Thermo-mechanical deformation behavior of a cast nitrogen-strengthened austenitic stainless steel was investigated over deformation temperatures ranging from 900 °C to 1200 °C and strain rates between 0.01 and 10 s−1 using a MMS-300 thermal simulation testing machine. Based on the obtained true stress–strain curves, a constitutive equation and a thermal processing map were established for the experimental steel. Microstructural evolution during deformation was characterized by electron backscatter diffraction (EBSD). The results indicate that the peak stress of the experimental steel decreases with increasing deformation temperature and decreasing strain rate. The Arrhenius-type constitutive relationship is given by \(\dot{\varepsilon } = 1.70 \times 10^{23 } [\sinh (0.0047\sigma_{p} )]^{10.62} \exp [ - 619387/(RT)]\) . The optimal thermo-mechanical deformation range is identified as a deformation temperature of 1070 °C to 1120 °C and a strain rate of 6 to 10 s−1, where dynamic recrystallization is sufficient, and stress distribution is uniform. At strain rates of 0.1 and 10 s−1, the degree of dynamic recrystallization (DRX) increases with increasing deformation temperature, with the dominant softening mechanism being DRX. The nucleation mechanism transitions from discontinuous DRX (DDRX) to continuous DRX (CDRX) and twin-induced DRX (TDRX) as temperature increases. When deforming at 1100 °C and 1150 °C, the degree of DRX initially decreases and then increases with increasing strain rate. At a low strain rate of 0.01 s−1, dynamic recovery (DRV) is the primary softening mechanism, whereas at 10 s−1, DRX dominates, with nucleation occurring by CDRX and TDRX. Precipitates are mainly distributed within deformed grains and are less frequent in recrystallized areas, with their content inversely correlated to the fraction of recrystallized grains. Notably, Nb(C, N) precipitates play a key role in inhibiting dynamic recrystallization. These findings provide a theoretical foundation for designing high-temperature thermomechanical processing routes for cast nitrogen-strengthened austenitic stainless steels.
