W.-K. ZOU et al.: CORROSION BEHAVIOR OF HRB 400 REINFORCING STEEL WELDING JOINT ...
329–338
CORROSION BEHAVIOR OF HRB 400 REINFORCING STEEL
WELDING JOINT IN SIMULATED CONCERT ENVIRONMENT
BASED ON SVET
KOROZIJSKO OBNA[ANJE ZVARNEGA SPOJA IZ OJA^ANEGA
JEKLA VRSTE HRB 400 V SIMULIRANEM OKOLJU IZ BETONA
TEMELJE^EM NA TEHNOLOGIJI SVET
WenKai Zou
1
, Chuanbo Zheng
1*
, Han Ma
2
, JiaQi He
1
, XiaoBing Li
1
,
JiMing Zhang
2
, DianChun Ju
1
, ChaoYang Zhou
1
,Guo Yi
1
1
School of Metallurgical and Material Engineering, Jiangsu University of Science and Technology, Zhangjiagang, 215600, Jiangsu, CHINA
2
Jiangsu Shagang Group Co., Ltd. Shagang Research Institute, Zhangjiagang257343, Jiangsu, China
Prejem rokopisa – received: 2023-12-07; sprejem za objavo – accepted for publication: 2024-04-08
doi:10.17222/mit.2024.1069
Based on SVET technology, the corrosion tendency of HRB400 steel welded joint and its base metal in simulated concrete envi-
ronment and the influence of corrosion products were studied in this paper. The results show that the microstructure of the weld
metal and base metal are ferrite+pearlite, and the microstructure of the heat affected zone is incompletely transformed
bainite+ferrite+pearlite. Since the region produces smaller grains and more grain boundaries after welding, it becomes the most
prone area for corrosion of welded joints. The addition of Cl
–
inhibited the passivation of HRB400 steel welded joint in the sim-
ulated concrete pore fluid. Through the analysis of Nyquist curve and polarization curve, it was found that under high chloride
ion concentration, the base metal is more sensitive to chloride ions compared to welded joints.With the increase of Cl
–
concen-
tration, the current density in the welded joint area gradually increased, but after reaching the chloride concentration of 0.5
mol/L, the current density tended to be flat. The occurrence of this phenomenon confirms the above conclusion. Further
more,through SVET testing of the filler metal, it can be found that the filler metal has good adaptability to the HRB400 welding
joint, forming a welding joint with better performance.
Keywords: corrosion of reinforced concrete, SVET, welded joints for reinforcing steel
Na osnovi tehnike vrsti~ne vibrirajo~e elektrode(SVET; angl.: Scanning Vibration Electrode Technique) so avtorji tega ~lanka
simulirali oziroma ugotavljali nagnjenost zvarnega spoja iz jekla vrste HRB400 h koroziji in njegove osnovne kovine v
simuliranem okolju iz betona. V tem ~lanku avtorji opisujejo vpliv nastalih korozijskih produktov. Rezultati preiskave ka`ejo,
da imata kovina za varjenje in osnovni materialferitno-perlitno mikrostrukturo in, da ima toplotno vplivana cona (HAZ; angl.:
heat affected zone) nepopolnoma transformirano bainitno-feritno-perlitno mikrostrukturo. Ker je po varjenju podro~je zvara bolj
drobno zrnato z ve~ kristalnih mej, je jasno da jele-to tudi bolj nagnjeno h koroziji. Dodatek klorovih ionov (Cl
–
) ovira oziroma
ustavi pasivacijo zvara iz jekla HRB400 v simuliranem okolju iz raztopine betona. Z analizo Nyquistove in polarizacijske
krivulje so ugotovili, da visoka koncentracija kloridnih ionov bolj vpliva na osnovno kovino (izbrano jeklo) kot na varjeni spoj
(zvar). Z nara{~anjem koncentracijeCl
-
ionov, gostota elektri~nega toka v zvaru postopoma nara{~a, toda nad koncentracijo
kloridnih ionov 0,5 mol/L ostaja le-ta konstantna. Pojav tega fenomena potrjujejo zgoraj navedeni zaklju~ki. Nadalje so avtorji s
pomo~jo tehnologije SVET testirali material za varjenje in ugotovili, da se dobro ujema z zvarom iz jekla HRB400 in pri tem
tvori zvarni spoj z bolj{imi lastnostmi.
