Tetsu-to-Hagane
Online ISSN : 1883-2954
Print ISSN : 0021-1575
Improvement of Ω Method to Estimate Creep Behavior of a Mod.9Cr-1Mo Steel
Kyu Seop PARKFujimitsu MASUYAMATakao ENDO
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1999 Volume 85 Issue 6 Pages 492-499

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Abstract

In order to predict creep behavior of a Mod.9Cr-1 Mo steel, an equation for logarithmic creep giving below has been exploited to describe pronounced primary creep.
ε=(1/Ω*)ln(Ω*ε*0t+1),
whereε*0 is the initial strain rate and Ω*is the gradient between logarithm of strain rate and true strain in a primary creep stage. Differentiation of the above equation with respect to time yields the following equation:
ε=lnε*0-Ω*ε.
Designating a primary creep duration by t*, creep life tr can be expressed by the following equation:
tr=t*+e-Ωε*/(Ωε0),
where t* is given below:
t*=(eΩ*ε*-1)/(Ω*ε*0).
Since relatively good correlations were seen between ε*0 and ε0 and between Ω*and Ω as below, the total creep life under a given condition can be described as a function of Ω and ε0.
ε*0=0.138·ε0.7250,
and
Ω* /Ω=AΩ* Ω·σ0-nΩ*Ω·exp(QΩ* Ω/RT),
where AΩ* Ω is temperature and stress independent constant, nΩ*/Ω is the stress exponent of Ω*/Ω, and QΩ*/Ω is the temperature-dependent parameter of Ω*/Ω. They are, respectively, 2.82×103/S, 2.0±0.1 and 21±1kJ/mol. Furthermore, since there is a correlationship between Ω and ε0, creep life tr can be expressed by a single parameter out of four parameters, ε*0, ε0, Ω* and Ω.

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© The Iron and Steel Institute of Japan
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