Solid lubrication coating of FeS layer on the surface of SKD 61 steel produced by plasma sulfnitriding

Plasma sulfnitriding technology has been employed to harden the surface of SKD 61 steel. In this plasma sulfnitriding method, a small amount of H2S gas has been added in the mixture of N2 and H2 used in the plasma nitriding method. This process has been performed under 3 torr pressure at 580 °C for 20 h. The plasma sulfnitriding yielded the very thin FeS iron sulfide layer 2–3 μm in thickness on the top of a 15–20 μm thick compound layer, which consisted of ɛ-Fe2–3N and a second phase of γ′-Fe4N. In comparision with commercial plasma nitriding treatment, the plasma sulfnitriding treatment has showed better surface roughness and corrosion resistance due to the presence of the thin FeS layer, which filled microvoids and microcracks in the outside of the compound layer. It has also been found that plasma sulfnitrided sample revealed better wear resistance due to the presence of the thin FeS layer which acted as a solid lubricant.