Coupled effects of TRIP and TWIP in metastable austenitic stainless steel via optimization of stacking fault energy

Metastable austenitic stainless steel (MASS) with combined transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects has attracted significant attention due to its excellent strength and ductility. However, simultaneously achieving both TRIP and TWIP effects has been challenging. Herein, we developed a Fe-13.5Cr-10.2Mn-2.4Ni-0.1C MASS with appropriate stacking fault energy. After the steel was performed 80 % cold rolling followed by short-term annealing for 100 s at 600 °C–900 °C, the grains were refined to 0.37–2.27 μm, with 14–17 mJ/m2 SFE, resulting in a coupled TRIP + TWIP effects. The high strength of the experimental steel is attributed to grain refinement strengthening and the rapid increase in the density of geometrically necessary dislocations during plastic deformation (dislocation strengthening). The high ductility is ascribed to the TRIP+TWIP coupling effects, which provide more nucleation sites for the transformation of γ to α' phase at strains greater than 0.14 and the coordinated deformation between coarse grains and surrounding fine grains in the bimodal grain distribution. This study proposes a method for optimizing stacking fault energy through rolling and annealing. Within the obtained range of stacking fault energy, MASS exhibits coupled TRIP and TWIP effects, thereby enhancing its strength and ductility. •By controlling the grain size, the stacking fault energy of austenitic stainless steels is adjusted to 14–17 mJ/m2, enabling both TRlP and TWIP effects.•The residual α' phase and twin boundaries also hinder dislocation movement, resulting in a yield phenomenon.•Deformation twins provide new nucleation sites for the γ → α' phase transformation at strains greater than 0.14.•At deformation twin locations, the γ, α', and ε phases exhibit orientation relationships of {111}γ||{0001}ɛ, {0001}ɛ||{101}α′, and {111}γ||{101}α′.