共查询到20条相似文献,搜索用时 15 毫秒
1.
Yasuharu Sakuma David K. Matlock George Krauss 《Metallurgical and Materials Transactions A》1992,23(4):1221-1232
Steels containing 0.15 pct C and 1.2 pct Si-1.5 pct Mn or 4 pct Ni were intercritically annealed and isothermally transformed
between 300 °C and 500 °C for 1 to 60 minutes. The specimens were subjected to tensile testing at room temperature, and the
microstructures were evaluated by light microscopy, scanning and transmission electron microscopy (SEM and TEM, respectively),
and X-ray diffraction (XRD). The microstructures consist of dispersed regions of bainite, martensite, and austenite in a matrix
of ferrite, and a maximum of 11.6 pct austenite is retained after isothermal holding at 450 °C in the Si-Mn steel. In specimens
where austenite transforms to martensite during quenching after isothermal holding, the stress-strain curves show continuous
yielding, high ultimate tensile strength (UTS), and relatively low ductility. In specimens where higher volume fractions of
austenite transform to bainite during isothermal holding, the stress-strain curves show discontinuous yielding, low UTS, and
high ductility. 相似文献
2.
Erin J. Barrick Divya Jain John N. DuPont David N. Seidman 《Metallurgical and Materials Transactions A》2017,48(12):5890-5910
10 wt pct Ni steel is a high-strength steel that possesses good ballistic resistance from the deformation induced transformation of austenite to martensite, known as the transformation-induced-plasticity effect. The effects of rapid heating and cooling rates associated with welding thermal cycles on the phase transformations and microstructures, specifically in the heat-affected zone, were determined using dilatometry, microhardness, and microstructural characterization. Heating rate experiments demonstrate that the Ac3 temperature is dependent on heating rate, varying from 1094 K (821 °C) at a heating rate of 1 °C/s to 1324 K (1051 °C) at a heating rate of 1830 °C/s. A continuous cooling transformation diagram produced for 10 wt pct Ni steel reveals that martensite will form over a wide range of cooling rates, which reflects a very high hardenability of this alloy. These results were applied to a single pass, autogenous, gas tungsten arc weld. The diffusion of nickel from regions of austenite to martensite during the welding thermal cycle manifests itself in a muddled, rod-like lath martensitic microstructure. The results of these studies show that the nickel enrichment of the austenite in 10 wt pct Ni steel plays a critical role in phase transformations during welding. 相似文献
3.
M. Arbab Rehan Anna Medvedeva Lars-Erik Svensson Leif Karlsson 《Metallurgical and Materials Transactions A》2017,48(11):5233-5243
Retained austenite transformation was studied for a 5 wt pct Cr cold work tool steel tempered at 798 K and 873 K (525 °C and 600 °C) followed by cooling to room temperature. Tempering cycles with variations in holding times were conducted to observe the mechanisms involved. Phase transformations were studied with dilatometry, and the resulting microstructures were characterized with X-ray diffraction and scanning electron microscopy. Tempering treatments at 798 K (525 °C) resulted in retained austenite transformation to martensite on cooling. The martensite start (M s ) and martensite finish (M f ) temperatures increased with longer holding times at tempering temperature. At the same time, the lattice parameter of retained austenite decreased. Calculations from the M s temperatures and lattice parameters suggested that there was a decrease in carbon content of retained austenite as a result of precipitation of carbides prior to transformation. This was in agreement with the resulting microstructure and the contraction of the specimen during tempering, as observed by dilatometry. Tempering at 873 K (600 °C) resulted in precipitation of carbides in retained austenite followed by transformation to ferrite and carbides. This was further supported by the initial contraction and later expansion of the dilatometry specimen, the resulting microstructure, and the absence of any phase transformation on cooling from the tempering treatment. It was concluded that there are two mechanisms of retained austenite transformation occurring depending on tempering temperature and time. This was found useful in understanding the standard tempering treatment, and suggestions regarding alternative tempering treatments are discussed. 相似文献
4.
