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1.
The effect of heat treatment on microstructure and cryogenic fracture properties in 5Ni and 9Ni steel 总被引:2,自引:0,他引:2
Heat treatments were utilized in 5Ni and 9Ni steel which resulted in the development of tempered microstructures which contained
either no measurable retained austenite (<0.5 pct) or approximately 4 to 5 pct retained austenite as determined by X-ray diffraction.
Microstructural observations coupled with the results of tensile testing indicated that the formation of retained austenite
correlated with a decrease in carbon content of the matrix. Relative values ofK
IC
at 77 K were estimated from slow bend precracked Charpy data using both the COD and equivalent energy measurements. In addition,
Charpy impact properties at 77 K were determined. In the 9Ni alloy, optimum fracture toughness was achieved in specimens which
contained retained austenite. This was attributed to changes in yield and work hardening behavior which accompanied the microstructural
changes. In the 5Ni alloy, fracture toughness equivalent to that observed in the 9Ni alloy was developed in grain refined
and tempered microstructures containing <0.5 pct retained austenite. A decrease in fracture toughness was observed in grain
refined 5Ni specimens containing 3.8 pct retained austenite due to the premature onset of unstable cracking. This was attributed
to the transformation of retained austenite to brittle martensite during deformation. It was concluded that the formation
of thermally stable retained austenite is beneficial to the fracture toughness of Ni steels at 77 K as a result of austenite
gettering carbon from the matrix during tempering. However, it was also concluded that the mechanical stability of the retained
austenite is critical in achieving a favorable enhancement of cryogenic fracture toughness properties.
Formerly with Union Carbide Corporation, Tarrytown, NY 相似文献
2.
The microstructures and mechanical properties of a series of vacuum melted Fe/(2 to 4) Mo/(0.2 to 0.4) C steels with and without
cobalt have been investigated in the as-quenched fully martensitic condition and after quenching and tempering for 1 h at
673 K (400°C) and 873 K (600°C); austenitizing was done at 1473 K (1200°C) in argon. Very good strength and toughness properties
were obtained with the Fe/2 Mo/0.4 C alloy in the as-quenched martensitic condition and this is attributed mainly to the absence
of internal twinning. The slightly inferior toughness properties compared to Fe/Cr/C steels is attributed to the absence of
interlath retained austenite. The two 0.4 pct carbon steels having low Mo contents had approximately one-half the amount of
transformation twinning associated with the two 0.4 pct carbon steels having high Mo contents. The plane strain fracture toughness
of the steels with less twinning was markedly superior to the toughness of those steels with similar alloy chemistry which
had more heavily twinned microstructures. Experiments showed that additions of Co to a given Fe/Mo/C steel raisedM
S
but did not decrease twinning nor improve toughness. Molybdenum carbide particles were found in all specimens tempered at
673 K (400°C). The Fe/Mo/C system exhibits secondary hardening after tempering at 873 K (600°C). The precipitate is probably
Mo2C. This secondary hardening is associated with a reduction in toughness. Additions of Co to Fe/Mo/C steels inhibited or eliminated
the secondary hardening effect normally observed. Toughness, however, did not improve and in fact decreased with Co additions. 相似文献
3.
The microstructures and mechanical properties of a series of vacuum melted Fe/(2 to 4) Mo/(0.2 to 0.4) C steels with and without
cobalt have been investigated in the as-quenched fully martensitic condition and after quenching and tempering for 1 h at
673 K (400°C) and 873 K (600°C); austenitizing was done at 1473 K (1200°C) in argon. Very good strength and toughness properties
were obtained with the Fe/2 Mo/0.4 C alloy in the as-quenched martensitic condition and this is attributed mainly to the absence
of internal twinning. The slightly inferior toughness properties compared to Fe/Cr/C steels is attributed to the absence of
interlath retained austenite. The two 0.4 pct carbon steels having low Mo contents had approximately one-half the amount of
transformation twinning associated with the two 0.4 pct carbon steels having high Mo contents. The plane strain fracture toughness
of the steels with less twinning was markedly superior to the toughness of those steels with similar alloy chemistry which
had more heavily twinned microstructures. Experiments showed that additions of Co to a given Fe/Mo/C steel raised Ms but did not decrease twinning nor improve toughness. Molybdenum carbide particles were found in all specimens tempered at
673 K (400°C). The Fe/Mo/C system exhibits secondary hardening after tempering at 873 K (600°C). The precipitate is probably
Mo2C. This secondary hardening is associated with a reduction in toughness. Additions of Co to Fe/Mo/C steels inhibited or eliminated
the secondary hardening effect normally observed. Toughness, however, did not improve and in fact decreased with Co additions. 相似文献
4.
