Journal of the Korean Society for Heat Treatment (열처리공학회지)

The Korean Society for Heat Treatment (한국열처리공학회)
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Resistance to Hydrogen Embrittlement of Ultra-high Strength Pearlitic Bolt

펄라이트 조직을 갖는 초고강도 볼트의 수소취성 저항성

  • Ahjeong Lyu (Department of Materials Science and Engineering, Yonsei University) ;
  • Young-Kook Lee (Department of Materials Science and Engineering, Yonsei University)
  • 유아정 (연세대학교 신소재공학과) ;
  • 이영국 (연세대학교 신소재공학과)
  • Received : 2023.01.04
  • Accepted : 2023.01.15
  • Published : 2023.01.30
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Abstract

Recently, ultra-high strength bolts have been developed for weight lightening of a vehicle and fuel efficiency. However, some amount of diffusible H is absorbed into the bolt during its manufacturing process so that H embrittlement (HE) often occurs particularly in high strength bolts with a tempered martensitic microstructure. This brings attention to ultra-high strength pearlitic bolts with a high resistance to HE. Therefore, in this study the HE resistance of the 1.6 GPa grade pearlitic bolt was evaluated through tightening tests and slow strain rate tests (SSRTs), and fracture surfaces of failed bolts were comparatively observed. A critical H content for the tightening test turned out to be ~0.23-0.35 mass ppm. The bolt with a diffusible H content of ~0.35 mass ppm was fractured during the tightening test, showing a quasi-cleavage fracture surface, indicating the occurrence of HE. In addition, the bolt underwent premature elastic failure during the SSRT. This implies that the HE resistance of high strength bolts can be evaluated by both tightening test and SSRT.

Keywords

Acknowledgement

이 연구는 2020년도 산업통상자원부 및 산업기술평가관리원(KEIT) 연구비 지원에 의한 연구임(No. K0001343).

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