To study the influence of melting and pouring temperatures upon the chilling tendency of permanent mold cast iron, plate shaped specimens of 20mm in thickness were poured into a metallic mold coated with acetylene soot and preheated at 150°C, and their hardness and microstructures were tested. Irons of Sc 1,04, 0.95 and 0.89 were melted in a high frequency induction furunace with alumina crucible. The melting temperatures were 1,500°C, 1,450°C and 1,400°C and the pouring temperatures were 1,400°C, 1,350°C and 1,300°C.
  The results obtained are as follows :
  1) Chilling tendency increases with increasing melting temperature. Chill depth is especially large when the melting temperature is 1,500°C.
  2) It is considered that the above mentioned phenomenon is due to the fact, which is established in sand mold casting, that the superheating of molten iron limits graphitization during solidification.
  3) Chiling tendency increases with increasing tapping temerature.
  4) This phenomenon is caused by the cooling velocity at solidification; cooling velocity increases with the increase in the temperature difference between the iron and the metallic mold.
  5) From the above mentioned results, it may be said that low temperature melting and low temperature pouring are recommended in order to prevent the chill of permanent mold cast iron.

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  An experiment was conducted to investigate the correlation between the shapes of external shrinkage defect and the expansion curves measured during soldification of the 75mm spherical test castings produced by the shot-backed and the metal-backed shellmolds using hypereutectic spheroidal graphite cast irons of different carhon equivalent.
The results were as follows :
  (1) In conventional shellmolds which are not as rigid as the metal-backed shellmolds, the test castings presented a marked expansion immediately after the pouring, and as the eutectic solidification proceeded the degree of expansion gradually decreased. Gross cavity was formed on the top surface of the castings at an early stage of solidification which expanded by the enlargement of the casting during eutectic solidification, but there were no purged plug observed in the cavity.
  (2) In metal-backed shellmolds which are more rigid than shellmolds, the resulting test castings initially contracted due to liquid contraction which was subsequently followed by expansion during eutectic solidification, resulting in smaller shrinkage defect and smaller overall expansion of the casting compared with those obtained by the shellmolds. Perfectly sound castings were sometimes obtained by the metal-backed shellmolding process. In this case, the earlier the initical contraction was completed and the smaller the contraction accompanied by the greater eutectic expansion, the sounder the castings were. In contrast to this the later the initial contraction was completed and the greater the contraction accompanied by the less eutectic expansion, the more unsound the castings with purged plugs in initially formed pipes were.
  (3) It was found that there is a significant correlation between the shapes of external top surface shrinkage and the changes of the test casting diameter during solidification.

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  Troubles in the foundry industry, such as pinhole-problems, have been solved by depending on traditional experience or intuition of field engineers.
  An algorism for automatical solution of such troubles was formulated based on a diagnostic model derived from statistical analyses.
  The algorism was applied to the solution of pinhole-problems in spheroidal graphite cast iron. Several-teens factors which were picked up as the principal causes of pinholes from the analyses were well consistent with the metallurgical knowledge on countermeasures for removal of pinholes in the products.

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  Cast iron for high temperature use grows by repeated heating and as a result weakens and fails easily. Another characteristic change due to growth is the decrease of thermal conductivity. The decrease of thermal conductivity adversely influences the thermal efficiency of an apparatus. Moreover, the change of temperature gradient within the material due to the decrease of conductivity will increase thermal stress and weaken the iron indirectly by thermal shock and thermal fatigue.
  Thermal conductivity of grown cast iron was measured with rod specimens set horizontally in still air with one end contacting the heat source. Axial temperature distribution by natural cooling was measured and the relative value of conductivity was calculated. For the experiment, six specimens of grown flake graphite cast iron were prepared by cyclic heating to 950°C in air. The linear growth of specimens was from 2% to 9% by heating of 10 and 50 cycles respectively. Specific weight, hardness and microstructure were alse examined.
  Results may be summarized as follows;
  1. The thermal conductivity of cast iron decreases continuously with growth, and it was about 50% of as-cast iron when the liner growth reached 8% by 40 cycles of heating to 950°C.
  2. With more than 50 cyles of heating, the decrease in thermal conductivity slowed down and showed a tendency of saturation.
  3. The decrease in thermal conductivity of grown cast iron is mainly due to the porosities caused by growth, and the graphite flakes changing to porosities acting as barriers for thermal current.
  4. Changes in microstructure such as ferritization and graphite-redistribution may also have some effects on the thermal conductivity.
  5. On the other hand, since the conductivity of a specimen held at 950°C for 25 hrs. in air was not remarkably reduced, the influence of oxidation will not be as important as repetitive heating.

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  Strength against fatigue is one of the most important factors in using a material under repeated stress. In considering the fatigue strength of spheroidal graphite cast iron, the influences of the matrix structure and the graphite structure must be taken into consideration. as the first step in our study the influence of pearlite content on the matrix structure was investigated. The chemical composition of the s. g. cast iron used here was: C:3.60%, Si:2.80%, Mn:0.18%, P:0.041%, S:0.012%, Cr:0.02%, Mg:0.038%. Nine variations to the pearlits content was used ranging from all pearlite matrix to all ferrite matrix by changing the conditions of heat treatment.
  The fatigue strength and other mechanical properties are shown on Table 1.
      Table 1 Mechanical Properties
[Written in non-displayable characters.]
From the results of the experiment the author obtained the following conclusions.
  1) The tensile strength and hardness increase in proportion to the increase in the pearlite content.
  2) The elongation and impact strength measured at room temperature decrease with the increase in the pearlite content up to 50% but become constant after the 50% mark is passed.
  3) Rotation bending fatigue limit was obtained for fatigue strength. Two kinds of specimens were used: the unnotched specimen (with a diameter of 8mm) and the notched specimen (with a radius of the notch of 1mm). The relation between fatigue strength and pearlite content is shown on Fig. 1. The increase in fatigue strength is proportional to the increase on the pearlite content between 23 kg/mm² (ferrite matrix) to 32 kg/mm² (pearlite matrix). However, on closer observation of the changes, it was found that the increase in the fatigue strength was smaller in the pearlite content range between 20% and 8% compared to other ranges. This range corresponds to the range of bulls' eye structure under microscopic observation. This observation can be explained on considering the fact that the fatigue phenomena is two fold i.e., the start of a crack and its propagation.
  4) The fatigue notch factor of pearlite matrix is equal to that of ferrite matrix both being of minimum value.

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