Metallographic studies have been conducted on a 0.024 pct C-16 pct Cr-1.5 pct Mo-5 pct Ni stainless steel to study the phase reactions associated with heat treatments and investigate the strengthening mechanisms of the steel. In the normalized condition, air cooled from 1010 °C, the microstructure consists of 20 pct ferrite and 80 pct martensite. Tempering in a temperature range between 500 and 600 °C results in a gradual transformation of martensite to a fine mixture of ferrite and austenite. At higher tempering temperatures, between 600 and 800 °C, progressively larger quantities of austenite form and are converted during cooling to proportionally increasing amounts of fresh martensite. The amount of retained austenite in the microstructure is reduced to zero at 800 °C, and the microstructure contains 65 pct re-formed martensite and 35 pct total ferrite. Chromium rich M23C6 carbides precipitate in the single tempered microstructures. The principal strengthening is produced by the presence of martensite in the microstructure. Additional strengthening is provided by a second tempering treatment at 400 °C due to the precipitation of ultrafine (Cr, Mo) (C,N) particles in the ferrite. 相似文献
5.
《Acta Metallurgica》1983,31(12):2037-2042
Tensile tests were conducted on a vanadium containing dual phase steel at temperatures between −53 and + 187°C to determine the effect of retained austenite stability on tensile properties. The transformation of retained austenite to martensite with stress/strain was shown to be a contributing factor in the yielding and strain hardening behavior of the dual phase steel. Increasing the stability of the austenite, by increasing the test temperature, caused the expected shift in the austenite to martensite strain transformation to higher strains. This led to a lower initial strain hardening exponent which increased with strain, compared to the ambient and sub-zero temperature deformation where the initial strain hardening exponent was higher but decreased with strain. The former behavior, which accentuated the strain hardening ability at higher strains, led to an increase in the uniform and total elongations, suggesting that the ductility of dual phase steels can be further improved by optimizing the stability of the retained austenite. 相似文献
6.
Tempered martensite-retained austenite microstructures were produced by direct quenching a series of 41XX medium carbon steels,
direct quenching and reheating a series of five 0.8C-Cr- Ni-Mo steels and intercritically austenitizing at various temperatures,
and quenching a SAE 52100 steel. All specimens were tempered either at 150 °C or at 200 °C. Specimens were subjected to compression
and tension testing in the microstrain regime to determine the elastic limits and microplastic response of the microstructures.
The retained austenite and matrix carbon content of the intercritically austenized specimens were measured by X-ray diffraction
and Mossbauer spectroscopy. The elastic limit of the microstructures decreases with increasing amounts of retained austenite.
Refining of the austenite distribution increases the elastic limit. Low elastic limits are mainly due to low flow stresses
in the austenite and not internal stresses. The elastic limit correlates with the largest austenite free-mean path by a Hall-Petch
type equation. The elastic limit increases with decreasing intercritical austenitizing temperature in the SAE 52100 due to
(1) a lower carbon content in the matrix reducing the retained austenite levels and (2) retained carbides that refine grain
size and, therefore, the austenite distribution in quenched specimens. The microplastic response of stable austenite-martensite
composites may be modeled by a rule of mixtures. In the microplastic region, the strain is accommodated by successively smaller
austenite regions until the flow strength matches that of the martensite. Reheating and quenching refines the microstructure
and renders the austenite unstable in the microplastic regime, causing transformation of the austenite to martensite by a
strain-induced mechanism. The transformation of austenite to martensite occurs by a stress-assisted mechanism in medium carbon
steels. The low elastic limits in medium carbon steels were due to the inability of the strain from the stress-assisted transformation
of austenite to martensite to balance the plastic strain accumulated in the austenite. 相似文献
7.
