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<p>A systematic investigation was conducted on the influence of residual nitrogen (0.003–0.008&#xa0;wt.%) on the microstructure, mechanical properties, and strain aging behavior of scrap-electric arc furnace produced SAPH440 low-alloy steel. Through internal friction spectroscopy, transmission electron microscopy, and atom probe tomography, the occurrence state of nitrogen and its interaction with dislocations under simulated industrial pre-strain (2%, 10%) and aging conditions (250&#xa0;°C/h) were elucidated. Increasing nitrogen content was found to refine ferrite grain size and enhance strength, but it also drastically reduced ductility and impact toughness due to heightened strain aging sensitivity. Nitrogen levels ≥ 0.008&#xa0;wt.% promoted extensive Cottrell atmosphere formation, which pinned dislocations and caused severe embrittlement after aging, leading to additional yield strength increments of up to 147&#xa0;MPa (2% strain) and 164&#xa0;MPa (10% strain), while elongation fell below 16% and 8.3%, respectively. Critically, even 2% pre-strain immobilized virtually all nitrogen atoms ≤ 0.008&#xa0;wt.%, precipitating significant property degradation. Nitrogen segregation at grain boundaries and dislocation networks after strain aging was directly observed.</p>

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Effect of residual element nitrogen on microstructure and strain aging behavior of low-alloy steel

  • 期刊论文

  • 发表日期：

    2026年1月20日

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  • Yu-He Huang,
  • Hai-Sheng Yang,
  • Jun Lu,
  • Jun-Heng Gao,
  • Hai-Tao Zhao,
  • Hong-Hui Wu,
  • Chao-Lei Zhang,
  • Wang Hui,
  • Guang Xu,
  • Jiang-Hua Qi,
  • Shui-Ze Wang,
  • Xin-Ping Mao

摘要

A systematic investigation was conducted on the influence of residual nitrogen (0.003–0.008 wt.%) on the microstructure, mechanical properties, and strain aging behavior of scrap-electric arc furnace produced SAPH440 low-alloy steel. Through internal friction spectroscopy, transmission electron microscopy, and atom probe tomography, the occurrence state of nitrogen and its interaction with dislocations under simulated industrial pre-strain (2%, 10%) and aging conditions (250 °C/h) were elucidated. Increasing nitrogen content was found to refine ferrite grain size and enhance strength, but it also drastically reduced ductility and impact toughness due to heightened strain aging sensitivity. Nitrogen levels ≥ 0.008 wt.% promoted extensive Cottrell atmosphere formation, which pinned dislocations and caused severe embrittlement after aging, leading to additional yield strength increments of up to 147 MPa (2% strain) and 164 MPa (10% strain), while elongation fell below 16% and 8.3%, respectively. Critically, even 2% pre-strain immobilized virtually all nitrogen atoms ≤ 0.008 wt.%, precipitating significant property degradation. Nitrogen segregation at grain boundaries and dislocation networks after strain aging was directly observed.