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Journal Articles

Mechanical properties and microstructure of dissimilar friction stir welds of 11Cr-ferritic/martensitic steel to 316 stainless steel

Sato, Yutaka*; Kokawa, Hiroyuki*; Fujii, Hiromichi*; Yano, Yasuhide; Sekio, Yoshihiro

Metallurgical and Materials Transactions A, 46(12), p.5789 - 5800, 2015/12

Dissimilar friction stir welding (FSW) of an 11% Cr ferritic/martensitic stee (PNC-FMS) to 316-grade austenitic stainless steel was attempted with a view to its potential application to the wrapper tubes of next-generation fast reactors. The mechanical properties and microstructure of the resulting welds were systematically examined, which revealed that FSW produces a defect-free stir zone in which material intermixing is notably absent. That is, both steels are separately distributed along a zigzagging interface in the stir zone when PNC-FMS is placed on the retreating side, with the tool plunging at the butt line. This interface did not act as a fracture site during small-sized tensile testing of the stir zone. Furthermore, the microstructure of the stir zone was refined in both the PNC-FMS and 316 stainless steel sides, resulting in improved mechanical properties over the respective base material regions.

Journal Articles

Mechanical properties of friction stir welded 11Cr-ferritic/martensitic steel

Yano, Yasuhide; Sato, Yutaka*; Sekio, Yoshihiro; Otsuka, Satoshi; Kaito, Takeji; Ogawa, Ryuichiro; Kokawa, Hiroyuki*

Journal of Nuclear Materials, 442(1-3), p.S524 - S528, 2013/09

 Times Cited Count:10 Percentile:26.48(Materials Science, Multidisciplinary)

Friction stir welding was applied to the wrapper tube materials, 11Cr-ferritic/martensitic steel, intended for fast reactors and defect-free welds were successfully produced. Then, the mechanical and microstructural properties of the friction stir welded steel were investigated. The hardness values of the stir zone were about 550 Hv, and they had hardly any dependence on the rotational speed, although they were much higher than that of the base material. However, tensile strengths and elongations of the stir zones were better at 298 K, compared to those of the base material. These excellent tensile properties were attributable to the fine grain formation during friction stir welding. A part of this study is the result of "Friction stir welding of the wrapper tube materials for Na fast reactors" carried out under the Strategic Promotion Program for Basic Nuclear Research by the Ministry of Education, Culture, Sports, Science and Technology of Japan.

Journal Articles

Effect of welding parameters on microstructure and mechanical properties of a friction stir welded 11Cr-ferritic/martensitic steel

Sato, Yutaka*; Kokawa, Hiroyuki*; Yano, Yasuhide; Sekio, Yoshihiro

Friction Stir Welding and Processing, 7, p.91 - 99, 2013/03

PNC-FMS is a newly developed 11Cr-ferritic/martensitic steel with good swelling resistance, designed for the wrapper tubes of fast reactors. In this study, friction stir welding (FSW) was attempted as a welding process of PNC-FMS because fusion welding of this steel significantly reduced mechanical properties through formation of brittle microstructure. FSW was applied to PNC-FMS at 100 to 300 rpm using Q60 tool, and defect-free welds were obtained. The stir zones had fine microstructure with ferrite and martensite, and the grain size and fraction of martensite increased with rotational speed. Since all welds were overmatched, all transverse tensile specimens were broken at the base material region. The tensile test of the stir zone clarified that the stir zone produced at 100 rpm exhibited higher strengths and elongation than the base material. This study showed that FSW at lower rotational speed produced the stir zone having better mechanical properties in PNC-FMS.

Journal Articles

Corrosion-erosion test of SS316L grain boundary engineering materials (GBEM) in lead bismuth flowing loop

Saito, Shigeru; Kikuchi, Kenji*; Hamaguchi, Dai; Tezuka, Masao*; Miyagi, Masanori*; Kokawa, Hiroyuki*; Watanabe, Seiichi*

Journal of Nuclear Materials, 431(1-3), p.91 - 96, 2012/12

 Times Cited Count:9 Percentile:36.56(Materials Science, Multidisciplinary)

To evaluate lifetime of structural materials for ADS, corrosion tests in LBE have been done at JAEA. The corrosion test was performed by using JAEA lead-bismuth flowing loop (JLBL-1). Experimental condition was as follows; The temperature of high and low temperature parts of the loop were 450$$^{circ}$$C and 350$$^{circ}$$C, respectively. Flowing velocity at the test specimens was about 1m/s. Plate type SS316L-BM and SS316L-GBEM were used as a specimens. After the 3,000 hours operation, the test specimens were cut and macroscopic observation was carried out. The result showed that both materials were intensively eroded. Corrosion depth and LBE penetration through grain boundaries of GBEM were smaller than these of 316SS-BM.

