New steels with different carbon contents were self-developed by thermo-mechanical controlled processing. The effects of the carbon content and the microstructure on the corrosion properties of new steels were investigated by immersion test and SEM. The results indicated that the ferrite phase （both the proeutectoid and eutectoid ferrite） dissolved preferentially. Cementite reserved and accumulated on the surface. As carbon content increased, the content of ferrite decreased and cathode/anode area ratio increased. Therefore, the corrosion rate of new steels increased from 0.30 to 0.90 mm/years when the carbon content rose from 0.05 to 0.13 wt%. The corrosion process of new steels was studied using electrochemical impedance spectroscopy experiments during 72 h. It indicated that the impedance modulus IZlo.ol nz of the new steels reduces with the increase of the immersion time. While the corrosion process of the new steel with 0.11 wt% C developed faster than that with 0.07 wt% C, although their IZlo.ol nz was similar at the initial stage.
A new type of corrosion-resistant steel consisting of ferrite and bainite phases was developed for cargo oil tanks of crude oil tankers. The corrosion rate of this new steel was 0.22 mm/a, which was equivalent to ca. 1/5 of the criterion（≤1 mm/a） for corrosion-resistant steels. The composition and element distribution of the corrosion products were investigated by micro-Raman spectrometry and energy dispersive spectrometer. The results demonstrated that the corrosion product wascomposed of α-FeOOH, Fe3O4 and a continuous Cu enrichment layer. This kind of corrosion product was protective to the steel matrix and accounted for the enhancement of the corrosion resistance of the new developed steel.
