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1.
The effect of carbon level on the tempering behavior at 700°C of 2.25 pct Cr-1 pct Mo steels having typical weld metal compositions
has been investigated using analytical electron microscopy and X-ray diffraction techniques. The morphology, crystallography
and chemistry, of each of the various types of carbides observed, has been established. It has been shown that each carbide
type can be readily identified in terms of the relative heights of the EPMA spectra peaks for iron, chromium, molybdenum,
and silicon. A decrease in the carbon level of the steel increases the rate at which the carbide precipitation reactions proceed,
and also influences the final product. Of the carbides detected, M23C6 and M7C3 were found to be chromium-based, and their compositions were independent of both the carbon level of the steel and the tempering
time. The molybdenum-based carbides, M2C and M6C, however, showed an increase in their molybdenum contents as the tempering time was increased. The rate of this increase
became greater as the carbon content of the steel was lowered. 相似文献
2.
3.
J.N. Mohapatra J. Swaminathan M.K. Ghosh A. Mitra 《Metallurgical and Materials Transactions A》2010,41(4):900-905
Water-quenched modified 9Cr-1Mo steel was creep tested in the laboratory at a temperature of 600 °C and 125 MPa stress. Magnetic
Barkhausen emissions (MBE) measurements were carried out by interrupting the test at different lengths of time. Creep damage
in such steel was observed by an increase in root mean square (RMS) voltage of the MBE. The magnetic softening was corroborated
with the decrease in pinning density in the material for the coarsening of carbides (M23C6) and formation of massive phases (Fe2Mo), which comes at the expense of a large number of finer carbides. Before failure, the rate of increase in RMS voltage of
the MBE decreased due to the demagnetizing field offered by the massive phases. The microstructural analysis was carried out
using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) study. 相似文献
4.
X. J. Wu X. Z. Zhang R. Liu M. X. Yao 《Metallurgical and Materials Transactions A》2020,51(3):1134-1147
In this study, the deformation-mechanism-based true-stress (DMTS) creep model is modified to include oxidation influence on the long-term creep performance of modified 9Cr-1Mo steels. An area-deduction method is introduced to evaluate oxide scale formation on the creep coupons, which is incorporated into the DMTS model formulated based on intragranular dislocation glide (IDG), intragranular dislocation climb (IDC), and grain boundary sliding (GBS) mechanisms, in modifying the true stress. Thus, the modified DMTS model can not only describe the creep curve, but also predict the long-term creep life and failure mode, which is shown to be in good agreement with the creep data generated in the authors’ laboratory as well as by the National Institute for Materials Science (NIMS) of Japan for long-term (> 104 hours) creep life prediction on Grade 91 steels. In particular, the predictability of the model is demonstrated in comparison with the Larson–Miller parameter method. In addition, the modified DMTS model provides quantitative information of mechanism partitioning, insinuating the failure mode via intragranular/intergranular deformation. Therefore, it has advantages over the empirical models in providing physical insights of creep failure, which can be useful to material design for performance optimization. 相似文献
5.
6.
Karthikeyan Rajan Nandani Rai Subramanya Sarma Vadlamani B. S. Murty 《Metallurgical and Materials Transactions A》2014,45(4):1684-1688
Analysis of isothermal grain growth kinetics of nanocrystalline Fe-9Cr-1Mo and Fe-9Cr-1W-based ferritic oxide dispersion strengthened alloys is reported. Fe-9Cr-1Mo-0.25Ti-0.5Y2O3 alloy exhibited ~900 and ~250 pct enhancement in grain-coarsening resistance at 1073 K (800 °C) in comparison with Fe-9Cr-1Mo-0.5Y2O3 alloy and Fe-9Cr-1W-0.5Y2O3 alloy, respectively. Comparison of grain growth time exponents also revealed that addition of Ti and Y2O3 to nanocrystalline Fe-9Cr alloy has significantly enhanced the grain growth resistance. This is attributed to the possible presence of Y-Ti-O-based nanoclusters (<5 nm). 相似文献
7.
