC group) consist of tungsten carbide (WC) and cobalt. The alloys of this group differ in their cobalt content, tungsten carbide grain sizes, and manufacturing technology. To equip the cutting tool, alloys with a cobalt content of 3-10% are used. In table. 2.3 shows the composition and characteristics of the main physical and mechanical properties of hard alloys, in accordance with GOST 3882-74.

Table 2.3 - Composition and characteristics of the main physical and mechanical properties of alloys based on WC-Co (VK group)

AT symbol alloy figure shows the percentage of cobalt binder. For example, the designation VK6 shows that it contains 6% cobalt and 94% tungsten carbides. With an increase in the cobalt content in the alloys in the range from 3 to 10%, the tensile strength, impact strength and plastic deformation increase, while the hardness and elastic modulus decrease. With an increase in the cobalt content, the thermal conductivity of the alloys and their coefficient of thermal expansion increase.

Figure 2.2 - Influence of cobalt on the properties of the hard alloy of the group (VK)

Of all existing hard alloys, alloys of the VK group with the same cobalt content have higher impact strength and flexural strength, as well as better thermal and electrical conductivity. However, the resistance of these alloys to oxidation and corrosion is much lower, in addition, they have a high tendency to seize with chips during cutting. With the same cobalt content, the physical, mechanical and cutting properties of the alloys are largely determined by the average grain size of tungsten carbide (WC). The developed technological methods make it possible to obtain solid

alloys in which the average grain size of the carbide component can vary from fractions of a micrometer to 10-15 microns.

Alloys with carbide sizes from 3 to 5 microns are classified as coarse-grained and are designated by the letter B (VK6-V), with carbide sizes from 0.5 to 1.5 microns by the letter M (fine-grained VK6-M), and with sizes when 70% grains less than 1.0 microns - OM (especially fine-grained VK6-OM). Alloys with a smaller size of the carbide phase are more wear-resistant and heat-resistant, and also make it possible to sharpen a sharper cutting edge (allow a cutting edge rounding radius of up to 1.0–2.0 µm).

Physical and mechanical properties of alloys determine their cutting ability in various operating conditions.

These regularities form the basis of practical recommendations for the rational use of specific grades of alloys. So, VK3 alloy with a minimum cobalt content, as the most wear-resistant, but the least durable, is recommended for finishing with the maximum allowable cutting speed, but with low feed and depth of cut, and VK8, VK10M and VK10-OM alloys - for roughing at a reduced speed cutting and increased cross-section of the cut in conditions of shock loads.

3.2 Titanium-tungsten-cobalt alloys (TC)

Alloys of the second group TK consist of three main phases: a solid solution of titanium and tungsten carbides (TiC-WC), tungsten carbide (WC) and a cobalt binder. They are intended mainly for equipping tools for cutting steels that produce continuous chips. Compared to alloys of the VK group, they have greater resistance to oxidation, hardness and heat resistance, and at the same time lower thermal and electrical conductivity, as well as lower modulus of elasticity.

The ability of alloys of the TK group to resist wear under the influence of sliding chips is also explained by the fact that the setting temperature with steel for alloys of this type is higher than for alloys based on WC-Co, which makes it possible to use higher cutting speeds when machining steel and significantly increase tool life. .

In table. 2.4 shows the composition and characteristics of the main physical and mechanical properties of alloys in accordance with GOST 3882-74.

Table 2.4 - Composition and characteristics of the physical and mechanical properties of alloys based on WC-TiC-Co, TK group

As with WC-Co based alloys, flexural and compressive strength and toughness increase with increasing cobalt content.

The thermal conductivity of the alloys of the TK group is significantly lower, and the coefficient of linear thermal expansion is higher than that of the alloys of the VK group. Accordingly, the cutting properties of the alloys also change: with an increase in the cobalt content, the wear resistance of the alloys during cutting decreases, and with an increase in the content of titanium carbide, the operational strength decreases (Fig. 2.3).

1) Bending strength - izg; 2) Hardness - HRA

Figure 2.3 - Influence of cobalt on the properties of a hard alloy of the TK group

Therefore, alloys such as T30K4 and T15K6 are used for finishing and semi-finishing of steel with high cutting speeds and low tool loads. At the same time, T5K10 and T5K12 alloys with the highest cobalt content are designed to work under severe conditions of shock loads with a reduced cutting speed.

By introducing alloying additives, alloys were obtained that are used for cutting steel with high shock loads.

The T4K8 alloy was developed to replace the standard T5K10 alloy. Its ultimate strength in bending is 1600 MPa, while for the T5K10 alloy it is 1400 MPa. The limiting plastic deformation of T4K8 is 1.6%, and for the T5K10 alloy it is 0.4%.

The T4K8 alloy, to a greater extent than the T5K10 alloy, resists shock loads and can be used in rough turning of steel castings at a cutting speed of 30-70 m/min, a cutting depth of up to 40 mm and a feed of 1-1.2 mm/rev. Tool life, equipped with T4K8 alloy, is 1.5-2.0 times higher than tool life, equipped with T5K10 alloy.

3.3 Titanium-tantalum-tungsten-cobalt alloys (TTK)

Industrial tantalum-containing hard alloys based on TiC-WC-TaC-Co consist of three main phases: a solid solution of titanium, tungsten and tantalum carbides (TiC-TaC-WC), as well as tungsten carbide (WC) and a cobalt binder.

