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1.
A statistical mechanical-based high temperature and high pressure equation-of-state for methane has been developed using the
McQuarrie and Katz formulation based on Leonard-Jones (n, 6) intermolecular potential. Fugacity coefficients for methane have
been estimated, and it is shown that for plain carbon steels during hydrogen attack the methane pressures are considerably
lower than the fugacities and fall into a physically meaningful range (≤2500 MPa). Further, simple, but reasonably accurate,
expressions for both the equation-of-state and fugacity coefficient have been developed for the purpose of modeling hydrogen
attack kinetics in ferritic steels. 相似文献
2.
Three high strength low alloy steels with low carbon contents and varying alloy contents were exposed to 21 MPa (3000 psi)
hydrogen pressure in the temperature range 350 to 510°C. The resulting sample expansion rate was measured using a highly sensitive
capacitance dilatometer. In all three HSLA steels, the early expansion rate was found to be independent of exposure time,
but a function of exposure temperature and pressure. The temperature dependence of the sample expansion rate was similar for
all three HSLA and the reference carbon steels, and corresponded roughly to an activation energy (Q) of 190 KJ/mole. The later accelerating expansion rate fitted aQ of 160 KJ/mole. Though the sample expansion rates exhibited the same temperature dependence, they varied by as much as two
orders of magnitude among the three HSLA and the carbon steels. This marked variation in rate was proportional to the estimated
carbon activity in each steel. Comparison between the Nelson curves published by the Americal Petro-leum Institute (API) for
1/2 pct Mo steel and the experimental curves constructed for HSLA steels indicated that these steels should provide comparable
or better resistance to hydrogen attack than the 1/2 pct Mo steel. 相似文献
3.
The hydrogen attack of steel involves the formation of methane bubbles along the grain boundaries and their subsequent link-up
to form fissures. This paper presents a detailed model for the kinetics of growth of such methane bubbles. The model considers
two parallel processes which can control the growth—one involving the bubble growth by direct power-law creep and the other
involving combinations of surface diffusion, grain boundary diffusion and matrix accommodation processes. The proposed model
is more general and complete than the earlier ones and considers for the first time the possibility of bubble growth being
controlled by surface diffusion and accommodation processes. The predictions of the model are shown to compare well with the
experimental results obtained in our lab and with the literature data. The model also indicates the relative importance of
lower carbon activity and increased creep stength of steel to its hydrogen attack resistance. 相似文献
4.
Murray John Stewart 《Metallurgical and Materials Transactions A》1976,7(3):399-406
Superplasticity has been investigated in three carbon-manganese steels with small additions of Nb, V, Al and Ti. Superplasticity was observed from 800 to 1000°C at strain rates from 0.002 to 0.01 min-1. Strain rate sensitivities above 0.7 have been observed; however elongations to fracture are quite low with a maximum value observed of 184 pct. The strain rate sensitivity did not vary with strain although it was very dependent on strain rate and temperature. Cold work prior to hot tensile testing enhanced the superplasticity in the vanadium steel. The premature failure of these steels with large strain rate sensitivities has been attributed to crack nucleation due to the fine particle network from the Nb and V precipitation. 相似文献
5.
Murray John Stewart 《Metallurgical and Materials Transactions A》1976,7(2):399-406
Superplasticity has been investigated in three carbon-manganese steels with small additions of Nb, V, Al and Ti. Superplasticity
was observed from 800 to 1000°C at strain rates from 0.002 to 0.01 min-1. Strain rate sensitivities above 0.7 have been observed; however elongations to fracture are quite low with a maximum value
observed of 184 pct. The strain rate sensitivity did not vary with strain although it was very dependent on strain rate and
temperature. Cold work prior to hot tensile testing enhanced the superplasticity in the vanadium steel. The premature failure
of these steels with large strain rate sensitivities has been attributed to crack nucleation due to the fine particle network
from the Nb and V precipitation. 相似文献
6.
7.
