Additive manufacturing of novel heterostructured martensite-austenite dual-phase steel through in-situ alloying

The interplay between the martensite and austenite phases in steels has critical effects on the mechanical properties. To tune the phase constitutions of martensite and austenite phases, this work in-situ alloyed martensitic C300 maraging steel (MS) with austenitic 316 L stainless steel (SS) by laser directed energy deposition (LDED). The microstructures, mechanical properties and deformation behaviour of the novel MS-12 wt% SS (MS12) and MS-24 wt% SS (MS24) dual-phase steels were investigated. The as-built samples achieve a relative density above 99.9%, and martensite-austenite dual-phase heterostructures are observed. Micro-segregation of molybdenum is considered the dominant reason for the face-centred cubic (FCC) phase formation. The fractions of the FCC phase were 5.8% and 16.8% in the MS12 and MS24 alloys, respectively. Moreover, the unique thermal history of LDED induces the heterostructured microstructure with FCC-rich and FCC-lean regions, which contributes to the high work hardenability of the steel. Compared with MS12, MS24 shows a much higher elongation (14.3%) and a superior work-hardening capability. The in-situ digital image correlation (DIC) observations reveal the strain partitioning within the two alloys during the initial deformation stage. The findings highlight a new approach to developing new materials by in-situ alloy commercially available materials using LDED.