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1.
Li Zhao-Dong Miyamoto Goro Yang Zhi-Gang Furuhara Tadashi 《Metallurgical and Materials Transactions A》2011,42(6):1586-1596
Substitutional alloying effects on reversion kinetics from pearlite structure at 1073 K (800 °C) in an Fe-0.6 mass pct C binary
alloy and Fe-0.6C-1 or 2 mass pct M (M = Mn, Si, Cr) ternary alloys were studied. Reverse transformation in the Fe-0.6C binary
alloy at 1073 K (800 °C) was finished after holding for approximately 5.5 seconds. The reversion kinetics was accelerated
slightly by the addition of Mn but retarded by the addition of Si or Cr. The difference of acceleration effects by the addition
of the 1 and 2 mass pct Mn is small, whereas the retardation effect becomes more significant by increasing the amount of addition
of Si or Cr. It is clarified from the thermodynamic viewpoint of carbon diffusion that austenite can grow without partitioning
of Mn or Si in the Mn- or Si-added alloys. On the one hand, austenite growth is controlled by the carbon diffusion, whereas
the addition of them affects carbon activity gradient, resulting in changes in reversion kinetics. On the other hand, thermodynamic
calculation implies that the long-range diffusion of Cr is necessary for austenite growth in the Cr-added alloys. It is proposed
that austenite growth from pearlite in the Cr-added alloys is controlled by the diffusion of Cr along austenite/pearlite interface. 相似文献
3.
While the kinetics of intermetallic phase formation in duplex stainless steel have been extensively studied for a wide range of compositions, relatively little research has been done on the mechanisms by which the phases nucleate and grow. In this research the emphasis was on the diffusional growth of the sigma (σ) and chi (χ) phases. Intermetallic phase precipitation in a standard DSS type EN 1.4462 was studied in detail at two temperatures: at 850 °C where large amounts of σ phase are formed, and at 650 °C where χ is the main intermetallic phase. The redistribution of the substitutional alloying elements Cr, Mo, Ni, Mn and Si between the ferrite, the austenite and the intermetallic phases was followed by means of scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDX). Mn and Si showed no distinct partitioning between the several phases. The diffusion paths of the other elements were found to be determined by two phenomena. On the one hand, the ferrite to austenite transformation causes Mo and Cr to enrich in the ferritic phase and Ni to enrich in the austenite. On the other hand, Mo (σ, χ) and Cr (σ) are removed from the ferrite by intermetallic phase precipitation. At 650 °C, strong Mo enrichments appear at the α‐γ phase boundaries indicating that grain boundary diffusion could be an important mechanism for Mo to diffuse to the growing χ phase. 相似文献
4.
The parabolic rate constant for the thickening of grain boundary ferrite allotriomorphs at the faces of austenite grain boundaries
was measured as a function of isothermal transformation temperature in three Fe-C-X1-X2 alloys where X1 is Mn and X2 is successively Si, Ni, and Co. The results were compared with the predictions of the local equilibrium model for multi-component
systems and with those derived from the theory of growth under paraequilibrium conditions. The distribution of Mn and Si in
ferrite and austenite in the Fe-C-Mn-Si alloy was also measured as a function of reaction temperature with transmission electron
microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The observed temperature below which alloying element partition
ceased was in good agreement with the local equilibrium model. Whereas the parabolic rate constant for thickening was considerably
larger than the amount predicted by this theory in the alloying element diffusion-controlled regime, the opposite was true
in the carbon diffusion-controlled regime. Similarly, the calculated paraequilibrium constant was usually considerably larger
than that measured experimentally. Synergistic enhancements of the effects of Mn and X2 in diminishing thickening kinetics were observed for each X2. The time-temperature-transformation (TTT) curves for the beginning of transformation were calculated from a modified Cahn
analysis for the overall kinetics of grain-boundary-nucleated reactions using values of the nucleation rate and the parabolic
growth rate constant computed from various models and compared with experimentally determined TTT curves. Substantial discrepancies
between the calculated and measured curves were ascribed to synergistic effects of Mn and X2 upon nucleation and growth kinetics.
