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1.
Lakshmiprasad Maddi D. Barbadikar M. Sahare A. R. Ballal D. R. Peshwe R. K. Paretkar K. Laha M. D. Mathew 《Transactions of the Indian Institute of Metals》2015,68(2):259-266
P92 steel (9Cr–0.5Mo–1.8W) was subjected to a heat treatment of 1050 °C/30 min/air cooling/780 °C/120 min/air cooling followed by 1080 °C/30 min/air cooling/740 °C/60 min/air cooling to obtain tempered martensite microstructure, for better creep strength. Stress rupture tests carried at 600 °C in the range of 250–350 MPa resulted in rupture times in the range of 200–3000 h. Straight line plot of stress rupture curve indicated no major change in deformation mechanism. Coarsening of precipitates and substructure development were the main reasons for microstructure degradation, consequently leading to reduced hardness of the sample. Gauge and grip portions of the same sample were sectioned to comparatively evaluate the effects of stress and aging. Gauge portion of 3000 h sample showed considerable change in the microstructure in terms of boundary migration, while that of grip portion hardly evolved. The ruptured samples exhibited predominantly ductile fracture with elongated cavities at higher rupture times. 相似文献
2.
R. Viswanathan 《Metallurgical and Materials Transactions A》1975,6(6):1135-1141
A program to study the effect of Sb, P, Sn and B on creep properties of four normalized and tempered 1.25 Cr−0.5 Mo steels
at 538°C (1000°F) has been completed. Results show that even a combined addition of large amounts of Sb, P and Sn does not
affect short time creep strength or ductility of the steel at 538°C (1000°F). Addition of B resulted in an increase or decrease
of creep strength depending on the nature of the impurity species present, presumably due to B-impurity interactions. Regardless
of the effect on creep strength, B additions caused sharp reductions in rupture ductility in all cases. Comparison of the
present results on the four laboratory steels (100 pct bainite) with results of a previous study on a commercial steel (60
pct bainite + 40 pct ferrite) show that the effect of microstructure becomes negligible and rupture strength values of the
various steels at 538°C (1000°F) approach each other at rupture times in excess of 104 h. 相似文献
3.
R. Viswanathan 《Metallurgical and Materials Transactions A》1975,6(7):1135-1141
A program to study the effect of Sb, P, Sn and B on creep properties of four normalized and tempered 1.25 Cr-0.5 Mo steels
at 538°C (1000°F) has been completed. Results show that even a combined addition of large amounts of Sb, P and Sn does not
affect short time creep strength or ductility of the steel at 538°C (1000°F). Addition of B resulted in an increase or decrease
of creep strength depending on the nature of the impurity species present, presumably due to B-impurity interactions. Regardless
of the effect on creep strength, B additions caused sharp reductions in rupture ductility in all cases. Comparison of the
present results on the four laboratory steels (100 pct bainite) with results of a previous study on a commercial steel (60
pct bainite + 40 pct ferrite) show that the effect of microstructure becomes negligible and rupture strength values of the
various steels at 538°C (1000°F) approach each other at rupture times in excess of 104 h. 相似文献
4.
R. L. Mehan E. C. Duderstadt E. H. Sayell 《Metallurgical and Materials Transactions A》1975,6(4):885-889
The creep-rupture properties of annealed arc-cast iridium were determined between 982°C and 1288°C for times less than 1000 h. It was found possible to fit the rupture and creep results by the Sherby-Dorn parameter method using an activation energy of 70,600 calJmole. It was found that under creep deformation, failure was at least partially intercrystalline, and the failure elongation decreased with increasing temperature and time. 相似文献
5.
R. L. Mehan E. C. Duderstadt E. H. Sayell 《Metallurgical and Materials Transactions A》1975,6(3):885-889
The creep-rupture properties of annealed arc-cast iridium were determined between 982°C and 1288°C for times less than 1000
h. It was found possible to fit the rupture and creep results by the Sherby-Dorn parameter method using an activation energy
of 70,600 calJmole. It was found that under creep deformation, failure was at least partially intercrystalline, and the failure
elongation decreased with increasing temperature and time. 相似文献
6.
