Formation and Deformation Mechanism of Al2O3-CaS Inclusions in Ca-Treated Non-Oriented Electrical Steels
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Industrial trials were performed to study the effect of calcium treatment on inclusions in non-oriented electrical steels. The evolution and characterization of inclusions in both molten steel and rolled steel were investigated, including a thermodynamic analysis using FactSage 7.1. In the Ca-treated steel, alumina inclusions were transformed into Al2O3-CaO-CaS, with a mass fraction of CaO that increased with increasing the Ca/S ratio. Inclusions of Al2O3-CaO-CaS were classified into wrapping and adhesion type according to their morphologies. Adhesion-type Al2O3-CaO-CaS inclusions were observed only in the steel with Ca/S > 0.84. The two types of Al2O3-CaO-CaS inclusions were transformed into Al2O3-CaS with distinctive morphologies. The mass fraction of Al2O3 and CaS in the inclusions was experimentally found to depend on the Ca/S ratio of the steel and confirmed by thermodynamic analysis. The two types of Al2O3-CaS inclusions could hardly be deformed during the hot-rolling process of the steel but showed different deformation behavior during the cold-rolling process of the steel. The component of CaS in the adhesion-type Al2O3-CaS inclusions was more easily separated from Al2O3 and formed a tail along the rolling direction of the steel, while only a little part of the CaS component broke off from the wrapping-type Al2O3-CaS inclusions.
The authors are grateful for the support from the National Science Foundation China (Grant Nos. U1860206 and 51725402), Beijing International Center of Advanced and Intelligent Manufacturing of High Quality Steel Materials (ICSM), Beijing Key Laboratory of Green Recycling and Extraction of Metals (GREM), and High Quality Steel Consortium (HQSC), School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing (USTB), China.
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