Atomic Cluster Aggregates in Nucleation of Solid Alumina Inclusion in the Aluminum Deoxidation for Liquid Iron
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INTRODUCTION
SOLID alumina inclusion with high melting point and low deformability is commonly detrimental to the quality of products, the castability, and the processability of high-quality Al-killed steel. Lowe and Mitchell suggested that nonmetallic inclusions have almost no hazard to the mechanical properties of steel, if the size of the inclusion particle is less than 1 lm and the distance between particles is longer than 10 lm in the steel matrix.[1] At the same time, many studies on using nonmetallic inclusions positively show that species oxide and sulfide with fine size (such as Ti2O3, Al2O3, and CuxS) can effectively enhance the formation of acicular intragranular ferrite.[2–5] Therefore, it is important to control the size and size distribution of solid alumina inclusions in Al-killed steel.
GUOCHENG WANG, CHANGMING ZHAO, and JING LI 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] YUANYOU XIAO is with the School of Materials and Metallurgy, University of Science and Technology Liaoning. DELI SHANG is with the Anshan Iron and Steel Group Company, Anshan 114021, Liaoning, P.R. China. Manuscript submitted October 5, 2016. Article published online November 27, 2017. 282—VOLUME 49B, FEBRUARY 2018
Alumina inclusions are almost originated from the Al-deoxidation reaction in liquid iron. The Al-deoxidation reaction has been intensively studied since the 1950s because of its complexity.[6–22] The consenting reaction equation and its standard Gibbs free energy change[23,24] can be written as 2Al + 3O = a-Al2O3(s), DrGH m = 1202.00 + 0.386T, kJ mol1. The knowledge on the Al deoxidation can be summarized as follows: (1) the Al-deoxidation reaction has difficulty reaching thermodynamic equilibrium and (2) primary alumina inclusions are mainly a-Al2O3 in the Al-deoxidation steel. In the Al-deoxidation reaction process, the nucleation of deoxidation products plays a decisive role in determining the structure, size, and size distribution of alumina inclusions. However, the knowledge on the Al deoxidation does not provide a clear picture about the nucleation pathway of deoxidation products from liquid iron. Little is known about the structures and thermodynamic properties of metastable alumina phase (MAP), as intermediates probably appeared in the nucleation stage of alumina products. Consequently, it is crucial to learn about the fundamentals of formation and transformation of MAP in the Al deoxidation for liquid iron in order to reveal the nucleation pathway and control alumina inclusions. In this work, the authors have studied the thermodynamics on formation and transformation of a species of MAP-alumina atomic cluster aggregates (AACAs) as intermediates in the nucleation of alumina deoxidation products on the basis of the sum
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