According to the production process of 20g steel(120t BOF→ LF→ CC), some system analysis are introduced to research on the content of T[O] and [N] and the type, source, composition and quantity of micro inclusions in refining process, pouring process and casting billet. The results of the study show: the content of T[O] is 93.2ppm in the normal billet which is 37.8ppm more than that at steady state in the export of tundish. The content of T[O] is 140.5ppm in the compound casting billet which is 70.133ppm more than that at non-steady state in the export of tundish. The secondary oxidation of mould is serious at casting progress. In billet, the quality of CaS-SiO2-Al2O3 complex inclusion is the most, the quality of MnS inclusion is the second, and the quality of Al2O3 inclusion is the least. The sulphur content in micro-inclusion of billet is higher. The sulphur content in CaS-SiO2-Al2O3 complex inclusion is 3~15%, the sulphur content in MnS inclusion is 25%. The particle size of less than 10μm in micro-inclusions is the largest. The particle size of 0~5μm is about 60%, the particle size of 5~10μm is about 35%, the particle size of 10~15μm is about 5%. The average total volume rate of micro-inclusion is 0.149% in normal billet. The average total volume rate of micro-inclusion is 0.184% in compound casting billet which is 1.23 times than normal billet. The number of micro-inclusion is 36.5/ mm2 in normal billet. The number of micro-inclusion is 58.5/ mm2 in compound casting billet which is 60.27% higher than normal billet. The non-steady state casting has serious influence on billet cleanliness.
The research about the macro-inclusions of three processes: BOF→ LF→ CC, BOF→ RH→ CC and BOF→ LF→ RH→ CC, shows that: The types of inclusion are SiO2-Al2O3-CaO-TiO2-MnO, SiO2 and SiO2-Al2O3. The content of SiO2-Al2O3- CaO-TiO2-MnO in the three processes are 34.2%、23.5% and 27%; The content of SiO2 are 24.4%、47% and 27%; The content of SiO2-Al2O3 are 26.8%、17.6% and 9%. Large inclusion>300μm takes up 69.8%~85% of the total inclusion in billet in three technological processes, and the inclusion, containing K and Na, is the most; slag entrapment in mould is really serious. Considering the cleanliness and cost, the better technological process of MRT3-BA stamping steel is BOF→ RH→ CC.
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