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1.
The kinetics of hydrogen-induced slow crack growth (SCG) under constant load was studied in two stainless steel alloys containing
mixtures of bcc and fcc phases. FERRALIUM 255, a duplex stainless steel, consisting of ∼50 pct austenite in a ferrite matrix,
was tested in hydrogen gas at 0 to 100 °C with the loading axis both perpendicular and parallel to the rolling direction.
In addition, specimens of AISI 301 were deformed in air in different ways to produce various amounts of bcc phase in an austenite
matrix prior to testing in H2 gas at room temperature. The kinetics of subcritical slow crack growth (SCG) in these alloys was compared with that for austenitic
and for ferritic stainless steels. The SCG rates were rationalized in terms of differences in hydrogen permeation in the two
phases. The results confirm that a higher rate of supply and accumulation of hydrogen in the region ahead of the crack tip
allows a higher cracking velocity. 相似文献
2.
The effects of small amounts of dissolved hydrogen on crack propagation were determined for two austenitic stainless steel
alloys, AISI 301 and 310S. In order to have a uniform distribution of hydrogen in the alloys, they were cathodically charged
at high temperature in a molten salt electrolyte. Sustained load tests were performed on fatigue precracked specimens in air
at 0 ‡C, 25 ‡C, and 50 ‡C with hydrogen contents up to 41 wt ppm. The electrical potential drop method with optical calibration
was used to continuously monitor the crack position. Log crack velocityvs stress intensity curves had definite thresholds for subcritical crack growth (SCG), but stage II was not always clearly delineated.
In the unstable austenitic steel, AISI 301, the threshold stress intensity decreased with increasing hydrogen content or increasing
temperature, but beyond about 10 wt ppm, it became insensitive to hydrogen concentration. At higher concentrations, stage
II became less distinct. In the stable stainless steel, subcritical crack growth was observed only for a specimen containing
41 wt ppm hydrogen. Fractographic features were correlated with stress intensity, hydrogen content, and temperature. The fracture
mode changed with temperature and hydrogen content. For unstable austenitic steel, low temperature and high hydrogen content
favored intergranular fracture while microvoid coalescence dominated at a low hydrogen content. The interpretation of these
phenomena is based on the tendency for stress-induced phase transformation, the different hydrogen diffusivity and solubility
in ferrite and austenite, and outgassing from the crack tip. After comparing the embrittlement due to internal hydrogen with
that in external hydrogen, it is concluded that the critical hydrogen distribution for the onset of subcritical crack growth
is reached at a location that is very near the crack tip.
Formerly Research Assistant, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign. 相似文献
3.
A fracture mechanics study of stress corrosion cracking (scc) of cold worked AISI 310 austenitic steel, and an experimental
metastable austenite, was conducted in hot aqueous solutions of 44.7 wt pct MgCl2 and the results compared with previous studies on AISI 316 steel. Attention was directed towards Region II behavior where
crack propagation rate (v) was independent of stress intensity (KI). The apparent activation energy of Region II was found to be in the range ~65 to 75 kJ/mol, independent of the relative
proportions of intergranular and transgranular cracking. Also, electron diffraction studies of fracture surfaces showed that
α′-martensite formation was not a pre-requisite for scc, although it may influence crack propagation rates. Cracking was discussed
in terms of a hydrogen embrittlement model under hydrogen transport control in the austenite lattice. However, adsorption
(chemisorption) effects on repassivation and dissolution behavior could not be eliminated from consideration.
Alan J. Russell, Formerly Research Student, University of British Columbia. 相似文献
4.
