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1.
Iron alloys containing 20 and 30 pct Ni and 3 to 4 cu cm H per 100 g metal have been subjected to slow strain-rate tensile tests in a study of hydrogen embrittlement. In the lower nickel massive martensite alloy, embrittlement is manifest as the cracking of prior austenite grain boundaries and is severe at room temperature but less marked at -196°C; while in the higher nickel acicular martensite alloy, the embrittlement observed at 20°C does not occur at —196°C. Hydrogen embrittlement in these materials is believed to be the result of high hydrogen contents in the vicinity of the prior austenite grain boundaries combined with stress concentrations caused by boundary perturbations which result from the impact of the martensite shears. During deformation, microcracks form and propagate in the prior austenite grain boundaries, probably assisted by internal hydrogen pressure and the lowering of crack surface energy by hydrogen adsorption. The temperature dependence and the effect of the type of martensite on the embrittlement can be explained by their effects on the hydrogen content and stress concentrations at prior austenite grain boundaries during deformation. 相似文献
2.
W. W. Gerberich T. Lvne X. F. Chen M. Kaczorowski 《Metallurgical and Materials Transactions A》1988,19(5):1319-1334
Internal hydrogen effects on stage II crack growth rates in AISI 4340 steel have been studied as a function of test temperature.
A model is developed that is physically based in that classical thermodynamics relates to solubility and trapping and Fick’s
second law controls hydrogen transport. Both of these are microstructurally related to how trapping affects both the crack
initiation site and diffusion to it. For two tempered conditions of 4340 steel, it is shown that there is a test temperature,T
0, for stage II crack growth, above which the crack does not grow. The fractography associated with test temperatures approachingT
0 tends toward 100 pct intergranular for both 1340 MPa and 1620 MPa strength levels. At lower test temperatures, there is as
much as 50 pct microvoid coalescence or 30 pct quasi-cleavage. In the lower strength condition, hydrogen traps at oxysulfide
particles with a binding energy near 75 kJ/mol. Where these intersect the prior austenite grain boundaries, this promotes
fingers of intergranular fracture which later triggers tearing of 100 μm size ligaments by microvoid coalescence. For the
higher strength material, it is proposed that hydrogen traps along martensite lath intersections with prior austenite grain
boundaries, the binding energy being near 27 kJ/mol. This promotes 1 μm size striations along intergranular facets. In both
cases the fractography is consistent with a proposed model of stress field concentration of hydrogen, further concentration
along trap sites, fracture nucleation at trap sites, and local, discontinuous fracture instabilities. 相似文献
3.
铁素体作为酸性环境用管线钢的主要组织类型之一,探究其晶界结构与管线钢氢致开裂(HIC)敏感性之间关系,可为进一步优化管线钢的抗HIC性能提供指导。对热轧态管线钢进行不同工艺热处理,采用扫描电子显微镜(SEM)、电子背散射衍射(EBSD)、透射电子显微镜(TEM)观察了试样的晶界、位错结构及氢鼓泡、氢致裂纹形貌,用电化学充氢及动态充氢方法对试样的HIC敏感性及氢致塑性损失进行了测试,用电化学氢渗透及氢微印实验对试样的氢捕获效率及氢原子分布进行了观察与分析,探索了铁素体晶界结构与HIC敏感性之间内在关联。其结果表明:当材料中以小角度晶界占主导或大小角度晶界比例约为1∶1时,对氢原子的捕获效率较高,HIC敏感性也相对较大;大小角度晶界均能捕获氢原子,但与氢的作用机制不同,大角度晶界主要促进氢致裂纹萌生,而小角度晶界主要促进氢致裂纹扩展。 相似文献
4.
