Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality
Carbon distribution in the as-quenched Fe—C martensite obtained after cooling down to 4.5 K is studied using Mössbauer spectroscopy. The location of carbon atoms in the one of three available sublattices of octahedral interstitial sites is established, whereas the partial occupation by carbon atoms...
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Інститут металофізики ім. Г.В. Курдюмова НАН України
2016
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nasplib_isofts_kiev_ua-123456789-1125012025-02-23T17:03:22Z Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality Розподіл вуглецю в низькотемпературному мартенситі на основі заліза та його тетрагональність Распределение углерода в низкотемпературном мартенсите на основе железа и его тетрагональность Gavriljuk, V.G. Firstov, S.O. Sirosh, V.A. Tyshchenko, A.I. Mogilny, G.S. Дефекты кристаллической решётки Carbon distribution in the as-quenched Fe—C martensite obtained after cooling down to 4.5 K is studied using Mössbauer spectroscopy. The location of carbon atoms in the one of three available sublattices of octahedral interstitial sites is established, whereas the partial occupation by carbon atoms of tetrahedral sites or octahedral sites in other sublattices is not confirmed. The ageing of virgin isothermal martensite starts during heating at temperatures above -50°C and leads to disappearance of single carbon atoms and their clustering in the α solid solution. In comparison with martensite obtained at room temperature, a decreased tetragonality of the low-temperature isothermal martensite and its partial recovery during ageing is observed. Based on the estimation of dislocation density and the absence of ε-carbide precipitation during subsequent tempering, a conclusion is made that plastic deformation occurs in the course of isothermal martensitic transformation because of the softness of the virgin martensite. Finally, a new interpretation of the abnormally low tetragonality is proposed, of which the essence is the capture and transport of immobile carbon atoms by gliding dislocations. As a result, a part of carbon is removed from the α solid solution and forms carbon atmospheres around the dislocations. The comparison of this hypothesis with available other ones is presented. Two possible reasons for partial recovery of tetragonality during ageing of virgin martensite are discussed: (i) the unfreezing of Snoek atmospheres created by gliding dislocations crossing the immobile carbon atoms at low temperatures and (ii) coherent stresses at the boundaries of the intermittent carbon-rich and carbon-depleted domains in the modulated structure of the aged martensite. Розподіл вуглецю у свіжозагартованому Fe—C-мартенситі, одержаному в процесі охолодження до 4,5 К, досліджено методом Мессбауерівської спектроскопії. Встановлено розташування атомів Карбону в одній із трьох підґратниць октаедричних міжвузлів і не підтверджено часткову зайнятість ними інших підґратниць або тетраедричних міжвузлів. Розпад свіжозагартованого ізотермічного мартенситу починається при нагріванні вище -50°C і приводить до зникнення поодиноких атомів вуглецю в α-твердому розчині та утворення їх кластерів. У порівнянні з мартенситом, одержаним гартуванням за кімнатної температури, свіжозагартований низькотемпературний ізотермічний мартенсит характеризується зменшеною тетрагональністю, яка частково відновлюється при наступному нагріванні вище -50°C. Ґрунтуючись на оцінках густини дислокацій в одержаному низькотемпературному мартенситі та відсутності виділень ε-карбіду при наступному відпусканні, зроблено висновок, що, внаслідок низької міцности утвореного незастареного мартенситу, ізотермічне мартенситне перетворення супроводжується пластичною деформацією. В результаті запропоновано нову інтерпретацію аномально низької тетрагональности низькотемпературного мартенситу, суть якої полягає у захопленні та транспортуванні дислокаціями ковзання нерухомих атомів Карбону з видаленням їх із твердого розчину і утворенням Карбонових атмосфер в полі напружень дислокацій. Наведено її співставлення з наявними гіпотезами. Проаналізовано дві можливі причини часткового відновлення тетрагональности при старінні низькотемпературного мартенситу: (i) розморожування атмосфер Снука, утворених дислокаціями ковзання за низьких температур, і (ii) когерентні напруження на межах переміжних областей, збагачених та збіднених Карбоном у модульованій структурі застареного мартенситу. Распределение углерода в свежезакалённом Fe—C-мартенсите, полученном в процессе охлаждения до 4,5 К, исследовано методом мёссбауэровской спектроскопии. Установлено размещение атомов углерода в одной из трёх подрешёток октаэдрических междоузлий и не подтверждена частичная занятость ими других подрешёток или тетраэдрических междоузлий. Распад свежезакалённого изотермического мартенсита начинается при нагреве выше -50°C и приводит к исчезновению одиночных атомов углерода в α-твёрдом растворе и образованию их кластеров. В сравнении с мартенситом, полученным закалкой при комнатной температуре, свежезакалённый низкотемпературный изотермический мартенсит характеризуется пониженной тетрагональностью, которая частично восстанавливается при последующем нагреве выше -50°C. Основываясь на оценках плотности дислокаций в полученном мартенсите и отсутствии выделения ε-карбида при последующем отпуске, сделан вывод, что, вследствие низкой прочности образованного несостаренного мартенсита, изотермическое мартенситное превращение сопровождается пластической деформацией. В результате предложена новая интерпретация аномально низкой тетрагональности низкотемпературного мартенсита, суть которой заключается в захвате и транспорте дислокациями скольжения неподвижных атомов углерода с удалением их из твёрдого раствора и образованием углеродных атмосфер в поле напряжений дислокаций. Приведено её сопоставление с существующими гипотезами. Обсуждены две возможные причины частичного восстановления тетрагональности при старении низкотемпературного мартенсита: (i) размораживание атмосфер Снука, созданных движущимися дислокациями при низких температурах, и (ii) когерентные напряжения на границах чередующихся областей, обогащённых и обеднённых углеродом в модулированной структуре состаренного мартенсита. 2016 Article Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality / V. G. Gavriljuk, S. O. Firstov, V. A. Sirosh, A. I. Tyshchenko, and G. S. Mogilny // Металлофизика и новейшие технологии. — 2016. — Т. 38, № 4. — С. 455-475. — Бібліогр.: 67 назв. — англ. 1024-1809 DOI: 10.15407/mfint.38.04.0455 PACS: 61.05.cp, 61.72.Hh, 62.20.fq, 64.70.kd, 81.30.Hd, 81.30.Kf, 81.40.Lm https://nasplib.isofts.kiev.ua/handle/123456789/112501 en Металлофизика и новейшие технологии application/pdf Інститут металофізики ім. Г.В. Курдюмова НАН України |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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| topic |