Journal Articles

Correlation effects among thermal displacements of atoms from diffuse neutron scattering measurements

Sakuma, Takashi*; Mohapatra, S. R.*; Yokokawa, Jo*; Shimizu, Norifumi*; Isozaki, Nobuhiro*; Uehara, Hiroyuki*; Xianglian*; Basar, K.*; Takahashi, Haruyuki*; Kamishima, Osamu*; et al.

Proceedings of 12th Asian Conference on Solid State Ionics and 15th Chinese Conference on Solid State Ionics, p.439 - 445, 2010/00

Diffuse neutron scattering intensities from ionic crystals, covalent crystals and metal crystals are analyzed by including the correlation effects among thermal displacements of atoms into the function describing background intensity. The obtained values of correlation effects among first nearest neighboring atoms are 0.7 near room temperature. The values of the correlation effects do not depend much on the type of the crystal binding near room temperature. The values of correlation effects decrease rapidly with the increase of inter-atomic distances. The correlation effects also decrease with the decrease of temperature.

JAEA Reports

Inhibition of sensitization in reactor pipe materials by grain boundary structure control, JAERI's nuclear research promotion program, H11-023 (Contract research)

Kokawa, Hiroyuki*; Shimada, Masayuki*; Wang, Z.*; Sato, Yutaka*; Sato, Yoshihiro*; Kiuchi, Kiyoshi

JAERI-Tech 2003-014, 22 Pages, 2003/03

JAERI-Tech-2003-014.pdf:1.68MB

no abstracts in English

Oral presentation

Irradiation resistance property of austenitic stainless steels prepared by grain boundary engineering processing, 1

Tanikawa, Ryusuke*; Sakaguchi, Norihito*; Watanabe, Seiichi*; Kinoshita, Hiroshi*; Kokawa, Hiroyuki*; Kawai, Masayoshi*; Yamashita, Shinichiro

no journal, , 

no abstracts in English

Oral presentation

Research and development of high performance FBR core materials based on grain boundary engineering, 1; Trial production

Yamashita, Shinichiro; Yano, Yasuhide; Endo, Masaki*; Sakaguchi, Norihito*; Watanabe, Seiichi*; Miyagi, Masanori*; Sato, Shinya*; Sato, Yutaka*; Kokawa, Hiroyuki*; Kawai, Masayoshi*

no journal, , 

no abstracts in English

Oral presentation

Research and development of high performance FBR core materials based on grain boundary engineering, 2; Evaluation of tensile properties

Yano, Yasuhide; Yamashita, Shinichiro; Endo, Masaki*; Sakaguchi, Norihito*; Watanabe, Seiichi*; Miyagi, Masanori*; Oyamada, Tetsuya*; Sato, Shinya*; Sato, Yutaka*; Kokawa, Hiroyuki*; et al.

no journal, , 

no abstracts in English

Oral presentation

Corrosion test of SUS316L grain boundary engineering material in lead bismuth flowing loop

Saito, Shigeru; Kikuchi, Kenji; Hamaguchi, Dai; Tezuka, Masao; Miyagi, Masanori*; Kokawa, Hiroyuki*

no journal, , 

no abstracts in English

Oral presentation

Crystal rotation measurement after high temperature creep in a single-crystal nickel-base superalloy

Shiota, Yoshinori; Akita, Koichi; Suzuki, Hiroyuki*; Kitazawa, Hideaki*; Yokokawa, Tadaharu*; Koizumi, Yutaka*; Harada, Hiroshi*

no journal, , 

no abstracts in English

Oral presentation

Dependence evaluation on grain boundary characteristic for corrosion effects after irradiaion

Endo, Masaki*; Sakaguchi, Norihito*; Kinoshita, Hiroshi*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Yamashita, Shinichiro; Yano, Yasuhide; Kawai, Masayoshi*

no journal, , 

no abstracts in English

Oral presentation

Effect of irradiation in grain boundary character distribution optimaized austenitic steel

Sakaguchi, Norihito*; Tanikawa, Ryusuke*; Endo, Masaki*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Kawai, Masayoshi*; Yamashita, Shinichiro; Yano, Yasuhide

no journal, , 

no abstracts in English

Oral presentation

Study on material damage in the high energy quantum beam fields and development of high performance materials, 4; Ion and HVEM irradiation of grain boundary engineered material and its properties

Sakaguchi, Norihito*; Endo, Masaki*; Kinoshita, Hiroshi*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Yano, Yasuhide; Yamashita, Shinichiro; Kawai, Masayoshi*

no journal, , 

no abstracts in English

Oral presentation

High performance FBR core material development by means of grain boundary engineering

