In 1962, the American Foundry Society (AFS) proposed classifying the graphite morphology of cast iron into morphology I (flake graphite), morphology II (graphite with sharp tip), morphology III (quasi flake graphite), morphology IV (lump graphite), morphology V (irregular spheroidal graphite), and morphology VI (spheroidal graphite). Furthermore, the American Society for Testing and Materials (ASTM International) proposed that morphology I (flake graphite) should be classified into A type, B type, C type, D type, and E type. Graphite in flake graphite cast iron is generally evaluated by morphology and not numerically. In this study, we proposed K-FGI, which is an index showing the number of graphite grains with an average diameter of 5 μm or more. For graphite of 50 μm or more and less than 150 μm, we propose the degree of thickness-thinness (hereafter abbreviated as DTT) as an index showing the thickness of graphite from the relationship between the graphite area and length of the maximum diameter. As the category of minimum graphite size increases, the number of graphite decreases. The degree of thickness-thinness decreases with increasing illuminance.

  The microstructure of graphite in gray cast iron is generally evaluated according to ISO-945 and not calculated numerically. On the other hand, K-FGI (KIRIU-Flake Graphite Structure Index) which is a measure of the number of graphites, and DTT (Degree of thickness - thinness) which is a measure of the thickness of graphite, was proposed by H. Ichimura. However, with these indices, there were some variations in the results depending on the measurement equipment and conditions even when the same graphite microstructure was measured. In this study, we propose a method to reduce the variability of K-FGI measurements by setting a reference value using general-purpose software and a master chart (micro-patterned pseudo-graphite structure). In order to confirm the effect of adjusting the microscope using master charts, two types of real-microstructural specimens were measured by seven organizations participating in the Graphite Shape Quantification Study Group of the Japan Foundry Engineering Society. The results of the measurements show that the dispersion of K-FGI is within ± 10%, the dispersion of DTT is within ±25% of the average.

  Mechanical, physical, and electrical properties of cast iron are greatly influenced by the morphology and distribution of graphites. The microstructure of graphite in flake graphite cast iron is generally evaluated according to ISO-945 and is not calculated numerically. On the other hand, K-FGI (KIRIU-Flake Graphite Structure Index) which is a measure of the number of graphite, and DTT (Degree of thickness - thinness) which indicate a measure of the thickness of graphite, was proposed. In this study, the relation between the tensile strength, Brinell hardness, and thermal conductivity of flake graphite cast iron and K-FGI, degree of thickness-thinness were investigated. There were a correlation between degree of thickness-thinness, tensile strength, hardness, and thermal conductivity. The tensile strength of cast iron depends on the continuity of the matrix due to the distribution of graphite. Therefore, as the degree of thickness-thinness increased, the tensile strength decreased. As the degree of thickness-thinness increased, Brinell hardness decreased. As the degree of thickness-thinness increased, the thermal conductivity increased.

  Thermal analyzer was manufactured using a data logger with a resolution of 20 bits. With this thermal analyzer, cooling rate curve, which is differential curve, can be calculated for measured cooling curve without moving average processing, and accurate inflection point and its occurrence time can be captured. The difference between the cooling curve and zero curve measured by this device was taken as the amount of latent heat released by solidification, and amount of latent heat released by solidification at each phase was quantified. There was correlation between graphitization ability and amount of latent heat released during the graphite growth phase. It can also be estimated that there is a correlation between K-FGI, which quantifies graphite structure and graphitization ability. The quantifying amount of latent heat released from solidification seems to be a useful method for identifying the properties of molten metal.