Abstract: The influence of mould level fluctuation, scarfing depth on the surface quality of hot rolled coil were analyzed by tracking the whole process of steelmaking, hot rolling and cold rolling，and the heredity of defects on the cold coil was studied. The results show that the defects of steelmaking contain four categories, such as mold powder entrapment, cluster Al₂O₃, blisters and blisters+Al₂O₃. The occurrence rate of the defects of the mold powder entrapment with the fluctuation of the mould liquid level ≥5 mm on the hot-rolled coil is 100 %. The part of mold powder entrapment can be eliminated after pickling, which will not affect the surface quality in the subsequent rolling process. The mold powder entrapment with spills and the spills have good heredity on the cold-rolled coil, which not be eliminated through pickling , rolling and galvanizing. According to the above statistical analysis, on the one hand, the optimization of the process parameters during casting for the high-level automobile outer panel was provided. The control window of steel-making process parameters of automobile outer plate production was put forward. On the other hand, the standard for releasing the defects without heredity was determined according to the customer requirements.

Key words: cold-rolled plat, surface quality, mold powder entrapment, blisters, Al₂O₃, heredity