Microstructure evolution and mechanical property enhancement of high-Cr hot work die steel manipulated by trace amounts of nano-sized TiC

Simultaneously increasing the strength and ductility of hot work die steels is of significant interest for broad applications. The in-situ development of a nano-phase in steels is a promising method for achieving this objective. However, little success has been reported so far. In this study, trace amounts of TiC nanoparticles were successfully introduced into a high-Cr hot work die steel (HHD) through an innovative method using a nano-TiC/Al master alloy. Upon adding 0.02 wt% nano-TiC, an incompletely recrystallized ferrite phase was observed in the HHD containing nano-TiC. Moreover, more globular pearlite was distributed at the ferrite grain boundaries in the HHD with nano-TiC than in the unmodified HHD. The added nano-TiC provided nucleation sites for γ-Fe dendrites and prevented γ-Fe growth during solidification and an austenitizing heat treatment. Furthermore, it noticeably increased the precipitation of more uniform nanoscale chromium carbides and significantly refined the carbides in the HHD during quenching and tempering. Finally, adding nano-TiC simultaneously enhanced the strength and toughness of the HHD. After quenching at 1353 K and tempering at 833 K, the yield strength, tensile strength, tensile strain, and impact toughness of the HHD with nano-TiC were 1330 MPa, 1620 MPa, 14.4 % and 460 J/cm2, respectively, which are all higher than those of the HHD without nano-TiC.