Abstract
In order to investigate the growth characteristics of spheroidal graphite cast iron, the fracture surface of irons which grew up to 10% linearly in air was observed by scanning electron microscope and electron probe microanalyser. From SEM-XMA fractography and composition-analysis, in addition to other experimental results on the growth of spheroidal graphite iron, the growth can be understood well as a metallurgical phenomenon occuring by the irreversible graphite migration during heating and cooling. Evidences for the growth mechanism are the grown micro-voids around graphite nodules observed on the SEM-fractograph and the redistributed graphite particles adjacent to graphite nodules confirmed by optical microscope and XMA. Dilatation curve also indicated the metallurgical behavior and the nominal increase in dimension even after the 10% growth.
No effect of oxidation was observed in the central area of the specimens, in spite of the iron becoming porous in structure after heavy growth. The results of analysis by XMA for O and Si also showed that the distribution of these elements was not changed by oxidation in the grown iron as compared with as-cast iron. This is very important in discussing the mechanism of growth in relation to oxidation.
