Shielding gas effects on double-sided synchronous autogenous GTA weldability of high nitrogen austenitic stainless steel

Acceptable weld formation in high nitrogen austenitic stainless steel (HNASS) was achieved when nitrogen gas (N2) was added to the Ar-based shielding gas. Although a relatively unstable process, in double-sided synchronous autogenous gas tungsten arc (GTA) welding (DSSAGW), added N2 enabled the arc plasma to shrink and accordingly heightened the arc voltage, leading to increased fusion areas of welds. Added N2 in the shielding gas was very beneficial for suppressing nitrogen loss in welded joints, with the nitrogen content in the weld zone (WZ) increased to 1.25% with pure N2 shielding gas, while the δ-ferrite content slightly decreased. With increased N2 in shielding gas, both the primary and secondary dendrite arm spacing in the WZ increased, while the equiaxed austenite in heat-affected zone (HAZ) varied rather little. The WZ microhardness increased with N2 addition to the shielding gas, indicating nitrogen's strong solid solution strengthening effects. Based on these results, N2 was considered to be a promising shielding gas for HNASS welding in DSSAGW and the optimal N2 and Ar proportions judged to be below 2/8 (by vol.).