Дефекты кристаллической решётки Дефекты кристаллической решётки |
| spellingShingle |
Дефекты кристаллической решётки Дефекты кристаллической решётки Gavriljuk, V.G. Firstov, S.O. Sirosh, V.A. Tyshchenko, A.I. Mogilny, G.S. Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality Металлофизика и новейшие технологии |
| description |
Carbon distribution in the as-quenched Fe—C martensite obtained after cooling down to 4.5 K is studied using Mössbauer spectroscopy. The location of carbon atoms in the one of three available sublattices of octahedral interstitial sites is established, whereas the partial occupation by carbon atoms of tetrahedral sites or octahedral sites in other sublattices is not confirmed. The ageing of virgin isothermal martensite starts during heating at temperatures above -50°C and leads to disappearance of single carbon atoms and their clustering in the α solid solution. In comparison with martensite obtained at room temperature, a decreased tetragonality of the low-temperature isothermal martensite and its partial recovery during ageing is observed. Based on the estimation of dislocation density and the absence of ε-carbide precipitation during subsequent tempering, a conclusion is made that plastic deformation occurs in the course of isothermal martensitic transformation because of the softness of the virgin martensite. Finally, a new interpretation of the abnormally low tetragonality is proposed, of which the essence is the capture and transport of immobile carbon atoms by gliding dislocations. As a result, a part of carbon is removed from the α solid solution and forms carbon atmospheres around the dislocations. The comparison of this hypothesis with available other ones is presented. Two possible reasons for partial recovery of tetragonality during ageing of virgin martensite are discussed: (i) the unfreezing of Snoek atmospheres created by gliding dislocations crossing the immobile carbon atoms at low temperatures and (ii) coherent stresses at the boundaries of the intermittent carbon-rich and carbon-depleted domains in the modulated structure of the aged martensite. |
| format |
Article |
| author |
Gavriljuk, V.G. Firstov, S.O. Sirosh, V.A. Tyshchenko, A.I. Mogilny, G.S. |
| author_facet |
Gavriljuk, V.G. Firstov, S.O. Sirosh, V.A. Tyshchenko, A.I. Mogilny, G.S. |
| author_sort |
Gavriljuk, V.G. |
| title |
Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality |
| title_short |
Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality |
| title_full |
Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality |
| title_fullStr |
Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality |
| title_full_unstemmed |
Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality |
| title_sort |
carbon distribution in low-temperature isothermal iron-based martensite and its tetragonality |
| publisher |
Інститут металофізики ім. Г.В. Курдюмова НАН України |
| publishDate |
2016 |
| topic_facet |
Дефекты кристаллической решётки |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/112501 |
| citation_txt |
Carbon Distribution in Low-Temperature Isothermal Iron-Based Martensite and Its Tetragonality / V. G. Gavriljuk, S. O. Firstov, V. A. Sirosh, A. I. Tyshchenko, and G. S. Mogilny // Металлофизика и новейшие технологии. — 2016. — Т. 38, № 4. — С. 455-475. — Бібліогр.: 67 назв. — англ. |
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Металлофизика и новейшие технологии |
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455
PACS numbers:61.05.cp, 61.72.Hh,62.20.fq,64.70.kd,81.30.Hd,81.30.Kf, 81.40.Lm
Carbon Distribution in Low-Temperature Isothermal
Iron-Based Martensite and Its Tetragonality
V. G. Gavriljuk, S. A. Firstov*, V. A. Sirosh, A. I. Tyshchenko,
and G. S. Mogilny
G. V. Kurdyumov Institute for Metal Physics, N.A.S. of Ukraine,
36 Academician Vernadsky Blvd.,
UA-03680 Kyiv, Ukraine
*I. M. Frantsevich Institute for Problems of Materials Science, N.A.S. of Ukraine,
3 Academician Krzhyzhanovs’kyy Blvd.,
UA-03680 Kyiv, Ukraine
Carbon distribution in the as-quenched Fe—C martensite obtained after cool-
ing down to 4.5 K is studied using Mössbauer spectroscopy. The location of
carbon atoms in the one of three available sublattices of octahedral intersti-
tial sites is established, whereas the partial occupation by carbon atoms of
tetrahedral sites or octahedral sites in other sublattices is not confirmed. The
ageing of virgin isothermal martensite starts during heating at temperatures
above 50C and leads to disappearance of single carbon atoms and their clus-
tering in the solid solution. In comparison with martensite obtained at
room temperature, a decreased tetragonality of the low-temperature iso-
thermal martensite and its partial recovery during ageing is observed. Based
on the estimation of dislocation density and the absence of -carbide precipi-
tation during subsequent tempering, a conclusion is made that plastic defor-
mation occurs in the course of isothermal martensitic transformation be-
cause of the softness of the virgin martensite. Finally, a new interpretation
of the abnormally low tetragonality is proposed, of which the essence is the
capture and transport of immobile carbon atoms by gliding dislocations. As a
result, a part of carbon is removed from the solid solution and forms carbon
atmospheres around the dislocations. The comparison of this hypothesis with
available other ones is presented. Two possible reasons for partial recovery of
Corresponding author: Valentin Gennadievich Gavriljuk
E-mail: gavr@imp.kiev.ua
Please cite this article as: V. G. Gavriljuk, S. A. Firstov, V. A. Sirosh,
A. I. Tyshchenko, and G. S. Mogilny, Carbon Distribution in Low-Temperature
Isothermal Iron-Based Martensite and Its Tetragonality, Metallofiz. Noveishie
Tekhnol., 38, No. 4: 455—475 (2016) (in English), DOI: 10.15407/mfint.38.04.0455.
Металлофиз. новейшие технол. / Metallofiz. Noveishie Tekhnol.
2016, т. 38, № 4, сс. 455—475 / DOI: 10.15407/mfint.38.04.0455
Оттиски доступны непосредственно от издателя
Фотокопирование разрешено только
в соответствии с лицензией
2016 ИМФ (Институт металлофизики
им. Г. В. Курдюмова НАН Украины)
Напечатано в Украине.
456 V. G. GAVRILJUK, S. A. FIRSTOV, V. A. SIROSH et al.
tetragonality during ageing of virgin martensite are discussed: (i) the un-
freezing of Snoek atmospheres created by gliding dislocations crossing the
immobile carbon atoms at low temperatures and (ii) coherent stresses at the
boundaries of the intermittent carbon-rich and carbon-depleted domains in
the modulated structure of the aged martensite.
