Corrosion behaviour of high chromium white irons in high temperature caustic

High chromium white cast irons are used in a number of applications in alumina refineries where wear is a significant issue. However, recent case studies of failures of white irons in high temperature digestion have suggested that significant corrosion of these materials is occurring and this may be leading to accelerated wear rates. In this paper, the corrosion behavior of a series of high chromium (Cr) white irons in concentrated caustic solutions is studied in the laboratory at temperatures from up to 280°C. The morphology of the oxide films is studied along with corrosion rates measured using weight loss measurements, and this is correlated with compositional and microstructural variations in the white irons. The failure mechanisms of these white irons involve preferential corrosion of the matrix, particularly in circumstances where the matrix is pearlitic. Recommendations regarding the heat treatment and compositions of white irons for use in high temperature digestion are made.