Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Initialising ...
Wakai, Takashi; Onizawa, Takashi; Obara, Satoshi; Nakashima, Takashi*; Yokoyama, Tetsuo*; Iseda, Atsuro*; Ogumo, Shinya*; Futagami, Satoshi*
Tainetsu Kinzoku Zairyo Dai-123-Iinkai Kenkyu Hokoku, 52(2), p.171 - 181, 2011/07
To enhance the economic competitiveness, high-Cr ferritic steels are adopted as the structural materials for JSFR, because the steels have both excellent high temperature strength and thermal properties. Among the high-Cr ferritic steels, modified 9Cr-1Mo steel (compatible to ASTM A213 T91) is a candidate of the structural material for the demonstration facility of JSFR, because the steel has superior microstructure stability at elevated temperature for long time. As for the steam generator tubes, to enhance the safety, straight double-walled tubes will be employed. In this study, the following technical issues were investigated; (1) Industrial manufacturability of thin-walled small bore tubes made of modified 9Cr-1Mo steel, (2) performance demonstration of the thin-walled small bore tubes, (3) industrial manufacturability of double-walled tubes using the thin-walled small bore tubes and (4) extraction of technical problems to manufacture the double-walled tubes for the JSFR steam generator. As a result, thin-walled small bore tubes made of modified 9Cr-1Mo steel were successfully manufactured by using the existing industrial facilities, up to 17m in length. The mechanical properties of the tubes satisfy the requirements from plant designing, as well as those from the material strength standards. Further, double walled tubes were also manufactured, up to 15m in length. The surface conditions of the tubes and the contact pressure between inner and outer tubes should be optimized.
Wakai, Takashi; Nagae, Yuji; Takaya, Shigeru; Obara, Satoshi; Date, Shingo*; Yamamoto, Kenji*; Kikuchi, Koichi*; Sato, Kenichiro*
Tainetsu Kinzoku Zairyo Dai-123-Iinkai Kenkyu Hokoku, 52(2), p.147 - 159, 2011/07
By employing high-Cr ferritic steels to the structural materials for JSFR, a compact plant designing can be achieved. It contributes to reduce the construction cost and to enhance the freedom of designing. Among the high-Cr ferritic steels, modified 9Cr-1Mo steel (compatible to ASTM A335 P91) is a candidate of the structural material for the demonstration facility of JSFR, because the steel has superior microstructure stability at elevated temperature for long time. However, remarkable creep strength degradation has been observed in the welded joint of high-Cr ferritic steels, especially in long-term region. It is known as "Type-IV damage". In the elevated temperature designing for the fast reactors, such creep strength degradation must be taken into account properly. Therefore, the creep strength assessment procedure and the allowable stress for the welded joints made of modified 9Cr-1Mo steel have been proposed. In this study, (1) a series of creep rupture tests to verify the validity of the creep strength assessment procedure was performed. (2) Applicability of the creep strength assessment procedure to the creep fatigue strength assessment of the welded joints made of modified 9Cr-1Mo steel was investigated. (3) Metallurgical examinations of creep ruptured specimens were carried out to confirm the contribution of "Type-IV damage". As a result, it was demonstrated that the creep strength assessment procedure was validated using the long-term creep rupture test results less than 30,000h and that the creep strength assessment procedure was applicable to the creep-fatigue strength assessment based on some uniaxial creep-fatigue test results.
Obara, Satoshi; Takaya, Shigeru; Wakai, Takashi; Asayama, Tai; Suzuki, Hiroshi; Saito, Toru; Martin, L.*
Kensa Gijutsu, 16(3), p.24 - 30, 2011/03
For the commercialization of fast breeder reactors (FBR), it is essential to enhance the economic competitiveness by reduction of total cost by elongation of plant service period. In this point of view, it is important to establish the assessment method of integrity of aged weld joint and repair welding for the components of future long life FBR. In the present study, evolution of microstructure is evaluated for the 304SS-304SS weld joint which was used for 88,000h at 526-545
C in the French proto-type fast reactor Phenix (as secondary pipes), and for the repair weld joint made from the 304SS of Phenix and new 316LSS plate. In addition, residual stress of the joints were measured by means of RESA and RESA-II. As the results, the microstructure and the residual stress of the joints had changed in the high temperature-long service environment and by the repair welding, and those of the repair weld joint were correlated with its hardness.
