Evaluation of mechanical and corrosion properties of resistance spot welded AISI 409 M ferritic stainless steel under welding parameters optimized conditions

`Resistance spot welding of ferritic stainless steels is influenced by heat input that controls the weld nugget formation, microstructural changes, and subsequent mechanical and corrosion properties. In this investigation, resistance spot-welding parameters were optimized to attain maximum Tensile Shear Fracture Load (TSFL) in AISI 409 M ferritic stainless steel sheets using Response Surface Methodology (RSM). Further, the influence of welding power, electrode pressure, and holding time was investigated in the present study. The optimized process resulted in a maximum TSFL of 11.03 kN, and the predicted and experimental values agreed well with a deviation of ±5%. The quadratic regression model analysis showed predictive capability of R² = 0.9938 and revealed electrode pressure as the most significant factor. In addition, microstructural analysis of weld joints indicated that the weld nugget contained refined equiaxed grains and controlled width of heat-affected zone. Furthermore, Potentiodynamic polarization test results showed that base metal corrosion rate increased from 3.20 ± 0.33–7.03 ± 0.24 mpy in the neutral medium and from 26.67 ± 0.52–58.24 ± 0.50 mpy in the acidic medium, whereas comparatively low corrosion rates were obtained in the alkaline medium. The optimized welding parameters reduced excessive sensitization and helped to develop a stable passive film which reduced corrosion degradation. Under the optimized conditions, optical microscopy and scanning electron microscopy analyses showed the good metallurgical bonding and the absence of significant defects.