Effects of High-Temperature Aging on Precipitation and Corrosion Behavior of a Ni-Cr-Mo-Based Hastelloy C276 Superalloy

The effects of short-term aging on the precipitation and corrosion behavior of a Ni-Cr-Mo-based superalloy Hastelloy C276 were studied in this work. Aging treatments were performed at 800 degrees C for 1 h, 2 h, 4 h, 8 h, 12 h and 15 h. It is found that M6C carbide, which is rich in Mo and W, is prone to precipitate at grain boundary when the aging time exceeds 4 h, associated with the formation of a Mo and W depletion zone adjacent to the grain boundary. The potentiodynamic polarization curves in 3 wt.% NaCl solution show no obvious differences among the aged samples. But the surface morphologies of samples after double-loop electrochemical potentiodynamic reactivation method (DL-EPR) tests in HCl solution present typical intergranular corrosion attack. The calculated degrees of sensitization based on the DL-EPR curves increase dramatically with the increase in aging time, which is consistent with the precipitation trends. It is recommended that hot working of Hastelloy C276 superalloy should avoid high temperature exposure (e.g., at 800 degrees C more than 4 h) or do heat treatment again after high-temperature processing.