Internal hydrogen embrittlement was studied in two nickel-base superalloys (IN718 and IN625) and one iron-base superalloy
(A286). Subcritical crack growth (SCG) measurements were made on uniformly precharged specimens containing up to 50 weight
parts per million (wt ppm) hydrogen, and the behavior was correlated with metallographic observations. For intermediate hydrogen
concentrations, three-stage SCG ratevs stress intensity behavior was observed in IN718 and IN625 but not in A286. For all alloys, the threshold stress intensity
decreased with increasing hydrogen concentration. Cracking in the nickel alloys was transgranular, and there was a transition
from dimpled to faceted failure as the hydrogen concentration increased. Failure in A286 was mainly by intergranular microvoid
coalescence at high hydrogen concentrations. Enhanced localization of plasticity and void pressurization due to hydrogen are
proposed to explain the observed hydrogen embrittlement of these alloys. The effects of hydrogen on the stacking fault energy,
trapping sites, microstructure, and cracking ahead of the main crack front are discussed with reference to the above alloys
and their hydrogen embrittlement.
Formerly Research Assistant, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign 相似文献
5.
A study of the correlation between crack paths and crack growth response was undertaken to define better the elemental processes
involved in gaseous hydrogen embrittlement. AISI 4340 steel fractured under sustained load in hydrogen and in hydrogen sulfide
over a range of temperatures and pressures, whose crack growth kinetics have been well characterized previously, was chosen
for study. Fractographic results showed that crack growth followed predominantly along prior-austenite grain boundaries, with
a small amount of quasi-cleavage, at low temperatures. At high temperatures, crack growth occurred primarily by microvoid
coalescence. The fracture surface morphology, which is indicative of the micromechanisms for crack growth, was essentially
the same for hydrogen and hydrogen sulfide. Changes in fracture morphology,i.e., crack paths, corresponded to changes in crack growth kinetics, both of which depended on pressure and temperature. There
was no evidence for crack nucleation in advance of the main crack, and this suggests that the fracture process zone is located
within one prior-austenite grain diameter from the crack tip. The experimental results indicate that microstructure plays
an important role in determining crack growth response. The prior-austenite grain boundaries are seen to be most susceptible
to hydrogen embrittlement, followed by the (110)α’ and (112)α’ cleavage planes. The martensite matrix, on the other hand, is relatively immune. The observed changes in crack growth rate
with temperature and pressure in the higher temperature region are explained in terms of the partitioning of hydrogen into
the different microstructural elements and the consequent changes in the micromechanisms for fracture.
Leave from the Department of Materials Science, Shanghai Jaio Tong University, Shanghai, People’s Republic of China.
Formerly Research Associate, Department of Mechanical Engineering and Mechanics. 相似文献
6.
N. J. Marchand J. -P. Baïlon J. I. Dickson 《Metallurgical and Materials Transactions A》1988,19(10):2575-2587
The fatigue propagation rates and fatigue threshold ( ΔK
th) values were studied (R = 0.1 and frequency = 20 Hz) on copper and 70-30 α-brass of two different grain sizes in laboratory air and dry argon. With
decreasing grain size, the threshold increased in copper, while it decreased in α-brass. These results suggest that in copper,
crack tip plasticity considerations were more important in determining the threshold values than crack closure effects. Dry
argon increased ΔK
th slightly in copper and more significantly in α-brass. A transition from completely transgranular to partially intergranular
and back to completely transgranular cracking was observed with decreasing crack growth rates in both materials and environments.
The growth rates for which intergranular cracking was obtained were found to be consistent with a hydrogen embrittlement mechanism,
associated with adsorption of water molecules and dislocation transport of hydrogen. 相似文献
7.
A “hydrogen partitioning” model has been developed to account for the pressure and temperature dependence for hydrogen-assisted
crack growth. The model gives explicit recognition to the role of hydr en-microstructure interactions in determining the distribution
(or partitioning) of hydrogen among the various microstructural elements (principally between the prior-austenite grain boundaries
and the matrix) and the rate of crack growth along the elements. It also takes into account the role of various rate controlling
processes in determining the rate that hydrogen is being supplied to the fracture process (or embrittlement) zone. Quantitative
assessment of the model indicates very good agreements between the model predictions and the observed crack growth responses
for AISI 4340 and 4130 steels tested in hydrogen and for AISI 4340 steel tested in hydrogen sulfide. This model accurately
characterizes the reduction in crack growth rate and the concomitant change in fracture mode at “high” temperatures. Through
its integration with the earlier models, based on rate controlling processes, the model predicts the pressure and temperature
dependence for K-independent crack growth over the entire range of environmental conditions. 相似文献
8.
