J. LI et al.: THE INFLUENCE OF HOT-ROLLING REDUCTIONS AND PASSES ON THE MICROSTRUCTURE ...
827–833
THE INFLUENCE OF HOT-ROLLING REDUCTIONS AND PASSES
ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES
OF Mn18Cr18N ESR STEEL
VPLIV STOPENJ REDUKCIJE IN [TEVILA PREHODOV MED
VRO^IM VALJANJEM NA MIKROSTRUKTURO IN MEHANSKE
LASTNOSTI JEKLA Mn18Cr18N ESR
Juan Li
1
, Fengming Qin
1
, Guanghui Zhao
1.2
, Huiqin Chen
1*
1
Taiyuan University of Science and Technology, no. 66 Liuliu Road, Wanbailin District, Taiyuan 030024, Shanxi, China
2
Shanxi Provincial Key Laboratory of Metallurgical Device Design Theory and Technology, no. 66 Liuliu Road, Wanbailin District,
Taiyuan 030024, Shanxi, China
chen_huiqin@126.com
Prejem rokopisa – received: 2018-08-28; sprejem za objavo – accepted for publication: 2018-10-30
doi:10.17222/mit.2018.188
The single-pass hot-rolling process with height reductions of 15 %, 30 %, 40 % and 50 %, and the three-pass and the five-pass
hot-rolling processes with 60 % total reduction, were carried out for Mn18Cr18N ESR steel slabs. The influence of the
hot-rolling reductions and passes on the microstructure and mechanical properties of the rolled samples was investigated. For
the single-pass rolled process, the volume fraction of the refined dynamically recrystallized grains increased with the increasing
of the reduction, both the tensile strength and elongation also increased with the increasing of the reduction, and the fracture
morphology transformed to ductile at higher reductions. For the three-pass and the five-pass rolling processes, strain-hardening
structures containing a large number of slip/shear bands and fewer refined dynamically recrystallized grains were present. The
tensile strength increased with the increasing number of passes, but the elongation decreased with the increasing number of
passes. The fracture morphologies were also characterised by brittle fractures. After the solid-solution treatment, uniform
refined static recrystallized grains were obtained in the three-pass rolled part, while grain growth following static recrys-
tallization occurred in the five-pass rolled part.
Keywords: Mn18Cr18N, rolling, microstructure, mechanical property
Avtorji ~lanka so izvajali preizkuse vro~ega valjanja slabov iz jekla pretaljenega pod `lindro Mn18Cr18N ESR (angl.: Electro
Slag Remelting) pri enem prehodu in z razli~nimi stopnjami redukcije (15 %, 30 %, 40 % in 50 %), kakor tudi preizkuse s tremi
in petimi prehodi pri celotni 60 % redukciji. Pri tem so ugotavljali vpliv stopenj redukcije in {tevila prehodov na mikrostrukturo
in mehanske lastnosti vro~e valjanih vzorcev jekla. Pri vro~em valjanju z enim prehodom so ugotovili, da se z nara{~ajo~o
stopnjo redukcije (deformacije) pove~uje volumski dele` udrobljenih dinami~no rekristaliziranih kristalnih zrn. Posledi~no sta
se tako pove~ali natezna trdnost in raztezek jekla, prav tako pa je morfologija preloma pre{la v duktilno. Pri vro~em valjanju s
tremi in petimi prehodi je deformacijsko utrjena struktura vsebovala veliko {tevilo drsno/stri`nih pasov in manj{e {tevilo
udrobljenih dinami~no rekristaliziranih zrn. Natezna trdnost jekel se je povi{evala s pove~evanjem {tevila prehodov, medtem ko
se je raztezek manj{al. Nastala je tipi~no krhka morfologija preloma. Po raztopnem `arenju so pri postopku valjanja s tremi
prehodi ustvarili enovito rafinirano mikrostrukturo s stati~no rekristaliziranimi kristalnimi zrni, medtem ko je pri postopku
valjanja s petimi prehodi rasti zrn sledila stati~na rekristalizacija.
Klju~ne besede: jeklo Mn18Cr18N, valjanje, mikrostruktura, mehanske lastnosti
1 INTRODUCTION
Mn18Cr18N, a high-nitrogen austenitic stainless
steel, is widely used to manufacture the retaining rings of
generators due to its distinctive advantages such as high
strength and toughness, non-magnetic property and ex-
cellent stress corrosion resistance.
