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Effect of segregation bands on corrosion of steel plate for ship hull

Mazur M., Kadłuczka A.

Archives of Foundry Engineering

2010

Vol. 10, iss. 3 spec.

157--162

Despite significant progress in the manufacturing of sheet metal ships carried both by optimizing the chemical compositions of steel mills as well as rolling and heat treatment, it still fails to remove the effects of persistent segregation. As a result we observed anisotropy of mechanical properties of the material which essentially complicates the process of construction for shipbuilding industry. Anisotropy of mechanical properties occurring in sheet metal hull is even more dangerous, that during their work, they are exposed to continuous exposure variable charges arising from sea surface waves. Another factor weakening the resistance to cracking metal ship is sea-water, which in the surface layer is highly aerated and very aggressive corrosion. The purpose of this study is to clarify the role of the segregation bands in the process of corrosion of low alloy steels used for ship hull. It was estimate a rate of corrosion in aerated sea water areas of the metal with or without segregation bands. After corrosion tests were made observations of specimens surfaces. Inside the segregation bands were found phosphorus. The contents of it were exceeded the average this element content in the steel. At the same time areas of the sheet metal with segregation bands were slowly corroded than areas without bands, although the changes of corrosion rate was similar in nature. Corrosion activity of rich in phosphorus segregation band is similar to phosphate corrosion inhibitors. These are effective in the presence of chloride in seawater to form a protective layer that protects against corrosion segregation band. Under the observation on scanning electron microscope there was no change in the appearance of surface samples after corrosion tests. A future direction of research will be estimate the stress corrosion in the same species – with and without segregation bands.