Ultrafine martensite/bainite heterostructure achieves synergistic strength and toughness of bearing steel

The martensitic 100Cr6 bearing steel suffers from severe strength-toughness trade-off, restricting its service reliability. Herein, ultrafine martensite/bainite heterostructure was fabricated via rolling-induced grain refinement and austempering-enabled heterostructure. Microstructure, mechanical performance, strengthening contributions and heterogeneous deformation-induced toughening behaviors were systematically investigated via multi-scale characterization and crystal plasticity simulation. Ultrafine martensite/bainite heterostructure was obtained to achieve synergistic strength of 2150 MPa and toughness of 14.5 J/cm2. Strain mismatch at M/B interfaces induces dispersed microcracks, interfacial back stress reduces crack-tip stress intensity and induces crack deflection, while tortuous and bifurcated crack propagation paths dissipate additional fracture energy, realizing prominent strength-toughness synergy. This work provides a facile strategy for high-performance bearing steel design.