| Final electromagnetic stirring (FEMS) is an effective method for improving center segregation and porosity of high-carbon and high-alloy steel. This subject is in the light of the FEMS installation of Baoshan Iron and Steel Company Limited. With the New-type multi-functional electromagnetic stirring installation, the process of FEMS of the continuous casting was simulated in the experiment conditions. Low melting hypereutectic alloy Pb-80%Sn was selected as the simulation medium of the steel. Effect of spiral magnetic field (SMF) on solidification structure, segregation and shrinkage porosity of the alloy was investigated with OM and XRF, with comparison of alloys solidified and component distribution in the conventional condition and rotating magnetic field (RMF). Mechanism of action of the SMF was studied and the optimal stirring parameters of the FEMS was selected which would provide a guide for the practical application of the spiral magnetic field stirrer in the factory.Firstly, the electromagnetic stirrer was measured to investigate the spiral and rotating magnetic field with their distributions of magnetic induction at different excitation current and frequency, regularity of distribution and relationship between the stirring parameters and magnetic induction were summarized according to the measuring datas. The measuring results indicate that, the magnetic induction increases with the excitation current as well as increases with the frequency within limits; the magnetic induction decreased gradually from the centre to the upper or lower part of the stirrer along the axial direction and from the inwall to the centre in the same height section along the radial direction; the coverage area of spiral magnetic field was wider along the axial direction than the rotating one and the decrease speed of rotating magnetic field was lower along the radial direction, though spiral magnetic field showed a more stationary distribution when R<60mm.Secondly, effect of spiral magnetic field on solidification structure of Pb-80%Sn hypereutectic alloy was studied and mechanism of action of SMF was also studied in depth, which provided reliable references of stirring parameters for the following simulated experiments of FEMS. The experimental results show that, compared with RMF, SMF can lead to a more uniform stirring in a larger zone of the ingot, which is more beneficial to break and refine the dendrites structure, thus promote the formation of ellipsoidal or equiaxed grains, reduce macrosegregation and lead less macro defects of the ingot. Both of the two magnetic field had a same optimal stirring frequency with10Hz.Finally, relationship between the solidified shell thickness and solidified time was measured in the experimental condition by simulating the process of FEMS in the continuous casting. Rotating and spiral magnetic field were stirred on the melt with a certain shell thickness and the stirring effect of spiral magnetic field was analysed comparatively, furthermore, the optimal stirring parameters of RMF and SMF were selected. The experimental results show that, at a fixed frequency, the grains size of primary phase increases with the excitation current and an optimal effect can be achieved when the current reaches125A for both RMF and SMF, while higher excitation current will lead to the growth of grains. Macrosegregation can be substantially eliminated by spiral magnetic field and a lower current (100A) is effective to obtain the same optimal stirring effect (125A) of rotating magnetic field. At a fixed excitation current, the optimal stirring time of RMF and SMF are10min and15min respectively and the action effect of SMF is more excellent than RMF whether on refining grain, decreasing macrosegregation or improving the macro defects with shrinkage porosity and so on. |
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