AISI O2 steel also can be called JIS SKS31 and DIN 1.2842 steel. It is the better type compare with the O1 tool steel. Its content of carbon, chromium and tungsten has been raised. So it has a higher hardenability characteristic, the deformation is small during the quenching. It is a low alloy tool steel which is better than carbon steel at the point of the mechanical property. It has high hardness and wearing resistance. Because of the certain account of vanadium element, the crystal grain is smaller then decrease the overheating sensitivity of the steel. At the meantime, the carbide is getting smaller and the distribution is uniformity.