Abstract: Submerged arc surfacing is a key technology for the repair and remanufacturing of cast-iron pipe molds. In this study, 21CrMo10 steel was used as the substrate, together with JY504S flux-cored wire and HJ260 flux, to systematically investigate the effects of welding current, voltage, and welding speed on the macroscopic bead geometry, dilution rate, and microhardness distribution of single-pass submerged arc surfacing layers. The results show that welding current has the most pronounced influence on penetration depth, with increasing current leading to significant increases in both penetration and reinforcement height. Arc voltage mainly affects bead width and reinforcement, where higher voltage results in wider beads and reduced reinforcement. Increasing the welding speed reduces the overall dimensions of the surfacing layer. Hardness measurements indicate that the maximum hardness appears in the heat-affected zone near the fusion line. Moreover, the hardness of both the surfacing layer and the heat-affected zone decreases with increasing current and voltage, while it first increases and then decreases with increasing welding speed. Furthermore, a finite element model established in Abaqus successfully simulates the temperature field distribution during surfacing, providing a theoretical basis for the optimization of submerged arc surfacing processes.