Characterization and corrosion behavior of high-chromium white cast irons

Erosion-resistant high-chromium white cast irons (CWIs) are widely used in hydrotransport components, particularly in oil-sand operations. Due to the acceptance that corrosion processes can accentuate material degradation by erosion processes and vice versa, it is important to understand the corrosion resistance of these materials in the environments in which they are used. Three CWI alloys with different chemical compositions-chromium (26 to 40 wt pct) and carbon (2.5 to 4.3 wt pct)-were investigated in this study. Electrochemical DC potentiodynamic polarization and potentiostatic tests were carried out in a solution of 1000 ppm Cl- at a pH of 8.5 (obtained by adding NaOH) that simulates a recycle cooling water. A detailed characterization of the microstructures was also performed. There are significant effects of microstructural features and alloy composition on the corrosion behavior of CWIs. Two key factors have been shown to determine the corrosion behavior: the primary carbide area fraction and the amount of chromium as well as other elements in the matrix. The corrosion resistance of the CWI alloys strongly depends on the ratio of chromium content in the M7C3 carbide to that in the matrix (Cr-M7C3/Cr-matrix).