Key words: isothermal martensitic transformation, plastic deformation,
short-range atomic order, dislocations, tetragonality.
Розподіл вуглецю у свіжозагартованому Fe—C-мартенситі, одержаному в
процесі охолодження до 4,5 К, досліджено методом Мессбауерівської спе-
ктроскопії. Встановлено розташування атомів Карбону в одній із трьох
підґратниць октаедричних міжвузлів і не підтверджено часткову зайня-
тість ними інших підґратниць або тетраедричних міжвузлів. Розпад сві-
жозагартованого ізотермічного мартенситу починається при нагріванні
вище 50C і приводить до зникнення поодиноких атомів вуглецю в -
твердому розчині та утворення їх кластерів. У порівнянні з мартенситом,
одержаним гартуванням за кімнатної температури, свіжозагартований
низькотемпературний ізотермічний мартенсит характеризується змен-
шеною тетрагональністю, яка частково відновлюється при наступному
нагріванні вище 50C. Ґрунтуючись на оцінках густини дислокацій в
одержаному низькотемпературному мартенситі та відсутності виділень -
карбіду при наступному відпусканні, зроблено висновок, що, внаслідок
низької міцности утвореного незастареного мартенситу, ізотермічне мар-
тенситне перетворення супроводжується пластичною деформацією. В ре-
зультаті запропоновано нову інтерпретацію аномально низької тетраго-
нальности низькотемпературного мартенситу, суть якої полягає у захоп-
ленні та транспортуванні дислокаціями ковзання нерухомих атомів Кар-
бону з видаленням їх із твердого розчину і утворенням Карбонових атмо-
сфер в полі напружень дислокацій. Наведено її співставлення з наявними
гіпотезами. Проаналізовано дві можливі причини часткового відновлення
тетрагональности при старінні низькотемпературного мартенситу: (i) ро-
зморожування атмосфер Снука, утворених дислокаціями ковзання за ни-
зьких температур, і (ii) когерентні напруження на межах переміжних об-
ластей, збагачених та збіднених Карбоном у модульованій структурі за-
стареного мартенситу.
Ключові слова: ізотермічне мартенситне перетворення, пластична дефо-
рмація, близький атомовий порядок, дислокації, тетрагональність.
Распределение углерода в свежезакалённом Fe—C-мартенсите, получен-
ном в процессе охлаждения до 4,5 К, исследовано методом мёссбауэров-
ской спектроскопии. Установлено размещение атомов углерода в одной из
трёх подрешёток октаэдрических междоузлий и не подтверждена частич-
ная занятость ими других подрешёток или тетраэдрических междоузлий.
Распад свежезакалённого изотермического мартенсита начинается при
нагреве выше 50C и приводит к исчезновению одиночных атомов угле-
рода в -твёрдом растворе и образованию их кластеров. В сравнении с
мартенситом, полученным закалкой при комнатной температуре, свеже-
закалённый низкотемпературный изотермический мартенсит характери-
зуется пониженной тетрагональностью, которая частично восстанавлива-
CARBON DISTRIBUTION IN LOW-TEMPERATURE IRON-BASED MARTENSITE 457
ется при последующем нагреве выше 50C. Основываясь на оценках
плотности дислокаций в полученном мартенсите и отсутствии выделения
-карбида при последующем отпуске, сделан вывод, что, вследствие низ-
кой прочности образованного несостаренного мартенсита, изотермиче-
ское мартенситное превращение сопровождается пластической деформа-
цией. В результате предложена новая интерпретация аномально низкой
тетрагональности низкотемпературного мартенсита, суть которой заклю-
чается в захвате и транспорте дислокациями скольжения неподвижных
атомов углерода с удалением их из твёрдого раствора и образованием уг-
леродных атмосфер в поле напряжений дислокаций. Приведено её сопо-
ставление с существующими гипотезами. Обсуждены две возможные
причины частичного восстановления тетрагональности при старении
низкотемпературного мартенсита: (i) размораживание атмосфер Снука,
созданных движущимися дислокациями при низких температурах, и (ii)
когерентные напряжения на границах чередующихся областей, обога-
щённых и обеднённых углеродом в модулированной структуре состарен-
ного мартенсита.
Ключевые слова: изотермическое мартенситное превращение, пластиче-
ская деформация, ближний атомный порядок, дислокации, тетрагональ-
ность.
(Received February 10, 2016)
1. INTRODUCTION
First time, the isothermal martensitic transformation in the iron-
based solid solutions was studied in detail by Kurdyumov and Maxi-
mova [1], although some indications were reported earlier (see, e.g., [2—
5]). Its main feature is the transformation in the course of time at low
temperatures. Since the first study by Kurdyumov and Maximova, it
was the object of intensive research on the ferrous and nonferrous al-
loys, of which results were, e.g., summarized by Lobodyuk and Estrin
[6, 7]. The following features of the isothermal martensite in Fe—C sol-
id solutions are distinctive in comparison with that obtained in the
nonferrous alloys and with the athermal Fe—C martensite.
First, it is characterized by a low yield and ultimate strength and
rather high plasticity [8—10]. Moreover, being integral part of the
athermal iron—carbon martensitic transformation at ambient tempera-
tures, the cracks are absent in the low-temperature isothermal marten-
site. Cracking starts only during its heating above 50C [9].
Second, the carbon atoms are essentially immobile during the iso-
thermal martensitic transformation (e.g., [11]), which results in a vir-
gin non-aged iron—carbon martensite. Its ageing starts during heating
above 50C and results in the martensite decomposition into the areas
rich and depleted in carbon alternately.
Third, the isothermal iron—carbon martensite is characterized by
458 V. G. GAVRILJUK, S. A. FIRSTOV, V. A. SIROSH et al.
decreased tetragonality [12] in comparison with that formed at ambi-
ent temperatures. The tetragonality is partially recovered during heat-
ing to room temperature, although never reaches its expected value
described by the relation c/a 1 0.046сС, where cC is the carbon con-
centration in mass %. The abnormally low tetragonality was found af-
ter low-temperature martensitic transformation in Fe—Mn—C [12], Fe—
Ni—C at a moderate Ni content of 8% [13], Fe—Re—C [14] and plain
high carbon [15] martensites.
Two main hypotheses have been proposed to interpret the abnormal-
ly low tetragonality of the virgin iron—carbon martensite: (i) a partial
location of carbon atoms in the tetrahedral interstitial sites resulted
from the martensitic transformation through the intermediate
-phase [16]; (ii) a redistribution of carbon atoms among three sublat-
tices of octahedral sites in the bcc crystal lattice due to a twinning on
the (011) planes in the course of the low-temperature martensitic
transformation [17]. According to the calculations [18], the occurrence
of thin twin layers in the -iron lattice on the ]110)[011( system can
shift the maximum of intensity in the X-ray reflections, which seems
to be consistent with the second hypothesis.
