The basic research of the coated steel plate about the relationship between the coating durability and the characteristics of the rust

One of the reasons why under-film corrosion occurs in the painting steel structure, is that repainting is performed although the rust still remains at the base material adjustment. Firstly we observed the rust of corroded steel sheet which is prepared by the Salt Spray Test( SST) before painting. The appearance of the specimen which is performed the base material adjustment after SST, is classified into bright area, dark area, and the steel exposed area. As a result of corrosion tests after the painting, it is confirmed that the under-film corrosion occurs in the dark area and the neighborhood.