International Journal of Modern Manufacturing Technologies

ISSN 2067–3604, Special Issue, Vol. XII, No. 3 / 2020

115

CORROSION RESISTANCE, STRUCTURE AND PROPERTIES OF

AUSTENITIC TIG WELD JOINTS

Tomasz Poloczek1, Jacek Górka

1, Aleksandra Kotarska

1, Monika Kciuk

2

1Silesian University of Technology, Welding Department

Konarskiego 18A, 44-100 Gliwice, Poland 2Silesian University of Technology, Department of Engineering Materials and Biomaterials

Konarskiego 18A, 44-100 Gliwice, Poland

Corresponding author: Tomasz Poloczek, Tomasz.Poloczek@polsl.pl

Abstract: The aim of the research was to examine

corrosion resistance, structure and properties of 50.8 mm

diameter and 1.8 mm thick austenitic steel X5CrNi8-10

(1.4301) tubes weld joints. The welding process was

carried out using manual and automatic Tungsten Inert Gas

(TIG) welding process without additional material. The scope of the research included microscopic observations of

welds cross-sections, hardness tests on welds cross-

sections, bending and static tensile tests, salt spray

corrosion tests. The samples tested in the salt chamber

were then investigated by macroscopic observations,

surface morphology evaluation and chemical composition

analysis of micro areas. The non-destructive and

destructive tests of weld joints revealed higher quality and

properties of automatically welded joints. The salt spray

corrosion tests allowed to determine the type and degree of

destruction of the material surface. Numerous oxidized areas with lower chromium and nickel content, chloride

precipitation and pitting were observed on the surface of

TIG manually welded samples. No significant corrosion

products were observed on the surfaces of TIG

automatically welded samples.

Key words: austenitic steel, TIG welding, corrosion

resistance.

1. INTRODUCTION

Nowadays, for steels used in industry very high

properties requirements are imposed. The materials should be characterized by high mechanical

properties, good weldability and machinability, as

well as high resistance to the destructive effects of corrosion [1-4]. A number of operations are used to

obtain the properties that are required. Some of these

operations are the proper selection of material,

processing technology and welding parameters. These and other operations guarantee the

improvement of the physicochemical and mechanical

properties of metals and alloys allowing long time use of steel constructions [5-9]. The durability of

materials is an important feature that affects the

further use and design of constructions and machines.

Material destruction is mainly caused by corrosion

processes. In addition to steel materials, corrosion also relates to plastics, ceramics and composites [10-

13]. Corrosion processes are common and cannot be

eliminated, but it is possible to reduce their harmful effects. Corrosion-resistant steel grades show high

resistance to the destructive effects of corrosion

processes. Such steel grades contain in chemical

composition elements such as chromium (min. 10 %), which in the presence of oxygen are able to form a

passive layer on the steel surface [14-18]. Corrosion-

resistant steels have found a wide range of industrial applications as a result of their properties. They are

used for manufacturing equipment for the chemical

industry, petrochemical, refining, pharmaceutical

production and for food processing equipment [19-24].

The austenitic steels (Cr-Ni) are characterized by

very good weldability, however in case of incorrect welding or heat treatment, it can be significantly

reduced. The metallurgical weldability of Cr-Ni

austenitic steels may be decreased by the reduction of the resistance to intergranular corrosion of welded

joint, the tendency to hot cracking or the formation of

the brittle σ phase [25-30]. Preventing the

deterioration of the weldability of austenitic steels is mainly based on the selection of the appropriate

welding technology with low linear energy in order to

limit overheating of the welded joint. Welding with low heat input reduces the chromium diffusion

phenomenon which causes intergranular corrosion.

The reduction in heat input also reduces the risk of hot cracking. In order to reduce the risk of brittleness

caused by σ phase precipitation, the presence of δ

ferrite in the weld should be limited to 2-8%, the

filler metal with a high content of austenite stabilizing elements should be used together with low

linear energies during welding and the joint heating

to the temperatures at which the σ phase separates (600 – 900°C) should be avoided [31-35].

