Effects of Heat Treatment on Microstructure, Mechanical Properties, and Residual Stress of Oscillation Laser-Tungsten Inert Gas Hybrid Welded Joints for SA-738Gr.B Steel

This paper adopted the new process of double-sided oscillation laser autogenous backing welding and double-sided oscillation laser-TIG hybrid filling welding to achieve 80 mm thick SA-738Gr.B steel narrow gap welding in the horizontal position. The microstructure, mechanical properties, and residual stress of the welded joints in the as-welded (AW) state and in the post-weld heat treatment (PWHT) state were analyzed comparatively. The results show that because of the high-temperature tempering effect of PWHT, the microstructure of the welded joint is transformed into a high-temperature tempered microstructure with the increase in alloy carbide precipitation. The grains growth of the backing weld and the base material is obvious. The relative frequency of the high-angle grain boundary of the weld increases. Under the PWHT, the tensile strength of the welded joint decreases, and the residual stresses of the welded joint are redistributed and reduced significantly.