Effects of heat treatment, aluminum, copper and magnesium content on the tensile strength, elongation and fracture toughness of Zn-27%Al-1%Cu-0.05%Mg alloys cast into metallic mold were studied. Specimens heat-treated at 365°C for 2 hrs, followed by air cooling result in 20 to 30% improvement in tensile strength with decreased elongation. Aging at 150°C for 20 hrs causes a decrease in tensile strength by 20% to 30% for as-cast alloys and alloys heat-treated at 365°C for 2 hrs, followed by water quenching. Heat treatment at 365°C, followed by water quenching resuls in about 13% decrease in fracture toughness for as-cast alloys. However, heat treatment at 365°C, followed by air cooling and aging at 150°C for 10 hrs dose not lower the fracutre toughness. Tensile strength (about 40 kg/mm²) for as-cast alloys is independent of aluminum, copper and magnesium content which is 15∼31%, 0.3∼3%, 0∼0.2% respectively. Above 0.1%Mg, there is rapid decrease in elongation.

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  Ten percent slip-rolling contact tests for spheroidal graphite cast iron and 0.4% carbon steel were carried out with lubrication in order to examine the effect of graphite on surface spalling. Spheroidal graphite cast irons of varying hardness value, H_B 143, 174 and 262, and annealed 0.4% carbon steel with a hardness of H_B 140 were used as test pieces. It was found that the rolling fatigue limit of spheroidal graphite cast iron, the Haztzian stress without surface spalling at 10⁷ revolutions, increased linnearly with increasing hardness. At the same hardness level, the rolling fatigue limit of spheroidal graphite cast iron is lower than that of 0.4% carbon steel. Cracks are initiated from the spheroidal graphite on the rolling surface and propagate via graphites in the bulk. It is considered that graphite in the matrix dose not improve the rolling fatigue limit even though it decreases friction.

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  The purpose of the present work is to clarify and consider in detail the effect of oxidation on the growth of spheroidal graphite cast iron by investigating the whole structure up to 10% linear growth in air. (1) The diameter of the iron decreased gradually due to the formation and loss of the oxide scale by repeated heating between room temperature and 950°C in air. (2) The grown iron has a four layer structure: the outer layer is composed of pure iron oxides; the second layer, ferrite; the third, pearlite, and the central area is composed of pearlite and ferrite. Each layer increased in its thickness with the progress of repeated heating except the central part. (3) In the primary growth stage of the iron, the oxidizing atmosphere formed only a slight oxide and decarburization layer. But the atmosphere gradually penetrate into the inside starting from 4% linear growth. (4) As the supply of oxygen became smaller from external atmosphere to the third layer, the atmosphere formed with the reaction of porous graphite nodules turned carburizing rather than oxidizing and denser pearlite was formed due to the carburizing phenomenon during cyclic heating. (5) No effect of oxidation was observed in the central area of the iron even after 10% linear growth. A metallurgical behavior was shown on the dilatometric curves. Furthermore, the tensile strength retained was 43.5 kg/mm² compared to 55.6 kg/mm² of the as-cast iron. This may be the result of the oxygen being consumed to form a carburizing atmosphere in the third layer, eliminating the effect of oxidation at the center. (6) Except for the extreme outer layer, redistribution of graphite and diffusion porosity due to graphite migration were observed by the scanning electron microscope but the spheroidal graphite nodule in the outer layer affected strongly by the external atmosphere lost its shape and the internal surface of the cavity became smoother.

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  The fatigue limit was shown to be highest in spheroidal graphite cast iron and lowest in flake graphite cast iron whereas compacted vermicular cast iron took the value between the two. Even if these values changed due to matrix structure, when considering the large difference of tensile strength in the microstructure, the fatigue limit can be accounted as the same value. In the crack propagation test, at the same ΔK level, crack propagation rate was high for flake graphite cast iron, low for spheroidal and medium for compacted vermicular cast iron. When considering the differences in these values within the matrix microstructure, crack growth rate in ferritic matrix was higher than in as-cast condition and pearlitic matrix. Furthermore, the acoustic emission can be used to monitor the propagation of fatigue crack which characterized the difference in the matrix microstructure of the spheroidal graphite cast iron.

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  A hypo-eutectic Fe-C-Si alloy was melted in a Tammann furnace and inoculated with Ca-Si alloy or oxidized with Fe₂O₃ powder after which it was cooled slowly in the furnace or rapidly in water. Chilling test pieces were also taken and a quantitative observation was made on the shape and distribution of primary austenite. Solid models of primary austenite were built from the test pieces and the dendritic structures were observed three-dimentionally using those models. Dendritic structure in Ca-Si inoculated iron is not very much affected by the cooling rate, and the dendrite size and distribution are uniform. Dendritic struture in oxidized iron becomes extremely fine with rapid cooling, but becomes extremely coarse with slow cooling. Almost every dendrite element seen in microstructures is three-dimentionally connected with each other.

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  Thermal fatigue test of two kinds of gray cast irons, FC25 and FC15 was carried out under completely constrained strain at constant mean temperature. The selected mean temperature was 300°C, 400°C and 500°C for FC25, and 400°C for FC15. The effect of the initial temperature of test pieces on the thermal fatigue life was investigated. The relation between experimented data and low cycle fatigue was considered. It was shown that thermal fatigue life could be estimated from the low cycle fatigue at the mean or upper temperature. Difference in life between FC15 and FC25 was not noticed. Thermal fatigue life of gray cast iron was not effected by the strain ratio.

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