Formation Reason for Surface Cracks of Q235B Steel Plate with Thickness of 22 mm

Longitudinal cracks were found on the surface of some set of Q235 B steel plate with thickness of 22 mm during the quality inspection process. The cracks formation reason was analyzed by using metallographic microscope and scanning electronic microscope. The results show that there were origin deep surface crack defects on the continuous cast slab which were flattened and extended during the rolling process. When the origin surface cracks was so deep that they could not be seamed together, the longitudinal surface cracks on the rolled steel plate formed.