Optimisation of Flux and Weld Parameters During Flux Bounded Tungsten Inert Gas Welding (FBTIG) of Nickel Based Superalloy Inconel 600

Abstract

Superalloys are used in the strategic sectors of aerospace, defence and nuclear in view of their high specific strength at elevated temperatures, good weldability and excellent oxidation resistance. Inconel 600 is a nickel–chromium alloy with good oxidation resistance at higher temperatures and resistance in carburizing and chloride containing environments. Tungsten inert gas (TIG) welding is the most versatile fabrication process used due to its efficiency and high level of process control. However, the depth of penetration obtained in the weld joint is quite low making multi-pass welding inevitable for thick-section welding. To improve depth of penetration of TIG welded joints, flux bounded tungsten inert gas (FBTIG) welding was developed, that uses thin layer of activating flux on top of the surface of the workpiece, by maintaining gap along the weld line. The present work focuses on the effect of nature of flux and flux gap on the weld bead geometry and mechanical properties of FBTIG welded Inconel 600 alloy. Optimization of weld and flux parameters was carried out through bead-on-plate welding and butt weld joints of Inconel 600 was fabricated using the optimized parameters. Radiographically qualified aerospace quality welds were fabricated and depth of penetration has increased three times for FBTIG welds coated with SiO2 flux using flux gap of 2.5 mm. The room-temperature tensile strength of FBTIG weldments is comparable to that of TIG welds and it was concluded that single-pass FBTIG welding can replace multi-pass TIG welding, to join thicker sections of Inconel 600.