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<p>In this study, a gradient nanostructure (GNS) is prepared on the surface of 45CrNiMoVA ultra-high-strength steel by large-load, multi-pass ultrasonic surface rolling process (USRP). The effect of GNS on low-cycle torsional fatigue was studied, and the evolution of GNS under low-cycle fatigue loading was also discussed. After USRP treatment, the turning marks of the specimens are eliminated. The surface roughness Ra is reduced to 94&#xa0;nm, and the roughness is reduced by 89% compared with the fine turning surface. The surface compressive residual stress is as high as -1174.90&#xa0;MPa. The thickness of the gradient strain layer induced by USRP is more than 1&#xa0;mm, where the thickness of the gradient nanolayer is more than 150&#xa0;μm. The surface grain size of the USRP specimens is nano-scale, and the dislocation density is significantly increased. The maximum hardness of the USRP specimens is 6.46 GPa, which is 40% higher than that of the untreated (UT) specimens. Due to the improvement of surface gradient strengthening, compressive residual stress and surface finish, the low-cycle torsional fatigue life of the USRP specimens are increased by 4.54 times at the maximum torsional shear stress of 933&#xa0;MPa, reaching 207.8 thousand cycles, compared with the UT specimens. Under low-cycle torsional fatigue loading, micro-cracks associated with turning traces appear on the surface of USRP specimens. The compressive residual stress continues to relax, the grain size of the GNS tends to grow, the dislocation density decreases, and the hardness decreases significantly. This indicates that the inhibitory effect of surface GNS on crack initiation and propagation would continue to degrade as the number of fatigue loading cycles increases. This study will be useful and informative for the further improvement of low-cycle fatigue performance of ultra-high strength steel components treated by USRP.</p>

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Effect of ultrasonic surface rolling process on microstructure and low-cycle torsional fatigue properties of 45CrNiMoVA ultra-high-strength steel

  • 期刊论文

  • 发表日期：

    2025年7月14日

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  • B. Ma,
  • J. X. Fang,
  • H. T. He,
  • T. Sun,
  • Z. Yang,
  • H. T. Chen,
  • T. T. Guo,
  • T. Fu,
  • X. Y. Zhou,
  • W. B. Wang,
  • J. T. Wei,
  • Y. L. Wang,
  • M. Wen,
  • P. He

摘要

In this study, a gradient nanostructure (GNS) is prepared on the surface of 45CrNiMoVA ultra-high-strength steel by large-load, multi-pass ultrasonic surface rolling process (USRP). The effect of GNS on low-cycle torsional fatigue was studied, and the evolution of GNS under low-cycle fatigue loading was also discussed. After USRP treatment, the turning marks of the specimens are eliminated. The surface roughness Ra is reduced to 94 nm, and the roughness is reduced by 89% compared with the fine turning surface. The surface compressive residual stress is as high as -1174.90 MPa. The thickness of the gradient strain layer induced by USRP is more than 1 mm, where the thickness of the gradient nanolayer is more than 150 μm. The surface grain size of the USRP specimens is nano-scale, and the dislocation density is significantly increased. The maximum hardness of the USRP specimens is 6.46 GPa, which is 40% higher than that of the untreated (UT) specimens. Due to the improvement of surface gradient strengthening, compressive residual stress and surface finish, the low-cycle torsional fatigue life of the USRP specimens are increased by 4.54 times at the maximum torsional shear stress of 933 MPa, reaching 207.8 thousand cycles, compared with the UT specimens. Under low-cycle torsional fatigue loading, micro-cracks associated with turning traces appear on the surface of USRP specimens. The compressive residual stress continues to relax, the grain size of the GNS tends to grow, the dislocation density decreases, and the hardness decreases significantly. This indicates that the inhibitory effect of surface GNS on crack initiation and propagation would continue to degrade as the number of fatigue loading cycles increases. This study will be useful and informative for the further improvement of low-cycle fatigue performance of ultra-high strength steel components treated by USRP.