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1.
Effect of quenching,tempering, and cold rolling on creep deformation behavior of a tempered martensitic 9Cr-1W steel 总被引:1,自引:0,他引:1
Fujio Abe 《Metallurgical and Materials Transactions A》2003,34(4):913-925
The effect of quenching, tempering, cold-rolling, and aging treatments, which produce different dislocation substructures
and different carbide distributions, on the creep-deformation behavior is investigated for a tempered martensitic 9Cr-1W steel
at 873 K, mainly. The creep rate vs time curves indicate transient creep, where the creep rate decreases with time, and accelerating creep, where the creep rate
increases with time. The minimum creep rate is closely correlated with the onset time of acceleration creep and is inversely
proportional to the duration of the transient creep region. The onset of acceleration creep shifts to shorter times for the
specimens subjected to the quenching, 20-hour tempering (long-term tempering) at 1023 K, and cold-rolling treatments than
that for the specimen subjected to the standard quenching and tempering (QT) treatment. The onset of acceleration creep is
closely correlated with the migration of lath or subgrain boundaries, causing the coarsening of laths or subgrains. Dislocation
cells produced by cold rolling are free of M23C6 carbides. The migration and recovery of dislocation cells significantly promote the onset of acceleration creep. The preferential
distribution of M23C6 carbides along lath boundaries is effective for the retardation of the onset of acceleration creep for up to longer times
by the stabilization of lath boundaries. In the acceleration creep region, after reaching a minimum creep rate, the logarithm
of the creep rate increases linearly with strain for a wide range of strains. The time to rupture (tr) is inversely proportional to the minimum creep rate
times the acceleration of the creep rate (d ln
/dε) in the acceleration creep region, but is not proportional to only the minimum creep rate, as given by
This equation is derived on the basis of the exponential function of strain in the acceleration creep region. 相似文献
2.
Dejun Li Kenji Shinozaki Hidemasa Harada Kenji Ohishi 《Metallurgical and Materials Transactions A》2005,36(1):107-115
This article is aimed at investigating the difference in precipitation behavior in the fine-grained heat-affected zone (FGHAZ),
coarse-grained heat-affected zone (CGHAZ), and base metal for the welded joint of high Cr ferritic heat-resistant steel (11Cr-0.4Mo-2W-1Cu-V-Nb,
normalized 1323 K×1 h and tempered 1033 K×1 h). Simulated HAZ (SHAZ) specimens were used, whose thermal cycles were controlled
to be the same as those in the actual welded joint with peak temperatures of 1523 and 1173 K to represent CGHAZ and FGHAZ,
respectively. Based on scanning electron microscopy (SEM) observation, it looks that the precipitates in FGHAZ specimens (1173
K) were fewer and larger than those in CGHAZ (1523 K) specimens and base metal specimens. This phenomenon implied that the
growth and coarsening of precipitates in FGHAZ may play a role in the deterioration of creep properties and type IV cracking,
which was observed in previous creep tests. X-ray diffraction analysis for the electrolytic extraction showed that the types
of precipitates are the same for the 1173 K specimens and base metal specimens, including M23C6, MX, Laves phase, and μ phase. Further, the elemental analysis of the extraction showed that the mass percentages of Cr, W, and Mo in the precipitates
to specimen mass were higher in the FGHAZ specimen than those in the base metal specimen, especially during the period between
600 and 2464 hours. Finally, a two-dimensional (2-D) model was proposed to simulate the precipitation behavior of the Laves
phase. 相似文献
3.
4.
采用Gleeble-1500D热模拟试验机研究了9Cr低活化马氏体钢在950~1200℃、应变速率为10-2~10s-1变形条件下的热压缩变形行为,并用金相显微镜观察了相应显微组织的变化.回归分析得出在0.15~0.8真应变量范围内变形激活能和材料常数随真应变量变化的关系式,并得出双曲正弦本构方程;利用数学方法直接从真应力-真应变曲线获得动态再结晶的峰值应力、临界应力、峰值应变和临界应变;回归得出了峰值应力、临界应力、峰值应变、临界应变和动态再结晶晶粒大小与Zener-Hollomon参数的关系式. 相似文献
5.
