共查询到20条相似文献,搜索用时 724 毫秒
1.
M. Sarikaya A. K. Jhingan G. Thomas 《Metallurgical and Materials Transactions A》1983,14(6):1121-1133
Electron microscopy, diffraction and microanalysis, X-ray diffraction, and auger spectroscopy have been used to study quenched and quenched and tempered 0.3 pct carbon low alloy steels. Somein situ fracture studies were also carried out in a high voltage electron microscope. Tempered martensite embrittlement (TME) is shown to arise primarily as a microstructural constraint associated with decomposition of interlath retained austenite into M3C filMs upon tempering in the range of 250 °C to 400 °C. In addition, intralath Widmanstätten Fe3C forms from epsilon carbide. The fracture is transgranular with respect to prior austenite. The sit11Ation is analogous to that in upper bainite. This TME failure is different from temper embrittlement (TE) which o°Curs at higher tempering temperatures (approximately 500 °C), and is not a microstructural effect but rather due to impurity segregation (principally sulfur in the present work) to prior austenite grain boundaries leading to intergranular fracture along those boundaries. Both failures can o°Cur in the same steels, depending on the tempering conditions. 相似文献
2.
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
3.
An investigation into the mechanisms of tempered martensite embrittlement (TME), also know as “500°F” or “350°C” or one-step
temper embrittlement, has been made in commercial, ultra-high strength 4340 and Si-modified 4340 (300-M) alloy steels, with
particular focus given to the role of interlath films of retained austenite. Studies were performed on the variation of i)
strength and toughness, and ii) the morphology, volume fraction and thermal and mechanical stability of retained austenite,
as a function of tempering temperature, following oil-quenching, isothermal holding, and continuous air cooling from the austenitizing
temperature. TME was observed as a decrease in bothK
Ic and Charpy V-notch impact energy after tempering around 300°C in 4340 and 425°C in 300-M, where the mechanisms of fracture
were either interlath cleavage or largely transgranular cleavage. The embrittlement was found to be concurrent with the interlath
precipitation of cementite during temperingand the consequent mechanical instability of interlath films of retained austenite during subsequent loading. The role of silicon
in 300-M was seen to retard these processes and hence retard TME to higher tempering temperatures than for 4340. The magnitude
of the embrittlement was found to be significantly greater in microstructures containing increasing volume fractions of retained
austenite. Specifically, in 300-M the decrease inK
Ic, due to TME, was a 5 MPa√m in oil quenched structures with less than 4 pct austenite, compared to a massive decrease of 70
MPa√m in slowly (air) cooled structures containing 25 pct austenite. A complete mechanism of tempered martensite embrittlement
is proposed involving i) precipitation of interlath cementite due to partial thermal decomposition of interlath films of retained
austenite, and ii) subsequent deformation-induced transformation on loading of remaining interlath austenite, destabilized
by carbon depletion from carbide precipitation. The deterioration in toughness, associated with TME, is therefore ascribed
to the embrittling effect of i) interlath cementite precipitates and ii) an interlath layer of mechanically-transformed austenite,i.e., untempered martensite. The presence of residual impurity elements in prior austenite grain boundaries, having segregated
there during austenitization, may accentuate this process by providing an alternative weak path for fracture. The relative
importance of these effects is discussed.
Formerly with the Lawrence Berkeley Laboratory, University of California. 相似文献
4.
Alexandra Fedoseeva Nadezhda Dudova Rustam Kaibyshev 《Metallurgical and Materials Transactions A》2017,48(3):982-998
The effect of tempering on the mechanical properties and fracture behavior of two 3 pct Co-modified 9 pct Cr steels with 2 and 3 wt pct W was examined. Both steels were ductile in tension tests and tough under impact tests in high-temperature tempered conditions. At T ≤ 923 K (650 °C), the addition of 1 wt pct W led to low toughness and pronounced embrittlement. The 9Cr2W steel was tough after low-temperature tempering up to 723 K (450 °C). At 798 K (525 °C), the decomposition of retained austenite induced the formation of discontinuous and continuous films of M23C6 carbides along boundaries in the 9Cr2W and the 9Cr3W steels, respectively, which led to tempered martensite embrittlement (TME). In the 9Cr2W steel, the discontinuous boundary films played a role of crack initiation sites, and the absorption energy was 24 J cm?2. In the 9Cr3W steel, continuous films provided a fracture path along the boundaries of prior austenite grains (PAG) and interlath boundaries in addition that caused the drop of impact energy to 6 J cm?2. Tempering at 1023 K (750 °C) completely eliminated TME by spheroidization and the growth of M23C6 carbides, and both steels exhibited high values of adsorbed energy of ≥230 J cm?2. The addition of 1 wt pct W extended the temperature domain of TME up to 923 K (650 °C) through the formation of W segregations at boundaries that hindered the spheroidization of M23C6 carbides. 相似文献
5.