Bruce D. Craig 《Metallurgical and Materials Transactions A》1984,15(3):565-572
Earlier work on AISI 4130 steels showed that phosphorus segregation to prior austenite grain boundaries was the primary cause
for intergranular fracture of these steels when exposed to hydrogen. Reduction of P segregation to grain boundaries by removing
the strong segregation couples of Mn-P and Si-P was expected to increase the hydrogen stress cracking resistance of 4130 type
steels. Elimination of Mn and/or Si did reduce the concentration of P at prior austenite grain boundaries, but allowed segregation
of S and N which acted in the same manner as P, promoting intergranular hydrogen stress cracking. 相似文献
5.
Bruce D. Craig 《Metallurgical and Materials Transactions A》1982,13(5):907-912
A series of four 4130 base steels with various phosphorus concentrations was subjected to cathodic charging to determine the
effect of P on hydrogen stress cracking resistance. Static fatigue curves for several different yield strengths were obtained
for each alloy. At high yield strengths under applied loads of 60 to 80 pct of the yield, 50 ppm P (bulk concentration) was
enough to provide sufficient grain boundary P for an impurity-hydrogen interaction which produced intergranular fracture along
prior austenite grain boundaries. Decreasing yield strength and applied stress caused a transition in fracture mode to transgranular
while the resistance to hydrogen stress cracking increased with decreasing P. Microhardness measurements of prior austenite
grain boundaries were made to establish the role of P. The role of P is not apparently related to its capacity as a strengthening
element but more probably as a hydrogen recombination poison. Grain boundary hardness measurements for low temperature tempers
(200 °C) appear to be valid while those at 500 °C were not. 相似文献
6.
The structure of tempered martensite and its susceptibility to hydrogen stress cracking 总被引:3,自引:0,他引:3
A series of 4130 steels modified with 0.50 pct Mo and 0.75 pct Mo were tempered at temperatures between 300 and 700 °C for
one hour. The changes in the carbide dispersion and matrix substructure produced by tempering were measured by transmission
electron microscopy. These measurements were correlated with resistance to hydrogen stress cracking produced by cathodic charging
of specimens in three-point bending. Scanning electron microscopy showed that specimens tempered between 300 and 500 °C failed
by intergranular cracking while those tempered at higher temperatures failed by a transgranular fracture mode. Auger electron
spectroscopy showed that the intergranular fracture was associated with hydrogen interaction with P segregation and carbide
formation at prior austenite grain boundaries. Transgranular cracking was initiated at inclusion particles from which cracks
propagated to produce flat fracture zones extending over several prior austenite grains. The 4130 steels modified with higher
Mo content resisted tempering and showed better hydrogen stress cracking resistance than did the unmodified 4130 steel. The
transition in fracture mode is attributed to a decohesion mechanism in the low temperature tempered samples and a pressure
mechanism in the highly tempered samples. 相似文献
7.
Hydrogen thermal analysis experiments have been employed to study the trapping and transport phenomena of hydrogen in nickel.
Dislocations in nickel act as trapping sites of hydrogen, and the hydrogen trap activation energy at dislocations appears
to be lower than the activation energy for the bulk diffusion of hydrogen. It is suggested that both hydrogen trapping at
grain boundaries and short-circuit diffusion through grain boundaries in nickel are present. The trap binding energy at grain
boundaries is estimated as 20.5 kJ ⋅ mol-1. Using the hydrogen thermal analysis experiments, the solubility and diffusivity of hydrogen in nickel have been measured.
The temperature dependences of those are described by C (H atoms/Ni atom) = 1.57 × 10-3 exp(-11.76 kJ ⋅ mol-1/RT) and D (m2 s-1) = 7.5 × 10-7 exp(-39.1 kJ ⋅ mol-1/RT), respectively. 相似文献
8.
Isothermal tempering at 500 °C (within the region rendering low alloy steels susceptible to reversible temper embrittlement)
induced acoustic emission activity in A533B steel during indentation loading. Samples, when sectioned, were found to contain
small (∼10 μm long) MnS inclusions, some of which had debonded from the matrix material when they were near the indentations.
