Effect of Slag Composition on MgO·Al2O3 Spinel-Type Inclusions in Molten Steel

• Published in: ISIJ International Vol. 57; no. 9; pp. 1546 - 1552
• Main Authors: Harada, Akifumi, Matsui, Akitoshi, Nabeshima, Seiji, Kikuchi, Naoki, Miki, Yuji
• Format: Journal Article
• Language: English
• Published: The Iron and Steel Institute of Japan 2017
• Subjects: inclusion; kinetic calculation; slag composition; spinel
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.ISIJINT-2017-174

It is well known that the formation of MgO·Al2O3 spinel-type inclusions is affected by the slag composition. To clarify the effect of the slag composition on the formation of spinel-type inclusions, laboratory-scale experiments were carried out in 30 kg-scale induction furnace. Changes in the composition of inclusions were investigated with different slag compositions. As the CaO/SiO2 and CaO/Al2O3 of the slag increased, spinel-type inclusions were observed, and the total Mg content and average composition of MgO in the inclusions were also higher. On the other hand, the total Mg content and average composition of MgO in inclusions decreased with decreasing CaO/SiO2 and CaO/Al2O3 of the slag, and most inclusions were Al2O3-type inclusions including a small amount of MgO. Based on the experimental results, a kinetic analysis was carried out using a calculation model to simulate the reactions between the molten steel, slag, refractory and inclusions in order to evaluate the effect of the slag composition on inclusions. The calculated results of the inclusion composition were in good agreement with the experimental results. In this experimental system, the total Mg content and spinel-type inclusions were suppressed due to a decrease in the activity of MgO in the slag and an increase in the oxygen activity at the interface between the molten steel and slag when the CaO/SiO2 and CaO/Al2O3 of the slag were lower. Therefore, the formation of spinel-type inclusions can be determined by the relationship between the MgO activity of the slag and the interfacial activity of oxygen.