Preserving Mechanical Properties in Fiber Laser Welded 1.6 GPa-Class Ultrahigh-Strength Steel Plates

Motivated by the significant tensile-strength loss reported for gas metal arc (GMA) and friction stir (FS) welds of 1.6 GPa-class ultrahigh-strength steel, this study assesses whether autogenous fiber laser beam (LB) welding can better preserve base-metal performance. Compared with GMA and FS welding, fiber LB welding produced joints with tensile strength essentially matching the base metal while maintaining sufficient impact toughness. Laser power and travel speed were optimized to balance heat input, weld quality, and productivity. A defect-free, full-penetration joint with a markedly narrow fusion zone was achieved in 6.0 mm plates (base-metal UTS = 1635 MPa) using a laser power of 2.9 kW and a travel speed of 1.2 m/min. The reduced heat input limited heat-affected-zone over-tempering and promoted a more homogeneous martensitic microstructure, thereby reducing the mechanical-property mismatch between the weld metal (WM) and the heat-affected zone (HAZ). This maintains the welded joint mechanical properties at a level comparable to the base steel (BM).