Abstract Undesirable fracture resistance has led to critical safety concerns in ultra-high strength quenching and partitioning (Q&P) steels. The present work proposes a new heat treatment method of tailoring simultaneously martensite matrix and retained austenite to enhance the fracture resistance of ultra-high strength Q&P steels, while keeping the good strength-ductility combination. To this end, both conventional and pre-cracked tensile tests are conducted on different Q&P steels with various microstructures consisting of different martensite matrix and retained austenite. Microstructure is analysed by neutron diffraction, atom probe tomography, transmission electron microscopy and dilatometry. For the optimum microstructure, the volume fraction of retained austenite play an important role in enhancing the strength-ductility combination, with an ultimate tensile strength reaching 1500 MPa and uniform elongation over 10%. In addition, the dislocation mobility in the martensite matrix of the optimum microstructure is enhanced due to the dislocation recovery, solute carbon depletion, and the transformation of transition carbides into cementite. The enhanced dislocation mobility reduces the flow stress and results in an improvement of intrinsic toughness of the martensite matrix. Furthermore, the size of cementite at grain boundaries of the optimum microstructure is so small (tens of nanometres) that brittle intergranular fracture is prevented. In summary, the new heat treatment method suggests that the optimal treatment should tailor simultaneously the martensite matrix and the retained austenite to optimise the strength, ductility and fracture resistance combination of ultra-high strength Q&P steels.

中文翻译：

---

通过调整马氏体基体和残余奥氏体优化超高强度淬火和分隔钢的强度-塑性-韧性组合

摘要 超高强度淬火隔断 (Q&P) 钢的不良抗断裂性已导致严重的安全问题。目前的工作提出了一种新的热处理方法，即同时调整马氏体基体和残余奥氏体，以提高超高强度 Q&P 钢的抗断裂性，同时保持良好的强度-延展性组合。为此，对具有由不同马氏体基体和残余奥氏体组成的各种显微组织的不同 Q&P 钢进行了常规和预开裂拉伸试验。通过中子衍射、原子探针断层扫描、透射电子显微镜和膨胀计分析显微结构。为获得最佳微观结构，残余奥氏体的体积分数对增强强度-塑性组合起着重要作用，极限抗拉强度达到1500 MPa，均匀伸长率超过10%。此外，由于位错恢复、溶质碳耗竭和过渡碳化物向渗碳体的转变，最佳显微组织的马氏体基体中的位错迁移率增强。增强的位错迁移率降低了流动应力并导致马氏体基体的内在韧性提高。此外，最佳微观结构的晶界处渗碳体的尺寸非常小（几十纳米），可以防止脆性晶间断裂。总之，