TO Category:

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 the steel grade does not have a letter designation, and its content (in tenths of a percent) is indicated at the beginning of the marking. 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 those 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, KhGS, KhVG, KhVGS, etc. These steels, containing 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 combine with carbon to 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-alloyed 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 produced by 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 - when machining hard-to-cut materials, corrosion-resistant and heat-resistant steels and alloys, titanium alloys, during rough turning and milling steel billets. 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.

The cutting wedge, when interacting with the material of the workpiece, carrying out continuous deformation and separation of the material, is subjected to force and heat, as well as abrasion. These operating conditions allow us to formulate the basic requirements for the material of the cutting part of the tool. The suitability of such materials is determined by their hardness, heat resistance, mechanical strength, wear resistance, manufacturability and cost.

1. Hardness. The introduction of one material (wedge) into another (workpiece) is possible only with the prevailing hardness of the wedge material, therefore, the hardness of tool materials, as a rule, is higher than the hardness of the materials being machined. However, as the temperature of the tool material increases, its hardness decreases and may not be sufficient to effect deformation and separation of the material. The property of materials to maintain the required hardness at high temperatures is called heat resistance.

2. Heat resistance. It is determined by the critical temperature at which the change in hardness occurs. If the temperature is above critical, the tool will not work. In general, heat resistance determines the new cutting speed.

3. Mechanical strength. The importance of mechanical strength for a tool material is explained by its operating conditions, which are characterized by bending, compressive and impact loads, and therefore the material's bending strength, compression and impact strength are the main indicators of the strength of the tool material.

4. Wear resistance. The ability of the material to resist wear determines the life of the tool material. Wear resistance is characterized by the work of the friction force related to the value of the worn mass of the material. The importance of this characteristic is that it determines the preservation of the initial geometry of the tool in time, since in the process of work, there is a constant abrasion of the tool (surface of the wedge).

5. Manufacturability. Manufacturability of the material - its ability to meet the requirements of heat treatment technology, pressure treatment, machining, etc., is a property that determines the possibility of manufacturing a tool of a given design.

6. Cost. The material of cutting tools should not be of high cost, because. this ultimately determines the breadth of its use.

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Groups of tool materials,
used to make cutting tools

1. Tool steels

U7, U7A, U13, U13A

Carbon steels are used for the manufacture of tools that operate at low cutting speeds of 15-18 m / min, as well as at temperatures not lower than 200-230 ° C. This is a bench tool (chisel, files, taps, dies, etc.). The hardness of carbon steels after heat treatment reaches HRC 62-64.

2. Alloy steel

To improve the technical or other properties of carbon steels, alloying elements are introduced into them. So, for example:

(Ni) Nickel (H) - increases ductility and toughness, increases hardenability

(Mn) Manganese (G) - increases strength, hardenability, wear resistance

(Cr) Chromium (X) - hardens steel

(W) Tungsten (B) - increases hardness, wear resistance, heat resistance

· (V) Vanadium (F) limits the change in properties when heated, improves surface quality and weldability, but worsens grindability.

(Mo) Molybdenum (M) increases hardenability, strength, ductility, toughness

· (Si) Silicon (C) increases hardenability.

The heat resistance of alloyed steel is not more than 300-350 ° C. Low-alloy steels (X) with chromium are used for the manufacture of metalwork tools. High alloy steels KhVG, HSVG for shaped cutters, small diameter drills, broaches, reamers and other tools operating at cutting speeds up to 25 m/min.

3. High speed steels

A special group of tool steels are high-speed steels with a tungsten content of 6-18% with high heat resistance (up to 650 ° C). They are suitable for making tools operating at cutting speeds up to 60 m/min.

Drills, taps, cutters, countersinks, reamers, dies, etc. are made from high-speed steel of normal productivity R9, R18, and tools for processing high-strength and difficult-to-machine materials are made from high-performance steels R18F2, R18F5, R10K5F5 or R9F5, since these types of steel have increased wear resistance and allow you to work at speeds up to 100 m/min.

In view of the scarcity of tungsten, as a rule, only the cutting part is made of the tool material (plates welded to the holders), and the body part is made of ordinary structural steel. After heat treatment, the hardness of high speed steel reaches HRC 64 or more.

4. Metal-ceramic hard alloys

These materials are alloys of refractory metal carbides with pure metallic cobalt acting as a binder (TiC, TaC, WC).

Hard alloys are obtained by pressing followed by sintering the molded material. They are used in the form of plates obtained by sintering at 1500 o -1900 o. This material has a heat resistance of 800 o -1000 o, which allows processing at a speed of 800 m/min. In industry, multifaceted plates are used (3, 4, 6). The disadvantage is that the material does not withstand impact loads well due to brittleness (the more cobalt in the composition, the higher the ductility).

All metal-ceramic alloys are divided into three groups:

Single carbide. Tungsten-cobalt hard alloys VK2, VK6, VK8, where the numbers after the letters indicate the percentage of cobalt. Increasing the percentage of cobalt increases the toughness. Alloys of this group are the most durable. They are used for processing cast iron, non-ferrous metals and their alloys, non-metallic materials. Heat resistance 250-1000 o C.

· Two-carbide. In these alloys, in addition to the components of alloys of the VK groups, it includes titanium carbide T5K10, T15K6, where 6% cobalt, 15% titanium carbide, and the rest is tungsten carbide. It is used in the processing of carbon and alloy steels. Limit heat resistance 1050 o C.

· Three-carbide. Additionally introduced tantalum carbide in addition to those listed above. TT17K6, TT17K12, where 17 is the total content of titanium and tantalum carbides, 12 is the content of cobalt, i.e. 71-tungsten carbide. These alloys have high strength, are used in the processing of heat-resistant steels and titanium alloys.

Group R- (blue)

Group P alloys are needed for processing materials that give drain chips (steel)

Group M - (yellow)

When machining stainless, heat-resistant steels and titanium alloys

M40-TT7K12, VK10-OM

M - small, OM - very small

Group K - (red)

Group K alloys are used for processing low-plastic materials, non-ferrous alloys, plastics, wood, cast iron

5. Mineral-ceramic tool alloys

These alloys are prepared on the basis of aluminum oxide Al 2 O 3 with small additions of magnesium oxide, and are sintered at 1700 o. For example, TsM332 is used for semi-finishing and finishing of steel and cast iron blanks, has high wear resistance, good cutting properties, is cheaper than hard alloys, but brittle. The material has heat resistance up to 1200 o.

6. Superhard tool materials.

These are materials based on cubic boron nitride (CBN) with high hardness and heat resistance. An example is elbor-R, which is used in the finishing of cast iron and hardened steels. This achieves the roughness characteristic of grinding. The cutting part of the tool is made of single crystals with a diameter of 4 mm and a length of 6 mm.

For the manufacture of the cutting part of the tool, natural diamonds (A) and synthetic (AC) diamonds weighing from 2 to 0.85 carats * are used. Natural diamonds are used for fine turning of non-ferrous metals and alloys of plastics and other non-metallic materials. Synthetic diamonds are used in the processing of high-silicon materials, fiberglass and plastics. Diamonds have high hardness, low coefficient of friction and slight ability to stick with chips, high wear resistance. The disadvantage is its low heat resistance and high cost.

Comparative characteristics
tool materials

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Turning tool geometry

When processing materials by cutting distinguish the following surfaces:

1- processed

2 - processed

3 - cutting surface

A common tool for processing external and internal surfaces is turning tool, it consists of a working part - I and a body - II. The working part is supplied with tool material, the body is made of structural steels. The latter is needed to mount the tool in the holder.

