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Journal Articles

Research of estimation method of thermal aging embrittlement on cast austenitic stainless steel

Abe, Teruyoshi; Nogiwa, Kimihiro*; Onitsuka, Takashi*; Nakamura, Takahisa; Sakakibara, Yasuhide

E-Journal of Advanced Maintenance (Internet), 6(4), p.146 - 152, 2015/02

Thermal embrittlement of cast austenitic stainless steel components from the decommissioned advanced thermal prototype reactor Fugen has been characterized. Cast stainless steel materials were obtained from recirculation pump casing. The actual time at temperature for the materials was 138,000 h at 275$$^{circ}$$C. The "Fugen" material show modest decrease in Charpy-impact properties and a small increase in micro-Vickers hardness in ferrite phase because of thermal aging at relatively low service temperatures. The fracture toughness prediction method (H3T model) predicts slightly lower values for Charpy-impact energy obtained from the Fugen material. The results from microstructural analysis suggest that the prediction method have the potential to provide higher accuracy by considerations of the activation energy for embrittlement at low service temperatures.

Journal Articles

Effect of local segregation of phosphorous on intergranular corrosion of type 310 stainless steel in boiling nitric acid

Komatsu, Atsushi; Motooka, Takafumi; Makino, Masashi; Nogiwa, Kimihiro; Ueno, Fumiyoshi; Yamamoto, Masahiro

Zairyo To Kankyo, 63(3), p.98 - 103, 2014/03

The effect of phosphorous on intergranular corrosion of type 310 stainless steel at transpassive potential was investigated using phosphorous added ultra high purity type 310 stainless steel. Intergranular corrosion depth was measured by scanning electron microscopic observation. Grain boundaries were observed using three dimensional atom probe. Intergranular corrosion was observed on phosphorous added stainless steel. The sample heat treated at 600$$^{circ}$$C showed severe integranular corrosion morphology. Observation by three dimensional atom probe revealed that grain boundary with high dissolution rate had segregated zone of chromium and phosphorous about 5nm in width, on the other hand, grain boundary with low dissolution rate had no segregated zone. From these results, it is suggested that intergranular corrosion of phosphorous added type 310 stainless steel at transpassive potential is affected by segregation of phosphorous and chromium along grain boundaries.

Journal Articles

Influence of thermal aging on cast stainless steels used in JAEA's nuclear reactor Fugen

Nogiwa, Kimihiro; Onitsuka, Takashi; Abe, Teruyoshi; Sakakibara, Yasuhide; Horie, Kaoru; Nakamura, Takahisa

Journal of Nuclear Science and Technology, 50(9), p.883 - 890, 2013/09

 Times Cited Count:2 Percentile:77.96(Nuclear Science & Technology)

The degree of influence of thermal aging on cast stainless steels over a protracted time at low temperatures was investigated by means of a toughness test and microstructural characterization performed on components dismantled from the advanced thermal proto-type reactor "Fugen". The thermal embrittlement mechanism was examined using data obtained dismantled from the materials that had aged on site. The results of a Charpy impact test and microstructural characterization performed using 3DAP analysis reveal early signs of a thermal aging effect over a protracted period at low temperatures corresponding boiling-water reactor (BWR).

Journal Articles

Characterization of the microstructure of dual-phase 9Cr-ODS steels using a laser-assisted 3D atom probe

Nogiwa, Kimihiro; Nishimura, Akihiko; Yokoyama, Atsushi; Otsuka, Satoshi; Kaito, Takeji; Inoue, Masaki; Okubo, Tadakatsu*; Hono, Kazuhiro*

Journal of Nuclear Materials, 417(1-3), p.201 - 204, 2011/10

 Times Cited Count:7 Percentile:45.23(Materials Science, Multidisciplinary)

Du se 9Cr-ODS (oxide dispersion-strengthened) steel consisting of residual-$$alpha$$ ferrite and $$alpha$$ prime martensite has excellent high-temperature strength. This study describes the microstructure of dual-phase 9Cr-ODS steels characterized by atom-probe tomography in order to compare oxide-particle dispersion states in each phase. This revealed that nano-size oxide particles were of the same chemical composition and that their mean size was about 3 nm in each phase. On the other hand, the number density in the residual-$$alpha$$ phase was about four times higher than that of the $$alpha$$ prime phase. These results indicate that the dense distribution of the oxide particles in the residual-$$alpha$$ phase contribute to the excellent high-temperature strength of 9Cr-ODS steel.

