Abstract: Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of SKD 61 steel. Plasma nitrocarburizing was conducted for 12 h at 540℃ in the nitrogen, hydrogen and methane atmosphere to produce the ε-Fe2–3 (N,C) phase. The compound layer produced by plasma nitrocarburising was predominantly composed of ε-phase, with a small proportion of γ′-Fe4(N,C) phase. The thickness of the compound layer and the diffusion layer are about 10 μm and about 200 μm, respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of 500℃ for 1 h. The very thin magnetite (Fe3O4) layer of 1–2 μm in thickness on top of the compound layer was obtained. Anodic polarization test revealed that plasma nitrocarburizing process contributed a significant improvement of corrosion resistance of SKD 61 steel. However, the corrosion characteristics of the nitrocarburized compound layer was deteriorated by oxidation treatment.

Key words: Plasma nitrocarburizing, Post oxidation, ε-Fe2–3 (N, C), γ′-Fe4 (N, C)