Investigation of anisotropic damage evolution in dual phase steels

Dual phase (DP) steels have been extensively used in automotive industry due to combination of versatile properties such as; high strength to weight ratio and good formability. The origin of these properties are based on the complex microstructural features. In DP steels, it is very common to have banded microstructural features due to production conditions. DP steels are composed of mainly soft ferrite and 15-20 vol\% hard martensite phases. During metal forming processes, the contrast in mechanical properties leads to strong and highly heterogeneous strain partitioning which in turn causes anisotropic damage nucleation and evolution, and different damage mechanisms. Therefore, it is both scientifically and industrially important to understand main reasons and consequences of damage anisotropy. In this research, the effect of microstructural anisotropy of DP600 on damage is studied by conducting tensile tests along rolling and transverse directions and evolution of damage is investigated by means of microscopical characterization techniques. Three different damage mechanisms have been observed during deformation of DP600 steel; void formation between ferrite-martensite interface, around unwanted inclusions and cracking of martensite.