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Journal Articles

Synergistic effect of aluminum lactate and sodium molybdate on freshwater corrosion of carbon steel under irradiation

Otani, Kyohei; Kato, Chiaki; Igarashi, Takahiro

Corrosion, 79(11), p.1277 - 1286, 2023/11

Journal Articles

Microstructural evolution of intermetallic phase precipitates in Cr-coated zirconium alloy cladding in high-temperature steam oxidation up to 1400$$^{circ}$$C

Mohamad, A. B.; Nemoto, Yoshiyuki; Furumoto, Kenichiro*; Okada, Yuji*; Sato, Daiki*

Corrosion Science, 224, p.111540_1 - 111540_15, 2023/11

Journal Articles

Hydrogen embrittlement and its prevention in 7XXX aluminum alloys with high Zn concentrations

Shimizu, Kazuyuki*; Toda, Hiroyuki*; Fujihara, Hiro*; Yamaguchi, Masatake; Uesugi, Masayuki*; Takeuchi, Akihisa*; Nishijima, Masahiko*; Kamada, Yasuhiro*

Corrosion, 79(8), p.818 - 830, 2023/08

7xxx aluminum alloys are representative high-strength aluminum alloys; however, mechanical property degradation due to hydrogen hinders further strengthening. We propose the dispersion of Mn-based second-phase particles as a novel technique for preventing 7xxx aluminum alloy hydrogen embrittlement. In this study, the deformation and fracture behaviors of high hydrogen 7xxx alloys containing 0.0% Mn and 0.6% Mn are observed in situ using synchrotron radiation X-ray tomography. The obtained macroscopic hydrogen embrittlement is quantitatively analyzed based on hydrogen partitioning in alloys. Adding 0.6% Mn, generating second-phase particles with high hydrogen trapping abilities, significantly suppresses hydrogen-induced quasicleavage fracture.

Journal Articles

Introduction of Cu$$^{2+}$$ to the inside of the crevice by chelation and its effect on crevice corrosion of Type 316L stainless steel

Aoyama, Takahito; Kato, Chiaki

Corrosion Science, 210(2), p.110850_1 - 110850_10, 2023/01

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

The chelated complex of Cu$$^{2+}$$: [Cu(EDTA)]$$^{2-}$$ was used to introduce Cu$$^{2+}$$ from outside to the inside of crevice. The introduced Cu$$^{2+}$$ was expected to act as an inhibitor for the crevice corrosion on stainless steels. Crevice corrosion tests, confirmed the introduction of Cu$$^{2+}$$ to the inside of the crevice via electromigration of [Cu(EDTA)]$$^{2-}$$ was confirmed. Migrated [Cu(EDTA)]$$^{2-}$$ reacted with H$$^{+}$$ and inhibited decrease in pH inside the crevice, where Cu$$^{2+}$$ was separated from [Cu(EDTA)]$$^{2-}$$ and suppressed active dissolution of the stainless steel.

Journal Articles

Characterization and corrosion behavior of Al-added high Mn ODS austenitic steels in oxygen-saturated lead-bismuth eutectic

Haoran, W.*; Yu, H.*; Liu, J.*; Kondo, Sosuke*; Okubo, Nariaki; Kasada, Ryuta*

Corrosion Science, 209, p.110818_1 - 110818_12, 2022/12

 Times Cited Count:1 Percentile:20.58(Materials Science, Multidisciplinary)

The corrosion behavior of newly developed Al$$_{2}$$O$$_{3}$$ forming high Mn oxide dispersion strengthened (ODS) austenitic steels was examined in oxygen-saturated lead-bismuth eutectic at 450$$^{circ}$$C for 430 h. Compared with non-ODS steels, the ODS steels possessed superior resistance to corrosion and spallation. The high density grain boundaries in the ODS steels acted as channels for the rapid outward diffusion of metallic elements, forming an internal continuous Cr$$_{2}$$O$$_{3}$$ scale at the original surface. Accelerated Al diffusion, along with oxidation prevention by the external (Fe, Mn) oxide scale and the internal Cr$$_{2}$$O$$_{3}$$ scale, jointly resulted in the formation of a continuous Al-rich oxide scale in ODS-7Al steel, contributing to its superior corrosion resistance.

