B. AYDEMIR et al.: INVESTIGATION OF PORTEVIN-LE CHATELIER EFFECT OF HOT-ROLLED ...
511–516
INVESTIGATION OF PORTEVIN-LE CHATELIER EFFECT OF
HOT-ROLLED Fe-13Mn-0.2C-1Al-1Si TWIP STEEL
PREISKAVA PORTEVIN-LE CHATELIER U^INKA PRI VRO^EM
VALJANJU Fe-13Mn-0.2C-1Al-1Si TWIP JEKLA
Bulent Aydemir1, Havva Kazdal Zeytin2, Gokhan Guven2
1Tubitak National Metrology Institute (UME), P.K. 54, Gebze, Kocaeli 41470, Turkey
2Tubitak MRC, Materials Institute, P.K. 21, Gebze, Kocaeli 41470, Turkey
bulent.aydemir@tubitak.gov.tr
Prejem rokopisa – received: 2015-02-07; sprejem za objavo – accepted for publication: 2015-07-08
doi:10.17222/mit.2015.034
This study was undertaken to investigate the microstructure and mechanical properties of hot rolled Fe-13Mn-0.2C-1Al-1Si
TWIP steel. Tensile tests were carried out at different strain rates to determine the Portevin-Le Chatelier (PLC) effect during
deformation. Subsequently, the samples were investigated by light microscopy and SEM. The sample microstructures revealed
inhomogeneous dislocation zones, deformation twinning and twin-dislocation interactions. Consequently, the PLC effect during
deformation was determined to be responsible for the excellent mechanical properties of the TWIP steel.
Keywords: TWIP steel, mechanical properties, microstructure, Portevin Le Chatelier effect
V {tudiji je bila preiskovana mikrostruktura in mehanske lastnosti vro~e valjanega Fe-13Mn-0.2C-1Al-1Si TWIP jekla. Natezni
preizkusi so bili izvedeni pri razli~nih hitrostih obremenjevanja. Kot rezultat nateznega preizkusa je bil ugotovljen u~inek Porte-
vin-Le Chatelier (PLC) med deformacijo. Vzorci so bili nato preiskani s svetlobnim mikroskopom in s SEM. Mikrostruktura
vzorcev ka`e nehomogena podro~ja dislokacij, deformacijske dvoj~ke in interakcije dvoj~kov z dislokacijami. Ugotovljeno je,
da so odli~ne mehanske lastnosti TWIP jekla posledica vpliva PLC med deformacijo.
Klju~ne besede: TWIP jeklo, mehanske lastnosti, mikrostruktura, vpliv Portevin Le Chatelier
1 INTRODUCTION
Higher automotive safety standards have led to a
strong interest in advanced high strength steel and "super
tough", high manganese steel characterized by Twin-
ning-Induced Plasticity (TWIP). The high-manganese
austenitic TWIP steels present excellent properties,
combining a very large strain-hardening rate and ducti-
lity. The TWIP effect is responsible for the observed
high maximum stress (600 MPa – 1100 MPa) and good
elongation (50 % – 95 %).1,2 Extensive research has al-
ready investigated on high Mn TWIP steels with slightly
different compositions. For example: Fe18Mn0.6C,
Fe22Mn0.6C, Fe–17Mn–0.6C, Fe–17Mn–0.8C etc.1–9
TWIP steels have a high manganese (Mn) content.
Manganese tends to stabilize austenite, although its role
in the TWIP microstructure is still a subject of active
research. Twinning promotes retention of the austenitic
microstructure but competes with dislocation glide by
impeding dislocation motion at twin boundaries and
other dislocation-dislocation interactions (e.g. forest
hardening). Twin formation is associated with Stacking
Fault Energy (SFE) at room temperature. Deformation
twinning in low SFE austenitic steels leads to high
strain-hardening and improved ductility of TWIP steel.
In low SFE austenitic steels, the increased partial
dislocation separation results in ease of twin nucleation.
