In the heavy section spheroidal graphite cast iron, abnormal graphite so called chunky often appears in case molten metal is processed by the spheroidizer with high rare earth metal (REM) content or insufficiently inoculated. However, the formation mechanism of chunky graphite has not been made clear because of few leading studies up to this time. In this study, therefore, in order to make clear the formation mechanism of chunky graphite, solidification conditions of heavy castings was reproduced by keeping small quantity of molten metal at the eutectic temperature for a long time. As the result, it has been found that chunky graphite appeared remarkably with increasing amount of Ce added, which segregated near the eutectic cell boundary during keeping at the eutectic temperature. It has also been found that chunky graphite was formed by the growth of graphite with sufficient spheroidizing ability in the direction where basal plain expands predominantly.

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  The shrinkage defect, mechanical properties in shrinkage specimens and chilling tendency in thin sections of spheroidal graphite cast iron were investigated. Nodularization treatment was carried out at 1773K by the addition of Fe-Si-Mg alloys containing high and low RE content. The addition of spheroidized agent containing high RE reduced chilling tendency in spheroidal graphite cast irons Containing 0.015 % sulfur. The shrinkage tendency was not considerably different between the spheroidized agents containing high and low RE content, but the spheroidized agent contain of bismuth should an extreme increase in the shrinkage tendency. A high tensile strength of 600 MPa or above was obtained in the thick sections of spheroidal graphite cast iron containing RE. Considerable elongation and low brinell hardness were obtained in the specimens treated with the agent containing low RE.

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  Dissolution of metallic plate, cylinder and sphere into contacting liquid metal was studied through simulation using Direct Finite Difference Method. One-dimensional displacement of solid-liquid interface due to dissolution follows parabolic law, the rate of which is formulated in terms of relative solubility of liquid metal. Relationship between dissolution rate and the relative solubility obtained was found to be in complete agreement with that of Danckwerts’ equation. The time for complete dissolution of metallic solid is shown by the melt down index, which depends on shape and initial size of the solid, and on diffusion coefficient and relative solubility of contacting liquid metal.

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  Sand inclusion and gas defect are main defects of green sand castings and both are related to with moisture in green sand. It’s quantity of the moisture changes during and after mixing. In this study, the relationship between moisture and oolitics is observed. Moist oolitics has high compactability and low evaporation during and after mixing than moistless oolitics. A cross section of sand adhered with oolitics was observed by SEM. (Porous structures were seen, and these structures coated were found to store moisture when with bentonite.) That is why dryness is prevented. Moistless oolitics require a long time for mixing and have low compactability because they need extra time for moisture to move into porous structure. It is therefore very important that oolitics are moistened before mixing.

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  As a result of Analysis of green sand properties on 100 lines of system sand in 1985 and 1998 respectively, it showed a tendency that green sand, analyzed in 1998, had lower compactability and higher strength compared with those in 1985. Also lower deviation was recognized. So it can be said that green sands in 1998 have changed to higher quality one with better flowability, while they are almost same properties among them. This change corresponds to an improvement of recent molding machine which have higher productivity and better dimensional precision. Green sand properties in 1998 were assorted into each type of molding machine. As a result, it has experienced that they have such properties as higher strength in case of shock wave type of molding machine. Then, green sand control indexes for each molding machine have been obtained. The relationship between green sand properties and additional volume of green materials, used volume of core sand, and sand-metal ratio were checked. As a result, additional volume of each green materials such as bentonite, starch and sea coal has been able to be calculated by remained volume of each materials, used volume of new sand and core sand, and sand-metal ratio. Then, objective standard of judgment for additional volume has been clear by comparing calculated and measured volume.

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