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1.
This research studied the effect of a two-step austempering process on the fracture toughness of ductile iron and compared
it to that of the conventional upper- and lower-ausferrite austempered ductile irons (ADIs). The results showed that such
a two-step austempering heat-treatment process yielded a fracture-toughness value equivalent to that of the upper-ausferrite
ADI, while the hardness was maintained at the level of lower-ausferrite ADI. This provided a unique combination of high toughness
with good hardness (strength) properties for the ADI with a two-step austempering. Optical microscopy, scanning electron microscopy
(SEM), and X-ray diffraction analysis were performed to correlate the properties attained to the microstructural features. 相似文献
2.
B. V. Cockeram 《Metallurgical and Materials Transactions A》2005,36(7):1777-1791
The high-temperature strength and creep resistance of low carbon arc cast (LCAC) unalloyed molybdenum, oxide dispersion strengthened
(ODS) molybdenum, and molybdenum-0.5 pct titanium-0.1 pct zirconium (TZM) molybdenum have attracted interest in these alloys
for various high-temperature structural applications. Fracture toughness testing of wrought plate stock over a temperature
range of −150 °C to 1000 °C using bend, flexure, and compact tension (CT) specimens has shown that consistent fracture toughness
results and transition temperatures are obtained using subsized 0.5T bend and 0.18T disc-CT specimens. Although the fracture
toughness values are not strictly valid in accordance with all ASTM requirements, these values are considered to be a reasonable
measure of fracture toughness. Ductile-to-brittle transition temperature (DBTT) values were determined in the transverse and
longitudinal orientations for LCAC (200 °C and 150 °C, respectively), ODS (<room temperature and −150 °C), and TZM (150 °C
and 100 °C). At test temperatures > DBTT, the fracture toughness values for LCAC ranged from 45 to 175 MPa√m, TZM ranged from
74 to 215 MPa√m, and the values for ODS ranged from 56 to 149 MPa√m. No temperature dependence was resolved within the data
scatter for fracture toughness values between the DBTT and 1000 °C. Thin sheet toughening is shown to be the dominant toughening
mechanism, where crack initiation/propagation along grain boundaries leaves ligaments of sheetlike grains that are pulled
to failure by plastic necking. Specimen-to-specimen variation in the fraction of the microstructure that splits into thin
sheets is proposed to be responsible for the large scatter in toughness values at test temperatures > DBTT. A finer grain
size is shown to result in a higher fraction of thin sheet ligament features at the fracture surface. As a result finer grain
size materials such as ODS molybdenum have a lower DBTT. 相似文献
3.
Cheng-Hsun Hsu Shen-Chih Lee Hwei-Yuan Teng 《Metallurgical and Materials Transactions A》2004,35(2):471-480
This research studied the effects of heat treatment and testing temperature on fracture mechanics behavior of Si-modified
CA-15 martensitic stainless steel (MSS), which is similar to AISI 403 grade stainless steel, which has been widely used in
wall and blanket structures and in the pipe of nuclear power plant reactors, turbine blades, and nozzles. The results indicated
that fracture toughness of low-Si CA-15 MSS is better than that of AISI 403. The specimens of the low-Si CA-15 MSS after austenitization
at 1010 °C and then tempering at 300 °C have higher plane-strain fracture toughness (K
IC
) values for both 25 °C and −150 °C testing temperatures. However, the specimens tested at 150 °C cannot satisfy the plane-strain
fracture toughness criteria. The fatigue crack growth rate is the slowest after austenitization at 1010 °C for 2 hours and
tempering at 400 °C. Observing the crack propagation paths using a metallographic test, it was found that the cracking paths
preferred orientation and branched along ferrite phase, owing to martensite-phase strengthening and grain-boundary-carbide
retarding after 300 °C to 400 °C tempering. Also, transmission electron microscopy (TEM), scanning electron microscopy (SEM),
and X-ray diffraction analysis were performed to correlate the properties attained to the microstructural observation. 相似文献
4.
