Various pig irons which producing conditions and chemical composition had been different were melted at 1450°C under low pressure of 7∼9×10⁻⁴ mmHg and the change in structure and chemical composition by vacuum-melting were examined. The properties such as graphite spheroidization by magnesium of the irons melted in vacuum were investigated. (1) The precipitation of eutectic graphite was accelerated by vacuum-melting, and the less the iron contained impurities, the easier the precipitation of eutectic graphite took place. (2) The amounts of elements such as Mn, S, Cu and Sn in irons were decreased by vacuum-melting. (3) The graphite in irons melted in vacuum was generally nodulized easily by addition of magnesium, but in irons containing elements such as Ti, As and Sb was not nodulized so easily.

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  To investigate the defects in heavy castings, we took cast-block specimens. These specimens were made of molten irons with additions of K₃Fe(CN)₆, Fe₂O₃ and SiO₂. By these tests, we found that nitrogen in molten iron formed blow-holed which increased as the degree of eutecticity decreased.
  In this report and the former report (Rept. 1), we have shown that casting defects are mainly caused by nitrogen in molten iron and the types of defects vary depending on the shape of the castings, i. e. the form of heat center and temperature gradient in castings.

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  The authors made experiments on producing cast iron with cast-in-steel inserted, which is coated with machine oil, red lead, water glass and silicon powder, or with such cast-in-steel as is covered with oxidation scale or hydration scale inserted. The results obtained are as follows : —
  1. In all cases, the results are worse than in case of using naked and polished steel cores.
  2. Worse adherent conditions were shown, in particular, when steel-cores coated with machine oil, red lead or water glass were used.
  3. While it has been a general method to use machine-oil coated cores to prevent blow occurence, it proved to be a bad one by our experiment.

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  Saitama pref. possesses some of better deposits of green sand found in Japan. Their distribution favours certain restricted areas. They have been obtained along the river from Kawaguchi to Misasa. The results of fundamental studies on Kawaguchi sand obtained are as follows.
  The difference of grain distribution ranging from 100 to 200 mesh was recognized by the position of the sand stratum.
  Kawaguchi sand has better uniformity in both grain size and alkali content, which is improved in quality by sand preparing remarkably. While raw Kawaguchi sand shows 430 g/cm² in green compressive strength, the sand after preparing shows 785 g/cm².

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  Spectrographic analysis method is well adapted for the determination of segregation, and taking its benefits the investigation of segregation was made on various kinds of alloys by the local spectrographic analysis method.
  As has already mentioned in reports 1∼5, it has been clarified that the segregation in castings is very complex due to the combination of both normal and inverse segregations in a single castings.
  Such a complicated segregation should be expressed by a concentration vs. distance segregation curve.
  The shape of the segregation curve can be regarded as representing a segregation pattern.
  Through the investigation of the theoretical or constitutional pattern of normal and inverse segregations, it has been revealed that the shape of segregation curve may make a considerable change with various conditions of solidification of the castings not only with cooling rate of alloy.
  In order to substantiate the theoretical mechanism of the forming segregation pattern, the basic experiment on segregation was conducted this time.
  The solidification process of the samples was completely controlled. Four kinds of samples solidified at the different travelling rate of solidification were prepared.
  Aluminium of 98.65% purity was used for the preparation of the samples and segregations of the four elements such as copper, magnesium, iron and silicon were determined.
  The gists of the results are as follows :
  (1) Both inverse and normal segregations were pronounced in the first and last regions to solidify.
  (2) Inverse segregation can be occurred in slowly cooled castings of the alloy having a relatively narrow range of solidification.
  Datails of experiments and theoretical considerations to the results are given in this paper.

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