Charged Specimens Research Articles

ショットピーニング後に人工腐食ピット加工を施した懸架ばね用鋼の疲労特性に及ぼす水素の影響

In order to reduce the weight of the suspension springs by increasing the steel strength, it is necessary to improve the corrosion fatigue property. However, the dominant factor governing the corrosion fatigue property of the suspension spring has not been satisfactorily revealed yet. Therefore, the investigation into elucidating the mechanism has been carried out to independently evaluate the influences of corrosion pits, shot peening, hydrogen, prior-austenite grain size, and so forth on the corrosion fatigue property. In this study, the influence of hydrogen on rotary bending fatigue test was investigated using specimens with artificial corrosion pits after shot peening. The dominant factors governing the corrosion fatigue property of the suspension spring were discussed based on the result of the present study in conjunction with the results of the previous study on the influences of shot peening and corrosion pit depth. The conclusions obtained were as follows: (1) In the case of the specimen without corrosion pit or with only shallow corrosion pits having still large compressive residual stress at the bottom of the pits, the fatigue property was fairly good but declined with the increment of charged hydrogen due to the diffusible hydrogen. On the other hand, in the case of the specimen with deep corrosion pits having only small compressive residual stress, the fatigue property was poor regardless of the charged hydrogen content. We inferred from this result that the deep corrosion pit releases the compressive residual stress at the bottom of pits. (2) The effect of prior-austenite grain size on fatigue properties of hydrogen charged specimens turned out to be almost negligible.

Effect of hydrogen and low temperature on fatigue crack growth of pipeline steels

In the presence of gaseous hydrogen or of H2S, metallic materials, such as carbon and low alloy steels, may suffer hydrogen damage and hydrogen embrittlement. In this paper the influence of hydrogen and low temperature on fatigue crack growth properties of two pipeline materials, X65 micro-alloyed and F22 low alloy steels, is studied. An electrochemical charging method has been adopted and fatigue propagation tests were carried out on hydrogen charged and uncharged specimens, by varying the test temperature and the frequency of the load application cycle. The experimental results show an evident effect of the hydrogen presence on the fatigue crack growth. The diffusion rate of hydrogen in the steels seems to be the most important parameter in order to explain the influence of temperature and frequency on the fatigue crack propagation rate. Fracture surface examination has been correlated with the results of mechanical testing.

A new mechanism in hydrogen-enhanced fatigue crack growth behavior of a 1900-MPa-class high-strength steel

This paper presents a new mechanism controlling the acceleration of fatigue crack growth of a hydrogen-charged high-strength steel (bearing steel SAE52100, σ ult > 1, 900MPa, HV = 569). Three- dimensionally complicated shape of a primary crack and secondary cracks were observed in hydrogen- charged specimens. Marked acceleration of fatigue crack growth in the presence of hydrogen was observed particularly at low test frequency, and was attributed to the initiation and successive coalescence of secondary cracks formed ahead of primary crack. These secondary cracks were produced along prior-austenite grain boundaries and carbide boundaries, or by direct cracking of carbides. Surprisingly, secondary cracks were observed outside the ordinary plastic zone ahead of the crack tip. TEM observation elucidated that the secondary cracks outside the crack tip plastic zone were produced by hydrogen-induced deformation twins impinging on grain boundaries and carbides. These results suggest a new mechanism of the acceleration of fatigue crack growth rates in high-strength steels caused by hydrogen-induced deformation twins, rather than due to hydrogen- enhanced localized plasticity. The phenomena associated with time dependent fatigue crack growth are presumed to be correlated with the initiation and coalescence of secondary cracks in the presence of hydrogen.

Phase transformations and micro cracks induced by hydrogen in cold-rolled and annealed AISI 304 stainless steels

The effect of hydrogen and stress on the phase transformation and surface cracking in cold-rolled and annealed AISI 304 stainless steels was investigated. Hydrogen was introduced by cathodic charging in 0.1 M H2SO4 + 1 g/L Na2HAsO4·7H2O. Scanning electron microscopy was used to observe structural changes and surface cracks of the specimens. X-ray diffraction analysis was used to investigate phase transformations in the uncharged and charged specimens immediately after charging or during aging. Cathodic charging can cause ε martensite phase transformation and aging after cathodic charging can induce the ε and α′ martensite transformation. There are a certain amount of surface cracks on the specimens surface after hydrogen charging or during aging. The surface morphology of the specimens is studied, and the mechanism of the hydrogen-induced phase transformation and the surface cracking formation in the charged specimens immediately after charging or during aging is discussed.

