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<p>Failure analysis is essential for identifying the root causes of component fractures and implementing preventive measures to avoid catastrophic failures. This study investigates the premature failure of locomotive traction gearbox gears used in indigenous trains in Pakistan. These gears underwent gas carburizing with a target case depth of 1.6–2.0&#xa0;mm and surface hardness between 57.4 HRC (653&#xa0;HV) and 59.9 HRC (697&#xa0;HV). Analysis of a fractured gear revealed that, while it met dimensional and chemical composition requirements, it failed to satisfy metallurgical and heat treatment specifications. Specifically, the gear exhibited insufficient case depth and improper hardness distribution, leading to early fatigue failure. The investigation included collecting operational and manufacturing histories from the indigenous factory, verifying material specifications using optical emission spectroscopy, and examining macro-fractographic patterns via stereomicroscopy to evaluate fracture patterns. Microstructural analysis assessed the quality of case hardening, while Vickers hardness testing determined the uniformity of case depth, with results converted to HRC for comparison. Chemical analysis confirmed that the gears were manufactured from FIAT 19CN5 steel. Macro-fractography revealed beach marks on the fracture surface, characteristic of fatigue failure, with cracks initiating at the gear tooth surface and propagating inward. Metallographic examination showed significant decarburization at the fractured surfaces, reducing surface hardness. Hardness testing on intact teeth also showed considerable variation, ranging from 49.5 HRC (503&#xa0;HV) to 56.0 HRC (613&#xa0;HV), indicating non-uniform carburization. The findings indicate deficiencies in the heat treatment process, particularly during carburizing and quenching. Inadequate case hardening and surface decarburization were the primary causes of premature fatigue failure. The study highlights the need for strict control and optimization of heat treatment parameters to ensure consistent case depth and hardness, thereby enhancing the service life of locomotive traction gears.</p>

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Failure Analysis of a Locomotive Traction Gear: Metallurgical and Fractographic Insights

  • 期刊论文

  • 发表日期：

    2025年12月4日

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  • Muhammad Ali Siddiqui,
  • Syed Amir Iqbal,
  • Syed Osman Shah,
  • Saquib Hesham,
  • Alishba Masood Siddiqui,
  • Aena Malik,
  • Syed Zain Ali Abbas

摘要

Failure analysis is essential for identifying the root causes of component fractures and implementing preventive measures to avoid catastrophic failures. This study investigates the premature failure of locomotive traction gearbox gears used in indigenous trains in Pakistan. These gears underwent gas carburizing with a target case depth of 1.6–2.0 mm and surface hardness between 57.4 HRC (653 HV) and 59.9 HRC (697 HV). Analysis of a fractured gear revealed that, while it met dimensional and chemical composition requirements, it failed to satisfy metallurgical and heat treatment specifications. Specifically, the gear exhibited insufficient case depth and improper hardness distribution, leading to early fatigue failure. The investigation included collecting operational and manufacturing histories from the indigenous factory, verifying material specifications using optical emission spectroscopy, and examining macro-fractographic patterns via stereomicroscopy to evaluate fracture patterns. Microstructural analysis assessed the quality of case hardening, while Vickers hardness testing determined the uniformity of case depth, with results converted to HRC for comparison. Chemical analysis confirmed that the gears were manufactured from FIAT 19CN5 steel. Macro-fractography revealed beach marks on the fracture surface, characteristic of fatigue failure, with cracks initiating at the gear tooth surface and propagating inward. Metallographic examination showed significant decarburization at the fractured surfaces, reducing surface hardness. Hardness testing on intact teeth also showed considerable variation, ranging from 49.5 HRC (503 HV) to 56.0 HRC (613 HV), indicating non-uniform carburization. The findings indicate deficiencies in the heat treatment process, particularly during carburizing and quenching. Inadequate case hardening and surface decarburization were the primary causes of premature fatigue failure. The study highlights the need for strict control and optimization of heat treatment parameters to ensure consistent case depth and hardness, thereby enhancing the service life of locomotive traction gears.