Measurements of the amount of graphite in cast irons quenched during freezing were carried out by means of structure analysis. The amount of graphite in the flake graphite cast iron was more than that in the spheroidal graphite cast iron of the same carbon equivalent. The amount of graphite in spheroidal graphite iron casting was much affected by its freezing rate ; the lower the rate, the more was the amount of graphite. Moreover, the amount of graphite was affected by the spheroidizing and inoculation treatments of the molten iron.

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  The property of wear resistance in high chromium cast iron was investigated. One kind of iron was 10 percent chromium alloy that crystallizes primary iron carbide as (Fe, Cr)₃C type, and the other was 30 percent chromium alloy that crystallizes the same as (Fe, Cr)₇C₃ type. In the dry wear condition under constant load in air, the specimens of metal mold casting and casting solidified unidirectionally were worn with emery papers of different grain size.
  Wear property varied with chromium content and the grain size of emery paper. Wear quantity of the harder 30 percent chromium alloy was less than that of 10 percent chromium alloy. Improvement of wear property in both types of cast iron is expected by controlling the solidification structures. Selection of wear surface from the structure perpendicular to the direction of solidification, controlled crystallization of larger primary iron carbide, and dispersed precipitation of eutectic matrices have good effect on wear resistance.

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  The size and shape of SiO₂ particles dispersed in colloidal silica were first measured using an electron microscope. The variation of the distance between individual silica was examined by small angle scattering of X-ray. Based on these examinations, the process of formation of solid amorphous silica (silica gel) produced by evaporation was discussed. The apparent density and the knoop hardness of the silica gel produced in the above process were measured. In addition, the knoop hardness of silica gel was measured after firing the gel at an elevated temperature.
  Two kind of colloidal silica, colloidal-L and colloidal-S, were used in this experiment. The mean diamter of SiO₂ particles dispersed in the colloidal silica-L proved to be 9.6 mμ, while that of the colloidal silica-S turned out to be 16.1mμ. The degree of roundness of SiO₂ particles was better in colloidal silica-L than in colloidal silica-S. The results of small angle scattering of X-ray was that each SiO₂ particle dispersed in the colloidal silica approached one another to almost collide at approximately 45% evaporation of water, resulting in the residual colloidal silica remarkably destabilizing and hardening in a short time. About 5−6% of water still remained in the lump of silica gel produced in the colloidal silica and dried in a desiccator sufficiently at room temperature. The apparent density and knoop hardness of this silica gel were 1.2−1.3g/cm³ and 63−67, respectively. The knoop hardness of the dried silica gel increased in proportion to the rise of firing temperature. When it was fired at the temperature above the crystallization point (800−840°C), the knoop hardness almost reached 500 after complete crystallization.

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  To clarify the mechanism of Si-inoculation, the diffusion passes between high carbon and low silicon liquid alloys and high silicon liquid alloys (high carbon/high silicon diffusion) were compared with that of low carbon and low silicon range (low carbon and low silicon range diffusion). In addition, solution and diffusion process of Fe-Si inoculant into cast iron melt was observed by the liquid quenching method.
  A characteristic difference was observed between the high carbon/high silicon diffusion and low carbon and low silicon range diffusion. In the former, carbon atoms cannot get into the high silicon side and the process is controlled only by the diffusion of silicon atoms into the high carbon side. As a result of this process, two carbon super-saturated regions are formed. In the latter, remarkable interaction was not observed. Only the lower silicon content (about 10%) region of the two carbon super-saturated ones described above was observed by liquid quenching after inoculation. Considering the width of the super-saturated area, this lower silicon region must be more effective for inoculation. In the Si-inoculation, fine graphite crystals would be nucleated upon the interfaces of silica and liquid in this carbon super-saturated region during the solution and diffusion process of the inoculant.

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  The fracture toughness of several cast irons of different tensile strength were investigated experimentally. Static and dynamic three point bending tests of notched bar specimens were carried out, and the load-deflection curve of each test was analysed to get the critical stress intensity factor, K_c, and J-integrals.
  K_c was found to increase as the tensile strength of the iron increased, without any difference in the static and dynamic tests of each iron. The elastic J-integral, J_e, calculated from the load-deflection curve showed almost the same value as the critical strain-energy release rate G_c=(1−ν²)K_c²/E, and increased with the increased tensile strength. However, the plastic J-integral, J_p, was found to have maximum value in the iron which contained sufficient ferrite and had medium strength of about 20kg/mm². The critical J-integral, J_c, calculated as the sum of J_e and J_p, proved to be valid as J_Ic for each iron, and showed a maximum value of about 2kg/mm in the irons of the tensile strength above 20kg/mm². The crack propagation energy per unit ligament area, J_prop, was very alike to J_p in each static test. And the total fracture energy per unit ligament area showed slightly less value than Charpy value in each test, and had a maximum value of 2.7kg/mm² in 20−25kg/mm² class irons, without any significant difference between the static and the dynamic tests. J_e/J_Ic was considered to be a criterion of brittleness of the fracture, and the lowest value was 0.25 in 20kg/mm² class iron and higher values went up to 0.5 in the irons of lower and higher strength.

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  The mechanism of retardation of mottling tendency in white iron castings by a small addition of bismuth has not been clarified yet. With a view to analysing this mechanism, the effect of bismuth addition on the morphological change of primary graphite in hypereutectic Ni-C alloy was studied using scanning electron microscope, electron probe microanalyser and quantitative television microscope.
  Primary graphite consisting of hexagonal stacking structure was obtained in this alloy when cooled slowly at the cooling rate of 15 and 5°C/min. From the morphological study of graphite structure which appeared in hypereutectic Ni-C alloy, it is obvious that there is adsorption of bismuth on the plane of graphite structure which is perpendicular to the basal plane. This behaviour affects the formation of hexagonal structure resulting from the appearance of anisotropy in the graphite crystal, retards the growth of graphite, and then leads to the formation of stacking structure which may be attributed to two dimensional nucleation.

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