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1.
The relative effects of austenite stacking fault energy and austenite yield strength on martensite morphology have been investigated
in a series of three Fe-Ni-Cr-C alloys. Carbon content (0.3 wt pct) andM
6 temperature (− 15°) were held constant within the series. Austenite yield strength atM
s was measured by extrapolating elevated temperature tensile data. Austenite stacking fault energy was measured by the dislocation
node technique. Martensite morphologies were characterized by transmission electron microscopy and electron diffraction techniques.
A transition from plate to lath martensite occurred with decreasing austenite stacking fault energy. The austenite yield strength
atM
s for the low SFE, lath-forming alloy was found to be higher than previously reported for lath-forming alloys. The relative
effects of these variables on martensite morphologies in these alloys is discussed. 相似文献
2.
The effect of austenite yield strength on the transformation to martensite was investigated in Fe-10 pct Ni-0.6 pct C alloys.
The strength of the austenite was varied by 1) additions of yttrium oxide particles to the base alloy and 2) changing the
austenitizing temperature. The austenite strength was measured at three temperatures above theM
s temperature and the data extrapolated to the experimentally determinedM
s temperature. It is shown that the austenite yield strength is determined primarily by the austenite grain size and that the
yttrium oxide additions influence the effect of austenitizing temperature on grain size. As the austenite yield strength increases,
both theM
s temperature and the amount of transformation product at room temperature decrease. The effect of austenitizing temperature
on the transformation is to determine the austenite grain size. The results are consistent with the proposal1 that the energy required to overcome the resistance of the austenite to plastic deformation is a substantial portion of the
non-chemical free energy or restraining force opposing the transformation to martensite. 相似文献
3.
A series of dispersion strengthened Fe-Ni alloys has been prepared by powder metallurgical techniques. This series was designed
to permit evaluation of the relative effects of Ms temperature, chemical driving force, and austenite yield strength on resultant martensite morphology without altering matrix
chemistry. Using a carefully selected lath-forming Fe-27Ni-.025C base alloy, incremental additions of an inert oxide dispersion
resulted in a decrease in Ms temperature, an increase in the thermodynamic driving force at Ms, and an increase in the austenite yield strength at Ms to values beyond those previously associated with the lath-to-plate morphology transition. As the Ms temperature dropped below about 0 °C, martensite morphology shifted from lath to an intermediate “twinned lath” to plate,
while holding constant both matrix chemistry and thermal history. Previous correlations of thermodynamic driving force and
austenite yield strength with martensite morphology have been shown to break down. It is concluded that the observed transition
from lath to plate martensite in the present alloy series was induced primarily by the depression of Ms temperature into the plate-forming temperature regime of the Fe-Ni system. 相似文献
4.
J. R. Strife M. J. Carr G. S. Ansell 《Metallurgical and Materials Transactions A》1977,8(9):1471-1484
The effect of austenite prestrain above theM
d
temperature on the structure and transformation kinetics of the martensitic transformation observed on cooling was determined
for a series of Fe-Ni-Cr-C alloys. The alloys exhibited a shift in martensite morphology in the nondeformed state from twinned
plate to lath while theM
s
temperature, carbon content, and austenite grain size were constant. The transformation behavior was observed over the temperature
range 0 to -196°C as a function of tensile prestrains performed above theM
d
temperature. A range of prestrains from 5 pct to 45 pct was investigated. It is concluded that the response of a given alloy
to austenite prestrain above theM
d
temperature can be correlated with the morphology of the martensite observed in the nondeformed, as-quenched state. For the
range of prestrains investigated, the transformation of austenite to lath martensite is much more susceptible to stabilization
by austenite prestrain above theM
d
temperature than is the transformation of austenite to plate martensite. 相似文献
5.
The resistance of austenite to plastic deformation (austenite flow stress) was measured using a high temperature tensile apparatus.