Hydrogen charging prior to testing greatly enhanced the acoustic emission activity. It also resulted in the formation of small
(∼20 to 200 μm) microcracks in samples tempered at 500 °C. These microcracks, when examined by optical metallography, appear
to have propagated along prior austenite grain boundaries, consistent with fractographic observations of temper embrittlement
in other low alloy steels. Many were nucleated by MnS inclusion debonding and all were confined to within a few hundred micrometers
of the sample surface and within two or three indenter diameters from the indent. It is proposed that trace impurities (P,
As, Sb, Sn) diffuse during the 500 °C temper to both the MnS inclusion interfaces and the prior austenite grain boundaries,
reducing local cohesive strength. The tensile field created by the indenter debonds inclusions to form crack nuclei. Moderate
acoustic emission results. In the absence of hydrogen these void nuclei may grow but do not coalesce to form observable cracks.
The prior austenite grain boundaries, which in contrast to the dispersed inclusions can provide continuous crack paths, are
not sufficiently temper embrittled to fracture without the assistance of hydrogen at these stresses. Hydrogen charging induces
a high hydrogen concentration in a surface layer of the sample. This reduces further the grain boundary cohesion, and cracks
initiated at inclusions are able to propagate along continuous grain boundary paths, generating additional energetic acoustic
emission signals. This process can continue after unloading the indenter due to hydrogen diffusion to the residual stress
field. 相似文献
9.
Atomistic computer simulations of the trapping of hydrogen and helium at defect free grain boundaries in nickel are presented.
Three symmetrical tilt boundaries that encompass a number of compact polyhedra of atoms are considered as regions of potential
trapping sites. By employing the structural unit model, these boundaries are shown to be representative of a wide range of
grain boundary structures. A general correspondence of trap locations in regions of expansion for both hydrogen and helium
has been found; however, the binding energy for helium trapping is much greater than that for hydrogen. Consequently, clean
grain boundaries in nickel appear to be important trapping sites for helium, but not significant sites for hydrogen binding.
These results are consistent with experimental autoradiography, thermal desorption, and transmission electron microscopy observations.
They imply that grain boundary trapping plays an important role in mechanisms of helium embrittlement, but not in hydrogen
embrittlement of nickel. 相似文献
10.
Dongliang Lin Jiangsheng Wu Yun Lan 《Metallurgical and Materials Transactions A》1988,19(9):2225-2231
Measurements of the threshold stress intensity for stress corrosion cracking (SCC), KISCC, and crack growth rate,da/dt, in distilled water were made, respectively, on bolt-loaded WOL and precracked three-point-bending specimens of a 4330M steel.
A significant improvement of resistance to SCC was obtained by increasing quenching temperature and it is due to a reduction
of segregated impurities of P and S at prior austenite grain boundaries. Intergranular cracking tendency increases with inter-granular
concentration of impurities and the fracture mode changes from intergranular separation along prior austenite grain boundaries
to transgranular quasi-cleavage as the segregated impurity becomes low enough. The combined effects of hydrogen and intergranular
impurities on reducing intergranular cohesion and the time for approaching the critical concentration of hydrogen are dis-cussed
in terms of a dynamic model which takes into account the accumulation of hydrogen ahead of a moving microcrack.
Formerly with Shanghai Jiao Tong University, Shanghai, China 相似文献
11.
SymbolList DA———Apparentdiffusioncoefficient; DL———Latticediffusioncoefficient; EaD———Diffusionactivationenergyofhydrogeninnormallattice ; EaT———Trapactivationenergy ; EB———Trapbindingenergy ; ES———Saddlepointenergy ; 相似文献
12.