Dependence of fracture toughness of austempered ductile iron on austempering temperature 总被引:1,自引:0,他引:1
Ductile cast iron samples were austenitized at 927 °C and subsequently austempered for 30 minutes, 1 hour, and 2 hours at
260 °C, 288 °C, 316 °C, 343 °C, 371 °C, and 399 °C. These were subjected to a plane strain fracture toughness test. Fracture
toughness was found to initially increase with austempering temperature, reach a maximum, and then decrease with further rise
in temperature. The results of the fracture toughness study and fractographic examination were correlated with microstructural
features such as bainite morphology, the volume fraction of retained austenite, and its carbon content. It was found that
fracture toughness was maximized when the microstructure consisted of lower bainite with about 30 vol pct retained austenite
containing more than 1.8 wt pct carbon. A theoretical model was developed, which could explain the observed variation in fracture
toughness with austempering temperature in terms of microstructural features such as the width of the ferrite blades and retained
austenite content. A plot of K
IC
2
against σ
y
(X
γ, C
γ)1/2 resulted in a straight line, as predicted by the model. 相似文献
5.
B. V. Cockeram 《Metallurgical and Materials Transactions A》2002,33(12):3685-3707
Oxide dispersion-strengthened (ODS) and molybdenum-0.5 pct titanium-0.1 pct zirconium (TZM) molybdenum have excellent creep
resistance and strength at high temperatures in inert atmospheres. Fracture toughness and tensile testing was performed at
temperatures between − 150 °C and 450 °C to characterize 6.35-mm-thick plate material of ODS and TZM molybdenum. A transition
from low fracture-toughness values (5.8 to 29.6 MPa√m) to values >30 MPa√m is observed for TZM molybdenum in the longitudinal
orientation at 100 °C and in the transverse orientation at 150 °C. These results are consistent with data reported in literature
for molybdenum. A transition to low fracture-toughness values (<30 MPa√m) was not observed for longitudinal ODS molybdenum
at temperatures >−150 °C, while a transition to low fracture-toughness values (12.6 to 25.4 MPa√m) was observed for the transverse
orientation at room temperature. The fine spacing of La-oxide precipitates which are present in ODS molybdenum results in
a transition temperature that is significantly lower than any molybdenum alloy reported to date, with upper-bound fracture-toughness
values that bound the literature data. A comparison of fracture-toughness values obtained using 1T, 0.5T, and 0.25T three-point
bend specimens shows that a 0.5T bend specimen could be used as a subsized geometry. 相似文献
6.
In an attempt to understand the role of retained austenite on the cryogenic toughness of a ferritic Fe-Mn-AI steel, the mechanical
stability of austenite during cold rolling at room temperature and tensile deformation at ambient and liquid nitrogen temperature
was investigated, and the microstructure of strain-induced transformation products was observed by transmission electron microscopy
(TEM). The volume fraction of austenite increased with increasing tempering time and reached 54 pct after 650 °C, 1-hour tempering
and 36 pct after 550 °C, 16-hour tempering. Saturation Charpy impact values at liquid nitrogen temperature were increased
with decreasing tempering temperature, from 105 J after 650 °C tempering to 220 J after 550 °C tempering. The room-temperature
stability of austenite varied significantly according to the(α + γ) region tempering temperature;i.e., in 650 °C tempered specimens, 80 to 90 pct of austenite were transformed to lath martensite, while in 550 °C tempered specimens,
austenite remained untransformed after 50 pct cold reductions. After tensile fracture (35 pct tensile strain) at -196 °C,
no retained austenite was observed in 650 °C tempered specimens, while 16 pct of austenite and 6 pct of e-martensite were
observed in 550 °C tempered specimens. Considering the high volume fractions and high mechanical stability of austenite, the
crack blunting model seems highly applicable for improved cryogenic toughness in 550 °C tempered steel. Other possible toughening
mechanisms were also discussed.
Formerly Graduate Student, Seoul National University. 相似文献
7.
