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Journal Articles

Thermal aging effect for creep properties on Ni base refractory alloys

Ishijima, Yasuhiro; Ueno, Fumiyoshi

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 4 Pages, 2015/05

In this study, to evaluate the effect of thermal aging on creep properties of Alloy 625, we carried out creep tests on aged and solution-treated Alloy 625 at 1073 K. According to the creep test results, time-to-rupture decreased by thermal aging when test stress was more than 100 MPa, but did not change when test stress was less than 100 MPa for any specimens. In the solution-treated alloy, creep deformation behaviors changed over 100 MPa. These results show that time-to-rupture was constant because intermetallic compounds precipitated when the test stress was less than 100 MPa in solution-treated alloy. The observed relationship between creep strain rate and test time showed that the precipitation started after 100 hr for solution treated alloys. These results suggest that intermetallic compounds precipitate immediately after furnace operation. And it is appropriate to use creep data of thermal-aged Alloy 625 for the reducing roasting furnace lifetime prediction.

JAEA Reports

Residual stresses and aging degradation of stainless steel weld overlay clading for nuclear reactor pressure vessel (Contract research)

Nishiyama, Yutaka; Onizawa, Kunio; Idei, Yoshio; Suzuki, Masahide

JAERI-Research 2000-047, 32 Pages, 2000/10

JAERI-Research-2000-047.pdf:1.69MB

no abstracts in English

JAEA Reports

Evaluation of charpy impact property in high strength ferritic/martensitic steel (PNC-FMS)

;

JNC-TN9400 2000-035, 164 Pages, 2000/03

JNC-TN9400-2000-035.pdf:3.67MB

High Strength Ferritic/Martensitic Steel (PNC-FMS : 0.12C-11Cr-0,5Mo-2W-0.2V-0.05Nb), developed by JNC, is one of the candidate materials for the long-life core of large-scale fast breeder reactor. Ductile brittle transition temperature (DBTT) was tentatively determined in 1992 in material design base standard of PNC-FMS. Howevcr, specimen size effect on impact property and upper shelf energy (USE) have not been evaluated. ln this study, effects of specimen size, thermal aging and neutron irradiation on the charpy impact property of PNC-FMS were evaluated, using together with recently obtained data. The design value of USE and DBTT as fabricated and each correlation of aging and irradiation effects were determined. The results are summarized as follows. (1)lt was found that USE is related to (Bb) as USE=m(Bb)$$^{n}$$, where B is specimen width, b is ligament size and both m and n are constant. For PNC-FMS, n value is equal to 1.4. It's possible to determine n value from USE (J) for full size specimen using the correlation: n=1.38$$times$$10$$^{-3}$$ USE + 1.20. (2)lt was clarified that DBTT is correlated with (BKt) as DBTT=p(log$$_{10}$$BKt)+q, where Kt is elastic stress concentration factor and both p and q are constant. For PNC-FMS, the correlation is as follows: DBTT=119(log$$_{10}$$BKt)-160. (3)DBTT estimated at the irradiation temperature from 350 to 650 $$^{circ}$$C for sub size specimen (width and height are 3 and 10 mm, respectively), was below 180 $$^{circ}$$C, based on the design value of DBTT as fabricated and each correlation of aging and irradiation effects.

Journal Articles

Microstructure and hardening in thermally aged and neutron-irradiated Fe-Cu model alloy

Kawanishi, Hiroshi*; Suzuki, Masahide

Effects of Radiation on Materials (ASTM STP 1366), p.492 - 515, 2000/03

 Times Cited Count:1 Percentile:33.86

no abstracts in English

Journal Articles

Thermal stress ratcheting analysis of time-hardening structure

Hada, Kazuhiko

Nippon Kikai Gakkai Rombunshu, A, 65(636), p.108 - 115, 1999/08

no abstracts in English

Oral presentation

Effect of long term thermal aging on SCC susceptibility in austenitic stainless steels

