During an investigation of D-type graphite iron cast in metal mold, it was recognized that the mechanical properties were affected by the melting condition, and as a result the fracture surface features sometimes changed. Especially it was shown that network patterns in the fracture surface were observed only when the mechanical properties of the iron are superior to those of the ordinary ones. In order to clarify this phenomenon, experiments were carried out in a 50 kg high frequency electric furnace. In the investigation reported herein, the following experimental factors were considered : melting and holding temperatures, holding time of melt, S and Ti content in iron and carburizing process. The results indicated that the mechanical properties of the iron are improved by increasing Ti content, melting temperature and holding time, although the melt tends to solidify as white iron under such conditions. It was also found that the chilling tendency of the melt carburized in a ladle in a way similar to inoculation is less than that of the melt carburized in furnace. The observation of the network-patterned surface shows that the network size and eutectic cell size coincide with each other and austenite dendrites grow to a great extent at the cell the boudary. At the cell boundary steadite is observed in place of graphite. It may be suggested that the structure of D-type graphite cast iron is similar to that of ductile cast iron, if the graphite colonies are regarded as spheroidal graphite. The superior mechanical properties of the iron can be explained by considering the D-type graphite colonies as being similar to spheroidal graphite in ductile cast iron.

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  Effects of casting variables on structures and tensile properties of ceramic shell mold castings were studied using plate-shaped specimens. Structures and tensile properties were almost uniquely correlated to the effective moduli of the castings calculated from their edge effect distances. As for effects of test piece sampling positions, there was a sharp drop in tensile strength elongation and reduction of area at the border between the edge effect zone and the defect zone, with a gradual increase towards the riser effect zone. When the effective moduli of the castings were increased by the effects of such casting variables as pouring temperature or ceramic fiber covering, the castings were prone to show more uniform tensile properties throughout, and to show slightly lower tensile properties in the sound zones. There was no difference in tensile properties between the edge effect zones and the riser effect zones.

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  A self-hardening molding process using aquous solution of polyvinyl alcohol (P.V.A) and boron compound was investigated. Because moisture in the mold affected the properties of the mold, control of moisture was very important in this process. Therefore, we tried to use cement for the purpose of controlling moisture in the mold. Of the binding materials, it was recognized that cement acted as an agent to reduce moisture in the mold and improve mold strength. Furthermore, the cement was effective to control bench life of the mold sand. Two types of cement were examined to study their effect on the properties of the mold. When jet cement was used, the properties of the mold were better than those with portland cement.

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  Oxidation behavior of Fe-25Cr-12Ni cast steels containing 0 to 1% rare earth metals (RE) and Co-base alloy has been studied by thermobalance and EPMA, while the alloys were being coated with cement clinker. The presence of the cement clinker accelerated the oxidation rate of these alloys. It changed the temperature dependence of oxidation of the RE-free cast steel and the Co-base alloy. The oxide of Co-base alloy was more adherent than those of the Fe-Cr-Ni cast steels after five cycles of heating to 1,000 deg C. Therefore the weight gain of the Co-base alloy decreased consistently at each heating cycle, while those of the Fe-Cr-Ni cast steels were inconsistent. The Fe-Cr-Ni steels under-going isothermal oxidation at 1,000 deg C with cement clinker without any wear were superior in heat resistance to Co-base alloy. The oxidation rate of the cast steel was reduced by adding 1.0% RE but was little affected by 0.2% RE. In the experiment with constant heating rate, the oxidation rate at 1,000 deg C was saturated at the amount of the cement clinker coating of 10 mg·cm^-2, while that at 1,100 deg C was saturated at 20mg·cm^-2 coating. At higher temperatures, the more the cement clinker was applied, the more the oxidation rate increased. The minimum temperature of observable weight gain was reduced to 700 deg C by cement clinker coating.

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  In this paper, the process of hot crack formation has been simulated by utilizing a testing unit designed by the authors. The hot tearing temperature and the critical fracture stress have been investigated for Al-Cu alloy. It was found that both the critical fracture stress and the hot tearing temperature were closely associated with the deformation velocity. The hot tearing temperature increases with a rise in the deformation velocity. On the other hand, there appears a peak value in the critical fracture stress when the deformation velocity is increased. Further, the condition for hot crack formation has been analyzed. The hot cracks will not be formed when the condition V<(KR/Es+β/τ−γR). l is satisfied, where V, R and l are deformation velocity, cooling rate and length of the heated zone of the specimen, respectively ; K and γ are increasing rate of strength and decreasing rate of elongation, respectively, of the alloy in the semi-solid state region ; Es and β are Young's modulus and elongation of the alloy at the semi-solidus temperature ; τ is time elapsed after the beginning of contraction.

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  Irons containing various amount of C and Si were melted in a high frequency induction furnace with a 12kW, 3,000Hz motor generator unit. The melt was superheated to 1,530 deg C for nodularization treatment in a crucible using 1.6wt% of Fe-Si-Mg alloy. After the nodularizing reaction subsided, the melt was post-inoculated with Fe-Si and was poured in CO₂ process sand mold with section sizes of 3mm, 6mm and 9mm. The presence of carbides and nodule count were determined with an image analyzing computer. The nodule count depended strongly on carbon equivalent and the relationship was expressed in a linear equation. For each cooling rate of specimen there was a characteristic nodule count (the critical nodule count) above which free carbide did not appear. The relationship between the critical nodule count and the cooling rate was expressed in the following quadratic equation ; N=0.58R²+19.07R+1.01, where N is the nodule count and R is the cooling rate.

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