Effect of GTAW flux on the microstructure and properties of austenitic, super austenitic and super duplex stainless steel welds

Fluxes have been developed to increase penetration when used in conjunction with the gas tungsten arc welding (GTAW) process. This process has been referred to as the active flux process (A-TIG), and high penetration gas tungsten arc welding (HP-GTAW). HP-GTAW fluxes are typically comprised entirely of oxides, entirely of fluorides/chlorides, or a combination of oxides and fluorides. This investigation documents the effect of flux composition on microstructural evolution and corrosion resistance in three alloys of small-bore stainless steel tubing, 316L, 254 SMO and SAF 2507, and with microstructure/CVN toughness in 6.35-mm (0.25-in) thick SAF 2507 plate. In this study welds were produced using HP-GTAW fluxes comprised exclusively of oxides, fluorides, and a 90 wt. pct. fluoride/10 wt pct oxide flux. This study shows that the HP-GTAW flux composition can have a significant influence on microstructure evolution in super duplex welds. When compared to autogenous GTA welds or welds produced using oxide-based HP-GTAW fluxes are shown to have a beneficial effect on mechanical properties, and corrosion resistance. This study represents the first phase of an ongoing investigation focused on understanding how HP-GTAW fluxes influence microstructure-property relationships in super duplex stainless steel.