Effects of antimony addition and section size on formation of chunky graphite in ductile iron

The combined effects of section size together with antimony addition on formation of chunky graphite in ductile iron were investigated by characterising graphite morphology, nodule count and size. Results show that the increased casting section size leads to an increase in spheroidal graphite diameter and a decrease in graphite nodule count. Meanwhile, all the graphite is spheroidal except in 90 mm thickness casting, in which chunky graphite clearly emerges. Moreover, the same tendency concerning graphite nodule count and size is observed in castings with 0·012 mass-% antimony addition as cooling rate decreases. However, the graphite nodule is refined compared with the Sb free castings, and chunky graphite is absent in 90 mm thickness casting effectively. It is believed that high graphite nodule count suppresses chunky graphite formation in thicker casting because of antimony addition, which has no evident effect on graphite morphology when the casting thickness sizes are less than 90 mm.