Steel In High Temperature Water Research Articles

OS0821 高温水中におけるステンレス鋼の低サイクル疲労寿命におよぼす表面粗さと荷重条件の影響

OS0821 高温水中におけるステンレス鋼の低サイクル疲労寿命におよぼす表面粗さと荷重条件の影響

Nanostructure and Local Properties of Oxide Layers Grown On Stainless Steel in High Temperature Water

not Available.

Crack initiation behavior of neutron irradiated model and commercial stainless steels in high temperature water

The objective of this study was to isolate key factors affecting the irradiation-assisted stress corrosion cracking (IASCC) susceptibility of eleven neutron-irradiated austenitic stainless steel alloys. Four commercial purity and seven high purity stainless steels were fabricated with specific changes in composition and microstructure, and irradiated in a fast reactor spectrum at 320°C to doses between 4.4 and 47.5dpa. Constant extension rate tensile (CERT) tests were performed in normal water chemistry (NWC), hydrogen water chemistry (HWC), or primary water (PW) environments to isolate the effects of environment, elemental solute addition, alloy purity, alloy heat, alloy type, cold work, and irradiation dose. The irradiated alloys showed a wide variation in IASCC susceptibility, as measured by the relative changes in mechanical properties and crack morphology. Cracking susceptibility measured by %IG was enhanced in oxidizing environments, although testing in the lowest potential environment caused an increase in surface crack density. Alloys containing solute addition of Ni or Ni+Cr exhibited no IASCC. Susceptibility was reduced in materials cold worked prior to irradiation, and increased with increasing irradiation dose. Irradiation-induced hardening was accounted for by the dislocation loop microstructure, however no relation between crack initiation and radiation hardening was found.

Thermo-Mechanical and Isothermal Low-Cycle Fatigue Behavior of Type 316L Stainless Steel in High-Temperature Water and Air

Two unique facilities for isothermal low-cycle fatigue (LCF) and in-phase (IP) or out-of-phase (OP) thermo-mechanical fatigue (TMF) testing of tubular specimens under boiling water reactor (BWR) and pressurized water reactor (PWR) coolant conditions were set up and successfully tested. The systems allow both strain- and stress-controlled fatigue experiments with very small strain amplitudes or complex stress/strain profiles with superimposed rather rapid temperature changes (100°C to 340°C) under flowing conditions. The present article introduces the new test facility and briefly discusses the first results of these experiments. In contrast to air, a strong effect of temperature on LCF and TMF lives was observed in deoxygenated and hydrogenated high-temperature water environment, where both lives decrease with increasing temperature above 100°C. The TMF life is between that of the isothermal LCF tests at minimum and maximum temperature. The IP TMF life is shorter than that of OP TMF and close to the LCF l...

冷間加工炭素鋼の高温水中応力腐食割れに及ぼすキャビティ生成の役割:2.き裂発生試験からの検討

冷間加工炭素鋼の高温水中応力腐食割れに及ぼすキャビティ生成の役割:2.き裂発生試験からの検討

Determination of Electrochemical Corrosion Potential along the JMTR In-Pile Loop - I: Evaluation of ECP of Stainless Steel in High-Temperature Water as a Function of Oxidant Concentrations and Exposure Time

In-pile loop experiments are one of the key technologies that can provide an understanding of corrosion behaviors of structural materials in nuclear power plants (NPPs). The experiments should be supported not only by reliable measurement tools to confirm corrosive conditions under neutron and gamma-ray irradiations but also by theoretical models for extrapolating the measured data to predict corrosion behaviors in NPPs.The relationships among electrochemical corrosion potential (ECP), metal surface conditions, exposure time, and other environmental conditions have been determined from in situ measurements of corrosion behaviors of stainless steel specimens exposed to H2O2 and O2 in high-temperature water. Based on the relationships, a model to evaluate the ECP of stainless steel was developed by coupling an electrochemical model and a double-oxide layer model.Major conclusions obtained from the evaluation model are as follows: (a) The difference in ECP behaviors of the specimens exposed to H2O2 and O2 were mainly from the thickness and developing rate of the inner oxide layers. (b) Calculated ECP behaviors, e.g., the different responses to H2O2 and O2 and hysteresis and memory effects, agreed with the measured ones. (c) Neutron exposure might decrease ECP due to radiation-induced diffusion in the oxide layer.The ECP evaluation model will be applied to evaluation of corrosive conditions in the JMTR in-pile loop.

