Research On Reactivity Calculation And Melting Flow Properties Of Mold Fluxes For Continuous Casting Of High-titanium Steel

Due to excellent mechanical properties,titanium-containing steel is widely used in the fields,such as ships,medical equipment,automotive light weighting and so on.With the development of various grades for industrialization,a series of problems appeare that impede the actual production of titanium-containing steels.Titanium-containing steel contains much more alloying element,Ti,which has a strong reducibility.During the continuous casting,[Ti]reacts with the oxide(Si O₂)in the mold slag,resulting in the raise of melting temperature,and the sharply increased viscosity,which deteriorate the lubricating performance of the mold slag.In addition,the heat controlling performance of the mold flux is affected,causing cracks and depressions on the strand surface.Aiming to weakening the reaction between the steel containing high content of Ti and the molten slag,this paper firstly studied the reactivity of traditional mold flux with titanium-containing steel.Then,the slag systems with non/low reactivity were proposed to avoid the steel-slag reaction and make the continuous casting smooth.First,the thermodynamic models,be based on the molecular ion coexistence theory were established to calculate the thermodynamic activities of various components in slag systems of CA,CS,CAS and CAST.The activity of[Ti]in molten steel was determined by applying the Henrys law.The influences of different factors on the reactivity beteween the titanium-containing steel and the liquid slag at 1550^oC were discussed.Main results indicate that the components,such as Si O₂ and Al₂O₃,had strong reactivity with[Ti],while Ba O and CaO were not able to react with the molten steel.In addition,the reactivity was also related to the contents of certain compositions.The higher content of reactive components(Si O₂ and Al₂O₃),the greater reactivity of steel with liquid slag.Moreover,the reactivity was determined by the combination of multi components.For example,the reactivity of[Ti]with(Al₂O₃)was affected by Si O₂,Ti O₂ and other components.When the activity of Si O₂ was relative large,[Ti]could firstly react with(Si O₂)and then was able to react with(Al₂O₃).To weakening and even avoid the reaction between titanium-containing steel and traditional slag during the continuous casting,the current study has designed new slag systems that had low or no reactivity with titanium-containing steel.Firstly,the interested compositions were selected by the calculation of standard Gibbs free energy of reaction between[Ti]and compositions that could be included in mold slag.Then,the components of low/non-reactive slag systems were determined.It is found that the addition of Ti O₂into the slag was able to inhibit the reactivity with steel to a certain extent,depending on the amount of Ti O₂ content.In addition,the reduction of the Al₂O₃content in the slag could also weaken the reactivity with molten steel,and when the content of Al₂O₃ in the mold slag was less than 8%,[Ti]was not able to react with the developed mold slags.On the basis of screening out the non-reactive mold flux components,the simplex method is used to design the composition of the experimental slag sample,and the melting and flow characteristics of the designed slag sample are tested.At the same time,refer to different continuous casting process parameters to determine the range of physical and chemical properties of the titanium-containing steel mold flux,and make the measured data into different types of contour maps,and make the contours of the slag series The graph is analyzed to obtain the range of the mold flux for titanium-containing steel.The study found that under the premise that(Li₂O)in the fixed slag is 5%,the section area 1can meet the range of titanium-containing steel casting:Sr O:45.37-45.67wt%,Sr F₂:11-13.49wt%,Al₂O₃:2.75-3.8wt%,Ti O₂:37.99-41.26wt%.Section 2 can meet the range of titanium-containing steel casting:Sr O:47.42-48.51wt%,Sr F₂:9.9-15.07wt%,Al₂O₃:4.07-5.98wt%,Ti O₂:31.53-38.43wt%.Section 4 can meet the range of titanium-containing steel casting:SrO:47.9-50%,SrF₂:10.58-12.03wt%,Al₂O₃:2.13-2.8wt%,TiO₂:32.67-37.09wt%.