Abstract: The morphology and microstructure of the fish scale defects on the surface of continuously annealed plates were analyzed by means of scanning electron microscopy and focused ion beam analysis. The results show that the essence of the scale defects is a kind of surface micro scratch. The formation mechanism of the defects can be attributed to the water leakage of the thermometer water jacket, which causes the local oxidation of the strip surface at high temperature. And then, the micro scratch formed when the oxidation part was pressed by the furnace roll and the strip tension. A large number of nanocrystalline structures were observed at the defect section cutting by focused ion beam technology, which confirmed that the surface of the strip was quenched and oxidized. The results of the microstructure analysis provide a theoretical basis for the investigation and solution of the scale defects.

Key words: continuous annealed plate, fish scale defect, focused ion beam