The introduction of tantalum carbide additives into alloys improves their physical, mechanical and operational properties, which is expressed in an increase in bending strength at a temperature of 20C and 600-800C.

An alloy containing tantalum carbide has a higher hardness, including at 600-800C. Tantalum carbide in alloys reduces creep, significantly increases the fatigue limit of three-phase alloys under cyclic loading, as well as heat resistance and oxidation resistance in air. In table. 2.5 shows the composition and characteristics of the main physical and mechanical properties of alloys in accordance with GOST 3882-74.

Table 2.5 - Composition and characteristics of the physical and mechanical properties of alloys based on TiC-WC-TaC-Co (TTK group)

Increasing the content of tantalum carbide in the alloy increases its cutting resistance, especially due to a lower tendency to cratering and failure under thermal cycling and fatigue loads. Therefore, tantalum-containing alloys are recommended mainly for severe cutting conditions with large shear sections, when significant force and temperature loads act on the cutting edge of the tool, as well as for interrupted cutting, especially milling. The most durable for steel processing in particularly unfavorable conditions (interrupted turning, planing, rough milling) is the TT7K12 alloy. Its use instead of high-speed steel makes it possible to increase the cutting speed by 1.5-2 times.

3.4 Tungsten-free hard alloys (BVTS)

Due to the scarcity of tungsten and cobalt, the industry produces tungsten-free hard alloys based on titanium carbides and carbonitrides with a nickel-molybdenum binder (Table 2.6).

Table 2.6 - Composition and characteristics of the physical and mechanical properties of tungsten-free hard alloys

In terms of hardness, BVTS are at the level of tungsten-containing alloys (VK group), in terms of strength characteristics and especially in terms of elasticity modulus, they are inferior to them. The Vickers hardness of BVTS at elevated temperatures in the temperature range of 293-1073K is slightly lower than the hardness of the T15K6 tungsten-containing alloy.

BVTS have low oxidizability. The highest heat resistance of the alloy KNT16, the alloy TN20 it is much lower. Therefore, it is advisable to manufacture a tool from the KNT16 alloy that works with interrupted cutting, for example, milling. The average "breaking feed" (at which the blade is destroyed) is 0.3 mm/tooth for the TN20 alloy, and 0.54 mm/tooth for the KNT16 alloy. When choosing cutting modes, the feed should not exceed these values, and the depth of cut should not exceed 5mm.

The TN20 alloy has the highest wear resistance. When turning steel 45 and steel 40X at t=1mm and S=0.2mm/rev, the resistance of the TN20 alloy is higher than that of the T15K6 alloy, over the entire cutting speed range (from 200 to 600 m/min).

Heating of a tool made of BVTS in HDTV installations, which are commonly used in tool soldering, degrades its performance. Therefore, for cutting from BVTS, mainly replaceable non-regrindable inserts (SMPs) are made.

Due to the reduced thermal conductivity, the greatest resistance of BVTS is in the case of the use of four-, five-, and six-sided SMPs, and not trihedral ones. in this case, the optimal geometric parameters of the plates are the front angle of 10, the clearance angle of 8-10, the radius at the top of 0.8 mm.

The effectiveness of the use of BVTS depends on the correct preparation of the tool, the choice of cutting conditions and processing conditions. The inserts must have a high-quality finishing on the cutting edges and the bearing surface and lie against the support without play.

The workpiece to be machined should not have a runout exceeding half of the machining allowance, as well as traces gas welding, slag inclusions.

Coolant should be used whenever possible when turning.

To prevent catastrophic tool breakage, it is recommended that the plate be forced to rotate after a certain number of blanks have been processed. Permissible wear of the cutters on the back face is 1.5-1.8 mm.

When milling, BVTS can be operated up to wear of 2.5-3.0 mm along the back edge.

With their high strength, WC-Co alloys are better able to resist the pulsating high load that occurs under these machining conditions. The prevailing type of wear in this case is adhesive-fatigue wear, and in the machining of white cast irons and fiberglass, it is abrasive, in which an important factor determining tool life is not only the cobalt content in the alloy, but also the grain size of the WC phase. And the higher the hardness of the material being machined, the more significant is the effect of the carbide grain size on the tool life.

Ni-based alloys with high strength and significant creep resistance at high temperatures, as well as low thermal conductivity, with with great difficulty processed by cutting. On the cutting surface of the tool-workpiece, very high temperatures and stresses are generated, seizure and subsequent detachment of hard alloy particles occur. The best resistance under these conditions is shown by especially fine-grained high-cobalt alloys.

Carbide grades based on WC-TiC-Co are recommended in the case of steel machining at high cutting speeds, when continuous chips are formed. The chips are constantly in contact with the front surface of the tool under conditions of significant temperature and pressure, which leads to the intensive formation of wear holes on the front surface of the cutter. In this case, diffusion wear prevails. A solution of tungsten carbide in titanium carbide dissolves in steel at a higher temperature and much more slowly than tungsten carbide. In addition, the presence of the WC-TiC-Co phase helps to reduce the rate of dissolution of tungsten carbide grains in steel, and thereby reduces the wear rate.

With the diffusion nature of wear, its rate, determined by the rate of dissolution of carbide grains in steel, depends to a greater extent on the chemical properties of the alloy than on its hardness associated with grain size. Under such conditions, tungsten-free alloys based on titanium carbide or carbonitride have a much greater resistance. They interact with steel less intensively than complex carbide WC-TiC.