Kaji, Yoshiyuki; Aoki, So; Kondo, Keietsu; Yamamoto, Masahiro

no journal, , 

The influence of long term thermal aging on SCC susceptibility in L-grade austenitic stainless steels (SSs) has been investigated using Creviced Bent Beam (CBB) tests. Test materials were type 304L and 316L SSs, and aging heat treatments were conducted at 288$$^{circ}$$C in air for up to 14000 hours followed by solution-annealing (SA) or 20% cold-working (CW). The evaluation of the SCC initiation susceptibility was conducted by CBB tests in BWR simulated high-temperature water at 288$$^{circ}$$C for 1000 hours. It was revealed by CBB tests that long term aged 304L-SA, 304L-CW, and 316L-SA showed low susceptibility of cracking, whereas long term aged 316L-CW showed high SCC susceptibility. And so far, it is considered that the low temperature sensitization was not the main cause of SCC in long term aged 316L-CW, because the previous TEM/EDX analysis on the long term aged 316L specimen showed no chromium depletion in the vicinity of grain boundaries. Further investigations are in progress from the viewpoint of mechanical properties, cold-rolling texture, microstructure and michrochemistry after the long term thermal aging in order to discuss the factors increasing SCC susceptibility.

Oral presentation

The Two step nucleation of G-phase in ferrite; The Critical size and composition

Matsukawa, Yoshitaka*; Takeuchi, Tomoaki; Nagai, Yasuyoshi*

no journal, , 

no abstracts in English

Oral presentation

Microstructure analysis on thermally aged stainless overlay cladding using X-ray absorption

Iwata, Keiko; Takamizawa, Hisashi; Ha, Yoosung; Okamoto, Yoshihiro; Shimoyama, Iwao; Kojima, Hiroshi*; Mayumi, Ren*; Iwase, Akihiro*; Nagai, Yasuyoshi*; Nishiyama, Yutaka

no journal, , 

Microstructure analysis for thermally aged stainless overlay cladding was conducted by using X-ray absorption. X-ray absorption fine structure analysis was adapted, which was possible to obtain the average information of a material and to identify the bond length and chemical state by the selected atoms. In this study, changes of coordination number and bond length around the Mn atom were recognized.

Oral presentation

Atomistic modeling of hardening in thermally-aged Fe-Cr binary alloys

Suzudo, Tomoaki; Nagai, Yasuyoshi*; Alfredo, C.*

no journal, , 

It is widely known that Fe-Cr binary alloys undergo spinodal decomposition when they are thermally aged, and that this microstructural evolution causes hardening and loss of ductility of the material. The present study is about the first attempt to tackle this problem by exploiting atomistic modeling techniques. We apply Monte Carlo simulation to creating spinodally-decomposed microstructure and molecular dynamics to simulating edge dislocations moving through this microstructure by imposing shearing deformation. We then measure the critical stress as a measure of hardness for many cases over the progress in spinodal decomposition, and succeed in reproducing an experimentally-discovered proportionality between the phase separation parameter and the hardening.

Oral presentation

Effect of long term thermal aging on SCC initiation susceptibility in L-grade austenitic stainless steels

Kaji, Yoshiyuki; Aoki, So; Kondo, Keietsu; Yamamoto, Masahiro

no journal, , 

The influence of long term thermal aging (LTA) on SCC initiation susceptibility in L-grade austenitic stainless steels (SSs) has been investigated using Creviced Bent Beam (CBB) tests. Test materials were type 304L and 316L SSs, and aging heat treatments were conducted at 288$$^{circ}$$C in air for up to 14000 hours followed by solution-annealing (SA) or 20% cold-working (CW). The evaluation of the SCC initiation susceptibility was conducted by CBB tests in BWR simulated high-temperature water at 288$$^{circ}$$C for 1000 hours. It was revealed by CBB tests that 304L-SA, 304L-CW, 304L-SA+LTA, 304L-CW+LTA, 316L-SA 316L-CW and 316L-SA+LTA showed no SCC initiation susceptibility, whereas 316L-CW+LTA showed high SCC susceptibility. To clarify the cause of SCC initiation in 316L-CW+LTA, several investigations are in progress from the viewpoint of mechanical properties, cold-rolling texture, microstructure and michrochemistry after LTA. It is considered that the low temperature sensitization was not the main cause of SCC in 316L-CW+LTA, because the TEM/EDX analysis on the 316L+LTA and 316L-CW+LTA specimens showed no chromium depletion in the vicinity of grain boundaries. In this presentation, we will explain the further investigation results for effect of LTA on SCC initiation susceptibility in L-grade austenitic SSs.

