Influence of Work Hardening on Tensile and Fatigue Behavior of Resistance Spot-Welded Dual-Phase Steel

In the current study, 1.4 mm thick dual-phase (DP600) steel sheets were prestrained at 0, 5, 10, and 15% prestrain levels followed by spot-welding in lap-shear configuration. The load carrying ability and fatigue properties of the joints were studied. Besides, the dislocation density of the deformed specimens was estimated by x-ray diffraction (XRD) as well as transmission electron microscopy (TEM). Additionally, in-depth examinations were carried out in terms of microstructure, hardness profiles, as well as fractography. The results indicated that the load carrying ability of joints increased with attendant reduction in energy absorption, with increase in prestrain level. The prestraining of sheets has insignificant influence on the high-cycle fatigue strength of the joints. In case of tensile–shear loading, the initiation of crack occurred at the base metal, while under cyclic loading, crack initiation took place from the heat-affected zone (HAZ). The majority of the dislocations produced owing to the prestraining are annihilated at HAZ during joining process, so there is no noteworthy influence of prestrain on the high-cycle fatigue strength of spot-welds.