The main requirements for tool materials are the presence of hardness, resistance to wear, heat, etc. Compliance with these criteria allows cutting. To implement the introduction into the surface layers of the product being processed, the blades for cutting the working part must be made of durable alloys. Hardness can be natural or acquired.
For example, factory-made tool steels are easy to cut. After mechanical and thermal processing , as well as grinding and grinding, the level of their strength and hardness rises.
How is hardness determined?
A characteristic can be defined in various ways. Tool steels have Rockwell hardness, hardness has a digital designation, as well as the letter HR with a scale of A, B or C (for example, HRC). The choice of tool material depends on the type of metal being processed.
The most stable level of functioning and low wear of blades that have undergone heat treatment can be achieved with an HRC of 63 or 64. At a lower rate, the properties of tool materials are not so high, and at high hardness they begin to crumble due to brittleness.
Metals with a hardness of HRC 30–35 are excellently treated with iron tools that have undergone heat treatment with an HRC of 63–64. Thus, the ratio of hardness is 1: 2.
For processing metals with HRC 45–55, devices based on hard alloys should be used. Their indicator is HRA 87–93. Materials based on synthetics can be used in the treatment of hardened steels.
Tool strength
During the cutting process, a force of 10 kN and higher acts on the working part. It provokes high voltage, which can lead to the destruction of the tool. To prevent this, cutting materials must have a high coefficient of strength.
Tool steels have the best combination of strength characteristics. The working part made of them perfectly withstands heavy loads and can function during compression, torsion, bending and tension.
Exposure to critical heating temperature on tool blades
When heat is released during the cutting of metals, their blades are subject to heating, and to a greater extent - surfaces. When the temperature is below the critical level (for each material it is different), the structure and hardness do not change. If the heating temperature rises above the permissible norm, then the level of hardness drops. The critical temperature is called red resistance.
What does the term "red resistance" mean?
Redness is the property of a metal to glow dark red when heated to a temperature of 600 ° C. The term implies the preservation of the metal hardness and resistance to wear. At its core, it is the ability to withstand high temperatures. There is a limit for various materials, from 220 to 1800 ° C.
How can the working capacity of a cutting tool be increased?
Tool materials of the cutting tool are characterized by increased functionality while increasing temperature resistance and improving the heat dissipation generated on the blade during cutting. Heat contributes to a rise in temperature.
The more heat removed from the blade deep into the device, the lower the temperature indicator on its contact surface. The level of thermal conductivity depends on the composition and heating.
For example, the content of elements such as tungsten and vanadium in steel causes a decrease in its level of thermal conductivity, and an admixture of titanium, cobalt and molybdenum causes its increase.
What determines the coefficient of sliding friction?
The index of the coefficient of sliding friction depends on the composition and physical properties of the contacting pairs of materials, as well as on the value of the stress on the surfaces subjected to friction and sliding. The coefficient affects the wear resistance of the material.
The interaction of the tool with the material that has been processed proceeds with constant movable contact.
How do tool materials behave in this case? Their views wear out equally.
They are characterized by:
- the ability to wash the metal with which it is in contact;
- ability to show wear resistance, that is, to resist the abrasion of another material.
Blade wear is ongoing. As a result of this adaptation, they lose their properties, and the shape of their working surface also changes.
The wear resistance may vary depending on the conditions under which the cutting proceeds.
What groups are tool steels divided into?
The main tool materials can be divided into the following categories:
- cermets (hard alloys);
- cermets, or mineral ceramics;
- boron nitride based on synthetic material;
- synthetic-based diamonds;
- carbon steel tool steels.
Tool iron can be carbon, alloy and high speed.
Carbon-based tool steels
Carbon substances began to be used for the manufacture of tools. Their cutting speed is low.
How are tool steels labeled? Materials are indicated by a letter (for example, “U” means carbon), as well as a number (tenths of a percent of carbon content). The presence of the letter “A” at the end of the marking indicates the high quality of the steel (the content of substances such as sulfur and phosphorus does not exceed 0.03%).
Carbon material characterizes hardness with an HRC of 62–65 and a low level of resistance to temperature.
Grades of tool materials U9 and U10A are used in the manufacture of saws, and the U11, U11A and U12 series are designed for hand taps and other tools.
The temperature resistance level of the steels of the U10A and U13A series is 220 ° C; therefore, it is recommended to use tools made of such materials at a cutting speed of 8-10 m / min.
Alloyed iron
The doped instrumental material can be chromium, chromosilicon, tungsten and chromotungsten, mixed with manganese. Such series are indicated by numbers, and they also have an alphabetic marking. The first left digit indicates the carbon content coefficient in tenths if the element content is less than 1%. The right digits symbolize the average indicator of the alloying component in percent.
The grade of tool material X is suitable for the manufacture of taps and dies. Steel B1 is applicable for the manufacture of small drills, taps and reamers.
The level of resistance to temperature in doped substances is 350-400 ° C; therefore, the cutting speed is one and a half times higher than for a carbon alloy.
What are high alloy steels used for?
Various quick cutting tool materials are used in the manufacture of drills, countersinks and taps. They are marked with letters as well as numbers. Important components of the materials are tungsten, molybdenum, chromium and vanadium.
High-speed steels are divided into two categories: normal and with a high level of productivity.
