오스테나이트계 경량철강의 냉각 조건에 따른 미세조직, 기계적 특성 이해 및 대형 슬라브 내부 특성 분포 예측 연구

• Published in: 대한금속·재료학회지, 58(12) Vol. 58; no. 12; pp. 830 - 842
• Main Authors: 김태하, Tae-ha Kim, 최윤석, Yoon Suk Choi, 김경원, Kyeong-won Kim, 박성준, Seong-jun Park, 박준영, Jun Young Park, 정경재, Kyeongjae Jeong, 한흥남, Heung Nam Han, 신종호, Jong-ho Shin
• Format: Journal Article
• Language: Korean
• Published: 대한금속재료학회 05.12.2020; 대한금속·재료학회
• Subjects: cooling rate; finite element analysis; light-weight steel; mechanical properties; κ-carbide; 재료공학
• ISSN: 1738-8228; 2288-8241

The effects of the cooling rate, after solution heat treatment, on the microstructures and mechanical properties of Fe-22Mn-8Al-0.8C-0.02Nb (low carbon) and Fe-20Mn-8Al-1.1C-0.1Nb (high carbon) light-weight steels were systematically investigated. The cooling process was controlled to achieve six different cooling rates, ranging from -0.016 to -465.1 ℃/s. Under the slowest cooling rate (furnace cooling), intra-granular and inter-granular precipitations of κ-carbides were observed throughout the austenite grains. The higher the C content was, the larger the size of the inter-granular κ-carbides was. The formation of κ-carbides resulted in an increase in yield strength, and a decrease in elongation and impact absorbed energy. In the Fe-20Mn-8Al- 1.1C-0.1Nb, the inter-granular precipitation of κ-carbides caused a drastic decrease in the impact absorbed energy and the inter-granular brittle fracture. To predict the distribution of yield strength and impact absorbed energy at production scale (a 10-ton scale slab), finite element analysis was conducted for water cooling and air cooling conditions. The average cooling rates at the center of the slab under water cooling and air cooling were predicted to be -0.126 and -0.031 ℃/s, respectively. Based on predicted cooling rates, the distribution of mechanical properties was determined. The prediction suggested that a large-scale slab of the light-weight steel with low C content would have good toughness at the center of the slab regardless of cooling condition. (Received November 2, 2020; Accepted November 23, 2020)