To prevent chill and improve ductility in spheroidal graphite cast iron, it is effective to generate many heterogeneous nuclei as the substrate of graphite crystallization, and to increase the graphite nodule count. It is known well that adding a rare earth (RE) element increases graphite nodule count in cast iron, resulting in improved mechanical properties. The spheroidizer and inoculant used for cast iron manufacture also have a possibility of using the RE-Si alloy which extracted from RE to neodymium (Nd), praseodymium (Pr) and samarium (Sm) for cost reduction and a possibility of using the RE-Si alloy which made 100% lantern or 100% cerium as RE. In this study, the spheroidization treatment was carried out by mixture in which the RE-Si alloy was near 100%La or 100%Ce as RE and by the spheroidizer which does not contain RE, and the influence of RE mixture on the graphite nodule counts and on the mechanical properties of thin-section spheroidal graphite cast iron was considered. The results showed that the graphite nodule count of 3mm thick specimens was higher with Re-Si alloy added with only Ce or La, than those added with both Ce and La as RE. The graphite nodule count was the highest in the specimens added with Ce alone. Compared to the specimens containing Ce and La (50 : 50), the specimens containing only Ce showed smaller sulfide particles, which act as the substrate of graphite crystallization, and a higher number of these particles. This is considered the reason for the increased graphite nodule count.

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  Spheroidal graphite cast iron is used widely as the casting material of windmill parts for wind power generation, and thus often requires high toughness at low temperatures. Due to its high thickness sensitivity, the mechanical properties of spheroidal graphite cast iron (FCD400) are easily affected by the shape of the parts used for, especially thickness. Depending on the environment used in, these parts are exposed to low temperatures below freezing, therefore requiring absorbed energy above 10J below 253K.
  This study investigated the impact properties of spheroidal graphite cast iron prepared by a variety of inoculation methods. Due to rising rare earth prices in recent years, we attempted to use rare earth-less inoculants. As a result, pouring inoculation was found to improve microstructure, and rare earth-less inoculant containing calcium was effective against brittleness at low temperatures.

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  Recently, high tensile strength steel with high manganese (Mn) content is used as a raw material for manufacturing cast iron. But, it is becoming increasingly difficult to recycle high Mn content steel scrap for the production of cast iron, because Mn is known as an element promoting the chilling tendency of cast iron melt. In this study, the effects of Mn/S ratio and inoculants such as pure Si, Fe-Si and Ca-Si on chilling tendency and mechanical properties in high manganese (2%) flake graphite cast iron with different carbon equivalents (CE) corresponding to FC150, FC250 and FC350 of JIS were investigated for the purpose of recycling high Mn steel scrap. Chilling tendency decreased, and tensile strength and Brinell hardness increased with increasing Mn/S ratio in high Mn flake graphite cast iron with 2％ Mn content. A difference in tensile strength of more than 100MPa was obtained in high Mn flake graphite cast iron compared to cast iron with standard Mn content, although they had the same CE. Possible reasons for the strengthening of high Mn flake graphite cast iron may be the reduction of the eutectic graphite and ferrite matrix and refinement of pearlite lamellar spacing. It was also found that when Ca-Si was added to high Mn cast iron melts, spherical sulfide in the form of (Mn, Ca) S formed in the melt and this sulfide acted as a substrate for graphite formation in eutectic solidification, resulting in remarkable graphitization and high strength.

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