Cemented Tungsten Carbide

The main use of tungsten (in the form of tungsten carbide) is in the manufacture of cemented carbide. After Scheele discovery of "Tungsten" in 1781, it took an additional 150 years before his and his successors? Efforts led to the application of tungsten carbide in the industry.

Cemented carbide, or hard metal as it is often called, is a material made by "cementing" very hard tungsten monocracies (WC) grains in a binder matrix of tough cobalt metal by liquid phase sintering.

The combination of WC and metallic cobalt as a binder is a well-adjusted system not only with regard to its properties, but also to its sintering behavior.

The high solubility of WC in cobalt at high temperatures and a very good wetting of WC by the liquid cobalt binder result in an excellent densification during liquid phase sintering and in a pore-free structure. As a result of this, a material is obtained which combines high strength, toughness and high hardness.

The beginning of tungsten carbide production may be traced to the early 1920抯, when the German electrical bulb company, Osram, looked for alternatives to the expensive diamond drawing dies used in the production of tungsten wire.

These attempts led to the invention of cemented carbide, which was soon produced and marketed by several companies for various applications where its high wear resistance was particularly important. The first tungsten carbide-cobalt grades were soon successfully applied in the cutting and milling of cast iron and, in the early 1930, the pioneering cemented carbide companies launched the first steel-milling grades which, in addition to tungsten carbide and cobalt, also contained carbides of titanium and tantalum.

By the addition of titanium carbide and tantalum carbide, the high temperature wear resistance, the hot hardness and the oxidation stability of hard metals have been considerably improved, and the WC-TiC-(Ta, Nb) C-Co hard metals are excellent cutting tools for the machining of steel. Compared to high speed steel, the cutting speed increased from 25 to 50 m/min to 250 m/min for turning and milling of steel, which revolutionized productivity in many industries.