https://doi.org/10.3311/PPme.

19568
Creative Commons Attribution b |1
Periodica Polytechnica Mechanical Engineering

The Effect of Welding Parameters on the Corrosion Resistance

of Austenitic Stainless Steel

Dávid Miklós Kemény1*, Dorina Kovács1

1
Department of Materials Science and Engineering, Faculty of Mechanical Engineering, Budapest University of Technology and
Economics, Műegyetem rakpart 3., 1111 Budapest, Hungary
*
Corresponding author, e-mail: kemeny.david@gpk.bme.hu

Received: 19 November 2021, Accepted: 17 February 2021, Published online: 23 February 2022

Abstract
Electricity produced in power plants is essential in our everyday life. In general, the energy transfer takes place after processing the
energy source in boilers or steam generators. Steam is generated through this process, that operates the turbines and they generate
electricity through the generators. As such equipment operates in a high pressure, corrosive and high temperature environment, these
circumstances may damage the tubes in the heat exchangers. Our research examines the potential of corrosion of heat exchanger
tubes after welding. The typical corrosion process is pitting. The corrosion resistance of stainless steel depends on a protective,
passive film formed on the surface of the steel exposed to the service environment. The use of fusion welding for fabrication leads
to local variations in the chemical composition inside the material, which may significantly alter the stability of the passive layer and
hence the corrosion behavior. The impact of welding parameters (shielding gas, amperage) was examined on corrosion resistance
of X6CrNiTi18-10 austenitic stainless steel. The corrosion test was performed according to ASTM G48 standard. The weight loss was
measured in Fe(III)-chloride solution by the first corrosion test. The results showed that the corrosion resistance of stainless steel
was better at 50 A and 10 l/min welding parameters. During the second test, a potentiodynamic corrosion test was made, and the
potentiodynamic curve was measured in 9% saline solution. In this solution, the stainless steel had a better corrosion property because
it was measured in a less aggressive medium.
Keywords
X6CrNiTi18-10, welding, corrosion, ASTM G48, shielding gas, potentiodynamic curve

1 Introduction
There are many areas of application for stainless steel. It is the surface than inside of the material. The alloy needs to
preferred in the food and pharmaceutical industries but is be homogeneous and contains appropriate Cr concentra-
also used in power plants [1]. The power plant use comes tion to avoid rust formation. The stainless steel has high
to the fore in this article. There are many types of power resistance to pitting, crevice and chloride stress corrosion
plants to generate electricity, for example, wind turbines, cracking because of the passive surface film [8–10]. This
hydroelectric, thermal and nuclear power plants. The ther- passive film must be very thin, about 2–3 nm [3, 11].
mal and nuclear power plants use fossil fuels (which can The heat exchangers could be damaged due to the high
be natural gas or uranium) [2]. From fossil fuel, energy pressure and temperature during operation. It is possi-
is retrieved to generate steam in the generator and boil- ble to correct the failure by the repair welding of the heat
ers. The saturated steam operates the turbines, and the tur- exchanger tubes. It is important to repair the affected area
bines operate the generator to produce electricity. to avoid the release of the heat transfer medium into the
The energy transfer goes by the corrosion resistant heat environment. This solution is possible at thermal power
exchanger tubes. The condition for corrosion resistance plants, but due to the high radiation level, it cannot be
is a stable, contiguous, passive layer on the steel surface. applied in nuclear power plants. The repair through weld-
This is met when Cr ≥ 12% and C ≤ 1.2% [3–6]. This resis- ing is more favorable, as buying a new exchanger because
tance is provided by the chromium-oxide ( Cr2O3 ) [7] on it is more expensive. The passive layer may be damaged
the surface of the steel if the amount of Cr is higher on during welding; thus, the corrosion resistance of some

Cite this article as: Kemény, D. M., Kovács, D. "The Effect of Welding Parameters on the Corrosion Resistance of Austenitic Stainless Steel", Periodica
Polytechnica Mechanical Engineering, 2022. https://doi.org/10.3311/PPme.19568
2|Kemény and Kovács
Period. Polytech. Mech. Eng.

