Hot deformation behavior and hot working window of a solid solution strengthened Ni-Cr-Fe-based superalloy

The hot deformation behavior of Ni-Cr-Fe-based ChS57 alloy was investigated by isothermal compression tests in the temperature range of 1000-1200 degrees C with strain rates covering 0.001-10 s-1. Based upon the hyperbolic sine function and dynamic material model, the constitutive model and processing maps of the alloy were established, the microstructure evolution was systematically analyzed and the optimization of the hot working window was completed. The results indicate that the flow stress increases remarkably with increasing strain rate and decreasing deformation temperature, while the amount of strain required to reach peak stress also gradually increases. The hot deformation process of this alloy is the result of the competition between dynamic softening and work hardening, with a deformation activation energy of 451.34 kJ/mol; dynamic recrystallization (DRX) is the main softening mechanism, while both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) exist; the low temperatures and medium strain rates (1000-1025 degrees C, 0.045-0.37s- 1) are the instability zone parameters of the alloy when flow localization and deformation bands are the microstructural manifestations of unstable hot working. The optimum hot working window for ChS57 alloy is the medium -low temperatures and low strain rates(1050-1100 degrees C, 0.001-0.003s-1)and the medium -high temperatures and high rates(1125-1175 degrees C, 1-10s-1 or 1100 degrees C/10s-1), where the microstructure appears as randomly oriented and uniformly distributed full DRX grains.