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www.me‐journal.org Journal of Metallurgical Engineering (ME) Volume 4, 2015
doi: 10.14355/me.2015.04.003
18
Effect of Manganese Sulphide Shapes on the
Work‐hardening Coefficient of Hot Rolled
Structural Steel Ahmed I. Z. Farahat, Zainab Abdel‐hamid and Nasser Gomaa
Central Metallurgical Research and Development Institute, CMRDI, P.O.Box 87 Helwan, Egypt
Abstract
This paper studied the effect of non‐metallic inclusions shapes (manganese sulphides on the tensile testing behavior, the work‐
hardening coefficient and rate. Longitudinal and Transverse tensile testing was carried out. The fracture surface was studied
after tensile testing. Chemical analysis for the non‐metallic solution was conducted using EDS‐SEM. Tensile testing was carried
out in thickness direction and in parallel to the direction of rolling. The work‐hardening coefficient (with tensile samples of the
thickness) increases with the types II and III. It is found that the work‐hardening rate for types of non‐metallic inclusions is
similar and has critical change. It is also observed that the non‐metallic inclusions Type II and III can resist the crack
propagation due to crack tip or plastic zone at the onset of crack.
Keywords
Non‐Metallic Inclusions Shapes, Longitudinal And Transverse Tensile Testing, Fracture Surface, Work‐Hardening Coefficient
Introduction
Non‐metallic inclusions are very harmful in steel practice. After Oxygen, Sulpher is the most important non‐
metallic element in the field of steel metallurgy [1]. Therefore, sulphides form a second important group of
inclusions. Morphology of suphides inclusions has significant effect on the various properties of steels [2].
1. Sulfides are precipitated during solidification due to the solute elements (such as Mn and S) segregation;
2. Sulfides are precipitated during the δ ̸γ transformation due to the redistribution of solute elements and the
different sulfide solubility in δ‐Fe and γ‐Fe;
3. Sulfides are precipitated in γ‐Fe due to the decrease in solubility of sulfur in the matrix with decreasing
temperature;
4. Sulfides are precipitated during the γ/α transformation due to the difference of sulfur solubility in γ‐Fe and
α‐Fe.
Simms and Dhale, in 1938, classified the non‐metallic inclusions into three types depending on the morphology of
manganese sulphides [3]:
1. Type I that exist when there is practically no aluminum content, usually in silicon‐killed steels.
2. Type II is that appear with the first traces of aluminum, above 0.005 wt%.
3. Type III is that initially appears alongside type II at levels of 0.01 to 0.03 wt% total aluminum.
4. Type III is practically assured as the only type to occur with total aluminum of ≈0.04 wt%.
The type of manganese sulphide inclusions in wrought steels depends on the type of sulphide formed in the
original cast steel.
Type I manganese sulphide inclusions are much harder than the other types. During rolling, type I manganese
sulphide deforms to a ʹlozengeʹ shape. Any silicates usually deform more, ending up at the tips of the lozenge [4].
Elongated (Types II and III) inclusions also act as initiation sites for lamellar tearing. Farrar in 1979 found that
Journal of Metallurgical Engineering (ME) Volume 4, 2015 www.me‐journal.org
19
lamellar tearing could also be initiated by type I manganese sulphides, but the volume fraction of Type I
manganese sulphides required for initiation was very high, and such a high level of only type I inclusions is
unlikely to be found in structural steels. In such (high oxygen) steels, susceptibility to lamellar tearing is generally
controlled by oxides [5,6].
The final shape of the inclusions in wrought steel is particularly important with reference to hydrogen induced
cracking in sour service and lamellar tearing [7,8]. The elongated manganese sulphide inclusions in wrought steel
(Type II, III) act as initiation sites for hydrogen induced cracking in sour (H2S containing) environments. However,
type I manganese sulphide inclusions have been reported to trap hydrogen, inhibiting hydrogen diffusion and thus
inhibiting hydrogen induced cracking both at the initiation and propagation stage. Types II and III MnS inclusions
become much more elongated than type I upon rolling [9].
It is much more difficult to distinguish between these types in wrought steels than in cast steels. Type II is
characteristically in clusters, rather than isolated inclusions [10].
