Fundamental Research On The Solidification Structure Features And Segregation Of H13 Billet By ESRR

H13 steel, a king of high-quality steel, is a widely used. In order to improve the quality of H13 billet, produced by ESRR, the morphology features of solidification structure and segregation for H13 billet were analyzed carefully. Then the relationship between solidification condition and solidification structure or segregation was also investigated. At last of carbon distribution of H13 billet along the casting direction was discussed.Firstly, secondary grain spacing, area, perimeter of solidification structure were measured, and fractal dimension, dimensionless perimeter were introduced to analyze the morphology feature of solidification structure and segregation points. It can be found that the SDAS average in equiaxed zone is greater than columnar zone. Under remelting rate 400kg/h, 450kg/h and 500kg/h, the area ratio of solidification structure in equiaxed zone is less than columnar zone, then it can be found that the perimeter and area of solidification structure negatively correlated. Secondly, study found that the fractal dimension of solidification structure in equiaxe zone is smaller than that in the columnar zone, while dimensionless perimeter average of solidification structure in equiaxed zone is higher than the columnar zone, which is attributed to the different theory of two methods. Then by measuring the area ratio, number, fractal dimension, dimensionless perimeter of segregation points, divided into three type according to their area, the segregation morphology features of H13 billet were studied. It can be found that the number of segregation points in columnar zone is more than equiaxed zone, which indicate the distribution of segregation points in columnar zone is more diffuse than that in equiaxed zone. Then the results of diffusion feature for different segregation point show that a larger area of segregation points seen more in equiaxed zone. And, the analysis results show that the fractal dimension average and dimensionless perimeter average in equiaxed zone segregation point is less than the columnar zone, which indicate that segregation point morphology in equiaxed zone is more complex than the columnar zone, which may be caused by the higher R in equiaxed zone. Finally, by comparing the relationship between fractal dimension, dimensionless perimeter and segregation, it can be found that dimensionless perimeter of solidification structure is suitable for characterizing the whole segregation degree of billet. And fractal dimension of solidification structure is suitable for characterizing the dispersion degree of segregation points.The calculating results show that LST(local solidification time) in equiaxed zone is larger than that in columnar zone. At the same time, by analyzing the growth direction under different remelting rate, it can be found that the solidification angle of columnar crystal decreases and then increases and then decreases, which demonstrate that the heat transfer along transverse and longitudinal direction are competing when the remelting rate increases, but on the whole heat transfer along the transverse direction is stronger than that along longitudinal direction. Then analysis revealed that fractal dimension and dimensionless perimeter of segregation points will decrease with increased LST. Secondly, when the LST increases, the total area of segregation will increase, while the total number of segregation points will decrease. Meanwhile, by investigating the relationship between the area ratio, the number ratio of different segregation points and LST, which indicate that it is more likely to appear a large area of segregation point when the LST increases. Finally, by analyzing and comparing the area and the number of segregation points under different remelting rate, the quality of billet, produced under the remelting rate 450 kg / h is best.Finally, in this paper the author uses the gray scale of image to obtain the carbon distribution on billet. Then the standard deviation, CCF and Hurst index were calculated. The standard deviation results of the carbon distribution showed that in addition to individual melting rate, the carbon distribution in the equiaxed zone fluctuate stronger than that in columnar zone. Then the CCF results of carbon distribution time series show when the lag is 0, the carbon content distribution is significant correlation between C ET transform position and the center position on billet under remelting rate of 400 kg / h, 450 kg / h, 500 kg / h. Hurst index shows that carbon distribution curve hold obvious self-similarity.