The flow stress was then correlated with the Ms temperature as determined magnetically during subsequent cooling. In one part of the study, the flow stress of the austenite
was varied only by work hardening the austenite, allowing the austenite composition, which is known to affect Ms, to be held constant. A decrease in Ms temperature with increasing austenite flow stress was observed. This observation was supported by the observation of a decrease
in the amount of austenite transformed at 25°C. In the other part of the study, a series of alloy steels of different chemical
compositions was tested. A decrease in Ms temperature with increasing austenite flow stress was again observed. Strengthening of austenite by plastic deformation was
shown not to change the chemical driving force for transformation. The effect of deformation on Ms temperature thus results from its influence on either the nucleation or the growth process. While the effect of austenite
deformation on martensite nucleation is uncertain, specific nucleation models can account for only approximately one-third
of the nonchemical free energy change which accompanies transformation. A proposal, consistent with the observations, was
made that the energy expended for the deformation of austenite during martensite plate growth could reasonably account for
a substantial part of the nonchemical free energy change. 相似文献
6.
Dieter Fahr 《Metallurgical and Materials Transactions B》1971,2(7):1883-1892
The effects of deformation-induced formation of martensite have been studied in metastable austenitic stainless steels. The stability of the austenite, being the critical factor in the formation of martensite, was controlled principally by varying the amounts of carbon and manganese. The formation of martensite was also affected by different test and rolling temperatures, rolling time, and various reductions in thickness. The terms “stress-induced” and “strain-induced” formation of martensite are defined. Experimental results show that low austenite stability resulted in stress-induced formation of martensite, high work-hardening rates, high tensile strengths, low “yield strengths,” and low elongation values. When the austenite was stable, plastic deformation was initiated by slip, and the work-hardening rate was too low to prevent early necking. A specific amount of strain-induced martensite led to an “optimum” work-hardening rate, resulting in high strengthand high ductility. For best results processing should be carried out aboveM d and testing betweenM d andM s. Mechanical working aboveM d had a negligible effect on the yield strength betweenM d andM s when the austenite stability was low, but its effect increased as the austenite became, more stable. Serrations appeared in the stress-strain curve when martensite was strain induced. 相似文献
7.
《Acta Metallurgica Materialia》1994,42(12):4117-4133
The stabilization effect of retained austenite has been studied using FeNiC alloys with Ms temperatures below 0°C via a two-step cooling procedure, i.e. the samples were first cooled to a temperature (Ta) below Ms temperature and then heated to room temperature (RT), after being held at RT for a while, the samples were recooled to low temperatures (23 or 82 K) and then heated to RT. It was found that, during the second step of cooling, the martensitic transformation occurred at a temperature of Ms′ which was lower than Ta. With increasing the amount of martensite formed during the first cooling, the difference in the martensitic transformation starting temperatures, ΔMs = Ms − Ms′, increased. The mechanism of the stabilization of retained austenite during the second step of cooling is proposed to be mainly due to the inhibition effect produced by the previously formed martensite. The aging processes, which retard the growth of the previously formed martensite plates and reduce the number of the available nucleation sites, are the necessary conditions for the above mechanism to operate. By simplifying the internal resisting stress acting on the retained austenite due to the existence of martensite phase as a hydrostatic compressive stress, which increases with increasing the amount of martensite, the change in ΔMs is discussed from a thermodynamic point of view. 相似文献
8.
D. A. Colling 《Metallurgical and Materials Transactions B》1971,2(10):2889-2896
The martensite ⇌ austenite transformations were investigated in Fe-Ni-Co alloys containing about 65 wt pct Fe and up to 15
wt pct Co. A change in morphology of martensite from plate-like to lath-type occurred with increasing cobalt content; this
change in morphology correlates with the disappearance of the Invar anomaly in the austenite. The martensite-to-austenite
reverse transformation differed depending on martensite morphology. Reversion of plate-like martensite was found to occur
by simple disintegration of the martensite platelets. Reverse austenite formed from lath-type martensite was not retained
when quenched from much aboveA
s, with microcracks forming during theM→γ→M transformation. 相似文献
9.
