PLASMA-DIFFUSION TREATMENT OF STELLITE

Stellite, a Co-base superalloy, exhibits good resistance to wear and corrosion. However, this good resistance to wear is sometimes less pronounced in some industrial applications such as steel mill equipment. The present study was therefore conducted to improve this impoverishment of wear property of Stellite. The maximum hardness after plasma nitriding was measured as 1300 HK 0.01, which was facilitated by the formation of CrN. It was found that plasma nitriding at 823 K exhibited relatively higher hardness and a thinner compound layer than plasma nitriding at 973 K. However, the hardness decreased drastically at 1073 K. Plasma nitrocarburizing was also applied with the parameters of optimized conditions for plasma nitriding with the addition of methane gas to are 80%N-2-H-2 gas mixture. The maximum hardness after plasma nitrocarburizing was about 1200 HK 0.01 and the thickness of layer was about 30 mu m while it was 8 mu m after plasma nitriding. It was indicated that carbon was uniformly distributed in the diffusion layer while the distribution of nitrogen was rich only at the compound layer. Surface conditions after plasma diffusion treatment are also discussed.