Yamashita, Shinichiro; Yano, Yasuhide; Sakaguchi, Norihito*; Watanabe, Seiichi*; Kokawa, Hiroyuki*; Kawai, Masayoshi*

no journal, , 

In this study, grain boundary character distribution (GBCD)-optimized Type 316 corresponding austenitic stainless steel has been developed as a nuclear material for next generation energy systems. Some of steel sheets were cold-rolled additionally for making the GBCD-optimized and cold-worked (GBCD+CW) specimens. These specimens, including as GBCD-optimized, were examined tensile strength property, phase stability during high temperature thermal ageing and irradiation property. The GBCD was assessed by orientation imaging microscopy (OIM) and also the microstructure by TEM. The OIM results showed that the average grain sizes and the frequencies of CSL boundaries in the typical specimens were 40-47 $$mu$$m and more than 70%. Totally considered all experimental results, it was indicated that it is highly possible to develop high performance FBR core material by means of grain boundary engineering.

Oral presentation

Microstructures and mechanical properties of friction stir welded 11Cr-ferritic/martenstic steel

Sato, Yutaka*; Kokawa, Hiroyuki*; Yano, Yasuhide; Sekio, Yoshihiro

no journal, , 

no abstracts in English

Oral presentation

Mechanical properties of friction stir welded 11Cr-ferritic/martensitic steel

Sekio, Yoshihiro; Yano, Yasuhide; Sato, Yutaka*; Kokawa, Hiroyuki*

no journal, , 

The applicability of friction-stir welding (FSW) which was already put into practical use with nonferrous-metal materials was examined to the 11Cr-ferrite/martensite steel (PNC-FMS) wrapper material in order to improve the welding performance of fast reactor core materials. In this research, the effect of FSW on mechanical and microstructural properties of the Stir Zone (SZ) was investigated. From the experimental results, there was no remarkable decrease in tensile property of the SZ as compared with the base material even though the hardness of the SZ increased due to the influence of very fine grains. This suggests that a post weld heat treatment which was required on the conventional fusion welding might be unnecessary. This study is the result of "Friction stir welding of the wrapper tube materials for Na fast reactors" carried out under the Strategic Promotion Program for Basic Nuclear Research by the Ministry of Education, Culture, Sports, Science and Technology of Japan.

Oral presentation

Microstructures and mechanical properties of dissimilar friction stir weld of 11%Cr ferritic/martensitic steel to SUS316 stainless steel

Sato, Yutaka*; Kokawa, Hiroyuki*; Yano, Yasuhide; Sekio, Yoshihiro

no journal, , 

no abstracts in English

Oral presentation

High-temperature tensile properties of the grain boundary engineered NIMONIC PE16

Sekio, Yoshihiro; Yamashita, Shinichiro; Sakaguchi, Norihito*; Shibayama, Tamaki*; Watanabe, Seiichi*; Tokita, Shun*; Fujii, Hiromichi*; Sato, Yutaka*; Kokawa, Hiroyuki*

no journal, , 

In order to improve ductility loss by helium embrittlement (or grain boundary embrittlement) induced under high temperature and neutron irradiation dose in nickel alloys which are expected to have high-temperature phase stability under non-irradiation, the grain boundary engineering was applied for NIMONIC PE16 to enhance the grain boundary strength. And, its high temperature tensile properties under non-irradiation were investigated as the first approach. As a result, the temperature dependence of the yield stress in the grain boundary engineered (GBE) PE16 was similar to that in NIMINIC PE16, but the yield stress was slightly lower and the uniform elongation was slightly higher at each temperature in GBE PE16 comparing to NIMINIC PE16. This would be caused by grain coarsening due to some heat treatments. If the gain size of GBE PE16 is optimized, tensile properties of GBE PE16 would be the same or more than that of NIMONIC PE16.

Oral presentation

Evaluation of mechanical property in grain boundary character distribution-optimized Ni-based alloy

Yamashita, Shinichiro; Sekio, Yoshihiro; Sakaguchi, Norihito*; Shibayama, Tamaki*; Watanabe, Seiichi*; Kokawa, Hiroyuki*

no journal, , 

Recent grain boundary structure studies have shown that optimal distribution of a high frequency of coincidence site lattice boundaries and consequent discontinuity of random boundary network in the material is one of very effective methods to enhance the intergranular corrosion resistance. This advantageous property, one of important ones for structural material of nuclear reactor, can be obtained through simple thermomechanical treatment process without any change of original chemical composition. In this study, grain boundary character distribution(GBCD)-optimized Ni-based alloy (PE16) has been developed as a prospective high-performance nuclear reactor material by grain boundary engineering processing, and then tensile behavior of GBCD-optimized Ni-based alloy was investigated to evaluate the effect of grain boundary engineering processing on mechanical property. The result of tensile test at room temperature showed that tensile strength of GBCD-optimized PE16 was somewhat lower than that of as-received PE16. However, no significant change was confirmed in elongation property. Details on tensile behavior analyses would be discussed in the conference.

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