Materials Sciences and Applicatio ns, 2011, 2, 1285-1292
doi:10.4236/msa.2011.29173 Published Online September 2011 (http://www.SciRP.org/journal/msa)
Copyright © 2011 SciRes. MSA
1285
Effect of Nano Size TiO2 Particles on Mechanical
Properties of AWS E 11018M Type Electrode
Tapan Kumar Pal, Utpal Kumar Maity
Welding Technology Centre, Metallurgical and Material Engineering Department, Jadavpur University, Kolkata, India.
Email: tkpal.ju@gmail.com
Received February 21st, 2011; revised May 16th, 2011; accepted July 1st, 2011.
ABSTRACT
Addition of nano size particles of TiO2 in the coating of shielded metal arc welding electrode (E 11018M) pa rtia lly sub-
stituting the con ventional micro size TiO2 was studied for possible enhanced electrode characteristics. The results show
that the nano size particle of TiO2 improved recovery of elements such as Mn, Ni, Mo, Ti etc. as well as increased
all-weld-metal tensile and ch arp y impa ct properties a t –51˚C. Furthermore, the charpy impact properties were found to
be very sensitive to variations in Ti content of the weld deposit.
Keywords: High Strength Steel, Coated Electrode, Nano Size Tio2, Strength and Toughne ss
1. Introduction
High strength steels are increasingly employed in many
applications due to the advantage they offer such as size
and weight reduction along with greater load bearing
capacities [1]. Increased use of high strength structural
steels poses a need for adequate welding consumable for
such materials. This leads to a significant advance in
electrode formulation to obtain weld deposits with high
values for strength and good toughness [2]. Structural
safety in welded joints are obtained by imposing re-
quirement on toughness by setting charpy V-notch levels
at the lowest design temperature [3]. The achievement of
adequate toughness value increasingly difficult as the
weld metal tensile strength increases. It has been well
established that maintaining good toughness become
more problematic as strength increases above in the re-
gion of 690 Mpa [1,4]. One way to obtain improved weld
metal toughness is through micro structural control,
which requires taking into account the weld metal chem-
istry.
Steel manufacturers have addressed the challenges of
increasing toughness in steel through grain refinement,
precipitating hardening, solid solution hardening, thermo
mechanical treatment and the promotion of low tem-
perature transformation products such as martensite and
bainite. Since weld metals are not usually given any
thermo mechanical or special heat treatment, many re-
search works have carried out by varying elemental
compositions or welding parameters with the aim of op-
timizing weld metal properties [5-7]. For the weld metal
of 780 MPa or lower strength steel, the effect of micro-
structure and oxygen content has been clearly demon-
strated. Acicular ferrite is an ideal microstructure for
these weld metals, and the increase in the amount of
acicular ferrite leads to improvement both in strength and
toughness [8,9]. The prior austenite grain size, inclusion
and specific alloying addition that hinder grain boundary
ferrite nucleation all are important consideration in
achieving optimum weld metal acicular ferrite and prop-
erties [10].
Weld consumables generally contain a small amount
of Ti to achieve stabilized transfer of molten droplets
during arc welding and it had been well known that Ti
bearing weld metal is preferably refined. Watanabe et al.
[11] experimentally changed oxygen contents in Ti bear-
ing gas metal arc weld metals and found that Ti oxides
effectively nucleate fine intragranular acicular ferrite.
Mori et al. [12] also proposed that oxide particles having
surface coating of TiO or those particles which are
wholly TiO would be the most potent site for nucleation
of acicular ferrite since disregestry between TiO and fer-
rite is only three percent.
In the present investigation, a novel approach has been
attempted to develop AWS E11018M electrode. The
study consisted of an addition of nano size particles of
TiO2 to the coating of shielded metal arc welding elec-
trode (E11018M) partially substituting the original (mi-
cro size) TiO2 and the effect of such addition on micro-
Effect of Nano Size TiOParticles on Mechanical Properties of AWS E 11018M Type Electrode
1286 2
structure and mechanical properties of all-weld metal.
2. Experimental
2.1. Preparation Coated Electrode
The AWS E11018M is a basic coated high strength steel
electrode. The core wire used for electrode was non-
rimming (semi killed) electrode quality steel of 3.15 mm
diameter and 450 mm length with a nominal composition
of C = 0.05%, Mn = 0.48%, Si = 0.018%, S = 0.018%, P
= 0.022%. The composition of the flux ingredients for
E11018 M was kept constant as given in Table 1, except
the micro size TiO2 particles which were partially re-
placed with nano size TiO2 particles. In the present in-
vestigation, out of 1.5% micro size TiO2 particles in total
flux ingredient, 1/3rd (33.33%) of it was replaced by the
nano size TiO2 particles for experimentation.