Z. P. Xing Y. F. Han J. T. Guo L. G. Yu 《Metallurgical and Materials Transactions A》1997,28(4):1079-1087
The microstructure, interfaces, and mechanical properties of NiAl-matrix composites reinforced by 0 and 20 vol pct TiC particles
have been examined. The composites were prepared by the hot-pressaided exothermic synthesis (HPES) technique. Portions of
the HPES-processed samples were hot isostatically pressed (“hipped”) at 1165 °C/150 MPa for 4 hours or annealed at 1400 °C
for 48 hours. In the as-fabricated state, TiC particles were generally polygonal and faceted, and the interfaces between TiC
and NiAl were atomically flat, sharp, and generally free from any interfacial phase. At least two orientation relationships
between TiC and NiAl were observed. In some cases, thin amorphous layers existed at NiAl/TiC interfaces. After “Hipping,”
the TiC particles tended to become round and the TiC/NiAl interfaces became overlapped. Annealing at 1400 °C for 48 hours
did not affect the microstructure or the interfacial structure of the composite in most cases. The compressive yield strengths
(YSs) from room temperature to 1100 °C of the composite were considerably higher than that of the monolithic NiAl. At 980
°C, the tensile YS of the composite was approximately 3 times that of the monolithic NiAl. In addition, the ambient fracture
toughness of the composite was 50 pct higher than that of the monolithic NiAl. 相似文献
8.
The tensile properties, fracture toughness and stress corrosion cracking (SCC) behavior of HY-180 M steel at 22 °C were studied
after final 5 h overaging treatments >510 ≤650 °C. SCC tests were conducted for 1000 h with compact tension specimens in aqueous
3.5 pct NaCl solutions at a noble (anodic) potential of −0.28 VSHE ( −0.48 VAg/AgC1) and a cathodic protection potential of −0.80 VSHE (−1.0 VAg/AgC1). The SCC resistance improved at aging temperatures >565 °C, the most significant improvement being at −0.80 VShe, especially after 650 ° aging whereK
ISCC was raised to at least 110 MPa · m1/2. However, this was at the expense of mechanical properties. Provided low crack propagation rates of ∼3 X 10−11 m/s at −0.80V
SHEmay be tolerated, the best compromise between strength, toughness, and SCC resistance was obtained after 594 °C aging. Under
these conditions, stress intensities as high as ∼ 110 MPa · m1/2 can be used, with a yield strength of ∼ 1150 MPa and fracture toughness of ∼ 170 MPa · m1/2. The retained austenite content after aging increased with aging temperature up to 25 pct by vol at 650 °C. It appeared to
correlate with improved SCC resistance, but other microstructural effects associated with aging may be involved.
Formerly Research Associate with theDepartment of Metallurgical Engineering , University of BritishColumbia 相似文献
9.
The effects of microstructure, impurity content, and testing temperature on the fracture toughness (as measured by the crack
tip opening displacement (CTOD)) and microcrack extension resistance curves (R curves) of Ti-6Al-4V alloys were examined. At 0 °C, microstructure is the most influential factor in the toughness-strength
relationship. Acicular microstructure specimens have a higher CTOD than specimens with equiaxed microstructures, regardless
of strength (0.2 pct proof stress) and impurity content. At −196 °C, impurity content becomes a controlling factor in the
toughness-strength relationship. Extra-low impurity (ELI) specimens, which have a lower impurity content, show a higher CTOD,
irrespective of microstructure. Microcracks extended from the notch tip before the maximum load was reached during testing
were investigated, and crack initiation (δ
i) and extension-resistance properties were evaluated by obtaining exact R curves of the microcracks. At 0 °C, specimens with different microstructures and different impurity contents have almost
the same δ
i. But acicular-microstructure specimens with a higher CTOD at a given strength show a greater crack extension resistance.
At −196 °C, ELI specimens, which have a higher CTOD, show a larger crack extension resistance. It is concluded that the crack
extension-resistance property of the microcracks extended from the notch tip before the maximum load is a controlling factor
for the fracture toughness of Ti-6Al-4V alloys. 相似文献
10.
