Abstract: In this study, the pure erosion behaviour of pure iron and its erosion-corrosion behaviour under different anodic polarization currents were investigated in various cathodic reactions (oxygen reduction, hydrogen ion reduction, and water reduction) using a cylindrical stirring system. The corrosion-enhanced erosion (C-E) rates were determined for each condition. The results revealed that pure iron displayed similar pure erosion behaviour across all three cathodic reactions. When the cathodic reactions involve hydrogen ion reduction or water reduction, the erosion-corrosion of pure iron manifested as uniform damage, with the reduction in hardness being the main cause of the C-E in this case. Conversely, in the case of oxygen reduction reaction as the cathodic reaction, the erosion-corrosion presented as pitting damage, with the reduction in hardness resulting from localized concentration of anodic current and the formation of easily worn protruding flaky iron structures at the edges of the pits as the main mechanism of the C-E. Moreover, linear and exponential relationships were found between the C-E rate and the anodic current density for uniform damage and pitting damage, respectively. Finally, the concept of surface equivalent hardness was proposed, along with the establishment of a mathematical model for surface equivalent hardness based on the relationships between the C-E rate and the anodic current density. Utilizing the surface equivalent hardness enables the evaluation of the erosion rate on material surfaces considering the coupled effect.

Key words: Corrosion-enhanced erosion, Cathodic reaction, Pitting damage, Uniform damage, Hardness