Stress-Assisted and strain-induced martensites in FE-NI-C alloys 总被引:3,自引:0,他引:3
P. C. Maxwell A. Goldberg J. C. Shyne 《Metallurgical and Materials Transactions B》1974,5(6):1305-1318
A metallographic study was made of the martensite formed during plastic straining of metastable, austenitic Fe-Ni-C alloys
withM
s
temperatures below 0°C. A comparison was made between this martensite and that formed during the deformation of two TRIP
steels. In the Fe-Ni-C alloys two distinctly different types of martensite formed concurrently with plastic deformation. The
large differences in morphology, distribution, temperature dependence, and other characteristics indicate that the two martensites
form by different transformation mechanisms. The first type, stress-assisted martensite, is simply the same plate martensite
that forms spontaneously belowM
s
except that it is somewhat finer and less regularly shaped than that formed by a temperature drop alone. This difference
is due to the stress-assisted martensite forming from cold-worked austenite. The second type, strain-induced martensite, formed
along the slip bands of the austenite as sheaves of fine parallel laths less than 0.5μm wide strung out on the {111}γ planes of the austenite. Electron diffraction indicated a Kurdjumov-Sachs orientation for the strain-induced martensite relative
to the parent austenite. No stress-assisted, plate martensite formed in the TRIP steels; all of the martensite caused by deformation
of the TRIP steels appeared identical to the strain-induced martensite of the Fe-Ni-C alloys. It is concluded that the transformation-induced
ductility of the TRIP steels is a consequence of the formation of strain-induced martensite.
Formerly a graduate student at Stanford University 相似文献
10.
Xiang-Mingh He Li-Jian Rong Yi-Yi Li De-Sheng Yan Zhi-Min Jiang 《Metallurgical and Materials Transactions A》2004,35(9):2783-2788
The shape-memory characteristics in the Ni41.3Ti38.7Nb20 alloy have been investigated by means of cryogenic tensile tests and differential scanning calorimetry measurement. The martensite
start temperature M
s
could be adjusted to around the liquid nitrogen temperature by controlling the cooling condition. The reverse transformation
start temperature A′
s
rose to about 70 °C after the specimens were deformed to 16 pct at different temperatures, where the initial states of the
specimens were pure austenite phase, martensite phase, or duplex phase. The shape-memory effect and the reverse transformation
temperatures were studied on the specimens deformed at (M
s
+30 °C). It was found that once the specimens deformed to 16 pct, a transformation hysteresis width around 200 °C could be
attained and the shape recovery ratio could remain at about 50 pct. The Ni41.3Ti38.7Nb20 alloy is a promising candidate for the cryogenic engineering applications around the liquid nitrogen temperature. The experimental
results also indicated that the transformation temperature interval of the stress-induced martensite is smaller by about one
order of magnitude than that of the thermal-induced martensite. 相似文献
11.
The effect of high quench rate on theM
s
temperature, percent transformed, martensite morphology and austenite hardness has been studied for several Fe-Ni-C steels.
For these steels the quench rate was varied only in the austenite region. TheM
s
temperature was found to increase with increased quench rate for both high- and low carbon steels while the percent transformation
increased or decreased depending upon the morphology of the steel. No variations in martensite hardness were found in the
as-quenched condition, but a difference in tempering rate was found between fast and slow quenched specimens. Austenite hardness
decreased slightly with increasing quench rate while the martensite morphology changed from lath to plate. Parallel aligned
plate structures were observed which resemble a twinned lath morphology. It was demonstrated that the actual difference between
this morphology and a true lath morphology is the self-accommodating nature of the lath structure. The morphology changes
were compared to the measured changes in martensite properties in order to identify the mechanism of the morphology shift.
It was concluded that for these alloys the morphology was controlled by the austenite shear mode.
S. J. Donachie was formerly a Graduate Assistant. 相似文献
12.
