Effects of warm forming on deep drawability of a TRIP-aided dual-phase sheet steel

To improve the deep drawing of high-strength TRIP-aided dual-phase (TDP) sh eet steel, Swift cup test uf a 0.19C-1.54Si 1.52Mn (mass%) TDF steel was in vestigated at temperatures between 20 degrees C and 250 degrees C. The stee l exhibited a larger limiting drawing ratio (LDR) than those of the convent ional ferrite-bainite and ferrite-martensite dual-phase steels without reta ined austenite. Furthermore, the LDR was enhanced by warm drawing at about 150 degrees C, at which the strain-induced transformation of the retained a ustenite particles is suppressed most. Such excellent deep drawability was caused by large local necking resistance due to "the transformation hardeni ng" and "the stress relaxation" resulting from the strain-induced martensit e transformation at the cup wall just above the punch bottom, as well as lo w drawing resistance of the shrinking flange.