In the previous report-"On the Solidification Process of Mg Cast lron"-the author studied the effect of Mg on the solidification process of Fe-C system. In this paper the experiments of the effect of Si on the solidification process of hypo-eutectic Fe-C system were carried out. By some addition of Si eutectic graphite structure, which never existed in Fe-C system, appeared by rapid cooling with or without ledeburite structure. Some relations were detected experimentaly between them, and the relations were seen over by the reference of Fe-C-Si system diagram. Lastly, a several changes of shapes of graphite except eutectic graphite are indicated briefly.

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  The suitability of foundry sand is assessed by the feel of the sand as it is pressed and deformed in the hand. The foundry workers who have long experience considerably develope skill in the preparation and treatment of their sand.
  We take a proper quantity of the sand and ram up the specimen by the sand rammer and then take y₁ or y₁₀ as the height of this specimen which the number of blow is one or ten respectively and ε(%)=(y₁−y₁₀/y₁) × 100．
  The value of ε rises to the maximum and then falls as the water content of the specimen is increased. The water content which ε is about 12∼14% coincides with one which the above mentioned feel of the sand is most suitable for making a mould.

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  It appears reasonable that in a two phase alloy such as malleable cast iron physical properties might well be a function of the size of particles of the discontinuous phase. In order to determine the effect of nodule size of temper carbon on mechanical properties of malleable iron, the author firstly carried out a tensile test of perforated iron plates which had the constant perforated area but different hole diameters. Then, melleable iron specimens containing nodules of various sizes were tested. These bars were prepared from a same melt of white iron and given a different heat-treatment. In both cases, results showed that the finer the size of hole and temper carbon, the higher their tensile strength, elongation, and reduction of area were.

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  We have troubled ourselves about the pinholes of steel castings cast in green sand moulds, so studied the cause of the pinholes and made them clear to be in the relation to hydrogen gas.
  We made efforts chiefly to examine the influeuces of green sand factors on the pinholes, casting the samples of molten steel in various conditions of green sand moulds. And after analysed hydrogen gas of the samples, we checked up the fractures of them whether there were pinholes or not.
  The results obtained are as follows.
 1) It's proved that the pinholes of green sand mould castings are caused by hydrogen gas when it is contented over 8 cc.⁄100 gr. in the cast samples.
 2) When the clay % of green sand is 12% and moisture % is varried from 5% to 8%, hydrogen gas in cast samples increases with the increase of moisture, and the increased amounts are under 2 cc.⁄100 gr.
 3) When the moisture of green sand is 5% or 7%, and clay % is varried from 11% to 17%, hydrogen gas is most contented in the samples at about 15% of clay.
 4) Hydrogen gas shows some increases with the decrease of permeability from 400 to 140 A. F. A.
 5) The relation among moisture, clay and pinholes is cleared, and 5% moisture and 12% clay of green sand are standard % in order to get sound steel castings.
 6) The samples cast in green sand moulds are (3 c.c. ⁄ 100 gr hydrogen gas) more rich than samples cast in a copper mould from a ladle. Therefore the hydrogen gas in molten steel just before tapping must be kept under 4 c.c. ⁄ 100 gr, considering the increase of 1 c.c. ⁄ 100 gr during the interval from the furnace to the ladle.

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