Effect of Post-weld Heat Treatment on the Microstructure and Corrosion Resistance of Deposited Metal of a HighChromium Nickel-Based Alloy

The evolution of Cr23C6 carbides in the deposited metal (DM) of a high-chromium nickel-based alloy was investigated after the post-weld heat treatment (PWHT) at 650, 750, 850, and 950 °C, respectively. With the increase in temperature, the morphology of the Cr23C6 carbides at the grain boundaries was transformed from the continuous lamellar-like to the semi-continuous rod-like and then to the discontinuous granular. Besides, the needle-like Cr23C6 carbides precipitated from γ matrix after PWHT at 850 °C. The coarsening kinetics of the needle-like Cr23C6 carbides obeyed the Lifshitz-Slyozov-Wagner law with the growth speed of 4.93 μm3/h in length and 5.56 × 10-3 μm3/h in width. Moreover, the ratio of the carbide length to width increased rapidly at first and then flattened as the holding time increased to 850 °C. The results of electrochemical corrosion experiment indicated that the needled-like Cr23C6 carbides impaired the corrosion resistance of DM due to the formation of chromium depletion around the carbides.