Collaborative Optimization Of Ladle Refining Process For Rapid Desulfurization And Controlling Nitrogen Content In Molten Steel

In order to adapt to the development of refining-continuous casting-continuous rolling process with low cost and high efficiency and the production of high performance steel,it is urgent to further optimize the process of rapid desulfurization and control the content of nitrogen in ladle refining,further reduce the content of sulfur and nitrogen in steel and its harm to the quality of billet and Slab in continuous casting and rolling.In this paper,with high performance bridge steel Q370 and the Q235 steel by argon blowing refining direct up process in a domestic plant was taken as the research object.Thermodynamics and kinetics of slag desulfurization and nitrogen absorption and their influencing factors were analyzed in tapping and refining processes.The cooperate optimization of technological measures were put forward about rapid desulfurization and the control the content nitrogen of molten steel.The main conclusions are as follows:(1)The slagging processes of desulfurization in tapping and deep desulfurization in LF furnace were analyzed.The calculation showed that the optical basicity of desulfurization slag were 0.74 and 0.77 respectively,and the sulfur distribution ratios were 501 and 631 respectively.the melting point of refining slag was lower than the refining temperature of molten steel,The refining slag used in the field has better desulfurization performance.(2)Under the condition of tapping desulfurization process of Q235 steel,desulfurization and nitrogen absorption models during tapping and argon blowing were established respectively,and the desulfurization and nitrogen absorption of molten steel were calculated.The results showed that the ratio of desulfurization during tapping and argon blowing was about 1:2,the desulfurization efficiency during deoxidization alloying was high,which accounting for more than 50% of the total desulfurization during tapping,and the total nitrogen absorption during tapping and argon blowing was 9.2 ppm,of which 81% was in tapping.(3)Under the condition of deep desulfurization in LF refining process of Q370 steel,the models of desulfurization and nitrogen absorption of liquid steel during LFsteel were calculated.The results showed that the proportion of desulfurization in the stages of large stirring,electrode heating and soft stirring was the same;the total amount of nitrogen absorbed in tapping-LF refining process was 20 ppm,the amount of nitrogen absorbed in tapping process accounted for 62% of the total amount of nitrogen absorbed,The deoxidizing alloying and electrode heating stages were respectively the maximum nitrogen absorption stages in tapping and LF refining stages,and their respective proportions were 60% and 57% respectively.Reducing the molten steel exposed during deoxidization alloying and improving the protective effect of foam slag during the heating process could effectively reduce the nitrogen uptake of molten steel.(4)Under the condition of steel tapping desulfurization process,raising the large stirring time for 2 minutes(the total argon station processing time remains unchanged)could achieve the desulfurization of molten steel with initial [S] ≤ 0.035%.Increasing the stirring time in a short time could neglect the nitrogen increment of molten steel.Increasing the stirring of molten steel during steel tapping could also improve the qualified rate of desulfurization,but it could lead to an increase of nitrogen absorption in steel by 5 ppm.(5)Under LF refining deep desulfurization conditions,early slagging(adding refining slag during tapping)operation could not only achieve desulfurization of molten steel with initial [S] ≤0.035%,but also reduce the nitrogen uptake of molten steel by 5 ppm.Increasing the large stirring time(the total refining time remains unchanged)could also improve the qualified rate of desulfurization,but increasing the stirring time would lead to the increase of nitrogen in molten steel on the one hand,On the other hand,it is harmful to temperature drop and slag entrapment.In LF refining process,calcium treatment operation could increase nitrogen uptake of molten steel.Inclined wire feeding could prevent a large number of calcium bubbles from overflowing from the exposed surface and cause disturbance on the exposed surface,thus avoiding the increase of nitrogen uptake in molten steel.