The influence of stacking fault energy on the microstructural and strain-hardening evolution of Fe–Mn–Al–Si steels during tensile deformation

Understanding the relationship between the stacking-fault energy (SFE), deformation mechanisms, and strain-hardening behavior is important for alloying and design of high-Mn austenitic transformation- and twinning-induced plasticity (TRIP/TWIP) steels. The present study investigates the influence of SFE on the microstructural and strain-hardening evolution of three TRIP/TWIP alloys (Fe–22/25/28Mn–3Al–3Si wt.%). The SFE is increased by systemically increasing the Mn content from 22 to 28 wt.%. The Fe–22Mn–3Al–3Si alloy, with a SFE of 15 mJ m−2, deforms by planar dislocation glide and strain-induced εhcp-/αbcc-martensite formation which occurs from the onset of plastic deformation, resulting in improved work-hardening at low strains but lower total elongation. With an increased SFE of 21 mJ m−2 in the Fe–25Mn–3Al–3Si alloy, both mechanical twinning and εhcp-martensite formation are activated during deformation, and result in the largest elongation of the three alloys. A SFE of 39 mJ m−2 enables significant dislocation cross slip and suppresses εhcp-martensite formation, causing reduced work-hardening during the early stages of deformation in the Fe–28Mn–3Al–3Si alloy while mechanical twinning begins to enhance the strain-hardening after approximately 10% strain. The increase in SFE from 15 to 39 mJ m−2 results in significant changes in the deformation mechanisms and, at low strains, decreased work-hardening, but has a relatively small influence on strength and ductility.