球状黒鉛鋳鉄の黒鉛生成とけい素の偏析との関係

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With a view to investigating the influences of silicon on graphite formation during freezing in spheroidal graphite cast irons, various combinations of molten iron with molten or solid Fe-20%Si alloys at various temperatures were tested in a specially designed CO2 process mold. From the results obtained by controlled potential electrolytic etching, it became clear that two types of segregation, i.e. normal and ring or halo, occur in the matrix simultaneously. Normal segregation shows a concentric circular band of highly concentrated silicon like a halo around the spheroidal graphite, whilst the ring type one shows a halo formed by the high silicon concentration some distance apart from the spherulite. By a more detailed analysis using EPMA, it was surmised that the graphite existing in normal silicon segregation begins to crystallize in the melt in the high silicon concentration after silicon addition, while the graphite in high silicon halo had already crystallized in the melt before the addition of silicon. In these cases, it appears that the silicon which segregate normally contributes to graphite nucleation and its growth, while silicon showing ring or halo type segregation does not have a role in affecting graphite nucleation or its growth. Quenching of specimens from the molten state clarified the fact that austenitic halo formation surrounding graphite in molten iron obstructs the diffusion of silicon to the central graphite through austenite, which then results in the formation of the silicon concentrated area surrounding the austenitic halo which are found around the primary graphite spherulite.
Japan Foundry Engineering Societyの論文

著者

大番屋嘉一
(株)神戸製鋼所加古川製鉄所

球状黒鉛鋳鉄の黒鉛生成とけい素の偏析との関係

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