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<p>In this paper, the torsional fatigue failure mechanism of a medium-carbon quenched and tempered structural steel designated as 45 steel (Chinese standard GB/T 699-1999, equivalent to AISI 1045) blower shaft under variable-frequency operation was elucidated. The analysis combined scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), mechanical testing, and fractographic observation, enabling a comprehensive multiscale characterization of the failure process. The fracture surface displayed three distinct stages: crack initiation at a stress-concentrated fillet transition (stress concentration factor Kt ≈ 2.1–3.5), stable propagation with transgranular secondary cracks, and final rupture exhibiting dynamic fracture features. Key material deficiencies were identified, including substandard yield strength (307&#xa0;MPa, 13.5% below specifications) and a brittle Widmanstätten ferrite–sorbitic pearlite microstructure. Columnar grains (&lt;50&#xa0;μm) and high-angle grain boundaries (76.9% HAGBs) facilitated crack propagation, while variable-frequency operation (32.5&#xa0;Hz) induced torque fluctuations and multiaxial stress coupling, accelerating fatigue damage. EBSD analysis revealed preferential crack advancement along the {111} &lt; 110 &gt; slip system, with Σ3 grain boundaries partially deflecting crack paths (average angle: 55°). The failure analysis was performed under representative operating conditions of the F3101BGFJ blower in a PTA production unit, where the shaft fractured during variable-frequency drive operation at 32.5&#xa0;Hz (≈65% rated speed), a current of 200 A, and an air discharge pressure of 260&#xa0;Pa. The shaft material was 45 steel with a measured yield strength of 307&#xa0;MPa. A synergistic failure mechanism is proposed, emphasizing interactions among material embrittlement, geometric stress concentration, and dynamic loading. The findings highlight that the premature failure of the blower shaft was driven by the combined effects of substandard yield strength, brittle Widmanstätten ferrite–sorbitic pearlite microstructure, severe geometric stress concentration, and multiaxial stresses induced by variable-frequency operation. These results provide direct guidance for material substitution, geometric optimization, and operational load control in blower shafts under similar service conditions.</p>

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Multi-Factor Coupled Fatigue Fracture Mechanism and Failure Analysis of a 45 Steel Blower Shaft Under Variable-Frequency Operation

  • 期刊论文

  • 发表日期：

    2025年10月6日

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  • Ting Yu,
  • Meng Yuan,
  • Liuyi Huang,
  • Fangfang Zhang,
  • Yilin Zhu

摘要

In this paper, the torsional fatigue failure mechanism of a medium-carbon quenched and tempered structural steel designated as 45 steel (Chinese standard GB/T 699-1999, equivalent to AISI 1045) blower shaft under variable-frequency operation was elucidated. The analysis combined scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), mechanical testing, and fractographic observation, enabling a comprehensive multiscale characterization of the failure process. The fracture surface displayed three distinct stages: crack initiation at a stress-concentrated fillet transition (stress concentration factor Kt ≈ 2.1–3.5), stable propagation with transgranular secondary cracks, and final rupture exhibiting dynamic fracture features. Key material deficiencies were identified, including substandard yield strength (307 MPa, 13.5% below specifications) and a brittle Widmanstätten ferrite–sorbitic pearlite microstructure. Columnar grains (<50 μm) and high-angle grain boundaries (76.9% HAGBs) facilitated crack propagation, while variable-frequency operation (32.5 Hz) induced torque fluctuations and multiaxial stress coupling, accelerating fatigue damage. EBSD analysis revealed preferential crack advancement along the {111} < 110 > slip system, with Σ3 grain boundaries partially deflecting crack paths (average angle: 55°). The failure analysis was performed under representative operating conditions of the F3101BGFJ blower in a PTA production unit, where the shaft fractured during variable-frequency drive operation at 32.5 Hz (≈65% rated speed), a current of 200 A, and an air discharge pressure of 260 Pa. The shaft material was 45 steel with a measured yield strength of 307 MPa. A synergistic failure mechanism is proposed, emphasizing interactions among material embrittlement, geometric stress concentration, and dynamic loading. The findings highlight that the premature failure of the blower shaft was driven by the combined effects of substandard yield strength, brittle Widmanstätten ferrite–sorbitic pearlite microstructure, severe geometric stress concentration, and multiaxial stresses induced by variable-frequency operation. These results provide direct guidance for material substitution, geometric optimization, and operational load control in blower shafts under similar service conditions.