Fracture toughness of the lean duplex stainless steel LDX 2101 总被引:1,自引:0,他引:1
Henrik Sieurin Rolf Sandström Elin M. Westin 《Metallurgical and Materials Transactions A》2006,37(10):2975-2981
Fracture toughness testing was performed on the recently developed lean duplex stainless steel LDX 2101 (EN 1.4162, UNS S32101).
The results were evaluated by master curve analysis, including deriving a reference temperature. The master curve approach,
originally developed for ferritic steels, has been used successfully. The reference temperature corresponds to a fracture
toughness of 100 MPa√m, which characterizes the onset of cleavage cracking at elastic or elastic-plastic instabilities. The
reference temperature, T
0, was −112 °C and −92 °C for the base and weld materials, respectively. In addition, the fracture toughness is compared with
impact toughness results. Complementary crack tip opening displacements (CTODs) have also been calculated. The toughness properties
found in traditional duplex stainless steels (DSS) are generally good. The current study verifies a high fracture toughness
for both base and weld materials and for the low alloyed grade LDX 2101. Even though the fracture toughness was somewhat lower
than for duplex stainless steel 2205, it is still sufficiently high for most low-temperature applications. 相似文献
11.
Superplastic behavior and microstructure evolution in a commercial Al-Mg-Sc alloy subjected to intense plastic straining 总被引:1,自引:0,他引:1
F. Musin R. Kaibyshev Y. Motohashi G. Itoh 《Metallurgical and Materials Transactions A》2004,35(8):2383-2392
A commercial Al-6 pct Mg-0.3 pct Sc-0.3 pct Mn alloy subjected to equal-channel angular extrusion (ECAE) at 325 °C to a total
strain of about 16 resulted in an average grain size of about 1 μm. Superplastic properties and microstructural evolution
of the alloy were studied in tension at strain rates ranging from 1.4 × 10−5 to 1.4 s−1 in the temperature interval 250 °C to 500 °C. It was shown that this alloy exhibited superior superplastic properties in
the wide temperature range 250 °C to 500 °C at strain rates higher than 10−2 s−1. The highest elongation to failure of 2000 pct was attained at a temperature of 450 °C and an initial strain rate of 5.6
× 10−2 s−1 with the corresponding strain rate sensitivity coefficient of 0.46. An increase in temperature from 250 °C to 500 °C resulted
in a shift of the optimal strain rate for superplasticity, at which highest ductility appeared, to higher strain rates. Superior
superplastic properties of the commercial Al-Mg-Sc alloy are attributed to high stability of ultrafine grain structure under
static annealing and superplastic deformation at T ≤ 450 °C. Two different fracture mechanisms were revealed. At temperatures higher than 300 °C or strain rates less than 10−1 s−1, failure took place in a brittle manner almost without necking, and cavitation played a major role in the failure. In contrast,
at low temperatures or high strain rates, fracture occurred in a ductile manner by localized necking. The results suggest
that the development of ultrafine-grained structure in the commercial Al-Mg-Sc alloy enables superplastic deformation at high
strain rates and low temperatures, making the process of superplastic forming commercially attractive for the fabrication
of high-volume components. 相似文献
12.
Chongmin Kim A. Richard Johnson William F. Hosford 《Metallurgical and Materials Transactions A》1982,13(9):1595-1605
The influence of microstructural variations on the fracture toughness of two tool steels with compositions 6 pct W-5 pct Mo-4
pct Cr-2 pct V-0.8 pct C (AISI M2 high-speed steel) and 2 pct W-2.75 pct Mo-4.5 pct Cr-1 pct V-0.5 pct C (VASCO-MA) was investigated.
