Study on hot deformation characteristics of 12%Cr ultra-super-critical rotor steel using processing maps and Zener–Hollomon parameter

The hot deformation behavior of a 12%Cr ultra-super-critical rotor steel was investigated in the temperature range of 900–1200 °C and strain rate range of 0.01–10 s− 1. The processing maps of the material were derived by using dynamic materials model and Prasad instability criterion. The deformation mechanisms of different regions in the processing maps and corresponding microstructures were discussed in combination of the change in Zener–Hollomon parameter. The results showed that for 12%Cr ultra-super-critical rotor steel, the flow stress, microstructural evolution and efficiency of power dissipation are closely related to the Zener–Hollomon parameter. The lower the Zener–Hollomon parameter is, the larger the extent of flow softening becomes, the more easily the dynamic recrystallization may occur, and the bigger the dynamic recrystallization grain size is. Moreover, the higher the Zener–Hollomon parameter, the lower the power dissipation rate. Flow instability occurring under high Zener–Hollomon parameter is manifested as flow localization. During the hot tension at 1 s− 1, the thermoplasticity of 12%Cr ultra-super-critical rotor steel is the worst at 950 °C.