Corrosion Behavior of Chromium Cast Iron and Steel in Hot Concentrated Alkaline

Hot concentrated alkaline corrosion and wearing corrosion environment exists in alumina metallurgical industry. Iron and steel materials with outstanding alkaline corrosion resistance are strongly demanded for their fabrication equipments. In this paper, corrosion resistance in static hot concentrated alkaline solution of several kinds of martensite chromium cast iron and steel was studied through polarization curves, potential-time curves, weight loss in the corrosion, and corrosive morphology analysis. Experimental results indicated that corrosion processes can be divided into three stages: dissolving of passivating films, exposed surface corrosion, and corrosion beneath the corroded product. Protection effect of the passivating films was transitory, and the corrosion rate during the exposed surface corrosion reached the maximum. Corrosion of the testing materials was composed of active dissolving corrosion of the metal matrix and caustic embrittlement cracking of the matrix, as well as grain boundary corrosion for the cast iron. Dissolving corrosion of the metal matrix was the main cause that induced the weight loss, while severe caustic embrittlement cracking of the metal matrix was disadvantageous. With an increase of the chromium content in the cast iron or steel, active dissolving corrosion of the metal matrix increased. However, the tendency of caustic embrittlement cracking decreased.