In order to investigate the behavior of elevated temperature low cycle fatigue crack propagation in Type 304 stainless and 2.5Ni-0.5Mo-0.1V ferritic steels, load-controlled low-cycle fatigue tests were carried out on notched specimens under four kinds of loading waveform (
i, e., PP-, PC-, CP- and CC-types).
The results obtained were summarized as follows:
(1) Type 304 stainless steel
The crack propagation rate,
dl/dN, was correlated well with the fatigue J-integral range, Δ
Jf, in P-type (
i, e., PP- and PC- types) fatigue tested at 973K and 823K. The striations, of which width was found to be nearly equal to
dl/dN, were observed on their fracture surfaces.
On the other hand,
dl/dN in C-type (
i. e., CC- and CP-types) fatigue tested at 973K was correlated well with the creep J-integral range, Δ
Jc. The fracture mode in this case was of intergranular type. However, good correlation of
dl/dN with Δ
Jc as well as Δ
Jf wasn't obtained in C-type fatigue at 823K, where the fracture mode was of mixed (
i, e., intergranular and transgranular) type. This appeared to be caused by creep-fatigue interaction.
(2) Ni-Mo-V steel
In the same way of the above stainless steel,
dl/dN in P- and C-type fatigue at 823K were correlated well with Δ
Jf and Δ
Jc, respectively. However, there was no difference in fracture mode between these two types, both of which exhibited the transgranular fracture mode.
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