Formerly Graduate Student, Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA
Formerly Mehl Professor Emeritus at Carnegie Mellon University. 相似文献
5.
6.
The influence of the Si and Mn concentrations on the kinetics of the bainite transformation in Fe-C-Si-Mn alloys 总被引:1,自引:0,他引:1
Five Fe-C-Si-Mn alloys were investigated by dilatometry, optical microscopy, and transmission electron microscopy (TEM) analysis
to determine the effects of Si and Mn content and austenitizing temperatures on the kinetics of bainite transformation. Segregation
of Mn at prior austenite grain boundaries at a temperature below Bs was detected by the scanning transmission electron microscopy + energy dispersive spectroscopy (STEM + EDS) and secondary
ion mass spectroscopy (SIMS) techniques. The fraction of intragranular ferrite increases with Mn content. The time needed
for the initiation of the bainite transformation tends to decrease as the austenitizing temperature decreases. The results
obtained were compared with those from Fe-0.38C-1.73Si and Fe-0.38C-3.11Mn alloys. Equilibrium and nonequilibrium segregation
of Mn at prior austenite grain boundaries and the effect of the interaction between Si and Mn on the segregation of Mn are
used to explain the results obtained and the large difference between the kinetics of the two ternary alloys and those of
the Fe-C-Si-Mn alloys.
This paper is based on a presentation made in the symposium “International Conference on Bainite” presented at the 1988 World
Metals Congress in Chicago, IL, on September 26 and 27, 1988, under the auspices of the ASM INTERNATIONAL Phase Transformations
Committee and the TMS Ferrous Metallurgy Committee. 相似文献
7.
Joon Jeong Yi In Sup Kim Hyung Sup Choi 《Metallurgical and Materials Transactions A》1985,16(7):1237-1245
Partial austenitization during the intercritical annealing of an Fe-2.2 pct Si-1.8 pct Mn-0.04 pct C steel has been investigated on four kinds of starting microstructures. It has been found that austenite formation during the annealing can be interpreted in terms of a carbon diffusion-limited growth process. The preferential growth of austenite along the ferrite grain boundaries was explained by the rapid carbon supply from the dissolving carbide particles to the growing fronts of austenite particles along the newly formed austenite grain boundaries on the prior ferrite grain boundaries. The preferential austenitization along the grain boundaries proceeded rapidly, but the austenite growth became slowed down after the ferrite grain boundaries were site-saturated with austenite particles. When the ferrite grain boundaries were site-saturated with austenite particles in a coarse-grained structure, the austenite particles grew by the mode of Widmanstätten side plate rather than by the normal growth mode of planar interface displacement. 相似文献
8.
Parabolic rate constants for the thickening (α) and lengthening (β) kinetics of grain boundary allotriomorphs of proeutectoid ferrite have been measured as a function of isothermal transformation
temperature in several Fe-C-X’ alloys whereX = Si, Ni, Mn, and Cr. These constants have been corrected approximately for the growth inhibition produced by facets on the
allotriomorphs. The corrected α values are compared with those calculated on the basis of three models: equilibrium at α:γ
boundaries with partition ofX, local equilibrium with “pile-up” ofX rather than bulk partition, and paraequilibrium. Values calculated from both the paraequilibrium and the “pile-up” models
were in order of magnitude or better agreement with the corrected experimental α’s. Similar levels of agreement were obtained
for the equilibrium model in the Si and Cr alloys and also in one Ni alloy at lower reaction temperatures. However, an estimate
of the maximum possible diffusion distance of alloying element into austenite during growth supported only the paraequilibrium
model under nearly all conditions investigated. Even for this model, however, measured rate constants are significantly less
than those calculated for Fe-C-Mn and Fe-C-Cr and greater for Fe-C-Si and the higher Ni, Fe-C-Ni alloy. The Mn and Cr discrepancies
seem best explained at present by a solute drag-like effect; an accompanying paper indicates that interphase boundary precipitation
of carbides is involved in the Si and Ni alloys, though an inverse solute drag-like effect may also be operative.
