Dynamic Recrystallization Behavior and Kinetics Model of a New Developed Austenitic Heat Resistant Steel CHDG-A

The deformation behavior and microstructural evolution of a new developed austenitic heat resistant steel CHDG-A were investigated by hot compression tests with strain rate in the range of 0.01-10 s-1 at 900~1100℃. The results show that either increasing the deformation temperature or decreasing the strain rate, the flow stress level reduces remarkably. Accurate constitutive equations were established between peak stress and deformation parameters, i.e., temperature and strain rate by the regression analysis of sine hyperbolic function. The hot deformation activation energy of CHDG-A was calculated to be 515.618 kJ/mol. From the deformed microstructures it is found that dynamic recrystallization (DRX) is the principal softening mechanism during hot working. The DRX process may initiate from nucleus formed at bulging out of grain-boundaries, which can be promoted by the increase of temperature and the decrease of strain rate. The values of peak stress, critical stress, peak strain and critical strain for DRX were determined from the true strain-true stress curves and their equations related to the Zener-Hollomon parameter were obtained. The critical strain and corresponding stress for DRX can be expressed through the parameter Z. The critical ratios of ε c/ε p and σ c/σ p are also identified, which are 0.52 and 0.98, respectively. Moreover, the DRX kinetics for CHDG-A can be represented in the form of Avrami equation, and the predicted volume fraction of new grains based on the developed model agrees well with the experimental results. © 2020, Editorial Office of Chinese Journal of Materials Research. All right reserved.