実機で長時間使用された 2.25Cr-1Mo 鋼のクリープ挙動解析

概要

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For the remaining creep life assessment, it is essential to evaluate the degree of structural degradation. In the present study, accelerated creep tests have been employed to assess the degree of structural deterioration of a 2.25 Cr-1Mo steel which was service-exposed for 11 years as a power plant component. The experimental results showed that strain rate over a wide rage of strain is expressed by the equation ; ln ε=ln ε_o+Sε, where ε_o is the imaginary initial creep rate and S is the strain rate acceleration factor. The magnitudes of ε_o and S are given by the following equations ; ε_o=A_oσ_o^nexp(-Q_o/RT). and S=A_sσ_o^<-n_s>exp(Q_s/RT), where A_o is the mechanically defined structure factor, σ_o is the initial stress, n is the stress exponent (9.5), Q_o is the activation energy (429 kJ/mol), Q_s is 24kJ/mol, A_s is a constant, and n_s is 0.98. Comparing these results with those of prestrained materials, it was found that the magnitudes of A_o, A_s and n_s are dependent upon the structural deterioration while those of n, Q_o and Q_s are independent of thermo-mechanical history. This means that the rate controlling mechanism is independent of structural deterioration. These historydependent parameters allow us the quantitative assessment of the structural deterioration of service-exposed materials.
1995-08-01