Assessment of the effect of nitriding treatment on physical and mechanical properties of stainless steels

Abstract

The Aim of this study is to apply a low-temperature plasma nitriding to AISI 304 and 316L stainless steels to evaluate its impact on structural, mechanical, and electrochemical properties. X-ray diffraction (XRD) confirmed the formation of expanded austenite (γN), which is responsible for the hardness improvement. Nanoindentation tests showed a reduction in penetration depth from ~1150 to 1100 nm in 304 and from ~1100 to 1070 nm in 316L under a 100 mN load. Electrochemical analysis revealed divergent behaviors. In AISI 304, corrosion resistance decreased significantly, with corrosion potential shifting from –28.7 to –306.9 mV and corrosion current density rising from 7.76 nA to 3.97 μA. This deterioration is attributed to unstable passive films and microstructural discontinuities caused by heterogeneous nitrogen saturation. In contrast, AISI 316L exhibited improved corrosion behavior: despite an increase in current density from 10.5 nA to 6.69 μA, impedance spectroscopy confirmed a strong capacitive response, indicating the formation of a more stable and homogeneous γN layer. The presence of molybdenum in 316L played a key role in enhancing passive film stability. These results indicate that plasma nitriding improved hardness in both alloys through interstitial nitrogen strengthening but affected corrosion differently depending on alloy composition: degradation in 304 due to passive film instability, and reinforcement in 316L thanks to molybdenum’s stabilizing effect.