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<p>The bulging process of high-strength thin-walled tubes is an effective alternative to traditional tube sheet welding. However, the fatigue damage at the bulges of the thin-walled tubes seriously affects the safe service of the components. A stress-relief annealing process with different heating/cooling rates (100 and 200 °C/h) and holding times (1, 2, and 3&#xa0;h) was proposed to optimize the microstructure and fatigue performance of thin-walled bulges. The experimental results indicate that the added annealing at 520 °C at a heating/cooling rate of 100 °C/h and holding 3&#xa0;h can decrease residual stress from 480 to 74.5&#xa0;MPa and improve fatigue cycle number from 984 to 2727 without affecting the ultimate tensile strength of about 550&#xa0;MPa. Stress-relief annealing only delays the fracture process of the regions I and III, but it hardly suppresses the fracture of region II as microcracks. In addition, the existence of initial microcracks is the main factor leading to a shortened fatigue life. This study can provide theoretical support and technical reference for low-cost optimization of the fatigue performance of high-strength thin-walled steel tubes in the aerospace and automotive manufacturing industries.</p>

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Adjusting Stress-Relief Annealing: Enhancing the Fatigue Performance of Hoop in High-Strength Thin-Walled Steel Tubes

  • 期刊论文

  • 发表日期：

    2025年2月10日

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  • Junfeng Wu,
  • Yukui Gao

摘要

The bulging process of high-strength thin-walled tubes is an effective alternative to traditional tube sheet welding. However, the fatigue damage at the bulges of the thin-walled tubes seriously affects the safe service of the components. A stress-relief annealing process with different heating/cooling rates (100 and 200 °C/h) and holding times (1, 2, and 3 h) was proposed to optimize the microstructure and fatigue performance of thin-walled bulges. The experimental results indicate that the added annealing at 520 °C at a heating/cooling rate of 100 °C/h and holding 3 h can decrease residual stress from 480 to 74.5 MPa and improve fatigue cycle number from 984 to 2727 without affecting the ultimate tensile strength of about 550 MPa. Stress-relief annealing only delays the fracture process of the regions I and III, but it hardly suppresses the fracture of region II as microcracks. In addition, the existence of initial microcracks is the main factor leading to a shortened fatigue life. This study can provide theoretical support and technical reference for low-cost optimization of the fatigue performance of high-strength thin-walled steel tubes in the aerospace and automotive manufacturing industries.