The constant embrittlement curve for constant segregation concentration on grain boundary of impurity element P and relationship between equilibrium grain boundary segregation concentration and operation time for 225Cr-1Mo steel were derived based on the theory of equilibrium grain boundary segregation. The mechanism of step-cooling test and mechanism of de-embrittlement for 225Cr-1Mo steel were explained. The segregation rate will increase but equilibrium grain boundary segregation concentration of impurity element P will decrease as temperature increases in the range of temper embrittlement temperature. There is one critical temperature of embrittlement corresponding to each embrittlement degree. When the further heat treating temperature is higher than critical temperature, the heat treating will become a de-embrittlement process; otherwise, it will be an embrittlement process. The critical temperature of embrittlement will shift to the direction of low temperature as further embrittlement. As a result, some stages of step-cooling test would change into a de-embrittlement process. The grain boundary desegregation function of impurity element P was deduced based on the theory of element diffusion, and the theoretical calculation and experimental results show that the further embrittlement or de-embrittlement mechanism can be interpreted qualitatively and quantitatively by combining the theory of equilibrium grain boundary segregation with constant embrittlement curve. 相似文献
8.
T. A. Parthasarathy H. F. Lopez P. G. Shewmon 《Metallurgical and Materials Transactions A》1985,16(6):1143-1149
The kinetics of Hydrogen Attack (HA) of the base metals and the weld metals of two Q&T 2.25 Cr-1 Mo steel weldments made by
different techniques (SMAW and SAW) were studied in the temperature range 460 to 590°C (860 to 1094 °F) and 10 to 23 MPa of
hydrogen. A sensitive dilatometer used to measure the rate of HA showed that the weld metals suffered HA at significantly
higher rates than the base metals. The SMAW weld metal was inferior to the SAW weld metal and swelled nearly an order of magnitude
faster than the base metal. This behavior is due to a significantly higher bubble density, and a resulting higher contribution
of power law creep of the matrix. The SAW behavior was intermediate between those of the base metals and the SMAW. For the
same hydrogen pressure the operating limit of the SMAW weld would be roughly 100°C lower than that of the base metals, and
that of the SAW roughly 50°C lower. 相似文献
9.
Metallographic studies have been conducted on 2.25Cr-lMo steel specimens taken from pressure vessels after long term service
exposures at 500 to 650 °C. The loss of strength in the 2.25Cr-lMo steel after the service exposure consists of two parts:
(1) the strength loss accompanying the change in the carbide morphology as usually occurs during tempering, and (2) a strength
loss which occurs without any noticeable microstructural change. This second part of the strength loss can also be produced
by relatively short term thermal treatment such as step-cooling from the tempering temperature, and is reversible by retempering
followed by air-cooling. This type of strength loss is associated with a reduction of molybdenum content in solid solution
in the ferrite. It is hypothesized that the strength loss and recovery of 2.25Cr-lMo steel are produced by changes in the
solid solution strengthening mainly due to molybdenum, carbon, and possibly nitrogen.
Subsidiary of AMAX Inc. 相似文献
10.
Wendell B. Jones J. A. Van Den Avyle 《Metallurgical and Materials Transactions A》1980,11(8):1275-1286
The substructures of thermally aged, creep deformed and fatigued 2.25 Cr-1 Mo steel have been studied using optical and transmission
electron microscopy. In agreement with earlier work, the substructure of the proeutectoid ferrite was found to be very stable
when exposed to thermal aging or creep deformation. This stability is explained based on the tendency of molybdenum atoms
to form pairs in the ferrite matrix. Nucleation and growth of additional carbide particles during creep testing was not observed.
