THE EFFECT OF ELECTRODES ON THE MECHANICAL

PROPERTIES OF WELDED STEELS

BY

FRIDAY AJE OVAT

JULY, 2004

THE EFFECT OF ELECTRODES ON THE MECHANICAL

PROPERTIES OF WELDED STTEELS

BY

FRIDAY AJE OVAT ( MENG/1251/2000 )

PGD, MARKUDI

(MECHANICAL ENGINEERING)

University of Agriculture

Thesis submitted to

The Department of Mechanical Engineering in partial

fulfillment of the requirements for the award of

degree of Master of Engineering.

University of Agriculture

Makurdi.

JULY, 2004

ii

DECLARATION

I declare that the work described in this thesis represent my original

Work and has not been previously submitted for any degree or

diploma to any university or similar institution.

Name of Candidate: Friday Aje Ovat

Signature of candidate.......................................................

Date....................................................................................

iii

SIGNATURE PAGE

NAME OF CANDIDATE: FRIDAY AJE OVAT

REGISTRATION NUMBER: M.ENG/1251/00

CERTIFICATE OF APPROVAL

We the undersigned hereby certify that the thesis presented by the

above named candidate be accepted as fulfilling

part requirement for the degree of master in engineering.

Title: The effect of electrodes on the mechanical properties of

welded steels.

....................... .......................................

Dr.E.E. Nnuka Date

Major Supervisor

........................... ..........................................

Dr. L. T. Tuleun Date

Minor Supervisor

............................ ...........................................

Dr. E. E. Nnuka Date

Head of Department

.............................. ...........................................

Prof. A. O. Nwankiti Date

Dean Post Graduate School.

iv

DEDICATION

I dedicate this work to the Almighty God for the knowledge and to

my parents and my late sister Miss Christiana Aje

whose prayers and encouragement during my study saw me through

the successful end.

v

ACKNOWLEDGEMENT

I wish to express my deep gratitude and appreciation to my

supervisor Dr. E. E. Nnuka, Head of department, Mechanical

Engineering, University of Agriculture Makurdi and my second

supervisor, Dr. L. T. Tuleun for their contributions and the pains they

took in seeing me through this research work.

I am equally grateful to Mr. M. I. Oseni, department of mechanical

engineering, University of Agriculture Makurdi for his

insurmountable input throughout the course of the work.

I also appreciate the efforts of Mrs. A. I. Nnuka, Dr. Mrs. C. D.

Tuleun, Engr. Popoola of the National Metallurgical Development

Centre ( NMDC ) Jos and Mr. Uquo of the civil Engineering

department, Cross River State University of Technology, Calabar for

assisting me in testing the prepared samples used in the research

work.

I am very much indebted to the family of my colleague and friend

Pastor Martins Okosun, for their hospitality and co-operation

throughout the duration of the study. Dr. F. A. Mboto was also

indispensable and his effort was worthwhile.

I am also grateful to my well wishers too numerous who in one way

or the other have contributed in no small way in making this work a

huge success.

vi

ABSTRACT

The research investigated the mechanical properties of welds in

relation to the different kinds of electrodes used in producing the

weldments, the different mechanical properties investigated were

hardness, impact, comprehension and tensile strength. The

electrodes that were used as the filler metals included two different

classes of mild steel electrodes. The tests carried out to measure the

mechanical properties of the welded included the tensile and

compressive tests using the hardness test using the Rockwell testing

machine. The samples were prepared using low and medium carbon

steels since they find wider application in the engineering Industry.

The joints made were butt joints and the welding process was

metallic arc welding.

