METHOD FOR SPHEROIDIZING MOLTEN METAL OF SPHEROIDAL GRAPHITE CAST IRON

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The present invention uses a graphite spheroidizing agent containing : 30-80 wt% of Si, Mg, one RE (rare earth element) selected from 80-100 wt% pure Ce or 80-100 wt% pure La, Ca, and Al. This graphite spheroidizing agent is added so as to satisfy the following conditions : the amounts added are such that in relation to the molten metal overall, the RE constitutes 0.001-0.009 wt%, the Ca constitutes 0.001-0.02 wt%, and the Al constitutes 0.001-0.02 wt%; and after the graphite spheroidizing treatment, the molten metal contains 0.03-0.07 wt% of Mg. As a result, it is possible to inexpensively suppress the crystallization of chunky graphite and the decline in mechanical properties in a thick product comprising spheroidal graphite cast iron.