Assessment of weld quality in blue laser light fiber welding of DP1000 dual-phase steel butt joint

This study evaluates the weldability of 0.8 mm DP1000 steel using Blue Laser Light Fiber (B-LLF) welding. Experiments varying laser power and welding speed achieved full penetration at heat inputs between 17.5 J/mm and 26.7 J/mm. The best samples reached welding joint efficiencies of 86–92% relative to the base material. Hardness testing and Scanning Electron Microscopy confirmed Heat Affected Zone (HAZ) softening, due to tempered martensite, and a 58–67% hardness increase in the Fusion Zone (FZ). The results show that B-LLF welding enables high-quality joints with lower energy consumption than conventional lasers, though HAZ softening remains a key limitation in DP1000 steels.