J. Janovec A. Vyrostková M. Svoboda A. Kroupa H. J. Grabke 《Metallurgical and Materials Transactions A》2004,35(3):751-759
The influence of both bulk vanadium content and aging conditions on the evolution of secondary phases in Cr-V low-alloy steels
was studied. Three 0.1C-0.9Cr-V steels with different vanadium contents (0, 0.258, and 0.512 wt pct) were aged for 100 to
5,000 hours at 773, 853, 953, and 993 K. In the investigation, a limited experimental program (transmission electron microscopy
(TEM)) was combined with credible thermodynamic predictions (ThermoCalc). Going out from the good agreement between the predicted
and experimental results, behavior of the iron-rich M7C3 carbide in time-temperature scale was characterized. The influence of bulk vanadium content was determined on appearance
of the M3C carbide in equilibrium, temperature of the M7C3 carbide precipitation, metal compositions of M3C or M7C3 carbides, and vanadium portion in the metallic part of the MX phase. 相似文献
8.
An experimental investigation of the internal methane pressure that is the driving force for bubble growth in hydrogen attack
(HA) was done on pure iron (204 ppm C) and on two low carbon steels of slightly different compositions. The methane contentN (c.c gas/g. material) in attacked specimens was measured by a vacuum extraction technique. The total void volumeV (c.c) was determined from density measurements before and after HA exposure. The two values,N andV, were then used in an equation of state to calculate an average methane pressureP for the attack stages beyond a density loss (d.l.) greater than 0.05 pct. It was determined thatN andP depend on hydrogen exposure conditions and the presence of traces of strong carbide forming alloying elements (in steel).
They are independent of specimen size and grain size over a limited range.P varies as the bubble volume increases, showing a generally decreasing trend which brings it to values lower than calculated
equilibrium pressures, although well within the same order of magnitude. Possible reasons for this behavior are discussed. 相似文献
9.
10.
Hardness of tempered martensite in carbon and low-alloy steels 总被引:3,自引:0,他引:3
R. A. Grange C. R. Hribal L. F. Porter 《Metallurgical and Materials Transactions A》1977,8(11):1775-1785
This paper presents the results of a systematic study of the effect of carbon, manganese, phosphorus, silicon, nickel, chromium,
molybdenum, and vanadium on the hardness of martensite in low to medium carbon steels tempered for one hour at 100°F (56°C)
intervals in the range 400 to 1300°F (204 to 704°C). Results show that the as-quenched hardness depends solely on carbon content.
On tempering, the effect of carbon on hardness decreases markedly with increasing tempering temperature. Studies of carbon-0.5
manganese steels showed that the incremental increase in hardness from 0.5 pct manganese after a given tempering treatment
was independent of carbon content. Based on this result, studies of the effects of the other alloying elements were made using
a 0.2 or 0.3 pct carbon, 0.3 to 0.5 pct manganese steel base composition. The hardness of the resulting tempered martensite
was assumed to be due to a given alloy addition, and when two or more alloying elements were added, their effects were assumed
to be additive.
Each of the seven alloying elements increased the hardness of tempered martensite by varying amounts, the increase being greater
as more of each element was present. Nickel and phosphorus have substantially the same effect at all tempering temperatures.
Manganese has essentially the same hardening effect at any temperature in the range 700 (371°C) to 1300°F; silicon is most
effective at 600°F (316°C), chromium at 800°F (427°C), molybdenum at 1000 to 1100°F (538 to 592°C), and vanadium at 1200°F
(649°C).
Using the data obtained, a procedure is established for calculating the hardness of tempered martensite for carbon and alloy
steel compositions in the range studied and for any combination of tempering time and temperature.
R. A. GRANGE was formerly with U. S. Steel Corporation (retired) 相似文献
11.
12.
A model for the stability of dispersed austenite in low alloy triple-phase steels has been developed. The model was based on the dislocation dissociation model for classical heterogeneous martensitic nucleation by considering stress effects on the nucleation site potency distribution. The driving force for martensitic transformation has been calculated with the aid of computational thermodynamics. The model allows for the effects of chemical composition of austenite, mean austenite particle size, yield strength of the steel and stress state on austenite stability. Chemical enrichment in C and Mn, as well as size refinement of the austenite particles lead to stabilization. On the contrary, the increase in the yield strength of the steel and triaxiality of the stress state lead to destabilization. The model can be used to determine the microstructural characteristics of the austenite dispersion, i.e. chemical composition and size, for optimum transformation plasticity interactions at the particular stress state of interest and can then be useful in the design of low-alloy triple-phase steels. 相似文献
13.
