High temperature compressive strength and Vickers hardness as well as bending strength at room temperature were measured on high C high speed steel type alloys (HCHS) and high Cr cast iron. As the temperature rises, the compressive strength and hardness fall in every specimen. The strength of HCHS maintains a higher level up to 823K, while the strength of high Cr cast iron lowers significantly over 773K. In HCHS with 5% Co, higher strength is kept even at 873K. Both the addition of Ni and precipitation of graphite reduce the strength of HCHS, while W shows little influence. The compressive strength is proportional to the hardness at 293∼923K. Co raises the bending strength of HCHS too. Since the crack propagates along eutectic M₂C carbides, to control the distribution of M₂C carbide is also important for getting the high strength. The distribution as well as the amount of M₂C carbide are dependent on Mo and W contents.

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  The Partial Melt Treatment Process was developed by the authors. A plate-like mold cavity was separated into a reaction chamber and product cavity by a thin dam. The alloy of FeSiMg alloy for spheroidization of base molten metal was prepared in the chamber. The base molten metal was poured up into an ingate from the bottom of the product cavity. A part of the molten metal flowed into the reaction chember over the dam. After spheroidization reaction in the chamber, spheroidized molten metal counterflowed over the dam and filled the upper part of the whole cavity. As a result of flow and replacement of both melts, a transitional graphite structure layer from spheroidal to flake downward was formed in the product. The effects of dam height, reaction chamber shape and treatment alloy on the quantitative control of the graphite layer ratio in the product were investigated.

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  Using a thermal analysis system consisting of three cups, the eutectic graphitization ability (ΔT₁/ΔT_E) which shows the melt quality was investigated. From the viewpoint of graphite type and the tensile strength, it was tried to verify that this ability serves as a useful a good value for evaluating the quality of cast iron. Various composition melts were inoculated and held in a furnace, after which they were cast at various fading times into three cups (First : Inoculated, Second : Base melt, Third : Tellurium added) and transverse test bar mold (φ30×500mm). Using the cooling curves of eutectic temperature obtained by three cups, eutectic graphitization ability was calculated and the relation between this ability and graphite types and mechanical properties was investigated. A good relationship was found between eutectic graphitization ability and graphite types, excepting for Ti added melts. And this ability is well related to tensile strength. Compared to the degree of normality which is suggested by Patterson, the eutectic graphitization ability is much better in predicting the quality of cast iron.

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  Aluminum matrix composites materials are utilized in many products such as the brake rotor etc due to abrasion resistance and light weight. However, several problems such as uniform dispersion of particles, machinability, reclamation have been occurred during the fabrication process of metal matrix particulate composites. Intermetallic compounds such as NiAl are suitable candidates for use as dispersoids for the purpose of resolving these problems due to the hardness, high temperature resistance and better wetting properties. In this study, aluminum alloy matrix composites dispersion strengthened by the addition of NiAl intermetallic particles were prepared by homogeneously mixing the dispersoid into the melt by a novel technique just prior to die casting. The mechanical properties such as tensile strength and elongation were obtained. Dissolving tests of NiAl dispersoids into aluminum alloy by stirring and melting the composites were conducted to investigate whether they can be used for reclaimed alloys.

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  With applying ultrasonic vibration the refinement mechanism of primary crystals in Al-Si alloy isothermally maintained at a semi-solid state was examined. The mechanical destruction of primary crystals and promoted formation of solidification nucleus have been considered as a refinement mechanism of ultrasonic vibration. It was confirmed that the application of ultrasonic vibration dose not cause the segmentation of grown primary dendrite crystals of the hypoeutectic Al-Si alloy by EBSD analysis. Neither is the case for primary Si crystals in hypereutectic Al-Si alloy. No particle size changes were detected by SEM observation and a coulter counter method of Si powder in water, when the ultrasonic vibration was applied. Refinement of primary crystals by ultrasonic vibration during solidification hardly depends on the mechanical destruction due to vibration energy. It was, therefore, concluded that both the molten metal vibration and the large acoustic stream formed in molten metal are considered to promote the nucleation and mechanical segmentation of primary dendrite crystals immediately after their nucleation.

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