parts of the weld seam may differ from the basic mate- Table 1 The identification of the samples and the varied welding
rial [12, 13]. Therefore, it is important to know the param- parameters

eters of the welding in order to produce a sufficient quality Sample Shield gas (l/min) Amperage (A)
weld seam with the highest corrosion resistance. 1 6 50

The aim of this research is to examine the effect of weld- 2 6 55

ing parameters on the X6CrNiTi18-10 austenitic stainless 3 6 60

steel weldability. Different shielding gas and amperage 4 10 50

5 10 55
were used during the welding to determine the optimum
6 10 60
parameters for the best corrosion property.

2 Materials and methods The macroscopic images were taken with Olympus
The tests were conducted on the X6CrNiTi18-10 SZX16 stereomicroscope. The optical microscope inspec-
(1.4541) austenitic stainless steel in the aspect of cor- tion was performed by using an Olympus PMG 3 micro-
rosion resistance. The typical chemical composition of scope. Kalling reagent was used to etch the surface to
X6CrNiTi18-10 stainless steel by weight percentage is: show the structure of the material. The ferrite content was
C ≤ 0.08%; Cr: 17–19%; Si ≤ 1%; Mn ≤ 2%; Ni: 9–12%; measured with Fisher FMP30 ferritscope.
P ≤ 0.045%; S ≤ 0.015%; Ti ≤ 0.7% [14]. The corrosion The first corrosion test was generated by following the
resistance steel pipe was used with 40 mm diameter and ASTM G48-11(2020)e1 standard [16]. The 6% Fe(III)-
2 mm wall thickness. The filler wire was 316. The welding chloride solution was used. The mass was measured with
equipment was Tungsten Inert Gas (TIG) and the shield APX – 200 type precision balance (max 200 g, measuring
gas was 100% Argon. The penetration depth is about accuracy: 0.1 mg) after the corrosion test.
5–6 mm using the TIG welding [15]. Different param- The second corrosion test was performed with Biologic
eters were used regarding the amperage and shield gas SAS type SP-150 potentiostat. The solution was 9% saline
quantity for instance by welding procedure. The amount solution. The EDS (energy dispersive X-ray spectrometry)
of shield gas was set to 6 or 10 l/min, and in the case of of Zeiss EVO MA10 scanning electron microscope was
each gas setting, the amperage was altered and set to 50, used to determine the atomic and weight percent of the
55 or 60 A. The other parameters of weld have not been corroded samples.
changed. The designation of the corresponding samples
(shown in Fig. 1) and the applied welding parameters are 3 Results and discussion
listed in Table 1. Sludge formation and slag on the welded Macrographs about the welded joint can be seen in Fig. 1.
samples can be seen and Kor-Fel Px picking paste was The discoloration in Fig. 1 is caused by Cr and Ni. As it
used to remove the discoloration. is discernible, the amount of Cr and Ni were higher in the
corrosion area (at the HAZ) than in the weld or base mate-
rial. The main components of stainless steel are Fe, Ni and
Cr, so the main parts of these elements originate from the
austenitic stainless steel [17].
The appearance of pitting after corrosion is clearly vis-
ible on the surface of samples in Fig. 2.
The ferrite content was determined in the welded joints
and its immediate vicinity with ferritscope after welding.
As it can be seen in Table 2, by using 10 l/min shield gas,
the ferrite content was less than at the other (lower) shield
gas quantity. The delta-ferrite can cause an increase in the
sensitivity of hot cracking [18]. It has to be noted that no
hot cracks were generated.
Table 2 shows the ferrite content of sample 4. This sam-
Fig. 1 The discolouration after weld on sample 2 ple showed the least weight loss (Table 3). Corrosion tests
 Kemény and Kovács
Period. Polytech. Mech. Eng.|3