Formerly graduate student, Department of Metallurgical Engineering, Michigan Technological University.
Formerly Professor at Michigan Technological University. 相似文献
9.
The nucleation kinetics of proeutectoid ferrite allotriomorphs at austenite grain boundaries in Fe-0.5 at. Pct C-3 at. Pct
X alloys, where X is successively Mn, Ni, Co, and Si and in an Fe-0.8 at. Pct C-2.5 at. Pct Mo alloy have been measured using
previously developed experimental techniques. The results were analyzed in terms of the influence of substitutional alloying
elements upon the volume free energy change and upon the energies of austenite grain boundaries and nucleus: matrix boundaries.
Classical nucleation theory was employed in conjunction with the pillbox model of the critical nucleus applied during the
predecessor study of ferrite nucleation kinetics at grain boundaries in Fe-C alloys. The free energy change associated with
nucleation was evaluated from both the Hillert-Staffanson and the Central Atoms Models of interstitial-substitutional solid
solutions. The grain boundary concentrations of X determined with a Scanning Auger Microprobe were utilized to calculate the
reduction in the austenite grain boundary energy produced by the segregation of alloying elements. Analysis of these data
in terms of nucleation theory indicates that much of the influence of X upon ferrite nucleation rate derives from effects
upon the volume-free energy change,i.e., upon alterations in the path of theγ/(α + γ) phase boundary. Additional effects arise from reductions in austenite grain boundary energy, with austenite-forming alloying
elements being more effective in this regard than ferrite-formers. By difference, the remaining influence of the alloy elements
studied evidently results from their ability to diminish the energies of the austenite: ferrite boundaries enclosing the critical
nucleus. The role of nucleation kinetics in the formation of a bay in the TTT diagram of Fe-C-Mo alloys is also considered.
Formerly Graduate Student, Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University 相似文献
10.
The formation of austenite from different microstructural conditions has been studied in a series of 1.5 pct Mn steels that
had been heated in and above the intercritical (α+ γ) region of the phase diagram. The influence of variables such as cementite morphology, initial structural state of the ferrite
and the carbon content has been assessed in terms of their respective effects on the kinetics of austenite formation and final
microstructure. Austenite was found to form preferentially on ferrite-ferrite grain boundaries for all initial structures.
The results of this study have shown that the 1.5 pct Mn has lowered both the AC3 and AC1, lines causing large amounts of austenite to form in low carbon steel. The kinetics of austenite formation at 725 °C were
not only very slow but also were approximately independent of the amount formed. Austenite appeared to form slightly more
rapidly from cold rolled ferrite than from recrystallized ferrite or ferrite-pearlite structures. 相似文献
11.
Ferrite nucleation and growth during continuous cooling 总被引:7,自引:0,他引:7
M. Militzer R. Pandi Ph.D. Student E. B. Hawbolt 《Metallurgical and Materials Transactions A》1996,27(6):1547-1556
The austenite decomposition has been investigated in two hypoeutectoid plain carbon steels under continuous cooling conditions
using a dilatometer on a Gleeble 1500 thermomechanical simulator. The experimental results were used to verify model calculations
based on a fundamental approach for the dilute ternary system, Fe-C-Mn. The austenite-to-ferrite transformation start temperature
can be predicted from a nucleation model for slow cooling rates and small austenite grain sizes, where ferrite nucleates at
austenite grain corners. The nuclei are assumed to have an equilibrium composition and a pillbox shape in accordance with
minimal interfacial energy. For higher cooling rates or larger austenite grain sizes, early growth has to be taken into account
to describe the transformation start, and nucleation is also encouraged at the remaining sites of the austenite grain boundaries.