T. C. Totemeier H. Tian J. A. Simpson 《Metallurgical and Materials Transactions A》2006,37(5):1519-1525
The effect of normalization temperature from 850 °C to 1050 °C on the structure and creep-rupture properties of modified 9Cr-1Mo
steel was studied. Normalization at temperatures below 925 °C resulted in structures containing significant polygonized, recovered
ferrite. The ferrite structures had poor creep-rupture strength: roughly two orders of magnitude increase in minimum creep
rate or decrease in rupture life for 850 °C compared to 1050 °C normalization at test conditions of 600 °C and 145 MPa. Room-temperature
strength and hardness were also reduced. The microstructure after normalization at the standard 1050 °C temperature consisted
of tempered martensite with fine M23C6 carbide along prior austenite and lath boundaries and fine MX carbonitride precipitates within the laths. Normalization at
temperatures between 925 °C and 1000 °C also resulted in reduced creep strength in comparison with 1050 °C normalization,
even though tempered martensite microstructures were formed and little change in room-temperature strength was observed; the
reduction was attributed to subtle differences in the MX precipitates. The effect of reduced normalization temperature was
more pronounced for higher-temperature, lower-stress creep-rupture conditions. 相似文献
6.
R. L. Klueh 《Metallurgical and Materials Transactions A》1978,9(11):1591-1598
The strength of 2 1/4 Cr-1 Mo steel depends on the microstructure, which, in turn, de-pends on the heat treatment. In the
fully annealed and isothermally annealed conditions, the microstructure is primarily proeutectoid ferrite with varying amounts
of bainite and pearlite. The relative amounts of the latter constituents depend on the cooling rates during the anneal. The
creep and rupture properties were determined for steel plates (from a single heat) given three different annealing treatments:
two were fully annealed, but cooled at different rates from the austenitizing temperature, and the third was iso-thermally
annealed. Properties were determined at 454, 510, and 566°C. At 454 and 510°C, the cooling rate had a significant effect on
the creep and rupture properties, with the ma-terial cooled fastest being the strongest. Although at 510°C strengths at short
rupture times differed widely, the properties approached a common value at longer rupture times. The properties differed very
little at 566°C, even for short rupture times. The effect of heat treatment was concluded to be the result of interaction
solid solution hardening, a dislocation-drag process. This process gave rise to nonclassical creep curves (as op-posed to
classical curves with single primary, secondary, and tertiary stages). By examining the creep-curve shape, it was possible
to interpret the heat treatment effects on the creep-rupture properties. 相似文献
7.
Anish Kumar K. Laha T. Jayakumar K. Bhanu Sankaro Rao Baldev Raj 《Metallurgical and Materials Transactions A》2002,33(6):1617-1626
Modified 9Cr-1Mo ferritic steel (T91/P91) has been subjected to a series of heat treatments consisting of soaking for 5 minutes
at the selected temperatures, starting from the α-phase region (1073 K) to the γ + δ-phase region (1623 K), followed by oil quenching. Hardness measurements, microstructural features, and grain-size measurements
by the linear-intercept method have been used for correlating them with the ultrasonic parameters. Ultrasonic velocity and
attenuation measurements, and spectral analysis of the first backwall echo have been used for characterization of the microstructures
obtained by various heat treatments. As the soaking temperature increased above Ac
1, the ultrasonic velocity decreased because of the increase in the volume fraction of martensite in the structure. There were
sharp changes in the ultrasonic velocities corresponding to the two critical temperatures, Ac
1 and Ac
3. Ultrasonic longitudinal- and shear-wave velocities were found to be useful in identifying the Ac
1 and Ac
3 temperatures and for the determination of hardness in the intercritical region. However, ultrasonic attenuation and spectral
analysis of the first backwall echo were found to be useful to characterize the variation in the prior-austenitic grain size
and formation of δ ferrite above the Ac
4 temperature. The scattering coefficients have been experimentally determined for various microstructures and compared with
the theoretically calculated value of the scattering coefficients for iron reported in literature. 相似文献
8.