Klju~ne besede: korozija oja~anega betona, tehnika vrsti~ne vibrirajo~e elektrode, zvarni spoji za oja~ano jeklo
1 INTRODUCTION
Reinforced concrete is currently widely used in vari-
ous construction fields around the world.
1
Generally, Re-
inforced concrete has high durability and can withstand
different harsh working environments.
2
The high-alkalin-
ity concrete pore liquid will provide strong protection for
the rebars, keep the rebars in a passivated state, and ef-
fectively avoid corrosion of the rebars.
3
However, in the
actual construction process, factors such as improper de-
sign, lax construction, and the intrusion of corrosive ions
in the environment often accelerate the corrosion of
rebars,
4
causing significant loss of steel bar sections,
which in turn leads to the destruction of reinforced con-
crete structures. As the most important form of damage
to reinforced concrete structures,
6
the various direct and
indirect safety and economic losses caused by steel cor-
rosion cannot be ignored.
7
According to a special re-
search conducted by the Committee on Transportation
Research of the United States National Research Coun-
cil,
8
the annual economic damages incurred by concrete
bridges in the United States due to the utilization of
de-icing salt range from $0.35 billion to $1 billion.
9
It
can be seen that studying the corrosion behavior of
rebars in concrete is of great significance to the construc-
tion field.
The scanning vibration electrode technique (SVET)
used in this article is an electrochemical testing method
Materiali in tehnologije / Materials and technology 58 (2024) 3, 329–338 329
UDK 620.193.2:669.1:621.791 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(3)329(2024)
*Corresponding author's e-mail:
zhengchuanbo@just.edu.cn (Chuanbo Zheng)

that has several significant advantages and innovations
compared to traditional electrochemical techniques:
High sensitivity and spatial resolution: SVET can
achieve real-time monitoring of electrochemical reac-
tions at the microscopic scale, with spatial resolution
reaching sub micron level. According to literature re-
view,
10
the spatial resolution of general electrochemical
testing can only reach the millimeter level. This high
sensitivity and spatial resolution give SVET unique ad-
vantages in studying micro electrochemical processes,
corrosion behavior, and corrosion protection materials.
Non destructive: SVET technology does not require
destructive operations on the tested sample, as it only in-
volves scanning a tiny probe on the surface of the sam-
ple.
11
This makes SVET an ideal tool for studying mate-
rial corrosion, anti-corrosion coating performance, and
other aspects
Real time performance: SVET can monitor electro-
chemical processes in real time,
12
providing real-time in-
formation about reaction kinetics and process dynamics,
which is crucial for a deeper understanding of electro-
chemical reaction mechanisms.
Multifunctionality: SVET technology can be com-
bined with other technologies,
13
such as scanning elec-
tron microscopy (SEM), to achieve multi angle and
multi-scale characterization of electrochemical pro-
cesses, providing the possibility for deeper research.
The innovation of SVET technology mainly lies in its
application to vibration probes. Traditional electrochemi-
cal testing methods often use static probes,
14–17
while
SVET utilizes the characteristics of vibration probes to
achieve high sensitivity electrochemical testing through
the electrochemical interaction between the vibration
probe and the electrolyte solution.
18
In addition, the de-
velopment of SVET also benefits from the advancement
of micro nano technology, making the preparation and
operation of SVET systems more convenient and accu-
rate.
19
At present, the general corrosion tendency of
HRB400 reinforced concrete has been clarified, but there
is little research on the corrosion behavior of its welded
joints in concrete systems, and there is little research us-
ing SVET methods. Therefore, this study aims to study
the corrosion tendency and reasons of HRB400 steel
welded joints in concrete systems using SVET method,
in order to provide further process optimization ideas for
construction engineering and materials fields, and to pro-
mote the further development of reinforced concrete
anti-corrosion engineering.
2 EXPERIMENTAL PART
2.1 Preparation of the welded joint
The welding materials utilized comprise HRB400
threaded steel and MG-51T low-carbon solid welding
wire, with their compositions as illustrated in Table 1.
