Comparison of nitrided austenite and nitrided martensite stainless steel produced with Rf-De high dense plasma nitriding

Abstract

High density RF-DC plasma nitriding was applied to make surface treatment both of austenitic and martensitic stainless steels: AISl-316L and AISl-420. The nitriding conditions were varied: the duration time was held for 7.2 ks (or 2 H), 14.4 ks (or 4 H), and 28.8 ks (or 8 H), and the holding temperature, at 673 K (or 400°C) and 753 K( or 480°C). A mixture of nitrogen (N2) and hydrogen (H2 ) was utilized as a carrier gas with the gas flow rate ratio of 70%N2 to 30%H2. Vickers micro-hardness testing was utilized to examine the change of surface hardness, and the corresponding microstructural analysis was carried out by utilizing X-Ray Diffraction Analysis. Hardening of the nitrided AISl-316L is attributed to formation of fine y-Fe4N and CrN precipitates in the matrix. On the other hand, the hardening of AISl-420 must be driven by extraordinary solid solubility of nitrogen and formation of intermediate iron nitrides or Fe2+xN without formation of y-phase and CrN