【摘要】：M50NiL steel was plasma nitrocarburized at 480 °C with and without rare earth(RE) addition. The microstructures of the surface layer were characterized by optical microscopy, X-ray diffraction and scanning electron microscopy. The mechanical properties and corrosion resistances of the surface layer were studied by Vickers microhardness measurements and polarization tests in 3.5% NaC l solution. The results showed that RE atoms could diffuse into the surface layer of the steel and inhabit the formation of ε-Fe_(2–3)(N,C) phase. As compared to the treatment without RE addition, RE addition further increased the surface hardness by 143 HV0.1, and further increased the thickness of the nitrocarburized layer by 39 μm. Compared with the quenched bearing steel, the corrosion resistance of the samples nitrocarburized with and without RE addition could be significantly improved. Especially, the sample plasma nitrocarburized with RE addition exhibited the highest corrosion resistance.