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<p>The austenitization phase transformation temperature of Q550qENH steel was measured using a thermal simulation testing machine. The continuous cooling transformation curve (SH-CCT) of the experimental steel under welding conditions was plotted by combining optical microscopy and Vickers hardness tester. The present study investigates the variation in laws of microstructure and hardness in the heat-affected zone (HAZ) under different cooling rates. The results demonstrated that at reduced cooling rates (1 to 3 °C/s), the transformation products of the experimental steel were identified as granular bainite, pearlite and a minor amount of ferrite. It was observed that the bainite content increased, and the hardness value increased, ranging from 224.6 to 241HV. At elevated cooling rates (5 to 15°C/s), the transformation products of the experimental steel were identified as granular bainite and pearlite. It was noted that the hardness increased significantly at a cooling rate of 10 °C/s, and the proportion of bainite gradually increased, with the hardness value increasing, ranging from 252HV to 290HV. At accelerated cooling rates (20 to 45 °C/s), the transformation products of the experimental steel were identified as lamellar bainite, granular bainite and a minor amount of martensite. Within this specified cooling rate range, the hardness and microstructure demonstrated stability, with the Vickers hardness maintaining consistency within the range of 282 to 310 HV. This stability ensured optimal weldability. In the absence of preheating at ambient temperature, the experimental steel demonstrated a suitable welding energy range of 8 to 27 kJ/cm. This work provides systematic SH-CCT data for Q550qENH steel, offering guidance for welding design in bridge applications.</p>

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Study on Q550qENH Steel SH-CCT and Optimal Welding Heat Input

  • 期刊论文

  • 发表日期：

    2026年3月1日

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  • H. L. Chang,
  • Y. Q. Fu,
  • J. Zhang,
  • J. Li,
  • D. Zhang,
  • J. M. Lai,
  • F. Feng,
  • D. Z. Ma

摘要

The austenitization phase transformation temperature of Q550qENH steel was measured using a thermal simulation testing machine. The continuous cooling transformation curve (SH-CCT) of the experimental steel under welding conditions was plotted by combining optical microscopy and Vickers hardness tester. The present study investigates the variation in laws of microstructure and hardness in the heat-affected zone (HAZ) under different cooling rates. The results demonstrated that at reduced cooling rates (1 to 3 °C/s), the transformation products of the experimental steel were identified as granular bainite, pearlite and a minor amount of ferrite. It was observed that the bainite content increased, and the hardness value increased, ranging from 224.6 to 241HV. At elevated cooling rates (5 to 15°C/s), the transformation products of the experimental steel were identified as granular bainite and pearlite. It was noted that the hardness increased significantly at a cooling rate of 10 °C/s, and the proportion of bainite gradually increased, with the hardness value increasing, ranging from 252HV to 290HV. At accelerated cooling rates (20 to 45 °C/s), the transformation products of the experimental steel were identified as lamellar bainite, granular bainite and a minor amount of martensite. Within this specified cooling rate range, the hardness and microstructure demonstrated stability, with the Vickers hardness maintaining consistency within the range of 282 to 310 HV. This stability ensured optimal weldability. In the absence of preheating at ambient temperature, the experimental steel demonstrated a suitable welding energy range of 8 to 27 kJ/cm. This work provides systematic SH-CCT data for Q550qENH steel, offering guidance for welding design in bridge applications.