Analysis of the plasticity characteristics of progressively drawn steel wires
Changes in the plasticity characteristics in air and in a hydrogenating environment of prestressing steel wires due to cold drawing process are investigated on the basis of slow strain rate tests on smooth specimens. The tested pearlitic steel is highly susceptible to hydrogen embrittlement at al...
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Фізико-механічний інститут ім. Г.В. Карпенка НАН України
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| Цитувати: | Analysis of the plasticity characteristics of progressively drawn steel wires / М.І. Hredil, J. Toribio, H.M. Nykyforchyn // Фізико-хімічна механіка матеріалів. — 2015. — Т. 51, № 4. — С. 71-75. — Бібліогр.: 12 назв. — англ. |
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Hredil, М.І. Toribio, J. Nykyforchyn, H.M. 2018-06-16T08:43:12Z 2018-06-16T08:43:12Z 2015 Analysis of the plasticity characteristics of progressively drawn steel wires / М.І. Hredil, J. Toribio, H.M. Nykyforchyn // Фізико-хімічна механіка матеріалів. — 2015. — Т. 51, № 4. — С. 71-75. — Бібліогр.: 12 назв. — англ. 0430-6252 https://nasplib.isofts.kiev.ua/handle/123456789/136274 620.193:691.328 Changes in the plasticity characteristics in air and in a hydrogenating environment of prestressing steel wires due to cold drawing process are investigated on the basis of slow strain rate tests on smooth specimens. The tested pearlitic steel is highly susceptible to hydrogen embrittlement at all stages of cold drawing. The inconsistency is revealed between the changes of two plasticity characteristics: reduction in area and uniform elongation. The obtained results are analysed distinguishing the contribution of resistance to crack initiation and crack propagation. Susceptibility to crack initiation increases as a result of cold drawing with simultaneous improvement of the crack propagation resistance. За результатами механічних випроб на повільний розтяг гладких зразків досліджено зміну характеристик пластичності у повітрі та наводнювальному середовищі прутків з перлітної сталі внаслідок холодного волочіння. Сталь високочутлива до водневого окрихчення на усіх етапах обробки. Виявлено невідповідність між змінами відносних звуження та рівномірного видовження. Отримані результати проаналізовано з виокремленням вкладу опору зародженню і поширенню тріщини. Внаслідок холодного волочіння підвищується чутливість до тріщиноутворення, при цьому опір поширенню тріщини дещо зростає. На основании результатов механических испытаний на медленное растяжение гладких образцов исследовано изменение характеристик пластичности на воздухе и в наводороживающей среде прутков из перлитной стали после холодного волочения. Сталь высокочувствительна к водородному охрупчиванию на всех этапах обработки. Обнаружено несоответствие между относительным сужением и равномерным удлинением. Полученные результаты проанализировали, выделяя отдельно сопротивление зарождению и распространению трещины. Вследствие холодного волочения повышается чувствительность к трещинообразованию, при этом сопротивление распространению трещины повышается. en Фізико-механічний інститут ім. Г.В. Карпенка НАН України Фізико-хімічна механіка матеріалів Analysis of the plasticity characteristics of progressively drawn steel wires Аналіз зміни характеристик пластичності прутків зі сталі внаслідок холодного волочіння Анализ изменения характеристик пластичности прутков из стали вследствие холодного волочения Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| title |
Analysis of the plasticity characteristics of progressively drawn steel wires |
| spellingShingle |
Analysis of the plasticity characteristics of progressively drawn steel wires Hredil, М.І. Toribio, J. Nykyforchyn, H.M. |
| title_short |
Analysis of the plasticity characteristics of progressively drawn steel wires |
| title_full |
Analysis of the plasticity characteristics of progressively drawn steel wires |
| title_fullStr |
Analysis of the plasticity characteristics of progressively drawn steel wires |
| title_full_unstemmed |
Analysis of the plasticity characteristics of progressively drawn steel wires |
| title_sort |
analysis of the plasticity characteristics of progressively drawn steel wires |
| author |
Hredil, М.І. Toribio, J. Nykyforchyn, H.M. |
| author_facet |
Hredil, М.І. Toribio, J. Nykyforchyn, H.M. |
| publishDate |
2015 |
| language |
English |
| container_title |
Фізико-хімічна механіка матеріалів |
| publisher |
Фізико-механічний інститут ім. Г.В. Карпенка НАН України |
| format |
Article |
| title_alt |
Аналіз зміни характеристик пластичності прутків зі сталі внаслідок холодного волочіння Анализ изменения характеристик пластичности прутков из стали вследствие холодного волочения |
| description |
Changes in the plasticity characteristics in air and in a hydrogenating environment of
prestressing steel wires due to cold drawing process are investigated on the basis of slow
strain rate tests on smooth specimens. The tested pearlitic steel is highly susceptible to
hydrogen embrittlement at all stages of cold drawing. The inconsistency is revealed
between the changes of two plasticity characteristics: reduction in area and uniform elongation.
