Effects of Holding Time on Haz-Softening in Resistance Spot Welded DP980 Steels

Resistance spot welding (RSW) of dual-phase (DP) steel subjected to various conditions of cooling rate (holding time) is studied in this work. Lap-shear tensile testing is used in order to evaluate the mechanical performance of the weldments. The microstructure is analyzed through optical and electron microscopy and the hardness is obtained through Vickers method. Results indicate an effective tempered region along the sub-critical heat affected zone in all the samples. A broken morphology accompanied with presence of small carbides within tempered martensite phase is consistently observed. Variations in the cooling rate (holding time) indicate minimal effect on the degree of softening and on the mechanical performance of the welds.