Study On Dephosphorization For Medium And High Phosphorus Hot Metal Of 80t Converter In CISC

In recent years, due to the market downturn and massive overcapacity, the form of iron and steel industry is very serious. In order to better survival and development, many domestic steel enterprises had focused on the development and utilization of high phosphorus iron ore to improve competitiveness by reducing cost. Phosphorus is harmful for most kinds of steel, and the use of high phosphorus iron ore will greatly increase the phosphorus content in hot metal. At the same time, with the development of the industry, it is set higher requirements for phosphorus content in steel. In current steelmaking process, the dephosphorization was occurred in converter, so it is meaningful to study the highly efficient dephosphorization in converter.Together with highly efficient dephosphorization in 80 t converter of CISC, through to deal with the data of field, the dephosphorization thermodynamics and dynamics analysis, it was studied that the effect of two parameters on the dephosphorization rate. The first is difference between the end-point temperature of BOF molten steel and C-P selective oxidation temperature, and the second is superheat of slag. Also,the temperature of the process and the end slag composition control requirements were studied, At last, a field test was carried out.1 When dealing with the data of field, the results can be got:The phosphorus content in the hot metal is high and uneven, and the average value is 0.166%. So task of dephosphorizationi s hard. Dephosphorization rate and decarburization rate of the whole process is not stable, and the dephosphorization rate is relatively low which is 87.8% at the end point. In order to achieve better dephosphorization effect, the initial bath temperature should be controlled in the range 1150 to 1210?, the bath temperature should be in 1580? of tapping with turning down at one time, the bath temperature should be control in 1645? at end point, and slag basicity is controlled in the range of 3.9~4.3, w(Fe O) is in the range of 22%-25%.2 Thermodynamics and dynamics analysis results:1)It should be considered that(Fe O) transfer oxygen when calculating the C-P selective oxidation temperature at the later blowing stage of BOF. When slag basicity increase 0.1, the temperature increase 2?. And when the(Fe O) content in slag increase, the temperature show a trend that increased first and then decrease, while its influence is relatively small. And when P content in liquid steel increase 0.001%, the temperature increase 5.3?. While when C content in liquid increase 0.01%, the temperature decrease about 7.3?.2)Two parameters can be used to reflect the thermodynamics and kinetics conditions of dephosphorization reaction, one is the difference between the end-point temperature of BOF molten steel and C-P selective oxidation temperature, another is superheat of slag. For sintering production of 80 t converter, when the difference reduce 10?, the dephosphorization rate increases by about 1.2%, when the difference is less than 30?, the dephosphorization rate is more than 90%.With the increase of superheat, the dephosphorization rate showed a trend of decrease after the first increase, in order to ensure the dephosphorization rate is greater than 90%, superheat of slag should be 205 ~ 235?.3)The decomposition temperature of ferrous phosphate is 1358?, while it is about 1370? in actual slag. The laboratory experiment results dephosphorization show that it has effect on phosphorus fixation to add lime before ferrous phosphate decompose. Due to the effect of low temperature on the melting property of slag, the best time to put lime is at 1400?(after the decomposition of iron phosphate) for dephosphorization. And this provides guidance for the addition time of second batch of lime to converter.3 Industrial test results:The converter single slag test results in 80 t of CISC show that when the end-point temperature of BOF molten steel is about 1640?, basicity is controlled in the range of 4.2 to 4.55, and w(Fe O) of end steel slag is between 23% and 27%, it can achieves better effect of dephosphorization and keeping carbon. The average value of P and C content are 0.013% and 0.07% respectively, and the dephosphorization rate reaches over 90%.