Because the flow rate of the emulsion during high-speed rolling is too small, the thermal deformation generated cannot be taken away in time, so that the temperature of the roll rises, the emulsion oil film on the surface of the strip is broken, and the surface of the strip is scratched. In addition, the roll slips at high speed, and the strip and the roll produce relative friction, which will also cause thermal scratches. Thermal scratches have a lighter scratch depth on the surface of the strip, and basically have no feel.