Ultrastrong and ductile additively-manufactured medium-carbon steel via modulating austenite stability

Selective laser melting (SLM) is a very promising near net shape approach to manufacture metallic complex-shaped parts. However, it is highly challenging to manufacture ultrahigh strength medium-carbon steels via SLM due to the cracking and low ductility issues. In this contribution, the mechanisms of crack and limited ductility in the conventional medium-carbon H13 steels by SLM were investigated, which was likely attributed to the poor stability of retained austenite (RA) and the resultant formation of brittle fresh martensite. A modified crack-free H13 steel for SLM was successfully additively manufactured via in-situ minor alloying of 316 L powders, leading to the substantially enhanced austenite stability with heterogeneity. The modified SLM-fabricated H13 steel exhibited an ultrahigh tensile strength (UTS) of ∼2.0 GPa with a fractured elongation of ∼19%. This work demonstrates the critical role of austenite stability in cracking behavior and ductility of the SLM-fabricated medium-carbon steels.