Hydraulic electrode extrusion machine was used to
produce the experimental electrodes of size 4mm. No
apparent effect was observed with nano size TiO2 parti-
cles on the extrusion behavior of the electrodes. The flux
coating has sufficient green strength and having smooth
appearance. The electrodes were dried in the oven to the
following sequence: at room temperature for 24 hours, at
60˚C for 30 min, at 90˚C for 10 min., at 120˚C for 15
min., at 200˚C for 5 min., at 300˚C for 5 min. and finally
at 420˚C for 50 min.
2.2. All-Weld—Metal Test Coupons
Four different all-weld metal samples were made with
electrodes having two without nano size TiO2 particles
i.e. MMAW-I and MMAW-II and two with nano size
TiO2 particles i.e. MMAWN-I and MMAWN-II in flat
position according to ISO 2560-73.Welds were deposited
on a groove of carbon steel (ASTM A131 grade B) plate
of 16 mm thick using the different developed electrodes.
The groove design is shown in Figure 1. The welding
parameters as given in Table 2 were used as per AWS A
5.5 - 1996. The electrode was inclined approximately at
50˚ - 60˚ along the welding direction using DC (+). Six-
teen no.s of passes in eight layers were required to
Table 1. Composition of flux ingredients used for coating in
E11018M type electrode.
Note: Liquid silicates used (for 1000 gm flux ingredients powder): Potas-
sium silicate = 130 gm, Sodium silicate = 55gm and Water = 10 gm.
Table 2. Welding parameters used.
Current type
Welding current
Open circuit voltage
Welding voltage
Welding speed
Inter-pass temperature
DC (+)
126 amp.
76 volt.
22 volt.
90 mm./minute
100˚C
completely fill up the groove of an experimental weld
test block.
2.3. Test Weld Block and Location of Test
Specimen
From each test weld block, all-weld tensile specimens,
transverse V-notch charpy impact specimens and metal-
lographic specimens were extracted. The location for
each type of specimen is shown in Figure 2.
2.4. Metallographic Study
Specimens for metallographic analysis from the weld
metal cross section, perpendicular to the welding direction,
were cut, ground and polished by standard methods. They
were then etched with 2% nital and examined under op-
tical microscope and scanning electron microscope
(SEM).
2.5. Tensile Testing
All-weld tensile specimens were machined longitudinally
from the weld deposits with dimension as per AWS A
5.5-1996. The tensile tests were carried out in a Servo-
Figure 1. Groove design.
Figure 2. Test weld block and location of the test specimens.
Flux constituent Wt %
Limestone 30.45
Fluorspar 22.75
Iron Powder 22.50
Ferro alloys 15.05
Other Minerals 6.25
Extrusion Agents 1.50
TiO2 1.50
Copyright © 2011 SciRes. MSA
Effect of Nano Size TiO2 Particles on Mechanical Properties of AWS E 11018M Type Electrode
Copyright © 2011 SciRes. MSA
1287
variations in the behaviour of the flux system, which in
turn leads to large variations in the metallurgical proc-
esses occurring in the weld pool.
Electric (Instron 8862) type 100 kN capacity universal
testing machine at a cross head speed of 0.5 mm/min.
Tensile test data such as YS, UTS and % elongation was
recorded for each all-weld sample. For each electrode
three samples were tested and average of three samples
was reported.
Although chemical equilibrium is not achieved in a
weld pool, a trend toward equilibrium is generally ob-
served that can be estimated using fundamental thermo-
dynamic principles. Oxidation reactions in the weld pool
can be described by the following generic reaction:
2.6. Vickers Hardness Testing
Hardness test was performed on metallography samples
using Vicker’s hardness testing m/c with a square based
diamond pyramid indenter having an included angle of
136˚ under a load of 30 kg.
xy
XMyOM O
(1)
According to the law of Mass Action, the equilibrium
constant, k, for Equation (1) can be written as follows:
x
MOy
y
x
MO
a
k
aa




(2)
2.7. Charpy Impact Testing and Fracture
Surface Study
For charpy impact testing, standard 55 × 10 × 10 × mm
size transverse specimens were machined and notch was
kept in weld metal perpendicular to the weld direction.
Charpy impact specimens were tested at –51˚C which
was achieved by adding acetone in liquid nitrogen. The
temperature was measured with electronic thermometer.
