共查询到20条相似文献,搜索用时 31 毫秒
1.
Dynamic deformation behavior of ultrafine-grained low-carbon steels fabricated by equal-channel angular pressing 总被引:1,自引:0,他引:1
Byoungchul Hwang Yang Gon Kim Han Sang Lee Sunghak Lee Byoung Doo Ahn Dong Hyuk Shin Chang Gil Lee 《Metallurgical and Materials Transactions A》2005,36(2):389-397
The dynamic deformation behavior of ultrafine-grained low-carbon steels fabricated by equal-channel angular pressing (ECAP)
was investigated in this study. Dynamic torsional tests, using a torsional Kolsky bar, were conducted on four steel specimens,
two of which were annealed at 480 °C after ECAP, and then the test data were compared in terms of microstructures, tensile
properties, and adiabatic shear-band formation. The equal-channel angular pressed specimen consisted of very fine, equiaxed
grains of 0.2 to 0.3 μm in size, which were slightly coarsened after annealing. The dynamic torsional test results indicated that maximum shear
stress decreased with increasing annealing time, whereas fracture shear strain increased. Some adiabatic shear bands were
observed at the gage center of the dynamically deformed torsional specimen. Their width was smaller in the equal-channel angular
pressed specimen than in the 1-hour-annealed specimen, but they were not found in the 24-hour-annealed specimen. Ultrafine,
equiaxed grains of 0.05 to 0.2 μm in size were formed inside the adiabatic shear band, and their boundaries had characteristics of high-angle grain boundaries.
These phenomena were explained by dynamic recrystallization due to a highly localized plastic strain and temperature rise
during dynamic deformation. 相似文献
2.
Yang Gon Kim Byoungchul Hwang Sunghak Lee Woo Gyeom Kim Dong Hyuk Shin 《Metallurgical and Materials Transactions A》2005,36(11):2947-2955
In the present study, ultrafine-grained microstructures of a conventional 5083 aluminum alloy were fabricated by equal-channel
angular pressing, and their dynamic deformation and fracture behavior were investigated. Dynamic torsional tests were conducted
on four aluminum alloy specimens using a torsional Kolsky bar, and then the test data were analyzed in relation to microstructures,
tensile properties, and adiabatic shear-banding behavior. The equal-channel angular-pressed (ECAP) specimens consisted of
ultrafine grains and contained a considerable amount of second-phase particles, which were refined and distributed homogeneously
in the matrix as the equal-channel angular pressing pass number increased. The dynamic torsional test results indicated that
the maximum shear stress increased, while the fracture shear strain remained constant, with increasing equal-channel angular
pressing pass number. Observation of the deformed area beneath the dynamically fractured surface showed that a number of voids
initiated mainly at second-phase particle/matrix interfaces and that the number of voids increased with increasing pass number.
Adiabatic shear bands of 200 to <300 μm in width were formed in the as-extruded and 1-pass ECAP specimens having coarser particles, whereas they were hardly formed
in the four-pass and eight-pass ECAP specimens having finer particles. The possibility of adiabatic shear-band formation was
explained by concepts of absorbed deformation energy and void initiation. 相似文献
3.
Dong-Geun Lee You Hwan Lee Chong Soo Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2005,36(3):741-748
The effects of the volume fraction of tempered martensite on the tensile and dynamic deformation properties of a Ti-6Al-4V
alloy having a bimodal microstructure were investigated in this study. Five microstructures having various tempered-martensite
volume fractions were obtained by varying heat-treatment conditions. Dynamic torsional tests were conducted on them using
a torsional Kolsky bar. The test data were analyzed in relation to microstructures, tensile properties, and adiabatic shear-band
formation. Under a dynamic loading condition, the maximum shear stress increased with increasing tempered-martensite volume
fraction, whereas the fracture shear strain decreased. Observation of the deformed area after the dynamic torsional test indicated
that a number of voids initiated mainly at α-phase/tempered-martensite interfaces, and that the number of voids increased with increasing martensite volume fraction.
Adiabatic shear bands of 6 to 10 μm in width were formed in the specimens having lower martensite volume fractions, while they were not formed in those having
higher martensite volume fractions. The possibility of adiabatic shear-band formation was explained by concepts of absorbed
deformation energy and void initiation. 相似文献
4.