Crack growth in 2.25Cr-lMo steels exposed to 3000 psi hydrogen has been investigated in the temperature range 440 °C to 500
°C, using modified wedge-opening loaded specimens to vary stress intensity. Under conditions of temperature and hydrogen pressure,
where general hydrogen attack does not occur, the crack propagated by the growth and coalescence of a high density of methane
bubbles on grain boundaries, driven by the synergistic influence of internal methane pressure and applied stress. Crack growth
rates were measured in base metal, and the heat-affected zones (HAZs) of welds were tempered to different strength levels.
The crack growth rate increased with material strength. Above a threshold of about Kl = 20 MPa√m (at 480 °C), the crack growth rate increased rapidly with stress intensity, increasing as roughly Kl
6.5. Because of better creep resistance, stronger materials can sustain higher levels of stress intensity to drive crack growth
and nucleate the high density of voids necessary for crack growth. Stress relaxation by creep reduces the stress intensity,
and thus the growth rate, especially in weaker materials. The crack growth rate in the heat-affected zone was found to be
substantially faster than in the base metal of the welds. Analysis indicates that Kl rather than C* is the appropriate crack-tip loading parameter in the specimen used here and in a thick-walled pressure vessel.
The DC potential drop technique met with limited success in this application due to the spatially discontinuous manner of
crack growth and limited crack-tip opening displacement.
Formerly Graduate Student, Materials Science and Engineering Department, The Ohio State University 相似文献
14.
15.
Hugo F. López 《Metallurgical and Materials Transactions A》1987,18(11):1971-1977
The hydrogen attack (HA) kinetics of an electroslag refined (ESR) and a rare earth metal (REM)-treated steel in the Q. and
T. condition were investigated by a highly sensitive dilatometer. Measured activation energies for bubble growth of 108 to
203 kJ/mol and pressure exponents of 0.9 to 1.6 are rationalized in terms of surface or grain boundary self-diffusion of iron
as the rate controlling mechanisms depending on the external hydrogen pressure and temperature. Comparisons of the HA susceptibility
of these steels with published work show that although the HA resistance of the ESR steel is not influenced by the heat treatment,
the REM steel shows a significant decrease in the rate of sample expansion. SEM observations indicate that the improvement
in the HA resistance of the REM steel is related to the presence of a very low density of methane bubbles. 相似文献
16.
Gregory N. Haidemenopoulos 《国际钢铁研究》1996,67(3):93-99
Tr ansformation i nduced p lasticity (TRIP) effects associated with austenite dispersions in low alloy Fe-Mn-Si steels can be enhanced by austenite stabilisation. Austenite which forms during conventional intercritical annealing does not possess the required stability in order to exhibit TRIP effects. In this work, thermodynamic calculations indicated that it is feasible to form austenite by a cementite to austenite conversion which occurs under paraequilibrium conditions, i.e with partition of carbon but with no partition of substitutional alloying elements. In this way the austenite inherits the manganese content of cementite and is chemically stabilised. A treatment consisting of a two-step annealing has been examined. In the first step, soft annealing, an Mn-enriched cementite dispersion in ferrite is formed. In the second step, intercritical annealing, austenite nucleates on the cementite particles, which are consumed to form austenite. It was experimentally determined that this austenite has been enriched in manganese and carbon and, therefore, is stabilised. The conversion reaction is followed by the conventional austenite nucleation at ferrite grain boundaries. This austenite is lean in manganese and is not stable. The net effect of the two-step annealing treatment is a significant austenite stabilisation relative to simple intercritical annealing, indicating a potential for enhanced TRIP effects in this class of steels. 相似文献
17.