1–2
Nitrogen, as an
important alternative alloying element instead of nickel,
can contribute to improve the stability of the austenitic
structure, the mechanical properties and the corrosion
resistance.
3–4
The conventional manufacturing route of
heavy retaining rings involves smelting, ingot conso-
lidation, forging, heat treatment and machining.
5
The
forging process includes ingot breakdown, upsetting,
punching, mandrel drawing and mandrel expanding
operations, which are complex and hard to control. The
compact route for manufacturing retaining rings has been
put forward; it involves only smelting and consolidation,
electro-slag re-melting (ESR) a hollow ingot and ring
rolling operations.
6
Compared to the conventional manu-
facturing route, the compact route is simple, energy-
saving, material-saving and convenient to control. This
compact route can be used to manufacture all kinds of
rings and hollow parts, especially for large rings and
hollow components. ESR ingots are generally compact,
homogenized and pure. However, coarse grains, espe-
cially coarse columnar grains, are more prominent in
ESR ingots.
7–8
Therefore, the coarse columnar grain
refinement during ring-rolling processes of lager hollow
Materiali in tehnologije / Materials and technology 52 (2018) 6, 827–833 827
UD.K 67.017:669.14:669.056:621.73.047 ISSN 1580-2949:
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 52(6)827(2018).

ingots has become a challenge for manufacturing high-
quality retaining rings, and the investigation of coarse
columnar grain refinement during the ring-rolling
processes of the steel plays an important role with
regards to optimizing the ring-rolling process para-
meters.
For austenitic stainless steels with a lower stacking
fault energy (SFE), grain refinement can be realized by
dynamic recrystallization (DRX) during hot deformation
and/or static recrystallization (SRX) during the inter-pass
of hot deformation. Qin found that DRX controlled by
dislocation and twining mechanisms occurs during the
hot deformation of ESR Mn18Cr18N ingots, which
depends mainly on the strain rates.
9
DRX controlled by
dislocation slipping and a climbing mechanism occurs at
lower strain rates, in which the equiaxed recrystallized
grains are composed of recovered sub-grains with low-
angle boundaries and various dislocation configurations;
DRX controlled by a twinning mechanism occurs at
higher strain rates, in which most of the recrystallized
grains are composed of twins, micro-twins and dislo-
cation cells in twins. However, grain refinement by DRX
usually needs large deformations. Therefore, the hot
workability is a major concern for the hot deformation of
ESR ingots. Based on hot-processing maps, the hot-
working windows of an ESR as-cast Mn18Cr18N ingot
steel should be in the temperature and strain-rate ranges
of 1050–1200 °C, 0.001–0.01 s
–1
and 1100–1200 °C,
0.1–1 s
–1
, in which the DRX controlled by the dislo-
cation slip mechanism and the twinning mechanism
occur, respectively.
10
The alternative method for the grain
refinement of austenitic stainless steels is SRX during
the inter-pass of deformation or heat treatments after hot
deformation, in which the deformation and duration
during the inter-pass of the hot deformation or the
parameters of the heat-treatment process have to be
matched.
In the present work, different hot-rolling reductions
and passes have been designed to investigate the micro-
structure evolution and the mechanical properties of
Mn18Cr18N ESR steel, which can provide a scientific
basis for designing and optimizing the ring-rolling
process in the compact route for manufacturing large
retaining rings.
2 MATERIALS AND EXPERIMENTAL PART
The material in this investigation was Mn18Cr18N
austenitic stainless steel with 0.61 % (w/%) nitrogen
received as an ESR ingot with a diameter of 300 mm and
a height of 130 mm. The chemical composition of the
steel is shown in Table 1. The original microstructure of
the ESR ingot is shown in Figure 1. The ingot steel was
composed of coarse columnar grains with sizes of
500–1000 μm at about 60° to the axis of the ingot, in
which uniform and fine sub-grains with a size of 50 μm
can be observed.
The rectangular rolling slabs were 100 mm in length,
90 mm in width and 12 mm in thickness, machined from
the ESR ingot. The length direction is parallel to the axis
of the ESR ingot. The rolling tests were conducted on a
rolling mill with rollers of 320 mm in diameter. The
slabs were heated to 1200 °C and held for 15 min for the
rolling. The single-pass rolling processes with 15 %,
30 %, 40 % and 50 % reductions were designed for
investigating the influence of single reductions on the
microstructure evolution and the mechanical properties
of the rolling parts. The three-pass and five-pass rolling
processes with 60 % total reductions and an 8 s
inter-pass duration were designed for investigating the
influence of passes on the microstructure evolution and
the mechanical properties of the rolling parts. For the
three-pass rolling process, the rolling path was 20 % –
4 0%–2 0% .F o rt h ef i v e - p a s srolling process, the
rolling path was 10%–20%–30%–20%–10%.For
all the rolling processes, the rolling velocity was 0.2 m/s.