With applied deformation, the grains are progressively
subdivided by the twinning process, and the internal twin
boundaries increase the strain hardening. Though the
actual twinning strain is limited, and the twin formation
itself may actually cause softening, the twin boundaries
decrease the dislocation slip distances progressively and
promote dislocation accumulation and storage, especially
at grain boundaries.1 This dynamic Hall–Petch effect
may not be the only cause for the observed strain hard-
ening of TWIP steel. In fact, the mechanism leading to
high strain hardening in TWIP steel is still a matter of
debate.
Austenitic steels usually reveal dynamic strain aging
(DSA); a form of unstable plastic flow found in the
dilute metal alloys.10–13 Portevin-Le Chatelier bands (or
the PLC effect) and serrated flow curves are usual mani-
festations of DSA, which occurs over a large temperature
range.14 The bands, which are regions of localized plas-
ticity, are commonly divided in three groups. As: Type A
(continuously propagates across the gage length of a
tensile specimen); Type B (discontinuous propagation or
"hop"); and Type C (no spatial correlation). A common
explanation of DSA in metals centers on disloca-
tion-solute interactions in which solute atoms diffuse to
dislocations temporarily arrested at obstacles (or trapped
by the local energy landscape in the lattice) thereby in-
creasing the stress required to release the dislocations.10
With aging, the dislocations are suddenly released, and
Materiali in tehnologije / Materials and technology 50 (2016) 4, 511–516 511
UDK 620.181:67.017:621.77:669.14.018.584 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(4)511(2016)
the process repeats elsewhere. There have been many
publications on dynamic strain aging and the PLC effect
in TWIP steels.15–17 The microstructure and mechanical
properties of the hot rolled Fe-13Mn-0.2C-1Al-1Si
TWIP Steel is investigated in this study. The conclusion
of the study was expected to be an aid for future indu-
strial manufacture of TWIP steel.
2 MATERIAL AND EXPERIMENTAL
PROCEDURE
The chemical composition of the newly developed
Fe-13Mn-0.2C-1Al-1Si TWIP steel is given in Table 1.
The TWIP steel was melted by induction melting under
an inert gas atmosphere in a furnace. Then, it was cast in
a ceramic mold with a thickness of about 20 mm. The
ingot was homogenized at 1200 °C for 6 h and then
hot-rolled to a thickness of 5 mm i.e. a total deformation
of 75 % by thickness. In addition, no annealing was
carried out.
Table 1: Chemical composition of investigated alloy in mass frac-
tions, (w/%)
Tabela 1: Kemijska sestava preiskovane zlitine, v masnih odstotkih
(w/%)
C Mn Si Cr N Al
0.23 12.73 1.08 0.12 0.10 0.95
The tensile samples were prepared mechanically in
accordance with the EN ISO 6892 Standard.18 The
experiments were conducted with a Zwick Z250 tensile
tester at the Material Institute in TUBITAK. The force
accuracy class of the machine was "class 0.5" according
to EN ISO 7500-1 standard.19 The extensometer was
used together with a strain measurement system. The
extensometer accuracy class of the machine was "class
0.5" according to EN ISO 9513 standard.20 All tests were
performed at 23±1 °C and 50±10 % humidity. The spe-
cimen was gripped by jaws and preload applied. Then,
the extensometer was automatically attached to the
specimen. The gage length of the applied extensometer
was 50 mm. The tensile test was carried out with test
speeds of (2, 5 and 10) mm/min. In addition, the Charpy
impact energy of 3 samples was tested at room tem-
perature by Charpy V-notch measurements on 55 mm ×
10 mm × 5 mm specimens.
The samples’ microstructures were examined by light
(Nikon) and scanning electron microscopes (SEM-Jeol-
JSM 6335F-Japan). The samples for microstructure inve-
stigations were cut suitably and mounted, mechanically
polished, and etched using a nital solution.
3 RESULTS AND DISCUSSION
Figure 1 shows a typical room temperature
stress–strain curve of the Fe-13Mn-0.2C-1Al-1Si TWIP
steel at different test speeds. Mechanical property values
obtained from the data in Figure 1 are listed in Table 2.
Average Charpy impact energy values in Joules are given
in Table 2. Figure 2 presents the tensile true stress–true
strain curves at different test speeds.
