The fine eutectic graphite structure occurs in the pure cast iron solution without other inclusions. Such a kind of solution is not sensitive to nitrogen which promotes the separation of large graphite flakes, so that the latter would not appear even in case the solution comes in contact with nitrogen. The cast iron specimen which has been solidified into a fine eutectic structure and specially treated, does not show the same structure again, when remelted in the similar manner as before. However, the fine eutectic graphite structure may be recovered, when such a specimen is melted and the solution is oxidized by passing CO
2 or O
2 through it, or when the solution is overheated to 1350°C in the hydrogen atmosphere. Seeing from these facts, it is presumed that the remelted solution contains very minute particles of the non-dissolved graphite suspended in the solutionthe so-called graphite nuclei-which are, according to the author's experiment, stable against heat and does not dissolve in the solution at temperatures up to 1400°C; and that in the presenee of CO
2, O
2 or H
2 with the solution, they would disappear by being oxidized to CO
2 or changing into hydrocarbons, and, on cooling, the fine graphite structure would be separated.
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