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MULTICOMPONENT Fe-C-Si-Mn-S-etc. alloys, known in industry as cast irons, solidify with a stable austenite/graphite (c/Gr), or metastable c/Fe3C eutectic. The stable form of the carbon-rich phase, the graphite, crystallizes from the liquid with a variety of morphologies, depending on the chemical composition and the solidification conditions (cooling rate). The main morphologies include lamellar (LG), compacted or vermicular (CG), and spheroidal (SG) graphite. Other ‘‘degenerated’’ or intermediate forms include, but are not limited to, chunky and exploded graphite. An LG-to-CG-to-SG transition can be triggered through the addition of small amounts of Mg, Ce, or lanthanides

D.M. STEFANESCU, Professor Emeritus, is with The Ohio State University, Columbus, OH, and also with The University of Alabama, Tuscaloosa, AL. Contact e-mail: [email protected] R. HUFF, Technical Team Leader, is with Manufacturing Technology, PD>, Caterpillar, Peoria, IL. G. ALONSO and P. LARRAN˜AGA, Project Leaders, and E. DE LA FUENTE, Junior Researcher, are with the A´rea Ingenierı´ a, I+D y Procesos Metalu´rgicos, IK4-Azterlan, Durango, Spain. R. SUAREZ, Manager R&D of Metallurgical Processes, is with the Veigalan Estudio 2010, Durango, Bizkaia, Spain. Manuscript submitted January 27, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A

to a low sulfur iron. The process is reversible: SG will revert to LG with sulfur addition or through loss of magnesium by evaporation and/or oxidation. The CG-to-LG transition is sensitive to the specific elements used to produce it. It was found that the transition from compacted to lamellar shape was continuous for Mg treatment, whereas a sharp transition was found when lanthanides were used for graphite shape modification.[1] This work is concerned with the crystallization of compacted and chunky (CHG) graphite. Typical examples of these morphologies are presented in Figure 1 after Reference 2 and 3. It is seen that both forms of graphite are highly interconnected and appear to grow radially outward. Earlier SEM investigation conducted on deep-etched Fe-C-Si samples of industrial composition, obtained through interrupted solidification, revealed the sequence of evolution of graphite aggregates morphology as the amount of magnesium in the composition increases. It was demonstrated that when the residual magnesium increases from