Ductility and strain-induced transformation in a high-strength transformation-induced plasticity-aided dual-phase steel 总被引:7,自引:0,他引:7
Koh-Ichi Sugimoto Mitsuyuki Kobayashi Shun-Ichi Hashimoto 《Metallurgical and Materials Transactions A》1992,23(11):3085-3091
The influence of forming temperature and strain rate on the ductility and strain-induced transformation behavior of retained
austenite in a ferritic 0.4C-1.5Si-1.5Mn (wt pct) dual-phase steel containing fine retained austenite islands of about 15
vol pct has been investigated. Ex- cellent combinations of total elongations (TELs), about 48 pct, and tensile strength (TS),
about 1000 MPa, were obtained at temperatures between 100 °C and 200 °C and at a strain rate of 2.8 X 10-4/s. Under these optimum forming conditions, the flow curves were characterized by intensive serrations and increased strain-hardening
rate over a large strain range. The retained austenite islands were mechanically the most stable at temperatures between 100
°C and 200 °C, and the retained austenite stability appeared to be mainly controlled by strain-induced martensite and bainite
transformations (SIMT and SIBT, respectively), with deformation twinning occur- ring in the retained austenite. The enhanced
TEL and forming temperature dependence of TEL were primarily connected with both the strain-induced transformation behavior
and retained aus- tenite stability. 相似文献
8.
Temperature Dependent Deformation Mechanisms of a High Nitrogen‐Manganese Austenitic Stainless Steel
The influence of temperature on the deformation behaviour of a Fe‐16.5Cr‐8Mn‐3Ni‐2Si‐1Cu‐0.25N (wt%) austenitic stainless steel alloy was investigated using transmission electron microscopy and X‐ray diffraction measurements. Recrystallized samples were deformed under tension at ?75°C, 20°C, and 200°C and the microstructures were characterized after 5% strain and after testing to failure. Deformation to failure at ?75°C resulted in extensive transformation induced plasticity (TRIP) with over 90% α′‐martensite. The sample deformed to 5% strain at ?75°C shows that the austenite transformed first to ?‐martensite which served to nucleate the α′‐martensite. Transformation induced martensite prohibits localized necking providing total elongation to failure of over 70%. At room temperature, in addition to some TRIP behaviour, the majority of the deformation is accommodated by dislocation slip in the austenite. Some deformation induced twinning (TWIP) was also observed, although mechanical twinning provides only a small contribution to the total deformation at room temperature. Finally, dislocation slip is the dominant deformation mechanism at 200°C with a corresponding decrease in total elongation to failure. These changes in deformation behaviour are related to the temperature dependence on the relative stability of austenite and martensite as well as the changes in stacking fault energy (SFE) as a function of temperature. 相似文献
9.
Martensite formation,strain rate sensitivity,and deformation behavior of type 304 stainless steel sheet 总被引:1,自引:0,他引:1
The strain and strain rate dependence of the deformation behavior of Type 304 stainless steel sheet was evaluated by constant
temperature tensile testing in the temperature range of −80 °C to 160 °C. The strain rate sensitivity, strain hardening rate,
and ductility reflected the compctition of two strengthening mechanisms: strain-induced transformation of austenite to martensite
and dislocation substructure formation. At low temperatures, the strain rate sensitivity and strain hardening rate correlated
with the strain-induced transformation rate. A maximum in total ductility occurred between 0 °C and 25 °C, and the contributions
of strain rate sensitivity and strain hardening to independent maxima with temperature of the uniform and post-uniform strains
are discussed.
Formerly Visiting Scientist, Department of Metallurgical Engineering, Colorado School of Mines. 相似文献
10.
G. R. Speich A. J. Schwoeble G. P. Huffman 《Metallurgical and Materials Transactions A》1983,14(5):1079-1087
Changes in the yield behavior, strength, and ductility of a Mn and a Mn-Si-V dual-phase (ferrite-martensite) steel were investigated after tempering one hour at 200 to 600 °C. The change in yield behavior was complex in both steels with the yield strength first increasing and then decreasing as the tempering temperature was increased. This complex behavior is attributed to a combination of factors including carbon segregation to dislocations, a return of discontinuous yielding, and the relief of residual stresses. In contrast, the tensile strength decreased continuously as the tempering temperature was increased in a manner that could be predicted from the change in hardness of the martensite phase using a simple composite strengthening model. The initial tensile ductility (total elongation) of the Mn-Si-V steel was much greater than that of the Mn steel. However, upon tempering up to 400 °C, the ductility of the Mn-Si-V decreased whereas that of the Mn steel increased. As a result, both steels had similar ductilities after tempering at 400 °C or higher temperatures. These results are attributed to the larger amounts of retained austenite in the Mn-Si-V steel (9 pct) compared to the Mn steel (3 pct) and its contribution to tensile ductility by transforming to martensite during plastic straining. Upon tempering at 400 °C, the retained austenite decomposes to bainite and its contribution to tensile ductility is eliminated. 相似文献
11.
