Generally, the bonding structure of green molding sand controls the green properties of sand mold. Many investigators have considered that the bonding material on sand grain surfaces adhered to the surfaces smoothly and uniformly.
    Some investigators have studied the distribution of bonding material on sand grain surfaces and explained that adhesion was not smooth, but they did not go so far as to discuss the relation between green properties and bonding structure of sand mold.
    The authors have considered that the observation of grain surface and its bonding structure by stereoscopic microscope will not be difficult when glass beads are used with water-bentonite mixture as bonding material. Accordingly, we first observed the bonding structure and green properties of glass beads-water-bentonite mixture. Next, we used silica sand and studied the relation between its bonding structure and green properties. The results were as follows:
  (1) Bonding structure of green glass beads mold was observed more easily than sand green mold by stereoscopic microscope, because there was no need to consider the influence of grain size, fineness of sand and distribution of grain size which must be considered for silica sand.
  (2) Surface hardness and green compressive strength increased with the increase of bonding material in a fixed water content of the bonding material. We considered the reason behind this to be the gradual increase of the bonding material in the gaps preventing the movement of grains.
  (3) Bulk density increased according to the increase of bonding material in a fixed water content of bonding material. The reason for this was considered to be the gradual increase of the bonding material in the gaps with the increase of the bonding material.
  (4) Permeability decreased with the increase of water content of the bondig material. We considered the reason to be in that more bonding material got into the gaps with the increase of water content of the bonding material.
  (5) Permeability decreased when there was little water in the bonding material, or when the proportion on fine grains in coarse increased. We considered the reaason to be in that powdered bentonite or fine grains got into the gaps.
  (6) In both glass beads and silica sand, permeability was small when there was plenty of bonding material, but the difference in permeability between abundant and little bonding material was greater when glass beads were used than when silica sand was used.
  (7) When glass beads were used, there was no large difference between three ramming piece and high pressure compacted piece. We reasoned that this was because spherical glass beads were compacted densely with comparatively small pressure.
  (8) When the ratio of coase to fine in the molding sand was almost the same, compactibility of the mixture was greatest in both glass beads and silica sand.

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    Solidification of high-purity Fe-C and Fe-C-Si alloys was studied by thermal analysis and metallographic techniques to investigate the relationships of the solidification process, the chemical composition and the cooling rate. The experiments were conducted in a specially designed high vacuum high frequency induction furnace under controlled coditions. The alloys studied were of hypo-eutectic, eutectic and hyper-eutectic compositions with carbon content and silicon content varying from 2.64% to 4.48% and 0.0% to 3.6%, respectively. The cooling rates employed were varied from 10 to 150°C/min (at the temperature range between 1,170 and 1,200°C) .
    The results obtained can be summarized as follows:
  (1) Eutectic solidification was undercooled with increasing cooling rate. The degree of undercooling was proportional to the 0.5th power of the cooling rate. The undercooling decreased with increasing carbon equivalent at a constant cooling rate.
  (2) The solidification rate increased in proportion to the cooling rate.
  (3) Consequently, the solidification rate was proportional to the square of the undercooling.
  (4) The primary crystallization rate of the hypo-eutectic alloy increased in proportion to the 1.3th power of the cooling rate.
  (5) The diameter of the eutectic cell of the eutectic alloy was smaller than that of the hypoeutectic or the hyper-eutectic alloys. With increasing cooling rate, eutectic cell diameter decreased, that is, the number of eutectic cells increased.
  (6) With the increase in the cooling rate, quasi-spheroidal graphite was formed in Fe-C-Si alloys containing a large amount of silicon and mottle iron structure by two eutectic reactions was observed in hypoeutectic alloys. These phenomena were observed clearly when the degree of undercooling, the rate of solidification and the rate of cooling increased.

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  Elastic behaviors of cast irons under low stress is not clear. Therefore, the authors have conducted investigtions to find this out using several cast irons of various tensile strengths and graphite structures and comparing the modulus of elasticity calculated from the propagating velocity of supersonic waves with the modulus of elasticity in zero region stress obtained by extrapolating from a mechanical method.
  The results obtained are summerized as follows:
  The flake graphite cast irons with low tensile strengths between 10 to 15kg/mm² do not show any elastic behavior even under low stress and their modulus of elasticity decreases uniformly with the increase of stress. But cast irons with high tensile strength do show elastic behaviors and their modulus of elasticity is constant for a considerables tress range. In cases of high strength cast irons, the constant value of the modulus of elasticity and the stress range of the constant modulus of elasticity are larger, and the rate of decrease of the modulus of elasticity under high stress is smaller.

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    Siliconizing to increase the resistance of metals and alloyse to corrosion and oxidation is widely performed in modern industry. But there are many difficulties in the siliconizing of cast iron, with either gas or powder methods. There has been no application of the process on any considerable scale to industry because of defects rough surface, a porous layer and detachment from the siliconized surface. The authors have discovered the possibility of siliconizing cast iron with the powder method, using Fe-Si-Cr alloy prepared in high purity. A good heat resistant layer on cast iron was obtained by packing the cast iron in the powder of Fe-Si-Cr alloy containing 20-30%Si and keeping it at 1,100°C in H₂ for 4 to 10 hours. This siliconizing process was good for producing silicon coating on cast iron containing 6-11%Si in the thickness range of 30-80μ. Recently, the metal mold process for producing cast iron castings is employed on a large scale because of its economic and technical advantages. However, the short service life of the metal mold which is one of the demerits of the process does not allow for the development of this process. The authors studied the applicability of the siliconized cast iron as a new metal mold material by examing oxidation resistance, degree of degradation of mechanical properties (thermal stability), high temperature hardness and thermal shock resistance. The conclusions obtained from the experiment are as fallows:
  (1) The thickness of the siliconized layer was 50-60μ in the case of siliconizing for 4 hours at 1,100°C.
  (2) The oxidation risistance in air for 30 hours at 900°C was about 8 times greater than that of the nonsiliconized cast iron.
  (3) The thermal stability and high temperature microhardness tests showed the siliconized cast iron to be substantially superior to untreated cast iron.
  (4) In the thermal shock resistance test, heating the cast iron to 1,000°C for 2 minutes and cooling it in the blasted air for 2 minutes, crack appeared at 325 cycles, while the siliconized cast iron did not initiate cracking even after 1,500 cycles.
(5) The siliconized cast iron showed good properties as a metal mold material. The service life of the metal mold will be prolonged by siliconizing it.

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