J. LI et al.: THE INFLUENCE OF HOT-ROLLING REDUCTIONS AND PASSES ON THE MICROSTRUCTURE ...
828 Materiali in tehnologije / Materials and technology 52 (2018) 6, 827–833
Figure 1: Microstructure of Mn18Cr18N ESR Figure 2: Schematic of the tensile-test specimen after rolling
Table 1: Chemical composition of the Mn18Cr18N steel (w/%)
CM nS iPSN iC rM oVA lNT iF e
0.074 19.21 0.59 0.014 0.001 0.14 20 0.022 0.053 0.023 0.6 0.016 Balance

The rolled parts were quenched by water after rolling.
The RD–ND sectional samples were taken longitudinally
to the rolling direction and prepared for microscopic and
fractographic observations by SEM and EBSD on a
ZEISS SIGMA. In the EBSD grain-boundary reconstruc-
tion maps, low-angle grain boundaries (2–15°, LAGB)
were expressed by white lines; and the high-angle grain
boundaries (%15°, HAGB) were expressed by black
lines. The mechanical property test samples were
machined according to GB/T 6396–2008 and tested on a
WDW–200 tensile testing machine. As the sample
thickness after rolling is different, the dimensions of the
tensile samples are shown in Figure 2 and Table 2.
Table 2: Dimensions of the tensile samples
Rolling pass Reduction /% Lc /mm Lt /mm
1
15 84 144
30 76 136
40 71 131
50 65 124
3/5 60 63 123
3 RESULTS
3.1 Microstructure evolution during different rolling
passes
Figure 3 shows the microstructures for the single-
pass rolled samples with 15 %, 30 %, 40 % and 50 %
reductions. It is clear that the refined grains and twins
increase with the increasing of the reductions. In Figure
3a there were no refined grains observed due to the
lower reduction of 15 %. However, the original as-cast
coarse grains elongated with the waved grain boundaries.
Two groups of cross-slip lines were also observed, which
is often observed in lager grains during deformation.
11
In
addition, waved grain boundaries have often been
considered as an early stage of nucleation for the DRX
grains.
12
In the sample compressed up to 30 % reduction
(Figure 3b), some refined grains located at the grain
boundaries formed, while the center part of the original
grains remains un-refined due to a smaller DRX fraction.
When the reduction was up to 40 % (Figure 3c), the
DRX was almost completed. However, the DRX-refined
grains were not uniform and  ferrite remains as the
original grain boundaries and morphology, which is not
beneficial to the mechanical properties of the rolled
parts. As shown in Figure 3d, when the reduction was
up to 50 %, the near fully DRX refined grains were
obtained and  ferrite could hardly be observed. This
suggests that the 40 % reduction in the single-pass roll-
ing process is enough for DRX; but the greater reduction
over 40 % is necessary for the uniformly refined DRX
grain structure that is nearly free of  –ferrite. Because
the rolling process was a non-isothermal and non-con-
stant strain-rate process, the size of the refined DRX
grains decreases with the increasing of the reduction. At
a reduction of 50 %, the size of the refined DRX grains
was about 50 μm, which almost equals the size of the
sub-grains in the parent as-cast coarse grains. This
implies that the refined DRX grains might be evolved
from the sub-grains of the parent as-cast grains directly,
which needs to be further confirmed.
For metals with a low or medium stacking-fault
energy (SFE), DRX is considered to be the dominant
microstructure-evolution mechanism during hot defor-
mation. The SFE of Mn18Cr18N steel has been calcu-
lated to be about 24 mJ/m
2
,
9
which also suggests that
DRX might take place during the hot rolling of the steel.
In DRX, nucleation generally prefers to occur at original
grain boundaries (the yellow arrows in Figures 4a and
4b), slipping bands or shear bands (the white arrows in
Figures 4a and 4b). This is because the dislocations slip
and pile up at the grain boundaries, which induces
orientation evolution and preferential nucleation at the
boundaries.