The welding experiments were conducted using a
Metal Inert Gas (MIG) composite welding method, em-
ploying a flat butt joint configuration.
20
The welding
wire used was a low-carbon solid welding wire, and a
0.5 mm gap was maintained during assembly to ensure
the alignment of the two plates as closely as possible.
Throughout the entire welding process, both the front
and back sides of the weld were shielded with pure Ar
gas. The gas flow rate at the front was set at 30 L/min,
while at the back, it was 5 L/min. The welding parame-
ters were as follows: welding current ranging from
130–150 A, welding voltage from 23–25 V, and welding
speed at 0.667 cm/s.
2.2 Corrosion system simulation
This paper uses the method of simulating concrete
pore fluid to study the corrosion process of HRB400 re-
inforcement welded joints and the effect of adding differ-
ent concentrations of NaCl on joint corrosion. Take the
saturated Ca(OH)
2
supernatant with a pH value of 12.5
as the simulated concrete pore liquid, and add NaCl to
obtain a chlorine-containing salt simulated concrete pore
liquid.
Following this, Cut out the parts of the HRB400 rein-
forcement welded joint that need to be tested and encap-
sulate them with denture-based resin; connect copper
wires behind them. After encapsulation, polish the test
surface with 240#, 400#, 600#, 800#, 1000#, 1500# and
2000# sandpaper in sequence until the surface is bright.
After polishing, use alcohol to remove surface stains,
rinse with distilled water, and blow dry. use. In the ex-
periment, P.O 42.5 ordinary Portland cement and lime-
stone mineral powder were used as composite cement-
itious materials, and carbon nanotubes and PAN-based
carbon fibers were used as conductive fillers. The com-
position and proportion of conductive concrete are
shown in Table 2. (Conductive fillers will only play a
role in electrochemical testing.) The working surface of
the specimen was then evenly covered with a layer of
concrete with a thickness of 0.5 cm. Conduct electro-
chemical tests after one day of curing. The encapsulated
samples were placed in a saturated Ca(OH)
2
solution
with a concentration of 0.5 mol/L NaCl for one day and
then electrochemical tests were performed,
20
The work-
ing electrode is shown in Figure 1.
W.-K. ZOU et al.: CORROSION BEHAVIOR OF HRB 400 REINFORCING STEEL WELDING JOINT ...
330 Materiali in tehnologije / Materials and technology 58 (2024) 3, 329–338
Table 1: Main chemical composition of HRB400 and welding wire
Materials C Si Mn P S Protective gas
HRB400 0.2302 0.4351 1.4324 0.0135 0.0177
Welding wire 0.10 0.64 1.26 0.011 0.012 80%Ar-20%CO2

2.3 Electrochemical testing
The electrochemical workstation utilized for the mac-
roscopic electrochemical testing was the Donghua elec-
trochemical workstation. For macroscopic electrochemi-
cal measurements, a corrosion cell with three electrodes
was utilized. The working electrode was the reinforce-
ment welded joint, the counter electrode was a platinum
sheet electrode, and the reference electrode was a mer-
cury oxide electrode.Following the attainment of a stable
open-circuit potential (OCP), a series of electrochemical
impedance spectroscopy (EIS) and potentiodynamic po-
larization curve experiments were conducted in a se-
quential manner. In the context of Electrochemical Im-
pedance Spectroscopy (EIS), the frequency range
utilized for impedance testing spanned from 10
5
Hz to 10
mHz. This range was subjected to a sine wave excitation
signal with an amplitude of 10 mV. During the process of
conducting polarization curve measurements, the begin-
ning potential relative to the open circuit potential (OCP)
was established at –0.8 V (HgO), whereas the final po-
tential relative to the OCP was set at 1.2 V (HgO). EIS
data obtained by equivalent circuit fitting based on
ZSimpWin software. Microelectrochemical tests were
performed using a Princeton VersaSCAN microscopy
scanning electrochemical workstation (AMETEK Inc.,
California, USA). The surface vibrational spectroscopy
and electrochemical technique (SVET) method is used to
quantify the difference in potential within the solution,
thereby indicating the local current present on the sample
surface, and reflecting the inhomogeneity of the electro-
chemical activity on the sample surface through three-di-
mensional images. To ensure accuracy, multiple mea-
surements were taken for each test, repeated at least
three times(include SVET tests). The presented results
are representative of the selected ones.In addition, the
test temperature is always maintained at 20 °C.