Analysis and prevention of cracking phenomenon occurring during cold forging of two AISI 1010 steel pulleys 总被引:2,自引:0,他引:2
Dong-Kuk Kim Suk Young Kang Sunghak Lee Kyung Jong Lee 《Metallurgical and Materials Transactions A》1999,30(1):81-92
This study is concerned with the effects of microstructural parameters on the cracking phenomenon occurring during cold forging
of two AISI 1010 steels that were fabricated by converter steel making and electric furnace steel making, respectively. This
allowed a comparison between microstructures that contained a small or large amount of nitrogen. Detailed microstructural
analyses of the cracked region showed that a number of adiabatic shear bands, along which cracks initiated and propagated,
were formed in the top interior part of the cold-forged pulley. Dynamic torsional tests were conducted using a torsional Kolsky
bar in order to investigate the dynamic deformation behavior during cold forging, and then the test data were compared via microstructures, mechanical properties, adiabatic shear banding, and fracture mode. From the dynamic shear stress-strain
curves, the steel containing a considerable amount of nitrogen showed a smaller shear strain of 0.2 at the maximum shear stress
point, after which the shear stress decreased rapidly prior to fracture, whereas the other steel containing a smaller amount
of nitrogen showed relatively homogeneous shear deformation. This dynamic torsional behavior correlated well with the cracking
and adiabatic shear banding behavior, together with the yield-point phenomenon occurring in the steel containing more nitrogen.
Because the cracking occurring during cold forging was associated with the adiabatic shear banding and the yield-point phenomenon,
the minimization of nitrogen and the fast cooling rate after hot rolling were suggested to prevent the cracking. 相似文献
5.
Effects of volume fraction of tempered martensite on dynamic deformation properties of a Ti-6Al-4V alloy having a bimodal microstructure 总被引:1,自引:0,他引:1
Dong-Geun Lee You Hwan Lee Chong Soo Lee Sunghak Lee 《Metallurgical and Materials Transactions A》2005,36(13):741-748
The effects of the volume fraction of tempered martensite on the tensile and dynamic deformation properties of a Ti-6Al-4V
alloy having a bimodal microstructure were investigated in this study. Five microstructures having various tempered-martensite
volume fractions were obtained by varying heat-treatment conditions. Dynamic torsional tests were conducted on them using
a torsional Kolsky bar. The test data were analyzed in relation to microstructures, tensile properties, and adiabatic shear-band
formation. Under a dynamic loading condition, the maximum shear stress increased with increasing tempered-martensite volume
fraction, whereas the fracture shear strain decreased. Observation of the deformed area after the dynamic torsional test indicated
that a number of voids initiated mainly at α-phase/tempered-martensite interfaces, and that the number of voids increased
with increasing martensite volume fraction. Adiabatic shear bands of 6 to 10 μm in width were formed in the specimens having
lower martensite volume fractions, while they were not formed in those having higher martensite volume fractions. The possibility
of adiabatic shear-band formation was explained by concepts of absorbed deformation energy and void initiation.
jointly appointed with the Materials Science and Engineering Department, Pohang University of Science and Technology 相似文献
6.
Effects of microstructural morphology on quasi-static and dynamic deformation behavior of Ti-6Al-4V alloy 总被引:2,自引:0,他引:2
Dong-Geon Lee Sangho Kim Sunghak Lee Chong Soo Lee 《Metallurgical and Materials Transactions A》2001,32(2):315-324
The effects of microstructural morphology on quasi-static and dynamic deformation behavior of a Ti-6Al-4V alloy were investigated in this study. Quasi-static and dynamic torsional tests were conducted using a torsional Kolsky bar for Widmanstätten, equiaxed, and bimodal microstructures, which were processed by different heat treatments, and then, the test data were analyzed in relation to microstructures, tensile properties, and fracture mode. Quasi-static torsional properties showed a tendency similar to tensile properties and ductile fracture occurred in all three microstructures. Under dynamic torsional loading, maximum shear stress of the three microstructures was higher and fracture shear strain was lower than those under quasi-static loading, but the overall tendency was similar. In the Widmanstätten and equiaxed microstructures, adiabatic shear bands were found in the deformed region of the fractured specimens. The possibility of the adiabatic shear band formation under dynamic loading was quantitatively analyzed, depending on how plastic deformation energy was distributed to either void initiation or adiabatic shear banding. It was found to be most likely in the equiaxed microstructure, whereas it was least likely in the bimodal microstructure. 相似文献
7.
