Secondary cooling method for improving surface quality of super-thick plate blank

The invention discloses a secondary cooling method for improving the surface quality of a super-thick slab, which is characterized in that a continuous casting slab with the thickness of more than 400mm is produced, the optimal cooling density of casting blank cooling water is adopted, the cooling density is gradually reduced from top to bottom according to the solidification characteristic of the casting blank, the surface temperature of the casting blank in the length direction is ensured to be uniformly reduced, and the surface quality of the casting blank is improved. Casting blank subsurface cracks caused by periodic rising of the surface temperature of the casting blank and repeated phase change of a solidified blank shell are avoided. And meanwhile, the cooling water amount of the edge part and the central area of the casting blank is controlled within an optimal proportion range, so that the temperature uniformity of the casting blank in the width direction is ensured, and the problem of supercooling