The microstructure of X6CrNiTi18-10 austenitic steel

can be seen in Figs. 3–4. The austenitic particles can be
well distinguished, and the shaping lines are well observ-
able after etching the base material with Kalling reagent,
as shown in Fig. 3.
A typical cross-section of pitting corrosion in the base
material is seen in Fig. 4. It shows the pitting of austenitic
stainless steel X6CrNiTi18-10 resulting from insufficient
corrosion resistance in a very aggressive chlorinated envi-
ronment. The formation of pitting can be influenced by
various parameters such as environment, chemical com-
position and metallurgical condition [20].
Corrosion is one of the typical damage processes
regarding welded joints. The weight loss occurs in the
welded joint, the seam and the base material and in the
heat-effect zone (HAZ), which can be well observed in
Fig. 5. Pitting was formed next to the weld joint typically
in the HAZ (Fig. 4)

Fig. 2 The welded samples after corrosion test

Table 2 The ferrite content (in percentage) of the samples at the

welded joints
Ferrite content (Ferrite number)
Sample
Material HAZ Weld seam HAZ Material
1 0.77 3.1 3.2 1.6 0.47
2 0.46 1.3 3.6 2.8 0.42
3 0.26 2.6 3 2.7 0.37
4 0.3 1.9 2.3 2.8 0.34 Fig. 3 Microstructure of austenitic stainless steel with the shaping lines
5 0.29 2.1 3.1 2.7 0.27
6 0.43 1.4 2.2 1.6 0.34

Table 3 The samples masses in the beginning and after 24 hours, and
the corresponding weight losses
Mass (g) Weight loss ( g/year/cm3 )
Sample
0. hour 24. hour 24.hour
1 18.8983 18.5292 5.73
2 16.6738 16.3142 5.94
3 14.9801 14.6136 7.35
4 22.5622 22.1625 5.11
5 16.0077 15.6329 6.47
6 17.6556 17.2563 6.51

were performed on the welded samples corresponding

Fig. 4 Pitting in the basic material
to the ASTM G48 standard [19]. The measured data are
shown in Table 3.
4|Kemény and Kovács
Period. Polytech. Mech. Eng.

Fig. 5 Pitting in the HAZ next to the seam of the welded joint Fig. 7 Delta-ferrite in the HAZ

The pitting is growing into the material, making a deep

and windy hole under the surface, as shown in Fig. 6. That
makes the pitting corrosion so dangerous because under
the visual inspection cannot be seen all of the weight
decreases, making the structure less resistant against the
mechanical impacts. Ongoing investigations are needed to
explore the pitting localization because predicting the pit-
ting tendency is still complicated [21].
The HAZ and the delta-ferrite can be observed in Fig. 7
at higher magnification. Different welding parameters
can be the shielding gas, heat input, the number of weld
passes and the filler metal [22, 23]. Uneven cooling results
in areas with different chemical composition areas and
Fig. 8 Microstructure of austenitic stainless steel and the titanium nitride
weaker corrosion resistance.
It is important to note that large amounts of titanium The EDS measurement was performed in order to ascer-
can cause excessive stabilization, causing rust and iron tain the nature of the precipitation (TiN). An environment
oxide [24] on the surface of stainless austenitic steels. full of precipitation can be seen in Fig. 9. The EDS result of
The typical appearance of titanium nitride (TiN) is seen
in Fig. 8 [25].

Fig. 6 Pitting in the base material of sample 4 Fig. 9 SEM image of the precipitation (TiN) area
 Kemény and Kovács
Period. Polytech. Mech. Eng. |5

