Unveiling Hot Deformation Behavior and Dynamic Recrystallization Mechanism of 654SMO Super-Austenitic Stainless Steel

The hot deformation behavior and dynamic recrystallization (DRX) of super-austenitic stainless steel were investigated by uniaxial compression in the temperature ranges of 1223 to 1523 K and strain rate ranges of 0.01 to 0.1 s(-1). The apparent activation energy for hot deformation was calculated to be 556 kJ/mol by the regression analysis of sine hyperbolic Arrhenius function. The processing map based on dynamic materials modeling was divided into different hot working domains. DRX fractions and grain sizes of each domain were evaluated to understand the relationship between dissipation efficiency, flow instability, and recrystallization. It was observed that the dynamic precipitation of sigma at low-temperature and low-strain rate domain inhibited the development of DRX leading to the flow instability in this domain. DRX at high-strain rate domains was predominantly governed by high nucleation resulting in a finer grain size. DRX at low-strain rate domains was controlled by growth of grains leading to high DRX fraction with larger grain size. By analyzing the DRX mechanisms of different domains, it was found that the softening of austenite was mainly achieved by discontinuous dynamic recrystallization, and continuous dynamic recrystallization only occurred at low-strain rate and high-temperature domain. Moreover, multiple twinning was first observed in dynamic recrystallization, which suggested that the twin boundaries could propagate not only by growth accident but also by interactions between pre-existed twin boundaries.

Automated summary

The hot deformation behavior and dynamic recrystallization of super-austenitic stainless steel were studied through uniaxial compression tests. The apparent activation energy for hot deformation was determined to be 556 kJ/mol. A processing map based on dynamic materials modeling was used to analyze the different hot working domains and their corresponding dynamic recrystallization fractions and grain sizes. It was observed that the formation of sigma phase at low-temperature and low-strain rate inhibited the development of dynamic recrystallization. High-strain rate domains showed predominantly high nucleation resulting in a finer grain size, while low-strain rate domains had a higher dynamic recrystallization fraction and larger grain size due to grain growth. The softening of austenite was mainly achieved through discontinuous dynamic recrystallization, and continuous dynamic recrystallization occurred only at low-strain rate and high-temperature domain. Furthermore, multiple twinning was observed in dynamic recrystallization, suggesting the propagation of twin boundaries through interactions with pre-existing twin boundaries.