A. Nasajpour - Effect of molybdenum on mechanical and abrasive wear properties of coating of as weld hadfield steel with flux-cored gas tungsten arc welding.pdf

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Journal of Alloys and Compounds 659 (2016) 262e269
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Journal of Alloys and Compounds
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Effect of molybdenum on mechanical and abrasive wear properties of
coating of as weld hadeld steel with
ux-cored
gas tungsten arc
welding
Ali Nasajpour
*
, AmirHossein Kokabi, Parviz Davami, Siamak Nikzad
a
Department of Materials Science and Engineering, Sahrif University of Technology, Tehran, Iran
a r t i c l e i n f o
Article history:
Received 11 June 2014
Accepted 11 November 2015
Available online 17 November 2015
Keywords:
Hadeld steel
Flux-cored wire
Abrasive wear
Work hardening
Surface hardening
a b s t r a c t
In this study, the variation of microstructure, yield and ultimate strength, strain hardening index, and
abrasive wear resistance of the hadeld steel cladded on st40 steel by the
ux-cored
gas tungsten arc
welding process protected by argon gas was investigated. The chemical composition of cladded hadeld
Steel contains Carbon, Manganese, and Silicon. Amount of Carbon, Manganese, and Silicon is constant in
all experiments, and Amount of Molybdenum ranged from o to 2.2 percent. Hence microstructure of
samples with the optical microscope and fractography with SEM as well as the formed phases with X-ray
diffraction and energy dispersive x-ray (EDX) were analyzed. To survey mechanical properties, tensile
and impact tests were carried out. Abrasive wear resistance was measured by dry sand/rubber wheel
apparatus. The results showed that the higher the percentage of Molybdenum is, the higher the yield and
ultimate strength will be, while the strain hardening index does not decrease. By increasing the per-
centage of molybdenum, the impact energy of the specimens and abrasive wear resistance has also
increased.
©
2015 Elsevier B.V. All rights reserved.
1. Introduction
Austenitic manganese steel, also called hadeld steel, contain-
ing Fe-1.2%C-13%Mn has the high intrinsic toughness, the high
strain hardening index, and an excellent wear resistance against
adhesive and abrasive wear for hard inorganic material
[1].
Because
of the low yield strength, it is possible to occur distortion and super
plastic deformation before activating and hardworking
[2].
The yield strength can be increased by adding alloy elements to
typical hadeld steel. For example, an addition of vanadium to
hadeld steel results in an increase in its yield stress and a decrease
in its ductility
[3].
G. Moghaddam et al.
[4]
were studied hadeld
steel containing 10%.wt V, ranging its carbon from 2.6%.wt to
3.3%.wt, and then has compared its mechanical properties and
microstructure to the standard hadeld steel.
G.Moghdam's observations show that a change in the percent-
age of carbon leads to a change in morphology and distribution of
carbide vanadium in matrix. Increasing the carbon percentage
causes an overwhelming increase in metal-to-metal wear
*
Corresponding author.
E-mail address:
Alinasajpour@hotmail.com
(A. Nasajpour).
http://dx.doi.org/10.1016/j.jallcom.2015.11.071
0925-8388/© 2015 Elsevier B.V. All rights reserved.
resistance and hardness, but decreases toughness and strain
hardening index in the same level. This steel is not suitable alter-
native when high wear resistance and toughness are needed
simultaneously.
Abbasi
[5]
compared standard hadeld steel to the hadeld steel
alloying with 1.5%.wt Al in terms of mechanical and wear properties
and reported that addition of aluminum enhances the yield stress,
primary hardness, and metal-to-metal wear resistance under low
stress. Although it decreases the ultimate tensile strength, elon-
gation, strain hardening index, and metal-to-metal wear resistance
under high stress.
Smith and Mackay
[2]
observed that the hadeld steel con-
taining 2%.wt Tungsten has more toughness and hardness than that
of typical hadeld steel.
It is also stated that addition of Molybdenum from 0.5%.wt to
2%.wt to a hadeld steel improves toughness, cracking resistance in
casting, yield stress, and toughness of cast large component during
solution heat treatment and quenching procedure. Molybdenum
changes the morphology of primary carbide and turns continuous
carbide into discontinuous that around austenite grain. Then car-
bides in grain boundaries become more spherical and less detri-
mental, especially in amounts of more 1.5%.wt Mo
[3,6].
A. Nasajpour et al. / Journal of Alloys and Compounds 659 (2016) 262e269
263
Finding an optimum composition of the hadeld steel are of an
abundant importance while it is accompanied high strain hard-
ening index and yield strength in the industries where high wear
resistance and toughness are needed. In this present paper, to make
surfacing properties suitable on low-carbon steel, the
ux-cored
wire of different amount of Mo was used while composition of
surface become that of hadeld. Addition of molybdenum not only
increases wear resistance but raises toughness of hadeld steel.