Journal Articles

Influence of laser irradiation condition on a femtosecond laser-assisted tomographic atom probe

Nishimura, Akihiko; Nogiwa, Kimihiro; Otobe, Tomohito; Okubo, Tadakatsu*; Hono, Kazuhiro*; Kondo, Keietsu; Yokoyama, Atsushi

Ultramicroscopy, 109(5), p.467 - 471, 2009/04

 Times Cited Count:6 Percentile:71.01(Microscopy)

Influence of femtosecond laser pulse condition on the performance of an energy compensated tomographic atom probe (ECOTAP) was investigated. Chirping ratio for laser pulses was controlled by a compressor stage. We have succeeded to get tomographic images of oxide dispersion strengthen steel, which will be used as fast breeder reactors. The ECOTAP successfully observed that the instability of the femtosecond laser pulses make the mass peaks slightly sifted or broadened to higher mass number. To investigate insulator materials, numerical simulation of conductivity increase on diamond has been successfully demonstrated.

Journal Articles

Characterization of microstructures in ODS steel by a laser assisted 3DAP

Nogiwa, Kimihiro; Nishimura, Akihiko; Oba, Hironori; Yokoyama, Atsushi; Okubo, Tadakatsu*; Hono, Kazuhiro*

Materia, 47(12), P. 626, 2008/12

no abstracts in English

Oral presentation

Improvement of 3D atom probe assisted by femtosecond laser ionization

Nishimura, Akihiko; Nogiwa, Kimihiro; Kondo, Keietsu; Otobe, Tomohito; Yokoyama, Atsushi; Okubo, Tadakatsu*; Hono, Kazuhiro*

no journal, , 

We successfully improved the performance of 3- Dimensional atom probe by using femtosecond laser ionization. A reflectoron type atom probe was applied due to its high mass spectroscopy. Laser system has a specially designed pulse compressor to change the laser pulse duration. An OPA wave length converter was installed to the laser system. We selected ODS steel and Zr metal for 3D atom probe analysis with numerical simulation. Femtosecond laser assisted 3D atom probes can overcome the performance of voltage pulsing 3D atom probes completely.

Oral presentation

Developments of a femtosecond laser assisted 3D atom probe for characterization of microstructure in structural materials in nuclear power plants

Nogiwa, Kimihiro; Nishimura, Akihiko; Oba, Hironori; Yokoyama, Atsushi; Okubo, Tadakatsu*; Hono, Kazuhiro*

no journal, , 

no abstracts in English

Oral presentation

A Microstructural study of 9Cr-ODS steel for FBRs core materials using a laser-assisted-3DAP

Nogiwa, Kimihiro; Nishimura, Akihiko; Inoue, Masaki; Otsuka, Satoshi; Yokoyama, Atsushi; Okubo, Tadakatsu*; Hono, Kazuhiro*

no journal, , 

Japan Atomic Energy Agency (JAEA) has developed 9Cr-ODS martensitic steel and has succeeded in manufacturing thin-walled tubes that overcome highly anisotropic properties. Previous studies revealed that the 9Cr-ODS steel has a dual phase structure consisting of residual-ferrite and martensite. Improvement in creep strength is apparently caused by the retention of the phase, in which ultrafine oxide particles are dispersed. In this study, we have investigated the nanometer-scale microstructure of a dual phase 9Cr-ODS steel by the 3D atom probe operated with femtosecond laser pulses and compared the dispersion state of oxide particles in residual-ferrite and martensite phases.