Wakai, Takashi; Nagae, Yuji; Onizawa, Takashi; Obara, Satoshi; Xu, Y.*; Otani, Tomomi*; Date, Shingo*; Asayama, Tai
Proceedings of 2010 ASME Pressure Vessels and Piping Conference (PVP 2010) (CD-ROM), 9 Pages, 2010/07
Obara, Satoshi; Takaya, Shigeru; Wakai, Takashi; Asayama, Tai; Suzuki, Hiroshi; Saito, Toru*; Martin, L.*
Hozengaku, 9(1), p.32 - 38, 2010/04
For the commercialization of fast breeder reactors (FBR), it is essential to enhance the economic competitiveness by reduction of total cost by elongation of plant service period. In this point of view, it is important to establish the assessment method of integrity of aged weld joint and repair welding for the components of future long life FBR. In the present study, evolution of microstructure is evaluated for the 304SS-304SS weld joint which was used for 88,000h at 526-545C in the French proto-type fast reactor Phenix (secondary pipes), and for the repair weld joint made from the 304SS of Phenix and new 316LSS plate. In addition, residual stress of the joints were measured by means of RESA and RESA-II. As the results, the microstructure and the residual stress of the joints had changed in the high temperature-long service environment and by the repair welding, and those of the repair weld joint were correlated with its hardness.
Obara, Satoshi; Wakai, Takashi; Asayama, Tai; Yamada, Yoshiyuki*; Nakazawa, Takanori*; Yamazaki, Masayoshi*; Hongo, Hiromichi*
Tetsu To Hagane, 96(4), p.172 - 181, 2010/04
This paper describes the effect of heat treatment on mechanical properties of 9Cr-W-Mo-V-Nb steel as a part of development of high Cr steel for fast breeder reactor (FBR). The effects of normalizing temperature and tempering temperature and time on creep properties were investigated from the viewpoint of microstructures. Creep strength increased with increase in normalizing temperature from 950C to 1200C. The microstructural factors that improve creep strength are increased amount of MX which precipitated during tempering process and increased dislocation density. In addition, coarsening of prior austenite grain size also contribute to increasing creep strength. Although creep rupture time of 780C-1h tempering specimen was greater than that of 700C-1h and 750C-1h tempering specimen in a long-term region exceeding 20000h at 650C, creep ductility and reduction of area of the former remarkably degraded compared to those of the latter.
Obara, Satoshi; Wakai, Takashi; Asayama, Tai; Yamada, Yoshiyuki*; Nakazawa, Takanori*
Tetsu To Hagane, 95(5), p.417 - 425, 2009/05
Times Cited Count：7 Percentile：43.17(Metallurgy & Metallurgical Engineering)This paper describes the effect of heat treatment on mechanical properties of high chromium (Cr) ferritic steel 9Cr-W-Mo-V-Nb steel as a part of development of high Cr steel for fast breeder reactor (FBR). The effects of normalizing temperature and tempering temperature and time on high temperature tensile properties and Charpy impact properties were investigated from the viewpoint of microstructures.
Obara, Satoshi; Onizawa, Takashi; Wakai, Takashi; Asayama, Tai
Proceedings of Workshop on Structural Materials for Innovative Nuclear Systems (SMINS), p.115 - 126, 2008/07
This study investigates the influence of normalising temperature on metal carbonitride (MX) precipitation behavior and mechanical property of high chromium (Cr) ferritic steel for sodium cooled fast reactor (SFR) structures. Generally, mechanical strength in high Cr steel is increased addition of vanadium (V) and niobium (Nb), because V and Nb play a role of precipitation strengthening elements as metal carbonitride (MX) particles. However, precipitation behavior depends not only on the amount of V and Nb but also on the heat treatment conditions. In this presentation, in order to investigate the optimum heat treatment conditions for FBR structural materials, several kinds of high Cr steels with different heat treatments were produced and a series of mechanical tests and metallurgical examinations were conducted.
