Laser beam welding of dual-phase DP1000 steel

Autogeneous laser beam welding is an efficient process to join ferritic-martensitic dual-phase steels without large dimensional distortions. Localized softening may occur in the heat affected zone, particularly in DP1000 steel with a high martensite volume fraction. DP1000 steel was welded in bead-on-plate configuration varying the welding power between 0.4 and 2.0 kW and the welding speed between 20 and 150 mm/s. Light optical microscopy, scanning electron microscopy, and X-ray diffraction were used to perform the microstructural characterization of the welded joints. High-quality laser beam welds of thin sheets of DP1000 steel can be produced using appropriate welding parameters. The optimal welding condition was a nominal laser power of 2.0 kW and a welding speed of 150 mm/s. This condition minimizes the amount of softening of prior martensite and yields a narrow heat affected zone and a small volume fraction of retained austenite in the weld.