Austenitic plasma nitrocarburising of carbon steel in N2–H2 atmosphere with organic vapour additions

Austenitic plasma nitrocarburising treatments of a medium carbon steel (0.47 wt.% C) have been carried out using a modified DC plasma furnace in a gas mixture of nitrogen, hydrogen and organic vapour of C6H6. Various gas compositions and treatment procedures have been used in order to produce a thicker monophase ε carbonitride compound layer on the carbon steel surface. The nitrocarburised layers have been examined with several analytical techniques including X-ray diffraction, glow discharge spectrometry, metallographic and microhardness tests. It has been found that austenitic plasma nitrocarburising with organic vapour as the carbon source can readily produce a desirable monophase ε compound layer on the investigated plain carbon steel surface. The ε compound layer is supported by an austenite layer followed by a diffusion layer which is expected to give higher load bearing capacity. It has also been found that the “two-step” plasma nitrocarburising process is advantageous over the “one-step” process since the monophase ε compound layer produced by the two-step process can be thicker, and the treatment temperature or the total treatment time can be reduced.