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<p>This study investigates the relationship between the microstructures and low-temperature impact toughness of S355NL low-alloy steel at intercritical normalizing temperatures. It was subjected to 800 °C, 850 °C, 900 °C, and 950 °C normalizing heat treatments followed by low-temperature (− 50 °C) impact tests. The results indicated that the low-temperature impact toughness initially increased and then decreased; the lowest impact toughness (102.7&#xa0;J) was observed at 800 °C, while the highest value (161&#xa0;J) is achieved at 850 °C. As the normalizing temperature further increases to 900 °C and 950 °C, the low-temperature impact toughness exhibited a gradual deterioration trend. At 800 °C, the phase transformation is insufficient to achieve complete austenitization, leading to coarse and inhomogeneous grains, which weaken grain boundary strengthening and consequently reduce low-temperature impact toughness. This improvement of toughness at 850 °C is attributed to grain refinement, the increased fraction of high-angle grain boundaries, and the reduced dislocation density, all of which synergistically improve strain compatibility and resistance to crack propagation. This study highlights the critical role of intercritical normalizing temperature in tailoring microstructural characteristics for optimizing low-temperature impact toughness, providing valuable insights for enhancing the reliability of S355NL low-alloy steel in low-temperature environments.</p>

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Effect of Intercritical Normalizing Temperature on Microstructure and Low-Temperature Impact Toughness of S355NL Low-Alloy Steel

  • 期刊论文

  • 发表日期：

    2025年11月1日

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  • Yanbin Li,
  • Qiaolong Ji,
  • Yi Ma,
  • Wujing Fu,
  • Guojian Cao,
  • Qihang Han,
  • Hao Wu,
  • Chao Ding,
  • Xuewen Li,
  • Guohua Fan

摘要

This study investigates the relationship between the microstructures and low-temperature impact toughness of S355NL low-alloy steel at intercritical normalizing temperatures. It was subjected to 800 °C, 850 °C, 900 °C, and 950 °C normalizing heat treatments followed by low-temperature (− 50 °C) impact tests. The results indicated that the low-temperature impact toughness initially increased and then decreased; the lowest impact toughness (102.7 J) was observed at 800 °C, while the highest value (161 J) is achieved at 850 °C. As the normalizing temperature further increases to 900 °C and 950 °C, the low-temperature impact toughness exhibited a gradual deterioration trend. At 800 °C, the phase transformation is insufficient to achieve complete austenitization, leading to coarse and inhomogeneous grains, which weaken grain boundary strengthening and consequently reduce low-temperature impact toughness. This improvement of toughness at 850 °C is attributed to grain refinement, the increased fraction of high-angle grain boundaries, and the reduced dislocation density, all of which synergistically improve strain compatibility and resistance to crack propagation. This study highlights the critical role of intercritical normalizing temperature in tailoring microstructural characteristics for optimizing low-temperature impact toughness, providing valuable insights for enhancing the reliability of S355NL low-alloy steel in low-temperature environments.