The working part of the cutter is formed by a number of surfaces, which, intersecting, form the cutting edge and the top of the cutter-6. 1 - the surface on which the chips come off. Back surfaces 2 and 3 face the workpiece. Intersecting with the front surface 1, they form cutting edges: main - 4 and auxiliary - 5. Accordingly, the rear surface 2 (it faces the cutting surface) is the main one, and 3 is the auxiliary one (directed towards the machined surface). The tip of the cutter is the point of intersection of the cutting edges.

Important role in the physical processes occurring in the processes of cutting, play cutter angles(cutting angles)

a - relief angle reduces friction between the back surface of the tool and the working surface, increasing the angle leads to a decrease in strength

a 1 - the presence of this angle reduces friction

g - the rake angle can be both positive and negative or zero, with a decrease in the angle, the deformation of the cut layer decreases, since the tool cuts into the material more easily, cutting forces decrease, chip flow conditions improve, and with a strong increase in the angle, thermal conductivity decreases, chipping increases

b - taper angle - the angle between the front and main rear surfaces of the cutter

d - cutting angle - the angle between the front surface of the cutter and the cutting plane

j- main angle in the plan determines the surface roughness, this decrease improves the quality of the surface, but at the same time the thickness decreases and the width of the cut material layer increases, with a decrease in this angle, vibration may occur

j 1 - auxiliary angle in the plan, with a decrease in the angle, strength increases

e - angle at the top of the cutter angle between the projections of the cutting edges on the main plane = 180°- (j+j1)

l - the angle of inclination of the cutting edge is positive when the top of the cutter is the highest point, and negative when the top of the cutter is the lowest point, affects the direction of chip flow

The angle values ​​change due to the error of the cutter.

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2 Yu. M. ZUBAREV MODERN INSTRUMENTAL MATERIALS APPROVED by the Educational and Methodological Association of Universities for Education in the Field of Automated Mechanical Engineering (UMO AM) as a textbook for students of higher educational institutions students in the specialty of the direction of training "Design and technological support of machine-building industries" ST. PETERSBURG MOSCOW KRASNODAR 2008

3 BBK 34 Z 91 Zubarev Yu. M. Z 91 Modern instrumental materials: Textbook. St. Petersburg: Lan publishing house, p.: ill. (Textbooks for universities. Special literature). ISBN The compositions and properties of modern domestic and foreign instrumental materials are considered in the book, their classification is given, properties and technological recommendations for their effective choice and application are stated. The methods of hardening and increasing the wear resistance of the blade cutting tool are given. The book will be useful for senior students of engineering specialties, teachers and graduate students. It is also designed for engineering and scientific workers of machine-building enterprises, design institutes and research institutes, technologists associated with the design, manufacture and use of cutting tools. BBK 34 Reviewer: V. V. MAKSAROV head. Department of Automated Engineering Technologies, Northwestern Technical University, Professor, Doctor of Technical Sciences Cover A. Yu. LAPSHIN Protected by the RF copyright law. Reproduction of the entire book or any part of it is prohibited without the written permission of the publisher. Any attempt to break the law will be prosecuted. Lan publishing house, 2008 Yu. M. Zubarev, 2008 Lan publishing house, artwork, 2008

4 INTRODUCTION General progress in mechanical engineering and metalworking is closely related to the development of the design of cutting tools and the improvement of tool material. Tool cutting materials are the materials from which the working part of cutting tools is made. The properties of the tool cutting material have a significant effect on the chip formation process and have a decisive influence on the cutting properties of the tool and the achievable level of cutting speeds. Efficient cutting of one material by another is possible if the following requirements are met: The tool material must have a strength sufficient for the cutting tool to withstand without brittle fracture (cleavage) the loads that arise and act on it when cutting this workpiece material. Possessing sufficient ability to resist brittle fracture, the tool material must at the same time provide sufficient dimensional stability of the cutting part of the tool, i.e., the ability not to change the shape given to it by sharpening in any significant way under the action of loads arising during cutting. The latter implies that the tool material has sufficient ductile strength. With sufficient brittle and ductile strength, the tool cutting material should also have the highest possible wear resistance, i.e., the ability to resist. INTRODUCTION 3

5 removal of small particles from the working surface of the tool by the outgoing chips and the machined surface of the part. The tool material meets the specified requirements if it has: high hardness, significantly exceeding the hardness of the material being processed, the ability to maintain hardness for a long time when heated, i.e. heat resistance, and sufficient compressive, bending and shear strength. Also important is the ability not to collapse under the influence of the so-called thermal shocks, i.e., repeatedly repeated sudden changes in temperature. At the same time, it is necessary to take into account the technological properties of the material, i.e. those properties that affect its ability to be processed in various operations. technological process manufacturing of cutting tools. Improving the quality and improvement of tool material are the most important factors in increasing the efficiency of machine-building production, since it is the cutting tool that determines the achievable level of cutting conditions and the degree of equipment utilization. The accuracy and quality of the cutting tool have a direct impact on the accuracy and performance characteristics of the parts of machine assemblies, as well as on the overall service life of the unit or machine. For tool materials, the concept of productivity of the processing process should be differentiated. When optimizing the properties of tool materials, one should take into account not only the cutting ability of the tool, but also consider in a complex a number of criteria that affect manufacturing process. As the main properties of tool materials, the following are indicated: low wear intensity, high tool life while ensuring quality, wear stability (low tool life variation). The use of workpieces with minimal allowances and the need to process hardened materials put forward new challenges related to ensuring the required dimensional accuracy and geometric shape of products, as well as improving the quality of their surface. To perform such operations, tool materials must provide high cutting edge and backing strength, wear resistance, and low tool life variation. If one tool material possesses these properties, then it can be considered ideal and universal in application.

6 changes. However, due to the fundamental contradiction between hardness and strength, such a material cannot be created. In this regard, the main direction of work in the tool industry should be focused on the creation and optimization of the technology for the production of such materials that would best meet specific tasks. modern production. The tool production faces the responsible task of providing the entire machine-building complex with high-quality, high-performance and at the same time wear-resistant tools. The quality and efficiency of using a metal-cutting tool depend on the following main factors: a) the choice of optimal designs and geometric parameters of its cutting part; b) right choice material of the cutting part of the tool; c) rational technology of its manufacture and features of the technology of finishing (grinding) operations; d) the use of various methods of hardening and coatings that increase the performance of the cutting part of the tool; e) appointment of rational modes of its operation; f) monitoring the state of the cutting part of the tool during its operation. The development of technological processes for the production of metal-cutting tools is based on general principles and patterns of engineering technology. Along with this, in the technology of production of metal-cutting tools, there are specific features associated with the use of expensive and scarce tool materials. Cutting tools operate under the influence of a complex set of factors, such as high contact stresses and temperatures, as well as under conditions of active physical and chemical processes. Contact stresses acting on the front and back surfaces of the tool during processing various materials, can vary from 700 to 4000 MPa. At the same time, temperatures arise in the cutting zone and at the contact boundaries between the tool and the material being processed, the values ​​of which vary from 200 to 1400 C. In this case, the contact pads of the tool wear out intensively under conditions of abrasive, adhesive-fatigue, corrosion-oxidation and diffusion processes. Under these conditions, instrumental INTRODUCTION 5