measured precipitation is the following in weight percent: The first was the ASTM G48 standard corrosion test, as it
Fe: 1.61%, Ti: 80.09%, N: 17.67%, Cr: 0.58%, Si: 0.06%. was described in the previous chapter, and the second was
the potential-difference measurement with Biologic SAS
3.1 Determination of weight loss and pitting numbers type SP-150 potentiostat. The examined welded joint was
The phenomenon of pitting is valued by loss of weight made with 50 A and 10 l/min shielding gas.
according to the standard. Unfortunately, the evaluation is Table 4 shows the weight loss due to corrosion. The cal-
not accurate because of the specifics of pitting. culated weight loss was 0.2 g/year/cm3.
Fig. 10 shows that 6 l/min gas caused higher weight loss General corrosion was observed on the entire surface
than the 10 l/min gas quantity (except for 55 A). The weight of the sample after the corrosion test. Pitting appeared on
loss was the least at 50 A for both 10 and 6 l/min shield the welded joint.
gas. It can be determined with the help of bar graphs that The aim was to determine the potentiodynamic curve
the weight loss increases with the growth of amperage. and calculate the corrosion rate with 24 hours experi-
The pitting numbers on the weld, HAZ, and base mate- ments. The sample was put into the 9% saline solution.
rial were measured after 24 hours corrosion test. The pit- In the beginning and at the end, the difference in the solu-
ting number as a function of current for 6 and 10 l/min of tion can be seen in Fig. 12.
shielding gas is shown in Fig. 11. The explanation of the discolored solution is the disso-
The pitting numbers were decreased with increasing lution of metal (Fe) into the liquid because of the potential
current, and the worst value was at 50 A, as can be seen difference. The following potentiodynamic curves were
in Fig. 11. obtained (Fig. 13) at the end of the measurement.
It was necessary to measure the weight and atomic
3.2 Corrosion rate percent to determine the corrosion rate. The sample sur-
The main purpose of this measurement was to com- face was equal by base material, HAZ and welded joint.
pare the corrosion resistance by two different methods. Consequently, the correct data can be obtained if the aver-
age atomic and weight percent of these three areas were
used. From these values, the equivalent weight and density
can be calculated. The results are shown in Table 5.
The corroded surface was 139.96 cm 2. After soft-
ware evaluation, the corrosion rate was determined,
0.045 mm/year in a 9% saline solution.

Table 4 The sample mass before and after corrosion

Before corrosion After corrosion
test (g) test (g)
X6CrNiTi18-10 21.9289 21.8520

Fig. 10 The weight loss according to the amperage and shield gas

Fig. 11 The pitting numbers according to the amperage and shield gas Fig. 12 The solution before a) and after b) corrosion test
6|Kemény and Kovács
Period. Polytech. Mech. Eng.

loss was associated with a low number of holes which

occurred by 50 A and 10 l/min shielding gas. Counting
the amount of pitting on corroded surfaces the least pit-
ting was measured at 60 A. It should be noted that the
least weight loss was at 50 A, but there was the most pit-
ting on the surface. This can be attributed to the nature of
pitting caused by 60 A, the number of pitting was less, but
it shows much deeper characteristics so that more weight
loss can occur.
It can be concluded that based on the ferrite content val-
ues, the optimal value is also 50 A amperage and 10 l/min
shielding gas.
Fig. 13 Potentiodynamic curve of austenitic steel welded joint The corrosion rate could be determined as 0.045 mm/year
Table 5 Calculated results of the sample of the austenitic stainless steel welded joint using a poten-
Sample Equivalent weight (g/eq) Density ( g/cm3 ) tiodynamic corrosion test. The amperage and the shield gas
Basic material 18.4424 7.7639 were optimal, which is based on previous measurements.
Heat affected zone 18.6114 9.9342 The weight loss was different by the two corrosion tests
Welded joint 9.6652 4.3365 because of the solution. The Fe(III)-chloride solution is an
Average 15.5734 7.3449 aggressive corrosion environment, and the weight loss of the
samples was about 5…7 g/year/cm3, and the saline was a less
4 Conclusions corrosive medium, and the weight loss was 0.2 g/year/cm3.
Pitting is one of the most dangerous corrosion types, which
a very corrosive environment can cause. Pitting sensitivity Acknowledgement
can be increased by welding, so choosing the right welding The research reported in this paper and carried out at BME
parameters is necessary. has been supported by the NRDI Fund (TKP2020 IES,
Investigations revealed that pitting corrosion was more Grant No. BME-IE-NAT and TKP2020 NC, Grant No.
significant in weld than in the base material. The same BME-NC) based on the charter of bolster issued by the
phenomenon was observed in the article of Chuaiphan and NRDI Office under the auspices of the Ministry for
Srijaroenpramong [26]. Furthermore, the smallest weight Innovation and Technology.

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