CREEP-BEHAVIOR ANALYSIS OF A SERVICE-EXPO SED 2.25CR-1MO STEEL

For the remaining creep life assessment, it is essential to evaluate t he degree of structural degradation. In the present study, accelerated creep tests have been employed to assess the degree of structural det erioration of a 2.25 Cr-1Mo steel which was service-exposed for 11 yea rs as a power plant component. The experimental results showed that st rain rate over a wide rage of strain is expressed by the equation; In epsilon = In epsilon(0) + S epsilon, where epsilon(0) is the imaginary initial creep rate and S is the strain rate acceleration factor. The magnitudes of epsilon(0) and S are given by the following equations; e psilon(0) = A(0) sigma(0)(n)exp(-Q(0)/RT), and S = A(s) sigma(0)(-n5)e xp(Q(s)/RT), where A(0) is the mechanically defined structure factor, sigma( )is the initial stress, n is the stress exponent (9.5), Q(0) is the activation energy (429 kJ/mol), Q(s) is 24kJ/mol, A(5) is a const ant, and n(s) is 0.98. Comparing these results with those of prestrain ed materials, it was found that the magnitudes of A(0), A(s) and n(s) are dependent: upon the structural deterioration while those of n, Q(0 ) and Q(s) are independent of thermo-mechanical history. This means th at the rate controlling mechanism is independent of structural deterio ration. These history-dependent parameters allow us the quantitative a ssessment of the structural deterioration of service-exposed materials .