通过光学显微镜、透射电子显微镜、X射线衍射仪以及显微硬度仪研究Fe-13Cr-5Ni马氏体不锈钢在加热过程中的组织转变行为.结果表明,Fe-13Cr-5Ni钢在10℃·s-1的加热速率下,加热至奥氏体单相区,冷却至室温后具有明显的“组织遗传冶现象.奥氏体以“针状冶形式在马氏体板条界处形核并沿着马氏体板条界长大,与母相间保持Kurdjumov-Sachs (K-S)位向关系.加热至两相区不同温度然后淬火至室温,奥氏体的量随两相区保温温度的升高先增加再减少,650℃时对应室温下残余奥氏体的极大值,并且这一变化趋势与试样显微硬度测试结果所得结论一致. 相似文献
9.
The effects of aluminum content on mechanical properties of a 9Cr-0.5Mo-1.8W steel have been investigated. It was found that
aluminum addition had a beneficial effect on toughness, but significantly reduced the creep resistance of the steel, especially
on the long-term side. Examination of the microstructure and precipitation characteristics revealed that almost all of the
aluminum added existed as AIN-type nitrides after normalizing and tempering. The undissolved AIN in high aluminum steels resulted
in a dramatic refinement of prior austenite grains, which contributed to the improvement of toughness and was also partially
responsible for the decreased creep rupture strength. The formation of AIN suppressed the precipitation of VN-type nitride;
AIN also provided formation sites for Nb(C, N) and M23C6 type, which had an equivalent effect to the coalescence of these precipitates on AIN, resulting in the reduction of precipitate
density and, therefore, decreased creep resistance. 相似文献
10.
The microstructure of 9Cr-2W-0.25V-0.1C (9Cr-2WV), 9Cr-2W-0.25V-0.07Ta-0.1C (9Cr-2WVTa), 7Cr-2W-0.25V-0.07Ta-0.1C (7Cr-2WVTa),
and 5Cr-2W-0.25V-0.07Ta-0.1C (5Cr-2WVTa) steels (all compositions are in wt pct) have been characterized by analytical electron
microscopy (AEM) and atom probe field ion microscopy (APFIM). These alloys have potential applications in fusion reactors
because they exhibit reduced neutron activation in comparison to the conventional Cr-Mo steels. The matrix in all four alloys
was 100 pct martensite. The precipitate type in the steels depended primarily on the chromium level in the alloy. In the two
9Cr steels, the stable phases were blocky M23C6 and small spherical precipitates previously identified as MC. The two lower-chromium steels contained blocky M7C3 and small needle-shaped carbonitrides in addition to M23C6. The AEM and APFIM analyses revealed that, in the steels containing tantalum, the majority of the tantalum was in solid solution.
With the exception of a few of the small spherical precipitates in low-number densities in the 9Cr-2WVTa, none of the other
precipitates contained measurable tantalum. The experimentally observed phases were in agreement with those predicted by phase
equilibria calculations using the ThermoCalc software. However, a similar match between the experimental and predicted values
of the phase compositions did not occur in some instances. Atom probe analyses directly confirmed the crucial role of trace
amounts of nitrogen in the formation of vanadium-rich carbonitrides as predicted by thermodynamic equilibrium calculations. 相似文献
11.
