Journal of Welding and Joining

The Korean Welding and Joining Society (대한용접접합학회)
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Effect of Chemical Composition of Nut Material on the Fracture Behavior in Nut Projection Welding of Hot-Stamped Steel Sheet

핫스탬핑강의 너트 프로젝션 용접시 너트 재질이 용접부 파단모드 변화에 미치는 영향

  • Lim, Sung-Sang (Dept. of Marine Equipment Engineering, Korea Maritime and Ocean University) ;
  • Kim, Young-Tae (Hyundai Motor Company, Sheet Metal Development Team) ;
  • Chun, Eun-Joon (Hyundai Motor Company, Sheet Metal Development Team) ;
  • Nam, Ki-Sung (Advanced Technology Team, SUNGWOO HITECH) ;
  • Park, Young-Wan (Dept. of Mechanical Engineering, Pukyong National University) ;
  • Kim, Jae-Wan (Dept. of Mechanical Engineering, Pukyong National University) ;
  • Lee, Sun-Young (Dept. of Mechanical Engineering, Pukyong National University) ;
  • Choi, Il-dong (Dept. of Marine Equipment Engineering, Korea Maritime and Ocean University) ;
  • Park, Yeong-Do (Dept. of Advanced Materials Engineering, Dong-Eui University)
  • 임성상 (한국해양대학교 조선기자재공학과) ;
  • 김영태 (현대자동차 강판재료개발팀) ;
  • 천은준 (현대자동차 강판재료개발팀) ;
  • 남기성 (성우하이텍 선행기술팀) ;
  • 박영환 (부경대학교 기계공학과) ;
  • 김재완 (부경대학교 기계공학과) ;
  • 이선영 (부경대학교 기계공학과) ;
  • 최일동 (한국해양대학교 조선기자재공학과) ;
  • 박영도 (동의대학교 신소재공학과)
  • Received : 2016.03.12
  • Accepted : 2016.04.04
  • Published : 2016.04.30
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Abstract

The use of materials for modern lightweight auto-bodies is becoming more complex than hitherto assemblies. The high strength materials nowadays frequently used for more specific fields such as the front and rear sub frames, seat belts and seats are mounted to the assembled body structure using bolt joints. It is desirable to use nuts attached to the assembled sheets by projection welding to decrease the number of loose parts which improves the quality. In this study, nut projection welding was carried out between a nut of both boron steel and carbon steel and ultra-high strength hot-stamped steel sheets. Then, the joints were characterized by optical and scanning electron microscope. The mechanical properties of the joints were evaluated by microhardness measurements and pullout tests. An indigenously designed sample fixture set-up was used for the pull-out tests to induce a tensile load in the weld. The fractography analysis revealed the dominant interfacial fracture between boron steel nut weld which is related to the shrinkage cavity and small size fusion zone. A non-interfacial fracture was observed in carbon steel nut weld, the lower hardness of HAZ caused the initiation of failure and allowed the pull-out failure which have higher in tensile strengths and superior weldability. Hence, the fracture load and failure mode characteristics can be considered as an indication of the weldability of materials in nut projection welding.

Keywords

References

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