Research progress on solidification behavior and segregation control of continuous casting billet along casting direction
Continuous casting billet is the main base material of rod and wire steel products.The defects such as macro/semi-macro segregation reflect the uneven microstructure and composition distribution of the billet to a cer-tain extent,which is an important factor affecting the quality improvement of high-end steel.At present,it is the main means to control the segregation defects in the billet by characterizing,analyzing and optimizing the macrostruc-ture in the billet from the two-dimensional cross section.However,both the solidified dendrites and the center segre-gation inside the billet have three-dimensional spatial morphology and distribution characteristics,so there may be some errors in the study only by two-dimensional cross section.At the same time,the fluctuation characteristics of solidified dendrites and segregation in the direction of continuous casting billet(perpendicular to cross section)can more directly reflect the fluctuation of internal microstructure and quality along the length direction of continuous casting billet,which is also one of the keys to affect the quality stability of continuous casting billet of high-quality steel and subsequent products.The research progress on the casting direction of continuous casting billets in recent years is summarized from three aspects:solidification behavior,structure fluctuation and center segregation control.CET transition is the key point of solidification structure control of casting billet,and its determination basis and its correlation with segregation show that the CET position along casting direction fluctuates and is related to the mor-phology of center segregation.The fluctuating characteristics of solidification dendrites and the periodic fluctuation of solidification end point are caused by the asymmetric flow field and temperature change in the liquid phase.Mean-while,the actual casting billet and related qualitative and quantitative models also show that the distribution of segre-gation elements along casting direction is characteristic of fluctuation feature,and can be analyzed by using time series technology.The development of center segregation control technology has obviously improved the internal quality uniformity of continuous casting billet,and segregation can be reduced from the casting direction based on segregation characterization method and heredity behavior model.Finally,as to the three-dimensional solidification mechanism,fluctuation characteristics of various kinds of blanks,surface quality,structure characterization,high casting speed,intelligent analysis and prediction,fine control,more and more analysis may be carried out along the casting direction of continuous casting in the future.
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