Microstructure Based Analysis of Plasticity and Failure of Dual Phase Steels

The formability and performance of dual-phase (DP) steel are determined by its microstructural characteristics. A banded martensitic microstructure can lead to premature failure during forming operations. In this study, two DP800 steel samples, one with a banded martensite structure and the other with an evenly dispersed martensite structure, are characterized through Nakazima and hole expansion experiments. Although both samples exhibit similar levels of ductility in tensile tests, their performance in forming experiments differs significantly. To further investigate the effect of microstructural banding, finite element models are generated from micrographs of the two samples using an in-house script. The plastic responses of the ferrite and martensite phases are calibrated to experimental data. These representative models are analysed under different loading scenarios to examine the impact of banding on the plasticity and failure of DP steels. The study concludes that martensite banding can induce anisotropic material behavior locally, leading to premature strain localization and, ultimately, early failure of the specimen.