3 RESULTS
3.1 Microstructure analysis
Microstructural analysis explains the corrosion sus-
ceptibility of the welded joint. This is attributed to local
differences in the microstructure, such as grain size and
elemental composition, which can result in varying cor-
rosion performance. Figure 2 depicts microstructural im-
ages of the reinforcement welded joint, where the weld
metal and base material is primarily composed of ferrite
and pearlite, while the heat-affected zone comprises par-
tially untransformed bainite, quasi-polygonal ferrite,
acicular ferrite, and pearlite. The microstructure of the
heat-affected zone indicates that its surface is more ac-
tive, with smaller grains and more grain boundaries,both
of which make it more susceptible to corrosion.
21–24
Moreover, when taking into account the phase composi-
tion, The coexistence of ferrite and bainite phases in the
heat affected zone is expected to lead to more corrosion
than in other parts of the welded joint (ferrite + pearlite).
W.-K. ZOU et al.: CORROSION BEHAVIOR OF HRB 400 REINFORCING STEEL WELDING JOINT ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 329–338 331
Figure 1: Schematic diagram of working electrode
Figure 2: Microstructural Morphology of the Welded Joint
Table 2: Conductive concrete ratio
Raw material consumption (kg/m
3
) Carbon nanotubes
/%
PAN-based carbon
fiber /%
Water reducing
agent /%
Defoamer
/% Cement Coal ash Mineral powder Water
280 33.6 50.4 140 0.2 0.3 1 0.1

3.2 Local corrosion behavior in different parts of joint
Figure 3 shows the polarization curves of welded
joints, and base metal under simulated concrete pore so-
lution of 0.5 mol/L NaCl. The graphic illustrates that
both the welded joint and the base material undergo three
separate zones, namely the activation region, the
passivation region, and the overpassivation region. In the
activation zone, there is a rapid occurrence of the devel-
opment of surface passivation film products, and the re-
actions on the metal surface proceed at a high rate.Once
the passivation region is reached, corrosion becomes sta-
ble within this specific range of potential, resulting in
smaller fluctuations in current values. The main factor
contributing to this phenomenon is principally associated
with the significantly alkaline properties of the simulated
concrete pore solution, which effectively stabilizes the
existence of calcium aluminate chloride. The presence of
corrosive anions, such as chloride ions (Cl
–
), is effec-
tively impeded by the passivation film at defects in the
welded joint.
25
In the region of overpassivation, when the
potential reaches a specific threshold, the passivation
film on the metal surface is compromised, leading to pit-
ting corrosion and a substantial escalation in the corro-
sion rate.
26
The passivation range of the welded joint has
a noticeably smaller scope in comparison to that of the
base material. Indicating that it is difficult to form a
complete passivation film on welded joints under simu-
lated pore fluid conditions.
27
In addition, it is observed
that the self-corrosion potential of the welded joint is
comparatively lower, suggesting a significantly dimin-
ished level of corrosion resistance in comparison to the
base material.
27
Detailed corrosion parameters are shown
in Table 3. According to previous research,
28
the partial
microstructure contained in welded joint is more likely
to become the area where corrosion begins. In order to
visually understand the corrosion resistance performance
of each area of the welded joint, the joint is divided into
weld metal (i.e. fusion zone), base metal, and heat af-
fected zone for SVET testing.
Table 3 Corrosion parameters of welded joints and base material
Specimens i
corr
/Acm
–2
E
corr
/V
Joint 7.02 × 10
–5
–0.869
BM 1.45 × 10
–5
–0.795
The results of the SVET (Surface Vibrational Spec-
troscopy and Electrochemical Technology) test for dif-
ferent locations of the welded joint under 0.5 mol/L sim-
W.-K. ZOU et al.: CORROSION BEHAVIOR OF HRB 400 REINFORCING STEEL WELDING JOINT ...
