Effect of Laser Welding on Formability of DP980 steel

Limiting dome height (LDH) tests were used to evaluate the formability of laser butt welded blanks of the dual phase 980 steel in comparison with the base metal. Two different lasers were used: diode and Nd:YAG, giving a wide range of welding thermal cycles. A sharp decrease in LDH was observed in the welded specimens due to the formation of a softened zone in the outer heat affected zone. Softened zone characteristics were correlated with the LDH. Larger softened zones led to a larger reduction in the LDH. The welding orientation relative to the rolling direction or to the punch surface did not influence the formability, as the softened zone dominated the formability behavior. It was observed that in both uniaxial and biaxial strain tests, the fracture occurred in the softened zone of the welded samples consistently slightly farther out from the weld centerline than in the location of the minimum hardness.