The solidification mechanism of hypoeutectic cast iron treated with Mg has been investigated by the microscopic examination of specimens quenched in the cold agent at various stages of solidification and the time-temperature curve.
  Consequently, it was found that the solidification of Mg-treated hypoeutectic cast iron proceeded with the initial precipitation of primary austenite dendrites, is followed by the direct appearance of graphite nodules as the kish graphite at the liquid of the highest carbon concentration near the primary austenite dendrites in the supersaturated liquid, and the process of graphite nodule growth is the same as in Mg-treated hypoeutectic cast iron mentioned in the previous paper. And then in this paper, the author commented on the theories so far reported on this subject.

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  Mechanical properties of aluminium - silicon - zinc alloys for castings are closely conected with their composition or their micro - structure. These relations are detailed on several figures, as to pure alloys cast in sand or permanent moulds and alloys containing a modifying agent of 0.5 per cent chromium cast in permanent moulds.
  Larger contents of zinc along the eutectic line in the diagram increase the tensile strength, or α of aluminium - rich solid solution and eutectic silicon is the main variable on the strength. The hardness becomes higher with increasing contents of zinc & silicon almost regardless the eutectic line. Chromium addition to the alloys enlarges equi-strength ranges (25 kg / mm² and 30 kg / mm²) and equi-hardness ranges in the figures. The alloys cast in sand moulds give less tensile strength by 20 per cent and less hardness than the alloys cast in permanent moulds. Silicon contents in sand castings which give the maximum strength are less than in permanent mould castings. Such differences may be caused by structural changes of silicon with different cooling rate.

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  Cracking of the mould by drying depends upon the shrinkage of sand, water and clay under 400°C. Clay is the most important material and the too much use of clay and the too small are causes of cracking.
  Water content increases the clay shrinkage and the pressure of vaparized water promotes cracking.
  The use of a high temperature to increase the drying speed becomes a cause of cracking by a difference of the surface and internal expansion and shrinkage.

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  In drying of moulds emphasis must be placed on the uniformity of temperature distribution in the furnace as well as the economy in fuel.
  To this aim the author made experiments on two methods. The one is the recirculating combustion method of the exhaust gas (hereafter be referred to as the recirculating combustion method) which uses a part of the exhaust gas in the coal-fired furnace together with the combustion air, and the other is a method which recirculates and diffuses the exhaust gas in the combustion chamber by means of a blower (hereafter be called as the recirculating diffusion method.)
  The recirculating combustion method effected on an economy of coal by 35 to 40 per cent. This was due to the lowered igniting temperature resulted from the increase in the air temperature, the reduction in the loss heat of the exhaust gas, and the diminition of cinder.
  The uniformity of temperature distribution in the furnace, however, showed no difference from the old method.
  Since it could be realized simply and effectively by increasing the drying hot air quantity, the hot air was increased by recirculating and inducing the exhaust gas in addition to its simultaneous forced diffusion.
  The adoption of the recirculating diffusion method enabled a better uniformity of the temperature by reducing the temperature variation from 130∼100°C to 60∼90°C, but the consumption of coal increased due to the use of the low temperature exhaust gas.
  From the above experiments the combination of recirculating diffusion and recirculating combustion (hereafter be called as the recirculating diffusion combustion) was employed to obtain a better uniformity of temperature distribution in the furnace without increasing the consumption of coal.
  The moisture in the drying hot air was doubled by the recirculation of the exhaust gas without delaying the crying time. The drying of moulds became uniform, and the formation of cracks and adhesion of soot on mould surfaces were prevented.

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  Welding repair work on steel castings needs various special conditions which are different from those of welding work on general steel, and the researches on it are comparatively few.
    The author investigated the effects of two methods such as carbon arc welding and electcic welding repair work on the properties, especially the strength and microscopic structure of steel castings. Results obtained were as followings :
  (1) A. C. electric welding in the normal method can be effectively applied for both welding repair work and welding of steel castings. Welded steel castings are not inferior to a proper steel casting on the structure and mechanical properties.
  (2) Carbon arc welding repair work is a little inferior to A. C. electric welding on the strength, so it can be applied only for welding repair work of the parts which strength can be disregarded.
  (3) The fact that carbon arc welding is inferior on strength was recognized on the structure, and is influenced by nitrogen.

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