The obtained results are analysed distinguishing the contribution of resistance to
crack initiation and crack propagation. Susceptibility to crack initiation increases as a
result of cold drawing with simultaneous improvement of the crack propagation resistance.
За результатами механічних випроб на повільний розтяг гладких зразків
досліджено зміну характеристик пластичності у повітрі та наводнювальному середовищі
прутків з перлітної сталі внаслідок холодного волочіння. Сталь високочутлива до водневого окрихчення на усіх етапах обробки. Виявлено невідповідність між змінами відносних звуження та рівномірного видовження. Отримані результати проаналізовано з виокремленням вкладу опору зародженню і поширенню тріщини. Внаслідок холодного волочіння підвищується чутливість до тріщиноутворення, при цьому опір поширенню тріщини дещо зростає.
На основании результатов механических испытаний на медленное растяжение гладких образцов исследовано изменение характеристик пластичности на воздухе
и в наводороживающей среде прутков из перлитной стали после холодного волочения.
Сталь высокочувствительна к водородному охрупчиванию на всех этапах обработки. Обнаружено несоответствие между относительным сужением и равномерным удлинением.
Полученные результаты проанализировали, выделяя отдельно сопротивление зарождению и распространению трещины. Вследствие холодного волочения повышается чувствительность к трещинообразованию, при этом сопротивление распространению трещины
повышается.
|
| issn |
0430-6252 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/136274 |
| citation_txt |
Analysis of the plasticity characteristics of progressively drawn steel wires / М.І. Hredil, J. Toribio, H.M. Nykyforchyn // Фізико-хімічна механіка матеріалів. — 2015. — Т. 51, № 4. — С. 71-75. — Бібліогр.: 12 назв. — англ. |
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2025-11-25T22:46:40Z |
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2025-11-25T22:46:40Z |
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| fulltext |
71
Ô³çèêî-õ³ì³÷íà ìåõàí³êà ìàòåð³àë³â. – 2015. – ¹ 4. – Physicochemical Mechanics of Materials
UDK 620.193:691.328
ANALYSIS OF THE PLASTICITY CHARACTERISTICS
OF PROGRESSIVELY DRAWN PEARLITIC STEEL WIRES
М. І. HREDIL 1, J. TORIBIO 2, H. M. NYKYFORCHYN 1
1 Karpenko Physico-Mechanical Institute of the NAS of Ukraine;
2 University of Salamanca, E.P.S., Zamora, Spain
Changes in the plasticity characteristics in air and in a hydrogenating environment of
prestressing steel wires due to cold drawing process are investigated on the basis of slow
strain rate tests on smooth specimens. The tested pearlitic steel is highly susceptible to
hydrogen embrittlement at all stages of cold drawing. The inconsistency is revealed
between the changes of two plasticity characteristics: reduction in area and uniform elon-
gation. The obtained results are analysed distinguishing the contribution of resistance to
crack initiation and crack propagation. Susceptibility to crack initiation increases as a
result of cold drawing with simultaneous improvement of the crack propagation resistance.
Keywords: prestressing steel, plasticity parameters, crack initiation and propagation.
