The effect of potassium chloride and potassium carbonate on the high temperature corrosion of 304L steel

The influence of both solid KCl as well as K₂CO₃ on the oxidation of the 304L steel has been investigated in the laboratory. Three temperatures were used; 500, 550, and 600°C. The steel samples were covered either with KCl or K₂CO₃ under two different atmospheres; dried air and air with 30% water content. Also exposures with no salt were carried out. The exposure time in every test was 168 h. The extent of corrosion, the elemental distribution as well as the identification of corrosion products was determined using a scanning electron microscope equipped with an energy dispersive x-ray analyzer (SEM/EDXA).

Both salts were found to be corrosive. The structure of the formed oxide layer was similar with both salts, i.e., the outermost iron oxide layer was followed by an oxide layer containing chromium, iron and nickel, still followed by a nickel-rich region before the bulk metal. With both salts indications of a potassium-chromium compound, most likely potassium chromate (K₂CrO₄) was found to be formed as an intermediate. The oxide layer thickness distributions showed some differences between the salts as well as differences within a salt under different conditions.