Double Pulse Process of Resistance Spot Welding of Ferritic/Martensitic Dissimilar Stainless Steels

Dissimilar joints made of AISI 409L ferritic stainless steel and AISI 410 martensite stainless steel are joined by double pulse resistance spot welding process. Macrostructure, microstructure, microhardness, and tensile shear performance of joints are studied. The nugget size increases to 2.4 mm in diameter under the role of the second pulse and changes a little with the second pulse when 4 kA welding current is applied. The nugget is remelted and microstructure is coarsened during the second pulse. Hardness of nugget decreases to 330.7 to 386.5 HV. The combination of strengthening from bigger nugget and softening from coarsen microstructure contributes to the ignorable change in peak load and enhancement of ≈150% in failure energy. However, when 8 kA welding current is applied, the nugget used single pulse is 5.4 mm in diameter and the second pulse has a negligible effect on the nugget size. The microstructure in nuggets is tempered during the second pulse. Hardness of nugget and peak load of joints are similar among the samples. Martensite decomposition and carbides precipitation during tempering contribute to the 95% enhancement in failure energy. All the joints fail in button mode and significant deformation occurs on the propagation path of crack on samples used double pulse.