Saiji Matsuoka

Development of a {111} Recrystallization Texture Associated WithDynamic Strain Aging During Hot Rolling in the Ferrite Region

Hot rolling in the ferrite region is applied in an extra-low C sheet steel without cold rolling by employing dynamic strain aging. When the amount of solute C is about 10 ppm before rolling, the r-value and {222} intensity ratio of sheet steel annealed after rolling are maxima at the rolling temperature of 773K, during which dynamic strain aging occurs. The {222} residual strain in the specimen rolled at 773K is higher than that in specimens rolled at other temperatures. It is proposed that dynamic strain aging would provide high stored energy in the {111} component of an as-rolled specimen, with the result that the region of high stored energy would recover and nucleate rapidly so that a strong {111} recrystallization texture develops.

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 remarkable increase in tensile strength as well as yield strength after strain age hardening without addition of special elements. The new sheet steel possesses excellent crash-worthiness and high fatigue strength, and also shows good formability almost equal to that of conventional high strength sheet steels. 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 steel is applied to crash-resistant parts and underbody parts.