Abstract: The cleanliness of battery case steel is an important factor affecting the deep drawing performance. Characterization methods such as metallographic microscopy (OM) and scanning electron microscopy (SEM) were used to sample different parts of the slab and cold rolled plate of a certain factory's battery case steel, and samples of battery cases with sand hole defects were taken to analyze the cleanliness level of battery case steel and identify the causes of quality defects in battery case steel sand holes. The results show that the part which has the largest and densest inclusions in the battery case steel slab is the inner arc 1/4. The part which has the largest size of inclusions in the cold rolled plate is the center, and it also has the lowest density of inclusions. Compared with the battery case steel of other six factories, the larger size of inclusions in this sample is the main reason for the difference from other factory products. Through research,the unreasonable desulphurization process is the main reason for the cracking defects of the battery case steel. After optimizing the production process to pretreat the hot metal and direct casting after converter smelting, the product has no significant cracking problem.

Key words: battery case steel, inclusions, cleanliness, stamping crack