W and C can form two compounds: WC and W2C, which have different physical and chemical properties. WC has two crystal forms, one is simple hexagonal structure, the other is face centered cubic structure, which is formed by peritectic reaction at 2785 ℃ and only stable at high temperature. W2C is a close packed hexagonal structure with high hardness and brittleness.
W2C has higher melting point and hardness than WC. It can form W2C + WC eutectic mixture with WC. The melting point of W2C is lower and it is easy to cast, which is called "cast tungsten carbide" or "fusible tungsten carbide". The carbon content of W2C is 78% ~ 80% (mass) and WC is 20% ~ 22% (mass). This cast tungsten carbide is the hardest and most wear-resistant material with lower cost.
