Ladle Lining With The Mgo Substrate And Al <sub> 2 </ Sub> O <sub> 3 </ Sub>-based Refractories For Steel Quality Impact Study

With the development and requirements of clean steel, low carbon and ultra-lowcarbon steel in recent years, the study of refractory focus on the impacts of refractoryon the steel quality at high temperature, including C, S, P, N, H, T[O] and inclusions,rather than corrosion resistance and long life, i.e., refractory cost and consumption inthe past.The intermediate frequency furnace with type of Consarc.Co.VIM is adopted inthe study. The MgO based and Al₂O₃ based refractorys are used for the lining, includingAl₂O₃-MgO(13.81%MgO), MgO-Al₂O₃ (82.93%MgO)and MgO-CaO with CaOcontent variation from 10% to 40%. The following steel grades, 82B, ML15 and pureiron are remelted with aluminum deoxidization and slag protection. The samplers aretaken by silica glass tube and steel cup during the melting process. Afterwards, theimpacts of refractory on steel, P, S and inclusions are analyzed by image analyzer, SEM,SLIM etc. Moreover, the phenomenon and mechanism of carbon pick-up areinvestigated with static method and different types of carbon by chemical analyses,optical microscope and SEM. Finally, the thermodynamic calculation is used forinclusions composition prediction.The MgO based and Al₂O₃ based refractorys, including Al₂O₃-MgO, MgO-Al₂O₃and MgO-CaO lining have greatly impacts on steel quality, P, S, inclusions and carbonpick-up. It can be ranked as follows, Al₂O₃-MgO＜MgO-Al₂O₃＜MgO-CaO.The results demonstrate that Al₂O₃-MgO and MgO-Al₂O₃ lining contribute little toP and S removal in the melt, however, MgO-CaO lining shows strong ability ofremoving P and S due to the dissociated CaO. P can dissolve into the steel infinitely,nevertheless,P can only be removed by the reaction between P₂O₅ and dissociated CaOto form stable compound, Ca₄P₂O₉. The mechanism of S removal is through liquid, inother words, the dissociated CaO in MgO-CaO lining reacted with sulphur to form CaS.Afterwards, Ca₄P₂O₉ and CaS is absorbed on the surface of MgO-CaO lining or float to the slag, and then the S and P is eliminated from the molten steel.Al₂O₃-MgO has no effect on inclusion removal; on the contrary, it can increaseinclusions in the molten steel due to its erosion. MgO-Al₂O₃ lining contributes tocleaning the steel a little, in other words, it doesn't contaminate molten steel at least.MgO-CaO lining has strong ability of reducing inclusions, and it become obvious withCaO content increasing. The best effect appeared at 30% CaO in present trial.The free energy AG at certain temperature can be calculated by element activity inthe melt and Van't Hoff isothermal equationΔG=ΔG^θ+RTlnJ, thus inclusion type andcorresponding condition can be predicted. The theorchical calculation is in a goodagreement with trial results, i.e., the inclusions composition can be forecasted bythermodynamic calculation while the composition of molten steel, slag and refractoryand the content of oxygen are predictable.The investigation the influence of MgO-CaO-C bricks on carbon pick-up in thesteel indicates that the amount of carbon pick-up goes up with carbon content inMgO-CaO-C bricks, which promote the rate and total amount of carbon dissolution intomolten steel. By substituting charcoal for flake graphite, the extent of carbon pick-up inthe melt is reduced.