Study On The Effect Of Direct Electro-Pulsing On Crystallization Behavior Of CaO-SiO₂ Based Mold Flux

Because of the"thermal effect"and"electric effect",electro-pulsing can reduce inclusions in molten steel and regulate the solidification structure,which will become another external field applied in the continuous casting process of steel.In the process of continuous casting production,the different steels have different requirements for lubrication and heat transfer performance of mold flux.Generally,the effective lubrication and controlling heat transfer are closely related to the phase transformation and distribution of mold flux between the copper mold and shell.Changing the cooling condition or composition,these are main methods to adjust the phase of mold flux at present.The disadvantages are time-consuming and poor pertinence.When the electro-pulsing is applied as external filed,it is possible to quickly and accurately control the phase transformation process of mold flux in mold,optimize the distribution of slag film and ensure the process running smoothly without affecting the normal production.Therefore,it is of great theoretical significance and engineering practical value to research the influence of electro-pulsing on the crystallization property of mold flux in accordance with the application trend of electro-pulsing technology in steel continuous casting production.In this paper,the influence of key components on the melt structure and conductivity of Ca O-Si O₂ based mold flux and the variation of melt structure under different pulse voltage and treatment time were studied by FTIR,Raman and XPS.SEM,EDS,XRD and other testing methods were used to analyze the influence of the crystallization properties of the mold flux under the electro-pulsing treatment,and the mechanism of these influence was explained with the perspective of thermodynamics and dynamics.The main conclusions are as follows:With the increase of basicity,the conductivity of the melt at 1573 K increases from 0.159 S·cm^-1 to 0.383 S·cm^-1,and the activation energy decreases from 134.21±12.41 k J·mol^-1 to 65.37±3.45k J·mol^-1.With Al₂O₃content increases from 2 wt.%to 4 wt.%,the activation energy decreases from 55.12±1.20 k J·mol^-1 to 41.09±0.38k J·mol^-1 and conductivity increases.With the increase of Al₂O₃ content to 8 wt.%,conductivity decreases and the activation energy increases to 98.99±1.42 k J·mol^-1.After electro-pulsing treatment,the precipitated grains are transformed from fine to massive,and the overall crystallinity increases obviously.The average grain size increases from 15.0±1.31μm to26.9±1.58μm with the rise of pulse voltage,and the precipitation content of Alumoakermanite increases from 7.4 wt.%to 14.7 wt.%,while that of Cuspidine decreases.With rise of pulse widths,the precipitated phase gradually changed into massive,and the average grain size increased from14.1±1.01μm to 24.7±2.07μm,but effect on the precipitated phase content was not obvious.The addition of electro-pulsing has an additional contributionΔG_E to crystal nucleation,influencing the free energy of nucleation.The results of non-isothermal crystallization kinetic show that the precipitated phase nucleates at a constant nucleation number with a growth of 1 dimension and was controlled by diffusion reaction when the melt is not treated by electro-pulsing,while the precipitated phase nucleates at a constant nucleation number with a growth of 2 dimension and is controlled by interface reaction when the melt was treated by electro-pulsing.The content of Q⁰（Si）,Q¹（Si）and Q²（Si）in melt increases with the increase of basicity of mold flux and Al₂O₃ content from 2 wt.%to 4 wt.%,while the content of Q³（Si）decreases,and the degree of polymerization of melt decreases.However,with further addition of Al₂O₃ content from 4 wt.%to 8 wt.%,the variation tendency is completely opposite.With the increase of pulse voltage and treatment time,the degree of polymerization of mlet decrease,the content of O^2-and O^-increase.