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1.
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
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Basic mechanical properties for four kinds of low carbon and low alloy steels, including S355, S275, Q345D, Q345E, were examined by means of tension toughness and plane strain fracture toughness tests at room temperature to -100 °C Test results of yield strength, tensile strengh, tension toughness, fracture toughness and ductile-brittle transition temperature for each steel were obtained for the sake of identifying the relationship between tension toughness and fracture toughness. More than 200 groups of samples were tested and analysed. It shows that there is a linear relationship between tension toughness Uk and fracture toughness J0.2BL for each steel at a tempearture which is greater than its own ductile-brittle transition temperature respectively. And this sastis-fied the requirement of the linear equation. 相似文献
5.
The fracture behaviors of low alloy steels with similar grain sizes but different sizes of carbide particles were investigated
using precracked and notched specimens. The results indicate that in precracked specimens (COD), steel with coarser carbide
particles has a lower toughness than steel with finer carbide particles over a temperature range from –196 °C to – 90 °C.
However, in notched specimens (four-point bending (4PB) and Charpy V), these two steels shows similar toughness at low temperature
where specimens are fractured by cleavage without fibrous cracking. In the transition temperature range, the steel with coarser
carbide particles conversely shows a little higher toughness due to the longer extension length of the fibrous crack. This
phenomenon indicates that in precracked specimens, the second-phase particles play a leading role in cleavage fracture, while
in notched specimens, the grain size dominates the fracture behavior. 相似文献
6.
The effect of quenching temperatures on microstructure and fracture toughness of high carbon steel was investigated. Plane strain fracture toughness was tested with compact tension specimen. Microstructure and fracture morphology of KIC samples after quenching and tempering treatment were examined by scanning electron microscope (SEM).The results show that the residual carbides of steel in hardened state decreasea with the quenching temperature increasing and totally disappear after quenched at 920??;the grain size grows up obviously when the quenching temperature is more than 960??. The microstructure in high temperature tempered state is composed of residual carbides, precipitated carbides and ferrite matrix;plasticity decreases monotonically; the fracture toughness gradually decreases in the range from 800?? to 960??,and then almost invariant; the fracture type of KIC specimens is gradually changed from cleavage fracture to intergranular fracture. The main reason for the changes of fracture toughness has close relationship with the plasticity. 相似文献
7.
The fracture behavior of an Fe-12 Ni-0.25 Ti alloy, grain refined through thermal cycling was studied down to liquid helium
temperature using a simple method of cryogenic fracture toughness testing. Comparison tests were also made with two other
common cryogenic alloys. Ultrafine grained Fe-12 Ni-0.25 Ti alloy, which is 100 pct ferritic, behaved in a ductile manner
similar to 304 austenitic steel. It was shown that the ductile-brittle transition temperature of the ferritic steel specimen
can be suppressed below liquid helium temperature by grain refinement even in the presence of a sharp crack. Yield strength
of 149 ksi with fracture toughness of 307 ksi√in. at liquid nitrogen temperature, and yield strength of 195 ksi with fracture
toughness of 232 ksi√in. at liquid helium temperature were obtained. 相似文献
8.
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
9.
The addition of 0.06 monolayers of antimony to the grain boundaries of iron with 0.3 monolayers of sulfur was found to have
no effect on the fracture toughness or subcritical crack growth behavior at cathodic potentials. Tests were conducted using
compact tension type samples tested in 1N H2SO4 at cathodic potentials of −0.6V (SCE) to −1.25V (SCE). The absence of any effect of antimony on the fracture toughness was
related to iron being in a “minimum” fracture toughness condition such that further segregation of an embrittling element
had no effect. Also, the subcritical intergranular crack growth threshold was found to decrease with increasing cathodic potential
consistent with results reported by others for transgranular fracture of steels in gaseous hydrogen. 相似文献
10.
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
11.
Correlation of rolling condition,microstructure, and low-temperature toughness of X70 pipeline steels 总被引:2,自引:0,他引:2
Byoungchul Hwang Young Min Kim Sunghak Lee Nack J. Kim Jang Yong Yoo 《Metallurgical and Materials Transactions A》2005,36(7):1793-1805
Correlation of rolling conditions, microstructure, and low-temperature toughness of high-toughness X70 pipeline steels was
investigated in this study. Twelve kinds of steel specimens were fabricated by vacuum-induction melting and hot rolling, and
their microstructures were varied by rolling conditions. Charpy V-notch (CVN) impact test and drop-weight tear test (DWTT)
were conducted on the rolled steel specimens in order to analyze low-temperature fracture properties. Charpy impact test results
indicated that the energy transition temperature (ETT) was below −100 °C when the finish cooling temperature range was 350
°C to 500 °C, showing excellent low-temperature toughness. The ETT increased because of the formation of bainitic ferrite
and martensite at low finish cooling temperatures and because of the increase in effective grain size due to the formation
of coarse ferrites at high finish cooling temperatures. Most of the specimens also showed excellent DWTT properties as the
percent shear area well exceeded 85 pct, irrespective of finish rolling temperatures or finish cooling temperatures, although
a large amount of inverse fracture occurred at some finish cooling temperatures. 相似文献
12.