In contrast to nucleation, growth of the ferrite is characterized by paraequilibrium;i.e., only carbon can redistribute, whereas the diffusion of Mn is too slow to allow full equilibrium in the ternary system. However,
Mn segregation to the moving ferrite-austenite interface has to be considered. The latter, in turn, exerts a solute draglike
effect on the boundary movement. Thus, growth kinetics are controlled by carbon diffusion in austenite modified by interfacial
segregation of Mn. Employing a phenomenological segregation model, good agreement has been achieved with the measurements.
This article is based on a presentation made during TMS/ASM Materials Week in the symposium entitled “Atomistic Mechanisms
of Nucleation and Growth in Solids,” organized in honor of H.I. Aaronson’s 70th Anniversary and given October 3–5, 1994, in
Rosemont, Illinois. 相似文献
12.
The kinetics of ferrite nucleation at austenite grain edges in Fe-C and Fe-C-X alloys 总被引:1,自引:0,他引:1
M. Enomoto W. F. Lange H. I. Aaronson 《Metallurgical and Materials Transactions A》1986,17(8):1399-1407
Nucleation kinetics of proeutectoid ferrite allotriomorphs at the edges of austenite grains in Fe-C and Fe-C-X alloys, where
X is successively Mn, Ni, Co, and Si, have been measured using a modification of the techniques previously developed to study
nucleation at grain faces. Analysis of these data with classical heterogeneous nucleation theory has shown that ferrite nuclei
formed at grain edges have low energy interphase boundaries. An equivalent conclusion was reached during our previous studies
of ferrite nucleation at austenite grain faces. The influence of alloying elements on nucleation rates was also found to follow
a pattern similar to that demonstrated for grain face nucleation.
Formerly Graduate Student with the Department of Metallurgical Engineering and Materials Science, Carnegie-Mellon University, 相似文献
13.
H. Guo G. R. Purdy M. Enomoto H. I. Aaronson 《Metallurgical and Materials Transactions A》2006,37(6):1721-1729
A low-carbon balloy steel with relatively high Mn and Si concentrations (0.04 wt pct C-3 wt pct Mn-1.9 wt pct Si) has been
used to explore the effects of alloy chemistry and austenite grain size on ferrite growth. Even at high levels of supersaturation,
the volume fraction of ferrite is found to increase slowly relative to the relaxation time for carbon diffusion. A series
of scanning transmission electron microscopy (STEM) analyses for Mn indicates that initial unpartitioned ferrite growth is
replaced by partitioned growth, accompanied by a dramatic drop in growth rate, and a persistent level of residual supersaturation
in the remaining austenite. The results are interpreted in terms of a transition from an initial paraequilibrium interfacial
condition to partitioned ferrite growth.
This article is based on a presentation made in the “Hillert Symposium on Thermodynamics & Kinetics of Migrating Interfaces
in Steels and Other Complex Alloys,” December 2–3, 2004, organized by The Royal Institute of Technology in Stockholm, Sweden. 相似文献
14.
The overall kinetics of the isothermal transformation of austenite to ferrite and bainite at intermediate temperatures and
the microstructure of the transformation products in Fe-C-Ti, Fe-C-Ti-Si, Fe-C-Ti-Mn, and Fe-C-Ti-Mn-Si alloys were investigated
with dilatometry, quantitative metallography, and TEM. The rate of transformation of austenite is retarded and the precipitation
of carbide is inhibited in Ti-containing alloys by additions of Si, Mn, or Si + Mn. In addition to bainite and degenerate
ferrite plates, a large amount of granular structure consisting of martensite and retained austenite (so-called granular bainite)
is observed in these alloys if the isothermal reaction time is not long enough to complete austenite decomposition. It is
suggested that the inhibiting effect of Si on carbide precipitation, the segregation of carbideforming elements to prior γ
grain boundaries and interphase interfaces, and the enhancing effect of Si on the segregation of these elements lead to the
results obtained. The results also support the view that so-called granular bainite is a mixture of transformation products
produced by the partial decomposition of austenite.