Later on, the abnormally high tetragonality was found in Fe—Al—C
[19, 20] and, at rather high Ni contents, in Fe—Ni—C [21, 22] marten-
sites. Based on these findings, the hypothesis [17] of carbon distribu-
tion among different sublattices of octahedral interstitial sites has
been updated [23], so that the occupation by carbon atoms of the only c-
sublattice was supposed in case of high tetragonality, whereas the
‘normal’ tetragonality was attributed to a partial occupation of the a-
and (or) b-sublattices, and the abnormally low tetragonality suggested
an increase in this fraction of carbon atoms.
The attempt of a critical experiment was undertaken using the neu-
tron diffraction [24], of which results supported the interpretation
given in [17, 23] and rejected the hypothesis in [16]. However, the both
hypotheses were at variance with results of studies carried out using
Mössbauer spectroscopy (see, e.g., [25—27]).
This paper aims at the analysis of a mechanism for the abnormally
low tetragonality of the low-temperature isothermal martensite taking
into account its aforementioned properties, namely low strength of
virgin martensite and immobility of carbon atoms at temperatures of
the isothermal martensitic transformation. The occurrence of plastic
deformation in the course of the isothermal transformation was the
main idea tested in this study.
2. EXPERIMENTAL
The tool steel X153CrMoV12 containing (% mass) 1.55C, 11.90Cr,
0.70V, 0.86Mo, 0.38Si, 0.33Mn, 0.05N, 0.00S, 0.02P, 0.00Al and a
CARBON DISTRIBUTION IN LOW-TEMPERATURE IRON-BASED MARTENSITE 459
reference steel 100Mn6 were studied. The first one was chosen be-
cause, aiming the increase of their wear resistance, the tool steels are
subjected to a deep cryogenic treatment where the isothermal marten-
sitic transformation is expected. The second one has the fully austenit-
ic structure and was first time used by Kurdyumov and Maximova [1]
for studies of the isothermal martensitic transformation. Moreover,
the abnormally low tetragonality of the low-temperature Fe—C marten-
site was observed just on this steel by Lysak and Vovk [12].
For Mössbauer study of carbon distribution in the Fe—C solid solu-
tion, the binary Fe—2.03% mass C alloy was obtained by the carburiza-
tion of a pure iron foil of 20 m in thickness at 1150C under flowing
methane followed by quenching in water. The obtained fully austenitic
specimen was cooled down to 4.5 K in the cryostat of Mössbauer spec-
trometer. Mössbauer measurements at 4.5 K revealed (68 1)% of the
virgin martensite and (32 1)% of retained austenite. Thereafter, the
sample was heated to 65 K and studied at this temperature after suc-
cessive heating—cooling cycles within the temperature range between
65 and 293 K with holding for 10 min at each temperature.
The martensitic transformation in the above-mentioned tool steel
was studied using Mössbauer spectroscopy, X-ray diffraction and me-
chanical spectroscopy. In addition, the TEM study of quenched sam-
ples after the low-temperature tempering was carried out aiming to
clarify the effect of isothermal martensitic transformation on the pre-
cipitation of transient carbides.
Specimens of steel X153CrMoV12 with a size of 10100.03 mm3
for
Mössbauer spectroscopy, 10100.1 mm3
for X-ray diffraction and
TEM, 0.70.760 mm3
for internal friction were solution treated at
1150C under protective argon atmosphere for 20 min followed by
quenching at room temperature (RT) using the argon flow. After
quenching at room temperature, the samples were subjected to deep
cryogenic treatment for different times at temperatures of 196 and
150C. A feature of this experiment was a rapid immersion in liquid
nitrogen, measurements at this temperature, subsequent heating and
holding at 150C and measurements at 196C. Such a technique al-
lowed one to keep the same cooling rate in the temperature range be-
tween RT and the temperature of the isothermal treatment. As shown
in [28], the holding at 196C is not accompanied by any transfor-
mation because of too low thermal activation.
A WISSEL Mössbauer spectrometer and a source of -quanta
57Co in
a Cr matrix with an activity of 50 mCi were used for the measure-
ments. The equipment was characterized by a line-width of 0.22 mm/s
for the line of the -quanta source.
The X-ray diffraction measurements were carried out with FeK-
radiation using a Huber diffractometer with the operating voltage of
30 kV and one-circle —2-goniometer. A computer program con-
460 V. G. GAVRILJUK, S. A. FIRSTOV, V. A. SIROSH et al.
trolled the angular movement of both the goniometer and the counter.
A cryosystem LN-3 produced by Cryo Industries of America Inc. was
used for measurements at low temperatures. In contrast to standard
cryostats, this system allows a rapid cooling of the sample installed in
the diffractometer, its holding and measurements at any temperature
within the range of 20 to 196C. With our samples, the lowest
achieved temperature was 182C.
An automated inverted pendulum with frequencies close to 1 Hz was
used for obtaining the IF spectra within the temperature range of 190
to 600C. The heating/cooling rate was about 1.5 K/min.
A JEM-2000 FXII transmission electron microscope, operating at a
voltage of 200 kV, was used for structural studies in the transmission
mode. Diffraction patterns from the areas of about 0.5 m in size were
obtained by the conventional selected area diffraction (SAD) tech-
nique.
3. CARBON DISTRIBUTION IN THE VIRGIN MARTENSITE
Mössbauer spectra of Fe—2.03% C solid solution are presented in Fig.
1, a after cooling down to 4.5 K, measuring at this temperature, heat-
ing up to 65 K (208C) and subsequent measuring at this temperature
after holdings for 10 min at temperatures within the range in between
208C and RT. Figure 1, b shows the outer lines of these spectra (nu-
clear transition 1/2 3/2).
It is worth noting that either the fraction of the retained austenite,
(32 1)%, or that of the martensite, (68 1)%, be measured at 4.5 K,
were not changed due to heating to 65 K (208C) and subsequent hold-
ings in between this temperature and RT. This result is at variance
with the data presented in [29], where, using the uniaxial dilatometry,
the inverse martensite-to-austenite transformation at low tempera-
tures was mentioned to occur in the alloy of similar composition Fe—
1.95% C, as well as in the alloy Fe—1.60% C—2.24% Mn. Possibly, the
relaxation of stresses during heating should be taken into account, if
the dilatometry is used for studies of metastable martensitic phases.