There isn’t a yield point nor a yield plateau observed
on the stress-strain curve, though some remarkable
serrated flows are found at strains above 5 %. As can be
seen the steel retains high strength and elongation with-
out necking at these strain rates. The main differences
between the stress–strain curves are the morphologies of
B. AYDEMIR et al.: INVESTIGATION OF PORTEVIN-LE CHATELIER EFFECT OF HOT-ROLLED ...
512 Materiali in tehnologije / Materials and technology 50 (2016) 4, 511–516
Figure 2: True stress–true strain curves of Fe-13Mn-0.2C-1Al-1Si
TWIP steel at different test speeds at room temperature
Slika 2: Prava krivulja napetost-raztezek TWIP jekla Fe-13Mn-0.2C-1
Al – 1Si pri razli~nih hitrostih preizkusa na sobni temperaturi
Figure 1: Stress-strain curves of Fe-13Mn-0.2C-1Al-1Si TWIP steel
at different test speeds at room temperature (2 mm/min, 5 mm/min, 10
mm/min)
Slika 1: Krivulje napetost-raztezek Fe-13Mn-0.2C-1Al-1Si TWIP
jeklo pri razli~nih hitrostih preizkusa, pri sobni temperaturi (2 mm/min,
5 mm/min, 10 mm/min)
the serrations. The fluctuations on the stress-strain curve
result from the dynamic strain aging (DSA) which is
consistent with earlier work on cold-rolled TWIP
steel.21–23
Table 2: Mechanical properties of Fe-13Mn-0.2C-1Al-1Si TWIP steel
at room temperature
Tabela 2: Mehanske lastnosti Fe-13Mn-0.2C-1Al-1Si TWIP jekla pri
sobni temperaturi
Test speed Rp 0.2 Rm A Eimpact
(mm/min) (MPa) (Mpa) (%) (J)
10 308 1075 17
23,95 307 844 14
2 306 999 16
Evidence of the appearance of deformation bands and
the coherent evolution of the serration is seen at room
temperature. In Figure 3 the magnified stress–strain
curve at 10 mm/min test speed is shown. The stress–
strain curve shows clear stress jumps and dips of the
same type described by K. Renard et al.17 The observed
serrations correspond to those of type A i.e. the bands
propagate continuously after nucleation.
An image of the hot rolled Fe-13Mn-0.2C-1Al-1Si
TWIP Steel obtained with a Nikon L150 light micro-
scope is given in Figure 4. The microstructure shows
B. AYDEMIR et al.: INVESTIGATION OF PORTEVIN-LE CHATELIER EFFECT OF HOT-ROLLED ...
Materiali in tehnologije / Materials and technology 50 (2016) 4, 511–516 513
Figure 4: Microstructure of the TWIP steel: a) as cast, b) hot rolled
Slika 4: Mikrostruktura TWIP jekla: a) lito, b) vro~e valjano
Figure 5: Microstructure of the TWIP steel (SEM): a) 2000×, b) 5000×
Slika 5: Mikrostruktura TWIP jekla (SEM): a) 2000 ×, b) 5000 ×
Figure 3: The room-temperature tensile response (magnified) of
Fe-13Mn-0.2C-1Al-1Si TWIP steel at 10 mm/min test speed
Slika 3: Pove~an odziv pri nateznem preiskusu Fe-13Mn-0.2C-
1Al-1Si TWIP jekla pri hitrosti preizkusa 10 mm/min na sobni tem-
peraturi
Figure 6: Diffraction pattern of the TWIP steel
Slika 6: Rentgenogram vzorca TWIP jekla
austenite grains containing a secondary precipitate
phase. The precipitates are mostly observed at grain
boundaries. Hot-rolling of the TWIP steel resulted in
annealing of the austenite grain twins, presenting as
mechanical twins. Deformation twins and twin-dis-
location interactions are observed in the deformed TWIP
steel. This twinning produces high strain hardening and
higher ductility, and is responsible for the excellent
mechanical properties of the hot-rolled TWIP steel.
SEM images of this sample are shown in Figure 5.
