| High aluminum steel is beneficial to the development of lightweight steel materials due to the addition of aluminum in steel as an alloying element.However,the aluminum in the molten steel is easily reacts with SiO2 in the mold flux during continuous casting process,which leads to the deterioration of the physical and chemical properties,affecting the lubrication and heat transfer functions,and causing the slab surface quality problem.In this paper,the slag-steel reaction kinetic and mold flow field were simulated,and the kinetic control mechanism influence on the flow field velocity,surface fluctuation and slag entrainment were studied systematically to provide theoretical guidance for the further optimization of the high aluminum steel continuous casting process.Research works in this paper are summarized as follows:(1)It was found by slag-steel reaction equilibrium experiments that the mold slag had completed the evolution from CaO-SiO2-Al2O3 to CaO-Al2O3 in the 10 min.With the consumption of SiO2 and the formation of Al2O3,the melting temperature of the mold slag increased rapidly and then stabilized,while the viscosity increased firstly and then decreased,then slowly rised and tended to be stable.In addition,the mold slag crystal phase evolution tendency was:dendritic CaF2?faceted CaF2,calcium silicate?calcium aluminate.(2)Combining the two-film mass transfer theory and the slag-steel reaction experiments,the mass transfer of Al in steel was determined as the limiting part of the reaction.A kinitic model for slag-steel reaction was established and the(%Al2O3)prediction results were consistent with the experiments and an actual continuous casting.In addition,a water model experimental system was established to simulate the mass transfer phenomenon at slag-steel interface and its kinetic control mechanisms was analyzed.It was found that the reaction rate could be decreased by reducing surface velocity and fluctuation in mold.(3)The influences of slag-steel reaction kinetic conditions on the high alumina steel mold flow field were studied.PIV(Particle Image Velocity System)results reflected that there was a risk of shear slag entrainment in the 1/4 wide surface and a risk of vortex slag entrainment near SEN.FFT(Fast Fourier Transform)and wavelet entropy analysis indicated that the fluctuations could be decomposed into low,medium and high according to frequency,and the low frequency wave causes the disorder of the meniscus fluctuation.Increasing SEN(Submerged Entry Nozzle)outlet angle and immersion depth,decreasing the casting speed could reduce the molten steel velocity in the mold.A wider mold could expand steel-slag contact area,leading to faster slag-steel reaction rate and longer reaction time.(4)The mechanisms of the surface slag entrainment in mold were analyzed.It is found that the squeezing of upper flow center caused the instability of the slag-steel interface,inducing the shearing slag entrainment;the low frequency fluctuation,which was easily influenced by periodic bias in mold,caused vortex entrainment.The orthogonal experimental results indicated that the theoretical optimal SEN conditions were-20°+concave bottom+145 mm.The surface fluctuation,flow velocity,the frequency and depth of vortex near SEN,slag-steel reaction rate were significantly reduced after using optimized SEN.The industrial experiments also reflected that the T[O],macro-inclusions and suface defects in the slab samples were also significantly reduced.As a whole,the optimization of SEN condition in this study can not only control the slag-steel reaction rate,but also reduce the risk of slag entrainment risk in the mold. |
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