To obtain reliable resistance spot welds that guarantees their satisfactory mechanical performance and improved crashworthiness in the vehicle autobody, it is vital to study the causes, conditions, and welding parameters resulting in the formation of defects and discontinuities in the welds. This work studies the weld discontinuities and defects that are likely to occur in resistance spot welding of 1-GPa transformation-induced plasticity steel. The causes of the formation of weld discontinuities and defects are discussed here. It is found that the rich chemistry and complex thermomechanical processing and thus special thermophysical properties of the alloy have significant impacts on the susceptibility of the welds to defects. The amount of heat input induced by the welding process also plays an important role on the defect formation. From the ductility ratio results, it can be said that there are critical heat input and critical nugget size for occurrence of the weld discontinuities and defects. The susceptibility of the resistance spot welds of the experimental alloy to early expulsion, liquation cracking, surface breaking cracks and their consequences on weld quality and performance are discussed here.
