Damage evolution during tensile test of austempered ductile iron partially austenized

The goal of this work is to analyze the damage evolution at microstructural scale of an austempered ductile iron partially austenized during tensile loading. The analysis is carried out by means of step-by-step tensile tests and the specimen's surface observation with optical and scanning electron microscopy. The results show that cracks initiate and propagate firstly at the matrix-nodule interface. Then, as the strain is increased, the initiation and propagation in the metallic matrix take places preferentially inside the ausferritic areas and along the ausferritic-ferritic interface. Despite the internodular zones tend to localize the plastic deformation, particularly in the ferritic zones, the ausferrite-ferrite interfaces, and the ausferrite itself acts as preferentially sites of cracks propagation. The final fracture is produced by the coalescence of multiple cracks into a single dominant crack leading to the material final fracture.