7, the material must also simultaneously have a sufficient margin of strength in compression and bending, the application of shock pulses and alternating stresses. The listed properties of tool materials are often mutually exclusive. Therefore, the creation of an instrumental material with an ideal set of these properties in the volume of a homogeneous body is currently not possible. With the accumulation of theoretical knowledge and practical experience in the processing of materials by cutting, mankind created new tool materials, improved their thermal and physico-chemical processing, which made it possible to constantly increase the productivity of the manufacturing process of machine parts. The history of the development of metalworking shows what a sharp increase in labor productivity was achieved during the transition from tool carbon and alloy tool to high speed steel or from high speed steel to hard alloys. For example, an increase in cutting speed during the transition from tool alloyed to high-speed steel and then to hard alloys, respectively, is characterized by the ratios 1 (1.6 ... 1.8) (4.9 ... 5.6), while the cutting speed for tools made of tool alloy steel are taken as a unit. Consequently, as a result of replacing the material of the tool, labor productivity increases. Currently, cobalt and vanadium high-speed steel grades R9F5, R18F2, R9K5, R9K10, R10K5F5 and others are widely used in the processing of hard-to-cut materials. Abroad, high-speed steels alloyed with molybdenum or both tungsten and molybdenum have been widely developed. Full or partial replacement of tungsten with molybdenum noticeably changes the technological properties of high-speed steel (less carbide heterogeneity, good grindability and ductility, less tendency to chipping of the cutting edge of the tool). Behind Lately a number of laboratories in our country and abroad carried out work to improve existing materials and to find new materials for the manufacture of tools. Research was carried out in all major groups of modern tool materials (Fig. 1): 1) in the field of high-speed and other tool steels; 2) in the field of sintered hard alloys; 6 MODERN TOOL MATERIALS

8 Fig. 1 Development of tool materials Fig. Fig. 2 The ratio of changes in cutting speed and process productivity in the processing of steels and alloys 3 Classification of existing tool materials 3) in the field of precipitation hardening alloys based on Cr and Co; 4) in the field of mineral ceramics; 5) in the area over hard materials(STM). The use of new tool materials made it possible to increase the processing speed. So, for example, over the past hundred years, the cutting speed has increased by about 10 times, while the processing time has decreased by 50 times (Fig. 2). INTRODUCTION 7

9 However, most tool materials known today have only a partial set of the above properties, which makes the area of ​​their rational application very limited. On fig. 3 shows the classification of existing tool materials according to their strength and hardness. Mechanical, physical and cutting properties of tool materials (average values) hardness, HRA Mechanical properties tensile strength in N/mm2 bending Impact strength in Nm/cm2 Physical properties Grade of material compression thermal conductivity in m deg density in kg/m .0 1.0 Tungsten hard alloys VK8 VK6 87.5 88.88 5.88 58.6 14.9 3.4 Titanium-tungsten hard alloys T5K5 T14K8 T15K6 T30K4 88.5 89.94 2.45 33.5 29 .3 29.7 11.7 11.3 9.0 3.5 4.5 5.5 TsM Mineralokeramika,784 16.7 3.8 5.8 n/a n/a n/a 3.5 3, Synthetic diamond AC n/a n/a 3, MODERN TOOL MATERIALS

10 The main properties of domestic tool materials are given in Table. 1. The following basic materials are used in tool production: 1. Tool steels: a) high-speed (GOST); b) alloyed (GOST); c) carbonaceous (GOST); d) precipitation hardening alloys. 2. Hard sintered alloys (GOST). 3. Mineral ceramics (cermets). 4. Diamonds (natural and artificial). 5. Superhard synthetic materials (STM) composites. The choice of material is influenced by the type of tool, its purpose, dimensions and working conditions, as well as tool manufacturing technology. INTRODUCTION 9

11 CHAPTER 1 TOOL STEELS Tool steels are subject to the following main characteristics: 1. Cutting ability. 2. Red resistance (heat resistance) Cold wear resistance. 4. Mechanical properties. 5. Cold and hot workability. The steels from which cutting tools are made must have: 1) high strength, since the tools experience great forces during the cutting process; 2) high hardness, since the cutting process can be carried out only if the hardness of the tool material is much greater than the hardness of the material being processed; 3) high wear resistance, since tool life depends on the degree of abrasion of the cutting edges; 4) high heat resistance, since during the cutting process, a large number of heat, part of which goes to heat the cutting surfaces of the tool, and the latter, when heated, lose their original hardness and quickly fail. In addition, the cyclic effect of temperatures during intermittent heat resistance is characterized by that highest temperature, when heated to which and for a sufficiently long exposure, the material does not irreversibly lose its hardness, i.e., restores it to its original value after cooling. 10 MODERN TOOL MATERIALS

12 cutting leads to the initiation of fatigue cracks in the cutting wedge of the tool and, ultimately, to its destruction (chipping). Tool materials are not equally resistant to heat: some lose their cutting properties when heated to a temperature of C, while others are able to cut at temperatures up to 1000 C or more. Steels for measuring tools must have a high wear resistance necessary to maintain the size and shape of the tools during operation, as well as good machinability to obtain a high surface quality. The required wear resistance is provided by quenching and tempering steels of certain grades, after which they acquire high hardness and retain the martensitic structure. In the manufacture of dies for cold deformation, two main requirements are imposed on steels: 1. High strength. 2. High wear resistance. Compared with cutting tools, the hardness of die parts, depending on the operating conditions, is chosen over a wider range (HRC). The steels from which the stamp for hot deformation is made must have: 1) high strength necessary to maintain the shape of the stamp at high specific pressures and deformation; 2) a certain heat resistance to maintain increased strength properties when heated; 3) viscosity to prevent breakage and chipping and obtain high heat resistance; 4) heat resistance to prevent cracks that occur during repeated alternation of heating and cooling; 5) wear resistance; 6) scale resistance (if the surface layer of the die parts is heated above a temperature of 600 C); 7) thermal conductivity for better removal of heat transferred from the workpiece; 8) hardenability must be obtained over the entire section, since many die parts are large and have high strength properties. CHAPTER 1. TOOL STEELS 11

13 1.1. CARBON STEELS At the beginning of mechanical engineering, cutting tools were made using simple carbon tool steels with a carbon content of 0.65 to 1.35%. In order for carbon tool steel to acquire cutting properties, it is quenched at a temperature of C (hardening temperature is specially set for each steel grade) and tempered at a temperature of C. The latter is used to eliminate brittleness. In the hardened state, carbon tool steels have a martensite structure (hypoeutectoid and eutectoid steel) and martensite with excess carbides (hypereutectoid steel) with a small amount of retained austenite. The nature of the distribution of carbides significantly affects the properties of steel: the tool is the better, the more evenly distributed the carbides in the structure, or, as they say, the lower the carbide heterogeneity of the steel. A significant local accumulation of carbides in the steel structure makes it impossible to manufacture high-quality tools from it, since in this case the cutting surface turns out to be uneven and low-strength due to increased brittleness. Carbide inhomogeneity can be eliminated or reduced by forging the tool steel before it is made into a cutting tool. After heat treatment, carbon tool steels have quite sufficient hardness (HRC), but their heat resistance is low: they irreversibly lose their hardness even at relatively low temperatures (C). In addition to low heat resistance, a significant disadvantage of carbon tool steels is their low and uneven hardenability, increased sensitivity to overheating, and relatively large surface decarburization. Carbon steels are divided into high-quality and high-quality. Each of these groups has eight steel grades. The chemical composition of tool carbon steels is given in table. 2. Carbon quality steel U7, U8, U8G, U9, U10, U11, U12, U13. Carbon high-quality steel U7A, U8A, U8GA, U9A, U10A, U11A, U12A, U13A. 12 MODERN TOOL MATERIALS