Vinay Kumar Tewari Ren Winand Jacques Charlier Jean-Pierre Elinck Jean van Muylder 《国际钢铁研究》1982,53(8):329-333
Based on the data of the literature for intercrystalline stress corrosion cracking (SCC) and hydrogen embrittlement of the High Strength AISI 4340 steel, determination of the so far unknown effects of tempering treatment around the low temper martensite embrittlement range (between 175 and 285°C) on the crack growth rates in 0.5 N NaCl solution. Effect of variation of stress intensity and applied potentials on crack growth rates. Effect of initial applied stress intensity and crack tip sharpness on crack growth characteristics. Discussion on crack growth rates for a better understanding of the SCC mechanism. 相似文献
9.
The effect of stress history on stress corrosion cracking of AISI 4340 steel in an aqueous environment has been studied with
the use of double-cantilever beam specimens. The stress history effect was found to influence the incubation time period with
changes in the stress intensity. When the stress intensity was decreased, the incubation time period was dependent on the
△K and finalK
f during stress corrosion testing. When the stress intensity was increased, the incubation time period was independent of the
applied stress intensity. However, the stress history effect did not influence the steady-state crack growth rates. In this
report, the stress history effect is explained by using the hydrogen embrittlement mechanism. 相似文献
10.
Fatigue crack growth rates (FCGR) in AISI 301 and 302 austenitic stainless steel alloys have been measured in controlled load
cycles withR = 0.05. Both annealed and cold rolled conditions were examined. The austenite phase of the AISI 301 alloy was unstable under
stress and transformed martensitically to α′ to a much greater extent than the AISI 302 alloy. At low values of mean stress
the unstable alloy had a lower FCGR than the more stable 302 alloy. The FCGR increased with mean stress until values of mean
stress ⪞70 MPa, where the FCGR was independent of mean stress and was the same for both alloys. Various metallographic and
macroscopic measurements were made to try to understand this behavior. It was concluded that residual compressive stress due
to transformation at the crack tip was responsible for the lower crack growth rates of the unstable 301 alloy. Cold worked
specimens had significantly lower crack growth rates than the annealed specimens, and both alloys behaved identically.
Formerly with the Department of Metallurgy, University of Illinois at Urbana-Champaign 相似文献
11.
Small crack size accelerates corrosion fatigue propagation through high strength 4130 steel in aqueous 3 pct NaCl. The size
effect is attributed to crack geometry dependent mass transport and electrochemical reaction processes which govern embrittlement.
For vacuum or moist air, growth rates are defined by stress intensity range independent of crack size (0.1 to 40 mm) and applied
maximum stress (0.10 to 0.95 Φys). In contrast small (0.1 to 2 mm) surface elliptical and edge cracks in saltwater grow up to 500 times faster than long (15
to 40 mm) cracks at constant δK. Small cracks grow along prior austenite grain boundaries, while long cracks propagate by
a brittle transgranular mode associated with tempered martensite. The small crack acceleration is maximum at low δK levels
and decreases with increasing crack length at constant stress, or with increasing stress at constant small crack size. Reductions
in corrosion fatigue growth rate correlate with increased brittle transgranular cracking. Crack mouth opening, proportional
to the crack solution volume to surface area ratio, determines the environmental enhancement of growth rate and the proportions
of inter- and transgranular cracking. Small cracks grow at rapid rates because of enhanced hydrogen production, traceable
to increased hydrolytic acidification and reduced oxygen inhibition within the occluded cell. 相似文献
12.