13
However, the slipping band and the shear
band can accelerate the dislocation movement and its
evolution in preference to nucleation. As shown in
Figure 4a, a few new recrystallized grains at the parent
J. LI et al.: THE INFLUENCE OF HOT-ROLLING REDUCTIONS AND PASSES ON THE MICROSTRUCTURE ...
Materiali in tehnologije / Materials and technology 52 (2018) 6, 827–833 829
Figure 4: EBSD grain-boundary reconstruction maps of the single-
pass rolled samples a) 15 %, b) 30 %, c) 40 %, d) 50 % (2–15°–White,
>15°–Black)
Figure 3: Microstructures of the single-pass rolled samples with
different reductions: a) 15 %, b) 30 %, c) 40 %, d) 50 %

grain boundaries formed due to the lower reduction.
Meanwhile, a large number of low-angle grain boun-
daries and slipping bands appeared in the interior of the
parent grains, which are characteristics of the sub-struc-
tures in strain-hardening and DRV materials. With the
increasing of the reduction, the first layer of the newly
recrystallized grains formed at the elongated parent grain
boundaries and slipping bands (Figure 4b). The higher
the reduction was, the more recrystallized grain layers
there were (Figures 4c and 4d). When the reduction was
high enough, the DRX completed and a fully recrys-
tallized grain structure was present. And new cycles of
recrystallization formed at the grain boundaries and the
three-grain junctions (the pink arrows in Figure 4d).
The binomial misorientation distributions in Figures 5
indicated that discontinuous DRX occurred during the
single-pass rolling processes. Most of low-angle grain
boundaries (LAGBs) were less than 10°, while most of
the high-angle grain boundaries (HAGBs) were between
40°–50° or at 60°. With the increasing of the reduction,
the average misorientation increased from 9.5° to 45.5°.
When the reduction was less than 30 % (Figures 5a and
5b), the average misorientation was less than 10.5°,
which suggests that the DRV dominates. As shown in
Figures 5c and 5d, the DRX dominates when the
reduction was greater than 40 %. The misorientation of
60° predominated in the HAGBs in Figures 5b to 5d.It
was reported that the 60° misorientation is related to
twin boundaries,
14
which implies that twining plays an
important role in DRX. This is in agreement with the
research results in the literature.
9
Figure 6 shows the microstructure and its charac-
teristics for the three-pass rolled sample. It is clear that
the original as-cast coarse grains elongated along the
deformation direction, in which a large number of defor-
mation bands were observed in Figure 6a. The EBSD
grain-boundary reconstruction map of the three-pass
rolled sample in Figure 6a also reveals that a certain
amount of refined grains formed at the original coarse
J. LI et al.: THE INFLUENCE OF HOT-ROLLING REDUCTIONS AND PASSES ON THE MICROSTRUCTURE ...
830 Materiali in tehnologije / Materials and technology 52 (2018) 6, 827–833
Figure 7: a) EBSD grain-boundary reconstruction map and b) the
corresponding misorientation distributions after five rolling passes
Figure 5: Misorientation distributions of the single-pass rolled
samples a) 15 %, b) 30 %, c) 40 %, d) 50 %
Figure 6: EBSD grain-boundary reconstruction map (a) and the
corresponding misorientation distributions (b) after three rolling
passes

grain boundaries and the intra-granular deformation
bands. However, Figure 6b shows that low-angle grain
boundaries predominated in the microstructure, which
suggests that the microstructure of the three-pass rolled
sample was almost in the deformation-hardening state
after the three-pass rolling process with the 20 % –40 %
–20 % reduction sequence in the experiment.
Figure 7 shows the microstructure and its charac-
teristics for the five-pass rolled sample. It can be seen
that the original as-cast coarse grains elongated severely
along the deformation direction in Figure 7a, compared
to that of the sample after the three-pass rolling process
in Figure 6a. The intra-granular deformation bands were
even thinner, and a small amount of refined grains
formed at the original coarse grain boundaries and the
intra-granular deformation bands. Figure 7b also shows
that low-angle grain boundaries also predominated in the
microstructure, which suggests that the microstructure of
the five-pass rolled sample was almost in the deforma-
tion hardening state after the five-pass rolling process
with the 10%–20%–30%–20%–10%reduction
sequence in the experiment.
3.2 Mechanical properties of the rolled parts
The mechanical properties of the hot-rolled parts
were tested and shown in Table 3. It is clear that both of
the strength indexes (the yield strength and the tensile
strength) and the plasticity index (the elongation ratio)
increased with the increasing reductions in the single-
pass process. Although the strength indexes also
increased with the increasing number of hot-rolling
passes, the plasticity index decreased with the increasing
number of hot-rolling passes.
