Formability of Dual-Phase Steels

Abstract

The mechanical behavior of dual-phase steels depends on a broad range of metallurgical phenomena. The initial hardening reflects the volume fraction of the martensitic phase via a back stress, but this also depends on the local strength of the martensite. Formability is related not only to strain hardening and other continuum properties such as normal plastic anisotropy, but may also be influenced by fracture phenomena associated with discrete microstructural events such as decohesion of the ferrite-martensite interface. Various micromechanisms of duplex systems are discussed and the influence of the related mechanical behavior in determining formability in different technological forming process is described. The low yield-to-tensile-strength ratio of dual-phase steels is of particular benefit in stamping shallow components such as autobody skin panels; however, denting resistance requires a high yield strength emphasizing the importance of aging after forming.