Study On The Characteristics And Control Of Inclusions In 50W350 Grade Non-oriented Electrical Steel

Non-metallic inclusions in steel have an important effect on the magnetic properties of non-oriented electrical steel plates, so the content of non-metallic inclusions should be reduced as far as possible in the refining process. At present, the stability of inclusion control in high grade non-oriented electrical steel is poor. In order to improve cleanliness of high grade non-oriented electrical steel, the evolution of inclusions in 50W350 grade non-oriented electrical steel produced by BOF-RH-CC process was studied, and the range of refining slag suitable for non-oriented electrical steel refining process was explored by analyzing the physical properties of the refining slag and the composition optimization model of CaO-MgO-MnO-FeO-SiO2-Al2O3 refining slag. The conclusions are as follows:Through analyzing the inclusions in the steel during the refining process, the results show that Al2O3 inclusions exist in each process, in the refining process the number of Al2O3 inclusions is lagre and its quantity decreased with the production.There is a small amount of smaller size AIN inclusions in the ladle and tundish.Inclusions containing sulfur elements and composite inclusions containing Na?K exist in continuous casting slab. The results of statistical analysis show that the number of inclusions in steel after argon treatment is 306.26 ?/mm2, the number of inclusions in the ladle is 140.96 ?/mm2, the number of inclusions in the tundish is 188.42 ?/mm2,the number of inclusions in the continuous casting slab is 145.12 ?/mm2. The size of the inclusions during the production process is mainly below 3?m and it is about 90%.The content of large inclusions in continuous casting slab obtained by electrolysis analysis averaged 6.20mg/10kg and large inclusions size is between 140?m to 300?m.The inclusions in the continuous casting slab mainly include composite oxides and some inclusions contain Na?K elements.Through analyzing the physical properties of refining slag, it is concluded that the composition of refining slag suitable for RH refining process of non-electrical steel is WCaO=40%?55%,WSiO2=10%?20%,WAl2O3=20%?30%,WMgO=50%?10,and select the typical refining slag composition to verify whether to meet the refining slag low melting point and low viscosity requirements during refining process.The model for optimizing the composition of CaO-MgO-MnO-FeO-SiO2-Al2O3 slag system was established based on the coexistence theory. When the composition of non-oriented electrical steel is W[si]=2.50%?2.8%?W[Als]=0.430?0.46%?W[Mn]=0.2%?0.3%,according to the model the composition of the slag which is suitable for non-oriented electrical steel RH refining is WCaO=40%?55%,WSiO2=8%?10%,WAl2O3=25%?35%,WMgO=6%?10%,W(FeO+MnO)?0.15%.