Nb是现代高性能钢铁材料中重要的微合金化元素,其在晶界有强偏聚特性。采用3种Nb-空位复合体扩散系数分别对非平衡晶界偏聚进行拟合,根据铁-铌二元合金中Nb在晶界偏聚实验的EPMA测量结果筛选出最终的复合体扩散系数,并据此讨论了低温恒温温度,基体Nb含量,原奥氏体晶粒尺寸对非平衡晶界偏聚动力学的影响,得出了最符合实验结果的铌-空位复合体扩散系数公式。结果表明,在1 000℃恒温过程,Nb非平衡晶界偏聚的临界时间在15 min左右,临界时间常数为6.57×105。从1 200℃固溶态冷却至某低温等温时,随着等温温度的升高临界时间迅速减小,Nb在晶界的最大偏聚量逐渐越小;随着基体Nb含量增加晶界Nb的最大偏聚量线性增加;随着原奥晶粒尺寸的增加临界时间逐渐增大。 相似文献
13.
The quenchedandtemperedlowalloysteelswithtensilestrengthexceeding 12 0 0MPaaresus ceptibletohydrogen induceddelayedfracture(HIDF )wheninuse[1,2 ] .Despitetheenormousamountofresearchworkperformedondelayedfrac tureofhighstrengthsteelintheseyears ,thesolu tiontothisproblemstillhasnotbeenobtained .TheresistanceofanalloytoHIDFisstronglyaffectedbytheinteractionofhydrogenwithmicrostructuralhet erogeneitiesthatactashydrogentraps ,andthere foreinasearlyas 1980s ,GMPressouyre[3 ] suggest edtheappli… 相似文献
14.
To understand and control hydrogen induced cracking and stress corrosion cracking, the processes of hydrogen absorption, diffusion and trapping are of interest. Fundamentals of these processes are described and of the determination of permeation coefficient, diffusivity and solubility of H in iron and steels, using the electrochemical double cell. With this method trapping parameters are also obtained, i.e. numbers of traps and binding energies. Extended studies were conducted on hydrogen in ternary alloys Fe‐Me‐C or N (Me = Ti, Zr, V, Nb, Mo) and in pipeline steels. Flat traps with binding energies around ?19kJ/mol H can be discerned from deep traps with binding energies around ?57kJ/mol H. As shown by constant extension rate tests with the pipeline steels, only the mobile hydrogen in ideal solution and in the flat traps is involved in hydrogen induced stress corrosion cracking, not the hydrogen tied up in deep traps. 相似文献
15.
Jeremy L. Caron Sudarsanam Suresh Babu John C. Lippold 《Metallurgical and Materials Transactions A》2011,42(13):4032-4044
BlastAlloy160 (BA-160) steel, with a nominal composition of Fe-0.05C-3.65Cu-6.5Ni-1.84Cr-0.6Mo-0.1V (wt pct), is strengthened
by Cu-rich precipitates and M2C carbides. This alloy was subjected to several weldability tests to assess its susceptibility to certain weld cracking mechanisms.
Hot ductility testing revealed a liquation cracking temperature range (LCTR) of 148 K (–125 °C), which suggested moderate
susceptibility to heat-affected zone (HAZ) liquation cracking. The enrichment of Ni and Cu was measured along the prior austenite
grain boundaries in the simulated partially melted zone (PMZ) and was consistent with similar enrichment at interdendritic
boundaries of the simulated fusion zone (FZ). Good wetting and penetration of liquid films along the austenite grain boundaries
of the PMZ was also observed. Associated with that finding were thermodynamic calculations indicating a completely austenitic
(face-centered cubic) microstructure at elevated temperatures. In testing to determine reheat cracking susceptibility, ductility
values of 41 to 78 pct RA were established for the 723 K to 973 K (450 °C to 700 °C) temperature range. The good ductility
values precluded susceptibility to reheat cracking according to the test criterion. Dilatometric measurements and thermodynamic
calculations revealed the formation of austenite in the reheat cracking temperature range, which was attributed to the high
Ni content of the BA-160 alloy. 相似文献
16.
