Ultra-high strength and ductility of low-Mn lightweight steel achieved through a four-phase lamellar structure design

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Low-Mn lightweight steels typically face challenges in achieving high strength and ductility due to the presence of δ-ferrite, which also severely limits transverse elongation when present as long-strip formations. This study successfully overcame these limitations by constructing a four-phase lamellar structure, resulting in an optimal strength-ductility balance (∼1.0 GPa YS, ∼1.45 GPa UTS, and 14.0% UE) and a notable improvement in transverse elongation. The introduction of a soft phase and a strain transition zone near δ-ferrite and martensite enhanced strain distribution uniformity, while retained austenite, precipitation strengthening, and heterogeneous strengthening further contributed to the superior mechanical properties.