Effect of Slag Composition on Inclusions in High Carbon Steel
Akifumi HaradaAkitoshi MatsuiNaoki KikuchiYuji MikiSeiji Nabeshima
Steel Research Laboratory, JFE Steel CorporationSteel Research Laboratory, JFE Steel Corporation.Now at Mizushima Ferroalloy Corporation
摘要：MgO?Al2O3 spinel-type inclusions have a harmful effect on the fatigue resistance of steel products. In order to clarify the effect of the slag composition on the formation of spinel-type inclusions in high carbon steel, laboratory-scale experiments were carried out in a 30 kg-scale induction furnace. The changes in the composition of the inclusions were investigated with different slag compositions. As the experimental results, spinel-type inclusions were reduced and the Mg content in the molten steel and average MgO content in the inclusions were lower with decreasing CaO/SiO2 and CaO/Al2O3 of the slag. 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 the inclusions. The calculated results of the inclusions were in good agreement with the experimental ones. The effects of the slag composition on the inclusions were evaluated by using this model, and the slag compositions without formation of spinel-type inclusions were clarified. According to the model calculation results, the Mg content and spinel-type inclusions in the molten steel were suppressed by decreasing the MgO activity in the slag and increasing the oxygen activity at the interface between the molten steel and slag, which were caused by lower CaO/SiO2 and CaO/Al2O3. 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.