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<p>Although cold radial forging is an effective manufacturing process for producing large-scale Cr–Mn–N austenitic steel rods with excellent mechanical properties, the influence of the resulting radial microstructural heterogeneity on deformation and fracture behavior remains insufficiently understood. In this work, a Cr–Mn–N austenitic steel rod with a diameter of 188&#xa0;mm fabricated by a final cold radial forging process is systematically investigated to elucidate the relationship between processing-induced microstructural gradients and mechanical properties. A pronounced radial gradient in grain size and dislocation structure is observed, with the grain size increasing from ~ 31.6&#xa0;μm at the surface to ~ 170.1&#xa0;μm at the center, accompanied by a reduction in dislocation pile-ups near grain boundaries toward the center. These microstructural variations lead to significant radial differences in strength, plasticity, and impact toughness. Yield strength follows a two-stage Hall–Petch relationship, indicating a transition from dislocation-dominated strengthening in the fine-grained surface region to a regime in which grain-boundary strengthening becomes increasingly important in the coarse-grained center region. The increase in elongation from the surface to the center is attributed to sustained work hardening, enabled by unsaturated dislocation storage near grain boundaries that allows for continued dislocation accumulation. Impact toughness also exhibits a two-stage Hall–Petch trend. In the fine-grained region, dislocation pile-ups near grain boundaries are associated with strain incompatibility and earlier crack initiation, while improved strain compatibility in the coarse-grained region contributes to increased crack-initiation energy and enhanced resistance to crack propagation.&#xa0;These findings provide mechanistic insights into microstructure evolution during cold radial forging and offer guidance for optimizing the mechanical performance of large-scale Cr–Mn–N austenitic steel components.</p>

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Radial microstructural heterogeneity governing two-stage Hall–Petch behavior of cold radial forged Cr–Mn–N austenitic steel rod

  • 期刊论文

  • 发表日期：

    2026年7月18日

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  • Bin Li,
  • Shenghu Chen,
  • Xuexin Pan,
  • HaiChang Jiang,
  • Lijian Rong

摘要

Although cold radial forging is an effective manufacturing process for producing large-scale Cr–Mn–N austenitic steel rods with excellent mechanical properties, the influence of the resulting radial microstructural heterogeneity on deformation and fracture behavior remains insufficiently understood. In this work, a Cr–Mn–N austenitic steel rod with a diameter of 188 mm fabricated by a final cold radial forging process is systematically investigated to elucidate the relationship between processing-induced microstructural gradients and mechanical properties. A pronounced radial gradient in grain size and dislocation structure is observed, with the grain size increasing from ~ 31.6 μm at the surface to ~ 170.1 μm at the center, accompanied by a reduction in dislocation pile-ups near grain boundaries toward the center. These microstructural variations lead to significant radial differences in strength, plasticity, and impact toughness. Yield strength follows a two-stage Hall–Petch relationship, indicating a transition from dislocation-dominated strengthening in the fine-grained surface region to a regime in which grain-boundary strengthening becomes increasingly important in the coarse-grained center region. The increase in elongation from the surface to the center is attributed to sustained work hardening, enabled by unsaturated dislocation storage near grain boundaries that allows for continued dislocation accumulation. Impact toughness also exhibits a two-stage Hall–Petch trend. In the fine-grained region, dislocation pile-ups near grain boundaries are associated with strain incompatibility and earlier crack initiation, while improved strain compatibility in the coarse-grained region contributes to increased crack-initiation energy and enhanced resistance to crack propagation. These findings provide mechanistic insights into microstructure evolution during cold radial forging and offer guidance for optimizing the mechanical performance of large-scale Cr–Mn–N austenitic steel components.