Korean Journal of Metals and Materials (대한금속재료학회지)

The Korean Institute of Metals and Materials (대한금속재료학회)
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Effect of Fine Copper Sulfides on the High Cycle Fatigue Properties of Bake Hardening Steels for Automotive

자동차용 소부경화형(BH) 강의 고주기 피로 특성에 미치는 미세 황화물의 영향

  • Kang, Seonggeu (Dept. of Materials Eng., Korea Maritime University) ;
  • Kim, Jinyong (Dept. of Materials Eng., Korea Maritime University) ;
  • Choi, Ildong (Dept. of Materials Eng., Korea Maritime University) ;
  • Lee, Sungbok (Surface Treatment Department, POSCO Kwangyang works) ;
  • Hong, Moonhi (Surface Treatment Department, POSCO Kwangyang works)
  • 강성규 (한국해양대학교 재료공학과) ;
  • 김진용 (한국해양대학교 재료공학과) ;
  • 최일동 (한국해양대학교 재료공학과) ;
  • 이승복 (POSCO 광양제철소 도금부) ;
  • 홍문희 (POSCO 광양제철소 도금부)
  • Received : 2010.07.14
  • Published : 2011.03.25
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Abstract

Bake hardening steels have to resist strain aging to prevent the yield strength increment and stretcher strain during press process and to enhance the bake hardenability during baking process after painting. The bake hardening steels need to control the solute carbon and the solute nitrogen to improve the bake hardenability. Ti and/or Nb alloying for nitride and carbide precipitation and low carbon content below 0.003% are used to solve strain aging and formability problem for automotive materials. However, in the present study, the effect of micro-precipitation of copper sulfide on the bake hardenability and fatigue properties of extremely low carbon steel has been investigated. The bake hardenability of Cu-alloyed bake hardening (Cu-BH) steel was slightly higher (5 MPa) than that of Nb-alloyed bake hardening (Nb-BH) steel, but the fatigue limit of Cu-BH steel was far higher (45 MPa) than that of Nb-BH steel. All samples showed the ductile fracture behavior and some samples revealed distinct fatigue stages, such as crack initiation, stable crack growth and unstable crack growth.

Keywords

Acknowledgement

Supported by : POSCO

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