Influence of Surface Roughness on Pitting Corrosion Behaviors of 304 Stainless Steel Passivated with Nitric Acid

After passivation in 10vol% HNO3 solution, the corrosion resistance of 304 stainless steel samples with different surface roughnesses were studied with potentiodynamic scan, electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN). The results show that when the surface roughness decreased from 0.25 μm to 0.1 μm, the charge-transfer resistance raised from 6.51 kΩ·cm2 to 19.17 kΩ·cm2, current standard deviation and potential standard deviation decreased, but noise resistance increased. The slopes of line segment in power spectral density (PSD) curves of potential and current increased, but the slope of noise spectrum curve decreased with the increase of surface roughnesses of samples, indicating that compact and stable passivation film was easily formed on the smooth surface of stainless steel. HNO3 passivation could markedly improve the pitting corrosion resistance of 304 stainless steel.