116

2. MATERIALS AND METHODOLOGY

The aim of the research was to examine corrosion

resistance, structure and properties of 50.8 mm diameter and 1.8 mm thick austenitic steel

X5CrNi18-10 (1.4301) tubes weld joints. The

welding process was carried out using manual and

automatic Tungsten Inert Gas (TIG) welding process without additional material. The chemical

composition and mechanical properties of tested steel

are presented in Table 1, the structure of tested steel is presented in Figure 1.

Fig. 1. The austenitic structure of X5CrNi18-10 steel,

etching: nitro-hydrochloric acid

Table 1. Chemical composition of the tested steel according to PN-EN 10088-1

Steel Grade Chemical composition, wt.%

Designation Number C Si Mn Pmax S N Cr Ni

X5CrNi18-10 1.4301 ≤0.07 ≤1 ≤2 0.045 ≤0.015 ≤0.11 17.5-19.5 8-10.5

Mechanical properties in room temperature

Designation Number Yield point [MPa] Tensile strength [MPa] Longitudinal elongation

[%]

X5CrNi18-10 1.4301 Rp0,2 min. Rp0,1 min. Rm A min.

195 230 500-700 40

2.1 Welding process

The material was degreased using acetone and prepared for "I" before welding. Test joints were

made in accordance with the Welding Procedure

Specification prepared on the basis of preliminary

tests. The automatic welding process was carried out on an ORBIMAT 165 CA welding machine by

Orbitalum (power source with built-in orbital

controller) equipped with an ORBIWELD 76S closed head. The manual welding process was

carried out using CastoTIG2020 equipment. Photos

of automatically and manually welded samples are

shown in Figures 2 and 3.

Fig. 2. Automatically TIG welded joints

Fig. 3. Manually TIG welded joints

2.2 Weld joints testing

The obtained weld joints were subjected to the following tests:

chemical composition tests using the BRUKER S1

TITAN X-ray spectrometer,

delta ferrite content tests using FISCHER FMP30

type ferrite meter – the tests were carried out on each weld circumference, at the weld face and in the base

material,

visual tests according to PN-EN ISO 17637: 2017 standard,

117

radiographic tests using the ICM SITEX CP200D X-ray tube – the samples were scanned

using an elliptical technique, which is used to scan

the circumferential joints and allows both walls of the joints to be x-rayed,

static tensile and bending tests using R20 type

testing machine with 4 kN load – the static tensile test was carried out in accordance with PN-EN ISO

6892-1: 2016 and the transverse bending test with

root-side (RBB) and face (FBB) stretching of the butt weld in accordance with PN-EN ISO 5173:

2010, for the bending test, 10 mm diameter bend

former was used,

metallographic macroscopic and microscopic

tests – macroscopic observations were carried out

on Olympus SZX9 stereoscopic microscope, for specimens etching Adler’s Reagent was applied,

microscopic observations were carried out on

Nikon Eclipse light microscope, for specimens etching nitro-hydrochloric acid was applied,

Vickers hardness HV0.2 tests in accordance with PN-EN ISO 9015-1:2011 using Wolpert

Wilson Micro-Vickers 401MVD device – the tests

were carried out along one measuring line passing

through the cross-section of the weld joint,

salt spray corrosion tests in CCP 450ip chamber – the tests were carried out in accordance with PN-

EN 9227:2017 in a 5 % NaCl, for 96h in the

temperature of 35 °C. For an initial assessment of the corrosion degree after a full 96h cycle in salt

spray chamber, the macroscopic observations on

ZEISS Discovery V12 stereoscopic microscope

were carried out. The surface topography observations of the samples after the corrosion test

were carried out using ZEISS scanning electron

microscope SUPRA 35 equipped with an EDAX X-ray microanalyzer.

Fig. 4. Radiograph of automatically welded joints

Fig. 5. Radiograph of manually welded joints

3. RESULTS AND DISCUSSION

The study of delta ferrite content in tested weld

joints revealed that base material has a ferritic

number of approximately 0.73 FN, while TIG weld has a ferritic number of 7.03 FN. The obtained

measurement values indicate that the delta ferrite

content in the weld is in the range of 3-15 FN

(according to PN-EN 1011-3). Below this range, the weld would be exposed to hot cracking, while delta

ferrite content above 15 FN would reduce hardness,

ductility and corrosion resistance of joints. Visual tests have shown that the tube joints obtained in the

process of TIG orbital welding were characterized

by linearity. The weld had a regular scale lined in the weld line and a face width of approximately 5

mm. In the case of manual welding, an uneven face

can be observed. On the heat-affected zone surface

occurrence of temper colours formed by chromium oxidation was observed (imperfection 610 in

accordance with PN-EN ISO 6520-1: 2009).

