W. ZHANG et al.: MICROSTRUCTURE AND MECHANICAL PROPERTIES OF WIRE ARC ADDITIVE-MANUFACTURING ...
359–364
MICROSTRUCTURE AND MECHANICAL PROPERTIES OF WIRE
ARC ADDITIVE-MANUFACTURING HIGH-CARBON CHROMIUM
BEARING STEEL
MIKROSTRUKTURA IN MEHANSKE LASTNOSTI Cr-Mo
LE@AJNEGA JEKLA IZDELANEGA Z DODAJNO TEHNOLOGIJO
NA OSNOVI @I^NEGA OBLOKA
Wenjie Zhang
1
, Weining Lei
1,2*
, Yang Zhang
1,2
, Xiao Liu
1,2
1
School of Materials Engineering, Jiangsu University of Technology, No. 1801 Zhongwu Road, Changzhou, Jiangsu 213001, China
2
Key Laboratory of Advanced Materials Design and Additive Manufacturing of Jiangsu Province, No. 1801 Zhongwu Road, Changzhou,
Jiangsu 213001, China
Prejem rokopisa – received: 2019-07-22; sprejem za objavo – accepted for publication: 2019-10-11
doi:10.17222/mit.2019.168
Wire arc additive-manufacturing technology (WAAM) was conducted successfully on a high-carbon chromium bearing steel
with an ER55-Ni welding wire and a GCr18Mo substrate. It is found that the microstructure of the cross-section of the WAAM
sample is divided into three parts, i.e., the deposition layer, the transition layer and the substrate. The microstructure of the
deposition layer mainly consists of needle-like tempered martensite and cementite, with a small quantity of ferrite. The
transition zone is composed of coarse bainite and ferrite. In the deposition layer, the hardness gradually decreases from the top
to the root, and the hardness of the transition layer is close to 350 HV. The arc-cladding sample exhibits a higher yield strength
and tensile strength but lower elongation than the substrate sample. The necking is formed and a failure occurs at the transition
layer of the WAAM sample. The maximum depth values of wear scars on WAAM and substrate samples are close to each other.
The wear is more uniform on the WAAM sample but the cross-sectional area of its wear scar is larger than that of the substrate
sample. The wear resistance of the WAAM sample is lower than that the substrate sample, which is mainly attributed to the low
hardness of the WAAM sample.
Keywords: additive manufacturing technology, high-carbon chromium bearing steel, microstructure, mechanical properties
Avtorji so uspe{no nanesli prevleko na podlago iz visoko oglji~nega Cr-Mo le`ajnega jekla GCr18Mo z dodajalno tehnologijo
na osnovi obloka (WAAM) varilne ER55-Ni `ice. Ugotovili so, da je mikrostruktura v preseku WAAM-vzorca razdeljena na tri
dele. Ti so: na nane{eno (navarjeno) plast, prehodni pas in podlago. Mikrostruktura na podlago nane{ene plasti je v glavnem
sestavljena iz igli~astega popu{~enega martenzita in cementita z majhno vsebnostjo ferita. Prehodna cona je sestavljena iz
grobega bainita in ferita. Trdota nane{ene plasti se postopno zmanj{uje od vrha proti podlagi in v povpre~ju zna{a okoli 350 HV.
Oblo~no nane{ena plast ima vi{jo mejo plasti~nosti toda manj{i raztezek kot podlaga. Med nateznim preizkusom je pri{lo do
zo`evanja (nastanka vratu) na WAAM-vzorcu in do njegove poru{itve je pri{lo v prehodni coni. Maksimalna globina raz nastalih
s preizkusi obrabe je pribli`no enaka na WAAM-vzorcu in vzorcu iz podlage. Obraba je bolj enakomerna na WAAM-vzorcu
vendar je v preseku nastale ve~je {tevilo raz zaradi obrabe kot tiste, ki so nastale na podlagi. Odpornost proti obrabi
WAAM-vzorca je manj{a od tiste na podlagi, kar avtorji v glavnem pripisujejo ni`ji trdoti WAAM-vzorca.
Klju~ne besede: dodajna tehnologija, nanos prevleke na osnovi obloka varilne `ice, kromovo le`ajno jeklo z visoko vsebnostjo
ogljika, mikrostruktura, mehanske lastnosti
1 INTRODUCTION
Additive-manufacturing (AM) technology is a
bottom-up and layer-by-layer manufacturing method,
which has the advantages of a fast forming speed, high
utilization of the material and high production
efficiency.
