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<p>A new multi-scale gradient structure has been successfully fabricated in medium Mn steel via cyclic torsion and aging treatments. Within millimeter-sized specimens, this structure exhibits hierarchical gradient characteristics: at the nanoscale, it encompasses gradients of B₂ precipitates, while at the microscale, it comprises gradients of grain size and austenite content. The tailored gradient distribution of B2 particles induces localized variations in the stacking fault (SF) energy of austenite across distinct gradient layers. This, in turn, activates multiple deformation mechanisms, such as SF formation and the twinning-induced plasticity effect. Moreover, the multi-gradient structure facilitates cross-scale dynamic strain partitioning during plastic deformation, thereby triggering a continuous austenite-to-martensite phase transformation from the sample’s center to its surface. This unique structural evolution preserves the integrity of gradient layers under high-strain conditions, notably enhancing hetero-deformation-induced hardening. Compared with its annealed counterpart, the multi-scale gradient medium Mn steel exhibits remarkable improvements in mechanical properties: the yield strength and ultimate tensile strength are increased by 39% and 21%, respectively, while the uniform elongation and static toughness are improved by 18% and 52%, respectively.​ This study provides a promising paradigm for designing ultra-strong and ductile medium Mn steel by leveraging controlled multi-scale microstructural gradient strategies.</p>

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Multi-scale gradient microstructure enabling simultaneous improvement of strength and ductility in medium Mn steel

  • 期刊论文

  • 发表日期：

    2026年4月22日

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  • Tao Liu,
  • Yindong Shi,
  • Xiliang Zhang,
  • Hongji Liu,
  • Yanru Zhang,
  • Zheng Lv,
  • Tong Su,
  • Yanhui Wang

摘要

A new multi-scale gradient structure has been successfully fabricated in medium Mn steel via cyclic torsion and aging treatments. Within millimeter-sized specimens, this structure exhibits hierarchical gradient characteristics: at the nanoscale, it encompasses gradients of B₂ precipitates, while at the microscale, it comprises gradients of grain size and austenite content. The tailored gradient distribution of B2 particles induces localized variations in the stacking fault (SF) energy of austenite across distinct gradient layers. This, in turn, activates multiple deformation mechanisms, such as SF formation and the twinning-induced plasticity effect. Moreover, the multi-gradient structure facilitates cross-scale dynamic strain partitioning during plastic deformation, thereby triggering a continuous austenite-to-martensite phase transformation from the sample’s center to its surface. This unique structural evolution preserves the integrity of gradient layers under high-strain conditions, notably enhancing hetero-deformation-induced hardening. Compared with its annealed counterpart, the multi-scale gradient medium Mn steel exhibits remarkable improvements in mechanical properties: the yield strength and ultimate tensile strength are increased by 39% and 21%, respectively, while the uniform elongation and static toughness are improved by 18% and 52%, respectively.​ This study provides a promising paradigm for designing ultra-strong and ductile medium Mn steel by leveraging controlled multi-scale microstructural gradient strategies.