Suppression of hydrogen-assisted fatigue crack growth in austenitic stainless steel by cavitation peening

In this paper we demonstrate the suppression of hydrogen-assisted fatigue crack growth in type 316L austenitic stainless steel by cavitation peening employing a cavitating jet in air. Plate bending fatigue tests on pre-cracked samples were conducted after cathodic hydrogen charging with and without cavitation peening. Without cavitation peening, the hydrogen effect on the crack growth behavior at low applied stress was clearly demonstrated compared with high applied stress in the fatigue test. The coalescence of sub-cracks and the main crack propagating from the pre-crack were observed in the hydrogen charged specimen. This phenomenon significantly accelerated the crack growth. This unexpected fracture was suppressed by introducing compressive residual stress by cavitation peening regardless of the length of processing time. In addition, lengthier treatment reduced the crack growth rate of the hydrogen charged specimen by 75% compared to an untreated one.

Fundamental differences in model cell-surface polysaccharides revealed by complementary optical and spectroscopic techniques

The propensity of two classes of polysaccharides, charged heparins and uncharged dextrans serving as models of those found in the extracellular matrix, to form ordered arrangements in solids and in solution, were explored employing polarising optical microscopy and reflection anisotropy spectroscopy. The fundamental modes of molecular vibration in the solid state, which relate to the occupancy of conformational states at ambient temperatures, were also investigated using terahertz (1–15 THz) spectroscopy on purpose built beam lines at SRS, Daresbury and ANKA, Karlsruhe. In the solid state, evidence for the anisotropic arrangement of ion centres was observed for the Na, Ca and Mg ion forms of heparin by RAS but, this was absent in aqueous solution at 100 mg ml−1 and the absence of molecular ordering in solution was confirmed by polarised optical microscopy. The ion charged heparin specimens showed very strong absorption of THz radiation indicating the accessibility of unoccupied higher energy conformational states in these materials whereas the uncharged dextrans showed only weak THz absorption, implying that the majority of conformational states are occupied and there are few unoccupied higher energy states in these materials. This suggests the two classes of material will have very different conformational properties, particularly in response to temperature changes in the extracellular matrix.

HYDROGEN ABSORPTION BEHAVIOR OF 1500 MPa--GRADE HIGH STRENGTH STEEL 42CrMoVNb

Hydrogen absorption behaviors of a newly developed 1500 MPa-grade high strength steel 42CrMoVNb at different austenitizing temperatures and tempering temperatures were studied using cathodic charging and hydrogen thermal desorption analysis,which were also compared with commercial structural steel 42CrMo.The results show that the hydrogen escape peak temperatures (θ_p) in hydrogen evolution curves of hydrogen charged 42CrMoVNb specimens are between 200℃to 300℃both at as-quenched condition and as-tempered condition.The absorbed hydrogen content of 42CrMoVNb specimen increases slowly with increasing tempering temperature up to 500℃.When the tempering temperature exceeded 500℃,the absorbed hydrogen content increases sharply and reaches its peak,6.6×10~(-6),for the specimen tempered at 600℃,which is 5 times as much as that of the as-quenched specimen.Thereafter the absorbed hydrogen content declines sharply as the tempering temperature was gone up sequentially.When the specimen was tempered at 400℃,the absorbed hydrogen content decreases slightly with austenitizing temperature increasing,and in the microstructure no fine dispersed(V,X)C carbide precipitated,while when the specimen was tempered at 600℃, the absorbed hydrogen content increases sharply with austenitizing temperature increasing,and more fine dispersed(V,X)C precipitated.These results indicate that fine dispersed(V,X)C precipitate could be regarded as a strong hydrogen trap,and the trap activation energy,E_a,is equal to about 28.7 kJ/mol,which was obtained by change heating rate.

