Characterization of nitrocarburized surface layer on AISI 1020 steel by electrolytic plasma processing in an urea electrolyte

In this study, electrolytic plasma processing (EPP) was employed for surface nitrocarburizing of AISI 1020 steel in a urea electrolyte, where the substrate samples were connected cathodically to a high-voltage DC current power supply. The structural, mechanical, wear and corrosion properties of the samples treated for 3–5 min were investigated. The results show that the surface layers formed on the samples by this treatment at 220 V have a ferritic nitrocarburizing characteristic which consists of a compound layer and diffusion zone. The surface layers of the treated samples at 240 V consisted of a compound layer, martensitic layer and diffusion zone, respectively, which is a marker of austenitic nitrocarburizing. The compound layers formed at 220 V and 240 V consisted of ɛ-Fe2-3 (N,C) and γ′-Fe4 (N,C) phases. The hardness value of the compound layer on the substrate was about 930 HV which was 4.5 times higher than that of the substrate. The thickness of the surface layer formed on the samples was a function of time and applied voltage. The wear and corrosion resistances of the samples were improved due to the surface treatment.