A Study On Slag Resistance And Anti-hydration Properties Of Calcia-rich Magnesia-Calcia Refractories Used For VOD

Following the testing on site of the import bricks, the reaction and erosion between calcia-rich MgO-CaO system refractory and VOD slag of a stainless steel refining furnace are discussed in this paper by analyzing micrograph and chemical mineral composition of residual brick after serving in VOD. The results are as follows: The service lining life of MgO-CaO materials is about twice that of magnesia-chrome materials and when the content of CaO is above 50%, the erosion resistance of MgO-CaO samples will be considerably higher;With increasing basicity of VOD slag, the erosion rate of magnesia-chrome materials increased, whereas that of MgO-CaO samples decreased. The technological secret of designing import MgO-CaO product has been revealed ,the production parameters and design of the MgO-CaO product (CaO≥50%) are provided.The main objective of the research was to study the influence of Y₂O₃, rare metal mixtures and zircon as additives on the sintering, anti-hydration and microscopic structures of MgO-CaO materials. In laboratory conditions, for MgO-CaO product (CaO≥50%), to which was added 1wt%Y₂O₃ or 0.5wt% rare metal mixture and sintered at 1650oC for 5hours,the product, which density can attain more than 3.19g/cm3, cold and hot modulus of rupture are respectively 110Mpa,14Mpa and hydration rate of MgO-CaO product (CaO≥50%) is lowest when tested at 0.2MPa pressure and kept at 130 oC for 2 hours, can be firstly developed. With synthesizing method for full powder of chemical pure, the dynamic on MgO and CaO crystal growth in MgO-CaO materials was discussed and the results are as follows:As the content of additive Y₂O₃ reaches 1wt% at 1650 oC, Y₂O₃ forms a full solid solution together with calcium oxide resulting in the deformation of the crystals of calcium oxide, therefore promoting the sintering of the MgO-CaO product (CaO≥50%) and the reason for addition of Y₂O₃ is that it can promote theanti-hydration ability of MgO-CaO materials (CaO≥50%), this is significant for reducing the cost of synthetic MgO-CaO clinker. The effect of zircon additive on the microstructure of calcia-rich magnesia-calcia materials has also been studied. The results are as follows: the hydration resistance of material is improved by zircon addition and the best quantity is 4%. The crystal size of MgO is grown bigger compared with no zircon addition. With the formation of CaZrO3, the specimen is beneficial to improve its anti-hydration.Magnesia-Calcia materials containing 22-53wt% CaO have been investigated for the corrosion and penetration resistances to refining slag by selection the slags on site .The corrosion and penetration resistances of MgO-CaO materials against AOD slag are stronger than against VOD slag and are enhanced with the increase of CaO content in specimens. Owing to the higher content of Al₂O₃ and CaF2 in the slag for VOD, CaF2 has reduced the viscosity and the melting point of slag. Consequently, the corrosion for VOD is stronger than that for AOD. The resistance to slag of self-made crucible is superior to import products. This is because that, there is a dense layer composed of high melting point C3S and C2S, which may hamper the penetration of slag. On the basis of the quaternary phase diagram of CaO-SiO2-Al₂O₃-MgO, the saturation concentration and slag viscosity on the boundary layer between the Magnesia-Calcia materials and slag were calculated. No matter what kinds of slag, the penetration depth of the slag decreased with the increase of CaO content.