Four kinds of multi-component white cast irons with different combinations of carbide type were poured into furan molds with different diameters, and cooling curves were taken using a R thermocouple inserted at the center of each mold cavity. The microstructural components in as cast iron, such as γ dendrite arm spacing (D_p), diameter (D_MC) of MC carbide, lamellar spacing (λ_M2C) of M₂C carbide, area fraction (S_eut) of (γ + M₂C) eutectic or that of both (γ + M₂C) plus ( γ + M₇C₃) eutectics, were well related to each characteristic cooling rate, while the area fraction of MC carbide was little affected by the cooling rate. The relations are expressed by, D_P = 25.1 ⋅ V_P^-0.36 (V_P : cooling rate during precipitation of primary γ ), D_MC = 4.4⋅ V_E-MC^-0.18 (V_E-MC : cooling rate during precipitation of ( γ + MC) eutectic), λ_M2C = (1.1∼2.0)⋅V_E-M2C^{-0.28∼-0.21} (V_E-M2C : cooling rate during precipitation of (γ + M₂C) eutectic, S_eut = (2.0∼15.3)⋅V_A^{-0.23∼-0.16} (V_A : average cooling rate from start to end of solidification)

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  The relationship between water embrittlement and the austempering temperature of austempered spheroidal graphite cast irons (ADI) with different graphite nodule diameters were investigated in this study. The following results were obtained. (1) Both the tensile strength and elongation of the ADI are decreased drastically, i. e. remarkable water embrittlement was observed when in contact with water. But the 0.2 % proof stress of ADI showed the same value with it in air. (2) The water embrittlement of ADI could be restrained by decreasing the diameter of the graphite nodule. (3) A white spot region regarded as the starting point of the fracture was formed on the fracture surface tested in contact with water. The range of white spot region showed the tendency that was increased with increasing the graphite nodule diameter. (4) The percentage reduction of the fracture energy was decreased with the increasing of austempering temperature under constant diameter of graphite nodule and the water embrittlement of ADI was restrained. (5) The remarkable water embrittlement of the ADI was thought principally by the martensitizing of unreacted retained austenite during tensile plastic deformation.

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  The microstructure and tensile properties of cast iron obtained by semi-solid casting were investigated under the conditions of chilled-cooling, air-cooling and furnace-cooling respectively. The primary solid particles decreased in size with stirring. The remaining liquid transformed into fine ledeburite structures under chilled-cooling. Fine graphite particles were found throughout the heat treated semi-solid cast iron specimens. The tensile strength and elongation of the specimens were 383 MPa, 3.4 % and 414 MPa, 4.1 % at the stirring speeds of 10 and 16.7 rotations per second over respectively. The tensile properties obtained by the semi-solid casting were improved comparing with the ordinary casting samples. The microstructure and tensile properties of semi-solid cast iron were found to differ considerably depending on the cooling conditions.

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  This paper presents a novel cast joining method of aluminum matrix composite (AMC) made by molten aluminum alloy to aim at manufacturing of partially reinforced components. Ultrasonic vibration was applied to resolve the main difficulties of the process such as an oxide film formed on the molten aluminum surface and pores appeared adjacent to the solidified interface, which prevent the joining pair from its soundness. In order to eliminate an oxide film and pores at the interface during the process, the application of ultrasonic vibration is required until the full remelting of the initially solidified aluminum alloy region due to the direct contact of the AMC. Ultrasonic vibration makes not only to accelerate the remelting, but also to disappear the thermal contact resistance between the joined portion. Resultantly, sound interface with high strength is achieved. The effects of the vibrational amplitude and cooling rate during the process on the soundness of cast joining are also discussed.

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  Fatigue tests were carried out on austempered spheroidal graphite cast iron (ADI) and ferritic spheroidal graphite cast iron (ferritic SG iron) to clarify the influence of exposure to water on fatigue strength. In wet condition, i. e. the test condition of exposure to water during testing, ADI and ferritic SG iron showed the same fatigue strength as that of irons tested at stress amplituds above the fatigue limits in air. While at the value of stress values below the fatigue limit in air, specimens of ADI and ferritic SG iron had no fatigue limit. Even though the number of cycles exceeded 10⁷ cycles, the fatigue strength decreases continuously. The decrease of the fatigue strength of ADI results largely from the preferential dissolution of acicular ferrite, which is induced by corrosion fatigue. Therefore, the fatigue strength of 10⁷ cycles for ADI exposed to water was reduced to 50 % of the fatigue limit 310 MPa in air. However, the fatigue strength of 10⁷ cycles for ferritic SG iron was decreased only 10 % from the fatigue limit 205 MPa in air, because there is no preferential dissolution of ferrite. On the other hand, specimens of ADI and ferritic SG iron dried after dipping in water for 480 hours, showed obvious fatigue limits, and the fatigue limits were reduced by 32 % for ADI and 25 % for ferritic ferritic SG iron than that tested in air. The reduction of fatigue limits results from the corrosion pits, which act like a notch.

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