Analysis of secondary precipitated phases observed at
the grain boundaries yields 
 and ’ particles. A secon-
dary phase precipitated within austenite matrix is also
seen. The 
 and ’ martensite transformations occurred
B. AYDEMIR et al.: INVESTIGATION OF PORTEVIN-LE CHATELIER EFFECT OF HOT-ROLLED ...
514 Materiali in tehnologije / Materials and technology 50 (2016) 4, 511–516
Figure 8: Microstructure of the TWIP steel necked region after
applying the tensile test with test speed: a) 2 mm/min, b) 5 mm/min,
c) 10 mm/min
Slika 8: Mikrostruktura podro~ja vratu pri TWIP jeklu po nateznem
preizkusu s hitrostjo preizkusa: a) 2 mm/min, b) 5 mm/min, c) 10
mm/min
Figure 7: Microstructure of the TWIP steel necked region after
applying the tensile test at different speeds: a) 2 mm/min, b) 5
mm/min, c) 10 mm/min
Slika 7: Mikrostruktura podro~ja vratu pri TWIP jeklu, po nateznem
preizkusu pri razli~nih hitrostih preizkusa: a) 2 mm/min, b) 5 mm/min,
c) 10 mm/min
after hot rolling. In the present work, the steel is cooled
in air after being hot rolled. Large parallel laths crossing
the micrograph correspond to  martensite, with ’
martensite also forming. With a relatively low stability,
the austenite transformation proceeds by     ’
martensitic transformations, resulting in a high work-
hardening rate. Stability against the    martensite
transformation is usually considered to imply stability
against the   ’ martensite transformation since  mar-
tensite laths form as an intermediate phase.8,24 The
Diffraction Pattern is given in Figure 6.
I. Gutierrez-Urrutia and D. Raabe25 in their study of
FeMnAlC steels, and many other researchers, reported a
form of carbides at the grain boundaries in the sedi-
ments, the k-carbides (Fe, Mn)3AlC.24,25 SEM images of
the second phase are precipitated in the grain boundary
(Fe,Mn)3AlC phase. This phase is reported in the
austenite grain boundaries of FeMnAl steel with high
carbon content after hot-rolling, and is deposited after an
aging process. Optical microscopy, SEM, and XRD
studies show the k-carbides to be precipitated in the
austenite grain boundary phase.
The microstructures of this TWIP steel at the necked
region in parallel with the tension force direction after
applying the tensile test with (2, 5, and 10) mm/min test
speed were analyzed. These fracture surface images are
shown in Figures 7 and 8. The cleavage regions in the
fracture surface images increased with test speed in-
creases, and there was a growth of cracks. SEM photos
clearly demonstrate the typical ductile pattern of surface
fracture. Cleavage fracture areas and micro-cracks in the
grain developed when the test speed increases. Unfilled
areas formed by pouring of inclusions can be observed
on the fracture surface.
Figure 8 shows a local deformation region with
many parallel deformation twins. Moreover, the high dis-
location density found in the micro-scale mechanical
twins, indicate that the twin boundaries could play a
similar role to grain boundaries as short range obstacles
for gliding dislocations and strongly delay the necking of
the sample. Thus the samples in this study showed high
strength and moderate elongation.
This evolution of the serrations with the strain level is
the commonly expected behavior in a classical PLC
scheme. This reflects an increase of DSA effectiveness
due to a rise in the dislocation density when the strain
increases. The evolution of the serration type with strain
rate is also a characteristic of DSA. Indeed, when the
strain rate decreases, that is, the waiting time of the dis-
locations increases, the magnitude of the serrations was
enhanced. As a consequence, the jerky flow was mostly
of type A when the test speed was sufficiently large, as
was the case at 10 mm/min. Finally, DSA should be
avoided in sheets during manufacturing as it gives rise to
non-homogeneous plastic flow during sheet forming
processes and may lead to surface defects on formed
parts.
