次世代革新的鉄鋼材料開発のためのスピネル系介在物の生成・変質メカニズムの解明

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The purpose of present study is to clarify the source of Mg and Ca for the formation of MgOAl2O3 (MA) spinel and CaO-Al2O3 type inclusions. For the formation of MA spinel type inclusion, the dissolution behavior of Mg from both MgO-based refractory and MgO-containing slag were studied. Here, about the MgO-based refractory, both the MgO-Cr2O3 refractory and MgO-C refractory were used. For the formation of CaO-Al2O3 type inclusion, the dissolution behavior of Ca from CaO-containing slag was studied. Both MgO and CaO in slag of different compositions were reduced by Al in steel, and Mg and Ca were dissolved into the steel. In the experiments using slag only saturated with MgO, when the Al content was 0.25%, the MgO-rich inclusion formed, while when the Al content was 2.5%, the MgO content of spinel inclusions increased to saturation.In order to confirm the above conclusions, an industrial experiment was conducted. During the actual LF treatment, the Al2O3 inclusion transformed to MgOAl2O3 spinel inclusion and few CaO-Al2O3 inclusion. Therefore, By the slag-steel reaction, CaO-Al2O3 inclusion could not form under the condition of industrial operation. Then, we found that the Ca for the formation of CaO-Al2O3 inclusion was from the added alloy, especially Fe-Si.Based on these results, we found that during the refining process of steelmaking, the inclusion only transformed through the routine of Al2O3 to MgOAl2O3 spinel. In order to hinder the formation of CaOAl2O3 inclusion, the impurity in the added alloy should be strictly controlled.