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Nakano, Junichi; Nemoto, Yoshiyuki; Tsukada, Takashi; Uchimoto, Tetsuya*
Journal of Nuclear Materials, 417(1-3), p.883 - 886, 2011/10
Times Cited Count：2 Percentile：18.29(Materials Science, Multidisciplinary)To examine the effects of minor elements on stress corrosion cracking (SCC) susceptibility of low carbon stainless steels with work hardened layer, a high purity type 304 stainless steel was fabricated and minor elements, Si, S, P, C or Ti, were added. Work hardened layer was introduced by shaving on the surface of stainless steels. The specimens were exposed to a boiling 42% MgCl
solution for 20 hours and the number and the length of initiated cracks were examined. SCC susceptibility of the specimen with P was the highest and that of the specimen with C was the lowest in all specimens. By magnetic force microscope examination, magnetic phase expected to be martensitic phase was detected near surface. Since corrosion resistance of martensite is lower than that of austenite, the minor elements additions would affect SCC susceptibility through the amount of the transformed martensite, i.e. austenite stability.
Nemoto, Yoshiyuki; Keyakida, Satoshi*; Uchimoto, Tetsuya*; Takaya, Shigeru; Tsukada, Takashi
International Journal of Applied Electromagnetics and Mechanics, 35(2), p.123 - 139, 2011/02
Times Cited Count：1 Percentile：11.16(Engineering, Electrical & Electronic)JP, 2008-301850
Patent publication (In Japanese)
This paper presents a study conducted to develop a diagnostic system that can detect IASCC precursors in stainless steels by measuring the magnetic properties of the material. The eddy current method and alternating current (AC) magnetization method were used, as these will be more practical for use in actual reactors. Probes were developed for these measurement methods, providing sufficient tolerance for environments in nuclear reactors. An attempt was also made to improve spatial resolution by manufacturing a smaller probe. A sensor system was designed for remote control, performance tests were conducted by measuring neutron-irradiated specimens and mock specimens, and magnetic data were evaluated by comparing the IASCC susceptibility of the specimens. It was proved that the sensor system developed in this study is capable of detecting IASCC precursors. Further developments necessary for application in actual nuclear reactors and the mechanism of correlation between magnetic properties and IASCC susceptibility were also discussed.
Oikawa, Ryota*; Uchimoto, Tetsuya*; Takagi, Toshiyuki*; Urayama, Ryoichi*; Nemoto, Yoshiyuki; Takaya, Shigeru; Keyakida, Satoshi*
International Journal of Applied Electromagnetics and Mechanics, 33(3-4), p.1303 - 1308, 2010/10
Times Cited Count：5 Percentile：35(Engineering, Electrical & Electronic)This paper discusses feasibility of non-linear eddy current method to evaluate material degradations of austenitic stainless steels associated with irradiation assisted stress corrosion cracking (IASCC). For the purpose, tensile test at elevated temperature was conducted using model alloys simulating radiation induced segregation (RIS), then magnetization curve of the specimens was measured by vibrating sample magnetometer (VSM), and microstructure of magnetization was observed by magnetic force microscopy (MFM). Moreover non-linear eddy current method was carried out. It was shown that the 3rd higher harmonic ration of the pick-up signal would relate to nominal strain of the specimens.
Takaya, Shigeru; Nemoto, Yoshiyuki; Uchimoto, Tetsuya*; Keyakida, Satoshi*
Nihon AEM Gakkai-Shi, 17(1), p.156 - 161, 2009/03
In a previous study, authors showed experimentally the correlation between leakage magnetic flux density and irradiation assisted stress corrosion cracking susceptibility of high purity model austenitic stainless steels. This study aimed to investigate mechanism of the correlation. Tensile test at elevated temperature and aging test were conducted on materials simulating irradiation-induced segregation, and leakage magnetic flux density was measured before and after these tests in order to study the influence of chemical composition change and lattice defect to leakage magnetic flux density. Furthermore, dependency of magnetic moment on chemical composition and vacancy was evaluated by first principle calculation. As result, it was shown that leakage magnetic flux density of irradiated materials is thought to increase in severe irradiation-induced segregation region with and without vacancy.
