Influence of Electromagnetic Stirring in Mold on the Quality of Bearing Steel Slab

Due to the electromagnetic stirring (M-EMS), the liquid core in the crystallizer generates rotational motion, which improves the heat transfer rate in the crystallizer, and also produces some other beneficial effects.

    (1) The movement of the liquid core makes the temperature of the molten steel uniform and reduces the temperature gradient, which is beneficial to eliminate overheating and improve the uniformity of solidification of the billet shell; (2) The liquid movement close to the solid phase interface makes the solidification front a large number of unstable The dendrites are transferred into molten steel, part of which is remelted, and part of which forms the growth core of equiaxed crystals to expand the equiaxed crystal region of the slab, improving the center looseness and center segregation; (3) Electromagnetic force can enhance the The upward stream brings the high-temperature steel flow to the upper part, shortens the initial solidification shell of the meniscus, and thus makes the vibration marks shallower; the upward stream creates the condition of "hot top" in the mold, which is also conducive to the mold slag Melting and lubricating to prevent surface cracks; (4) Stirring can also continuously clean up the slag inclusions and large inclusions in the surface area and bring them into the mold slag, so as to obtain a clean surface.

    The penetration depth of the magnetic field of the electromagnetic stirrer is large when the current frequency is low, and the penetration depth is shallow when the frequency is high, and the stirring intensity increases with the increase of the coil current. Only when pouring at low superheat, using stirring can have a good effect, otherwise it is difficult to expand the equiaxed grain area inside the slab, and the effect of improving central segregation is poor

Foreign studies have shown that: the direction of electromagnetic stirring at the end of solidification, bidirectional is more conducive to the improvement of central carbon segregation than unidirectional. Validation experiments also illustrate this point.

    Using M-EMS, the shell is formed more uniformly, and the reduction of the amount of slag in the surface layer is conducive to the growth of the shell. Because the slag has a heat insulating effect, it will hinder the growth of the shell. Using S-EMS, the maximum carbon segregation value can be reduced from 1.68 to 1.38. The use of F-EMS can interrupt the bridging of the central part and better supply the liquid steel required for solidification and shrinkage.