Journal Articles

Effects of potential on the electrical conductivity of a solution within a crevice of stainless steel in high-temperature water

Soma, Yasutaka; Komatsu, Atsushi; Ueno, Fumiyoshi

Corrosion, 78(6), p.503 - 515, 2022/06

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

The effects of electrochemical potential (ECP) on water chemistry within a crevice are of critical importance for understanding stress corrosion cracking (SCC) of Fe-Cr-Ni alloys in high temperature water. In this study, the effects of ECP on the electrical conductivity of a solution within a Type-316L stainless steel crevice ($$sigma$$$$_{crev}$$) have been studied in 288$$^{circ}$$C and 8 MPa water containing 10 ppb Cl$$^{-}$$ as major anionic species. In situ measurements of $$sigma$$$$_{crev}$$ in a rectangular crevice with a gap of 15 $$mu$$m and a depth of 23 mm have been conducted using small sensors installed at different crevice depths. An increase in ECP from -0.49 V (vs. standard hydrogen electrode) to -0.12 V resulted in an increase in $$sigma$$$$_{crev}$$ from 12 $$mu$$Scm$$^{-1}$$ to 160 $$mu$$Scm$$^{-1}$$ at a distance of 21 mm from the crevice mouth. The increase in $$sigma$$$$_{crev}$$ reached a maximum at about 0.15 V (about 300 $$mu$$Scm$$^{-1}$$) and then tended to decrease with increasing potential. Finite element model analysis taking into account the electrochemical reaction quantitatively reproduced this behavior. It is considered that Cl$$^{-}$$ is the major anionic species transported into the crevice at relatively low potentials, and that $$sigma$$$$_{crev}$$ increases monotonically with increasing ECP. On the other hand, when ECP exceeds around 0 V, a sufficient amount of HCrO$$_{4}$$$$^{-}$$ generated by transpassive dissolution also transported into the gap. Since this chemical species is highly oxidizing, unlike Cl, it is assumed that it reacts with metal cations to oxidize and precipitate them, thereby lowering conductivity.

Journal Articles

Three-dimensional computational modeling and simulation of intergranular corrosion propagation of stainless steel

Igarashi, Takahiro; Komatsu, Atsushi; Motooka, Takafumi*; Ueno, Fumiyoshi; Yamamoto, Masahiro

Corrosion Science and Technology, 20(3), p.105 - 111, 2021/06

We constructed three dimensional computational model using cellular automata method to simulate the intergranular corrosion propagation of stainless steel. In the model, the computational system was constructed by three types of cells: grain (bulk), grain boundary (GB), and solution cell. Our simulations revealed that the surface roughness calculated by the model adopted distributed dissolution rates of GBs was greater than that adopted constant dissolution rates of GBs. The cross-sectional images obtained by our simulation were comparable with that obtained by corrosion tests. These results indicate that the surface roughness during corrosion relates the distribution of corrosion rate.

Journal Articles

Electrochemical behavior of carbon steel with bentonite/sand in saline environment

Kitayama, Ayami; Taniguchi, Naoki; Mitsui, Seiichiro

Materials and Corrosion, 72(1-2), p.211 - 217, 2021/01

 Times Cited Count:0 Percentile:0(Materials Science, Multidisciplinary)

Journal Articles

Corrosion resistance of a cast steel overpack for high-level radioactive waste disposal in Japan

Ogawa, Yusuke*; Suzuki, Satoru*; Taniguchi, Naoki; Kawasaki, Manabu*; Suzuki, Hiroyuki*; Takahashi, Rieko*

Materials and Corrosion, 72(1-2), p.52 - 66, 2021/01

 Times Cited Count:2 Percentile:13.49(Materials Science, Multidisciplinary)

Cast steel is one of the promising alternative to forged steel that is the current reference material for carbon steel overpack. In this study, the full-scale cast steel overpack was produced experimentally and the distribution of casting defects were investigated. The corrosion test regarding corrosion rate and stress corrosion cracking (SCC) susceptibility were also conducted using samples taken from the full-scale cast steel overpack and the corrosion resistance of cast steel was compared with that of forged steel. From above two corrosion tests, it can be said that the corrosion resistance of cast steel is mostly the same as that of forged steel.

Journal Articles

Stress corrosion cracking of copper in swollen bentonite simulating nuclear waste disposal environment

Fujimoto, Shinji*; Tsuchiya, Hiroaki*; Ogawa, Soma*; Iida, Yoshihisa; Taniguchi, Naoki

Materials and Corrosion, 72(1-2), p.333 - 338, 2021/01

 Times Cited Count:2 Percentile:13.49(Materials Science, Multidisciplinary)

The stress corrosion cracking (SCC) of pure copper in bentonite was examined by a slow strain rate test (SSRT). The bentonite was swollen with pure water or aqueous solutions containing NH$$_{3}$$ of 0.05 M and 0.1 M. The thick corrosion films and particulate deposits were formed on copper surface after SSRT. Typical tarnish rupture type SCC occurred on pure copper in swollen bentonite with and without NH$$_{3}$$. Crack propagation rate was enhanced by NH$$_{3}$$. It is confirmed thick oxide layer is formed on copper during plastic deformation which resulting in the tarnish crack type SCC. The many particulate deposits observed on the surface might be formed as a results of rapid dissolution of Cu$$^{2+}$$ to form porous CuO at locallized deformed sites.