Carbide grades based on WC-TiC-TaC-Co are recommended for interrupted cutting, such as milling, when numerous short cracks appear on the working surfaces of the tool, perpendicular to the cutting edge. These cracks are caused by periodic expansion during heating during cutting and contraction during cooling of the surface layers of the hard alloy. With further development, cracks lead to chipping and chipping and become main reason tool failure.

Therefore, to equip a milling tool, hard alloys are used that are the least sensitive to thermal fatigue and dynamic cyclic loads, alloys containing tantalum carbide in their composition, i.e. alloys based on WC-TiC-TaC-Co.

3.6 Classification of modern hard alloys according to the international standard ISO513 and determination of the conditions for their effective use

When determining the applications of hard alloys, the recommendations of the international organization of standards ISO (ISO) are usually used, which provide for their use taking into account the materials being machined and the type of chips, the type of processing (finishing, semi-finishing, light roughing and roughing), machining conditions (good, normal and heavy), as well as types of processing (turning, boring, milling, etc.).

According to (ISO), all processed materials are divided into three groups: P (indicated in blue), M (yellow) and K (red). The P group includes steels and steel castings, during the processing of which drain chips are obtained. The M group includes stainless steels, titanium and heat-resistant alloys, during the processing of which fracture and drain chips are obtained. Group K includes cast irons, non-ferrous metals and their alloys, materials with high surface hardness, during the processing of which fracture and elemental chips are obtained (Table 2.7).

Table 2.7 - Classification of processed materials by cutting groups

Each application group is divided into subgroups, and as the subgroup index increases from 01 to 40 (50), the processing conditions become more severe, ranging from fine cutting to roughing with impacts. This consideration is convenient for the selection of recommended grades of hard alloys according to their properties. The higher the application subgroup index, the lower the required carbide wear resistance and allowable cutting speed, but higher strength (impact strength) and allowable feed and depth of cut (Table 2.8).

Table 2.8 Subgroups of Carbide Applications

* Work with variable depth of cut, with intermittent feed, with shocks, vibrations, with the presence of a casting skin and abrasive inclusions in the material being processed

Thus, small indices correspond to finishing operations, when high wear resistance and heat resistance are required from hard alloys, and large indices correspond to roughing operations, i.e. when the hard alloy must have high strength. In this regard, each grade has its own preferred application in which it provides the maximum workability of the alloy and machining performance.

The cutting speed, the continuity of processing, the rigidity of the AIDS system, the method of obtaining the workpiece (the state of the machined surface) allows you to determine the processing condition and formulate requirements for the basic properties of the hard alloy. Processing conditions can be good, normal and heavy.

GOOD - High speeds. Continuous cutting. Pre-finished workpieces. High rigidity of the AIDS technological system.

Requirements for hard alloy - high wear resistance.

NORMAL - Moderate cutting speeds. contour turning. forgings and castings. Sufficiently rigid AIDS system.

The requirements for hard alloys are good strength combined with sufficiently high wear resistance.

HEAVY - Low speeds. Interrupted cutting. Thick crust on castings or forgings. Non-rigid AIDS system.

Requirements for hard alloy - high strength.

In addition to subgroups of application, it is necessary to know the type of processing (finishing, semi-finishing, light and roughing), which allows you to navigate in terms of depth of cut (t, mm) and feed (S 0, mm / rev). The type of processing is given in table. 2.9.

Table 2.9 Treatment type

The scope of hard alloys can be represented by a summary table 2.10.

Table 2.10 Defining Carbide Applications

From Table. 2.10 it can be seen that the scope of use of the grade of hard alloy will depend on the material being processed, the conditions and type of processing. Areas of rational use of hard alloys of domestic production are given in table. 2.11.

Table 2.11 Carbide applications

Note. Wear resistance of alloys increases from bottom to top, strength - vice versa.

Hard alloys of the MS series are produced at the Moscow Plant of Hard Alloys (MKTO) according to the technology of the Sandik Coromant company.

4. Cutting ceramic

The industry produces four groups of cutting ceramics: oxide (white ceramics) based on Al 2 O 3 , oxycarbide (black ceramics) based on Al 2 O 3 -TiC composition, oxide-nitride (cortinite) based on Al 2 O 3 -TiN and nitride ceramics based on based on Si 3 N 4 .

The main feature of cutting ceramics is the absence of a binder phase, which significantly reduces the degree of its softening when heated during wear, increases plastic strength, which predetermines the possibility of using high cutting speeds that are much higher than the cutting speeds of a hard alloy tool. If the limiting level of cutting speeds for carbide tools when turning steels with thin sections and small blunting criteria is 500-600 m/min, then for a tool equipped with cutting ceramics, this level increases to 900-1000 m/min.

The compositions of the main types of cutting ceramics and some physical and mechanical properties are presented in Table. 2.12.

Table 2.12 Composition, properties and applications of ceramics

The disadvantage of oxide ceramics is its relatively high sensitivity to sharp temperature fluctuations (thermal shocks). Therefore, cooling when cutting with ceramics is not used.

This is the main reason for micro- or macro-cracking of cutting ceramics and tool pads already at the stages of running-in or initial stage of steady-state wear, leading to failures due to brittle fracture of the tool. The mentioned wear mechanism of the ceramic cutting tool is prevailing.

In recent years, new grades of oxide ceramics have appeared, which include zirconium oxide (ZrO 2) and its reinforcement with "filamentary" silicon carbide (SiC) crystals. Reinforced ceramics has high hardness (HRC A -92) and increased strength (up to 1000 MPa).

