| Abstract Scope |
The complex-phase steel is a material composed of a ductile ferrite phase and high-strength martensite phase. It is widely used as a structural material such as automobiles and ships. Despite these advantages, complex-phase steel has low formability. According to previous studies, significant differences in mechanical properties, such as ductility, hardness, and strain hardening rate, between ferrite and martensite phases. Additionally, during phase transformation, volume expansion occurs, forming geometrically necessary dislocations at phase interfaces, which leads to localized work hardening at these interfaces. As a result, the material exhibits strain disparity, with the interfaces experiencing the highest stress concentrations and crack initiation.
In this study, nanoindentation was conducted to measure the hardness of the complex-phase steel depending on its phases. Hole expansion ratio test was conducted to evaluate the correlation between the hardness of each phase and hole expansion ratio. This study suggests an optimal microstructure for enhancing hole expansion ratio. |