The effect of dissolved oxegen on the potential of coated steel was investigated in neutral solutions. The potential difference of coated steel between in aerated solutions and in deaerated solutions was relatively large, for example, 480mY. The value was much larger compared with that of uncoated steel, which suggested that the steel surface beneath paint film had some characteristic behaviors. The electrochemical behaviors of dissolved oxygen are shown below. (I) The potential of coated steel

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... in aerated solutions and in reaerated solutions was noble and almost equal, and that in deaerated solutions was less noble. The polarization resistance of coated steel in aerated solutions was largest, and that in both deaerated and reaerated solutions became smaller. (II) The potential behavior of coated steel was as same as the case (I). The polarization resistance in deaerated solutions was largest, and that in both aerated and reaerated solutions became smaller. (III) The range of potential difference between in aerated and deaerated solutions was relatively small in the initial stage of immersion or in case of thicker paint film These results suggest that passivate film is formed on the steel surface under paint film in neutral solutions. The model of polarization diagram of coated steel was proposed, considering the effect of dissolved oxygen.