332 Materiali in tehnologije / Materials and technology 58 (2024) 3, 329–338
Figure 3: Polarization curves of joint and base metal under 0.5 mol/L
NaCl saturated
Figure 4: SVET images of welded joints immersed in 0.5 mol/L NaCl
simulated concrete pore solution for 24 h

ulated concrete pore liquid are depicted in Figure 4. The
examination utilizes a blend of three-dimensional repre-
sentations and two-dimensional planar images for the
purpose of visualization. The three-dimensional repre-
sentations provide a comprehensive depiction of the vari-
ations in current density over the surface of sample. The
use of Scanning Vibrating Electrode Technique (SVET)
enables the deduction of corrosion activity at regions
where defects are present by continuous scanning. The
fluctuations observed in the data are indicative of micro
anode and microcathode currents, with the peaks repre-
senting the former and the troughs representing the lat-
ter.
29
The chosen micro-area three-dimensional map dis-
plays a prominent anode peak, indicating that the current
fluctuations around the anode peak are large. These areas
are likely to be the areas where corrosion occurs around
the sample,
30
dissolution occurs earlier in the corrosive
solution, destroying the passivation film on the joint sur-
face, causing the substrate to be exposed in the solution,
becoming the anodic phase and starting to activate corro-
sion. It can be found that the fluctuations in the three-di-
mensional diagram of the weld metal are relatively gen-
tle, and the difference in current density values is small,
indicating that the anode current changes slowly in this
area, the probability of surrounding corrosion is low, and
the sample surface still has a good layer of protection in
the solution to inhibit the occurrence of corrosion. Si-
multaneously, in the three-dimensional image of the
heat-affected zone, it can be clearly seen that the anode
peak is lower away from the weld area, and the anode
peak gradually becomes larger after approaching the
weld area. The complete three-dimensional image exhib-
its a fluctuating and irregular pattern, whereas the anode
current displays a significant disparity. This is because
the local area near the fusion line has higher thermal
stress and is more prone to corrosion.
31
Upon comparing
the SVET images of the three distinct portions, it be-
comes apparent that the weld metal region exhibits a
lower susceptibility to corrosion in comparison to both
the base material and the heat-affected zone. In contrast,
it can be shown that the heat-affected zone exhibits the
highest susceptibility to corrosion start, a finding that is
consistent with the outcomes derived from the polariza-
tion tests. In order to accurately evaluate the corrosion
behavior of each part of the welded joint using SVET
data,
32
the data in Table 4 are calculated using the fol-
lowing formulas:
[]
Ij x yx y
z
Y X
c
dd =<
∫ ∫
(,)
max max
0
0 0
(1)
[]
Ij x yx y
z
Y X
a
dd =>
∫ ∫
(,)
max max
0
0 0
(2)
I
II
=
+
ac
2
(3)
Table 4: SVET data in 0.5 mol/L NaCl saturated Ca (OH)
2
solution in
each region of the welded joint
Specimens J /(mA·cm
–2
)
HAZ 1.25
Weld metal 0.442
BM 0.881
3.3 Corrosion products
Before studying the micro effects of chlorides on
welded joints, it is best to first understand what corrosion
products are present in the welded joints in this concrete
system, in order to conduct a reasonable analysis of sub-
sequent experimental results. Therefore, XRD experi-
ments were conducted, and the results are as follows:
The X-ray diffraction (XRD) spectra of the welded joint
following a 10-day corrosion period in a 0.5 mol/L so-
dium chloride (NaCl) Simulated concrete pore fluid is
depicted in Figure 5. Figure 5 illustrates that the constit-
uents present on the surface of the welded joint predomi-
nantly consist of CaCO
3
,F e
2
O
3
, and CaCl
2
.F e
2
O
3
is a
corrosion product in this system.
33
The presence of Fe
2
O
3
suggests that corrosion has taken place on the surface of
the welded joint.
3.4 Impact of chloride ion concentration on local cor-
rosion resistance
EIS experiment and Tafel polarization curve are the
most common experiments reflecting corrosion tendency.
