Although many factors such as the concentration difference of O_2 between the occluded area and bulk surface may initiate the localized corrosion of low alloy steels in sea water, the degree of the "self catalysis effect" is the direct and intrinsic factor which takes effects in the Occluded Corrosion Cavity (OCC) determines greatly the localized corrosion rate of low alloy steels in sea water. A new OCC simulated cell with varied dimensions of the occluded cavity was designed for appraising the degree of the "self catalysis effect" by measuring the short circuit current and calculating the relative quantity of coulomb, the results presented was in good accordance with that of low alloy steels immersed in sea water, 902>A3>945>907>921. A new multi-cycles scanning potentiostatic polarization (MCSPP) method was invented to appraise rapidly the relative degree of the "self catalysis effect". The microscopic studies of the sample after the occluded experiment presented that properties of films and the surface patterns of the low alloy steels and mild steel differ greatly from each other. The "microscopic area difference" (MAD) effect was initiated to explain the effect of the microscopic area difference on the degree of "self catalysis effect", and the "carbides dispersively strengthening" (CDS) effect to explain the effect of the distributions and quantities of carbide. According to the macroscopic and microscopic studies of the "self catalysis effect", we explained satisfactorily some complex phenomena. The general corrosion rate of different low alloy steels in sea water is approximately equal; the localized corrosion of steel 902 is much higher than other low alloy steels; the steel 921 presents a fairly good localized corrosion resistant property. Based on the microscopic analyses of the "self catalysis effect", some viewpoints on how to lower the localized corrosion rate of low alloy steels in sea water were presented.
修改评论