Microstructure evolution and hot deformation characteristics of 15Cr-22Ni iron-base superalloy

Abstract

The hot deformation behavior and microstructure evolution of a newly designed 15Cr-22Ni iron-based superalloy containing 0.6 wt %Nb was studied. The strain-compensated constitutive equations were established, which can accurately predict the high-temperature flow behavior of the superalloy. The dynamic recrystallization kinetic model was developed. The degree of dynamic recrystallization gradually increases with decreasing strain rate and increasing deformation temperature. The hot processing map of designed superalloy was developed and the optimum hot processing range has been determined to be 1050–1150 °C/0.01 s−1. Hot deformation induces the precipitation of nano-sized NbC at grain boundaries and dislocations in the designed superalloy. Nano-sized NbC particles act as nucleation sites for dynamic recrystallization. The dynamic recrystallization behavior is compared with that of 15Cr-22Ni-1 Nb alloy. The starting of dynamic recrystallization of designed superalloy is later than that of 15Cr-22Ni-1 Nb alloy, which is attributed to the lack of active sites in the early recrystallization nucleation. However, the recrystallization kinetics of designed superalloy is faster than that of 15Cr-22Ni-1 Nb alloy. Due to the weak pinning force of nano-sized NbC precipitates to the grain boundaries and dislocations, the movement of grain boundaries and dislocations is less hindered, which is beneficial to the growth of dynamic recrystallization grains.