Effect of Ni on the Microstructure and Mechanical Property of Annealing and Tempering Pre-hardened Plastic Mould Steel

The microstructure and mechanical property of pre-hardened plastic mould steel that had gotten forged and heated treatment were studied.The microstructure of annealed steel witch was composed of granular bainite,lower bainite and martensite.The toughness and the elongation were increased when the volume of granular bainite was reduced.The residual austenite did not improve the toughness for the little content.The decomposition of residual austenite had resulted in the increasing of the yield strength.The hardness of martensite was reduced and meanwhile increased the hardness of bainite and tempering microstructure after anealling because of the increase of Ni.This possible reason is that the Ni lowered the precipitation of carbide.The residual austenite was the important reason of hardness change.