Journal Articles

Effects of residual stress and plastic strain on hydrogen embrittlement of a stretch-formed TRIP-aided martensitic steel sheet

Hojo, Tomohiko*; Akiyama, Eiji*; Saito, Hiroyuki*; Shiro, Ayumi*; Yasuda, Ryo*; Shobu, Takahisa; Kinugasa, Junichiro*; Yuse, Fumio*

Corrosion Science, 177, p.108957_1 - 108957_9, 2020/12

 Times Cited Count:15 Percentile:76.55(Materials Science, Multidisciplinary)

Hydrogen assisted cracking on hemispherically-stretch-formed specimens of transformation induced plasticity-aided martensitic steel was investigated. Hydrogen charging induced cracking around the foot of the impression formed on the steel sheet, and the cracks propagated along the radial direction toward the hillside and the plains. Distributions of stress, plastic strain and volume fraction of retained austenite were analyzed employing the energy-dispersive X-ray diffraction method utilizing the synchrotron X-ray radiation at SPring-8. It was notable that the crack initiation took place in the region where the measured tensile stress was the highest. Influences of plastic strain and resulted martensitic transformation were also suggested.

Journal Articles

Relationship between the microstructure and local corrosion properties of weld metal in austenitic stainless steels

Tokita, Shun*; Kadoi, Kota*; Aoki, So; Inoue, Hiroshige*

Corrosion Science, 175, p.108867_1 - 108867_8, 2020/10

 Times Cited Count:19 Percentile:84.05(Materials Science, Multidisciplinary)

The purpose of this study is to evaluate the corrosion resistance of weld metal by electrochemical methods and discuss the relationship between microstructure and corrosion resistance. Intergranular and pitting corrosion resistances were measured using electrochemical potentiokinetic reactivation (EPR) test and pitting potential measurement respectively. The reactivation ratio and pitting potential corresponded to its chemical composition. The specimens containing more Cr and Mo showed higher resistance. In the EPR test, the dendrite core with a relatively low Cr content was corroded. In the pitting corrosion test, Nb carbide became the initiation site of pitting corrosion which propagated along the cell structure.

Journal Articles

Corrosion behaviour of Al-added high Mn austenitic steels in molten lead bismuth eutectic with saturated and low oxygen concentrations at 450$$^{circ}$$C

Wang, H.*; Yu, H.*; Kondo, Sosuke*; Okubo, Nariaki; Kasada, Ryuta*

Corrosion Science, 175, p.108864_1 - 108864_12, 2020/10

 Times Cited Count:19 Percentile:85.18(Materials Science, Multidisciplinary)

Corrosion tests were performed on newly developed alumina-forming austenitic (AFA) steels in stagnant lead bismuth eutectic (LBE) with saturated and low oxygen concentrations at 450$$^{circ}$$C for 430 h. The steels exhibited enhanced corrosion resistance to the LBE environments with the increasing of Al content. A continuous and protective Al-rich oxide scale formed on the steel specimens that were exposed to LBE with a low oxygen concentration, whereas a non-protective and stratified oxide scale formed in the oxygen saturated LBE.

Journal Articles

Modelling of intergranular corrosion using cellular automata, 1; Characteristics and corrosion rates of stainless steels in modified nuclear reprocessing solution

Yamamoto, Masahiro; Irisawa, Eriko; Igarashi, Takahiro; Komatsu, Atsushi; Kato, Chiaki; Ueno, Fumiyoshi

Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2019) (Internet), 5 Pages, 2019/09

Intergranular corrosion phenomena were analysed using modified reprocessing solution. The data indicated that corrosion rates increased with time at the initial stage, and these stayed at constant value. Intergranular corrosion propagated at grain boundary in the initial stage and then attacked whole grain boundary causing drop out of grains. Corrosion rates of steady state were sum of intergranular corrosion amounts and weight losses of dropped grains. Surface appearances and cross sections of corroded samples were analyzed. The results indicated that the initial stage of intergranular corrosion was characterized by the ratio of corrosion rates between grain boundary and matrix. These ratios differed from individual grain boundaries. Total corrosion rates were affected by the distribution of these ratios. These data were based on the numerical modelling of intergranular corrosion using cellular automata. And also, calculated results were compared with these analytical data.