Imperfection 610 may be allowed or not depending on the application. In case of exceeding the

permissible level of oxide films, they must be

always removed. In some installations (e. g. pharmaceutical, chemical and food industries) the

oxide layer on the surface must be removed. No

other surface imperfection was found on the face of

the weld. The root of welds observation also showed the presence of temper colours. Radiographic tests

did not reveal any internal imperfections in weld

joints (Figures 4 and 5). Bending and tensile tests showed a difference in

mechanical properties of weld joints.

Manually welded joints revealed average tensile

strength at break of 658 MPa and average elongation of 32 %, while automatically welded joints revealed

average tensile strength at break of 703 MPa and

average elongation of 52 %. Figure 6 shows a comparison of tensile strength at break values of

tested samples.

118

Fig. 6. The comparison of tensile strength at break of a)

manually TIG welded joint nr 1, b) manually TIG

welded joint nr 2, c) automatically TIG welded joint nr

3, d) automatically TIG welded joint nr 4

The macroscopic observation did not reveal internal

imperfection such as lack of fusion and penetration

(Figures 7 and 8).

The microscopic observations of weld joints revealed twin boundaries in the base material and

heat-affected zone. The presence of twins is a result

of plastic deformation to which the material was subjected in the manufacturing process. The

microstructure of welds was characterized by a

vermicular structure of delta ferrite. In the root area

of the weld, locally increased occurrence of delta ferrite due to welding method was observed (Figures

9 and 10).

The hardness tests of welds cross-sections revealed almost even hardness distribution in automatically

and manually TIG welded joints. The difference of

hardness was found in the heat-affected zone of

automatically and manually welded joints. In the case of the manual process, the average hardness in

HAZ was 168 HV0.2, while for automatic process

average hardness in HAZ was 188 HV0.2 (Figure 11).

Fig. 7. Macrostructure of automatically welded joint

Fig. 8. Macrostructure of manually welded joint

Fig. 9. The microstructure of automatically welded joint

Fig. 10. The microstructure of manually welded joint

119

Fig. 11. The hardness distribution in weld joints

The salt spray corrosion tests allowed to determine the type and degree of material surface damage (Figures 12

and 13). No significant corrosion products were

observed on the surface of the automatically welded

joints. On the other hand, numerous oxidized areas with lower chromium and nickel content, chloride

precipitation and pitting were observed on the manually

welded joint surface (Figures 14-16). In addition, some mechanical damage caused by grinding (Figure 17)

together with solidified tungsten inclusion (Figure 18)

were observed on the manually welded joint surface.

Fig. 12. The macrostructure of the automatically welded

joint after salt spray corrosion test

Fig. 13. The macrostructure of the manually welded joint

after salt spray corrosion test

Fig. 14. Topography view of the manually welded joint

surface after salt spray corrosion test with a visible oxidize

area with a lower chromium content

Fig. 15. Topography view of the manually welded joint

after salt spray corrosion test with visible chloride

120

a)

b)

Fig. 16. a) The chemical composition analysis (EDS) of chloride precipitations on the manually welded joint surface after

salt spray corrosion test, b) spectrometric spectrum of chlorides

Fig. 17. Topography view of the manually welded joint

surface after salt spray corrosion test with a visible

mechanical damage

Fig. 18. Topography view of the manually welded joint

surface after salt spray corrosion test with a visible

solidified tungsten inclusion, formed during the welding

process

121

4. CONCLUSIONS

The chemical composition tests of X5CrNi18-10

revealed estimated contents of elements in tested steel: chromium – 17.5 %, nickel – 8.4 %, manganese – 1.5