This study is concerned with a correlation between the microstructure and fracture behavior of two AISI 4340 steels which
were vacuum induction melted and then deoxidized with aluminum and titanium additions. This allowed a comparison between microstructures
that underwent large increases in grain size and those that did not. When the steels were tempered at 350°C,K
Ic and Charpy impact energy plots showed troughs which indicated tempered martensite embrittlement (TME). The TME results of
plane strain fracture toughness are interpreted using a simple ductile fracture initiation model based on large strain deformation
fields ahead of cracks, suggesting thatK
Icscales roughly with the square root of the spacing of cementite particles precipitated during the tempering treatment. The
trough in Charpy impact energy is found to coincide well with the amount of intergranular fracture and the effect of segregation
of phosphorus on the austenite grain boundaries. In addition, cementite particles are of primary importance in initiating
the intergranular cracks and, consequently, reducing the Charpy energy. These findings suggest that TME in the two 4340 steels
studied can be explained quantitatively using different fracture models. 相似文献
6.
A. Reguly T. R. Strohaecker G. Krauss D. K. Matlock 《Metallurgical and Materials Transactions A》2004,35(1):153-162
Charpy V-notch (CVN) specimens from experimental heats of 5160 steel containing 0.001 and 0.034 mass pct phosphorus were austenitized
at temperatures between 830 °C and 1100 °C, quenched to martensite, and tempered at temperatures between 100 °C and 500 °C.
Scanning electron microscopy (SEM) was used to characterize the fracture surfaces of tested CVN specimens and carbide formation
on prior austenite grain boundaries. Quench embrittlement, the susceptibility to intergranular fracture in as-quenched and
low-temperature tempered high-carbon steels due to cementite formation as affected by phosphorus segregation on austenite
grain boundaries, developed readily in specimens of the high phosphorus steel austenitized at all temperatures. The low phosphorus
steel developed quench embrittlement only after austenitizing at 1100 °C. Intergranular fractures correlated with low room-temperature
CVN impact toughness. The results are discussed with respect to the dissolution of carbides during austenitizing and the effect
of phosphorus on grain boundary, carbide formation, and stability. 相似文献
7.
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
8.
Fe-12 Mn alloys undergo failure by catastrophic intergranular fracture when tested at low temperature in the as-austenitized
condition, a consideration which prevents their use for structural applications at cryogenic temperatures. The present research
was undertaken to identify modifications in alloy composition or heat treatment which would suppress this embrittlement. Chemical
and microstructural analyses were made on the prior austenite grain boundaries within the alloy in its embrittled state. These
studies failed to reveal a chemical or microstructural source for the brittleness, suggesting that intergranular brittleness
is inherent to the alloy in the as-austenitized condition. The addition of 0.002 to 0.01 wt pct boron successfully prevented
intergranular fracture, leading to a spectacular improvement in the low temperature impact toughness of the alloy. Autoradiographic
studies suggest that boron segregates to the austenite grain boundaries during annealing at temperatures near 1000 °C. The
cryogenic toughness of a Fe-12Mn-0.002B alloy could be further improved by suitable tempering treatments. However, the alloy
embrittled if inappropriate tempering temperatures were used. This temper embrittlement was concom-itant with the dissolution
of boron from the prior austenite grain boundaries, which reestablishes the intergranular fracture mode. 相似文献
9.
Shoji Fujiwara Takatoshi Ogawa Yoshifumi Ohmura Imao Tamura 《Metallurgical and Materials Transactions A》1983,14(6):1067-1077
In Fe-4 pct Mo-0.2 pct C martensite which is a typical secondary hardening steel, premature failure o°Curred in tensile test
at 600 °C to 700°C where solute atoms could diffuse easily. To clarify this phenomenon, the quenched specimens were tempered under applied stress
and tensile-tested at room temperature. The following results were obtained: (1) Typical intergranular fracture was observed
in specimens tempered in a temperature range of 600 °C to 650 °C with tempering times of five minutes to 10 minutes and applied
stress (70 MPa to 140 MPa). (2) Based on Auger analysis, this phenomenon was considered to be caused by segregation of P,
S, and Mo on prior austenite grain boundaries due to applied stress. (3) The direction of applied stress was found to be very
significant. Namely, when the tensile direction was parallel to the applied stress during tempering, the specimen was more
brittle, and when tensile direction was normal to the applied stress, the specimen was not so brittle. (4) To reduce this
embrittlement, solution treatment temperature was adjusted, and it was found that the embrittlement was considerably reduced
both in specimens with fine prior austenite grains and with some ferrite phase on prior austenite grain boundaries.