Along with the improvement ceramic materials on the basis of aluminum oxide, new grades of cutting ceramics based on silicon nitride (silinit-R) have been created. Such a ceramic material has a high bending strength (bend = 800 MPa), a low coefficient of thermal expansion, which distinguishes it favorably from oxide ceramic materials. This makes it possible to successfully use silicon nitride tools for rough turning, semi-finishing of cast iron, as well as finishing turning of complexly alloyed and heat-treated (up to HRC 60) steels and alloys.

Cutting ceramics are produced in the form of non-regrindable replaceable inserts. Plates are made with negative chamfers around the perimeter on both sides. chamfer size f = 0.2 ... 0.8 mm, its angle of inclination is negative from 10 to 30. The chamfer is necessary to harden the cutting edge.

The allowable wear of ceramic inserts is much less than that of carbide inserts. The maximum wear on the back surface should not exceed 0.3 ... 0.5 mm, and during finishing operations 0.25 ... 0.30 mm.

When assigning cutting conditions for ceramics, there are recommendations:

1. The preferred square shape of the insert with the maximum possible sharpening angle and the largest radius at the top of the insert r b .

2. The width of the chamfer f is selected depending on the hardness of the material being processed, the harder the material being processed, the wider the chamfer.

3. The cutting speed must be set to the maximum allowable based on the rigidity of the AIDS system and the characteristics of the equipment.

4. Workpieces machined with cutting ceramic inserts must have chamfers at the inlet and outlet of the cutter, the width of which exceeds the machining allowances, as well as grooves at the transition points from cylindrical surface to the end.

Currently, ceramic tools are recommended for finishing gray, ductile, ductile and chilled cast irons, low and high alloy steels, including improved, heat-treated (HRC up to 55-60), non-ferrous alloys, structural polymer materials(K01-K05, P01-P05). Under these conditions, a tool equipped with cutting ceramic inserts significantly outperforms a carbide tool in terms of performance.

The use of a ceramic tool in machining with increased shear cross-sections (txS), with interrupted cutting, sharply reduces its efficiency due to the high probability of sudden failure due to brittle fracture of the cutting part of the tool. This largely explains the relatively low volume of ceramic tools used in Ukrainian industry (up to 0.5% of the total volume of cutting tools), for developed Western countries this volume ranges from 2 to 5%.

5. Super hard synthetic polycrystalline tool materials

Superhard materials are considered to have microhardness higher than the microhardness of natural corundum (Al 2 O 3) (i.e., Vickers hardness of more than 20 GPa). Materials whose hardness is higher than metals (i.e. 5-20 GPa) can be considered as highly hard. Of the natural materials, only diamond is classified as superhard. In 2000, a new superhard phase, cubic boron carbonitride (BC 2 N), was obtained by direct transformation of a graphite-like solid solution of BN-C at a pressure of 25 GPa and a temperature of 2100 K at the ISM Academy of Sciences of Ukraine, which received the designation kanb. The hardness and modulus of elasticity of kanb is intermediate between diamond and cubic boron nitride, making it the second hardest material after diamond and opening up new perspectives.

5.1 Features of obtaining tool materials based on diamond and cubic boron nitride

The tool industry produces synthetic superhard materials based on diamond and cubic boron nitride (CBN).

Natural diamond is the most solid material on Earth, which has long been used as a cutting tool. The fundamental difference between single-crystal natural diamond and all other tool materials with a polycrystalline structure, from the toolmaker's point of view, is the possibility of obtaining an almost perfectly sharp and straight cutting edge. Therefore, at the end of the 20th century, with the development of electronics, precision engineering and instrumentation, the use of natural diamond cutters for micro-turning of mirror-clean surfaces of optical parts, memory disks, copier drums, etc. increases. However, due to the high cost and brittleness, natural diamonds are not used in general engineering, where the requirements for the quality of part processing are not so high.

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Locksmith and tool work

Basic properties of tool materials

The materials used for the manufacture of cutting tools can be divided into three main groups:
1) tool steels;
2) hard alloys;
3) non-metallic tool materials.

The tool material must have certain performance properties that correspond to the operating conditions of the cutting tool. The hardness and strength of the tool material must be higher than the similar parameters of the processed material (steel and cast iron). When cutting, the working part of the tool is heated to high temperatures, and its cutting edges are subjected to intense wear, so the tool material must have high heat resistance and wear resistance.

Tool steels. An alloy of iron with carbon (the content of the latter is 0.1-1.7%) is called steel. Steels containing more than 0.65% carbon and due to this high hardness are called tool steels.

To improve the operational or technological properties of tool steel, alloying (improving) elements are introduced into its composition. Such steels are called alloyed and their designation (grade) includes a Russian letter corresponding to the name of the alloying element: X - chromium (Cr); F - vanadium (V); H - Nickel (Ni); K - cobalt (Co); G - manganese (Mn); T - titanium (Ti); M - molybdenum (Mo); B - niobium (No); C - silicon (Si); Ta - tantalum (Ta); B - tungsten (W), etc.

Carbon in steel grade letter designation does not have, and its content (in tenths of a percent) is indicated at the beginning of the labeling. The content of the alloying element is indicated as a percentage after the corresponding letter. For example, alloyed chromium-silicon steel grade 9XC contains 0.9% carbon, 1% chromium and 1% silicon. If the content of carbon or an alloying element in steel is equal to or approximately equal to 1%, then the unit in the marking is omitted. For example, HVG grade steel contains 1% carbon, 1% chromium, 1% tungsten and 1% manganese.