Results obtained from the tests indicated that the required level of

hardness could be achieved when low and medium carbon steels

were welded with stainless electrode while impact strength level can

be achieved when joints are produced with guage-12 electrodes on

low carbon and medium carbon steels. Acceptable level of tensile

strength and compression strength can be obtained when low and

medium carbon steels are welded with stainless electrodes. The

designer is therefore given an opportunity to choose the appropriate

electrodes on the different steels when designing to achieve the

appropriate level of mechanical properties.

vii

TABLES OF CONTENTS PAGE

Title page i

Declaration ii

Signature page iii

Dedication iv

Acknowledgement v

Abstract vi

Table of contents vii

List of Figures xii

List of plates xiii

Symbols xiv

Abbreviations xiv

1.0 INTRODUCTION-- - - - - - - - 1

1.1 Background - - - - - - - 1

1.2 Objectives of the research work - - - - 5

1.3 Significance of the research -- - - - - 5

1.4 Scope of the research-- - - - - - - 6

2.0 LITRATURE REVIEW-- - - - - - - 7

2.1 Joining process- - - - - - - - - 7

2.1.1 Mechanical - - - - - - - - - 7

2.1.2 Welding - - - - - - - - - 8

2.1.3 Brazing - - - - - - - - - 10

viii

2.1.4 Adhesive - - - - - - - - - 11

2.1.5 Soldering- - - - - - - - - - 12

2.2 Welding process - - - - - - - - 15

2.2.1 Gas welding - - - - - - - - 16

2.2.2 Resistance welding - - - - - - 17

2.2.3 Arc welding process - - - - - - - 19

2.2.4 Metallic arc welding - - - - - - - 21

2.3 Consideration for selection of a joining process` - - 22

2.4 Electrodes - - - - - - - - 22

2.4.1 American welding society specifications for

Filler materials - - - - - - - - - 23

2.5 The weld - - - - - - - - 29

2.6 Development of a weld in arc welding - - - - 31

2.6.1 Heat sources - - - - - - - - 32

2.6.2 Metal transfer -- - - - - - - - 37

2.6.3 Heat flow - - - - - - - - 40

2.6.4 The weld metal - - - - - - - - 42

2.7 Weld pool solidification and contraction - - - 43

2.8 Weld cracking - - - - - - - - 45

2.8.1 Measurement of crack sensitivity - - - - 45

2.9 Dilution and uniformity of the weld pool - - - - 46

2.10.1 Weld quality - - - - - - - - 46

2.10.2 Weldability - - - - - - - - 47

X

3.3.1 Specimen preparation - - - - - - - -67

3.3.2 Test method - - - - - - - - - 69

3.4 Tensile test - - - - - - -- - 69

3.4.1 Specimen preparation - - - - - -- - 69

3.4.2 Test method - - - - - - - - 71

3.5 Comprehension test - - - - - - - 71

3.5.1 Specimen preparation - - - - - - 71

3.5.2 Test method -- - - - - - - - - 73

3.6 Preparation of specimens for micrographs - - 73

3.6.1 Specimen preparation - - - - - - - 73

3.6.2 Microscopy - - - - - -- -- - - 75

3.7 Summary of specimen preparation - - - - 75

4.0 RESULTS - - - - - - - - - - 77

4.1 Introduction- - - - - - - - - - 77

4.2 Hardness test - - - - - - - - - 77

4.3 Impact test - - - - - - - - - 81

4.4 Tensile test - - - - - - - - - 85

4.5 Compression test - - - - - - - - 89

5.0 DISCUSSION - - - - - - - - - 92

5.2 Hardness Results - - - - - - - - 92

5.2.2 Medium Carbon steel - - - - - -- - 93

5.3 Impact results - - - - - - - - 93

xi

5.4 Tensile results - - - - - - - - 95

5.5 Compression results - - - - - - - 97

5.6 Micrography - - - - - - - - - 99

6.0 CONCLUSIONS AND RECOMMENDATIONS - - - 116

6.1 Conclusion - - - - - - - - - 116

6.1.1 Hardness test - - - - - - - - - 116

6.1.2 Impact test - - - - - - - - - 116

6.1.3 Tensile test - - - - - - - - - 117

6.1.4 Compression test - - - -- - - - - 117

6.2 Recommendations - - - - - - - 118

References - - - - - - - - 119

xii

LIST OF FIGURES

FIGURE TITLE

PAGE

NO.

