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

摘要

Acceptable weld formation in high nitrogen austenitic stainless steel (HNASS) was achieved when nitrogen gas (N-2) 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 N-2 enabled the arc plasma to shrink and accordingly heightened the arc voltage, leading to increased fusion areas of welds. Added N-2 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 N-2 shielding gas, while the 8-ferrite content slightly decreased. With increased N-2 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 N-2 addition to the shielding gas, indicating nitrogen's strong solid solution strengthening effects. Based on these results, N-2 was considered to be a promising shielding gas for HNASS welding in DSSAGW and the optimal N-2 and Ar proportions judged to be below 2/8 (by vol.).