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1.
The temperature change due to the conversion of mechanical deformation to internal heat and its effect on the as-measured
stress-strain behavior of alloy 304L was investigated by means of initially isothermal (compression specimen, dies, and environment
at same temperature at initiation of test), constant strain rate, uniaxial compression of laboratory-sized cylindrical specimens.
Strain rate was varied in the range 0.01 to 1 s−1, where the thermal state of the test specimen varied from nearly isothermal to nearly adiabatic, respectively. Specimens
were deformed in the temperature range of 750 °C to 1150 °C to a strain of 1. The change in specimen temperature with applied
strain was calculatedvia finite-element analysis (FEA) from the asmeasured stress-strain data. Selected predictions were confirmed with embedded thermocouples
to verify the model employed. Temperature was found to increase monotonically with strain at a strain rate of 1 s-1, consistent with what is theoretically expected for the adiabatic case. At the 0.1 and 0.01 s-1 rates, the sample temperature initially increased, peaked, and then decreased as the sample thinned and the contact area
between the sample and the cooler dies increased. As-measured stress was corrected for softening associated with deformational
heating by interpolation between the various instantaneous stress-temperature behaviors. The resulting isothermal flow data
are compared to those predicted by a conventional method that employs an empirical estimate of the heat retention efficiency
of the test specimen, assumed dependent on strain rate but independent of strain, to reduce the increase in temperature calculated
for the adiabatic case. Differences between the calculated isothermal stress-strain data from the two methods are discussed.
Values for the apparent activation energy of deformation and the strain to the peak in the flow curve, which is associated
with the onset of dynamic recrystallization, determined from isothermal stress-strain data differed significantly from those
obtained from the as-measured compression test data.
Formerly Senior Systems Engineer with EG&G Rocky Flats, Inc., is retired. 相似文献
2.
Yeon-Seung Jung Young-Kook Lee David K. Matlock Martin C. Mataya 《Metals and Materials International》2011,17(4):553-556
Tensile tests were used to investigate the effect of grain size on the strain-induced martensitic transformation start temperature
in metastable austenitic steel with special attention to ultrafine grain size. The austenite grains were refined to submicron
size by the strain-induced martensite and its reverse transformations (SIMRT), which occurred during a conventional cold rolling
and annealing process. The start temperature of the straininduced martensitic transformation was linearly lowered with a decrease
in austenite grain size, even down to submicron grain sizes. This result is due to the decrease in grain size causing an increase
in the temperature dependency of the strain-induced martensitic transformation and higher austenite stability brought about
by grain refinement. 相似文献
3.
Deformation-induced phase transformation and strain hardening in type 304 austenitic stainless steel 总被引:1,自引:0,他引:1
Amar K. De John G. Speer David K. Matlock David C. Murdock Martin C. Mataya Robert J. Comstock Jr. 《Metallurgical and Materials Transactions A》2006,37(6):1875-1886
Deformation-induced phase transformation in a type 304 austenitic stainless steel has been studied in tension at room temperature
and −50 °C. The evolution of transformation products was monitored using X-ray diffraction (XRD) line profile analysis of
diffraction peaks from a single XRD scan employing the direct comparison method. Crystallographic texture transitions due
to deformation strain have been evaluated using (111)
γ
pole figures. The tensile stress-strain data have been analyzed to explain the influence of underlying deformation-induced
microstructural changes and associated texture changes in the steel. It is found that the initial stage of rapidly decreasing
strain hardening rate in type 304 steel is primarily influenced by hcp ɛ-martensite formation, and the second stage of increasing
strain hardening rate is associated with an increase in the α′-martensite formation. The formation of ɛ-martensite is associated
with a gradual strengthening of the copper-type texture components up to 15 pct strain and decreasing with further strain
at −50 °C. Texture changes during low-temperature deformation not only change the mechanism of ɛ-martensite formation but
also influence the strain rate sensitivity of the present steel. 相似文献
4.