Visit Thaveeprungsriporn Gary S. Was 《Metallurgical and Materials Transactions A》1997,28(10):2101-2112
The objective of this study is to understand and quantify the role of the coincidence-site-lattice boundary (CSLB) population
on creep deformation of Ni-16Cr-9Fe at 360 °C. It is hypothesized that an increase in the CSLB population decreases the annihilation
rate of dislocations in the grain boundary, leading to an increase in the internal stress and a decrease in the effective
stress. The result is a reduction in the creep strain rate. The role of CSLBs in deformation is, thus, to increase the internal
stress by trapping run-in lattice dislocations at the grain boundaries as extrinsic grain boundary dislocations (EGBDs), creating
backstresses on following dislocations rather than annihilating them, as in the case of high-angle boundaries (HABs). The
hypothesis was substantiated by showing (1) that dislocation absorption kinetics differ substantially between a CSLB and an
HAB, and (2) that the CSLB fraction strongly affects the internal stress in the solid. Dislocation absorption kinetics were
measured by comparing EGBD density in transmission electron microscopy (TEM). Results showed that CSLBs contain an EGBD density
which is 3 times higher than HABs at 1.25 pct strain. Internal stress was measured by the stress dip test and was found to
be ≈ 30 MPa higher in the CSLB-enhanced sample. Steady-state creep rates of Ni-16Cr-9Fe in 360 °C argon were also found to
be strongly affected by the grain boundary character distribution. Increasing the CSLB fraction by approximately a factor
of 2 resulted in a decrease in steady-state creep rates by a factor of 8 to 26 in coarse-grain (330 μm) samples and a factor of 40 to 66 in small-grain (35 μm) samples. It is postulated that annihilation of EGBDs only occurs at triple lines where at least two HABs intersect. By
using a geometric relationship to evaluate the probability of EGBDs annihilating at a triple line, the model predicts a non-linear
dependence of the creep rate with CSLB fraction, yielding excellent correlation with measurement. The model provides a physical
basis for measurements which show that increasing the CSLB fraction by only moderate amounts can greatly reduce the steady-state
creep rate in Ni-16Cr-9Fe. 相似文献
12.
Toshihiro Ohtani Hirotsugu Ogi Masahiko Hirao 《Metallurgical and Materials Transactions A》2005,36(2):411-420
We studied the microstructural evolution of 2.25Cr-1Mo steels subjected to tensile creep at 923 K through monitoring of shear-wave
attenuation and velocity, using electromagnetic acoustic resonance (EMAR). Contactless transduction based on the magnetostrictive
mechanism is the key to establishing a monitor for microstructural change in the bulk of the metals with a high sensitivity.
In the short interval, 50 to 60 pct of the creep life, attenuation experiences a peak, being independent of the applied stress.
This novel phenomenon is interpreted in terms of the drastic change in dislocation mobility and rearrangement, which is supported
by transmission electron microscopy (TEM) observations for dislocation structure. At this particular period, the dense dislocation
structure starts to transform to subgrain boundaries, which temporally accompanies long, free dislocation, absorbing much
ultrasonic energy to produce the attenuation peak. The EMAR has the potential to assess the damage advance and to predict
the remaining creep life of metals. 相似文献
13.
V. Karthik K. Laha K. S. Chandravathi P. Parameswaran K. V. Kasiviswanathan Baldev Raj 《Transactions of the Indian Institute of Metals》2010,63(2-3):431-436
The Ball-Indentation (BI) testing based on multiple cycles of loading-unloading using a spherical indenter is a useful technique for evaluating tensile properties from a very small volume of material. In this study, the BI technique has been used in a novel way to evaluate the changes in mechanical properties of Modified (Mod) 9Cr-1Mo caused by creep exposures. Microstructural degradation of varying degrees in Mod 9Cr-1Mo steel is simulated by conventional creep test terminated at various strains. By carrying out BI tests on unstressed head and stressed gage portions of the creep specimens, the changes in the strength and ductility are evaluated. Microstructural evolution in the creep exposed conditions studied using transmission electron microscopy is related to the strength changes caused by the stressed exposures. 相似文献
14.
B. K. Choudhary S. Saroja K. Bhanu Sankara Rao S. L. Mannan 《Metallurgical and Materials Transactions A》1999,30(11):2825-2834
Detailed investigations have been performed to examine the creep-rupture behavior of a 1000-mm diameter and 300-mm-thick tube
plate forging of 9Cr-1Mo ferritic steel in quenched and tempered (Q + T), simulated postweld heat treatment (SPWHT), and thermally
aged (TA) conditions. Creep tests were conducted over a wide stress range (50 to 275 MPa) at 793 and 873 K. The alloy exhibited
well-defined primary, steady-state, and extended tertiary creep stages at all test conditions. At 793 K, no significant difference
in the creep-rupture properties was noted between Q + T, SPWHT, and TA conditions. On the other hand, SPWHT specimens exhibited
lower creep-rupture strength than that of Q + T specimens at 873 K. Applied stress (σ
a
) dependence of rupture life (t
r
) exhibited two-slope behavior. Both the Monkman-Grant (ε
s
.t
r
= C
MG) and modified Monkman-Grant (ε
s
.t
r
/ε
f
= C
MMG) relationships were found to be valid for 9Cr-1Mo steel, where ε
s
is the steady-state creep rate and ε
f
is the strain to failure. The two-slope behavior was also reflected as two constants in the Monkman-Grant relationship (MGR)
and modified Monkman-Grant relationship (MMGR) in the two stress regimes. Further, two creep damage tolerance factors (λ = 1/C
MMG) of 5 and 10 were also observed in the high and low stress regimes, respectively. The alloy exhibited high creep ductility,
which was retained for longer rupture lives at low stresses, and the creep ductility increased with increase in test temperature.
