Challenges in the formability of the next generation of automotive steel sheets

Improving strength may lightweight car bodies by thinning the structure gauge while bearing the same crash loads. Development of the third generation advanced high-strength steels aiming to boost material ductility to over 30% total elongation has become the common sense of potential solutions for stamping. Not only total elongation but also several other parameters, involving presswork hardening, anisotropy ratio, strain rate sensitivity, uniform elongation, edge sensitivity and internal stress between phases, are critical in determining the formability under the complex stress and strain distributions during stamping. We clarify here the logic of formability and difficulties in this context of three types of steel: quenching and partitioning, delta-transformation-induced plasticity and medium Mn-TRIP.