Journal of Welding and Joining

The Korean Welding and Joining Society (대한용접접합학회)
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Microstructural Characteristics of 800 MPa Grade High Strength Steel Weld Metals

800 MPa급 고강도강 용접금속의 미세조직 특성 비교 연구

  • 이재희 (한양대학교 신소재공학부) ;
  • 김상훈 (한양대학교 신소재공학부) ;
  • 윤병현 (포항산업과학기술연구원) ;
  • 김환태 (한국과학기술정보연구원) ;
  • 길상철 (한국과학기술정보연구원) ;
  • 이창희 (한양대학교 신소재공학부)
  • Received : 2010.04.30
  • Accepted : 2010.11.17
  • Published : 2011.02.28
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Abstract

Microstructural characteristics of two high strength (600 MPa & 800 MPa) weld metals produced by flux-cored arc welding process (FCAW) were evaluated. The 600 MPa grade weld metal was consisted of 75% acicular ferrite and 25% ferrite which was formed at relatively high temperature (grain boundary ferrite, widmanstatten ferrite, polygonal ferrite). However, the 800 MPa grade weld metal was composed of about 85% acicular ferrite and 15% low temperature forming phases (bainite, martensite). The prior austenite grain size of 800 MPa grade weld metal was decreased by solute drag force. The compositions and sizes of inclusions which are the dominant factors for the formation of acicular ferrite were analyzed by a transmission electron microscopy (TEM). In both 600 MPa and 800MPa grade weld metals, the inclusions were mainly consisted of Ti-oxide and Mn-oxide, and the average size of inclusions was $0.7{\mu}m$. The 800 MPa grade weld metal exhibited higher tensile strength and similar toughness compared with the 600 MPa grade weld metal. This result is mainly due to a higher fraction of low temperature products and a lower fraction of grain boundary ferrite in the 800 MPa grade weld metal.

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References

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