Facing the quality problems of transverse surface crack at the comer of 150 mm x 150 mm continuous casting billet of 60Si2Mn spring steel(/% ：0.56-0.64C

1.50-2.00Si

0.70-1.00Mn

≤0.025P

≤0.020S)

the transverse surface crack defects at the comer of casting billet are analyzed by metallographic microscope and SEM and it is carrying out test comparison. The result indicates that the defect is caused by the large drag force of the large taper of crystallizer copper tube and the poor lubrication effect of shielding flux and the uneven secondary cooling. By reducing the mold steel tube taper from 2.2 mm to 1.6 mm and the melting temperature of protective slag from 1 182 °C to 1 072 °C and its viscosity from 0.76 Pa·s to 0.52 Pa·s and the secondary specific water from 0.45 L/kg to 0.32 L/kg

to reduce the drag of casting billet in copper tube and improve the cooling heat transfer of the mold

the cooling effect of the secondary cooling section and the cooling uniformity of casting billet

the defects of casting billet have been effective controlled

and the qualified pass rate for casting billet surface defect detection increases from 35% to 92%.