Si 및 Al 함량과 항온열처리조건이 초고강도 마르텐사이트-베이나이트 Fe-0.2C-2.0Mn 복합조직강의 미세조직과 인장특성에 미치는 영향

• Published in: 대한금속·재료학회지, 59(9) Vol. 59; no. 9; pp. 602 - 612
• Main Authors: 이응혁, Eung Hyuk Lee, 유창재, Chang Jae Yu, 이홍범, Hong-bum Lee, 김지훈, Ji-hoon Kim, 서동우, Dong-woo Suh
• Format: Journal Article
• Language: Korean
• Published: 대한금속재료학회 05.09.2021; 대한금속·재료학회
• Subjects: complex phase steels; hardening; isothermal heat treatment; martensite-bainite; transformation; 재료공학
• ISSN: 1738-8228; 2288-8241

This study investigated the influence of partial replacement of Si by Al on the microstructure and tensile properties of ultra-high strength steels with martensite-bainite complex microstructure produced by austenitization and subsequent isothermal heat treatment around M s temperature. When the isothermal heat treatment was done below the M s temperature, the fraction of martensite increased with the lower isothermal temperature, but the fractions of constituent phases in the final microstructure were not significantly affected by the partial replacement of Si by Al. Nevertheless, the increase in Al content in the complex phase steel accelerated the bainite transformation, which is thought to be associated with the increase of the free energy difference between FCC and BCC. The enhancement of the bainite transformation not only effectively suppressed the martensite formation upon final cooling when the isothermal temperature was above the M s temperature but also helped refine the final microstructure when subjected to isothermal heat treatment below the M s temperature. The yield strengths of the investigated complex phase steels were little influenced by the partial replacement of Si with Al, as long as the fractions of the constituent phases were comparable. This possibly originates with the solid solution hardening and the microstructure refinement with Al addition. (Received June 8, 2021; Accepted June 30, 2021)