Hot Deformation Behavior of a Powder Metallurgy Superalloy with High γ′ Content

The hot deformation behavior of a powder metallurgy superalloy EP741NP is studied using isothermal compression testing on a Gleeble-3500 thermomechanical simulator. Constitutive equations and processing maps are then constructed based on the experimental stress–strain data, and microstructural changes are analyzed by sectioning the compressed samples. The results show that most stress–strain curves are characterized by rapid work hardening and slow flow softening. Steady-state flow stress is achieved under low strain rates and at high temperatures. Based on experimental stress–strain data, a constitutive equation compensated by strain is constructed, which provides an accurate prediction of flow stress behavior. Due to the dissolution of γ′, the effects of temperature on the processing map are more significant than strain rate and strain. The recrystallization rate at low temperature is limited by the γ + γ′ nucleation mechanism around grain boundaries and prior particle boundaries (PPBs), forming a unique necklace structure. The optimal processing conditions for the EP741NP superalloy are at temperatures of 1150–1170 °C and strain rates of 0.005–0.02 s⁻¹, which produces a significantly refined microstructure free from PPB.