In this study two different heat treatments were conducted on an X 37 Cr Mo V 5‐1 hot‐work tool steel, resulting either in a tempered fully martensitic matrix or a matrix almost consisting of tempered bainite. Short‐term creep tests were performed at a high stress level of 800 MPa and at temperatures in the range from 450 °C to 500 °C. Creep specimens consisting of a tempered fully martensitic microstructure exhibited a three times longer creep‐to‐rupture time, than those consisting of a tempered almost bainitic microstructure. Microstructural investigations of creep specimens were performed by transmission electron microscopy. Results of these investigations revealed that due to a lower cooling rate, which is necessary to form bainite, the tempered bainitic microstructure consists of large former bainitic plates, whereas tempered martensite shows fine former martensitic laths. Tempered bainite also exhibits a higher number density of large M3C, M7C3 and MC carbides than tempered martensite. Small M2C carbides appear in both microstructures in the same quantity, however, nanometer‐sized MC carbides could only be found in tempered martensite. Thus poor short‐term creep behavior of the tempered almost bainitic microstructure can be explained by the lesser amount of strengthening relevant precipitates, a smaller size‐effect due to distance of bainitic interfaces as well as lower solid solution hardening. 相似文献
7.
I. Holzer E. Kozeschnik H. Cerjak 《Transactions of the Indian Institute of Metals》2010,63(2-3):137-143
Modern advanced 9–12 % Cr steels are complex alloys with excellent creep strength even at high temperatures up to 620°C. The mechanical properties of these steels are significantly influenced by the presence and stability of various precipitate populations. Numerous secondary phases grow, coarsen and, sometimes, dissolve again during heat treatment and service, which leads to a varying obstacle effect of these precipitates on dislocation movement. In this work, the experimentally observed creep rupture strength of an modified 9–12% Cr steel developed in the European COST Group is compared to the calculated maximal obstacle effect (Orowan stress) caused by the precipitates present in these steels for different heat treatment conditions. It is shown that the differences in creep rupture strength caused by different heat treatments disappear after long time service. This observation is discussed on the basis of the calculated evolution of the precipitate microstructure. The concept of boosting long-term creep rupture strength by maximizing the initial creep strength with optimum quality heat treatment parameters for precipitation strengthening is critically assessed. 相似文献
8.
Metallographic studies have been conducted on a 0.024 pct C-16 pct Cr-1.5 pct Mo-5 pct Ni stainless steel to study the phase reactions associated with heat treatments and investigate the strengthening mechanisms of the steel. In the normalized condition, air cooled from 1010 °C, the microstructure consists of 20 pct ferrite and 80 pct martensite. Tempering in a temperature range between 500 and 600 °C results in a gradual transformation of martensite to a fine mixture of ferrite and austenite. At higher tempering temperatures, between 600 and 800 °C, progressively larger quantities of austenite form and are converted during cooling to proportionally increasing amounts of fresh martensite. The amount of retained austenite in the microstructure is reduced to zero at 800 °C, and the microstructure contains 65 pct re-formed martensite and 35 pct total ferrite. Chromium rich M23C6 carbides precipitate in the single tempered microstructures. The principal strengthening is produced by the presence of martensite in the microstructure. Additional strengthening is provided by a second tempering treatment at 400 °C due to the precipitation of ultrafine (Cr, Mo) (C,N) particles in the ferrite. 相似文献
9.
A new Ti-Al-Nb alloy with a composition of Ti-27.5Al-13Nb (at. pct) was proposed. The density of this alloy was 4.7 g/cm3, which is about 13 pct lower than that for O+B2 alloys. After hot processing, the alloy was heat treated under two conditions: directly aged at 850 °C (DA treatment), or cooled from above the β-transus temperature with a cooling rate of 3 °C/min and then aged at 850 °C (BCA treatment). Under the present heat-treatment conditions, the phase constitution was primarily O+α 2. A very fine Widmanstätten microstructure was obtained after the DA treatment, while a microstructure with coarse O plates was obtained after the BCA treatment. The tensile properties were investigated at 20 °C to 950 °C, and the creep behavior was investigated at 650 °C to 750 °C/90 to 380 MPa. The elongation to fracture at room temperature for the DA-treated tensile specimen was as high as 2.6 pct, despite the high Al content in this alloy. In comparison with the O+B2 ternary alloys, this alloy showed higher specific proof stress at temperatures over 800 °C and higher creep strength. The stress exponent and the apparent activation energy for creep were calculated. The fracture mechanism was discussed. 相似文献
10.
