Optimization of the Plasma Nitrocarburizing Temperature on the Surface Characteristics of AISI 316L Austenitic Stainless Steel after Post Oxidation

In this experiment, post-oxidizing treatments were implemented on AISI 316L stainless steel which was plasma nitrocarburized previously at various temperatures. Plasma nitrocarburizing was performed on AISI 316L stainless steel at various temperatures (400°C, 450°C, 500°C) with a gas mixture of H₂, N₂, and CH₄ for 15 h. Additionally, the post oxidation treatment was carried out at 400°C for 1 h in a gas mixture of O₂ and H₂. After treatment, the behavior of the duplex layer was investigated by optical microscopy, X-ray diffraction, scanning electron microscopy and micro-hardness testing. A Potentiodynamic polarization test was also used to evaluate the corrosion resistance of the samples. The X-ray diffraction confirmed the development of a Cr₂N, γ_N phase and magnetite (Fe_3O4) phase under plasma nitrocarburizing and post-oxidizing processes. Additionally, it was found that the thickness and surface hardness increased with an increasing nitrocarburizing temperature. The experiment revealed that 316L stainless steel had better hardness and excellent corrosion resistance than the bare sample, when both the nitrocarburizing and oxidizing treatment temperatures were 400°C.