Study on the hot deformation behavior and microstructure evolution of as-forged GH3625 alloy

GH3625 alloy is widely used in aviation, nuclear power and other fields of hot section components. However, the high alloying level, significant deformation resistance, and narrow hot working window of the alloy bring great challenge to the plastic deformation of the alloy. The hot deformation behavior and microstructure evolution of as-forged GH3625 alloy were studied by hot compression tests with deformation temperatures of 930–1180 °C, strain rates of 0.001–1 s−1 and true strain of 0.92. The results show that the flow stress of the alloy exhibits noticeable characteristics of temperature-negative sensitivity and rate-positive sensitivity. The true stress-strain curves are of two types: dynamic recovery (DRV) and dynamic recrystallization (DRX). The strain-compensated Arrhenius constitutive model was used to predict the alloy's flow behavior, with a linear fitting correlation coefficient (R) of 0.9872 and an average relative error (AARE) of 8.92%. The hot processing map of the alloy based on Prasad was constructed and superimposed. It was found that there were two instability regions, which were located in the low temperature and high strain rate region and the high temperature and low strain rate region respectively. The optimal processing region was 1154∼1180 °C/0.75–1 s−1 combined with the true stress-strain curves and the microstructure. Continuous dynamic recrystallization (CDRX) at subgrains rotation and discontinuous dynamic recrystallization (DDRX) at grain boundaries were identified during thermal deformation. As the η value decreases, the dynamic recrystallization grain size decreases under the deformation condition of 930–1180 °C/1 s−1, and the microstructure evolution mechanism changes from DDRX→ DDRX + CDRX→ DDRX + CDRX + DRV → CDRX + DRV, and ∑3 TBs also reduces.