Steel samples with size of 10 mm×10 mm×5 mm were cut down from a hot-rolled Mn-steel microalloyed by Ti, Cr and Nb and produced by compact strip production (CSP) technology. The samples were annealed at 950 °C for different time firstly, and then hot rolled or cooled in the air, in water and in furnace, respectively. Auger electron spectroscopy (AES) was used to study the effects of annealing and hot rolling on the segregation of arsenic at grain boundary (GB) in the steel. The results indicated that a higher content of arsenic was found at grain boundaries than in the matrix when the steel was annealed at 950 °C for 2 h and then cooled to room temperature by water quenching. But the content of arsenic at grain boundaries was similar to that in the matrix when the steel was annealed at 950 °C for 2 h and then cooled to room temperature by furnace cooling. A longer holding time, such as 12 h and 36 h at 950 °C, resulted in a similar arsenic content at grain boundaries to that in the matrix of the steels. Hot rolling led to a similar content of arsenic at grain boundaries and within grains in the steels as well. 相似文献
11.
The present study examined the influence of chrome-aluminide coatings on the creep and stress rupture properties of a wrought
Udimet-520 nickel-base superalloy used in gas turbine blade applications. Creep and stress rupture tests were conducted at
802 °C (1475 °F) on coated and uncoated wrought bars in the fully heat treated condition. The tests showed that the application
of the chrome-aluminide coatings caused a marked deterioration in rupture strength and ductility. Masking procedures used
to protect the turbine blade roots during coating of the Ni-base superalloy also affected the rupture strength or rupture
ductility. The mechanical behavior in the coated creep resistant alloy was correlated with the microstructure and is discussed
in terms of possible controlling processes. 相似文献
12.
The transverse creep and stress rupture behavior of a number of Borsic®-aluminum composites was investigated at temperatures from 200° to 400°C. The cpmposites studied consisted of nominally 50 vol pct Borsic fiber and included matrices of 6061, 2024, 2219, and 5052 aluminum alloys. The effect of heat treatment was studied in the heat-treatable alloys. Where transverse composite behavior differed from matrix alloy behavior, the difference was found to be due primarily to a change in fracture mode at higher matrix strength levels from matrix failure to one which involves longitudinal fiber splitting. Of the four basic matrix alloys tested, the best creep resistance was obtained with the 2024 matrix. Additional improvement of transverse creep and stress rupture resistance was realized by incorporating transverse reinforcements such as SAP alloy foil, titanium alloy foil, and 0.002 in. stainless steel wire in the composites. These reinforcements made possible good transverse properties at 400°C with density increases of ≤15 pct. The two best additions were 21 pctβ III titanium foil and 6 pct AFC-77 stainless steel wire. A transverse fracture mode incorporating longitudinal fiber splitting was documented and characterized, and its effect on composite behavior determined. The use of nonsplitting fibers such as 5.6 mil B and 5.7 mil Borsic in preventing this fracture mode was investigated. 相似文献
13.
Manuel Carsi Oscar A. Ruano Felix Peñalba Qleg D. Sherby 《Metallurgical and Materials Transactions A》1997,28(9):1913-1920
The elevated temperature mechanical properties of a 1.8 pct C-1.6 pct Al ultrahigh carbon steel (UHCS-1.8C-1.6Al) is described
in the temperature range from 750 °C to 1150 °C and in the strain rate range from 0.2 to 26 s−1. A torsion test apparatus was used which permitted rapid cooling (50 °C per second) immediately after fracture to establish
microstructure-processing-property relations. The strength-strain rate relation of the UHCS-1.8C-1.6Al material correlates
well with a lattice diffusion-controlled dislocation creep process. The present data, together with other high carbon steels
data, predict that austenite containing a high amount of carbon in solution has a high stacking fault energy. The ductility
of the UHCS-1.8C-1.6Al is maximum at 1050 °C. This indicates that successful deep die forging and other mechanical processing
operations at high strain rates should be performed at this temperature. The microstructure of the deformed samples consisted
of a matrix of pearlite with some undissolved spherical carbides when rapidly cooled from 900 °C and 1050 °C and of a thin
network of proeutectoid carbides when cooled from 1150 °C. High hardnesses in the range of Rockwell C 42 to 50 are obtained
for such structures. 相似文献
14.
