Dual-phase (DP) steels with a microstructure consisting of ferrite and martensite phases have high tensile strength and good ductility compared with the conventional HSLA steels with ferrite-pearlite microstructures. The main purpose of this research was to evaluate the void formation process in a low carbon DP steel with approximately 32% martensite during tensile straining. The quantitative examinations were conducted in the post-neck region of the fractured tensile specimen using the Clemex image analyzing software. Having analyzed different images taken from the fractured tensile specimen parallel to loading direction, different stages of void formation process were examined. For this reason, the microstructure of the investigated DP steel was studied using optical and scanning electron microscopes. The number of voids nucleated during non-uniform deformation up to the fracture point as well as their area fractions as a function of the applied axial true strain, determination of the neck point and predominant mechanism of voids nucleation were the main results of this study. The results showed that fracture of martensite islands during tensile straining was the main mechanism controlling the void nucleation stage. Furthermore, voids growth in the post-neck region and their subsequent coalescence leading to final fracture confirmed the occurrence of ductile fracture in dual-phase steel in such a way similar to the composite materials with a ductile matrix.

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