Journal Articles

Mass transfer inside narrow crevice of SUS316L in high temperature water

Yamamoto, Masahiro; Soma, Yasutaka; Igarashi, Takahiro; Ueno, Fumiyoshi

Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2018) (USB Flash Drive), 7 Pages, 2018/09

In order to clarify the SCC behavior of SUS316L under BWR environment, mass transfer inside crevice of SUS316L in high temperature water using various crevice gap samples was investigated. The samples were prepared by put together two SUS316L sheets. Crevice gap differs from 0.005 mm to 0.1 mm. Corrosion tests were conducted in 8 ppm dissolved oxygen (DO) conditions. Surface oxide film was analysed by laser Raman spectroscopy (LRS) after immersion. Numerical simulations were also conducted by using COMSOL Maltiphysics. Diffusion process of DO and the other chemical species were calculated with connected to electrochemical process. Electrical conductivities inside the crevice were 100 times larger than these of outer water. The reason of high conductivity is existence of Fe$$^{2+}$$ ions at the DO depletion crevice.

Journal Articles

Study on oxidation model for Zircalloy-2 cladding in SFP accident condition

Nemoto, Yoshiyuki; Kaji, Yoshiyuki; Onizawa, Takashi*; Kanazawa, Toru*; Nakashima, Kazuo*; Tojo, Masayuki*

Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2018) (USB Flash Drive), 8 Pages, 2018/09

The authors proposed oxidation models based on oxidation data which previously obtained in high temperature oxidation tests on small sample of Zircalloy-2 (Zry2) cladding in dry air and in air/steam mixture environment. The oxidation models were implemented in computational fluid dynamics (CFD) code to analyse oxidation behavior of long cladding sample in hypothetical spent fuel pool (SFP) accident conditions. The oxidation tests were conducted using Zry2 cladding sample 500 mm in length. The oxide layer growth in dry air was well reproduced in the calculation using the oxidation model, meanwhile which in air/steam mixture was overestimated atmosphere composition change anticipated in the spent fuel rack during the accident, and its influence on the oxidation behaviour of the cladding were discussed in consideration of the oxidation model improvement.

Journal Articles

Effects of environmental factors inside the crevice on corrosion of stainless steel in high temperature water

Yamamoto, Masahiro; Sato, Tomonori; Igarashi, Takahiro; Ueno, Fumiyoshi; Soma, Yasutaka

Proceedings of European Corrosion Congress 2017 (EUROCORR 2017) and 20th ICC & Process Safety Congress 2017 (USB Flash Drive), 6 Pages, 2018/09

The authors have studied the differences between outer surface and the crevice-like portion of SUS316L in high pressurized and high temperature water containing dissolved oxygen. We have already introduced that changes in the characteristics of corrosion products along the crevice directions and gap width. It is suggested that the environmental conditions are different with the features of crevice from these results. In this report, we introduce the changes in oxide films with crevice gaps and comparison with the numerical simulation data utilizing of FEM calculation.

Journal Articles

Corrosion inhibition effects of metal cations on SUS304 in 0.5 M Cl$$^{-}$$ aqueous solution

Islam, M. S.*; Otani, Kyohei; Sakairi, Masatoshi*

Corrosion Science, 140, p.8 - 17, 2018/08

 Times Cited Count:11 Percentile:55.08(Materials Science, Multidisciplinary)

The corrosion characteristics of SUS304 exposed to 0.5M Cl$$^{-}$$ aqueous solution containing different metal cations were studied with immersion tests, surface analysis and electrochemical tests. The mechanism of corrosion with metal cations was clarified by the XPS analysis results together with the hard and soft acid and base (HSAB) concept and the passive films structure. It is supposed that metal cations with large hardness make a layer by chemical bonding with the passive films. The passive films are protected by the metal cation layer from Cl$$^{-}$$ attack, and consequently corrosion reactions are inhibited.

Journal Articles

An Empirical model for the corrosion of stainless steel in BWR primary coolant

Uchida, Shunsuke*; Hanawa, Satoshi; Naito, Masanori*; Okada, Hidetoshi*; Lister, D. H.*

Corrosion Engineering, Science and Technology, 52(8), p.587 - 595, 2017/10

 Times Cited Count:4 Percentile:21.84(Materials Science, Multidisciplinary)

Based on the relationship among ECP, metal surface conditions, exposure time and other environmental conditions, a model to evaluate the ECP and corrosion rate of steel was developed by coupling a static electrochemical analysis and a dynamic oxide layer growth analysis. Major conclusion obtained on the model are as follows. The effect of H$$_{2}$$O$$_{2}$$ and O$$_{2}$$ concentrations on ECP were successfully explained as the effects of oxide layer growth. Hysteresis of ECP under changes in water chemistry conditions were successfully explained with the model. Decreases in ECP due to neutron exposure were explained well by radiation-induced diffusion in the oxide layers.

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