Effects of heat treatments on the microstructure and mechanical properties of Rene 80

Abstract

Effects of heat treatments on room temperature mechanical properties and stress-rupture properties of Rene 80 have been investigated. The microstructures were analyzed by optical microscope and scanning electron microscope after each step of heat treatments. With the decrease of aging temperature, the average size of γ′ phase decreases, but the volume fraction of γ′ phase increases. The lower aging temperature suppresses the growing of the coarse γ′ particles, but facilitates the growth of the fine γ′ particles. After the optimum heat treatment, the ultimate tensile strength and yield strength are respectively higher than 1040MPa and 950MPa, the stress-rupture life at 871°C/310MPa is higher than 170h with excellent ductility. The improved tensile strength and stress-rupture life are primarily due to the increased volume fraction of γ′ phase. The borides precipitate at grain boundaries at about 913°C. The primary MC is found to decompose into M6C at about 873°C and M23C6 at 840–873°C at grain boundaries. The precipitate of the carbides may partly contribute to the improved mechanical properties.