B2 phase controlling method of austenitic Fe-16Mn-10Al-5Ni-0.86C lightweight steel using laser powder bed fusion process and its microstructure and mechanical properties

초록

Fe-Mn-Al-C lightweight steels have attracted extensive attention due to their high specific strength and good ductility, with strengthening primarily relying on x-carbides. However, the shearable nature of x-carbides restricts work-hardening capacity and limits the achievement of an optimal strength-ductility synergy. The addition of Ni enables the formation of non-shearable B2 ordered intermetallic phases, thereby improving mechanical performance, but their refinement typically requires complex processing routes such as hot rolling, cold rolling, and tempering. Laser powder bed fusion (L-PBF), an advanced additive manufacturing technique characterized by extremely high cooling rates (103-106 K/s), provides a promising pathway to directly precipitate nanoscale B2 phases during solidification, eliminating the need for conventional multistep treatments. In this study, Fe-16Mn-10Al-5Ni-0.86C lightweight steel was fabricated via L-PBF, and its microstructure and mechanical properties were investigated. The results revealed that rapid solidification promoted the uniform precipitation of nanoscale B2 phases within the austenitic matrix, with an average size below 200 nm and a volume fraction of 24.46 %. Room-temperature tensile testing demonstrated a yield strength of 1.214 GPa combined with an elongation of 22.3 %, presenting a markedly superior strength-ductility synergy compared with hot-rolled counterparts of identical composition and approaching that of cold-rolled and tempered steels. Furthermore, comparative analysis elucidated the intrinsic relationship between B2 precipitation behavior and strengthening mechanisms under different processing conditions.

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