共查询到20条相似文献,搜索用时 15 毫秒
1.
R. Garber I. M. Bernstein A. W. Thompson 《Metallurgical and Materials Transactions A》1981,12(2):225-234
The effects of hydrogen on ductile fracture were studied in two spheroidized plain carbon steels, containing 0.16 and 0.79
pct C. A combination of fractography and quantitative metallography on sectioned, deformed specimens permitted separation
of the effects of hydrogen on the initiation, growth, and link-up of voids. In both steels, hydrogen was found to have no
significant effect on either the initiation of voids at carbides, or early growth of voids, prior to link-up. In the higher
carbon steel the fracture surface dimple size increased after hydrogen exposure with no other evident change in the fracture
surface appearance; it is therefore inferred that hydrogen primarily assists void growth during link-up in this steel. In
the lower carbon steel the fracture appearance changed and a decrease in void size due to hydrogen was found fractographically;
thus, both initiation and growth of voids are apparently enhanced during the link-up phase of fracture in this steel. It is
hypothesized that these effects may be due largely to a void pressure mechanism if hydrogen is transported by mobile dislocations.
Formaly Graduate Student, Department of Metallurgy and Materials Science, Carnegie-Mellon University 相似文献
2.
3.
S. Yu. Nastich 《Russian Metallurgy (Metally)》2013,2013(10):765-771
The formation of the products of bainitic transformation in pipe steels of strength classes K60 (X70) and K65 (X80) during thermomechanical treatment is considered. It is shown that the structural factors that affect the ductile-fracture resistance of steel are the bainite morphology and the carbon distribution over structural constituents. 相似文献
4.
In this report we consider the problem of hydrogen induced ductility losses in a plain carbon spheroidized steel. Specifically,
the effect of internal hydrogen on the formation of voids from second phase (cementite) particles and their subsequent growth
and coalescence was studied by careful microscopic inspection of uniaxially strained bars, both initially cylindrical and
circumferentially notched, with and without hydrogen. Void initiation occurred with lower strains and stresses with hydrogen,
although an equally important contribution to the ductility loss was from hydrogen accelerated void growth and coalescence.
This latter process takes place by the propagation of voids along the grain, and possibly subgrain, boundaries which interlink
the cementite spheroids. The results indicate that hydrogen facilitates interface separation, possibly by accumulating at
the boundaries during hydrogenation of the specimen and lowering the cohesive strength, thereby making void initiation and
growth along them easier. 相似文献
5.
研究了不同碳含量和显微组织的低合金钢的耐腐蚀性能和腐蚀行为,并与商业耐候钢09CuPCrNi进行了相应的比较.通过金相显微镜、扫描电镜观察,轧后水冷钢的主体组织为板条状贝氏体,轧后空冷钢为针状铁素体、粒状贝氏体、M/A小岛和少量渗碳体(珠光体)的混合物.用干湿循环加速腐蚀实验对耐蚀性测定结果表明:低碳钢(0.03%C)和轧后水冷的较高碳含量钢(0.1%C)的耐蚀性均明显优于09CuPCrNi;低碳含量钢的组织类型对其耐蚀性影响不大;较高碳含量情况下,单相贝氏体钢的耐蚀性优于由铁素体、渗碳体(珠光体)等构成的复相组织钢;轧后水冷时,不同碳含量的钢耐蚀性差别不大;轧后空冷时,低碳含量钢的耐蚀性优于较高碳含量钢.用扫描电镜对锈层进行观察,可以看出耐蚀性较好的样品在腐蚀后期形成了致密的内锈层. 相似文献
6.
《Acta Metallurgica》1987,35(7):1415-1432
Fatigue crack growth behavior of 4340 steels was investigated in four gaseous environments; laboratory air, wet hydrogen, dry hydrogen and dry helium. Specimen orientation does not affect crack propagation rate results. The effects of R-ratio (load ratio) and environment on crack growth rate properties are interrelated. Increasing R -ratio increases the rates of near-threshold crack propagation. Nevertheless, the effect of R-ratio on crack growth rates in air is much more significant than that in the two dry environments. Interestingly, the R-ratio effect in wet hydrogen is comparable to that in dry environments. At an R-ratio of 0.1, the rates of crack propagation in air are slower than those in dry environments while crack growth rates are essentially identical in wet hydrogen and dry environments. Increasing R -ratio was found to decrease the environmental effect. Furthermore, increasing yield strength from 700 to 1040 MPa does not affect crack propagation behavior. While surface roughness-induced crack closure is thought to be minimal in affecting gaseous-environment near-threshold crack growth behavior of 4340 steels, oxide-induced crack closure governs crack propagation kinetics. It is suggested that in moisture-containing environments, thick oxide deposits measured on fracture surfaces may not result in high crack closure levels. Nevertheless, oxide-induced crack closure rationalized the effects of R-ratio and environment on near-threshold crack growth rate properties. Furthermore, hydrogen embrittlement is believed not to play an important role in influencing wet-hydrogen environment near-threshold crack propagation behavior. At higher ΔK levels (⩾ 12 MPa √m), an “intrinsic” dry hydrogen effect seems to be present, and crack closure, however, cannot account for the environmental effect. 相似文献
7.