14 Chemical composition of carbon steels for cutting tools according to GOST (%) Steel grade Carbon Manganese Silicon Chromium Carbon high-quality steel U7A 0.65 0.74 0.15 0.30 0.15 0.30 0.15 U8A 0.75 0, 84 0.15 0.30 0.15 0.30 0.15 U8GA 0.80 0.90 0.35 0.60 0.15 0.30 0.15 U9A 0.85 0.94 0.15 0, 30 0.15 0.30 0.15 Y10A 0.95 1.04 0.15 0.30 0.15 0.30 0.15 Y11A 1.05 1.14 0.15 0.30 0.15 0, 30 0.15 U12A 1.15 1.24 0.15 0.30 0.15 0.30 0.15 U13A 1.25 1.35 0.15 0.30 0.15 0.30 0.15 Quality carbon steel U7 0.65 0.74 0.20 0.40 0.15 0.35 0.20 U8 0.75 0.84 0.20 0.40 0.15 0.35 0.20 U8G 0.80 0 .90 0.35 0.60 0.15 0.35 0.20 U9 0.85 0.94 0.15 0.35 0.15 0.35 0.20 U10 0.95 1.04 0.15 0 .35 0.15 0.35 0.20 U11 1.05 1.14 0.15 0.35 0.15 0.35 0.20 U12 1.15 1.24 0.15 0.35 0.15 0 ,35 0.20 U13 1.25 1.35 0.15 0.35 0.15 0.35 0.20 fractions of a percent). In addition, steels contain manganese from 0.15 to 0.6%, silicon from 0.15 to 0.35%, chromium from 0.15 to 0.20%. The letter G is steel with a high manganese content. High-quality steels are cleaner than high-quality ones, i.e., with a lower content of sulfur, phosphorus and other impurities, as well as non-metallic inclusions. An increase in the carbon content of steel increases its hardness, but at the same time increases its brittleness. Carbon steels have high hardness after heat treatment and low hardness in the annealed state, which ensures their good machinability by cutting and pressure (see Table 3). CHAPTER 1. TOOL STEELS 13

15 Steel grade Table 3 Hardness standards of carbon tool steel hardness HB (no more) After annealing, the indentation diameter at Dmax = 10 mm and P = 3000 kgf U8 and U8A 187 4, U8G and U8GA 187 4, U9 and U9A 192 4, U10 and U10A 197 4, U11 and U11A 207 4, U12 and U12A 207 4, U13 and U13A 217 4, Steel grades U7, U7A, U8, U8GA, U9, U9A are used for the manufacture of chisels, scissors and saws for cutting metals and wood, cutters for processing copper and its alloys. Steel grades U8A and U10A are used for the production of punches, dies, scissors and other die parts. From steel grades U10A, U11, U11A, U12 and U12A, small-diameter drills, taps, reamers, dies, small-diameter cutters, metal saws, hacksaw blades, chisels for notching files are made. U13 and U13A steels are used to make tools of especially high hardness: cutters, chisels for notching files, scrapers, files, etc. Carbon steels are supplied in the annealed state in the form of hot-rolled, forged or calibrated bars of various sections or in the form of strips. the properties of tool steels (and along with this equally its other qualities, including: heat resistance, hardness and toughness) increase when one or more of the following elements are added to their composition: chromium, manganese, tungsten, silicon and vanadium. Chromium provides less carbide heterogeneity, better hardenability and deep hardenability of steel; 14 MODERN TOOL MATERIALS

16 tungsten also contributes to a more uniform distribution of carbides, although to a lesser extent than chromium, and improves the hardenability and hardenability of steel; the positive effect of manganese is that it greatly lowers the hardening temperature and increases hardenability; silicon is an alloying element that delays the second stage of martensite decay and increases the heat resistance of steel; vanadium forms the hardest and most wear-resistant carbides, and also contributes to obtaining a fine-grained structure. Tool steels in the presence of one or more of the listed elements in their composition are called alloyed tool steels. The latter are used for the manufacture of cutting tools of large cross-section, as well as more complex in shape; in particular, drills, reamers, cutters, broaches, taps and round dies are made from them, designed for processing non-hard materials (non-ferrous metals, low-strength steels and cast iron). The chemical composition of the most common alloyed tool steels is given in Table. 4(c). In the manufacture of cutting tools from alloyed tool steels, they are subjected to stepwise hardening at a temperature of C (depending on the steel grade) and tempering at temperatures of C. Back in the 1960s. of the last century, it was found that the maximum amount of tungsten and manganese that can be introduced into tool steel if it is quenched at a temperature of C, respectively, is: 5 ... 8% and 1.5 2.5%. Being added in such quantity, these metals give the steel significant heat resistance when heated to C and the ability to harden when cooled not in special cooling media, but in air. In connection with this last property, such steel is called self-hardening. Depending on the purpose and properties, alloyed tool steels are divided into two groups: 1. Steels for the production of cutting and measuring tools. 2. Steel for stamping tool. Steels of the 1st group are divided into steels: shallow hardenability (7ХФ, 11Х, ХВ5, В1, Ф); deep hardenability (Х, 9ХС, ХВГ, 9ХВГ, 9Х5ВФ). CHAPTER 1. TOOL STEELS 15

17 Chemical composition of tool steel Grade Carbon Manganese Silicon I. Steel for cutting a) shallow 7HF 0.63 0.73 0.30 0.60 0.15 0.35 8HF 0.70 0.80 0.15 0.40 0 ,15 0.35 9HF 0.80 0.90 0.30 0.60 0.15 0.35 11X 1.05 1.14 0.40 0.70 0.15 0.35 13X 1.25 1.40 0.30 0.60 0.15 0.35 XB5 1.25 1.45 0.15 0.40 0.15 0.35 V1 1.05 1.20 0.15 0.40 0.20 0.35 F 0.95 1.05 0.15 0.40 0.15 0.35 b) deep Х 0.95 1.10 0.15 0.40 0.15 0.35 9ХС 0.85 0.95 0, 30 0.60 1.20 1.60 CVH 0.90 1.05 0.80 1.10 0.15 0.35 9CVG 0.85 0.95 0.90 1.20 0.15 0.35 CVSH 0 .95 1.05 0.60 0.90 0.65 1.00 9Kh5F 0.85 1.00 0.15 0.40 0.15 0.40 9Kh5VF 0.85 1.00 0.15 0.40 0 .15 0.40 8Kh4V4F1 (RF) 0.75 0.85 0.15 0.40 0.15 0.40 II. Steel for a) for deformation 9X 0.80 0.95 0.15 0.40 0.25 0.45 X6VF 1.05 1.15 0.15 0.40 0.15 0.35 X12 2.00 2, 20 0.15 0.40 0.15 0.35 X12M 1.45 1.65 0.15 0.40 0.15 0.35 X12F1 1.20 1.45 0.15 0.40 0.15 0, 35 b) for deformation 0.15 0.40 0.15 0.35 8X3 0.75 0.85 0.15 0.40 0.15 0.35 5XHM 0.50 0.60 0.50 0.80 0.15 0.35 16 MODERN TOOL MATERIALS

