Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming
The current paper reports the new solutions intended to enhance the complex of mechanical properties and tendency to the press forming of the hot-rolled low-carbon and ultralow-carbon steels with subsequent cold deformation via upsetting and torsion under hydrostatic pressure (THP). У роботі одержан...
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Інститут металофізики ім. Г.В. Курдюмова НАН України
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| Cite this: | Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming / Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, V.V. Prutchykova // Progress in Physics of Metals. — 2019. — Vol. 20, No 2. — P. 213-284. — Bibliog.: 184 titles. — eng. |
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Projdak, Yu.S. Kutsova, V.Z. Kotova, T.V. Stetsenko, H.P. Prutchykova, V.V. 2020-04-16T16:48:34Z 2020-04-16T16:48:34Z 2019 Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming / Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, V.V. Prutchykova // Progress in Physics of Metals. — 2019. — Vol. 20, No 2. — P. 213-284. — Bibliog.: 184 titles. — eng. 1608-1021 DOI: https://doi.org/10.15407/ufm.20.02.213 https://nasplib.isofts.kiev.ua/handle/123456789/167926 The current paper reports the new solutions intended to enhance the complex of mechanical properties and tendency to the press forming of the hot-rolled low-carbon and ultralow-carbon steels with subsequent cold deformation via upsetting and torsion under hydrostatic pressure (THP). У роботі одержано нові розв’язки науково-практичної задачі, яка полягає у підвищенні комплексу механічних властивостей і схильності до штампування гарячевальцьованих низько- та ультранизьковуглецевих сталей з подальшою холодною деформацією методами осаду та кручення під гідростатичним тиском (КГТ). В работе получены новые решения научно-практической задачи, которая заключается в повышении комплекса механических свойств и склонности к штамповке горячекатаных низко- и ультранизкоуглеродистых сталей с последующей холодной деформацией методами осадки и кручения под гидростатическим давлением (КГД). en Інститут металофізики ім. Г.В. Курдюмова НАН України Успехи физики металлов Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming Закономірності формування структури, текстури та властивостей при комбінованій пластичній деформації низько- й ультранизьковуглецевих сталей для холодного штампування Закономерности формирования структуры, текстуры и свойств при комбинированой пластической деформации низко- и ультранизкоуглеродистых сталей для холодной штамповки Article published earlier |
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| title |
Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming |
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Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming Projdak, Yu.S. Kutsova, V.Z. Kotova, T.V. Stetsenko, H.P. Prutchykova, V.V. |
| title_short |
Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming |
| title_full |
Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming |
| title_fullStr |
Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming |
| title_full_unstemmed |
Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming |
| title_sort |
regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming |
| author |
Projdak, Yu.S. Kutsova, V.Z. Kotova, T.V. Stetsenko, H.P. Prutchykova, V.V. |
| author_facet |
Projdak, Yu.S. Kutsova, V.Z. Kotova, T.V. Stetsenko, H.P. Prutchykova, V.V. |
| publishDate |
2019 |
| language |
English |
| container_title |
Успехи физики металлов |
| publisher |
Інститут металофізики ім. Г.В. Курдюмова НАН України |
| format |
Article |
| title_alt |
Закономірності формування структури, текстури та властивостей при комбінованій пластичній деформації низько- й ультранизьковуглецевих сталей для холодного штампування Закономерности формирования структуры, текстуры и свойств при комбинированой пластической деформации низко- и ультранизкоуглеродистых сталей для холодной штамповки |
| description |
The current paper reports the new solutions intended to enhance the complex of mechanical properties and tendency to the press forming of the hot-rolled low-carbon and ultralow-carbon steels with subsequent cold deformation via upsetting and torsion under hydrostatic pressure (THP).
У роботі одержано нові розв’язки науково-практичної задачі, яка полягає у підвищенні комплексу механічних властивостей і схильності до штампування гарячевальцьованих низько- та ультранизьковуглецевих сталей з подальшою холодною деформацією методами осаду та кручення під гідростатичним тиском (КГТ).
В работе получены новые решения научно-практической задачи, которая заключается в повышении комплекса механических свойств и склонности к штамповке горячекатаных низко- и ультранизкоуглеродистых сталей с последующей холодной деформацией методами осадки и кручения под гидростатическим давлением (КГД).
|
| issn |
1608-1021 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/167926 |
| citation_txt |
Regularities of formation of structure, texture and properties under the combined plastic deformation of the low-carbon and ultralow-carbon steels for cold press forming / Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, V.V. Prutchykova // Progress in Physics of Metals. — 2019. — Vol. 20, No 2. — P. 213-284. — Bibliog.: 184 titles. — eng. |
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ISSN 1608-1021. Usp. Fiz. Met., 2019, Vol. 20, No. 2 213
© Yu.S. ProjdAK, V.Z. KUtSoVA, t.V. KotoVA,
H.P. StetSeNKo, V.V. PrUtcHYKoVA, 2019
https://doi.org/10.15407/ufm.20.02.213
Yu.S. Projdak, V.Z. kutSoVa, t.V. kotoVa,
H.P. StetSenko, and V.V. PrutcHYkoVa
National Metallurgical Academy of Ukraine,
4 Gagarin Ave., UA-49000 Dnipro, Ukraine
regUlarities of forMation
of strUctUre, textUre and ProPerties
Under the coMbined Plastic deforMation
of the low-carbon and Ultralow-
carbon steels for cold Press forMing
the current paper reports the new solutions intended to enhance the complex of
mechanical properties and tendency to the press forming of the hot-rolled low-carbon and
ultralow-carbon steels with subsequent cold deformation via upsetting and torsion
under hydrostatic pressure (tHP). Using state-of-the-art research methods, the fea-
sibility of forming an ultra-fine-crystalline structure through the combined plastic
deformation is established. the dependence of the change in mechanical properties
on the structural and textural parameters as well as phase composition is estab-
lished. this research is the first wherein the mechanical properties have been deter-
mined by the method of nanoindentation for the 08пс, 01Ют, 01Ют (Са), 01ЮтА
steels, which were initially hot-rolled and afterwards underwent the cold deforma-
tion by the tHP method. the increase in the indentation hardness by 2 times (5.5–
6.0 GPa) is revealed along with the decrease of the modulus of elasticity by 1.5 times
(150–190 GPa), but with the opportunity to sustain the satisfactory ductility
(δ = 0.75–0.8). this provides a great suitability to the cold press forming of the
steels as compared to their initial hot-rolled state.
Keywords: ultra-low carbon steels, nanoindentation, severe plastic deformation, torsion
under hydrostatic pressure, press forming, texture.
1. Introduction
the world achievements in the sphere of automobile industry demand
that the manufacturers decrease their product weights and lower the
pro duction costs but increase the operational safety degree. the most
214 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
suitable for these applications are low-alloy steels with conventional me-
cha nisms of strengthening as well as much promising IF-steels (inter-
stitial free steel). Manufacturing volumetric blanks of various metals
and alloys with nanocrystalline structures or ultra-fine crystalline struc-
tures by means of severe plastic deformation (SPd) is one of the direc-
tions being actively developed in the nanomaterials sphere. Among the
SPd methods, torsion under hydrostatic pressure and equal channel an-
gular pressing are most widely applied.
the development of the materials with ultra-fine-crystalline struc-
ture and the new level of properties via the SPd methods is impossible
without the profound knowledge of the regularities according to which
the structures change under the treatment regime influence. From the
above considerations, it is easily deduced why more and more topical are
becoming the researches addressing the development of new steels for
automotive sheets in terms of their quality as well as their production
technologies. the developments of such kind could be performed if based
on grounded fundamental researches and those of the applied nature for
the sake of the processes and the phenomena occurring during the manu-
facturing procedure and further operations with the metal produced.
However, the higher strength normally means decrease in ductility for
metals. Attaining high strength along with high ductility for develo-
ping new promising construction and operation materials is one of the
fundamental challenges for the material science. concerning ultra-fine-
crystalline structure metals and alloys, this problem can be solved by
means of control over their microstructures.
the influence of the structure fineness on the set of properties in
steels is described in the publications of V.V. rybin, V.I. trefilov,
K.d. Potomkin, Yu.V. Milman, S.o. Firstov, V.F. Moiseiev. considering
the fact that the cold plastic deformation is widely recognized to be
the efficient way for strengthening steels, there are publications (by
r.Z. Va liev, V.M. Sehal, S.V. dobatkin, Yu.Ya. Meshkov, M.L. bern-
shtein, A.A. baranov, t.G. Langdon) devoted to the analysis of the
struc tural changes of the metal under deforming conditions, but the
information on the influence produced on the structures and the tex-
tures of low carbon and ultralow carbon steel is still not comprehensive.
therefore, there is still a true need in the researches aiming at
establishing the regularities between the deformation regimes and the
properties of thin-sheet rolled stock of low-carbon and ultralow carbon
steels, namely their structures, textures, phase compositions and ma-
chinability properties.
After the introduction, the second section of this publication re-
views the contemporary researches reporting on the methods of plastic
defor mation for low carbon and ultralow carbon steels, the regularities
of their structure formation, their properties, the contemporary interpre-
ISSN 1608-1021. Usp. Fiz. Met., 2019, Vol. 20, No. 2 215
Regularities of Formation of Structure, Texture and Properties of Steels
tation of the deformation process occurring in metals and alloys. the
papers addressing the problem of the deformation degree influence on
the properties of thereof steels are also regarded in this section. based
on the information obtained from the scientific and the patented sour-
ces, the solution stages for this urgent scientific and engineering prob-
lem have been determined and they are considered as the development
of the rational regimes of combined plastic deformation for the low car-
bon and the ultralow carbon steels with the purpose to improve their
properties.
the third section provides the data on the material and research
methods. the object of the research is the samples of the hot-rolled
low carbon and the hot-rolled ultralow carbon 08пс, 01ЮтА, 01Ют,
01Ют (Са) steels, which are subjected to the additional cold plastic
deformation by means of the torsion under hydrostatic pressure.
the fourth section deals with the specific character of the structure
formation for hot rolled low carbon and hot rolled ultralow carbon steels
subsequently deformed by the methods of torsion under hydrostatic
pressure. Here, we report on the materials concerned with the influence
of the additional plastic deformation on the sizes of the crystallites, the
density of dislocations, the lattice parameters, and microstrength for the
investigated steel samples.
the fifth section describes the electronic microscopy studies con-
ducted with thin foil samples of the hot-rolled steels of 01ЮтА, 01Ют,
01Ют(са), 08пс grades. this allows observing the structural changes in
the process of combined plastic deformation.
Finally, in the sixth section, the characteristics of the strength and
the ductility of the hot-rolled low-carbon and the hot-rolled ultralow
carbon steels, which have been subsequently cold deformed, are inves-
tigated by the methods of torsion under hydrostatic pressure.
2. Structure, Properties and Methods of the Study
for thin-Sheet Low-carbon and ultralow-carbon Steels
for automobile Industry
2.1. Low-Carbon Construction Steels for Cold Press Forming
the world’s automobile industry is dynamically developing and consu-
mes a significant part of the global steel thin sheet production. the
products manufactured from these sheets are produced by the methods
of plastic deformation (press forming, deep drawing) and they can make
up to half of a modern wheel vehicle. the main requirement for sheet
steels in drawing is to provide a high degree of formability when the
manufacture of the components to possess intricate shapes and high
quality surface after the deformation, which is a strict requirement for
protective coatings.
216 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
the high plasticity of the solid parts prevents their brittle frac tures
in the events of accidents and decreases the weight of the car.
Ferrite is the main phase of low carbon and ultralow-carbon steels of
structural type for cold press forming. It undergoes aging during its
structural transformations triggered by the manufacturing process and
as the result, ductility is reduced but strength is increased. this ham-
pers or even makes it not feasible to carry out press forming by conven-
tional effort of the press, especially when the manufacture of solid parts
is commonly performed in two or three operations according to the
techno logy. the process of aging proceeds spontaneously: from the un-
stable oversaturated state of the ferrite to the maximum equilibrium
(natural aging), or because of plastic deformation (deformation aging).
For example, low carbon steel at the temperature of 400 °c can contain
approximately 0.02% of nitrogen in a solid ferrite solution, but once it
is cooled down to 100 °c and rolled, it loses all its nitrogen from the
solid solution into the Cottrell clouds. thus, this steel is capable of aging
and actually is not suitable for the manufacture of the car solid parts
[1]. Further, in order to prevent the deformation ageing of steel, the
carbide-forming and nitride-forming elements are introduced into its con-
tent; it is aluminium in priority that is able to neutralize the harmful
effects of excessive c and N. Furthermore, the steel acquires non-ageing
properties and is assigned 08Ю grade. If the increased strength is re-
quired, it is achieved by doping with phosphorus or with other elements
and this is marked as 08ЮП steel grade. this steel is demanded by the
automobile plants and meets the requirements of ГОСТ (State Standard)
9045-93 [2].
carbon is known as one of those elements, which greatly changes
almost all the properties of sheet steel, and it bears the special effect on
its formability. In the case of the carbon content less than 0.03%, the
matrix structure is to consist of relatively large ferrite grains that grow
after cold rolling during recrystallization annealing in a bell furnace
(Fig. 1). the ferrite grains are able to cause surface defect of so-called
orange peel during the press forming process when the automobile solid
parts being produced. that plays not in favour of the sheet steel quality.
the content of silicon in steels of 08Ю grade is not to exceed 0.02% as
Fig. 1. the effect of carbon
con tent in steel on the grain
size of a ferrite in the matrix
structure [2]
ISSN 1608-1021. Usp. Fiz. Met., 2019, Vol. 20, No. 2 217
Regularities of Formation of Structure, Texture and Properties of Steels
the presence of silicon within the metal strengthens it and makes it brit-
tle. therefore, the production route for the steel with the silicon con-
tent within 0.008–0.012% includes controlled deoxidation since alu-
minium reduces the silicon from the converter slag having entered the
teeming ladle before the tapping completion and the ladle refractories
are also capable of providing the additional silicon penetrating into steel.
Manganese exhibits both direct and indirect effect on a wide range
of properties of low carbon steels. First and foremost, it strengthens the
ferrite matrix, which is not desirable in 08Ю steel. However, alloying
with manganese is necessary for binding sulphur into the sulphides,
thus preventing the formation of the defect of the so-called band struc-
ture during the hot rolling operation. Moreover, manganese has a no-
ticeable effect on the kinetics of steel aging, as it slows down the rate
of nitrogen coming off from the ferrite lattice.
thanks to the above-said influence produced by manganese on steel,
manganese amounts introduced into steel are to exceed by 10–15 times
the sulphur content and are commonly within the range of 0.17–0.21%.
Similar to sulphur, phosphorus tends to worsen the ductility of low-
carbon steels and its content is required to be limited to meet the ap-
propriate standard demand.
the character and the degree of the interconnection between alumi-
nium and nitrogen in 08Ю steel have a powerful influence on the capa-
bility of low carbon steel for deep drawing and to extra deep drawing, that
is, formability without defects on the automobile solid parts.
Aluminium is introduced into steel with the purpose to remove that
oxygen from the melt, which enters it during the period of tap-to-tap
time and tapping. At the same time, aluminium interacts with nitrogen
Fig. 2. Schematic representation of the virtual compromise between the aluminium and
nitrogen contents in the sheet steel for an extra deep drawing [4], where 1 — increase
of the yield strength and temporary resistance, 2 — fine grain, 3 — working area
Fig. 3. the effect produced by low contents of chemical elements on the temporary
resistance of cold-rolled an nealed steel intended for deep drawing [4]
218 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
dissolved in the ferrite
and forms the nitrides,
which are released in the
form of dispersed parti-
cles. this inhibits the
growth of ferrite grains
during recrystallization
annealing operation and strengthens steel but insignificantly. by facili-
tating the removal of nitrogen from the ferrite lattice, aluminium even
at the stage of the molten steel heat production eliminates the possi-
bilities for this steel to undergo deformation aging at deformation and
heat treatment.