J. Beswick 《Metallurgical and Materials Transactions A》1984,15(2):299-306
Numerous publications refer to the phase transformations and properties of SAE 52100 steel, and this paper concerns itself
with the effect of prior cold deformation on the martensitic hardening response. TheA
c1
and Ac3 temperatures are lowered due to cold work as is theM
s
with a resultant increase in the retained austenite content for a given hardening cycle. Significantly, the prior cold deformation
results in a refinement of the austenite grain size. The low angle dislocation cells produced by the cold deformation recover
during the heating to the austenitizing temperature to form fine ferrite subgrains. The intersections of the fine ferrite
subgrains with the spheroidal carbides in the soft annealed microstructures are preferential sites for nucleation of austenite.
This results in finer austėnite grains, which produces accelerated carbide dissolution and austenite alloy enrichment compared
to un worked, soft annealed structures. The mechanism for the accelerated austenitization is significant in predicting heat
treatment response from published phase transformation data for SAE 52100 steel. 相似文献
5.
Jerzy Pacyna 《国际钢铁研究》1987,58(2):87-92
The aim of this work was to find the quantitative dependences between fracture toughness Klc and the volume fraction of retained austenite in the matrix of quenched high-speed steels. The tests were carried out on three model alloys of a different content quotient of Mo: W which, after quenching, were gradually supercooled up to ? 196°C and then tempered at 450°C. Also the measurements of the content of retained austenite in the vicinity of the surface of a sample fracture were carried out. It was determined that after tempering at 450°C the fracture toughness of the matrix of high-speed steels is directly proportional to the content of retained austenite in it. Every 1 % by volume of retained austenite increases the fracture toughness Klc of the matrix by about 5%, despite the fact that most probably it is completely transformed into fresh martensite in front of a propagating crack. Higher fracture toughness of the matrix of high-speed steels rich in molybdenum should be explained exlusively by a larger content of retained austenite. Transformations in the martensitic part of the matrix of the alloys richer in molybdenum clearly reduce the advantageous effect of retained austenite on this steel feature. 相似文献
6.
The fatigue crack growth rates,da/dN, and the fracture toughness, KIc have been measured in two high-carbon martensitic stainless steels, 440C and BG42. Variations in the retained austenite contents
were achieved by using combinations of austenitizing temperatures, refrigeration cycles, and tempering temperatures. In nonrefrigerated
440C tempered at 150 °C, about 10 vol pct retained austenite was transformed to martensite at the fracture surfaces duringK
Ic testing, and this strain-induced transformation contributed significantly to the fracture toughness. The strain-induced transformation
was progressively less as the tempering temperature was raised to 450 °C, and at the secondary hardening peak, 500 °C, strain-induced
transformation was not observed. In nonrefrigerated 440C austenitized at 1065 °C,K
Ic had a peak value of 30 MPa m1/2 on tempering at 150 °C and a minimum of 18 MPa m1/2 on tempering at 500 °C. Refrigerated 440C retained about 5 pct austenite, and did not exhibit strain-induced transformation
at the fracture surfaces for any tempering temperature. TheK
Ic values for corresponding tempering temperatures up to the secondary peak in refrigerated steels were consistently lower than
in nonrefrigerated steels. All of the BG42 specimens were refrigerated and double or quadruple tempered in the secondary hardening
region; theK
Ic values were 16 to 18 MPa m1/2 at the secondary peak. Tempered martensite embrittlement (TME) was observed in both refrigerated and nonrefrigerated 440C,
and it was shown that austenite transformation does not play a role in the TME mechanism in this steel. Fatigue crack propagation
rates in 440C in the power law regime were the same for refrigerated and nonrefrigerated steels and were relatively insensitive
to tempering temperatures up to 500 °C. Above the secondary peak, however, the fatigue crack growth rates exhibited consistently
lower values, and this was a consequence of the tempering of the martensite and the lower hardness. Nonrefrigerated steels
showed slightly higher threshold values, ΔKth, and this was ascribed to the development of compressive residual stresses and increased surface roughening in steels which
exhibit a strain-induced martensitic transformation. 相似文献
7.
