Theoretical And Experimental Study Of Slag Forming Path During Duplex Dephosphorization Processing

With the increasing high demands of our consumer for the steel quality, steelworkers are faced with important engineering problems of the harmful elementphosphorous removal in steel. The industries production shown that the duplexprocessing was efficient processing, which was used to produce lower or ultra-lowphosphorous higher quality steel and the tap-to tap time was shorted and reduced theproduction cost. The duplex dephosphorization processing is a tremendous success toemploy in some steel plant. However, there are short of the theoretical studying of theduplex dephosphorization processing, which is limited it was extensively used by steelplant. Hence, in our work, the duplex dephosphorization converter, higher temperaturedecarbonrization converter were investigated as the research object, the slag formationpath during duplex processing wa studied。The CaO-SiO₂-FeO-MgO-MnO-P₂O₅as hexatomic slag was adopted in thedephosphorization converter, and adopted CaO-FeO-MnO-SiO₂-MgO-Al₂O₃-P₂O₅asheptabasic slag in the decarburization converter. The effect of slag composition onliquilid line was calculated by the Factsage thermol soft and combined with contourmap on the phosphorus distribution ratios or contour map on the manganese distributionratios. The theoretical slag formation path of lower temperature dephosphorizationconverter and higher temperature decarbonrization converter was obtained, respectively.In experimental condition, the effect of phosphorus、silicon in hot metal and the slagcomposition on dephosphorization were studied, the slag forming path was obtainedbased on the above studying, detailed work was summarized as follows:â‘ The L_Pincreased with increased basicity （1.5².1）, the basicity of finial slagwas controlled about2.1because the smelting temperature in dephosphorizationconverter was lower than the decarbonrization converter. The L_Pincreased withincreased FeO （5%³0%） in final slag, however, the theoretical L_Pincreased and thendecreased with increased FeO content in final slag, the theoretical L_Preached maximumvalue when the FeO content was about25%. Hence, in practical processing, the FeOcontent in final slag was controlled about25%. The L_Pincreased with increased MnO（3%¹2%） in final slag, however, the theoretical L_Pdecreased with increased MnOcontent in final slag, the smelting point of slag could be reduced when the MnO existedin slag, the MnO content in final slag was controlled among6%⁸%in consideration of reducing the smelting temperature of slag. The MgO content in final slag shoul becontrolled among4.0%⁵.0%, which was beneficial of reducing the smeltingtemperature of slag.â‘¡The dephosphorization ratio increased from21%to90%when the [Si] in hotmeatl was increased from0.1%to0.4%and then kept90%continually increased to0.8%when the baisicity was2.1. The basicity of final slag can not much higher than thedecarbonrization converter because the lower smelting temperature was indephosphorization converter, and reduced the cost of production. Hence, the content ofSi among0.2%⁰.4%was appropriate, which was beneficial of dephosphorization. L_Pdecreased with increased phosphorus （0.1%⁰.2%） in hot metal, in order to realize theefficient dephosphorization the [P] was controlled under0.12%.â‘¢The theoretical and practical slag formation path were higher irony line in thedephosphorization of converter via theoretical calculation and experimental studying,and the theoretical and practical initial slag composition were15%CaO-44%SiO₂-41%FeO, approximately. The process slag composition was passed the higher FeO of20%CaO-20%SiO₂-60%FeO. The theoretical and practical final dephosphorization slagcomposition was close by53%CaO-25.5%SiO₂-21.5%FeO and50.8%CaO-24.2%SiO₂-25%FeO, respectively. The last solid phosphorus slag was closeby63.6%CaO-30.3%SiO₂-6.1%FeO. However, in the practical smelting process, thecomposition of initial slag should be obtained via blowing system.â‘£In order to improve the recovery ratios of manganese, the requirement forcontrollable composition of final slag in the decarburization converter：The basicity offinial slag was controlled among4⁵, and the content of FeO, MnO and MgO in finalslag was controlled among20%,14%¹7%,8%¹0%, respectively.The theoretical slagformation path was irony line in the decarburization converter, and composition ofinitial slag was15%CaO-65%FeO-20%MnO, approximately. The composition of finaldecarburization slag was close by40%CaO-35%FeO-25%MnO.