Journal of the Korean Society for Heat Treatment (열처리공학회지)

The Korean Society for Heat Treatment (한국열처리공학회)
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Microstructures and Hardness Distributions of a Large-sized High Strength H-sectional Steel with Both V and Nb

V, Nb 첨가 고강도 대형 H 형강의 부위별 미세조직과 경도 분포

  • Ha, Yangsoo (Department of Materials Science and Engineering, Yonsei University) ;
  • Jung, Jae-Gil (Department of Materials Science and Engineering, Yonsei University) ;
  • Lee, Young-Kook (Department of Materials Science and Engineering, Yonsei University)
  • 하양수 (연세대학교 공과대학 신소재공학과) ;
  • 정재길 (연세대학교 공과대학 신소재공학과) ;
  • 이영국 (연세대학교 공과대학 신소재공학과)
  • Received : 2013.01.03
  • Accepted : 2013.03.08
  • Published : 2013.03.30
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Abstract

The microstructures and hardness distributions of a large-sized high strength H-sectional steel with both V and Nb were systematically examined. The outer surface of the flange part was composed of martensite and bainite due to faster cooling, and had a high hardness value of approximately 310 Hv. However, the amounts of ferrite and pearlite increased and the hardness decreased with increasing the distance from the outer surface at the flange part, except the inner surface. High hardness value of about 290 Hv was measured at the upper surface of the web part having martensite and bainite. The hardness drastically decreased with increasing the web thickness, and then greatly rose again at the lower surface due to bainite formation caused by fast air cooling. The hardness of the flange part was higher than that of the web part due to the larger amount of low-temperature transformed phases, except for the lower surface of the web part. Nb-rich precipitates of 30 to 50 nm and V-rich precipitates less than 20 nm were observed at both flange and web parts. However, the particle size was smaller at the flange part than the web part, resulting in the higher strength of the flange part.

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References

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