The intergranular corrosion (IGC) and electrochemical characteristic of carbon steel in carbonic acidand sodium nitrite solutions was studied with methods of potentiodynamic polarization andmetallographic microscope. The relation between intergranular corrosion and electrochemicalcharacteristic was discussed. The occurrence of IGC was observed on the steel surface when the steelwas potentiodynamic polarized in carbonic acid and sodium nitrite mixed solution. Carbon steelshowed the typical electrochemical characteristic of active-passive-transpassive in the mixed solution,and the initiation and propagation of IGC was observed only when the steel was potentiodynamicpolarized in active-passive transition region, passive region and transpassive region. For carbon steel inthe mixed solution, the occurrence of IGC was very closely related to the electrochemicalcharacteristic of active-passive transition: carbonic acid induced the dissolution of grain boundariesand sodium nitrite promoted the passivation of crystal grains.
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