Corrosion process of carbon steel in aqueous solution under the atmospheric environment and the oxygen depleted environment has been reviewed by focusing the corrosion film formed on carbon steel in neutral pH. In the neutral solution under the atmospheric condition which contains oxygen, the critical pH to form the corrosion film and the precipitation ratio of dissolved iron ions depending on pH and the parabolic growth rate law were discussed. Under oxygen depleted environment, H
2O works as oxidizing agent to oxidize Fe to produce Fe
3O
4 film with production of H
2 gas. At high temperatures, the dissolution process of the Fe
3O
4 film controls the corrosion rate, whereas, at lower temperatures, the film growth process controls the corrosion rate and a steady dissolution rate of Fe
3O
4 film determines the corrosion rate after long exposure time.
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