engleski

Influence of chemical removal of oxide films, formed by exposure of high-alloy steel to air at high temperatures, on their pitting liability

Oxide film or scale, formed on stainless steels in hot air during manufacture or in exploitation, affect their corrosion resistance harmfully. This effect has been studied by testing the liability of stainless steels with thermal oxides to pitting in FeCl3-solution according to ASTM G48-99a. For evaluation of results eight pitting criteria, based on determination of pits number, their depths and mouths areas, have been used. Stainless steel specimens were exposed to testing solution - in the initial state (ie. without thermal oxides), - after heating in air (ie. with thermal oxides), and - after heating in air and subsequent pickling in agents containing HNO3 and HF. Beside sheet specimens, welded pipe specimens have been tested, too. Thereby it was established that pitting criteria vary considerably on the weld itself, on heat tints zones and on base metal. The discussion of results shows that the removal of thermal oxides by pickling decreases general pitting tendency but it is impossible to achieve initial localised corrosion resistance therewith. After all, it may be concluded that the investigation confirms modern concepts about nucleation and growth of pits on stainless steels, elaborated by G.T.Burstein and collaborators.

pitting corrosion; high-alloy steel; oxide film

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