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

概要

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In order to predict creep behavior of a Mod.9Cr-1Mo steel, an equation for logarithmic creep giving below has been exploited to describe pronounced primary creep. ε=(1/Ω^*)ln(Ω^*ε^^.^*_0t+1), where ε^^.^*_0 is the initial strain rate and Ω^* is the gradient between logarthm 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^^.=1nε^^.^*_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^*>/(Ωε^^._0), where t^* is given below : t^*=(e^<Ω^*ε^*>-1)/(Ω^*ε^^.^*_0). Since relatively good correlations were seen between ε^^.^*_0 and ε^^._0 and between Ω^* and Ω as below, the total creep life under a given condition can be described as a function of Ω and ε^^._0. ε^^.^*_0=0.138・ε^^.^<0.725>_0, and Ω^*/Ω=A_<Ω^*/Ω>・σ_0^<-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, 2.82×10^3/s, 2.0±0.1 and 21±1 kJ/mol. Furthermore, since there is a correlationship between Ω and ε^^._0, creep life t_r can be expressed by a single parameter out of four parameters, ε^^.^*_0, ε^^._0, Ω^* and Ω.
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