Characteristics of Precipitation Hardened Extra Low Carbon Steels

석출강화형 극저탄소강의 특성에 대한 고찰

  • Yoon, Jeong-Bong (Sheet products & process research group, Technical research Laboratories, POSCO) ;
  • Kim, Sung-il (Automotive steel product research group, Technical research Laboratories, POSCO) ;
  • Kim, In-Bae (School of Material science & Engineering, Pusan University)
  • 윤정봉 (포스코 기술연구소 박판연구그룹) ;
  • 김성일 (포스코 기술연구소 자동차소재그룹) ;
  • 김인배 (부산대학교 재료공학부)
  • Received : 2008.06.23
  • Published : 2008.10.25

Abstract

Conventional bake-hardenable(BH) steels should be annealed at higher temperatures because of the addition of Ti or/and Nb which forms carbides and raises recrystallization start temperature. In this study, the development of new BH steels without Ti or Nb addition has been reviewed. The new BH steels have nearly same mechanical properties as the conventional BH steels even though it is annealed at lower temperature. The steels also show smaller deviation of the mechanical properties than that of the conventional BH steels because of the conarol of solute carbon content during steel making processes. The deviation of mechanical properties in conventional BH steels is directly dependent on the deviation of solute carbon which is greatly influenced by the amount of the carbide formers in conventional BH steels. Less alloy addition in the newly developed BH steels gives economical benefits. By taking the advantage of sulfur and/or nitrogen which scarenge in Interstitial-Free or conventional BH steels, fine manganese sulfides or nano size copper sulfides were designed to precipitate, and result in refined ferrite grains. Aluminum nitrides used as a precipitation hardening element in the developed steels were also and resull in fine and well dispersed. As a result, the developed steels with less production cost and reduced deviation of mechanical properties are under commercial production. Note that the developed BH steels are registered as a brand name of MAFE(R) and/or MAF-E(R).

Keywords

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