Exploring Fe–Mn–Al–C lightweight steels via in-situ alloying in direct energy deposition
Seungjin Nam, Chahee Jung, Hyun Chung, Heechan Jung, Young Mok Kim, Hyoung Seop Kim, Hyunjoo Choi, Seok Su Sohn
Abstract
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/cm 3 ) 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∙%. 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.