ＳＵＳ３０４鋼およびＮｉ‐Ｍｏ‐Ｖ鋼の高温低サイクル疲労き裂伝ぱ特性と破壊形態

Abstract

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 steelThe crack propagation rate, dl/dN, was correlated well with the fatigue J-integral range, ΔJf, 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, ΔJc. The fracture mode in this case was of intergranular type. However, good correlation of dl/dN with ΔJc as well as ΔJf 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 steelIn the same way of the above stainless steel, dl/dN in P- and C-type fatigue at 823K were correlated well with ΔJf and ΔJc, respectively. However, there was no difference in fracture mode between these two types, both of which exhibited the transgranular fracture mode.