18 Alloy Steel (%) Table 4 Chromium Tungsten Vanadium Molybdenum Nickel and Measuring Tool Hardenability 0.40 0.70 0.15 0.30 0.40 0.70 0.15 0.30 0.40 0.70 0.15 0.30 0.40 0.70 0.40 0.70 0.40 0.70 4.0 5.0 0.15 0.30 0.40 0.70 0.80 1.20 0.15 0, 30 0.20 0.35 0.20 0.40 hardenability 1.30 1.65 0.95 1.25 0.90 0.80 1.20 1.60 0.50 0.80 0.50 0.80 0.60 1.10 0.70 1.00 0.05 0.15 4.50 5.50 0.15 0.30 4.50 5.50 0.80 1.20 0.15 0.30 4, 00 5.00 4.00 5.00 0.90 1.40 cold die tool 1.40 1.70 5.50 7.00 1.10 1.50 0.40 0.70 11.50 13, 00 11.00 12.50 0.15 0.30 0.4 0.6 11.00 12.50 0.70 0.90 hot 2.20 2.70 7.50 9.00 0.20 0 .50 7.00 9.00 2.00 3.00 3.20 3.80 3.20 3.80 0.50 0.80 0.15 0.30 1.40 1.80 CHAPTER 1. TOOL STEELS 17

19 Steel grade Carbon Manganese Silicon 5HNV 0.50 0.60 0.50 0.80 0.15 0.35 5HNSV 0.50 0.60 0.30 0.60 0.60 0.90 5HGM 0.50 0, 60 1.20 1.60 0.25 0.65 4Kh5VChFSM 0.35 0.45 0.15 0.40 0.60 1.00 4Kh3V2F2M2 0.35 0.45 0.30 0.50 0.15 0, 35 4Kh2V5FM 0.30 0.40 0.15 0.40 0.15 0.35 4Kh5V2FS 0.35 0.45 0.15 0.40 0.80 1.20 c) for shock 4KhS 0.35 0.45 0.15 0.40 1.20 1.60 6ХС 0.60 0.70 0.15 0.40 0.60 1.00 4ХВ2С 0.35 0.44 0.15 0.40 0.60 0.90 5ХВ2С 0.45 0.54 0.15 0.40 0.50 0.80 6ХВ2С 0.55 0.65 0.15 0.40 0.50 0.80 6ХВГ 0.55 0.70 0.90 1, 20 0.15 0.35 Steels of the 2nd group are divided into steels: for cold deformation (9Kh, Kh6VF, Kh12, Kh12M, Kh12M1); for hot forming (3Kh2V8F, 7Kh3, 5KhNM, 5KhNSV, 5KhGM); for percussion instrument (4ХС, 4ХВ2С, 6ХВ2С, 6ХВГ). In the designations of steel grades, the first digits indicate the average carbon content in tenths of a percent. They may not be indicated if the carbon content is close to unity or greater than unity. The letters behind the numbers indicate: G manganese; With silicon; X chrome; into tungsten; F vanadium; H nickel; M molybdenum. The numbers after the letters indicate the average content of the corresponding element in whole percent. The absence of numbers means that the content of this alloying element is approximately 1%. The content of sulfur and phosphorus in steel should not exceed 0.030% (of each element). Alloy steels, in comparison with carbon steels, have an increased toughness in the hardened state, a lower tendency to deformation and cracks during hardening. The cutting properties of alloyed steels are approximately the same as those of carbon steels.

20 Continuation of the table. 4 Chromium Tungsten Vanadium Molybdenum Nickel 0.50 0.80 0.40 0.70 1.40 1.80 1.30 1.60 0.40 0.70 0.80 1.20 0.60 0.90 0, 15 0.30 4.00 5.00 3.50 4.20 0.30 0.60 0.40 0.60 3.00 3.70 2.00 2.70 1.50 2.00 2.00 2 .50 2.00 3.00 4.50 5.50 0.60 1.00 0.60 1.00 4.50 5.50 1.60 2.40 0.60 1.00 tool 1.30 1, 60 1.00 1.30 1.00 1.30 2.00 2.50 1.00 1.30 2.00 2.50 1.00 1.30 2.20 2.70 0.50 0.80 0 .50 0.80 remote instrumental. They have low heat resistance (C). Alloyed tool steels are widely used in the manufacture of tools and technological equipment (devices). Alloy steels are used to produce circular and band saws, knives for cold cutting of metals, punches, cores, cutters and milling cutters for processing hard materials at low cutting speeds, twist drills, taps, dies, reamers, combs, broaches. The hardness of alloy steel in the state of delivery (after annealing) and the hardness after hardening must comply with the standards specified in Table. 5. Circular band saws, knives for cold cutting of metals, chisels, punches, cores and other tools that work with shock loads are made from steel grades 7HF, 8HF and 9HF. From steel grades ХВ5, 9ХС, ХВГ, В1 and ХВСГ, cutters and milling cutters for processing hard materials at a low cutting speed, twist drills, taps, reamers, dies, combs, broaches are made. Particularly widespread were steel grades KhVG and 9XC. CVG steel is hardened and deforms little, but at the same time it is sensitive to formation CHAPTER 1. TOOL STEELS 19

21 Steel grade Table 5 Hardness standards of alloy tool steel Steel after annealing hardness HB indent diameter at Dball = 10 mm and Р = 3000 kgf 7ХФ No more than 229 Not less than 4.0 8ХФ Not more than 255 Not less than 3.8 less than 3.8 Steel after hardening temperature (C) and hardening medium, oil, water, oil, water, oil, water hardness HRC (not less than) 11X.1 4, oil 62 13X.9 4, water 62 XB.6 4 , water 62 V.0 4, water 62 F.1 4, water 62 X.0 4, oil 62 9XC.9 4, oil 62 HVG.8 4, oil 62 9HVG.9 4, oil 62 HVSG.9 4, oil 62 9Kh5F,9 4, oil 59 9Kh5VF,9 4, oil 59 8Kh4V4F1(RF), 8 4.2 1150, oil 60 9Kh.1 4, oil 62 Kh6VF,9 4.3 1000, oil 61 Kh12, Kh12M, 8 4, oil 58 Х12Ф,8 4, oil 58 3Х2В8Ф,8 4, oil 46 4Х8В,8 4, oil 45 7Х.0 4, oil 54 8Х.8 4, oil 55 5ХНМ,9 4, oil 47 5ХНВ,8 4, oil 56 5KhNSV,8 4, oil 56 5KhGM,9 4, oil MODERN TOOL MATERIALS

22 Steel grade Steel after annealing hardness HB indent diameter at Dball = 10 mm and P = 3000 kgf 4Kh5V2FS,0 4.5 Continuation of Table. 5 Steel after hardening temperature (C) and hardening medium, oil or air hardness HRC (not less than) 4Kh5V4FSM Not more than 255 Not less than 3, oil 50 4Kh2V5FM,0 4, oil 50 4Kh3V2F2M,7 4, oil 50 4KhS,2 4, oil 47 6ХС,0 4, oil 56 5ХВ2С,8 4, oil 55 6ХВГ,1 4, oil 57 4ХВ2С,1 4, oil 53 6ХВ2С,6 4, carbide grid oil. For this reason, cracks and chipping of the cutting edge of the tool often occur. This steel requires strict structural control in the state of delivery of each batch of blanks and after hardening of each batch of tools. In addition, tools made of CVG steel working with increased specific pressures (drills, broaches, knives) quickly lose the shape of the working edge (dull). CVG steel cannot provide high resistance to complex shaped tools. Steel 9XC, along with good hardenability, is characterized by high resistance to heating. It retains high hardness and wear resistance when heated to 250 C. Due to the uniform distribution of carbides, 9XC steel is used in the manufacture of tools with a thin cutting edge. However, 9XC steel is difficult to process due to its high annealed hardness (HB). In addition, it has an increased sensitivity to decarburization, including when heated in a salt melt, which requires careful deoxidation of the melt. End cutting tools, threaded gauges, patterns of complex shape, complex and precise dies for cold deformation are made from steel grade 9KhVG, which

