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| Evolution of inclusions in steelmaking process for #br# ultra low carbon BH auto exposed panel |
| PAN Xiaoqian1，YANG Jian1，ZHI Jianjun2，WANG Ruizhi2，FAN Zhengjie2，XU Longyun1#br# |
(1. School of Materials Science and Engineering， Shanghai University， Shanghai 200444， China；
2. Baoshan Iron and Steel Co.， Ltd.， China Baowu Steel Group Co., Ltd., Shanghai 201901， China)
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Abstract In order to study the specific evolution of inclusions for ultra low carbon steel in steelmaking process，the inclusions automatic analyze system was used to study the ultralow carbon bake hardening (BH) steel of automobile exposed panel for two heats (S100 and S150) with sulfur mass percent of 0.010% and 0.015%， respectively. The evolution of the morphology，composition，number and size of inclusions from the end point of RH to the slab for two heats was analyzed. The refining slag of RH and tundish flux were also analyzed in the way of Xray fluorescence spectrometer and Xray diffractometer. The results show that the main types of inclusions in BH steel are Al2O3，MnS，Al2O3+MnS and Sicontaining inclusions (Sicontaining inclusions are mainly SiAlO inclusions，excluding pure Si，SiC，SiO2). Because of the high mass percent of Mn and S in BH steel，a large amount of MnS precipitates during solidification，which makes the number density of MnS inclusions and the total number density of inclusions in slab increase significantly. There is no significant difference in the number densities of MnS inclusions in RH and tundish between two heats with the sulfur mass percent of 0.010% and 0.015%. As MnS precipitates mainly in solidification process，the number density of MnS in slab for S150 heat is obviously higher than that for S100 heat. The higher w(（FeO+MnO）) in the refining slag and the lower ratio of w(（CaO）)/w(（Al2O3）) lead to more Al2O3 inclusions at the end of RH. In the casting process，the flow of ladle filler sand into tundish flux will lead to the increase of its SiO2 mass percent and the increase of SiAlO inclusions in molten steel. During the mold process，the Al2O3 inclusions aggregate and grow up continuously and are removed by floatation，which reduces the number density of Al2O3 and Al2O3+MnS inclusions and increases the size of the inclusions.
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