Effects of Quenching and Tempering Temperature on Microstructure and Hardness of P/M Tool Steel for Hot Working

The effects of quenching and tempering temperatures on microstructure and hardness of 0.35C-5Cr-Mo-V hot working tool steel processed by powder metallurgy were studied. I/M tool steel having the same chemical composition was also used for discussion. P/M tool steels have fine microstructure with uniformly dispersed carbides, though I/M tool steels have banded structure caused by macrosegregation during the freezing process. The hardness of both I/M and P/M tool steels quenched from various temperatures increased with increasing austenitizing temperature, then saturated at > 1350K. The hardness of tempered P/M tool steel was slightly lower than that of I/M tool steel. The austenite grain growth of P/M tool steel was inhibited, i.e. grain coarsening temperature was more than 50K higher than that of I/M tool steel.