For the initial corrosion behaviour of spheroidal graphite cast iron in atmospheric corrosion environment, it is quite different from that of carbon steel and weathering steel. This study focused on the initial corrosion behaviours affected by the graphite and Cu in the spheroidal graphite cast iron, the atmospheric exposure test and wet-dry cyclic test were conducted. After two years of atmospheric exposure, the mean corrosion depth of spheroidal graphite cast iron is smaller than that of carbon steel and comparable to that of weathering steel. According to the test results under wet-dry cyclic conditions, the initiation points and area at the initial corrosion stage of spheroidal graphite cast iron are larger than those of carbon steel and weathering steel. Furthermore, the precipitation of Cu was observed in this stage. In addition, the cross-sectional observation on the spheroidal graphite cast iron, carbon steel, and weathering steel were carried out on the two years atmospheric exposed specimens. The EPMA, XRD, and open circuit potential measurements were also performed. Test results shows that the concentration of Si and Cu, has been confirmed existing at the lower part of compact rust near the substrate of spheroidal graphite cast iron, which has contribution to the formation of a high protective rust layer. For the crystalline rust composition, the amount of αFeOOH is more than γ-FeOOH in spheroidal graphite cast iron. Comparing with carbon steel, the rust layer of spheroidal graphite cast iron showed a more noble potential, because of the high proportion of passiving α-FeOOH.
Ichiro Dote (Department of Civil Engineering, Kyushu University Japan)
Ichiro Dote has studied in the Department of Civil Engineering, at Kyushu University as a working doctor from 2018. Where his major field of study is atmospheric corrosion of cast iron. Right now, he is living in Fukuoka, Japan.