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 ε_hcp-/α_bcc-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 ε_hcp-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 ε_hcp-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.