Alternating electromagnetic force of two cycles per second was applied to solidifying melts of pure aluminum, aluminum with titanium addition, aluminum-copper and aluminum-silicon alloys so as to study the effects of stirring of molten metal on as-cast structures. Grain structures of aluminum below 99.9% in purity were significantly refined by stirring and the degree of refinement was proportional to the intensity of stirring. Grain structures of high purity aluminum, however, were only slightly changed by stirring. Although stirring also refined grain structures of aluminum with titanium addition, the relative degree of refinement by stirring was less than that in 99.9% aluminum. It was observed that primary silicon of hypereutectic aluminum-silicon alloy with stirring was markedly segregated and eutectic showed mixed structure of fine and coarse silicon particles. In case of aluminum −7.5% silicon alloy stirring gave rise to a divorced structure in which eutectic was separated from primary aluminum. As a whole stirring of molten aluminum-silicon alloys did not result in refinement both of primary and of eutectic silicon except the fine silicon particles in the mixed structure of the hypereutectic alloy.

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  Sand molds were frozen by liquid nitrogen contained in a copper box. Freezing rate of the molds increased either as the moisture content increased, the mold density increased or the molding sand became coarser. The consumption rate of liquid nitrogen for freezing silica sand molds corresponded to the freezing rate of the molds. Freezing rate of various sand molds increased in the order of chamotte sand, chromite sand, olivine sand, zircon sand and silica sand. Consumption ratio of liquid nitrogen per unit volume of frozen mold increased in the order of silica sand, chamotte sand, olivine sand, chromite sand and zircon sand. Thus silica sand is the most economical aggregate to be frozen among the sands studied.

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  Austempered ductile iron has superior properties in tensile strength and elongation. However, since it contains much retained austenite, there was an uncertainty as to the stability of the properties at high and low temperatures. Therefore, the properties of austempered ductile iron at low temperature were studied. Tensile tests at 0, −20, and −40°C did not show any noticeable change in tensile strength, but yield point and elongation decreased at low temperature. Hardness measured at 10mm from the fractured surfaces at room temperature increased and quantity of retained austenite decreased at lower temperature of tensile testing, while no change in structures was recognized. These phenomena may come from partial transformation of the retained austenite to martensite. On the other hand, the mechanical properties and quantity of retained austenite did not change by tensile tests performed at room temperature after cooling the specimens to 0, −20 and −40°C. Furthermore, when specimens were cooled down to −50°C and kept for four hours, hardness and quantity of retained austenite did not change. When specimens were cooled down to −120 and −196°C and kept for one hour, hardness increased and quantity of retained austenite decreased, the change at −196°C being larger than that at −120°C. These phenomena suggest also partial transformation of retained austenite to martensite like in sub-zero treatment of steel. After repeated cooling of 60 times from room temperature to −40°C hardness and quantity of retained austenite did not change. Therefore, it is concluded that the austempered ductile iron is stable at temperature down to −40 to −50°C but unstable at temperature below −120°C.

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  X-ray and γ-ray inspections have been used to detect near surface flaws of castings such as blow holes or pin holes. Ultrasonic testing, on the other hand, is widely used as a more handy method of detecting surface flaws. Although many types of ultrasonic probes are on market, they are associated with various problems such as dead zone and Fresnel zone of probe, scattering echo between casting surface and probe or grass and attenuation caused by graphites in matrix. Thus it was considered necessary to develop a detection method which is not affected by dead zone and surface roughness of specimens. The authors developed a special ultrasonic probe to detect near surface flaws of castings and named it Multitransducer. This paper describes the flaw detection sensitivity and signal-to-noise ratio of the probe. The results indicated the effctiveness of the probe.

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  Density and ultrasonic sound velocity of as-cast, ruptured and heat treated specimens of flaky, CV and spheroidal graphite cast iron were measured and the following results were obtained.
(1) Density and sound velocity were decreased by tensile stress or heat treatment, while they were also affected by chemical composition and matrix structure. Sound velocity was proportional to density. (2) The main reason for the reduction of density and sound velocity was attributed to voids generated in the cast iron during the application of tensile stress or heat treatment. The effect of density upon sound velocity was explained to the most part by graphite content and the amount of voids induced in cast iron. (3) Young's modulus E(kgf/mm²) of cast iron was approximately expressed by the equation (1).
    E=21500(A_ef−x)+1000(1−A_ef)…………………………………………(1)
where A_ef is the effective area fraction of the matrix in as-cast state and x is the area fraction of cracks or voids formed by stress or heat treatment. The order of the amount of opening of cracks in ruptured specimens with the same x value was calculated by equation (1) using the measured density and sound velocity as FC20<FC25, 30<CV<FCD45.

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  Castability and section thickness sensitivity of CV graphite cast iron were studied in comparison with flaky and spheroidal graphite cast irons. CV graphite cast iron was made by using a graphitizing agent containing calcium, while carbon equivalent and pouring temperature were varied. Shrinkage decreases with increasing carbon equivalent and with decreasing pouring temperature. Shrinkage susceptibility of CV graphite cast iron is more favorable than that of spheroidal graphite cast iron and is comparable to that of flaky graphite cast iron. Fluidity of CV graphite cast iron is in between those of the other two irons. Section thickness sensitivity of CV graphite cast iron is less favorable to those of the other two irons. This is because CV graphite cast iron is affected by both the graphite shape and areal percentage of pearlite, while flaky or spheroidal graphite cast irons are affected by only either of the two factors. It is concluded that the castability of CV graphite cast iron is in between the other two irons.

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  It is well known that austempered ductile iron shows good toughness and strength. To further raise these properties effects of various heat treatments and alloying elements were investigated in this study. It was found that the best result is obtained when alloys containing Ni or Mn are austempered from (α+γ) range.

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