A. Bojack L. Zhao P. F. Morris J. Sietsma 《Metallurgical and Materials Transactions A》2014,45(13):5956-5967
The formation of austenite during tempering of a 13Cr6Ni2Mo supermartensitic stainless steel (X2CrNiMoV13-5-2) was investigated using an in situ thermo-magnetic technique to establish the kinetics of the martensite to austenite transformation and the stability of austenite. The austenite fraction was obtained from in situ magnetization measurements. It was found that during heating to the tempering temperature 1 to 2 vol pct of austenite, retained during quenching after the austenitization treatment, decomposed between 623 K and 753 K (350 °C and 480 °C). The activation energy for martensite to austenite transformation was found by JMAK-fitting to be 233 kJ/mol. This value is similar to the activation energy for Ni and Mn diffusion in iron and supports the assumption that partitioning of Ni and Mn to austenite are mainly rate determining for the austenite formation during tempering. This also indicates that the stability of austenite during cooling after tempering depends on these elements. With increasing tempering temperature the thermal stability of austenite is decreasing due to the lower concentrations of austenite-stabilizing elements in the increased fraction of austenite. After cooling from the tempering temperature the retained austenite was further partially decomposed during holding at room temperature. This appears to be related to previous martensite formation during cooling. 相似文献
12.
S. Zhou K. Zhang Y. Wang J. F. Gu Y. H. Rong 《Metallurgical and Materials Transactions A》2012,43(3):1026-1034
The designed steel of Fe-0.25C-1.5Mn-1.2Si-1.5Ni-0.05Nb (wt pct) treated by a novel quenching-partitioning-tempering (Q-P-T)
process demonstrates an excellent product of strength and elongation (PSE) at deformed temperatures from 298 K to 573 K (25 °C
to 300 °C) and shows a maximum value of PSE (over 27,000 MPa pct) at 473 K (200 °C). The results fitted by the exponent decay
law indicate that the retained austenite fraction with strain at a deformed temperature of 473 K (200 °C) decreases slower
than that at 298 K (25 °C); namely, the transformation induced plasticity (TRIP) effect occurs in a larger strain range at
473 K (200 °C) than at 298 K (25 °C), showing better mechanical stability. The work-hardening exponent curves of Q-P-T steel
further indicate that the largest plateau before necking appears at the deformed temperature of 473 K (200 °C), showing the
maximum TRIP effect, which is due to the mechanical stability of considerable retained austenite. The microstructural characterization
reveals that the high strength of Q-P-T steels results from dislocation-type martensite laths and dispersively distributed
fcc NbC or hcp ε-carbides in martensite matrix, while excellent ductility is attributed to the TRIP effect produced by considerable retained
austenite. 相似文献
13.
