Study On Converter Steelmaking Technology Based On High Silicon Hot Metal

In this paper,the two converter steelmaking process for high silicon([Si]>1.5%)hot metal,the double slag process for high silicon(0.8%<[Si]<1.5%)hot metal and the lining protection of desilication converter were analysed and optimized.The production problems of high silicon and high phosphorus hot metal produced by COREX furnace were solved.For the high silicon([Si]>1.5%)hot metal,the two converter steelmaking process is proposed.High silicon hot metal was desilicicated in converter 1,then sent to converter 2 for decarbonization and dephosphorization.The carbon-silicon oxidation reaction in the desilication furnace was studied,and a prediction model for the composition of semi-steel was established.The equilibrium temperature of carbon-silicon oxidation reaction is about 1550?.When the temperature of the molten bath is higher than 1550? the oxidation of the carbon will be promoted,which leads to the lack of heat in the decarbonization converter.When the temperature of hot metal is higher than 1550?,it will cause carbon oxidation in the early stage of smelting in converter 2.Also it will result in the difficulty of slag formation and a large amount formation of gas which cause the slag overflow or spatter.In order to ensure the smelting of converter 2,the end point[Si]content of the desilication converter should be controlled between 0.5?0.7%,and the temperature should be less than 1500?.The slag basicity of desilication furnace should be 1-1.2 to relieve the effect of 45%(SiO2)content in the slag on the separation of slag and iron.The slag retention operation is adopted to reduce the addition of the first batch of slag materials and promote the formation of the initial slag to realize the high dephosphorization rate in the early stage of decarbonization furnace.Considering the influence of hot metal temperature,carbon content,silicon content and semi-steel temperature on the amount of scrap steel addtion,the charging amount model of scrap was developed.Through the studies above,the stable smelting of high-silicon hot metal is realized.Compared with the double slag process,the spatter rate can be effectively reduced,the average consumption of lime and dolomite are reduced by 31 kg/t?23kg/t,the average loss of iron and steel is reduced by 5.5%,and the ratio of converter scrap is 35%.For hot metal of which[Si]content is 0.8?1.5%and[P]content is higher than 0.12%,the double slag steelmaking process is adopted.In the early stage,the temperature should be controlled at 1350?1400?,and the silicon content of semi-steel should be controlled at 0.05%to avoid the spatter caused by(FeO)concentration of slag.To ensure the dephosphorization in early stage,the basicity of slag should be high.The ideal route of slag basicity in the early stage is to increase from about 1.0 to 1.6 gradually.The slag basicity should controlled at 1.4-1.6,(FeO)should be at 16-20%,which can realized a 50%rate of liquid phase and[P]concentraction in Ca2SiO4·Ca3P2O5 solid phase.It is found that there is a limit value in the early stage dephosphorization,the phosphorus content in the liquid steel is reduced to 0.06%at most,the highest dephosphorization rate is 60%,which is 50%in actual production.A better dephosphorization effect can be realized by increasing the slag basicity at early stage.When low phosphorus steel is produced,the carbon content less than 0.06%can promote the end point dephosphorization by further utilization of the slag.The double slag process model is developed,and average content of carbon at end point is 0.0575%,the average content of phosphorus is 0.008%,and the dephosphorization rate at end point is more than 93%.During steelmaking of high silicon hot metal,the corrosion of furnace lining is serious which is caused by low basicity,low melting point and high MgO dissolution of slag.For better slag splashing,slag basicity should be controlled at 1?1.2,(MgO)content should between 5-7%and(FeO)content should be about 5%.In order to relive the upper lining erosion of desilication furnace,when splashing slag the top blowing volumn should be controlled about 32000 m3/h,the low bottom blowing flow rate is adopted,the oxygen lance position should be 1600-2000 mm,the amount of slag should be controlled at 110-120 kg/t.After adoption of the measures above,the lining area below 400 thickness is reduced to 3.65 m2 for 87 heats which is less than before(1.73 m2 after producing 74 heats),and the erosion degree of front large surface and slag line part is obviously reduced.