The Effect of Trace Nitrogen on Microstructure and Property of Cr-Mo-V Hot-Working Die Steel

The effect of trace nitrogen on microstructure, hardness, toughness, and tempering stability of Cr-Mo-V hot-working die steel was investigated in this study. Results show that trace nitrogen promotes the precipitation of V(C, N), increasing the amounts of undissolved carbides in tempered steel. The undissolved carbides exert a stronger pinning effect on refining austenitic grains during the quenching process and refine the final tempered microstructure. The solid solubility of alloying elements and lattice distortion of matrix decreased obviously by trace nitrogen. Trace nitrogen could increase the hardness and toughness of hot-working die steel by refining the microstructure. However, the tempering stability would be decreased obviously due to the decrease of solid solubility of alloy elements, especially V. The results of this research can be used to provide a scientific basis for applications of nitrogen in hot-working die steel.