Nitrogen content decreasing in steel is a way to reduce the yield
strength, which contributes to the formability of the thin sheet steel. At
the same time, it is a way to dec rease the anisotropy of the thin sheet
structure and proper ties, to decrease the normal ani sotropy coefficient
(r), which com p lica tes the metal forming for the vehicle parts [3]. the
appropriate amounts of aluminium intro duced into that steel which con-
tains the predicted or measured amounts of nitrogen are the path of a
tried and tested compromise capable, as well as whatever compromise
does, of partial forming a satisfactory sheet formability. An example of
the virtual compromise is schemed in Fig. 2. the content of nitrogen in
08Ю steel does not nor mally exceed 0.006–0.007% on condition that
the cold-rolled metal is to be subjected to annealing in a bell furnace.
If the annealing of cold-rolled strips is carried out on continuous
lines, the steel is to contain less than 0.004% of nitrogen. According to
the recommendations for the cold-rolled strips passing the annealing
operation in bell furnaces through their production route, the alumini-
um content for introduction into the molten metal is to be 5 times more
than the content of its nitrogen. While the aluminium as much as 10
times nitrogen content is to be observed if annealing is of a continuous
type (at least one third of aluminium is consumed for binding the oxy-
gen of the melt and subsequent oxide formation).
optimally, the content of the dissolved aluminium within low-car-
bon steel of 08Ю grade is to be wit hin 0.03–0.04%, in accor dance to the
technology adop ted in a steelmaking shop.
the chemical elements, introduced into the melt by means of the
charge con stituents (iron, scrap, ca sual additives), except those intro-
Fig. 4. the influence of low
contents of chemical elements
on the ferrite grain size within
cold-rolled strips after anneal-
ing in a bell furnace [4]
ISSN 1608-1021. Usp. Fiz. Met., 2019, Vol. 20, No. 2 219
Regularities of Formation of Structure, Texture and Properties of Steels
duced into the charge calculation, are able to influence drastically both
the mechanical properties and the microstructure of the rolled products
made of 08Ю steel.
the character and the degree of this effect are shown in Figs. 3
and 4. the majority of the chemical elements can be considered as those
which strengthen the solid solution during recrystallization annealing
carried out for cold-rolled low carbon steels in bell furnaces as the pro-
longed treatment of the rolled stock is inherent to them, providing the
structure state and the stress level close to the equilibrium. this is
mostly expressed for phosphorus, weaker for manganese, silicon, copper
and nickel.
No less pronounced is the influence of various elements on the grain
size: niobium and titanium are the most strong ferrite grain refiners
while molybdenum and chrome are less effective in this.
the above data allow us to conclude that in order to achieve the
required properties of 08Ю steel, we have to maintain the minimum
contents of the elements for solid solution strengthening (phosphorus,
manganese, silicon, copper and nickel) and control the contents of the
elements affecting grain size (niobium, titanium, chromium and molyb-
denum). In addition, we have to coordinate carefully the content of the
elements that contribute to the formation of the particles of carbides,
nitrides, carbonitrides [5, 6]. thus, the very low contents of the men-
tioned elements are an important prerequisite for the production of
08Ю steel suitable for thin sheets, capable of deep formability. In this
case, the steel is to contain miserable amounts of nitrogen and the alu-
minium amounts corresponding to them.
the national standards do not limit the contents of nitrogen, chro-
mium, nickel, copper, molybdenum, titanium, vanadium within 08Ю steel.
However, the metallurgical plants utilizing their many-year expe rience
in the production of thin sheet steels with good formability properties
establish the requirements for the contents of those chemical elements,
which are non-standardized for 08Ю steel. As an example, can serve the
fact that in low-carbon steels for automobile industry, the chromium
content should not exceed 0.03%, while copper and nickel should not
exceed 0.06%. the weight content of niobium in steel is not to exceed
0.005%, while titanium is to be within 0.003%. Molybdenum and vana-
dium are allowed in an amount not more than 0.01% each of them.
2.2. The Automotive Steel without Atom
Introduction into Ferrite Lattice
the quality of cold-rolled products made of low-carbon thin sheet steel
of non-aging type do not satisfy the increased market demands of the
XXI century for automotive metal. the development of new steels should
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meet the goals of the new century, the rhythm of its fast life, high
speeds of movement, the necessary degree of the safety and the envi-
ronmental friendliness [7, 8].
the ІF steels are widely applied for their rather high strength and
sufficient ductility, their application enables the decreases in the auto-
mobile weight, fuel consumption, and carbon dioxide exhaust. From
year to year, the technological process of their production is being im-
proved. the plastic anisotropy of the cold-rolled sheet invariably in-
creases. the coefficient of the normal anisotropy for the cold-rolled
sheets for some grades of steel has increased to R = 2.2–2.4 [9].
thin sheet steel used in automobile construction, can be divided
into three groups: conventional steels for cold press forming (yield
strength <210MPa, tensile strength <340 MPa); high strength steel
(yield strength >210 MPa, tensile strength >340 MPa); high-specific-
strength steels (yield strength >550 MPa, tensile strength >750 MPa).
both cold-rolled and hot-rolled pickled automotive sheet steels are
usually supplied in a relatively narrow range of thicknesses (0.5–
4.0 mm) with appropriate quality indicators, which are intended for the
manufacture of specific parts, knots and car panels. the quality of auto-
motive steel is evaluated, above all, by its formability, strength, degree
of the destruction energy absorption, elastic modulus value, and ability
to perceive the process of parts connecting with a laser beam, reliability
of the adhesion of its surface with paint and corrosion resistance.
the composition and the level of car sheet quality parameters deter-
mine the use of appropriate steel grades for internal and external solid
panels (IF, VH, dP, Sr), for passive safety elements (HSLA, trIP) and
for the manufacture of bearing units and power components (Mart,
Mnb). In Ukraine, there have been no class of IF until recently, this is
explained by the absence in a steelmaking shop equipment feasible to pro-
vide an appropriate system of technologies for these type of steel (steel
heating, secondary metallurgy and steel teeming). currently, PjSc Al-
chevsk Iron & Steel Works is building a modern converter workshop with
two 300-ton converters of combined blowing. the station for pig iron
desulphurisation in the mixers is foreseen within the converter shop.
However, even presently steel is there produced in twin-bath steelmak-
ing units with a capacity of 2 × 300 t, is refined at a ladle fur nace and
Vd/Vod, and is cast at two-strand slab continuous casters.
the relative amounts of microalloying elements (titanium and nio-
bium) to be introduced into steel depend on the actual contents of car-
bon, nitrogen and sulphur in the melt and are determined by the calcu-
lations as follows. (a) For steels microalloyed with titanium: ti = (4c +
+ 1.5S + 3.43N)%. (b) For steels, microalloyed with titanium and niobium:
ti = (2.4S + 3.43N)%; Nb = 7.75c%. the deviation in the titanium con-
tent is allowed to be +0.03%, while that in niobium content of +0.02%.
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Regularities of Formation of Structure, Texture and Properties of Steels
2.3. Methods of Processing Automotive Thin-Sheet
Low-Carbon and Ultralow-Carbon Steels
2.3.1. Technologies of Hot Rolling and Cold Rolling,
Thermal Processing of Thin Sheets from Automotive IF-Steels
the required characteristics of a thin sheet IF-steel are developed predo-
minantly at the stage of the controlled rolling technique at a broad strip
hot rolling mill. Its temperature regime and force conditions of metal
deformation are determined during the experimental rolling processes
for the experimental strip lots. Moreover, the main attention here is
paid to the experimental determination of the optimal heating tempe-
ratures for slabs, the concluding stage of rolling and the operation of a
strip rolling into a roll. these temperatures are interrelated with the
amounts of microalloying steels with Nb or ti or both and at the same
time with numerous mechanisms of structure formation (niobium the
pre dominantly responsible for this). (1) during the inhibition of the re-
crys tallization process and consequent refinement of the matrix grain
with NbX particles, which despite their significant dissolution in γ-iron
lattice at slab heating, partly precipitate again under thermal mechani-
cal effect of the rolling process. (2) the polymorphic transformation,
strengthening of steels with the dispersion phenomena, heterogeneous
diffusion, which does not develop completely due to atomic radius un-
suitability (the atomic radius of niobium is large if compared to that of iron).
We cannot emphasizing the role of Nb in the matrix grain size for-
mation, since the recrystallization process is retarded by the carbo-
nitrides of the microalloying elements, released from the solution dur-
ing hot rolling and subsequent cooling of the IF-steel strips on the
reverse roller of a broad strip hot rolling mill.
the microstructural processes in IF-steels often overlap with each
other in time and have a mutual effect on each other. they occur at the
time when a slab is in a furnace as well as when the slab is in the rough-
ing group of the broad strip hot rolling mill, and when the broad strip
is in the finishing group or on the reverse roller. during these proc-
esses, the concentration of the solid solution increases while the grain
size decreases, the matrix is undergoing strengthening by means of so-
lidification, the structure transformation regions and those of the phas-
es are expanding, which have a cumulative effect on the entire set of
properties of the finished rolled metal.
by the targeted change in the pro cess parameters of IF-steel hot
rolling, one can control the microstructure that means producing sheets
with the necessary mechanical properties, texture and anisotropy, name-
ly, the control over the steel formability.
the temperature regime for hot-rolled strips (produced from IF
steels) is commonly developed for a possibility and necessity to obtain
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Fig. 6. Properties of annealed strips (at the estimated length of test samples, 50
mm) and heating temperature of slabs [11]
Fig. 5. the dynamics of austenite grain
growth at heating microalloyed steel
[18]
Fig. 7. effect of temperature of end of
rolling on the size of grain of cold-rolled
strip: а — coefficient of plastic anisotro-
py; b and c — with a thickness of 1.6 mm
(●, ○) and 1.2 (∆, ∆) at fast cooling after
rolling (●, ▲) and usual (○, ∆) [12]
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Regularities of Formation of Structure, Texture and Properties of Steels
the metal with a relatively fine grain microstructure of the ferrite ma-
trix. this is facilitated by its microalloying to inhibit the growth of the
austenite grains during preheating the dedicated slabs for rolling opera-
tions. the degree of ferrite grain growth restrain is illustrated by the
curves in Fig. 5.
In accordance with the graphs, that type of ti that forms resistant
nitrides at the crystal boundaries at steel heating, retards austenite
grain growth most intensively. the relatively low speed of austenite grain
growth occurs in case of steel heating to the temperature not exceeding 1000 °с.
the anisotropy coefficient (r) and relative elongation (δ) are noticeably
higher after cold-rolled strip annealing than that of the strips rolled
from the slabs and heated to the temperature of 1200 °с as it is implied
by the data in Fig. 6. However, force and energy conditions of hot roll-
ing for strips predetermine the necessity of heating IF steels slabs to the
temperatures of 1180–1210 °с.
the finishing temperature of strips rolling, the rate of their cooling
on a rolling mill roller table and the coiling temperature produce a notice-
able effect on the finished steel properties. the degree of this effect can
be calculated by the curves in Fig. 7.
2.3.2. Severe Plastic Deformation. Structure Formation at SPD of Steels
the processes of obtaining submicrocrystalline and nano-microcrystal-
line materials (with grains size less than 1 µm and less than 100 nm) by
means of plastic deformation are often called by the generic term of
SPd. the severe plastic deformation technique involves compression
with high degrees of deformation along with the application of high-
pressure values at the temperatures less than the temperature of recrys-
tallization [13, 14]. Y.e. Beygelzimer introduces the definition [15] of strain
accumulation processes, which occur at SPd. their main goal is the ac-
cumulation of strain in the blanks, but not their shape change. When
preparing nanocrystalline structures, the obtained level of the true de-
gree of strain can reach 4 and more. In order to describe these processes,
it is suggested to use the term of megaplastic deformation. obtaining
bulk nanostructured metals and alloys via SPd becomes an important
rapidly developing branch of the contemporary material science. this
process is aimed at creating materials with high mechanical and physi-
cal properties. the dispersion of a microstructure to a submicro crys-
talline or nano-microcrystalline level causes a significant increase in
strength, in fatigue strength and a decrease in the transition tem-
perature into the material superplastic state [15, 16].
the most popular techniques of SPd include high-pressure torsion
(HPt), based on the Bridgman anvil method and equal channel angular
pressing (ecAP), the latter was suggested by V.M. Segal in 1972 and
further developed by Valiev [17].
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the principal effect of ultra-fine-crystalline structure in the mate-
rials after SPd is the increase in the final material strength due to the
refining initial coarse-grained texture. the experimental results in
refs. [18–22] confirm the possibility of applying SPd methods to both
readily deformed materials and many difficult-to-deform ones. Among
the pecu liarities of the final structure, one can obviously distinguish a
fine grain size, predominantly high-angle boundaries with disordered
structural elements, a low density of the dislocation inside the grains
and non- equilibrium grain boundaries. With the objective to understand
the processes of structuring during severe plastic deformation, the
large-scale studies of the single-phase materials as well as the materials
with a small quantity of the second phase [23–27] have been carried out.
In accordance with these studies, two main mechanisms of grain re fi-
nement during SPd have been defined. the first mechanism is based,
first of all, on the dislocation activity, that is the accumulation of the
dislocations, their interaction and spatial rearrangement. this results
in the refinement of the coarse grains into numerous fine grains by
forming dislocations, and the evolution of the boundaries with a low
angle of disorientations into those with the high-angle grain boundaries
[28–29]. In the course of structuring within the areas of high density
of the dislocations, there occurs the arrangement of the dislocations
into the dislocation ‘walls’, which transform into deformation bands
at defor mation degree increasing [29]. the dislocation walls surro unding
the regions with a relatively low dislocation density form a cellular
structure. the peculiarities and the physical form of such structures
depend on the material and are determined by the stacking-fault ener -
gy (SFe) and the degree and temperature of deformation. When the
tem perature increases, the thickness of the dislocation walls decrea -
ses until the subgrain boundaries formation and, accordingly, the
number of the internal dislocations decreases. the deformation degree
affects the size and the disorientation of the adjacent cells: the increa -
se in the defor mation degree leads to the decrease of the average cell
size but the increase in the angle of the disorientation between the
adjacent cells.
the second mechanism of structuring during SPd, where the defor-
mation of twinning dominates, is commonly observed in f.c.c. metals
with low stacking-fault energy, for example, in tWIP steels [30, 31],
cu–Zn [43] and cu–Al alloys [32, 33]. the mechanisms of deformation
twinning have been studied widely enough. Several mechanisms of the
deformation-twins’ formation have been suggested for f.c.c. materials
in refs. [34–39]. Information that is more detailed is provided in the
review paper [40].