The failure mode remained trangranular under all test conditions. The extensive tertiary creep in the alloy has been attributed
to microstructural degradation associated with precipitates and dislocation substructure. The creep-rupture strength of the
forging was found to be lower than that of thin section bars and tubes. 相似文献
15.
R. Sandhya R. Kannan V. Ganesan M. Valsan K. Bhanu Sankara Rao 《Transactions of the Indian Institute of Metals》2010,63(2-3):553-557
Mod.9Cr-1Mo ferritic-martensitic steel is the material chosen for the steam generator of the Prototype Fast Breeder Reactor being built at Kalpakkam, India. The use of sodium as a heat transfer medium for Liquid Metal Fast Breeder Reactors (LMFBRs) necessitates a comprehensive understanding of the effects of dynamic sodium on the Low Cycle Fatigue (LCF) behaviour of structural components. Moreover welds being the weak links in any structure, it is necessary to evaluate the LCF behaviour of joints in sodium environment, more so in Mod.9Cr-1Mo steel because of the well established Type — IV cracking in this material. With this aim in view, a programme has been initiated to evaluate the LCF properties of weld joints of this steel in dynamic sodium environment. A facility has been developed in-house for mechanical property evaluation in dynamic sodium. LCF tests conducted in flowing sodium environment at 823 and 873 K showed a similar trend in cyclic stress response in air and sodium environments exhibiting a continuous cyclic softening behaviour. The fatigue lives are significantly improved in sodium environment when compared to the data obtained under identical testing conditions in air environment. The lack of oxidation in sodium environment is considered to be responsible for the delayed crack initiation and consequent increase in fatigue life. Comparison with RCC-MR code shows that the design curve based on air tests is conservative. 相似文献
16.
Qiang Li 《Metallurgical and Materials Transactions A》2006,37(1):89-97
Precipitation of Fe2W Laves phase in a 12Cr-2W power plant steel is investigated by using transmission electron microscopy (TEM). Fe2W Laves phase is found to be coherent with the matrix and has a stacking fault structure. The influence of formation of Fe2W Laves phase on the yield strength of the steel is quantitatively evaluated. The modeling result indicates that the strengthening
effect from the formation of Laves phase particles is diminished by the loss of solid solution strengthening of alloying elements,
and, as a result, the strength of the steel remains similar. The effect of clustering and coarsening of Laves precipitates
on the strength of the steel is also studied. It is showed that clustering and coarsening decreases the strengthening effect
of Laves phase. The limitation of the modeling approach currently adopted is also discussed. 相似文献
17.
B. K. Choudhary C. Phaniraj Baldev Raj 《Transactions of the Indian Institute of Metals》2010,63(2-3):675-680
The paper presents the validity of several interesting relationships examined for better understanding of creep behaviour of 9Cr-1Mo ferritic steel. Creep rate-rupture time relationships of Monkman-Grant type have been found to be valid. Like stress dependence of creep rate and rupture life, both Monkman-Grant and modified Monkman-Grant relations (MGR and MMGR) exhibited distinct constant values of C MG and C MMG , respectively for low and high stress regimes. The validity of MGR and MMGR is a consequence of the creep deformation behaviour of 9Cr-1Mo ferritic steel obeying first order kinetics. On the basis of creep rate-rupture time relationships of Monkman-Grant type, several other relationships involving transient and tertiary creep parameters have been evolved and their applicability have been examined for the steel. Analogous to MGR and MMGR, a relationship involving transient creep parameters and the other involving tertiary creep parameters were found to be valid. Further, 9Cr-1Mo steel obeyed a recently introduced critical damage criterion interrelating time to reach Monkman-Grant ductility with rupture life, and the criterion depends only on creep damage tolerance factor. This unique relationship is evolved based on the seminal concept of time to reach Monkman-Grant ductility as the time at which the useful safe creep life is exhausted and damage attains a critical level. The important implications of this concept have been discussed. 相似文献
18.
