高Mn片状黒鉛鋳鉄のチル化傾向と機械的性質に及ぼすMn/S比及び接種剤の影響

抄録

  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.