Comparison Study of Hot Deformation Behavior and Microstructure Evolution of Rack Steels with and without Segregation

In order to compare the hot deformation behavior and microstructure evolution of the rack steels with and without segregation, hot compression tests are carried out in the temperature range of 1173-1423 K and the strain rate range of 0.01-10 s(-1) on a DIL805A/D quenching and deformation dilatometer. The flow stress, constitutive relation, processing map, and microstructure characterization are investigated. The results show that the flow stress increases with the increase of strain rate and the decrease of deformation temperature. The calculated activation energy (Q) and stress exponent (n) for the segregated samples are 395.245 kJ mol(-1) and 6.046, which are higher than segregated samples, showing 376.815 kJ mol(-1) and 5.930. The processing maps show that the workability of the nonsegregated steel is significantly more excellent than segregated steel. The segregated steel shows a higher kernel average misorientation angle and local strain. Complete dynamic recrystallization occurs at a high strain rate, and high deformation temperature can refine the grains.