The effects of chemical compositions and processing factors on the bake-hardenability have been studied on the box-annealed rephosphorized steels and the steels strengthened by silicon and manganese. The effects of bake-hardening on the dent and crush resistance have been also studied.
Lowering carbon content, increasing hot coiling temperature, and increasing annealing temperature are shown to be effective for the improvement of bake-hardenability. Bake-hardenability also increnses with increassing silicon and phosphorus contents and decreasing manganese content. The influence of these elements is diminished by lowering carbon contents.
In order to meet the demands of automobile manufacturers, bake-hardenable rephosphorized steel sheets are successfully produced on an industrial scale in Unitized Annealing Department.
Application of bake hardening is effective to improve dent and crush resistance. Dent resistance is more improved than crush resistance due to bake-hardening.
