Achieving ultrahigh yield strength and decent toughness in an in-situ alloyed H13 steel via laser powder bed fusion

It is highly challenging to simultaneously achieve ultrahigh yield strength (YS) and decent toughness in the H13 steel via laser powder bed fusion (L-PBF). In this contribution, a double tempering strategy is used to optimize the microstructure and mechanical performance of an in-situ alloyed H13 steel fabricated via L-PBF. The primary tempering can result in the formation of fresh martensite and the relatively unstable retained austenite (RA), which substantially deteriorates impact toughness and yield strength (YS). The appropriate double tempering can effectively eliminate fresh martensite and reduce the fraction of the unstable RA to below 5%, successfully realizing decent mechanical properties with an ultrahigh YS of ~1.8GPa, an ultimate tensile strength (UTS) of ~2.05GPa, and a Charpy V-notch (CVN) value of 17J in an in-situ alloyed H13 steel via L-PBF, which is comparable with those of the wrought H13 steel. The current study demonstrates that the elimination of fresh martensite and optimization of austenite stability are the key to improve the mechanical performance of L-PBF ultra-high strength steels with medium carbon content.