Effect of Ti Contents and Welding Current on the Mechanical Properties of Electrical Resistance Spot Welds in Complex-Phase Steel Sheets

When complex-phase (CP) steel with a tensile strength of more than 1 GPa grade is joined using resistance spot welding (RSW), the optimum Ti content should be chosen in order to satisfy the weldability and mechanical properties. Therefore, in this study, the effect of the Ti content (0 similar to 300 ppm) on the tensileshear load of the RSW in CP steels is investigated. Because the resistivity of the base metal is independent of the Ti content, it does not affect the nugget diameter. Regardless of the Ti content, the specimens under 5t(1/2) (t = sheet thickness) are fractured in the interfacial failure mode. In the low welding current condition (lower than 6.4 kA), the measured nugget diameters are smaller than the calculated critical nugget diameter regardless of the amount of Ti addition in order that the fracture mode is interfacial failure. Pull-out failure occurs at the softened zone, which is the boundary between the base metal and heat-affected zone. The tensile-shear load of the specimen failure in the pull-out mode increases as the fractured diameter and hardness of the softened zone increase. The shear load is only dependent on the fractured diameter.