STATE-EQUATION OF A 2.25CR-1MO STEEL UNDER CONSTANT-LOAD CREEP TESTING

Creep testing was conducted on the pre-crept specimens of a 2.25Cr-1Mo steel under constant load. The amount of pre-strain was between 4.4 and 12.0%, and the range of temperature and initial stress was 853 to 903 K and 78.4 to 127.4 MPa, respectively. The relation between creep rate, epsilon and creep strain, epsilon was expressed as below over a wide range of creep strain: epsilon = epsilon0exp(Sepsilon), where s is the acceleration factor, epsilon0 is the imaginary initial strain rate, and the stress and temperature dependence of epsilon0 is given as: epsilon0 = Asigma(n)exp(- Q(o)/RT), where Q(o) is the apparent activation energy for creep of the magnitude of 400+/-10kJ . mol-1, sigma is the true stress, n is the stress exponent of the magnitude of 9.7 and A is the mechanically defined structure factor expressed as below: A = A(o)exp [(m - n)epsilon(p)], where A(o) is the structure factor for virgin specimens and m is the constant. These experimental facts lead to the conclusion that pre-strain and creep strain do not alter the creep mechanism but cause the increase in the mechanically defined structure factor, and creep life, t(r) is given by t(r) = 1/(Sepsilon0).