TAKATOSHI OGAWA, formerly with Kyoto University.
YOSHIFUMI OHMURA, formerly with Kyoto University.
This paper is based on a presentation made at the “pcter G. Winchell Symposium on Tempering of Steel” held at the Louisville
Meeting of The Metallurgical Society of AIME, October 12-13, 1981, under the sponsorship of the TMS-AIME Ferrous Metallurgy
and Heat Treatment Committees. 相似文献
10.
Shoji Fujiwara Takatoshi Ogawa YOshifumi Ohmura Imao Tamura 《Metallurgical and Materials Transactions A》1983,14(5):1067-1077
In Fe-4 pct Mo-0.2 pct C martensite which is a typical secondary hardening steel, premature failure occurred in tensile test
at 600 °C to 700 °C where solute atoms could diffuse easily. To clarify this phenomenon, the quenched specimens were tempered
under applied stress and tensile-tested at room temperature. The following results were obtained: (1) Typical intergranular
fracture was observed in specimens tempered in a temperature range of 600 °C to 650 °C with tempering times of five minutes
to 10 minutes and applied stress (70 MPa to 140 MPa). (2) Based on Auger analysis, this phenomenon was considered to be caused
by segregation of P, S, and Mo on prior austenite grain boundaries due to applied stress. (3) The direction of applied stress
was found to be very significant. Namely, when the tensile direction was parallel to the applied stress during tempering,
the specimen was more brittle, and when tensile direction was normal to the applied stress, the specimen was not so brittle.
(4) To reduce this embrittlement, solution treatment temperature was adjusted, and it was found that the embrittlement was
considerably reduced both in specimens with fine prior austenite grains and with some ferrite phase on prior austenite grain
boundaries.
Formerly with Kyoto University
Formerly with Kyoto University
This paper is based on a presentation made at the “Peter G. Winchell Symposium on Tempering of Steel” held at the Louisville
Meeting of The Metallurgical Society of AIME, October 12-13, 1981, under the sponsorship of the TMS-AIME Ferrous Metallurgy
and Heat Treatment Committees. 相似文献
11.
The limits of strength and ductility of a medium‐carbon silicon chromium spring steel are investigated for the case of conventional heat treatment including austenitization, quenching and tempering. The effect of phosphorus and austenite deformation prior to quenching was studied by measuring mechanical properties after quenching and tempering and by microstructural investigation. Strong influence of phosphorus on the ductility is observed for the quenched and tempered martensite without prior austenite deformation. The minimum in ductility found after tempering at 350°C is explained by the formation of cementite and grain boundary segregation of phosphorus. Two thermomechanical treatments were tested involving different austenite conditions produced by variation of the deformation temperature. The deformed conditions, recrystallized or work‐hardened, exhibit higher ductility at all tempering temperatures tested. A combined thermomechanical treatment is proposed that provides the highest ductility after tempering at 300°C independent of the phosphorus content. All thermomechanical treatments described in this study refine or eliminate carbide films at prior austenite grain boundaries. It was found possible to increase the tensile strength and the fatigue limit by deformation of austenite prior to quenching while maintaining or increasing the ductility level. 相似文献
12.
Retained austenite and tempered martensite embrittlement 总被引:4,自引:0,他引:4
The problems of detecting the distribution of small amounts (5 pct or less) of retained austenite films around the martensite
in quenched and tempered experimental medium carbon Fe/c/x steels are discussed and electron optical methods of analysis are
emphasized. These retained austenite films if stable seem to be beneficial to fracture toughness. It has been found that thermal
instability of retained austenite on tempering produces an embrittlement due to its decomposition to interlath films of M3C carbides. The fractures are thus intergranular with respect to martensite but transgranular with respect to the prior austenite.
The temperature at which this occurs depends upon alloy content. The effect is not found in Fe/Mo/C for which no retained
austenite is detected after quenching, but is present in all other alloys investigated. 相似文献
13.
