In this study, two types of thick steel plates are prepared by controlling carbon equivalent and nickel content, and their microstructures are analyzed. Tensile tests, Vickers hardness tests, and Charpy impact tests are conducted to investigate the correlation between microstructure and mechanical properties of the steels. The H steel, which has high carbon equivalent and nickel content, has lower volume fraction of granular bainite (GB) and smaller GB packet size than those of L steel, which has low carbon equivalent and nickel content. However, the volume fraction of secondary phases is higher in the H steel than in the L steel. As a result, the strength of the L steel is higher than that of the H steel, while the Charpy absorbed energy at -40 °C is higher than that of the L steel. The heat affected zone (HAZ) simulated H-H specimen has higher volume fraction of acicular ferrite (AF) and lower volume fraction of GB than the HAZ simulated L-H specimen. In addition, the grain size of AF and the packet sizes of GB and BF are smaller in the H-H specimen than in the L-H specimen. For this reason, the Charpy absorbed energy at -20 °C is higher for the H-H specimen than for the L-H specimen.

Abstract
1. 서 론
2. 실험 방법
    2.1 시편 제조
    2.2 미세조직 분석 및 기계적 특성 평가
3. 결과 및 고찰
    3.1 모재의 미세조직과 기계적 특성
    3.2 HAZ의 미세조직과 기계적 특성
4. 결 론
References

• 박지원(울산대학교 첨단소재공학부)
• 조성규(현대제철 R&D Center) | Sung Kyu Cho (Technical Research Center, Hyundai Steel Company)
• 조영욱(현대제철 R&D Center) | Young Wook Cho (Technical Research Center, Hyundai Steel Company)
• 신건철(울산대학교 첨단소재공학부) | Gunchul Shin (School of Materials Science and Engineering, University of Ulsan)
• 권용재(울산대학교 첨단소재공학부) | Yongjai Kwon (School of Materials Science and Engineering, University of Ulsan)
• 이정구(울산대학교 첨단소재공학부) | Jung Gu Lee (School of Materials Science and Engineering, University of Ulsan)
• 신상용(울산대학교 첨단소재공학부) | Sang Yong Shin (School of Materials Science and Engineering, University of Ulsan) Corresponding author