Hydrogen In Stainless Steel Research Articles

On the estimation of the diffusion coefficient and distribution of hydrogen in stainless steel

In this work, the localisation of hydrogen in an electrochemically charged stainless steel was investigated by Scanning Kelvin Probe Force Microscopy and Glow Discharge Optical Emission Spectroscopy analysis. Both techniques indicated a high hydrogen content at less than 90 micrometres under the charged surface. Thermal Desorption Spectroscopy was used to calibrate the data from both techniques and thus to calculate the hydrogen concentration. Finally, after assuming certain hypotheses, Fick's laws were used to calculate the coefficient of diffusion and subsurface concentration of hydrogen in cathodic charging conditions.

On the Estimation of the Diffusion Coefficient and Distribution of Hydrogen in Stainless Steel

In this work, the localisation of hydrogen in an electrochemically charged stainless steel was investigated by Scanning Kelvin Probe Force Microscopy and Glow Discharge Optical Emission Spectroscopy analysis. Both techniques indicated a high hydrogen content at less than 90 micrometres under the charged surface. Thermal Desorption Spectroscopy was used to calibrate the data from both techniques and thus to calculate the hydrogen concentration. Finally, after assuming certain hypotheses, Fick's laws were used to calculate the coefficient of diffusion and subsurface concentration of hydrogen in cathodic charging conditions.

Structure of the Oxide Films Formed on Hydrogen-Charged and Uncharged 316L Stainless Steels in Oxygenated High Temperature Water

Austenitic stainless steels (SSs) are commonly used in pressurized water reactors (PWRs) nuclear power systems as key structural materials. The corrosion resistance are closely related to the passive film formed on the surfaces of austenitic alloys in high-temperature aqueous environments. It has been reported that hydrogen can affect corrosion, localized corrosion as well as stress corrosion cracking of materials in aqueous solutions. It is necessary to investigate the influence of hydrogen on the corrosion behavior of stainless steels material in high temperature water environments. In the present study, the oxide films formed on 316L SS with uncharged (316L) and hydrogen-charged (316L-H) in oxygenated simulated PWR primary water at 300℃were investigated. Oxygen was added in high temperature water to simulated occlude region condition or faulted water chemistry. The aim of this work is to clarify the effect of hydrogen in stainless steel on the corrosion behavior. The surface morphologies of the oxide films formed on 316L (uncharged) and 316L-H (charged) specimens after exposure to oxygenated PWR primary water at 300 oC for168 h were observed. The regular and irregular oxides particles homogeneous distributed on the outer surface of 316L specimen, and compact filamentary oxides in the sub-surface. On 316L-H specimen, large oxides dispersed and inhomogeneous distributed on the outer surface, and compact minor polyhedral oxide particles packed on the sub-surface. The number of the large oxides on the outermost surface of 316L specimen was more than that on the 316L-H sample. The cross-section of the oxide films formed on 316L specimens after exposed to oxygenated PWR primary water was analyzed by FIB-TEM. The interface front between the inner oxide layer and the base metal was wavy-shaped. There were compact Cr-rich oxides in the inner layer, and filamentary (Fe, Ni)-rich oxides in the outer layer. There was slightly Ni-enrichment near the inner oxides/matrix interface and Fe-enrichment beneath the inner oxides/matrix interface from EDS line scan profile. Some discontinuous cellular oxides distributed on the inner oxides/matrix interface on 316L-H after the exposure test, which was Fe-rich oxides identified by EDS maps and line scan. Similar to the 316L specimen, the inner layer oxide was compact and Cr-edriched, showing a slightly Fe-enriched beneath the inner oxides/matrix interface, but no Ni-enrichment close to the interface of inner oxides/matrix was observed. Figure 1

Laser surface melting of stainless steel anodes for reduced hydrogen outgassing

Anodes of 304 stainless steel have been processed by a continuous wave Yb fiber laser with a wavelength of 1.064μm and subjected to 50keV electron bombardment in order to determine the extent to which hydrogen outgassing is reduced by the laser surface melting treatment. The results show a reduction in outgassing, by approximately a factor of four compared to that from untreated stainless steel. This is attributed to a reduction in the number of grain boundaries which serve as trapping sites for hydrogen in stainless steel. Such laser treated anodes do not require post-processing to preserve the benefits of the treatment and are excellent candidates for use in high power source devices.

