Influence of hot deformation on dynamic recrystallization behavior of a novel austenitic stainless steel

During the fabrication of large parts by forging, dynamic recrystallization (DRX) is the primary softening mechanism that affects the microstructure and properties of austenitic stainless steel, and an in-depth analysis of this process is necessary. The isothermal hot compression tests were conducted to investigate the hot deformation behavior of Fe-21Cr-15Ni-5Mn-2Mo steel, a novel austenitic stainless steel, at strain rates from 0.01 to 10 s^-1 and temperatures ranging from 950 to 1200 °C. Based on the true stress-strain curves derived from the tests, the constitutive model and hot working map for the steel were constructed, and the microstructure evolution of the steel was systematically analyzed. The critical deformation conditions for the occurrence of DRX were determined using the plotted work hardening rate curve. The findings indicate a significant rise in flow stress as strain rate increases or deformation temperature decreases. Concurrently, the strain needed to attain peak stress progressively grows. The activation energy for deformation of the steel is 595.511 kJ/mol, which results from the competition between dynamic softening and work hardening during its hot deformation process. Low strain rate and low temperature (0.01 s^-1, 950 °C) are the parameters for the instability zone of the steel, and localized flow and deformation bands are the microstructure manifestations of unstable hot processing. The optimal hot working window for the experimental steel is the medium to high strain rate range and medium to high temperature (0.1-10 s^-1, 1100-1200 °C), where the microstructure exhibits randomly oriented, uniformly distributed DRX grains. The bulging of the initial grain boundaries is primarily associated with the nucleation mechanism of DRX. Furthermore, based on the critical strain and peak strain, the kinetics of DRX are predicted by the Avrami equation.