%, molybdenum – 0.3 %, cobalt – 0.2 %, copper – 0.5

% and titanium – 0.03 %. The welding processes

carried out in the research resulted in a change of the microstructure in the area of the heat-affected zone in

which the grain growth was observed due to

overheating during the welding process. It was also observed that in the case of manually welded joints,

the grain growth was higher than in the case of

automatically welded joints. This structural change

affected the deterioration of the strength properties and hardness in the heat affected zone. As a result of the

corrosion resistance tests, it was observed that despite

slight differences in hardness and strength as well as changes in the structure of the corrosion-resistant

X5CrNi18-10 austenitic steel, the manually welded

sample showed significantly lower corrosion resistance.

5. REFERENCES

1. Adamiak, M., Wyględacz, B., Czupryński, A.,

Górka, J. (2017). A study of susceptibility and

evaluation of causes of cracks formation in braze-

weld filler metal in lap joints aluminum – carbon steel made with use of CMT method and high power

diode laser, Archives of Metallurgy and Materials,

62, pp. 2113-2123. 2. Ahmadi, E., Ebrahimi, A.R. (2012). The effect of

activating fluxes on 316L stainless steel weld joint

characteristic in TIG welding using the Taguchi

method, Journal of Advanced Materials and Processing, 1, 55-62.

3. Aichele, G. (2005). Orbital welding – solutions for

demanding tasks (Part 1), Welding and Cutting, 4, pp. 176-178.

4. Benway, A.A. (2000). Advancements in automatic

orbital welding expand its use, provide welders with more option, Industrial Maintenance & Plant

Operation, 61(7), p. 22.

5. Chih-Yu, H., Kuang-Hung, T. (2011).

Performance of activated TIG process in austenitic stainless steel weld, Journal of Materials Processing

Technology, 211, 503–512.

6. Emmerson, J. (1999). Multipass orbital welding of pipe, The Tube & Pipe Journal, 10(1), 22-26.

7. Ghetiya, N., Pandya, D. (2014). Mathematical

Modeling for the Bead Width and Penetration in Activated TIG Welding Process, International

Conference on Multidisciplinary Research &

Practice, 1, pp. 247-252.

8. Gietka, T., Ciechacki, K., Kik, T. (2016). Numerical simulation of duplex steel multipass

welding, Archives of Metallurgy and Materials, 61, 1975-1983.

9. Górka, J., Janicki, D., Fidali, M., Jamrozik, W.

(2017). Thermographic Assessment of the HAZ Properties and Structure of Thermomechanically

Treated Steel, International Journal of

Thermophysics, 38, p. 183.

10. Górka, J., Przybyła, M,. Szmul, M., Chudzio, A., Ładak D. (2019). Orbital TIG welding of

titanium tubes with perforated bottom made of

titanium-clad steel, Advances in Materials Science, 19 (3), 55-64.

11. Grajcar, A., Opiela, M., Fojt-Dymara, G. (2009).

The influence of hot-working conditions on a

structure of high-manganese steel, Archives of Civil and Mechanical Engineering, 9(3), pp. 49-58.

12. Gucwa, M., Winczek, J., Giza, K., et. Al. (2019).

The Effect of Welding Methods on the Corrosion Resistance of 304 Stainless Steel Joints, Acta Physica

Polonica A, 135(2), 232-235.

13. Henon, B.K. (1997). Fabrication techniques for successful orbital tube welding, The Tube and Pipe

Quarterly, 7(1-2), pp 40-51.

14. Henon, B.K., Brond, A., Mosciaro, H. (2002).

Orbital welding best competition, Welding Design & Fabrication, 75(8), pp. 28-54.

15. Huang, H.Y. (2009). Effects of shielding gas

composition and activating flux on GTAW Weldments, Material and Design, 30(7), pp. 2404–

2409.

16. Janicki, D. (2013). Fiber laser welding of nickel based superalloy Rene 77 Proceedings of SPIE, 8703,

87030Q, Laser Technology 2012: Applications of

Lasers.

17. Janicki, D. (2013). Fiber laser welding of nickel based superalloy Inconel 625. Proceedings of SPIE,

8703, 87030R, Laser Technology 2012: Applications

of Lasers. 18. Kciuk, M., Lasok, S. (2017). Corrosion

resistance of X5CRNI18-10 stainless steel,

Archives of Metallurgy and Materials, 62(4), pp.