Role of Cavity Formation in Crack Initiation of Cold-Worked Carbon Steel in High-Temperature Water

Crack initiation behavior was studied to understand the underlying processes during the incubation period for prediction of crack initiation after long-term exposure in high-temperature water. Tests were performed using blunt-notched compact tension-type specimens of cold-worked carbon steel (ASTM A106 [UNS K03006]) exposed under static load condition in hydrogenated pure water and in air in the range of temperatures between 320°C and 450°C. Five important patterns were observed. First, intergranular cracking was observed in both water and air, even in static load conditions when steel specimens had been cold-worked. Second, 1/T-type temperature dependencies of initiation times were observed for cold-worked (CW) carbon steel (CW carbon steel), and the crack initiation time in an operating plant (Point Lepreau Nuclear Generating Station, Point Lepreau, New Brunswick, Canada) seemed to lie in the extrapolated line of the experimental results. Third, cavities were identified at the grain boundaries at the bottom of a notch (highly stressed location) before cracks initiated both in water and air. The cavities seem to result from the condensation of vacancies and affected the bond strength of grain boundaries. Consequently, the bond strength is assumed to be weakened during the incubation period. Fourth, the rate of formation of cavities in water was more than 10 times the rate in air. This suggests that the rate of diffusion of vacancies may be enhanced by the absorption of hydrogen, which results from the reduction of water on the surface. Fifth, an excellent correlation was observed between the rates of crack growth and cavity formation both for stress corrosion cracking (SCC) and creep cracking. This suggested that the rate limiting process of crack growth is the formation of cavities at grain boundaries both in creep cracking and for SCC in high-temperature water. Finally, to assess the mechanism of intergranular stress corrosion cracking (IGSCC) initiation and growth at high-temperature water, the diffusion of vacancies driven by stress gradients was studied using a specially designed compact tension (CT)-type specimen. As a model for IGSCC in cold-worked carbon steel in high-temperature water, the formation of cavities from the collapse of vacancies seems to be the best interpretation of the present data.

Stress corrosion cracking of Ru doped 304 stainless steel in high temperature water

In pressurised water reactor primary water, there is generally growing concern that stress corrosion cracking (SCC) may occur in occluded locations where residual oxygen and other impurities may be trapped. For these critical components, the deployment of more SCC resistant materials is desirable. In this paper, the effect of 1 wt-%Ru additions on the SCC susceptibility of 304 austenitic stainless steels was investigated in high temperature water. Slow strain rate tensile tests were performed on standard and 1 wt-%Ru modified 304 stainless steels in both sensitised and cold worked conditions. Preliminary results showed that, although both ruthenium doped and standard 304 stainless steels exhibited intergranular SCC, the former was less susceptible as indicated by a greater strain to failure. The results obtained suggest an improved performance of the Ru doped 304 stainless steel towards SCC susceptibility in these environments.

Stress Corrosion Cracking of Sensitized Type 304 Stainless Steel in High-Temperature Water with Anionic Impurities Contamination

This paper describes some results selected from a larger program that was aimed at understanding the stress corrosion cracking (SCC) initiation of Type 304 stainless steel (UNS S30400) in high-temperature deaerated water. Out of a large number of statically loaded samples, only a small minority of the tested samples underwent SCC. The occurrence of SCC indicates a synergism between sensitization, ionic impurities (mainly chloride and sulfate), and/or superficial defects and cold work. In fact, none of the nonsensitized materials initiated cracking (within the time scale of the tests), while only three sensitized samples underwent extensive SCC. The crack morphology of the fractured sample was predominantly inter-granular with some transgranular regions. Transmission electron microscopic samples containing crack tips were, in most respect, in line with the literature: a magnetite/spinel duplex layer on the crack surfaces, a Cr-rich oxide at the crack tip, and Ni enrichment at the metal/oxide interface and oxidized deformation bands intercepting the crack flanks. Also, finger-like features protruding several hundreds of nanometers along the slip planes intersecting the intergranular crack were found on grain boundaries with a high degree of localized deformation. These results support the theory that cracking initiation and propagation might be associated with the formation of oxide on crystallographic planes inside the material.