4 CONCLUSIONS
This study investigated the microstructure and me-
chanical properties of hot rolled Fe-13Mn-0.2C-1Al-1Si
TWIP steel. The conclusions are summarized in the
following:
a) The hot-rolled Fe-13Mn-0.2C-1Al-1Si TWIP steel
exhibited excellent mechanical properties with an
ultimate strength of 1075 MPa and an elongation of
17 %.
b) Many deformation twins and twin-dislocation
interactions were observed in the deformed TWIP
steel microstructure. This is due to the influence of
the PLC effect. The PLC effect during deformation
was determined to be responsible for the excellent
mechanical properties of the hot-rolled TWIP steel.
c) From a technological point of view the PLC effect,
and hence DSA, must be avoided. DSA gives rise to
non-homogeneous plastic flow during sheet forming
processes and may lead to surface defects on formed
parts.
5 REFERENCES
1 S. Allain, J. P. Chateau-Cornu, O. Bouaziz, A physical model of the
twinning-induced plasticity effect in a high manganese austenitic
steel, Mater. Sci. Eng. A, 387–389 (2004), 143, doi:10.1016/
j.msea.2004.01.060
2 L. Chen, H. S. Kim, S. K. Kim, B. C. De Cooman, On the Transition
of Internal to External Selective Oxidation on CMnSi TRIP,
Metallurgical and Materials Transactions A, 47 (2007) 12,
1804–1812, doi:10.2355/isijinternational.47.1804
3 Y. N. Dastur, W. C. Leslie, Mechanism of work hardening in
Hadfield manganese steel, Metal. Trans. A, 12A (1981) 5, 749–759,
doi:10.1007/BF02648339
4 O. Grassel, L. Krüger, G. Frommeyer, L. W. Meyer: Int. J. Plast.,
Microstructure–deformation relationships in fine grained high
manganese TWIP steel–the role of local texture, International
Journal of Materials Research, 16 (2000) 10–11, 1391, doi:10.1016/
S0749-6419(00)00015-2
5 M. Koyama, T. Sawaguchi, T. Lee, C. S. Lee, K. Tsuzaki, Work
hardening associated with -martensitic transformation deformation
twinning and dynamic strain aging in Fe–17Mn–0.6C and
Fe–17Mn–0.8C TWIP steels, Materials Science and Engineering A,
528 (2011), 7310–7316, doi:10.1016/j.msea.2011.06.011
6 I. Karaman, H. Sehitoglu, K. Gall, Y. I. Chumlyakov, H. J. Maier,
Deformation of single crystal Hadfield steel by twinning and slip,
Acta Mater., 48 (2000), 1345, doi:10.1016/S1359-6454(99)00383-3
7 S. Kibey, J. B. Liu, M. J. Curtis, D. D. Johnson, H. Sehitoglu, Effect
of nitrogen on generalized stacking fault energy and stacking fault
widths in high nitrogen steels, Acta Mater., 54 (2006), 2991,
doi:10.1016/j.actamat.2006.02.048
8 E. Bayraktar, F. A. Khalid, C. Levaillant: J. Mater., Deformation and
fracture behaviour of high manganese austenitic steel, Process.
Technol., 147 (2004), 145, doi:10.1016/j.jmatprotec.2003.10.007
9 B. X. Huang, X. D. Wang, Y. H. Rong, L. Wang, L. Jin, Mechanical
behavior and martensitic transformation of an Fe–Mn–Si–Al–Nb
alloy, Mater.Sci. Eng. A, A438–440 (2006), 306, doi:10.1016/
j.msea.2006.02.150
10 L. G. Hector, P. D. Zavattieri, Nucleation And Propagation Of Porte-
vin-Le Chatelier Bands In Austenitic Steel With Twinning Induced
Plasticity, Proceedings of the SEM Annual Conference, Indianapolis,
USA 2010
B. AYDEMIR et al.: INVESTIGATION OF PORTEVIN-LE CHATELIER EFFECT OF HOT-ROLLED ...
Materiali in tehnologije / Materials and technology 50 (2016) 4, 511–516 515
11 S. Kumar, E. Pink, Dynamic strain aging in a tungsten heavy metal,
Scripta Mat., 35 (1996), 1047–1052, doi:10.1016/1359-6462(96)
00262-X
12 J. M. Robinson, M. P. Shaw, Microstructural and mechanical influ-
ences on dynamic strain aging phenomena, Int. Materials Reviews,
39 (1994), 113–121, doi:10.1179/imr.1994.39.3.113
13 J. A. Yakes, C. C. Li, W. C. Leslie, The Effect of Dynamic Strain
Aging on the Mechanical Properties of Several HSLA Steel, SAE
Trans., SAE 790009 (1980), 44–59
14 B. Skoczen, J. Bielski, S. Sgobba, D. Marcinek, Constitutive Model
of Discontinuous Plastic Flow at Cryogenic Temperature, Int. J.
