investigation of mig welding to the corrosion
TRANSCRIPT
INVESTIGATION OF MIG WELDING TO THE CORROSION BEHAVIOUR OF
CARBON STEEL
NG WAI LOON
Report submitted in partial fulfilment of the requirements for the award of the degree of
Bachelor of Mechanical Engineering
Faculty of Mechanical Engineering
UNIVERSITI MALAYSIA PAHANG
JUNE 2012
vii
ABSTRACT
A welding process was performed on the low carbon steel based on different welding
parameters in this experiment. The main objective of this study was to investigate the
effect of welding voltages (19 V, 20 V, 21 V, and 22 V) and wire feed rates (90 ipm,
100 ipm, 110 ipm, and 120 ipm) to the corrosion behaviour of welded carbon steel in
synthetic seawater environment (3.5 wt% NaCl). Besides that, the microstructure
changes in the weldments of maximum and minimum voltages were analysed and
compared with the as-received sample before welding process. On the other hand, the
penetration level of the weldments was analysed due to the different welding parameter.
The welding method in this experiment was metal inert gas (MIG) with filler metal (ER
70S-6 with 1.2 mm diameter). Based on the results obtained, the corrosion rate
decreased when the welding voltage was increased from 19 V to 22 V or when the wire
feed rate was increased from 90 ipm to 120 ipm until the full penetration level of
weldment occurred. In conclusion, the lowest corrosion rate occurred at highest welding
voltage and highest wire feed rate when full penetration of weldment occurred. The
corrosion product that formed on the surface of the sample was iron oxides and pitting
was found on the surface of the exposed area after the corrosion test.
viii
ABSTRAK
Satu proses kimpalan telah dijalankan ke atas keluli karbon rendah berdasarkan
beberapa parameter kimpalan yang berlainan dalam eksperimen ini. Objektif utama bagi
kajian ini adalah untuk mengkaji kesan voltan kimpalan (19 V, 20 V, 21 V dan 22 V)
dan kadar suapan wayar (90 ipm, 100 ipm, 110 ipm, and 120 ipm) kepada kelakuan
kakisan kimpal dalam persekitaran air laut sintetik (3.5wt % NaCl). Selain itu,
perubahan mikrostruktur dalam hasil kimpal voltan maksimum dan minimum telah
dianalisis dan dibandingkan dengan sempel yang diterima sebelum proses kimpalan. Di
samping itu, tahap penembusan daripada hasil kimpal yang disebabkan oleh parameter
kimpalan berbeza dianalisis. Kaedah kimpalan dalam eksperimen ini adalah
menggunakan mesin kimpalan MIG (metal inert gas) dengan logam pengisi (ER 70S-6
berdiameter 1.2 mm). Berdasarkan keputusan yang diperolehi, kadar kakisan akan
menurun apabila voltan kimpalan meningkat dari 19 V ke 22 V dan kadar suapan wayar
meningkat dari 90 ipm ke 120 ipm sehingga tahap penembusan penuh hasil kimpal
terjadi. Kesimpulannya, kadar kakisan terendah berlaku pada voltan kimpalan dan kadar
suapan wayar yang tertinggi ketika penembusan penuh kimpal berlaku. Hasil kakisan
yang terbentuk di permukanan sampel adalah oksida besi dan bopeng telah dijumpai di
permukaan kawasan yang terdedah selepas ujian kakisan.