The stability of the retained austenite in the course of heating to RT
gives also the evidence that the isothermal martensitic transformation
in the studied binary Fe—C alloy proceeded only in the course of cooling.
3.1. Interpretation of Mössbauer Spectrum
The virgin and aged Fe—C martensites were the object of a number of
Mössbauer studies (see, e.g., [25—27, 30—38]). So far, it is hardly possi-
ble to carry out ab initio calculations of hyperfine structure parame-
ters in such multicomponent spectra. As a test for validity of their in-
CARBON DISTRIBUTION IN LOW-TEMPERATURE IRON-BASED MARTENSITE 461
terpretation, the change in the spectra caused by heating the virgin
martensite to RT, can be used, taking into account the corresponding
redistribution of carbon atoms and their additive effect on the hyper-
fine field Hi at the nuclei of nearest iron atoms, 0.3 T per one carbon
atom [26, 39].
As a first approximation, the martensitic spectrum in Fig. 1, b can
be divided into 3 components A, B and C characterized by different hy-
perfine fields Hi and belonging to iron atoms having no, one and two
carbon atoms as nearest neighbours, respectively. At the same time,
because of high sensitivity of the hyperfine field to local dilatations of
the crystal lattice, different values of the isomeric shift and, particu-
larly, the quadrupole interaction, can be revealed in each of these com-
ponents.
The component A is approximated by sextets 1 and 2 with different
values of the hyperfine field, Hi, and a rather close isomer shift, , and
quadrupole interaction, . Sextet 1 with the highest Hi comes from
pure iron atoms in the martensite. Its increased hyperfine field in
comparison with that in the pure -iron is obviously caused by dilata-
tion of the crystal lattice at the distances far from carbon atoms, in ac-
Fig. 1. Mössbauer spectra of the alloy F—2.03% mass C after quenching in wa-
ter, cooling to 4.5 K, measurements at this temperature (as-quenched) and
subsequent heating to different temperatures with holding for 10 min within
the range of 208C to RT (a); outer lines (nuclear transition 1/2 3/2) of
selected spectra (b). All measurements after heating were carried out at 65 K
(208C).
462 V. G. GAVRILJUK, S. A. FIRSTOV, V. A. SIROSH et al.
cordance with the Bethe—Slater dependence of atomic magnetic mo-
ments on the interatomic distance. Sextet 2 can be attributed to atoms
1Fe in Fig. 2, configuration a, which are the third neighbours of the
carbon atoms and only slightly subjected to the effect of carbon atoms.
After ageing at RT, the intensity of both sextets 1 and 2 decreases,
see Fig. 1, b, and a new sextet 7 with the Hi typical for pure -iron be-
comes dominant in this component, because the decomposition of the
supersaturated carbon solid solution due to ageing is accompanied by
formation of rather large not dilated domains of pure iron atoms.
Sextets 3 and 4 in the component B correspond to the iron atoms as
second and first neighbours, respectively, of a single carbon atom in
the octahedral site on the c axis (atoms 1Fe and 1Fe in the configura-
tion a, see Fig. 2). The sign of the quadrupole interaction is different
for these two kinds of atoms because of the different angle between
the electric field gradient q and direction of the axis of easy magneti-
zation axis H. The quadrupole interaction is described by the formula
8/)1cos3( 22 qQe , where e and Q are the electron charge and the
iron nuclear quadrupole moment, respectively. As Q is positive in the
b.c.c. iron [40] and q is negative [41, 42], the quadrupole interaction
for 1eF atoms should be negative and twice larger in comparison with
1eF atoms (see Fig. 2, a and Table 1).
Sextets 5 and 6 are characterized the same hyperfine fields, smaller
by 3 T than that for atoms 1eF , and different quadrupole interactions
in their sign and by two times in the value. They belong to the iron at-
Fig. 2. Configurations of iron and carbon atoms as derived from the interpre-
tation of Mössbauer spectra. H is the axis of easy magnetization; q is the elec-
tric field gradient.
CARBON DISTRIBUTION IN LOW-TEMPERATURE IRON-BASED MARTENSITE 463
oms Fe2 with two carbon atoms as nearest neighbours in the configura-
tions c and d, where the angle is equal to zero or 90, respectively.
After cooling within the temperature range in between 208C and
50C, the spectra remain unchanged. A redistribution in the intensity
of the components starts after heating above 50C (see Fig. 1, b). The
component B caused by single carbon atoms essentially disappears,
whereas the cluster component C increases its intensity. Due to ageing
at RT, the outer lines are shifted to the gravity centre of the spectrum
and the component 7 appears in the spectrum.
3.2. Carbon Distribution in the Virgin and Aged Martensites
The obtained data of Mössbauer studies allow carrying out the follow-
ing analysis of available hypotheses about carbon distribution in the
virgin low-temperature martensite and its change in the course of the
ageing.
If some part of carbon atoms could be located in the a- or b-
sublattices of the octahedral interstitial sites, as proposed in [17], an
additional component is expected in the spectrum having the hyperfine
field equal to that for spectrum 4 but different quadrupole interaction
in the sign and by two times in the value (see configurations a and b in
Fig. 2). This component should disappear in the course of heating with-
in the temperature range of 50C up to RT when tetragonality starts
to increase. However, such a component is not found in the spectrum.
Ino et al. [26] have analysed a hypothetic case of local turn in the ax-
is of easy magnetization to follow the shift of carbon atoms into the a-
or b-sublattices in the martensite. These authors have shown that the
gain in the exchange energy for the alignment of the iron atom spins
along the c axis, 1.410
20
J, is by two orders of magnitude higher than
TABLE 1. Parameters of hyperfine structure in Mössbauer spectrum of Fe—
2.03% mass C for the virgin martensite. Sextet 7 appears after ageing at
20C. Measurements at 65 K (208C).
Sextet Hyperfine field Hi, T
Isomer shift (in relation to
-iron) 0.005, mm/s
Quadrupole interac-
tion 4, mm/s
1 37.4 0.2 0.207 0.027 0.005
2 35.7 0.3 0.157 0.012 0.005
3 33.5 0.4 0.124 0.076 0.01
4 31.6 0.4 0.229 0.210 0.01
5 28.0 0.3 0.197 0.512 0.01
6 27.8 0.3 0.005 0.273 0.01
7 34.6 0.15 0.096 0.009 0.01
464 V. G. GAVRILJUK, S. A. FIRSTOV, V. A. SIROSH et al.
the anisotropic energy, 1.010
22
J, by which the spin direction of
neighbouring iron atoms could be locally turned along the a or b axes,
if the carbon is located in those sublattices. Therefore, such local mi-
crodomains of differently oriented spins cannot exist within the -iron
martensitic crystals.
