The Corrosion Resistance of Ductile Iron★

The internal structure of ordinary grey iron, pearlitic ductile iron, ferritic ductile iron, malleable iron and mild steel are compared. Differences in the amount of carbon present and in the form in which it occurs are responsible for some differences in the corrosion behavior of these materials. This is explained on the basis of the electrochemical reactions which occur during corrosion. As corrosion proceeds, the graphite which is present in the cast materials may accumulate as a graphitic layer on the surface. The adherence and permeability of such graphitic layers and their influence on subsequent corrosion and on galvanic behavior are discussed. Corrosion data in acids, in neutral and alkaline solutions, in sea water, in the atmosphere and underground, in miscellaneous environments, and under conditions involving erosion are presented and interpreted in the light of the principles outlined above. By and large, it is concluded that ductile iron has satisfactory corrosion resisting properties which permit its use where grey iron, malleable iron, or steel are regularly employed. 6.2.2