Influence of fillers and welding processes on the microstructural evolution, mechanical properties and corrosion behavior of dissimilar Hastelloy C-22/AISI 321 joints

This investigation deals with the dissimilar joining of Hastelloy C-22/AISI 321 austenitic stainless steel by employing gas tungsten arc welding (GTAW) and pulsed current-gas tungsten arc welding (PC-GTAW) employing two different fillers (ERNiCrMo-4 and ERNiCrMo-3). This investigation article attempts to study in detail the structure-property relationship of these dissimilar weldments. The results attested that a finer dendritic morphology at the molten zone (MZ) was obtained employing PC-GTAW process over GTAW process. In addition, the presence of Mo and Nb in ERNiCrMo-4 and ERNiCrMo-3 fillers responsible for amplifying the constitutional supercooling resulted in a significant disparity in the morphology from cellular to columnar and an equiaxed dendritic structure. In addition, the spread of the inter-dendritic precipitates rich in Mo and Nb (due to their low solubility in austenitic matrix) were quite lesser for MZ welded with PC-GTAW process due to the high cooling rates compared to GTAW process. However, Nb-rich fillers showed higher precipitation tendency irrespective of the welding processes. Furthermore, weldment made by employing Mo-rich ERNiCrMo-4 filler in combination with PC-GTAW process resulted in superior mechanical properties. Therefore, for dissimilar welding of Hastelloy C-22/AISI 321 austenitic stainless steel, PC-GTAW consuming ERNiCrMo-4 filler offers better-quality joints for use in industrial applications. (paper)