A study has been carried out on the effects of isothermal heat treatment at 475 and 550‡C and of continuous cooling at different
rates from 850°C on the brittleness (as assessed by the ductile-brittle impact transition temperature) of a vacuum melted
Fe-25 Cr alloy. The ductile-brittle transition temperature was found to be the lowest for the water quenched condition and
highest for the furnace cooled condition and for material aged at 475‡C for long times (~500 h). An increase of brittleness
with decreased cooling rate in the continuously cooled samples is attributed to the formation of more continuous and larger
amounts of chromium nitrides and carbonitrides at the grain boundaries. Very little or no body centered cubic chromium-rich
phase (alpha prime), associated with 475°C embrittlement, was observed. On aging at 550°C, the increased brittleness with
time is also accounted for by the formation of grain boundary nitrides and carbonitrides. Although a similar effect takes
place in the alloy heat treated at 475°C, the precipitation of alpha prime after long aging times enhances the brittleness.
The tendency towards a more brittle condition with aging treatment and slower cooling rate is explained in terms of the Cottrell
theory for brittle fracture. 相似文献
15.
A study has been carried out on the effects of isothermal heat treatment at 475 and 550‡C and of continuous cooling at different
rates from 850°C on the brittleness (as assessed by the ductile-brittle impact transition temperature) of a vacuum melted
Fe-25 Cr alloy. The ductile-brittle transition temperature was found to be the lowest for the water quenched condition and
highest for the furnace cooled condition and for material aged at 475‡C for long times (~500 h). An increase of brittleness
with decreased cooling rate in the continuously cooled samples is attributed to the formation of more continuous and larger
amounts of chromium nitrides and carbonitrides at the grain boundaries. Very little or no body centered cubic chromium-rich
phase (alpha prime), associated with 475°C embrittlement, was observed. On aging at 550°C, the increased brittleness with
time is also accounted for by the formation of grain boundary nitrides and carbonitrides. Although a similar effect takes
place in the alloy heat treated at 475°C, the precipitation of alpha prime after long aging times enhances the brittleness.
The tendency towards a more brittle condition with aging treatment and slower cooling rate is explained in terms of the Cottrell
theory for brittle fracture. 相似文献
16.
Creep Rupture Strength and Microstructure of Low C-10Cr-2Mo Heat-Resisting Steels with V and Nb 总被引:1,自引:0,他引:1
T. Fujita K. Asakura T. Sawada T. Takamatsu Y. Otoguro 《Metallurgical and Materials Transactions A》1981,12(6):1071-1079
The new ferritic heat-resisting steels of 0.05C-10Cr-2Mo-0.10V-0.05Nb (Cb) composition with high creep rupture strength and
good ductility have already been reported. The optimum amounts of V and Nb that can be added to the 0.05C-10Cr-2Mo steels
and their effects on the creep rupture strength and microstructure of the steels have been studied in this experiment. The
optimum amounts of V and Nb are about 0.10 pct V and 0.05 pct Nb at 600 °C for 10,000 h, but shift to 0.18 pct V and 0.05
pct Nb at 650 °C. Nb-bearing steels are preferred to other grades on the short-time side, because NbC precipitation during
initial tempering stages delays recovery of martensite. On the long-time side, however, V-bearing steels have higher creep
rupture strength. By adding V to the steels, electron microscopic examination reveals a stable microstructure, retardation
during creep of the softening of tempered martensite, fine and uniform distribution of precipitates, and promotion of the
precipitation of Fe2Mo. 相似文献
17.
