Development of Hot-Rolled Sheet Steel with the Significant Increase in Tensile Strength Induced by Strain Age Hardening

A new type of bake-hardenable high strength hot-rolled sheet steel was developed, which shows a remarkable increase in tensile strength as well as yield strength after strain age hardening without addition of special elements. The new sheet possesses excellent crashworthiness and high fatigue strength, and also shows good formability, equal to that of conventional high strength sheets. This unique combination of properties makes it possible to reduce the weight of the car body by using thinner gauge material when the new sheet is applied to crash-resistant parts and underbody parts.