Facing the quality problems of low pass rate and crack defects on the surface of the Φ44 mm metal rolling 45 with sulfur(/% ：0.42 ~ 0. 50C

0.17 ~ 0. 37Si

0. 50 ~ 0. 80Mn

≤ 0.035P

0. 035 ~ 0. 045S)

the analysis is that the defects are caused by defects in the 150 mm x 150 mm casting billet. The crack defects are found on the surface of the slab and analyzed by metallographic microscope. The result indicates that the defect is caused by the strong cooling of the small R of crystallizer copper tube and the poor heat transfer and lubrication effect of the shielding flux and the asymmetrical secondary cooling. The process optimization of the crystallizer copper tube and the shielding flux and the second cooling is carried out. It improves the cooling heat transfer of the mold and the cooling effect of the secondary cooling section and the cooling uniformity of casting billet. The result shows the defects of casting billet have been effective controlled and the qualified rate of rolled material has been greatly improved.