Transactions of the Korean Society of Mechanical Engineers A (대한기계학회논문집A)

The Korean Society of Mechanical Engineers (대한기계학회)
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Environmental Fatigue Behaviors of CF8M Stainless Steel in 310℃ Deoxygenated Water - Effects of Hydrogen and Microstructure

산소가 제거된 310℃ 순수환경에서 CF8M 주조 스테인리스강의 환경 피로거동 - 수소 및 미세구조의 영향

  • 장훈 (카이스트 원자력 및 양자공학과) ;
  • 조평연 (카이스트 원자력 및 양자공학과) ;
  • 장창희 (카이스트 원자력 및 양자공학과) ;
  • 김태순 (한국수력원자력 (주) 중앙연구원)
  • Received : 2013.04.27
  • Accepted : 2013.10.20
  • Published : 2014.01.01
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Abstract

The effects of environment and microstructure on low cycle fatigue (LCF) behaviors of CF8M stainless steels containing 11% of ferrites were investigated in a $310^{\circ}C$ deoxygenated water environment. The reduction of LCF life of CF8M in a $310^{\circ}C$ deoxygenated water was smaller than 316LN stainless steels. Based on the microstructure and fatigue surface analyses, it was confirmed that the hydrogen induced cracking contributed to the reduction in LCF life for CF8M as well as for 316LN. However, many secondary cracks were found on the boundaries of ferrite phases in CF8M, which effectively reduced the stress concentration at the crack tip. Because of the reduced stress concentration, the accelerated fatigue crack growth by hydrogen induced cracking was less significant, which resulted in the smaller environmental effects for CF8M than 316LN in a $310^{\circ}C$ deoxygenated water.

CF8M (11% ferrite) 주조 스테인리스강의 $310^{\circ}C$ 순수환경에서의 저주기피로 수명에 미치는 수소 및 미세구조의 영향을 분석하였다. CF8M 의 경우, 공기환경 대비 $310^{\circ}C$ 순수환경에서의 피로수명의 감소는 단조재인 316LN 에 비해 다소 작았다. 미세구조 및 파면 분석을 통해, CF8M 의 저주기피로 수명의 감소는 316LN 의 경우와 마찬가지로 수소유기균열에 의한 것으로 판단되었다. 그러나, CF8M 의 경우, 페라이트상 경계에 수소유기균열에 의한 2 차 균열이 빈번히 발생함에 따라 균열 선단에서의 응력집중이 저하되는 효과가 있었다. 이러한 응력집중의 완화로 인해 수소유기균열에 의한 피로균열진전이 둔화되어 결과적으로 저주기피로 수명의 저하가 완화되는 것으로 판단되었다.

