Effects of multi-pulse tempering on resistance spot welding of DP590 steel

Multi-pulse tempering (MPT) on the resistance spot welding (RSW) is a considerable method to improve the quality of spot weld joints. For its uncertain tempering temperature and large temperature fluctuation, some stable sequential coupling finite element (FE) models for RSW and MPT of DP590 dual phase steel are developed to control the tempering temperature and further determine the experimental parameters. The nugget shape and size of simulation are verified by experimental observation, and the effects of MPT on microstructure, microhardness, and mechanical property during tensile-shear loading condition are experimentally investigated. The results show that MPT and its tempering temperature have no effect on the tensile-shear failure mode and have slight impact on nugget size and tensile-shear peak load. Besides, MPT leads to lower nugget hardness and better mechanical properties of spot weld joints than that of ordinary RSW due to the formation of a tempered martensite, and the higher tempering temperature expands these effects of MPT. However, the extent of the impact by MPT temperature on microstructure and mechanical property of spot weld joints is inferior to that of the impact by the MPT process itself.