2101-2106. 19. Kik, T., Moravec, J., Novakova, I. (2017). New

method of processing heat treatment experiments

with numerical simulation support, 5th International Conference on Modern Technologies

in Industrial Engineering (ModTech) Book Series:

IOP Conference Series-Materials Science and Engineering, 227, 012069.

20. Kurc-Lisiecka, A., Ozgowicz, W.S., Kalinowska-

Ozgowicz, E., Maziarz, W. (2016). The

microstructure of metastable austenite in X5CrNi18-10 steel after its strain-induced martensitic

transformation, Materials and Technologies, 50(6),

837-843. 21. Lisiecki, A., Burdzik, R., Siwiec, G., Konieczny,

Ł., Warczek, J., Folęga, P., Oleksiak, B. (2015). Disk

122

laser welding of car body zinc coated steel sheets, Archives of Metallurgy and Materials, 60(4), 2913–

2922.

22. Lisiecki, A. (2016). Effect of heat input during disk laser bead-on-plate welding of

thermomechanically rolled steel on penetration

characteristics and porosity formation in the weld

metal, Archives of Metallurgy and Materials, 61(1), 93–102.

23. Lothongkum, G., Chaumbai, P.,

Bhandhubanyong, P. (1990). TIG pulse welding of 304L austenitic stainless steel in flat, vertical and

overhead positions, Journal of Materials Processing

Technology, 89-90, 410-414.

24. Lothongkum, G., Viyanit, E., Bhandhubanyong, P. (2001). Study on the effects of

pulsed TIG welding parameters on delta-ferrite

content, shape factor and bead quality in orbital welding of AISI 316L, Journal of Materials

Processing Technology, 110, 233-238.

25. Lukkari, J. (2005). Orbital – TIG – a great way to join pipes, Svetsaren, 60(1), pp. 3-6.

26. Mannion, B. (2000). The fundamentals of orbital

welding, Gases & Welding Distributor, 44 (1), p. 42-

44. 27. Morawiński, Ł., Chmielewski, T., Olejnik, L.,

Buffa, G., Campanella, D., Fratini, L. (2018).

Welding abilities of UFG metals, AIP Conference Proceedings, 1960(1), 050012, ESAFORM, Palermo,

Italy.

28. Parkitny R., Winczek J., (2013). Analytical solution of temporary temperature field in half-

infinite body caused by moving tilted volumetric heat

source, International Journal of Heat and Mass

Transfer, 60, 469 – 479. 29. Rogalski, G., Swierczyńska, A., Landowski, M.,

Fydrych, D. (2020). Mechanical and Microstructural

Characterization of TIG Welded Dissimilar Joints between 304L Austenitic Stainless Steel and Incoloy

800HT Nickel Alloy, Metals, 10(5), 559.

30. Sagues, P. (2010). Adaptive control techniques

advance automatic welding, Welding Journal, 89(8), 26-28.

31. Skowronska, B., Chmielewski, T., Pachla, W., et.

al. (2019). Friction weldability of UFG 316L stainless steel, Archives of Metallurgy and Materials,

64(3), pp. 1051-1058.

32. Swierczynska, A., Labanowski, J., Michalska, J. et al., (2017). Corrosion behavior of hydrogen

charged super duplex stainless steel welded joints,

Materials and Corrosion-Werkstoffe und Korrosion,

68(10), pp. 1037-1045. 33. Tsai, C.H., Hou, K.H., Chuang, H.T. (2006).

Fuzzy control of pulsed GTA welds by using real-time

root bead image feedback, Journal of Materials Processing Technology, 176(1-3), 158-167.

34. Weman, K. (2004). A History of Welding,

Svetsaren, 1, pp. 32-35. 35. Widgery, D. J. (2005). Mechanised welding of

pipelines, Svetsaren, 60(1), pp. 23-26.

Received: April 23, 2020 / Accepted: December 20,

2020 / Paper available online: December 25, 2020 ©

International Journal of Modern Manufacturing Technologies