In order to clarify the quenching crack phenomenon in cast steel, a disk shaped low alloy cast steel specimen with an opening was quenched in water at 1123 K. The generation of quench crack was studied by microstructure observation and analyzed by heat treatment simulation. The results obtained were as follows. (1) Quenching cracks form easily as the specimen volume increases. Quenching cracks occur due to time lag in martensitic transformation at the surface side and inner side of the quenched specimen. (2) Minute quenching cracks occur first at the boundary, alter which each microcrack joined together and grew into a maincrack. (3) Moreover, the quenching crack showed a very sharp grain boundary fracture, and since the grain boundary strength was lower than that in transgranular, quenching cracks of low alloy steel casting materials are considered due to martensitic transformation stress in that mid and high temperature regions. (4) Heat treatment simulation showed quenching occurs at maximum principal stress concentration positions. The stress concentration location and quenching crack position are influenced by specimen shape. (5) Quenching crack generation was demonstrated by the heat treatment simulation, clarifying that the crack is generated not by heat stress but by martensite transformation stress.

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  The relation between crack nucleation and stress-induced martensitic transformation in retained massive austenite (RM-γ) of austempered ductile iron (ADI) was examined in detail by means of tensile deformation tests and SEM observations for an ADI material. SEM observations revealed that cracks were not nucleated on boundaries between spheroidal graphites and matrix, but in RM-γ. Surface relieves due to stress-induced martensitic transformation were observed in RM-γ near the cracks. Surface relieves were also observed in RM-γ in which cracks were not nucleated. Consequently, the cracks were concluded to be nucleated in RM-γ subject to stress-induced martensitic transformation.

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  Bismuth-bearing bronze alloy is drawing attention as a lead-free copper alloy substitute for CAC406 alloy. Effects of the bismuth content and cooling rate on the casting structure and mechanical properties of bronze alloys were investigated. The decrease in the liquid us line reduced with increasing bismuth content, resulting in a large change in the alloying components such as zinc and bismuth. The bismuth content of 3 mass% is appropriate for controlling composition and obtaining a good castability under the same casting conditions as CAC406 alloy. Small pores are formed in the bismuth-bearing bronze alloy. The amount of pores was found to increase with increasing bismuth content. In addition, higher cooling rates of the alloy during casting diminished the amount of pores and increased bulk density. Uniform dispersion of fine bismuth particles (about 10 μm) and grain refinement led to higher strength and higher elongation of the alloy. A 3 mass% bismuth-bearing bronze alloy of 2 mm in thickness showed more than 50% elongation and 300 MPa tensile strength.

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  Cast irons with hard phases such as steadite and cementite have been widely used for cylinder-liners of marine engines. The hard phases are formed due to the addition of P or B, and their morphology strongly influences, sliding properties (scuffing resistance, wear resistance, etc.), machinability and mechanical properties. In order to understand metallurgical features, the effects of small amounts of P and B on the formation of the hard phases were discussed using cast iron with 3.3%massC, 1.3%massSi, 0.8%massMn, 0.05%massS, and 1.4%massCu. Microstructural observation, SEM/EDS or SEM/WDS quantitative analysis, and volume fraction measurement of hard phases were performed. From the experimental results it was found that P leads to the crystallization of steadite, while B leads to that of cementite. This work also discussed the morphology of each hard phase and the mutual dependence of P and B when cast iron contained both elements. As for the volume of the hard phases, the establishment of a quantification method is also desirable from an industrial point of view. The relationship between the volume fraction of the hard phases and P and B contents was investigated, and it was clarified that the volume fraction of steadite and cementite increases with an increase in the P and B contents respectively. The feasibility to predict the volume fraction of these phases as a function of the P and B contents was also evaluated using Shceil's equation.

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  We have developed a high vacuum die casting technique using horizontal clamping vertical squeeze casting machine and applied this technique to the mass production of a suspension parts for a sportscar. This technique principally consists of steadily evacuating air in the die cavity using a new shutoff valve and closely sealing the gaps of the die parting planes by a new sealing method. By this method, sufficiently high vacuum condition under 3KPa was obtained in a cavity. Moreover, since the quality of molten aluminum remarkably affects the occurrence of cracks by severe plastic deformation during the clinching of the ball joint part for fixing parts, we developed a new system of pouring from bottom of the ladle to prevent air entrapment in the molten aluminum, etc.

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