A ductile-brittle-ductile (DBD) transition behavior in an age-hardenable Fe-8Mn-7Ni alloy has been analyzed in light of segregation
and desegregation of alloying elements at prior austenite grain boundaries. The DBD transition in the alloy can be distinguished
by two C-type curves: one corresponding to the start of zero tensile elongation and the other to the finish. The activation
energies for ductile-to-brittle and brittle-to-ductile transitions are in close agreement with that for age hardening. Manganese
content at the prior austenite grain boundaries was analyzed by Auger electron spectroscopy, and intergranular fracture strength
at the brittle fracture region showed inverse trends with Mn concentration at the grain boundaries. All these observations
strongly suggest that manganese segregation and its desegregation are responsible for the DBD transition of this alloy.
Formerly Graduate Student, Department of Metallurgical Engineering, Seoul National University 相似文献
17.
The effect of oxygen content on the susceptibility of high-strength weld metal to hydrogen cracking is examined. Increasing
oxygen content had a detrimental effect on the cracking susceptibility of weld metal containing a dψusible hydrogen content
of 4.7 ppm. In weld metal containing a much lower dψusible hydrogen content (0.87 ppm), increasing weld metal oxygen content
had no detrimental effect on hydrogen cracking susceptibility. These results are explained by a model which proposes that
hydrogen cracking occurs when a critical oxide inclusion density promotes intergranular fracture at prior austenite grain
boundaries and when a critical level of hydrogen is present in the weld metal. For the same level of hydrogen (moisture) contamination,
high-strength weld metals containing oxygen contents greater than 200 ppm will be much more susceptible to hydrogen cracking
than deposits made using inert gas-shielded or vacuum-operated welding processes.
Formerly Visiting Scientist, Department of Metallurgy and Materials Science, University of Toronto 相似文献
18.
The effect of oxygen content on the susceptibility of high-strength weld metal to hydrogen cracking is examined. Increasing
oxygen content had a detrimental effect on the cracking susceptibility of weld metal containing a dψusible hydrogen content
of 4.7 ppm. In weld metal containing a much lower dψusible hydrogen content (0.87 ppm), increasing weld metal oxygen content
had no detrimental effect on hydrogen cracking susceptibility. These results are explained by a model which proposes that
hydrogen cracking occurs when a critical oxide inclusion density promotes intergranular fracture at prior austenite grain
boundaries and when a critical level of hydrogen is present in the weld metal. For the same level of hydrogen (moisture) contamination,
high-strength weld metals containing oxygen contents greater than 200 ppm will be much more susceptible to hydrogen cracking
than deposits made using inert gas-shielded or vacuum-operated welding processes.
Formerly Visiting Scientist, Department of Metallurgy and Materials Science, University of Toronto 相似文献
19.
Nonequilibrium segregations of substitutional solute and impurity elements to austenite grain boundaries during cooling from the austenitizing temperature have been measured in thin foil specimens of ferritic 2.25 pct Cr 1 pct Mo, 2.25 pct Cr 1 pct Mo 0.08 pct Sn and austenitic Type 316 steels using scanning transmission electron microscopy combined with energy dispersive X-ray spectrometry (STEM-EDS). The results are discussed and compared with the predictions of a theoretical analysis which describes the segregation in terms of a quench-induced diffusion of vacancy-solute atom pairs to the grain boundaries. 相似文献
20.
Nonequilibrium segregations of substitutional solute and impurity elements to austenite grain boundaries during cooling from
the austenitizing temperature have been measured in thin foil specimens of ferritic 2.25 pct Cr 1 pct Mo, 2.25 pct Cr 1 pct
Mo 0.08 pct Sn and austenitic Type 316 steels using scanning transmission electron microscopy combined with energy dispersive
X-ray spectrometry (STEM-EDS). The results are discussed and compared with the predictions of a theoretical analysis which
describes the segregation in terms of a quench-induced diffusion of vacancy-solute atom pairs to the grain boundaries. 相似文献