23 heat treatment should not be subject to significant volumetric changes (warping). Thread-rolling tools, hand hacksaw blades, dies, punches and other tools intended for cold deformation are made from steel grades X6VF. Steel grades Kh12M and Kh12F1 are less deformed during heat treatment than other tool steels. They are used to make dies of complex shape and high wear resistance, reference gears, rolling dies, drawing dies. From steel grades 3Kh2V8F and 4Kh8V2, press-injection molds are made for the manufacture of plastic parts, molds for injection molding parts from aluminum alloys. From steel grades 7X3 and 8X3, dies are made for hot heading of bolts on presses and horizontal forging machines with replaceable working inserts, forming and piercing punches for hot bending and trimming. From steel grades 5HNM, 5HNV, 5HNSV and 5HGM, hammer dies of medium and large sizes are produced. From steel grades 4Kh5V2FS, 4Kh5V4FSM, 4Kh2V5FM and 4Kh3V2F2M2, tools for hot deformation of stainless, heat-resistant and other hard-to-form alloys, as well as molds for injection molding, are made. Pneumatic chisels, crimps, scissors for hot and cold cutting of metals, die parts for cold deformation are made from steel grades 4XC, 6XC, 4XV2C. From steel grades 5XV2S and 6XV2S, thread-rolling dies and molds for injection molding are made. Punches of complex shape are made from steel of the 5KhVG grade for cold piercing of predominantly shaped holes in sheet material, small dies for hot stamping, mainly when a minimum change in size is required during heat treatment. From steel grades 9X5F, 9X5VF, 8X4V4F1 and 9X, all kinds of cutting tools for woodworking are made. The choice of multicomponent steels with a high content of alloying elements for woodworking tools is caused by the stressful conditions of its operation. Applied in modern equipment high cutting speeds (m/s) and feeds (up to 100 m/min) intensively wear out the tool. Wear increases especially as a result of strong 22 MODERN TOOL MATERIALS

24 tool heating (above 400) when rubbing against wood. In some cases, this leads to irreversible structural changes in the surface layers of the blade. The choice of tool material with very high wear resistance, toughness, strength and heat resistance is also dictated by the widespread use of wood chip, fibrous, and adhesive blanks at the present time. During their processing, abrasive action, increased bending and shock loads occur. Significantly reduce the strength of the cutting edge and small taper angles. Alloying tool steel with several elements has become one of the main directions for improving its properties, since the complex of necessary properties cannot be provided with only one alloying element, even if in an increased amount (6 ... 12%). Elements are introduced into the steel composition that effectively increase hardenability and hardenability (Cr, Mn, Si), elements that prevent grain growth during heating and provide high mechanical properties (V, W, Mo). MSTU "STANKIN" created complex alloyed tool steel 7KhG2VM. According to the test data, the strength of steel 7KhG2VM is 50% higher, and the sensitivity to heating is two times less than that of high-chromium steels with % Cr (Kh6VF and Kh12M). The impact strength of the new steel is two to three times higher than that of Kh6VF steel, and five to six times higher than that of Kh12M and Kh12F1 steels; its wear resistance is lower than that of high-chromium steels. The heat resistance of steel 7KhG2VM, at which the hardness is not less than HRC57, is 250 C. The sensitivity to overheating is negligible. Due to cooling in air, the new steel has smaller volumetric changes than high-chromium steels. Steel 7KhG2VM has passed industrial tests at a number of enterprises. Complex-shaped punches, punching die matrices and other tools were made from it. The deformation during hardening did not exceed 0.05% (less than Kh12M steel), and the resistance is 25% higher. For steel 7KhG2VM, the following heat treatment modes are recommended: isothermal annealing (heating to C, holding at this temperature for hours, cooling at a rate of 30 deg / h to C, holding at this temperature for at least CHAPTER 1. TOOL STEELS 23

25 5 h, cooling at a rate of up to 30 deg/h to 600 C and further cooling with a furnace; hardness HB, structure granular perlite); quenching at C (lower temperature allows parts to be heated in conventional furnaces and baths used for hardening carbon steels) and tempering at C to obtain hardness HRC chromium, vanadium, molybdenum, which form stable carbides after heat treatment. In addition to carbide-forming elements, cobalt is also included in some grades of high-speed steels. High-speed steels have found a very wide application for the manufacture of a wide variety of tools. This is due to their high, compared to other tool steels, heat resistance () and high hardness after heat treatment (HR C), in some new grades HRC High speed steels have the highest bending strength of all tool materials (ó and = MPa) and the highest impact strength. Due to this, they successfully compete with hard alloys and even outperform them in cutting conditions with strong dynamic loads and large shear sections. ALLOYING AND PROPERTIES OF SPEED STEELS ) and carbide-forming elements: tungsten (W), vanadium (V), molybdenum (Mo), chromium (Cr). Some steels are alloyed with a sufficiently large amount of cobalt (Co). Below we consider the nature of the influence of alloying elements on the properties of high-speed steels. Increasing the carbon content improves the hardenability of steel, i.e., provides higher hardness after heat treatment, but somewhat reduces ductility. Until recently, the optimal carbon content in high-speed steels with 18% tungsten was considered to be 0.7 ... 0.8%. Recent studies have established that the carbon content can be 24 MODERN TOOL MATERIALS

26 increase to 1.3...1.4% without changing the content of other alloying elements. In this case, the hardness of the steel increases from HRC to.5 HRC (in some cases up to 68 HRC), and its heat resistance from C to 630 C. In such steels, there is no noticeable deterioration in toughness, strength, hot ductility and weldability. Grindability deteriorates slightly. This provides an increase in tool life during processing, mainly blanks made of simple structural steels, at low cutting speeds by about %. An increase in the content of vanadium contributes to an increase in heat resistance and hardness, obtaining a fine-grained structure, but reduces the grindability of steel. The content of vanadium must be consistent with the content of carbon required for the formation of vanadium carbides. It has been experimentally established that the quantitative ratio between vanadium and carbon should be in the range of 2...2.7. In modern high-speed steels with % W and increased carbon content, the optimum vanadium content is about 3%. Steel R12F3 of all vanadium steels has an optimal combination of properties. With high HRC hardness, it has increased strength and toughness, good processing properties and high wear resistance. Tools made of R12F3 steel, when machining materials with increased abrasion ability at low cutting speeds, have a tool life times greater than tools made of R18 and R12 steels. Tungsten increases the hardness and heat resistance of steels, but worsens the technological properties of malleability and machinability. Currently, steels are produced containing 18, 12, 9, 8, 6, 2 ... 0% tungsten. In the latter case, tungsten is partially or completely replaced by molybdenum. Steels with 18% tungsten are indispensable in the processing of heat-resistant materials, when a high temperature occurs in the cutting zone. These steels are insensitive to overheating during heat treatment, due to which the range of hardening temperatures for them is quite wide (10 C). Heat treatment of such steels is well mastered. However, in recent years, molybdenum-alloyed steels have been increasingly used. This is due to both the shortage of tungsten and a number of valuable qualities of molybdenum steels. Molybdenum increases the strength and toughness of steels, improves ductility, and reduces carbide inhomogeneity. CHAPTER 1. TOOL STEELS 25