G. R. Speich A. J. Schwoeble G. P. Huffman 《Metallurgical and Materials Transactions A》1983,14(6):1079-1087
Changes in the yield behavior, strength, and ductility of a Mn and a Mn-Si-V d11Al-phase (ferrite-martensite) steel were investigated
after tempering one hour at 200 to 600 °C. The change in yield behavior was complex in both steels with the yield strength
first increasing and then decreasing as the tempering temperature was increased. This complex behavior is attributed to a
combination of factors including carbon segregation to dislocations, a return of discontinuous yielding, and the relief of
resid11Al stresses. In contrast, the tensile strength decreased continuously as the tempering temperature was increased in
a manner that could be predicted from the change in hardness of the martensite phase using a simple composite strengthening
model. The initial tensile ductility (total elongation) of the Mn-Si-V steel was much greater than that of the Mn steel. However,
upon tempering up to 400 °C, the ductility of the Mn-Si-V decreased whereas that of the Mn steel increased. As a result, both
steels had similar ductilities after tempering at 400 °C or higher temperatures. These results are attributed to the larger
amounts of retained austenite in the Mn-Si-V steel (9 pct) compared to the Mn steel (3 pct) and its contribution to tensile
ductility by transforming to martensite during plastic straining. Upon tempering at 400 °C, the retained austenite decomposes
to bainite and its contribution to tensile ductility is eliminated.
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
14.
Effect of thermomechanical processing on the retained austenite content in a Si-Mn transformation-induced-plasticity steel 总被引:1,自引:0,他引:1
The influence of hot deformation on the microstructure of a hot-rolled Si-Mn transformation-induced-plasticity (TRIP) steel
was evaluated in an effort to better control retained austenite content. In this study, axial compressive strains varying
in amounts from 0 to 60 pct were imposed in the austenite phase field, and effects on the formation of polygonal ferrite,
bainite, and retained austenite were determined. In addition, modifications in simulated coiling temperature from 420 °C to
480 °C and cooling rates from the rolling temperature, between 10 °C/s and 35 °C/s, were assessed. Fast cooling rates, low
coiling temperatures, and low degrees of hot deformation were generally found to decrease the amount of polygonal ferrite
and increase retained austenite fraction. Unexpectedly, a sharp increase in polygonal ferrite content and decrease in retained
austenite content occurred when the fastest cooling rate, 35 °C/s, was coupled with extensive hot deformation and high coiling
temperatures. This effect is believed to be due to insufficient time for full recovery and recrystallization of the deformed
austenite, even in the absence of intentional microalloying additions to control recrystallization kinetics. The resultant
decrease in hardenability allowed the ferrite transformation to continue into the holding time at high (simulated) coiling
temperatures. 相似文献
15.
P. J. Gibbs E. De Moor M. J. Merwin B. Clausen J. G. Speer D. K. Matlock 《Metallurgical and Materials Transactions A》2011,42(12):3691-3702
Manganese enrichment of austenite during prolonged intercritical annealing was used to produce a family of transformation-induced
plasticity (TRIP) steels with varying retained austenite contents. Cold-rolled 0.1C-7.1Mn steel was annealed at incremental
temperatures between 848 K and 948 K (575 °C and 675 °C) for 1 week to enrich austenite in manganese. The resulting microstructures
are comprised of varying fractions of intercritical ferrite, martensite, and retained austenite. Tensile behavior is dependent
on annealing temperature and ranged from a low strain-hardening “flat” curve to high strength and ductility conditions that
display positive strain hardening over a range of strain levels. The mechanical stability of austenite was measured using
in-situ neutron diffraction and was shown to depend significantly on annealing temperature. Variations in austenite stability between
annealing conditions help explain the observed strain hardening behaviors. 相似文献
16.
17.
Cyclic deformation behavior of a transformation-induced plasticity-aided dual-phase steel 总被引:1,自引:0,他引:1
Koh-Ichi Sugimouto Mitsuyuki Kobayashi Shin-Ichi Yasuki 《Metallurgical and Materials Transactions A》1997,28(12):2637-2644
Cyclic hardening-softening behavior of a TRIP-aided dual-phase (TDP) steel composed of a ferrite matrix and retained austenite plus bainite second phase was examined at temperatures ranging from 20
°C to 200 °C. An increment of the cyclic hardening was related to (1) a long-range internal stress due to the second phase
and (2) the strain-induced transformation (SIT) behavior of the retained austenite, as follows. Large cyclic hardening, similar
to a conventional ferrite-martensite dual-phase steel, appeared in the TDP steel deformed at 20 °C, where the SIT of the retained
austenite occurred at an early stage. This was mainly caused by a large increase in strain-induced martensite content or strain-induced martensite hardening, with a small contribution of the internal stress. In this case, shear and expansion strains on the SIT considerably decreased
the internal stress in the matrix. With increasing deformation temperature or retained austenite stability, the amount of
cyclic hardening decreased with a significant decrease in plastic strain amplitude. This interesting cyclic behavior was principally
ascribed to the internal stress, which was enhanced by stable and strain-hardened retained austenite particles. 相似文献
18.