2. Experimental procedure
To fabricate the
ux-cored
wire, the St12 steel strip was used as
a tube in which alloying powders
ll.
These powders contain pure
Fe, graphite, ferromanganese, and ferromolybdenum. To produce
the
ux-cored
wire,
rst
strip was deformed in shape of U by a wire
drawing die, and then alloying powders of the suitable percentage
were put into U-shape strip. By deforming further, the
ux-cored
wire seam was completely closed, and consequently powders
were compacted with 5 steps of drawing.
Fig. 1
shows the proce-
dure of production of the
ux-cored
wire.
Afterwards the weld wire with size of 4 mm in diameter is made.
Therefore one pass of welding dilution of 7% was cladded on St40
steel when using gas tungsten arc welding with argon gas. Speci-
cations
of welding are 30 V, 110 A, and speed of 2.13 mm/s. To
reduce effect of dilution on composition of weld metal, the second
weld pass was cladded on the
rst
weld pass. The chemical analysis
of St40 steel is observed in
Table 1.
In order to obtain the compo-
sition of surface of samples, the spectrometric analysis was carried
out. As shown in
Table 2,
ve
compositions of different amounts of
molybdenum were obtained.
2.1. Microstructure
Because of high hardness and harden ability, the samples were
cut with wire-cut apparatus and then were grounded and polished
with alumina suspension. To etch samples and observe the optical
microstructure, samples were
rst
suspended in naital reagent of
2% within 20 s and later in ferric chloride (Fe
3
Cl) within 60 s.
Olympus BX51 optical microscope was applied for studying the
section that recognizes surface. To distinguish the phases with the
same chemical composition and calculate volume fraction of car-
bides, seven images were taken from surface of each sample using
scanning electron microscope, Tescan VEGA 2. Meanwhile, energy
dispersive x-ray and x-ray diffraction were used to obtain chemical
composition of carbides. The x-ray diffraction analysis was done
with specication of CueK
a
radiation (
l
¼
1.5406 A) at 2ѳ-step of
0.02
and scanning duration of 0.5 s from 10 to 100.
2.2. Impact and tensile test
To fabricate specimens for the charpy impact test and tensile
test, two plates with bevel of 30
were used while gap distance was
Table 1
Chemical composition of substrate to weld.
Fe
Bal
C
0.18
Mn
1.5
Si
0.4
S
0.015
P
0.025
Al
0.02
Cr
0.3
Mo
0.08
Table 2
Chemical composition of weld metal after cladding.
Sample.no
1
2
3
4
5
Fe
Bal
Bal
Bal
Bal
Bal
C
1.38
1.41
1.36
1.39
1.42
Mn
12.9
13.1
12.8
12.7
13.2
Si
0.07
0.06
0.07
0.05
0.05
S
<0.005
<0.005
<0.005
<0.005
<0.005
P
<0.05
<0.05
<0.05
<0.05
<0.05
Al
0.002
0.003
0.002
0.004
0.002
Cr
0.04
0.02
0.04
0.03
0.03
Mo
e
0.75
1.22
1.65
2.22
7 mm, and a backing material of St40 steel was applied as it was
welded to two plates in spot weld with GTAW. The root of V-shape
bevel is
lled
by two passes with GTAW process. As observed in
Fig. 2,
three specimens for impact test and two specimens for
tensile test were made from each of the welded samples.
The subsize specimens for tensile test were made by wire-cut
apparatus according to E8M-O4ASTM standard. Based on ASTM
E23-96, the specimens for impact test were prepared with a
specication of 3.8 mm
Â
55 mm
Â
10 mm and notch of 45
with
2 mm depth. Impact test was carried out using AVERY apparatus.
Fig. 2.
Procedure of making specimens for tensile test and impact test after welding.
Fig. 1.
Sequence of production of
ux-cored
wire.
264
A. Nasajpour et al. / Journal of Alloys and Compounds 659 (2016) 262e269
2.3. Abrasive wear test
To survey abrasive wear resistance of the samples, the standard
of ASTM G65-04 was used. Having cladded on ST40 steel in
dimension 8 cm
Â
3 cm, the surface of each of the samples was
smoothened such that the whole samples have the same condition.
The round-shape sands have specication of 50e70 mesh particle
size and an existing rate of 300e400gr/min as an abrasive agent
while in applied force of 130 N.
The distance of wear is considered 1440 m for each test such
that measuring procedure of weight was done in every 360 m. It is
noted that measuring was done with accuracy of 0.001gr.
