Study On Optimization Of Refining Slag And Its Mechanism On Removal Of Inclusions In Spring Steel

60Si2Mn spring steel is the most widely used spring steel in China.The main task of improving the fatigue performance of the spring steel is to reduce the inclusion in the molten steel or to change the Al₂O₃ inclusion into a plastic inclusion of less damage to the steel.This paper uses FactSage 7.0 software to calculate equilibrium of 60Si2Mn steel and CaO-Al₂O₃-Si O₂-MgO slag reaction,and[O],[Al],[Ca],[Mg]equilibrium relationship between molten steel and slag composition is discussed.The inclusions in molten steel are studied by thermodynamic calculation,and verified by the balance experiment between molten steel and slags.The results follows:As w（SiO₂）is controlled under 30%,and w（CaO）/w（Al₂O₃）in the control between1.2～2 of CaO-SiO₂-Al₂O₃-MgO slag and dissolved oxygen content will be controlled under 10ppm;Over 87%of inclusions are smaller than 10μm and 50%smaller than4μm;Al₂O₃ will be transitioned to 3Al₂O₃-2SiO₂ inclusions in molten steel,but it is difficult to be low-melting point liquid inclusions of CaO-Al₂O₃-2Si O2,the main reason is due to the reduction of[Ca]from refining slag is not enough to make 3Al₂O₃-2SiO₂transformed completely,calcium wire feeding process or other means to increase the content of[Ca]should be used in refining.The thermodynamics results showed that[Ca]content control is related to[O],[Al]content in liquid steel.In order to get better understanding the mechanism of removal inclusions from slag,physicochemical properties and interfacial properties of slag are studied in this paper,while using the sessile drop experiments to study the interface wettability between spring steel and refine slag.The results indicate that the rate of w（CaO）/w（Al₂O₃）plays an increasing role in reducing the viscosity of slag,and with the decreasing of the w（SiO₂）of slag,the viscosity of slag is also reduced,but when the rate of w（SiO₂）/%decreased to a certain extent,the effect is not obvious.Comparing the relationship between the interfacial tension between slag and steel and T.[O]in molten steel,it shows that the stronger the interfacial tension between slag and steel is,the lower the T.[O]in the molten steel.