27 The disadvantage of molybdenum steels is their tendency to decarburize the surface layer and overheat during hardening. As a result, the range of hardening temperatures for these steels is narrower than for tungsten steels, and is 5 C. These steels are more capricious during heat treatment than tungsten steels. A number of tungsten steels (0...8% W) have been developed in our country and abroad. An example is domestic steel R6M5, steel groups AT T and M4O (USA). These steels are characterized by high hardness and heat resistance at high level mechanical properties and good sandability. The optimal content of tungsten and molybdenum in high-speed steels was experimentally established: W + 2Mo = %. Conventional high speed steels contain about 4% chromium. Chromium, like tungsten, molybdenum and vanadium, is a carbide-forming element. However, it does not have such a strong effect on the properties of high-speed steels as the above elements. It has now been established that reducing the chromium content to 2% somewhat increases impact strength and promotes grain refinement, but reduces hardness by 1.0...1.5 HRC and reduces strength. As a result, the cutting properties remain unchanged. Alloying with cobalt in the amount of % provides a significant increase in the heat resistance of steels up to C and makes it possible to obtain hardness up to 70 HRC. Cobalt-alloyed steels are steels of increased and high productivity, because they provide a % increase in cutting speed compared to steels of normal productivity (P18, P12), especially when cutting hard-to-cut materials. In the first half of the twentieth century, it was found that if the hardening temperature of tungsten steels is increased and brought to approximately 1300 C, the amount of tungsten in steel can be increased up to %, the amount of chromium up to 4 ... 5% and vanadium up to 1 ... 1.5 %. Such a highly alloyed steel, having heat resistance when heated to temperatures of about 600, made it possible to increase cutting speeds by a factor of times compared to an allowable tool made of carbon tool steel. In this regard, it was called high-speed cutting. First brand 26 MODERN TOOL MATERIALS

28 high speed steel in their own way chemical composition corresponded to the R18 grade according to GOST Recently, research and development of new grades of high-speed steels has been carried out with great intensity in many countries of the world. As a result, cobalt-alloyed steels appeared, which have higher heat resistance than P18 steel; it became possible to partially replace tungsten with molybdenum (at a ratio of 1% Mo instead of 4% W) or vanadium (at a ratio of 1% V instead of 8% W) while maintaining heat resistance at the same level. It has been established that increased alloying of steel with vanadium (up to 4...5%) contributes to an increase in its wear resistance. The heat treatment of high speed steel includes hardening after heating to temperatures of the order of C (depending on the steel grade and tool dimensions) and subsequent high multiple (three or four) tempering at C. After such heat treatment, the hardness of the tools is HRC, and for steels with the addition of cobalt or vanadium up to HRC The structure of hardened and repeatedly tempered high speed steel consists of acicular martensite and excess carbides. In order to further increase the hardness and wear resistance of the surface layers of tools made of high-speed steels of normal productivity, some special methods of chemical-thermal treatment are currently used additionally (cyanidation, chromium plating, surface carbon saturation, sulfiding, phosphating, tempering in a steam atmosphere at a temperature of C, as well as electrohardening with hard alloys and upholstery with balls). Studies have also found that small additions of titanium (Ti), boron (B) and nitrogen (N) only slightly increase the wear resistance of steels. Aluminum (Al) has practically no effect on the properties of steels. Recently, steels with the addition of silicon (R8M3K6S) and niobium (R3M3FB2) have appeared. foreign countries(USA, Germany, France, England, Sweden, Japan, etc.) a large number of different high-speed steels are produced. The chemical composition of steels produced in our country CHAPTER 1. TOOL STEELS 27

29 according to GOST, GOST and according to some specifications, is presented in table. 6. In it, steels of normal heat resistance are steels with heat resistance up to 620 C, and steels of increased heat resistance are steels with heat resistance C. Table 6 Chemical composition of high-speed steels Content of alloying elements,% Steel grade C W Mo Cr V Co Steels of normal heat resistance 1. Tungsten P18 0.7 0.5 1 3.8 4.4 1 1.4 Р12 0.8 0, up to 1 3.2 3.7 1.5 1.9 Р9 0.85 0.95 8.5 10 up to 1 3.8 4.4 1.3 1.7 R9F (EP347) 0.7 0.8 8.5 10 to 1 4 4.6 1.3 1.7 2. Tungsten-molybdenum R6M3 0.85 0.95 5.5 6.5 3 3.6 3 3.6 2 2.5 Р6М5 0.8 0.9 5.5 6.5 4.5 5.5 3.8 4.4 1.8 2.2 Р9М1 (EP344) 0.8 0.9 8.6 3.5 4.1 1.8 2.2 Steels with increased heat resistance 8 2.4 R14F4 1.2 1.5 to 1 4 4.6 3.4 4.1 R12F3 (EP597) 0.94 1.5 0.5 1 3.5 4 2.5 3 R9F5 1.4 1 .5 9 10.5 up to 1 3.8 4.4 4.3 5.1 B. Cobalt steels 1. Tungsten-cobalt R18F2K5 0.85 0.5 1 3.8 4.4 1.8 2.4 5 6 R15F2K5 (EP599) 0.75 0.85 12.5 14 0.5 1 3.5 4 1.7 2.2 5 6 R9K5 0.5 to 1 3.8 4.4 2 2.6 5 6 R9K10 0.5 to 1 3.8 4.4 2 2.6 9.5 10.5 .6 2.1 2.5 5 6 R6M5K5 0, Cobalt steels with high vanadium content R10K5F5 1.45 1.55 10.5 11.5 up to 1 4 4.6 4.3 5.1 5 6 R12K5F4 1.25 1.4 12.5 14 0.5 1 3.5 4 3.2 3 MODERN TOOL MATERIALS

30 In addition to the steels given in table. 6, a number of new high speed steels have been developed in recent years. Below is a brief description of them. High-performance steel R18F2K8M (EP379) has a hardness after HRC heat treatment at a heat resistance of 640 C. When machining titanium and heat-resistant alloys, tools made of EP379 steel have a tool life several times higher than that of steel R18, and when threading and drilling hardened steels, it is times higher. Steel R18F3K8M (EP380) can be hardened to HRC hardness and has a heat resistance of 650 C, however, it is characterized by poor ductility and therefore can only be used for the manufacture of simple-shaped tools. Having hardness HRC, steel R18F4K8M (EP381) is somewhat superior to the previous one in terms of strength and toughness. R9F4K8M steel has even higher strength properties. Its hardness is equal to HRC. For processing austenitic steels and heat-resistant alloys, it is recommended to use R12M3F2K8 (EP657) steel, which has a hardness of up to 68.5 HRC and heat resistance of up to 640 C with good technological properties. Steel R6M5F2K8 (EP658) has a hardness HRC at a heat resistance of 640 C and is designed for processing high-strength steels under shock loading conditions. For the same purpose, steel R6M5K14F2 (EP804) is also recommended. All of these steels were developed at Saint Petersburg State Technical University. A number of new grades of high-speed steels were developed at MGTU "STANKIN": R18F2K5M, R12F4K8, R8M3S, R9MCHK8 (EP688), R8M3K6S (EP722). EP688 steel has a hardness of up to 5 HRC, and EP722 steel of up to 5 HRC. Steel EP688 is recommended for processing heat-resistant alloys, where the tool life of this steel is several times higher than that of R18 and R12 steels, and 1.5 ... 2.5 times higher than that of R9K5 and R9K10 cobalt steels. EP722 steel tools are recommended for cutting high-strength steels and titanium alloys. The recently produced steels 10R6M5 and 10R8M3 have increased wear resistance and are used for cutting hardened structural steels with HRC hardness. The tool life of steel 10R6M5 when processing blanks of machine parts with a strength of V MPa is 1.3 ... 2 times higher than that of steel R6M5. Steel R6M5F3 is recommended for finishing CHAPTER 1. TOOL STEELS 29