Hydrogen induced cracking (HIC) and sulphide stress cracking (SSC) represent two kinds of a specific hydrogen
provoked damage that are frequently met in petroleum and refinery industry. In the first case (HIC), it is generally
recognized that resistance of steels depends mainly on their microstructure features‐non‐metallic inclusions and
segregation bands. Elongated manganese sulphides are considered as the most dangerous initiation sites [4,11]. In
the second case sulphide stress cracking (SSC), it is believed that resistance of steels can be preferentially related to
their strength level while microstructure characteristics are less important [5‐8, 10, 12].
Manganese sulphide inclusions are responsible for the initiation coarse micro‐voids as a result of the separation of
the inclusion matrix interface. The subsequent growth of micro‐voids and the propagation of the cleavage cracks
depend on effective ferrite grain size and matrix strength [13].
This paper is a trial to detect the effect of sulphide shape on the opening of cracks especially in the direction of
rolling and thickness and to compare their work‐hardening coefficients.
Experimental Work
The Received Material
Plate of heats of steel with the thick plate were received and used for experimental studies. The chemical
composition of the studied heats is given in Table 1
TABLE 1CHEMICAL COMPOSITION OF STEEL (WT%)
Sample C Si Mn P S Al
1 0.172 0.267 1.69 0.0065 0.0086 0.0403
2 0.170 0.265 1.71 0.0600 0.0080 0.0401
3 0.171 0.270 1.68 0.0063 0.0084 0.0400
The tensile testing was carried out at room temperature to determine the tensile strength in the rolling direction
and in the thickness direction to evaluate the effect of non‐metallic inclusions on the work‐hardening coefficient.
Polished samples were metallographically prepared to determine the non‐metallic inclusions type and size. Optical
and SEM microstructure were used to recognize the different phases. The ASTM standard (E45‐97) was used to
recognize and to compare the different size of non‐metallic inclusions for the received plates. ASTM E8 ‐ Standard
Test Methods for Tension Testing of Metallic Materials was used to machine the tensile specimens. The tensile rate
was 5mm/minutes.
Optical Microstructure
The microstructure consists of ferrite (white phase) and pearlite (dark phase) as shown in Figs.1&2. The matrix
consists of banded layers of ferrite and pearlite.
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RELATIONSH
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Consequently
EMENTS
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.
S.Sahoo, M.G
the Charpy
ing A613(2014
Hart, PHM;
3 Offshore Tec
HIP BETWEEN T
esting, the w
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Egyptian Na
Ghosh, R.N.Gh
impact prope
4)37–47.
Bailey, N; Fa
chnology Con
THE REDUCTIO
work‐harden
aximum valu
e the non‐me
rection.
pe II & III)
not cause sev
ions highly
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ulphide (typ
by type II or
e II and II)
asier to detec
tional Steel F
hosh, D.Chakr
erties of low
arrar, JCM ʹM
ference, Hous
J
ON OF TENSIL
ning coefficie
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) causes sev
ct the cracks
Factory and
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Material Aspect
ston, Texas, 30
Journal of Met
LE AREA AND W
ent (n) high
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ases the cross
ere cracks du
nitiations and
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ads to sudd
vere crack
before they
Head of Qu
t of microstru
LA steel con
ts Controlling
0th April‐2nd
tallurgical Eng
WORK‐HARDE
hly increases
type I. the T
s section und
uring Z‐test
d consequen
ning coefficie
ch highly res
ere crack ini
en catastrop
initiation as
reach the cri
ality Contro
ctural parame
taining MnS
g Weld Defect
May 1973, Vo
gineering (ME
ENING COEFFI
s with enha
Type II and
der stress an
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ntly does not
ent where in
sists the cra
itiation, how
phically failu
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itical size.
ol Departmen
eters, microte
inclusions M
ts In Offshore
ol.2, Paper No.
E) Volume 4, 2
ICIENT
ncing the n
III decrease
d the elonga
decreasing
t deteriorate
n the transve
ck propagat
wever, the cr
ure. Meanwh
ith slow cr
nt are gratefu
xture and ma
Materials Scie
e Structuresʹ P
. OTC 1908, p8
2015
non‐
the
ated
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ack
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Pre‐
823‐
Journal of Metallurgical Engineering (ME) Volume 4, 2015 www.me‐journal.org
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