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ODUCTION

IN steelmaking, alumina, spinel, and calcium aluminate inclusions are the common types of inclusions in Al-killed steels.[1–4] Alumina and spinel inclusions are irregular, and hard to deform, which may cause defects in final products,[1,5,6] while most of calcium aluminate inclusions are globular and sometimes are considered harmful for the fatigue property of steel.[7,8] Therefore, the control of these inclusions becomes extremely important for steelmaking industry. Many studies have been conducted aiming at a better control of inclusions in steelmaking process. A number of publications have pointed out that refractory has great impact on the formation and evolution of inclusions during refining process.[2,3,9–23] Three types of refractories—alumina, spinel, and MgO—are widely used in industrial production. For MgO refractory, Brabie et al.[9,10] proposed that carbon in refractory could reduce MgO into Mg gas, and then Mg gas would lead to the formation of spinel inclusions. A number of studies[2,3,11–18] also indicated that some of the dissolved Mg in Al-killed steel is supplied from the reduction of MgO refractory by dissolved Al. Some researchers[13,19] suggested that the carbon in high-carbon steels, e.g., bearing steels, could

also reduce MgO refractory, resulting in the dissolution of Mg into the liquid metal. MgO inclusions have also been found in liquid steel. The MgO inclusions may come from refractory. Some researchers[20–22] considered that the MgO refractory was also one of the sources of the inclusions with MgO islands inside the calcium aluminate liquid phase. In fact, the effects of alumina and spinel refractories on the inclusions have rarely been reported, though a few studies have briefly touched this area.[23] Moreover, the slag-steel-refractory system has usually been chosen to study the effect on inclusions. Hence, the individual effects of slag and refractory have not been clearly identified. Further systematical investigation is needed to understand the effects of different refractories on different types of inclusions. The present work focuses on the effect of refractory on inclusions in Al-killed steel. Steel samples were taken from industry to identify the types of inclusion. Laboratory experiments were carried out to study the effects of different refractories on different inclusions. Based on the comparison of the results of laboratory experiments with industrial findings, the effect of refractory on different types of inclusions in real production was discussed.

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EXPERIMENTAL

A. Industrial Sampling ZHIYIN DENG, Lecturer, is with the School of Metallurgy, Northeastern University, Shenyang 110819, P.R. China, and also with the Department of Materials Science and Engineering, KTH Royal Institute of Technology, 110819 Stockholm, Sweden. Contact e-mail: [email protected] MIAOYONG ZHU, Professor, is with the School of Metallurgy, Northeastern University, China. DU SICHEN, Professor, is with the Department of Materials Science and Engineering, KTH Royal Institute of Technology. Manuscript submitted