Cemented carbides are powder metallurgical products sintered with Co, Mo and Ni as binder. The room temperature can reach 78 ~ 78 HRC hardness, which can withstand temperatures up to 850 ~ 1000 ℃, the cutting speed 4 ~ 10 times higher than high speed steel. However, its impact toughness and bending strength are far worse than those of high-speed steel, so it is rarely made into integrated cutter.
Tungsten carbide is the raw material of cemented carbide family. Pure tungsten carbide is not commonly used. It is black hexagonal crystal with metallic luster and similar hardness to diamond. Melting point 2870 ℃, boiling point 6000 ℃, relative density 15.63 (18 ℃). Tungsten carbide is insoluble in water, hydrochloric acid and sulfuric acid. Pure tungsten carbide is fragile. If mixed with a small amount of metals such as titanium and cobalt, brittleness can be reduced. Tungsten carbide, used as a cutting tool for steel, is often added with titanium carbide, tantalum carbide, or a mixture of them, to enhance the ability to resist explosion. Tungsten carbide is chemically stable.
In tungsten carbide, a carbon atom is inserted into the gap of a tungsten metal lattice without damaging the lattice of the original metal and forming a solid solution of the gap. Tungsten carbide can be made by heating a mixture of tungsten and carbon at high temperatures, and the presence of hydrogen or hydrocarbons can accelerate the reaction. If use oxygen containing compounds in the preparation of tungsten, vacuum products must eventually in 1500 ℃, and to remove carbon oxides. Tungsten carbide is suitable for machining at high temperatures. Cutting tools, structural materials of kilns, jet engines, gas turbines, nozzles, etc.
