DEFECT SENSITIVITY OF DUAL-PHASE STEELS: A STATISTICAL MICROMECHANICAL INVESTIGATION OF THE DUCTILITY LOSS DUE TO PREEXISTING DEFECTS

Abstract

As a result of their heterogeneous two-phase microstructure, dual-phase (DP) steels reveal various damage mechanisms leading to the nucleation of voids, microcracks, and other defects at all stages of deformation. Defects may also preexist in the microstructure due to thermomechanical processing of the material. The literature has ample evidence that DP steels, while offering a good compromise between ductility and strength, are sensitive to these types of preexisting defects. However, the quantitative dependency of mechanical properties of DP steels on such preexisting defects is still to be explored. In this paper, a systematic statistical analysis of this sensitivity is carried out using an idealized microstructural model of randomly generated two-phase volume elements with embedded preexisting defects. The proposed model also enables a methodological study probing the influence of mechanical phase contrast (i.e., the hardness difference between the constituent phases) and volume fractions. It is observed that high phase contrast microstructures are less sensitive to initial defects since the inherent extreme heterogeneity of the microstructure leads to the nucleation of new damage incidents irrespective of the presence of preexisting defects. At constant contrast, the volume fraction of the hard phase has less influence. These conclusions are insensitive to the precise type of defect considered.