Effect of Continuous and Pulsed Current GTA Welding on the Performance of Dissimilar Welds Involving Aerospace Grade Alloys

Dissimilar joints involving Inconel 718 and the martensitic grade stainless steel AISI 416 have been employed in gas turbine applications. In the present study, an attempt has been made to compare the effect of continuous current and pulsed current gas tungsten arc welding of this dissimilar joint. These dissimilar alloys were welded using a low cost, Nb free stainless steel filler, with a view of controlling or eliminating the deleterious Laves phase. Microstructure studies performed at the fusion zones of both CCGTA and PCGTA weldments revealed the formation of martensite at the cap zones. The unmixed zone containing Nb rich phases, observed at the weld interface of Inconel 718 was found to be lower for PCGTA weldments. Tensile failures were experienced at the parent metal of AISI 416 for both the cases. Impact toughness of the weldments were lower than that of parent metals employed in the study. High temperature corrosion studies were performed on the weld coupons by exposing them to an aggressive molten salt environment containing K2SO4 - 60% NaCl at 650 A degrees C. Owing to the recrystallization and grain refinement, the PCGTA weldments experienced better corrosion resistance compared to the CCGTA weldments. Surface analytical techniques were employed to determine the hot corroded species formed and attempts have been made to establish the corrosion kinetics.