Hydrogen in Stainless Steel as Killing Agent for UHV: A Review

Due to the small size of hydrogen atom, its interstitial diffusion accompanied by high mobility of hydrogen atoms in materials. For metals, H diffusivity may reach values as known for ions in aqueous solutions. Thus, thermodynamic equilibrium is reached within comparably short times even at room temperature. Therefore, metal–hydrogen systems are often used as model systems to study physical or chemical properties and their change with concentration. The high mobility of hydrogen further allows studying the impact of defects that usually annihilate at elevated temperatures. Austenitic stainless steels are the most common choice for high vacuum and ultra-high vacuum systems. Not all alloys are suitable; e.g. the free-machining 303 steel contains sulfur, which tends to outgas. Alloys with good weldability under argon arc welding are usually chosen. Stainless steel materials and their properties for manufacturing Ultra-high vacuum (UHV) chambers has found use in the l0-8Pa pressure region, standard cleaning procedures and mild vacuum baking is sufficient in most instances. Vacuum chambers for use in the lower 10-9-10-10Pa region are frequently pretreated by vacuum firing in order to reduce the hydrogen outgassing, which is the main residual gas in that pressure range. Vacuum firing is a heat treatment of the vacuum vessels in a vacuum oven to 950°C for l-3h, depending on thickness of the material, at a pressure less than 10-3Pa, which results in an outgassing of the material. Heat treatment in ambient air is both simpler and cheaper to perform than vacuum firing. Therefore it is of interest to investigate the feasibility of an air bake as an alternative, to accomplish lower outgassing rates which is discussed in this paper.

716 ステンレス鋼中の水素挙動に及ぼす応力負荷の影響(OS4-5 オーガナイズドセッション《材料・組織と加工》)

As for most stainless steels, use under the stress, corrosive and hydrogen environments is aimed for. The stress frequently promotes hydrogen embrittlement. Local plastic deformation takes place because of stress concentration, resulting in the formation of large amount of lattice defects. These defects become the trap sites of hydrogen leading to possible increase in hydrogen concentration. In addition, stress gradient is expected to promote the hydrogen diffusion. Thus, it is important to study hydrogen behavior in some stainless steels affected by stress loading, because hydrogen embrittlement is related with hydrogen concentration at a crack initiation site. However, the mechanism for the embrittlement and the behavior of hydrogen in stainless steels have not been clarified yet. In this study, the behavior of hydrogen in two stainless steels (ferritic and austenitic) was investigated by means of the hydrogen microprint technique (HMPT). As a result, it has been confirmed that cathodic electrolytic charging causes hydrogen invasion and that hydrogen is emitted from the steels during holding after charging.

Behavior of hydrogen in stainless steel under irradiation

A nondestructive method of the simultaneous analysis of hydrogen and helium in combination with the technique of studying hydrogen migration provides fundamentally new information about the hydrogen behavior in metal-hydrogen systems: about hydrogen migration in metals directly under irradiation and about the mutual effect of implanted hydrogen and helium in constructional materials of nuclear and thermonuclear reactors. The irradiation of metals and alloys with ionizing radiation (ion beams, electrons, and x-ray quanta) causes intense hydrogen migration due to the excitation of electron states from metal-hydrogen bonds whose lifetime is sufficient for hydrogen to leave its regular positions and for nonequilibrium migration. Hydrogen migration over and escape from metals and alloys under the action of electrons and x-ray quanta with an energy below the threshold of defect formation are accompanied by the rearrangement of the defect structure of the material: the annealing of defects of the hydrogen origin due to the annihilation of defects (interstitial atoms and hydrogen-free vacancies). Hydrogen dissolved in metals and alloys reduces the trapping coefficient of the implanted helium, which is due to the formation of fine complexes HV and HV2 and, as a result, to a decrease in the probability of formation of large vacancy complexes which are effective traps for helium.