For each electrode five samples were tested and average
of five samples was reported. The broken charpy impact
specimens were examined under Scanning Electron Mi-
croscope to understand fracture micro-mechanism.
where, M
a
and O
a
are the activities of the weld
metal alloying element, M and oxygen, respectively, and
x
MOy
a
is the activity of the metal-oxide inclusion in the
weld metal. For equilibrium considerations, the activity of
the metal-oxide can be taken as unity, which leads to the
following relation:


y
x
MO
1
k
aa
(3)
3. Results and Discussion With knowledge of the oxidation reactions that will
occur in the solidified weld pool, it is possible to predict
the direction toward which these reactions will go as
changes are made in the welding flux.
3.1. Chemical Composition of Weld Deposits
The chemical composition of different weld deposits is
given in Table 3. The final weld metal chemical compo-
sition is determined by the slag-metal reactions that oc-
cur in the weld pool [13-15]. Research into slag-metal
reactions has generally been done within the limited
scope of a single flux system. However, the complexity
of the welding environment as well as the nonideal be-
haviour of the reactions that occur in the arc, lead to too
many variables, which make accurate prediction of the
effect of specific changes in system parameters difficult.
Even small changes in the flux coating can result in large
Competing chemical reactions within the weld pool
will also affect the final weld metal chemical composi-
tions. As local concentrations of alloy elements vary with
solidification [16,17], the local activity of the alloying
elements will change, altering the amount of alloying
additions that will be oxidized. As a result, these com-
petitive reactions will alter the predicted weld metal
chemical composition.
Results of all-weld metal chemical composition as
presented in Table 3 demonstrate that the recovery of the
Table 3. All-weld metal chemical composition (wt %).
Weld Element MMAW-I MMAWN-I MMAW-II MMAWN-II E11018M (AWS A5.5 - 1996)
C 0.053 0.046 0.058 0.051 0.10 max
Mn 1.49 1.76 1.62 1.73 1.3 - 1.8
Si 0.58 0.46 0.60 0.40 0.60 max
S 0.02 0.02 0.019 0.018 0.03 max
P 0.025 0.028 0.024 0.028 0.03 max
Cr 0.158 0.152 0.160 0.156 0.40 max
Ni 2.31 2.45 2.23 2.47 1.25 - 2.50
Mo 0.412 0.451 0.391 0.432 0.25 - 0.50
Cu 0.021 0.027 0.025 0.023 -
Al 0.003 0.005 0.005 0.005 -
V 0.012 0.019 0.019 0.020 0.05 max
Ti 0.0023 0.0040 0.0088 0.0200 -
Effect of Nano Size TiOParticles on Mechanical Properties of AWS E 11018M Type Electrode
1288 2
elements such as Mn, Ni, Mo, Ti etc. have improved in
weld metal with the addition of nano size TiO2 particles
(sample MMAWN-I and MMAWN-II). When alloying
elements are transferred from the coating (slag) to weld
metal, the equilibrium is [18]
do slox
MM MM  (4)
where Md is the amount of alloy transferred to deposit, Mo
is the initial amount of the alloy in the electrode (Core and
flux coating), Ms is the remaining amount of the alloy in
the slag and Mox is the amount of the oxidised alloy. The
unique physical properties of nano particles, resulting
from quantum size and surface effects presumably en-
hance the recovery of the alloying elements by facilitating
the slag-metal reactions. Arguments based on high reac-
tivity of nano particles suggest that nano size TiO2 would
dissociate resulting in more instant generation of O2 which
is likely to provide more stirring effect of the weld pool.
This in turn will improve slag-metal reaction. A similar
behaviour was reported for nano scale marble added in a
hardfacing electrode [19]. However, increasing oxygen
concentration with dissociation of TiO2 should increase
the loss of alloying elements by oxidation. The chemical
composition of weld deposit as presented in Table 3
rather shows opposite trend except Cr which shows some
loss. This observation suggests that the two potentially
competing effects would determine the final amount of
alloy components transferred to the weld pool. However,
considering affinity of Ti towards oxygen compared to Cr,
it appears that gain of Ti can be attributed due to 1) neg-
ligible difference between the partial pressure of oxygen
in the arc atmosphere and dissociation pressure of TiO2 at
high temperature and 2) reduction of TiO2 at the boundary
of metal/slag in the reaction zone of welding as per fol-
lowing equation:
2
TiO2(Si)2(SiO) (Ti)
 (5)
This is not unexpected considering some loss of Si in
the weld deposit with addition nano size TiO2.