Study of hydrogen effusion in austenitic stainless steel by time-resolved in-situ measurements using neutron radiography

Abstract The purpose of the present study was to show the feasibility of measuring hydrogen effusion in austenitic stainless steel (1.4301) using neutron radiography at the facility ANTARES of the research reactor FRM II of the Technische Universitat Munchen. This method is appropriate to measure in-situ hydrogen effusion for hydrogen concentrations as small as 20 ppm H . Experiments were carried out in the temperature range from room temperature up to 533 K. The measurement principle is based on the parallel comparison of electrochemically hydrogen charged specimen with hydrogen-free reference specimen at the same temperature. This allows the determination of the hydrogen concentration in the specimens as a function of time and temperature. Separate hot carrier gas extraction experiments using the same temperature–time profiles as the radiography experiments have been used to calibrate the grey values of the neutron transmission images into hydrogen concentrations. It can be stated that the hydrogen effusion correlates with the specimen temperature.

Fatigue Behavior Of Pipeline Steel Under Hydrogen Environment And Low Temperature

In the presence of H2S, metallic materials, such as carbon and low alloy steels, may suffer hydrogen damage and hydrogen embrittlement. In this paper the influence of hydrogen and low temperature on mechanical properties of two pipeline materials, X65 micro-alloyed and F22 low alloy steels, is studied. An electrochemical hydrogen charging method has been setup. Diffusible hydrogen content of steels is in the range 0.6 to 2 ppm. Fatigue propagation tests were carried out on charged and uncharged specimens, by varying the test temperature and the frequency of the load application cycle. The experimental results show an evident effect of the hydrogen presence on the fatigue crack growth. The diffusion rate of hydrogen in the steels seems to be the most important parameter in order to explain the influence of temperature and frequency on the fatigue crack propagation rate. Fracture surface examination confirms the results of mechanical testing.

The Effect of Hydrogen on the Master Failure Curve of APL 5L Gas Pipe Steels

The effect of hydrogen on the material failure curves of APL 5L gas pipe steels was analysed from viewpoint of the notch fracture mechanics. The material failure curves based on two-parameter fracture criterion have been determined for API 5L X52, X70 and X100 gas pipe steels. The notch fracture toughness Kp,c and the effective T-stress were employed to describe the material failure curve. Tests were carried out on electrolytic hydrogen charged SENT, CT, RT (Roman Tile) and DCB specimens with a notch. Fracture initiation was detected by acoustic emission. Material failure curves for hydrogen charged steels and steels without hydrogen were constructed. It was shown that there is critical hydrogen concentration, which causes significant reduction of local fracture resistance of pipe steels.

G030063 水素封入試験片の疲労条件下におけるき裂成長挙動の負荷波形特性([G03006]材料力学部門一般セッション(6):高温・環境)

G030063 水素封入試験片の疲労条件下におけるき裂成長挙動の負荷波形特性([G03006]材料力学部門一般セッション(6):高温・環境)

Effects of deformation on hydrogen absorption and desorption properties of titanium

In this study, we analyzed the effects of deformation on hydrogen absorption and desorption properties of titanium to improve such properties. Hydrogen was introduced into commercially pure (99.5%) titanium by the electrochemical method. The amount and existing state of hydrogen were examined using hydrogen desorption curves obtained by thermal desorption spectroscopy. Hydrogen absorption was promoted by applying tensile deformation prior to charging, which leads to hydride formation within a short charging time. The amount of hydrogen absorbed decreased when the volume fraction of deformation twins exceeded about 0.2. It was considered that hydrogen was mainly trapped by dislocations forming hydride while a large fraction of deformation twins hindered dislocation motion, thus reducing dislocation density leading to a decrease in the amount of absorbed hydrogen. Almost half the charged hydrogen was released when in-plane compressive stress was applied to a charged plate specimen at room temperature due to hydride decomposition under compressive stress.

Hydrogen Evolution Behavior during Tensile Deformation in Austenitic Stainless Steels Exposed to High Compressed Hydrogen Atmospheres

Hydrogen embrittlement sensitivity of austenitic stainless steels, SUS316L and SUS310S exposed to high compressed hydrogen gas atmospheres was evaluated by means of a slow strain rate testing (SSRT) in air. Hydrogen evolution behavior during tensile deformation and fracture was also investigated by using a testing machine equipped with a quadrupole mass spectrometer installed in an ultrahigh vacuum chamber. When the SUS 316L specimen with hydrogen gas charging were deformed at a very slow crosshead speed of 1.67 nm/s, local deformation was promoted as compared to the specimen without hydrogen gas charging. On the other hand, no decrease of the ductility was observed in the SUS310S specimen with hydrogen gas charging even in the SSRT. In the hydrogen charged SUS316L specimen, the amount of continuous hydrogen evolution throughout deformation was much higher than that in the specimen without hydrogen gas charging. In addition, sudden hydrogen evolutions were sometimes identified in the SUS316L specimen with hydrogen gas charging during the deformation.

