Study on “Black Line” on the Edge of SPHC Hot-rolled Strip

In order to eliminate the black line defect occurring on the edge of SPHC hot-rolled strip after pickling,the reasons for producing black line were investigated by means of microscope,scanning electron microscopy,energy dispersive spectroscopy and other related test equipment.The results show that the main element in defect area is Fe,and the microstructures are dominated by ferrite and a small amount of pearlite,accompanied by coarse crystal and mixed crystal.It is found that the black line is formed from edge cracks which are turned over and brought to the strip surface due to tensile stress.By improving the strip's edge and corner quality and optimizing vertical roll type and rolling process,the black line can be effectively eliminated,which ensures good product quality and yield,thus satisfying the need of market.