During the single-pass rolling process, the greater is
the reduction, the higher is the dislocation density, so
that the higher is the strength. When the reduction
increased up to the critical strain for the DRX of the steel
at the experimental deformation parameters, the DRX
occurred as shown in Figure 3. Therefore, new refined
DRX grains formed. Although, refined DRX grains with
a lower dislocation density compared to the strain-
hardened parent grains can decrease the strain hardening
rate, the strength of the deformation material can be
improved by the refined DRX grains based on the
Hall–Patch relationship at room temperature, and the
plasticity of the deformation material can also be
improved by the refined DRX grains.
For DRX, the critical strain is needed to initiate the
DRX. During the three-pass and five-pass rolling pro-
cesses, the microstructures in the rolled parts were
elongated, hardening the coarse grains with fewer DRX
refined grains at the grain boundaries and slipping bands
(as shown in Figures 6 and 7) due to the lower reduction
of each pass and the shorter holding time between the
inter-pass, and the DRX or static recrystallization (SRX)
can hardly occur. Therefore, the strength indexes in-
creased with the increasing number of rolling passes, but
the the plasticity of the elongation ratio decreased with
the increasing number of rolling passes.
The tensile test results also indicate that no obvious
necking occurred in the tensile samples machined from
the three-pass and five-pass rolled parts, which was
similar to that of the tensile samples machined from the
single-pass rolled part with a reduction of 15 %. The
necking increased with the increasing reduction of the
single-pass rolled parts. Figure 8 shows the fracture
morphologies of the single-pass and multi-pass rolled
parts. It can also be seen that the fracture transformed
from brittle fracture to ductile fracture with the increas-
ing reductions of the single-pass parts corresponding to
the fracture morphologies from Figures 8a to 8d. And
the fracture in Figure 8d with the maximum reduction of
50 % after the single-pass rolling process was a typical
ductile fracture. However, the fractures of Figures 8a, 8e
and 8f were more likely brittle fractures.
4 DISCUSSION
During the hot-rolling process, the initial microstruc-
ture state and the deformation parameters of the tem-
perature, strain rate, reduction, pass and inter-pass
holding times, have a comprehensive influence on the
microstructure and the mechanical properties of hot-
rolled parts.
15–16
Therefore, it is a challenge to optimize
the rolling process for improving the microstructure and
the mechanical properties of the ESR as-cast billets.
For metals with a low SFE, shear bands could often
be observed in the deformed grains, except for the dis-
location slipping and twinning.
17
During the hot-rolling
process, the reduction in each pass plays an important
role in refining the grains of the rolled parts. When the
reduction is lower than the critical strain of DRX, as
indicated in Figure 3a, the initial as-cast coarse grains
will be elongated along the rolling direction with various
dislocation configurations inside. Meanwhile, the as-cast
coarse grains can be divided into several parts by
slipping and shear bands for matching the deformation of
the adjacent grains with different misorientations, and
the grain boundaries could be waved due to grain-boun-
dary slipping (Figure 3a). When the reduction increased
up to the critical strain of DRX, dislocations piling up at
the grain boundaries and the slipping bands could be
evolved into regular configurations such as sub-grains,
where DRX nuclei formed preferentially, as shown in
Figure 3b and Figure 4. Then the DRX volume fraction
increased with the increasing amount of reduction, as
shown in Figures 3c and 3d. Although the newly formed
DRX refined grains have a lower dislocation density, the
strength of the deformation material can be improved by
the refined DRX grains based on the Hall–Petch relation-
ship at room temperature; and the plasticity of the
deformation material can also be improved by the refined
DRX grains, as shown in Table 3. Satio found that a
high strain rate and a low final rolling temperature
J. LI et al.: THE INFLUENCE OF HOT-ROLLING REDUCTIONS AND PASSES ON THE MICROSTRUCTURE ...
Materiali in tehnologije / Materials and technology 52 (2018) 6, 827–833 831

provide time and energy that is not enough for merging
and the growth of sub-grains, and DRX/SRX occurs
slowly.
