Microstructural and mechanical evaluation of a dissimilar gas metal arc-welded AISI 304/AISI 409M Joint using ER308L filler

Dissimilar welding of austenitic and ferritic stainless steels is essential in industrial applications that require both corrosion resistance and cost-effectiveness. However, differences in thermal expansion coefficients and phase stability between these alloys often cause premature failure in heat-affected zones, particularly on the ferritic side, where grain coarsening compromises joint integrity. Despite extensive research, the metallurgical–mechanical relationships governing AISI 304/AISI 409M weld performance remain inadequately understood. This study establishes correlations between welding parameters, microstructural evolution, and mechanical performance in gas metal arc-welded butt joints of AISI 304 austenitic to AISI 409M ferritic stainless steel using ER308L filler material. Welding was performed at optimized parameters (current—150 A, voltage—20 V, welding speed—250 mm/min) corresponding to 0.72 kJ·mm⁻¹ heat input. Comprehensive characterization included radiographic inspection, optical microscopy, X-ray diffraction, microhardness mapping, tensile testing, and bend testing. Results showed defect-free welds with dendritic fusion zone structure. The high-temperature heat-affected zone on AISI 409M exhibited significant grain coarsening from 8 µm to 65 µm (7.12-fold increase). X-ray diffraction detected only austenite and ferrite phases without deleterious intermetallics. The microhardness peaked at the fusion zone with 379.52 HV, with nearly a 37.89% reduction in heat-affected zones due to grain growth with respect to the fusion zone. Tensile tests showed failure in the softened ferritic zone at 85% of base metal strength, while bend tests demonstrated excellent ductility without cracking. This work demonstrates that ER308L produces metallurgically compatible joints between AISI 304 and AISI 409M. The key contribution is quantitatively establishing that controlled heat input (0.72 kJ·mm⁻¹) limits grain coarsening and maintains joint performance above 85% capacity, providing practical guidelines for industrial applications.