Oral presentation

Evaluation of the fine tantalum rich particles in Fe-C-Ta model alloy

Kano, Sho; Enomoto, Masato*; Sakasegawa, Hideo; Tanigawa, Hiroyasu; Kondo, Keietsu; Nogiwa, Kimihiro; Toyama, Takeshi*; Nagai, Yasuyoshi*

no journal, , 

no abstracts in English

Oral presentation

Influence of thermal aging on cast duplex stainless steels in Fugen served materials

Nogiwa, Kimihiro; Onitsuka, Takashi; Abe, Teruyoshi; Sakakibara, Yasuhide; Nakamura, Takahisa; Horie, Kaoru

no journal, , 

no abstracts in English

Oral presentation

Study of thermal ageing behaviour of duplex stainless steels by positron annihilation lifetime technique

Onitsuka, Takashi; Nogiwa, Kimihiro; Abe, Teruyoshi; Sakakibara, Yasuhide; Nakamura, Takahisa; Horie, Kaoru

no journal, , 

no abstracts in English

Oral presentation

A Microstructural study of 9Cr-ODS steel for 9Cr-ODS steels using a laser-assisted-3DAP

Nogiwa, Kimihiro

no journal, , 

no abstracts in English

Oral presentation

Study of thermal ageing behaviour of duplex stainless steels by positron annihilation lifetime spectroscopy

Onitsuka, Takashi; Nogiwa, Kimihiro; Abe, Teruyoshi; Sakakibara, Yasuhide; Nakamura, Takahisa; Horie, Kaoru

no journal, , 

no abstracts in English

Oral presentation

Research of estimation method of thermal aging embrittlement on cast austenitic stainless steel

Nogiwa, Kimihiro; Onitsuka, Takashi; Abe, Teruyoshi; Sakakibara, Yasuhide; Nakamura, Takahisa

no journal, , 

Thermal embrittlement of cast austenitic stainless steel components from the decommissioned advanced thermal prototype reactor "Fugen" has been characterized. Cast stainless steel materials were obtained from recirculation pump casing. The actual time at temperature for the materials was 138,000 h at 275$$^{circ}$$C. The Fugen material show modest decrease in Charpy-impact properties and a small increase in micro-Vickers hardness in ferrite phase because of thermal aging at relatively low service temperatures. The fracture toughness prediction method (H3T model) predicts slightly lower values for Charpy-impact energy obtained from the Fugen material. The results from microstructural analysis suggest that the prediction method have the potential to provide higher accuracy by considerations of the activation energy for embrittlement at low service temperatures.

Oral presentation

Study of thermal aging embrittlement on stainless steels used Fugen nuclear reactor

Nogiwa, Kimihiro; Onitsuka, Takashi; Takeuchi, Tomoaki; Abe, Teruyoshi; Sakakibara, Yasuhide; Horie, Kaoru; Nakamura, Takahisa

no journal, , 

no abstracts in English

Oral presentation

EBSD analysis of fracture behaviour of cast duplex stainless steels used in JAEA's nuclear reactor Fugen

Takeuchi, Tomoaki; Nogiwa, Kimihiro*; Sakakibara, Yasuhide*; Tsuchiya, Kunihiko

no journal, , 

Analyses on fracture behavior of cast duplex stainless steels sampled from piping of primary loop recirculation system of JAEA's nuclear reactor Fugen were performed. The samples were composed of primary austenite phase, and minor ferrite phase with from a few to few tens percent of volume fraction. It is known that thermal aging at about 300-500$$^{circ}$$C causes hardening of only the ferrite phase. Therefore, electron back-scattered diffraction (EBSD) analysis, which can observe individually the properties of the two phases, was applied so as to reveal its fracture mechanism. The results indicated that the crystallographic orientation relationship between the austenite and ferrite was hybrid, and that the Charpy absorbed energy depended on the deformation behavior of not only the austenite phase but also the minor ferrite phase near the fracture surface.

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