Diversified Aggregated Patterns of Alumina Inclusions in High-Al Iron Melt
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INTRODUCTION
HIGH-AL steel is one of the alternative materials to achieve automotive lightweight through both reducing the density of steel materials and keeping the material strength. The main differences in metallurgical processes between the high-Al steel and the conventional Al-killed steel lie in the Al-deoxidation reaction resulting in alumina inclusions and the segregation of high-concentration Al element in steel solidification process. Many studies on the conventional Al-killed steel suggested that alumina inclusion is easy to aggregate into the large-sized particle agglomerates with various shapes, such as plate-like, dendritic, and clustered, et al., because of the high interfacial energy between alumina inclusions and iron melt, which have an extremely negative effect on continuous casting and steel product performances.[1–6] The Al-deoxidation reaction and agglomerations of alumina inclusions in the conventional Al-killed steel have been extensively investigated GUOCHENG WANG and YUANYOU XIAO are with the School of Materials and Metallurgy, University of Science and Technology Liaoning, Anshan 114051, Liaoning, P.R. China and also with the Key Laboratory of Chemical Metallurgy Engineering Liaoning Province, University of Science and Technology Liaoning, Anshan, 114051, Liaoning, P.R China. Contact e-mail: [email protected] YANG ZHAO, PENGLIANG JIN, and SHENGLI LI are with the School of Materials and Metallurgy, University of Science and Technology Liaoning. SEETHARAMAN SRIDHAR is with the Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO, 80401. Manuscript submitted May 5, 2020; accepted September 10, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
in recent decades.[7–16] Research on production of high-Al steel has become a hot spot at present.[17–22] However, there are less known about the characteristics, formation, and agglomeration of alumina inclusions formed by high-concentration Al reacting with O in high-Al iron melt. Peak et al.,[23] Kang et al.,[24] and Jung et al.[25] studied the thermodynamic equilibrium of Al-deoxidation reaction with the Al concentration of 0.0027 to 100, 0.01 to 10.0, 0.0001 to 10.0 mass pct in iron melt, respectively. Their results indicated that the dissolved O concentration decreases first and then increases with the increasing of Al concentration in iron melt. There is still not a unified quantitative understanding on the reaction equilibrium between O and Al with high concentration in iron melt. It is obvious that the reaction of O and Al with high concentration in iron melt affects the formation and agglomeration of Al-deoxidation products, probably resulting in a feasible new morphology and mechanism of agglomeration. In the current work, the experiments of high-concentration Al deoxidation for iron melt were carried out by the confocal laser scanning microscope (CLSM) controlling different holding times of high-temperature melts and cooling rate. The diversified aggregated patterns of alumina inclusions in the samples we
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