<p>This study explores the impact of WC nanoparticles on the structure and properties of laser fusion-coated Ni45 coatings, aiming to enhance their corrosion resistance. The experiment utilized ZG42CrMoA alloy steel as the substrate, and a composite coating was applied using a 5kW CO₂ laser, a four-axis CNC machine, and a coaxial powder feeding system. The microstructure of the coatings was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), a microhardness tester, and an optical microscope. The performance of the coatings was evaluated through electrochemical corrosion tests. The findings indicate that increasing the nano-WC content leads to the enrichment of WC nanoparticles at grain boundaries, which strengthens these boundaries and refines the grains. This refinement increases the energy required for grain fracture along the boundaries, enhances the uniformity of Cr element distribution, and enlarges the eutectic zone, thereby improving both the tensile strength and corrosion resistance of the coating. However, an excessive amount of nano-WC can cause agglomeration, resulting in increased C element production and exacerbating Cr depletion at the grain boundaries. This, in turn, diminishes the diffusion strengthening effect of the nano-WC particles. Optimal results were observed at a nano-WC content of 6.0 wt.%, where the coating exhibited a refined and uniform grain structure, maximum tensile strength, and minimum corrosion current density.</p>