Prestressed concrete structures are a very important part of infrastructure of any
country. They include buildings, transportation network, energy production, nuclear
power plants, water and waste-water treatment systems etc. There is a lot of long-term
service objects that have been in operation for 50 years and more. Their increasing age,
the environmental impact, increasing traffic loads may change their serviceability [1].
Damage during service, frequently appearing after several years or decades of exploi-
tation, is usually most consequential. The lack of sufficient protection resulting from
the alkaline nature of the cement matrix in as-received state or the loss of alkalinity due
to carbonation and/or depassivation caused by the chloride attack are the major causes
of corrosion initiation. Failures of prestressing steel in structures are predominantly
attributed to hydrogen-induced stress corrosion cracking [1] under simultaneous action
of aqueous corrosive environment and static tensile stresses. In such conditions not
only concrete coating fracture occurs but also prestressing steel wires could suffer in-
service degradation similarly to other steels [2–5].
Mechanical behaviour and fracture peculiarities of prestressing steels under diffe-
rent environmental conditions have been studied thoroughly using both notched and
pre-cracked specimens [6–9], paying attention to the stress state in the vicinity of the
crack tip [7–9]. Meanwhile, there is a lack of data concerning smooth specimens and
they are not clear/monosemantic due to a big scatter of results [6, 10]. This paper is
aimed at fulfilling this gap and finding out some regularities of hydrogenation effect on
cracks initiation and propagation in the prestressing steel wires without pre-cracking.
Materials and methods. Materials used were cylindrical specimens of cold drawn
pearlitic steel wires from different steps of the real manufacturing process, and also the
initial hot rolled steel bar. The steel conventionally called E, which passes through
seven cold drawing steps has been studied. The chemical composition of the steel is the
following (mass.%): 0.88 C, 0.69 Mn, 0.22 Si, 0.010 P, 0.024 S, 0.239 Cr, 0.076 Ni,
0.010 Mo, 0.129 Cu, 0.118 V, Fe is balance. Plastic strain accum 0ε 2ln( / )P
iD D= accu-
mulated by steel at each stage of the cold drawing process and corresponding diameter
Corresponding author: M. I. HREDIL, e-mail: mysya@ipm.lviv.ua
72
of the wires are shown in the Table. The hot rolled bar was marked E0 and the follo-
wing steels as E1…E7 according to a cold drawing step.
Diameter D of the steels E and accumulated plastic deformation level εεεε
p
accum
Steel E0 E1 E2 E3 E4 E5 E6 E7
D, mm 11.03 9.90 8.95 8.21 7.49 6.80 6.26 5.04
ε
p
accum 0.00 0.22 0.42 0.59 0.78 0.97 1.13 1.57
Mechanical investigations consisted in slow strain rate testing (10–7 s–1) in air and
in a model environment using smooth cylindrical specimens with diameters equal to
wires thickness and with length 300 mm. Surface of the tested wires was not grinded
but only degreased by acetone and washed with water to approach the real working
conditions. Specimens were tested on the MTS Alliance RT/100 testing machine with
software TESTWORKS 4. The initial distance between grips was 220 mm.
For the study of hydrogenation effect on the mechanical behaviour of the steel an
electrochemical cell of 8 mm height was fixed around a specimen. In this electrochemi-
cal three-electrode scheme a tested wire (working electrode) was connected to a poten-
tiostat by its negative pole and served as cathode. The platinum spiral as a counter
electrode was used for polarization providing uniform distribution of current along the
specimen surface. Constant cathodic potential –1.2 V was maintained by the potentio-
stat AMEL VOLTALAB PGP 201. Reference electrode was saturated calomel – SCE
(Hg|Hg2Cl2). Tests were performed in the solution containing 1 g/l Ca(OH)2 + 0.1 g/l
NaCl (pH 12.5) with free oxygen access modelling a pore solution in concrete [6, 11].
At least three specimens were tested in air and for each “metal–environment” system.
The object of the analysis was the true stress– true strain curves σ–ε and reduction
in area (RA), ψ. Curves in air were recorded using an extensometer and presented up to
the moment of reaching the ultimate tensile strength σUTS (the stage of uniform elon-
gation). For the tests in hydrogenating medium the whole tensile curves are shown.
