| According to investigate a steel mill, in order to improve the effect of deoxidationand desulphurization in the refining process, shorten refining cycle and control the hard,brittle and large particle inclusions in molten steel for reducing the refining energyconsumption and the corresponding refining costs, with42CrMoA crankshaft steel as anexample, the multi-systems slags in the process of refining desulphurization have beenresearched. It is very important to choose the reasonable slags and determine thecomposition and ratio of slags and slags quantity.In this paper, the thermodynamics study of refining desulphuration has beenintroduced using four types of CaO-Al2O3-SiO2-MgO, CaO-Al2O3-SiO2-MgO-FeO,CaO-Al2O3-SiO2-MgO-MnO and CaO-Al2O3-SiO2-MgO–MnO-FeO slags systemssmelting42CrMoA crankshaft steel. The sulphide capacity (CS) model using KTH,sulphur equilibrium distribution ratio (LS) and activity model by thermodynamicsoftware Factsage6.3.1and Origin8.5have been built. Combining the result of modelcalculation, the effect factors on desulphuration have been analysis, finally the bestdesulphuration components are obtained optimizing the maximum CSand LSandgenerating low poin compound inclusions.For CaO-Al2O3-SiO2-MgO slag, the CSincreases by the rising of basicity andtemperature, decreases by the rising of MgO and Al2O3contents. When the basicity is4-6, the capacity of desulphuration is better. CaO/Al2O3effect on CSis seldom,available large sulphur capacity at1-2. When LSis large, the corresponding bestcomponents are CaO=50~55%, SiO2=4~6%, Al2O3=40~43%, MgO=4~8%. When theMgO content increases, the liquid phase region of CaO is reduced. The activity of Al2O3 increases by the rising of CaO, but decreases by the rising of Al2O3. When the contentof MgO is respectively4%,8%,12%,15%, and the corresponding SiO2is respectively20~30%,25~45%,27~40%and about40%, the effect of CaO and Al2O3on Al2O3activity appeared inflection point. The rising of CaO content leads to the increase ofCaO activity, but with the increase of SiO2, the CaO activity decreases. The targetrefining slag compositions suited to generate low melting point compound calciumaluminate inclusions are CaO=45~55%, SiO2=0~8%, Al2O3=30~45%, MgO=4~8%.For CaO-SiO2-Al2O3-MgO-FeO slag, the effect of Al2O3content on the CSthroughorthogonal design method is biggest. With the increase of FeO, CShas little change.When basicity is equal or greater than4.7and CaO/Al2O3is0.7-1.25, low point isachieved by slags. LSalong with the increase of FeO content decreases. When LSachieving the maximum, the corresponding compositions are CaO54~57%, SiO27~10%, Al2O328~35%, MgO6%and CaO51~58%, SiO23~10%, Al2O330~38%,MgO8%. Suitable for the production of low melting point compound calciumaluminate salts, refining slag compositions are CaO48~60%, SiO2≤10.28%, Al2O329~40%, MgO6%, FeO0.5%.For CaO-SiO2-Al2O3-MgO-MnO, CSdecreases by increasing MnO content withhigh basicity. When basicity is equal or greater than4.7and CaO/Al2O3is0.7-1.22, lowpoint is achieved by slags. When LSat maximum, refining slag compositions arerespectively CaO53~58%, SiO28~11%, Al2O335~40%, MgO6%, MnO0.5%and CaO51~55%, SiO25~10%, Al2O334~38%, MgO10%, MnO0.5%. Refining slagcompositions Suitable for the production of low melting point compound calciumaluminate salts are CaO46~57%, SiO2≤9.91%, Al2O326~42%, MgO6%, MnO0.5%.For CaO-SiO2-Al2O3-MgO-MnO-FeO, FeO and MnO have seldom an effct on CS.When basicity is equal or greater than4.5and CaO/Al2O3is0.67-1.25, low point isachieved by slags. LSat maximum, refining slag compositions are respectively CaO52~58%, SiO29~13%, Al2O330~40%, MgO6%, MnO0.5%, FeO0.5%and CaO50~56%, SiO25~10%, Al2O332~38%, MgO8%, MnO0.5%, FeO0.5%and CaO50~55%, SiO25~8%, Al2O335~40%, MgO10%, MnO0.5%, FeO0.5%. Refining slagcompositions Suitable for the production of low melting point compound calciumaluminate salts are CaO52~55%, SiO2≤10.7%, Al2O337~40%, MgO6~8%, FeO0.5%, MnO0.5%. |
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