Thermal desorption study of selected austenitic stainless steels

Residual hydrogen in stainless steel results in a steady outgassing from vacuum chamber walls, hindering the achievement of ultrahigh vacuum conditions. The total content, the binding states, and the diffusivity of residual hydrogen in austenitic stainless steels, which together define the room temperature hydrogen outgassing rate, have been investigated by thermal desorption spectroscopy (TDS). Seven different steel types have been studied by means of two different TDS systems. The study has been extended to include the effects of various postproduction treatments, aimed at reducing the hydrogen content and/or outgassing, namely vacuum firing and baking both in air and under vacuum. A large variety of hydrogen desorption peaks have been observed, which have been attributed to diffusible hydrogen, hydrogen trapping in the surface oxides or in lattice defects induced by precipitates, and steel recrystallization. The hydrogen depletion effectiveness of vacuum baking at different temperatures has been quantified, and the consequences of air baking have been clarified, leading to practical guidelines for technological applications.

Hydrogen bulk states in stainless-steel related to hydrogen release kinetics and associated redistribution phenomena

Hydrogen represents the main residual gas in UHV and EHV stainless-steel chambers and to suppress its outgassing rate, the material is usually thermally treated in vacuum. In an attempt to prove the hypothesis that hydrogen in stainless steel is located in more than one bulk state, the thermal extraction method for concentration determination was applied from 305 to 1000°C. A thin AISI 304 sample was inductively heated and released gases were accumulated and subsequently analysed by a quadrupole mass spectrometer (QMS). Measurements began at low temperature and several cycles were repeated until the outgassing rate approached the detection limit of the set-up. The same procedure was used at higher temperatures. The observed outgassing behaviour cannot be explained by a model where the diffusion in the bulk over single states limits the kinetics nor by a model where only surface reactions limit it. The amount of extracted hydrogen was 5.1×10 19 H atom/cm 3 (total heating time 59.3 h) which greatly exceeded the value calculated on the basis of published data for solubility. At higher temperatures more hydrogen atoms were available to escape from the bulk than at lower temperatures although the sample seemed to be previously “outgassed”. The redistribution occurred even at room temperature and diminished the effect of previous treatments. A simple second-order kinetics model was introduced to obtain some relevant parameters, which may be applied for a more accurate prediction of hydrogen release kinetics.

Study on the bulk diffusion of hydrogen in stainless steels

The concentration of hydrogen in stainless-steel cylinders that had been exposed to hydrogen gas many times was calculated, based on the diffusion equation and the numerical method of finite difference. The concentration of hydrogen in 316L and 22-13-5 stainless-steel cylinders that had been exposed to hydrogen gas at temperatures of 400°C and 740°C and stored in air at room temperature were determined by SIMS to test the calculation. The calculation was in good agreement with determination. Some discussions on the bulk diffusion of hydrogen are made in this report.

Study on the bulk diffusion of hydrogen in stainless steels

Study on the bulk diffusion of hydrogen in stainless steels

Migration of hydrogen in steel and alloys, stimulated by ionizing radiation

A study is made of the behavior of hydrogen in stainless steel and alloys of titanium and vanadium during exposure of the metals to ionizing radiation (accelerated nitrogen ions, γ-quanta). It is shown that the radiation stimulates intensive migration of hydrogen. The cross section of the accelerated ions is 10−16 cm2. This shows that hydrogen is released from traps as a result of excitation of the electronic subsystem and vibrational degrees of freedom of the hydrogen bonds, with the excitation energy subsequently being transferred to the nuclear subsystem. A phenomenological model is proposed to describe the ionization-accelerated migration of hydrogen in metals. Gamma- and electron-stimulated dissociation of hydrogen-containing bonds inside a solid occur by the Mensell — Homer and Auger mechanisms, as well as by nonadiabatic transition and vibrational-translational exchange. The calculated probability of the migration of hydrogen by these mechanisms is found to agree well with the experimental data.