Effect of hydrogen absorption on strain-induced low-cycle fatigue of low carbon steel

The effects of hydrogen have been studied on low carbon steel (JIS S10C), which contains limited amount of pearlite. Fatigue life and its strain rate dependence have been examined. The possible mechanism of hydrogen effect on those properties has been discussed. The hydrogen absorbed was 0.5–1.5 mass-ppm, according to the thermal desorption analysis (TDA). Main part of the hydrogen is dissolved in the matrix; the rest part is trapped by pearlite. This small hydrogen severely reduces the fatigue life, even in S10C steel that is considered to be less susceptible to hydrogen embrittlement. The more the hydrogen is absorbed, the less the fatigue life is. Hydrogen absorption also causes the increase in stress amplitude. Fractographic examination revealed the fracture process as the followings. The hydrogen gasifies at the interface between the non-metallic inclusion and matrix. Then the high pressure hydrogen gas atmosphere maintains hydrogen content in the matrix around inclusion. This assists the crack initiation at the interface of inclusion, and also assists the crack propagation through producing the fish-eye fracture. According to the published works on non-hydrogen charged specimens, vacancy plays an important role in both crack initiation and propagation, and determines the fatigue life. The stress amplitude is believed also influenced by the vacancy that is produced by the movement of jogged dislocation. When these vacancies are stabilized by hydrogen, fatigue life will be decreased with the increased stress amplitude. Fatigue life is decreased with slower strain rate test. Stress amplitude shows the negative dependence to the strain rate. These are claimed as the features of dynamic strain aging (DSA). Considering the above mentioned knowledge on vacancy stabilized by hydrogen, the DSA is brought about by the interaction between dislocation and vacancy-hydrogen pair.

Effect of Absorbed and Environmental Hydrogen on Short Fatigue Crack Propagation near Threshold in Low Alloy Steel

The effects of hydrogen on fatigue crack propagation behavior of short fatigue crack and crack closure behavior were studied using low alloy steel SCM440H. Fatigue crack propagation test using specimen which has a 50µm deep pre-crack was conducted at a frequency of 28Hz in air, vacuum and hydrogen gas. Hydrogen pre-charge was done by cathodic polarization method. The concentration of absorbed hydrogen was 0.83 ppm in hydrogen charged specimen and 0.06 ppm in uncharged specimen. The fatigue crack propagation rate of uncharged material was dependent on environments. The acceleration of fatigue crack propagation rate by absorbed hydrogen was about 2 to 5 times irrespective of environment. As a consequence, the fatigue crack propagation rate of hydrogen pre-charged material tested in air was the highest. The crack opening stress was higher in hydrogen gas and in vacuum compared with that in air. Fatigue crack propagation rate was summarized in two independent bands when plotted against effective stress intensity factor range. This means that the effects of environment (vacuum, air and hydrogen) and stress ratio (R = -1, 0, 0.6) could be explained by crack closure phenomenon. However, the acceleration of crack propagation by absorbed hydrogen could not be explained only by crack closure phenomenon.

低合金鋼の下限界近傍の微小疲労き裂進展に及ぼす水素侵入と水素雰囲気の影響

The effects of hydrogen on fatigue crack propagation behavior of short fatigue crack and crack closure behavior were studied using low alloy steel SCM440H. Fatigue crack propagation test using specimen which has a 50µm deep pre-crack was conducted at a frequency of 28Hz in air, vacuum and hydrogen gas. Hydrogen pre-charge was done by cathodic polarization method. The concentration of absorbed hydrogen was 0.83 ppm in hydrogen charged specimen and 0.06 ppm in uncharged specimen. The fatigue crack propagation rate of uncharged material was dependent on environments. The acceleration of fatigue crack propagation rate by absorbed hydrogen was about 2 to 5 times irrespective of environment. As a consequence, the fatigue crack propagation rate of hydrogen pre-charged material tested in air was the highest. The crack opening stress was higher in hydrogen gas and in vacuum compared with that in air. Fatigue crack propagation rate was summarized in two independent bands when plotted against effective stress intensity factor range. This means that the effects of environment (vacuum, air and hydrogen) and stress ratio (R = -1, 0, 0.6) could be explained by crack closure phenomenon. However, the acceleration of crack propagation by absorbed hydrogen could not be explained only by crack closure phenomenon.