For the same reason, a possible partial localization of carbon atoms
in the tetrahedral sites of virgin martensite should be accompanied by
two additional components in Mössbauer spectra with the hyperfine
field close to that of component 4 and different quadrupole interac-
tions (see configuration e in Fig. 2).
Therefore, the hypotheses attributing the abnormally low tetrago-
nality of virgin martensite to the localization of carbon atoms in the
tetrahedral sites [16] or their distribution on the a-, b-, or c-sublattices
of octahedral sites [17] (see configurations e and b in Fig. 1) are not
consistent with the hyperfine structure of Mössbauer spectra of virgin
martensite and their evolution during the heating.
The decrease in intensity of sextets 3 and 4 caused by single carbon
atoms and the growth of sextets 5 and 6 belonging to carbon clusters at
temperatures above 50C is consistent with the available observations
of the decomposition and even formation of the modulated structure in
the aged high-carbon martensites (e.g., [43, 44]).
4. PLASTIC DEFORMATION IN THE COURSE
OF ISOTHERMAL MARTENSITIC TRANSFORMATION
As follows from the X-ray diffraction measurements, Fig. 3, a, and da-
ta of mechanical spectroscopy, Fig. 3, b, the isothermal martensitic
transformation in the studied steel X153CrMoV12 proceeds within the
temperature range in between 100C and 170C during cooling or
heating with the maximal intensity at 150C.
As a rule, due to the volume effect of phase transformations in sub-
stitutional solid solutions, they are accompanied by plastic defor-
mation. This deformation is often used in cyclic heat treat-
ments for the accumulation of crystal lattice defects and correspond-
ing strengthening.
However, it is not the case in carbon steels. Because of high mobility
of carbon atoms at temperatures below Ms down to 50C, the ageing of
the freshly formed martensite occurs just in the course of its for-
mation, which increases strength and hardness and, thereby, prevents
plastic deformation. Moreover, it is ageing that causes cracking dur-
ing martensitic transformation [9].
As mentioned above, the low-temperature isothermal martensite in
carbon steels possesses a decreased strength and it is free of mi-
crocracks [8, 9]. This feature along with the immobility of carbon at-
oms at temperatures below 50C is a hint that, like martensitic trans-
CARBON DISTRIBUTION IN LOW-TEMPERATURE IRON-BASED MARTENSITE 465
formations in the substitutional solid solutions, plastic deformation
can occur during martensitic transformations at sufficiently low tem-
peratures.
Because of a complicated defect structure in the high-carbon steels
and, having no possibility for TEM study in situ at low temperatures,
two indirect experiments were carried out for testing this idea based
on estimation of a change in dislocation density due to isothermal mar-
tensitic transformation and studies of the low-temperature -carbide
precipitation during subsequent tempering. The latter aimed to test a
Fig. 3. Fragments of X-ray diffraction patterns of steel X153CrMoV12 after
quenching from 1150C at RT, holding at 170C for 15 and 240 min and sub-
sequent holding at 100C for 30 min. Evolution of the austenitic reflection
(200) is shown in the upper left corner. Measurements at temperatures of
holding (a); temperature dependence of internal friction in steels
X153CrMoV12 and X220CrMoV13-4 in the course of heating after quenching
in liquid nitrogen (b).
466 V. G. GAVRILJUK, S. A. FIRSTOV, V. A. SIROSH et al.
possible competition between the binding enthalpy of carbon atoms in
dislocation atmospheres and the enthalpy of -carbide formation.
In the first experiment, the Snoek—Köster (S—K) relaxation was
measured, of which the source are the vibrations of dislocation seg-
ments. At other equal conditions, e.g. the strain amplitude and fre-
quency, the relaxation strength is proportional to the density of dislo-
cations. In Figure 4, the S—K relaxation is presented for steel
X153CrMoV12 after quenching at RT without or with subsequent
holding at 196C or 150C for 24 hours. The highest relaxation peak
indicating to a largest dislocation density is obtained after holding at
150C, where the isothermal transformation is the most intensive. As
shown in [45], this growth of S—K relaxation strength, 9%, is much
higher than the increment of the isothermal martensite fraction, 4%,
which could be another source of the increased dislocation density.
The idea of the second experiment is based on the old studies carried
out by Wilson [46] who has shown that Vickers indentation test on the
as-quenched Fe—0.8% C martensite prevents the precipitation of -
carbide during subsequent tempering.
The precipitation of the low-temperature -carbide during temper-
ing of steel X153CrMoV12 is compared in case of quenching at RT,
Fig. 5, and isothermal martensitic transformation at 150C, Fig. 6.
The -carbide is clearly identified in Fig. 5 and is absent in Fig. 6,
which is consistent with the observations made by Wilson. A reason for
this phenomenon is the higher enthalpy of binding between disloca-
tions and carbon atoms, 0.8 eV, and the heat solution of -carbide in
the ferrite, 0.26 eV.
The distorted shape of reflections, see Fig. 6, c, can be related to the
Fig. 4. Snoek—Köster relaxation in steel X153CrMoV12 after holding at 196
and 150C for 24 hours in comparison with conventional quenching at room
temperature.
CARBON DISTRIBUTION IN LOW-TEMPERATURE IRON-BASED MARTENSITE 467
formation of satellites due to spinodal decomposition during the age-
ing of the low-temperature martensite, like it was observed earlier in
Fe—Ni—C [43] and Fe—C [44] alloys.
The total suppression of -carbide precipitation due to the isother-
mal martensitic transformation gives the evidence that, be initiated by
the softness of virgin martensite, plastic deformation involves the to-
tal structure of steel including also the athermal martensite, in spite of
its brittleness. This case can be compared with drawing or rolling of
eutectoid steels containing the brittle plate cementite along with the
soft ferrite.
5. A MECHANISM FOR DECREASE OF TETRAGONALITY
Plastic deformation in the course of the low-temperature isothermal
martensitic transformation is expected to be accompanied by the cap-
ture and transport of immobile carbon atoms by gliding dislocations,
which removes a part of carbon from the solid solution. If so, the te-
tragonality of the virgin martensite should be decreased. The main
point in this hypothesis is a possibility for the transport of interstitial
atoms by dislocations.