1–2
Over the years, AM researches have been
focused on improving the mechanical properties of
forming components so that they can be used directly. As
one kind of the AM technology, wire arc additive-
manufacturing technology (WAAM) takes arc as the heat
source and inert gases (such as Ar) as the protection
atmosphere.
3–4
By layer-by-layer manufacturing, near-net
shape forming is achieved in WAAM.
5–6
The direct-form-
ing technology based on an arc heat source has the
advantages of low production costs and good mechanical
properties and has been widely used in various industrial
fields, such as the automobile industry, aerospace, food
and medical treatment.
7–8
In recent years, WAAM has attracted great attention
with the formation and repair of various kinds of metallic
materials, including Mg alloys, Al alloys and Ti
alloys.
9–10
For example, Y. Y. Guo et al.
11
studied the
microstructure and tensile properties of an AZ80M Mg
alloy made with WAAM, and the results showed that the
microstructure of the WAAM AZ80M alloy was inhomo-
geneous, containing micro-defects, which influenced the
mechanical properties. T. T. Wang et al.
12
studied the
microstructure and tensile properties of WAAM die-steel
components made of an H13 steel welding wire, and the
Materiali in tehnologije / Materials and technology 54 (2020) 3, 359–364 359
UDK 620.1/.2:620.17:669.1.017:621.7 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(2)359(2020)
*Corresponding author's e-mail:
leiweining@jsut.edu.cn (Weining Lei)

results showed that the components were well formed
with a uniform hardness distribution.
High-carbon chromium bearing steel is widely used
as a rolling-bearing material, due to its high toughness,
good wear resistance, suitable elasticity, good corrosion
resistance and good machinability.
13–14
However, the
repair of high-carbon chromium bearing steel in a
service environment is difficult once damage occurs. So
far, there has been little research on the AM of
high-carbon chromium bearing steel. In this paper, an
ER55-Ni welding wire was used for WAAM on a
GCr18Mo substrate, which was a typical bearing steel.
The microstructure, mechanical properties and wear
behavior of the WAAM sample were investigated. The
reasons for the difference between the WAAM sample
and the substrate were analyzed.
2 EXPERIMENTAL PART
2.1 Materials
The chemical compositions of the ER55-Ni welding
wire and GCr18Mo bearing steel used in this study are
listed in Table 1. The diameter of the ER55-Ni welding
wire was 1.2 mm and the dimensions of the GCr18Mo
bearing-steel plate was 200 mm × 200 mm × 14 mm.
2.2 WAAM process
A schematic of the WAAM process is shown in
Figure 1. A tungsten-inert-gas (TIG) welding machine
and alternating-current power supply were used in this
study. The welding parameters used in this study are
listed in Table 2. The length of the weld bead deposited
on the substrate is 150 mm and 12 layers were deposited.
The final weld-bead height was about 20 mm.
Table 2: WAAM processing parameters used in this study
Processing parameter Value
Welding current (A) 190
Wire feed speed (mm/s) 3.2
Travel speed (mm/s) 4
Wire feeding angle (°) 55
Tungsten electrode diameter (mm) 3.2
Flow rate of 99.99-% argon shielding gas (L/s) 1.7
Interval time between two layers (s) 30
2.3 Testing and characterization
The cross-section specimens of the WAAM sample
were cut with wire-cut electrical-discharge machining
and treated with the standard metallographic preparation
method. The microstructure was observed with a light
microscope (LM) and scanning electron microscope
(SEM). The hardness of the specimens was measured
with a digital microhardness tester (HVS-1000B). The
sampling place of the tensile specimens is shown in
Figure 1; the gauge dimensions were 10 mm in length, 3
mm in width and 1 mm in thickness. A tensile test at
room temperature was conducted with an electronic
universal tensile-testing machine (WDW3200) and the
tensile rate was 2 mm/min. In the tensile test, two groups
of samples were drawn and one set of data was selected.
The strain evolution during the tensile test was charac-
terized with a digital image correlation (DIC) system.
The wear behavior was tested with a friction-wear tester
(Nanovea Tribometer). A micro-profilometer (Nanovea
PS50) and SEM were used to observe the surface
morphology of the tensile specimens and wear marks.
3 RESULTS AND DISCUSSION
3.1 Microscopy
As shown in Figure 2a, the microstructure of the
cross-section is divided into three parts, i.e., the
deposition layer, transition layer and substrate. As shown
in Figure 2b, the microstructure of the deposition layer
mainly consists of tempered martensite and cementite,
with a small quantity of ferrite. The morphology of
tempered martensite exhibits a fine needle-like pattern,
which grows irregularly in multiple directions. It can be
seen from the SEM image of the deposition layer in
Figure 2c that some carbides are distributed at the grain
boundaries and in the tempered-martensite matrix.
