Hot Deformation Behavior and Dynamic Recrystallization Characteristics of 12Cr Ultra-Super-Critical Rotor Steel

In this paper, the constitutive model and dynamic recrystallization characteristics of 12Cr ultra-super-critical rotor steel were investigated quantitatively during hot deformation. A series of axisymmetric hot compression tests at temperatures from 900 to 1200 °C under strain rates of 0.001–1 s⁻¹ were conducted on a Gleeble−1500D thermal simulator. Based on the experimental true stress–strain curves varying with temperature and strain rates, a complete constitutive model was established and all material parameters in the model could be expressed as a function of strain using a fifth order polynomial fit. The proposed model was verified so as to have the capability of accurately predicting the flow behaviour with an average absolute relative error of < 2.82%. Meanwhile, after hot deformation the microstructure was observed via electron backscatter diffraction technology. Then, the dependence of the characteristic parameters on the Zener–Hollomon parameter were confirmed. Furthermore, the kinetics equation of dynamic recrystallization was obtained, which included the flow stress calculated based on the evolution equation of the dislocation density during the work hardening-dynamic recovery stage. The result indicated that the predicted values for dynamic recrystallization volume fraction and flow stress were in line with the experimental values.