Effect of Fiber Laser Welding on the Fatigue Properties of Dissimilar Welded Joints between DP980 and HSLA Steels

Advanced high strength steels (AHSS) such as dual phase (DP) steels are now being extensively used to achieve light weighting goals of vehicles because of their attractive combination of formability and high strength. High strength low alloy (HSLA) steels are also used in lightweight bodies-in-white; DP and HSLA steels are therefore often laser butt-welded together into tailor welded blanks and to create other joints. Among the laser welding processes, fiber laser welding (FLW) has been shown to provide excellent quality welds, including superior weld mechanical properties, at higher speeds than those possible with other laser welding processes. Using dissimilarly welded DP980-HSLA blanks made with different welding parameters, the tensile properties were found to not change in spite of the HSLA being weaker than the soft zone on the DP980 side of the weld. The high heat input weld was found to have more softening in comparison to its base metal (BM) (55 HV versus 46 HV) and less bainite (8% versus 15%) in its FZ in comparison to the low heat input weld. The fatigue properties of the high heat input weld were also found to be better than those of the low heat input weld.