In Situ Observation of Crystallization in CaO-Fe 2 O 3 System with Different Cooling Rates and Chemical Compositions Usi
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The crystallization behaviors of the CaO-Fe2O3 system in the nonequilibrium state with different chemical compositions and cooling rates were investigated. In addition, the CCT and nonequilibrium phase diagram of CaO-Fe2O3 system were derived at various cooling rates. As the cooling rate increased, the nonequilibrium state of the CaO-Fe2O3 system moved in a left-downward direction as a whole. In addition, the Darken’s excess stability function was introduced in order to understanding the change of phase diagram phenomena. Sinter ore is one of the main charge materials in Blast Furnace operation (BF). The productivity of BF is governed by the qualities of sinter ore such as reducibility and mechanical strength. As the properties of sinter ore mainly depend on mineralogy, understanding the mineralogical characteristics of sinter ore is necessary to design the optimal microstructure, especially that of Silico-Ferrite of Calcium and Aluminum (SFCA). However, owing to the complexity of the sintering process caused by its inhomogeneous and nonequilibrium nature, the formation mechanism of iron ore sinter is not fully understood yet. Furthermore, the sinter mineralogy has a complicated nature, and its behaviors vary significantly and depend on various factors.[1–6] Numerous investigations[7–10] have aimed to determine the formation mechanisms of the sinter bonding phases of SFCA. SFCA phases influence the strength, reducibility, and reduction degradation index. Therefore, research has been extensively conducted on the
TAE JUN PARK, JOON SUNG CHOI, and DONG JOON MIN are with the Department of Materials Science and Engineering, Yonsei University, 50, Yonsei-ro, Seodaemun-gu, Seoul 03722, Republic of Korea. Contact e-mail: [email protected] Manuscript submitted March 19, 2018. METALLURGICAL AND MATERIALS TRANSACTIONS B
formation mechanism of SFCA. Webster and Scarlett et al.[11–14] studied the reaction sequences involved in the formation of SFCA using in situ X-ray diffraction techniques. Their studies indicate that, during cooling in a liquid state, the initial crystallization is determined by the reaction between FeOx and the melt, and the formation of SFCA is determined by the reaction of the CaO-Fe2O3 system. Edstrom et al.[15] reported the temperature interval of the phases generated in the CaO-Fe2O3 system and Phillips et al.[16] demonstrated the phase diagram of CaO-Fe2O3 in air and at an O2 pressure of 1 atm, in which the phase stability, decomposition of Fe2O3, and melting of 2CaOÆFe2O3 were fully discussed. However, as the actual sintering process is a nonequilibrium and heterogeneous condition with rapid temperature changes and various chemical compositions, previous studies provide scant information in this regard. In this study, the crystallization behaviors of the CaO-Fe2O3 system, which determine the shape of SFCA, were investigated in the nonequilibrium state with different chemical compositions. Crystallization behaviors were observed by using a confocal laser scanning microscope, which can simulate rapid h
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