Wang et al. [41] have noted that not only the primary, but also the
secondary deformation twinning is characteristic of the second mecha-
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Regularities of Formation of Structure, Texture and Properties of Steels
nism of grain refinement in the process of SPd. this deformation twin-
ning refines coarse f.c.c. grains by means of the interaction between the
dislocations and the twins’ boundaries, thus transforming the twins’
boundaries into conventional high-angle grain boundaries. In publica-
tion [41], it is reported that the minimum achievable grain size is deter-
mined by the minimum thickness of the twins. It is known that the av-
erage thickness of a twin in the highly deformed materials is the function
of the stacking-fault energy of material [41]. obtaining a twin thickness
less than 2 nm in the material with low stacking-fault energy is feasible
[42]. However, until now, grain size of less than 10 nm has not been
obtained. this indicates the great complexity of the grain refinement
process in those f.c.c. materials where the stacking-fault energy is even
lower than that described by Wang for the cu–Zn alloy [43]. Moreover,
there have been cases registered wherein deformation produced not only
the effect of twinning, but also untwining [43–48].
Additionally, the deformation temperature effect on the mechanism
of structuring during deformation should be specified. the cross slip
and the dislocation mobility require thermal activation. However, the
twinning phenomenon during cold working can appear to be more be-
neficial than the dislocation mobility. therefore, the structuring mecha-
nisms can be different even at the deformation of the same material if
the deformation temperatures are different.
2.3.3. Torsion under Hydrostatic Pressure as One
of the Main SPD Techniques. Structuring
and Mechanical Properties of Steels during THP
the basic deformation during torsion under hydrostatic pressure (tHP)
technique is produced due to the torsion of a sample. the applied uniax-
ial pressure, which usually reaches several GPa, plays two roles. Firstly,
the pressure creates a quasi-hydrostatic compression region in the cen-
tral part of the sample, which prevents its destruction. Secondly, it in-
creases the friction between the strikers and the sample. due to the high
friction, the sample transmits the moment of torsion from the moving
striker and the latter is deformed by torsion.
currently, tHP is commonly used for the studies of the SPd phys-
ics. At room temperature or at lower ones, tHP is applied for producing
nanocrystalline structures in metals, alloys, intermetallics and ceram-
ics. the sizes of the samples before deformation are commonly less than
20 mm in diameter and 1 mm in height. After the deformation, the
height of the sample decreases down to 0.2–0.5 mm. the significant
refinement in the structure is already observed after one-half turn de-
formation, but in order to create a uniform nanostructure there, as a rule,
the deformation of several turns is required.
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the tHP of pure metals leads to formation of an equated structure
with the average grain size of 50–100 nm. In the alloys, the grain size
can be much smaller. the mechanism of severe deformation depends on
many factors, particularly, on the crystal lattice type and the stacking-
fault energy. A strong phasic character characterizes the process of
nanostructure formation.
In the pure f.c.c. metals, with a high stacking-fault energy (cu, Ni),
the sequence of structural transformations is as follows. While the tor-
sional deformation increases up to n ≈ 0.1 (where n is the number of
turns of the mobile striker), the dislocations are concentrating within the
boundaries of the subgrains (centres), which are almost dislocation-free
grain regions of arbitrary form separated from the other regions by low-
angle boundaries. At the further increase in deformation up to n ≈ 1,
the sizes of the subgrains are decreasing, and the degree of their diso-
rientation is increasing. At that, there occurs a gradual transition from
the subgrain structure into the grains, which mainly contain high-angle
grain boundaries.
the severe plastic deformation of alloys together with the formation
of nanostructures can also cause the formation of metastable states, for
example, the supersaturated solid solutions and the metastable phases.
In intermetallic compounds after tHP, there can be observed the long-
range order destruction that can lead to the complete disordering.
the materials obtained by tHP are characterized by a high level of
in ternal stresses and significant crystal lattice distortions. In such ma-
te rials, there can be found the anomalies of some fundamental proper-
ties, for instance, elastic moduli, the curie and debye temperatures,
satu ration magnetization. As a rule, the materials obtained by tHP are
characterized by the high strength at relatively low temperatures, high
plasticity and superplasticity at elevated temperatures.
the scheme of a contemporary plant for processing by the method
of torsion under hydrostatic pressure described in refs. [49–54], is
shown in Fig. 8. It differs from bridgman anvil [55] by a deepening in
the lower bar of the plant. It prevents metal creeping, which results in
providing quasi-hydrostatic pressure that allows the samples to be de-
formed for a long time without destruction. When the lower anvil is
rotating, the sample is being deformed by a non-precision offset owing
to the surface friction.
the deformation degree produced by tHP can be calculated by the
for mulae presented in ref. [55]. the same formulae have been used in
the earlier studies for cr–Ni steels [56] and f.c.c. metals [57] after tHP.
the first important results of these studies are obtaining an average
grain size of dav less than 100 nm under tHP (P = 6 GPa, ε = 7.1), the
decrease of dav with the decrease of stacking-fault energy [58], the pos-
sibility of a low-temperature recrystallization of nickel and copper sin-
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Regularities of Formation of Structure, Texture and Properties of Steels
gle crystals, which have been deformed
by tHP (ε is more than 5) at the tempe-
rature lower than the homologous tempe-
rature of ∝ 0.4Tmelting [58], and the possi-
bility of phase transformations in Fe–Ni
alloy caused by tHP (at P = 8–10 GPa
ε ≈ 5) [59]. to obtain this effect under
static compression it would be necessary
to apply a load of about 20–22 GPA.
Shear in the centre of the sample
equals zero and increases with the radius
extension, provided if the thickness of
the workpiece remains constant. Howev-
er, the close values of microhardness at different points indicate that
the structure in the centre of the sample is refined in a way similar to
those in the other areas of the radius [60–62]. the di salignment of the
strikers or other deviations from the ideal tHP scheme may be the rea-
son why the area of the reduced microhardness disappeared within the
sample centre [63]. Moreover, during tHP, the initial sample thickness
somewhat decreases after deformation, and the use of the ini tial thick-
ness data in the formula makes the estimated value of defor mation
lower as compared with the true value. In actual practice, the calcula-
tion formulae can be considered as only approximately equal to the ac-
tual deformation degrees. Additionally, it should be taken into account
that the nanocrystalline structure is formed under the influence of not
only external stresses, but also internal ones as well, that are not re-
lated to the true deformation. the tHP method provides rather high-
applied stresses for obtaining practically homogeneous structures with
the maximum refined grain [64–67].
In the early publications (see ref. [68] and references therein), the
sequence of structural transformations in tHP process has been studied
with such materials as Ni, cu with the f.c.c. lattice and the high stack-
ing-fault energy. based on the obtained results [68, 69], the following
phasic model of structuring has been proposed. the first stage of the
reinfor cement is characterized by the higher density of dislocations that
rear range in the boundaries of the cells with the higher deformation.
their sizes stabilize at the value less than 1 µm when reaching the de-
formation ε = 1.5–2. Further, with deformation ε = 2–4, the process is
characterized by the dislocations accumulation in the cell boundaries.
one can observe an increase in the angles of the cell boundaries disori-
Fig. 8. Scheme of severe plastic deformation
(SPd) of torsion under hydrostatic pressure
(HPt) [57]
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Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
entation up to the angles of approximately 10°. When embedding the
dislocations into the subboundaries exceeds the possible limits, the fur-
ther accumulation of dislocations inside the cell begins, which is accom-
panied by mechanical reinforcement at ε = 4–5. Under conditions of
tHP, the high level of internal stress causes the formation of the high-
angle boundaries with disordered structural elements, which serve as a
warehouse for a large number of excessive dislocations. this expression
of rotational defor mation modulus extends over the whole sample and
the deformation acquires the stable stage.
the study of the armco iron in ref. [70] confirms the stages of
nano structures formation under the torsional severe plastic deforma-
tion. At the first stage, with deformation N from 1/4 up to 1 turn, a
cell structure appears with low-angle boundaries, disordered structural
elements and a cell size of about 400 nm. Further, at the second stage,
which proceeds from 1 turn to 3 turns, the transition structure with the
signs of a cellular and a granular one is formed. With the increase in
the deformation degree, an average size of cells decreases, while the
angles of boundaries disordering increase, evolving gradually into a
homogeneous ultra-fine grained structure of granular type at the third
stage. Furthermore, the lattice of grains at the third stage is strongly
deformed, because of distant stresses from the non-equilibrium grain
boundaries with a high density of grain boundary dislocations.
the electron-microscopic studies after tHP procedure carried out
for [70] have revealed the similarity of the nanostructure formation
stages in the armco iron, in the single-phase steels of 13Х23т and AISI
316L grades. the only difference between them is the formation of the
finer grains in the steels at the third stage. thus, it can be stated that
the process of structuring under tHP has common features for pure
metals and alloys.
Ivanisenko et al. [71–74] observes a similar nanostructure forma-
tion, as well as the dissolution of pearlite plates in the industrial pearl-
ite steel (≈ 0.7% c) under tHP operation. After the shear that equals
100 at room temperature, the sample microstructure has been develop-
ing into the cell structure and contains partially dissolved cementite
plates. the further increase in the shear up to the level of 200 leads to
the nonhomogeneous grain structure formation. during this deforma-
tion, the grains of 100 nm in length and 15 nm in thickness have been
obtained. the dislocation walls separate the elongated grains with the
high density of dislocations. during the deformation, the distance be-
tween the cementite plates is reducing. After the shear that equals 300,
there develops a homogeneous nanostructure with the grain sizes of
about 10 nm and complete cementite dissolution. However, in the alloy
of ХН77тЮр with low stacking-fault energy [75] of disordering, the
cell structure has not been formed even at very high degrees of defor-
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Regularities of Formation of Structure, Texture and Properties of Steels
mation. the structure refinement occurs with the emergence and spread
of the shear bands, which with the increase in deformation are filling
the whole sample. For the stable deformation stage of ε ≥ 5, the struc-
ture with the regions that practically do not contain dislocations or
high-angle disordering is found to be characteristic. the sizes of the struc-
tural elements decrease with the decrease in the stacking-faultenergy.
In ref. [76], the structural changes of the ferrite and the austenitic
steels during the torsion under hydrostatic pressure (tHP) at room tem-
perature have been investigated. With the equivalent strains that are
equal to εv = 8 and εv = 32, the publication reports on obtaining a micro-
structure with an average structural element size less than 100 nm. on
comparing the obtained results with the armco iron, the austenitic and
the ferrite steels, it has been shown that the refinement of the initial
grains into the small crystals within the structure in case of both steels
has been shifted toward the lower deformation degrees. Any significant
changes have not been noted for equivalent strains above εv = 16 for
steel, but the sizes of the structural elements are less than in the armco
iron. the publication [76] has concluded that the grain size reduction is
conditioned by the increase of the alloying elements number as well as
the decrease in the stacking-fault energy. both factors are clearly de-
fined for these steels.
the research reported in ref. [77] presents the results with the ul-
tra-fine grained structure formation in carbon steels of 20 and 45 steel
grades under torsion in SPd at certain pressure and the temperatures
of 20 and 400 °с. It has been shown that an almost homogeneous struc-
ture with crystal sizes of 100–200 nm forms in both steels at room
temperature, while at elevated temperature the deformation localization
occurs in the sample periphery along with the formation of the nonho-
mogeneous microstructure in its diameter. SPd by torsion leads to the
increase in the material microhardness, the microhardness value after
deformation carried out at 400 °с is 2.5 times higher than that after the
deformation at 20 °c.
thus, SPd with carbon steels of 20 and 45 grades causes the for-
mation of the nanocrystalline structure with the grain or the fragment
size of 100–200 nm. during SPd by torsion, the nonhomogeneous defor-
mation occurs, the degree of inhomogeneity of this deformation increas-
es towards the peripheral area of the samples.
the deformation degree localization increases with the increase in
deformation temperature. However, despite the microstructure inhomo-
geneity, which can be detected by the optical metallography, the elec-
tron-microscopic research shows the refinement of the grains across the
diameter of the samples both on the periphery and in the central sample
area. It should be noted, that the increase of the deformation tempera-
ture does not lead to the increase in the sizes of the fragments, though
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they have non-equilibrium boundaries, capable of the offset or migra-
tion [78–87]. Probably, this deformation scheme with the shear compo-
nent predominance does not ensure any conditions for the grain-bound-
ary and the fragments migration that could lead to an increase of their
sizes. the other factor to prevent the growth of the grains could be the
disperse carbide particles that cause Ziner inhibition [87].
thus, the structuring process is staged at tHP and the average size
of the structural elements depends on the parameters of deformation as
well as on the material itself and its chemical composition.
3. research Materials and Methods
3.1. Materials
As the research materials, we selected the sheet metal cards of 2.07 mm
thick made of 08пс steel grade and rolled on a continuous sheet rolling
mill 1680 at the industrial plant of open joint stock company Zapor-
izhzhya metallurgical plant ‘Zaporizhstal’ (Ukraine, Zaporizhzhya). the
samples of 01ЮтА, 01Ют, 01Ют(са) steels were taken from the cards
with 3.5 mm of thickness after hot rolling on the continuous hot-strip
mill 2000 and pickling on the continuous pickling line, both operations
conducted at the industrial shop at the open joint stock company ‘Li-
petsk metallurgical works’ (russia, Lipetsk). the chemical composition
of the studied steel grades is given in table 1.
3.2. Methods
the experimental studies on the temperature rolling conditions were
carried out in the rolling laboratory of the Institute for Ferrous Metal-
lurgy named after Z. I. Nekrasov of the National Academy of Sciences
of Ukraine. table 2 presents the rolling deformation modes for the stud-
ied grades of steel. the procedure of the samples’ preparation is as fol-
lows. Metal heating before rolling was conducted in electric furnace
cH 1.62.51/11-и2 at the rate of 3 °с/s and holding time of 2–4 sec-
onds. the rolling was carried out on the laboratory single stand double-
high mill 280 in one or two passes (at the rolling speed of 1.4 m/s, the
pause between the passes made up the interval of 13–15 seconds). After
rolling, the cards of steels underwent air-cooling (from the temperature
of the rolling completion to the ambient temperature (Vcooling ≈ 5–8 °с/s).
In order to simulate the process, the coil was charged into electric fur-
nace of 25414/11-и1 type, where the temperature corresponded to the
coiling temperature, and it was cooled along in the furnace to the ambi-
ent temperature (Vcooling ≈ 0.05 °с/s).
the severe plastic deformation for the samples was carried out through
the method of torsion under hydrostatic pressure on the plant similar in
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Regularities of Formation of Structure, Texture and Properties of Steels
its type to the bridgman anvil; the experiment supervision was con-
ducted by the head of the department of technological engineering
V.F. bala kin, doctor of engineering science, professor at the National
Metallurgical Academy of Ukraine. the samples had been subjected to
cogging at room temperature by compression and then by torsion to dif-
ferent degrees of deformation.