A simple two-step thermal processing technique was devised to impart a microduplex structure in a high strength 250 grade
commercial maraging steel. A martensite grain size of approximately 1μm was obtained with interspersed islands of retained austenite whose volume fraction and mechanical stability could be controlled
by varying the thermal processing conditions. The microstructure and mechanical properties of the microduplex structure were
compared to those of the alloy in the maraged, martensitic condition. Due to the presence of the austenite phase, the microduplex
structure showed a much smaller temperature and strain rate dependence of deformation than the martensitic structure. A remarkable
increase in uniform elongation was observed below theM
d
temperature of retained austenite. The microduplex structure did not show any significant advantage in fracture toughness
over the martensitic structure when compared at similar strength levels. By suitably adjusting austenitic stability a deformation-induced
phase transformation (TRIP) of the retained austenite in the microduplex structure could be made to occur; however, the transformation
did not lead to any evident increase in toughness. The microduplex structure exhibited a slight improvement in fracture toughness
at high strain rate in contrast to the martensitic structure in which the rate effect significantly reduced the toughness. 相似文献
8.
An investigation was carried out to examine the influence of microstructure on the plane strain fracture toughness of austempered
ductile iron. Austempered ductile iron (ADI) alloyed with nickel, copper, and molybdenum was austenitized and subsequently
austempered over a range of temperatures to produce different microstructures. The microstructures were characterized through
optical microscopy and X-ray diffraction. Plane strain fracture toughness of all these materials was determined and was correlated
with the microstructure. The results of the present investigation indicate that the lower bainitic microstructure results
in higher fracture toughness than upper bainitic microstructure. Both volume fraction of retained austenite and its carbon
content influence the fracture toughness. The retained austenite content of 25 vol pct was found to provide the optimum fracture
toughness. It was further concluded that the carbon content of the retained austenite should be as high as possible to improve
fracture toughness. 相似文献
9.
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
10.
James P. Materkowski George Krauss 《Metallurgical and Materials Transactions A》1979,10(11):1643-1651
The toughness of SAE 4340 steel with low (0.003 wt pct) and high (0.03 wt pct) phosphorus has been evaluated by Charpy V notch
(CVN) impact and compact tension plane strain fracture toughness (K
1c) tests of specimens quenched and tempered up to 673 K (400°C). Both the high and low P steel showed the characteristic tempered
martensite embrittlement (TME) plateau or trough in room temperature CVN impact toughness after tempering at temperatures
between 473 K (200°C) and 673 K (400°C). The CVN energy absorbed by low P specimens after tempering at any temperature was
always about 10 J higher than that of the high P specimens given the same heat treatment. Interlath carbide initiated cleavage
across the martensite laths was identified as the mechanism of TME in the low P 4340 steel, while intergranular fracture,
apparently due to a combination of P segregation and carbide formation at prior austenite grain boundaries, was associated
with TME in the high P steel.K
IC values reflected TME in the high P steels but did not show TME in the low P steel, a result explained by the formation of
a narrow zone of ductile fracture adjacent to the fatigue precrack during fracture toughness testing. The ductile fracture
zone was attributed to the low rate of work hardening characteristic of martensitic steels tempered above 473 K (200°C). 相似文献
11.
C. A. Stickels 《Metallurgical and Materials Transactions B》1974,5(4):865-874
The life of through-hardened 52100 anti-friction bearing components is improved if the excess carbides, undissolved during
austenitization, are small and uniformly dispersed. One kind of carbide-refining heat treatment consists of 1) dissolving
all carbides, 2) isothermally transforming the austenite to pearlite or bainite, and 3) austenitizing, quenching and tempering
in the usual manner. Each step in this sequence of treatments was investigated, and the behavior of pearlitic and bainitic
microstructures during subsequent austenitization was contrasted with the behavior of ferrite/spheroidized-carbide microstructures.
It was shown that: 1) The usual hardening treatments given spheroidize-annealed bearing components result in an inhomogeneous
microstructure, possibly due to the faster dissolution of carbides near austenite grain boundaries. 2) Austenitization of
pearlite or bainite produces very uniform dispersions of ultra-fine carbides on the order of 0.1 μm diameter or less. 3) Specimens
with ultra-fine carbides tend to have more retained austenite. 4) The rate of coarsening of ultra-fine carbides at austenitizing
temperatures of 840°C and below, is slow enough so that conventional furnace heat treatments are satisfactory for producing
this microstructure. 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.
