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<p>SAE 9254 chromium–silicon alloy steel is widely used for automotive coil springs due to its high strength and excellent fatigue resistance. However, premature fatigue failures observed during validation testing have raised concerns regarding manufacturing robustness. This study investigates the root cause of fatigue failure in SAE 9254 coil springs supplied to an automotive spring manufacturer. Two failed springs were examined using mechanical testing, fractography, and advanced microstructural and compositional analyses. Fractographic examination revealed characteristic thumbnail-type fatigue features with well-defined beach marks, indicating crack initiation from surface defects. Scanning electron microscopy identified distinct crack initiation, propagation, and final fracture regions, while energy-dispersive spectroscopy detected oxygen, silicon, and traces of chromium and manganese at the crack origin, suggesting surface oxidation and scale formation. Metallographic analysis showed a tempered martensitic microstructure in the core; however, a decarburized surface layer and surface irregularities acted as stress concentrators, reducing surface hardness and fatigue resistance. The average hardness was approximately 576.17 HV, and bulk chemical composition complied with SAE 9254 specifications, eliminating material chemistry as the cause of failure. The results indicate that the premature fatigue failure was primarily process-induced, associated with surface defects, oxidation, and decarburization during wire preparation and heat treatment. Improved surface quality control, optimized heat treatment parameters, and enhanced coating practices are recommended to extend the service life and improve the fatigue performance.</p>

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Root Cause Analysis of Fatigue Fracture in Chromium–Silicon Alloy Coil Springs for Automotive Applications

  • 期刊论文

  • 发表日期：

    2026年5月7日

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  • Souvik Das,
  • Md Saif Anwar,
  • Sandip Talukder,
  • Sasmita Behera,
  • Tanmay Bhattacharyya,
  • Goutam Mukhopadhyay

摘要

SAE 9254 chromium–silicon alloy steel is widely used for automotive coil springs due to its high strength and excellent fatigue resistance. However, premature fatigue failures observed during validation testing have raised concerns regarding manufacturing robustness. This study investigates the root cause of fatigue failure in SAE 9254 coil springs supplied to an automotive spring manufacturer. Two failed springs were examined using mechanical testing, fractography, and advanced microstructural and compositional analyses. Fractographic examination revealed characteristic thumbnail-type fatigue features with well-defined beach marks, indicating crack initiation from surface defects. Scanning electron microscopy identified distinct crack initiation, propagation, and final fracture regions, while energy-dispersive spectroscopy detected oxygen, silicon, and traces of chromium and manganese at the crack origin, suggesting surface oxidation and scale formation. Metallographic analysis showed a tempered martensitic microstructure in the core; however, a decarburized surface layer and surface irregularities acted as stress concentrators, reducing surface hardness and fatigue resistance. The average hardness was approximately 576.17 HV, and bulk chemical composition complied with SAE 9254 specifications, eliminating material chemistry as the cause of failure. The results indicate that the premature fatigue failure was primarily process-induced, associated with surface defects, oxidation, and decarburization during wire preparation and heat treatment. Improved surface quality control, optimized heat treatment parameters, and enhanced coating practices are recommended to extend the service life and improve the fatigue performance.