Although embrittlement of spheroidal graphite cast iron is caused by heating at about 450°C, it is the same as the temper embrittlement known in black-heart malleable cast iron. There have been many studies on this problem without any clear conclusion on the cause of this phenomenon. In this study, therefore, temper embrittlement in ferritic spheroidal graphite cast iron was re-examined from using new techniques such as instrumented Charpy impact test, scanning electron microscopy and ion microanalysis.
  It was found that temper embrittlement appeared mainly as the transition temperature rose, impact fracture loads at each position of the temperature transition curve decreased with the progress of embrittlement and intergranular type fracture occurred. No abnormality such as precipitation was observed on the surface by scanning electron microscope, but segregation of phosphorus and sulfur was observed clearly as a result of ion microanalysis. From this, it appeared that temper embrittlement was mainly due to normal segregation of phosphorus and sulfur at the grain boundary.

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  The present paper is a study on the relationship of green sand mold properties such as tensile strength and springback in high pressure molding to grain size distribution of base sand and considers some aspects of grain size distribution in high pressure molding.
  The following results were obtained on compaction by squeezing at 7kg/cm² or adding simultaneous jolting; 1) green tensile strength in 4 screen sand was higher than in 1 screen sand, 2) springback in 1 screen sand was smaller than in 4 screen sand, 3) green permeability in 1 screen sand was higher than in 4 screen sand, 4) no conclusion was obtained on comparison of density uniformity, because there was a great difference depending on the ratio of moisture to bentonite.
  The following results were obtained on compaction by squeezing at pressure beyond 10kg/cm² ; 1) it could not be concluded whether 4 screen sand or 1 screen sand was higher in green strength because approximately the same maximum strength was indicated within a certain squeeze pressure, 2) springback in 4 screen sand was somewhat lower than in 1 screen sand, and springback at 10kg/cm² in 4 screen sand was lower than at 7kg/cm², 3) permeability in 1 screen sand was always higher than in 4 screen sand, 4) density uniformity in 4 screen sand changed a little with compactability, but it in 1 screen sand lowered remarkably with increasing compactability and rose remarkably with decreasing compactability.

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  Heat absorbing characteristics of sand casting molds were examined theoretically with particular emphasis on the effect of geometrical shape of the mold cavity.
  Dimensionless heat absorbed by a mold plotted against dimensionless time was defined as the characteristic heat absorbing curve of a given mold shape. Heat absorbing curves for several typical shapes were calculated by finite difference method. Difference of solidification time of castings as affected by the shape was judged from the curves to be in the range of ±25%.
  A simplified method of constructing heat absorbing curves was proposed where a given shape was devided into several unit shapes such as plane, internal corner or external corner and heat absorption by the unit shapes was added together to obtain the total heat absorption. The range of influence of internal and external corners was determined as a function of time and the temperature diffusivity of the mold material. This knowledge was essential in deciding the division of a given shape into unit shapes.
  Although the method was found sufficiently precise for determining heat absorption by molds, a considerable error was introduced when the method was directly used for determining the solidification time of the castings, since temperature difference within the castings was neglected in the calculation. The method needs future improvement in this respect.

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  The coarsening of primary dendritic crystals in hypo-eutectic cast iron during freezing was investigated by using synthetic irons with a pure electrolytic iron base.
  Primary dendrites are coarsened by holding them in the solid-liquid coexistence range of freezing for some time. The rate of coarsening is higher at the beginning of holding and at a higher holding temperature. Dendrites become fine when the cooling rate of iron is high in the freezing temperature range. Dendrites in the slow cooling iron are refined with carbon and phosphorus, and coarsened with sulfur. The coarsening effect of sulfur is attributed to the change of diffusion coefficient.

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  The effect of the mechanical properties of the moisture condensed layer on scabbing were investigated, and the relation of the green and hot properties of the sand to scabbing was also examined. In order to determine the fundamental causes of scabbing, the mechanism of scab formation was theoretically discussed based on experimental data.
  No distinct relation between the scabbing tendency and the sand properties such as compressive strength, and deformation at room temperature and high temperature, could be found. The thermal expansion and expansion force of the dried sand layer in the mold, assumed to be main factors of scabbing, were estimated based on the mechanism of the scab formation, and the correlations between these values and the scabbing tendency were examined. According to these results, the mold fracture, which causes the scab defect, occures at the moisture condensed layer when the thermal expansion of the dried sand layer exceeds the formation of the moisture condensed layer. The scabbing may be reduced by increasing the deformation of the moisture condensed layer and the modulus of green deformation, and by reducing the shock heat expansion and the modulus of hot deformation.

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  In cast iron, it is well known that the bending strength σ_b, obtained by the rupture moment and the section modulus, is almost twice the tensile strength σ_t. In the previous paper, theauthors proposed a new theoretical formula, σ_b=(2.0-σ_t/100)×σ_t (σ_b, σ_t : kg/mm²) to relate σ_b to σ_t for a rectangular beam. But strictly speaking, such a bending strength defined by the section modulus varies according to the geometry of the cross section of the beam.
  In the present paper, the bending strength of a cast iron round bar was analyzed theoretically, taking into consideration the non-elastic stress-strain relationship of cast iron. The theoretical ratio of the bending strength of a round bar to that of a rectangular beam was calculated on the numerous stress-strain curves using an electronic computer.
  Calculated results showed that the bending strength of a round bar was 10% higher than that of a rectangular beam, independent of the strength and the profile of the stress-strain curve of the material. In effect, a new formula for the estimation of the bending strength, σ_b = 1.1×(2.0-σ_t/100)×σ_t, was obtained for a round bar. The formula was recognized valid after comparing with the experimental values offered by fourteen perfectural industrial laboratories. The empirical formulas by Mackenzie and Auguss lay between the two formulas by the authors in the range of σ_t>20kg/mm². It was also confirmed experimentally that the as-cast specimens had lower strength and wider scattering range than lathed specimens.

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