While it has long been accepted that stainless steels, have the inherent ability to passivate in air or under other oxidizing conditions, investigation indicates that the rate of film growth and the “degree of passivity” attained vary considerably under different conditions. Solution potential measurements offer a convenient means of following the progress of the film formation. Data show the behavior of stainless steel specimens in various solutions and in air after a prior chemical activation. A 30 per cent nitric acid solution rapidly produces a passive potential as compared to air. A comparison of several stainless steel types in regard to their passivating characteristics is given and the effect of surface finish is also considered. Results suggest that in some instances stainless steels probably owe their corrosion resistance to the formation of a protective film of corrosion product on the surface rather than to the passive film which, according to the usual concept, is caused by an oxidizing environment.

Subject
Acids, Surface finishing, Steel surfaces, Materials, Potential measurements, Nitric acid, Solutions, Specimen preparation, Electric potential, Passivation, Corrosion resistance, Stainless steel, Passivity
Copyright 1951 by the National Association of Corrosion Engineers.
1951
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