Theoretical and experimental studies of the transport of hydrogen
atoms by dislocations were carried out mainly in the seventies [47—49].
In relation to carbon, it is worth to note the striking difference be-
tween the decrease of carbon mobility in the deformed steels and the
enhanced carbon migration in the course of plastic deformation [50—
Fig. 5. Precipitates of -carbide after tempering at 100C of steel
X153CrMoV12 quenched at RT. The -carbide was identified by diffraction
from the area marked with a circle (a); the same after tempering at 200C (b);
diffraction pattern after tempering at 200C, zone axes ]311[ and ]121[ (c).
468 V. G. GAVRILJUK, S. A. FIRSTOV, V. A. SIROSH et al.
52]. This enhancement significantly exceeds the expected increase in
the mechanical driving force for the diffusion flux. A non-activated
mechanism for formation and transport of a ‘dislocation—interstitial
atom’ complex was analysed within the scope of the Frenkel—Kontoro-
va model in [53].
An indirect confirmation of carbon transfer by dislocations is pre-
sented by the phenomenon of cementite decomposition during plastic
deformation of pearlitic steels by drawing or rolling. About 50% of ce-
mentite is decomposed due to severe plastic deformation of the eutectoid
steel [54—56]. The degree of decomposition is controlled by the competi-
tion between Fe—C bonding in the cementite lattice and the enthalpy of
binding of carbon atoms to dislocations in the ferrite (see [57, 58]).
As shown in the quoted studies, the thin plate cementite is inten-
sively decomposed during plastic deformation, whereas a smaller de-
composition is found in case of the coarse plate cementite and no ce-
mentite decomposition occurs for the coarse grain cementite. The total
cementite decomposition is obtained due to severe plastic deformation
by the high-pressure torsion (e.g. [59]).
At the same time, there is no indication to any increase in the ferrite
lattice parameter, and, therefore, practically no carbon from the de-
composed cementite is dissolved in the solid solution. This conclusion
is also supported by Mössbauer studies [55—58], where the spectra are
shown to consist of only two sextets from ferrite and cementite. No
components caused by carbon in the solid solution are present in
Mössbauer spectra of cold worked pearlitic steels and only their inten-
sity is changed due to partial decomposition of cementite.
Recently, using Local Electron Atom Probe study [60], it was found
that carbon atoms of decomposed cementite in the severely deformed
steel are located at the dislocations in the ferrite. Such a huge carbon
concentration at the dislocations cannot be reached by a pulling of car-
bon atoms out of cementite lattice by dislocations with formation of
Fig. 6. Martensite after deep cryogenic treatment, DCT, at 150C and tem-
pering at 100C for 2 h (a); electron diffraction, zone axis [133] (b); diffrac-
tion spot ]101[ asymmetrical in directions ]313[ and ]213[ (c).
CARBON DISTRIBUTION IN LOW-TEMPERATURE IRON-BASED MARTENSITE 469
Cottrell’s atmospheres because, in contrast to Cottrell and Bilby analy-
sis [61], these atmospheres are rather diluted [62].
In other words, to be decomposed, the cementite should be involved
in deformation of pearlitic steels. As shown using transmission elec-
tron microscopy [63, 64], the cementite of plate morphology in pearlit-
ic steels is plastically deformed during the drawing or rolling.
Therefore, a mechanism for the strain-induced cementite decomposi-
tion amounts to the cutting of cementite plates by the gliding disloca-
tions followed by the capture of carbon atoms and their transfer into the
ferrite with formation of carbon segregations around the dislocations.
Based on the aforementioned analysis, one can assume that a similar
mechanism is operating in case of the low-temperature isothermal
martensitic transformation, i.e. the plastic deformation results in the
capture and transport of carbon atoms by gliding dislocations.
If so, it is particularly interesting to analyse the partial recovery of
tetragonality during subsequent heating of the virgin martensite. The
point is that, as mentioned above, because of a high enthalpy of bind-
ing between carbon atoms and dislocations, the atoms in dislocation
atmospheres cannot contribute to the ageing of virgin martensite.
Even the precipitation of the low-temperature -carbide is suppressed,
if carbon atoms are located in the field stress of dislocations.
Steel 100Mn6 having Ms 93C and subjected to the isothermal
martensitic transformation during holding at 150C was used for this
study. The change in the martensite tetragonality during subsequent
heating up to 70C is presented in Fig. 7. It is seen that tetragonality
c/a 1.026 is much smaller of its value 1.047 expected for the Fe—C
martensite with 1.0% mass C. Its partial recovery up to c/a 1.036
occurs due to heating to RT. At 70C, the c/a ratio starts to decrease.
According to hypotheses of [16, 17], the heating leads to jumping of
carbon atoms from the tetrahedral to octahedral interstitial sites [16]
or disappearance of (011) twins [17]. However, as shown in Section 3.2,
no corresponding components appear in Mössbauer spectra of the vir-
gin martensite and disappear in the course of its heating to RT. The
effect of heating amounts only to the decrease in the fraction of single
carbon atoms and increase in that of carbon clusters.
In view of the decisive role of plastic deformation in the decreased
tetragonality of the low-temperature isothermal martensite, as pro-
posed in this study, two possibilities for its partial recovery during
heating can be analysed.
The first one concerns the interaction between gliding dislocations
and immobile carbon atoms at low temperatures. One can imagine that
some carbon atoms are not captured by crossing dislocations. In this
case, the so-called Snoek atmospheres are formed, of which essence is a
change in the ordering of carbon atoms, i.e., their jumping from the
interstitial sites in the c-sublattice into those in the a- or b-sublattices.
470 V. G. GAVRILJUK, S. A. FIRSTOV, V. A. SIROSH et al.
In case of mobile carbon atoms, the Snoek atmospheres disappear im-
mediately after dislocation passage because the Zener ordering returns
carbon atoms into the c-sublattice. However, at temperatures below
50C, this reverse jumping is impossible, which decreases tetragonal-
ity like it is proposed in hypothesis [17]. In the course of subsequent
heating, at temperatures above 50C, Zener ordering starts to be op-
erating and results in jumping of carbon atoms back into the c-
sublattice and recovery of tetragonality.
The only objection against this interpretation is that, like the case in
Fig. 7. Low-temperature X-ray diffraction of steel 100Mn6 after solution
treatment at 1000C, isothermal martensitic transformation at 150C and
subsequent heating: fragments of diffraction patterns obtained in the course
of heating from 120 to 70C and evolution of the austenitic (200) reflection
in the course of holding at 150C (the insert in the upper right corner) (a),
corresponding change in tetragonality of martensite (b).