Carbon tool steels, depending on the carbon content, are assigned grades U7A, U8A, U9A, U10A, UNA, U12A, U13A. For example, steel grade U7A: carbon (letter U), contains 0.7% carbon (number 7); high-quality (letter A), i.e., having a low content of harmful impurities (sulfur and phosphorus). Heat resistance (QK = 180-L220°C) and wear resistance of carbon tool steels are lower than similar parameters of other tool materials. The higher the carbon content, the higher these parameters.

Hardness (after annealing) 187-207 HB is low, so these steels are well machined by cutting.

Hardened carbon steels grind well. These steels (the cheapest of tool materials) are used for the manufacture of tools operating at low cutting temperatures: woodworking and fitter's tools; templates and calibers of reduced accuracy; files, scrapers, rolling rollers, taps, etc.

Low-alloyed tool steels include steel grades 9XC, HGS, HVG, HVGS, etc. These steels contain about 1% carbon, as well as chromium (1%), manganese (1%), silicon (1%) and tungsten (1% ), are characterized by better hardenability, increased hardenability and heat resistance, less tendency to grain growth.

The heat resistance of these QK steels is 250-260 ° C, the hardenability is 40-50 mm, the hardness (after annealing) is 241-255 HB. The machinability of low-alloy steels is somewhat worse than carbon steels, they are more prone to burns during grinding.

These steels are used for the manufacture of dies, taps, drills, reamers, etc., as well as cold stamping dies.

High-speed steels are used for the manufacture of cutting tools operating at high speeds, forces and cutting temperatures. These steels are characterized by high wear resistance, heat resistance, strength and toughness. High-speed steels are divided into two groups: 1) steels alloyed with tungsten and molybdenum and containing up to 2% vanadium (P18, P12, P9, P6M5, P6MZ, etc.); 2) steel alloyed with tungsten and cobalt and containing more than 2% vanadium (R18F2, R14F5, R9F5, R10F5K5, R9K5, R9KYu, etc.).

The first group belongs to steels of normal productivity, and the second - to steels of increased productivity.

At the beginning of the marking of these steels is the letter P (which means high-speed), the number following it indicates the average content of tungsten ( ), subsequent letters and numbers indicate the names of other alloying elements and, accordingly, their average content (). In addition, high-speed steels contain carbon (0.7-1.5%), chromium (3-4.4%) and some other elements that are not indicated in the marking. For example, high-speed steel grade P18 contains 0.7-0.8% carbon, 17-18.5% tungsten, 3.8-4.4% chromium, 1-1.4% vanadium.

The high performance properties of high-speed steels are ensured by their alloying with tungsten, vanadium and molybdenum, which, when combined with carbon, form the corresponding carbides (WC, VC and MoC). The wear resistance of high-speed steels is 3-5 times higher than that of carbon and low-alloy steels; heat resistance is 620 °C, and when alloyed with cobalt 640 °C. The presence of vanadium contributes to the formation of a fine-grained structure, which increases the strength and reduces the brittleness of the steel.

High-speed steels also have high technological properties: they are hardened in heated oil, molten salts and when cooled in air (i.e., they do not require rapid cooling); calcined over the entire cross section, regardless of the size of the workpiece.

The disadvantages of these steels are high hardness in the state of delivery (255-269 HB); tendency to carbide heterogeneity; reduced grindability (especially for steels alloyed with vanadium).

The most common is R6M5 grade steel, used for the manufacture of all types of cutting tools intended for processing (at a cutting speed of up to 1-1.2 m/s) carbon and medium-alloy structural steels.

Hard alloys are metallic materials, characterized by high heat resistance, wear resistance and hardness. The heat resistance and hardness of these alloys are, respectively, twice and 1.3-1.4 times higher than the similar parameters of high-speed steel grade P18. Therefore, the durability of carbide tools is much higher than the durability of high-speed tools, and this advantage is greater, the higher the cutting speed.

Hard alloys manufactured by the method of powder metallurgy (by pressing in the form of crushed metal powders and their subsequent sintering at high temperatures) are called cermets.

The basis of ceramic-metal hard alloys are grains of tungsten carbides (WC), titanium (TiC) and tantalum (TaC), which are interconnected by cobalt (strong and ductile material). The grain size is usually not more than 1-2 microns. Cobalt fills the entire space between the grains, leaving no voids (pores), and cements them.

Hard alloys are divided into three groups: tungsten (B); titanium-tungsten (TV); titanotan-tal-tungsten (TTV). Group B alloys consist of tungsten carbides bonded with cobalt. This group includes alloys of grades VK.Z, VK4, VK6, VK8, etc. Here the letter B means tungsten; K - cobalt; the number following the letter, the content of cobalt in . For example, an alloy of grade VK8 contains 8 cobalt and 92% tungsten carbides.

Hard alloys of the TV group consist of titanium carbides and tungsten carbides bonded with cobalt. This group includes alloys of grades T5K.Yu, T15K8, T15K6, T30K4. The T15K6 grade alloy contains 15% titanium carbides, 6% cobalt and 79% tungsten carbides.

The third group includes hard alloys grades TT7K12, TT10K8, TT20K9, etc., consisting of tungsten carbides, titanium carbides, tantalum carbides bonded with cobalt. The TT7K12 hard alloy contains 12% cobalt, 7% titanium and tantalum carbides, and 81% tungsten carbides.

