In-situ monitoring of the corrosion behaviour of austempered ductile iron (ADI) under cyclic salt spray exposure

The corrosion behavior of austempered ductile iron (ADI) under cyclic salt spray exposure was studied using a specific three-electrode cell located in the salt fog chamber. Three steps were identified, namely pitting corrosion of ferrite (very first cycles), followed by inward oxidation of the ausferrite matrix and then (iii) mixed oxidation of the matrix associated with the formation of a rust layer at the specimen surface. Evolution of the corrosion rate calculated from in-situ electrochemical measurements was correlated with surface changes quantified from optical and field emission scanning electron (FE-SEM/EDS) microscopies. Corrosion products were identified by means of micro-Raman spectroscopy.