ix
TABLE OF CONTENTS
Page
EXAMINER DECLARATION ii
SUPERVISOR’S DECLARATION iii
STUDENT’S DECLARATION iv
DEDICATION v
ACKNOWLEDGEMENTS vi
ABSTRACT vii
ABSTRAK viii
TABLE OF CONTENTS ix
LIST OF TABLES xiii
LIST OF FIGURES xiv
LIST OF SYMBOLS xvii
LIST OF ABBREVIATIONS xviii
CHAPTER 1 INTRODUCTION
1.1 Introduction 1
1.2 Background of Study 1
1.3 Problem Statement 3
1.4 Objectives 4
1.5 Scopes 4
1.6 Thesis Outline 4
CHAPTER 2 LITERATURE REVIEW
2.1 Introduction 6
2.2 Material 7
2.2.1 Carbon Steel 7
2.2.2 Types of Carbon Steel 7
2.2.3 Application of Carbon Steel in Seawater 9
2.2.4 Welding Wire 10
2.3 Corrosion Concepts 11
2.4 Electrochemical Corrosion Measurement 13
x
2.5 Types of Corrosion 16
2.5.1 Galvanic Corrosion 16
2.5.2 Stress Corrosion Cracking (SCC) 17
2.5.3 Hydrogen-induced Cold Cracking 18
2.5.4 Pitting 19
2.6 Factors Influencing Corrosion of Weldments 20
2.6.1 Welding Factors 20
2.6.2 Metallurgical Factors 22
2.7 Weld Microstructures 23
2.7.1 The Fusion Zone 24
2.7.2 Heat Affected Zone (HAZ) 25
2.7.3 Base Metal 26
2.8 Effect of Heat Input on Low Carbon Steel 27
2.8.1 Weld Microstructure 27
2.8.2 Geometrical Factors 35
CHAPTER 3 METHODOLOGY
3.1 Introduction 38
3.2 Material 40
3.3 Sample Preparation 41
3.4 Compositional Analysis 41
3.5 Welding 43
3.6 Metallorgraphic Analysis 45
3.7 Electrochemical Test 55
3.8 Scanning Electron Microscopy (SEM) 57
CHAPTER 4 RESULTS AND DISCUSSION
4.1 Introduction 59
4.2 Compositional Analysis 60
4.3 Microstructural Examination of As-Received Sample 61
4.4 Optical Microscopy of Welded AISI 1010 Carbon Steel 63
4.5 Visual Inspection of Welded AISI 1010 Carbon Steel 65
4.6 Polarization Results of Electrochemical Test 69
xi
4.7 Effect of Welding Voltage and Wire Feed Rate on Corrosion Rate 77
4.7.1 Effect of Wire Feed Rate on Corrosion Rate 78
4.7.2 Effect of Welding Voltage on Corrosion Rate 79
4.8 Scanning Electron Microscopy (SEM) Result 82
CHAPTER 5 CONCLUSION AND RECOMMENDATIONS
5.1 Introduction 85
5.2 Conclusions 85
5.3 Recommendations 86
REFERENCE 87
APPENDICES
A1 AISI-SAE Standard Carbon Steels 90
A2 Compositional Analysis of Sample Material 91
B Sample Calculation of Corrosion Rate for Electrochemical Test 92
C1 Optical Microscopy of Welded Sample 1 93
C2 Optical Microscopy of Welded Sample 2 94
C3 Optical Microscopy of Welded Sample 3 95
C4 Optical Microscopy of Welded Sample 4 96
C5 Optical Microscopy of Welded Sample 5 97
C6 Optical Microscopy of Welded Sample 6 98
C7 Optical Microscopy of Welded Sample 7 99
C8 Optical Microscopy of Welded Sample 8 100
C9 Optical Microscopy of Welded Sample 9 101
C10 Optical Microscopy of Welded Sample 10 102
C11 Optical Microscopy of Welded Sample 11 103
C12 Optical Microscopy of Welded Sample 12 104
C13 Optical Microscopy of Welded Sample 13 105
C14 Optical Microscopy of Welded Sample 14 106
C15 Optical Microscopy of Welded Sample 15 107
C16 Optical Microscopy of Welded Sample 16 108
D1 Visual Inspection of Welded Samples 1, 2, 3 and 4 109
xii
D2 Visual Inspection of Welded Samples 5, 6, 7 and 8 110
D3 Visual Inspection of Welded Samples 9, 10, 11 and 12 111
D4 Visual Inspection of Welded Samples 13, 14, 15 and 16 112
E1 Gantt Chart PSM 1 113
E2 Gantt Chart PSM 2 114
xiii
LIST OF TABLES
Table No. Page
2.1 Types of carbon steel 8
2.2 Chemical composition of AWS ER70S-6 10
3.1 Welding parameter 45
3.2 Parameter setup in electrochemical test 56
4.1 Composition analysis of AISI 1010 carbon steel 60
4.2 Visual inspection of welded AISI 1010 carbon steel 66
