Superalloy Inconel 718 is an important material used for aero-engine high temperature turbine disks. The grain refining of Inconel 718 becomes critical because of the improvement in the quality and reliability of aero-engine. Inconel 718 turbine disks are manufactured by multi-stage hot deformation processes, in which the recrystallized grain grows up in next passes. Therefore, it is difficult to obtain a uniform and refined microstructure by recrystallization refining. The delta phase in Inconel 718 can control grain size through the strong pinning effect. Thus, the Delta process (DP) has been applied for the forging of Inconel 718. In this paper, for the DP of Inconel 718, the evolution of delta phase during isothermal compression deformation at temperature of 950 degrees C and strain rate of 0.005 s(-1), was studied by using optical microscope (OM), scanning electron microscope (SEM) and quantitative X-ray diffraction (XRD) technique. The results show that spherical or rod-shaped delta phase particles in the interior of grains precipitated in the aging treatment disappear during the heating and holding time before deformation, and the content, of delta phase decreases from 8.14% to 7.05%. Dissolution of delta phase occurs during the deformation, and the content of delta phase decreases from 7.05% to 5.14%. The spheroidization of plate-like or needle-like delta phase takes place due to the effect of deformation and dissolution breakages, and the plate-like or needle-like delta phase transferrs to spherical or rod-shaped delta phase. In the centre with the largest strain, the plate-like or needle-like delta phase disappears and spherical or rod-shaped delta phase appears in the interior of grains and grain boundaries.
