The occurrence and propagation of cracks during solidification of the alloy is an important problem in the casting. Hot tearing is rather common but is one of the serious defects in aluminium alloy and in steel castings. As hot tearings are supposed to occur only when the stresses produced in the casting exceeded the strength snd ability to deform in hot tearing temperature range, several kinds of investigations were done in aluminium and in aluminium-copper alloys in order to establish a correlation between the contracting stresses and metallurgical and mechanical properties which lead to hot tearing.
  An apparatus for measuring the contracting stress during solidification and the load necessary to break the casting at high temerature was set up and it was recorded by means of automatic null balance recorder connected to a strain gauge on the rod. These data were then correlated with the hot tearing behaviour observed under the condition restrained contraction. Moreover, the effects of Ti as a grain refiner and Sn as an impurity were investigated and discussed.
  The results of these experiments can be summerized as follows:
  1) The temperatues, at which contraction stress generates, approximately agree with the contraction beginning temperatures and they are different by the treatment of the melt.
  2) The larger the range of solidification is, the wider is the range of hot shortness, so hot tearings are apt to occur.
  3) Since the grain refinement with the addition of Ti lowers the temperature at which the contraction stress generates and increases the strength for temperature lowering, hot tearing unlikely occurs.
  4) The addition of Sn to Al and Al-5%Cu alloy decreases high temperature strength and increases hot tearing tendency.
  5) Although the healing phenomenon is recognized by the recovery of contracting stress, it was observed only by the microscopic examination that there was a partial healing depend on the freeging of residual melt flowed in to the cracks.

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  The heat absorption of casing mold is mostly inftueced by some thermal qualities of the molding sands.
It was clear that the Krischer's method and its extension were to be quite useful for investigating such qualitities of molding sands with moisture or at high temperature.
In this paper, we clarified the meaured values of heat transfer concerning some olivine sands, silicate sands, back sand, etc.,

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  During the graphite-austenite eutectic solidification of iron melt, the solute elements, such as manganese and sulfur, are rejected from growing eutectic as solute in the melt and are concentrated in retained melt. Consequently, when all sulfur in the iron exists as solute in the iron melt at the beginning of the eutectic solidification, the distribution of sulfur in the iron after solidification becomes a network, shown by a sulfur print, corresponding to the eutectic cells boundary. While, when a part of sulfur forms manganese sulfide suspended in the melt, the distribution of sulfur in the iron after solidification is random. On the basis of this phene-menon, the maximum amounts of manganese and sulfur as solute in iron melt at the eutectic temperature during solidification were measured by the change in the types of sulfur distribution in the gray iron with different contents of manganese and sulfur after solidification. These amounts obtained are in good agreement with those calculated from the solubility products given by an equilibrium experiment for the reaction, Mn+S=(MnS).

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  As a part of the study on hot tearing in white cast iron, the author took up five types of specimens, and investigated statistically the influence of various factors such as chemical compositions, melting and molding conditions, on their hot tearing. The characteristics of specimens which are called A-, B-, C-, D- and E- type are as follows.
A-type : Specimen whose contraction at the solidification stage and cooling stage followed, is restrained by mold.
B-type : Specimen which has abrupt change in cross-sectional area.
C-type : Specimen which resembles to that of C. T. Moore’s.
D-type : Shift fork for an auto-tricycle, partially modified to be more sensitive to hot tearing.
E-type : Specimen which is selected as typical types of castings containing disk-like or ring-like parts.
  In this paper the experimental results on the influence of carbon, silicon and boron on hot tearing occured in specimens were described, And the following conclusions were obtained.
  (1) Carbon is an element which has a great effect on hot tearing. But the way of its influence differs with specimen. To know the cause it is neceasary to investigate not only the degree of contraction and the conditions of restraint but hot temperature strength and feeding characteristics of side riser in relation to carbon content and the shape of castings.
  (2) Silicon has less effects on hot tearing than carbon. In B-, and D- type specimen, hot tearing tendency increases with increasing silicon content, but in E- type specimen the reverse effect is obtained.
  (3) In some specimen, the more quantity of boron is added to molten metal, the more hot tearing occurs.

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  An investigation was done on two problems in 800 kg low frequency induction furnace operation.
  The results obtained were summarized as follows
  (1) It was found that carbon contents of melt in the low frequency induction furnace were very variable by melting temperature, treating time, carbon pick up process and its control was most improtant.
  (2) On the carbon pick up, the effects of various factors upon it in melting operation was studied. It was found that the treating temperature and carbon contents of melt were referred to the carbon pick up especially, and these factor should be controled correctly.
  (3) On the speciality of the low frequency induction furnace melt, the measurement of Oxygen and Nitrogen contents in melt were done as well as mechanical properties, section sensibility, shrinkage property etc., and it was confirmed that the property of the molten cast iron which was melt in low froquency induction furnace was not inferior to that of Cupola.

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