The results of these creep tests and those of Klueh have been interpreted on the basis of Mo pair stability and the affinity
between molybdenum and carbon. Fatigue tests at 866 K, however, did produce a fine Mou2C precipitate which contributed to secondary cyclic hardening in tests lasting longer than 200 h. The alloy was found to undergo
early cyclic hardening followed by abrupt softening within the first tens of cycles. 相似文献
11.
Dae Whan Kim Gyeong Geun Lee Woo-Seog Ryu 《Transactions of the Indian Institute of Metals》2010,63(2-3):523-527
Low cycle fatigue tests of 9Cr-1Mo steel aged at 600°C for 5000 h and 10000 h were conducted at RT-600°C. Fatigue life was not decreased with aging. Cyclic softening was seen with cycles in both unaged and aged specimens. Aging decreased the amount of softening at RT and 400°C but increased it at 600°C. The precipitate species were not changed with aging upto 5000 h but Laves phase was precipitated after 10000 h aging. Fatigue life of 9Cr-1Mo steel aged to 10000 h is dependent on dislocation slip behavior rather than the amount and coarsening of precipitate. 相似文献
12.
Temper embrittled 2.25 Cr-1 Mo steel was tested by slow bending of notched specimens at various temperatures, and the fracture
mode was examined by SEM fractography. Comparison of the local fracture mode with the load-displacement curves showed that
intergranular fracture occurred most prominently in the region where cracking initiated, but that the fracture mode tended
to change to cleavage as the cracking propagated and accelerated. When the area fraction of intergranular fracture was plotted
as a function of test temperature, a maximum appeared, and the temperature of this maximum tended to increase with specimen
hardness. It is argued that the gap between the cleavage fracture stress (σ
F
CL
) and that of intergranular fracture (σ
F
IG
) was greatest at some particular temperature, allowing a maximum amount of grain boundary fracture. However, the gap (σ
F
CL
-σ
F
IG
) diminished as cracking accelerated, and the fracture mode tended to switch to cleavage. The contrast in behavior between
temper embrittled CrMo and NiCr steels is discussed. 相似文献
13.
Thermodynamic properties of carbides present in 2.25Cr-lMo steel were determined at 985 K by a gas flowing method with fixed
CH4/H2 gas mixtures and by a silica capsule method with reference alloys. The carbon activity range was from 0.06 to 0.5. Total
carbon content, carbide species, and Cr and Mo partitionings between the matrix and carbides were measured as a function of
the carbon activity. Both M6C and M23C6 carbides were present after 1000 to 3000 hours at the test temperature and in the carbon activity range studied. The amount
of M6C was greater in the low carbon activity range, while M23C6 carbide became the major carbide with increasing carbon activity. The M6C carbide contained Mo as a major element and Cr
and Si as minor elements; approximately 13 pct of the metal constituent was (Cr + Si). The stability of M6C carbide in this steel is significantly higher than M6C formed in the Fe-Mo-C system. The M23C6 carbide contained Cr as a major metal component and Mo as a minor. The M23C6 carbide is more stable in an extended range of the carbon activity in 2.25Cr-lMo steel than in the Fe-Cr-C system. The presence
of Si is apparently low in M23C6. Thermodynamic parameters were computed for M6C and M23C6 carbides using a regular solution model of component carbides, FeCx, CrCx, and MoCx. 相似文献
14.
为了研究核电用2.25Cr-1Mo钢的抗蒸汽氧化性能,在500 ℃、0.1 MPa水蒸气条件下,对2.25Cr-1Mo耐热钢进行了600 h的氧化试验,利用分析天平测定样品氧化增重,获得氧化动力学曲线,通过扫描电镜观察分析了氧化膜的形貌和结构,结合X射线衍射和能谱分析对氧化产物进行物相分析。试验结果表明,2.25Cr-1Mo耐热钢的氧化增重曲线符合立方规律;氧化膜为双层结构,氧化膜内层较为致密的主要物相为(Fe,Cr)3O4尖晶石,氧化膜外层疏松多孔主要物相为Fe3O4和少量Fe2O3;腐蚀速率测定结果表明,该材料具有较好的抗蒸汽氧化性能。 相似文献
15.