3. Results and discussion
3.1. Microstructure
Fig. 3
shows the optical microstructure of as-weld samples
containing 0, 0.75, 1.2, 1.65, and 2.2%.wt Mo. As shown in
Fig. 3,
the
microstructure of as-weld includes austenite as a matrix in which
three unique phases disperse in terms of apparent shape. The
rst
one is the massive-shaped phase that is primary carbide into which
grains of austenite were formed. The second one is a needle-shaped
phase. It is the carbide that precipitates in grain boundaries of
austenite. The third one is a linear-shape phase of which thickness
is much low. They are secondary carbides of which preferred sites
to nucleate are on mechanical twins. The third one grows in matrix
in parallel lines
[7].
Fig. 4
Shows the results of XRD and EDS tests of the samples
welded with the
ux-cored
wire containing 2.2%.wt Mo. It is
concluded that part, a, is the carbide enriched in molybdenum with
chemical composition of Mo
2
C, and the part, b, is complex carbide
of Fe and Mn, Mn
1.2
C Fe
1.8
, and the part, c, is matrix of austenite,
and the part, d, is carbides in grain boundaries
[4].
Based on the backscatter image captured by SEM in
Fig. 5
and
chemical analysis of EDS and XRD, It can be stated that colonies of
primary carbide consist of two kinds of carbide. Molybdenum
carbides in spherical shape are always into complex carbide of Fe
and Mn. The higher the percentage of molybdenum carbide is, the
lower amount of complex carbide of Fe and Mn will be, Conse-
quently the complex carbides detrimental decrease in grain
boundary
[3].
This is illustrated in
Fig. 5
that is the backscatter image of surface
of samples. As shown in
Fig. 5,
an increase in amount of Mo in-
creases carbide colonies, as a result decreases average length of
carbide in grain boundaries.
Seven back scatter images with magnication of 1500 were
prepared. These images show the section including surface. These
Fig. 3.
Microstructure of samples in magnication of 50 a) without Mo b) 0.75% Mo c) 1.2%Mo d) 1.65%Mo e)2.2%Mo.
A. Nasajpour et al. / Journal of Alloys and Compounds 659 (2016) 262e269
265
Fig. 4.
The result of XRD and EDS test of the sample containing 2.2%Mo.
results have been brought in
Table 3.
According to
Table 3,
total volume fraction of carbides is the
same amount in all amounts of molybdenum. Increasing molyb-
denum causes a decrease in average length of carbide in grain
boundary and an increase in volume fraction of molybdenum
carbide.
3.2. Impact test
Fig. 6
shows impact energy as a function of amount of molyb-
denum. As amount of Mo increases up to 2.2%, impact energy in-
creases from 11.2% to 17.7%. In other words, impact energy of
sample welded without Mo is 58% less than that with 2.2% of Mo.
According to
Table 3,
increasing amount of Mo does not vary the
266
A. Nasajpour et al. / Journal of Alloys and Compounds 659 (2016) 262e269
Fig. 5.
Electron backscattered image of surface of samples a) without Mo b) 0.75%Mo c) 1.2%Mo d) 1.65%Mo e) 2.2%Mo.
Table 3
Volume fraction of carbide in samples.
Sample
0% Mo
0.75% Mo
1.2% Mo
1.65% Mo
2.2% Mo
Volume fraction of Mn
1.2
C Fe
1.8
18.4
18.1
18.3
17.8
18.2
e
e
e
e
e
0
¼
18.4
2.2
¼
15.9
3.7
¼
14.6
4.6
¼
13.2
5.3
¼
12.9
Volume fraction of Mo
2
C
e
2.2
3.7
4.6
5.3
Average length of carbide in grain boundaries(
m
m)
572
518
365
153
98
Volume fraction of total carbide
18.4
18.1
18.3
17.8
18.2
Fig. 6.
Impact energy as a function of amount of molybdenum.
total volume fraction of carbides, but decreases length of carbide
put in grain boundary. As a result an increase in amount of Mo
causes an increase in hardness and toughness simultaneously.
Fig. 7
shows the image of fracture surface of the sample welded with the
ux-cored
wire without Mo after impact test. Fracture surface on
the right of notch is observed in
Fig. 7(a).
This fracture is brittle, and
cracks are formed through carbides in grain boundaries.
Fig. 7(b)
shows fracture surface below notch.
Fig. 7(b)
is a mixture of
intergranular and intergranular facets
[8].
The white arrow denotes
the site of crack nucleation in
Fig. 7(b).
It is concluded that the
lowest impact energy is attained when the most carbides are in
grain boundaries, or namely the
ux-cored
wire is free of Mo.
Fig. 8
shows the secondary electron image of fracture surface of
the sample welded with the
ux-cored
wire containing 2.2%.wt Mo
after impact test. Although large dimples are observed in
Fig. 8
(a)
that is fracture surface of the right of notch, it can be stated shear
brittle fracture occurred
[9,10]. Fig. 8(b)
presents fracture surface
below notch. Existence of many dimples demonstrates that ductile

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