Temperature-dependent strengthening mechanisms in Mn- and Si-alloyed low carbon ferritic steels for cylindrical battery case

Enhancing the mechanical performance of casing materials is essential to mitigate thermal runaway risks in cylindrical electric vehicle (EV) batteries. This study investigates the effects of Mn and Si additions on the microstructure and tensile properties of low carbon ferritic steels at room and high temperatures (500 °C). Without phase transformations, the additions of Mn and Si led to distinct differences in grain size, strain hardening, and dislocation behavior. At room temperature, the Si-added alloy exhibited the highest tensile strength (399 MPa), primarily due to increased dislocation density and enhanced strain hardening. In contrast, at 500 °C, the tensile strength of the Si-added alloy was significantly lower than that of Mn-added alloy as a result of dynamic recovery and extensive subgrain formation. The Mn-added alloy maintained higher strength at elevated temperature by suppressing recovery and preserving dislocation structures. These findings highlight a temperature-dependent trade-off in strengthening mechanisms, where Si enhances tensile strength at room temperature and Mn contributes to strength also at elevated temperatures, offering a guideline for designing thermally robust ferritic steels for EV battery casing applications.