Numerical Simulation Of Flow And Solidification Behavior In Continuous Casting Of Stainless Steel With EMS

The electromagnetic stirring technique can strengthen the flow of molten steel in billet in the process of continuous casting, make the flow state of molten steel in mold be beneficial to the rise and decrease of nonmetallic inclusions and bubbles, and homogenize the temperature of molten steel in liquid core. At the same time, it can also improve the solidification structure and enlarge the equiaxed crystal zone of billet. Presently, researches on the influence of M-EMS and F-EMS on flow and heat transfer of molten steel in continuous casting of stainless steel billet are not sufficient. In this paper, the author studied the continuous casting process of stainless steel billet. By using the numerical simulation method, the author investigated the distribution of magnetic flux density and electromagnetic force of M-EMS and F-EMS. The influence of M-EMS on behavior of the interface between molten steel and slag was investigated by using the VOF model. Through the coupling calculation of flow and solidification, the solidification process of billet with different stirring intensity was described. At the same time, the effect of casting speed and superheat on the solidification process of billet was also investigated.The main conclusions are as follows:In out-mold electromagnetic stirrer, the small square billet is located in the center of stirrer where the magnetic flux density is well-distributed. The variation of current intensity has no effect on the distribution of magnetic flux density on cross section of billet. The decay rate of magnetic flux density along the central axis of F-EMS is very low near the center of F-EMS. The magnetic field distributes uniformly and maintains a relatively high value from the center of the stirrer in a certain distance. Thus it makes sure that the molten steel at the solidification end of billet stirred by enough intensity of electromagnetic force.Under the effect of centrifugal force with M-EMS, the interface between molten steel and slag concaves down from the center. Meanwhile, the molten steel velocity and turbulence kinetic energy on the interface increase obviously, and two other new recirculation zones formed under the center zone of the stirrer. When the current intensity is 376A and the center of the stirrer deviates from the interface by 355mm, slag will be entrapped into molten steel. The shear on the nozzle wall increase with the stirring intensity increasing. Thus the wall of the nozzle will be eroded faster. The wall shear of nozzle will be decreased when the stirring method changed from one-way stirring to forward and backward alternant stirring. In alternant stirring, the shorter of continuous stirring time, the more stable of the free surface. The deformation degree of free surface is the largest in round billet mold with the same stirring intensity. The deformation degree of free surface in curved billet mold is similar to that of straight billet mold, and the deformation of free surface in straight billet is the weakest.The solidification rate of molten steel increases obviously and the length of liquid core shortens considerably with the effect of M-EMS and F-EMS. Meanwhile, with the molten steel washing the solidifying front, the shell thickness is fluctuant. The stronger of the stirring intensity is, the greater of the fluctuation is. Therefore, it is more reasonable to set the current intensity of M-EMS and F-EMS as 300A and 260A considering the uniformity of the shell thickness and the length of liquid core. With the increase of casting speed, the shell thickness is decreased and the length of liquid core is increased. During production, the F-EMS has no obvious effect on solidifying process of billet when the casting speed is 1.2m/min. So using the upper limit of casting speed in production is suggested. Besides, excessive intensity of F-EMS may result in the fluctuation of temperature at the solidification end, and the shrink and deformation of liquid core at the solidification end is excessive, which is harmful to molten steel feeding. With the degree of superheat enhanced, the solid fraction at the solidification end reduces. But the temperature on the surface and at the center of the billet doesn't change obviously. Therefore, improving the superheat of molten steel appropriately will be beneficial to F-EMS.