改良9Cr-1Mo鋼のクリープ挙動を推定するためのΩ法の改良

抄録

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 t_r can be expressed by the following equation:
t_r=t^*+e^-Ωε*/(Ωε₀),
where t^* is given below:
t^*=(e^Ω_*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·ε^0.725₀,
and
Ω^* /Ω=A_{Ω^* Ω}·σ₀^-n_Ω*Ω·exp(Q_{Ω^* Ω}/RT),
where A_{Ω^* Ω} is temperature and stress independent constant, n_Ω^*/Ω is the stress exponent of Ω^*/Ω, and Q_Ω^*/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 t_r can be expressed by a single parameter out of four parameters, ε^*₀, ε₀, Ω^* and Ω.