The Effect of Plasma Nitriding Time on Corrosion Behavior of 304 Stainless Steel

In order to improve the local corrosion performance of 304 stainless steel in Cl-environment, hotwire enhanced plasma unbalanced magnetron sputtering technology was used for ion nitriding. The microstructure,structure and corrosion resistance of the nitrided layer of 304 stainless steel under different nitriding time were stud-ied by SEM, XRD and electrochemical workstation. The corrosion process and corrosion resistance mechanism werediscussed. The results show that plasma nitriding has a significant effect on the corrosion resistance of 304 stainlesssteel. After nitriding for 2 h, the corrosion potential of 304 stainless steel increases from -257 to -128 m V, and theimpedance modulus increases by three orders of magnitude compared with the substrate. The corrosion current den-sity decreased from 7.94×10^-7to 5.21×10^-8A/cm², and the corrosion weight loss decreased from 837.65 to 159.46g/m²·a^-1. The corrosion resistance of stainless steel was significantly improved. However, when nitriding time is ex-tended to 4 h, Fe₃N is formed due to the combination of N and Fe atoms. The galvanic couple of γ_N and Fe₃N phaseforms the corrosion microcell, which reduces the corrosion potential, increases the corrosion current density andweight loss, and reduces the corrosion resistance of stainless steel. In this experiment, the corrosion resistance of 304 stainless steel nitrided for 2 h in Cl^-solution is the best.