Effects of Ageing and Forging on Short-term Creep Behaviors of Inconel-713C Superalloy at 850 °C

In this paper, the short-term creep behavior of the Inconel-713C superalloy after different pre-treatments including the ageing and forging processes has been studied at 850 °C. The ageing heat treatment was heating at 930 °C for 16 hours without solutioning process. The optical microscopy (OM) and the scanning electron microscopy (SEM) techniques were applied for microstructural evaluations. The results showed that although the ageing treatment increased the γ’ phase content, the age-hardened material had a lower creep lifetime (about 40%) with respect to the as-cast alloy. This was related to the decrease in the amount of M23C6-type secondary carbides precipitation. When the Inconel-713C superalloy specimen was forged at 1200 °C, the third stage of the creep curve (strain versus time) increased drastically and shortened the creep lifetime. The small grain size of the forged specimen was responsible for such inverse creep behavior. In addition, fractographs of this specimen indicated intragranular cracks on the ruptured surface. When the forged sample was age-hardened directly without the solutioning treatment, the creep lifetime increased about 4 times as compared to the forged specimen.