Effect of Nitrogen Content on Electrochemical Response and Pitting Behavior of New Austenitic Stainless Steels

The novel austenitic stainless steels containing 0.326%, 0.527% and 0.750% nitrogen respectively were subjected to potentiodynamic polarization tests in 2.5%, 3.5%, 4.5%, 5.5% and 10.5% NaCl solutions using an electrochemical workstation. Meanwhile impedance spectra was obtained from EIS tests in 3.5%NaCl solution.The standard pitting corrosion tests were performed in 6%FeCl3 solution to calculate the average corrosion rate of the specimens, and the corrosion morphology and three-dimensional images of the corroded specimens were observed by scanning electron microscopy(SEM) and laser confocal microscopy(LSM).The results show that the corrosion potential(E_corr) of the specimen presents a trend of increasing and then decreasing with the increase of the solution concentration, and the pitting potential(E_b) is greater than 1.2 V when the nitrogen content is 0.527%; The charge transfer resistance (R_ct) and passivation film thickness(Lss) also show a trend of increasing and then decreasing with the increase of the nitrogen content and the maximum value is obtained when the nitrogen content is 0.527%, the R_ct and Lss is 4.222×10⁵ Ω·cm² and 6.688×10^-8 m, respectively, which indicate that the alloy has the best corrosion resistance in NaCl solution.The average corrosion rate and corrosion pit depth of the alloy with 0.527% nitrogen content have the minimum value of 130.370 g/(m²·h) and 185.300 μm, respectively, it has the smallest corroded area in the same field of view, exhibiting good corrosion resistance.