Study On Desulfurization In RH By Input Method For Soft-killed Steel

In the modern steelmaking process of some lowcarbon and ultra-lowcarbonsteels, the production process of “BOF(basic oxygen furnace)+RH(Ruhrstahl-Heraeus)” are generally adopted. The molten steel is usually not deoxidized or only partially deoxidized during the converter tapping, and Al is added for final deoxidation after decarburization during RH refining. Thus, the Al consumption, Al2O3 generation, and the production cost can be reduced. However, it is practically impossible to remove the sulphur from the molten steel before RH degassing, due to the high oxygen activity in molten steel and high Fe O+Mn O content in top slag. As a result, desulfuration after Al deoxidation in the RH has become an important method to produce the steel with low [S] content.In the paper, desulfurizationin RH by input method is investigated during the production process of low-carbon steel and electrical steelwith ultra-lowcarbon content. First, thermodynamic analysis is carried on to obtain a slag with reasonable compositions. At the same time, the dynamics behavior of desulphuriser added from RH vacuum chamber is simulated through the physical modeling. Finally, the factors affect the dynamics behavior is analyzed, and the industrial experiment is carried out.Thermodynamic calculation shows thatthe sulphur partition decreases dramatically with increase in the Fe O content in slag, which is attributed to the increasing of Fe O activity. The Fe O+Mn O content should be controlled to less than 5%. Increasing the %Ca O/%Al2O3 ratio increases the sulphur partition between slag and steel, due to the decrease of Fe O activity and the increase of sulphide capacity.The %Ca O/%Al2O3 ratio should be controlled in the range of 1.8 to 2.0.The addition of Si O2 can decrease the sulphide capacity of the slag and increase the activity of Fe O in slag, so the Si O2 content in slag should be minimized.The results of physical modeling show that the desulphuriser added from vacuum chamber will be dragged into ladleby descending flow in the down snorkel, and then, it rises to the ladle surface quickly. Thus, the desulphurisertakes a few short moments tointeract with steel in the vacuum chamber, which is not in favor of desulfuration. Decreasing the vacuum pressure can increase the liquid level in the vacuum chamber, which favors increasing the duration time. However, increasing the gas flow has a contrary result.Based on the physical modeling, the amount of desulphuriser in the vacuum chamber is corrected, and the desulfurization kineticsin RH by input method is developed, which has a good prediction.The kinetics result shows that the final [S] content increases linearly with the initial [S] content in steel, and initial [S] content in steel should be reduced as much as possible to obtain the steel with low [S] content. Increasing the Ls to the benefit of desulfurization.Industrial experiment shows that, for low-carbon steel, desulfurization efficiency with desulphuriser of mechanical mixing is superior to that of pressing ball and premelting, and optimum desulfurization efficiency is obtained when the gas flow is 90 m3/h and the amount of desulphuriser is 1200 kg. In addition, compared to low-carbon steel, better desulfurization efficiency is gained for the electrical steel with ultra-lowcarbon content, due to the better thermodynamic conditions caused by high [Si] and [Al] contents.