Exploring Fe-Mn-Al-C lightweight steels via in-situ alloying in direct energy deposition

초록

This study explores the feasibility of in-situ alloying via direct energy deposition (DED) to tailor microstructures and strength-ductility balance of Fe-Mn-Al-C lightweight steels (LWSs) with independently varied composition of 8-12 wt% Al and 20-25 wt% Mn. As the Al content increased, the matrix phase was transformed from austenitic (8Al) to ferritic (10Al and 12Al), accompanied by the formation of secondary phases. The in-situ alloyed LWSs exhibited a reduced density (6.5-7.0 g/cm3) while exhibiting an exceptional strength-ductility synergy. Specifically, 20Mn8Al LWS exhibited an ultimate tensile strength of 883 MPa and an elongation of 43.8 %, resulting in a product of strength and elongation of 39 GPa center dot%. It also achieved a weight reduction of 10 % compared to conventional stainless steel. Strengthening was primarily governed by pre-existing dislocations and solid-solution strengthening effects, while deformation twinning in 20Mn8Al enhanced strain hardening and delayed necking. These findings highlight the potential of in-situ alloyed LWSs for lightweight structural applications, offering a superior combination of mechanical properties and density reduction. Furthermore, this study establishes DED-based in-situ alloying as a versatile strategy for microstructural and mechanical property optimization in additive manufacturing of advanced steels.

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