18
Therefore, only a few DRX/SRX refined grains
can be observed in Figure 6a and Figure 7a, and the
fractions of LAGB in Figure 6b and Figure 7b were
much higher. However, a large number of slipping or
shear bands can be observed in the elongated grains after
the three-pass and five-pass rolling processes, especially
after the five-pass rolling process due to the lower
reduction of each pass. The slipping bands or shear
bands with a higher energy can be seen as the prefe-
rential nucleation sites and accelerate the DRX during
the rolling processes.
19
Qin also found that a large num-
ber of deformation micro-bands were observed in the
interior of the deformed columnar grains at higher strain
rates.
9
The interfaces between deformed micro-bands can
serve as preferential nucleation sites for DRX. Chen
10
found that the hot-processing windows for ESR
Mn18Cr18 steel were 1050–1200 °C, 0.001–0.01 s
–1
and
1100–1200 °C, 0.1–1 s
–1
. It indicated that a high
individual pass reduction or a high final rolling tempe-
rature was necessary for refined recrystallized grains and
improved properties. During a subsequent solid-solution
treatment, DRX and SRX proceed continuously. Then
the fully recrystallized grain structure can be obtained in
Figure 9a, because the solid-solution treatment
temperature and time were appropriate (1050 °C/2 h).
However, the fully static recrystallized grains will grow
(Figure 9b) at higher temperatures after a prolonged
period. After the solid-solution treatment, the uniform
refined recrystallized grain structure can provide in-
creased plasticity of the rolled parts. The average grain
sizes in Figures 9a and 9b were about 83 μm and
130 μm, respectively.
Table 3: Mechanical properties of the rolled parts
Rolling
pass
Reduction
c/%
Yield
strength,
R
eL/MPa
Tensile
strength,
R m/MPa
Elongation,
A/%
1
15 694 882 40.7
30 719 886 43.4
40 724 920 50.2
50 740 930 51.5
3 60 894 1011 41.0
5 60 1027 1086 30.6
5 CONCLUSIONS
The influence of hot-rolling reductions and passes on
the microstructure and mechanical properties of the ESR
Mn18Cr18N steel was investigated by hot-rolling expe-
riments. The microstructures and mechanical properties
of the rolled parts were tested and analyzed by SEM,
EBSD and tensile tests. The conclusions can be drawn as
follows.
(1) For the single-pass rolled process, the volume
fraction of refined dynamically recrystallized grains
increased with the increasing of the reduction. The near
fully DRX refined grains with a size of about 50 μm
were obtained and ferrite could hardly be observed for
the reduction up to 50 %. Both the tensile strength and
J. LI et al.: THE INFLUENCE OF HOT-ROLLING REDUCTIONS AND PASSES ON THE MICROSTRUCTURE ...
832 Materiali in tehnologije / Materials and technology 52 (2018) 6, 827–833
Figure 8: Fracture morphologies of the single-pass rolled parts with reductions of: a) 15 %, b) 30 %, c) 40 %, d) 50 %, and e) of the three-pass
rolled part and f) of the five-pass rolled part
Figure 9: a) Solid-solution treated microstructures of the three-pass
rolled and b) five-pass rolled samples

the elongation also increased with the increasing of
reduction, and the fracture morphology transformed to
ductile at higher reductions.
(2) For the three-pass rolling processes, strain-hard-
ening structures containing a large number of slip/shear
bands and fewer refined dynamically recrystallized
grains were present. Compared to the single-pass rolled
part, the tensile strength increased, and the elongation
decreased. The fracture morphology was characterised
by brittle fracture. After the solid-solution treatment,
uniform refined static recrystallized grains with an
average grain size of about 83 μm were obtained in the
three-pass rolled part.
(3) For the five-pass rolling process, strain-hardening
structures containing a large number of slip/shear bands
and fewer refined dynamic recrystallized grains were
present. The tensile strength increased with the increas-
ing number of passes, but the elongation decreased with
the increasing number of passes. The fracture morphol-
ogy was characterised by brittle fracture. After the
solid-solution treatment, the grain growth following the
static recrystallization occurred in the five-pass rolled
part. The average grain size was about 130 μm.
Acknowledgments
This work was financially supported by the National
Natural Science Foundation of China (no. 51575372).
Sponsored by the Fund for Shanxi Key Subjects
Construction (20170401), Science and Technology
Research Plan (Industrial) Project of Shanxi Province,
China (no. 201603D121006-2).
Compliance with ethical standards
Conflict of interest. The authors declare that they
have no competing interests.
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J. LI et al.: THE INFLUENCE OF HOT-ROLLING REDUCTIONS AND PASSES ON THE MICROSTRUCTURE ...
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