Fundamental Application Research On Deslagging And Dephosphorization Of Conventer Slag-remaning And Double Slag Process

Currently, Chinese iron and steel industrises are facing the problems including overcapacity, thin margins and serious environmental pollution. Compared with traditional single slag or double slag process, it will reduce the consumption of lime during the converter slag-remaining and double slag process by substitute final slag in the last heat for some lime in the current heat. It has a great significance to reduce the production cost and improve the environmental pollution by decreasing the discharge of steel slag.There are two phases during this process, i.e. decarburization phase and dephosphorization phase. Two tasks should be completed during dephosphorization process which are the removal of most phosphorus and the extracting of dephosphorization flux from converter. Slag foaming is the important way of removing dephosphorization flux from converter. Deslagging and dephosphorization are the key parts of the whole slag-remaining and double slag process. Therefore, slag foaming during dephosphorization phase and dephosphorized theory were mainly studied in this paper which provide guidance to understand and improve the slag-remaining and double slag process.The statistic analysis of many production data during 50t converter slag-remaining and double slag process indicates that the quantity of deslagging, iron loss caused by deslagging, and dephosphorization during dephosphorization phase are key difficulties. It also provides a basis for related theoretical research.Samples were taken during deslagging process at the end of the 50t converter dephosphorization phase and the electronic microscope photographs of foaming slag were analyzed. The results indicate that the foaming slag are composed of foam, slag phase and iron shot. The number of bubbles in foaming slag increases, the bubble size and porosity decreases from up to down. The roundness of bubble are about 0.9～1.0 mostly. The favorable conditions of obtaining large quantity of deslagging was obtained by analyzing the formation process of foaming slag: reducing the drainage time, i.e. deslagging rapidly, increasing the reaction rate of carbon and oxygen.As to the large loss of iron and the foaming slag containing large amount of iron shot, the water/silicon oil system was used to simulate the bubble entrainment behavior during it going through steel/slag interface process. The results show that increasing the viscosity of slag and reducing the bubble size benefit the decrease of bubble entrainment rate. After the regression of relative parameters, the formula of bubble entrainment was obtained M=4.6EoB2.57(ηs/ηd) (ps/pd)-5 The mechanism of bubble entrainment was deeply studied and it indicates that large size droplets are entrained by high speed spherical crown-shaped bubbles and the small droplets are entrained by low speed cone-shaped bubbles.The thermodynamic theoretical calculation of Factsage and hot state experimental results show that the phase constitution of dephosphorization flux were phosphorus-rich phase, Fe-riched phase and substrate. When the basicity of slag was 1.5-2.5 and the composition of slag located in primary zone of dicalcium silicate, the precipitation of 2CaO·SiO2 reduced slightly which increased the phosphorus content in phosphorus-rich phase and it benefites dephosphorization in convertor. When the basicity of slag was lower than 1.5 and the composition of slag located in primary zone of CaSiO3, the precipitation of 2CaO·SiO2 reduced obviously which was unfavorable for dephosphorization. Considering the traditional dephosphorization theory that high basicity slag benefits dephosphorization reaction between steel and slag, the suitable basicity of slag should be 1.5～2.5.The optimal production results of 50t converter indicates that during the deslagging process, the carbon and oxygen reaction rate increased through adding ore 2～6kg/t in batch 0.5-1min before deslagging and the quantity of deslagging increased by 32.6% by controlling the deslagging time less than 3min. As to dephosphorization part, during dephosphorization phase, the blowing oxygen time, temperature, slag basicity and Fe2O3 content were respectively 4-6min、 1350～1400℃,1.6～2.2,20～25%. During decarburization phase, when the temperature was 1610-1700℃, the slag basicity was 17～30%, the decrease of temperature and increase of basicity and Fe2O3 content benefit dephosphorization. The composition of final slag and temperature should be adjusted according to the requirement of steel grade. The average dephosphorization rate reached 92.7%, the consumption of lime reduced by 30.3% and the iron and steel material consumption reduced by 0.55%.