4.3 Tafel polarization curve data of samples 1, 2, 3 and 4 (19 V) 70
4.4 Tafel polarization curve data of samples 5, 6, 7 and 8 (20 V) 72
4.5 Tafel polarization curve data of samples 9, 10, 11 and 12 (21 V) 74
4.6 Tafel polarization curve data of samples 13, 14, 15 and 16 (22 V) 76
4.7 Corrosion rate of samples with different wire feed rate and welding
voltages
77
xiv
LIST OF FIGURES
Figure No. Page
2.1 The basic corrosion cell 11
2.2 Corrosion process showing anodic and cathodic current components 14
2.3 Schematic diagrams showing the regions of a heterogeneous weld 23
2.4 Variation of weld structure with distance from the welding seam
centre
24
2.5 Iron-carbon phase diagram 27
2.6 Weld microstructure in low carbon steels 30
2.7 Continuous cooling transformation diagrams for weld metal of low
carbon steel
30
2.8 Weld microstructure in low carbon steels 31
2.9 HAZ microstructure in low carbon steels 32
2.10 Base metal microstructure in low carbon steels 32
2.11 Weld microstructure with heat input 1 (690 J/mm) 33
2.12 Weld microstructure with heat input 4 (2800 J/mm) 34
2.13 Effect of percentage of heat input to the corrosion current of weld
metal
34
2.14 Weld bead geometry 36
2.15 Effect of welding voltage on bead geometry 37
2.16 Effect of wire feed rate on bead geometry 37
3.1 A flow chart showing a summary of the research methodology 39
3.2 Photograph of carbon steel in laboratory 40
3.3 Shearing machine (MSV-C 31/6) 40
3.4 Sample preparation for welding process 41
3.5 Spectrometer machine 42
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3.6 Sample 17 (as-received material) 42
3.7 MIG welding machine 43
3.8 (a) Carbon dioxide cylinders and (b) Filler material
(AWS ER 70S-6)
44
3.9 Welded sample 44
3.10 Sectional cut-off machine 46
3.11 Sample after cutting process 46
3.12 Sample after connected with wire 47
3.13 Voltmeter 47
3.14 LECOSET 7007 (resin and liquid) 48
3.15 Mounting cup 49
3.16 LECOMAT pressure vessel 49
3.17 Sample 5 50
3.18 Grinding machine 51
3.19 Rotating polishing wheel 52
3.20 (a) 6 micron diamond suspension and (b) 1 micron diamond
suspension
52
3.21 0.05 micron alumina suspension 53
3.22 Etching solution 53
3.23 Optical microscope 54
3.24 A schematic diagram showing weldment, base metal and HAZ 54
3.25 Electrochemical measurement setup 56
3.26 WPG-100 potentiostat 57
3.27 Cleaning solution 58
3.28 Cleaning process 58
4.1 Sample 17 (as-received material): (a) Top view and (b) Bottom view 61
xvi
4.2 Optical micrograph of as-received AISI 1010 carbon steel (500x
Magnification)
62
4.3 Optical micrograph of weldment sample 4 (19 V and 120 ipm)
(500x Magnification)
63
4.4 Optical micrograph of weldment sample 16 (22 V and 120 ipm)
(500x Magnification)
64
4.5 Sample 13 (22 V and 90 ipm) 67
4.6 Sample 14 (22 V and 100 ipm) 67
4.7 Sample 16 (22 V and 120 ipm) 68
4.8 Polarization diagram of sample 1, 2, 3 and 4 (19 V) 69
4.9 Graph of corrosion rate versus wire feed rate of samples 1, 2, 3 and 4 71
4.10 Polarization diagram of sample 5, 6, 7 and 8 (20 V) 71
4.11 Graph of corrosion rate versus wire feed rate of samples 5, 6, 7 and 8 73
4.12 Polarization diagram of sample 9, 10, 11 and 12 (21V) 73
4.13 Graph of corrosion rate versus wire feed rate of samples 9, 10, 11
and 12
75
4.14 Polarization diagram of sample 13, 14, 15 and 16 (22V) 75
4.15 Graph of corrosion rate versus wire feed rate of samples 13, 14, 15
and 16
77
4.16 Graph of corrosion rate versus wire feed rate 78
4.17 Graph of corrosion rate versus welding voltages 79
