IVB, VB, VIB metal carbide, nitride, boride, etc, due to the particularly high melting point and hardness, collectively known as tungsten carbide. Here, with emphasis on the carbide to illustrate the structure of hard gold, characteristics and application.

IVB, VB, VIB metal and carbon type metal carbide formation, due to the carbon atom radius is small, can fill the gap in metal character and retain the original metal lattice form, the form filling between solid solution. Under appropriate conditions, this kind of solid solution can also continue to dissolve its constituent elements, until it is saturated. As a result, they can within a certain range of changes (such as the composition of titanium carbide in TiC0.5 ~ TiC change), chemical formula does not conform to the rules of valency. When dissolved carbon content exceeds a certain limit (such as titanium carbide in Ti: C = 1:1), lattice pattern will change, make the original metal crystal lattice transformed into another form of metal crystal lattice, at this time between the solid solution called filling filling compound.

Type metal carbides, especially IVB, VB, VIB metal carbide the melting point of 3273 k or more, including hafnium carbide, tantalum carbide, 4160 k and 4150 k respectively, is the current known substances with the highest melting point. Most of the carbide hardness is very big, the microhardness is greater than 1800 kg, was (microhardness is one of the hardness of representation, used in hard alloy and hard compound, microhardness, 1800 kg, was equivalent to Morse a diamond hardness of 9). Many carbide under high temperature is not easy to decompose, antioxidant ability stronger than the metal components. Titanium carbide in thermal stability is best in all of carbide, carbide is a very important metal type. However, in the oxidizing atmosphere, all carbide under high temperature easy to oxidation, can say this is a major weakness of carbide.

In addition to the carbon atoms, nitrogen and boron atoms can enter the metal lattice, the gap formed between the solid solution. Filling between them and the nature of the carbide, conductive, thermal conductivity, high melting point, high hardness, brittleness also big.