After hot rolling, the low carbon and the ultralow carbon steels
were subjected to the additional plastic deformation by torsion under
hydrostatic pressure (see table 3).
the true deformation under torsion has been estimated by the follo-
wing formulae according to publications [88–92]:
1 1
2
ln ln ,
r Nr
h h
ϕ π
ε = =
(3.1)
Table 1. Chemical composition of low-carbon and ultralow-carbon steels
Steel grade
(type)
chemical composition, wt.%
c Mn Si P S cr Ni cu Al ti N2 ca
01ЮтА 0.002 0.12 0.01 0.006 0.011 0.01 0.01 0.02 0.05 0.062 0.005 0.0002
01Ют 0.003 0.13 0.02 0.008 0.012 0.01 0.01 0.02 0.041 0.056 0.004 —
01Ют (са) 0.003 0.12 0.01 0.005 0.011 0.01 0.01 0.02 0.041 0.070 0.004 0.0003
08пс 0.080 0.30 0.01 0.023 0.030 0.04 0.03 0.03 0.020 — — —
Table 2. Rolling deformation modes
or 01ЮТА, 01ЮТ, 01ЮТ (Са), and 08пс steels
Steel type
Theating Т1rolling h0 h1 ∆h1 ε1 Т2rolling h2 ∆h2 ε2 Σ∆h Σε Тcooling
°c mm % °c mm % mm % °c
01ЮтА 1000 970–
980
3.5 1.8 1.7 48.6 730–
740
1.30 0.50 27.8 2.2 62.9 660–
680
01Ют 1000 970–
980
3.5 1.80 1.70 48.6 730–
740
1.35 0.45 25.0 2.15 61.4 660–
680
01Ют (са) 1000 970–
980
3.5 1.8 1.7 48.6 730–
740
1.40 0.40 22.2 2.10 60.0 660–
680
08пс 1000 750 2.07 1.9 0.17 8.2 — — — — — — —
N o t e: Here, Theating denotes the sheet steel heating temperature, T1rolling and T2rolling
are the temperatures of the steel sheet rolling in the first and second passes, h0 is
an initial thickness of the sample, h1 and h2 are the thicknesses of the sample after
the first and second passes, ∆h1 and ∆h2 are the metal reductions in the first and
second passes, Σh is the total metal reduction in two passes, ε1 and ε2 are the relative
degrees of the metal deformation in the first and second passes, Σε is the total
degree of the metal deformation in two passes, Tcooling is a coiling temperature
232 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
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0 2
1
ln 1 ,
r
h
h
ε = + ϕ
(3.2)
where r is the sample radius (mm), N is the turning number, h0 is the
sample height before the test (mm), h1 is the sample height after the test
(mm), ϕ is the rotation angle (radian).
the following formula is applied to calculate the shear γ for tHP
method:
2 ,
N
r
h
γ = π (3.3)
where N is the turning number, h is the sample thickness, r is the sam-
ple radius (mm).
the equivalent strain is used to compare the degree of the shear
during tHP with the deformation degree at other SPd methods; accord-
ing to Mises criterion, equivalent strain is calculated by the formula:
equiv ,
3
γ
ε = (3.4)
where γ is the shear.
the nanohardness measurements were performed by means of the
nanoindenter G200 (USA) with a diamond triangular berkovich pyra-
mid. the measurements were made on the depth of 200 nm. the im-
prints were applied at the distance of 15 µm from each other. each
sample undergone 10 measurements, then the results were averaged.
the inden tation curve was built to determine the hardness (practically,
the load curve) in the coordinate reference system of ‘indentation depth–
resistance force to the indenter penetration’.
the new indices and characteristics have been introduced into the
indentation diagram for the materials mechanical properties and their
correlations supplement the existing indices presented in the Interna-
tional Standard ISo 14577 [93]. In general, the method of the auto-
matic inden tation provides a practically complete picture of mechanical
properties and structural conditions of new contemporary materials of
Table 3. Parameters of torsion under hydrostatic pressure
for the hot-rolled low- and ultralow-carbon steels
Steel T, °с P, kgf/cm2 P, MPа h0, mm h1, mm d, mm N
08пс
20
155 15.2
0.7 0.5–0.4 9
5
01ЮтА 155 15.2 5
01Ют 194 19.02 5
01Ют (са) 350 34.32 3
Note: T is a deformation temperature, Р is a torsion pressure, h0 and h1 are the
sample thick nesses before and after the tests, d is the sample diameter, N a revolution
number
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Regularities of Formation of Structure, Texture and Properties of Steels
any phase compositions and in any structural conditions even at the
smallest samples.
the mechanical properties of the studied steels after tHP opera-
tions were determined experimentally by the indentation method. the
obtained data processing has been carried out by the calculation method
using the methodology by S.o. Firstov [94]. the application of the metho-
dology allows defining the indentation hardness, the indentation elastic
modu lus, the boundary hardness, the non-contact elastic deformation at
in den tation, the non-contact elastic deformation stress, etc. the metho-
dology enables us to overcome sufficient methodological difficulties
connected with obtaining true values for the mechanical characteristics
of elasticity, strength and deformation of materials with special pro per-
ties (including nanostructural materials), the difficulties of such sort
arise when the traditional methods of testing are applied.
the characteristics of plasticity for the hot-rolled steels after addi-
tional cold working have been determined according to the metho dology
of Yu.V. Milman [95].
For the studies on the sample microstructures, optical microscopes
of Neophot-21 and Nikon eclipse MA-200 were used and the certain
sample preparation procedure was observed. the metallographic sam-
ples were prepared in the intersection diametric to the rolling direction
using the sand paper (ГОст (State Standard) 6456-82 [96]) with consist-
ent reduction of abrasive grit. Polishing with the diamond paste re-
moved the small grooves left after the abrasion and smooth mirror-like
surfaces of the metallographic samples were obtained. the polished sam-
ples were subjected to etching in the concentrated nitric acid, or to
chemical etching in a saturated solution of ferrichloride in chlorhydric
acid with the addition of some quantity of nitric acid. the quantitative
metallo graphic analysis has been carried out using the dedicated soft-
ware for the data processing and data analysis NIS-elements.
the measurement of the microhardness for the low carbon and the
ultralow carbon steels both in the initial hot-rolled state and after tHP
were carried out via the Future tech automatic hardness tester FM-700
(japan) with a load of 500 gf, the microhardness indentation time
of 50 seconds, this allowed determining Vickers microhardness. the
method of the microhardness measurement is regulated by ГОст 9450-
76 [97].
the phase composition, the crystal lattice parameters, the crystal-
lite sizes, the dislocations concentration and the microstress values have
been studied through X-ray crystallography in FeKα radiation via дрОН-
3M equipment. the analysis of the shape of the diffraction arcs has been
carried out applying the least-squares method and by singling out phy-
sical extensions of the lines by the method of the approximations of the
line profile by Gaussian [98–102].
234 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
the study of the spatial distribution of the structure elements orien-
tations has been conducted via the automatic analysis of the diffrac tion
patterns of the back-scattered electrons (ebSd-analysis) with the appli-
cation of Kikuchi lines in the scanning electron microscope jeoL jSM-
6490 at a 500 times’ magnification [102–107]. the abrasion machining
and polishing were accompanied by plastic deformation of the surface
layers. In order to remove the deformation surface layer of the sample,
electrolytic brightening was applied within the chemical agent consist-
ing of 15% perchloric acid +85% acetic acid at the solution temperature
of 8–15 °c and under the voltage of 12.5 V. Further, the washing in the
dis tilled water and ethanol followed [108–109]. the automatic deter-
mination of the crystallographic orientation on the surface was con-
ducted at steps of 1 µm each; in each experiment, a region of 255 × 191
steps was chosen and it took 5 hours of the scanning time.
the fine-structural investigation of the low carbon steel samples has
been carried out on jeoL electron microscope jeM-100cXII (japan).
the electrochemical polishing was done in the teNUPoL plant in elect-
ro lytic conductor: 30 ml of Hclo4, 175 ml of n-butanol, 300 ml of
сН3ОН.
4. the Influence of combined Plastic deformation
on the Microstructure Formation of Low-carbon
and ultralow-carbon Steels
4.1. THP Effect on the Structure Formation
of the Hot-Rolled 08пс-Grade Steel
the microstructure of the sheet product determines the level of its me-
cha nical properties and the quality of the pressed parts. the structural
components of the hot-rolled low-carbon 08пс steel are presented by soft
plastic ferrite and hard brittle cementite. the level of the mechanical
properties and the ability of the hot-rolled metal to be drawn mainly
de pend on the size and the homogeneity of the ferrite grains and on the
type and the position of the precipitated cementite [110].
the ferrite grain size in the hot-rolled sheet produced by rolling
with the fuel-free mould powder can vary from 7 µm to 35 µm. the fine-
grained structure (the grain diameter is 7 µm to 15 µm) increases the
strength characteristics and reduces the ductility of the metal that de-
teriorates its formability. the ductility of the fine-grained steels is
lower than that in the steels with the grain of 25–35 µm in diameter
while it is 15–20% higher than the ductility of the coarse-grained steel
with the grain size of 110–140 µm in diameter [111]. the coarse-grained
structure leads to the metal tearing during stamping, and forms a de-
fect of the ‘orange peel’ on the surface of the pressed parts.
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Regularities of Formation of Structure, Texture and Properties of Steels
the quality of the hot-rolled products is regulated by the norms of
дсту 16523-97, in particular, for thin metal sheets. Accordingly, these
requirements to the microstructure are to provide better formability
and the necessary quality of the finished parts [112]. thus, the standard
regulates the ferrite grain size, which must not exceed 62 µm for the
hot-rolled superfine thin sheet, but the ferrite grain size inhomogeneity
is considered acceptable in the boundaries of the three adjacent grit
numbers. the high grain-size inhomogeneity leads to the nonuniform
metal deformation when drawing, which can cause the metal tearing.
the uniform structure is also necessary in the hot-rolled metal for
semi-finished rolled stocks of the cold rolling mills. the favourable
structure of the metal appears to be the main prerequisite for achieving
the high deep drawing with steels after their final heat treatment, as
the hot-rolled metal structure significantly affects the metal structure
pattern when it is after cold rolling and subsequent recrystallization
annealing. the degree of the metal deformation on the dedicated mills
can reach 70–80%, and due to this, the high grain-size inhomogeneity,
which worsens the metal formability at cold rolling temperatures, can
cause the cracks in the sheets, and, as a consequence, can lead to indus-
trial accidents. At that, the grain-size inhomogeneity is reduced neither
by cold rolling, nor by recrystallization annealing [112].
our research in this section aims at establishing the microstructure
formation regularities with regard to the hot-rolled low carbon and the
hot-rolled ultra-low carbon steels after severe plastic deformation by
tHP method at room temperature.
Figure 9 shows the microstructures of the initial blank of 08пс
steel: the minimum deformation degree is 8.2% in the region of the
ferrite–pearlite metal structure if the heat schedule is up to 750 °c and
rolling is carried out in one pass. this provides a uniform texture across
the intersection of the complete metal sheet while the ferrite grain sizes
are within 8–20 µm (Fig. 9).
the grains are mainly equiaxial. the fine ferrite grain within the
steel sheet structure increases its elastic properties, at that the sheet is
difficult to form, its surface becomes wavy and resistance to forming
increases [114]. the microstructure of the sample under research is by
nature a ferrite and a phase that contains carbon in the form of the
structure-free cementite in amount less than 10%, which meets the re-
quirements of дсту 5640-68 [115]. the cementite particles with a shape
close to a globular one are evenly arranged in the basic ferrite struc-
tural component, which appears to be a favourable factor for the hot-
rolled metal intended for deep drawing.
In order to increase the mechanical properties and the formability
of the hot-rolled 08пс steel, its sample was additionally deformed by
tHP method at room temperature (refer to Fig. 10 for the images of the
236 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
subsequent plastic deformation). the microstructure analysis has showed
that after tHP of 08пс steel, in the sample centre and in the middle of
its radius there is a smaller grain refinement respecting the periphery
of the sample, where the maximum grain size decrease with a clear met-
allographic texture is observed [115, 116].
the shear initiation is a local kinetic structural transition that oc-
curs only in the local area of a crystal due to the phenomenon of the
entropy. the subsequent plastic flow in the course of the deformation
can be regarded as an absolute relief process, which tends to withdraw
the local strong excitation from the volume of the deformed crystal,
having used all possible channels of the crystal lattice structural rear-
rangement. the further evolution determines the regularities of the
metal plastic flow, which is a vortex one by its nature [117]. According
to the synergetic approach, the convective current appears to be the
Fig. 10. Microstructure of the surface of the 8пс steel sample after HPt (×250) for
е = 1.14 (a), е = 2.53 (b), and е = 3.16 (c) (see also [114–116])
Fig. 9. Microstructure of the hot-rolled 08пс steel, ε = 8% [113]: a — surface of the
sample, b — sample centre
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Regularities of Formation of Structure, Texture and Properties of Steels
most effective channel of the equiaxial system motion to the balance.
the crystal being deformed tends to form a structure with the elements
capable of conducting a convective current.
An example of such structure can serve the cellular dislocation
structure in the crystals with the moderate stacking-fault energy. each
cell moves as an independent structural element, experiencing the trans-
lation and the rotational deformation modes. the motion of separate
dislocations accommodates interaction of the adjacent cells, during
the process of polycrystal deformation, the autonomous motion is active
in each grain. At high deformations, the mentioned is clearly expres -
sed. the grain-by-grain mass transfer underlies the structural su-
perplasticity of polycrystals [117]. the condition of maintaining the
integrity of the deformed solids determines the multiplicity of the
slip in the crystal because of which shear stagnation areas occur. during
the deformation, a single crystal is split into the regions with the lim-
ited shear stagnation areas, the latter concentrate large stresses and
become the regions of the strong excitation that produce defects, i.e.,
the process of the cross slip develops to determine the crystal behaviour,
acting as a structurally nonhomogeneous medium. thus, during that
deformation, which causes the crystal splitting, the following takes
place: the regions are formed with the boundaries functioning as the
regions of stagnated shears, which are defined by the density of defects
and contain powerful stress concentrators. It is commonly known that
these regions must accommodate shears that flow on their boundaries
while the conditions for the integrity maintenance are not neglected
[117]. the classical studies [118, 119] emphasize that when analysing
a stressed state of a solid it is extremely important to take into account
the shear stress required to create a residual displacement of the solid
particles since the effect of the relative shear on the flow often overcomes
the influence of the other factors such as normal stresses, anisotropy, etc.
the microstructure study in the sample cross sections has confirmed
the presence of the strong deformation localization on the periphery of
the samples. Figure 11, a clearly shows the metal flow lines in the proc-
ess of deformation; the lines lead to the clear metallographic texture
formation which coincides with the direction of torsion. the plastic dis-
tortion of the material is a special form of the mass transfer.
It can occur in a strictly or moderately organized fault motion of
the crystal structure connected with the presence of the local excess or
the lack of the mass (the interstitials, the vacancies, the dislocations,
and their more complex formations). the partial dislocations also satisfy
this condition, since they are formed because of the removal or the in-
troduction of the material wedges from the sample or to the sample.
therefore, the motion of the partial dislocations also causes plastic de-
formation of the material.
