Effect of carbon content on deep drawability of TRIP-aided dual-phase sheet steels

Effect of retained austenite on the deep drawing in high strength TRIP-aide d dual-phase (TDP) sheet steels with different carbon content were investig ated. The deep drawability based on the limiting drawing ratio (LDR=D-0/d(p )), where the D-0 and the d(p) are a maximum blank diameter and a punch dia meter respectively, was affected by the volume fraction of the retained aus tenite and by its stability (carbon concentration). Namely, the higher the volume fraction of the retained austenite and its stability, the larger str ength-deep drawability balance, i.e., the product of tensile strength and L DR. Furthermore, the higher blank folding force, the larger the strength-de ep drawability balance of high carbon TDP steel. The excellent deep drawabi lity was due to large local necking resistance at the cup wall just above t he punch bottom due to "the transformation hardening" and "the stress relax ation" resulting from the strain-induced martensite transformation, as well as a low drawing resistance of the shrinking flange.