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Hard alloys

The main feature of hard alloys is their high hardness and wear resistance, which determines their use as a material for the production of cutting and drilling tools, and also products with high requirements for wear resistance. The page contains a description of these alloys: physical and mechanical properties, application areas, grades of hard alloys, product types.

Basic information

Hard alloys are heterogeneous materials which particles of high hardness refractory compounds (most often carbides, less often nitrides or borides of transition metals; the most widely used carbides are tungsten, titanium, tantalum, chromium or their combinations) are cemented with a plastic metal (cobalt, nickel, iron and their alloys). Hard alloys have high hardness and wear resistance and retain these properties at a temperature of 900-1500 °C.


There are two types of hard alloys depending on the production method:
  • sintered;
  • cast.

Sintered alloys are obtained by powder metallurgy methods. This method gives a very high production precision of the resulting items and provides high values of various properties. Items produced by powder metallurgy methods require minimal mechanical processing, so they are processed by grinding or physical and chemical methods (laser, ultrasound, etching in acids, etc.). Sintered hard alloys are sometimes called metal-ceramic, since their production technology is similar to the production technology of ceramics. Alloys of this type are applied to the tool by soldering or mechanical fixing. The most common representatives of this group are VK alloys (for example, VK6, VK8), TK and TTK - the hard alloys based on tungsten carbide.

Cast hard alloys are obtained by casting. This group includes stellites (chromium, tungsten, nickel, carbon; the basis is cobalt), sormites (chromium, тickel, carbon; the basis is iron), stellite-like alloys (the basis is nickel). For surfacing, they are produced in the form of cast bars or rods of various chemical compositions.

The following groups of hard alloys are distinguished depending on the application area:
  • tool alloys used in the processing of materials by cutting, pressing or stamping, in drilling rocks, and so on;
  • structural alloys used for the production of wear-resistant parts of machines, mechanisms and devices, including those with special properties - high density, high time resistance and a significant modulus of elasticity;
  • heat-resistant and thermal stable alloys.

  • There are also another two large groups of hard alloys:
  • tungsten-containing;
  • tungsten-free.

  • The basis of all tungsten-containing alloys is tungsten carbide. Also, the composition must contain a binding metal, which can be cobalt, nickel or a mixture of nickel with molybdenum. In addition to tungsten carbide, such alloys may contain titanium carbides and tantalum carbides.

    In tungsten-free hard alloys, tungsten carbide is replaced either with some other solid material, such as nitride, boride, silicide, or with a carbide of another refractory metal, such as zirconium, hafnium, vanadium, niobium, tantalum, chromium or молибдена.

    Hard alloys properties

    The main practically useful properties of hard alloys are high hardness, wear resistance and strength. In some cases, heat resistance and thermal stability, and also refractoriness, play an important role.

    The properties of alloys vary depending on the group which a particular hard alloy belongs to. For VK alloys, the grain size of tungsten carbide plays an important role. As the grain size decreases, the hardness increases, but the bending strength and viscosity of the alloy decreases (with the same percentage of tungsten carbide and cobalt) and backwards, accordingly. Alloys of the TK group doped with titanium carbide have better resistance to oxidation, higher hardness and heat resistance compared to the VK group. However, they have lower viscosity, bending strength, and thermal and electrical conductivity. The simultaneous addition of tantalum and titanium carbides (TTK group) increases the bending strength of the alloys compared to the TK group.

    Grade Density, g/cm3 σИ, MPa, at least HRA, at least
    VK6 14.6-15.0 1500 88.5
    VK8 14.4-14.8 1600 87.5
    VK10 14.2-14.6 1650 87.0
    T30K4 9.5-9.8 950 92.0
    T15K6 11.1-11.6 1150 90.0
    T5K12 13.1-13.5 1650 87.0
    TT7K12 13.0-13.3 1650 87.0
    TT8K6 12.8-13.3 1250 90.5
    TT20K9 12.0-13.0 1300 89.0
    TN20 5.5-6.0 1100 90
    KNT16 5.6-6.2 1350 89.0

    Hard alloys grades

    The most common grades among tungsten-containing hard alloys are: VK - alloys based on tungsten carbide with cobalt as the binding metal, TK - alloys based on tungsten carbide with cobalt as the binding metal and the addition of titanium carbide, TTK - the same as TK plus tantalum carbide.

    In general, grades of tungsten-containing hard alloys are formed as follows: letter V - tungsten carbide (WC), T - titanium carbide (TiC), TT - titanium and tantalum carbides (TaC), KNT - titanium carbonitride, K - cobalt (Co), N - nickel (Ni); numbers after the letters mean the content of these elements as a percentage, and for the letters TT - the amount of content of titanium and tantalum carbides; the content of tungsten carbide is not specified, it is determined by the difference.

    In tungsten-free alloys, nickel is used as a binding metal mixed with 20-25% of molybdenum.

    The chemical composition of some grades is presented in the table.

    Grade Content, %
    WC TiC TaC Co
    VK6 94 - - 6
    VK8 92 - - 8
    VK10 90 - - 10
    T30K4 66 30 - 4
    T15K6 79 15 - 6
    T5K12 83 5 - 12
    TT7K12 81 4 3 12
    TT8K6 84 8 2 6
    TT20K9 71 8 12 9
    TН20 - 80 - (Ni+Mo) - 20
    KНT16 - 84 - Ti(C,N) - (Ni+Mo) - 20

    Advantages / disadvantages

    • high hardness and wear resistance;
    • quite high strength characteristics;
    • good values of heat resistance and thermal stability;
    • refractory materials.
    • tungsten carbide, which is the basis of most hard alloys, has a high cost;
    • they have a lower viscosity and are quite sensitive to shock loads compared to high speed steels.

    Application areas

    Sintered hard alloys are widely used for cutting materials, for equipping mining tools, wear machine parts, die assemblies, dragging tools, calibration tools, pressing tools, and so on. Cutters and drill heads are the examples of the most common products made of hard alloys. A tool made entirely of a hard alloy is very expensive, so only the cutting or wear part is made of it. Tool holders are made of ordinary structural or tool steel.

    Cast hard alloys are used much less frequently compared to sintered ones. They are widely used in the production of dies and some drilling tools.

    Hard alloy products

    The industry makes raw materials for the production of hard alloys in the form of powdered mixtures. The most widely used hard alloy mixtures are VK6 and VK8. The mixtures are formed and sintered further, resulting in billets or finished products of the desired shape. Billets serve as raw materials for the production of semi-finished products, such as sheets, plates, rods and other products.


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