CARBON DISTRIBUTION IN LOW-TEMPERATURE IRON-BASED MARTENSITE 471
hypotheses [16] and [17], such frozen Snoek atmospheres should cause
additional components in Mössbauer spectrum of the virgin Fe—C mar-
tensite and their disappearance during heating, which is not observed.
The second possibility is to attribute the partial recovery of tetrago-
nality to some coherent stresses appearing in the course of martensite
ageing. These stresses are supposed to be caused by spinodal-like de-
composition of the virgin martensite and formation of carbon-rich and
carbon-depleted areas.
The analogy to this case can be found in the studies of tetragonality
of the carbon-free Fe—Ni martensites with the Ni content in the invar
area. The spinodal-like decomposition in instead of I the Fe—Ni invar
alloys was demonstrated in [65]. The short-range decomposition in the
austenitic Fe—Ni alloy was also proven by X-ray diffraction and TEM
studies, based on the theoretical calculations of Fe—Fe, Fe—Ni and Fe—
Ni interatomic bonds and different hydrogen solubility, correspond-
ingly different dilatation in the Fe-rich and Ni-rich areas of the Fe—Ni
solid solution [66].
A fragment of diffraction pattern of the Fe—33.5Ni alloy after aus-
tenitizing at 1150C and cooling down to 10 K is presented in Fig. 8
(see about detail [67]). The doublet (112)/(211) in the as-quenched
state, see Fig. 8, a, is the evidence of tetragonality in the martensite
lattice in absence of carbon. A slight deformation at 40 K by a screw
mounted in the cryostat led to a decrease in the c/a ratio (Fig. 8, b). Af-
ter further slight deformation at 110 K, tetragonality disappears (Fig.
8, c). It also disappears without any deformation due to increase in mo-
bility of dislocations during heating in the temperature range between
110 K and 200 K.
This experiment clearly indicates to coherent stresses as a source for
tetragonality of the virgin martensite. The nature of this coherency
can be of two kinds: (i) coherent stresses at the interface between vir-
gin martensite and retained austenite, as proposed in [67] and (ii)
stresses caused by different dilatation in the Fe-rich and Ni-rich areas
because of the short-range decomposition. The Ni-rich areas in the aus-
tenitic invar alloy are characterized by Langevin superparamagnetism
and, correspondingly, a large volume magnetostriction in superpara-
magnetic clusters, which is inherited by the virgin martensite formed
due to quenching at low temperatures.
Similar way, the increase in the c/a ratio during heating of the iso-
thermal martensite from 50C to RT (see Fig. 7, b) can be related to
stresses caused in the aged martensite by its spinodal decomposition.
6. CONCLUSIONS
1. Mössbauer studies of the as-quenched binary Fe—C martensite
formed at temperatures below RT revealed the distribution of carbon
472 V. G. GAVRILJUK, S. A. FIRSTOV, V. A. SIROSH et al.
atoms solely in one of three sublattices of the octahedral interstitial
sites in the b.c.c. iron lattice, and no sign of carbon localization in oth-
er sublattices or in the tetrahedral sites was detected.
2. The low-temperature isothermal martensitic transformation in car-
bon steels is accompanied by plastic deformation, which can be ex-
plained by the softness of the transformed virgin martensite.
3. The abnormally low tetragonality of the virgin isothermal marten-
site is attributed to the capture and transport of immobile carbon at-
oms by gliding dislocations removing a part of carbon atoms from the
solid solution and resulting in formation of carbon atmospheres
around the dislocations.
4. Two possible reasons for partial recovery of tetragonality during the
Fig. 8. The effect of in situ deformation on the diffraction peaks (112) and
(211) of the virgin Fe—33.5% mass Ni martensite with Ms 125 K after aus-
tenitizing at 1150C and cooling down to 4 K: undeformed (a); deformed at
40 K (b); further deformed at 110 K (c). Measurements are carried out at
40 K.
CARBON DISTRIBUTION IN LOW-TEMPERATURE IRON-BASED MARTENSITE 473
heating of virgin isothermal martensite above 50C are discussed in
terms of the unfreezing of Snoek carbon atmospheres created by glid-
ing dislocations at low temperatures or coherent stresses arising from
the decomposition of the aged martensite into the carbon-rich and car-
bon-depleted domains with formation of the modulated structure.
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/NLD (Gebruik deze instellingen om Adobe PDF-documenten te maken die zijn geoptimaliseerd voor prepress-afdrukken van hoge kwaliteit. De gemaakte PDF-documenten kunnen worden geopend met Acrobat en Adobe Reader 5.0 en hoger.)
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/UKR <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>
/ENU (Use these settings to create Adobe PDF documents best suited for high-quality prepress printing. Created PDF documents can be opened with Acrobat and Adobe Reader 5.0 and later.)
>>
/Namespace [
(Adobe)
(Common)
(1.0)
]
/OtherNamespaces [
<<
/AsReaderSpreads false
/CropImagesToFrames true
/ErrorControl /WarnAndContinue
/FlattenerIgnoreSpreadOverrides false
/IncludeGuidesGrids false
/IncludeNonPrinting false
/IncludeSlug false
/Namespace [
(Adobe)
(InDesign)
(4.0)
]
/OmitPlacedBitmaps false
/OmitPlacedEPS false
/OmitPlacedPDF false
/SimulateOverprint /Legacy
>>
<<
/AddBleedMarks false
/AddColorBars false
/AddCropMarks false
/AddPageInfo false
/AddRegMarks false
/ConvertColors /ConvertToCMYK
/DestinationProfileName ()
/DestinationProfileSelector /DocumentCMYK
/Downsample16BitImages true
/FlattenerPreset <<
/PresetSelector /MediumResolution
>>
/FormElements false
/GenerateStructure false
/IncludeBookmarks false
/IncludeHyperlinks false
/IncludeInteractive false
/IncludeLayers false
/IncludeProfiles false
/MultimediaHandling /UseObjectSettings
/Namespace [
(Adobe)
(CreativeSuite)
(2.0)
]
/PDFXOutputIntentProfileSelector /DocumentCMYK
/PreserveEditing true
/UntaggedCMYKHandling /LeaveUntagged
/UntaggedRGBHandling /UseDocumentProfile
/UseDocumentBleed false
>>
]
>> setdistillerparams
<<
/HWResolution [2400 2400]
/PageSize [612.000 792.000]
>> setpagedevice
|