S. Sivaprasad S. Tarafder V. R. Ranganath S. K. Das K. K. Ray 《Metallurgical and Materials Transactions A》2002,33(12):3731-3740
The effects of prestrain on the ductile fracture behavior of two varieties of Cu-strengthened high-strength low-alloy (HSLA)
steels have been investigated through stretch-zone geometry measurements. It is noted that the ductile fracture-initiation
toughness of both the steels remained unaltered up to prestrains of ∼2 pct, beyond which the toughness decreased sharply.
A methodology for estimating the stretch-zone dimensions is proposed. Fracture-toughness estimations through stretch-zone
width (SZW) and stretch-zone depth (SZD) measurements revealed that the nature of the variation of ductile fracture toughness
with prestrain can be better predicted through SZD rather than the SZW measurements. However, for the specimen geometries
and prestrain levels that were investigated, none of these methods were found suitable for quantifying the initiation fracture
toughness. 相似文献
13.
The effects of heat treatment and of the presence of primary carbides on the fracture toughness,K Ic and the fatigue crack growth rates,da/dN, have been studied in M-2 and Matrix II high speed steels. The Matrix II steel, which is the matrix of M-42 high speed steel, contained many fewer primary carbides than M-2, but both steels were heat treated to produce similar hardness values at the secondary hardening peaks. The variation of yield stress with tempering temperature in both steels was similar, but the fracture toughness was slightly higher for M-2 than for Matrix II at the secondary hardening peaks. The presence of primary carbides did not have an important influence on the values ofK Ic of these hard steels. Fatigue crack growth rates as a function of alternating stress intensity, ΔK, showed typical sigmoidal behavior and followed the power law in the middle-growth rate region. The crack growth rates in the near threshold region were sensitive to the yield strength and the grain sizes of the steels, but insensitive to the sizes and distribution of undissolved carbides. The crack growth rates in the power law regime were shifted to lower values for the steels with higher fracture toughness. SEM observations of the fracture and fatigue crack surfaces suggest that fracture initiates by cleavage in the vicinity of a carbide, but propagates by more ductile modes through the matrix and around the carbides. The sizes and distribution of primary carbides may thus be important in the initiation of fracture, but the fracture toughness and the fatigue crack propagation rates appear to depend on the strength and ductility of the martensite-austenite matrix. 相似文献
14.
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
15.
R. O. Ritchie W. L. Server R. A. Wullaert 《Metallurgical and Materials Transactions A》1979,10(10):1557-1570
Critical fracture stress and stress modified fracture strain models are utilized to describe the variation of lower and upper
shelf fracture toughness with temperature and strain rate for two alloy steels used in the manufacture of nuclear pressure
vessels, namely SA533B-1 (HSST Plate 02) and SA302B (Surveillance correlation heat). Both steels have been well characterized
with regard to static and dynamic fracture toughness over a wide range of temperatures (−190 to 200°C), although validJ
Ic
measurements at upper shelf temperatures are still somewhat scarce. The present work utilizes simple models for the relevant
fracture micromechanisms and local failure criteria to predict these variations in toughness from uniaxial tensile properties.
Procedures are discussed for modelling the influence of neutron fluence on toughness in irradiated steel, and predictions
are derived for the effect of increasing fluence on the variation of lower shelf fracture toughness with temperature in SA533B-1.
An erratum to this article is available at . 相似文献
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R. D. K. Misra K. K. Tenneti G. C. Weatherly G. Tither 《Metallurgical and Materials Transactions A》2003,34(10):2341-2351
The relationship between microstructure and formability (also toughness) of industrially processed Cb-Ti and V-Cb steels with
similar yield strength of about 600 MPa and total elongation of 20 pct was examined. The steels were processed under similar
conditions and any variations in processing history were unintentional. Cb-Ti steels exhibited superior formability and toughness
in relation to V-Cb steels. The improved formability and toughness of Cb-Ti steels is attributed to the cumulative contribution
of relatively finer grain size, narrow ferrite grain size distribution, inherently more ductile behavior and microplasticity,
the reduced intensity of {100}〈011〉 texture, and slightly higher intensity of the desired {332}〈113〉 texture. 相似文献
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An investigation has been made to improve the low temperature mechanical properties of Fe-8Mn and Fe-12Mn-0.2 Ti alloy steels.
A reversion annealing heat treatment in the two-phase (α+ γ) region following cold working has been identified as an effective treatment. In an Fe-12Mn-0.2Ti alloy a promising combination
of low temperature (-196°C) fracture toughness and yield strength was obtained by this method. The improvement of properties
was attributed to the refinement of grain size and to the introduction of a uniform distribution of retained austenite (γ).
It was also shown that an Fe-8Mn steel could be grain-refined by a purely thermal treatment because of its dislocated α martensitic
structure and absence of ε martensite. As a result, a significant reduction of ductile to brittle transition temperature was
obtained.
formerly with the Lawrence Berkeley Laboratory, University of California. 相似文献