Determination of hydrogen in stainless steels by spark-source mass spectrometry

A spark-source mass spectrometric (SSMS) method capable of determining traces of hydrogen in micro-volumes of metals was developed by using a pointed metal probe technique. The hydrogen background was decreased to μg g −1 levels by the combination of a method in which the sample in the ion source is baked under vacuum at 323–343 K for more than 25 ks and a liquid nitrogen or liquid helium cryogenic pump method. This method was applied to the analysis of austenitic stainless steels at μg g −1 hydrogen levels, and the relative standard deviation was within 20% for samples with hydrogen concentrations ranging from 2 to 4 μg g −1. The relative sensitivity coefficent was 2.3 (Fe=1).

Prevention of ductility loss in hydrogen-charged steel by gamma-ray irradiation

Hydrogen is known as a constituent which degrades the mechanical properties of metals and alloys, particularly their ductility. The degradation of mechanical properties, called hydrogen embrittlement, is a serious problem in metals and alloys under a hydrogen environment, e.g., pickling, welding, plating, etc. Although many researches have been made to clarify the nature and the mechanism of hydrogen embrittlement in steels (1), little has been reported on the method of prevention of hydrogen embrittlement except for works by Pressouyre and Bernstein (2,3). They showed that the susceptibility of ferrous alloys to hydrogen embrittlement is reduced by addition of titanium. Recently, we found that hydrogen in stainless steels is outgassed upon exposure to ionizing radiation (4-7). Therefore, hydrogen embrittlement in steels is expected to be influenced by ionizing radiation. This study was undertaken to determine the extent of prevension of hydrogen embrittlement by examining the effect of gammairradiation on the ductility in a low carbon steel electrolytically charged with hydrogen.

Trapping and radiation-induced detrapping of hydrogen in stainless steel exposed to liquid lithium

The phenomenological model of non-equilibrium diffusion and release of hydrogen from metals under the effect of electron beam in the sub-threshold region is considered. It is shown that the radiation stimulates the release and diffusion of hydrogen at a rate, significantly exceeds the rate of thermal equilibrium processes in the metals. This can occur in the presence of long-lived, in a time scale of single phonon and electron relaxation, vibrationally excited H-bonds. The proposed model confirms the experimental results previously obtained.

Radiation enhanced diffusion and permeation of hydrogen in stainless steel

Radiation enhanced diffusion and permeation of hydrogen in stainless steel

Hydrogen in stainless steels: Isotopic effctss on mechanical properties

Hydrogen in stainless steels: Isotopic effctss on mechanical properties

Coulometric determination of microamounts of hydrogen in metal

Hydrogen in metal was extracted into a carrier gas (argon) by heating at about 1100°, and oxidized to water with copper(II) oxide. The water was converted into ammonia with sodium amide at 80°. The ammonia was then titrated with electrolytically generated hypobromite ion. The blank value of single determination could be reduced to less than 1 μg of water. Hydrogen in stainless steels, tantalum metal and pure tin metal could be determined satisfactorily, and some results were compared with those obtained by the ordinary vacuum extraction method.

Reduction of stainless-steel outgassing in ultra-high vacuum

The outgassing rate of a 2 mm thick stainless-steel sheet was measured in ultra-high vacuum at constant pressure to avoid the readsorption occurring in a `rate of pressure rise' determination. The rate was typically 10-12 torr l. cm-2 sec-1 and about 99% or more of the gas was hydrogen. Since stainless steel usually contains large amounts of hydrogen and the diffusion coefficient of hydrogen in stainless steel is high, it was suspected that the hydrogen diffuses to the surface from the interior of the metal and is released into the vacuum. Calculations show that the observed outgassing rate could be explained by such a process and should be reduced by several orders of magnitude by a high-temperature treatment. The effects of residual hydrogen in the treatment furnace and hydrogen permeation from the atmosphere are also considered in these calculations. The greater the thickness of the metal, the higher the temperature has to be. Measurements are in reasonable agreement with these calculations.