Erosion corrosion causes significant problems in various industrial environments through a synergistic effect which results in much greater weight loss than the sum of the weight losses in the individual processes. The erosion-corrosion behavior of three low-alloy steels was investigated in a simulated concrete slurry using the rotation method. The key influencing factors and mechanism of material degradation were analyzed. The experimental results indicate that the weight loss increases with the linear velocity according to a nearly exponential relationship (W = KVn), where n is 1. 40–2. 14. This weight loss is mainly caused by erosion in the alkaline slurry, and steels with higher tensile strengths show higher erosion-corrosion resistance. The formation of many platelets and ring cracks and their removal from the sample surface during erosion corrosion in the slurry are thought to constitute the mechanism responsible for this weight loss. These platelets and ring cracks are formed by solid particles striking the sample surface. Craters are initially produced and subsequently disappear as they grow and come in contact with each other. Fewer craters were observed on the surfaces of samples that exhibited higher weight loss. The surface of the material became work-hardened because of the effect of the particles striking and scratching, and a deformed layer was produced on the surface for steels of lower strengths, leading to deeper and more abundant gouges. 相似文献
18.
S. Sivaprasad S. Tarafder V. R. Ranganath S. K. Das K. K. Ray 《Metallurgical and Materials Transactions A》2002,33(12):3731-3740
The effects of prestrain on the ductile fracture behavior of two varieties of Cu-strengthened high-strength low-alloy (HSLA)
steels have been investigated through stretch-zone geometry measurements. It is noted that the ductile fracture-initiation
toughness of both the steels remained unaltered up to prestrains of ∼2 pct, beyond which the toughness decreased sharply.
A methodology for estimating the stretch-zone dimensions is proposed. Fracture-toughness estimations through stretch-zone
width (SZW) and stretch-zone depth (SZD) measurements revealed that the nature of the variation of ductile fracture toughness
with prestrain can be better predicted through SZD rather than the SZW measurements. However, for the specimen geometries
and prestrain levels that were investigated, none of these methods were found suitable for quantifying the initiation fracture
toughness. 相似文献
19.
利用全谱ICP -AES(CID检测器 )分析技术 ,对试样溶解方法、元素分析谱线、共存元素干扰、背景校正、仪器分析参数 (射频发生器功率、雾化器压力和泵提升量 )等因素进行了研究 ,综合确定了最佳实验条件 ,并采用稀硫酸溶样后 ,经硫磷酸冒烟 ,直接进行试样前处理 ,建立了一种可同时测定低合金钢中Zr和Nb含量的简单、快速和实用的分析方法。结果表明 :本法测定钢中锆和铌含量的分析误差和精密度符合国标GB2 2 3 3 0 -94和GB2 2 3 3 9-94的技术要求 ,其检出限均为0.0 0 0 相似文献
20.
Coarsening kinetics of multicomponent MC-type carbides in high-strength low-alloy steels 总被引:2,自引:0,他引:2
Kaori Miyata Takahiro Kushida Tomohiro Omura Yuichi Komizo 《Metallurgical and Materials Transactions A》2003,34(8):1565-1573
Morphology and coarsening kinetics of MC-type carbide (MC-carbide) precipitating during the tempering process have been investigated
in V- and Nb-bearing Cr-Mo martensitic steels. Detailed transmission electron microscopy (TEM) observations show that the
addition of V and Nb stabilizes the B1-type MC-carbide instead of L’3-type M2C-carbide. The morphology of the MC-carbide is characterized as disk-like with Baker and Nutting orientation relationships
with the matrix. When the specimens are fully solution treated followed by quenching, the MC-carbide precipitates as a multicomponent
system with continuous solid solution of VC, NbC, and MoC. The V-, Nb-, and Mo-partitioning control the lattice parameter
of MC-carbide and consequently affect the coherency between MC-carbide and the matrix. The coherent MC-carbide grows into
an incoherent one with the progress of tempering. The numerical analysis on TEM observations has shown that the coarsening
kinetics of MC-carbide is equated to (time)1/5 criteria, while the coarsening kinetics of the coexisting cementite is equated to (time)1/3 criteria. It is thus suggested that the Ostwald ripening of MC-carbide is controlled by pipe diffusion of V, Nb, and Mo along
dislocations. It has been confirmed that the coarsening rate of the multicomponent MC-carbide is affected by V, Nb, and Mo
content. Applying the thermodynamic solution database, the rate equation for MC-carbide coarsening can be expressed as a function
of V, Nb, and Mo content, and the activation energy for pipe diffusion can be estimated as ΔQ
v: ΔQ
Nb: ΔQ
Mo=1:3.9:0.6. 相似文献