238 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
the regions where the active flow of the metal occurs have been ob-
served in some areas of the sample. these are the regions with the ele-
ments of the turbulent or vortex flows and the regions of the laminar
flows. Such elements and those similar to them possess the nature of the
nonhomogeneous flows and are revealed at the relatively small optical
magnitudes (Fig. 11, b) [120].
the formation of such regions evidences that the different slip sys-
tems consistently enter the process of the plastic flow; it can be fixed in
Fig. 11. the cross-section microstructures of the hot-rolled steel samples after ad-
ditional deformation by tHP method (N = 5, d = 9 mm) [124]: a — general view
(×100), b–f — ×400, e–f — ×500
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Regularities of Formation of Structure, Texture and Properties of Steels
the phenomenological study of the metal deformation. According to
Schmid’s law [121], the slip is initiated within one or several planes,
where the shear stress reaches its maximum while the rest of the planes
are not active. then, the crystal axes turn because of the shear, and a
double shift, i.e., the simultaneous slip upon the two sets of planes, can
occur. With the increase in the stress, the deformation begins in less
favourably oriented planes. the similar turning leads to the generally
crystallographic orientation of the grains, which is one of the causes of
the mechanical properties anisotropy. thus, for the plastic deformation
compatibility, both the accommodation slip and accommodation turns of
the lattice are necessary.
the critical moment of the partial disclination initiated in the grain
boundaries can be considered as the moment of the rotational modes of
plasticity occurrence in the crystal and the beginning of its fragmenta-
tion [121]. A traditional description of the plastic deformation includes
the beginning of the metal plastic flow under stress; it considers only
homo geneous distribution of deformation in the sample volume and
takes into account only mechanical strengthening. this is a false state-
ment, which results from the fact that theory does not take into account
the main role of the temporal dependence of the gradient stress and the
dissipative nature of the metal plastic flow. considering them, one co-
mes to the fundamentally new conclusion anticipated by the theory:
without the emergence of an internal mechanical field of a vortex na-
ture within the deformed crystal, it is impossible to have the propaga-
tion of plastic deformation through the stable crystal. the plastic flow
of the metal with a stable structure is feasible only with the ‘estafette’
mecha nism of deformation. the relaxation of one stress concentrator is
to be spread throughout the sample, providing a local structural kinetic
crys tal transformation.
the microstructures of the sample surfaces of hot-rolled steel of
08пс grade after tHP are presented in Fig. 12; these microstructures
are characterized by the rotational modes presence. It means that at the
stage of the developed plastic deformation, the collective effects of the
evolution of the highly interacting dislocation assemblies cause rota-
tional modes of plasticity; their carriers are partial disclinations [122].
the elements of a nonuniform flow are revealed at relatively small opti-
cal magnitudes, but they represent the upper layer of the confinement
effect of the plastic deformation, that can also be clearly manifested at
deeper levels. to be exact, the movement of the individual dislocation is
the localization of plastic deformation, its primary spatial inhomogene-
ity. the plastic rotations are always accompanied by the shear. this
con clusion has been proved as based on the analysis of the peculiarities
of the fragmented crystal fine structure at the transition into the mac-
ro-level. thus, the rotational instabilities not only sharply reorient the
240 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
crystal lattice, but also lead to the directed transfer of substances in the
crystal being deformed [123]. At the late stages of the developed plastic
deformation, the powerful rotation and shear instabilities occur in the
fragmented structure; they are judged as the unexpected and abnor-
mally large plastic rotations and shifts of one fragment with respect to
the other one. these theory conclusions fully correlate both with the
general mechanical behaviour of the material and the structural trans-
formations under this discussion.
4.2. THP Effect on the Structure Formation
of Hot-Rolled Ultra Low Carbon Steels
the world experience in the IF-steels production shows the necessity of
their microalloying with niobium and titanium (in ref. [124] these ele-
ments are introduced in the amounts of 0.02–0.04%). According to the
data given in ref. [125], the titanium content must be as much as 4.5
times carbon content. In the current studies, the titanium content in the
ultralow carbon steels is higher (0.05–0.07%). the negative influence
of titanium (the strengthening of material, the formation of the acute-
Fig. 12. the sample surface microstructures of the hot-rolled 08пс steel after addi-
tional deformation via tHP, е = 5.30 (N = 5, d = 9 mm) [124]: a–c — ×200, d —
×500
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Regularities of Formation of Structure, Texture and Properties of Steels
angled carbonitride precipitation, which make the grain boun daries
brittle and reduce metal ductility) might have been compensated by the
presence of 0.0002–0.0003%of calcium in the ultralow carbon steels.
calcium is a surface-active element with increased horophility to pre-
vent the enrichment of the grain boundaries with titanium, copper and
phosphorus and combines sulphur and nitrogen, as well as to improve
plasticity and formability of steel [126].
the publications [127–130] presume that titanium carbides and ti-
ta nium carbonitrides that precipitate from austenite block the migra-
tion of the grain boundaries; due to this, the collective and secondary
ferrite recrystallization processes do not develop at steel slow cooling.
In ref. [131], the samples of the ultralow carbon steels and 08пс steel
have been analysed after the deformation in two passes in the auste-
nitic and ferrite or ferrite–pearlite temperature ranges, cooled in air
and in the furnace. the ultralow carbon steel structures turned out to
be similar (as the grains growth is restrained by the microparticles of
titanium carbides and titanium carbonitrides), but they differed from
the samples structure of 08пс steel rolled in two passes and the differ-
ence is in the size of the ferrite grains within the surface layers of the
sheet. the author explains this fact by the influence of microparticles
on the inhibition of the processes of the ferrite collective recrystalliza-
tion. the study of the microstructure evolution in the process of impos-
ing the load during torsion in bridgman anvils has revealed that with
the increase in the load there occurs the concentration of the disloca-
tions in the cells, the decrease of the cell sizes and the increase of the
disorientation between them. this leads to the activation of the defor-
mation rotational modes simultaneously throughout the sample, providing
a stable deformation stage [132, 133]. the elastic distortions also in-
crease due to the distant stresses from the non-equilibrium grain bound-
aries containing incor porated dislocations with high densities [134–136].
the microstructure of the hot-rolled ultralow carbon steels is shown
in Fig. 13. the microstructures of the 01ЮтА steel (Fig. 13, a, b) rolled
in two passes (the first — in the austenite temperature range, the se-
cond — in the ferrite temperature range with 60% deformation degree
and cooling in the furnace) is characterized by the presence of a fine-
grained layer of 150–200 µm thickness in the surface area of the sheet.
the ferrite grain size in this layer is 10–20 µm but in the central area,
the grain size reaches 20–130 µm. thus, the zonal grain-size inhomo-
geneity is obvious.
Further, for the microstructure of the 01Ют steel refer to Fig. 13,
c and d. this steel has been rolled in two passes: the first — in the
austenite temperature range, the second — in the ferrite temperature
range with 60% deformation degree and cooling in the furnace. the
micro structure is characterized by the presence of a fine-grained layer
242 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
of 150–200 µm in thickness in some regions of the stripped steel. the
ferrite grain size in the surface layer is 10–20 µm while in the central
layer the size makes up 15–130 µm.
the microstructure of the 01Ют (са) steel (Fig. 13, e and f ) has
been studied after the same preparation procedure as two previous
Fig. 13. the hot-rolled ultralow-carbon steel microstructures: а and b — 01ЮтА, c
and d — 01Ют, e and f — 01Ют (са)
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Regularities of Formation of Structure, Texture and Properties of Steels
steels: 01Ют (са) sample has been rolled in two passes: the first pass in
the austenite temperature range, the second pass in the ferrite tem-
peratures range, 60% deformation degree and cooling in the furnace.
the images in Fig. 13, e and f, evidence that the microstructure is cha-
racterized by the presence of a fine-grained layer of 100–200 µm in
thickness in some regions of the stripped steel. Its ferrite grain size in
the surface layer is 5–20 µm while the size in the central layer of the
stripped steel is 15–130 µm.
thus, the treatment of the ultralow carbon steels (in the austenite
range at the temperature of 970–980 °с, and in the ferrite range at the
temperature of 730–740 °c, cooling regime in the open air (Tcooling =
= 660–680 °c)) results to the formation of the zonal grain-size inho mo-
geneity that may be related to the static recrystallization process. dur-
ing the pause between the passes, there occurs restructuring in the
ferrite. In the more rapidly cooled surface areas, a recrystallized fine-
grained ferrite structure forms while the incomplete recrystallization
process results in the structure as in the central area.
Authors of the publication [137] claimed that a structure with elon-
gated ferrite grains is formed at low temperatures of the rolling comple-
tion in the surface areas of low-carbon steel sheets (at edges of the coils,
which are the rapidly cooled). the slow cooling does not faci litate the
completion of the recrystallization process in the central areas of the
ultralow carbon steel samples.
thus, the results of the study have shown that for obtaining a uni-
form structure in the ultralow carbon steel sheets treated in the last
pass within the ferrite temperature interval, the decrease in Tcooling is
possible. one of the possible variants of obtaining the elongated recrys-
tallized grains within the structure is the use of the additional heat
treatment operation (the annealing is to be not higher than the tempe-
rature of Ас1 at 690–710 °с for 3–5 hours). this will also increase the
fatigue resistance of steel and improve the condition of the rolled pro-
ducts surface.
After hot rolling, the steels of 01ЮтА, 01Ют and 01Ют (са) grades
were subjected to SPd by tHP method. Figure 14 shows their micro-
structures along the radii of the samples after tHP. during the torsion,
the deformation scheme of a simple shear type [138–140] was embodied.
this scheme is characterized by the constant change of the angle be-
tween the direction of the maximum shear stress and the direction of
the maximum elongation. In the process of torsion, there occurs the new
slip systems inclusion and the motion of dislocations is developing in
the systems that have not been previously applied. the microstructure
of the 01ЮтА steel is characterized by inhomogeneity of the strain dis-
tribution along the radius of the sample (Fig. 14, a–c). there are radial
lines of the plastic deformation localization on the periphery of the sam-
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ple, while the sample centre has a homogeneous microstructure. the
steel of 01Ют grade after tHP possesses a more homogeneous structure
from the sample centre to the middle of its radius (Fig. 14, d, e) while
on the periphery of the sample there are clearly defined strains of de-
Fig. 14. the microstructure of the surface of the hot-rolled steel samples after tHP:
a, b, c — 01ЮтА; d, e, f — 01Ют; h, i, j—01Ют (са) (×200). Here, a, d, g —
specimen centre; b, e, h — specimen middle part; c, f, i — specimen periphery
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Regularities of Formation of Structure, Texture and Properties of Steels
formation that coincide with the direction of torsion (Fig. 14, f ). At
that, the grain refinement increase is also observed. calcium in the com-
position of the 01Ют(са) steel affects the formation of a homogeneous
structure throughout the radius of the sample (Fig. 14, h–j), that indi-
cates about the uniform strain distribution.
5. combined Plastic deformation effect
on the Fine Structure and the texture Formation
of Low-carbon and ultralow-carbon Steels
5.1. The Fine Structure Formation
of the Low-Carbon08пс-Grade Steel after Hot Rolling
the electron-microscopic research on the thin foils of 08пс steel allows
us to detect the structural changes in the course of the combined plastic
deformation process. thus, the fine structure within the surface and in
the central areas of the hot-worked blank has been studied. the blank
was rolled under the Theating = 1000 °c, T1rolling = 750 °c (the two-phase
austenite–ferrite temperature range), the deformation degree was 8%,
the air-cooling.
Figure 15 demonstrates the electron microscopic images of the fine
structure of the middle areas (Fig. 15, a, b) and the surface areas
(Fig. 15, c, d) of the hot-rolled sheet steel of 08пс grade. the deforma-
tion for this steel was carried out at the temperatures of the lower range
of the intercritical interval; for this reason, a significant part of austen-
ite volume had already undergone γ → α conversion. this can serve as
an explanation why the noticeably deformed ferrite appears to be the
main structural component (Fig. 15, a). Figure 15 shows the individual
dislo cations, most of them are grouped into the polygonal walls that
separate the cells, and there are walls completely free of any disloca-
tions. the size of such cells in most cases is 0.5–1.5 µm, and the maxi-
mum is 5.0 µm. In the polygonal walls, the dislocation density is small,
there are individual dislocations observed, and even the regular (with
hexa gonal cells) fragments of the networks, which indicates active proc-
esses of diffusion at deformation temperature. due to this fact, such
dislo cation networks are the low-angle ones, this fact is confirmed by
the microdiffraction patterns in which the reflections are almost not
split, in some cases, they show disorientation not more than 1.5–2.0°
(Fig. 15, b).
the part of the austenite in the surface as well as in the central part
of the sample of the hot-rolled sheet steel of 08пс decomposes under
cooling by a diffusion mechanism to form the colonies of pearlite, which
are very rarely found at the electron-microscopic analysis of thin foils
(Fig. 16, a). Figure 16 confirms the pearlite colonies presence in the
sample central area of the 08пс hot-rolled steel; this pearlite has a typi-
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Fig. 16. the fine structure of the hot-rolled 08пс-grade steel: a — electron-micro-
scopic image of the pearlite colony in the middle layer, b — corresponding diffrac-
tion pattern
Fig. 15. the fine structure of the hot-rolled 08пс steel [155]: a, b — structure and
diffraction pattern of the surface area; с, d — structure and diffraction pattern of
the central area
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Regularities of Formation of Structure, Texture and Properties of Steels
cal laminar morphology. In general, pearlite consists of alternating pla-
tes of ferrite and cementite, and is the important structural component
of carbon alloys [141]. Within the boundaries of one colony, all ferrite
plates have a single ‘monocrystal’ orientation while, all cementite plates
are of a different orientation, which is clearly confirmed by the diffrac-
tion pattern from the central part of the colony (Fig. 16, b).
The dispersion of the pearlite is characterized by the interlamellar
spacing, i.e. defined as the sum of the thicknesses of the ferrite and the
cementite plates. The interlamellar spacing reduction is accompanied by
the steel strength increase. In the spheroidized state, the cementite ac-
quires the forms of ellipsoids or spheres of different sizes, due to which
such pearlite is less brittle [142]. If addressing the crystallography of
the pearlite component, in this case its microdiffraction pattern demon-
strates the presence of Petch-type orientation relationship between the
cementite and ferrite lattice [143]. Such pearlite structure is the result
of the growing in the hot-rolled austenite and it partly inherits its po-
lygonal substructure. It should be noted that the volume per cent of the
pearlite in 08ïñ steel is insignificant and its influence on the mechani-
cal properties is of no consequence, however, its structural pa ra meters
can have an effect on the structural changes that occur during the sub-
sequent intensive deformation by THP method [144]. Additionally, it is
worth saying that the existence of the pearlite colonies allows the fol-
lowing conclusion: the process of the austenitic phase enrichment with
carbon proceeds gradually and continuously from 0.08% and up to 0.8%.
5.2. Electron-Microscopic Analysis
of the Fine Structure of the Hot-Rolled 08пс-Type Steel
after Additional Deformation by THP
The severe plastic deformation of THP (at N 5, P 310 kgf/cm2) leads
to the fine-grain-structure formation if applied with the hot-rolled steel
of 08ïñ grade (Fig. 17). Due to the ununiformed deformation distribu-
tion along the radius of the sample, it is reasonable to carry out the fine
structure study on the middle of the sample radius (Fig. 17, a, b) and
on its periphery (Fig. 17, e, f ). The (ring) electron diffraction pattern
with point reflections implies the presence of the high-angle boundaries
(Fig. 17, b). The diffraction pattern obtained from the region located in
the middle of the sample radius indicates the presence of the textured
grains and their boundaries (Fig. 17, b). At that, the angle of the azi-
muthal blur is an important characteristic, which depends on the mea-
sure of the disorientation angle between the crystal lattices of individ-
ual subgrains on the image section of the sample structure. This measure
is the size or the diameter of the selector diaphragm, which under given
condition is 3.5 m on the image scale. The scheme to reveal the struc-
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ture peculiarities of reflections that are split into subreflections is
shown in Fig. 17, c, d. the region, heightened with a rectangle in Fig.
