Hot deformation behavior and microstructure analysis of 25Cr3Mo3NiNb steel during hot compression tests

The hot deformation behavior of 25Cr3Mo3NiNb steel was studied by means of isothermal hot compression tests. The constitutive equations were established based on strain compensated Arrhenius and modified Johnson-Cook models, respectively. The hot processing maps at different strains were constructed based on dynamic materials model. Then, the hot compressed microstructure was examined to study the effects of strain rate and temperature on the microstructure characteristics. The results show that the strain compensated Arrhenius model exhibits higher accuracy on predicting the flow stress than that of the modified JC model. The flow instability tends to occur under high strain rate, and the power dissipation efficiency with large values distributes homogenously with the strain rate from 0.001 s−1 to 0.1 s−1. The optimum condition for hot forming of 25Cr3Mo3NiNb steel was determined as the temperature range of 1350-1450 K and strain rate range of 0.001-0.03 s−1. When the strain rate is 1.0 s−1, the specimens are composed of homogeneous fine grains, and the temperature has slight influence on the microstructure. However, at the temperature of 1473 K, it is found that the strain rate significantly affects the characteristics of the microstructure.