Obara, Satoshi; Onizawa, Takashi
no journal, ,
no abstracts in English
Obara, Satoshi; Onizawa, Takashi; Wakai, Takashi; Aoto, Kazumi
no journal, ,
no abstracts in English
Obara, Satoshi; Yamada, Yoshiyuki*; Nakazawa, Takanori*
no journal, ,
This presentation shows the effect of heat treatment on high tensile property and toughness in W added high Cr ferritic heat resistant steel with several heat treatments. In the tensile test at evaluated temperature, the tensile strength was increased with increasing normalizing temperature. On the contrary, the tensile strength was decreased with increasing tempering temperature and time. In the Charpy impact test, fracture appearance transition temperature (FATT) was increased and upper shelf energy (USE) was decreased with increasing normalizing temperature. On the contrary, the FATT was decreased and USE was increased with increasing tempering temperature and time.
Obara, Satoshi; Yamada, Yoshiyuki*; Nakazawa, Takanori*; Yamazaki, Masayoshi*; Hongo, Hiromichi*
no journal, ,
no abstracts in English
Obara, Satoshi; Otsuka, Satoshi; Wakai, Takashi; Inoue, Masaki; Asayama, Tai; Suzuki, Junichi; Onuma, Masato*
no journal, ,
no abstracts in English
Obara, Satoshi; Takaya, Shigeru; Wakai, Takashi; Asayama, Tai; Suzuki, Hiroshi; Saito, Toru*; Lauernt, M.*
no journal, ,
For the commercialization of fast breeder reactors, it is considered reduction of total cost by elongation of plant service period. For this reason, it is needed to establish the aged weld joint integrity assessment method for future FBR components. Additionally, since it is expected to employ the repair weld for aged structural components, it is essential to investigate the effect of repair weld. To investigate the influence of high temperature-long service on weld joint, it is examined using microscopy, residual stress analysis and hardness tester. In addition, similar examinations are also conducted for repair weld joint to investigate the effect of repair weld.
Obara, Satoshi; Suzuki, Junichi; Wakai, Takashi; Inoue, Masaki; Asayama, Tai; Onuma, Masato*
no journal, ,
no abstracts in English
Onizawa, Takashi; Wakai, Takashi; Obara, Satoshi; Asayama, Tai
no journal, ,
High Cr steel for structural material of fast breeder reactors request high ductility and toughness during long term. V and Nb are believed to improve the high temperature strength of high Cr steels by precipitating as carbides and/or nitrides, namely fine MX particles. However, the long term efficiency and stability of such precipitation strengthening mechanisms provided by the fine MX particles have not been clarified yet. A series of trial products controlling V and Nb contents is produced and mechanical tests are conducted to investigate the effect of these elements on the mechanical properties and the long term stability of the MX strengthening mechanism. In this study, stability of NbX in high Cr steel under creep deformation was examined.
Miyashita, Yuta*; Nakazawa, Takanori*; Obara, Satoshi; Yamazaki, Masayoshi*; Hongo, Hiromichi*
no journal, ,
no abstracts in English
Obara, Satoshi; Wakai, Takashi; Asayama, Tai; Mogi, Masaru*; Miyashita, Yuta*; Nakazawa, Takanori*
no journal, ,
no abstracts in English
Obara, Satoshi; Wakai, Takashi; Asayama, Tai; Yamada, Yoshiyuki*; Nakazawa, Takanori*; Yamazaki, Masayoshi*; Hongo, Hiromichi*
no journal, ,
no abstracts in English
Onizawa, Takashi; Wakai, Takashi; Nagae, Yuji; Obara, Satoshi; Enuma, Yasuhiro*; Asayama, Tai
no journal, ,
no abstracts in English
