Effect of Strength Grades of Dual Phase Steels on Failure Location and Joint Efficiency of GMAW Lap Joints

Abstract: In this study, the effect of the material strength grades of cold rolled dual phase 590, 780, and 980 MPa steels on the weld strength of gas metal arc welding lap joints is investigated. With increasing strength grades of the base metal, the bead geometry is similar for identical welding currents and speeds. However, the failure location changes from a base metal to a fusion zone and the joint efficiency decreases with increasing material strength grades. This is attributed to the changes in the location of minimum hardness that result from the heat-affected zone softening phenomena. Joint efficiency is related to the ratio between the base metal hardness and minimum hardness of the welds. A prediction formula for joint efficiency (η) is obtained in terms of proportion of base metal hardness and minimum hardness (HMIN/HBM) as follows: η = 0.801 (HMIN/HBM) + 20.0.