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

Taking Ni60+20wt% Cr₃C₂ composite powders 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. With the increase of welding current to 130 A, the surface of the surfacing layer became smooth and flat, and the forming quality became good, but 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 current were composed of γ-Ni(Fe), Cr₇C₃, CrB, Cr₂₃C₆ and Cr₃C₂ phases. With the increase of welding current, the massive structure in the surfacing layer was refined and the number of carbides increased, but the structure became coarse and the number of carbides decreased under the welding current of 140 A; 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 no obvious defects with good forming quality, the finest structure, the largest number of carbides, the flower-like structure centered on chromium carbide, the highest hardness with Rockwell hardness and Vickers hardness of 62.6 HRC and 763 HV, respectively, the best wear resistance and the least wear mass loss with 65.8% lower than that of the substrate, and the lightest abrasive wear degree.