Radiation-Induced Stress Relaxation of Welded Type 304 Stainless Steel Evaluated by Neutron Diffraction

Abstract

The welded Type 304 stainless steel specimens were neutron-irradiated up to 2 × 1025 n/m2 (E > 1MeV) at 561K in the Japan Material Testing Reactor (JMTR). The residual stresses in the test specimens were measured by neutron diffraction, and the radiation-induced stress relaxation was evaluated from the change of stress distributions along the direction transverse to the weld bead. The magnitudes of σX (transverse to the weld) and σY (longitudinal to the weld) residual stresses decreased steadily with increasing neutron fluence. The irradiation dose dependence and the mechanism for the relaxation were examined using an equation derived from the irradiation creep equation. There was a steep stress relaxation, which might correspond to transient creep, at the early stage of neutron irradiation near the weld, and the different radiation-induced relaxation behaviors could be observed depending on the distance from the weld. The radiation-induced stress relaxation for welding-induced residual stress, which was generated under a three-dimensional restriction, indicated the tendency to be slower compared to the fundamental results for mechanically applied stress.

Current understanding of radiation-induced degradation in light water reactor structural materials

“…Understanding on irradiation creep has obtained mainly from data at temperatures higher than 400 • C [278] and experimental data at LWR-relevant temperatures (280-370 • C) are scarce [279,280]. Recently data on irradiation creep and stress relaxation at temperatures around 300 • C have been accumulated by MTR irradiation experiments in the last decade [281][282][283][284][285][286][287]. Figure 22 shows the data of irradiation stress relaxation in type 304 and 316L SSs at 288 • C [280][281][282][283][284].…”

“…Recently data on irradiation creep and stress relaxation at temperatures around 300 • C have been accumulated by MTR irradiation experiments in the last decade [281][282][283][284][285][286][287]. Figure 22 shows the data of irradiation stress relaxation in type 304 and 316L SSs at 288 • C [280][281][282][283][284]. The ratio of the measured stress (σ ) to the initial applied stress (σ 0 ) was decreased with dose and became less than 0.5 at ∼5 dpa.…”

Radiation-induced stress relaxation in high temperature water of type 316L stainless steel evaluated by neutron diffraction

“…12. Equation of radiation-induced stress relaxation obtained by regression approximation fit for the results of this study and literature data [13]. …”

“…• This study ○ Obata et al [13] • This study ○ Obata et al [13] • This study ○ Obata et al [13] /MPa/dpa *1: This study *2: Obata et al [13] Fig. 12.…”

“…In Ref. [13], stress ratio is defined as the stress ratio of the data after irradiation to the data before irradiation. On the other hand, stress ratio is defined as the stress ratio of the irradiated specimen to the un-irradiated specimen in this study.…”