1 Equilibrium diagrams of tin and copper rich alloys 14

after soldering operations

2 Arc appearance and structure 34

3 Typical voltage-current characteristics for various 36

Process with arc length about 6mm in each case

4 Weld macrostructure as a function of weld pool shape 44

5 Typical engineering stress-strain behavior to fracture 51

6 Graphic recording of fatigue properties 57

7 Standard specimen for Izod test for impact property 68

8 Standard tensile specimen with circular cross section 70

9 Specimen for compression test 72

xiii

LIST OF PLATES

PLATE TITLE PAGE

NO.

1 Micrograph of unwelded low carbon steels 101

2 Micrograph of low carbon steel welded with guage-10 electrode

103

3 Micrograph of low carbon steel welded with stainless steel electrode

105

4 Micrograph low carbon steel welded with guage-12 electrodes

107

5 Micrograph of unwelded medium carbon steel 109

6 Micrograph of medium carbon steel welded with guage-10 electrode

111

7 Micrograph of medium carbon steel welded with guage-12 electrodes

113

8 Micrograph of medium carbon steel welded with stainless steel electrodes

115

xiv

LIST OF TABLES

TABLE

NO. TITLE

PAGE

1 American welding society filler metal specification 24

2 characteristics of mild steel covered electrodes 26

3 Electrodes description and rods characteristics 27

4 Electrodes characteristics and their applications 28

5 Metal transfer types 39

6 Hardness of low carbon steel 78

7 Hardness of medium carbon steel 80

8 Impact strength for low carbon steel 82

9 Impact strength for medium carbon steel 84

10 Result of tensile test for low carbon steel 86

11 Result of tensile test for medium carbon steel 88

12 Compression strength for low carbon steel 90

13 Compression strength for medium carbon steel 91

xv

SYMBOLS

Sn - Tin

Cu - Copper

Ø - Temperature

Fe - Temperature

I - Iron

J - Current

K - Current density

α - Principal stress

P - Load

E - Modules of Elasticity

ρ - Density

xvi

ABBREVIATIONS

ABBREVIATIONS TERMS

LCS = Low carbon steel

MCS = Medium carbon steel

J = Joules

Mm = Millimeters

HRC = Hardness Rockwell Scale (c)

DCRP = Direct current reverse

polarity

DCRP = Direct current straight

polarity

AC = Alternating current

1

INTRODUCTION

1.1 BACKGROUND

Very few machines are fabricated without welding on some

components. To use welding effecting, a designer should have a

basic understanding of various welding process, the weldment and

the designs.

Welding is a process in which two materials usually metals are

permanently joined together through isolated coalescence, resulting

from a suitable combination of temperature, pressure and

metallurgical conditions. It is one of the major ways to fabricate

metal parts. It consists of permanently fastening together of two or

more pieces into a single homogenous part by the application of

pressure or heat. Most widely used types of welding processes are,

arc welding, gas welding and resistance welding. Each of these

processes is similar to each other in that metal parts are joined by

fusion in what is essentially a localized small casting operation. The

work pieces are melted along a common edge or surface so that

molten metal and often filler metals are allowed to form a common

pool or puddle (Benedict, 1987). The weldment is formed by the

permanent joint of the various pieces after the puddle solidifies.

The designer needs to know at least enough about a welding process

to determine if it is the best process to build into a particular design.

There are many instances in which materials have to be joined to

one another as joining is part of the fabrication process for a

complete

2

article. The shape of the finished component may be too complex to

manufacture in one place and several small parts may have to be

assembled and rigidly joined. Alternatively, a component may be too

large in one piece and again several parts may have to be joined

together. The joining process include the use of bolts, screws and

rivets, and also bonding by means of soldering, brazing, welding and

use of adhesive and cement ( Budinski, 1983, Carmichael, 1976, and

Higgins, 1985 ).

Metal may be joined by soldering, brazing, welding and bolts/screws.

In soldering and brazing, the bonding agent is metallic alloy that is

different from the metals being joined, while in wedding, filler

materials are used. Some thermoplastic materials, wood and

ceramic may be bonded using adhesive and cement. In the earliest

form, joining primarily consisted of component parts. Considering

the relative simplicity of the items or component being joined and

the materials constituent from which they were joined, forging was

adequate.