Former Graduate Student, Southwest Jiaotong University
This paper is based on a presentation made in the symposium “International Conference on Bainite” presented at the 1988 World
Metals Congress in Chicago, IL, on September 26 and 27, 1988, under the auspices of the ASM INTERNATIONAL Phase Transformations
Committee and the TMS Ferrous Metallurgy Committee. 相似文献
15.
Intragranular ferrite nucleation in medium-carbon vanadium steels 总被引:10,自引:0,他引:10
Fusao Ishikawa Toshihiko Takahashi Tatsurou Ochi 《Metallurgical and Materials Transactions A》1994,25(5):929-936
In this study, the mechanism of intragranular ferrite nucleation is investigated. It is found that “intragranular ferrite
idiomorphs” nucleate at vanadium nitrides which precipitate at manganese sulfide particles during cooling in the austenite
region. It is observed that intragranular ferrite has the Baker-Nutting orientation relationship with vanadium nitride which
precipitated at manganese sulfide. According to classical nucleation theory, the proeutectoid ferrite nucleation rate depends
on the following factors: (1) the driving free energy for ferrite nucleation, (2) the diffusivity of carbon atoms in austenite,
and (3) the increase in the interfacial energy associated with ferrite nucleation. In the Baker-Nutting orientation relationship,
the lattice mismatch across the habit planes is likely to be very small. Depleted zones of solute atoms such as vanadium are
assumed to be formed in the austenite matrix around precipitates. The effect of the depleted zones on factors (1) and (2)
is estimated thermodynamically and it is proved that those effects are negligibly small. Thus, we conclude that the most important
factor in nucleation kinetics of intragranular ferrite is the formation of precipitates which can develop coherent, low energy
interfaces with ferrite. 相似文献
16.
On the growth kinetics of grain boundary ferrite allotriomorphs 总被引:1,自引:0,他引:1
C. Atkinson H. B. Aaron K. R. Kinsman H. I. Aaronson 《Metallurgical and Materials Transactions B》1973,4(3):783-792
Previous work has shown that the thickening kinetics of proeutectoid ferrite allotriomorphs in an Fe-0.11 pct C alloy are
often more rapid than the kinetics calculated for volume diffusion-control from the Dube-Zener equation for the migration
of a planar boundary of infinite extent, assuming the diffusivity of carbon in austenite,D, to be constant at that of the carbon content of the Ae3. Recalculating the thickening kinetics, using a numerical analysis
of the infinite planar boundary problem previously developed by Atkinson in which the variation ofD with composition is taken fully into account, was found to increase this discrepancy. Measurements were then made of the
lengthening as well as the thickening kinetics of grain boundary allotriomorphs in the same alloy. Application to these data
of Atkinson’s numerical analysis of the growth kinetics of an oblate ellipsoid, in which the composition-dependence ofD is similarly considered, produced an acceptable accounting for nearly all of the data. It was concluded that the growth of
ferrite allotriomorphs is primarily controlled by the volume diffusion of carbon in austenite; the presence of a small proportion
of dislocation facets along one of the broad faces of the allotriomorphs, however, usually results in growth kinetics which
are somewhat slower. An alternate treatment of the lengthening and thickening data upon the basis of the theory of interfacial
diffusion-aided growth of allotriomorphs indicated that, in the temperature range investigated (735° to 810°C),the diffusivities
of carbon along γ:γ and γ:α boundaries required for this mechanism to make a significant contribution to growth are too high
to be physically plausible.
Formerly with Scientific Research Staff
Formerly with Scientific Research Staff, Ford Motor Company 相似文献
17.
