This study aims to research and develop applications of alloy tool steel (SKD11) castings with high C and high Cr, manufactured by the investment casting process. We systematically investigated the influence of amount, morphology, and distribution of M₇C₃ and/or MC type carbides on mechanical properties such as tensile and bending strength, elongation, and hardness. The steel castings were melted in a high frequency induction furnace, and melts varying from 0.3mass% V to 10mass% V were cast into an alumina mould 14mm in thickness, heated to 1,373K. With increasing V content, crystallized carbides in the castings were found to increase and change from plate-like eutectic M₇C₃ type to granular MC type, crystallizing randomly owing to stronger stabilization of the carbide of V than Cr. The hardness of quenched and subsequent tempered castings with 10mass% V was lower than that with less than 5mass% V. Because most of the C in castings with more than 5mass% V is used to form MC type carbide, there is a lack of C content in the matrix to maintain good hardening ability as a result of martensite transformation during quenching. The castings with 1.8mass% C and 5mass% V modified by increasing the C content according to amount of V added was found to exhibit higher strength and hardness than those with the SKD11 composition. Fracture crack was observed to propagate continuously along the M₇C₃ type carbide, suggesting that higher strength can be obtained by dispersing or separating continuous carbide.

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  Gravity die casting of AC4C aluminum alloy with mechanical vibration (0-120Hz) was conducted. Columnar rod specimens (Φ25mm × L210mm) were cast to investigate the effect of mechanical vibration on cooling rate. The cooling rate of the alloy melt increased by imposition of mechanical vibration, and increased with an increase in the vibration frequency. By imposition of mechanical vibration, the mold temperature increased quickly and reached higher temperature. The surface roughness of rod specimens cast with mechanical vibration was about 30μm (bottom of the rod) to 20μm (top of the rod), markedly more rough than that of specimens cast without vibration (20μm (bottom) to 11μm (top) ). When the vibration frequency was more than 80Hz, the scattering of surface roughness reduced, indicating the scattering reduction of the air gap layer.

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