Creep, Fatigue and Creep‐fatigue Crack Growth Rates in Parent and Simulated Haz Type 321 Stainless Steel

Abstract

&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.

Influence of Hydrogen on the Initiation of Creep-Fatigue Cracks in Plates Near Stress Concentrators

“…Consider a strip of 321 steel [4] with two side notches subjected to the action of cyclic loads, high temperature, and hydrogen-containing media (Fig. 2).…”

“…where b is the depth of the notches, L is the half width of the plate, and α 2 is the stress concentration fac-tor at the notch tip { α 2 = 2 p −1 (πr) −1/2 K max [1]}.Further, we determine the characteristics of high-temperature creep by analogy with[4]: K fC = 100 MPa m , K th = 7.5 MPa m , σ t = 450 MPa , E = 1.9 ⋅10 5 MPa , A 1 = 1.25 ⋅10 −5 m/h, m = 0.85 , t * = 12 h, t 1 = 0.0128 h, α 0 = 1.24 , and R = 0 and choose the following geometric parameters: b = 4 mm , L = 20 mm , and r = 1.3 mm . We assume that the characteristics of hydrogenation of 321 and 15Kh2MFA steels insignificantly differ and take the required quantities for 321 steel according to the results obtained in[6]: β 1 = 2.22 (ppm) −1 , β 2 = 0.22 h −1 , and C 0 = 0.9 ppm .…”

Method for calculating the operating life of a steam pipe with a creep-fatigue crack near a weld joint

“…Therefore, equation (12) together with initial and finite conditions (13), (14) is a computational model for the evaluation of the residual resource of the steam pipeline with semi-circular internal creepfatigue crack in the wall pipe near the ring weld joint.…”

High-temperature flaw assessment procedure

“…Creep-fatigue crack-growth data have been produced for both base and simulated heataffected zone (HAZ) type 321 stainless steel at 650°C in air and reported by Gladwin et al 5 Before testing, the type 321 stainless steel was aged for 200 h at 750°C. Further heat treatment was used to produce simulated HAZ material.…”

“…3 and 4 are applied to a typical LMR component in Chap. 5. Finally, experimental and analytical results are summarized, and concluding remarks are made in Chap.…”