Laser welding of modern automotive high strength steels

The paper demonstrates the correlation between the chemical composition of steel grades and the hardness as well as the formability of laser welds generated with modern automotive high strength steel grades. At the very low heat input of industrial laser welding and the resulting extremely high cooling rate, the weld hardness is fully controlled by the carbon content of the base materials and not by the carbon equivalent. Correspondingly, the ductility of the weld seam decreases with increasing carbon content as will be demonstrated by Erichsen cup testing on laser welded samples. Based on these results it is possible to derive guidelines in terms of influencing the alloy design, the welding process as well as the material selection for a given application. In particular cases, the benefits that can be obtained with niobium microalloyed materials will be highlighted.