Microstructure evolution and dynamic recrystallization mechanism during thermal deformation of N50 austenitic stainless steel

To optimize the thermal deformation behavior of N50 austenitic stainless steel for fusion reactor applications, uniaxial hot compression tests were conducted at temperatures of 950–1200°C, strain rates of 0.001–10 s⁻¹, and a true strain of 0.9. Constitutive models for both the dynamic recovery (DRV) and dynamic recrystallization (DRX) stages were established based on the Estrin-Mecking and modified Avrami equations, with all key parameters correlated to the Zener-Hollomon parameter, yielding high predictive accuracy (R = 0.991, AARE = 2.12%). A hot processing map was constructed, identifying an optimum processing window at 1100–1200°C and strain rates below 0.02 s⁻¹. Microstructural characterization reveals that the recrystallization fraction increases with temperature up to 1150°C but decreases at 1200°C due to enhanced DRV, which is consuming stored deformation energy. With increasing strain rate, the recrystallization fraction decreases from 0.001 to 1 s⁻¹ owing to insufficient time for diffusional processes, but partially shows a rebound at 10 s⁻¹, when adiabatic heating significantly accelerates grain boundary migration. The DRX mechanism is identified as predominantly discontinuous dynamic recrystallization (DDRX), supplemented by continuous dynamic recrystallization (CDRX). These findings provide an integrated framework linking constitutive modeling, processing window determination, and recrystallization mechanisms for optimizing the hot workability of N50 steel.