Influence of dissolved oxygen concentration on the oxide film formed on 304 stainless steel in high temperature water

Characteristics of the oxide films formed on 304 stainless steel under different dissolved oxygen (DO) concentrations in 290°C water were investigated. Less hematite and more spinel oxides form on fresh sample as DO decreases. Meanwhile, relative Cr content in the film increases. Spinel develops on the film preformed under 3ppm DO when it was further immersed under DO below 5ppb while the preformed hematite degrades. The spinel preformed under DO below 5ppb still grows up when further immersed under 3ppm DO while the base layer becomes more porous due to dissolution of Cr.

電気回路理論に基づく高温水中18-8ステンレス鋼の応力腐食割れ進展過程の評価方法の考察

冷間加工が高温水中における18Cr-8Ni（18-8）オーステナイトステンレス鋼の応力腐食割れ（SCC）進展過程に及ぼす効果を評価する方法が，電気回路モデルを用いて定量的に考察されてきた．本論文では導出されたSCC進展速度評価式において，き裂先端の分極抵抗に関連するパラメーターを考察することにより，冷間加工及び溶接HAZ部が高温水中のステンレス鋼のき裂進展速度に及ぼす効果及び鋭敏化処理との複合効果を当該導出式を用いて評価できることを確認した．

Work Hardening, Sensitization, and Potential Effects on the Susceptibility to Crack Initiation of 316L Stainless Steel in BWR Environment

After CBB testing, the structure and composition of surface oxide films on austenitic stainless steels in high-temperature water were examined by changing the metallurgical conditions in alloys and the concentration of dissolved oxygen and dissolved hydrogen in high-temperature water. SEM, X-ray diffraction, and Auger electron spectroscopy revealed that the water chemistry played a major role in the formation of the oxide film and in the crack initiation. The oxide film is composed of an outer layer formed with hematite and magnetite and an inner layer corresponding to the transition oxide/substrate, which is Cr-rich and Ni-rich. Dissolved hydrogen conditions reduced the thickness of the oxide and increased its nickel content. Dissolved oxygen conditions promoted the formation of numerous and bigger cracks compared with dissolved hydrogen conditions. Environmental conditions are preponderant compared with metallurgical conditions.

CORROSION FATIGUE OF NUCLEAR--GRADE STAINLESS STEEL IN HIGH TEMPERATURE WATER AND ITS ENVIRONMENTAL FATIGUE DESIGN MODEL

The high safety of light water reactor nuclear power plants (NPPs) requires very strict design standard and service property of pressure boundary components materials. The service degradation and life assessment of the components materials primarily depend on the understanding of environmentally assisted failure mechanism, accumulation of service property data and construction of evaluation models. Currently domestic NPPs are relying on foreign design, operation and life assess- ment standards. However, recent experimental data indicate that even the ASME design fatigue code may be deficient in safety margin under certain conditions of loading and environment. In the present work, based on the corrosion fatigue tests in simulated NPPs' high temperature pressurized water, the corrosion fatigue behavior and environmentally assisted failure mechanism of domestic nuclear-grade stainless steel have been investigated. The factors affecting fatigue life of nuclear grade stainless steel in high temperature water were evaluated. A design fatigue model was constructed by taking envi- ronmental degradation effects into account and the corresponding design curves were given for the convenience of engineering applications.

Work Hardening, Sensitization, and Potential Effects on the Susceptibility to Crack Initiation of 316L Stainless Steel in BWR Environment

After CBB testing, the structure and composition of surface oxide films on austenitic stainless steels in high-temperature water were examined by changing the metallurgical conditions in alloys and the concentration of dissolved oxygen and dissolved hydrogen in high-temperature water. SEM, X-ray diffraction, and Auger electron spectroscopy revealed that the water chemistry played a major role in the formation of the oxide film and in the crack initiation. The oxide film is composed of an outer layer formed with hematite and magnetite and an inner layer corresponding to the transition oxide/substrate, which is Cr-rich and Ni-rich. Dissolved hydrogen conditions reduced the thickness of the oxide and increased its nickel content. Dissolved oxygen conditions promoted the formation of numerous and bigger cracks compared with dissolved hydrogen conditions. Environmental conditions are preponderant compared with metallurgical conditions.

