Abstract
The effects of quenching and tempering temperatures on microstructure and hardness of 0.4C-4Cr-Mo-V-Nb hot-working tool steel processed by both ingot(I/M) and powder metallurgy(P/M) were studied. The aim of the addition of Nb to JIS SKD6 is to improve the toughness by refining prior austenite grains due to the pinning effect of NbC. In comparison with the conventional tool steel without Nb, the grain coarsening of Nb added I/M tool steel was inhibited considerably. The hardness of I/M tool steel tempered at 873K after quenched from 1303K was above 70HV higher than that of conventional tool steel. On the other hand, the hardness of quenched P/M tool steel was slightly lower than that of I/M tool steel, however, P/M tool steel had fine-grained structure in the case of quenching from high temperature, for example, from 1403K.