The study of adiabatic shear band instability in a pearlitic 4340 steel using a dynamic punch test 总被引:1,自引:0,他引:1
Anna K. Zurek 《Metallurgical and Materials Transactions A》1994,25(11):2483-2489
The formation of adiabatic shear band instabilities in a pearlitic 4340 steel using a dynamic punch test has been studied.
The dynamic punch-impact test produced white-etching adiabatic shear bands. The average strain of 0.5 was sufficient to produce
adiabatic shear bands in this steel at an average strain rate of 18,000 s−1. Nanohardness variations found across the adiabatic shear band are thought to be caused by the fragmentation and spheroidization
of the Fe3C and the overall deformation and work hardening of the pearlitic microstructure. The cracks formed at the termination of
the adiabatic shear band caused the sample to fracture in a ductile mode. 相似文献
8.
The effects of martensite morphology and volume fraction on the quasi-static and dynamic deformation behavior of dual-phase
steels were investigated in this study. Quasi-static and dynamic torsional tests were conducted using a torsional Kolsky bar
for four steel specimens, which had different martensite morphology and volume fraction, and then the test data were compared
via microstructures, tensile properties, and fracture mode. In the intermediate quenched (IQ) steel specimens, very fine fibrous
martensites were well distributed in the ferrite matrix, but bulky martensites were mixed with ferrites in the step quenched
(SQ) specimens. Quasi-static torsional properties were similar to tensile properties, and fracture occurred in a ductile mode
in IQ specimens, whereas cleavage fracture was predominated in SQ specimens. Under a dynamic loading condition, the fracture
mode of SQ specimens was changed from cleavage to ductile fracture, whereas IQ specimens had a ductile fracture mode, irrespective
of loading rate. These phenomena were analyzed using a shear lag model, phase continuity, and the thermal softening effect
of martensite. 相似文献
9.
Dong-Geun Lee Sunghak Lee Chong Soo Lee Sunmoo Hur 《Metallurgical and Materials Transactions A》2003,34(11):2541-2548
The effects of microstructural factors on the quasi-static tensile and dynamic torsional deformation behaviors in Ti-6Al-4V alloys with Widmanstätten structures were investigated in this study. Dynamic torsional tests were conducted using a torsional Kolsky bar for five Widmanstätten structures, in which microstructural parameters such as colony size and α lamellar spacing were varied by heat treatments, and then the test data were analyzed in relation to microstructures, tensile properties, and fracture mode. Under dynamic torsional loading, maximum shear stress was largely dependent on colony size, whereas shear strain at the maximum shear stress point was on colony size as well as α lamellar spacing. Adiabatic shear bands were found in the deformed area of the fractured torsional specimens, and their width was smallest in the structure whose colony size and α lamellar spacing were both large. The possibility of the adiabatic shear band formation was quantitatively analyzed in relation to microstructural factors. It was the highest in the coarse Widmanstätten structure, which was confirmed by the theoretical critical shear strain (υ c ) condition for the adiabatic shear band formation. 相似文献
10.
Effect of size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys 总被引:3,自引:0,他引:3
Dong-Kuk Kim Sunghak Lee Heung-Sub Song 《Metallurgical and Materials Transactions A》1999,30(5):1261-1273
The effect of the size and shape of tungsten particles on dynamic torsional properties in tungsten heavy alloys was investigated.
Dynamic torsional tests were conducted on seven tungsten alloy specimens, four of which were fabricated by repeated sintering,
using a torsional Kolsky bar, and then the test results were compared via microstructure, mechanical properties, adiabatic shear banding, and deformation and fracture mode. The size of tungsten particles
and their hardness were increased as sintering temperature and time were increased, thereby deteriorating fracture toughness.
