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 less-than-or-equal-to 3.6 X 10(5) s), 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, PHI 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, epsilonP as follows: PHI(P)=(a.epsilonP+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(tau)/s).(epsilon(m)/s-1)Y = KP where Y and KP are constant independent of stress, and their values are 1.63 and 4.18 X 10(-6), respectively.