31 and semi-finishing of alloy steels, including difficult-to-machine, stainless and austenitic steels. Tool life is % higher than that of steels R18 and R6M5. When optimizing the composition of alloying elements in high speed steels, mathematical modeling is often used to establish the relationship between composition and property. The content of alloying elements was chosen as the studied factors (input parameters), hardness, strength, impact strength, heat and wear resistance were considered as the target functions (output parameters), and the carbide inhomogeneity ball and the depth of the decarburized layer were considered as controlled parameters. Optimization of the obtained models made it possible to choose the composition of steel with the following concentration of alloying elements: 1.05...1.15% carbon; 1.7...2.2% tungsten; 3.3...3.8% molybdenum; 5.0...5.5% chromium; 2.5...3.0% vanadium; 3.3...3.8% cobalt; 0.7...1.2% silicon; 0.2...0.5% niobium; designated steel grade R2M3F3K3SB. Optimum mode of heat treatment of steel: hardening at C and double tempering at 560 C for 1 hour. After treatment, R2M3F3K3SB steel is characterized by the following properties: hardness HRC, strength MPa, impact strength 0.23 ... 0.28 MJ / m 2 , red hardness HRC 58, characterized by hardness after four hours of heating at 630 C. In the annealed state, the steel structure is polygonized ferrite and MC carbide, M 6 C and M 23 C 6, the distribution of which is more uniform than in high-alloy steels of the R6M5K5 grade. Austenization at 1220°C does not cause noticeable grain growth in the steel, since more than 90% of excess carbides based on vanadium and niobium MC remain undissolved and serve as a barrier to grain growth. Cobalt is almost completely contained in the solid solution, is not redistributed between it and the carbide phase, and does not affect the amount of the latter. However, upon tempering, cobalt together with silicon significantly changes the carbide coagulation kinetics. This explains the fact that the dimensions of the MC, M 2 C and M 3 C carbides released during tempering of R2M3F3K3SB steel are much smaller than in most high-speed steels. 30 MODERN TOOL MATERIALS

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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.

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 tough materials (steel, brass). Alloys of the titanotantalum-tungsten group are used under unfavorable working conditions of the tool with shock loads, when machining steel castings and forgings.

Mineral ceramic materials.

Mineral-ceramic materials for cutting tools are made in the form of aluminum oxide Al 2 O 3 (alumina) plates 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.

The use of hard-to-cut materials in industry and the constant growth of labor productivity, especially in metal cutting processes, require the creation of new processing methods and new metal-cutting tools from more efficient tool materials.

The performance of a tool depends to a large extent on its ability to maintain certain time cutting properties. Cutting properties deteriorate not only under the influence of high temperature, which rises during the cutting process and causes a decrease in tool hardness, but also under such phenomena as adhesion, diffusion, abrasive-mechanical wear of the cutting edge and tool surfaces.

The ability of an instrument to resist these phenomena is called wear resistance. Tool life is measured by the time during which its cutting properties are maintained and under certain working conditions. To avoid premature failure of the cutting edge, the tool material must also be sufficiently strong.

Therefore, tool materials, regardless of their chemical composition and production method, intended for use as cutting elements of tools, must have: hardness exceeding the hardness of the metals being processed; high wear resistance; red hardness; mechanical strength combined with sufficient ductility. The listed properties determine the physical and mechanical characteristics of tool materials. However, not all tool materials have equally high physical and mechanical properties. They vary depending on the chemical composition, structural state, on the conditions of interaction of the tool material with the metal of the workpiece during the cutting process, and on its stability at varying temperatures.

Classification of tool materials by chemical composition and physical and mechanical properties

The classification of tool materials by chemical composition and physical and mechanical properties is shown in fig. 1, from which it can be seen that at present the materials of cutting tools are divided into four groups and differ in a significant nomenclature. In accordance with this, various cutting materials should have their own rational areas of application.

Figure 1. Classification of modern tool cutting materials

Materials belonging to groups II - IV have increased cutting properties and therefore are progressive.

Progressive cutting materials, due to increased heat resistance and wear resistance, in comparison with tool steels, provide work at high cutting speeds when cutting with a tool, processing of metals with high hardness, which contributes to an increase in labor productivity and the efficiency of the technological process. The productivity of the machining process depends not only on the cutting speed, but also on the amount of feed and depth of cut. These parameters determine the cut area and, accordingly, the cutting force acting on the cutting part of the tool, causing complex stresses in the cutting wedge. Therefore, one of the main mechanical characteristics tool cutting material is bending strength. However, in nature there are no materials that simultaneously have high hardness, wear resistance and strength.

The relative arrangement of tool materials in terms of wear resistance and strength is shown in fig. 2.

Figure 2. Relative arrangement of cutting materials in terms of their wear resistance and bending strength of its design, taking into account the physical and mechanical properties of the material and cutting mode factors.

Materials scientists are working to create new materials and improve existing ones in the direction of simultaneously improving the above properties of materials.

Students-toolmakers and technologists are faced with the task of rational choice of cutting material for a specific tool and type of processing.

The main recent achievements in the field of progressive cutting materials include:

1. improving the quality of ceramic-metal tungsten-titanium-cobalt hard alloys;
2. development of low-tungsten hard alloys;
3. development and improvement of tungsten-free hard alloys;
4. increasing the cutting ability of alloys by applying coatings with titanium carbide, titanium nitride, carbonitrides and oxides of various metals;
5. development and improvement of oxide-carbide mineral ceramics;
6. creation of polycrystals of synthetic superhard materials based on carbon and boron nitride.

The quality of the tool material is determined by a complex of mechanical and physico-chemical properties:

• ultimate strength in uniaxial tension and compression;
• temperature dependence of the yield strength or hardness;
• temperature dependence of endurance limit;
• temperature dependence of the intensity of adhesion with the processed material;
• modulus of elasticity, temperature coefficient of linear expansion, Poisson's ratio;
• heat and thermal diffusivity;
• temperature dependence of the rate of mutual dissolution of instrumental and processed materials;
• temperature dependence of the oxidation rate.

Comparison of the main physical and mechanical properties of groups of cutting materials is given in Table. 1. Cermets, which occupy an intermediate value between hard alloy and high-speed steel in terms of cutting characteristics, are not included in Table. 1.

Material	Density ?, 10 3 kg / m 3	Microhardness HV,10 7 Pa	Compressive strength? szh. MPa	Bending strength? from, MPa	Modulus of longitudinal elasticity E, GPa	Thermal conductivity, W / (m * K)	Heat resistance, °C
Carbide						11…80
Mineral ceramics: oxide
oxide-carbide
Superhard cubic boron nitride
synthetic diamond

New tooling materials usually have a limited scope - so they will complement rather than replace the main types of tooling materials. The complexity of the chip formation process, especially under interrupted cutting conditions and at high temperatures, does not currently allow predicting the cutting ability of new tool materials under all machining conditions.

Improved existing and created new progressive cutting materials have improved cutting properties and allow cutting all structural materials.