Fracture behavior and multiple toughening mechanisms of low-Ni, low-Mn weathering bridge steel at low temperature based on crystallographic characteristics

The intrinsic relationships among the crystallographic characteristics, plastic deformation, and low-temperature fracture toughness of a low-Ni, low-Mn weathering bridge steel were investigated in this study. The evolution of grain boundary characteristics, crystallographic orientations, and textures during low-temperature quasi-static fracture was characterized using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). In addition, the fracture and toughening mechanisms were comprehensively elucidated from a microstructural perspective. Results indicated that the J 0.2BL value of the weathering bridge steel at −40 °C reached 1027.94 kJ/m 2 . This superior low-temperature fracture toughness is primarily attributed to multiple toughening mechanisms involving the synergistic effects of both intrinsic and extrinsic contributions. The intrinsic toughening mechanism arises from the coordinated deformation of the multiphase microstructure and the adaptive evolution of crystallographic texture. The increased plastic deformability within the crack-tip plastic zone facilitates deformation-induced grain refinement, thereby elevating the cleavage fracture stress. Extrinsic toughening is manifested through crack deflection jointly governed by high-angle grain boundaries (HAGBs) and crystallographic orientation. HAGBs and low-Schmid factor (SF) grains with large twist angles promote significant crack deflections during crack propagation. The repeated deflection of the crack substantially increases the energy dissipated during fracture, thereby inhibiting rapid crack growth. • Low-Ni, low-Mn steel exhibits superior plastic deformability and cryogenic toughness. • Adaptive evolution of texture in the plastic zone coordinates plastic deformation. • Deformation-induced grain refinement and adaptive texture evolution provide intrinsic toughening. • Synergistic control of crack deflection by HAGBs and crystallographic orientations enhances extrinsic toughening.