Abstract
In this work, the effect of preliminary mechanical surface treatment on the kinetics of formation, phase composition, and functional properties of the nitrided layer during electrolytic-plasma nitriding (EPN) of austenitic stainless steel 12Kh18N10T (AISI 321) was investigated. In contrast to traditional approaches, for the first time, this work establishes a direct correlation between the degree of surface deformation induced by shot peening and the formation of the expanded austenite (γN) phase under low-temperature plasma conditions. Quantitative X-ray phase analysis revealed a lattice parameter expansion of Δa/a0 ≈ 1.4–1.8% and a gradual transformation of γ-Fe → γN without the formation of CrN nitrides at moderate intensity of preliminary treatment. According to SEM/EDS data and microhardness profiles, a multilayer structure was formed, consisting of a thin surface film of CrN/Fe4N, a developed γN zone with a thickness of 12–15 µm, and a stable austenitic γ-Fe matrix. The surface microhardness increases to 880 ± 20 HV, while the friction coefficient decreases to 0.35–0.40, corresponding to a wear reduction of approximately 55% compared to the initial steel. The results provide a mechanistic understanding of nitrogen diffusion through defect-enriched subsurface layers and show that optimal preliminary deformation (d = 6 mm, v = 40 Hz, t = 20 min) promotes controlled formation of the γN phase with minimal lattice instability. The proposed combined approach—shot peening + EPN—is an effective method for producing wear- and corrosion-resistant surfaces of austenitic steels under atmospheric plasma conditions.