Heredity of segregation spot from the slab to the hot-rolled plate

Segregation spots in the slab and banded structures in the rolled plate were analyzed using etching and statistical analysis. A numerical model was developed to study the evolution of segregation spots during heat treatment and rolling process. The results show that the diameter of segregation spots increases with the distance from the slab surface, and the large spots are concentrated in the equiaxed zone. In the hot-rolled plate, bands are primarily observed in the inner part. The banded structure is closely associated with Mn segregation, since C diffuses more rapidly than Mn during heat treatment. The segregation spots near the slab surface have an average diameter of 30.0 μm and do not result in the formation of bands, due to Mn diffusion during heat treatment. However, in the center of the slab, the average and maximum diameters of segregation spots are 178.4 and 469.8 μm, respectively, indicating incomplete Mn diffusion during heat treatment. In the subsequent rolling process, the thickness of the segregation spots decreases and their length extends, while the width remains relatively unchanged. With the approximately spherical spot in the slab, the banded structure in the hot-rolling plate is semi-ellipsoidal. But it still appears to be band in the rolling direction, especially with significant reduction amount.