Abstract: This article analyzed the microscopic characteristics and microstructure types of black lines through sampling and scanning electron microscopy. The results showed that the main cause of black lines is the uneven plastic flow of metal during the rolling process of coarse rolling vertical rollers. The main form of black line defects is hot-rolled iron oxide scale, mainly composed of Fe3O4 and Fe-Si spinel compounds. By standardizing the heating temperature, optimizing the distribution ratio of the vertical roll side pressure, optimizing the control of the hot rolling process, and increasing the final rolling temperature of the hot-rolled strip to reduce the rolling in the two-phase zone, the proportion of black line defects at the edge of hot-rolled non oriented silicon steel has been reduced.

Key words: non-oriented silicon steel, black line, iron oxide scale, process control