The initiation and propagation behaviors of fatigue cracks on the surfaces of smooth specimens under completely reversed bending were investigated for a ferritized spheroidal graphite cast iron and an extremely low carbon steel. The main results obtained were as follows:
  1) The cycle ratio N/Nf at the initiation of small fatigue cracks is as small as 0.05 in case of the ferritized spheroidal graphite cast iron, comparing to about 0.3 of the extremely low carbon steel.
  2) Small fatigue cracks were observed to initiate from the edges of many graphite nodules in case of the ferritized spheroidal graphite cast iron. Therefore, the presence of many graphite nodules is considered to be the main cause of the fact that the crack density of the ferritized spheroidal graphite cast iron is much higher than that of the extremely low carbon steel.
  3) The ferritized spheroidal graphite cast iron is smaller than the extremely low carbon steel in both the propagation rate of the main fatigue crack and the value of m of the d(2a)/dN-ΔK curve.
  4) The fracture surface patterns at the crack initiation regions were observed to be quasi-cleavage fracture in case of the ferritized spheroidal graphite cast iron and slip plane decohesions in case of the extremely low carbon steel. The fracture patterns at the crack propagation regions were observed to consist of quasi-striation, intergranular fracture and quasi-cleavage fracture in case of the ferritized spheroidal graphite cast iron and slip plane fracture and ductile striation in case of the extremely low carbon steel.

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  The critical fraction solid, below which the primary solid and liquid flow concurrently during the solidification of Ai-Si alloy ingot, has been investigated in relation to the macrostructure of the ingot. The critical fraction solid was estimated by simulating the shape of the shrinkage depression of the conventionally cast ingots. The critical fraction solid varied from 0.05 to 0.40 when the macrostructure of the Al-3mass%Si alloy ingot changed from columnar to fine equiaxed morphology. It was also found that when the semi-liquid region disappeared, where the fraction solid was below the critical value, the remaining zone where the fraction solid is less than 0.67 had relatively high porosity.

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  A numerical technique for the quantitative prediction of shrinkage cavity is presented. In this technique the 3-dimensional heat balance equations are solved by Finite Difference Method independent of the formation of shrinkage cavity. Macroshrinkage is predicted in the region where bulk flow is easy and calculated in the elements where pressure head is minimum. The region where residual liquid flows in the dendrites is distinguished by a critical fraction solid. Microshrinkage forms where the fraction solid gradient is lower than a critical value in the assumed path of the interdendritic flow. Some numerical examples are analysed. The calculated shrinkage volumes agree well with the experimental ones in the steel plate castings and Al alloy casting. The computer cost of the proposed technique is not much more expensive than conventional technique such as the temperature gradient method. Therefore, it could be very useful for the evaluation of risers and the prediction of quantity of shrinkage in the castings.

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  Using the reduction refining and non-reduction refining flake graphite high grade cast iron having the thickness of 20mm diameter annealed at 550°C to relieve the strain, the evaluations for quality were carried out. Their evaluation methods are the reifegrad (RG), the relative bending load (RB), the relative hardness (RH), and the relative hardness related to bending load (RHb). The quantitative analysis of the tensile fracture surfaces by using their cast iron were performed by making use of a scanning electron microscope (SEM) photographs. And the relationship between the evaluation values for quality and the percentage of each fracture surface were obtaind. Their fracture surface are the percentage of graphite fracture surface and the microdimple-wrinkle like pattern fracture surface. As a result, the most reliable equation for the evaluation, RB=100/(1222-662 Sc), was deduced. The reduction refining specimens had more the microdimple-wrinkle like pattern than the fracture surface of the non-reduction refining specimens by fractography and it was found that RG value increased with increasing the percentage of microdimple-wrinkle like pattern fracture surface, while RH value decreased against increasing the percentage of that fracture surface.

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  The reaction between the molten Ni-base super alloy for single crystal casting, Alloy 454, and the high purity mullite on the market was examined at 1,500°C, 1,540°C and 1,580°C under the reduced pressure about 2×10^-10 Torr. The reacted layer is produced to 10-16μm at 1,500°C, 18-27μm at 1,540°C, 38-52μm at 1,580°C. The main product of the reaction is considered to Al₂O₃ from the result of X-ray microanalysis. Some of the products are contaminated as the inclusion at the near side of the reacted layer in the obtained ingot. Probably, the cause of reacting the mullite specimen with the molten alloy may be existing the mullite solid solution in the specimen, especially containing higher SiO₂ than the stoichiometric composition, which presumed to come from the problem of the preparing method of the raw material and the occurrence of the composition shifting while the contact with the molten alloy for a long time at high temperatures.

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