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Dual phase steels, a composite made of ferrite matrix and hard martensiteinclusions, are currently introduced as automotive structural parts owing to theirexcellent strength/ductility compromise while involving only small amounts ofalloying elements. Nevertheless, these alloys suffer sometimes from limiteddamage and fracture resistance, for instance during forming operations, due toearly void nucleation leading to small or moderate fracture strains dependingmostly on the characteristics of the martensite phase. Several DP steels,presenting various amounts of martensite and C content, with or withoutadditional tempering, are investigated by performing mechanical tests underdifferent loading conditions, in-situ micromechanical tests, nanoindentation, andin depth damage mechanism characterization. A micromechanical modelcombining an advanced Gurson model and homogenization theory is validated bycomparison to the experimental results and used to perform a comprehensiveparameter study with the objective of guiding microstructure optimization.