4.18 Sample 15 before cleaning process 82
4.19 Sample 15 after cleaning process 83
4.20 Corrosion product formed after corrosion test 83
4.21 Corrosion defect after corrosion test 84
xvii
LIST OF SYMBOLS
A Exposed area
d Density
Ecorr Corrosion potential
Eoc Open circuit potential
I Welding current
Icorr Corrosion current
K Constant value
Q Heat input
S Welding speed
V Welding voltage
% Percentage
xviii
LIST OF ABBREVIATIONS
AISI American Iron and Steel Institute
ASTM American Society for Testing and Materials
Ar Argon
C Carbon
CO2 Carbon dioxide
Cr Chromium
CR Corrosion rate
Cu Copper
e- Electron
EW Equivalent weight
Fe Iron
Fe2+
Ferrous ions
Fe3+
Ferric ions
Fe2O3·nH2O Iron (III) oxides
FeO(OH) Iron (III) oxide-hydroxide
Fe(OH)3 Iron (III) oxide-hydroxide
FHWA Federal Highway Administration
GMAW Gas Metal Arc Welding
HAZ Heat affected zone
HCL Acid hydrochloric
H2O Water
MIG Metal inert gas
Mn Manganese
xix
Mo Molybdenum
NACE National Association of Corrosion Engineers
NaCl Sodium chloride
Ni Nickel
No Number
O2 Oxygen
OH- Hydroxide irons
P Phosphorus
S Sulphur
SAE Society of Automotive Engineers
SCC Stress corrosion cracking
SEM Scanning electron microscopy
Si Silicon
UMP University Malaysia Pahang
V Vanadium
Wt% Weight percentage
CHAPTER 1
INTRODUCTION
1.1 INTRODUCTION
This chapter explains about the background of study, problem statement,
objectives, and scopes of this study. The purpose of this study can be identified by
referring at the problem statement of this study. Besides that, the detail of the study and
output can be obtained based on the objectives and scopes of this study.
1.2 BACKGROUND OF STUDY
Corrosion can be defined as degradation of quality and properties in a material
due to the chemical reaction between the components of the material and the
surrounding. In other words, corrosion can be described as deterioration of essential
properties such as mechanical properties and physical properties in a material (Seifedine,
2008). Corrosion can cause a variety of problems in our daily life, depending on the
application of the metals. The first common problem is the leakage of the metal such as
tanks and pipes, which allows leakage of fluids or gases out of the tanks or pipes.
Metals are widely used in the piping system either in underground or seawater condition
which corrosion is easily occurred. Besides that, the next effect of corrosion is the
degradation of quality and properties in a material. The strength of the metal where the
cross section of structural members is reduced due to the effect of the corrosion, leading
to a loss of strength of the structure and subsequent failure of the structures.
Millions of dollars are lost each year due to the effect of corrosion. Much of this
loss is due to the corrosion of iron and steel since the price of iron and steel is much
2
more expensive and both metals are widely used in the industry compared to other type
of metals (Osarolube et al., 2008). Based on the study entitled “Corrosion Costs and
Preventive Strategies in the United States”, the total annual estimated direct cost of
corrosion in the United State is a staggering $276 billion. Besides that, the indirect
corrosion costs are lost time, and thus lost productivity because of outages, delays,
failures, and litigation. The shipping industry cost of corrosion is $2.7 billion, broken
down into new ship construction ($1.1 billion), maintenance and repairs ($0.8 billion),
and corrosion-related downtime ($0.8 billion) (Koch et al., 2002).