Plasticity, (2010), doi:10.1016/j.ijplas.2010.02.003
15 P. Zavattieri, V. Savic, L. G. Hector Jr., J. R. Fekete, W. Tong, Y.
Xuan, Spatio-temporal characteristics of the Portevin-Le Châtelier
effect in austenitic steel with twinning induced plasticity, Int. J.
Plasticity, 25 (2009), 2298–2330, doi:10.1016/j.ijplas.2009.02.008
16 B. C. De Cooman, L. Chen, S. Kim, H. S. Estrin, Y. Kim, S. K.
State-of-the-Science of High Manganese TWIP Steels for Auto-
motive Applications, Springer, # 2010, 165–183
17 K. Renard, S. Ryelandt, P. J. Jacques, Characterization of the Porte-
vin-Le Chatelier effect affecting an austenitic TWIP steel based on
digital image correlation, Mat. Sci. Eng. A, 527 (2010), 2969–2977,
doi:10.1016/j.msea.2010.01.037
18 EN ISO 6892-1:2009, Metallic materials – Tensile testing –Part 1:
Method of test at room temperature
19 EN ISO 7500-1:2015 Metallic materials – Verification of static uni-
axial testing machines – Part 1: Tension/compression testing machi-
nes – Verification and calibration of the force-measuring system
20 EN ISO 9513:2012 Metallic materials - Calibration of extensometer
systems used in uniaxial testing
21 L. Zhang, X. H. Liu, K. Y. Shu, Microstructure and Mechanical
Properties of Hot-Rolled Fe-Mn-C-Si TWIP Steel, J. Iron. Steel. Res.
Int., 18 (2011) 12, 45–48, 64, doi:10.1016/S1006-706X(12)60008-9
22 O. Bouaziz, S. Allain, C. Scott, Effect of grain and twin boundaries
on the hardening mechanisms of twinning-induced plasticity steels,
Scripta Mater., 58 (2008) 6, 484, doi:10.1016/j.scriptamat.2007.
10.050
23 D. Barbier, N. Gey, S. Allain, N. Bozzolo, M. Humbert, Analysis of
the tensile behavior of a TWIP steel based on the texture and
microstructure evolutions, Mater. Sci., 500 (2009) 1–2, 196,
doi:10.1016/j.msea.2008.09.031
24 S. S. F., De Dafé, F. L. Sicupira, F. C. S. Matos, N. S. Cruz, D.R.
Moreira, D.B. Santos, Effect of cooling rate on (
, ’) martensite
formation in twinning/transformation-induced plasticity Fe-17Mn-
0.06C steel, Mat. Res., 16 (2013) 6, 1229–1236, doi:10.1590/S1516-
14392013005000129
25 I. Gutierrez-Urrutia, D. Raabe, High strength and ductile low density
austenitic FeMnAlC steels: Simplex and alloys strengthened by
nanoscale ordered carbides, Materials Science and Technology, 30
(2014) 9, 1099, doi:10.1179/1743284714Y.0000000515
26 Y. Minamino, Y. Koizuma, N. Tsujia, N. Hirohataa, K. Mizuuchib, Y.
Ohkandab, Microstructures and mechanical properties of bulk
nanocrystalline Fe–Al–C alloys made by mechanically alloying with
subsequent spark plasma sintering, Science and Technology of
Advanced Materials, (2004) 5, 133–143, doi:10.1016/j.stam.2003.
11.004
B. AYDEMIR et al.: INVESTIGATION OF PORTEVIN-LE CHATELIER EFFECT OF HOT-ROLLED ...
516 Materiali in tehnologije / Materials and technology 50 (2016) 4, 511–516