The hardness of cermet hard alloys is 87-92 HRA. With an increase in the cobalt content, the hardness and wear resistance of the alloys decrease, but at the same time their toughness and strength increase.

The heat resistance of alloys of the first and second groups is about 1000 °C; alloys of the third group - 1050-1100 °C.

Hard alloys of group B are used in the processing of workpieces made of cast iron, non-ferrous metals and their alloys and non-metallic materials (plastics, fiberglass, etc.); alloys of the TV group - when processing carbon and alloy steels; alloys of the TTV group - in the processing of hard-to-cut materials, corrosion-resistant and heat-resistant steels and alloys, titanium alloys, in rough turning and milling of steel blanks. Two types of carbide inserts are produced - for soldering onto holders and tool bodies and for mechanical fastening on them (the latter type of fastening is preferred). The purpose, shape, dimensions and degree of accuracy of carbide inserts are established by the standard.

Mineral-ceramic hard alloys consist of refractory oxides of aluminum (A1203) or zirconium (Zr02) bound by a vitreous substance. These alloys, produced by pressing powders of these oxides followed by sintering, have high hardness (91–92 HRA), heat resistance (1300°C), and wear resistance, but they are very brittle.

Cermets are somewhat less brittle - hard alloys in which refractory oxides are bound by metals (iron, nickel, titanium, etc.), Mineral-ceramics and cermets are used for fine turning (at a speed of 4-5 m / s) workpieces with a uniform allowance; wherein prerequisite is the high rigidity of the machine tool and technological equipment.

In recent years, single crystals of natural diamond and polycrystals of synthetic diamond and cubic boron nitride (CBN) have been used as tool materials for cutting tools (cutters, drills, milling cutters). Depending on the feedstock, alloying additives and production technology, various types of CBN are obtained, called composites.

Diamond blade tools are used for high-performance finishing and semi-finishing (at a cutting speed of 5-10 m/s) of non-ferrous metals and alloys, titanium and non-metallic materials.

Blade tools made of CBN are used for finishing (at a cutting speed of 0.7-1.7 m/s) hardened alloyed and hardened tool steels. Such performance is not possible when cutting with other tool materials. For example, when processing with CBN cutters, the cutting speed reaches 7-12 m / s, i.e., it approaches the grinding speed.

Tool materials must have a high hardness that remains sufficient even at high temperatures to enable the tool to be embedded in a less hard material. structural material. The hardness must be preserved even at high temperatures, that is, the tool materials must have high red hardness. Based on the features of loading tools (cantilever fastening, impact loads, bending, tension, compression), their main strength indicators are considered to be torsion, bending, and compression strengths, as well as impact strength. The need to resist intense abrasion poses the problem of creating wear-resistant tool materials. In addition, they must be technologically advanced and have a low cost.

Carbon tool steels grades U7A, U8A, U10A and others are used for the manufacture of tools with hardness HRC = 60-62 after heat treatment; red hardness of steels - up to 200-250 ° C, permissible cutting speeds - 15-18 m / min. They are used in the production of files, chisels, taps, dies, hacksaw blades and other tools.

The red hardness of alloyed tool steels reaches 250-300 °C, the allowable cutting speeds are 15-25 m/min. These steels are slightly deformed during heat treatment, so tools of complex configuration are made from them: dies, chisels, taps, reamers, drills, cutters, cutters, broaches, etc.

From high speed steels a cutting tool is made with a hardness of HRC = 62-65. After heat treatment, the red hardness of such steels is maintained up to 640 °C, the cutting speed is up to 80 m/min. Simple-shaped tools (cutters, milling cutters, countersinks, etc.) are made from P9 steel, complex tools with high wear resistance (tappers, dies, gear-cutting tools) are made from P18 steel. High-speed steel grade R6M5 is widely used. There are high-speed steels with a low tungsten content (11ARMZF2) or without it (11M5F). Increasingly, tools made of high-speed steels with wear-resistant coatings are being used. Thus, thin coatings of titanium nitride increase tool life by 2-5 times.

Carbide, which have high wear resistance, hardness (HRA = 86-92) and red hardness (800-1000 °C), are suitable for machining speeds up to 800 m/min. Single-carbide hard alloys grades VK2, VK4, VK6, VK8 have good resistance to impact loads, are used for processing cast irons, non-ferrous metals and their alloys, non-metallic materials. Two-carbide hard alloys of grades T5K10, T14K18, T15K6, T30K4 are less strong, but more wear-resistant than alloys of the first group. They are used in the processing of ductile and viscous metals and alloys, carbon and alloy steels. Three-carbide hard alloy grade TT7K12 has increased strength, wear resistance and toughness, it is used for processing heat-resistant steels, titanium alloys and other hard-to-cut materials.

In order to increase wear resistance without reducing the strength of hard alloys, especially fine grains of tungsten carbide (VK6-OM) are used. Tools are also equipped with plates with thin coatings (5-10 microns thick) made of wear-resistant materials (titanium carbide, nitride or carbonitride, etc.). This increases their durability by 5-6 times. There are also tungsten-free hard alloys of the TM1, TMZ, TN-20, KNT-16 grades, created on the basis of carbides or other titanium compounds with the addition of molybdenum, nickel and other refractory metals.

