High-temperature deformation mechanisms and physical-based constitutive modeling of ultra-supercritical rotor steel

This study presents an investigation that characterizes the evolution of the dynamically recrystallized structure and flow behavior of FB2 rotor steel during hot deformation in the temperature range from 900 degrees C to 1200 degrees C at strain rates from 0.001s(-1) to 0.1s(-1) using Gleeble-3500 thermo-simulation machine. Dynamic recrystallization (DRX) plays a key role in softening mechanism for hot deformed FB2 rotor steel. The fraction of LABs greatly increases with the decrease of deformation temperature. Low angle boundaries (LABs) always have higher local misorientation angle, which means the lower deformation temperature is capable of providing not enough driven force for the migration of LABs and thereby decelerates the DRX process to consume the dislocations. Furthermore, the critical stress and critical strain for initiation of DRX are calculated by setting the second derivative of the third order polynomial. Based on the classical stress-dislocation relation and the kinetics of dynamic recrystallization, a two-stage constitutive model is developed to predict the flow stress of FB2 steel. Comparisons between the predicted and measured flow stress indicate that the established physically-based constitutive model can accurately characterize the hot deformations for the studied steel.