Abstract
Exposure experiments in the presence of deposited matter were carried out with the aim of developing laboratory techniques for simulating corrosion conditions of stainless steels under atmospheric dusts. The tests were made on austenitic steels in salt-spray and in atmospheres contaminated with sulphur dioxide and hydrogen sulphide with and without sodium chloride present in the deposits. Carbon black, activated carbon, granulated graphite and silica powder were used as dusts. While no localised corrosion resulted under silica, all carbonaceous materials, in the presence of chloride ions, produced steel pitting in the following order of increasing severity: AISI 316 < 304 < 302. Hydrogen sulphide also led to localised attacks under carbon deposits in the absence of chloride ions.
Some potential measurements on specimens of the AISI Types 304, 316, 430 and 410, while exposed in a salt-spray cabinet, showed that carbon deposits caused a definite potential shift in the positive direction on all but the martensitic Type 410, suggesting that pitting may be induced by the potential-raising catalytic action of carbon on the cathodic reduction of oxygen.
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