3.2. Microstructure and Mechanical Properties
of Weld Deposit
Figure 3 shows the optical and Scanning Electron mi-
crographs of weld deposits with and without nano size
TiO2. The weld metal microstructure is affected by melt-
ing, gas dissolution, solidification and solid-state trans-
formations. Since the weld pool region is heated to tem-
perature as high as 2500 k, the liquid steel dissolves oxy-
gen. The extent of oxygen dissolution depends upon the
thermodynamic properties of liquid metal, gas and slag
phases [20]. As the liquid weld metal cools from this
temperature in the temperature range 2000˚C - 1700˚C,
(a) (b)
(c) (d)
Figure 3. Typical microstructures of all-weld metals: (a) optical micrograph (× 500) & (b) SEM micrographs without nano
ize TiO2, (c) optical micrograph (× 500) and (d) SEM micrographs with nano size TiO2.
s
Copyright © 2011 SciRes. MSA
Effect of Nano Size TiOParticles on Mechanical Properties of AWS E 11018M Type Electrode 1289
2
the dissolved oxygen and deoxidizing elements in the
liquid steel react to form complex oxide inclusions in the
range of 0.1 - 1.5 µm size range. In the temperature range
1700˚C - 1600˚C, solidification to δ-ferrite starts and
envelops these oxide inclusions and this δ-ferrite trans-
forms to austenite. The austenite may transform to sev-
eral microstructural constituents depending on chemical
composition, cooling rate, and austenite grain size. In
fact, the final microstructure in low carbon steel weld
metals depends on complex interactions between several
important variables such as inclusions, weld cooling rate
and weld metal hardenability.
Although the microstructures of weld deposits as
shown in Figure 3 appear to be similar i.e. acicular fer-
rite with some bainite, considerable difference in the
percentage of acicular ferrite and fineness of the structure
do exits. Weld deposits with nano size TiO2 addition
show more acicular ferrite and more fine grained struc-
ture compared with without addition of nano size TiO2.
The difference in microstructural characteristics is be-
lieved to be due to difference in chemical composition
and inclusion characteristics. The inclusions in weld de-
posits of without nano-size TiO2 particles are coarser
(Figure 4(b)) than that of with nano-size TiO2 particles
which are smaller and more in number (Figure 4(a)).
Growth and separation of oxide inclusions is influenced
by factors such as number density of the nuclei, interfa-
cial tensions and the extent of melt stirring [21]. The
separation of small oxide particles in weld deposit with
nano-size TiO2 particles is probably favoured by the tur-
bulent conditions existing in the hot part of the weld
pool.
If there are no inclusions, acicular ferrite formation
will not occur [22]. In addition, even if the inclusions are
present, acicular ferrite may not form if they are ineffec-
tive. The acicular ferrite constituent, which is character-
ized by small non-aligned ferrite grains found within
prior austenite grains, needs a greater degree of under
cooling than primary ferrite or side plate ferrite. Fur-
thermore, the size, type and number of weld metal inclu-
sions, the prior austenite grain size and specific alloying
additions are important considerations in achieving op-
timum weld metal acicular ferrite.
In a Fe-C-Mn structural steel inoculated with titanium
oxide the acicular ferrite microstructure was promoted by
increasing the manganese concentrations from 1.4 wt%
to 2.46 wt% [23]. It was suggested that Mn segregates to
austenite grain boundaries and reduces the driving force
for bainite nucleation at the interface and thus facilitates
the formation of acicular ferrite. Recently, He and Ed-
monds [24] speculated that the formation of Fe-V clus-
ters could act as nucleation sites for acicular ferrite in
addition to inclusions. Furthermore, Furahara et al. [25]
showed that addition of V and N to C-Mn steel contain-
ing MnS inclusions led to the formation of acicular fer-
rite. Above discussion probably suggests that increase in
hardenability elements in weld deposits with nano-size
TiO2 allows for greater under cooling as well as favor-
able inclusion characteristics for greater possibility of
acicular ferrite formation.
Considering that both bainite and martensite are prod-
ucts of austenite, one should ascertain that high strength
steel weld deposits will be free from martensite for im-
proved strength and toughness. It is well recognized that
steel will be free from martensite when the MS tempera-
ture of the steel is below its BF temperature. Interestingly,
the BS, BF and B50 temperatures as well as the MS and MF
temperatures are all related to the chemical composition
of the steel [26]. Recent constraint base model work [27]
on the metallurgical criteria related with chemical com-
position has been used to predict the microstructure/
strength of low carbon low-alloy weld deposits by the
(a) (b)
Figure 4. Effect of titanium on (a) YS & UTS and (b) Charpy-V-temperature.