Phosphorus as a tramp element deteriorates the toughness and enhances the brittle fracture in high strength steels. Even very low bulk concentrations can cause severe enrichment on the prior austenite grain boundaries. This seriously restricts the applicability of highly demanded vehicle components. Three approaches were chosen to reduce the detrimental effect of phosphorus in quenched and tempered high strength CrV‐steels for high power leaf springs: Change in the chemistry (addition of boron for repelling phosphorus from the grain boundaries), application of thermomechanical treatment (TMT) instead of conventional heat treatment (CHT) (producing lattice defects as intragranular traps for phosphorus atoms) and optimizing the tempering process (balancing grain boundary segregation and lattice restoration). Whereas no effect of boron was determined, TMT reduces the sensitivity to phosphorus and leads to better ductility, especially for the highest strength Rm > 2000 MPa. The best strength ‐ ductility combination was found for the range of tempering temperatures ?temp between 280 and 330 °C even for phosphorus contaminated steels. Outside of this range of ?temp, there is a significant deterioration of ductility for P ≥ 0.02 %. Independent of P‐content, there is a dramatic decrease in 0.2 % proof strength for ?temp decreasing below 280 °C due to residual internal stresses. 相似文献
14.
Isothermal tempering at 500 °C (within the region rendering low alloy steels susceptible to reversible temper embrittlement)
induced acoustic emission activity in A533B steel during indentation loading. Samples, when sectioned, were found to contain
small (∼10 μm long) MnS inclusions, some of which had debonded from the matrix material when they were near the indentations.
Hydrogen charging prior to testing greatly enhanced the acoustic emission activity. It also resulted in the formation of small
(∼20 to 200 μm) microcracks in samples tempered at 500 °C. These microcracks, when examined by optical metallography, appear
to have propagated along prior austenite grain boundaries, consistent with fractographic observations of temper embrittlement
in other low alloy steels. Many were nucleated by MnS inclusion debonding and all were confined to within a few hundred micrometers
of the sample surface and within two or three indenter diameters from the indent. It is proposed that trace impurities (P,
As, Sb, Sn) diffuse during the 500 °C temper to both the MnS inclusion interfaces and the prior austenite grain boundaries,
reducing local cohesive strength. The tensile field created by the indenter debonds inclusions to form crack nuclei. Moderate
acoustic emission results. In the absence of hydrogen these void nuclei may grow but do not coalesce to form observable cracks.
The prior austenite grain boundaries, which in contrast to the dispersed inclusions can provide continuous crack paths, are
not sufficiently temper embrittled to fracture without the assistance of hydrogen at these stresses. Hydrogen charging induces
a high hydrogen concentration in a surface layer of the sample. This reduces further the grain boundary cohesion, and cracks
initiated at inclusions are able to propagate along continuous grain boundary paths, generating additional energetic acoustic
emission signals. This process can continue after unloading the indenter due to hydrogen diffusion to the residual stress
field. 相似文献
15.
A study of the structure and mechanical properties of Fe-Cr-Mo-C martensitic steels with and without boron addition has been
carried out. Nonconventional heat treatments have subsequently been designed to improve the mechanical properties of these
steels. Boron has been known to be a very potent element in increasing the hardenability of steel, but its effect on structure
and mechanical properties of quenched and tempered martensitic steels has not been clear. The present results show that the
as-quenched structures of both steels consist mainly of dislocated martensite. In the boron-free steel, there are more lath
boundary retained austenite films. The boron-treated steel shows higher strengths at all tempering temperatures but with lower
Charpy V-notch impact energies. Both steels show tempered martensite embrittlement when tempered at 350 °C for 1 h. The properties
above 500 °C tempering are significantly different in the two steels. While the boron-free steel shows a continuous increase
in toughness when tempered above 500 °C, the boron-treated steel suffers a second drop in toughness at 600 °C tempering. Transmission
electron microscopy studies show that in the 600 °C tempered boron-treated steel large, more or less continuous cementite
films are present at the lath boundaries, which are probably responsible for the embrittlement. The differences in mechanical
properties at tempering temperatures above 500 °C are rationalized in terms of the effect of boron-vacancy interactions on
the recovery and recrystallization behavior of these steels. Although boron seems to impair room temperature impact toughness
at low strength levels, it does not affect this property at high strength levels. By simple nonconventinal heat treatments
of the present alloys, martensitic steels may be produced with quite good strength-toughness properties which are much superior
to those of existing commercial ultra-high strength steels. It is also shown that very good combinations of strength and toughness
can be obtained with as-quenched martensitic steels. 相似文献
16.
