Study On Cleanliness Of Steel In Non - Oriented Electrical Steel By BOF-RH-CSP Process

The paper using SEM-EDS(Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy) and bulk sample electrolysis to analyse the evolvement rules of T[O] content, [N] content, inclusions and slag composition in LGW800 brand non-oriented electrical steel by BOF-RH-CSP process of the Steel. Steel and slag samples were collected from BOF endpoint, RH refining process, tundish and casting blank. The paper also optimized the process. In addition, the prediction model of oxygen content in 30 tons of tundish was established through theoretical derivation, factors that affected oxygen in tundish were analysed in order to improve the steel cleanliness.Results were as follows:(1) Excessive content of dissolved oxygen(600ppm) in decarburization end remained to be futher reduced. Breaking a vacuum and casting casued the increase of T[O] and [N] content, it implied that protection measures for casting need to be strengthened.(2) The number of inclusions displayed a decreasing tendency during the process, most of inclusions in refining process were irregular shape of Al2O3 and MnO·Al2O3, most of inclusions in tundish were Large size and irregular shape of Al2O3 and Al2O3·SiO2·CaO·MnO, and content of large inclusions of billet was 5.46 mg per 10kg, the number was more, these included Al2O3, SiO2 and composite inclusions made up of MnO、MgO、CaO、Al2O3、SiO2, the size was in the range of 80-300μm, Some of these large inclusions containing K, Na element were caused by involved mold flux.(3) Slag basicity (%CaO/%SiO2) in the process increased firstly, reached the climax, then decreased; the value of (%CaO/%Al2O3) and (%MnO+%FeO) content gradually decreased, the content of (%MnO+%FeO) was high(12.5%) when vacuum degassing refining finished; the content of (%Al2O3) gradually increased.(4) The prediction formula of oxygen content in tundish showed that factors influencing oxygen content of steel in tundish were as follows:the oxygen content of steel in ladel, (%MnO+%FeO) content of ladel slags,casting time, SiO2 content in the refractory material, the absorbing nitrogen content in tundish, inclusion floatation removal rate constant k2, properly decrease the oxygen content of steel in ladel and (%MnO+%FeO) content of ladel slags, reduced the absorbing nitrogen content in tundish, improve the inclusion floatation removal rate constant, these above were good for decreasing oxygen content of steel in tundish.(5) Temperature drop of Converter tapping process was controlled better after the process optimization, but molten steel temperature at the end of vacuum degassing refining and superheat of molten steel during casting were a little high, which need to be further controlled; Controlling the content of oxygen in the molten steel during RH vacuum refining process and the stability were improved obviously; The stability of controlling carbon content in down of converter furnace and argon station was improved, the ratio of carbon content which was less than 35 ppm showed a trend of increase.