Joining process involves parts produced by other units, processes

and unites them into more complex part, hence it is regarded as a

method of assembly. In an effort to meet the production challenges,

several joining processes have been evolved to include the board

headings such as, welding, adhesive soldering and brazing. A similar

evolution has also been placed with the methods used to power the

various joining machines or tools.

3

Initially, tools were powered by muscles, either human or animals.

However, as the power of water, wind, stream and electricity were

harnessed mankind was able to further extend production capacities

with new machines, greater accuracy and faster production rates

(Benedict, 1987).

Every time, new machines or tools including materials and power

sources are utilized, the efficiency and capabilities have been

expanded with the use of high frequency sound waves and beams of

electrons and coherent light.

A weld arises from a joining method called welding. This process is

only peculiar to materials of metallic composition. Engineering

component, machine parts and machines are usually subjected to

varying loads and stresses. Many components when in service are

loaded, for example the steel component in an automobile axle and

other parts loaded in similar manners.

Therefore, it is necessary to know the characteristics of the materials

and to design the member from which it is made such that any

resulting deformation will not result to fracture. In machines and

tools whose materials are of metal origin, often sections and rods

may be welded before and during assembly.

The welded joint is subjected to either longitudinal or lateral loading.

When the load exceeds the yield strength, there is failure of

4

The joints, hence the need to ascertain the strength of the welded

joint with respect to the selected mechanical properties of metals

such as, tensile strength, hardness, impact, and compression

strengths. The mechanical properties of materials are determined by

performing carefully designed laboratory experiments that

replicates as nearly as possible the service conditions.

Steel is largely used in the manufacture of goods, but their finishing

could be by welding or other means of joining, which is an

engineering process involving the establishment of a metallurgical

bond. The means of achieving joining are resistance, gas, pressure

and arc welding. This research work shall be limited to the use of arc

welding process due to its availability, relative ease of operation, and

its usage of consumable electrodes. In this process, the steel shall be

raised to a high temperature to attain the desired degree of melting.

Steels are innumerable in their classification but this study is limited

to two classes of carbon steels namely: low carbon (0 to 0.3%C) and

medium carbon steel (0.3 to 0.45%C) due to their availability and

wide application in components production. Also given the

diversified kinds of electrodes, the research work shall be limited to

only three classes of electrodes because they are commonly found

and used in workshops, they include; E6013 mild steel electrode (

gauge 10 and gauge 12) and stainless steel electrode, joints shall be

of the butt type.

5

The effect of the different types of electrodes used on the welded

joint in relation to the different types of steels shall be carefully

examined through subjecting the joints to the different mechanical

tests.

1.2 objective of the research

The objectives of this study are to:

i. determine the strength of the welded steel joint,

ii. determine the effect of electrodes types on the mechanical

properties of welded steel,

iii. establish through mechanical tests the performance of an

economically completed weld service, and

iv. determine the appropriate electrode that is best suited for a

particular class of steel.

1.3 SIGNIFICANCE OF THE RESEARCH

The ideal weld is one in which there is complete continuity between

the parts being joined. Every part of the joint is indistinguishable

from the parent metal. Mechanical testing also enables the

investigation for improved properties through phase transfer and

phase transformation, so as to obtain the necessary data for design,

production, quality control and acceptance.

The research is intended to investigate the effect of electrodes on

the mechanical properties of the weld so as to enable the designer

and

6

the production engineer to predict a good and desirable weld even

before it is put to service condition.

1.4 SCOPE OF THE RESEARCH

The area and scope of this research was limited to the materials and

equipment specified which were expected to yield the desired

results.

Practical experiments and tests were carried out in the workshops

and laboratories of the University of Agriculture Makurdi, Civil

Engineering Workshops of the Cross River State University of

Technology, Calabar and the National Metallurgical Development

Centre (NMDC) Jos.

