| Incoloy825 alloy is a nickel-based corrosion-resistant alloy with many excellent properties and is widely used in aerospace,offshore engineering,energy and other important fields.However,due to the addition of strong reducing elements such as Al and Ti in the alloy,Al2O3,TiO2 and TiN inclusions are generated in the molten steel during the continuous casting production process,causing subsurface inclusions?cracks?the floaters in the mold and the nozzle clogging.The continuous casting process is the final step of production and the last means to remove inclusions in the steel.Therefore,the continuous casting mold fluxes should have excellent properties for absorbing inclusions in steel.When the mold flux absorbs the inclusions in the steel,the increase of the inclusion content will cause a large change in the viscosity?melting temperature and mineralogical phase,which will affect the smooth progress of the continuous casting process.Therefore,it is required that the mold flux has the ability to absorb inclusions in the steel,and the mold flux has no significant change in physical and chemical properties after the inclusions are absorbed.In this thesis,the phase transition and viscosity of the mold flux were calculated by FactSage thermodynamic simulation software.The surface tension of the mold was calculated by the modified Butler equation.The viscosity of the mold flux decreases with the increase of basicity and the increase of BaO and B2O3 content.When TiO2 enters the mold flux,the viscosity of the mold flux increases due to the precipitation of high melting point phase CaTiO3.The surface tension of the mold flux increases with the increase of basicity and BaO content,and decreases with the increase of B2O3 content.The rotating cylinder method was used to study the variation of the rate of dissolution and absorption of inclusions with the basicity of slag,BaO and B2O3 content.The increase of basicity and the addition of BaO and B2O3 will increase the absorption rate of Al2O3,TiO2 and TiN inclusions.When the BaO or B2O3 content is increased from 10%to 15%,the absorption rate of the inclusions to the inclusions no longer increases or decreases slightly.The rate at which the mold slag absorbs inclusions no longer increases or decreases slightly.The mold flux absorbs Al2O3 inclusions at a rate of 2.04×10-3?9.38×10-3g·cm-2·min-1,while the mold flux absorbs TiO2 and TiN at a rate of 2.41×10-1?6.31×10-1 g·cm-2·min-1,with a difference of 1?2 orders of magnitude.A boundary layer is formed between the inclusion rod and the slag during the absorption process,and the inclusions gradually diffuse into the slag through the boundary layer.In order to compare the change of melting temperature and precipitation phase before and after the inclusion of inclusions,the flux was measured by smelting temperature measuring instrument,scanning electron microscopy spectroscopy(SEM-EDS)and X-ray diffraction(XRD).After the slag absorbs Al2O3,TiO2 and TiN inclusions,the melting temperature increases,since the high melting point CaTiO3 is generated,the increase in the melting temperature after absorption of the TiO2 and TiN inclusions is greater than the increase in the melting temperature after the absorption of the Al2O3 inclusions.The increase of the basicity and the content of BaO can promote the crystallization of mold flux.The precipitated phases are mainly Ca2Al2SiO7,Na2Mg3Si2Al2O10F2 and Ca4Si2O7F2.The addition of BaO to mold flux can produce Ca2MgBaSi2O8.After the addition of B2O3,a large amount of borosilicate glass can produced in the slag,resulting in the reduction or even disappearance of other crystal contents.The slag has no obvious change in the crystal phase composition after absorption of Al2O3.After absorbing TiO2 and TiN,the high melting point phase of CaTiO3 appears,which affects the performance of the mold flux. |
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