Natural Graphite Spheroidization Phenomena in Arc Furnace Metallurgical Process for High-Silicon Cast Iron

Grey cast iron with spheroidal graphite has been known and widely used since the 20th century (since 1947). Numerous methods have been developed for the secondary metallurgy process to produce nodular graphite. Spontaneous crystallization of nodular graphite is known in foundry practice and other fields. Examples of cast iron with spheroidal graphite include pure alloys with low sulfur content and natural samples containing nodular graphite, formed by natural forces (meteorites and combustion ash). This article presents the results of two industrial experiments that led to the formation of nodular graphite precipitates without the addition of elements that promote spheroidization. Studies were carried out on high-silicon cast iron intended for corrosion-resistant castings. TDA, chemical composition analysis, light and scanning microscopy, EDS, X-ray spectroscopy, and digital image analysis were used to identify the nodular precipitates. The analyses confirmed the presence of nodular graphite precipitates, and known growth mechanisms were assigned to them. It is likely that deoxidation of the metal bath during the metallurgical process contributed to the spontaneous crystallization of graphite spheroids.