Abstract
A new concept, in which free magnesium might be a key indicator of the state of graphite spheroidization in spheroidal graphite irons, is proposed and verified in this study. Chilled samples containing different amounts of total magnesium were prepared. The total, inclusive and free state magnesium contents were analysed by a special procedure. Free magnesium increased in steps as total magnesium increased. On the other hand, inclusive magnesium was nearly equal among the chilled samples. The nodularity and the mechanical properties in 50 mm Y-blocks showed good correlation to the value of the free magnesium, but no relation to that of the inclusive magnesium. The quality of spheroidal graphite cast iron should be controlled by the content of free magnesium in practice. The experimental results well supported the site theory.
