Thermal conductivity of sand molds was expressed as the sum of effective thermal conductivities due to conduction and radiation. Equations of thermal conductivity of dry silica sand molds and furan resin bonded sand molds were obtained. The effective thermal conductivity due to radiation increases above 1,000°C constituting about 50% of the thermal conductivity at 1,500°C. Although the thermal conductivity of dry silica sand molds increases with the melting temperature of poured metal by the increase of radiative heat flux, that of furan resin bonded chromite sand molds is not affected by poured metal because of the small radiative heat flux. The thermal conductivity obtained by the steady method is lower below 600°C than that of this work determined by the pouring method, and being higher above 800°C. This is because the radiative heat flux increases with the decrease of temperature gradient in sand molds. It is reasonable to use thermal conductivity obtained by the pouring method for computer simulation of castings, because the thermal gradient in the pouring method is the same as those in practice. A radiative heat transfer model in sand molds which coincides well with the experimental results was derived from Hamaker's theory.

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  Changes in structure and mechanical properties of cast iron by different pressures of vacuum melting were examined to find out the conditions for Coral-type graphite formation. Desulfurizing, deoxidizing and denitriding occur, which leads to refining and rounding of the graphite tip. Ferritization of matrix structure proceeds with crystallization of the roundish graphite resulting in a rise of tensile strength and softening. Prolonged holding in vacuum has the same effect as the lowering of pressure. Pressure below 10^-2mmHg and holding time 30 min or more are required to obtain Coral-type graphite. These changes when casting under the atmosphere subsequent to vacuum melting were also examined from the industrial point of view. The effect of vacuum melting is weakened by casting under the atmosphere.

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  The optimum amount of coal dust addition to green sand mixture to prevent pinhole formation in spheroidal graphite iron castings and the mechanism of pinhole prevention were studied using cup-shaped test castings. Green sand was mixed with Simpson's muller. A jolt and squeeze type molding machine was used. The molten iron nodularized by the converter process was poured. Additions of coal dust 3% or more remarkably reduce pinhole formation. Pouring temperature, thickness of specimen and moisture of mold sand have some effects on pinhole formation, but additions of coal dust 3% or more weaken these effects. The volatile matter in the coal dust is greatly responsible for eliminating the pinholes. Pinhole prevention depends not only on the mass but also the kind of gases generated.

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  The susceptibility to temper embrittlement of cast steels was compared with that of forged steels. The degree of temper embrittlement of cast steels is closely related to the parameter, (Si+Mn)×(P+Sn)×10⁴, and is much greater than that of forged steels. Difference in temperature embrittlement susceptibility between cast steel and forged steel is caused by difference in Mn content and homogenizing. Moderated dendritic solute segregation due to homogenization lowers the susceptibility to temper embrittlement when heated at temperatures higher than 1,100°C.

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  Bending fatigue tests at −30°C were carried out on flake graphite cast iron with various graphite shapes. The graphite shape and matrix structure were converted into numerical expressions and the statistical analysis was conducted. The S-N curves at −30°C move parallel to higher number of repeated stress, and the fatigue limit lowers than that at room temperature. The fatigue limit is lowered by the presence of flake graphite.

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  A new blast granulation system of basic oxygen furnace slag has been developed for the utilization of slag, the recovery of the sensible heat and improvement in handling. Blast granulation facilities were constructed in Nov. 1981. The spherical particles produced by this system are greatly improved with respect to degraded property of B. O. F. slag and can be used as substitutes for sand. The utilization of these particles less than 0.5mm in diameter for molding sand for cast iron was studied. They have the advantages that:  (1) The slag particles are excellent in fluidity and are easily formed to a mold. Metal penetration into the cast mold hardly occurs.  (2) About 30% of binder is saved for each ton of casting.  (3) The slag particles are so antiabrasive that the loss is only 2.5% per casting.  (4) Proper facings must be used on the mold surface.  (5) High frequency dielectric heating is applicable for the dry mold.

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