Carbon steel is the most widely used engineering material despite its relatively
limited corrosion resistance. Carbon steel is used in large tonnages in marine
applications, nuclear power and fossil fuel power plants, transportation, chemical
processing, petroleum production and refining, pipelines, mining, construction and
metal-processing equipment. Carbon steel has been the most widely used structural
material which is abundantly available, inexpensive and has adequate mechanical
properties but has a high general corrosion rate (Kadhim, 2011).
Welding is a reliable and efficient metal-joining process which is widely used in
the industry. With the growing emphasis on the use of automated and robotic system
Metal Inert Gas (MIG) welding, with its all-position capabilities, Gas Metal Arc
Welding (GMAW) has been employed increasingly in mechanized surfacing in the
industry (Murugan and Parmar, 1994). However, during the welding process, due to the
different quantity of heat input as well as the quality of the weldments, many problems
arise from the process especially in corrosion (Funderburk, 1999). The cycle of heating
and cooling that occurs during the welding process affects the microstructure and
surface composition of welds and adjacent base metal. Metallurgical factor is one of the
primary concerns to the corrosion of welded carbon steel (Davis, 2006). Thus, the joint
is always considered as the weakest part of a component.
3
1.3 PROBLEM STATEMENT
Carbon steel is the most widely used engineering material in the overall of steel
production worldwide. Although carbon steel is highly related to the limited corrosion
resistance compared to other common types of steels such as stainless steel, carbon steel
is still used in large tonnages in applications which are highly related to the high
corrosion resistance requirement. Since carbon steels represent the largest single class
of alloys in use, both in terms of tonnage and total cost, it is easy to understand that the
corrosion of carbon steels is a problem of enormous practical importance. This is the
reason for the existence of entire industries devoted to providing protective systems for
irons and steel.
Carbon steels are commonly used in seawater for structural applications such as
ship hulls, offshore platforms, sheet piles and coastal facilities as well as sea water
piping systems. Millions of dollars are lost each year due to the effect of corrosion, thus
the corrosion behaviour of carbon steel is utmost important to be studied. Previously,
study of corrosion of welded carbon steels in seawater is always related to the type of
material used. However, welding parameters such as welding voltages applied and wire
feed rate play a big role in influencing the corrosion rate of the steel. Welding
parameters have a high influence on the quality of the welding which directly affects the
corrosion resistance of the material. Besides that, welding parameters have high
influence on the heat input to the material which directly alter the microstructure of the
weldments and indirectly affects the corrosion rate of the material. Although there are
many researches and studies about the corrosion of welded carbon steel carried out in
the past few decades in seawater environment, there is still no research came out which
accurately describes the trend of corrosion rate to welding parameters. Thus, in this
study, the effect of welding parameters on the corrosion rate of welded carbon steel in
seawater environment is investigated.
4
1.4 OBJECTIVES
The main objective of this study is to investigate the effect of welding voltage
and wire feed rate to the corrosion behaviour of weld carbon steel in synthetic seawater
environment.
1.5 SCOPE
i) The material used is low carbon steel (AISI 1010).
ii) The welding method employed is MIG.
iii) Different welding voltages (19 V, 20 V, 21 V, and 22 V) and wire feed rates
(90 ipm, 100 ipm, 110 ipm, and 120 ipm) are used to join the sample using
butt joints.
iv) Microstructure analysis of welding specimens by using optical microscope/
scanning electron microscopy (SEM).
v) Electrochemical test by using potentiostat.
vi) Corrosion rate of welded carbon steel in synthetic seawater (3.5 wt% NaCl)
environment.
