Analysis Of Manganese Removing And Dephosphorization Based On Slag-remaining And Double-slag Process

Dephosphorization and demanganization requires a large amount of slag in traditional BOF production,and the cost is relatively higher.Furthermore,the reversion phenomenon of rephosphorization and manganese occurs easily in the last period of blowing,which makes it difficult to control the residual manganese and phosphorus content in the steel.In recent years,many iron and steel enterprises use remaining slag-double slag steelmaking technology in the BOF,which can improve the dephosphorization and demanganization capability of converter and reduce the production cost significantly.However,there are still many problems need to be solved to improved in the process.For example,the removal effect of manganese and phosphorus is instability,and the flutuation of process is lager.Based on this background,firstly the thermodynamic and kinetic of Mn and P oxidation in converter steelmaking process were analyzed.Secondly combined with on-site smelting data,it was found that dephosphorization and demanganization behavior in remaining slag-double slag technology mainly concentrated in the first slag-blowing process,while decarburization occurred mainly in the second slag-blowing process.Therefore,the first slag-blowing process has great effective on dephosphorization and demanganization.The effects of basicity,iron oxide content in slag,silicon content in molten iron,blowing temperature,slag basicity and blowing time on the rate of demanganization and dephosphorization were statistically analyzed under the first slag-blowing process.The conclusions obtained are as follows:In order to inprove the oxidation of manganese in hot metal by using slag remaining-double slag process,it is necessary to guarantee a good oxidation of slag at the initial stage of steelmaking,suitable basicity and temperature to promote the reaction in liquid steel and emulsification in the slag.After the analysis of the field data,It was found that there could be a good effect on removing Mn when the first slag basicity is1.5～2.0,the temperature of first slag is 1350℃～1400℃ and the first slag-blowing time is 230s～260s.For the remaining slag-double slag technology,to obtain an optimum effect dephosphorization the first slag must be of high oxidation,low melting temperature,proper basicity and good fluidity.Field data analysis found that good dephosphorizationeffect can be obtained when a blowing time is about 240 s,primary blowing temperature is lower than 1400℃ and the first slag basicity is 1.5～2.0.