Analysis of the cracking causes of battery steel shell

Abstract

In this article, the causes of cracking defects are studied through the analysis of defective battery shell specimens. The defective specimens are analysed by a metallographic optical microscope and scanning electron microscope. It is found that large CaO–Al₂O₃–MgO inclusion is the main cause of battery shell cracking. The minimum size of inclusions observed in the cracking defect is 11 μm. The inclusions in the cold-rolled plate are mainly Al₂O₃ as well as CaS and CaO–MgO–Al₂O₃, and the average diameter of the inclusions is 3–4 μm. Inclusions larger than 10 μm are the main cause of cracking. Analysis of the refining slag shows that the basicity of the current slag is too high, resulting in a high melting point. Consequently, the slag cannot be completely melted. Besides, the Mannesmann index is also high, indicating poor fluidity. Both high melting point and poor fluidity of the slag are not conducive to the absorption of inclusions in steel, leading to the high possibility of larger inclusions in the steel, and therefore the formation of cracking during stamping.