In the as-hardened condition, the M2 steel has a higher fracture toughness than the MA steel, although the latter steel is
softer. In the tempered condition, MA is softer and has a higher fracture toughness than M2. When the hardening temperature
is below 1095 °C (2000 °F), tempering of both steels causes embrittlement,i.e., a reduction of fracture toughness as well as hardness. The fracture toughness of both steels was enhanced by increasing
the grain size. The steel samples with intercept grain size of 5 (average grain diameter of 30 microns) or coarser exhibit
2 to 3 MPa√m (2 to 3 ksi√in.) higher fracture toughness than samples with intercept grain size of 10 (average grain diameter
of 15 microns) or finer. Tempering temperature has no effect on the fracture toughness of M2 and MA steels as long as the
final tempered hardness of the steels is constant. Retained austenite has no influence on the fracture toughness of as-hardened
MA steel, but a high content of retained austenite appears to raise the fracture toughness of as-hardened M2 steel. There
is a temperature of austenitization for each tool steel at which the retained austenite content in the as-quenched samples
is a maximum. The above described results were explained through changes in the microstructure and the fracture modes.
CHONGMIN KIM, formerly with Climax Molybdenum Company of Michigan, Ann Arbor, MI. 相似文献
13.
E. Fleury J. H. Lee S. H. Kim W. T. Kim J. S. Kim D. H. Kim 《Metallurgical and Materials Transactions A》2003,34(13):841-849
This article presents the results of a study on the microstructure and mechanical properties of Al−Si−Cu−Fe specimens produced
by the spark plasma sintering (SPS) technique. The microstructure of the starting powder and bulk specimens was analyzed by
means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The formation
of the icosahedral and decagonal quasi-crystalline phases in the as-gas-atomized powders is described for the first time.
It is then shown that these metastable phases transformed into the 1/1 cubicapproximant phase upon heating at about 600°C.
Second, the effects of SPS process parameters such as the temperature and time have been investigated. Owing to the generation
of a spark discharge neighboring powder particles, dense cylindrical samples were obtained after a short sintering time of
30 minutes at the temperature of 650°C. The highest values of the Vickers microhardness, about 8.9 GPa, were obtained when
the powders were sintered in the temperature range of 600°C to 650°C for a holding time of 30 minutes, while the fracture
toughness was found to be inversely proportional to the sintering temperature. However, at the sintering temperature of 650°C,
the fracture toughness increased from about 1.40 to 1.52 MPa √m as the holding time increased from 10 to 60 minutes. As compared
to cast specimens, the enhanced mechanical properties are explained by the refined microstructure resulting from the low temperature
and short sintering time applied during SPS processing 相似文献
14.
K. A. Taylor 《Metallurgical and Materials Transactions A》1992,23(1):107-119
The segregation and precipitation of boron have been studied in two 0.2C−0.6Mn0.−5Mo steels containing (nominally) 10 and
50 ppm B. After heating to 1260 δC, samples were air-cooled to 870 °C and then held for times between 0 and 5000 seconds.
Additional samples were heated to 1260 °C, air-cooled to 900 °C, reduced in thickness by 50 pct, and then held for various
times at 870 °C, as above. The distributions of boron under these various conditions were investigated qualitatively by an
autoradiographic technique. In both steels, segregation and/or precipitation of boron at austenite grain boundaries was detected
under all conditions examined. Precipitation of iron borocarbide particles occurred along austenite grain boundaries in the
50 ppm B steel during cooling to the holding temperature of 870 °C, while in the 10 ppm B steel, such precipitation occurred
only after long times at 870 °C. Mechanical properties of single-pass-rolled samples were measured after tempering to assess
the effects of borocarbide precipitation on notch toughness. Such precipitation lowered the Charpy upper shelf energy and
increased the transition temperature. 相似文献
15.
H. Choe J. H. Schneibel R. O. Ritchie 《Metallurgical and Materials Transactions A》2003,34(2):225-239
The need for structural materials with high-temperature strength and oxidation resistance coupled with adequate lower-temperature
toughness for potential use at temperatures above ∼1000 °C has remained a persistent challenge in materials science. In this
work, one promising class of intermetallic alloys is examined, namely, boron-containing molybdenum silicides, with compositions
in the range Mo (bal), 12 to 17 at. pct Si, 8.5 at. pct B, processed using both ingot (I/M) and powder (P/M) metallurgy methods.
