Pure erosion and pure corrosion were intentionally superimposed and their interaction was observed, expecting that some useful information on the mechanism of erosion-corrosion might be obtained. As a pure erosion process cavitation erosion and slurry erosion were chosen. It has already been made clear in the previous chapter that the damage generation processes of the erosion are both pure mechanical. As a result of experiments, it was found that cavitation erosion was at the initial stage accelerated by corrosion but in the later stage it was inhibited through the adsorption of chloride ions on the metal surface. Alternatively, the erosion always accelerated corrosion by renewing the metal surface. Slurry erosion process, that is, the damage to the metal surface by the impact of solid particle was entirely enhanced by corrosion. Corrosion of the target material was sometimes enhanced and sometimes inhibited depending on the particle impact angle, which was in good accordance with the observation in the previous chapter. The most important discovery in the experiments was that under the superposition of erosion and corrosion the product of the cooperation of erosion and corrosion did not exist. Accordingly erosion-corrosion was judged as a pure electrochemical corrosion process.