| In our country,the steel industry has great pressure in resource shortage,energy consumption,smoke and slag waste discharge.In order to improve the efficiency of converter steelmaking,a new technology of converter steelmaking with " Double Slag+Remaining Slag" has been studied and developed.The steelmaking process is divided into dephosphorization period and decarburization period.The slag pour rate at the end of dephosphorization period is between 40%and 45%.The slag at the end of decarburization period is retained and solidified,then scrap is added to prepare the next furnace for smelting.The final slag in decarburization period has high basicity and low phosphorus content.Through solidification and reuse of the decarbonization slag and pouring out high phosphorus content slag in dephosphorization period,the efficiency of converter dephosphorization has been improved,and the consumption of lime and light-burned dolomite for steelmaking has been reduced.From 2011 to 2018,the process was applied to the 100t converter steelmaking plant of Shouqin Company.The proportion of application is between 70%and 85%,and the consumption of lime and light-fired dolomite is reduced by 45%and more than 55%respectively compared with the traditional process.The steel material consumption reduced more than 8kg/t.The main research work is as follows:(1)Research on the steelmaking process with Double Slag and Remaining Slag.After the dephosphorization period ends,the dephosphorized slag enters the decarburization period.After the decarburizing period,the decarburized slag is solidified in the converter to realize safe exchange of iron,and then the next smelting is started.By controlling the slag quantity,alkalinity and oxidizability of the slag in converter,the amount of dephosphorized slag at the end of the dephosphorization stage is about 60-80 kg ·t-1 steel,and all the slag accumulated in the furnace at the end of cycle is about 120-130 kg·t-1 steel,and all the slag accumulated at the end of the dephosphorization stage is about 60-80 kg·t-1 steel.The average slag produced is about 80 kg ·t-1 steel.With the increase of smelting furnaces,the consumption of lime in steelmaking decreases gradually,from 65 kg·t-1 steel to 31 kg ·t-1 steel.The phosphorus content in molten steel decreased from 0.018%to 0.005%.(2)Study on high efficiency dephosphorization process in dephosphorization periodUnder the condition of limited bottom blowing strength,the high efficiency dephosphorization process at low bottom blowing strength(0.03NM3·min-1·t-1)was studied.Different from the dephosphorization process of high bottom blowing flow rate and low top blowing flow rate in dephosphorization period,the effect of top blowing flow rate and gun position on the impact of molten pool is calculated by numerical simulation,and the bottom blowing low flow rate is developed in the dephosphorization period,which is different from that in Japan and other iron and steel plants,such as Japan and other iron and steel plants.The top blowing low lance position and high flow rate oxygen supply(the top blowing gas supply intensity 3.ONM3·min-1·t-1)is used to strongly stir the molten steel pool.Through the application of this process,the temperature of molten steel at the end of the dephosphorization period is about 1350℃,and the temperature of the molten steel at the end of the dephosphorization period is about 1350℃.Under the condition of low alkalinity and low iron oxide,the dephosphorization rate is about 70%during the dephosphorization period.The basicity of steel slag is controlled between 1.5 and 2.0,and the content of FeO in slag is controlled within 12%,which further reduces the consumption of metal material in slag.(3)Study on the enrichment of phosphorus in slag and its influencing factorsCombined with the phenomenon of high oxidation and high basicity in low phosphorus steel smelting with weak bottom blowing converter,the regularity and influencing factors of phosphorus enrichment in converter steel slag under the condition of rich phosphorus phase dicalcium silicate(expressed as C2S)were studied.It is found that the existence of solid-phase phosphorus-rich phase C2S can improve the ability of dephosphorization of steel slag.However,the high free FeO reacts with the rich phosphorus phase C2S,which results in the formation of low melting point liquid slag phase.With the disappearance of the solid state C2S,the phosphorus enriched in the liquid phase slag enters the liquid slag,and the increased phosphorus in the liquid phase slag participates in the distribution of phosphorus between the liquid phase slag and the molten steel,and the addition of phosphorus in the liquid phase slag participates in the distribution of phosphorus between liquid slag and molten steel.Then the phenomenon of phosphorus return was produced.The effect of Si content in slag on phosphorus-rich phase was studied.The enrichment phase of phosphorus in slag consisted of C2S,tricalcium silicate(expressed as C3S)and other phases containing Si,while other slag phases contained low or no phosphorus,so it was found that there was a reasonable amount of SiO2 in steel slag.When the amount of SiO2 in slag is lower than the reasonable amount,the amount of phosphorus-rich phase C2S will be reduced,and the efficiency of dephosphorization of slag will be affected.The excessive amount of SiO2 will affect the basicity and lead to the difficulty of dephosphorization.When the basicity is constant,the amount of slag is too large,resulting in unnecessary waste.The reasonable amount of SiO2 is reduced to the content of Si in hot metal,and the calculation method of w(Si)is:w(Si)≥3 ×(hot metal W(P)-end point of converter W(P)),without considering the addition of Si element into steel-making auxiliary material.From the point of view of phosphorus-rich phase,the relationship between the content of phosphorus in hot metal and the amount of slag has been established.In addition,if the temperature is too high,the amount of C2S in solid state will be reduced,and the dephosphorization will be adversely affected.(4)Study on the process of high efficiency dephosphorization with low alkalinity and low oxidation slagDephosphorization requires large amount of slag,high basicity and high oxidizability of slag system,but the existence of phosphorus-rich phase C2S does not completely need high basicity and high oxidizability environment.Under lower basicity condition,reducing the content of FeO in slag can produce more phosphorus-rich C2S phase.The basicity of steel slag is decreased by adopting low FeO slag system in the process of "Double Slag+Remaining Slag",and through the study of slag phase,it is found that the size of phosphorus-rich phase C2S of slag with low FeO content is relatively large,and the phosphorus content in slag is relatively high.In the steel slag with high FeO content,the size of phosphorus-rich phase C2S is relatively small and the phosphorus content in the slag is relatively low.The phosphorus partition ratio of low FeO,and low alkalinity slag system(FeO%:13.9,R:3.1)can be obtained.Under the same conditions,the phosphorus partition ratio of high basicity slag system(FeO%:19.0,R:4.0)is 167,and that of high FeO content is higher than that of high basicity slag system(FeO%:19.0,R:4.0).The application of this slag system can further reduce the consumption of iron and steel-making accessories.The average consumption of lime decreases more than 15kg/t steel,and the average consumption of light-fired dolomite reduces about 4.5kg/t steel.(5)Study on smelting process of ultra-low phosphorus steel based on Double Slag and Remaining Slag"The calculation and analysis of smelting slag of ultra-low phosphorus steel show that the theoretical phosphorus distribution ratio is between 100 and 200.When there is a sufficient amount of phosphorus-rich phase C2S phase in the slag,the actual phosphorus distribution ratio can reach 400-500.When the content of silicon in molten iron is low(Si<0.25%)and the amount of phosphorus-rich phase C2S formed in slag is less,every time the content of Si is increased by 0.10%in hot metal,the content of phosphorus in molten steel can be reduced to about 9-12ppm by increasing the amount of C2S in slag.At the end of smelting,ultra-low temperature drawing(1575℃,carbon content:0.10%),the content of phosphorus in molten steel is 30-40 ppm.Only lime is allowed to be added to the temperature-raising process in the after blowing.Free CaO is used to restrain the reaction of free FeO in slag to C2S,which can restrain a large amount of phosphorus return in this stage.It can be realized that the final phosphorus content of converter is lower than that of 50ppm. |
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