IN625 buttering assisted GMAW for high-integrity DSS 2205/AISI 4140 dissimilar welds

This research presents a comprehensive investigation into the fabrication and optimisation of dissimilar metal welds (DMWs) between Duplex Stainless Steel (DSS 2205) and High-Strength Low-Alloy (HSLA) AISI 4140 steel using a synergistic Gas Metal Arc Welding (GMAW) process integrated with a nickel-based Inconel 625 (IN625) buttering layer. The introduction of IN625 as a buttering material effectively suppressed the formation of Type II martensitic boundaries at the AISI 4140 steel-weld metal interface, ensuring metallurgical continuity and enhancing mechanical integrity. Welding parameters were systematically optimised through a Taguchi L9 orthogonal design by varying arc voltage, welding speed, and inter-pass temperature, followed by multi-response optimisation via Grey Relational Analysis (GRA) and desirability-based regression. The optimal parameter set (25 V, 500 mm/min, 150 °C) yielded a maximum ultimate tensile strength of 632 MPa and a notched tensile strength of 324 MPa with a composite desirability of 90.23%. The fracture morphology indicated ductile failure dominated by microvoid coalescence. Microstructural characterisation revealed an austenitic matrix reinforced with finely distributed ferrite stringers across the weld zone, and the absence of a distinct brittle interface confirmed complete metallurgical fusion. Micro-hardness mapping across the weldments confirmed a well-balanced hardness distribution, with peak hardness observed in the AISI 4140 heat-affected zone (HAZ) and moderate values maintained across the weld and IN625 buttering region. Overall, the study establishes IN625 buttering-assisted GMAW as a robust strategy for eliminating interfacial brittleness and achieving mechanically superior dissimilar joints between DSS 2205 and HSLA AISI 4140, suited for structural and petrochemical applications.