Abstract: Effectively mitigating local stress concentration is important for improving the mechanical performance of materials. Inspired by natural biological structures, this work introduces bamboo fiber ferrite into a bionic medium-carbon steel through warm rolling and short-time annealing. The resulting cementite presents multi-scale features spanning from tens of nanometers to hundreds of nanometers. The bionic steel has the characteristics of mitigating micro and macro local stress concentration, the yield strength achieves ∼800 MPa, which is ∼3 times that of conventional carbon steel, while maintaining excellent ductility (21.7 %). Extensive investigation reveals that the microscopic stress relief stems from hetero-deformation induced hardening and point-line topological stress transfer. Analysis of the fracture and the microstructures at crack tips indicates that the spherical cementite disperses the stress at the crack tip, making it difficult for cracks to expand, and mitigating macroscopic stress concentration. The results opening a pathway for designing metallic materials with excellent mechanical properties.

Key words: Biomimetic engineering, Microstructure design, Stress concentration, Medium carbon steel