Experiments were carried on the decarbonization of pig iron grains for making the low-carbon pure iron as substitute for steel scraps or Luppe. Various factors which influence the process, such as gas composition, temperature, grain size, time of contact, catalysers, etc. were studied.

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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 CO₂ or O₂ 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 CO₂, O₂ or H₂ with the solution, they would disappear by being oxidized to CO₂ or changing into hydrocarbons, and, on cooling, the fine graphite structure would be separated.

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In the present experiment to determine non-metallic inclusions in carbon steels tne author tested some samples by means of the chlorine method adopted by Roland Wasmuht or E.W. Colbeck. However, in this method it was found that since the residues had been washed only with hot water after chlorination, exceedingly large amount of residues contaminated by the ferric hydroxide and silica gel were obtained, which had been produced by the hydrolysis of ferric and silicic chlorides remaining on boat; and that the total oxygen content calculated from the value of these oxides was three or five times greater than that obtained by the vacuum fusion method Accordingly, in order to eliminate these contaminating substances the residues were washed in the following order: -first with hot water, then by turns with hot 5% hydrochloric acid, hot water, hot 5% sodium carbonate solution, hot water, hot 5% hydroch oric acid, and finally with hot water. The chlorine method with the aforementionel improved washing procedure was applied to a number of killed steels, and the total oxygen content was found to agree precisely with the residues obtained by the vacuum fusion method.
In the case of killed steels in which the ferrous and manganous oxides content were relatively low, non-metallic inclusions could be determined easily by the present method. However, steels with high content of these oxides were liable to be attacked, to some extent, by washing with the 5% hydrochloric acid washing. Therefore, the author extracted the residues after chlorination in the 5% sodium citrate solution (pH 7) to prevent ferric chloride from hydrolysis, then filtered and washed the residues with the 5% sodium carbonate solution to exclude the silica gel. In this procedure the total oxygen obtained by the chlorine method and the vacuum fusion method were in good agreement even in steels containing high percent inclusions of ferrous or manganous oxide.

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