Improving the strength-ductility synergy and corrosion resistance of Inconel 718/316L dissimilar laser beam welding joint via post-weld heat treatment

Inconel 718/316L dissimilar welding is widely used in nuclear power plants, which suffers from the deterioration of mechanical properties and corrosion resistance after welding, attributed to the formation of brittle phase and the existence of residual stress. In this paper, the impact of post-weld heat treatment (PWHT) on Inconel 718/316L welding joints is systematically investigated. By conducting PWHT after welding, notable reductions in residual stress in as-welded joints are significantly reduced and the microstructure is improved, resulting in an enhanced strength-ductility synergy and corrosion resistance. The as-welded joints exhibit the generation of brittle Laves phase and welding residual stress in the fusion zone. After PWHT at 650 degrees C, a substantial increase in the quantity of fine-scale y00 strengthening phases with a uniform dispersion distribution in weldment is observed, along with the release of residual stress. This combination yields an optimal strength-ductility synergy and corrosion resistance of the joint. However, the 8 phase precipitates along in Laves phase boundary after PWHT at 850 degrees C, which exhibits a semi-coherent interface with y matrix, and a non-coherent interface with the Laves phase, leading to severe stress concentration at the 8 phase interface. This severe stress concentration could be a preferred location for crack initiation and propagation, resulting in a substantial loss in mechanical behavior. Additionally, the increase in the phase boundary of y/y00, y/Laves, Laves/8 and y/8 reduces the corrosion resistance of the joint. The findings of this study provide an effective strategy for improving the performance of Inconel 718/316L dissimilar laser beam welding joint.(c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).