The author has studied the inhibitory effects of elements such as Se, Te, Ti, Al, B, Cu, As, Sn, Sb, Pb and Bi on the formation of spheroidal graphite to clarify the mechanism of preventation of graphite spheroidization. In this report, the inhibitory effects of these elements on the solidification process were discussed and summarized.
  Elements such as S, Se, Te, Pb and Bi consume Mg which is necessary to form spheroidal graphite, while Ti, Al, B, Cu, As, Sn and Sb do not. Harmful elements which have little or no solubility in molten iron and have small equilibrium distribution coefficients in austenite are more inhibitory than others. Elements such as S, Se and Te form vermicular, undercooled and flaky graphite with increased addition, while Ti, Al, B, Cu, As, Sn and Sb form degenerated graphite. Elements such as Pb and Bi form degenerated graphite when the amount is small but form vermicular, undercooled and flaky graphite when the content is high.
  Granular and thread-like degenerated graphite form at the austenite cell boundary at the last stage, quasi-spheroidal and vermicular graphite form at the austenite grain boundary at the middle stage and aggregated graphite form at the first stage of eutectic solidification. The formation of vermicular, undercooled and flaky graphite on the addition of S, Se, Te, Pb and Bi, is caused by the consumption of Mg by these elements, and the formation of degenerated graphites such as granular, thread-like, vermicular and quasi-spheroidal ones on the addition of Ti, Al, B, Cu, As, Sn, Sb, Pb and Bi, is caused by the concentration of these elements at the austenite grain and cell boundaries during eutectic solidification. Elements such as B, Cu, As, Sn, Sb, Pb and Bi improve the shape of the primary graphite within a certain range of addition. The harmful elements can be classified into the following three groups depending on the type of inhibition, i. e. the Mg-consume type (S, Se, Te), the boundary concentrating type (Ti, Al, B, Cu, As, Sn, Sb) and the mixed type (Pb, Bi).

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  The fluidity of tin bronze was estimated from the filling ratio in the permanent mold, and the influence of the amount of tin, casting conditions, thickness of the casting and mold on fluidity was investigated. Fluidity increases as the superheat of melt and the mold temperature increase. It is difficult to obtain sound castings less than 6mm in thickness when pouring into permanent mold at room temperature. The addition of phosphorus causes the transition from the columnar grains to equiaxed ones and makes the dendrite structure coarse, because the freezing range of the tin bronze alloy is widened. Thus, fluidity increases with the increase of the phosphorus content. Fluidity decreases as the tin content increases up to the solubility limit, and then increases with the increase of the tin content.

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  With a view to analyzing how to suppress mottling in white cast iron, the effect of both the amount and method of bismuth addition to molten iron on graphite formation during solidification of synthetic cast iron was investigated. By directly adding bismuth to molten iron the form of graphite changes from normal flake graphite to a highly branched type. If bismuth addition is sufficient a white iron structure can be obtained. In W-type molten metal joining test material, bismuth transported from a melt with a high bismuth content accelerate the precipitation of finer graphite. It became clear in Shear Cell Joining test piece that bismuth diffusing from pure bismuth melt causes precipitation of fine graphite during solidification of cast iron. Consequently, more than critical amount of bismuth to change the graphite morphology is required to prevent the nucleation and growth of graphite in cast iron.

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  In order to investigate the infiuence of graphite nodule on impact fracture characteristics of ferritic spheroidal graphite iron, Charpy impact test and fractographical study of the fracture surface were carried out on irons with varried carbon content and constant nodule size. On conducting the Charpy impact test, total absorbed energy was divided into two absorbed energies by using an instrumented impact tester, that is, crack initiation energy and propagation energy were determined from load-time curves. On fractographical study, the ductile and brittle fracture surfaces were observed with a scanning electron microscope.
  Void nucleation occurs at the graphite structures of the ductile cast iron that failed in a ductile manner at high temperature, and the graphite nodules facilitate the growth and coalescence of voids. Therefore, increasing the number of graphite nodules lowers the ductile impact value in all cases. Under the condition of brittle fracture at low temperature, cleavage crack initiates at the eutectic cell boundary. Graphite structures arrest the continuous propagation of a crack and causes the crack to branch.

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  The content of soluble oxygen during cooling, inoculation and solidification of Fe-C and Fe-C-Si alloy melts were measured by the oxygen concentration cells with the solid electrolyte of mullite. It was possible to detect the transitional critical temperature from C-O reaction to Si-O reaction during cooling. The transitional critiical temperature is lower than the critical equilibrium temperature. This means that considerable undercooling is required to accelerate the Si-O reaction. Above the critical temperature, the soluble oxygen content near the solid SiO₂ is higher than the equilibrium value. Immediately after the Si-inoculation, the soluble oxygen content falls abruptly and recover to the constant level. This means that the Si-inoculation process contains the deoxidization process of the melt. In the beginning of eutectic solidification, the soluble oxygen content of melt increases by its redistribution during the solidification.

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  In order to study crack initiation and its growth rate, a fatigue machine installed with a microscope was employed for continuous and direct observation of the polished surface of the specimen during fatigue.
  Iron with fine duplex strucure throughout the matrix tends to improve fatigue strength and endurance ratio as compared with lamellar pearlitic and spheroidal pearlitic ones although the ultimate tensile strength of these are higher than the iron of the duplex matrix. This tendency is especially remarkable in notched specimen in agreement with the fact that the fatigue notch factor of the fine duplex one is much lower.
  The analysis of the growth of the fatigue crack showed that there were three stages of growth and that the rate of growth in the second stage (constant growth rate stage) almost governed the fatigue life. Rapid crack propagation was accompanied by the linkage of isolated micro-cracks generating from the vicinity of the eutectic cell boundaries and graphite nodules ahead of the main crack. Because the eutectic cell boundary region tended to remain a coarse pearlite containing non-metallic inclusion and temper carbon, it has a high notch effect compared with that of graphite nodules. The fatigue strength of the iron with a fine duplex and spheroidal pearlite which were heat-treated for a short time decreased due to the formation of a defective region above mentioned. Consequently, when the matrix structure is fine and uniformly duplex throughout the matrix, a remarkable improvement in the fatigue properties may be achieved in spheroidal graphite cast iron.

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