Mineral ceramics - synthetic material, the basis of which is alumina (A1 2 O e), sintered at a temperature of 1720-1750 ° C. Mineral ceramics brand TsM-332 is characterized by a red hardness of 1200 °C. Tools made from this material have high wear resistance and dimensional stability, and are characterized by the absence of metal sticking to the tool; their disadvantage is low strength and brittleness. Plates made of mineral ceramics are fastened mechanically or by soldering, having previously subjected them to metallization. In order to improve the performance properties, tungsten, molybdenum, titanium, nickel, etc. are added to mineral ceramics. Such materials are called cermets. Plates made of mineral ceramics are used for non-impact processing of workpieces made of steels and non-ferrous alloys.

Find application in tools and superhard materials (SHM). These include materials based on cubic boron nitride, composites. Cutting plates made of composites are supplied with cutters and milling cutters.

Abrasives are powder fine-grained substances used for the production of abrasive tools: grinding wheels, belts, bars, segments, heads. Natural abrasive materials (emery, quartz sand, corundum) are characterized by a significant spread of properties, therefore they are rarely used.

Abrasive tools in mechanical engineering are made from artificial materials: electrocorundum, silicon carbides, boron carbides, chromium oxide and a number of new materials. All of them are distinguished by high properties: red hardness (1800-2000 °C), wear resistance and hardness. Thus, the microhardness of boron carbides is 43% of the microhardness of diamond, silicon carbides - 35% and electrocorundum - 25%. Processing with abrasive tools is carried out at speeds of 15-100 m/s at the final stages of technological processes for the manufacture of machine parts.

Grinding and polishing pastes contain chromium oxide in their composition. Of the new materials, elbor is used as abrasives for processing hard alloys, which is a polycrystalline formation based on boron nitride of a cubic or hexagonal structure.

Various diamond tools are widely used in industry. Natural (A) and synthetic (AC) diamonds are used, which are characterized by high hardness, red hardness, wear resistance and dimensional stability. Machining with diamond tools is characterized by high precision, low surface roughness and high productivity.

TEST QUESTIONS

• 1. What movements are carried out by the working bodies of the machine? Which one is called cutting motion?
• 2. What is the geometry of the turning tool?
• 3. What physical phenomena accompany the cutting process?

The main requirements for tool materials are as follows:

The tool material must have a high hardness in the state of delivery or achieved as a result of its heat treatment - at least 63 ... 66 HRC according to Rockwell.

It is necessary that at significant cutting temperatures the hardness of the tool surfaces does not decrease significantly. The ability of a material to maintain high hardness at elevated temperatures and its original hardness after cooling is called heat resistance. The tool material must have high heat resistance.

Along with heat resistance, the tool material must have high wear resistance at elevated temperatures, i.e. have good resistance to abrasion of the processed material.

An important requirement is a sufficiently high strength of the tool material. If the high hardness of the material of the working part of the tool is accompanied by significant brittleness, this leads to tool breakage and chipping of the cutting edges.

The tool material must have technological properties that provide optimal conditions for the manufacture of tools from it. For tool steels, this is good machinability by cutting and pressure; favorable features of heat treatment; good sandability after heat treatment. For hard alloys, good grindability is of particular importance, as well as the absence of cracks and other defects that occur in the hard alloy after soldering the plates, during grinding and tool sharpening.

16 Types of tool materials and areas of their application.

Previously, all materials began to be used carbon tool steels grades U7, U7A ... U13, U 13A. In addition to iron, they contain 0.2 ... 0.4% manganese, have sufficient hardness at room temperature, but their heat resistance is low, since at relatively low temperatures (200 ... 250С) their hardness decreases sharply.

Alloy tool steels in their chemical composition, they differ from carbon ones by an increased content of silicon or manganese, or by the presence of one or more alloying elements: chromium (increases the hardness, strength, corrosion resistance of the material, reduces its ductility); nickel (increases strength, ductility, impact strength, hardenability of the material); tungsten (increases the hardness and heat resistance of the material); vanadium (increases the hardness and strength of the material, promotes the formation of a fine-grained structure); cobalt (increases the impact strength and heat resistance of the material); molybdenum (increases the elasticity, strength, heat resistance of the material). For cutting tools, low-alloy steel grades 9ХФ, 11ХФ, 13Х, V2F, KhV4, KhVSG, KhVG, 9ХС, etc. are used. These steels have higher technological properties - better hardenability and hardenability, less tendency to warp, but their heat resistance is almost equal to that of carbon steels 350 ... 400С 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, reamers).

High-speed tool steels. From the group of high-alloy steels for the manufacture of cutting tools, high-speed steels with a high content of tungsten, molybdenum, cobalt, and vanadium are used. Modern high-speed steels can be divided into three groups.

To steels of normal heat resistance include tungsten R18, R12, R9 and tungsten-molybdenum R6M5, R6M3, R8M3. These steels have hardness in the hardened state of 63…66HRC, flexural strength of 2900…3400 MPa, impact strength of 2.7…4.8 J/m 2 and heat resistance of 600…650С. They are used in the processing of structural steels, cast irons, non-ferrous metals, plastics. Sometimes high-speed steels are used, additionally alloyed with nitrogen (P6AM5, P18A, etc.), which are modifications of conventional high-speed steels. Alloying with nitrogen increases the cutting properties of the tool by 20...30%, hardness - by 1 - 2 HRC units.

