Abstract
It has been understood from the results of the experiments heretofore carried out by the authors that shrinkage cavity is apt to occur when the molten iron is oxidized and that the inclement of SiO2, as an inclusion, is found simultaneously by the chlorine method for oxide determination. In order to clear up the relation between sirinkage cavity and the inclusion, the experiments this time were made to discriminate the form of SiO2 and the effect of that form on the graphite structure were also studied. The electron diffraction method was applied to discriminate the form of SiO2. On the plane of the oxidized iron specimen etched with bromine gas, the electron diffraction reflection pattern like α-crystobalite was observed indistinctly. This specimen was subsequently treated by chlorine gas of high temperature and then the residue drawn out from this treatment, the non-metalic substance, was investigated by the electron diffraction transmission method. This time, the diffraction transmission pattern of α-crystobalite was observed very clearly. In the case of treating the silicate, like 2FeO·SiO2, with chlorine gas, however, no transmission pattern of α-crystobalite was observed. Consequently, it has been confirmed that the SiO2 obtained from the oxidized specimen has the form of α-crystobalite and that the specimen does not give the form of the double salt with FeO. In the next step of the experiments, turning scrap of cast iron was melted in contacting with silicate powder, FeO powder and various sorts of SiO2-FeO silicates and the influence of those substances on graphite structure was investigated. The results taken are as follows : 1) Pure silica impedes the graphitization when it contacts with molten iron. 2) It seems that FeO and SiO2-FeO silicates also impede the graphitization. But, this can not be said confidently because the percentages of carbon and silicon in the iron decreased somewhat. 3) When the molten iron is oxidized at relatively low temperature, the percentage of SiO2 becomes greater. Therefore, in order to explain the cause of the occurence of shrinkage cavity, it will be necessary to confirm the effects of SiO2 which seems to impede the graphitization. (H. M.)