Determination of Orbital Location of Electron-Induced Secondary Electrons by Electric Field Visualization

The electric field around positively charged biological specimens is studied by electron holography. By the amplitude reconstruction process for holograms, the orbits of electron-induced secondary electrons are clarified on the nanometer scale. It is found that the stationary orbit of secondary electrons can be directly located without disturbing their motions under the condition that the current of secondary electrons in stationary orbit is considerably larger than that of incident electrons. The experimental conditions for the induction of the stationary orbit of secondary electrons are discussed, and furthermore the theoretical basis of the orbital location of secondary electrons through electric field visualization is discussed in the framework of quantum mechanics.

走査電子顕微鏡における絶縁物試料の帯電コントラスト (1) 正帯電コントラスト

走査電子顕微鏡における絶縁物試料の帯電コントラスト (1) 正帯電コントラスト

Hydrogen effects on pitting corrosion and semiconducting properties of nitrogen-containing type 316L stainless steel

Abstract The effects of hydrogen pre-charging on pitting corrosion resistance and semiconducting nature of passive film formed on two different nitrogen-containing type 316L stainless steel (0.076 and 0.086 wt% N) have been studied. Auger electron spectroscopy (AES) analysis of the alloys after passivation indicated weak nitrogen peak, but the presence of nitrogen and NH3/NH4+ was confirmed by the X-ray photoelectron spectroscopy (XPS) analysis. The results of pitting corrosion in 0.5 M NaCl (pH ≈ 5.7) solution revealed that hydrogen increased the passive current density and significantly reduced the pitting resistance. In 0.3 M H3BO3 + 0.075 M Na2B4O7·10H2O (pH ≈ 8.45) solution, increase in passive current density without affecting the breakdown or transpassive potential was observed for both the alloys. Electrochemical impedance spectroscopy (EIS) measurement after hydrogen pre-charging showed decrease in semi-circle radius of Nyquist plot, and the polarization resistance, RP associated with the resistance of the passive film. The decrease was significant with increasing hydrogen-charging current density (−50 to −100 mA/cm2). The results of the capacitance measurement and Mott–Schottky plots revealed that passive films exhibit n-type and p-type semiconductivity films for both the uncharged and hydrogen charged specimens of the investigated alloys. Doping densities obtained from Mott–Schottky plots increased with hydrogen pre-charging. The overall results indicated that hydrogen pre-charging deteriorated the passive film stability and lowered pitting corrosion resistance. The effects of hydrogen pre-charging on pitting corrosion, passive film and semiconducting properties are discussed in light of the above results.

Absorption of hydrogen in tensile strained iron and high-carbon steel studied by electrochemical permeation and desorption techniques

Absorption of hydrogen in gradually tensile strained Armco iron and high-carbon steel, cathodically charged in 0.1 M NaOH solution, was studied using the electrochemical permeation and desorption techniques. Measurements of hydrogen permeation through specimens in the form of a membrane allowed determining the lattice diffusivity and concentration of hydrogen (diffusible hydrogen). The lattice diffusivity of hydrogen in iron ( D = 6.2 × 10 −5 cm 2/s) was about 280 times higher than that in high-carbon steel ( D = 2.2 × 10 −7 cm 2/s). In turn, a detailed analysis of the desorption rate of hydrogen from previously hydrogen charged and strained, cylindrical specimens made it possible to characterize hydrogen reversibly attached to traps. This trapped hydrogen made nearly a whole and a majority (from 70% to 85%, depending on strain) of the reversibly absorbed hydrogen in iron and high-carbon steel, respectively. In both studied materials, the amount of the trapped hydrogen strongly increased with strain. Moreover, in contrast to the diffusible hydrogen, evenly distributed in the charged specimen, the trapped hydrogen was mainly located within a subsurface region of the specimen. The estimated thickness of this subsurface region in iron was about 0.44 mm, whereas that in high-carbon steel was only about 0.017 mm. Consequently, the subsurface concentration of hydrogen in high-carbon steel was extremely high. It may be one of the reasons for more intensive hydrogen embrittlement of high-carbon (high-strength) steels in comparison with that of iron.