Due to the coexistence of different micro structural components and their interactions, multiphase steels offer an excellent combination between high formability and strength. On the micro-scale, the fracture examination shows large influence of different phases and their distributions on the mechanical properties and failure mechanisms. Considering the influence of multiphase microstructure, an approach is presented using representative volume elements (RVE) in combination with continuum damage mechanics (CDM). Herein, the influence of the material properties of individual phases and the local states of stress on the material formability as well as the failure behavior can be examined. By means of the RVE-CDM approach, a precise criterion for the deformability characterization in sheet metal forming of multi phase steels is presented.