To assist in the understanding of micromechanisms for corrosion fatigue crack growth in metastable austenitic steels, the
relationships between the crack paths and the underlying microstructure were investigated for annealed and cold-rolled (CR)
304 stainless steels that had been tested in a deaerated 3.5 pct NaCl solution, air, and vacuum. Corrosion fatigue in the
deleterious environments (3.5 pct NaCl and air) was brittle and occurred primarily by {001}γ and other unidentified, quasi-cleavage (QC), accompanied by preferential cracking along {111}γ twin and grain boundaries. In contrast, fatigue cracking in vacuum was ductile, fully transgranular, and noncrystallographic.
Transformation to alpha prime (α′-) martensite by fatigue was found to be essentially complete in the CR steel, which contained
ε-martensite, and in the annealed steel tested in vacuum, but was substantially less in the annealed steel tested in air and
3.5 pct NaCl solution. These results, taken in conjunction with the crack growth and electrochemical reaction data, support
hydrogen embrittlement (HE) as the mechanism for corrosion fatigue crack growth in 304 stainless steels in 3.5 pct NaCl solution.
Martensitic transformation appears not to be the only responsible factor for embrittlement. Other microstructural components,
such as twin and grain boundaries, slip bands, and cold work-induced lattice defects, may play more important roles in enhancing
crack growth rates. 相似文献
13.
《Acta Metallurgica Materialia》1990,38(11):2031-2040
The mechanisms of hydrogen embrittlement in AISI type 316 austenitic stainless steel have been investigated by in situ straining in a high-voltage electron microscope (HVEM) equipped with an environmental cell. Hydrogen effects on strain-induced phase transformations, the generation rate and velocity of dislocation, and crack propagation rates were studied. The salient features of the fracture were similar for cracks propagating in vacuum and in hydrogen gas. In each case, ε and α′ martensite formed at the crack; the ε phase extended ahead of the crack while the α′ phase was restricted to high stress regions near the crack tip. The principal effect of hydrogen was to decrease the stress required for dislocation motion, for phase transformation of the austenite, and for crack propagation. 相似文献
14.
N. Narita C. J. Altstetter H. K. Birnbaum 《Metallurgical and Materials Transactions A》1982,13(8):1355-1365
The effect of hydrogen and stress (strain) on the stability of the austenite phase in stainless steels was investigated. Hydrogen
was introduced by severe cathodic charging and by elevated temperature equilibration with high pressure H2 gas. Using X-ray diffraction and magnetic techniques, the behavior of two “stable” type AISI310 steels and an “unstable”
type AISI304 steel was studied during charging and during the outgassing period following charging. Transformation from the
fcc γ phase to an expanded fcc phase, γ*, and to the hcp ε phase occurred during cathodic charging. Reversion of the γ* and
e phases to the original γ structure and formation of the bcc α structure were examined, and the kinetics of these processes
was studied. The γ* phase was shown to be ferromagnetic with a subambient Curie temperature. The γ⇆ε phase transition was
studied after hydrogen charging in high pressure gas, as was the formation of a during outgassing. These results are interpreted
as effects of hydrogen and stress (strain) on the stability of the various phases. A proposed psuedo-binary phase diagram
for the metal-hydrogen system was proposed to account for the formation of the γ* phase. The relation of these phase changes
to hydrogen embrittlement and stress corrosion cracking of stainless steel is discussed. 相似文献
15.