A. A. Hussein 《Metallurgical and Materials Transactions A》1982,13(5):837-846
Dual-phase (α + martensite) microstructures were produced in binary Cu-Al alloys by quenching from the (α + β) phase field.
A wide range of martensite volume fraction VM was obtained, depending on alloy composition and quench temperatureT. Linear dependence onT of VM was established. Predefined values for VM can thus be achieved by adjustment ofT and alloy composition. Furthermore, the size, shape, and distribution of component phases can be varied in a predetermined
fashion by means of controlled cooling from the β range. The properties of α and martensite were tracedvia microhardness measurements. The microhardness of martensite increases with quench temperature in spite of the accompanying
decrease of its solute content. This is in accord with previous work and emphasizes the dominating role of martensite ordered
structure on strength. Such strength depends only on quench temperature irrespective of overall alloy composition or morphology.
The α microhardness is not affected by alloy composition or quench temperature. The martensitic phase can be hardened by means
of short time tempering due to order hardening or solute clustering effects. Depending on quench temperature, optimum use
of such temper hardening can be achieved. Moreover, cold working of dual-phase structures followed by annealing at temperatures
around 300 °C achieves substantial strengthening of both α and martensite. The strengthening of α is a consequence of anneal
hardening. Although such high strength levels are accompanied by reduction of the ductility (as measured by thickness reduction
achieved by cold rolling), the heat treatment schedule can be optimalized to achieve high strength while restoring ductility. 相似文献
13.
An investigation of the phase transformation and the austenite stabilization in a high strength austenite has been made. An
Fe-29Ni-4.3Ti austenite age-hardened byγ′(Ni3Ti) precipitates showed a further increase of strength after martensitic and reverse martensitic phase transformations. The
stability of ausaged austenite as well as ausaged and transformation-strengthened austenite was improved significantly through
an isothermal treatment at 500°C. TheM
s
temperature of the strengthened austenite was restored to nearly that of annealed austenite while the austenite was hardened
toR
c
41 through precipitation and phase transformations. The observed austenite stabilization is attributed to the formation of
G.P. zones or short-range order of less than ∼10? size.
Formerly with University of California, Berkeley 相似文献
14.
A. I. Uvarov V. A. Sandovskii N. F. Vil’danova E. I. Anufrieva 《Russian Metallurgy (Metally)》2008,(4):347-353
The effect of the generator current frequency f on the magnetic permeability μ of the N30K10T3 invar is studied for its various structural states formed upon the following treatments: phase naklep (i.e., the phase-transformation-induced hardening of austenite), cold plastic deformation, and cooling in liquid nitrogen. The ferromagnetic austenite of the alloy is metastable with respect to the γ → α martensite transformation upon cooling to temperatures below the temperature of the onset of the martensite transformation (M s ≈ ?80°C) and represents a supersaturated solid solution ageable during heating. The types of treatment are shown not to change the linear character of the μ(f) dependence in the frequency range under study (15–50 kHz) and to decrease μ to a certain extent. 相似文献
15.
A. I. Uvarov V. A. Kazantsev N. F. Vil’danova E. I. Anufrieva 《Russian Metallurgy (Metally)》2010,(3):223-228
The N30K10T3 invar that has a temperature of the onset of martensite transformation of austenite M
s ≈ −80°C and a Curie point θC ≈ 200°C after water-quenching from 1150°C is studied. The decomposition of a supersaturated solid solution is shown to substantially
influence the linear thermal expansion coefficient. The alloy is studied in the following three initial states: after quenching,
after phase transformation-induced hardening (γ → αm → γp.h), and after cold (20°C) plastic deformation by 30%. 相似文献
16.
