Evolution of local grain boundary curvature and multi-mode nucleation mechanisms of dynamic recrystallization in 254SMO steel

To elucidate the dynamic recrystallization (DRX) mechanism of 254SMO superaustenitic stainless steel (SASS) during high-temperature deformation, isothermal compression tests were performed on a Gleeble-3800 simulator at deformation temperatures of 900–1200 °C, strain rates of 0.01–10 s⁻ 1 , and a true strain of 0.916. An Arrhenius-type constitutive model with strain compensation and a DRX kinetic model were developed, achieving a prediction accuracy with a correlation coefficient R of 0.99. The deformed microstructures were characterized using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results reveal that at 950–1050 °C, high curvature is mainly concentrated at grain boundaries, where local bulging and dislocation annihilation facilitate preferential nucleation, indicative of discontinuous dynamic recrystallization (DDRX). At 1050–1200 °C, the fraction and continuity of high-curvature segments decrease, and continuous dynamic recrystallization (CDRX) dominates, driven by subgrain rotation, grain fragmentation, and lattice rotation. At a strain rate of 10 s⁻ 1 , DRX grains are orderly distributed along Σ3 twin boundaries, with boundary orientations highly consistent with twin structures, suggesting the occurrence of twin-induced dynamic recrystallization (TDRX). In this study, local grain boundary curvature is introduced for the first time as a key internal variable to elucidate the transition of DRX mechanisms from grain boundary bulging to intragranular substructure evolution.