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<p>Achieving a favorable strength–toughness balance in thick-section low-alloy steels remains a critical challenge for structural applications. The effects of lamellarization annealing (L) and subsequent tempering (T) temperatures on microstructural evolution and mechanical performance were systematically examined in a 30-mm-thick thermo-mechanical controlled processing plate. The L temperature was varied from 800 to 860&#xa0;°C, followed by T at 400–550&#xa0;°C. Microstructural evolution was characterized using optical microscopy, scanning electron microscopy, electron backscatter diffraction, and X-ray diffraction (XRD), while tensile and Charpy V-notch impact tests were conducted to evaluate mechanical performance. Lower L temperatures (800 and 820&#xa0;°C) promoted the formation of heterogeneous lamellar structures composed of martensite/bainite and intercritical ferrite. This microstructural heterogeneity enhanced plastic deformation capability and low-temperature impact toughness by increasing the density of high-angle grain boundaries and promoting favorable dislocation configurations. In contrast, higher L temperatures (840 and 860&#xa0;°C) led to microstructural homogenization and dislocation accumulation, which improved strength but significantly deteriorated toughness. T at 400&#xa0;°C resulted in insufficient recovery and limited toughness improvement. An optimal strength–toughness balance was achieved at 500&#xa0;°C, whereas T at 550&#xa0;°C caused over-recovery, leading to a slight reduction in toughness despite enhanced ductility. XRD analysis revealed that a high fraction of screw dislocations combined with a moderate dislocation density enhanced crack-tip plasticity and ductile fracture behavior. The L<sub>810</sub>T<sub>500</sub> condition (810&#xa0;°C represents an intermediate L temperature within the optimal range of 800–820&#xa0;°C) achieved the best synergy: tensile strength ~900&#xa0;MPa, elongation of more than 17%, and impact toughness of more than 250&#xa0;J at −40&#xa0;°C.</p>

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Lamellarization–tempering induced heterogeneous lamellar structures achieving strength–toughness synergy in HSLA steel

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月5日

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  • Wen-Hao Zhou,
  • Zhen-Shan Zhang,
  • Zhong-Wen Wu,
  • Qing-Xue Zhang,
  • Hai-Tao Zhao,
  • Jun-Heng Gao,
  • Hong-Hui Wu,
  • Chao-Lei Zhang,
  • Shui-Ze Wang

摘要

Achieving a favorable strength–toughness balance in thick-section low-alloy steels remains a critical challenge for structural applications. The effects of lamellarization annealing (L) and subsequent tempering (T) temperatures on microstructural evolution and mechanical performance were systematically examined in a 30-mm-thick thermo-mechanical controlled processing plate. The L temperature was varied from 800 to 860 °C, followed by T at 400–550 °C. Microstructural evolution was characterized using optical microscopy, scanning electron microscopy, electron backscatter diffraction, and X-ray diffraction (XRD), while tensile and Charpy V-notch impact tests were conducted to evaluate mechanical performance. Lower L temperatures (800 and 820 °C) promoted the formation of heterogeneous lamellar structures composed of martensite/bainite and intercritical ferrite. This microstructural heterogeneity enhanced plastic deformation capability and low-temperature impact toughness by increasing the density of high-angle grain boundaries and promoting favorable dislocation configurations. In contrast, higher L temperatures (840 and 860 °C) led to microstructural homogenization and dislocation accumulation, which improved strength but significantly deteriorated toughness. T at 400 °C resulted in insufficient recovery and limited toughness improvement. An optimal strength–toughness balance was achieved at 500 °C, whereas T at 550 °C caused over-recovery, leading to a slight reduction in toughness despite enhanced ductility. XRD analysis revealed that a high fraction of screw dislocations combined with a moderate dislocation density enhanced crack-tip plasticity and ductile fracture behavior. The L810T500 condition (810 °C represents an intermediate L temperature within the optimal range of 800–820 °C) achieved the best synergy: tensile strength ~900 MPa, elongation of more than 17%, and impact toughness of more than 250 J at −40 °C.