A simple two-step thermal processing technique was devised to impart a microduplex structure in a high strength 250 grade commercial maraging steel. A martensite grain size of approximately 1 μm was obtained with interspersed islands of retained austenite whose volume fraction and mechanical stability could be controlled by varying the thermal processing conditions. The microstructure and mechanical properties of the microduplex structure were compared to those of the alloy in the maraged, martensitic condition. Due to the presence of the austenite phase, the microduplex structure showed a much smaller temperature and strain rate dependence of deformation than the martensitic structure. A remarkable increase in uniform elongation was observed below theM d temperature of retained austenite. The microduplex structure did not show any significant advantage in fracture toughness over the martensitic structure when compared at similar strength levels. By suitably adjusting austenitic stability a deformation-induced phase transformation (TRIP) of the retained austenite in the microduplex structure could be made to occur; however, the transformation did not lead to any evident increase in toughness. The micro-duplex structure exhibited a slight improvement in fracture toughness at high strain rate in contrast to the martensitic structure in which the rate effect significantly reduced the toughness. 相似文献
14.
An investigation was carried out to study the microstructure and mechanical properties of isothermally transformed AISI E
52100 steel. Heal treatments consisting of single and two cycle austenitization followed by isothermal holding resulted in
duplex structures of martensite and bainite. In addition, high temperature austenitization led to large amounts of retained
austenite at room temperature. Conventional oil quenching treatments were also performed for purposes of comparison. It was
found that isothermal holding aboveM
s after single cycle austenitization resulted in a microstructure which had strength and toughness properties equivalent to
quenched and tempered 52100. The two cycle austenitization treatment followed by isothermal holding led to a doubling of the
fracture toughness at equivalent hardness and ultimate tensile strength levels relative to the properties of conventional
quenched and tempered 52100 steel. The mechanical stability of retained austenite, present after two cycle austenitization,
was examined. Although it was found that the presence of unstable retained austenite was associated with the best combination
of strength and toughness, it cannot be unequivocally stated that the retained austenite influenced the mechanical properties.
R. M. HORN, formerly with University of California, Berkeley 相似文献
15.
This research program was carried out to evaluate the effects of surface hardening on the fracture toughness of carburized
steel. The materials AISI 8620 steel was machined into compact-tension (CT) specimens. The specimens were pack carburized
at 930°C (1706°F) for different periods of time, cooled to ambient temperature and subsequently tempered at various temperatures
for one hour. The fractured specimens were examined by hardness tests, metallography, X-ray diffraction analysis for retained
austenite in the case, and scanning electron microscope fractographic analysis of the fracture surfaces. The experimental
results revealed that theKIC values of the carburized, AISI 8620 steels were improved by the increase in case depth. Martensitic/tempered-martensitic
structure in the case was the major constituent contributing to the improved toughness. The amount of retained austenite at
the case increased as the thickness of the hardened layer increased. But retained austenite as well as large grain size were
found to have adverse effects on fracture toughness of the carburized steel. The tempering temperature of 500°C (932°F) provided
maximumKIC values. Higher tempering temperatures resulted in sharp decrease of fracture, toughness values.
W{upeio}-Y{upoue} H{upo}, formerly a Graduate Student, in the Department of Materials Engineering Tatung Institute of Technology,
is in compulsory 0 ROTC military
service of Republic of China. 相似文献
16.
TRIP‐assisted multiphase steels have been thoroughly studied in the cold‐rolled and annealed state. The effects of hot‐rolling conditions on these steels are much less studied even though these are of major importance for industrial practice. This study was carried out in order to understand the effect of the hot deformation of austenite on the tensile properties of TRIP‐assisted multiphase steels. Two different compositions and microstructures are investigated. The first one is a low‐carbon steel (mass content of 0.15 %) with a microstructure consisting of an intercritical ferritic matrix, bainite and retained austenite. The second one is a medium‐carbon steel (mass content of 0.4 %) that consists of bainite and retained austenite. Both steels were deformed to various strain levels below the non‐recrystallisation temperature of austenite. The medium carbon steel was deformed in the fully austenitic temperature range whereas the low‐carbon steel was deformed in the intercritical temperature range. In both cases, the prior hot deformation of austenite brings about a large enhancement of the work‐hardening capabilities. In the case of the medium‐carbon steel, this effect can be attributed to a much larger TRIP effect taking place during straining. In the case of the low‐carbon steel, the improvement of the work‐hardening behaviour was attributed to an Interaction between the martensitic transformation and the dislocations already present within the surrounding ferrite matrix. 相似文献
17.