7

2.1 JOINING PROCESSES

Joining processes involves the linking of two or more sections of

materials together for the purpose of performing a desirable

function. The sections to be linked could be of similar or dissimilar

type. There are varieties of joining processes. The Engineer chooses

the most appropriate and familiar joining option from those

available and be able to decide which process is applicable by

weighing the disadvantages and the advantages of each (John,

1980).

Welding traditionally has been emphasized with little attention given

to other joining processes and methods. It has fulfilled more

universal needs and has given more organized pool of information.

However, advancement has been made in other major areas such as,

mechanical fasteners, brazing and soldering (Callister Jr., 1996).

2.1.1 Mechanical

The mechanical joining process also known as mechanical fastening

involves the use of infinite variety of fasteners. One fastening

innovation begets another until it becomes difficult to keep track of

all the types available for the joining operation (Carmichael, 1976).

Mechanical fasteners are classified into five broad categories:

threaded fasteners, rivets, retaining rings, pin fasteners and quick

operating fasteners. Threaded fasteners include screws, bolts, stud,

nuts, and threaded inserts (Paul et al, 1988).

8

Permanent fastening is often done with rivets. Sizes are designated

by the body diameter and range from those for use in bridges to

those for small toys and watches. The forms and proportions of

small and large rivets are standardized and conform to ASA B18.1

and B18.4. There are different rivet heads such as cone head, button

head and countersunk (Paul et al, 1988).

Retaining rings are inexpensive stampings made to fit securely into

grooves, as axial locators on shafts (Parmley, 1977).

Pin fasteners are often used in place of rivets and bolts. The most

common types include groove, tapered, roll, cotter, and grip springs

pins (Parmley, 1977).

Quick operating fasteners or quick released fasteners are specialized

items to operate on or against spring pressure (Carmichael, 1976).

2.1.2 Welding

Welding is one of the major ways to fabricate metal parts. It consists

of permanently fastening together two or more pieces into a single

part by the application of heat, pressure or both (Yankee, 1988).

While there are over 40 separate welding processes, only a relatively

few processes are industrially important. The remaining processes

are used only in specialized fields of application or are rarely used at

all. Welding processes are categorized into three major types viz; arc

welding, gas welding, and resistance welding.

9

The choice of any of the welding methods stated above is a function

of the advantages and disadvantages considered by the design

engineer (Budinski, 1983).

Application of welding methods

Welding is extensively used for joining pressure vessels, heat

exchangers and piping in alloy steels. Pipelines are joined by welding

due their reliabilities.

In railways, welded metal railway vehicles are lighter, stronger and

more resistance to fire and more rugged with running and

maintenance costs.

Modern road vehicles utilize a considerable amount of welding

(various types) for chassis, wheels and body construction and for

assembly of pressed steel components (Davies, 1994).

Welding has been closely associated with the development of the

aircraft industry and the modern aeroplane in particularly

dependent on welding for the production and servicing of the sheet

metal fusing components involved in its construction (Jeffus, 1984).

The repairs and maintenance of parts and engineering equipment,

generally has been simplified by welding which enable broken and

worn out parts to be quickly repaired, very often at a fraction of the

cost of replacement (Jeffus, 1984).

10

2.1.3 Brazing

The term brazing was originally employed to describe the use of a

copper-zinc alloy as a filter material for joining two metal parts

(Higgins, 1980). Brazing includes a group of processes for joining

metal parts by heating them about 500⁰c using a filler metal with

melting temperature below that of the base metal. The filler metal

flows into the joint by capillary action (Higgins, 1980). Brazing is used

where a ductile joint is required, when not only good strength but

also resistance to fatigue and corrosion are demanded. Such joints

withstand higher service temperature than soft soldered joints.

Steel, cast iron, copper, bronze and brass are the alloys commonly

joined by brazing together dissimilar metals. Copper and aluminum

can be joined in this way if an aluminum silicon alloy is used as the

brazing solder (Higgins, 1977).

As with soft soldering, joints can be made singly or in mass

production by using a suitable method of heating work. Often two or

more parts are assembled by pressing, pinning, clamping or spot

welding before a permanent brazed joint is made between them

(Higgins, 1977).

