Notched Creep Damage Assessment Based on EBSD Observation for Austenitic Stainless Steel

Abstract:

Creep damage processes for smooth and notched specimen of austenitic stainless steel through interrupted creep tests using multiple specimens. The material used was 18-8 stainless steel for boiler tube use. The mid-sections of interrupted creep test specimens were observed through SEM(Scanning Electron Microscope) instrumented with EBSD(Electron BackScatter Diffraction patter) equipment. IPF(Inverse Pole Figure) maps, Phase maps and GOS(Grain Orientation Spread) maps were used for investigating creep damage process. For smooth specimen, the relationship between macroscopic creep time fraction and GOS averaged for all pixels showed linearity, while the relationship between creep strain and the averaged GOS showed non-linearity regressed by Green function successfully. For notched specimen, the EBSD maps became noisy possibly due to extensive phase transformation under highly concentrated notch stress. Obtained GOS data for gamma phase only showed non-monotonic change with time and nominal strain. The evaluated local strains in the vicinity of the notch showed relatively small amount, which might cause the very long creep life compared with smooth specimen under the same nominal stress condition.

• Periodical: Materials Science Forum (Volume 941)
• Pages: 420-425
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.941.420
• Online since: December 2018
• Authors: Kazunari Fujiyama, Shuhei Higashide, Kazuki Nomoto
• Keywords: Austenitic Stainless Steel, Creep Damage, Creep Strain, Creep Void, EBSD, GOS, Notched Creep

References

[1] A. J. Schwartz, M. Kumar, B. L. Adams and D. P. Field (Eds.), Electron Backscatter Diffraction in Materials Science, second ed., Springer, New York, (2009).

[2] K. Fujiyama, H. Ueno, H. Hagiwara, S. Ogino, A. Ogawa and H. Kimachi, The EBSD investigation on the grain structure of Mod.9Cr steel for estimating damage and creep strain under creep and creep-fatigue conditions, HIDA-6 Conference, Nagasaki, Japan, ETD. LTD., (2013) CD-ROM.

DOI: 10.1299/jsmemm.2013._os1509-1_

[3] K. Fujiyama, H. Kimachi, T. Tsuboi, H. Hagiwara, S. Ogino and Y. Mizutani, Damage Assessment of Heat Resistant Steels through Electron BackScatter Diffraction Strain Analysis under Creep and Cree-Fatigue Conditions, J. Solid Mechanics and Materials Engineering, JSME, 6, 6 (2012) 530-544.

DOI: 10.1299/jmmp.6.530

[4] E. Ott, Cgaos in Dynamical Systems, second ed., Cambridge University Press, UK, (2002).