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&Crack growth rate data are presented from a range of fully reversed displacement-controlled Fatigue and creep-Fatigue tests and from static load-controlled creep crack growth tests on aged 321 stainless steel (parent and simulated HAZ) at 650'C. In the creep Fatigue tests, constant displacement tensile hold periods of 12-192 h were used. Crack growth rates comprised both cyclic and dwell period contributions. Cyclic growth contributions are described by a Paris-type law and give faster crack growth rates than those associated with pure fatigue tests. Dwell period contributions are described by the C' parameter. The total cyclic crack growth rates are given by summing the cyclic and dwell period contributions. Estimates of C' using a reference stress approach together with the appropriate stress relaxation creep data are shown to correlate well with experimentally measured C * values. Crack growth rates during static load-controlled tests correlate well with C'. Good agreement is obtained between crack growth rates during the static tests and those produced during the hold period of the creep-fatigue tests. NOMENCLATURE(dtrid~Y),,,,,, = total crack growth rilte during crcep-fatigue test (du,'dN) = crack growth rate during pure fatigue test (du/diV),. = cyclic contribution to crack growth rate during creep-fatigue test du!di = hold period contribution to crack growth rate during creep-fatigue test u / W = crack length to specimen width ratio u. u,) = crack length. initial crack length B = thickness of compact tension specimen C' = creep crack growth correlation parameter D = constant in creep rate equation for stress relaxation E = Young's modulus f ( u / W ) = stress intensity function K , AK,,, = stress intensity factor. total stress intensity Factor range AKeK = stress intensity factor range for which cracks are open m = limit load ratio n = creep stress index qo = ratio of load range for which cracks are open to total load range R = ratio of minimum load in cycle to maximun load in cycle I = time ih =hold period duration W =width of compact tension specimen Y = compliance function A = load line displacement rate i = creep rate 1 = non-dimensional crack velocity parameter for determining the applicability of C' P, AP = load, load range u, urer = stress, reference stress 355 356 D. N. GLADWIN er ul.

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