A study of the influence of microstructure on fatigue crack growth in an AISI 1018 steel has been carried out. Two distinctly
different duplex microstructures were investigated. In one microstructure ferrite encapsulated islands of martensite; in the
other martensite encapsulated islands of ferrite. The latter structure resulted in a significant increase in threshold level
(18 MPa√mvs 8 MPa√m) together with an increase in yield strength. Fractographic analysis was used to investigate the influence of microstructure
on the mode of fatigue crack growth.
Formerly at the University of Connecticut 相似文献
8.
9.
《粉末冶金学》2013,56(4):345-349
AbstractFatigue crack propagation rates under plane strain conditions have been investigated for three PM low alloy steels consolidated to high densities by rotary compaction followed by sintering and heat treatment. It is shown that the densities and properties are intermediate between those of pressed and sintered materials and of powder forged materials. Threshold stress intensities compare satisfactorily with those for wrought counterparts, but resistances to crack growth are inferior to those of wrought steels. Possible reasons for the properties of the rotary compacted materials are considered in the light of their microstructures and the behaviour of other PM materials. 相似文献
10.
11.
Bainite formation in low carbon Cr-Ni steels 总被引:4,自引:0,他引:4
A low carbon Cr-Ni steel has been used to investigate the formation of upper bainite. Experimental results indicate that the
start temperatures of the three morphologies of upper bainite in this steel,i.e., carbide-free bainite, bainite with carbide between and within ferrite laths, are about 600°, 500δ, and 425 °C, respectively;
the habit plane of bainitic ferrite in this steel is close to (1 7 11)α, which is 13.3 deg away from (0 ll)α; and the orientation relationship between cementite and ferrite is consistent with Bagaryatskii’s. By means of the superelement
approach, a thermodynamic treatment which applies to Fe-C alloys is extended into that suitable for low alloy steels, and
calculation shows that the driving force for bainite formation at BS temperatures is insufficient to compensate for shear strain energy.
Formerly Graduate Student, Department of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai, People’s
Republic of China. 相似文献
12.
Tacke K.-H. 《钢铁冶炼》2013,40(4):317-323
AbstractStrip casting of low carbon steels has been investigated using a laboratory twin roll machine with copper rolls. The following grades have been studied: a deep drawing low carbon (LC) steel, a LC steel with titanium addition, and a high strength low alloy (HSLA) grade. The casting behaviour of these steels has been examined, and the observed surface defects classified. Defects are most pronounced for the LC grade and significantly less for the HSLA steel and the LC steel with titanium addition. The as cast structure has been analysed. It can be modified by post-cast treatment, e.g. by normalisation or in line rolling. The mechanical properties of cold rolled and annealed strip materials and their textures are presented. Satisfactory sheet properties can be achieved both as hot band and as cold rolled sheet when adequate treatment steps are applied. Consequences for strip casting applications and future research are discussed. 相似文献
13.
Low Nsol levels not only require reduced N contents (≤ 20 ppm) in steel but also Al/N ratios higher than 5 and C contents higher than 0.025% because of the synergic effect between N and C precipitations; scavenging of Al on nitrogen is far from complete even in steels coiled at 750°C. Low Csol levels are achieved either at very lowC contents (C ≤ 0.003%) or at C contents higher than 0.025%. Due to high Csol, carbon aging is expected in steels coiled at 750°C. Softer, bake hardenable steels with good aging resistance will be obtained in the range 0.025–0.030 % C independently of the coiling temperature. C supersaturation of the ferrite is reduced at higher cooling rates after continuous annealing. Changes in C and N supersaturation according to the steel composition and the continuous annealing process are explained, taking into account the carbides morphology and the annealing conditions. 相似文献
14.
J. B. Lupton S. Murphy J. H. Woodhead 《Metallurgical and Materials Transactions B》1972,3(11):2923-2931
The tempering behavior of three steels each containing 0.20 pct C and having tungsten contents of 2.1, 3.9 and 5.9 pct has
been followed by thermomagnetic analysis and electron microscopy. Using a Sucksmith Balance, the proportions of autotempered
carbide and retained austenite in as-quenched specimens were estimated, and the amount of cementite precipitated upon subsequent
tempering measured accurately. Solution of tungsten in cementite during tempering was monitored by observing changes in Curie
temperature. The magnetic nature of alloy carbides precipitating at high temperatures allowed tentative identification and
this directed and assisted the electron microscopy study which provided new information on the morphology of tungsten carbides.
J. B. LUPTON, formerly Research Student, Metallurgy Department, University of Sheffield, England,
S. MURPHY, formerly Research Fellow, Metallurgy Department, University of Sheffield, 相似文献
15.
