Age hardening behaviour of deep drawable and bake hardenable steel sheet produced by high–temperature continuous annealing

A bake hardenable and deep drawable high strength steel sheet for automotive use, 'CHRX–BH', has been developed. The metallurgical basis for producing this steel is summarised and then its bake hardening behaviour is discussed. The bake hardening behaviour of this steel strongly depends upon the type of prestrain applied before aging. While temper rolling can suppress age hardening, tensile strain or plane strain accelerate aging of the steel. After press–forming, but even before baking, remarkable age hardening was recognised in this steel. For optimising the bake hardening effect without incurring room temperature aging problems, not only controlling the amount of solute C and N but also controlling using conditions becomes important.