M. C. Mataya C. A. Perkins S. W. Thompson D. K. Matlock 《Metallurgical and Materials Transactions A》1996,27(5):1251-1266
The stress-strain behavior and the development of microstructure between 850 °C and 1150 °C in an austenitic stainless steel,
22Cr-13Ni-5Mn-0.3N, were investigated by uniaxial compression of cylindrical specimens at strain rates between 0.01 and 1
s-1 up to a strain of one. The measured (anisothermal) and corrected (isothermal) flow curves were distinctly different. The
flow stress at moderate hot working temperatures, compared to a number of other austenitic alloys, was second only to that
of alloy 718. Both static and dynamic recrystallization were observed. Recrystallization was sluggish in comparison to alloy
304L, apparently due to the presence of a fine Cr- and Nb-rich second-phase dispersion, identified as Z phase, which tended
to pin the high-angle grain boundaries even at a high temperature of 1113 °C. Recrystallization may also be retarded by preferential
res-toration through the competitive process of recovery, which is consistent with the relatively high stacking-fault energy
for this alloy. It is concluded that this alloy must be hot worked at temperatures higher than usual for austenitic stainless
steels in order to minimize flow stress and refine grain size. 相似文献
5.
Kester D. Clarke Robert J. ComstockJr. Martin C. Mataya Chester J. van Tyne David K. Matlock 《Metallurgical and Materials Transactions A》2008,39(4):752-762
The effect of strain rate on the yield stress of ferritic stainless steel sheet was experimentally determined and a previously
developed model was applied to the data. Five ferritic stainless steel alloys, including one in two thicknesses, were mechanically
tested at room temperature in uniaxial tension at strain rates ranging from 0.001 to 300 s−1, and low-strain-rate tests were selectively performed at nonambient temperatures. The hypothesis that ferritic stainless
steels react similarly to strain rate as mild steels was investigated by the application of a widely accepted strengthening
model, based on body-centered-cubic (bcc) crystal lattice deformation mechanisms, to the experimental data.[1] Yield stresses were compared to model predictions and good agreement was found. The results allow for the prediction of
yield stresses for these materials over strain rate ranges of 0.001 to 300 s−1, and as a function of test temperature. Model parameters for the ferritic stainless steels were reasonable relative to those
previously reported for pure bcc ferritic iron.[1] A correlation between the effect of alloying additions on solid solution strengthening and the athermal component of shear
stress is also suggested. The results allow prediction of yield stress of ferritic stainless steels over a wide range of strain
rates and temperatures.
This article is based on a presentation made in the symposium entitled “Dynamic Behavior of Materials,” which occurred during
the TMS Annual Meeting and Exhibition, February 25–March 1, 2007 in Orlando, Florida, under the auspices of The Minerals,
Metals and Materials Society, TMS Structural Materials Division, and TMS/ASM Mechanical Behavior of Materials Committee.
相似文献
Kester D. Clarke (Graduate Research Assistant)Email: |
6.
7.
The formability of austenitic stainless steels 总被引:1,自引:0,他引:1
S. F. Peterson M. C. Mataya D. K. Matlock 《JOM Journal of the Minerals, Metals and Materials Society》1997,49(9):54-58
This article reports the results of a study to determine the effects of austenite stability, with respect to the strain-induced
transformation to martensite, on the formability of 300 series stainless steels. The effects were evaluated as a function
of alloy content, deformation temperature, and deformation rate. Three stainless-steel alloys with different nickel contents
were evaluated as commercially cold-rolled and annealed sheet products. Tensile tests were performed at temperatures between
−60°C and +125°C and at strain rates from 0.00167 s−1 to 0.167 s−1. The combined effects of strain, strain state, deformation-induced temperature changes, and strain rate are considered to
explain the interrelationships between martensite formation and limit strains as observed in forming-limit diagrams.
S.F. Peterson earned his M.S. in metallurgical and materials engineering from the Colorado School of Mines in 1997. He is currently an
engineer at Case Corporation.