The chemical composition of precipitated austenite in 9Ni steel 总被引:1,自引:0,他引:1
B. Fultz J. I. Kim Y. H. Kim J. W. Morris 《Metallurgical and Materials Transactions A》1986,17(6):967-972
Analytical scanning transmission electron microscopy and a novel Mössbauer spectrometry technique were used to measure the chemical composition of austenite particles which precipitate during intercritical tempering of 9Ni steel. Both techniques showed an enrichment of Ni, Mn, Cr, and Si in the austenite. A straightforward analysis involving data on both austenite composition and austenite formation kinetics suggests that the growth of austenite particles is controlled by a 3-dimensional diffusion process. The segregation of solutes to the austenite accounts for much of its stability against the martensitic transformation at low temperatures. Composition inhomogeneities develop in austenite particles after long temperings; the central regions of the particles are lean in solutes and are first to undergo the martensitic transformation. However, changes in solute concentrations of the austenite during long temperings seem too small to account for the large changes in austenite stability. It appears that some of the stability of precipitated austenite must be microstructural in origin. 相似文献
18.
The selective oxidation of Twinning Induced Plasticity (TWIP) steel during annealing at 800 °C in a N2 + 10%H2 gas atmosphere with a dew point of ?17 °C and ?3 °C was investigated by means of high resolution transmission electron microscopy of cross‐sectional samples. The annealing resulted in the selective oxidation of Mn and Si and the austenite‐to‐ferrite phase transformation of the sub‐surface region. In the low dew point atmosphere, the annealing resulted in the formation of a MnO layer at the surface. Crystalline c –xMnO · SiO2 (x ≥ 2) particles and amorphous a –xMnO · SiO2 (x < 0.9) particles were found at the interface between the MnO layer and the steel matrix. In a narrow zone of the sub‐surface, the Mn depletion resulted in the transformation of the initial austenite. In the high dew point atmosphere, a thicker MnO layer was formed on the surface and no mixed manganese‐silicon oxides particles were observed at the MnO/steel matrix interface. In the sub‐surface, Mn was significantly depleted in the range of 2–3 µm below the surface and the initial austenite in this zone was transformed to ferrite. MnO particles were found at the grain boundaries and in the interior of grains. 相似文献
19.
The microstructural evolutions of the cold rolled Fe-0.1C-5Mn steel during intercritical annealing were ex- amined using combined advanced techniques. It was demonstrated that intercritical annealing results in an ultrafine granular ferrite and austenite duplex structure in cold rolled 0.1C-5Mn steel. The strong partitioning of manganese and carbon elements from ferrite to austenite was found during intercritical annealing by scanning transmission elec- tron microscopy (STEM) and X-ray diffraction (XRD). Strong effects of boundary characters on the austenite for- mation were indicated by austenite fast nucleation and growth in the high angle boundaries but sluggish nucleation and growth in the low angle boundaries. The ultrafine grained duplex structure in 0.1C-5Mn was resulted from the the sluggish Mn-diffusion and the extra high Gibbs free energy of ferrite phase. Based on the analysis of the micro- structure evolution, it was pointed out that the intercritical annealing of the medium Mn steels could be applied to fabricate an ultrafine duplex grained microstructure, which would be a promising approach to develop the 3rd genera- tion austomobile steels with excellent combination of strength and ductility. 相似文献
20.
M. M. Souza J. R. C. Guimarães K. K. Chawla 《Metallurgical and Materials Transactions A》1982,13(4):575-579
With the introduction of dual phase steels, it is increasingly becoming important to obtain a thorough understanding of intercritical
austenitization phenomena. Quantitative microscopy techniques were used to study the process of intercritical austenitization
(740°C) of two Fe-Mn-C steels, one of them being microalloyed with Nb. The two steels showed essentially the same kinetics,viz., three stages of intercritical austenitization: (i) austenite growth into pearlite until complete pearlite dissolution, (ii)
growth of austenite into ferrite, and (iii) equilibration of ferrite and austenite. However, compared to data published by
other researchers, the maximum amount of austenite, in our case, was reached much faster. Ferrite-ferrite interface processes
and preferred nucleation at particles in the ferrite boundaries accelerated the austenite growth. Austenite growth out of
pearlite colonies was asymmetric due to the fast ferrite-ferrite interface processes. 相似文献