Effect of nitrogen addition on formation of secondary austenite in duplex stainless steel weld metals and resultant properties

The gas tungsten arc (GTA) welding process is widely employed for fabricating duplex stainless steel (DSS) components. The microstructural phase balance is disturbed in DSS welds owing to the thermal cycles associated with welding and the desired phase balance is generally achieved either through control of heat input or by altering the composition. In GTA welding, the phase balance is obtained either via the use of nickel fortified fillers or by introduction of nitrogen. Control of ferrite in the welds is essential, since metastable ferrite may transform to secondary austenite during multiple pass welding. The present work describes the influence of nitrogen on the phase balance of DSS welds and also its controlling effect on the secondary austenite formation in multiple pass welds. It was observed that neither the nitrogen addition nor the secondary austenite formation influenced the hardness of the welds, but formation of secondary austenite led to a deterioration in corrosion resistance. The corrosion resistance of welds containing secondary austenite (SA) was observed to be inferior to that of SA free weld metals.