Study about the Behavior of Molten Steel Flow in a Continuous Casting Mold imposed the Magnetic Fields

Abstract

Molten steel flow in a mold of a continuous caster can control the meniscus temperature at position of forming the initial solidified shell and the inclusion behavior, and can be affected by the port size and angle of the immerged entry nozzle, argon gas flow rate, electro-magnetic fields. In particular, the electro-magnetic devices have been developed to improve the slab quality. A number of researchers in continuous casting process have conducted a study on the effect of molten steel by the electro-magnetic stirrer using traveling magnetic field and electro-magnetic breaker using static magnetic field respectively. The drawback of steel fluid flow phenomena for a continuous casting mold under an electro-magnetic stirrer with a traveling magnetic field is the severe meniscus fluctuations due to the high velocity and excessive downward flow in the casting direction. This can result in slab surface defects due to mold flux or inclusion entrainment. The disadvantages of the molten steel flow in the mold under only the static magnetic fields are the weaker deceleration ability for controlling the flow speed at meniscus, and it has only a deceleration function. So the operating conditions requiring the acceleration for wide width and lower casting speed cannot be reproduced. In the present study, the comparison between static and traveling magnetic fields for the deceleration ability of meniscus flow in order to avoid the mold slag entrapment was conducted. In addition, the downward flow which reduces the inclusion penetration depth according to the strength of the static magnetic fields was evaluated. Finally, the implementation of braking forces using static magnetic fields in a combination with a traveling magnetic field were studied to inhibit these defects in as-cast steel products. The numerical model for the computational fluid dynamics (CFD) and magneto hydro dynamics (MHD) is necessary to evaluate the molten steel behaviors, and is able to show more detailed flow phenomena by magnetic field. These numerical results were validated in the commercial-scale operations. The numerical results of the fluid flow in the mold under a combined traveling and static magnetic field operation show not only 50% lower downward flow speed, but also more enhanced rotational flow to improve the washing effects. The results suggest the optimized range of the ratio between the traveling and static magnetic flux density is 65 to 75% to ensure steel quality improvements; this range maintains a balance between the fluid forces from the jet flow and the magnetic forces in the mold.