Formation mechanism of chunky graphite in heavy section spheroidal graphite cast iron

摘要

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 tuetal 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.