Three stabilization mechanisms—the shortage of nuclei, the partitioning of alloying elements, and the fine grain size—of the
remaining metastable austenite in transformation-induced plasticity (TRIP) steels have been studied by choosing a model alloy
Fe-0.2C-1.5Mn-1.5Si. An examination of the nucleus density required for an athermal nucleation mechanism indicates that such
a mechanism needs a nucleus density as large as 2.5 · 1017 m−3 when the dispersed austenite grain size is down to 1 μm. Whether the random nucleation on various heterogeneities is likely
to dominate the reaction kinetics depends on the heterogeneous embryo density. Chemical stabilization due to the enrichment
of carbon in the retained austenite is the most important operational mechanism for the austenite retention. Based on the
analysis of 57 engineering steels and some systematic experimental results, an exponential equation describing the influence
of carbon concentration on the martensite start (M
s) temperature has been determined to be M
s (K)=273+545.8 · e
−1.362w
c(mass pct). A function describing the M
s temperature and the energy change of the system has been found, which has been used to study the influence of the grain size
on the M
s temperature. The decrease in the grain size of the dispersed residual austenite gives rise to a significant decrease in the
M
s temperature when the grain size is as small as 0.1 μm. It is concluded that the influence of the grain size of the retained
austenite can become an important factor in decreasing the M
s temperature with respect to the TRIP steels. 相似文献
17.
The characteristics of the B2(β) to L10(β′) martensitic transformation in NiAl base alloys containing a small amount of third elements have been investigated by
differential scanning calorimetry (DSC), X-ray diffraction (XRD), and transmission electron microscopy (TEM). It is found
that in addition to the normal Ll0 (3R) martensite, the 7R martensite is also present in the ternary alloys containing Ti, Mo, Ag, Ta, or Zr. While the addition
of third elements X (X: Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ta, W, and Si) to the binary Ni64Al36 alloy stabilizes the parentβ phase, thereby lowering the Ms temperature, addition of third elements such as Co, Cu, or Ag destabilizes theβ phase, increasing the Ms temperature. The occurrence of the 7R martensite structure is attributed to solid solution hardening arising from the difference
in atomic size between Ni and Al and the third elements added. The variation in Ms temperature with third element additions is primarily ascribed to the difference in lattice stabilities of the bcc and fcc
phases of the alloying elements. 相似文献
18.
E. Cingolani M. Ahlers J. Van Humbeeck 《Metallurgical and Materials Transactions A》1999,30(3):493-499
The two-way shape memory effect (TWME) induced by stabilization of the martensite phase during aging has been studied in Cu-13.4
Al-4.0 Ni (mass pct) single crystals. The influence of the degree of long-range order on the transformation has been determined
by using different heat treatments. The transformation temperatures are strongly influenced by the degree of order in the
austenite: annealing from above or below the second neighbor L21 ordering temperature changes the M
s
by more than 100 °C. It has been established that the diffusion in the austenite as well as in the martensite phase is considerably
slower in this alloy than in other Cu-based ones, due to the presence of Ni. The obtained TWME has a similar efficiency as
when other more complex thermomechanical trainings are made. In this alloy, the TWME by stabilization is not complete, in
contrast to that in Cu-Zn-Al single crystals. 相似文献
19.
Z. M. Shi Jian Li B. Chi J. Pu Y. S. Zhang M. Q. Wang J. Shi H. Dong 《Metallurgical and Materials Transactions A》2013,44(9):4136-4142
Non-isothermal compressive deformation was performed on high strength steel 22SiMn2TiB for the study of martensitic phase transformation from deformed austenite. The transformation start temperature M s decreased with the increase of deformation from 0 to 50 pct, and the variation of deformation rate (0.1 and 10 s?1) and the appearance of deformation-induced ferrite and bainite showed no influence on the change of M s temperature. The deformation at both the rates increased the volume fraction of retained austenite; however, the carbon content of retained austenite decreased at 10 s?1 and remained basically unchanged at 0.1 s?1. The yield strength of austenite at M s temperature and the stored energy in deformed austenite were experimentally obtained, with which the relationships between the change of M s temperature and the thermodynamic driving force for martensitic phase transformation from deformed austenite were established by the use of the Fisher-ADP–Hsu model. And finally, the transformation kinetics was analyzed by the Magee–Koistinen–Marhurger equation. 相似文献
20.
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