To elucidate the segregation behavior of solutes in Al-Si and Al-Cu binary alloys, specimens of several hypo-eutectic Al-Si alloys water-quenched at different stages of solidification or air-cooled from melt to room temperature were prepared and the distributions of Si concentration were analyzed across the primary dendrites. The Si distribution in the dendrites of the specimens water-quenched during primary solidification showed that Si concentration declined from the surface toward the center of the dendrite. In contrast, the specimens water-quenched after eutectic solidification or air-cooled from melt to room temperature showed that Si concentration increased from the surface toward the center of the dendrite. The diffusion distance of Si in the dendrites during the cooling process from the finish of solidification to room temperature was calculated according to Fick's second law and showed good agreement with the measured value. Therefore, the segregation behavior with high Si concentration in the center of the dendrite was attributed to the diffusion of Si from the center to the surface of the dendrite, resulting in the precipitation on the adjacent Si phase during eutectic solidification.

  Recently, high tensile strength steel with high manganese (Mn) content is used as a raw material for manufacturing cast irons. It is however becoming increasingly difficult to recycle high Mn content steel scraps for the production of cast iron, because Mn is well known as an element promoting the chilling tendency of cast iron melt. Thus in this study, to strengthen flake graphite cast iron with thin section and realize recycling of high Mn steel scrap, we investigated the effects of Mn content and cooling rate on the chilling tendency and mechanical properties of flake graphite cast irons with different Mn contents and carbon equivalents (CE) corresponding from FC100 to FC350 of JIS standards.

  Tensile strength and Brinell hardness increased as Mn contents and cooling rates increased, and as CE and graphite area ratio decreased in flake graphite cast iron. On the other hand, the amount of pearlite in the matrix increased and pearlite lamellar spacing decreased as Mn contents and cooling rates increased and CE decreased.

  High Mn content flake graphite cast iron was evaluated as good quality based on evaluation indices such as RG, RH and σ/HB. It was observed that when Ca-Si was added to high Mn cast iron melts, spherical shaped sulfide in the form of (Mn, Ca) S formed in the melt and this sulfide acted as a substrates for graphite formation in eutectic solidification, resulting in remarkable graphitization and high strength. The strengthening of high Mn flake graphite cast iron was considered due to the formation of A type graphite, reduction of graphite area ratio and ferrite matrix, refinement of pearlite lamellar spacing, solid solution strengthening by Mn in ferrite matrix and formation of martensite and retained austenite in the eutectic cell boundary.

  The influence of pouring temperature on the microstructure and high-temperature mechanical properties of Nb-added austenitic heat resistant cast steel was investigated for the purpose of extending the service life of jigs in heat treatment processes. The steel was manufactured by the sand mold casting process, and three pouring temperatures of 1753K, 1823K and 1883K were selected for the investigation. Thermal shock test and creep ruptured test were carried out at 1223K to evaluate high-temperature mechanical properties. Microstructural characterizations were done by qualitative / quantitative analyses of extracted primary carbides and microstructure observation. As a result, it was found that the amount and size of primary carbides (NbC and M₂₃C₆) depend on the pouring temperature, and this microstructure affects the high temperature mechanical properties. Besides, under a long-term thermal shock or creep environment, it voids where found to generate due to the decomposition of M₂₃C₆, precipitated ferrite and sigma phase increase with heating time. Propagation of cracks in cast steels was considered to proceed due to the coalescence of voids in addition to the difference in the amount of each precipitated phase. Moreover, it was clear that secondary carbides were less effective in restraining crack propagation than primary carbides. These findings suggest that pouring temperature is strongly related to high-temperature mechanical properties, and the pouring temperature of 1823K results in excellent thermal shock resistance and creep property.