Weld metal composition and aging influence on metallurgical, corrosion and fatigue crack growth behavior of austenitic stainless steel welds

AISI 316 austenitic stainless steel joints were fabricated using gas tungsten arc welding (GTAW) process selecting two filler compositions viz. AISI 316L (conventional) and AISI 347 (Nb-based). Both the welds were subjected to an aging treatment of 750 degrees C/24 h. AISI 316L aged weld metal microstructure exhibited interdendritically branched d-ferrite morphology which facilitated a strong network for the formation of carbides, whereas in 347 weld similar ferrite morphology occurred but branching effect was not observed. EPMA(Electron probe microanalyzer) results show that carbide precipitation in the dendritic regions of both the welds in the aged condition accounted for their respective corrosion that occurred interdendritically. Corrosion performance evaluation of the welds carried out by measuring their degree of sensitization using DLEPR (double loop electrochemical potentiokinetic reactivation) technique showed niobium contained 347 weld performed better than a 316L weld. Fatigue crack growth resistance of both the welds in the aged condition increased due to dispersion strengthening effect that occurred due to carbides formation. Further, 316L weld exhibited better fatigue performance than 347 weld, both in the as-welded as well as in the aged condition. This study establishes that if Nb addition to the weld metal can improve the sensitization performance of AISI 316 welds, it can at the same time; decrease their fatigue crack growth resistance also.