Abstract: As the tightening of environmental protection policies, environmental protection coating products of non-oriented silicon steel have increased rapidly in recent years. The surface of the environmental protection coating liquid, of which the composition is different from that of traditional chromium-containing coating liquid, is poor on the quality stability and prone to various defects. In the process of producing a certain non-oriented silicon steel, black spot defects appeared on the surface, which impacted greatly on the stability of the production line and the yield of the product. Through macroscopic observation, scanning electron microscope (SEM), energy spectrum analysis, on-site simulation experiments, the causes of black spots were analyzed and control measures for such defects were put forward, which effectively reduced the incidence of black spot defects.

Key words: non-oriented silicon steel, black spot defect, ECO-friendly coating, phosphate coating