M.C. Mataya earned his Ph.D. in metallurgy and materials science from Marquette University in 1976. He is currently an engineer at the
Rocky Flats Technology Site.
D.K. Matlock earned his Ph.D. in materials science and engineering from Stanford University in 1972. He is currently a professor at the
Colorado School of Mines. Dr. Matlock is also a member of TMS. 相似文献
8.
D. W. Brown S. P. Abeln W. R. Blumenthal M. A. M. Bourke M. C. Mataya C. N. Tomé 《Metallurgical and Materials Transactions A》2005,36(4):929-939
Weakly textured hot-pressed (HP) beryllium and strongly textured hot-rolled beryllium were compressed using a split-Hopkinson
pressure bar (SHPB) (strain rate ∼4500 s−1) to a maximum of 20 pct plastic strain as a function of temperature. The evolution of the crystallographic texture was monitored
with neutron diffraction and compared to polycrystal plasticity models for the purpose of interpretation. The macroscopic
response of the material and the active deformation mechanisms were found to be highly dependent on the orientation of the
load with respect to the initial texture. Specifically, twinning is inactive when loaded parallel to the strong basal fiber
but accounts for 27 pct of the plastic strain when loaded transverse to the basal fiber. In randomly textured samples, 15
pct of the plastic strain is accomplished by twinning. The role of deformation mechanisms with components out of the basal
plane (i.e., twinning and pyramidal slip) is discussed. 相似文献
9.
The development of microstructure and strength during forging in a γ′ strengthened austenitic stainless steel, JBK-75, was
investigated by means of forward extrusion of cylindrical specimens. The specimens were deformed in a strain range of 0.16
to 1.0, from 800°C to 1080°C, and at approximate strain rates of 2 (press forging) and 2 × 103 s-1 (high energy rate forging), and structures examined by light and transmission microscopy. Mechanical properties were determined
by tensile testing as-forged and forged and aged specimens. The alloy exhibited an extremely wide variety of structures and
properties within the range of forging pzrameters studied. Deformation at the higher strain ratevia high energy rate forging resulted in unrecovered substructures and high strengths at low forging temperatures, and static
recrystallization and low strengths at high temperatures. In contrast, however, deformation at the lower strain ratevia press forging resulted in retention of the well developed subgrain structure and associated high strength produced at high
forging temperatures and strains. At lower temperatures and strains during press forging a subgrain structure formed preferentially
at high angle grain boundaries, apparently by a creep-type deformation mechanism. Dynamic recrystallization was not an important
restoration mechanism for any of the forging conditions. The results are interpreted on the basis of stacking fault energy
and the accumulation of strain energy during hot working. The significance of observed microstructural differences for equivalent
deformation conditions (iso-Z, where Z is the Zener-Holloman parameter) is discussed in relation to the utilization of Z for
predicting hot work structures and strengths. Aging showed that the γ′ precipitation process is not affected by substructure
and that the strengthening contributions, from substructure and precipitation, were independent and additive. Applications
for these findings are discussed in terms of process design criteria.
Formerly with Rockwell International, Energy Systems Group 相似文献
10.
Flow localization and shear band formation in a precipitation strengthened austenitic stainless steel 总被引:2,自引:0,他引:2
Flow localization and shear band formation in a γ′ strengthened austenitic stainless steel, JBK-75, was investigated by means
of compression of reduced-gage-section, cylindrical specimens. The specimens were deformed in a strain rate range of 103 to l03s-1 and from 650 °C to 1100 °C. The alloy exhibited an extreme susceptibility for macroscopic localized flow when the microstructure
contained fine γ′ precipitates on the order of 10 nm. At high strain rates localized flow in the precipitate containing structures
took the form of macroscopic, transgranular shear bands. At low strain rates the localized flow occurred mainly in precipitate-free
zones along high angle grain boundaries. Localized flow was always associated with the occurrence of dynamic recrystallization.
Other mechanisms for flow localization, including the effects of adiabatic heating on γ′ precipitate dissolution, are discussed. 相似文献