The kinetics of sustained-load subcritical crack growth for 18 Ni maraging steels in high purity hydrogen are examined using
crack-tip stress intensity,K, as a measure of crack driving force. Crack growth rate as a function of stress intensity exhibited a clearly definedK-independent stage (Stage II). Crack growth rates in an 18 Ni (250) maraging steel are examined for temperatures from -60°C
to 100°C. A critical temperature was observed above which crack growth rates became diminishingly small. At lower temperatures
the activation energy for Stage II crack growth was found to be 16.7 ± 3.3 kJ/mole. Temperature and hydrogen partial pressure
are shown to interact in a complex manner to determine the apparentK
th
and the crack growth behavior. Comparison of results on ‘250’ and ‘300’ grades of 18 Ni maraging steel indicate a significant
influence of alloy composition and/or strength level on the crack growth behavior. These phenomenological observations are
discussed in terms of possible underlying controlling processes.
Formerly a Graduate Student and Research Assistant.
Based on a thesis submitted in partial fulfillment of requirements for the M.S. degree in Metallurgy and Materials Science,
Lehigh University, Bethlehem, PA. 相似文献
16.
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
17.
On macroscopic and microscopic analyses for crack initiation and crack growth toughness in ductile alloys 总被引:1,自引:0,他引:1
Relationships between crack initiation and crack growth toughness are reviewed by examining the crack tip fields and microscopic
(local) and macroscopic (continuum) fracture criteria for the onset and continued quasi-static extension of cracks in ductile
materials. By comparison of the micromechanisms of crack initiationvia transgranular cleavage and crack initiation and subsequent growthvia microvoid coalescence, expressions are shown for the fracture toughness of materials in terms of microstructural parameters,
including those deduced from fractographic measurements. In particular the distinction between the deformation fields directly
ahead of stationary and nonstationary cracks are explored and used to explain why microstructure may have a more significant
role in influencing the toughness of slowly growing, as opposed to initiating, cracks. Utilizing the exact asymptotic crack
tip deformation fields recently presented by Rice and his co-workers for the nonstationary plane strain Mode I crack and evoking
various microscopic failure criteria for such stable crack growth, a relationship between the tearing modulusT
R and the nondimensionalized crack initiation fracture toughnessJ
Ic is described and shown to yield a good fit to experimental toughness data for a wide range of steels.
An erratum to this article is available at . 相似文献
18.
Masazumi Tanaka 《Metallurgical and Materials Transactions A》1996,27(9):2678-2685
The influence of aqueous environments on fatigue crack propagation behavior was investigated for two types of structural steel
(SB42 and HT80) in pure and 3 pct NaCl water under freely corroding conditions. In the intermediate to high ΔK region, fatigue crack propagation rates were higher in both aqueous environments and in 1 atm hydrogen than in air for both
types of steel, and the acceleration effect increased power functionally with decreasing frequency from 5 to 0.0005 Hz. Such
a crack growth acceleration property was explained by the mechanism of cyclically induced hydrogen embrittlement, as shown
by the brittle striations formed on the fracture surfaces. On the other hand, in the lower ΔK region, both aqueous environments inversely suppressed crack growth and enhanced the threshold stress intensity factor range
ΔK
th just above the ΔK
th in air, while only in aerated 3 pct NaCl water was the crack observed to grow even under the condition below the ΔK
th in air, not showing the threshold. Probable mechanisms for such fairly complex environmental effects were also suggested. 相似文献
19.
Relationships between crack initiation and crack growth toughness are reviewed by examining the crack tip fields and microscopic
(local) and macroscopic (continuum) fracture criteria for the onset and continued quasi-static extension of cracks in ductile
materials. By comparison of the micromechanisms of crack initiationvia transgranular cleavage and crack initiation and subsequent growthvia microvoid coalescence, expressions are shown for the fracture toughness of materials in terms of microstructural parameters,
including those deduced from fractographic measurements. In particular the distinction between the deformation fields directly
ahead of stationary and nonstationary cracks are explored and used to explain why microstructure may have a more significant
role in influencing the toughness of slowly growing, as opposed to initiating, cracks. Utilizing the exact asymptotic crack
tip deformation fields recently presented by Rice and his co-workers for the nonstationary plane strain Mode I crack and evoking
various microscopic failure criteria for such stable crack growth, a relationship between the tearing modulusT
R and the nondimensionalized crack initiation fracture toughnessJ
Ic is described and shown to yield a good fit to experimental toughness data for a wide range of steels. 相似文献
20.
To enamel modern LC‐steels it is necessary to provide a sufficient amount of hydrogen recombination sites as well as hydrogen traps within the materials microstructure to keep the hydrogen inside the steel. Hence surface defects like fish scaling, which are related to the effusion of hydrogen, can be avoided. Therefore it is necessary to produce internal surfaces inside the steel In form of hard and brittle particles which can be fractured during cold rolling and produce voids. For LC‐steels these particles could be formed by iron carbides. Aiming at an increased amount of cementite particles inside the steel, the carbon content could be raised or the parameters of the thermomechanical treatment (TMT) could be adjusted for a given carbon content to form coarse cementite particles. In this investigation the TMT‐parameters were systematically varied in hot compression tests and the results were evaluated by quantitative metallography. The focus was laid on the variation of the final deformation temperature, the coiling temperature and the cooling rate after coiling. 相似文献