Copyright © 2011 SciRes. MSA
Effect of Nano Size TiOParticles on Mechanical Properties of AWS E 11018M Type Electrode
1290 2
following equations:
50 Cn
r
B(o)770(270C)(90M )
37(Ni)(70C )83(Mo)
 
 (6)
C
Ms(o )561(474C)(33Mn)
(17Ni)(21 Mo)
 
  (7)
The calculated metallurgical characteristics of differ-
ent weld deposits are presented in Table 4.
The calculated data of B50 temperature as given in Ta-
ble 4 indicates the presence of bainite in all the weld de-
posits as the higher strength bainitic steels exhibits a B50
temperature in the range of 420˚C to 550˚C. Furthermore,
weld deposits having lower B50 temperature attributes
higher strength [28,29], Since bainite is a transformation
product of austenite, lowering the transformation tem-
peratures allows one to refine the grain size of the trans-
formation product, leading to simultaneous increase in
both tensile strength and ductility.
The average measured tensile and impact properties
are summarized in Table 5 for four weld deposits with
and without nano size TiO2. The addition of nano size
TiO2 in the coating of E11018M electrode significantly
elevates both YS and UTS as well as low temperature
toughness. The fracture surfaces of with nano size TiO2
shows quasi-cleavage mode of fracture(Figure 5(a))
compared to fracture surface of without nano size TiO2
which exhibits almost smooth typical cleavage frac-
ture(Figure 5(b)). Beside microstructural control to
achieve mechanical property goal, it is necessary to con-
trol oxygen and nitrogen in the weld metal for low tem-
perature toughness. Prior investigation using experimen-
tal flux-cored wire electrodes has shown the beneficial
effect of titanium addition in controlling weld metal ni-
trogen content [30]. Titanium addition also served to
refine the weld metal grains. Using C-Mn steel weld de-
posits, Evans [31] determined that there are two optimum
Table 4. Calculated metallurgical characteristics of differ-
ent weld deposits.
Weld sample B50 Temperature (˚C) MS Temperature (˚C)
MMAW-I 491 439
MMAWN-I 460 430
MMAW-II 479 434
MMAWN-II 463 428
Table 5. Mechanical properties of different weld deposits.
Weld
deposits YS
(MPa) UTS
(MPa) % Elongation Cha rp y Impac t
toughness at
–51˚C (J)
MNAW-I
MMAWN-I
MMAW-II
MMAWN-II
690
710
701
734
765
791
770
823
23
24
22
25
28
33
29
35
titanium concentration regarding impact toughness e.g.
30 and 200 ppm as shown schematically in Figure 5(b).
Also both YS and UTS increased with increase in Ti
content in the weld metal (Figure 5(a)). Evans [32] also
reported a complex interaction between Mn and Ti. The
optimum impact toughness occurred at 35 ppm Ti and
1.4 pct. Mn. The effect of Ti was more pronounced at
higher level of Mn. Titanium therefore acts as deoxidizer,
grain refiner and nitrogen getter and at the same time it is
very sensitive to the performance of weld deposits. The
beneficial effect of Ti on mechanical properties of weld
deposits, toughness in particular, at some critical concen-
tration is supported in the present study. Thus, to enhance
the performance of weld deposits particularly the tough-
ness, it is very important to control the amount of Ti in
weld deposits.
4. Conclusions
The following conclusions may be drawn from the study:
1) The introduction of nano size TiO2 in the coating of
coated electrode (E11018M) improved recovery of ele-
ments such as Mn, Ni, Mo, Ti etc.
(a)
(b)
Figure 5. SEM fractographs (a) weld metal with nano size
TiO2 and (b) weld metal without nano size TiO2.
Copyright © 2011 SciRes. MSA
Effect of Nano Size TiOParticles on Mechanical Properties of AWS E 11018M Type Electrode 1291
2
(a)
(b)
Figure 6. Optical micrographs showing inclusions: (a) weld
metal with nano size TiO2 and (b) weld metal without nano
size TiO2.
2) A significant influence on microstructure and me-
chanical properties of weld deposits has been observed
with addition of nano size TiO2. Both strength and
toughness at –51˚C of weld deposits with nano size TiO2
increased compared to without nano size TiO2.
3) In order to enhance the performance of weld depos-
its particularly the toughness, it is very important to con-
trol the amount of Ti in weld deposits.
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