It is obtained by analysis that the edge cracks occur during bending and straightening of strip due to 70 mm thin slab horizontal plane non-homogeneous cooling and edge over-cooling during production of SS400 steel strip Coil with irrational secondary cooling water rate led to precipitation of AIN in austenite and grain boundary britle. The high-quality product rate of SS400 steel strip coil increased from 92.27% to 98.09% by improved technology measure including to control Al
S
content 0.02%~0.03% in steel
decrease nitrogen pick-up during concasting and secondary cooling water rate at plate slab edge.