Abstract： A variety of surface defects on continuous annealed or galvanized automotive steel sheets such as scratches, dents, coating pinhole, stamping orange peel, stamping streak and streaky mark were studied. The crystalline grains located in defects were observed by scanning electron microscope(SEM) and optical microscope(OM), and four types of grain characteristics were found including fine grains, coarse grains, non-recrystallized grains, and deformed grains. The results indicated that the grain characteristics at the defect position could be utilized to further determine the defect origination and reduce the scope of inspection. For the scratches or dents originated from the continuous annealing line, the local deformed grains indicated that the defect may originate in the cooling section. The local coarse grains suggested a strain-induced secondary recrystallization occurred in the ends of heating section or in the beginning of soaking section. The local fine grains meant that the defect probably occurred in the heating section, cleaning section or it might be brought by the as received cold rolled steel sheet.
2022, Vol. 40 
