Single pulse MIG welding of Inconel 625 with ER90S-B9-B9 filler: optimization and characterization

This study presents a novel application of a ferritic–martensitic steel filler (ER90S-B9, P91 grade) for joining Inconel 625 using a single pulse MIG welding process, addressing the limited exploration of dissimilar filler selection for Ni-based superalloys. Inconel 625 plates of 5 mm thickness were joined in butt joint configuration using 1.2 mm diameter ER90S-B9 filler wire (P91 steel grade). Experiments were conducted based on L9 Taguchi array with wire feed speed, pulse current ratio and dynamics as input parameters. Optimized welding parameters were identified using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) multi-objective optimization technique. Radiographic testing of the best and least optimized welds confirmed the absence of weld defects. Metallurgical analysis was done using Scanning Electron Microscope (SEM), Energy Dispersion Spectroscopy (EDS) and Electron Back Scatter Diffraction (EBSD) for correlating the mechanical property variations. The fusion zone (FZ) was dominated by equiaxed and columnar dendrites. The Low Angle Grain Boundaries (LAGB) were significantly reduced in the heat-affected zone (HAZ). The impact toughness, tensile strength and strain of the optimized weld were found to be 45 J, 670 MPa and 11.3% respectively.