Corrosion Resistance of Plasma-Nitrided AISI 316L Stainless Steel with Intermittent Nitrogen Flow

Low-temperature plasma nitriding of austenitic stainless steels produces an expanded austenite (γN) layer that enhances surface hardness but may generate high residual stress and cracking, compromising corrosion resistance. This work evaluates the influence of nitrogen flow duty cycle on the corrosion resistance of AISI 316L austenitic stainless steel plasma-nitrided at 425 ℃ for 2 h. Continuous nitrogen flow (2C) and intermittent flow at 50% (2P50) and 10% (2P10) nitrogen duty cycles were investigated, with untreated steel (UN) as reference. Samples were characterized by SEM, XRD, nanoindentation, OCP, EIS, potentiodynamic polarization in 3.5 wt.% NaCl and XPS. Reducing the nitrogen duty cycle produced layers with lower nitrogen incorporation and reduced cracking. However, excessive reduction in the duty cycle decreased corrosion resistance, indicating the importance of sufficient nitrogen incorporation for electrochemical performance. The 2C condition exhibited the most noble corrosion potential and the highest localized corrosion potential, whereas 2P10 showed lower corrosion resistance than UN. EIS indicated more stable, thicker passive films at 2C and 2P50. The results suggest that nitrogen availability influences passive-film stability and may contribute to the synergistic protective effect of nitrogen and molybdenum. Overall, 2P50 provided a balance between surface hardening, layer integrity, and corrosion resistance.