Optimal Property Of VOD Refining Slag Of Ultra Clean Ferritic Stainless Steel

The production of ultra clean ferritic stainless steel needs to reduce the content of C, N, Oto a lower level by VOD refining process, Aluminum, titanium oxide and titanium nitrideinclusions precipitate during refining process of stainless steel. The inclusions will have a badeffect on continuous casting, rolling process, surface quality of product and mechanicalproperties. Inappropriate treatment can reduce corrosion resistance of ferritic stainless steel.Therefore, the quality control of ultra clean ferritic stainless steel should focus on the control ofinclusions, the ability of refining slag to absorb the inclusion is particularly important forreducing inclusions and improve the purity of ferritic stainless steel during the VOD refiningprocess. This paper studied the dissolution mechanism of inclusions in VOD refining slag andoptimal property of VOD refining slag of ultra clean ferritic stainless steel, the results of presentwork supplied a theoretical foundation for the control of inclusions in ultra clean ferriticstainless steel.Melting temperature of CaO-SiO₂-Al₂O₃-MgO-CaF₂pentary VOD premelted refining slagwas obtained by the calculation of thermodynamics software FactSage, online observation withhigh temperature confocal scanning laser microscope and a DSC thermal analyzer, thecapability of deoxidization and desulfurization of refining slag in ultra clean ferritic stainlesssteel was obtained by the thermodynamics calculation, the composition of refining slag whichhas more appropriate melting temperature is w（CaO）／w（SiO₂）=4,25%～35%Al₂O₃,6%MgO,5%CaF₂.With the initial Al₂O₃content in refining slag reducing, the capability of deoxidizationand desulfurization of refining slag in ultra clean ferritic stainless steel is much better.The rate of refining slag to absorb the inclusion is studied through the determination of thedissolution rate of Al₂O₃in refining slag by the rotating cylinder method. The experimentstudied the influence of angular velocity of Al₂O₃rod, temperature, the basicity and initialAl₂O₃content of refining slag on the dissolution rate of Al₂O₃. It is concluded that the aluminadissolution is controlled by the diffusion of Al₂O₃into refining slag. The dissolution rate ofAl₂O₃will be increased by enhancing temperature, reducing the basicity and initial Al₂O₃content of refining slag. The basicity and temperature have a more significant effect on thedissolution rate of Al₂O₃.The experiment investigated the influence of various factors on the dissolution of TiO₂andTiN in refining slag by adjusting the composition of refining slag and temperature. Thedissolution of TiO₂can be promoted by enhancing temperature, increasing the basicity andCaF₂content of refining slag. High FeO and MgO content of refining slag can obviouslyincrease the dissolution of TiN in refining slag. Enhancing temperature will promote the titanium nitride dissolution, but at low FeO and MgO content of refining slag, the dissolutionof TiN is still small. Titanium exists in the form of compounds such as CaTiO3，Mg₂TiO₄,Ca₃Ti₂O₇et al after the dissolution of TiO₂and TiN in solidified refining slag.