17, b, is shown at 8-fold magnification in Fig. 17, c, where via contrast-
ing it became possible to calculate the number of the subreflexes from
the po ly gons that form the reflection. In this case, the number of the
Fig. 17. the fine structure of the hot-rolled 08пс steel after additional deformation
by tHP method [113]: a, b — the structure and diffraction pattern of the middle of
the specimen; c, d — the formation scheme for reflections; e, f — the structure and
diffraction pattern of the specimen periphery
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Regularities of Formation of Structure, Texture and Properties of Steels
subgrains suitable for the diaphragm of 3.5 µm in diameter is 21 ± 3
subgrains. the azimuthal blur of the reflections in the diffraction pat-
terns is 17–21° (Fig. 17, d) as related with the deformation localization
on the sample periphery.
this permits bringing the conclusion that the sizes of the cells are
within 0.21–1.0 µm. At that, the angles of disorientation (θazim) range
from 20.5° to 26.1° (Fig. 17, c, d). on the periphery, the azimuthal blur
of the reflections is rather significant, which complicates their meas-
urement (Fig. 17, f ). due to this, the measurement of these angles has
been carried out by the reflections of {110} type planes, which corre-
spond to the orientation of the primary electron jet along the direc tion
〈111〉. this gives us the chance to select the angle out of 6 blurred re-
flections or equivalent maximums; this angle characterizes the real val-
ues of the deformation degree in the selected area. the average value
has been counted by 4 microdiffraction patterns and θazim = 32.1° has
been obtained.
5.3. The Fine Structure Formation of the Low-Carbon
01ЮТ(Ca)-Grade Steel after Hot Rolling
the electron-microscopic research of the thin foils from the samples of
steel 01Ют (ca) steel ensures the structural change tracing in the proc-
ess of the tested deformation modes. the fine structure has been studied
both in the surfaces and in the central areas of the worked blank and the
sample rolled under the following regime: Theating = 1000 °c; T1rolling =
= 970–980 °c; T2rolling = 730–740 °c; deformation degree: 61.5%; air-
cooling. Figure 18 demonstrates the fine structure fragments of the
surface area of the hot-rolled sheet steel of 01Ют(ca). A similar sub-
grain structure of 01Ют steel is widespread in the hot-worked steels
(Fig. 18, a), it appears because of the cell formation of the deformed
ferrite component.
the electron-microscopic research of the sample central metal and
the sample surfaces indicates the absence of the pearlite colonies within
the steel, as well as the absence of the carbide precipitations both along
the boundaries of the ferrite grains and in their internal volumes. the
density of dislocations is somewhat increased (ρ ≈ 4.5 ⋅ 109 cm−2) in the
ferrite (Fig. 18, a), whereas there is an increased number of the low-
angle polygonal boundaries, as a significant amount of the excess fer-
rite having already precipitated in the structure during the deformation
in the intercritical interval (740 °c). the average cell size (the sub-
grains) reaches dsub = 2.5 µm. one of such boundaries is located between
the grains A and B in Fig. 18, a.
the diffraction pattern has been obtained from the region that con-
tains the edges of the boundary (Fig. 18, b), due to which it looks like a
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single-crystal one with the zone axis [0
–
13]f. on closer inspection of the
reflections in the magnified and contrasted form (refer to Fig. 18, c), it
becomes obvious that the boundary between the subgrains A and B has
an azimuthal component of disorientation υ = 1.02°, that corresponds to
the arc distance between the reflections from the subgrains A and B.
Moreover, the reflections themselves have the form of the ellipses elon-
gated along the arc, with the radius of the reciprocal lattice r*
hkl = 42 mm,
measured on the magnified imprint of the microdiffraction pattern im-
age (Fig. 18, c). this relates to the existence of the evenly distributed
dislocations that are not bound into the polygonal or low-angle or sub-
grain boundaries, although they contribute to the higher strength of the
ferrite phase.
5.4. The Electron-Microscopic Analysis
of the Fine Structure of the Hot-Rolled 01ЮТ (Са)-Type Steel
after Additional Deformation by THP
the electron-microscopic research on the thin foils of the hot-rolled ul-
tra low-carbon steel of 01Ют (са) grade allows detecting the structural
changes in the process of SPd by tHP method (N = 5, P = 310 kgf/cm2).
Fig. 18. the fine structure of the hot-
rolled 01Ют steel [145]: а — electron-
microscopic image; b — diffraction pat-
tern, zone axis [0
-
13]; c — reflection
fine structure [2
-
13]
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Regularities of Formation of Structure, Texture and Properties of Steels
the fine structure of the radius middle part of the disk sample made
from the hot-rolled ultralow-carbon steel of 01Ют (са) after additional
deformation by tHP method is given in Fig. 19, a.
the deformation after hot rolling is distributed directly along the
radius of the disk sample, and this inhomogeneity is evident in the dis-
location cell structure both in the fine structure images and in the
microdiffraction patterns. the effect of deformation is visible in the
change of the cell sizes, which are characterized by the presence of the
azimuthally blurred diffraction reflections of the microdiffraction pat-
terns (Fig. 19, b). due to the deformation localization at the periphery
of the sample, the azimuthal blurring of the reflections is 17–21° in the
diffraction patterns (Fig. 19, d). In this case, it should be noted that the
image of the main reflection splitting has a centrosymmetric nature
that is characteristic of the vortex flow of the metal when there are
micro regions of rotation accompanied by the emergence of the rota-
tional modes. the size of the microcells with such rotational character
is 2–5 µm in diameter and more. thus, it can be assumed, that in the
central part of such cyclonic formations the density of dislocations is
somewhat lower than on the periphery (Fig. 19, c).
Fig. 19. the fine structure of the hot-rolled 01Ют (са)-type steel after additional defor-
mation by tHP [145], where a and b — structure and diffraction pattern of the middle
of the sample, c and d — structure and diffraction pattern of the sample periphery
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5.5. The Study on the Texture of Low-Carbon
Hot-Rolled 08пс Steel after THP via EBSD Analysis
the preferential orientation of the texture has a significant effect on
the structure-dependent properties of the polycrystalline substance. the
survey of the publications [146, 147] devoted to the study of the texture
formation processes and the mechanisms of the polycrystals deforma-
tion with the b.c.c. arrangement has revealed that the systematic study
of the textures has not been carried out, though these data are of scien-
tific and practical interest. ebSd method probes different crystal planes
with the electrons. In these types of studies, there are especially high
requirements for the quality of the surface; due to this, the samples
have been subjected to the electrolytic polishing in order to obtain mir-
ror-like surfaces at high speed with the absence of the field distortion
in the surface layer. It is important to have a detailed description of the
deformation methods, since not only the sample microstructure but also
the methods of its surface preparation for the ebSd research depend on
the history of the sample processing. It is known that during the prepa-
ration of the polished sections, the non-deformed material and the de-
formed material behave differently. the results of the ebSd studies
depend on the quality of the structure preparation. A quality structure
with minimal distortion is obtained when using non-deformed material
while the deformed material requires more careful preparation at the
polishing stage.
the surface of each sample has been previously studied with an opti-
cal microscope in order to select the areas for the research among the
sample surface and its central zones. However, with the development of
the SPd methods, a number of specific problems arise related to the
identification of dynamically recrystallized grains formed during the
deformation process. the textured material can be considered as an in-
termediate state between a material with a chaotic distribution of its
orientations and the material with the ideal orientations. one of the
features of the texture is scattering, that is the deviation of the grain
orientations from a certain medium. one of the ways to define a texture
is to describe its ideal orientation of the single crystals with observance
for their scattering phenomenon. based on ebSd analysis for the orien-
tation scanning, the orientation distribution functions are constructed
at each point of its direction.
the data on the texture type and its scattering have been obtained
after determining the orientation of each grain individually. For the
known orientation of a larger number of grains, the direct pole figures
have been constructed for planes {100}, {110}, {111}. Aiming at the tex-
ture description, the direct pole figure and inverse pole figures are ap-
plied. every pole figure is the average value of the grain distribution
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Regularities of Formation of Structure, Texture and Properties of Steels
over the spatial orientations. the texture of polycrystals can be de-
scribed via four coordinates. three of them determine the grain orienta-
tions while the fourth defines its density (its possible orientation).
therefore, even the presence of several pole figures does not enable the
establishing the quantitative connection between the properties of the
material and its texture. the direct pole figures of the hot-rolled low-
carbon steel of 08пс after additional deformation by means of hydro-
static pressure are shown in Fig. 20.
If we assume that in the hot-rolling process, the friction stress in
the deformation zone causes the formation of certain shear bands on the
metal surface, and these shear bands possess the different crystallo-
graphic parameters than the internal metal [148] and the recrystalliza-
tion pro cesses are different within them as well. the development of
recrys tallization in the mentioned metal with, so-called Goss texture
[149], (110) (001), is characterized by faster rates of nuclei formation
than those within the metal with other texture parameters. the high
rate of growth in the ferrite grains in this case is conditioned by recrys-
tallization mechanism grounded on grain coalescence.
the components from the hot-rolled steel of 08пс grade acquire cer-
tain texture characteristic features after processing additionally with
tHP methods and these characteristics are: (100), (110), (111). In the
central zone of the sample, the Goss texture is obviously singled out and
Fig. 20. Quantitative direct pole figures intensity within the texture of
the hot-rolled 08пс steel after hydrostatic pressure processing: a — sample
central part, while b — sample periphery
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it is the feature of the hot-rolled state that is confirmed by inhe riting
the texture of hot-rolled metal with further cold SPd by tHP method.
the publication [150] notes that the lattices of the majority of Feα
crystals are arranged in a way to have the crystallographic directions of
sliding 〈111〉 within the plane parallel to the rolling plane. this enhanc-
es the elongation properties of the cold-rolled sheet. the shape of the
recrystallized ferrite grains facilitate this: they are elongated along the
rolling direction, that is, the ratio of the two axes of the grain is more
than 1. the analysis carried out for inverse pole figures evidences that
there is the presence of the texture components of (101) and (001), they
have their maximal intensity in the sample periphery in the directions
of 0Y and 0Z (Fig. 21, b).
5.6. The EBSD Analysis of the Texture of the Hot-Rolled
Ultralow-Carbon 01ЮТ(Са)-Grade Steel after THP
the texture characteristic (intensity, scattering, orientation ratio) chan-
ge before the sheet intersection. It is due to the deformation inhomoge-
neity via the influence of the friction forces acting from the rolling roll
on the surfaces in contact. therefore, the velocity of the metal flow in
the internal metal is higher than that on the surface. the resulting tex-
ture of the central metal is more precisely expressed. Moreover, the
surface layers are often characterized by new orientations, which are
Fig. 21. Inverse pole figures of hot-rolled 08пс steel subjected to the further SPd
by the tHP methods: a — sample central part, b — sample periphery
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Regularities of Formation of Structure, Texture and Properties of Steels
not typical for the deformation texture and their presence depends on
the deformation scheme, temperature and degree. If due to the sudden
temperature drop, the texture of recrystallization is formed along with
preserving the deformation texture within the internal metal, then the
inhomogeneity of the texture is more visible. For the material with
b.c.c. lattice, the transition to the surface layers shows the lower inten-
sity and greater scattering of the texture. the less is the deformation
degree and the thicker is the sample, the better the texture inhomogene-
ity is expressed in it.
the pole figures allow us to judge on the texture intensity and its
scattering. In order to compare to examples of direct pole figures with
different degrees of lattice distortions (different deformation degree
and processing regimes), let us construct the levels of pole density. the
intensity, which is averaged per the whole pole figure, is taken as a unit
of pole density level to correspond to the chaotic orientation of the crys-
tals [151].
one of the texture characteristics is its intensity that is the density
unit filling the dedicated orientation of the {hkl} lattice by planes. the pole
figures establish the ratios between the crystallographic elements and
the conventional external directions of the sample. the colour con tours
on the direct pole figures indicate the intensity of the texture as compa-
red with the chaotic texture. the yellow and the orange colours identify
the minimal and the maximal values of the pole density in the units divi -
sible by the chaotic distribution. the points with close values of intensity
are connected with isolines. the pole figures of hot-cold 01Ют (са) steel
for the planes of (100), (110), and (111) are shown in Fig. 22.
though for b.c.c. metals it is sufficient to demonstrate the changes
in the pole figures (110), we present the figures for three most signifi-
cant directions of the cubic crystal. the best expressed in the sample
central zone of 01Ют (са) steel is the texture with the dominating ori-
entation of the ferrite grains biplane {100} (Fig. 22, a). the structure
inhomo geneity is observed in the intersection of the sheet rolled in two
passes: in the central zone there is the best texture of {100} type while
for the surface zone there are texture structures unity of {100} and
{111}. the texture of the sample central zone is characterized by higher
intensity than the texture of fine grains: the orientation pole density of
〈100〉 decreases if compared with surface layer with Р〈100〉 = 6.2 until
Р〈100〉 = 4.3 (Fig. 22).
thus, according to the data submitted in ref. [152], the velocity of
metal flow in the internal metal is higher than that in the surface layer
due to the inhomogeneity of the deformation. As the result, the texture
in the central metal is better expressed. therefore, through the whole
cross-section of the sample processed in the regime, the ordinary textures
of rolling formed with better expressed orientation are {100} and {111}.
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As known from refs. [153–158], the favourable is that texture
wherein the large part of the grain lattices is orientated in a way to ar-
range their crystallographic plane {111} parallel to the sheet surface.
the technology of IF-steel has to provide the preparation of the maxi-
mal amounts of the grains with such orientation.
the plastic effect within the metal occurs on condition that the re-
sis tance to the shear is higher than the ultimate one in some of the lat-
tice zones. In this case, sliding occurs on the plane towards the closest
packed atoms. For ferrite, this direction is the cube diagonal (111).
Within the ferrite grains, the lines of sliding are rarely straight lines,
unlike those of austenite. the ferrite grains are covered with bent-up
lines that are arranged on one or several middle directions. If the new
system of sliding lines intersects the previously formed lines, then the
value of sliding can be determined through the shears of those lines,
which have appeared earlier.
In ref. [159], the differences in the textures of the surface and the
central zone of IF-samples are explained by decarburization of the sam-
ple surfaces under metallic scales.
Figure 23 demonstrates the direct pole figures of 01Ют (са) steel
after tHP processing at room temperature. the noticeable increase of
the intensity peaks is found and this leads to formation of the less blur
structure within the central zone of the sample (Fig. 23, a) as compared
with the central zone of the initial state (Fig. 23, a).
Fig. 22. Quantitative intensity of direct pole figures within the hot-rolled steel tex-
ture of 01Ют (са)-type: a — sample central part, b — sample periphery
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Regularities of Formation of Structure, Texture and Properties of Steels
the analysis of direct pole figures of 01Ют (са) steel after tHP
processing has shown that the deformation at torsion leads to the high-
er intensity values in the sample periphery and therefore to forming
more precisely distinguished texture. the specific feature of the texture
after additional cold deformation by tHP method is the inheriting the
rolling texture with the components of {100} and {111}. After tHP, the
new component of {110} changes the texture.
the interpretation of the data obtained for the textures is the given
in refs. [160, 161]. the action of the crystallographically observed
mechanisms of deformation, including sliding and twinning at certain
crystallographic planes and directions, leads to the development of the
crystallographic texture within the metal being deformed. While the
deformation due to the mutual shear of grains is developed at non-
crystallographic intergrain boundaries, it is not related to the forma-
tion of crystallographic texture and causes texture weakening and scat-
ting in the initial metal.
