Effect Of Rare Earth Oxides On Properties Of Magnesium Carbon Refractory

Rare earths play a role in microalloying and modifying inclusions in steel materials,and improve the quality of steel.With the increase of demand for rare earth steel,it is found that nozzle clogging affects continuous casting production when pouring rare earth steel.The erosion of rare earth in steel on nozzle material is the main cause of nozzle clogging.The common aluminum-carbon nozzle is easy to be corroded by rare earth in steel,and magnesium-carbon refractory is a kind of high-quality alkaline refractory,which has small wettability on slag and molten steel,and has excellent peeling resistance and corrosion resistance.It can be made into nozzle suitable for rare earth steel continuous casting.In this paper,magnesia-carbon refractories were taken as the research object.By doping rare earth oxides into magnesia-carbon refractories to promote sintering,the thermodynamic calculation and analysis of rare earth oxides in magnesia-carbon refractories,the improvement of magnesia-carbon refractories by rare earth oxides,and the influence of rare earth oxides on the microstructure of magnesia-carbon refractories were carried out.The influence of Y₂O₃coating on the corrosion resistance of Ce-based rare earth steel was discussed.The conclusions are as follows:（1）According to the volume density and apparent porosity of GB/T2997-2015 test materials,the effect of rare earth oxides on the compactness of materials was studied.It was found that rare earth oxides doped in magnesia-carbon refractories can react with silicon oxide and alumina in the material to form rare earth silicate and rare earth aluminate,which can promote the sintering of the material,improve the compactness and mechanical properties of the material,so as to reduce the infiltration of rare earth steel in the material,reduce the erosion of particles in the material,and improve the corrosion resistance of rare earth steel.The addition of 0.5%La-rich samarium slag had the best improvement effect on the material properties.The volume density increased by 3.6%,the apparent porosity decreased by 10.2%,the flexural strength and compressive strength increased by 22.5%and19.6%,respectively,and the corrosion resistance of Ce-based rare earth steel increased by10%.（2）The microstructure of Mg O-C refractories doped with Y₂O₃and lanthanum-rich samarium slag was detected.It is found that rare earth oxides are mainly concentrated around magnesium oxide and graphite particles,especially in the position where there are many pores around fine particles,which enhances the bonding degree between particles in the material,reduces the shedding of particles on the surface of Mg O-C material when eroded by rare earth steel,reduces the roughness of the eroded surface and reduces the retention of molten steel;and inhibiting the decarburization reaction of the material at high temperature,reducing the reaction between rare earth in molten steel and the decarburization products diffused to the surface of the material,forming the initial precipitation of rare earth compounds,which is beneficial to prevent nozzle clogging.（3）Through the study on the corrosion resistance of Y₂O₃coating refractory to rare earth steel,it is found that the porosity of Y₂O₃coating is far less than that of magnesia carbon material,which makes it difficult for rare earth steel to penetrate and diffuse in the coating,and slows down the corrosion rate of rare earth steel.The chemical properties of Y₂O₃coating are stable,and it does not react with rare earth in steel,which slows down the corrosion of rare earth in steel on refractory materials.The coating separates the magnesium carbon material from the molten steel,avoids the decarburization reaction of graphite,and effectively inhibits the corrosion of rare earth steel.The corrosion resistance of samples coated with Y₂O₃is higher than that of samples doped with rare earth oxides.