Nemoto, Yoshiyuki; Keyakida, Satoshi*; Uchimoto, Tetsuya*; Takaya, Shigeru; Tsukada, Takashi
Hozengaku, 7(4), p.57 - 68, 2009/01
Authors previously reported leakage magnetic flux density measured by flux gate (FG) sensor seems to depend on irradiation assisted stress corrosion cracking (IASCC) susceptibility of neutron irradiated austenitic stainless steels. This study aimed to evaluate possibility to develop diagnostic method to detect symptom of IASCC by more practical methods such as Eddy current method and AC magnetization method. Magnetic properties of neutron irradiated specimens and mockup specimens were studied and dependence on IASCC susceptibility was revealed. Microstructure observation using transmission electron microscope (TEM) was conducted to study magnetic phase formation by radiation induced segregation. It was shown that measurement of magnetic signal changed by magnetic phase formation along grain boundaries caused by radiation induced segregation would be a mechanism of the diagnostic method to detect symptom of IASCC.
Nemoto, Yoshiyuki; Uchimoto, Tetsuya*; Keyakida, Satoshi*; Nagae, Yuji; Takaya, Shigeru; Ebine, Noriya; Tsukada, Takashi
no journal, ,
It was suggested by the authors that electromagnetic method could detect irradiation assisted stress corrosion cracking (IASCC) of austenitic stainless steel in advance of crack initiation. Authors investigated the mechanism using mock specimens of radiation induced segregation (RIS). SCC susceptibility and electromagnetic properties of the mock specimens were studied. Results were compared with the data of irradiated specimens and mechanism of electromagnetic diagnosis were discussed. A sensor system will be developed by application of these mechanism.
Nemoto, Yoshiyuki; Takaya, Shigeru; Ebine, Noriya; Tsukada, Takashi; Uchimoto, Tetsuya*; Keyakida, Satoshi*
no journal, ,
no abstracts in English
Nemoto, Yoshiyuki; Miwa, Yukio; Takaya, Shigeru; Ebine, Noriya; Tsukada, Takashi; Uchimoto, Tetsuya*; Keyakida, Satoshi*
no journal, ,
Authors reported previously that magnetic parameter seems to depend on irradiation assisted stress corrosion cracking susceptibility of high purity model austenitic stainless steels. This study aimed to investigate mechanism of the dependence. Electron diffraction patterns obtained by transmission electron microscopy were evaluated to study precipitation in irradiated specimens. Influence of element segregation on electro magnetic property of austenitic stainless steel was investigated applying mockup specimens. It was shown that magnetic phases were formed in irradiated austenitic stainless steels. Mockup experiments showed that radiation induced segregation can bring magnetic phase formation along grain boundaries. The magnetic phase was thought to involve with mechanism of magnetic parameter dependence on irradiation assisted stress corrosion cracking susceptibility.
Nemoto, Yoshiyuki; Miwa, Yukio; Takaya, Shigeru; Ebine, Noriya; Tsukada, Takashi; Uchimoto, Tetsuya*; Keyakida, Satoshi*
no journal, ,
Authors reported previously that magnetic parameter seems to depend on irradiation assisted stress corrosion cracking susceptibility of high purity model austenitic stainless steels. This study aimed to investigate mechanism of the dependence. Electron diffraction patterns obtained by transmission electron microscopy were evaluated to study precipitation in irradiated specimens. Influence of element segregation on electro magnetic property of austenitic stainless steel was investigated applying mockup specimens. It was shown that magnetic phases were formed in irradiated austenitic stainless steels. Mockup experiments showed that radiation induced segregation can bring magnetic phase formation along grain boundaries. The magnetic phase was thought to involve with mechanism of magnetic parameter dependence on irradiation assisted stress corrosion cracking susceptibility.