From the above considerations, it is easily deduced that crystal -
lo graphic sliding leads to the sample texture enhancing while the
non- crystallographic mechanisms of plastic deformation cause the
blurred texture.
thus, in the process of deformation the following mechanism of
grain shears has been actively developed. Moreover, the influence of the
Fig. 23. Quantitative intensity of direct pole figures within the texture of the hot-
rolled 01Ют (са) steel after additional deformation by tHP methods: a — sample
central part, b — sample periphery
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crystallographic sliding cannot be neglected, though its contribution to
the texture formation is less expressed.
the maps of the inverse poles are united into the organization chart
with the crystallographic description of the single direction of refer-
ence. these maps indicate the principle directions within the sample and
the intersections of the directions. At each point of the map, the crys-
tallographic direction corresponds to the certain direction in the sam-
ple, and the colour is distributed in accordance to its position in b.c.c.
lattice. the orientations of certain crystallographic directions are en-
coded in the dedicated colours on the crystal orientation maps. the
analysis on the inverse pole figures provides information not only about
the presence of a texture within the sample, but also about the mecha-
nisms occurring during the processing. thus, as an example can serve
the case when the predominance of one of the pole densities can indicate
which relief me cha nism specifically prevails in the given sample: inter-
stitial or in ter granular slip while the changes in the texture can be re-
lated to the changes in the deformation mechanisms or the development
of dynamic recrystallization [162]. Moreover, if the maximum pole den-
sity is con centrated in the orientation range of 〈111〉 and 〈110〉, then
this evidences that the mechanisms of twinning have been actively
developed in the sample [163]. If the intensity of the normal yield
decreases and the distribution becomes more homogeneous, which is
observed in our case, and then we can speak about the texture blurring
Fig. 24. Inverse pole figures of hot-rolled 01Ют (ca) steel followed with further
SPd by tHP method: a — sample central part, b — sample periphery
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Regularities of Formation of Structure, Texture and Properties of Steels
and the activation of non-crystallographic mechanisms of plastic
deformation.
However, the texture analysis will not be complete without the anal-
ysis of direct pole figures. they show the density of the normal yield of
the corresponding crystallographic planes, in this case they are 〈111〉,
〈110〉, 〈100〉. consider the effect of tHP on the formation of a texture
in terms of inverse pole figures. In Figure 24, we demonstrate the
inverse pole figures in the crystal of the steel 01Ютt (ca) after they
have been subjected to tHP into different external directions: the di-
rection of deformation (0X), the transverse direction (0Y), the normal
direction (0Z) (direction of inverse pole figures) for cubic crystals 〈100〉,
〈110〉, and 〈111〉.
In the central zone of the sample (Fig. 24, a), the maximum density
is concentrated in the direction of 〈001〉 (inverse pole figures). the maxi-
mum pole density is observed in the direction of 〈101〉 and is concen-
trated near the direction of 〈111〉 (Fig. 24, b). In other directions (trans-
verse and axial), the principle changes have not been registered. Further,
the inverse pole figures becoming more acute indicate the presence of
crys tallographic deformation mechanisms during the proces sing proce-
dure, for example, internal grain slip (Fig. 24, b).
6. nanoindentation Method for defining Strength
and ductility of Hot-rolled 08пс-, 01ЮТА-, 01ЮТ-,
and 01ЮТ (СА)-Grade Steels after their additional
cold deformation
6.1. Strength Characteristics Determination by S.O. Firstov
Methodology Applied for Hot-Rolled 08пс, 01ЮТА, 01ЮТ,
and 01ЮТ (Са) Steels after Their THP Processing
Nanoindentation is currently reported to be the principle method for
determining the physical and mechanical characteristics of various ma-
te rials and coatings according to the nanoscale. Via this method, diffe-
rent mechanical characteristics of the material can be reported in a
num ber up to 20 [164, 165].
Aiming at determining how the method of nanoindentation reveals
the metallic material mechanical properties, international standards
(e.g. ISo 14577) have been developed and adopted. Moreover, a few
fac tors significantly affect the results of whatever mechanical tests
conduc ted by this method. they are surface roughness, temperature
drift, imperfect indenter geometry, peculiarities of the material struc-
ture and others. Further, there are the methods developed for data
processing and sample preparation, which take into account thereof fac-
tors [166, 167].
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the property of hardness is an issue of special concern among the
methods of material quality control. thereof is the fastest, simplest and
non-destructive method of analysis. Moreover, there exist methods ad-
dres sing to the other mechanical properties that have a correlation with
the hardness [168]. Further, the hardness measurements are used to test
the quality of sheet steel. these properties do not bring the con clusions
concerning the behaviour of steel during pressing, but very often, the
sheets with a low hardness are well pressed [169]. the publications [170,
171] utilize the assumptions [172] for the first purpose of ela borating the
detailed method for the Young’s modulus determining and for the second
purpose of obtaining reliable values of hardness. the particular attention
is drawn to the fact that the indenter penetration depth registered in the
indentation diagram does not coincide with the depth of its imprint dur-
ing which the contact between the indenter and the material takes place.
In this connection [173, 174], the value of the hc penetration depth is
introduced, wherein the contact between the indenter and the material
occurs after the complete load until Pmax. In this part of the indentation
imprint, there occurs an elastic-plastic deformation and possible destruc-
tion of the material, as well as the elastic deformation of the indenter.
In ref. [175], the possible physical causes of the scale effect within
the materials are considered during testing by nanoindentation. thus,
the experiments on nanoindentation enable the further studies on the
relation between the structure and the mechanical properties of a wide
range of materials at the nanoscale. these studies are important when
designing materials with a given set of properties.
6.1.1. Indentation Hardness Calculation
the indentation hardness with the applied force (Pmax) in the contact
area of the indentation imprint (hc) can be expressed as follows:
max
2
,
24.5IT
c
P
H
h
= (6.1)
where Pmax is an applied force (N), hc is a penetration depth formed by
the contact between the indenter and the material after the complete
load (until Рmax).
max
max
max
0.75 .
/c
p
h h
dp dh
= − (6.2)
the indentation hardness with utilization of the work (Wc) per-
formed by the applied force (Fmax) for the displacement of the material
by the indenter within the contact area of the indentation imprint can
be defined as follows:
HWc = 0.843 НIT, (6.3)
where НIT is indentation hardness (GPa).
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Fig. 25. distribution of the indentation hardness along the sample radius for ultral-
ow-carbon steel sample in the initial hot-rolled state and in the state after addi-
tional strain by the tHP method. Here, 1 — sample centre, 2 — sample middle ra-
dius, 3 — sample periphery; a—01ЮтА (N = 5), b — 01Ют (N = 5), c — 01Ют (са)
(N = 3)
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Figure 25 illustrates the distribution of the indentation hardness
and the hardness of the work along the sample radius after the tHP
operations with the 01ЮтА, 01Ют, and 01Ют (са) steels. It has been
established that after tHP processing, the steels of 01ЮтА and 01Ют
show the same type of the hardness change along the radius of the sam-
ple. From the sample centre to the sample middle metal, the hardness
increases in both steels: 2.1 and 2.6 GPa in 01ЮтА while 2.5 and
2.9 GPa in the 01Ют. At the periphery there is a decrease observed in
the hardness of 01ЮтА steel down to 2.0 and 2.3 GPa. the changes in
the hardness of 01Ют (са) and 01Ют at tHP are different in their na-
ture: the maximum hardness values are observed at the periphery of the
sample and reach 4.9 and 5.8 GPa 01Ют (са), and those for 01Ют are
2.9 and 3.4 GPa.
For all the cases studied with the ultralow-carbon steel, the hard-
ness increase has been found during the tHP processing both in the
centre and at the periphery of the sample. the nonhomogeneous distri-
bution of the hardness along the sample radius of the sample is ex-
plained as the result of the deformation localization at the periphery of
the sample.
In Figure 26, we demonstrate how are distributed the indentation
hardness and the hardness obtained via the work along the 08пс sample
radius after tHP processing. the attained results allow us to claim that
the hardness of the 08пс steel after tHP processing varies over the ra-
dius of the sample: from its centre to its periphery, the hardness in-
creases: H1 = 3.4 GPa and H4 = 6.0 GPa, respectively.
Fig. 26. distribution of the indentation hardness along the sample radius of 08пс
steel in the initial hot-rolled state and that after the additional strain by the tHP
method (N = 5): 1 — sample centre, 2 — middle of sample radius; 3, 4 — sample
periphery
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Regularities of Formation of Structure, Texture and Properties of Steels
the hardness values calculated per the work parameter are slightly
lower than the indentation hardness and vary from 2.9 to 4.8 GPa. the
value of the hardness on the sample periphery is 2 times higher than
the hardness of this steel in the initial hot-rolled state. this also con-
firms the fact of the deformation localization on the periphery of the
sample [176].
6.1.2. Calculation of Noncontact Elastic Strain and Corresponding Stresses
in the Hot-Rolled Low-Carbon and Ultralow-Carbon Steels Subjected
to Additional Deformation via THP Methods
the ref. [177] reports on the correlation revealed that determines the
elastic deformation of not completely recovered nature in the material
indentation imprint (when the elastic deformation is only a part of the
elastic-plastic deformation). It is able to describe only that part of the
elastic deformation which is manifested in the non-contact region of the
indentation imprint, that is, it is related to the material located within
the deepening around the indenter (the material ‘feels’ elastic defor-
mation, εes, only). In order to calculate the non-contact elastic deforma-
tion during the indentation the following formula is applied [176]:
εes = 0.0984 × (hs/hc) = 0.307 × (НIT/Е *), (6.4)
where hs is the indenter penetration depth (no contact with the material
resulting in the material deepening around the indenter), hc is the in-
denter penetration depth (contact between the material and the indenter
after complete load until Рmax), НIT/Е * is the material resistant to the
applied stress.
the non-contact elastic deformation of hot-rolled ultralow-carbon
steels after additional plastic deformation by torsion under hydrostatic
pressure has been calculated according to formula (6.4) and the results
are presented in Fig. 27.
the method of automatic indentation allows defining the limit value
of the elastic deformation, which can be reached within the material:
εes
limit = 0.5626 ln (sinα) (εes
limit ≈ 5.5% for a standard berkovich inden ter).
depending on the material and the conditions of its loading, this value
may be sufficient or insufficient to complete its real elastic properties.
the calculated values of the elastic deformation occurring along the
sample radius of ultra-low carbon steels are presented in Fig. 27.
the analysis on the image in Fig. 27 confirms the fact of the uni-
form distribution of deformation along the radius of the ultralow-car-
bon steel sample. In the initial hot-rolled state, the values of εes are as
follows: for 01ЮтА steel, εes = 0.00287; for 01Ют steel, εes = 0.00423,
while for 01Ют (са) steel, εes = 0.0033. In the process of tHP process-
ing, the value of εes increases from the sample centre to its periphery as
264 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
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Fig. 27. distribution of the calculated values of elastic deformation along the sam-
ple radius of the hot-rolled ultralow-carbon steel (in the initial hot-rolled state and
after additional strain by the tHP methods): 1 — sample centre, 2 — middle of
sample radius, 3 — sample periphery; a — 01ЮтА, b — 01Ют, c — 01Ют (са)
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Regularities of Formation of Structure, Texture and Properties of Steels
follows: from εes = 0.003955 to εes = 0.00832 for 01ЮтА steel, while the
values of εes = 0.005018 to εes = 0.1085 are detected for 01Ют steel. For
01Ют (са), which contains calcium, the value of εes also increases from
the sample centre to its periphery: from εes = 0.004287 to εes = 0.00795;
however, there is a decrease in this value found within the sample mid-
dle radius as εes = 0.003027.
the calculated values of the non-contact elastic deformation for
08пс-grade steel are demonstrated in Fig. 28 (hot-rolled material after
additional plastic deformation by the tHP methods).
the calculation of the elastic deformation values have been carried
out. they vary along the radius of the sample: the minimum value in
the centre is εes = 0.004, while the maximum one is at the periphery
εes = 0.011. It follows that both the elastic and the plastic properties of
the material, revealed by the indentation procedure, are controlled by
the value of the material elastic deformation.
6.2. Determining the Ductility Characteristics of 08пс Steel
and the Ultra-Low Carbon Steels in Hot-Rolled State
and after THP Processing by Yu. V. Milman Methodology
two fundamental properties can be distinguished in the physics of
strength. they determine the mechanical behaviour of materials in
terms of strength and plasticity. the strength of the material is deter-
mined by its ability to withstand the applied force [176]. More specifi-
cally, the strength of a solid can be defined as the resistance of a solid
to tearing into two or more parts. Strength is calculated in accordance
with thereof definitions when tested for tension by a destructive load
Fig. 28. calculated values of the elastic deformation for 08пс steel in the initial
hot-rolled state and after additional deformation by the tHP method along the
sample radius: 1 — specimen centre, 2 — middle of sample radius, 3 — sample
periphery
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divided by the sample cross-sectional area. In physics and in engineer-
ing, plas ticity is determined by the ability of the material to undergo
per manent deformation under loading [178]. In the russian conven-
tional physics of strength and physics of plasticity, A.N. orlov and V.r.
regel defined the plasticity as ‘the properties of solid bodies to be ir-
reversibly deformed under the influence of external forces or internal
stresses’ [177].
commonly, plasticity is characterized by elongation of ductility (δ)
when tested for tension or lateral narrowing of toughness (ψ) before the
fracture occurs. these parameters of the material are of great practical
importance, but they do not completely reflect the essence of the above
definitions of plasticity. this is because they determine the conditions
for the transition from a plastic deformation to destruction and do not
always correlate with the definition of plasticity in the sense of the ma-
terial ability to undergo the permanent deformations under load.
thus, the parameters of δ and ψ are determined not only by plastici-
ty, but also by, at least, two other conditions: the ratio between the yield
stresses and the destructive strain, as well as the strain strengthening.
the parameter of δ normally includes uniform deformation and defor-
mation after the formation of a stable “neck” and the deformation locali-
zation within it. According to the above-mentioned physical defi nition,
the plasticity of the material is to increase continuously with the tem-
perature increasing since the temperature increase facilitates the move-
ment of dislocations in solids (the exception is some inter metallides).
therefore, it is reasonable to introduce a new characteristic of plas-
ticity as a constituent of the plastic deformation within the general
elastic-plastic deformation [179]. Such a characteristic (in accordance
with the physical definition of plasticity as the ability of a material to
be plastically deformed) was proposed in ref. [180] in the form of a
dimensionless parameter.
this characteristic of plasticity can be determined by various me-
thods of mechanical testing (stretching, compression, bending), but it is
easier to determine it when the tests with a pyramidal indenter, as
shown in refs. [181–183].
When indentation is over the small amounts of material being de-
formed, the specific character of the stress fields reduces the ability to
the macroscopic destruction and dramatically reduces the temperature
of cold brittleness. this makes it possible to determine the hardness and
the characteristics of plasticity for most materials, even at cryogenic
temperatures.
For a standard berkovich indenter, the plasticity characteristics
(δH) can be determined by the following expression [184]:
21 10.2 (1 2 ) ,H v v HM Eδ = − × − − (6.5)
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Regularities of Formation of Structure, Texture and Properties of Steels
where v is Poisson’s ratio, НМ is a hardness of indentation (GPa), and
Е is modulus of elasticity (GPa).
the calculation of the plasticity characteristics of (δH) is required
for the studies when the scientists address the chemical composition
influence, thermal and mechanical processing and the structural state
in terms of hardness, microhardness and nanohardness of materials. It
can be defined as below. Uniting the characteristics of strength and
those of plasticity enables a more complete description of the material
mechanical behaviour than that involving only hardness phenomenon.
the plasticity characteristic (δА) is determined in accordance with ref.
