The temperature dependence of fatigue life from room temperature to 500°C was investigated by push-pull low cycle fatigue test in flake and spheroidal graphite cast irons. It was found that fatigue life of flake graphite cast iron was not dependent on temperature. But that of spheroidal graphite cast iron at total strain amplitude decreases with increasing temperature until it becomes minimum at 400°C and then reverts back again to its original life at 500°C. Therefore, the fracture condition taking the temperature dependence into account is also studied.

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  The relation between graphite shape and stereological parameter in spheroidal, compacted vermicular, flake and eutectic graphite cast irons was investigated using the texture analysing system. The analysis of standard structure diagrams relating to shape and dimension of graphite by Everest was carried out. Stereological parameters used in this study were surface area per unit volume (S_V), mean surface area of one particle per unit volume (S_VP) and three dimentional mean free distance (λ). It has been shown that these parameters relate to various graphite shapes. Therefore, graphite shape was quantitatively classified by stereological parameters. S_V has characteristic ranges corresponding to various graphite shapes. S_V of compacted vermicular graphite was 0.035 to 0.060μ⁻¹, compared to which the values of spheroidal graphite was lower and flake graphite was higher. S_VP and λ also have characteristic ranges.

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  The metal-mold interface reactions in steel casting were investigated by bringing sodium silicate-bonded mold of silica sand, olivine sand, zircon sand and chromite sand into contact with steel on the surface of which FeO was formed in mixed gas atmosphere of CO and CO₂. In these different sand molds, the reaction depth h is related to the reaction time t by the following equation; h²=Kt−α, where K and α are constants. And the steel-mold interface reactions are determined by the formation rate of FeO at steel-mold interface.

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  The mechanism of the remarkable expansion during tne austenitizing of ferritic cast irons has been studied dilatometrically and theoretically varying the silicon content and graphite shapes. The expansion tends to increase with decreasing silicon content and raising temperature. It also increases as the graphite shape becomes more spherical. According to the calculated results, the expansion occurs when more carbon than Ce dissolves in the austenite, and the amount of this expansion is proportional to the difference in the carbon content in the austenite, (C₂−C_e), at given temperature: where, C_e is the carbon content dissolved in austenite when the specific volume is equal to that of ferrite, and C₂ is the maximum carbon content dissolved in austenite. The calculated result coincides fairly well with the experimental result in spheroidal graphite cast iron. A further discussion taking the effect of graphite shape into consideration indicates that the graphite becomes porous in austenitizing, and that the amount of vacant space formed between the graphite and matrix depends on the graphite shape, where it is larger in spheroidal graphite than in compacted vermicular and flake graphite. Consequently, it has been proved that the expansion results from the volume increase of the matrix and generation of vacant space.

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