Specifically, the oxidation (“pesting”), fracture toughness, and fatigue-crack propagation resistance of four such alloys,
which consisted of ∼21 to 38 vol. pct α-Mo phase in an intermetallic matrix of Mo3Si and Mo5SiB2 (T2), were characterized at temperatures between 25 °C and 1300 °C. The boron additions were found to confer improved “pest”
resistance (at 400 °C to 900 °C) as compared to unmodified molybdenum silicides, such as Mo5Si3. Moreover, although the fracture and fatigue properties of the finer-scale P/M alloys were only marginally better than those
of MoSi2, for the I/M processed microstructures with coarse distributions of the α-Mo phase, fracture toughness properties were far superior, rising from values above 7 MPa √m at ambient temperatures to almost
12 MPa √m at 1300 °C. Similarly, the fatigue-crack propagation resistance was significantly better than that of MoSi2, with fatigue threshold values roughly 70 pct of the toughness, i.e., rising from over 5 MPa √m at 25 °C to ∼8 MPa √m at 1300 °C. These results, in particular, that the toughness and cyclic
crack-growth resistance actually increased with increasing temperature, are discussed in terms of the salient mechanisms of
toughening in Mo-Si-B alloys and the specific role of microstructure. 相似文献
16.
The temperature dependence of the critical stress intensity factor and of the fracture energy were measured on six low-carbon
iron alloys, one containing 0.002 wt pct C and five containing 0.02 wt pct C. Either Ni, P, Si, or Si and Mn were added to
four of the five 0.02C irons in quantities typically found in ferritic steels. The fracture tests were conducted at rapid
(but less than impact) speed of 1 ips on fatigue cracked, three-point bend beam specimens. Each alloy was tested over a temperature
range of —195° to 24°C in both furnace-cooled and quench-aged states. Both alloying and heat treatment produced wide differences
in the fracture resistance of these alloys. The quench-aged 0.002C iron and furnace-cooled phosphorus alloy failed by intergranular
separation, whereas the remaining alloys exhibited cleavage fractures. With the exception of 0.002C iron, an alloy in the
quench-aged condition had higher fracture toughness than the same alloy in the furnace-cooled state. The transition temperature,
however, was influenced by heat treatment only in the plain carbon irons. In this case the transition temperature was independent
of carbon content but the furnace-cooled specimen had a lower transition temperature than the quench-aged specimens.
D. C. A. R. COX, formerly Exchange Scientist at the Naval Research Laboratory 相似文献
17.
Structure and properties of a β solution treated,quenched, and aged si-bearing near-α titanium alloy
The microstructure, tensile properties, and fractographic features of a near-α titanium alloy, IMI 829(Ti-6.1 wt pct Al-3.2
wt pct Zr-3.3 wt pct Sn-1 wt pct Nb-05 wt pct Mo-0.32 wt pct Si) have been studied after aging over a temperature range of
550°C to 950°C for 24 hours following solution treatment in the β phase field at 1050°C and water quenching. Transmission
electron microscopy studies revealed that aging at 625°C and above produced discrete silicides at α′ interplatelet boundaries.
However, aging at 900°C and above has also resulted in the precipitation of β phase along the lath boundaries of martensite.
The silicides have been found to have a hexagonal structure withc=0.36 nm anda=0.70 nm (designated as S2 by earlier workers). There is a significant improvement in yield and ultimate tensile strength after aging at 625°C, but
there is less improvement at higher aging temperatures. The tensile ductility is found to be drastically reduced. While the
fracture surface of the unaged specimen shows elongated dimples, the aged samples show a mixed mode of fracture, consisting
of facets, featureless parallel bands, and extremely fine dimples. 相似文献
18.
