Multi-pass arc welding techniques of 12 mm thick super-duplex stainless steel

The fusion zone microstructure and mechanical properties of UNS S32750 joints obtained from gas tungsten arc (GTA), gas metal arc (GMA) and flux cored arc (FCA) welding processes were investigated. The formation of grain boundary, Widmanstatten and intragranular austenite were observed in the fusion zone of the weldments. Electron back scattered diffraction (EBSD) analysis confirmed the presence of chi (psi) and sigma (sigma) phases in the reheated fusion zones of all the weldments. Tensile failures occurred at the fusion zone for all the weldments and the joint efficiency was found to be greater for GTA welds than the others. The number of welding passes and heat input had a significant impact on the ferrite: austenite ratio. FCA weldments experienced inferior notch toughness at both room temperature and sub-zero temperature owing to the prominent amount of secondary austenite and precipitation of intermetallic phases compared to the other weldments.