Keywords

References

  1. Chopra, O. K. and Shack, W. J., 2006, Effect of LWR Coolant Environments on the Fatigue Life of Reactor Materials, NUREG/CR-6909, Argon National Laboratory.
  2. Higuchi, M., Sakaguchi, K., Nomura, Y. and Hirano, A., 2007, "Final Proposal of Environmental Fatigue Life Correction Factor ($F_{en}$) for Structural Materials in LWR Water Environment," Proc. of Pressure Vessel & Piping, ASME, Texas, USA, PVP2007-26100.
  3. Cho, H., Kim, B. K., Kim, I. S., Jang, C. and Jung, D. Y., 2007, "Fatigue Life and Crack Growth Mechanisms of the Type 316LN Austenitic Stainless Steel in $310^{\circ}C$ Deoxygenated Water," J. of Nucl. Sci. & Technol., Vol. 44, pp. 1007-1014. https://doi.org/10.1080/18811248.2007.9711340
  4. Cho, H., Kim, B. K., Kim, I. S. and Jang, C., 2008, "Low Cycle Fatigue Behaviors of Type 316LN Austenitic Stainless Steel in $310^{\circ}C$ Deaerated Water - Fatigue Life and Dislocation Structure Development," Mater. Sci. & Eng. A, Vol. 476, pp. 248-256. https://doi.org/10.1016/j.msea.2007.07.023
  5. Chopra, O. K. and Shack, W. J., 2002, Mechanism and Estimation of Fatigue Crack Initiation in Austenitic Stainless Steels in LWR Environments, NUREG/CR-6787, Argon National Laboratory.
  6. Jang, C., Cho, P. Y., Kim, M. Oh, S. J. and Yang, J. S., 2010, "Effects of Microstructure and Residual Stress on Fatigue Crack Growth of Stainless Steel Narrow Gap Welds," Mater. & Des., Vol. 31, pp. 1862-1870. https://doi.org/10.1016/j.matdes.2009.10.062
  7. Stolarz, J. and Foct, J., 2001, "Specific Features of Two Phase Alloys Response to Cyclic Deformation," Mater. Sci. & Eng. A, Vol. 319, pp. 501-505.
  8. Zhao, Y. X., Gao, Q. and Wang, J. N., 1999, "Microstructural Effects on the Short Crack Behavior of a Stainless Steel Weld Metal during Low-Cycle Fatigue," Fatigue, Fracture of Eng. Mater. & Struct., Vol. 22, pp. 469-480. https://doi.org/10.1046/j.1460-2695.1999.00196.x
  9. Rho, B. S., Hong, H. U. and Nam, S. W., 2000, "The Effect of ${\delta}$-Ferrite on Fatigue Cracks in 304L Steels," Int. J. of Fatigue, Vol. 22, pp. 683-690. https://doi.org/10.1016/S0142-1123(00)00043-8
  10. Mediratta, S. R., Ramaswamy, V. and Rama Rao, P., 1985, "Influence of Ferrite-Martensite Microstructural Morphology on the Low Cycle Fatigue of a Dual-Phase Steel," Int. J. of Fatigue, Vol. 7, pp. 107-115. https://doi.org/10.1016/0142-1123(85)90041-6
  11. Jang, H., Kim, J. H., Jang, C., Lee, J. G. and Kim, T. S., 2013, "Low-cycle Fatigue Behaviors of Two heats of SA508 Gr.1a Low Alloy Steel in $310^{\circ}C$ air and Deoxygenated Water - Effects of Dynamic Strain Aging and Microstructure," Submitted to Mater. Sci. & Eng. A.
  12. Cho, H., Kim, B. K., Kim, I. S., Oh, S. J., Jung, D. Y. and Byeon, S. C., 2005, "Environmental Fatigue Testing of Type 316 Stainless Steel in $310^{\circ}C$ Water," Proc. of Pressure Vessel & Piping, ASME Colorado, USA, PVP2005-71493.
  13. Higuchi, M., Tsutsumi, K., Hirano, A. and Sakaguchi, K., 2003, "A Proposal of Fatigue Life Correction Factor $F_{en}$ for Austenitic Stainless Steels in LWR Water Environments," J. of Pressure Vessel & Piping, Vol. 125, pp. 403-410. https://doi.org/10.1115/1.1613945
  14. Tsutsumi, K., Kanasaki, H., Umakoshi, T., Nakamura, T., Urata, S., Mizuta, H. and Nomoto, S., 2000, "Fatigue Life Reduction in PWR Water Environment for Stainless Steels," Proc. of Pressure Vessel & Piping, New York, USA, Vol. 410-2, pp. 23-34
  15. Chopra, O. K. and Shack, W. J., 2001, Environmental Effects on Fatigue Crack Initiation in Piping and Pressure Vessel Steels, NUREG/CR-6717, Argon National Laboratory.
  16. Jang, H., Cho, H., Jang, C., Kim, T. S. and Moon, C. K., 2008, "Effect of Cyclic Strain Rate and Sulfides on Environmentally Assisted Cracking Behaviors of SA508 Gr.1a Low Alloy Steel in Deoxygenated Water at $310^{\circ}C$," Nucl. Eng. Technol., Vol. 40, pp. 225-232. https://doi.org/10.5516/NET.2008.40.3.225
  17. Lynch, S. P., 2003, Mechanisms of Hydrogen Assisted Cracking - A Review, The Minerals, Metals & Materials Society (TMS), Warrendale, Pennsylvania, pp. 449-466.
  18. Murakami, Y. and Matsuoka, S, 2010, "Effect of Hydrogen on Fatigue Crack Growth of Metals," Eng. Fracture Mech., Vol. 77, pp. 1926-1940. https://doi.org/10.1016/j.engfracmech.2010.04.012
  19. Gerland, M., Alain, R., Ait Saadi, B. and Mendez, J., 1997, "Low Cycle Fatigue Behavior in Vaccum of a 316L-Type Austenitic Stainless Steel Between 20 and $600^{\circ}C$ - Part II: Dislocation Structure Evolution and Correlation with Cyclic Behavior," Mater. Sci. & Eng. A, Vol. 229, pp. 68-86. https://doi.org/10.1016/S0921-5093(96)10560-8
  20. Mannan, S. L., 1993, "Role of Dynamic Strain Ageing in Low Cycle Fatigue," Bull. Mater. Sci., Vol. 16, No. 6, pp. 561-582. https://doi.org/10.1007/BF02757656
  21. Robertson, I. M., 1999, "The Effect of Hydrogen on Dislocation Dynamics," Eng. Fracture Mech., Vol. 64, pp. 649-673. https://doi.org/10.1016/S0013-7944(99)00094-6
  22. Hong, S. G., Lee, K. O. and Lee, S. B., 2005, "Dynamic Strain Aging Effect on the Fatigue Resistance of Type 316L Stainless Steel," Int. J. of Fatigue, Vol. 27, pp. 1420-1424. https://doi.org/10.1016/j.ijfatigue.2005.06.037