Study on Formation Mechanism of CaO-SiO 2 -Based Inclusions in Saw Wire Steel
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TRODUCTION
DURING the production of high-quality saw wires for cutting silicon panels, thin and rheological inclusions were desirable to decrease breakages of the wires during fabrication.[1–5] Dissolved aluminum in liquid steel has to be strictly limited to prevent undeformable alumina-based or alumina-enriched oxides. Therefore, Fe-Si alloy containing quite low levels of aluminum should be chosen in deoxidation. Besides, refining slag of low basicity (mass percentage ratio of CaO to SiO2) should be
KUN-PENG WANG is with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing, 100083, P.R. China, and also with Xingtai Iron & Steel Co., Ltd., Xing-tai City, Hebei, 054027, P.R. China. MIN JIANG, XIN-HUA WANG, and ZHAN-MIN CAO are with the School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing. Contact e-mail: [email protected] YING WANG and HAO-QIAN ZHAO are with Xintai Iron & Steel Co., Ltd. Manuscript submitted July 26, 2016.
METALLURGICAL AND MATERIALS TRANSACTIONS B
used.[6–18] Formed oxide inclusions were usually either MnO-SiO2-Al2O3- or CaO-SiO2-based system.[6,7,9,13–18] The former type of inclusions was transformed from Si-Mn deoxidation products, viz., MnO-SiO2. Because of the chemical reactions among slag-steel inclusions, MnO-SiO2 inclusions were finally changed into MnOSiO2-Al2O3 system.[9,10] However, there are discrepancies/ ambiguities on the formation mechanisms and origins of CaO-SiO2-based inclusions. One of the important proposals insisted that they were transferred from MnOSiO2-Al2O3, because MnO in inclusions can be reduced by dissolved Ca ([Ca]) in steel with the proceeding of refining.[15–18] Theoretically, this would happen if [Ca] in steel was high enough. Nevertheless, it is difficult for it to occur in industrial practice, because activity of CaO in slag is extremely low. Hence, some other studies proposed that CaO-SiO2-based inclusions were entrapped slag particles.[7,11,12] In other studies, transformation of MnO-SiO2-Al2O3 into CaO-SiO2-Al2O3-MnO was also mentioned by discussing the effect of top slag. However, how CaO entered into inclusions, either directly by slag entrapment or indirectly by chemical reactions among
slag-steel inclusions, was not specified.[6,7,9,10] In a recent work by the present authors, it was found that CaO-SiO2-based inclusions can be greatly decreased by optimal slag-making operation, although their existence was not eradicated.[13,14] As a result, whether the CaO-SiO2-based inclusions were chemical reaction products or exogenous particles should be specified and deeper insights are needed. One of the key points was to make clear the origin of CaO in CaO-SiO2-based inclusions. Commonly, the rise of CaO in inclusions probably can be caused by chemical reaction between [Ca] in steel and the inclusions. In the production of saw wire, the source of [Ca] can be complex during steelmaking. Despite steel-slag chemical reactions, raw materials, such as added ferrous alloys,
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