Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Effects of Coiling Temperature and Carbides Behavior on Stretch-flangeability for 980MPa Hot-rolled Steels

980 MPa급 열연강의 권취온도와 탄화물 거동에 따른 신장플랜지성

  • Chun, Eun-Joon (Department of Materials Science and Engineering, Pusan National University) ;
  • Lee, Ju-Seung (Department of Materials Science and Engineering, Pusan National University) ;
  • Do, Hyeonghyeop (Technical Research Center, Hyundai Steel Company) ;
  • Kim, Seong-Ju (Technical Research Center, Hyundai Steel Company) ;
  • Choi, Yoon-Suk (Materials and Processing Division, UES, Inc.) ;
  • Park, Yong-Ho (Department of Materials Science and Engineering, Pusan National University) ;
  • Kang, Namhyun (Department of Materials Science and Engineering, Pusan National University)
  • Received : 2012.03.09
  • Published : 2012.07.25
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Abstract

To analyze the factors on stretch-flangeability for 980 MPa-grade hot-rolled steels, two types of steels (Fe-Cr and Fe-Mo) were manufactured by hot-rolling. Manufactured steels at the low coiling temperature, such as 400 and $500^{\circ}C$, had poor stretch-flangeability due to un-uniformly distributed carbides and a large deviation of interphase hardness. However, when the coiling temperature was set at $650^{\circ}C$ with Fe-Cr steel, 998 MPa of ultimate tensile strength, 19% of total elongation and 65% of the hole expanding ratio were achieved by microstructural constituents of polygonal ferrite (PF) and granular ferrite (GF) dispersed with fine carbides (<50 nm). Therefore, the material to attain 980 MPa with superior formability was the Fe-Cr steel that was precipitation-hardened in polygonal ferrite and granular ferrite at the coiling temperature $650^{\circ}C$.

Keywords

Acknowledgement

Supported by : 지식경제부

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