Direct water quenching technique can be used in hot stamping process to obtain higher cooling rate compared to that of the normal die cooling method. In the direct water quenching process, setting proper water flow rate in consideration of material thickness and the size of the area directly cooled in the component is important to ensure uniform microstructure and mechanical properties. In this study, to derive proper water flow rate conditions that can achieve uniform microstructure and mechanical properties, microstructure and hardness distribution in various water flow rate conditions are measured for 3.2 mm thick boron steel sheet. Hardness distribution is uniform under the flow condition of 1.5 L/min or higher. However, due to the lower cooling rate in that area, the lower flow conditions result in a drastic decrease in hardness in some areas in the hot-stamped part, resulting in low martensite fraction. From these results, it is found that the selection of proper water flow rate is an important factor in hot stamping with direct water quenching process to ensure uniform mechanical properties.

Abstract
1.서 론
2. 실험방법
    2.1 직수분사 핫스탬핑 성형 시험
    2.2 냉각속도 측정
    2.3 미세조직 관찰 및 경도 측정
3. 결과 및 고찰
    3.1 유량 조건에 따른 냉각속도
    3.2 유량 조건에 따른 경도분포
    3.3 유량 조건에 따른 미세조직
    3.4 냉각속도 및 조직 분율 예측 결과
4.결 론
Acknowledgements
References

• 박현태(한국생산기술연구원 탄소소재응용연구그룹, 전북대학교 기계설계공학과) | Hyeon Tae Park (Carbon & Light Materials Application R&D Group, Department of Mechanical Design Engineering)
• 권의표(한국생산기술연구원 탄소소재응용연구그룹) | Eui Pyo Kwon (Carbon & Light Materials Application R&D Group) Corresponding author
• 임익태(전북대학교 기계설계공학과) | Ik Tae Im (Department of Mechanical Design Engineering, Jeon-buk National University)