Effect of carbon addition on low-temperature plasma nitriding characteristics of austenitic stainless steel

Attempts have been made in the present work to investigate the influence of carbon in the treatment atmosphere on the low-temperature plasma nitriding characteristics of austenitic stainless steels. It was found that treatment gas composition has a significant effect on the structural characteristics of the nitrided layer. The addition of a small amount of carbon-containing gas such as methane (CH4) to the treatment atmosphere can alter the structural development in the alloyed zone and offer several beneficial effects to the nitriding process. Based on this discovery, a new process has been developed, which involves the simultaneous incorporation of both nitrogen and carbon into the alloyed zone to form a dual-layer structure, which is free from chromium nitride, and carbide precipitates. Such a hybrid structure not only possesses larger layer thickness, high hardness, and more favourable hardness gradient than nitrided-alone layers, but also exhibits much improved corrosion resistance. (c) 2006 Elsevier Ltd. All rights reserved.