Effects of Nb Content on Microstructure and Wear Resistance of Fe-Cr-C Alloy Surfacing Layer Based Carbon Arc

Using Fe-Cr-C alloy powder block containing 0-5wt% Nb as surfacing material, surfacing layer was prepared on Q235 steel substrate by carbon arc surfacing method, the effects of Nb content on microstructure, hardness and wear resistance of the surfacing layer were studied. The results show that, when mass fraction of Nb was 0-5%, all surfacing layers and base metal (Q235 steel) formed good metallurgical bonding. Microstructure of surfacing layer was composed of gray-black matrix and white hard phase, matrix was composed of martensite and retained austenite, white hard phase was consisted by primary carbides of M7C3, eutectic carbides and Cr23C6. With the increase of Nb content from 0 to 5wt%, microstructure of surfacing layer gradually refined, the quantity of hard phase gradually increased and they distributed more evenly; Meanwhile, hardness of surfacing layer increased and then decreased, and wear loss decreast and then increase. When the mass fraction of Nb was 3%, the hardness of surfacing layer was the highest, up to 63 HRC, the wear loss was minimum, only reached to 5.5 mg. When the mass fraction of Nb was 3%, scratch on surfacing layer surface was the shallowest and the scratch was not continuous, only a small amount of spot shape pits on wear surface, and the wear degree of the surfacing layer was lightest.