The effects of casting design and reduced pressure in the flask on the mold filling of molten aluminum alloy in the expendable pattern casting (EPC) process were investigated experimentally. An aluminum alloy plate was cast by the EPC process, and the arrival time of the molten metal was measured for three coats with different permeability. The use of a high permeability coat, or the condition of applying reduced pressure, led to a higher melt velocity. The melt velocity did not increase in proportion to the coat permeability. The experimental values of the arrival time of molten metal were compared with the calculated values based on the mold filling model used in the previous study. The values were in relatively good agreement except for when the coat permeability was very low. The arrival time in top pouring was almost the same as that in bottom pouring, except for when the coat permeability was very low. The melt velocity in the top pouring did not drop, even when the coat permeability was low.

  The purpose of this study is to investigate that effects of graphite spheroidization ratio and microstructure on the characteristics of fatigue limit in spheroidal graphite cast iron. Ferritic spheroidal graphite cast iron (FDI), pearlitic spheroidal graphite cast iron (PDI), and austempered spheroidal graphite cast iron (ADI) were used as specimens. The graphite spheroidization ratio was varied between 94～63% by the addition of a spheroidizing agent. Tensile test was carried out in air at room temperature. The experiment conformed to JIS (Japan Industrial Standards). Rotating bending fatigue test was also carried out using these materials. The experiment conformed also to JIS. Stress ratio R was －1, and the specimen used was type 1 (JIS) with a diameter of 8mm. The test was carried out in air at room temperature. The relationship between fatigue limit and graphite spheroidization ratio was investigated, as well as the correlation between fatigue limit and defect size.

  When the graphite spheroidization ratio was over 80%, the fatigue limit was not influenced. Fracture origins were microshrinkage, aggregate graphite, and unspheroidized graphite. When graphite spheroidization decreased, the ratio of unspheroidized graphite at the fracture origin increased. The defect size that transitioned from region Ⅰ to Ⅱ differed according to the microstructure: the defect size of PDI was the smallest, and that of FDI was larger than ADI. When there are no large defects in FDI, the fatigue limit can be estimated by tensile strength. However, in PDI and ADI, it must be estimated taking into account the size of existing defects in specimens.

  In-situ and time-resolve X-ray imaging was performed to observe the solidification of hypereutectic Fe-C-Si alloys containing 0.05 and 0.002mass%Mg. The crystallographic orientations of spherical graphite particles in conventional spheroidal graphite cast iron and specimen after the in-situ observation were measured by the EBSD technique. Mg concentration influenced nucleation frequency and the temperature range in which the primary graphite particles independently grew. The spherical graphite particles became approximately 40μm in diameter for 2-5s and then were engulfed in the eutectic of γ-Fe and graphite in the 0.05mass%Mg specimen. In the 0.002mass%Mg specimen, the nucleation frequency of primary graphite particles became lower. Most of the graphite particles exhibited spherical shape until diameter reached 40μm and then changed shape from spherical to a flake-like shape. The graphite particles grew for 20s until the engulfment by the eutectic solidification. EBSD analysis showed that the c-axis of graphite crystals tended to be parallel to the normal direction of spherical surface for both conventional alloys and the in-situ specimens. The results proved that the same growth mechanism operated in both specimens.

  Generally, thin-walled ductile cast iron (TWDI) is produced with a high carbon equivalent (CE), which is decided by the contents of silicon and carbon used, in order to control chilling. In this study, a TWDI plate with a thickness of 2mm was made with various CEs adjusted by varying the silicon and carbon contents. Casting was melted in a 15kg high frequency induction furnace. Before the melt was treated with graphite spheroidizing agent and inoculation, the CE value was measured using a CE meter. The specimens were divided into groups A and B according to the chemical composition. for group A, the silicon content was kept unchanged at 2.4mass% while the CE value was changed by only the addition of carbon. For group B, the silicon content was increased while keeping carbon content constant at 3.6mass%. Graphite nodule count and Vickers hardness were measured and the microstructure was also observed. As a result, microstructures with free-carbides were obtained when the silicon content exceeded 2.4mass% and CE was over 4.2. The peariite area ratio increased when the carbon content exceeded 3.7mass%. The ferrite area ratio and graphite nodule count increased with increasing silicon content. Moreover, the graphite nodule count exceeded 3000nod/mm² and peariite ratio dropped below 30% when the silicon content was over 2.7mass%. The graphite nodule count of the sample with hypereutectic composition varied in the range of 1700～2400nod/mm² as carbon content increased.

  Multi-component white cast irons containing Cr, Mo, W, V and Co have been widely popularized as roll materials for hot rolling mills because of their excellent wear performance. In this research, the effects of C and Co contents on mechanical properties and hot wear resistance were investigated using Fe-M (5%Cr-5%Mo-5%V-5%W) － Co-C (mass%) cast alloys. MC and M₂C carbides are crystalized in all specimens, and M₇C₃ carbide forms in specimens with high C and high Co. Martensitic matrix is obtained in specimens with C content of 1.5～2.5mass% and with Co content less than 7.5mass%. An increase of Co content promotes transformation of soft pearlite matrix. Martensitic matrix has over 600HV in micro-hardness, and the change of micro-hardness is similar to that of macro-hardness. Tensile strength, compressive 0.2% proof strength, and fracture toughness are high in cast irons with high hardness. Hot wear resistance is larger in cast irons with higher hardness and higher fracture toughness.