Behavior of Dual Phase steels in Stretch Bending

Abstract

In this study, the limit wall stretch was investigated to characterize the forming limit of dual phase (DP) steels under stretch bending conditions. A limit wall stretch analysis proposed by Yoshida[1] was used to describe the experiment. The results showed that limit wall stretch analysis was not appropriate for predicting the failure of DP steels because of its high yield strength and low work hardening property. An alternate parameter, the uniform strain limit ratio, was suggested to assess stretch bending limits experimentally. It was found that this parameter was proportional to the punch radius to sheet thickness ratio (R/t). Observations of the microstructure of DP980 steels revealed the existence of martensite bands along the rolling direction (RD). It was speculated that the low uniform strain limit ratio of DP980 stretched along the transverse direction (TD) is due to the weakening effect of the martensite bands.