Fatigue crack growth mechanism in aged 9Cr-1Mo steel: threshold and Paris regimes

Chaswal, Vibhor ; Sasikala, G. ; Ray, S. K. ; Mannan, S. L. ; Baldev Raj, (2005) Fatigue crack growth mechanism in aged 9Cr-1Mo steel: threshold and Paris regimes Materials Science and Engineering A, 395 (1-2). pp. 251-264. ISSN 0921-5093

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Official URL: http://linkinghub.elsevier.com/retrieve/pii/S09215...

Related URL: http://dx.doi.org/10.1016/j.msea.2004.12.026


Room temperature fatigue crack growth (FCG) testing was conducted after thermal aging for 500 and 5000 h at 823 K and for 500 h at 923 K, on 9%Cr-1%Mo steel normalized at 1323 K and tempered at 1053 K. Though crack growth behavior in Paris regime is not much affected by aging, stress intensity factor range for threshold (ΔKth) is found to increase monotonically. Acoustic emission signal analysis indicates identical crack propagation mechanisms in both threshold and Paris regimes. But SEM fractography reveals micro-voiding in the Paris regime only. Also, theoretical analysis of plastic zone size and inter-particle spacing (λm) predicts microcleavage in the threshold regime. This indicates FCG occurs as a two-step mechanism, but each regime has a different dominant step viz. initial micro-void nucleation and growth at precipitates, followed by eventual micro-cleavage of inter-particle ligaments. Aging induces solid solution dilution, precipitate coarsening and increases λm. In threshold regime, due to a tougher matrix, and a smaller cyclic crack increment (δaN) than λm, an increase in ΔKth values is observed. Conversely, Paris regime δaN is greater than λm, making it rather insensitive to aging.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Fatigue Crack Growth; Threshold Stress Intensity Factor; Transgranular Quasicleavage; Acoustic Emission; Aged 9Cr-1Mo Steel
ID Code:40365
Deposited On:24 May 2011 04:23
Last Modified:24 May 2011 04:23

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