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

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: Φp= (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: (tr/s)·(εm/s-1)Y=KP where Y and KP are constant independent of stress, and their values are 1.63 and 4.18 × 10-6, respectively.