The dynamic torsional test results indicated that in the specimens whose tungsten particles were coarse and irregularly shaped,
cleavage fracture occurred predominantly with little shear deformation, whereas shear deformation was concentrated into the
center of the gage section in the conventionally fabricated specimens. The deformation and fracture behavior of the specimens
having coarse tungsten particles correlated well with the observation of the in situ fracture test results, i.e., cleavage crack initiation and propagation. These findings suggested that there would be an appropriate tungsten particle
size because the cleavage fracture mode would be beneficial for the “self-sharpening” of the tungsten heavy alloys. 相似文献
11.
Han Sang Lee Byoungchul Hwang Sunghak Lee Chang Gil Lee Sung-Joon Kim 《Metallurgical and Materials Transactions A》2004,35(8):2371-2382
The effects of martensite morphology and tempering on the quasistatic and dynamic deformation behavior of dual-phase steels
were investigated in this study. Dynamic torsional tests were conducted on six steel specimens, which had different martensite
morphologies and tempering conditions, using a torsional Kolsky bar, and then the test data were compared via microstructures, tensile properties, and fracture mode. Bulky martensites were mixed with ferrites in the step-quenched (SQ)
specimens, but small martensites were well distributed in the ferrite matrix in the intermediate-annealed (IA) specimens.
Under a dynamic loading condition, the fracture mode of the SQ specimens was changed from cleavage to ductile fracture as
the tempering temperature increased, whereas the IA specimens showed a ductile fracture mode, irrespective of tempering. These
phenomena were analyzed in terms of a rule of mixtures applied to composites, microstructural variation, martensite softening
and carbon diffusion due to tempering, and adiabatic shear-band formation. 相似文献
12.
Yongjin Kim Sang Yong Shin Yang Gon Kim Nack J. Kim Sunghak Lee 《Metallurgical and Materials Transactions A》2010,41(8):1961-1972
This study aimed at investigating effects of strain rate and test temperature on deformation and fracture behavior of three
API X70 and X80 linepipe steels fabricated by varying alloying elements and hot-rolling conditions. Quasi-static and dynamic
torsional tests were conducted on these steels having different grain sizes and volume fractions of acicular ferrite and polygonal
ferrite, using a torsional Kolsky bar, and then the test data were compared via microstructures, tensile properties, and adiabatic shear band formation. The dynamic torsional test results indicated that
the steels rolled in the single-phase region had the higher maximum shear stress than the steel rolled in the two-phase region,
because their microstructures were composed mainly of acicular ferrites. Particularly in the API X80 steel rolled in the single-phase
region, increased dynamic torsional properties could be explained by the decrease in the overall effective grain size due
to the presence of acicular ferrite having smaller effective grain size. The possibility of the adiabatic shear band formation
at low temperatures was also analyzed by the energy required for void initiation and difference in effective grain size. 相似文献
13.
Effect of tungsten particle shape on dynamic deformation and fracture behavior of tungsten heavy alloys 总被引:1,自引:0,他引:1
Dong-Kuk Kim Sunghak Lee Heungsub Song 《Metallurgical and Materials Transactions A》1998,29(3):1057-1069
The effect of the tungsten particle shape on the dynamic deformation and fracture behavior of tungsten heavy alloys was investigated.
Dynamic torsional tests were conducted using a torsional Kolsky bar for five alloys, one of which was fabricated by the double-cycled
sintering process, and then the test data were compared via microstructures, mechanical properties, adiabatic shear banding, and fracture mode. The dynamic torsional test results indicated
that in the double-sintered tungsten alloy whose tungsten particles were very coarse and irregularly shaped, cleavage fracture
occurred in the central area of the gage section with little shear deformation, whereas shear deformation was concentrated
in the central area of the gage section in the other alloys. The deformation and fracture behavior of the double-sintered
alloy correlated well with the observation of the impacted penetrator specimen and the in situ fracture test results, i.e., microcrack initiation at coarse tungsten particles and cleavage crack propagation through tungsten particles. These findings
suggested that the cleavage fracture mode would be beneficial for the self-sharpening effect, and, thus, the improvement of
the penetration performance of the double-sintered tungsten heavy alloy would be expected. 相似文献
14.