Oral presentation

SCC initiation susceptibility in L-grade austenitic stainless steels after long-term thermal aging treatment

Kaji, Yoshiyuki; Kondo, Keietsu; Aoki, So; Hirade, Tetsuya; Yamamoto, Masahiro

no journal, , 

To clarify the causal relationship between the LTA treatment and the SCC initiation susceptibility, microstructural analyses on 316L CW specimens before and after the LTA treatment have been conducted. One of viewpoints in our research is the deformation microstructure. Results of the surface examination by SEM on CBB tested specimens suggested the difference in the deformation microstructure of 316L CW and CW+LTA. Coarse and planar slip steps were frequently observed on the surface of 316L CW+LTA specimens, indicating the localization of dislocation motion to limited slip planes. On the other hand, surface morphology observed in 316L CW was mainly fine and wavy slip step, indicating the occurrence of the homogeneous plastic deformation. The detail mechanism of the change in the deformation microstructure by the LTA treatment is unknown yet. Researches on its effect on the deformation microstructure and, furthermore, the SCC susceptibility is now in progress.

Oral presentation

Long term thermal aging effect on SCC initiation susceptibility of L-grade stainless steels

Kaji, Yoshiyuki; Aoki, So; Fujimura, Yuki; Kondo, Keietsu

no journal, , 

In this study, the influence of the long term thermal aging (LTA) on SCC initiation susceptibility of L-grade SSs was examined. Results of CBB testing on Type 316L CW and CW + LTA under the BWR simulated water condition showed the increase of SCC susceptibility to initiation after the LTA treatment. The material examinations on those materials were conducted to identify the SCC accelerating factors. The initial microstructure in Type 316L CW and CW + LTA was characterized to dislocation tangles and dislocation cell structures, respectively, indicating that the LTA treatment induced the rearrangement of dislocations toward the energetically favorable state. Whereas, no sensitization of the grain boundaries of Type 316L CW + LTA was confirmed by means of TEM/EDX analysis. The examination of surface deformation microstructure by bending deformation was conducted by the consecutive SEM observation before and after CBB testing. The more heterogeneous deformation was enhanced by the LTA treatment, that is, the reduction in dislocation motion and increase of deformation twinning. It was considered from those obtained results that the concentration of local stress around grain boundaries caused by the more heterogeneous deformation might be one of the promoting factors for increasing the SCC susceptibility in non-sensitized Type 316L CW + LTA.

Oral presentation

Aging effect for hydrogen embrittlement behavior of Ta/Zr explosive joint

Nakabachi, Kaito*; Yokoyama, Kenichi*; Ishijima, Yasuhiro; Ueno, Fumiyoshi; Abe, Hitoshi

no journal, , 

The effects of thermal aging on hydrogen embrittlement behavior were investigated for Zr/Ta/SUS explosive joints used in spent nuclear fuel reprocessing plants, especially at the Zr/Ta interface, which is considered to be susceptible to hydrogen embrittlement. The results showed that brittle fracture occurred at the Zr/Ta interface when the hydrogen concentration of Ta was over 20 ppm, and the ductility of the specimens with such hydrogen concentration was recovered when the hydrogen concentration of Ta decreased below 10 ppm by thermal aging at 300$$^{circ}$$C for 1000 hr, while the hydrogen concentration was reduced to The ductility of the Ta/Zr interface was not recovered without significant decrease in hydrogen concentration. These results suggest that the hydrogen concentration in Ta at the Ta/Zr interface affects the hydrogen embrittlement behavior of the explosion joint and that the hydrogen state changes with thermal aging.

Oral presentation

Effects of pre-strain on enhancement of hydrogen embrittlement induced by aging for pure Ta

Nakabachi, Kaito*; Yokoyama, Kenichi*; Ishijima, Yasuhiro; Ueno, Fumiyoshi; Abe, Hitoshi

no journal, , 

To investigate the effects of strain and thermal aging on hydrogen embrittlement of Ta, tensile tests and internal friction measurements were carried out on cold rolled Ta after hydrogen charging and thermal aging. As a result, the internal friction increased with cold rolling. The internal friction was further increased by hydrogen charging. However, the internal friction of these specimens decreased after thermal aging. These results suggest that aging causes the annihilation or re-arrangement of defects or a change in the hydrogen trapping. In addition, the ductility of the hydrogen-charged and cold-rolled specimens decreased after thermal aging, suggesting that the change in hydrogen and defect state due to thermal aging affects the mechanical properties.

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