Numerous authors consider that in nodular cast iron, the interface between the graphitic nodule and the α-matrix is so weak that nucleation appears suddenly at the beginning of plastic strain.^[1,2] Nevertheless, the present experimental study indicates that the nucleation of voids is a continuous process as a function of the imposed mechanical parameters (Σ_m, ε_eq). This result is explained in terms of interaction effects between closely spaced particles. A critical parameter for interaction is determined. Growth kinetics are also investigated and comparison with the Gurson–Tvergaard law allows identification of the q₁ and q₂ parameters of the potential. A critical void volume fraction f^c is finally defined and is shown to depend on the stress triaxiality level. At last, the role of the various microstructural heterogeneity levels on the damage kinetics is emphasized. Then, it is clearly demonstrated that all these heterogeneity levels must be considered to estimate a critical interfacial stress.