Robert S. Piascik Richard P. Gangloff 《Metallurgical and Materials Transactions A》1993,24(12):2751-2762
Microscopic fatigue crack propagation (FCP) paths in peak-aged unrecrystallized alloy 2090 are identified as functions of
intrinsicda/dN- δK kinetics and environment. The FCP rates in longitudinal-transverse (LT)-oriented 2090 are accelerated by hydrogen-producing
environments (pure water vapor, moist air, and aqueous NaCl), as defined in Part I. Subgrain boundary cracking (SGC) dominates
for δK values where the cyclic plastic zone is sufficient to envelop subgrains. At low δK, when this crack tip process zone
is smaller than the subgrain size, environmental FCP progresses on or near 100 or 110 planes, based on etch-pit shape. For
inert environments (vacuum and He) and pure O2 with crack surface oxidation, FCP produces large facets along 111 oriented slip bands. This mode does not change with δK,
and T1 decorated subgrain boundaries do not affect an expectedda/dN- δK transition for the inert environments. Rather, the complex dependence ofda/dN on δK is controlled by the environmental contribution to process zone microstructure-plastic strain interactions. A hydrogen
embrittlement mechanism for FCP in 2090 is supported by similar brittle crack paths for low pressure water vapor and the electrolyte,
the SGC and 100/110 crystallographic cracking modes, the influence of cyclic plastic zone volume (δK), and the benignancy
of O2. The SGC may be due to hydrogen production and trapping at T1 bearing sub-boundaries after process zone dislocation transport, while crystallographic cracking may be due to lattice decohesion
or hydride cracking.
Formerly Graduate Student, Department of Materials Science, University of Virginia 相似文献
16.
《Acta Metallurgica》1986,34(9):1771-1781
Transient and steady state fluxes of hydrogen were measured for annealed and deformed AISI 301, 304 and 310 austenitic and annealed AL 29-4-2 ferritic stainless steel membranes using a gas phase permeation technique at T = 100–350°C. Permeability and effective diffusivity and solubility constants were calculated from these data. Up to 80% deformation of the stable AISI 310 alloy made only a relatively small change in the transport parameters. Deformation of AISI 301 and 304 resulted in various amounts of stress-induced α′ martensite, which greatly enhanced the effective hydrogen diffusivity and permeability. The relationship between phase changes and hydrogen transport parameters was modeled using various assumptions about the microstructure. Effective solubility and diffusivity values are discussed in terms of dislocation trapping and transport. 相似文献
17.
The conditions of cathodic charging, gaseous hydrogen environment, and loading for which a TRIP steel may or may not be susceptible
to hydrogen embrittlement were investigated. In the austenitic state, the TRIP steel appeared to be relatively immune to hydrogen
embrittlement. It was shown that it is the strain-induced martensitic phase, α′, which is embrittled. In TRIP steel single-edge-notch specimens under fixed loads in gaseous hydrogen, slow crack growth
occurs when the stress intensity level exceeds a threshold level of about 25 ksi-in.1/2 and the growth rate varies approximately as the 2.5 power of the stress intensity level. The activation energy for this slow
crack growth was found to be about 10,000 cal/g-atom, the approximate activation for hydrogen diffusion in martensite. Thus
it was concluded that slow crack growth in TRIP steel loaded in gaseous hydrogen involves the diffusion of hydrogen through
the α′ phase.
Formerly with the Lawrence Berkeley Laboratory, Berkeley, Calif. 相似文献
18.
Howard G. Nelson Dell P. Williams Alan S. Tetelman 《Metallurgical and Materials Transactions B》1971,2(4):953-959
Gaseous hydrogen embrittlement of quenched and tempered 4130 steel was studied as a function of temperature from −42° to 164°C
in a partially dissociated hydrogen environment at low molecular hydrogen pressures (≈8 × 10−3 torr). Atomic hydrogen was created by dissociation of molecular hydrogen on a hot tungsten filament located near a crack
opening. The presence of atomic hydrogen was found to increase the rate of hydrogen-induced, slow crack growth by several
orders of magnitude and to significantly alter the temperature dependence of embrittlement from what is observed in the presence
of molecular hydrogen alone. Based on a previous study, these observations are interpreted in terms of a difference between
the hydrogen-transport reaction step controlling hydrogen-induced, slow crack growth in the molecular hydrogen and the atomic-molecular
hydrogen environments. Finally, a comparison is made between the kinetics of hydrogen-induced, slow crack growth observed
in the presence of atomic-molecular hydrogen and the kinetics of known, possible hydrogen-transport reactions in an effort
to identify the reaction step controlling hydrogen embrittlement in the presence of atomic hydrogen. 相似文献
19.