Fujio ABe 《Metallurgical and Materials Transactions A》2005,36(2):321-332
The effect of fine precipitation and subsequent coarsening of Fe2W Laves phase on the creep deformation behavior was investigated for simple 9Cr-W steels containing 0, 1, 2, and 4 wt pct
W. After tempering, the specimens were subjected to creep tests at 823, 873, and 923 K for up to 15,000 hours. The precipitation
of Fe2W Laves phase takes place during creep at boundaries from the supersaturated solid solution of the high-W steels, the 9Cr-2W
and 9Cr-4W steels, but not in the low-W steels, the 9Cr-0W and 9Cr-1W steels. The fine precipitation of Fe2W Laves phase decreases the creep rate in the primary or transient creep region, while the subsequent large coarsening of
Fe2W Laves phase reduces the precipitation strengthening and promotes the acceleration of creep rate in the tertiary or acceleration
creep region after reaching a minimum creep rate. The change in shape of creep rate curves with stress and temperature is
explained by taking fine precipitation and subsequent coarsening of Fe2W Laves phase into account. 相似文献
19.
Effect of initial microstructure on microstructural instability and creep resistance of XD TiAl alloys 总被引:1,自引:0,他引:1
Hanliang Zhu K. Maruyama D. Y. Seo P. Au 《Metallurgical and Materials Transactions A》2006,37(10):3149-3159
A number of lamellar structures were produced in XD TiAl alloys (Ti-45 at. pct and 47 at. pct Al-2 at. pct Nb-2 at. pct Mn+0.8
vol pct TiB2) by selected heat treatments. During creep deformation, microstructural degradation of the lamellar structure was characterized
by coarsening and spheroidization, resulting in the formation of fine globular structures at the grain boundaries. Grain boundary
sliding (GBS) was thought to occur in local grains with a fine grain size, further accelerating the microstructural degradation
and increasing the creep rate. The initial microstructural features had a great effect on microstructural instability and
creep resistance. Large amounts of equiaxed γ grains hastened dynamic recrystallization, and the presence of fine lamellae
increased the susceptibility to deformation-induced spheroidization. However, the coarsening and spheroidization were suppressed
by stabilization treatments, resulting in better creep resistance than the microstructures without these treatments. Furthermore,
well-interlocked grain boundaries with lamellar incursions were effective in restraining the onset of GBS and microstructural
degradation. In the microstructures with smooth grain boundaries, a fine lamellar spacing significantly lowered the minimum
creep rate but rapidly increased the tertiary creep rate for the 45 XD alloy. For the 47 XD alloy, well-interlocked grain
boundaries dramatically improved the creep resistance of nearly and fully lamellar (FL) structures, in spite of the presence
of coarse lamellar spacing or equiaxed γ grains. However, it may not be feasible to produce a microstructure with both a fine
lamellar spacing and well-interlocked grain boundaries. If that is the case, it is suggested that the latter feature is more
beneficial for creep resistance in XD TiAl alloys with relatively fine grains. 相似文献
20.
《Acta Metallurgica》1988,36(7):1855-1862
A study has been made of the effects of ageing at 550°C on the ductility and fracture mechanisms in a 9 Cr-1 Mo steel. Although the fracture mode remains ductile, ageing at times up to 5000 h causes a progressive reduction in ductility. Voids are nucleated at both coarsely distributed inclusions and at much more finely distributed precipitates, and the principal effect of ageing is to enhance void formation at precipitates. This enhancement is due to a combination of phosphorus segregation to carbide precipitate-matrix interfaces and, after ageing for 5000 h, to the precipitation of Fe2Mo (Laves phase). An important aspect of the observations is that void nucleation at precipitates occurs continuously with increasing strain until failure occurs and the results are consistent with a failure criterion based on the achievement of a critical void spacing. 相似文献