On Local Formability/Ductility of New Advanced High-Strength Steels: Temperature, Bake Hardening and Strain Rate Effects

New advanced high-strength steels (AHSSs) based on different microstructure-based concepts have been developed in the past decades to meet various needs in the automotive industry. Nevertheless, cracking issues in many practical forming and crash scenarios still limit the applications of these new AHSSs, despite their relatively high tensile elongations measured under laboratory test conditions. Accordingly, and inspired by the concept of the Local-Global Formability Diagram, this work started from comparing true fracture strain (TFS), a typical representative parameter of the local formability/ductility, of different AHSS sheet metal grades. Furthermore, possible TFS evolution by some critical application-based effects, such as temperature, bake hardening and strain rate, was investigated. Explanations and discussions of the material mechanisms based on the test results were also presented in this work. The objective of this study is to highlight the importance of local formability/ductility and provide the corresponding references to the future AHSS development strategy.