Steels of increased heat resistance characterized by an increased carbon content - 10P8M3, 10P6M5; vanadium - R12F3, R2M3F8; R9F5; cobalt - R18F2K5, R6M5K5, R9K5, R9K10, R9M4K8F, 10R6M5F2K8, etc.

The hardness of steels in the hardened state reaches 66…70HRC, they have higher heat resistance (up to 620…670С). This makes it possible to use them for processing heat-resistant and stainless steels and alloys, as well as structural steels of increased strength and hardened. The service life of tools made of such steels is 3–5 times higher than that of steels R18, R6M5.

Steels of high heat resistance characterized by a low carbon content, but a very large number of alloying elements - V11M7K23, V14M7K25, 3V20K20Kh4F. They have a hardness of 69…70HRC, and a heat resistance of 700…720С. The most rational area of ​​their use is the cutting of hard-to-cut materials and titanium alloys. In the latter case, the tool life is 30–80 times higher than that of R18 steel, and 8–15 times higher than that of VK8 hard alloy. When cutting structural steels and cast irons, the tool life increases less significantly (3-8 times).

hard alloys. These alloys are obtained by powder metallurgy methods in the form of plates or crowns. The main components of such alloys are tungsten carbides WC, titanium TiC, tantalum TaC and niobium NbC, the smallest particles of which are connected by relatively soft and less refractory cobalt or nickel mixed with molybdenum.

Hard alloys have high hardness – 88…92 HRA(72…76HRC) and heat resistance up to 850…1000С. This allows you to work with cutting speeds 3-4 times higher than with high-speed steel tools.

Currently used hard alloys are divided into:

for tungsten alloys VK groups: VK3, VK3-M, VK4, VK6, VK6-M, VK6-OM, VK8, etc. In the symbol, the number shows the percentage of cobalt. For example, the designation VK8 shows that it contains 8% cobalt and 92% tungsten carbides. The letters M and OM denote the fine-grained and especially fine-grained structure;

for titanium-tungsten alloys TK groups: T5K10, T15K6, T14K8, T30K4, T60K6, etc. In the symbol, the number after the letter T indicates the percentage of titanium carbides, after the letter K - cobalt, the rest - tungsten carbides;

for titanium-tantalum-tungsten alloys TTK groups: TT7K12, TT8K6, TT20K9, etc. In the symbol, the numbers after the letter T indicate the percentage of titanium and tantalum carbides, after the letter K - cobalt, the rest - tungsten carbides;

for non-tungsten hard alloys TM-1, TM-3, TN-20, KNT-16, TS20HN. Designations are conditional.

Carbide grades are available as standardized inserts that are brazed, bonded or mechanically attached to structural steel toolholders. Tools are also produced, the working part of which is entirely made of hard alloy (monolithic).

Alloys of the TK group have higher heat resistance than VK alloys. They can be used at high cutting speeds, so they are widely used in steel machining.

Hard alloy tools of the VK group are used in the processing of parts made of structural steels in conditions of low rigidity of the AIDS system, with interrupted cutting, when working with impacts, as well as in the processing of brittle materials such as cast iron, which is due to the increased strength of this group of hard alloys and not high temperatures. in the cutting area. They are also used in the processing of parts made of high-strength, heat-resistant and stainless steels, titanium alloys. This is explained by the fact that the presence of titanium in most of these materials causes increased adhesion with alloys of the TK group, which also contain titanium. Alloys of the TK group have significantly worse thermal conductivity and lower strength than VK alloys.

The introduction of tantalum carbides or tantalum and niobium carbides (TT10K8-B) into the hard alloy increases its strength. However, the heat resistance temperature of these alloys is lower than that of the two carbide alloys.

Particularly fine-grained hard alloys are used for processing materials with high abrasion ability. They are used for finishing and semi-finishing of parts made of high-strength tough steels with an increased tendency to hardening.

Alloys with a low cobalt content (T30K4, VK3, VK4) are used in finishing operations, with a high cobalt content (VK8, T14K8, T5K10) are used in roughing operations.

Mineral ceramics. It is based on aluminum oxides Al 2 O 3 with a small addition (0.5 ... 1%) of magnesium oxide MgO. High hardness, heat resistance up to 1200С, chemical inertness to metals, oxidation resistance in many respects surpass the same parameters of hard alloys, but are inferior in thermal conductivity and have a lower bending strength.

High cutting properties of mineral-ceramics are manifested during high-speed machining of steels and high-strength cast irons, and fine and semi-finish turning and milling increase the productivity of machining parts up to 2 times while increasing the tool life periods up to 5 times compared to machining with hard alloy tools. Mineral ceramics is produced in the form of non-regrindable plates, which greatly facilitates the conditions for its operation.

Superhard tool materials (STM)– the most promising are synthetic superhard materials based on diamond or boron nitride.

Diamonds are characterized by high hardness and wear resistance. In terms of absolute hardness, diamond is 4-5 times harder than hard alloys and tens and hundreds of times higher than the wear resistance of other tool materials in the processing of non-ferrous alloys and plastics. Due to their high thermal conductivity, diamonds better remove heat from the cutting zone, however, due to their brittleness, their area of ​​application is very limited. A significant drawback of diamond is that at elevated temperatures it enters into a chemical reaction with iron and loses its efficiency.

Therefore, new superhard materials were created that are chemically inert to diamond. The technology for obtaining them is close to the technology for obtaining diamonds, but not graphite, but boron nitride was used as the starting material.

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 on working part Since the tool is subjected to significant cutting forces that create 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.

Hard alloys 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.