A study on the nucleation of tensile cracks in high-purity ferritic and ferrite-pearlite steels

The initiation and evolution of cracks during deformation are regarded as core indicators for evaluating the structural integrity of steel materials. Microstructural evolution and crack nucleation mechanisms in single-phase ferrite (HYT2) and ferrite-pearlite steels (Q195 and Q235) during tensile deformation were systematically investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). It is shown that crack nucleation is strongly regulated by microstructural features and is explicitly classified into four categories: ferrite-ferrite (F/F) grain boundaries, ferrite-pearlite (F/P) phase boundaries, pearlite-pearlite (P/P) colony boundaries, and inclusion-matrix interfaces. Quantitative analysis indicates that the type of interface has a significant influence on crack initiation, with the interface nucleation stress exhibiting a prominent hierarchy: homophase interfaces > heterophase interfaces > inclusion interfaces. A foundation for understanding the initiation and evolution of cracks during the deformation of steel materials is established in this study, and a critical theoretical basis is provided for the material evaluation and failure prevention of engineering components, such as cathode steel bars used in aluminum electrolysis.