| The main factors that affected the slab internal quality were central segregation and porosity, and the final electromagnetic stirring was one of the effective methods to solve this problem. The F-EMS can distribute temperature and composition evenly by means of forced flow in the two-phase region of billet. So, it is significant to study the influence of electromagnetic stirring on the billet quality. Since the unpredictable velocity of liquid steel and the limitation of traditional analytical method, numerical simulation has become an effective way to deal with these difficult questions.Based on the process conditions of 160mm x 160mm billet continuous casting machine with final electromagnetic stirring, the solidification model, electromagnetic field model and flow field mode were established by using ANSYS13.0 software and the distribution laws of magnetic field, magnetic field and flow field were obtained. At the same time, the impacts of electromagnetic parameters and casting process parameters were investigated through numerical simulation and industrial experiment. The main conclusions were as follows:(1) With the casting speed increasing from 1.8m/min to 2.0m/min, the disappearance of liquidus line and solidus line postponed 0.99m and 1.37m respectively, and the temperature in the air cooling zone rise from1026.4℃ to 1078.4℃. With the superheat growing from 10℃ to 30℃, the disappearance of liquidus line and solidus line moved back 0.19m and 0.24m respectively, and the temperature in the air cooling zone increase from 1012.9℃ to 1026.4℃.(2) The magnetic flux density showed parabolic distribution along the axial line in the final electromagnetic stirring. It reached its maximum value in the centre of stirrer and decreased along the axial line. On the horizontal plane, the electromagnetic force distributes circumferentially and the magnitude was proportional to the distance from the center. The electromagnetic force increased with the current intensity and frequency. With the current intensity raising for each additional 50A, the electromagnetic force increased by about 117Gs when the current frequency was 6Hz. As the current frequency growing from 5Hz to 8Hz, the electromagnetic force increased from 2611N/m3 to 4155N/m3 with the current density fixed in 300A.(3) With electromagnetic stirring, the molten steel in the two-phase region swirl intensely and the stirring intensity reach its maximum in the center of the agitator. And the stirring velocity increase with the current intensity and frequency. As the final electromagnetic stirring current was fixed in 6Hz, the maximum stirring velocity raised from 11.2cm/s to 18.2cm/s with the increase of current intensity from 300A to 400A. Similarly, the maximum stirring velocity raised 1.7cm/s with increasing frequency of 1Hz.(4) The actual tests showed that the optimal frequency and current intensity for F-EMS were 6Hz and 380A when the continuous casting speed was 1.9m/min and the spray water ratio in the secondary cooling zone was 1.057L/kg. With these final electromagnetic stirring parameters, the maximum flow velocity of molten steel at the solidification front caused by electromagnetic force is 16.5cm/s and central carbon segregation index in billet can be controlled below 1.05. |
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