In this study, effects of carbon and nickel on microstructure and low temperature Charpy impact properties of HSLA (high strength low alloy) steels are investigated. To understand the complex phase transformation behavior of HSLA steels with high strength and toughness before and after welding processes, three kinds of HSLA steels are fabricated by varying the carbon and nickel content. Microstructure analysis, low temperature Charpy impact test, and Vickers hardness test are performed for the base metals and CGHAZ (coarse-grain heat affected zone) specimens. The specimens with the lowest carbon and nickel content have the highest volume fraction of AF, the lowest volume fraction of GB, and the smallest GB packet size. So, the low temperature Charpy absorbed energy of the CGHAZ specimen is the highest. The specimens with increased carbon and nickel content have the lowest volume fraction of AF, the highest volume fraction of GB, and the largest GB packet size. So, the low temperature Charpy absorbed energy of the CGHAZ specimen is the lowest.

Abstract
1. 서 론
2. 실험 방법
    2.1 강재 제조
    2.2 CGHAZ 모사 시험
    2.3 미세조직 분석 및 기계적 특성 평가
3. 실험 결과
    3.1 모재 미세조직 분석 및 비커스 경도
    3.2 CGHAZ 미세조직 분석 및 비커스 경도
    3.3 CGHAZ 샤르피 충격 특성 및 파면 분석
4. 고 찰
    4.1 미세조직 형성에 미치는 탄소의 영향
    4.2 미세조직 형성에 미치는 니켈의 영향
    4.3 기계적 특성에 미치는 CGHAZ 미세조직의 영향
5. 결 론
References

• 엄해원(울산대학교 중공업융합기술공학과) | Haewon Eom (Department of Convergence Technology for Heavy Industries, University of Ulsan)
• 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 중공업융합기술공학과/울산대학교 첨단소재공학부) | Sang Yong Shin (Department of Convergence Technology for Heavy Industries, University of Ulsan/School of Materials Science and Engineering, University of Ulsan) Corresponding author