Deformation inhomogeneity evolution and crack formation mechanism analysis in ultra-high strength steel by crystal plasticity simulations

Understanding deformation inhomogeneity and the formation mechanism of crack are crucial for fully exploiting the potential of ultra-high strength steel (UHSS). In this paper, the deformation inhomogeneity and microscopic crack formation mechanism of UHSS were investigated by combining high-fidelity crystal plasticity models with microscopic experiments. The simulation results at grain level show that the deformation strain of the UHSS is non-uniform, characterized by distinct deformation bands. A broad deformation band extends between multiple grains at an angle of approximately 40 degrees to the rolling direction, while a sharp deformation band is observed within a single grain. These features are intricately linked to the initial orientation (Taylor factor) distribution of the grains and their rotational behavior. The locations with greater Taylor factor deviations become potential crack initiation sites. In addition, as the deformation proceeds, the alpha-fiber reinforcement exacerbates the deformation inhomogeneity of the UHSS.