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Effect of Carbon Equivalent and Cooling Rate on Microstructure in A516 Steels for Pressure Vessel

압력용기용 A516 강의 미세조직에 미치는 탄소 당량과 냉각 속도의 영향

  • Lee, Hyun Wook (School of Materials Science and Engineering, University of Ulsan) ;
  • Kang, Ui Gu (Technical Research Center, Hyundai Steel Company) ;
  • Kim, Min Soo (Technical Research Center, Hyundai Steel Company) ;
  • Shin, Sang Yong (School of Materials Science and Engineering, University of Ulsan)
  • Received : 2019.04.22
  • Accepted : 2019.08.13
  • Published : 2019.08.27

Abstract

In this study, the effect of carbon equivalent and cooling rate on microstructure and hardness of A516 steels for pressure vessel is investigated. Six kinds of specimens are fabricated by varying carbon equivalent and cooling rate, and their microstructures and hardness levels are analyzed. Specimens with low carbon equivalent consist of ferrite and pearlite. As the cooling rate increases, the size of pearlite decreases slightly. The specimens with high carbon equivalent and rapid cooling rates of 10 and $20^{\circ}C/s$ consist of not only ferrite and pearlite but also bainite structure, such as granular bainite, acicular ferrite, and bainite ferrite. As the cooling rate increases, the volume fractions of bainite structure increase and the effective grain size decreases. The effective grain sizes of granular bainite, acicular ferrite, and bainitic ferrite are ~20, ~5, and ${\sim}10{{\mu}m$, respectively. In the specimens with bainite structure, the volume fractions of acicular ferrite and bainitic ferrite, with small effective grains, increase as cooling rate increases, and so the hardness increases significantly.

Acknowledgement

Grant : The Competency Development Program for Industry Specialist

Supported by : Hyundai Steel Company, Korea Institute for Advancement of Technology(KIAT)

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