Pseudo-passive films on cast irons: A strategy to mitigate corrosion by acting directly on microstructure

The effect of the microstructure on the corrosion resistance of four grades of cast irons was studied in an alkaline 0.03 M NaCl solution. The research was performed by combining microstructural analysis, electrochemical measurements and the characterization of the corroded surfaces. The structure underneath the corrosion layer determines the corrosion resistance of cast irons. It increases according to the following order: grey < chunky < spheroidal < high silicon ductile cast iron. The graphite morphology governs the rate of galvanic corrosion whereas the ferrous matrix controls the formation of non-disrupted oxide layers. A pseudo-passive layer explained the lowest corrosion rate of the high silicon ductile cast iron.