舞钢炼钢厂现有一台90t超高功率电弧炉、两台LF精炼炉和一台VD炉,工艺流程为UHP→LF→VD→CC(IC),主要生产硅含量≥0.15%系列钢种。为满足市场要求,生产了一批低硅钢种,在生产过程中存在一些问题,即部分炉次在精炼过程中涨[Si]严重,不能保证成品[Si]≤ 相似文献
16.
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
17.
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
18.
C. R. Das S. K. Albert A. K. Bhaduri B. S. Murty 《Metallurgical and Materials Transactions A》2013,44(5):2171-2186
The effect of initial heat treatment on microstructure and mechanical properties of boron-free and boron-containing modified 9Cr-1Mo steel (P91 and P91B, respectively) has been studied under different heat-treatment conditions. The prior austenite grains evolved in P91 steel, having different prior austenite grain sizes, were found to be similar in size after heat treatment in the range of 1073 K to 1448 K (800 °C to 1175 °C) for 5 minutes. The microstructural evolution in P91B steel having different prior austenite grain sizes appeared to be uniform when subjected to different heat-treatment temperatures with the prior austenite grain size being similar to that of initial grain size. Lath martensite was observed in P91B steel after all heat treatments. On the other hand, lath martensite was observed in P91 steel only when subjected to high-temperature heat treatment, whereas subgrain/substructure as well as coarse precipitates were observed after a lower temperature heat treatment. Large differences in the hardness/strength values between different microstructures corresponding to coarse-grained heat-affected zone (CGHAZ) and intercritical HAZ (ICHAZ) of P91 steel weldment were due to the distinct difference in these microstructures. The difference in hardness/strength values between the CGHAZ and ICHAZ was found to be insignificant in P91B steel under similar heat-treatment conditions. 相似文献
19.
本文主要研究了2.25C r-1M o钢正火处理后显微组织和回火过程中碳化物相对钢的强韧性的影响,奥氏体化处理后进行冷却(加速冷却和空冷),得到的显微组织为粒状贝氏体和先共析铁素体。对于2.25C r-1M o厚钢板,显微组织和碳化物相的变化是造成2.25C r-1M o钢强韧性能变化的主要原因。 相似文献
20.
T. Karthikeyan Manmath Kumar Dash S. Saroja M. Vijayalakshmi 《Metallurgical and Materials Transactions A》2013,44(4):1673-1685
The grain boundary character distribution (GBCD) and microstructure in 9Cr-1Mo ferritic/martensitic steel subjected to different heat treatments and thermomechanical treatments (TMTs) have been evaluated using electron backscatter diffraction (EBSD) technique. Microstructures obtained through displacive transformation of high-temperature austenite yielded higher amounts of Σ1-29 coincidence site lattice (CSL) boundaries (from 29 to 38 pct) compared with the ferrite grains obtained by diffusional transformation (~16 pct) or by recrystallization process (~14 pct). Specifically, the low-angle (Σ1), Σ3, Σ11, and Σ25b boundaries were enhanced in the tempered martensite substructure, whereas the prior austenite grain boundaries were largely of random type. Misorientation between the product ferrite variants for ideal orientation relationships during austenite transformation was calculated and compared with CSL misorientation to find its proximity based on Brandon’s criteria. The observed enhancements in Σ1, Σ3, and Σ11 could be interpreted based on Kurdjumov–Sachs (K–S) relation, but Nishiyama–Wassermann (N–W) relation was needed to understand Σ25b formation. The amounts of CSL boundaries in the tempered martensite structure were not significantly influenced by austenite grain size or the kinetics of martensitic transformation. In mixed microstructures of “polygonal ferrite + tempered martensite”, the frequencies of CSL boundaries were found to systematically decrease with increasing amounts of diffusional/recrystallized ferrite. 相似文献