Creep Strength Assessment of High Chromium Ferritic Creep Resistant Steels

Abstract:

Degradation mechanism and life prediction method of high chromium ferritic creep resistant steels have been investigated. In the high stress condition, easy and rapid extension of recovered soft region results in significant decrease in creep strength, however, ductility is high. In the low stress condition, extension of recovered soft region is mainly controlled by diffusion and it is slow, therefore, deformation is concentrated in the recovered soft region along grain boundaries and ductility is extremely low. Delta-ferrite produces concentration gap due to difference in equilibrium composition of austenite and ferrite phases at the normalizing temperature. It increases driving force of diffusion and promotes recovery of tempered martensite adjacent to delta-ferrite. Concentration gap may be produced also in heat affected zone (HAZ), especially in fine grain HAZ similar to dual phase steel, and it has possibilities to promote recovery and, therefore, to decrease creep strength. It has been confirmed the advantage of region splitting analysis of creep rupture strength for high chromium ferritic creep resistant steels, through a residual error analysis. It is important to avoid a generation of concentration gap in order to improve stability of microstructure and to maintain high creep strength.

• Periodical: Materials Science Forum (Volumes 539-543)
• Pages: 3112-3117
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.539-543.3112
• Online since: March 2007
• Authors: Kazuhiro Kimura, Kota Sawada, Yoshiaki Toda, Hideaki Kushima
• Keywords: Creep Strength Enhanced Ferritic Steel, Degradation, Long-Term Creep, Region Splitting

References

[1] V. Foldyna, Z. Kuboň, A. Jakobová and V. Vodárek, Development of Advanced High Chromium Ferritic Steels, Microstructural Development and Stability in High Chromium Ferritic Power Plant Steels, A. Strang and D. J. Gooch eds., The Institute of Materials, (1997).

DOI: 10.1007/978-94-011-1048-8_37

[2] A. Strang and V. Vodarek, Microstructural Stability of Creep Resistant Martensitic 12%Cr Steels, Microstructural Stability of Creep Resistant Alloys for High Temperature Plant Applications, The Institute of Materials, London, (1998), 117-133.

[3] K. Kimura, H. Kushima and F. Abe, Heterogeneous Changes in Microstructure and Degradation Behaviour of 9Cr-1Mo-V-Nb Steel During Long Term Creep, Key Engineering Materials, 171-174(2000), 483-490.

DOI: 10.4028/www.scientific.net/kem.171-174.483

[4] K. Kimura, H. Kushima and F. Abe, Degradation and Assessment of Long-term Creep Strength of High Cr Ferritic Creep Resistant Steels, Proc. Int. Conf. Advances in Life Assessment and Optimization of Fossil Power Plants, Orland, Florida, USA, Mar. 11-13, (2002).

DOI: 10.1115/pvp2005-71039

[5] K. Kimura, K. Sawada, K. Kubo and H. Kushima, Influence of Stress on Degradation and Life Prediction of High Strength Ferritic Steels, PVP-Vol. 476(2004), 11-18.

DOI: 10.1115/pvp2004-2566

[6] K. Kimura, Assessment of Long-term Creep Strength and Review of Allowable Stress of High Cr Ferritic Creep Resistant Steels, PVP2005-71039(2005).

DOI: 10.1115/pvp2005-71039

[7] NIMS Creep Data Sheet, National Institute for Materials Science, No. 51, (2006).

[8] NIMS Creep Data Sheet, National Institute for Materials Science, No. 52, (2006).

[9] NIMS Creep Data Sheet, National Institute for Materials Science, No. 43, (1996).

[10] B. Sundman, B. Jansson and J-O. Andersson, Calphad, 9(1985), 153.

[11] M. Tabuchi, M. Matsui, T. Watanabe, H. Hongo, K. Kubo and F. Abe, Creep Fracture Analysis of W Strengthened High Cr Steel Weldment, Mat. Sci. Res. Int., 9(2003), 23-28.

DOI: 10.2472/jsms.52.3appendix_23