Dong-Kuk Kim Sunghak Lee Heung-Sub Song 《Metallurgical and Materials Transactions A》1998,29(13):1057-1069
The effect of the tungsten particle shape on the dynamic deformation and fracture behavior of tungsten heavy alloys was investigated.
Dynamic torsional tests were conducted using a torsional Kolsky bar for five alloys, one of which was fabricated by the double-cycled
sintering process, and then the test data were compared via microstructures, mechanical properties, adiabatic shear banding, and fracture mode. The dynamic torsional test results indicated
that in the double-sintered tungsten alloy whose tungsten particles were very coarse and irregularly shaped, cleavage fracture
occurred in the central area of the gage section with little shear deformation, whereas shear deformation was concentrated
in the central area of the gage section in the other alloys. The deformation and fracture behavior of the double-sintered
alloy correlated well with the observation of the impacted penetrator specimen and the in situ fracture test results, i.e., microcrack initiation at coarse tungsten particles and cleavage crack propagation through tungsten particles. These findings
suggested that the cleavage fracture mode would be beneficial for the self-sharpening effect, and, thus, the improvement of
the penetration performance of the double-sintered tungsten heavy alloy would be expected. 相似文献
15.
Effect of surface carburization on dynamic deformation and fracture of tungsten heavy alloys 总被引:1,自引:0,他引:1
Sug-Woo Jung Suk-Joong L. Kang Dong-Kuk Kim Sunghak Lee Joon-Woong Noh 《Metallurgical and Materials Transactions A》1999,30(8):2027-2035
Effects of surface carburization on dynamic deformation and fracture behavior of tungsten heavy alloys were investigated in
order to improve the penetration performance. Dynamic torsional tests using a torsional Kolsky bar were conducted on four
specimens, three of which were carburized by the case carburization process. The test data were then compared with hardness,
Charpy impact energy, adiabatic shear banding, deformation and fracture mode, and penetration performance. With increasing
carburization temperature and time, surface hardness increased, but impact energy decreased. The dynamic torsional test results
indicated that for the carburized tungsten specimens, cleavage fracture occurred in the center of the gage section with little
shear deformation, whereas shear deformation was concentrated at the center of the gage section for the conventionally processed
specimen without carburization. The deformation and fracture behavior of the carburized specimens correlated well with the
observation of the impacted penetrator specimens, i.e., microcrack initiation at tungsten particles and cleavage crack propagation. Since the cleavage fracture mode is thought
to be beneficial for self-sharpening, these findings suggest the beneficial effect of the surface carburization on the penetration
performance. 相似文献
16.
Microscopic observations are made of the shear band material in three different steels: (1) an AISI 1018 cold-rolled steel
(CRS), (2) a structural steel (HY-100), and (3) an AISI 4340 vacuum arc remelted (VAR) steel tempered to either of two hardnesses,
RHC 44 or 55. To produce the shear bands, specimens were subjected to large shear strains at relatively high strain rates,
≈103/s, resulting in essentially adiabatic deformation conditions. It was found that whenever the shear band led to fracture of
the specimen, the fracture occurred by a process of void nucleation and coalescence; no cleavage was observed on any fracture
surface, including the most brittle of the steels tested (RHC = 55). This is presumably due to the softening of the shear
band material that results from the local temperature rise occurring during dynamic deformation. Differences in shear band
behavior between the various microstructures are also described.
Formerly Research Assistant, Brown University 相似文献
17.
Microscopic observations are made of the shear band material in three different steels: (1) an AISI 1018 cold-rolled steel
(CRS), (2) a structural steel (HY-100), and (3) an AISI 4340 vacuum arc remelted (VAR) steel tempered to either of two hardnesses,
RHC 44 or 55. To produce the shear bands, specimens were subjected to large shear strains at relatively high strain rates,
≈103/s, resulting in essentially adiabatic deformation conditions. It was found that whenever the shear band led to fracture of
the specimen, the fracture occurred by a process of void nucleation and coalescence; no cleavage was observed on any fracture
surface, including the most brittle of the steels tested (RHC = 55). This is presumably due to the softening of the shear
band material that results from the local temperature rise occurring during dynamic deformation. Differences in shear band
behavior between the various microstructures are also described.
