1. School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China; 2. State Key Lab of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, Hebei, China; 3. Technology Center, Kunming Iron and Steel Group Co., Ltd., Anning 650300, Yunnan, China
Abstract：In order to control the amount and type of inclusions in a Q235 steel and improve the impact toughness of the steel, the variation in morphologies and composition of inclusions in the production process of LF→tundish→bloom was analyzed using ASPEX. Thermodynamic analysis of the formation mechanism of different type inclusions was performed using FactSage. It is found that the evolution of non-metallic inclusions in steel was, homogeneous SiO2-MnO inclusions→homogeneous SiO2-Al2O3-MnO-TiOx inclusions→two-phase Al2O3-SiO2-CaO enveloping MgO·Al2O3 inclusions→multiphase TiOx-SiO2-Al2O3-CaO-MnO-MnS inclusions. The two-phase SiO2-MnO inclusions found in the steel at the beginning of LF refining are caused by the phase change of pure SiO2 in the SiO2-MnO inclusions during the cooling process. The two-phase Al2O3-SiO2-CaO found in the LF outbound steel sample encloses the MgO·Al2O3 inclusions because of the high aluminum content in the added silicon calcium strontium alloy, resulting in liquid inclusions in the molten steel,MgO·Al2O3 was precipitated. Titanium-containing inclusions would precipitate pure Ti3O5 during solidification and cooling of the continuous casting billet, and the precipitated phase of MnS will precipitate in the steel. Therefore, there were heterogeneous TiOx-SiO2-Al2O3-CaO-MnO-MnS inclusions in the continuous casting bloom.
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2020, Vol. 55 
