Abstract
The work-hardening behavior under strain path changes for dual phase (DP) steel has been investigated by using simple shear sequences, in comparison with that for interstitial free (IF) steel. The results show that a strong hardening followed by softening in an orthogonal path change, which is normally seen in IF steel, is not significant in DP steel. Based on these results, analytical approaches to predict forming limit strain and stress in monotonic and orthogonal paths by using Hill criterion have been conducted. It is known that stress based forming limit curves are path independent, while strain based forming limit curves are strongly path dependent. For IF steel, the localized necking is started just after the second loading in orthogonal sequence, which thus shows that even stress based forming limits are path dependent in IF steel. On the other hand, DP steel exhibits localized necking at the same amount of total strain both for monotonic and orthogonal paths and thus the stress based forming limits are path independent, which reflects differences in work-hardening under strain path changes in DP and IF steels. It might be pointed out that these differences are originated in the microstructural evolution of both steels.
