Tribological properties of a liquid nitrocarburised special purpose cold work tool steel

A special purpose Cr–Mo–V cold work tool steel, of commercial name “SLEIPNER”, was subjected to liquid nitrocarburising to enhance its wear behaviour. Nitrocarburising is performed in industrial liquid salt bath at 570 °C for 4 h. SLEIPNER is mostly used for cold work tooling (e.g. for the manufacture of blanking and shearing tools) due to its high wear and chipping resistance. It could be considered equivalent to X90CrMoV8 3, although there is no existing equivalent standard describing the exact chemical composition of this steel. The tribological properties were evaluated using the standard pin-on-disk wear testing method with tungsten carbide-based pin against steel under nitrocarburised and annealed conditions.The variation of friction coefficient and wear volume were recorded as a function of applied normal load (5, 8 and 10 N) and sliding distance for a constant running speed (0.6 m/s). Optical and scanning electron microscopy was also used to study the microstructure and the wear tracks of the tested materials. The friction coefficient of the nitrocarburised steels varied between 0.65 and 0.80, while the relative wear resistance is found 34–112 times higher than that of the annealed steels.