Effect of Si Content on Microstructure and Tensile Properties of Fe–Mn–Al–C Lightweight Steel

Fe–Mn–Al–C lightweight steels are promising candidates for weight‐sensitive structural components. However, the role of compositional tailoring in governing strength–ductility synergy remains to be fully clarified. In this study, Fe–Mn–Al–C steels with varying Si contents were designed and subjected to solution treatment to systematically investigate the effects of Si on microstructural evolution and tensile deformation behavior. As the Si content increased from 0.2 to 1.5 wt.%, all tested steels retained a single‐phase austenitic structure. The effective grain size increased from 40.5 to 62.4  μm, the fraction of annealing twins rose from 47.9% to 52.5%, and lattice distortion became more pronounced, while stacking fault energy decreased from 44.1 to 41.3  mJ/m ² . The reduced stacking fault energy promotes the nucleation and sustained multiplication of deformation twins during tensile deformation, strengthens the interaction between dislocation slip and mechanical twinning, and maintains high work‐hardening capability. Si‐induced solid‐solution strengthening, together with TWIP‐assisted dynamic subdivision of austenite grains, suppresses strain localization and enables simultaneous improvement in strength and ductility. Within the investigated composition range, the 1.5Si steel exhibits the optimal strength–ductility combination, with a yield strength of 378 MPa, an ultimate tensile strength of 761 MPa, and an elongation to fracture of 49.1%.