Before the subsequent test, the EIS test and Tafel polar-
ization can be used for macro and local comparison. The
EIS fitting data are shown in Tables 5 and 6.Inthe
equivalent circuit, R
s
is the solution resistance, R
f
is the
passivation film resistance, Q
1
is the common phase an-
gle element, which includes the passivation film capaci-
tance C
f
and the dispersion coefficient n
1
, R
dl
is the
charge transfer resistance, Q
2
is the common phase angle
W.-K. ZOU et al.: CORROSION BEHAVIOR OF HRB 400 REINFORCING STEEL WELDING JOINT ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 329–338 333
Figure 5: XRD Spectrum of the Welded Joint Surface After 10 Days
of Corrosion

element, These include the electric double layer capaci-
tance C
dl
and the dispersion coefficient n
2
. The value of
the diffusion coefficient n is usually between 0 and 1.
34
Research shows that the value of n is related to the uni-
formity and compactness of the surface passivation
film.
35
The smaller the value of n, the more grain bound-
aries, defects, and impurities exist on the surface of the
material. The worse the uniformity and density of the
passivation film.
36
In the circuit, Q
1
simulates the com-
plete area of the passivation film, and Q
2
simulates the
double electric layer at the rupture point of the
passivation film or the defect potential.
37
From Figure 6,
it can be seen that as the concentration of chloride ions
increases, the performance of the passive film formed by
the joint gradually decreases. However, the performance
of the passive film formed by the joint at 0.5 mol/L is
higher than that at 0.3 mol/L. According to the Nyquist
curve of the base material in Figure 7, the passivation
film performance of the base material rapidly decreases
with the increase of chloride ion concentration. When
reaching a high concentration, the capacitance arc of the
base material curve is already close to that of the joint
curve. This indicates that at high chloride ion concentra-
tions, the performance of the passivation film formed on
the surface of the base material and the joint is relatively
close.
According to the polarization curves shown in Fig-
ures 8 and 9, it can be observed that at low chloride ion
concentrations, corrosion of the joint and substrate mate-
rials does not occur significantly, and there is a phenom-
enon of secondary passivation in both the base material
and the joint,and it can be observed that there is a notice-
able decline in the corrosion resistance of the welded
joint as the concentration of Cl
–
increases. The observed
phenomenon can be attributed to the build-up of chloride
ions (Cl
–
) at the sites of defects during the passivation
process of the metal.
25
This buildup leads to the forma-
tion of localized activation spots and consequently accel-
erates the pace at which the material dissolves.
28
An in-
crease in the concentration of chloride ions (Cl
–
) results
in a corresponding increase in their adsorption onto the
substrate’s surface.
38
Consequently, this heightened ad-
sorption contributes to the exacerbation of corrosion.
39
W.-K. ZOU et al.: CORROSION BEHAVIOR OF HRB 400 REINFORCING STEEL WELDING JOINT ...
334 Materiali in tehnologije / Materials and technology 58 (2024) 3, 329–338
Figure 7: Impedance Spectrum of Base Material in Simulated Con-
crete Pore Solutions with Different Chloride Ion Concentrations
Figure 6: Impedance Spectrum of Welded Joints in Simulated Con-
crete Pore Solutions with Various Chloride Ion Concentrations
Table 5: EIS fitting parameters for corrosion of welded joints in simulated concrete pore fluids with different chloride ion concentrations
Cl
–
concentration
/mol·L
–1
R
s
/ ·cm
2
R
f
/ cm
2
Q
f
/ –1
·cm
–2
·s
–1
n
f
R
ct
/ cm
2
Q
dl
/ –1
·cm
–2
·s
–1
n
dl
0 3.04 2.18 × 10
4
1.34 × 10
–5
0.86 1.77 × 10
4
3.84 × 10
–5
0.68
0.1 3.12 2.47 × 10
4
5.82 × 10
–5
0.88 1.59 × 10
4
2.26 × 10
–4
0.71
0.3 4.76 4.98 × 10
4
8.13 × 10
–5
