The Flow Stress Behavior and Constitutive Model of Cr8Mo2SiV Tool Steel during Hot Deformation

The uniaxial hot compression tests of Cr8Mo2SiV tool steel are conducted by thermomechanical simulator in a wide strain rate range of 0.005-5 s(-1) and temperature range of 900-1150 degrees C to predict the hot deformation behavior. It is found that flow stress strongly depends on deformation temperature and strain rate under the mechanisms of dynamic softening and work hardening. Second, the Johnson-Cook model and modified Arrhenius-type equation considering the compensation of strain are proposed for the estimation of flow stress of the tool steel. Subsequently, the validity of the established constitutive models is verified by standard statistical parameters including correlation coefficient (R) and average absolute relative error (AARE). Finally, the hot deformed microstructure is analyzed using the constitutive model with strong predictive ability. With the decrease in lnZ (Z is the Zener-Hollomon [Z-H] parameter) value from 43.5 to 32.7 s(-1), microstructure evolution indicates that a remarkable increase in the high-angle grain boundaries (misorientation more than 15 degrees) from 19.1% to 32.6%, which also reflects the reliability of Z-H map in predicting dynamic recrystallization behavior under most thermal deformation conditions.