为改善高强度钢的塑性和韧性,对中碳低合金马氏体高强度钢分别采用常化后空冷+回火和常化后控冷+回火工艺,研究常化后冷却工艺对钢中残余奥氏体及力学性能的影响.采用扫描电镜获得钢的组织形态,利用X射线衍射和电子背散射衍射技术分析钢中残余奥氏体的体积分数、形貌和分布.发现两种工艺下均得到板条马氏体+残余奥氏体组织,残余奥氏体均匀分布在板条之间,随工艺参数不同,其体积分数在3%~10%变化.常化后加速冷却能显著细化马氏体板条,提高钢的屈服强度和抗拉强度100 MPa以上,冲击功下降4 J.残余奥氏体的体积分数随常化控冷终冷温度的升高呈现先升高后降低的变化,常化后的控制冷却也可以作为进一步改善马氏体类型钢组织和性能的方法 相似文献
18.
Steels containing about 12 pct Cr, 10 pct Mn, and 0.2 pct N have been shown to have an unstable austenitic microstructure
and have good ductility, extreme work hardening, high fracture strength, excellent toughness, good wear resistance, and moderate
corrosion resistance. A series of alloys containing 9.5 to 12.8 pct Cr, 5.0 to 10.4 pct Mn, 0.16 to 0.32 pct N, 0.05 pct C,
and residual elements typical of stainless steels was investigated by microstructural examination and mechanical, abrasion,
and corrosion testing. Microstructures ranged from martensite to unstable austenite. The unstable austenitic steels transformed
to α martensite on deformation and displayed very high work hardening, exceeding that of Hadfield’s manganese steels. Fracture
strengths similar to high carbon martensitic stainless steels were obtained while ductility and toughness values were high,
similar to austenitic stainless steels. Resistance to abrasive wear exceeded that of commercial abrasion resistant steels
and other stainless steels. Corrosion resistance was similar to that of other 12 pct Cr steels. Properties were not much affected
by minor compositional variations or rolled-in nitrogen porosity. In 12 pct Cr-10 pct Mn alloys, ingot porosity was avoided
when nitrogen levels were below 0.19 pet, and austenitic microstructures were obtained when nitrogen levels exceeded 0.14
pct. 相似文献
19.
C. A. Stickels 《Metallurgical and Materials Transactions A》1977,8(1):63-70
The compressive flow stress and rate of work hardening of quenched and tempered AISI 52100 steel were measured for a variety
of heat treatments. Both the flow stress and the work hardening index,n, increase with decreasing tempering temperature. Flow stresses increase initially with increasing austenitizing temperature,T
a, then decrease with a further increase inT
a as the amount of retained austenite increases.n tends to increase asT
a increases. In specimens temperared to eliminate retained austenite,n decreases to near zero as the strain increases. This behavior appears to be characteristic of tempered martensite. When less
than 10 pct retained austenite is present,n still decreases with increasing strain, but witn n ore than about 15 pct retained austenite,n increases with strain. Heat treatments which refine the primary carbides increase the flow stress forT
a≤840°C. Since fine primary carbides lead to more retained austenite at a givenT
a, n tends to be greater when primary carbides are refined. For one heat treatment, the retained austenite content was measured
by an X-ray method as a function of plastic strain. From changes in the relative intensities of austenite reflections, it
was found that austenite crystals most favorably oriented for deformation in compression transform most readily to martensite
on straining. 相似文献
20.
R. Chait 《Metallurgical and Materials Transactions B》1972,3(2):369-375
Room temperature tensile and compressive true stress-true strain curves of various high strength steels (quenched and tempered
4340 steel, 410 martensitic stainless steel, and H-11 steel; and aged 300-grade 18 Ni maraging steel) were analyzed to determine
the effect of the various microstructures, on what has been termed the strength differential (SD),i.e., the strength level difference between the tensile and compressive flow curves. Care was taken to insure that the compressive
deformation was homogeneous. Regardless of the amount of plastic deformation, the quenched and tempered steels exhibited a
higher flow stress in homogeneous compressive deformation than for tensile deformation. The extent of the SD was dependent
on tempering temperature. This observation is consistent with what others have observed regarding yield strength behavior
of quenched and quenched-and-tempered steels. Despite the low carbon content, aged maraging steel also showed a greater resistance
to homogeneous compressive deformation. Metallographic examination of the maraging steel revealed the banding that is indicative
of segregation. However, homogenization had little effect on the SD despite a change in austenite grain size, reverted austenite
content, and the austenite-to-martensite transformational strains shown by Goldberg to be present in segregated material. 相似文献