| Continuous casting greatly improves casting efficiency and saves energy compared with traditional ingot casting.Mold is the heart of continuous casting process and plays a decisive role in the continuous casting system.The application of electromagnetic stirrer in continuous casting can effectively improve the equiaxed crystal ratio and billet quality.The research of electromagnetic stirrer in mold makes it play the most important role in continuous casting production.In this paper,the 42 CrMo medium carbon steel of 300mm×360mm continuous casting bloom is taken as a research object.The finite element analysis method is used to establish a three-dimensional electromagnetic field model to study the influence of electromagnetic field distribution in continuous casting under different electromagnetic parameters(current intensity and current frequency).After that,the data of obtained electromagnetic force was imported into the flow field analysis to study the distribution of steel flow field and temperature field in the mold under different current intensity and current frequency,finally the optimum electromagnetic stirring parameters were obtained.Then,the traditional M-EMS was improved according to the characteristics of electromagnetic field,flow field and temperature field.A new type of electromagnetic stirrer for mold was designed so as to reduce the defects and improve the quality of the casting bloom which compare with the distribution of electromagnetic field,temperature field and flow field of the traditional M-EMS.In addition,the structure of the submerged nozzle used in the continuous casting production of the cooperative steel plant was improved.Two new nozzle structures(the wide-mouth and the fine-mouth submerged nozzle)were proposed to study the influence of different submerged nozzles on the temperature field and flow field distribution of steel in the mold.The results show that the rotating electromagnetic force of the traditional mold stirrer increases with the increase of the current intensity and current frequency.The magnetic induction increases with the increase of current intensity,but decreases with the increase of current frequency.With the increase of the current intensity and frequency of the electromagnetic stirrer in the mold,the flow of steel in the mold is strengthened and the floating condition of inclusions is improved.However,with the increase of the current intensity and frequency,the flow velocity of the free surface in the mold was rapidly which will cause slag entrapment seriously.The optimum electromagnetic parameters are 500 A and 3Hz.The depth of steel jet strand in wide-mouth submerged nozzle is shallower which conducive to the formation of initial solidified bloom shell,the reduction of surface cracks and corner cracks of bloom.The hot zone of the steel in the mold is moved upward,which is conducive to the equiaxed grains of bloom and the improvement of equiaxed rate.Moreover,the increase of the area of reflux zone of steel in mold is conducive to the floatation of inclusions and the cleanliness of steel in mold is improved.However,the temperature field and flow field distribution of steel in the fine submerged nozzle are similar to that of the straight nozzle,and the effect of improvements on the flow field and temperature field of steel in the fine submerged nozzle is not obvious.The electromagnetic stirrer of improved structure can produce better stirring effect with smaller current parameters(400A,3Hz),which compared with the traditional electromagnetic stirrer(500A,3Hz).Through comparative analysis,the electromagnetic force produced by the electromagnetic stirrer of improved structure is larger than that of the traditional stirrer,and the distribution of electromagnetic force on the surface of the slab is more uniform.Under the stirring action of the new mold electromagnetic stirrer,the disturbance of steel in the mold is strengthened,the hot zone of molten steel moves upward and the heat transfer efficiency in the mold increasingly,which can quickly eliminate the superheat of steel,contribute to the formation of initial solidified shell,reduce the generation of bloom cracks,facilitate the formation of equiaxed,improve the equiaxed rate and improve the quality of slab. |
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