EFFECT OF CHEMICAL COMPOSITION AND MICROSTRUCTURE ON THE GALVANIC CORROSION OF CAST IRON.

The corrosion of iron and steel has been much studied during some years past. However, the investigation on the galvanic corrosion or contact corrosion of iron and steel has been performed in comparatively small circles and very few reports published.The author studied the effect of chemical composition and micro-structures on the galvanic corrosion of cast iron specimens which had been immersed in the 3% Nacl solution, being made in contact with each other. According to the result of such simple test, some minute difference in the electrolytic solution pressure of different cast irons was distinctly recognized, which revealed that T.C and Si, by their graphitizing effect, increase the solution pressure, while Mn, Cr, Ni, and Cu decrease it. It was presumed that a high grade cast iron with low C and low Si which also contains nickel or chromium should more remarkably retard the corrosion velocity when made in contact with the equal volume of a plain cast iron with higher T.C and Si. FolloWing, therefore, the proper selection of combination of the materials in contact, galvanic corrosion of the main parts of marine engines would be more prevented. Investigations of such practical applications and the result of various cases of corrosion tests will be informed in the near future.