Percentage of RA was calculated after fracture of the specimens. The commercial wire
was not taken into consideration because of its thermal treatment after cold drawing to
remove residual stresses, which modified its plasticity characteristics. It did not allow
the comparison of the final stage of cold drawing with the previous ones. Macrofrac-
ture maps were obtained using scanning electron microscope JEOL JSM-5610 LV for
the identification of characteristic fracture zones, namely, crack initiation, subcritical
crack growth and final fracture area.
Results and discussion. Uniform elongation εu of the specimens tested in air
decreased sequentially with cold drawing degree with improving the strength characte-
ristics (Fig. 1, curves 0–6). Such mechanical behaviour corresponds to conventional
notion about strain hardening of materials. Concerning the tests with cathodic polariza-
tion (Fig. 1, curves 0′–6′), it should be noted that no visible transformations were fixed
related to subcritical crack growth, because it could be reflected in the curves shape. It
can be explained by a very low strain rate. In this case even if the stage of crack propa-
gation is prolonged it could be visible in the negligible increment of ε on the stress–
strain diagram. Hydrogenated material revealed divergent behaviour: firstly the para-
meter ε increased with cold drawing reaching the maximum value for the steel E3 and
then it reduced. The possible explanation will be done later involving another plasticity
parameter, reduction in area.
Reduction in area for the test in air, in contrast to relative elongation, is nonmono-
tonic function of accumulated plastic strain ε
p
accum exhibiting maximum at the later
stages of cold drawing (Fig. 2, curve 1). It means that two plasticity parameters, εu and
73
ψ, the former showing uniform deformation, and the latter – general plasticity under
fracture, revealed opposite tendencies with ε
p
accum increment.
On the basis of the principle of volume constancy of a metal during its plastic
deformation, it is possible to calculate its RA at the moment of reaching the σUTS value,
ψu, using well-known relation [12]:
1
2ln
1
ε =
− ψ
. (1)
Since εu used for calculation corresponds to the start of a neck formation because
of the crack nucleation inside a specimen, the obtained value ψu could be considered as
an indirect indicator of steel resistance to crack initiation under tension. Values calcu-
lated for the tests in air are plotted in Fig. 2 as curve 2. Thus, these data actually repre-
sent the material resistance to crack initiation which is relatively low for the tested
steel.
Likewise the subtraction ψ – ψu could characterise the stage of crack propagation
– the greater this value, the higher the plasticity margin of material. Thereby ψu and
(ψ – ψu) could be indicators of steel resistance to crack initiation and crack growth
correspondingly. Analysis of Fig. 2 (curves 1 and 2) reveals an opposite trend in the
changes of these values. Regularities at the stage of crack initiation correspond to the
expected results (εu decreases with cold drawing), while a positive effect of the steel
treatment on crack growth resistance could be found in the peculiarities of metal struc-
ture changes due to cold drawing.
Fig. 1. Fig. 2.
Fig. 1. Stress-strain curves of steel E in air (0–6) and under hydrogenation (0’–6’).
The numbers indicate the cold drawing steps of the steel.
Fig. 2. Plasticity of the tested steel in air (1, 2) and under cathodic polarization (3, 4):
1, 3 – experimentally obtained reduction in area;
2, 4 – uniform reduction in area calculated from (1).
The foregoing approach to the plasticity parameters analysis was used also for the
test results of hydrogenated specimens. In contrast to the test in air, stably low values
of reduction in area ψH were obtained under hydrogenation conditions (Fig. 2, curve 3),
revealing high sensitivity of the tested steel to hydrogen embrittlement, previously
described in [7]. Such behaviour was explained by progressive pearlite lamellas re-
orientation in a direction parallel to the longitudinal wire axis at each step of cold
drawing [8]. The maximum plasticity (in terms of ψ) corresponds to the total re-orien-
74
tation of structural units, and from this point the following increment of plastic strain
only reduces the parameter ψ.
