Tensile properties on dissimilar welds between 11Cr-ferritic/martensitic steel and 316 stainless steel after thermal aging

Yano, Yasuhide; Tanno, Takashi; Oka, Hiroshi; Otsuka, Satoshi; Kaito, Takeji

Journal of Nuclear Materials, 555, p.153105_1 - 153105_8, 2021/11

https://doi.org/10.1016/j.jnucmat.2021.153105

The aim of this study was to evaluate the tensile properties and microstructures of dissimilar welds between 11Cr-ferritic/martensitic steel and 316 stainless steel after thermal aging at temperatures between 400 and 600C up to 30,000 h. Characterization of microstructure was carried out by scanning electron microscopy and transmission electron microscopy. Microstructural analysis showed that the microstructure in the weld metals consisted of lath martensite containing a small amount of residual austenite. Thermal aging hardening of WMs occurred at 400 and 450C due to the effects of both a-a' phase separation and G-phase precipitation. However, there was no significant change in the total elongation, and fracture surfaces indicated that very fine dimpled rupture was predominant rather than the cleavage rupture. It was suggested that lath martensite phases enhanced the tensile strength due to phase separation, while residual austenite played a role in keeping elongation as a soft phase.

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.

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), 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=1.3810 USE + 1.20. (2)lt was clarified that DBTT is correlated with (BKt) as DBTT=p(logBKt)+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(logBKt)-160. (3)DBTT estimated at the irradiation temperature from 350 to 650 C for sub size specimen (width and height are 3 and 10 mm, respectively), was below 180 C, based on the design value of DBTT as fabricated and each correlation of aging and irradiation effects.

Thermal stress ratcheting analysis of time-hardening structure

Hada, Kazuhiko

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

no abstracts in English

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

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.

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.

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 300C 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.

Effect of cold-work and long-term aging on SCC initiation susceptibility of austenitic stainless steel

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

no journal, , 

The effect of the long-term thermal aging (LTA) on the SCC susceptibility to initiation in cold worked L-grade austenitic stainless steels has been investigated. The thermal aging treatments at 288C for more than 14,000h were conducted on Type 316L SS samples after cold rolling with 20% thickness reduction, and CBB testing was performed to both aged and unaged samples. The results showed that an obvious increase of IGSCC susceptibility was induced after the LTA treatment. In order to reveal the enhancement factor of the SCC susceptibility in LTA treated specimens microstructural examination was conducted by means of SEM/EBSD and TEM. Those results suggested that movement and rearrangement of dislocations toward the dislocation cell structure occurred during LTA treatment. It is presumed that the dislocation cell structure formed during the LTA process might cause the homogeneous plastic deformation and the localization of stress/strain, and consequently, enhance the SCC susceptibility to initiation.

Fracture toughness evaluation of martensitic steel for fast reactor wrapper tube thermal aged using miniaturized test technique

Tanno, Takashi; Shizukawa, Yuta; Fujita, Koji

no journal, , 

The evaluation of the fracture toughness of thermal-aged PNC-FMS was conducted using the miniature three-point bending fracture toughness evaluation technique under development. The results implied that although the Charpy impact properties of PNC-FMS after thermal aging for 6000 hours at 600C degraded, the fracture toughness at room temperature did not degraded. Furthermore, as a result of comparing the cases where fatigue pre-crack was introduced to the test specimen before and after thermal aging, it was found that there was no significant difference under the present thermal aging conditions.