Simultaneously enhancing strength and toughness of medium-carbon martensitic steel via nano precipitates and fine-grained structure

A medium-carbon martensitic mold steel with high strength and toughness is obtained based on the synergistic effect of nano precipitates and fine-grained (FG) structure. Treatment increases the length per unit area of the effective grain boundary by 37.9%. Compared with the untreated samples, the excellent properties of the steel include increases of 39.2% in impact energy and more than 110 Mpa in ultimate yield strength. The FG structure is produced by the interaction between the MC nano precipitates formed by V alloying and the subgrain structure formed by thermomechanical processing (TMP). Additionally, the anisotropy of the microstructure is eliminated through the innovative introduction of austenitization, resulting in the refinement and homogenization of the grain structure. MC nano precipitates not only prevent the growth of subgrain structure but also enhance the thermal stability of FG structure through a pinning mechanism during austenitization.