Steel with normal performance
To the category of iron with a normal level of performance can be classified P18, P9, P9F5 and tungsten alloys mixed with molybdenum of the P6MZ, P6M5 series, which retain a hardness of at least HRC 58 at 620 ° C. The material is suitable for processing steels with carbon content and low alloy category, gray cast iron and non-ferrous alloys.
High performance steels
This category includes the brands R18F2, R14F4, R6M5K5, R9M4K8, R9K5, R9K10, R10K5F5, R18K5F2. They are able to maintain HRC 64 at temperatures from 630 to 640 ° C. This category includes superhard tool materials. It is intended for iron and alloys that are difficult to process, as well as for titanium.
Hard alloys
Such materials are:
- ceramic-metal;
- mineral ceramic.
The shape of the plates depends on the properties of the mechanics. Such tools operate at high cutting speeds compared to high-speed material.
Cermets
Ceramic carbides are:
- tungsten;
- tungsten with a titanium content;
- tungsten with the inclusion of titanium and tantalum.
VK series includes tungsten and titanium. Tools based on these components have increased wear resistance, but they have a low level of shock resistance. Devices on this basis are used to process cast iron.
An alloy of tungsten, titanium and cobalt is applicable to all types of iron.
The synthesis of tungsten, titanium, tantalum and cobalt is used in special cases when other materials are ineffective.
Hard alloys are characterized by a high level of resistance to temperature. Tungsten materials can retain their property with HRC 83–90, and tungsten materials with titanium can with HRC 87–92 at temperatures from 800 to 950 ° C, which makes it possible to operate at high cutting speeds (from 500 m / min to 2700 m / min when processing aluminum).
To process parts that are resistant to rust and elevated temperature, tools from the series of fine-grained OM alloys are used. The VK6-OM brand is suitable for finishing, and the VK10-OM and VK15-OM are suitable for semi-finishing and roughing.
Superhard instrumental materials of the BK10-XOM and VK15-XOM series possess even greater efficiency when working with “difficult” parts. They replaced tantalum carbide with chromium carbide, which makes them more durable even when exposed to high temperature.
To increase the level of strength of a solid plate, resort to its coating with a protective film. Titanium carbide, nitride and carbonite are used, which is applied in a very thin layer. The thickness is from 5 to 10 microns. As a result, a layer of fine-grained titanium carbide is formed. The resistance level of such inserts is three times higher than that of plates without a special coating, which increases the cutting speed by 30%.
In some cases, cermet materials are used, which are obtained from aluminum oxide with the addition of tungsten, titanium, tantalum and cobalt.
Mineral ceramics
Mineral ceramics TsM-332 is used for cutting tools. It is inherent resistant to elevated temperatures. The hardness index of HRC is from 89 to 95 at 1200 ° C. The material is also characterized by wear resistance, which allows the processing of steel, cast iron and non-ferrous alloys at high cutting speeds.
Series B cermet is also used to make cutting tools. It is based on oxide and carbide. The introduction of metal carbide into the composition of mineral ceramics, as well as molybdenum and chromium, helps optimize the physicomechanical properties of cermet and eliminates its fragility. Increases cutting speed. The semi-finishing and finishing treatment with a cermet-based device is used for malleable gray cast iron, hard-to-work steel and a number of non-ferrous metals. The process is carried out at a speed of 435-1000 m / min. Ceramic for cutting is resistant to temperature. Its hardness on a scale is HRC 90–95 at 950–1100 ° .
For the treatment of hardened iron, cast iron, and fiberglass, a tool is used, the cutting part of which is made from solids containing boron nitride and diamonds. The hardness index of elbor (boron nitride) is approximately the same as that of diamond. Its resistance to temperature is two times higher than that of the latter. Elbor is characterized by inertness to iron materials. The tensile strength of its polycrystals during compression is 4-5 GPa (400-500 kgf / mm 2 ), and when bent, 0.7 GPa (70 kgf / mm 2 ). Resistance to temperature has up to a limit of 1350-1450 ° C.
Also worth noting is the synthetic-based diamond ballas of the ASB series and the carbonado series ASPK. The reactivity of the latter to carbon-containing materials is higher. That is why it is used for sharpening parts of non-ferrous metals, alloys with a high content of silicon, hard materials VK10, VK30, as well as non-metallic surfaces.
The index of durability of carbonade cutters is 20-50 times greater than the level of resistance of hard alloys.
What alloys are widespread in industry?
Tooling materials are available worldwide. Species used in Russia, the USA and Europe, for the most part do not contain tungsten. They belong to the series KNT016 and TH020. These models became a replacement for the T15K6, T14K8 and VK8 brands. They are used for processing steels for structures, stainless steel and tool materials.
New requirements for tool materials are due to a deficiency of tungsten and cobalt. It is precisely with this factor that the United States, European countries and Russia are constantly developing alternative methods for producing new tungsten-free hard alloys.
For example, tool materials manufactured by the American company Adamas Carbide Co Titan series 50, 60, 80, 100 contain carbide, titanium and molybdenum. The increase in number indicates the degree of strength of the material. Characterization of tool materials of this release implies a high level of strength. For example, the Titan100 series has a strength of 1000 MPa. She is a competitor to ceramics.