[185] and is calculated from the ratio of the planes to the continuous
plasticity (δА) determined by the method of continuous penetration dia-
gram (Fig. 29) by formula
1 ,p e
A
t t
A A
A A
δ = = − (6.6)
where Ae is area under the unloading curve, At is area under the load
curve, Ар = Аt − Ae.
the characteristics of plasticity (δА) determined by the method of
continuous penetration, is an analogue of the dimensionless plasticity
parameter (δH), the constituent of the plastic deformation within the
general elastoplastic deformation under the indenter, which character-
izes the ability of the material to formability under deformation.
the changes in the values of the plasticity characteristics of δH and
δА after tHP along the radius of the ultralow-carbon steel sample, cal-
culated by formulae (6.5) and (6.6), are shown in Figs. 30 and 31. For
steels of 01ЮтА and 01Ют, the same type of change in ductility δH is
observed: from the centre to the periphery, the plasticity characteristic
of ductility is reduced (Fig. 30, a and b), which agrees with the distri-
bution of the hardness along the radius of the sample. For the steel of
Fig. 29. Load–strain diagram
of a standard berkovich inden-
ter in the coordinates of the
load and displacement of the
in denter [185]
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Fig. 30. distribution of plasticity characteristics (δH) of the ultralow-carbon steel
along the sample radius in the initial hot-rolled state and after additional strain by
tHP methods: 1 — sample centre, 2 — middle of sample radius, 3 — sample periph-
ery; a — 01ЮтА, b — 01Ют, c — 01Ют (са)
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Fig. 31. distribution of plasticity characteristics (δА) of the ultralow-carbon steel
along the sample radius in the initial hot-rolled state and after additional deforma-
tion by tHP methods: 1 — sample centre, 2 — middle of the sample radius, 3 —
sample periphery; a — 01ЮтА, b — 01Ют, c — 01Ют (са)
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Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
01Ют (ca), there is a slight change in this dependence, the plasticity of
the sample middle metal is equal to the initial value, while in its centre
and at its periphery the ductility is lower (Fig. 30, с). despite a slight
decrease in the Young modulus, the increase in the hardness at the sam-
ple periphery of the ultralow-carbon steel being studied leads to a slight
decrease in the plasticity characteristics of ductility δH: up to 0.8–0.85
of the hot-rolled ultralow-carbon steel subjected to tHP. It has been
established that the ductility δА of the ultralow-carbon steel after tHP
decreases within the distance from the sample centre to its periphery.
the analysis of Figs. 30 and 31 has shown a good consistency of meas-
urement results in two plasticity characteristics (δН and δА). the maxi-
mum values of plasticity are observed in the sample central part
of 01ЮтА (Fig. 30, a, and Fig. 31, a), 01Ют (Figs. 30, b, and 31, b),
01Ют (ca) (Fig. 30, a, and Fig. 31, a). the ductility of δН and δА on the
sample periphery reaches the minimum values, but the plasticity re-
mains at a rather high level, despite the high values of its hardness. the
special methods have been developed; they allow improving the ductility
of nanostructural materials to some extent.
the most known methods [186] for increasing the plasticity of nano-
structured materials include the following. the formation of a duplex
structure consisting of nanoscale grains and a number of larger grains
in which plastic deformation is initiated; the formation of nanodispersed
particles of the second phase, able to cause the deformation strengthen-
ing and to increase deformation before the formation at the stable neck
stretching.
the possibility to characterize quantitatively the plasticity of the
ultra fine-grained ultralow-carbon steel (like other steels) opens up the
possibility of finding the ways to increase the plasticity of these materials.
For the 08пс steel (ε = 8.2%) in the initial state, the value of the
plasticity characteristic is δH = 0.901. the drop in the plasticity charac-
teristics after tHP processing is caused by an increase in hardness
values stipulated by the surface hardening. the uneven distribution
of the plasticity characteristics along the sample radius is explained by
the nature of the deformation localization in the tHP process at the
sample periphery. For е = 5.308 and H = 6.01 GPa (corresponds to the
value at the sample periphery), the ductility index is δH = 0.752; while
for е = 3.8 and H = 3.4 GPa (in the central sample zone) δH = 0.892,
which is very close to the value of the ductility index in the initial state
(Fig. 32) [186].
thus, the plasticity characteristic of δH is determined by the ratio of
HM/E. With the increasing hardness, the value of this plasticity charac-
teristic decreases at a constant elasticity modulus (E). Moreover, the effect
of the plasticity reducing along with the hardness increasing should en-
hance together with the simultaneous reduction of the Young modulus.
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Regularities of Formation of Structure, Texture and Properties of Steels
Figure 33 illustrates the variable value of δА along the radius of the
steel sample of 08пс. the experimental studies have shown that δН ≈ δА
with the sufficient accuracy. In the initial hot-rolled state, δА = 0.894.
there is observed a drop in the plasticity along the radius of the sample
from δА = 0.884 to δА = 0.727. At this, the plasticity δА is defined by
formula (6.6). Unlike the method applied for δН, it does not require the
defining of the Young modulus, the hardness and the Poisson ratio,
which are able to bring some error into the calculation.
Fig. 33. distribution of plasticity characteristics (δA) for 08пс steel along the sample
radius in the initial hot-rolled state and after additional strain by tHP methods
[186]: 1 — sample centre, 2 — middle of the sample radius, 3 and 4 — sample
periphery
Fig. 32. distribution of plasticity characteristics (δH) for 08пс steel along the sam-
ple radius in the initial hot-rolled state and after additional deformation by tHP
methods [186]: 1 — sample centre, 2 — middle of the sample radius, 3 and 4 —
sample periphery
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Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
In contemporary physics of the strength and plasticity, the materi-
als plasticity is commonly determined as the ability of the material to
un dergo the residual deformations under load. In practice, the material
stretching until the fracture commonly characterizes the plasticity.
7. conclusions
this review paper reports on the scientific and practical solutions of the
problem, which consist in the establishment of the patterns of the struc-
ture formation, the texture formation and the formation of the mecha-
nical properties of the low-carbon and ultralow-carbon 08пс-, 01Ют-,
01Ют (са)-, and 01ЮтА-grade steels at combined plastic deformation.
this makes it possible to establish rational regimes of complex process-
ing for 08пс, 01Ют, 01Ют (са), 01ЮтА steels to increase the complex
of their mechanical properties.
based on theoretical and experimental study, the following scien-
tific and practical conclusions appear.
I. the analysis of the scientific and technical literature along with
market demands has shown that the study of the structure of low-car-
bon and ultralow-carbon steels in combined deformation for improving
their mechanical properties is an urgent task.
II. the effect of combined plastic deformation on the structure for-
mation, the grain size, the dislocation density, the micro-stresses of the
hot-rolled low-carbon and ultralow-carbon 08ps-, 01Ют-, 01Ют (са)-,
and 01ЮтА-type steels has revealed as follows.
due to the torsion under the hydrostatic pressure of the low-car bon
and ultralow-carbon 08ps, 01Ют, 01Ют (са), and 01ЮтА steels, the
nonhomogeneous structure is formed and is characterized by the me tal
flow in the direction of torsion. this heterogeneity is stipulated by the
change of the deformation at torsion under hydrostatic pressure (N = 5)
in the sample area from its periphery (e = 5.867, γ = 353.250) to its
centre (e = 4.363, γ = 78.50).
X-ray structural analysis of the hot-rolled low and the hot-rolled
ultralow carbon 08пс, 01Ют, 01Ют (са), and 01ЮтА steels after addi-
tional deformation by torsion under hydrostatic pressure method con-
firms the formation of an ultra-fine-grained structure with coherent
scattering region of less than 100 nm in the (110) and (220) planes.
the value of the micro-stresses of 08ps-grade steel at torsion under
hydrostatic pressure (N = 5) is 1.14 times higher than that in the initial
state of this steel.
the density of the dislocations in the ferrite grains of steel 01Ют
after torsion under hydrostatic pressure at P = 300 kgf/cm2 and N = 5
increases in comparison with the initial state of this steel by 1.5 times
while for the 01Ют (ca) steel it makes 1.3 times, and for 01ЮтА steel
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Regularities of Formation of Structure, Texture and Properties of Steels
by 1.5 times. the values of micro-stresses developing within the ultral-
ow-carbon steel unit after the torsion under hydrostatic pressure in-
crease in comparison with the initial hot-rolled state in the 01Ют and
01Ют(ca) steels as much as 1.13 and 1.4 times, respectively. the re-
sulting diffe rences are probably related to the introduction of calcium
into 01Ют (ca) steel, which in comparison with other alloying elements
has the largest atomic radius.
III. by means of electronic microscopy and microdiffraction applied
for thin foils, the fine grain boundary, the dislocation, the polygoni -
sed and the deformed structures of the low-carbon and ultralow-carbon
08пс and 01Ют steels have been studied and the following has been
revealed.
the deformation after the hot rolling is distributed directly along
the radius of the sample disk and this inhomogeneity is manifested in
the dislocation-cell structure, as in the images of the fine structure, and
in the microdiffraction patterns.
the electron-microscopic analyses of the hot-rolled 08пс and
01Ют (ca) steels after torsion under hydrostatic pressure confirm the
de formation localization at the periphery of the sample and the forma-
tion of cells of 0.5–1.0 microns in the size.
In the course of the steel hot deformation during rolling, the tex-
ture with a pronounced component {110} is being formed because of
turning the body-centred cubic arrangement of the ferrite along the di-
rection of the frictional force action due to the shear tangential friction
force acting in the deformation zone within the surface layer.
In the central rolled zone, the force influence at the deformation is
symmetrical, therefore the usual texture of rolling with the most ex-
pressed orientations are {100} and {111} being formed.
the additional severe plastic deformation by torsion under hydro-
static pressure method for the ultralow-carbon steel of 01Ют (ca) re-
sults in the formation of the texture with {100}, {111}, and {110} com-
ponents.
Inverse pole figures of the hot rolled steels of 08пс and 01Ют (ca)
indicate the introduction of crystallographic deformation mechanisms
in the process of additional cold deformation by torsion under hydro-
static pressure method.
IV. the calculated characteristics of strength and plasticity of the
low-carbon and ultralow-carbon 08пс, 01ЮтА, 01Ют, 01Ют(ca) steels
on the basis of the data obtained by the nanoindentation method have
been revealed as follows.
the additional deformation for the hot-rolled steels of 01ЮтА-,
01Ют-, 01Ют(са)-, and 08пс-grade by torsion under hydrostatic pres-
sure methods leads to the increase in indentation hardness both in the
centre and at the periphery of the sample in 1.5–2 times.
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Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
the irregular distribution of the hardness along the radius of the
sample is due to the localization of the deformation at the periphery of
the sample.
because of precipitation of 01ЮтА, 01Ют, 01Ют (са) steels, there
is a decrease in plasticity observed with respect to the initial hot-rolled
state for all samples of the investigated steels. the maximum decrease
in plasticity properties is the feature for the 01Ют (ca) steel: δH = 0.66,
which is 71% lower than that in the initial hot-rolled state.
In severe plastic deformation by torsion under hydrostatic pressure
method, the plasticity of the hot-rolled low-carbon and ultralow-carbon
steels is kept at a rather high level with respect to the initial state. the
uneven distribution of the plasticity along the radius of the sample is
due to the nature of the deformation localization in torsion under hy-
drostatic pressure processes at the sample periphery.
reFereNceS
d. brandshtetter, 1. Tekhnologiya otzhiga v kolpakovykh pechakh. Sovremennye
kontseptsii proizvodstva kholodnokatanoy tonkolistovoy stali dlya avtomobiles-
troeniya [the annealing technology in bell-type furnaces. the modern concepts
for the production of cold rolled sheet steel for the automotive industry], trudy
IV Kongressa prokatchikov (Moscow: 2002), p. 227 (in russian).
State Standard 1997.01.01. 2. Prokat tonkolistovoy kholodnokatanyy iz nizkoug-
lerodistoy kachestvennoy stali dlya kholodnoy shtampovki. tekhnicheskie us-
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received october 24, 2018;
in final version, january 13, 2019
Ю.С. Пройдак, В.З. Куцова, Т.В. Котова,
Г.П. Стеценко, В.В. Прутчикова
Національна металургійна академія україни,
пр. Гагаріна, 4, 49000 дніпро, україна
ЗАкОНОМІрНОстІ ФОрМуВАННЯ структури, текстури
тА ВлАстиВОстей При кОМбІНОВАНІй ПлАстичНІй
деФОрМАцІї НиЗькО- й ультрАНиЗькОВуГлецеВиХ
стАлей длЯ ХОлОдНОГО штАМПуВАННЯ
у роботі одержано нові розв’язки науково-практичної задачі, яка полягає у під-
ви щенні комплексу механічних властивостей і схильности до штампування га-
ря чевальцьованих низько- та ультранизьковуглецевих сталей з подальшою хо-
лод ною деформацією методами осаду та кручення під гідростатичним тиском
(кГт). За допомогою сучасних метод дослідження встановлено можливість фор-
му вання ультрадрібнокристалічної структури при комбінованій пластичній де-
фор мації. Встановлено залежність зміни механічних властивостей від параметрів
структури, текстури та фазового складу. Вперше методом наноіндентування
визначено механічні характеристики гарячевальцьованих сталей 08пс, 01Ют,
01Ют (са), 01ЮтА з подальшою холодною деформацією методом кГт. Вста нов-
лено підви щен ня в 2 рази твердости індентування (5,5–6,0 ГПа), пониження
мо дуля пруж ности в 1,5 рази (150–190 ГПа) та збереження задовільної плас-
тичности (δ = 0,75–0,8), що ґарантовано забезпечує більшу схильність до штам-
пування досліджених сталей порівняно з гарячевальцьованим станом.
Ключові слова: ультранизьковуглецеві сталі, наноіндентування, інтенсивна плас -
тична деформація, кручення під гідростатичним тиском, штампування, текстура.
Ю.С. Пройдак, В.З. Куцова, Т.В. Котова,
А.П. Стеценко, В.В. Прутчикова
Национальная металлургическая академия украины,
пр. Гагарина, 4, 49000 днепр, украина
ЗАкОНОМерНОсти ФОрМирОВАНиЯ структуры, текстуры
и сВОйстВ При кОМбиНирОВАННОй ПлАстическОй
деФОрМАции НиЗкО- и ультрАНиЗкОуГлерОдистыХ
стАлей длЯ ХОлОдНОй штАМПОВки
В работе получены новые решения научно-практической задачи, которая зак-
лючается в повышении комплекса механических свойств и склонности к штамповке
горячекатаных низко- и ультранизкоуглеродистых сталей с последующей холодной
деформацией методами осадки и кручения под гидростатическим давлением
(кГд). с помощью современных методов исследования установлена возможность
формирования ультрамелкокристаллической структуры при комбинированной
284 ISSN 1608-1021. Prog. Phys. Met., 2019, Vol. 20, No. 2
Yu.S. Projdak, V.Z. Kutsova, T.V. Kotova, H.P. Stetsenko, and V.V. Prutchykova
пластической деформации. установлена зависимость изменения механических
свойств от параметров структуры, текстуры и фазового состава. Впервые ме-
тодом наноиндентирования определены механические характеристики горяче-
катаных сталей 08пс, 01Ют, 01Ют(са), 01ЮтА с последующей холодной
де формацией методом кГд. установлено повышение в 2 раза твёрдости ин-
дентирования (5,5–6,0 ГПа), снижение модуля упругости в 1,5 раза (150–
190 ГПа) и сохранение удовлетворительной пластичности (δ = 0,75–0,8), что
гарантированно обеспечивает большую склонность к штамповке исследуемых
сталей по сравнению с горячекатаным состоянием.
Ключевые слова: ультранизкоуглеродистые стали, наноиндентирование, ин тен-
сивная пластическая деформация, кручение под гидростатическим давлением,
штамповка, текстура.
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