Four commercial purity Ni-Cr-Mo-V steels of closely comparable bulk chemistry and grain size, but tempered to various strength
levels, were embrittled by exposure at 600°, 750°, and 850°F for times up to 35,000 hr. Maximum temper embrittlement occurred
at 850°F in all steels. Severe cases of embrittlement resulted in a marked decrease in tensile ductility and an intergranular
tensile fracture. Auger electron emission analysis showed that P, Sn, Ni, and Cr were segregated at prior austenite boundaries
in the steels exposed to 750° and 850°F. Increased segregation of phorphorus and tin was always accompanied by increased segregation
of nickel and chromium. The severity of grain boundary segregation increased with increasing values of fracture transition
temperature. Despite comparable bulk chemistry and grain size, the degree of segregation was different in different steels.
Under exposure conditions causing severe embrittlement, the FATT values displayed a strong dependence on the strength level
of the steel. In a giyen steel, while the composition and morphology of carbides at austenite boundaries were the same as
in the matrix, the density and size of carbides were much higher at the austenite boundaries. The preference of these boundaries
as fracture sites would seem to arise from two considerations, namely, a high degree of impurity and alloy element segregation
and the fact that the density and size of carbides at these boundaries is higher than that in the matrix.
On educational leave from Westinghouse Research Laboratories, Pittsburgh, Pa. 相似文献
17.
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
18.
Tempered martensite embrittlement (TME) was studied in vacuum-melted 4130 steel with either 0.002 or 0.02 wt pct P. TME was observed as a severe decrease in Charpy V-notch impact energy, from 46 ft-lb. at 200 °C to 35 ft-lb. at 300 °C in the low P alloy. The impact energy of the high P alloy was consistently lower than that of the low P alloy in all tempered conditions. Fracture was transgranular for all specimens; therefore, segregation of P to the prior austenitic grain boundaries was not a factor in the occurrence of TME. Analysis of load-time curves obtained by instrumented Charpy testing revealed that the embrittlement is associated with a drop in the pre-maximum-load and post-unstable-fracture energies. In specimens tempered at 400 °C the deleterious effect of phosphorus on impact energy became pronounced, a result more consistent with classical temper embrittlement rather than TME. A constant decrease in pre-maximum-load energy due to phosphorus content was observed. The pre-maximum-load energy decreases with increasing tempering temperature in the range of 200 °C to 400 °C, a result explained by the change in work hardening rate. Carbon extraction replicas of polished and etched as-quenched specimens revealed the presence of Fe2MoC and/or Fe3C carbides retained after austenitizing. Ductile crack extension close to the notch root was related to the formation of fine microvoids at the retained carbides. 相似文献
19.
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
20.
V. V. Berezovskaya R. A. Savrai E. A. Merkushkin A. V. Makarov 《Russian Metallurgy (Metally)》2012,2012(5):380-388
The structure, mechanical properties, and pitting corrosion of nickel-free high-nitrogen (0.8% N) austenitic 06Kh18AG19M2 and 07Kh16AG13M3 steels have been studied in various structural states obtained after hot deformation, quenching, and tempering at 300 and 500°C. Both steels are shown to be resistant to the ?? ?? ?? and ?? ?? ? martensite transformations irrespective of the decomposition of a ?? solid solution (06Kh18AG19M2 steel). Austenite of the steel with 19 wt % Mn shows lower resistance to recrystallization, which provides its higher plasticity (??5) and fracture toughness at a lower strength as compared to the steel with 13 wt % Mn. Electrochemical studies of the steels tempered at 300 and 500°C show that they are in a stable passive state during tests in a 3.5% NaCl solution and have high pitting resistance up to a potential E pf = 1.3?C1.4 V, which is higher than that in 12Kh18N10T steel. In the quenched state, the passive state is instable but pitting formation potentials E pf retain their values. In all steels under study, pitting is shown to form predominantly along the grain boundaries of nonrecrystallized austenite. The lowest pitting resistance is demonstrated by the structure with a double grain boundary network that results from incomplete recrystallization at 1100°C and from the existence of initial and recrystallized austenite in the 07Kh16AG13M3 steel. To obtain a set of high mechanical and corrosion properties under given rolling conditions (1200?C1150°C), annealing of the steels at temperatures no less than 1150°C (for 1 h) with water quenching and tempering at 500°C for 2 h are recommended. 相似文献