Abstract: A comprehensive study on the formation mechanisms and differences in the banded structure of commonly used automotive gear steels, namely SCr420H, 16MnCr5, 20CrMnTiH, SAE8620H and 22CrMoH, which possessed varying alloy element compositions but underwent similar smelting and rolling processes, was conducted. In addition, the process was optimized. The findings reveal that SCr420H, 16MnCr5 and 20CrMnTiH steels exhibit relatively less pronounced banded segregation, whereas 22CrMoH and SAE8620H steels display distinct banded structures. The alloying elements Mo and Ni in 22CrMoH and SAE8620H steels affect the microstructure transformation during rolling and cooling, resulting in the development of an abnormal microstructure, bainite, in the final rolled steel. By adjusting the continuous casting superheat to a range of 15-30 ℃, maintaining a consistent pulling speed, intensifying the crystallizer and secondary cooling, achieving a homogeneous rolling heating temperature of 1200-1240 ℃, ensuring a diffusion duration of at least 90 min, and maintaining a final rolling temperature of 910-960 ℃, the banded structure in SAE8620H round steel is effectively improved to a grade of ≤2.0.

Key words: gear steel, banded structure, alloy element content, process optimization