1.6 THESIS OUTLINE
This thesis consists of 5 chapters which illustrate the flow of the project from
introduction till the conclusion. Every chapter presents with different contents. After
read the entire chapters in the thesis, the viewer may understand the detail of the project
and obtains the output of the project.
Chapter 1 contains about the background of study, problem statement, objectives,
and scopes of this study.
Chapter 2 contains all the literature review and some presentation of the earlier
work. This chapter also presents about the information of the material that used in this
study. Some concepts which relate to the corrosion also discusses in this chapter.
5
Chapter 3 contains the summary of the research methodology of this project.
This chapter also explains about the flow of the project which includes the steps of
project conducted.
Chapter 4 contains the results that obtained during this study. This chapter also
explains the analysis and discussion of the result. The result obtained is discussed and
compared to previous study in this chapter.
Chapter 5 explains the conclusion of the project. This chapter also includes the
future recommendation of the project.
CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
This chapter presents about the material that used in this study which includes
type of material and some basic knowledge about the chosen material and the
application of the material in seawater environment. On the other hand, some concepts
which relate to the corrosion include the electrochemical reaction also discusses in this
chapter. The formation of the corrosion product also explains in this chapter based on
the chemical reaction. The corrosion determination method that used in this study which
is polarization diagram and some formula which relate to the corrosion determination
also include in this chapter. Different types of corrosion defects which relate to welding
also discuss in this chapter such as stress corrosion cracking (SCC), pitting and galvanic
corrosion. Besides that, this chapter also explains about the history background and
presentation of the earlier work.
7
2.2 MATERIAL
2.2.1 Carbon Steel
Carbon steel is the most widely used engineering material in the overall of steel
production worldwide (Morrow, 2010). Carbon steel can be defined as steel where the
main interstitial alloying element is carbon. Carbon steel can be described as the
structural material which is abundantly available, inexpensive, adequate formability and
weldability, and has adequate mechanical properties but has a high general corrosion
rate (Kadhim, 2011).
Although carbon steel is always related to the low corrosion resistance or high
general corrosion rate, it is still the most widely used engineering material in this world.
It is well known that carbon steel corrodes rapidly in seawater environment and requires
adequate protection depending on the type of application. Though carbon steel is the
most prone to corrosion, it is the least expensive of the most commonly perforated
metals compared to other type of structural material. Carbon steel is used in large
tonnages in marine applications, nuclear power and fossil fuel power plants,
transportation, pipelines, mining, and construction (Kadhim, 2011).
2.2.2 Types of Carbon Steel
Carbon steel can be divided into five groups based on its carbon content which
are low carbon steel, mild steel, medium carbon steel, high carbon steel and ultra-high
carbon steel. Typical groups of carbon steels are as tabulated in Table 2.1 and each
group of carbon steel is provided with some examples which start with American Iron
and Steel Institute (AISI). There are a total of five groups of carbon steel which shows
different characteristics as discussed in Table 2.1. Different groups of carbon steel are
applied in different application in worldwide and it depends on the characteristic of the
carbon steel and the requirement of the application.
8
Table 2.1: Types of carbon steel
Carbon
steel types
Example
AISI No.
% of
carbon
Explanation
Low carbon
steel
1010, 1012 0.05-0.15 It is neither ductile nor brittle.
It is normally used when huge
quantities of steel and high surface
finish are required.
It is used in the form of structural
steel such as sheets, strips, rods and
wires.
Mild steel 1018, 1020 0.16-0.29 Its price is usually low and it
provides the material properties
which are acceptable under many
circumstances.
It is characterized by a low tensile
strength, but it is malleable, good
machinability, and cheap
It is used to produce ship plates,
welded turbines, boiler tubes and
camshafts.
Medium
carbon steel
1035, 1038 0.30-0.59 It is stronger and possesses better
hardness and tensile strength but less
ductility than mild steel.
It has good machinability, deep
hardening properties and fantastic
wear resistance.
