Scholarlink

<p>This paper investigates the delayed brittle fracture of an austempered 50CrV4 (DIN 1.8159) conical spring washer utilized in the tread brake units of electric multiple units (EMUs). The failure occurred approximately seven months after assembly under a sustained static clamping load. The investigation was conducted using optical emission spectroscopy (OES), macroscopic and microscopic Vickers hardness testing, metallographic examination, scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDS). Fractographic examination revealed that the crack initiated at the subsurface near the bottom outer diameter, exhibiting brittle intergranular characteristics. Microstructural analysis identified distinct segregation bands at the crack origin, characterized by hard untempered martensite (~ 570 HV) and undissolved carbides, standing in sharp contrast to the bainite matrix (~ 460 HV) formed during the austempering process. EDS analysis confirmed significant enrichment of manganese (Mn), chromium (Cr), and vanadium (V) within these bands. The failure is attributed to the localized increase in hardenability caused by severe banded segregation, which prevented the bainitic transformation in the solute-rich zones during isothermal holding. Consequently, brittle martensite formed upon cooling, which could not accommodate the tensile hoop stresses generated during flattening. Comparative analysis confirmed that the defect originated from localized inconsistencies in the raw steel strip. Recommendations for prevention include implementing stricter raw material acceptance criteria regarding microstructural homogeneity (e.g., ASTM E1268).</p>

错误：搜索内容不能为空，请输入英文关键词
错误：关键词超出字数限制，请精简
高级检索

Delayed Brittle Fracture of Austempered 50CrV4 Spring Washers: The Role of Severe Banded Segregation

  • 期刊论文

  • 发表日期：

    2026年7月28日

查看全文
  • Jing Lyu,
  • Xin Xu,
  • Jie Hu,
  • Qian Zhang,
  • Xuwen Sun,
  • Qiquan Yang

摘要

This paper investigates the delayed brittle fracture of an austempered 50CrV4 (DIN 1.8159) conical spring washer utilized in the tread brake units of electric multiple units (EMUs). The failure occurred approximately seven months after assembly under a sustained static clamping load. The investigation was conducted using optical emission spectroscopy (OES), macroscopic and microscopic Vickers hardness testing, metallographic examination, scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDS). Fractographic examination revealed that the crack initiated at the subsurface near the bottom outer diameter, exhibiting brittle intergranular characteristics. Microstructural analysis identified distinct segregation bands at the crack origin, characterized by hard untempered martensite (~ 570 HV) and undissolved carbides, standing in sharp contrast to the bainite matrix (~ 460 HV) formed during the austempering process. EDS analysis confirmed significant enrichment of manganese (Mn), chromium (Cr), and vanadium (V) within these bands. The failure is attributed to the localized increase in hardenability caused by severe banded segregation, which prevented the bainitic transformation in the solute-rich zones during isothermal holding. Consequently, brittle martensite formed upon cooling, which could not accommodate the tensile hoop stresses generated during flattening. Comparative analysis confirmed that the defect originated from localized inconsistencies in the raw steel strip. Recommendations for prevention include implementing stricter raw material acceptance criteria regarding microstructural homogeneity (e.g., ASTM E1268).