In recent years, thin wall spheroidal graphite cast iron has been increasingly looked forward to reduce the weight of industrial products. Suitable evaluations of tensile properties are necessary for realizing practical application of this material. Standard test pieces with a diameter of 14mm are usually used for the tensile tests of spheroidal graphite cast iron, however they cannot be obtained from thin castings. To resolve this problem by using thin plate test pieces for testing instead, this paper studied the equivalence between evaluation by the thin plate and that by the standard test piece, both of which were taken from the same block samples. The results of the tensile tests showed that the influence of cross-section shape on tensile strength, 0.2% proof strength, and breaking elongation was quite small and negligible, while the elongation varied depending on measurement methods and gauge length. The larger the gauge length, the smaller was the elongation. The gauge length was set according to the equation L₀ ＝ 4√A₀, based on the similarity rule of Barba, where A₀ is the primary section of the test piece, to match the elongation of thin plate test pieces with standard ones. Moreover, the length of interspaces between butted fracture surfaces was not negligible in the measurement of the elongation. The breaking elongation was defined as plastic elongation obtained from the breaking point of the stresselongation curve without including the length of interspaces. In addition, the relation between Rockwell and Brinell hardness of ductile cast iron was found to correspond with that of steel by SAE J 417. The tensile strength of thin wall ductile cast iron can be estimated by Rockwell hardness, which can be used to measure the hardness of thin wall samples.

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  Flake graphite cast iron containing aluminum is known as a heat-resistant material. Heat-resistant material normally undergoes various temperature changes during service. It is known that flake graphite cast iron containing more than 6mass% of aluminum shows excellent heat-resistant property. In this research, the surface and microstructure of flake graphite cast iron containing 6mass% aluminum oxidized at elevated temperature were investigated.
  Flake graphite cast iron containing 6mass% aluminum was heat-treated in air at the temperature combination of 1073K and 1273K. The surface conditions and microstructures were examined by optical microscope, SEM and EPMA. Alumina precipitated at the positions where graphite existed during heat treatment. Internal oxidation advanced inward more rapidly at 1073K than at 1273K. Once, this cast iron was heat-treated at 1273K in air, internal oxidation did not easily advance inward by the next heat treatment, indicating that the heat-resistant property of this cast iron can be improved by simple heat treatment.

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  It is well known that the changes in added resin ratio affect mold compression strength. The results of this test show that changes in sand grain distribution also change mold compression strength. The influence of sand grain distribution change on mold strength was discussed by studying the changes in apparent specific gravity, permeability, and other elements which depend on characteristics of the contact point between sand grains.

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