Comparison of potassium chloride and potassium carbonate with respect to their tendency to cause high temperature corrosion of stainless 304L steel

The influence of both solid KCl as well as K2CO3 on the oxidation of the 304 L steel has been investigated in the laboratory. Three temperatures were used; 500 degrees C, 550 degrees C, and 600 degrees C. The steel samples were covered either with KCl or K2CO3 and held in two different atmospheres; dried air and air with a water content of 30%. Exposures with no salt were carried out as well. 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, followed by a nickel-rich region before the bulk metal. With both salt 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.