DISTRIBUTION OF NODULARIZING ELEMENTS IN R. E. TREATED SPHEROIDAL GRAPHITE CAST IRONS

The distribution of nodularizing elements such as cerium, yttrium, magnesiumor calcium and of subversive such as sulphur in R. E. treated spheroidal graphitecast irons has been studied by means of autoradiograph, electron probe and ionmass microanalysis. The blackness of autoradiography to a first approximationshowed the content of the radioactive components in graphite and in matrix. Cer-tain graphite spherulites each contained a nucleus, the composition of which wasdifferent with different nodularizing elements. The distribution of the different nod-ularizing elements cerium, magnesium, yttrium, calcium and the subversive agentsulphur in nodular cast iron occurred in many different ways, compounds ofnodularizing elements might exist as nuclei of graphite spherulites with yttrium,magnesium and calcium etc. around them. In certain spherulites, cerium was found-to distribute uniformly but yttrium irregularly. In cast irons treated separately bycerium, yttrium or other nodularizing elements, however, hardly any rare earthwas found to enrich around most of the spherulites. In view of the complex be-havior in rare earth distribution, it would appear that graphite spherulites are form-ed far from only in a single way. The interaction due to the nodularizingelements in fact may be the result of scavenging subversives (sulphur, oxygen, etc.),in its consequence the surface tension of melt and the interfacial tension at themelt-graphite boundaries thus facilitating the formation of graphite spherulites.The mechanism of duplex graphite spherulites formation has also been primarilyexamined.