Abstract:  In April 2021, the issue of black spots was particularly prominent in the production of silicon steel on Shagang's cold rolling and pickling line 1, with a total of 179 tons being rejected. To investigate the causes of these black spot defects, especially the batch occurrence in April, a comprehensive analysis was conducted covering various aspects such as silicon steel grades, defect locations, pickling production time, pickling speed, acid addition time, and acid addition amount. The results indicated that the black spot defects mainly occurred within the first 20 meters of the hot coil's ends, with over 90 % of the defects occurring on the lower surface of the hot coil's head (inner coil). The black spot defects in April were primarily caused by the combined effects of three factors: acid addition amount, regenerated acid concentration, and pickling speed. Through measures such as optimizing the acid addition amount, specifying the regenerated acid concentration, and improving the pickling speed, the black spot defects were effectively controlled.

Key words: acid rolling, silicon steel, black spot defect, analysis and improvement