The effect of testing temperature on retained austenite (RA) stability of industrially cold rolled CMnSi sheet steel treated by quenching and partitioning (Q&P) process has been investigated by observing the deformation and transformation behavior of RA at different testing temperatures. Uniaxial tensile properties at different temperatures were determined and a correlation between RA stability and mechanical properties were also established. Ultimate tensile strength increases monotonously when temperature decreases, while total elongation reaches an optimum value between 0 and 20°C, where RA exhibits the greatest TRIP effect. Work hardening rate was calculated to decrease through three different stages in an oscillation manner, leading to significant enhancement in both strength and ductility. The kinetic of deformation‐induced martensite transformation is also studied and the stability of RA can be evaluated by comparing the kinetic parameter β. 相似文献
19.
M. J. Cieslak C. R. Hills P. F. Hlava S. A. David 《Metallurgical and Materials Transactions A》1990,21(9):2465-2475
Differential thermal analysis (DTA), high-temperature water-quench (WQ) experiments, and optical and electron microscopy were used to establish the near-solidus and solidification microstructures in PH 13-8 Mo. On heating at a rate of 0. 33 °C/s, this alloy begins to transform from austenite to δ-ferrite at ≈1350 °C. Transformation is complete by ≈1435 °C. The solidus is reached at ≈1447 °C, and the liquidus is ≈1493 °C. On cooling from the liquid state at a rate of 0. 33 °C/s, solidification is completed as δ-ferrite with subsequent transformation to austenite beginning in the solid state at ≈1364 °C. Insufficient time at temperature is available for complete transformation and the resulting room-temperature microstructure consists of matrix martensite (derived from the shear decomposition of the austenite) and residual δ-ferrite. The residual δ-ferrite in the DTA sample is enriched in Cr (≈16 wt pct), Mo (≈4 wt pct), and Al (≈1. 5 wt pct) and depleted in Ni (≈4 wt pct) relative to the martensite (≈12. 5 wt pct Cr, ≈2 wt pct Mo, ≈1 wt pct Al, ≈9 wt pct Ni). Solid-state transformation of δσ γ was found to be quench-rate sensitive with large grain, fully ferritic microstructures undergoing a massive transformation as a result of water quenching, while a diffusionally controlled Widmanstätten structure was produced in air-cooled samples. 相似文献
20.
The process of ausform-finishing in gears involves the deformation of metastable austenite. A critical step in optimizing
the deformation process is to determine the link between material deformation behavior and final material properties, such
as hardness and microstructure. To this end, uniaxial compression testing was carried out on 1 pct carburized AISI 9310 steel
specimens in the low-temperature ausforming regime (85 °C to 230 °C). The work-hardening response of metastable austenite
and its relation to the hardness and microstructure was determined from these experiments. High work-hardening rates (work-hardening
exponent n=0.4 to 0.7) were caused by deformation-induced transformation of metastable austenite to either martensite or bainite or
both. It is postulated that, at the ausforming temperatures in the neighborhood of 230 °C, bainite formed at the highest achievable
strains of 50 pct while oriented martensite (loading induced) was detectable at lower strains of 20 pct. The hardness of the
resulting ausformed microstructure increased with degree of straining and with reduction in temperature of ausforming. An
X-ray determination of the retained austenite content showed that austenite tends to stabilize even after minimal ausforming.
A transmission electron microscopy study on ausformed specimens showed the presence of microtwinning and high-dislocation
densities. The effect of processing parameters on fatigue response under rolling contact conditions is discussed given current
understanding and available fatigue data. 相似文献