This study aims to investigate the corrosion characteristics of spheroidal graphite cast iron in an atmospheric environment and compare them with those of carbon steel and weathering steel. The atmospheric exposure test results showed that the corrosion rate of spheroidal graphite cast iron is significantly lower than that of carbon steel and less than or equal to that of weathering steel. The main reason for the differences in the corrosion rate of the three materials should be due to the high protectiveness of the rust layer.

  Previous research suggests that Si and Cu contribute to the rust protection of spheroidal graphite cast iron, but the details are unclear.

  In this study, an atmospheric exposure test was conducted using specimens with minimal additions of Si and Cu to confirm their effects on the corrosion behavior of spheroidal graphite cast iron in an atmospheric environment.

  The results showed that the corrosion rate of the specimens with added Si was significantly lower than that of the specimens with minimal addition of Si. It was also revealed that Si was concentrated in the oxide state in the inner layer of the rust, especially around graphite.

  In addition, the corrosion mechanism of spheroidal graphite cast iron in an atmospheric environment was studied, considering the effects of Si and Cu.

  The behaviors of the distributions of solidification velocity and cooling rate during solidification in pure metal and alloy castings were examined by casting simulation, and their mechanisms and relations with actual phenomena such as the generation of the shrinkage cavities in pure Al castings as an example were investigated. For the 2-dimentional solidification simulation of plate castings, the acceleration zone of solidification was observed out of the end and riser effective ranges, irrespective of the casting and mold materials and/or the critical solid fraction. This zone corresponds to low temperature gradient and low NIYAMA parameter region, where the shrinkage cavities along the zone was observed on the cross section of a pure Al plate casting. For the cross-sectional observation and 3-dimentional flow and solidification simulation of cylindrical pure Al castings, neither the acceleration zone of solidification nor centerline shrinkage cavities were observed, irrespective of the mold materials. These findings may be due to the formation of the longitudinal temperature gradient with decreasing melt temperature during mold filling. Meanwhile, high cooling rate zones in and around the end effective ranges of the plate castings were observed in 2-dimensional solidification simulation under the critical solid fraction of 0.99. This high cooling rate zone was caused by the cooling of the unsolidified mesh by the surrounding solidified mesh and end effect. Although shrinkage cavities could be prevented by the high temperature gradient in the high cooling rate zone, these results suggest that there exists a correlation between the zone and morphology of the solidification macro- and microstructures.

  For the purpose of further increasing the tensile strength of high-Mn flake graphite cast iron, the effects of graphitization promoting elements (Cu, Sb, Sn) and carbide-stabilizing elements (C, V, Mo) on the chilling tendency and mechanical properties of this cast iron were investigated. The following results were obtained.

  1) The addition of Cu to high Mn specimens decreased the chill depth and increased tensile strength (σ). The specimens to which 10% Cu was added had a D-type graphite structure, resulting in chill formation.

  2) In the 10% Cu-added specimen, spherical Cu crystals, including MnS crystallized by the binary monotectic reaction of the Fe-C-Cu ternary phase diagram, were crystallized.

  3) In high Mn specimens with Sb and Sn additions, σ did not change but the chill depth decreased up to a certain amount of these elements.

  4) In the specimens with increased amounts of Sb and Sn, formation of high-concentration phases of Sb and Sn was observed at the eutectic cell boundaries, respectively.

  5) In high Mn specimens with Cr and V additions, Chill depth and σ increased and complex carbides containing Cr, V and Mn as a solid solution formed, respectively.

  6) In high Mn specimens with Mo addition, the amount of bainite formed increased with increasing Mo addition, and a large increase in σ was observed accordingly.

  In this study, the characteristics of the supercooling reversal temperature of ductile cast iron were discussed, from the viewpoint of the supercooling reversal temperature (T_sc), which is obtained by thermal analysis system. Cooling curves in hypoeutectic, eutectic and hypereutectic were systematically measured. The eutectic graphitization ability (EGA), nodule count and presence of shrinkage in each were investigated in relation to the T_sc obtained from thermal analysis. Although the T_sc was similar in hypoeutectic and eutectic, it was higher in hypereutectic. Regardless of the T_sc, shrinkage was not observed in eutectic but was present in both hypoeutectic and hypereutectic. In addition, as a result of analyzing the thermal analysis results obtained from foundry operations, it was found that the relationship between graphitization ability and T_sc changes due to the influence of chemical components such as Si, and these influences are strong. However, regardless of solidification morphology, a strong linear correlation was observed between graphitization ability and T_sc.