During the working process, the mold is subjected to impact load. In order to reduce the damage of breakage or chipping during working, the mold steel is required to have certain toughness.

There are many factors to influence the toughness of mold steel, like: the chemical composition, grain size, purity, carbide, inclusions of the mold steel, the heat treatment system; also the metallographic structure after the heat treatment. Particularly, the purity of the mold steel and the deformation of the hot work have a great effect on the toughness. 
The toughness, strength and wear resistance of steel are often contradictory. Therefore, the chemical composition of steel should be selected reasonablly. And adopting reasonable refining, hot work and heat treatment processes can make the mold material good toughness, strength and wear resistance.