Laser powder bed fusion of crack-susceptible stainless maraging steel undergoing solid-state phase transformations

Abstract

For alloys that experience solid-state phase transformation upon cooling, the absence of as-solidified chemical segregation information makes the elimination of hot cracking challenging. One such material is the hot-crack-susceptible high-strength maraging steel C465. Here, we resolve its hot cracking problem under the laser powder bed fusion process through the addition of titanium nitride (TiN) particles. During solidification, TiN promotes grain refinement and reduces the formation of liquid films with low solidus temperatures. Under cooling, the partial dissolution of TiN lowers the martensite start temperature and yields more retained austenite. Upon subsequent annealing, the dissolved titanium slows down the austenite reversion kinetics, while the dissolved nitrogen improves the yield strength. Materials under tensile deformation follow a three-stage work-hardening behavior, indicative of strain-induced martensitic transformations. This work highlights that besides the nucleant's grain refinement potency, the effect of its partial dissolution during processing needs to be critically examined, when addressing the hot cracking problem for alloys prone to phase transformations.