Influence of Stress and Strain on the Creep Damage of a 2.25Cr-1Mo Steel

Abstract

The effect of pre-creep on the creep life has been investigated over a stress range from 78.4 to 125 MPa at 873K. It was found that the creep life was decreased with increasing pre-creep stress and strain. In the case where the time elaspsed for pre-straining is relatively short(t≤3.6 × 10⁵s), and thereby creep damage due to aging is unimportant, pre-creep strain has a dominant effect on the creep damage. Defining the creep damage parameter, Φ as the ratio of the minimum creep rate of a damaged specimen to that of an unused specimen, the extent of the structural deterioration is expressed as a function of pre-strain, εp as follows:
Φ_p= (a·εp + 1)^b
where a and b are constants of the magnitude of 0.60 and 0.74 at 873K, respectively. The Monkman-Grant rule was obeyed for the damaged specimens, and the relationship between creep life and minimum creep rate is expressed as follows:
(t_r/s)·(ε_m/s^-1)^Y=K_P
where Y and K_P are constant independent of stress, and their values are 1.63 and 4.18 × 10^-6, respectively.