Morphology Characteristics Of Solidification Structure And Carbon Segregation In High Carbon Steel Billet By Continuation Casting Based On Fractal Theory

High carbon steel has high strength and hardness,high elastic limit and fatigue limit.so it is widely used.However,because of the high carbon content,the macro/semi-macro carbon segregation is easy to be produced in the production process of high carbon steel continuous casting billet,and the segregation of carbon element will lead to various defects in the subsequent processing process,thus affecting the performance of high carbon steel.Under the background of improving the quality of high carbon steel continuous casting billet,taking 82 B cord steel as an example,the solidification structure and carbon segregation morphology are described based on the fractal dimension and other parameters.Finally,the relationship between solidification structure and carbon segregation itself was discussed through the relationship between solidification structure and carbon segregation morphology parameters.For the solidification structure of 82 B cord steel,secondary dendrite arm spacing,perimeter,dimensionless perimeter and fractal dimension of solidification structure were used to quantitatively describe the morphology of solidification structure.It is found that the solidification structure morphology has fractal characteristics,and the fractal dimension calculated by the box counting method can quantitatively characterize the self-similarity complexity of the main morphology of the solidification structure,and it increase first,then decrease,then increase of solidification structure from the surface to the center of the billet.The fractal dimension of solidification structure decreases with the increase of the superheat and the casting speed.Moreover,there is a certain relationship between the quantitative characterization parameters of solidification structure,the perimeter and dimensionless perimeter of solidification structure decrease with the increase of secondary dendrite arm spacing.The fractal dimension of solidification structure increases with the increase of secondary dendrite arm spacing,and the dimensionless parameters of solidification structure decreases with the increase of fractal dimension of solidified structure.In terms of carbon segregation characteristics,carbon segregation points are classified into ??? and ? three types according to the size of segregation point area.It is found that the contribution of the three types of segregation points to the overall segregation degree of the billet is different.The segregation ratio of the billet is mainly affected by the large segregation point,the larger or more of large segregation points,the greater the segregation rate.At the same time,the morphology of carbon segregation points has fractal characteristics,and the fractal dimension of the segregation point calculated by the perimeter-area method can be used as the quantitative index characterizing the self-similarity degree of the morphology of the segregation point,and the value of the fractal dimension from the surface to the center of billet gradually decreases.It is found that the dimensionless parameters of segregation points can be used to describe the degree of segregation dispersion,while the fractal dimension of segregation points is more suitable to describe the segregation ratio.Based on the analysis of solidification structure and carbon segregation morphology,the relationship between solidification structure and carbon segregation characteristic parameters is compared.It is found that there is no obvious relationship between secondary dendrite arm spacing and segregation morphology(except fractal dimension of segregation point).This indicates that there are a few limitations using secondary dendrite arm spacing to characterize the difference of solidification structure and the degree of segregation of the billet.At the same time,by studying the relationship between fractal dimension of solidification structure and segregation characteristic,it is found that segregation rate decreases with the increase of fractal dimension of solidification structure.The fractal dimension of segregation point decreases with the increase of fractal dimension of solidification structure.And the dimensionless parameters of solidification structure and fractal dimension of solidification structure can be used to describe the segregation ratio of billet.Through the study of the relationship of the morphology parameters between the solidification structure and of segregation points under different process parameters,it is found that the internal quality of 82 B cord steel with low superheat and low drawing speed is better.