Effects of water chemistry and loading conditions on stress corrosion cracking of cold-rolled 316NG stainless steel in high temperature water

The effects of electrode potential, stress intensity factor and loading history on stress corrosion cracking growth of a cold-rolled 316NG stainless steel in 288 °C pure water were investigated. Crack branching and intergranular stress corrosion cracking along random grain boundaries were observed by electron-back scattering diffraction. A strong dependence of crack growth rate on stress intensity factor is observed. A single-cycle overloading produced a retarded transient cracking growth period. The mild inhibiting effect of decreasing electrode potential on crack growth of cold-rolled 316NG SS is analyzed based on the interaction between crack tip mechanics and crack tip oxidation kinetics.

Stress Corrosion Cracking of Nitrogen-containing Stainless Steel 316LN in High Temperature Water Environments

Stress corrosion cracking(SCC) of stainless steels and Ni-based alloys in high temperature water coolant is one of the key problems affecting the safe operation of nuclear power plants(NPPs).The nitrogen-added stainless steel is a kind of possible candidate materials for mitigating SCC since reducing the carbon content and adding nitrogen to offset the loss in strength caused by the decrease in carbon content can mitigate the problem of sensitization.However,the reports of SCC of nitrogen-added stainless steels in high temperature water are few available.The effects of applied potential and sensitization treatment on the SCC of a newly developed nitrogen-containing stainless steel(SS) 316LN in high temperature water doped with chloride at 250 ℃ were studied by using slow strain rate tests(SSRTs).The SSRT results are compared with our data previously published for 316 SS without nitrogen and 304NG SS with nitrogen,and the possible mechanism affecting the SCC behaviors of the studied steels is also discussed based on SSRT and microstucture analysis results.The susceptibility to cracking of 316LN SS normally increases with increasing potential.The susceptibility to SCC of 316LN SS was less than that of 316 SS and 304NG SS.Sensitization treatment at 700 ℃ for 30 h showed little effect on the SCC of 316LN SS and significant effect on the SCC of 316 SS.The predominant cracking mode for the 316LN SS in both annealed state and the state after the sensitization treatment was transgranular.The presented conditions of mitigating stress corrosion cracking are some useful information for the safe use of 316LN SS in NPPs.

143 オーステナイト系ステンレス鋼酸化皮膜の高温水中組織変化に関する原子レベルシミュレーション(材料力学III,一般講演)

143 オーステナイト系ステンレス鋼酸化皮膜の高温水中組織変化に関する原子レベルシミュレーション(材料力学III,一般講演)

Formation of Cavities Prior to Crack Initiation and Growth on Cold-Worked Carbon Steel in High-Temperature Water

Abstract The rate of growth of stress corrosion cracking (SCC) was measured for cold-worked carbon steel (ASTM A106 [UNS K03006]) in hydrogenated pure water under static load condition. Four import...

Electrochemical Corrosion of Carbon Steel in High Temperature Water

not Available.

IGSCC of non-sensitized stainless steels in high temperature water

SCC studies in stainless steels and nickel alloys reveal that all grades and conditions are susceptible to SCC in high temperature water, whether deaerated or aerated, high H 2 or low, theoretical purity water or buffered/contaminated, lower temperature or higher. However, the kinetics of SCC growth vary enormously with stress intensity, yield strength, sensitization, water chemistry, irradiation, temperature, etc. The role of yield strength is especially important because it changes with surface cold work, bulk cold work, weld shrinkage strain, and irradiation hardening; the role of metallurgical strengthening mechanisms, e.g., nitrogen additions or precipitation hardening, may have a similar effect. SCC growth rate measurements were performed in high temperature water on unsensitized stainless steels (and alloy 600) of various grades and compositions. Little effect of grade/heat of stainless steel, martensite content or H 2 fugacity/permeation rate was observed, while large effects were observed for yield strength (cold work), stress intensity factor, corrosion potential, and temperature. A model ‘stainless steel’ containing 5% Si (and elevated Ni and reduced Cr) showed high growth rates and little effect of corrosion potential or stress intensity factor.