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In order to evaluate the influence of boundar y length(BL)between graphite nodule and matrix on the corrosion rate of spheroidal graphite cast iron, the corrosion test was performed in a sulfuric acid solution at pH 2. The presence of graphite nodule was considered to influence the corrosion at the boundary between matrix and graphite nodule. The contiguous length between graphite nodule and matrix per unit area was defined as BL. The corrosion potential and rate were measured. The surface morphology of the specimens was observed. Anodic dissolution of the matrix in the vicinity of the graphite nodules took place preferentially. As a result, the graphite nodules were detached from the matrix. The graphite nodules worked as cathode. However, no influence of BL on corrosion rate was seen.

The rate equation of hydrogen evolution reaction of spheroidal graphite cast iron with different pearlite area has been studied in sulphuric acid solutions at 298 K. The cathodic Tafel slope of 20?130 V/decade and the reaction order with respect to the activity of hydrogen ion of 1 are obtained by linear potential sweep technique. The rate equation of hydrogen evolution reaction does not depend on the area of pearlite. There is no difference in hydrogen evolution reaction mechanisms between pure iron and spheroidal graphite cast iron.

This study focused on the differences in initial corrosion behavior of spheroidal graphite cast iron, carbon steel and weathering steel in atmospheric corrosive environment, the atmospheric exposure test and dry/wet cyclic test were conducted to examine the effect of graphite and Cu of spheroidal graphite cast iron on its initial corrosion behavior. After exposure to the atmosphere for two years, the mean corrosion depth of spheroidal graphite cast iron is smaller than that of carbon steel and similar to that of weathering steel, whereas the initial corrosion of spheroidal graphite cast iron progresses earlier than carbon steel and weathering steel, regardless of the temperature, humidity, and the amount of sea salt. From the initial corrosion test results in the wet-dry cyclic test, that Cu precipitation was observed at the corrosion origin of the spheroidal graphite cast iron, which is same as that in weathering steel. Based on the findings obtained in this study, a schematic diagram of the initial corrosion mechanism of spheroidal graphite cast iron was speculated.

The old gray cast iron for water supply pipes in Yokohama City which was made in the UK in 1887 is highly corrosion resistant. The corrosion behavior of the old gray cast iron in soils was studied. For comparison, a gray cast iron used for modern pipes, a spheroidal graphite cast iron, and a carbon steel were tested. The corrosion potentials and corrosion rates were measured. The corrosion products and the base metals were analyzed by X-ray diffractometry and energy dispersion spectroscopy. The corrosion rate of the gray cast iron made in the UK in 1887 was lower than those of the others. The gray cast iron contains a large amount of steadite, which is a ternary eutectic (γ-Fe, Fe 3 C, and Fe 3 P). The network structure of steadite enclosed the corrosion products and decreased the corrosion rate.