0.93 1.89 × 10
4
4.17 × 10
–4
0.79
0.5 3.98 4.16 × 10
4
6.82 × 10
–5
0.91 1.72 × 10
4
3.43 × 10
–4
0.74
Table 6: EIS fitting parameters of base metal corrosion in simulated concrete pore fluids with different chloride ion concentrations
Cl
–
concentration
/mol·L
–1
R
s/ ·cm
2
R
f
/ ·cm
2
Qf / –1
·cm
–2
·s
–1
nf R
ct
/ ·cm
2
Qdl / –1
·cm
–2
·s
–1
ndl
0 3.01 1.82 × 10
4
1.05 × 10
–5
0.85 1.82 × 10
4
4.01 × 10
–5
0.66
0.1 3.09 2.15 × 10
4
5.74 × 10
–5
0.88 1.56 × 10
4
2.19 × 10
–4
0.57
0.3 3.55 3.68 × 10
4
6.79 × 10
–5
0.78 1.66 × 10
4
3.15 × 10
–4
0.67
0.5 3.97 4.17 × 10
4
7.83 × 10
–5
0.91 1.84 × 10
4
3.96 × 10
–4
0.77

According to the values in Table 7, in a solution contain-
ing NaCl at an equivalent concentration, it is seen that
the self-corrosion current density of the welded joint sur-
passes that of the base material. This difference means
that the base material exhibits greater corrosion resis-
tance. By comparing the absolute difference in i
corr
be-
tween the welded joint and the base metal at high con-
centrations (0.3–0.5 mol/L), it can be found that the
absolute difference in i
corr
between the welded joint and
the base metal is 1.75 × 10
–5
, and the absolute difference
in i
corr
between the base metal and the base metal is
1.771 × 10
–5
. It can be seen that the sensitivity of the
base metal to chloride ion concentration is higher than
that of the welded joint at high concentrations. It is
worth noting that when the chloride ion concentration
reaches 0.5 mol/L, the self corrosion current density of
welded joints decreases compared with 0.3 mol/L. A
similar situation occurred in the EIS test,which is not
consistent with the general rule of previous stud-
ies.
34
Although a large number of repeated tests have
been carried out, the possibility of contingency cannot be
ruled out. Therefore, Further detailed testing was con-
ducted on the corrosion trend in local areas of welded
joints using SVET technology.
Table 7: Corrosion parameters of base metal joints under different
chloride ion concentrations
Sample
Cl
–
concentra-
tion/mol·L
–1
i
corr
/A·cm
2
E
corr
/V
BM
0 4.06 × 10
–6
–0.784
0.1 4.23 × 10
–6
–0.796
0.3 4.79 × 10
–6
–0.813
0.5 2.25 × 10
–5
–0.824
Joint
0 3.56 × 10
–6
–0.506
0.1 1.08 × 10
–5
–0.817
0.3 4.17 × 10
–5
–0.884
0.5 2.42 × 10
–5
–0.828
Figure 10 shows the evolution of current density dis-
tribution of welded joints after soaking in simulated con-
crete pore solution of (0, 0.1, 0.3 and 0.5) mol/L NaCl
for 1 h respectively. It can be found that in four different
solutions, at the beginning of the corrosion stage,the cur-
rent density at the microlocation was not unified and
showed peaks and valleys, indicating that anodic and
cathodic localized corrosion occurred. When the concen-
tration of chloride ion is 0 mol/L, the local current is
generally flat without too much fluctuation, This is be-
cause under normal alkaline environment, the passivation
film on the surface of welded joints has high integrity,
and pitting corrosion will hardly occur.
40
With the chlo-
ride ion concentration continuously increasing to 0.3
mol/L, the average current density of each region of the
welded joint generally increased, and the anode peak ap-
peared in some regions.
41
When the current increases and
the current position increases, it can be confirmed that
pitting corrosion has occurred on the surface of the
welded joint.
19
And the pitting sites were more evenly
distributed and numerous,
42
with a large cathode and a
small anode.
43
This is related to the grain size changes
and possible residual stresses in the welded joints men-
tioned earlier.During the corrosion process, residual
stress easily causes chloride ions to migrate along the
stress gradient, making it easy for pitting corrosion to oc-
cur in the welded joint. However, when the concentration
of chloride ion reaches 0.5 mol/L, the current density in
the micro zone of the welded joint has a downward
trend.
