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Automotive OEMs are compelled by increasingly stringent global emissions standards to find economic solutions for building higher efficiency vehicles without compromising safety and ride quality. This challenge requires new advanced high strength steels (AHSS) that will significantly reduce vehicle weight and improve fuel economy. In addition to providing higher strength, these automotive sheet steels must have exceptional formability to produce reduced gauge parts with increasingly complex geometries. Formability is comprised of two components, global and local. Global formability represents the ability of a sheet material to be deformed under various stress conditions and to be formed into a part without failure. It can be estimated using forming-limit diagrams or ductility measurements from conventional uniaxial tensile tests. However, these tests cannot reliably assess the local formability at the edges or at the internal holes of the blanks during stamping.

The historical development of autobody steels has demonstrated a paradoxical relationship between strength and ductility, with increasing strength necessary for lightweighting commensurate with reductions in ductility necessary for cold formability. This in turn creates geometric constraints in part design and manufacturing, ultimately limiting usage of these higher strength steel grades in automobiles. Quench and tempering including variants such as quench, partitioning, and tempering are known approaches to increase strength while attempts to overcome the paradox have focused on increasing ductility through three distinct deformation mechanisms including; 1) shear band induced plasticity (SIP), 2) transformation induced plasticity (TRIP), and 3) twinning induced plasticity (TWIP).

Due to its affordability, excellent stiffness-to-density ratio, and predictable forming characteristics, steel has historically dominated the material selection for vehicle body structures. As light-weighting has gained momentum due to more stringent vehicle emissions standards, the usage of Advanced High Strength Steels (AHSS) has proliferated during the past two decades. In the last decade, significant efforts have been made in developing the “third generation” of AHSS with strength-ductility combinations significantly better than in the first generation AHSS. A paradigm changing nanostructured 3rd Generation AHSS has been developed by NanoSteel that will be described with a focus on the new mechanisms, enabling structures, and resulting mechanical properties.