Continuously annealing of cold rolled sheet offers the possibility of producing different steel grades with Bake Hardenability as a specific feature. Killed steel grades, from extra deep drawing (YS < 180 MPa) to drawing HSS (YS > 280 MPa) are obtained by adapting chemical analysis, rolling conditions and annealing treatment.
Aging at room temperature does hardly occur and is without any consequence even for the most critical outer panels. The effects of deformation, baking time and temperature are determined by tensile and indentation tests. The conclusions from both tests, are similar. In the as shipped condition (Temper rolled), substantial bake hardening (BH), even without prestrain, is obtained under industrial baking conditions. With increasing prestrain the baking temperature and the time to reach the maximum BH decrease. The highest BH is found in the lower prestrain levels. The loss in BH however at higher prestrain levels is compensated by a larger work hardening contribution.
Two industrial applications of Bake Hardenable Steel (Floor and Roof), are described.