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TRODUCTION

IN cast iron foundry shops, thermal analysis (TA) has slowly evolved over the years as an essential tool for melt control before pouring, but also as a predictive tool of microstructure and casting properties. The possibilities of thermal analysis have been often reviewed, e.g., in the recent works by Dioszegi et al.[1] and Stefanescu.[2–4] TA is expected first to give the so-called carbon equivalent, CE, which is used to locate hypoeutectic alloys with respect to the austenite-graphite eutectic but much more has been looked for, e.g., graphite shape and inoculation level. In practice, foundries rely on experimental calibration of their processing route and state that an alloy behaves as eutectic when the corresponding thermal record shows one single plateau that encompasses the whole solidification process.[5] However, results by Chaudhari et al.[6] M.J. CASTRO-ROMA´N and R. DEL CAMPO-CASTRO are with the Cinvestav Unidad Saltillo, Av. Industria Metalu´rgica 1062, Parque Industrial Saltillo-Ramos Arizpe, Ramos Arizpe, Coahuila, C.P. 25900, Mexico. J. LACAZE is with the CIRIMAT, Universite´ de Toulouse, 31030 Toulouse, France. Contact e-mail: [email protected] A. REGORDOSA and J. SERTUCHA are with the Azterlan, Basque Research Technological Alliance, Aliendalde Auzunea 6, 48200 Durango, Bizkaia, Spain. Manuscript submitted June 14, 2020.

METALLURGICAL AND MATERIALS TRANSACTIONS A

have long ago demonstrated that mildly hypereutectic alloys may show eutectic-type records while being of varying CE. This behavior could result from the solidification conditions in the TA cup, while other microstructures could be revealed in parts with varying size and cooling rate cast with such a melt, thus generating some confusions. As a matter of fact, the conditions for growth of graphite and austenite are affected by tiny changes in the process parameters, e.g., melt composition, graphite nucleation, and growth or else cooling rate. Accepting that growth of austenite is easier than that of graphite, graphite growth is thus the key in understanding TA records as it is for analyzing the microstructure of cast iron parts. In the literature, the basic knowledge of graphite growth was largely obtained in relation to the eutectic reaction, while little research has been done on the primary growth of graphite, i.e., the precipitation of graphite alone directly from the liquid. Rare studies on primary growth have been carried out by quenching samples during solidification or by investigating the microstructure of highly hypereutectic alloys.[7,8] There is also one outstanding experimental work based on TA analysis including highly hypereutectic cast irons which is of main concern for the present study. This work was performed over several years and led to two final contributions dedicated to the possibility of extending thermal analysis for predicting as-cast microstructure of

industrial cast irons[9] and laboratory alloys.[6] There were two essential outputs from this work which are as follows: (i) the thermal records of