Considering the wires suffering hydrogenation it was easy to note that fracture in
all cases took place before reaching σUTS, obviously, due to rapid growth of a macro-
crack. Therefore it could be assumed that values of rupture stress and stress for crack
initiation were very close, the corresponding strain values εH
u being slightly less than
εH. It could be accepted that εH
u = εH to simplify the calculation. Then according to (1),
curve 4 in Fig. 2, demonstrating the resistance of the investigated steels to initiation of
hydrogen induced cracking, was obtained. The curve exhibited maximum in the middle
stage of cold drawing, caused by a combined action of two competitive effects. Some
retardation of crack initiation from the surface could be a result of reduced surface
roughness as a result of cold drawing. Meanwhile, susceptibility to hydrogen assisted
cracking prevails at the final stages because of considerable increment in steel strength.
Obviously, surface roughness doesn’t matter in the case of fracture in air, therefore the
parameter ψu decreases sequentially with cold drawing degree (Fig. 2, curve 2). Con-
cerning the resistance to crack propagation under cathodic polarization ψH – ψH
u (see
Fig. 2, curves 3 and 4), it should be noted that evolution of this parameter due to cold
drawing is similar in both experimental conditions (air and hydrogenation) – it rises
slightly at the later stages of cold drawing process. Another situation could be expected
for the final prestressing steel (which is not considered in the present work) due to its
extremely high strength and essential susceptibility to hydrogen embrittlement [7].
Examples of typical fracture maps after both tests (in air and under cathodic pola-
rization) are presented in Fig. 3. Three characteristic zones should be distinguished on
the fracture surface of the specimen broken in air: a central zone, an intermediate zone
and a shear lip. For the
hydrogenated specimen all
three zones were also pre-
sent. Besides, a new zone
appeared, called tearing
topography surface (TTS),
and reported previously in
[9], which is situated near
the lateral surface and indi-
cates the place of crack ini-
tiation. In both cases radial
marks in the intermediate
zone were observed which
indicated crack growth di-
rection – from the centre of each specimen to its edge. It is derived from the compari-
son of the presented fracture maps that, despite of the appearance of TTS (which is ac-
tually tiny comparing to the whole fracture surface) and crack origin from the lateral
surface, fracture under cathodic polarization is suggested to be quasi symmetrical.
Therefore the tendency of RA changes due to cold drawing is similar in air and in
hydrogenating conditions.
CONCLUSION
Division of the values of reduction in area as a basic plasticity parameter of steel
into the components responsible for crack initiation and crack growth allows one to
consider the stage of crack initiation and crack propagation separately. It should be
noted that a tendency of its changes with strain increment ε are similar for both test
conditions, in particular, increase of susceptibility to crack initiation and simultaneous
improvement of resistance to crack propagation in heavily drawn steels.
Fig. 3. Microfracture maps of steel E4 after tensile test
in air (a) and under hydrogenation in the solution
containing1 g/l Ca(OH)2 + 0.1 g/l NaCl, pH 12.5 (b).
75
РЕЗЮМЕ. За результатами механічних випроб на повільний розтяг гладких зразків
досліджено зміну характеристик пластичності у повітрі та наводнювальному середовищі
прутків з перлітної сталі внаслідок холодного волочіння. Сталь високочутлива до водне-
вого окрихчення на усіх етапах обробки. Виявлено невідповідність між змінами віднос-
них звуження та рівномірного видовження. Отримані результати проаналізовано з виок-
ремленням вкладу опору зародженню і поширенню тріщини. Внаслідок холодного воло-
чіння підвищується чутливість до тріщиноутворення, при цьому опір поширенню тріщи-
ни дещо зростає.
РЕЗЮМЕ. На основании результатов механических испытаний на медленное растя-
жение гладких образцов исследовано изменение характеристик пластичности на воздухе
и в наводороживающей среде прутков из перлитной стали после холодного волочения.
Сталь высокочувствительна к водородному охрупчиванию на всех этапах обработки. Об-
наружено несоответствие между относительным сужением и равномерным удлинением.
Полученные результаты проанализировали, выделяя отдельно сопротивление зарожде-
нию и распространению трещины. Вследствие холодного волочения повышается чувстви-
тельность к трещинообразованию, при этом сопротивление распространению трещины
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Received 25.06.2015
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