Metastable pitting corrosion of 304 stainless steel in 3.5% NaCl solution

Metastable pitting corrosion of 304 stainless steel was studied by potentiostatic polarization and three-dimensional video microscope. The results showed that the dissolution rate of metastable pits increased with time, and peaked before repassivation. The average lifetime of metastable pits decayed with potential. Whereas maximum pit lifetime, average peak value of current transients and pitting nucleation numbers increased with potential. Metastable pits were transformed from cone-shaped to dish-shaped during metastable growth. The ohmic potential drop presented between the pit interior and bulk solution, but the growth controlling factor was metal cations diffusion.