Formation and thermodynamics of CaS-bearing inclusions during Ca treatment in oil casting steels

Xue-feng Bai; Yan-hui Sun; Rui-mei Chen; Yi-min Zhang; Yi-fan Cai

doi:10.1007/s12613-019-1766-0

Volume 26 Issue 5

May 2019

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Article Navigation > International Journal of Minerals, Metallurgy and Materials > 2019 > 26(5): 573-587

Xue-feng Bai, Yan-hui Sun, Rui-mei Chen, Yi-min Zhang, and Yi-fan Cai, Formation and thermodynamics of CaS-bearing inclusions during Ca treatment in oil casting steels, Int. J. Miner. Metall. Mater., 26(2019), No. 5, pp. 573-587. https://doi.org/10.1007/s12613-019-1766-0

Cite this article as:

Xue-feng Bai, Yan-hui Sun, Rui-mei Chen, Yi-min Zhang, and Yi-fan Cai, Formation and thermodynamics of CaS-bearing inclusions during Ca treatment in oil casting steels, Int. J. Miner. Metall. Mater., 26(2019), No. 5, pp. 573-587. https://doi.org/10.1007/s12613-019-1766-0

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Research Article

Formation and thermodynamics of CaS-bearing inclusions during Ca treatment in oil casting steels

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Corresponding author:
Yan-hui Sun E-mail: sunyanhui@metall.ustb.edu.cn
Received: 7 December 2018; Revised: 21 January 2019; Accepted: 24 January 2019

Abstract

Abstract

Industrial experiments were carried out to investigate the formation of CaS-bearing inclusion during Ca double modification in oil casting steels using polished cross sections and electrolytic extraction. Immediately after Ca addition, the role of newly generated CaS as an intermediate reaction product, which modified the Al₂O₃ inclusion into a liquid calcium aluminate, was confirmed. The formation of transient CaS was attributed to the high surface segregation of S at the liquid steel-calcium vapor interface, where a simple site coverage model based upon the Langmuir adsorption equation was established. Moreover, a CaS outer layer surrounding the liquid calcium aluminate was attained mainly in the tundish, which was distributed unevenly on the surface of liquid particles according to the three-dimensional mapping results. The surface of a well-modified calcium aluminate with higher CaO activity and Al₂O₃ activity under bulk composition conditions in the tundish acted as a favorable site for the generation of CaS. Additionally, CaS could be precipitated directly onto existing inclusions during solidification of the steel, which led to various morphologies of CaS-bearing inclusions in slabs. Furthermore, the phase transformation of inclusions during solidification was strongly influenced both by the S content and the Ca/S ratio in the tundish via thermodynamics.
- CaS inclusions;
- Ca treatment;
- electrolytic extraction;
- thermodynamics;
- three-dimensional investigations

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