The limit drawing ratio and formability prediction of advanced high strength dual-phase steels

Dual phase (DP) steels, being among advanced high-strength steels (AHSS), have been successfully used in the sheet metal stamping of automotive components for its great benefit in reducing vehicle weight while improving car safety. In their practical application, one of the major challenges is related to formability prediction of onset crack. This paper first conducts limiting drawing ratio (LDR) experiments to identify the maximum blank diameter of SPFC340, DP600, DP800 and DP1000 with onset crack. The fracture modes of these four types of blanks are then compared and classified into two categories: necking crack and shear crack. Further for DP1000, appropriate hardening formula is determined to fit the flow curve derived by the tensile test. Three yielding models (Hill-48, Batlat-89 and Banabic-2005) are compared with each other in the numerical simulation of DP1000 LDR onset crack. The investigation shows that a Swift and Hockett–Sherby combined formula is in good agreement with the flow curve of the tensile test and Batlat-89 yield model successfully predicts the onset shear crack of DP AHSS.

► Formability is evaluated for DP AHSS from 600 MPa to 1000 MPa.
► 600–1000 MPa DP AHSS encounter consistent shear crack.
► Latitudinal and longitudinal cracks are observed on DP800 and above steel grades.