Microstructure evolution of delta-processed IN718 during holding period after hot deformation

Two IN718 alloys with different initial delta phase contents have been used to study the microstructure evolution during the holding period after the hot deformation by the heat treatment at 950-1040 A degrees C after deformation at temperature of 950 A degrees C and strain rate of 0.005 s(-1). The results indicate that the grain growth is restrained due to the pinning effect of delta phase. The activation energy of grain growth for the alloys with initial delta phase content of 0 and 8.14 wt% in the heat treatment after hot working were 273.8 and 882.8 kJ/mol, respectively. In addition, the dissolution of delta phase occurred during the heat treatment after the hot deformation, and the delta phase dissolved largely as the temperature is higher than 980 A degrees C. Therefore, the heating and deformation temperature should be in the range of 950-980 A degrees C for the Delta Process and multi-stage hot working processes.