The effect of solitary addition of Mo, V and Nb and simultaneous addition of these elements on microstructure, hardness and impact strength in 16%Cr or 27%Cr cast iron was examined to evaluate the optimum service life under impact wear resistance. Cast iron with 16%Cr has martensite structure with K₂ type eutectic carbide at interdendrite region and fractured frailly. The absorbed energy was proportionate to the dendrite fracture ratio. In contrast, 27%Cr cast iron has a martensite structure with granular eutectic carbide, and coarse granular or hexagonal carbide in the boundary of the eutectic colony, and the absorbed energy was very low. Hardness of dendrite matrix decreased after the addition of Mo, but macro-hardness was not affected very much. The combined addition of 0.3%Mo and 0.1%V improved the impact characteristics without decreasing hardness. Addition of 0.15%-0.30%Nb alone and in combination with 0.3%Mo and 0.1%Nb improved the impact characteristics without sacrificing hardness.

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  A computer simulation program for axisymmetrical and three-dimensional thermal analysis of solidification of castings was developed allowing for the effects of metal flow and latent heat. The unsteady heat conduction was numerically analyzed using the finite element method. The calculated cooling curves agreed with those experimentally obtained for spheroidal and flake graphite cast iron specimens with the error between 10 to 30 percent. The location of shrinkage cavities of spheroidal graphite cast iron specimens and the size distribution of eutectic cells of flake graphite cast iron specimens were associated with the isothermal lines calculated.

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  Effect of microstructure on mechanical properties of test pieces of JIS AC4C and AC7A aluminum casting alloys, which-were cast into metal mold, were examined by a correlation analysis and multiple regression analysis using a biomedical computer program. Microporosity had a significant effect on ultimate strength, hardness and fatigue strength. The impact value was strongly affected by the number of eutectic compound and elongation was affected by micro-grain size and microporosity.

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  High manganese cast steel shows high toughness and high wear resistance values after work hardening, but it shows rather low hardness and poor wear resistance before work hardening. In order to get higher hardness of high manganese cast steel without work hardening, up to 0.28% boron was added to 13%Mn—2%Cr cast steel and the effect of boron on the mechanical properties and abrasive wear resistance of the steel were investigated. The hardness of high manganese cast steel was increased but the toughness of the steel was lowered by addition of boron and heat treatment after water toughening. Improvement of wear resistance of high manganese cast steel can be expected by selecting proper boron content and heat treatment in relation to the wear condition.

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  Shrinkage defect in steel disk castings of 25 mm thickness, which was cast in CO₂ sand mold, was examined by X-ray and SEM. The results including the experiments by Bishop et al were discussed based on numerical analyses by the direct finite difference method developed by the authors. It was shown that the sound zone by the end chill effect can be estimated by the progress of freezing front of solid fraction of 0.7 or progress of contours of temperature gradient during freezing. Shrinkage defect near the riser, however, can not be predicted by these parameters. The pressure gradient method, proposed in this paper, could best estimate the formation of shrinkage defect. The shrinkage defect near the riser was string-like and V-shaped. It disappeared by increasing aluminum content and it could be due to macro-blowholes created by H₂, N₂ and CO gas. The shrinkage near the chill end may be microporosity formed by rapid pressure drop resulting from solidification contraction. Furthermore, the shrinkage in the riser was estimated to some extent by the analysis with Darcy's law. More accurate prediction of shrinkage defect requires the consideration of the solid phase movement, examination of the gas content in the melt and heat transfer during pouring.

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