Effect of Welding Current on the Microstructure and Properties of Resistance Spot‐Welded Joints of SUS301L/H1000 Dissimilar Stainless Steels

This study investigates the influence of welding current on the resistance spot welding quality of SUS301L stainless steel and H1000 ultra‐high strength steel. Results show that as the welding current increases from 6 to 11 kA, the weld nugget diameter increases from 5 to 8 mm and the joint tensile strength increases by 15%. However, expulsion occurrence increases, and shrinkage cavities with internal crack defects also become more prevalent. Metallographic analysis indicates the weld nugget consists mainly of austenite with a small amount of ferrite. The heat‐affected zone (HAZ) width on the H1000 steel side is ≈2 mm. At currents of 9 kA and below, interfacial fracture occurs, primarily caused by microvoid aggregation near interfacial precipitates and defects. At 10 kA or higher, weakened interfacial bonding creates pre‐existing cracks. Crack propagation is accompanied by plastic deformation on the SUS301L side, eventually resulting in a button fracture with nugget extraction from the H1000 side. Finite element simulations of the temperature field show good agreement with experimental results, having a maximum relative error of less than 8.2%, mainly attributed to dynamic changes in the contact interface's heat dissipation coefficient and welding expulsion.