Development of welding technique to avoid the sensitization in the alloy 600 by conventional Gas Tungsten Arc Welding method

Abstract

Even though Nickel based superalloy (alloy 600) exhibits high corrosion resistance at elevated temperatures, the main limitation of this alloy is the formation of Cr-depleted zones in the grain boundary regions. In this regard, there is a constant demand for the reduction of Cr-depleted (sensitization) zones towards various applications. In order to achieve this, the present work is focussed on the fabrication of weld joints by Gas Tungsten Arc Welding (GTAW) and Pulsed Current Gas Tungsten Arc Welding (PCGTAW) using the filler wires such as ERNiCr-3, ERNiCrMo-3, and ERNiCrMo-14 to avoid sensitization. The fabricated materials were analyzed by optical and scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS). The macro examination of these welded materials clearly reveals the presence of defect-free weld joints. As per the results from the microstructural analysis, the rapid cooling was achieved in the pulsed current technique, and subsequently, the equiaxed dendrites were observed in the fusion zone. EDS analysis showed the presence of Nb-rich (MC) carbide phases near the joints fabricated by filler wires i.e. GTA ERNiCr-3 and ERNiCrMo-3 indicating the preferential formation of Nb-carbide over Cr-carbide. In a similar way, Mo-rich M23C6 phases were observed near the joint fabricated by the filler wire, GTA ERNiCrMo-14. There was no microsegregation observed during the fabrication through the PCGTA welding technique.