The magnesium-treated spheroidal graphite cast iron having ferritic matrix and containing approximately 3.6%C, 2.5%Si and 0.08%Mn, was made from a high purity pig iron, which was poured into a small size Y-block CO₂ sand mold heated at 450°C (weight of casting : 1.5kg).
  The specimen in the as-cast state, the specimen annealed to relieve the casting-stress and the specimen ferritized completely by decomposing small quantities of the remaining pearlite had almost the same impact properties, that is, the maximum impact value was approximately 3kg·m/cm² and the transition temperature was −13°C in all cases. After two stages-ferritizing-annealing (the ferritizing-annealing was done just below A_r1 after reheating to temperature of austenite range), both the specimen having as-cast ferritic matrix and the specimen having the bull's eye strucure showed the maximum impact values similar to that of the previous three specimens, but the transition temperatures were lowered to −34°C and −50°C, respectively. The lowering of the transition temperature corresponds well to the refinement of the ferrite grain size due to the two stages-ferritizing annealing.
  The low temperature brittleness of the cast iron with body centered cubic lattice structure may be enhanced by the interstitial atoms such as C or N, and the Stroh's equation was well applicable, where the ferrite grain size corresponds linearly with the reciprocal of the transition temperature.

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  The authors have made a thermal fatigue testing equipment which gives a mechanical load on the specimen. The thermal fatigue lives of gray cast iron, ductile cast iron and malleable cast iron were examined under completely restricted and mechanically loaded condition.
  The completely restricted thermal fatigue life of each ductile cast iron and malleable cast iron was longer than that of the gray cast iron. The relationship between strain amplitude (ε_t) and the completely restricted thermal fatigue life (N_f) was expressed by the following equation : ε_t·N_f^α=constant where α was 0.68 in gray cast iron, 0.82 in ductile cast iron and 0.75 in malleable cast iron.
  Thermal fatigue life under mechanical load was shortened with increase in both the heating temperature (T_H) and the mechanical load (σ_M). A T_H-σ_M diagram which shows a given thermal fatigue life (N_f=10³ cycles) was made for each cast iron. At higher σ_M, ductile cast iron and malleable cast iron with pearlitic matrix was resistant to a higher repeated thermal cycle temperature than those of ferritic matrix, but at lower σ_M, the results were reversed.

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  This experiment was designed to grasp the metallurgical characteristics of the solidification of zinc die casting alloy, especially AG40A, by comparing the solidification characteristics measured under two casting processes-gravity die casting and pressure die casting.
  The undercooling measured in gravity die cating was 10-15°C and that in pressure die casting was 120-180°C. The solidification structure of pressure die casting was smaller than that of gravity die casting, and the grain size of the former was approximately one half to one-third of the latter.
  Empirical equations which showed the relation between the solidification time t(sec), wall thickness d(mm) and molten metal temperature T(°C), were obtained by the following formula.
  gravity die casting process; t=d^1.56{0.224+0.002(T−380)}
  pressure die casting process; t=d^2.1{0.0297+0.00046(T−380)}
The chief factor that determined the fluidity of molten metal in gravity die casting was wall thickness, but in the case of pressure die casting wall thickness and plunger speed were the two chief factors.

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  With a view to investigating the effect of graphite on the strength of various cast iron, a series of model cast iron with various graphite-like constituents existing in the synthetic matrix was made. As substitutes of graphites in gray iron, spheroidal graphite iron and malleable iron, natural graphite, copper granule and carbon sand grain having a similar size and shape as the graphite in each iron respectively were mixed with epoxy resin matrices.
  An analysis of variance on the tensile test results showed that the influence of graphite shape is extremely large and the tensile strength increases in order of flake, lump and spheroidal shape. It was recognized that the tensile strength increases up to certain maximum value up to a certain graphite nodule fineness, then decreases gradually. The maximum value of tensile strength on the resin tensile specimen was obtained when the graphite size was No.6 in A.S.T.M. A247-47 or GShD 3 in GOST 3443-57 standard. It was also obtained that the effect of graphite volume on the tensile strength was not so large as that of the graphite shape. It seems that the strength decreases with the increase of notch effect and the decrease of effective area of matrix substance.
  When the graphite contents are the same, the increase of graphite nodule number increases the strength of specimen. In higher ranges of graphite content, however, the effect of nodule number is not large. An uniform distribution of graphite in the matrix to obtain the maximum ratio of graphite diameter to the distance between graphites in ductile iron sample resulted in higher tensile strength.

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  This study was made to clarify the phenomena of the transfer of sulfur from coke to metal when the metal is molten down in cupola.
  A sulfurous oxidized film is formed on the surface of the metal passing the preheating zone. This film is very thin and the diffusion of the sulfur in the film into the metal was not recognized. In the melting zone, the solid metal changes to a molten drop state, and sulfur absorption increases rapidly up to about 60-80% of total absorption. One of the source of supply of sulfur is the S₂ gas near the surface of the coke and the other is the SO₂ gas in the combustion atmosphere.
  It was confirmed that there is less sulfur pick-up in pig iron than in steel. The reason for this phenomenon was considered to be that there are plenty of C and Si in pig iron which activates desulfurization.

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  Grasping the retained strength change in sand molds is important for improving collapsibility of mold. In this work, the retained strength changes along the metal-mold interface in various sand molds (with facing) bonded with bentonite and Hibushi clay binders were investigated.
  There is no difference between bentonite and Kibushi clay with regard to the retained strength change in sand molds. However, as the bentonite swells with moisture, well-compacted sand molds bonded with bentonite have higher compressive strength than those with Kibushi clay. Consequently, the retained strength curves in sand molds with bentonite slide up to a higher strength side than in case of Kibushi clay.
  The primary factor working on the retained strentgh is the thermal expansion of molding sand. The molding sand which shows a larger thermal expansion has a larger volume change with heating and cooling, As a results, the bond between sand grains are disrupted and that lowers the retained strength of the part heated up to a high temperature. On the other hand, as molding sand with smaller thermal expansion shows intergranular sintering at high temperatures and moreover, as the bonds of sand grains are strengthened with fused binder, the retained strength increases rapidly at the part where it has been heated up to a high temperature. Silica sand and olivine sand belong to the former type, and chromite sand and zircon sand belong to the latter type. But, as olivine sand mold fuses above 1,300°C, the retained strength increases near the metal-mold interface. In chromite sand and zircon sand molds, rapid rises in the retained strength near the matal-mold interface take place without regard to binders, and it, therefore, seems difficult to improve collapsibility of such molds.

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  A formula of isothermal ferritization process in gray cast iron was devised on the assupmption that graphite flakes are randomly oriented in the iron, and the values thus obtained were compared with experimental results.
  Fraction of ferritization, F, in direct or indirect isothermal ferritization can be expressed by
      F=1−exp(−√8N_L²Kt)
where N_L, K and t denote number of interceptions of scanning line at the surface of graphite flakes per unit length, the growth rate constant of ferrite layer and the time of ferritization, respectively. Measured fractions of ferritization were somewhat lower than the calculated fractions when the number of interceptions of scanning line at the graphite-matrix interface was expressed as N_L. And they showed slightly higher values when the number of interceptions at thr graphite-ferrite interface was expressed as N_L. As a whole, however, the tendency of ferritization seems to be well expressed by the above formula.
  The fraction of graphite surface with which ferrite layers grow in contact got larger and approached unity as ferritization time increased. The growth rate constants of the ferrite layer obtained in gray iron were smaller than those in spheroidal graphite or black heart malleable irons at the same temperatures, which may be attributed to the differences in chemical composition of the irons.

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