Formerly Research Assistant, Brown University 相似文献
18.
《Acta Metallurgica Materialia》1991,39(11):2553-2563
A detailed study has been made of the localized adiabatic shear band formation in a plain carbon and a low alloy eutectoid rail steel subjected to high strain rate compression at initial deformation temperature of 298, 453 and 623 K. Localized adiabatic shearing due to impact is found to be favored with alloy steels and decreasing temperatures of deformation. It is shown that the deformed and transformed shear bands rather than being two separate phenomena are only an outcome of the extent of adiabatic strain localization occuring during deformation; the deformed bands forming with lesser localized flow and the transformed bands forming with extensive localized flow. This study explains convincingly the formation of the white phase on the surface of the rail heads during wheel-rail contact as due to the coalescence of the numerous adiabatic shear bands. 相似文献
19.
Dong-Geun Lee You Hwan Lee Sunghak Lee Chong Soo Lee Sun-Moo Hur 《Metallurgical and Materials Transactions A》2004,35(10):3103-3112
Effects of microstructural morphology on dynamic deformation behavior and ballistic impact properties of Ti-6Al-4V alloy plates
were investigated in this study. Dynamic torsional and ballistic impact tests were conducted on equiaxed and bimodal microstructures,
which were processed by different heat treatments, and then the test data were analyzed in relation to microstructures and
tensile properties. According to the dynamic torsional test data, maximum shear stress and fracture shear strain of the bimodal
microstructure were higher than those of the equiaxed microstructure, and the possibility of the adiabatic shear band formation
was more likely in the equiaxed microstructure than in the bimodal microstructure. In the ballistically impacted region of
the equiaxed microstructure, a number of adiabatic shear bands and cracks were observed to be formed along plastic flow lines,
and delamination occurred because of cracking along the flow lines or shear bands. In the case of the bimodal microstructure,
shear bands were found in limited areas near the penetrated surface without occurring delamination, and their number was smaller
than that of the equiaxed microstructure. Thus, ballistic performance of the bimodal microstructure was better than that of
the equiaxed microstructure, which was consistent with the dynamic torsional test results. 相似文献
20.
Manpreet Singh Anindya Das T. Venugopalan Krishnendu Mukherjee Mahesh Walunj Tarun Nanda B. Ravi Kumar 《Metallurgical and Materials Transactions A》2018,49(2):463-475
The effects of microstructure parameters of dual-phase steels on tensile high strain dynamic deformation characteristic were examined in this study. Cold-rolled steel sheets were annealed using three different annealing process parameters to obtain three different dual-phase microstructures of varied ferrite and martensite phase fraction. The volume fraction of martensite obtained in two of the steels was near identical (~ 19 pct) with a subtle difference in its spatial distribution. In the first microstructure variant, martensite was mostly found to be situated at ferrite grain boundaries and in the second variant, in addition to at grain boundaries, in-grain martensite was also observed. The third microstructure was very different from the above two with respect to martensite volume fraction (~ 67 pct) and its morphology. In this case, martensite packets were surrounded by a three-dimensional ferrite network giving an appearance of core and shell type microstructure. All the three steels were tensile deformed at strain rates ranging from 2.7 × 10?4 (quasi-static) to 650 s?1 (dynamic range). Field-emission scanning electron microscope was used to characterize the starting as well as post-tensile deformed microstructures. Dual-phase steel consisting of small martensite volume fraction (~ 19 pct), irrespective of its spatial distribution, demonstrated high strain rate sensitivity and on the other hand, steel with large martensite volume fraction (~ 67 pct) displayed a very little strain rate sensitivity. Interestingly, total elongation was found to increase with increasing strain rate in the dynamic regime for steel with core–shell type of microstructure containing large martensite volume fraction. The observed enhancement in plasticity in dynamic regime was attributed to adiabatic heating of specimen. To understand the evolving damage mechanism, the fracture surface and the vicinity of fracture ends were studied in all the three dual-phase steels. 相似文献