| Abstract |
| The effects of CH4 content at nitriding step in the low temperature two-step plasma treatment (carburizing+nitriding) on the surface characteristics of AISI304L stainless steel were investigated. The low temperature plasma carburizing was carried out at 550℃ for 5h in a gas mixture of H2, Ar and CH4. The thickness of a carburized layer increased up to about 30 μm and corrosion resistance of the layer decreased due to the precipitation formed at the grain boundary. After carburizing, a low temperature plasma nitriding was subsequently performed in the same chamber at 400℃ for 15 h to improve corrosion resistance and to further increase the surface hardness. The surface hardness of a N-enriched layer after nitriding reached up to 1,200 HV0.1, which is much higher than that of as-carburized layer (750 HV0.1). The post nitriding process had a beneficial effect on reducing the precipitates in the C-enriched layer. The thickness of the N-enriched layer was about 10 μm without containing CH4 in the nitriding atmosphere. With increasing the CH4 level in the atmosphere, the uniformity and thickness of the N-enriched layer decreased and finally reached 5 μm with 8% CH4. The amount of the precipitates in the N-enriched layer increased with increasing CH4 composition. |
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| Key Words |
| austenitic stainless steel, plasma carburzing, plasma nitriding, expanded austenitie |
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