Regulating precipitation behavior in an ultrahigh-strength, high-molybdenum maraging steel via laser powder bed fusion

In high-molybdenum (Mo) maraging steels, the formation of coarse Mo-enriched precipitates during conventional hot processing can significantly compromise both strength and ductility. In this contribution, we utilized the laser powder bed fusion (L-PBF) technique to produce a high-Mo maraging steel with a nominal chemical composition of Fe-13Ni-12Co-10Mo-1W-1Ti (wt.%). Notably, the ultrafast cooling rate inherent to L-PBF successfully suppresses the formation of coarse Mo-enriched precipitates. The co-precipitation of high-density Ni3Ti and Mo-enriched nanoprecipitates within the direct-aged martensitic matrix was observed. As a result, despite containing -16% soft reverted austenite, the direct-aged samples exhibit an ultrahigh yield strength (YS) of 2.34 GPa and an ultrahigh ultimate tensile strength (UTS) of -2.57 GPa, with an acceptable uniform elongation (UE) of around 2.7%. This work may provide a new pathway for the development of ultrahigh-strength maraging steels.