Mechanical and metallurgical aspects of spot-welded joints in heat-treated low-carbon mild steel sheet

Abstract

The optimum welding parameters for the spot welding of 0·030 in martensitic, bainitic, cold-rolled, and subcritically annealed low-carbon steel sheet of the same chemical composition, have been determined. The welds in the martensitic sheet are able to withstand almost double the tensile-shear loads that are supported by the welds in subcritically annealed sheet; the tensile-shear strengths of the welds in the bainitic and cold-worked sheet are intermediate to those in the other two sheet materials. The behaviour of the spot welds under fatigue stresses was determined, and, unlike the effects on the tensile-shear strength, the metallurgical condition of the parent sheet material appears to have very little significant effect upon the endurance limit of the spot welds.