44
According to the XRD test results, it is not diffi-
cult to infer that there are corrosion products in the joint
after 1 h immersion, namely:
Fe
2+
+ 2OH
–
 Fe(OH)
2
4Fe(OH)
2
+O
2
+2H
2
O  4Fe(OH)
3
2Fe(OH)
3
 Fe
2
O
3
+2H
2
O
At the same time, high concentration of OH
–
can ef-
fectively inhibit the accumulation of Cl
–
in the passive
film defects,
36
therefore, when the concentration rises to
0.5 mol/L, the current density in the micro region will
W.-K. ZOU et al.: CORROSION BEHAVIOR OF HRB 400 REINFORCING STEEL WELDING JOINT ...
Materiali in tehnologije / Materials and technology 58 (2024) 3, 329–338 335
Figure 9: Polarization curves of the welded joint in simulated con-
crete pore solutions with different chloride ion concentrations
Figure 8: Polarization curves of the base material in simulated con-
crete pore solutions with different chloride ion concentrations

tend to be flat.
45
This is also consistent with the polariza-
tion curve and EIS results.
4 DISCUSSION
Based on the research by Nedal,
3
it is not difficult to
find the general conclusion that as the concentration of
chloride ions invading the concrete system increases, the
corrosion rate of the entire reinforced concrete system
will increase. In this study, the results of the Nyquist
curve and polarization curve confirmed that the HRB400
steel bar welding joint will generate a better passivation
film than the base metal under high chloride ion concen-
tration. That is to say, at high chloride ion concentration
(0.5 mol/L), the HRB400 steel bar welding joint will
show better corrosion resistance. After further SVET
testing, this conclusion was also confirmed. Meanwhile,
through the comparison of SVET testing results, it was
found that the HRB400 steel bar welding joint made by
previous researchers showed higher anode current den-
sity in the fusion line area,
10
followed by HAZ. Accord-
ing to the SVET test results in this article, the anode cur-
rent density at the HAZ of the welded joint is much
higher than that in other areas, which means that the
filler weld metal used in this article has better phase with
the HRB400 steel reinforcement welded joint, making it
a higher quality welded joint in concrete environments.
5 CONCLUSIONS
(1) Observation results based on micro-appearance,in
HRB400 welded joints, The microstructure of the weld
metal and base metal is a ferrite+pearlite,and the struc-
ture of the heat-influencing area is bainite that are not
fully transformed+ferrite+pearlite. Combined with the
results of SVET test, it can be confirmed that this area in
the welded joint is most prone to corrosion, because
smaller grains and more grain boundaries are formed,the
probability of defects occurring is the highest.
(2) According to the results of the SVET test, the an-
ode corrosion current density in the heat affected zone of
HRB400 steel welded joint is the highest, reaching
1.25 mA·cm
–2
. The closer to the HAZ, the faster the an-
ode current changes, and the more prone to corrosion.
Based on other electrochemical test fitting data results,
compared to welded joints, the base metal has a higher
sensitivity to chloride ion viscosity at high concentra-
tions, and the performance of the passivation film
formed between the base metal and the joint tends to be
consistent at high concentrations. Moreover, based on the
W.-K. ZOU et al.: CORROSION BEHAVIOR OF HRB 400 REINFORCING STEEL WELDING JOINT ...
336 Materiali in tehnologije / Materials and technology 58 (2024) 3, 329–338
Figure 10: Current density distribution of welded joints after immersion for 24 h under different chloride ion concentrations: a) 0 mol/L, b) 0.1
mol/L, c) 0.3 mol/L, d) 0.5 mol/L

SVET test results of the weld metal, the corrosion resis-
tance of the filled area is relatively excellent, and it has
good compatibility with the joint.
(3) SVET and XRD results show that when the chlo-
ride ion concentration increases, the local current density
distribution on the welded joint surface changes from
uniform to uneven, but when it reaches 0.5 mol/L, the lo-
cal current density tends to be flat again. On the basis of
analyzing the formation process of corrosion products in
this experiment, considering that the OH
–
and Cl
–
in the
corrosion products are adsorbed and competed on the
surface of the welded joint, which makes the welded
joint more resistant to Cl
–
with a higher concentration
(0.5 mol/L).
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