Design And Development Of Fluorine-free Ladle Furnace Slag For Axle Steel

Axle steel is special steel used to make railway vehicles and locomotive axles,and LF refining is an important process for the performance of axle steel.Calcium fluoride can improve the forming speed and fluidity of refining slag,but the produced fluoride is not conducive to the improvement of production environment and the reduction of the fluoride-containing waste.In this paper,based on the smelting requirements of axle steel,a fluorine-free LF refining slag system was designed and developed by adjusting its composition to controll the basic physical properties and metallurgical properties of the slag.The research results will help reduce the emission of fluorine-containing waste and improve the working conditions.Taking the CaO-Al2O3-SiO2-MgO-CaF2 slag system as the research object,with the help of FactSage 7.1 software and phase diagram analysis,the influence of refining slag composition on the metallurgical properties of the slag system was predicted,and the components of the fluoride-free refining slag system are preliminarily designed.Based on the results of theoretical analysis,the basic physical properties of refining slag were experimentally determined to further optimize the composition of the slag system,and then the practical application effect of fluorine-free refining slag was investigated through industrial test.The results of thermodynamic calculation and analysis showed that when the composition of the refining slag without fluorine is in the range of w(CaO)=45?55%,w(MgO)=6?8%,w(Al2O3)=30?40%,w(SiO2)=2?10%,w(CaO)/w(Al2O3)=1.00?1.50,the resigned refining slag system presented theproper melting temperature,good fluidity and well ability of controllingthe activity of SiO2 and Al2O3 in the slag in a lower range.Through the basic physical property test experiment,the slag system composition was finally optimized in the range of w(CaO)=45?55%,w(MgO)=6?8%,w(SiO2)=2?6%,w(Al2O3)=30?40%,w(CaO)/w(Al2O3)=1.25?1.50,which can ensure that the melting and flow characteristics of the fluorine-free refining slag is similar to that of the original fluorine-free slag.The designed fluorine has predicted to achieve the refine effect,and it is expected to achieve the refining effect of axle steel.Industrial verification test results showed that the designed fluorine-free refining slag has good deoxidizing and desulfurizing ability and can meet the smelting demand of axle steel.