Effect of Welding Current on Microstructure and Properties of Ni60/Cr₃C₂ Plasma Surfacing Layer

With Ni60 alloy power+20wt% Cr₃C₂ powder as surfacing powder, a single-pass Ni60/Cr₃C₂ surfacing layer was prepared on the surface of Q235 low carbon steel by plasma surfacing technology. The effects of welding current (110–140 A) on the macromorphology, microstructure, hardness and wear resistance of the surfacing layer were studied. The results show that the Ni60/Cr₃C₂ surfacing layer exhibited a good metallurgical bond with the substrate. When the welding current increased to 130 A, the surface of the surfacing layer became smooth and flat, and the forming quality became good; when the welding current was too high (140 A), the surface oxidation and burning appeared, and the forming quality deteriorated. With the increase of welding current, the melting height, melting depth, melting width and dilution rate of the surfacing layer all increased. The surfacing layer under 110 A welding current was composed of γ-Ni(Fe), Cr₇C₃ and CrB phases. With the increase of welding current, the types of chromium compounds increased. The surfacing layers under 130,140 A welding currents were composed of γ-Ni(Fe), Cr₇C₃, CrB, Cr₂₃C₆ and Cr₃C₂ phases. With the increase of welding current, the structure of the surfacing layer was refined first and then coarsened, the number of carbides and the hardness of the surfacing layer first increased and then decreased, and the wear mass loss first decreased and then increased. When the welding current was 130 A, the surfacing layer had good forming quality without obvious defects, and had the finest structure, the largest number of carbides, the flower-like structure centered on chromium carbide, the highest hardness, the least wear mass loss , and the lightest abrasive wear degree.