Effect of rolling temperature on the annealing behavior of 304L austenitic stainless steel: grain boundary optimization, heterogeneous microstructure formation and mechanical response

Solution-treated 304L austenitic stainless steel (ASS) was rolled at −196 °C, 25 °C and 200 °C with thickness reductions of 10–70%, followed by short-time annealing at 1050 °C or 750 °C. The effects of rolling temperature on martensitic transformation, defect substructures, grain boundary character distribution (GBCD), texture evolution, recrystallization behavior and mechanical properties were systematically investigated. The stacking fault energy (SFE) increased with rolling temperature, promoting a deformation transition from TRIP-dominated martensitic transformation to TWIP/slip-assisted austenite deformation. Cryogenic rolling (CR) markedly accelerated martensitic transformation, the α′-martensite fraction increasing from 61.74% to 97.75% as the thickness decreased. Room-temperature rolling (RTR) produced an α′-martensite/retained-austenite dual-phase deformation structure, whereas warm rolling (WR) suppressed martensitic transformation and favored dislocation slip and deformation twinning in austenite. After 10% rolling and annealing at 1050 °C for 5 min, WR specimen exhibited the highest Σ3 and low-Σ CSL boundary fractions of 52.97% and 57.93%, respectively. After 70% rolling followed by annealing at 750 °C for 5 min, RTR70-750 exhibited a heterogeneous dual-scale austenitic structure and achieved the best strength–ductility balance, with a yield strength of 923.6 MPa, an ultimate tensile strength of 1102.2 MPa and an elongation of 7.2%. These results demonstrate that rolling temperature is an effective variable for tailoring short-time annealing responses, enabling grain boundary optimization after slight deformation and heterogeneous microstructure formation after heavy deformation.