Figure 2d shows the microstructure of the transition
zone, which is composed of coarse bainite and ferrite.
Due to the thermal-exposure influence during WAAM,
microcracks were formed in the transition zone and these
microcracks range in length from 40 μm to 50 μm,
leading to a great reduction in both plasticity and
toughness of the region.
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Table 1: Chemical compositions of the ER55-Ni welding wire and GCr18Mo bearing steel used in this study, (w%C)
Alloys C Si Mn P Ni Cr Mo Cu Fe
ER55-Ni2  0.12 0.4  1.25  0.025 0.80 1.10  0.15  0.35  0.35 Bal.
GCr18Mo 0.9 0.2 0.25 0.02 0.25 1.65 0.20 0.25 Bal.
Figure 1: Schematic presentation of WAAM

As shown in Figures 2d and 2e, the microstructure of
the transition zone is different from the deposition layer
or the substrate. There is an obvious difference in the
chemical composition between the welding wire and the
substrate. High-carbon steel usually exhibits high crack
sensitivity. Due to the high energy density and fast cool-
ing during the WAAM process, hardening and cracking
are easy to occur in the transition zone. In addition, the
heat exposure of bainite results in the precipitation and
coarsening of carbides. Figure 2f shows the microstruc-
ture of the substrate, which is composed of fine-grained
low bainite and cementite. The SEM image in Figure 2g
shows that the carbides are uniformly distributed in the
GCr18Mo substrate.
3.2 Hardness
Figure 3 shows the hardness distribution from the
top to the root at the center of the weld. According to the
hardness-distribution curve, the hardness gradually
decreases from the top to the root, and the hardness of
the transition layer is close to 350 HV. As the welding
joint is subjected to several thermal cycles, the marten-
site gradually changes into tempered martensite with a
relatively low hardness. Since the chemical composition
of the deposition layer is different from that of the
substrate, its amount of carbide is lower than that of the
substrate. Meanwhile, coarse grains are formed in the
W. ZHANG et al.: MICROSTRUCTURE AND MECHANICAL PROPERTIES OF WIRE ARC ADDITIVE-MANUFACTURING ...
Materiali in tehnologije / Materials and technology 54 (2020) 3, 359–364 361
Figure 2: Microstructure of the cross-section of a WAAM sample observed with LM and SEM: a) junction of WAAM, b), c) welding layer, d), e)
transition zone f), g) parent metal
Figure 3: Hardness distribution from the top to the root at the center
of the weld

deposition layer due to the thermal exposure. As a result,
the hardness of the deposition layer is lower than that of
the substrate.
3.3 Tensile properties
The specific data for the tensile properties are
summarized in Table 3. According to the tensile-test
results, the WAAM sample exhibits higher yield strength
(YS) and ultimate tensile strength (UTS) but lower
elongation (EL) than the substrate sample. The YS and
UTS of the WAAM sample reach 622 MPa and 998
MPa, higher by 102 % and 70 % than the substrate
sample, respectively, while its EL is 20 %, which is 46 %
higher than that of the substrate sample.
Table 3: Specific data for the tensile properties
Material YS/MPa UTS/MPa Elongation/%
Weld 622 998 20
Parent metal 308 588 37
Figure 4 shows images of the dynamic-failure
process of the tensile test obtained with the high-speed
digital image correlation (DIC) method. As shown in
Figure 4, there is an obvious neck shrinkage in both
specimens after the tensile test, which indicates a ductile
fracture in both the WAAM and substrate sample. The
three recording moments during the tensile test are the
initial moment, the intermediate moment and the
near-failure moment, respectively. It can be seen that, at
the initial moment, the axial strain field in the gauge part
of both the WAAM and substrate sample is uniform and
there is no obvious local strain. At the intermediate
moment, a local strain is observed and obvious necking
is seen in the WAAM sample. The necking is located at
the transition layer.
During the welding process, the fiber region in the
interface between the cladding layer and the substrate
undergoes a strong plastic deformation. This plastic
deformation not only leads to an increase in the
macroscopic strength of the sample, but also increases
the overall microhardness of different regions and
reduces the toughness. As for the substrate sample, there
is still no obvious strain concentration. At the near-
failure moment, the strain distribution in the WAAM
sample shows a little difference compared to the inter-
mediate moment. The necking is formed and the failure
occurs at the transition layer. As for the substrate sample,
the strain concentration is observed at the near-failure
moment and the corresponding necking and failure
occur.
