While the local passivation film is destroyed, the rest of the protective film remains intact, which makes the pitting corrosion conditions of stainless steel realized and strengthened. According to the electrochemical generation mechanism, the electrode potential of the activated stainless steel is much higher than that of the passive stainless steel, and the electrolyte solution satisfies the thermodynamic conditions of electrochemical corrosion. The activated stainless steel becomes the anode, and the passive stainless steel acts as the cathode.
Corrosion spots involve only a small part of the metal, the rest of the surface is a large cathodic area. In the electrochemical reaction, the cathodic reaction and the anodic reaction are carried out at the same speed, so the corrosion speed concentrated on the anodic corrosion point is very significant and has obvious penetration effect, thus forming pitting corrosion.
