Mechanism of twinning induced plasticity in austenitic lightweight steel driven by compositional complexity

Abstract

The current work investigated the mechanical behaviors of a novel austenitic lightweight Fe-Mn-Al-Si-C steel that combined the characteristics of lightweight steel and TWIP steel, due to compositional complexity. The critical design principle lay in the synergetic addition of Al and Si to obtain simultaneously a stacking fault energy of 49.5 mJ/m2, short-range ordering, and density reduction. The initial strain hardening in this steel proceeded by microband-induced plasticity slip featuring the substructure of Taylor lattices due to planar-slip dislocations. It contributed to a high Hall-Petch coefficient of 673 MPa·μm0.5. In the latter stage of deformation, even though the stacking fault energy was not low, stacking faults and deformation twins were triggered when the critical stress was achieved. This transition behavior was first observed in lightweight steel and the overall effects led to an outstanding work hardening rate of about 2.4 GPa. This lightweight TWIP steel with a density of 6.98 g/cm3 possessed ultimate tensile strength of 800-950 MPa and total elongation of 67-77%. This study focused on its mechanical behaviors and developed a confined dislocation model to clarify the transition from dislocation glide to mechanical twinning.