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Korean Journal of Metals and Materials > Volume 55(12); 2017 > Article
Korean Journal of Metals and Materials 2017;55(12): 825-835. doi: https://doi.org/10.3365/KJMM.2017.55.12.825
Fe-Mn-Al-C계 경량철강의 미세조직 및 기계적 물성 변화에 미치는 냉각속도의 영향
박준영1, 박성준1, 이재현1, 문준오1, 이태호1, 정경재2, 한흥남2, 신종호3
1재료연구소 철강재료연구실
2서울대학교 재료공학부
3두산중공업 주단기술고도화팀
Effect of Cooling Rate on the Microstructure and Mechanical Properties of Fe-Mn-Al-C Light-Weight Steels
Jun Young Park1, Seong-Jun Park1, Jae-Hyun Lee1, Joonoh Moon1, Tae-Ho Lee1, Kyeong Jae Jeong2, Heung Nam Han2, Jong-Ho Shin3
1Ferrous Alloy Department, Korea Institute of Materials Science, Changwon 51508, Republic of Korea
2Department of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National
3Casting & Forging Technology Development Team, Doosan Heavy Industries & Construction, Changwon 51711,
Correspondence  Seong-Jun Park ,Tel: +82-55-280-3341, Email: hyega@kims.re.kr
Received: 1 September 2017;  Accepted: 20 September 2017.  Published online: 4 December 2017.
ABSTRACT
The effects of cooling after solution heat treatment on the microstructure and mechanical properties of light-weight steels were investigated using Fe-30Mn-xAl-0.9C alloys containing 9.0–12.8 wt% Al. Lab-scale specimens (thickness: 10 mm) of the alloys were cooled by different cooling rates from -337 to -0.053 ℃/s using water, air, and furnace cooling. As the cooling rate decreased, hardness of the alloys increased due to precipitation of κ-carbides. However, reduction of the cooling rate induced the growth of intergranular κ-carbides. This resulted in the decrease of impact absorbed energy of the alloys at room temperature, and exhibited intergranular brittle fracture behavior. The 12.8 wt% Al alloy cooled at the slowest cooling rate in particular showed the formation of β-Mn. To estimate the cooling rates of large-scale slabs of light-weight steels, finite element simulations were conducted. The cooling rates at the center of the slab under air and water cooling (free convection) were calculated to be -0.049 and -0.15 ℃/s, respectively. The results indicated that water cooling could prevent the excessive formation of κ-carbides/β-Mn during fabrication of large-scale slabs of alloys containing an Al content lower than 10.5 wt%.
Keywords: light-weight steel, microstructure, cooling rate, κ-carbide, β-Mn
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