It is used in automotive components
which required higher strength such
as stronger nut, large forgings, and
high tensile tubes.
High carbon
steel
1055 0.6-0.99 It is very strong, utilized in high-
strength wires and springs.
Ductility and machinability of steel
decreases with the increase in carbon
content.
It is used in produce cold chisel,
wrenches, jaws, hacksaw blades and
railway service.
Ultra-high
carbon steel
1-2 It could be tempered for greater
hardness.
It is utilized for special purposes
such as non-industrial-purpose
knives, punches or axles.
Source: Ashby and Johnson (2009)
9
2.2.3 Application of Carbon Steel in Seawater
Although carbon steel is highly related to the limited corrosion resistance
compared to other common types of steels such as stainless steel, carbon steels are
commonly used in seawater for structural applications such as ship hulls, offshore
platforms, sheet piles and coastal facilities as well as seawater piping systems. All these
applications required high corrosion resistance material since the medium environment
of the applications is seawater which can increase the corrosion rate of the material
(Kadhim, 2011). Basically, seawater in the ocean in the world has a salinity which is
about 3.5 %. In other words, each litre by volume of seawater has approximately 35
grams of dissolved salts (predominantly sodium (Na+) and chloride (Cl
−) ions).
Carbon steel is preferred in a seawater environment compared other types of
material since carbon steel exhibit low initial cost compared with other materials, the
ready availability of material and components and the existence of widely used and
accepted welding procedures. However, the rate of corrosion of carbon steel is much
higher and this becomes the main barrier of the usage of carbon steel in seawater
environment. Basically, a system that produced or designed using carbon steel is much
cheaper since carbon steel is inexpensive but the system is larger, heavier and shorter
life compared to other structural material. Thus, the failures of the structure may occur
earlier and it is within a few years and complete replacement is required compared to
other better corrosion resistance structural material (Bennett, 2002).
However, in order to increase the corrosion resistance of carbon steel in
seawater environment, method of coatings is largely applied. Coating is a famous and
widely used method to protect the low corrosion resistance material such as plain
carbon steel but it also increases the initial costs since more process is needed compared
to plain carbon steel. Coating is applied on the both surfaces which are inner and outer
surface in order to increase the corrosion resistance of the material. However, by
applying a coating on the surface of the material, it introduces complications into the
fabrication procedures, such as the need for a local removal prior to welding and re-
application afterwards (Morrow, 2010). Besides that, heat treated carbon steel can be
used compared to plain carbon steel in order to improve the corrosion resistance of the
10
carbon steel. Heat treated carbon steel has better mechanical properties and corrosion
resistance compared to the plain carbon steel since different microstructure existed in
the material.
2.2.4 Welding Wire
In MIG welding, AWS ER70S-6 is a common wire types that used to join the
common steel. AWS ER70S-6 is a mild steel welding wire that contains a higher
percentage of manganese and silicon compared to other standard grades of MIG wire.
This welding wire is chosen in order to produce high quality welds when used on dirty,
oily, or rusty steel. The chemical composition of AWS ER70S-6 is shown in Table 2.2.
High percentage of silicon content increases the fluidity of the weld pool which create a
smoother bead appearance and resulting in minimal post-weld grinding. This wire is
engineered to provide trouble-free performance from heavy duty, high speed, spray
transfer applications all the way to light duty low speed, short-arc applications. ER70S-
6 is designed for use with various gas mixtures such as 100 % CO2, 75 %/25 % Ar/CO2
or 98 %/2 % Ar/O2 (Scholz, 1996).
Table 2.2: Chemical composition of AWS ER70S-6
Source: Scholz (1996)
Element Weight, %
C 0.06 to 0.15
Si 0.8-1.15
Ni 0.15 (max)
Mo 0.15 (max)
Cu 0.5 (max)
S 0.035 (max)
Cr 0.15 (max)
Fe Balance
Mn 1.40-1.85
V 0.025 (max)
P 0.03 (max)
Other 0.5 (max)