3.4 Wear behavior
Figure 5 shows a 3D wear scar and cross-sectional
images of the WAAM and substrate sample. The maxi-
mum depth, cross-sectional area and wear rate calculated
according to the cross-sectional images are shown in
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362 Materiali in tehnologije / Materials and technology 54 (2020) 3, 359–364
Figure 5: 3D wear scar and cross-section images of the WAAM and
substrate samples: a) substrate sample, b) WAAM sample
Figure 4: Images of the dynamic failure process of the tensile test
obtained with the high-speed digital image correlation (DIC) method:
a) substrate sample, b) WAAM sample

Table 5. It can be seen that the maximum depths of the
wear scars in the WAAM and substrate sample are close
to each other. The wear is more uniform on the WAAM
sample but its cross-sectional area of the wear scar is
larger than that of the substrate sample. The wear rate of
the WAAM sample is 26.42 mm
3
/(N·m), while the wear
rate of the substrate sample is only 8.33 mm
3
/(N·m).
This shows that the wear resistance of the WAAM
sample is lower than that of the substrate sample, which
is mainly attributed to the low hardness of the WAAM
sample. According to Archard’s law, materials with high
hardness always exhibit low wear rate and good wear
resistance.
15–16
Table 4: Wear results for the WAAM and substrate samples
Materials
Maximum
wear depth/
mm
Cross-sectional
area of wear
marks/mm
2
Wear rate
mm
3
/(N·m)
Substrate
sample
7.6×10
–3
8.33×10
–4
8.33
WAAM
sample
7.22×10
–3
2.642×10
–3
26.42
WAAM is applied to high-carbon steel. It takes about
12 min to form a cladding layer with a thickness of 20
mm and a length of 15 cm, which enables rapid additive
manufacturing. As shown in Figure 2, there are signi-
ficant differences between the microstructures of the
deposition layer, transition layer and substrate. During a
WAAM process, the transition zone is subjected to the
arc heat for several times and it is seriously affected by
it, which results in a strong plastic deformation occurring
in the fiber zone of the interface. As the height of the
deposition layer gradually increases during the WAAM
process, the heat dissipation and heat accumulation
change.
17,18
The heat-dissipation speed of the deposition
layer slows down along the substrate and the temperature
gradient gradually decreases along the vertical direction.
The microstructure at the bottom of the deposition layer
changes from martensite to tempered martensite, and the
grain size is slightly larger than that of the substrate.
As shown in Figure 3, as the temperature gradient
decreases, the grains grow coarse and the hardness is
decreased. The hardness usually decreases as the grain
size is increased. The hardness at the top of the depo-
sition layer is the highest and close to that of the
substrate. The microstructure evolution of the transition
layer inevitably influences the tensile properties of the
WAAM sample. The stress concentration and fracture
appear in the transition layer, and the bonding between
deposition layers is good. During a tensile test, a crack
initiated at the transition layer is continuously expanded
by the stress, resulting in a deteriorative elongation.
19,20
The research on the WAAM of high-carbon steel is still
new. For this reason, it is necessary to modify the test
procedure, including the preheating of the substrate
before the test and annealing after WAAM to reduce the
residual stress and improve the mechanical properties.
4 CONCLUSIONS
In this paper, the WAAM process was successfully
conducted on a high-carbon chromium bearing steel with
an ER55-Ni welding wire and GCr18Mo substrate. The
microstructure, mechanical properties and wear behavior
of the WAAM sample were investigated. The main
conclusions are as follows:
1) The microstructure of the cross-section of the
WAAM sample is divided into three parts, i.e., the
deposition layer, transition layer and substrate. The
microstructure of the deposition layer mainly consists
of needle-like tempered martensite and cementite,
with a small quantity of ferrite. The transition zone is
composed of coarse bainite and ferrite.
2) For the deposition layer of the WAAM sample, the
hardness gradually decreases from the top to the root,
and the hardness of the transition layer is close to 350
HV. The WAAM sample exhibits higher YS and UTS
but lower EL than the substrate sample.
3) The maximum depths of the wear scars in the
WAAM sample and substrate sample are close to
each other. The wear of the WAAM sample is more
uniform, but its cross-sectional area of the wear scar
is larger than that of the substrate sample. The wear
resistance of the WAAM sample is lower than that of
the substrate sample.
Acknowledgment
This research was funded by the National Natural
Science Foundation of China (No. 51275222), Major
Project of the Natural Science Foundation from the
Postgraduate Research & Practice Innovation Program of
the Jiangsu Province (No. SJCX18_1065).
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