抄録
In order to evaluate a shrinkage tendency of molten spheroidal graphite cast iron, test pieces having a variety of widths with a constant thickness were cast and the shrinkage areas were measured. Also, cooling curves of the surface and the inside of test pieces were prepared to find a relationship between the shrinkage area and the inside solidification ratio when the surface solidified (temporarily referred as S/I). The S/I value at the start of shrinkage occurrence is determined as a critical S/I to shrinkage, with which the shrinkage tendency for the molten iron has been evaluated. The critical S/I to shrinkage are determined for different contents of C, Mo, Sb, Cr and P and inoculation methods and Bi addition. Resultantly the higher amount of C makes the shrinkage lower and minimum at the C content approx. 3.7 %, and it becomes higher with the increase of the amount of alloy element and Bi addition and lower by inoculation. Also, it is found that the shrinkage tendency by adding an alloy element can be converted to C content. Other causes of shrinkage e.g. the lack of graphitization, worse fluidity due to primary graphite, or the difference of solidification time between the surface and the inside are also explained.
