A novel high nitrogen hot-work die steel 3Cr5Mo2SiVN achieving excellent hardness-strength-toughness balance

A novel high nitrogen hot-work die steel 3Cr5Mo2SiVN was manufactured by pressurized induction melting, possessing excellent hardness-strength-toughness balance under conventional heat treatment process. The results indicated that 3Cr5Mo2SiVN steel exhibited better hardness-toughness synergy compared with H13 steel. Meanwhile, its impact energy and elongation were improved by ca. 50% and 13% compared with H13 steel with similar hardness. The achievement of superior toughness of 3Cr5Mo2SiVN steel could be attributed to the following reasons: firstly, the higher fraction of operators 1 and 2, more uniform and refined close-packets and Bain groups as well as smaller effective grain size obtained a higher ratio of high angle grain boundaries, which resulted in the more changes of crack propagation direction and thus an increase of energy absorption. Secondly, the smaller size and number density of undissolved M(C, N) carbonitrides distributed along the prior austenite grain boundaries required greater tensile stress and then reduced grain boundary brittleness. For the strengthening mechanism, the precipitation strengthening increment was mainly provided by M(C, N) carbonitrides and M3C carbides for 3Cr5Mo2SiVN steel, and MC carbides for H13 steel, respectively. The smaller effective grain size and higher interstitial atom (C and N) content in the martensitic laths of 3Cr5Mo2SiVN steel were crucial factors in enhancing its strength.