Enhanced ductility and fracture classification maps for advanced high-strength steels considering local ductility and fracture toughness

Alternative classification diagrams considering global and local ductility have been introduced recently in order to better describe the overall formability of advanced high-strength steels (AHSSs). These diagrams combine different parameters obtained from uniaxial tensile tests to rank steel formability and establish objective performance indicators. However, such classification schemes may fail to estimate fracture performance in certain failure modes related to the material’s damage tolerance and crack propagation resistance, which is fundamental for a safe implementation of high-strength steels in structural and safety related applications. The present work proposes a new classification concept for AHSSs, considering not only global and local ductility but also fracture toughness. The proposed criteria aim to provide a more comprehensive definition of AHSSs formability and cracking resistance, considering intrinsic material parameters. Different strain- and energy-based parameters are analysed and their relevance to material ranking is discussed. The study is based on the analysis of 25 AHSSs, including Dual Phase, Complex Phase, TRIP, TRIP-aided Bainitic Ferritic, Press hardened steels, Quenching&Partitioning and Medium-Mn steels with tensile strengths ranging from 800 to 1500 MPa.