In order to study the failure of ingot mould due to repeated thermal stress a testing apparatus for producing crazing experimentally and a method for determining the amount of crazing were developed. In this study, the characteristics of this apparatus and method were examined, furthermore, 6 types of gray cast iron with different sulphur content (0.0015%S, 0.02%S and 0.118%S) and different cooling rate in solidification (ordinary and slow) were tested on crazing.
  The results may be summarized as follows.
  1. The whole crazing apparatus including high frequency electric induction furnace for heating and water cooler applied from outside of the test piece for cooling was placed in a vessel to control the atmosphere.
  2. A method for quantitative measurement of crazing based on the principle of the airmicrometer was developed.
  3. On experiment, the above apparatus and method were found to be satisfactory.
  4. It was observed in this experiment that the formation of crazing was influenced remarkably by the graphite structure of gray cast iron.

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  The authors studied influences of sand grain size distribution on green properties of several bentonite bonded sands with same grain fineness number compacted at high pressure.
  The results obtained are as follows:
(1) In any sand grain size distribution, bulk density, surface hardness and green compressive strength increased and permeability reduced with the increase in squeeze pressure.
(2) The changes of green properties were comparatively remarkable under 30kg/cm² squeeze pressure, but was not recognizable over this pressure.
(3) The green properties of sand mixture was influenced by ratio of fine sand to coarse one; and compactness of sand was greatest when:
  coarse sand: fine sand=(8∼6) : (2∼4)
(4) S.S.I. (Surface Stability Index) was influenced more by bentonite content than by squeeze pressure and the value thus increased with the increase of bentonite.
(5) The most precise surface on steel castings was produced by a coarse sand mixture containing a small amount of fine sand.

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  In order to understand the oxidation mechanism of iron alloys at high temperature, it is important to determine the concenrtation and the distribution of alloying elements on oxide scales. The determination is generally carried out with electron probe micro-analyzer because of the highest spacial resolution of this technique, but a standard method of quantitative analysis on oxide scales has not been determined as yet. The purpose of this work is to provide a basis for the oxide analysis utilizing pure metal as a standard is not established.
  The intensities of MeK_α and OK_α in the oxide of light elements (MgO, Al₂O₃ and SiO₂), iron oxides (FeO, Fe₃O₄ and Fe₂O₃) and their original pure metals were measured at various beam voltages (5∼30 KV), and their experimental values obtained with known correction formulas are com- pared with theoretical values.
  The accuracy of analysis of metal constituents of oxides is the same as in the case of alloys disregarding the peak shift caused by the change in chemical combination from metals to oxides. The nearest values are observed at 15 KV on the oxides of light elements and at 20 KV on the iron oxides. In general, the absorption correction formula of J. Philibert and the atomic number correction formula of J. V. Smith are valid.
  There are no accurate standards for quantitative oxygen analysis using OK_α because there is a shift in the peak of the wave length and the spectrum changes measurably in shape. Moreover each measured OK_α intensity of oxides exhibits a characteristic maximum value to the beam voltages. In principle, therefore, a quantitative oxigen analysis of oxides is impossible. But because the iron oxides have similar material parameters it may be said that the OK_α intensities are proportional to the oxygen weight percent of oxides.

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  In order to confirm the validity of the potentiostatic etching technique which was originally proposed for the purpose of detecting microsegregation of silicon in iron-carbon alloys, electron probe X-ray microanalysis was performed concurrently on some experiments.
  The results obtained are summarized as follows:
  (1) It was found that segregation can be detected in cast iron with martensitic matrix also under similar conditions as in the case of ferritic one, but the figures revealed were not as clear as in the case of the latter.
  (2) Segregation pattern of silicon was shown to be formed directly during solidification. It was not influenced by ferritization holding at around 48 hrs at 750 °C cr 24 hrs at 800°C.
  (3) Segregatin in ferritic cast irons containing 0.4% of silicon or less can be detected by prolonged electrolysis. But when the iron contains more than 4% silicon, the whole surface of the sample is stained too rapidly that the segregation pattern is not clearly revealed when etching at or close to +600mV v.s. Hg-HgO electrode.
  (4) Silicon in high carbon iron is enriched in the core of eutectic cells or dendrites in contrast to low carbon iron. In the latter case, it concentrates mainly in the interdendritic regions, regardless of the graphite structure.
  (5) Etching behavior and the nature of silicon distribution in the metallic matrix are not influenced by the coexistence of manganese up to 1% in content.
  (6) On the comparison of these results with the data obtained by X-ray microanalysis, it was concluded that the potentiostatic etching is a simple and useful technique for revealing the segregation pattern of silicon in irons, especially when they contain less than 4% silicon and relatively small amounts of foreign elements. But for a quantitative analysis of silicon distribution, a more detailed study of electrochemical characteristics of iron-silicon alloys is needed.

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  The term “ mass-effect ” in this paper signifies the effect of size and shape of castings on the deterioration of properties from the surface inwards or on the change in mechanical properties by section size, due to variations in the rate of cooling during casting or heat treatment. With a view to investigating the mass-effect of spheroidal graphite cast iron made by both magnesium and calcium bearing alloy treatment, the cooling rate of four protrusions having wall thicknesses of 18, 25, 45 and 60mm respectively, which are connected to one cross-shaped block specimen is measured by using two oscillographs with twelve sources. The relationship of the cooling rate, mechanical properties and micro-structure were investigated on both as-cast and heat treated specimens. Moreover, the cooling rate of Y-block specimens cooled in sodiumsilicate bonded sand mold maintained at temperatures of 150, 240, 475, 630 and 800°C was also investigated to obtain various cooling rates. Although in Y -block specimens the cooling rate as-cast is different, none of the mass-effect appeared during heat treatment, because the size and shape of these five Y-block specimens were the same.
  Summarization of the result obtained with the cross-shaped block, shows that both maximum tensile strength and elongation were gained in the specimen cut from original cross-shaped block having 25mm thickness. The influence of size on the strength and structure was cleariy marked in the group of normalized specimen. In as-cast specimens, however, the mass-effect in different rates of cooling within Ar₁ temperature range is small, since there is only a little difference in the rate of cooling in a cross-shaped block. The correlation between strength and micro-structure in spheroidal graphite cast iron is quite complicated, as the former is influenced not only by form and size of graphite but also by total area of ferrite in bull's eye structure. Besides, the difference of strength in calcium treated irons cast into Y-block mold is not so great compared with that of magnesium treated iron. The largest mass-effect in as-cast condition appeared in magnesium treated iron, causing a great difference in both tensile strength and hardness. When normalizing is performed by cooling from 930°C, however, the difference in hardnessis is minimized. It is also observed in calcium treated iron that a comparatively large difference in elongation is obtained by annealing at sub-critical temperature. This is because imperfect spheroidization of graphite during solidification occurs in calcium treated iron when slow cooled.
  From various straight regression lines showing correlation between mechanical strength and cooling rate, i.e. as diameter of bar assumed, values of tensile strength, yield strength, elongation and hardness of both types of spheroidal graphite cast iron can be estimated considerably precisely. Consequently, by the measurement of the rate of cooling in cast block, estimates can be made of strength, or hardness of spheroidal graphite cast iron as-cast and after normalizing by using various regression lines investigated in our laboratory. In commercial casting, however, it is rather difficult to estimate as-cast strength and others, since some complicated correlating factors affect both cooling rate and strength of castings.

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