Study on microstructure evolution in welded lap joint configuration of dissimilar advanced high-strength steels using low-frequency laser wobble welding

Laser wobble welding (oscillating laser beam) experiments were performed on high-strength micro-alloyed steels (HSLA) in both a low-carbon state (top plate) and carburized state (lower plate) using various process parameters. The welds were characterized regarding microstructure and microhardness. The cross sections of the welds had a predominantly symmetric geometry and were free of defects. Repeatable heating along an oscillating path resulted in a gradual transformation along heat-affected (HAZ) region of the top HC380LA plate from partial recrystallization through acicular and Widmanstätten ferrite formation to bainite. The microstructure of the lower 16MnCr5 plate experienced self-tempering of HAZ martensite along with bainite formation. The microhardness distribution across the entire fusion zone (FZ) of the dissimilar joint exhibited relatively consistent value, with the most significant variation of 80 HV attributed to the carburized layer of the lower plate.