Takaya, Shigeru; Nemoto, Yoshiyuki; Uchimoto, Tetsuya*; Keyakida, Satoshi*
no journal, ,
In a previous study, authors showed experimentally the correlation between leakage magnetic flux density and irradiation assisted stress corrosion cracking susceptibility of high purity model austenitic stainless steels. This study aimed to investigate mechanism of the correlation. Tensile test at elevated temperature and aging test were conducted on materials simulating irradiation-induced segregation, and leakage magnetic flux density was measured before and after these tests in order to study the influence of chemical composition change and lattice defect to leakage magnetic flux density. Furthermore, dependency of magnetic moment on lattice constant was evaluated by first principle calculation. As result, it was shown that leakage magnetic flux density of irradiated materials is thought to increase in severe irradiation-induced segregation region.
Uchimoto, Tetsuya*; Takagi, Toshiyuki*; Nemoto, Yoshiyuki; Takaya, Shigeru; Keyakida, Satoshi*
no journal, ,
This paper discusses feasibility of non-linear eddy current method to evaluate material degradations of austenitic stainless steels associated with irradiation assisted stress corrosion cracking. For the purpose, tensile test at elevated temperature was conducted on materials simulating radiation-induced segregation, and non linear harmonic analysis of eddy current was carried out for the tensile test specimens. In addition, microstructure of magnetization of the tensile test specimens was observed by magnetic force microscopy. It was shown that non linear harmonics of eddy current is associated with the Cr depletion and Ni enrichment at grain boundary and intragranular phase transformation.
Oikawa, Ryota*; Uchimoto, Tetsuya*; Takagi, Toshiyuki*; Urayama, Ryoichi*; Nemoto, Yoshiyuki; Takaya, Shigeru; Keyakida, Satoshi*
no journal, ,
no abstracts in English
Uchimoto, Tetsuya*; Oikawa, Ryota*; Takagi, Toshiyuki*; Urayama, Ryoichi*; Nemoto, Yoshiyuki; Takaya, Shigeru; Keyakida, Satoshi*
no journal, ,
Shibuya, Kentaro*; Uchimoto, Tetsuya*; Takagi, Toshiyuki*; Takaya, Shigeru
no journal, ,
Magnetic property of aged samples and creep rupture samples of mod. 9Cr-1Mo steel were measured by a nonlinear eddy current method and a magnetic Kerr effect method. Concerning the creep rupture samples, it was found that the equivalent remanent magnetization measured by the nonlinear eddy current method and that measured by the magnetic Kerr effect method are different. This difference may be introduced by change in precipitation of MX carbonnitride and dislocation.
Matsumoto, Takanori*; Uchimoto, Tetsuya*; Takagi, Toshiyuki*; Takaya, Shigeru
no journal, ,
Mod. 9Cr-1Mo steel is used in advanced fossil power plants. It becomes more important to manage creep damage because temperature and pressure in operating conditions become higher. In this study, it is an objective to evaluate microstructure change due to creep damage by nonlinear eddy current testing. Firstly, relationship between signal of nonlinear eddy current testing and microstructure of creep test samples of mod. 9Cr-1Mo steel was investigated. Next, nonlinear electro-magnetic analysis was performed by using FEM, and then models describe the relation between microstructure and magnetic property was discussed. As result, the possibility of quantitative evaluation of microstructure change due to creep damage by the proposed method is shown.
Matsumoto, Takanori*; Uchimoto, Tetsuya*; Takagi, Toshiyuki*; Takaya, Shigeru
no journal, ,
The aim of this study is to evaluate microstructure change by creep damage of mod. 9Cr-1Mo steels using electromagnetic nondestructive evaluation. For the purpose, AC magnetization curves of isothermal aging specimens are discussed. Through the comparison between experimental and numerical results, equivalent conductivity and relative permeability are evaluated, and the relationship between microstructure and magnetic properties is discussed.