Robert O. Ritchie 《Metallurgical and Materials Transactions A》1977,8(7):1131-1140
Interactions between hydrogen embrittlement and temper embrittlement have been examined in a study of fracture and low growth
rate (near-threshold) fatigue crack propagation in 300-M high strength steel, tested in humid air. The steel was investigated
in an unembrittled condition (oil quenched after tempering at 650°C) and temper embrittled condition (step-cooled after tempering
at 650°C). Step-cooling resulted in a severe loss of toughness (approximately 50 pct reduction), without loss in strength,
concurrent with a change in fracture mode from micr ovoid coalescence to inter granular. Using Auger spectroscopy analysis,
the embrittlement was attributed to the cosegregation of alloying elements (Ni and Mn) and impurity elements (P and Si) to
prior austenite grain boundaries. Prior temper embrittlement gave rise to a substantial reduction in resistance to fatigue
crack propagation, particularly at lower stress intensities approaching the threshold for crack growth(x0394;K
o). At intermediate growth rates (10-5 to 10-3 mmJcycle), propagation rates in both unembrittled and embrittled material were largely similar, and only weakly dependent
on the load ratio, consistent with the striation mechanism of growth observed. At near-threshold growth rates (<10−5 to 10−6 mmJcycle), embrittled material exhibited significantly higher growth rates, 30 pct reduction in threshold ΔKo values and intergranular facets on fatigue fracture surfaces. Near-threshold propagation rates (and ΔKo values) were also found to be strongly dependent on the load ratio. The results are discussed in terms of the combined influence
of segregated impurity atoms (temper embrittlement) and hydrogen atoms, evolved from crack tip surface reactions with water
vapor in the moist air environment (hydrogen embrittlement). The significance of crack closure concepts on this model is briefly
described. ntmis]formerly with the Lawrence Berkeley Laboratory, University of California in Berkeley.
Formerly with the Lawrence Berkeley Laboratery, University of California in Berkeley. 相似文献
20.
Robert S. Piascik Richard P. Gangloff 《Metallurgical and Materials Transactions A》1993,24(1):2751-2762
Microscopic fatigue crack propagation (FCP) paths in peak-aged unrecrystallized alloy 2090 are identified as functions of
intrinsicda/dN- ΔK kinetics and environment. The FCP rates in longitudinal-transverse (LT)-oriented 2090 are accelerated by hydrogen-producing
environments (pure water vapor, moist air, and aqueous NaCl), as defined in Part I. Subgrain boundary cracking (SGC) dominates
for ΔK values where the cyclic plastic zone is sufficient to envelop subgrains. At low ΔK, when this crack tip process zone is smaller than the subgrain size, environmental FCP progresses on or near (100) or (110)
planes, based on etch-pit shape. For inert environments (vacuum and He) and pure O2 with crack surface oxidation, FCP produces large facets along 111 oriented slip bands. This mode does not change with ΔK, andT
1 decorated subgrain boundaries do not affect an expectedda/dN- ΔK transition for the inert environments. Rather, the complex dependence ofda/dN on ΔK is controlled by the environmental contribution to process zone microstructure-plastic strain interactions. A hydrogen embrittlement
mechanism for FCP in 2090 is supported by similar brittle crack paths for low pressure water vapor and the electrolyte, the
SGC and 100/110 crystallographic cracking modes, the influence of cyclic plastic zone volume ( ΔK), and the benignancy of O2. The SGC may be due to hydrogen production and trapping atT
1 bearing sub-boundaries after process zone dislocation transport, while crystallographic cracking may be due to lattice decohesion
or hydride cracking.
Robert S. Piascik, formerly Graduate Student, Department of Materials Science, University of Virginia. 相似文献