Abstract—Resistance Spot Welding (RSW) is widely used in automotive and manufacturing industries for joining metallic sheets; however, welding dissimilar metals such as mild steel and stainless steel remains challenging due to their differing thermal and metallurgical properties. This study investigates the influence of preheating the stainless steel component at varying temperatures (100 °C, 120 °C, 150 °C, and 180 °C) on the mechanical and microstructural characteristics of dissimilar RSW joints with mild steel. Tensile testing, hardness profiling, and Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) analyses were conducted to evaluate joint performance. The results revealed that preheating significantly affects residual stress distribution, ductility, and joint homogeneity. Without preheating, joints exhibited high tensile strength (127.46 MPa) but low ductility due to rapid cooling and martensitic formation. Optimal conditions were achieved at 180 °C preheat, yielding the highest tensile strength (156.32 MPa), improved ductility (strain = 1.80% Gauge Length), and the lowest standard deviation (6.95 MPa), indicating enhanced process stability. Hardness analysis confirmed a balanced gradient across the weld, heat-affected zone, and base metal, while SEM observations identified reduced microcracks and improved microstructural uniformity at higher preheat levels. Overall, a preheat temperature of 180 °C effectively minimizes thermal gradients and residual stresses, improving weld integrity and consistency. These findings provide practical insights for optimizing preheating parameters in industrial RSW applications, particularly in the fabrication of automotive body structures and other dissimilar steel assemblies.

Keywords—preheat, dissimilar material, resistance spot welding

Cite: Kristiana Pasau, Nasaruddin Salam, Ahmad Yusran Aminy, and Azwar Hayat, "The Effect of Preheating on the Quality of Spot Welding Between Dissimilar Mild Steel and Stainless Steel 304," International Journal of Mechanical Engineering and Robotics Research, Vol. 15, No. 1, pp. 50-64, 2026. doi: 10.18178/ijmerr.15.1.50-64

Copyright © 2026 by the authors. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).