The Effect Of Electromagnetic Fields On Kinetic Behavior Of MgO-C Refractory Material In Contact With Slag

With development of the electromagnetic metallurgical technology and superconductingtechnology, electromagnetic field（EMF） is used widely in steel metallurgy industry. For example,during the process of long flow rout steelmaking（BOF） the electromagnetic force is used to heat,stir, separate and control flow velocity and shape of molten metal with the uncontact method.During the short flow route steelmaking, EMF exists in the field of arc/induction furnace andsecondary refining. All these areas is characterized by a high temperature environment, sharpquenching and snap heat, electromagnetic fields and serious slag erosion. Due to its high thermalshock resistance and good corrosion resistance, MgO-C refractories are often used in hightemperature environments with electromagnetic fields. At high temperature, refractory materialsare the semiconductor, and the molten slag contains a large number of free movement of ions.SoEMF have an great influence on both the properties of refractories and the interfacial reaction ofslag/refractories, which could be revealed by the oxidation reaction of graphite and the corrosionof the slag/magnesite in EMF. In this paper, the effect of EMF on the theory and experiment ofslag corrosion dynamics for MgO-C refractories has been investigated. Based on the erosion ratemeasurement, he kinetic mechanism of ecorrosion of MgO-C refractories in the static magneticfield has been researched. At the same time, effect of carbon content and FexO-rich slag oncorrosion mechamism of MgO-C refractories in EMF has also been studied. In the experiments,both X-ray diffraction（XRD）, scanning electron microscopy（SEM） and energy dispersivespectroscopy （EDS） are used to determine the phase, microstructure and micro-area compositionof the sample after the tests. The composition, phase, microstructure and porosity at theinterface btween slag and MgO-C refractory material have been studied furtherly.At1700℃and Ar atmosphere of0.1MPa, the effect of magnetic field strength（H=0,125,250,500mT） on the corrosion experiment of Low-carbon （6wt.%） MgO-C brick wereconducted. The corresponding reaction time is15min,30min,60min and120min in the staticmagnetic field respectively. The results show that: in static magnetic field a thick penetrationlayer is generated in MgO-C refractories at initial stage of corrosion. The cations of Ca and Si inslag infiltrate into MgO-C refractories along with the boundary of MgO particles. At final stageof corrosion, MgO dense layer is appeare obversly in refractories while the penetration layer isdisappear. At slag line, high temperature phase is Al-rich MgAl2O4spinel while the low-meltingphases are tricalcium silicate and magnesium melilite. The reaction of MgO and carbon is themain mechanism of the corrosion process and the reaction rate is controlled by diffusion of CO（g） and Mg （g） in penetration layer. In magnetic field-free, dense MgO protective layerconnected by a number of magnesia particles is apppeare in refractories at an initial stage of corrosion, which could prevent slag penetration further. The MgO protective layer is disappeareat final stage of corrosion and slag could penetrate into refractories. The thickness of thepenetration layer is small. At slag line, high temperature phase is MgAl2O4spinel andthelow-melting phases are forsterite and monticellite. The corrosion of the MgO-C brick iscontrolled by dissolution of MgO in the slag.At1600℃and Ar atmosphere of0.1MPa, The corrosion experiment of low-carbon （6wt.%）MgO-C brick is conducted in an induction furnace with EMF. The effect of EMF on corrosionmechanism of the low carbon MgO-C brick is studied. The results show that in EMF, a thickMgO-rich reaction layer is generated between slag layer and decarburized layer. Because EMFcould improve the diffusion of Fe^2+/3+and Mn²⁺ions in MgO, the MgO-rich layer containing alarge number of Mn-doped MgFe₂O₄phase could be formed. Decarburized layer contains alarge number of large pores while the particle of metal is small. This phenomenen comes fromthe high-temperature battery reaction between molten steel and graphite, which made CO gasand metal Fe in the corresponding district. Decarburized layer is thick and contains a little of slagpenetrated in refractories. At slag line, the high temperature phase is MgAl2O4spinel and thelow-melting phases are calcium, magnesium olivine and enstatite.At1600℃and Ar atmosphere of0.1MPa, the corrosion experiments of MgO-C brick wasconducted in induction furnace and resistance furnace respectively. The Effect of EMF on thecorrosion mechanism between slag containing different amount of Fe and MgO-C brickcontaining different amount of C has been investigated. The experimental results show that EMFpromote the formation and destruction of penetration layer in MgO-C brick corroded by iron-richslag and accelerate the corrosion of MgO reaction layer by Fe²⁺/3+in slag. In EMF, Fe content inthe slag improve the corrosion of decarburized layer greatly, reduce both the viscosity of slagand the partial pressure of Mg in the decarburized layer, and accelerate the erosion of thedecarburized layer. Carbon content of MgO-C refractories have a great influence on MgO-richreaction layer and the corrosion of decarburized layer. The increase of C content can reduce theMgO-rich reaction layer thinkness and accelerate the dissolution of MgO in the decarburizedlayer by convection.