Effect of Post-weld Heat Treatment on the Microstructure and Corrosion Resistance of Deposited Metal of a High-Chromium 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 degrees 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 gamma matrix after PWHT at 850 degrees C. The coarsening kinetics of the needle-like Cr23C6 carbides obeyed the Lifshitz-Slyozov-Wagner law with the growth speed of 4.93 mu m(3)/h in length and 5.56 x 10(-3) mu m(3)/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 degrees 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.