Hyo Kyung Sung Sang Yong Shin Byoungchul Hwang Chang Gil Lee Nack J. Kim Sunghak Lee 《Metallurgical and Materials Transactions A》2011,42(7):1827-1835
Six ultra-low-carbon high-strength bainitic steel plates were fabricated by controlling rolling and cooling conditions, and
effects of bainitic microstructure on tensile and Charpy impact properties were investigated. The microstructural evolution
was more critically affected by start cooling temperature and cooling rate than by finish rolling temperature. Bainitic microstructures
such as granular bainites (GBs) and bainitic ferrites (BFs) were well developed as the start cooling temperature decreased
or the cooling rate increased. When the steels cooled from 973 K or 873 K (700 °C or 600 °C) were compared under the same
cooling rate of 10 K/s (10 °C/s), the steels cooled from 973 K (700 °C) consisted mainly of coarse GBs, while the steels cooled
from 873 K (600 °C) contained a considerable amount of BFs having high strength, thereby resulting in the higher strength
but the lower ductility and upper shelf energy (USE). When the steels cooled from 673 K (400 °C) at a cooling rate of 10 K/s
(10 °C/s) or 0.1 K/s (0.1 °C/s) were compared under the same start cooling temperature of 873 K (600 °C), the fast cooled
specimens were composed mainly of coarse GBs or BFs, while the slowly cooled specimens were composed mainly of acicular ferrites
(AFs). Since AFs had small effective grain size and contained secondary phases finely distributed at grain boundaries, the
slowly cooled specimens had a good combination of strength, ductility, and USE, together with very low energy transition temperature
(ETT). 相似文献
18.
In the initial part the change of microstructure for steel X20 CrMoV 121 is discussed in terms of the distribution of carbide precipitates and its effects on accelerated creep resistance and hardness are presented. In the following, experimental results of microstructure and accelerated creep resistance are presented for the steels X20CrMoV 121 and P91 annealed for up to 8760 hours at 650°C and 750°C before the testing. A similar evolution of the distribution of carbide particles of a size above 102 nm is found for both steels, while the accelerated creep resistance is diminished much stronger for the steel X20CrMoV 121. This difference is due to a greater stability of NbC than that of VC precipitates, both related to the evolution of the chemical composition of complex chromium, molybdenum and iron carbide particles. 相似文献
19.
D. Eylon J. A. Hall C. M. Pierce D. L. Ruckle 《Metallurgical and Materials Transactions A》1976,7(12):1817-1826
To establish correlations between microstructure and mechanical properties for the Till alloy, twelve different combinations
of hot die forging and heat treatment, in the α+β and β phase regions, were investigated. The resulting heat treated forgings
were classified into four distinct categories based on their microstructural appearance. The room temperature tensile, post-creep
tensile, fracture toughness and fatigue crack propagation properties were measured along with creep and low cycle fatigue
at 566°C. The creep, tensile, fatigue crack propagation and fracture toughness properties, grouped in a manner similar to
the microstructural categories. The fracture appearance and behavior of the cracks during propagation in fatigue and in fracture
toughness tests were examined, and correlations with the microstructure discussed. In the case of the fully transformed acicular
microstructure, it was found that the size and the orientation of colonies of similarly aligned α needles are dominant factors
in the crack behavior. 相似文献
20.
Microstructure,creep properties,and rejuvenation of service-exposed alloy 713C turbine blades 总被引:1,自引:0,他引:1
T. M. Maccagno A. K. Koul J. -P. Immarigeon L. Cutler R. Allem G. L’espérance 《Metallurgical and Materials Transactions A》1990,21(12):3115-3125
A study was carried out on the microstructure and creep properties of aero engine first-stage turbine blades made from Alloy
713C nickel-base superalloy. Results are reported for new blades, blades in two service-exposed conditions, and service-exposed
blades subjected to one of three rejuvenation treatments: a recoating heat treatment, a hot isostatic pressing (HIP) + recoating
heat treatment, and a HIP + controlled cooling + recoating heat treatment. The blade microstructure undergoes significant
change during service, and this leads to a loss in creep properties exhibited by specimens machined from the blade airfoils.
Good correlations were observed between the rupture time and the amount of blade airfoil untwist and between the minimum creep
rate and the amount of untwist. The recoating heat treatment and the HIP + controlled cooling + recoating treatment were moderately
successful in restoring the microstructure and creep properties of the service-exposed blades. In comparison, the HIP + recoating
treatment was very successful in rejuvenating creep properties but only for blades having a chemical composition with a lower
propensity to form σ phase. For the blades with an unfavorable composition, σ phase was found to form preferentially near
the grain boundaries during creep testing, and this had a detrimental effect on the creep properties. Nonetheless, the degree
of rejuvenation for these blades was always at least as good as that obtained through the recoating heat treatment alone.
Formerly National Aeronautical Establishment 相似文献