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<p>High-speed railway fastening systems require spring steels with high fatigue resistance and reliable mechanical performance under severe service conditions. In this study, the mechanical performance of 38Si7 alloy spring steel coated with electroless NiB was investigated, with and without subsequent heat treatments at 250 and 400&#xa0;°C for 1&#xa0;h. Hardness measurements increased from approximately 500 HV for the substrate to about 650 HV for the NiB coating, and further to nearly 800 and 950 HV after heat treatments at 250 and 400&#xa0;°C, respectively. Fatigue tests demonstrated that NiB coatings significantly enhanced the fatigue resistance of the substrate, increasing the number of cycles to failure from approximately 6.3 million for uncoated 38Si7 to about 13.3 million for NiB-coated specimens. However, post-deposition heat treatments reduced the fatigue resistance, with the 400&#xa0;°C condition exhibiting the lowest fatigue life (approximately 4.8 million cycles). Fractographic analyses revealed four characteristic regions—crack initiation, crack propagation, fatigue zone, and sudden fracture—with symmetric fracture behavior observed on both arms of the specimens. Overall, the results indicate that NiB coating is highly effective in improving the fatigue performance of 38Si7 spring steel, whereas excessive heat treatment can adversely affect this enhancement.</p>

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Effects of Heat Treatment on the Fatigue Behavior of NiB-Coated 38Si7 Spring Steel for High-Speed Railway Applications

  • 期刊论文

  • 发表日期：

    2026年2月9日

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  • Mustafa Dursunlar,
  • Zakir Taş

摘要

High-speed railway fastening systems require spring steels with high fatigue resistance and reliable mechanical performance under severe service conditions. In this study, the mechanical performance of 38Si7 alloy spring steel coated with electroless NiB was investigated, with and without subsequent heat treatments at 250 and 400 °C for 1 h. Hardness measurements increased from approximately 500 HV for the substrate to about 650 HV for the NiB coating, and further to nearly 800 and 950 HV after heat treatments at 250 and 400 °C, respectively. Fatigue tests demonstrated that NiB coatings significantly enhanced the fatigue resistance of the substrate, increasing the number of cycles to failure from approximately 6.3 million for uncoated 38Si7 to about 13.3 million for NiB-coated specimens. However, post-deposition heat treatments reduced the fatigue resistance, with the 400 °C condition exhibiting the lowest fatigue life (approximately 4.8 million cycles). Fractographic analyses revealed four characteristic regions—crack initiation, crack propagation, fatigue zone, and sudden fracture—with symmetric fracture behavior observed on both arms of the specimens. Overall, the results indicate that NiB coating is highly effective in improving the fatigue performance of 38Si7 spring steel, whereas excessive heat treatment can adversely affect this enhancement.