Effect of Laser Power on Microstructure and Mechanical Properties of Laser Welded High-Nitrogen Steel

This study investigates the influence of laser welding process parameters on the weld bead formation, microstructure, and mechanical properties of high-nitrogen steel. Results indicate that as laser power increases, the weld bead width expands, while the cross-sectional porosity exhibits a trend of initially decreasing and then increasing. The lowest porosity is achieved at a power of 2.1 kW and a welding speed of 8 mm/s. Microstructural analysis revealed that higher laser power promotes grain coarsening, increases the proportion of high-angle grain boundaries, and raises the ferrite phase content. At 2.4 kW, the weld zone exhibits high dislocation density and significant lattice distortion. Regarding mechanical properties, the hardness of the weld metal gradually decreased with increasing laser power, while the tensile strength exhibited an initial increase followed by a decrease. The tensile strength (840.5 MPa) was also achieved under the process conditions of 2.1 kW and 8 mm/s.