The present study was undertaken to investigate the effect of solution treatment (in the temperature range 520 °C to 550 °C)
and artificial aging (in the temperature range 140 °C to 180 °C) on the variation in the microstructure, tensile properties,
and fracture mechanisms of Al-10 wt pct Si-0.6 wt pct Mg/SiC/10p composite castings. In the as-cast condition, the SiC particles are observed to act as nucleation sites for the eutectic
Si particles. Increasing the solution temperature results in faster homogenization of the microstructure. Effect of solution
temperature on tensile properties is evident only during the first 4 hours, after which hardly any difference is observed
on increasing the solution temperature from 520 °C to 550 °C. The tensile properties vary significantly with aging time and
temperature, with typical yield strength (YS), ultimate tensile strength (UTS), and percent elongation (EL) values of ∼300
MPa, ∼330 MPa, and ∼1.4 pct in the underaged condition, ∼330 MPa, ∼360 MPa, and ∼0.65 pct in the peakaged condition, and ∼323
MPa, ∼330 MPa, and ∼0.8 pct in the overaged condition. Prolonged solution treatment at 550 °C for 24 hours results in a slight
improvement in the ductility of the aged test bars. The fracture surfaces exhibit a dimple morphology and cleavage of the
SiC particles, the extent of SiC cracking increasing with increasing tensile strength and reaching a maximum in the overaged
condition. Microvoids act as nucleation sites for the formation of secondary cracks that promote severe cracking of the SiC
particles. A detailed discussion of the fracture mechanism is given. 相似文献
19.
Influence of tempering on the microstructure and mechanical properties of HSLA-100 steel plates 总被引:5,自引:0,他引:5
The influence of tempering on the microstructure and mechanical properties of HSLA-100 steel (with C-0.04, Mn-0.87, Cu-1.77,
Cr-0.58, Mo-0.57, Ni-3.54, and Nb-.038 pct) has been studied. The plate samples were tempered from 300 °C to 700 °C for 1
hour after austenitizing and water quenching. The transmission electron microscopy (TEM) studies of the as-quenched steel
revealed a predominantly lath martensite structure along with fine precipitates of Cu and Nb(C, N). A very small amount of
retained austenite could be seen in the lath boundaries in the quenched condition. Profuse precipitation of Cu could be noticed
on tempering at 450 °C, which enhanced the strength of the steel significantly (yield strength (YS)—1168 MPa, and ultimate
tensile strength (UTS)—1219 MPa), though at the cost of its notch toughness, which dropped to 37 and 14 J at 25 °C and −85
°C, respectively. The precipitates became considerably coarsened and elongated on tempering at 650 °C, resulting in a phenomenal
rise in impact toughness (Charpy V-notch (CVN) of 196 and 149 J, respectively, at 25 °C and −85 °C) at the expense of YS and
UTS. The best combination of strength and toughness has been obtained on tempering at 600 °C for 1 hour (YS-1015 MPa and UTS-1068
MPa, with 88 J at −85 °C). 相似文献
20.
Krishna Parameswaran Kenneth Metz Arthur Morris 《Metallurgical and Materials Transactions A》1979,10(12):1929-1939
Isothermal sections for the iron rich corner of the Fe−Cu−C system have been constructed at 1500, 1450, 1200, 1172, 1150,
1000, and 950°C. A ternary invariant point exists at 1172°C where an iron rich liquid, a copper rich liquid, austenite, and
graphite coexist. The iron rich liquid contains 3.7 wt pct Cu and 4.0 wt pct C. The austenite contains 7.3 pct Cu and 1.6
pct C. The copper rich liquid contains 2.4 pct Fe, and apparently very little carbon. The diagrams are used to explain the
phenomena of “inverse segregation” that occurs during the solidification of iron rich Fe−Cu−C alloys.
KRISHNA PARAMESWARAN, formerly Metallurgy Graduate Student, University of Missouri-Rolla
KENNETH METZ, formerly Metallurgy Graduate Student, University of Missouri-Rolla 相似文献