Microstructure evolution and mechanical properties of keyhole deep penetration TIG welds of S32101 duplex stainless steel

In this research, workpieces of 10.8 mm thickness S32101 duplex stainless steel (DSS) were welded using a novel keyhole deep penetration TIG (DP-TIG) welding system in a single pass without groove preparation and filler metals. The weld geometry profiles conducted with different welding currents and welding speeds were analyzed. The microstructure evolution of the welded joints was carefully observed by means of optical microscope (OM) and scanning electron microscopy (SEM). Microhardness and mechanical properties of the weldments were tested and investigated in detail. The results show that the misorientation angle distribution of ferrite and austenite gradually migrated from high angle grain boundaries (HAGBs, θ ≥ 15°) to low angle grain boundaries (LAGBs, 2° ≤ θ ≤ 5°) during the welding process. In addition, a large number of Σ3 CSL boundaries gradually disappeared and the texture of austenite evolved from the original cubic texture into copper texture. The phase fractions of the weld metal (WM) are close to that of the base metal (BM). The impact property of the WM was lower than that of the BM. However, the tensile strength and microhardness of the WM were superior in comparison to the BM. This indicates that the one-sided welding with double-sided shaping of 10.8 mm thickness S32101 DSS can be welded by using the high productivity, low-cost and defect-free DP-TIG welding equipment. It also implies that DP-TIG welding can be widely applied and has many advantages in industrial applications.