Characterization of Hot Deformation Behavior and Processing Maps Based on Murty Criterion of SAE8620RH Gear Steel

The hot deformation behavior and microstructure evolution of the SAE8620RH gear steel were investigated through a single-pass hot compression test at deformation temperatures between 850 and 1100 degrees C and strain rates between 0.02 and 8.0 s-1 by 60% reduction. A novel strain compensation constitutive model was developed, and the 2D processing maps were established by Murty's criterion. Results showed that the relationship between material-related parameters and strain can be mathematically expressed by a highly reliable 8th-order polynomial. The constructed strain compensation constitutive model demonstrated remarkable predictive precision, as evidenced by the correlation coefficient (R) and the absolute values of average relative error (AARE) of 0.978 and 4%, respectively. The flow instability domains considerably expanded towards the high deformation temperature region as the strain increased. Microstructure analysis confirmed the accuracy of the processing map constructed by Murty's criterion. The most noticeable optimum processing windows for SAE8620RH gear steel at a strain of 0.7 occurred within the temperature range of 1000-1100 degrees C and the strain rate range of 0.3-1.0 s-1, due to high eta values exceeding 0.3 and equiaxial dynamic recrystallization microstructure.