Brazing fluxes: The temperature attained in a brazing process is

much higher than that prevailing during soft soldering. As in the later

process, the presence of even a thin film of oxide prevents proper

bonding between the brazing solder and the work pieces (Higgins,

11

1985). The need for the suitable flux which will not only protect the

metal from oxidation but will also dissolve any existing oxide films on

the surface of the work therefore becomes apparent.

Ordinarily, borax which melts about 750⁰c, producing a mobile

liquid, is probably the most widely used brazing flux. It dissolves the

oxides of the common metals, with the exception of aluminum,

chromium and beryllium (Schwarts 1995, Benedict 1987, and

Beatson and Brooker, 1975).

Advantages of brazing: The advantages of brazing may be

summarized into the following:

i. materials of different thickness can be joined;

ii. brazed joints require little or no finishing;

iii. there is less danger in changing the metallurgical structure than

with fusion welding; and

iv. dissimilar metals can be brazed with a stress free condition

(Higgins, 1977).

2.1.4 Adhesive

Adhesive bonding or joining method started several years ago. The

early man used natural resigns to fasten the head of spears to the

shaft (Skeist, 1990). The Egyptians used glues to fasten veneers to

coffins. Some centuries ago, Isaac Newton wrote in this opticks that

``there are agents in nature able to make the particles of joints stick

together by strong attraction and it is the business of experimental

philosophy to find out” (Skeist, 1990).

12

Protein glues made from iron animal hides, hoof soya beans, have

been replaced by variety of epoxy and polyester resins add natural/

synthetic rubber. The phenomenal growth of adhesive as a bonding

agent has been part of the synthetic polymer explosion. It has been

a standard joining method (Skeist, 1990).

Allen (1988) classified adhesive materials under the following

heading; Natural adhesive examples: animal, vegetative mineral

synthetic, that is thermoplastic rubber, thermoplastic resins and

thermosetting resins.

Advantages of adhesive method: According to (Cagle, 1968 Cagle,

1973, Allen, 1988, and De Lollis, 1970) adhesive joints provide the

following advantages;

i. a good seal against moisture;

ii. good thermal and electrical insulation;

iii. some flexibility of the joint; and

iv. thin, delicate and heat sensitive parts, which heating methods of

joining would distort or destroy, can be bonded.

2.1.4 Soldering

Schwarts (1979) defined soldering as a process that uses nonferrous,

low melting point (under 427⁰c) alloy to join metal components. The

molten solder alloy fill the space between the surfaces with a

strength comparable to that of cohesive force in the solder itself.

The metal surface (of solderable metals) and the tin in the solder

react to form a layer of intermetallic compounds that permanently

wets the surface.

13

Tin-led alloys are the most widely used soldering alloys. They are

compatible with all types of base alloy metals. Since the solder is

drawn by the capillary action, a joint clearance of 0.08mm is usually

recommended.

Soldering processes differ from fusion welding in that there is no

direct melting of the metal parts being joined. The soldering alloy

melts and flows freely over a temperature range below the solidus

temperature of the material, though some solution of the material

alloy may occur. Capillary action causes the soldering alloy to flow

between the two closely adjacent surfaces of the materials (Higgins,

1994 and Stevens, 1990).

Before a metallic can be soldered, it must be `wettable’ (Higgins,

1977). In order for this to occur there must be liquid solubility

between the solder and one of the constituent metals of each

material. The atoms of at least one of the component metals of the

solder may form a solid solution with the metal surface being

soldered, but combination of the two metals from the liquid solution

may result in the formation of an intermetallic compound.

In ordinary tin-lead solders, it is the tin which alloys with the surface

being soldered. Tin forms intermetallic compounds with both iron

and copper, as indicated in the portion of their respective

equilibrium diagrams in figure 1, which represents tin-rich alloys.

14

0

T C

210

220

230

232

240

LIQUIDLIQ +

227

0

0

0

0

LIQ +Cu Sn6 5

0.006%Cu

+ CuSn0 6 5

COPPER % 0.70

IRON % 19.0

200

400

600

T C

Sn + FeSn2

LIQUID496

0

LIQ + FeSn

FeSn+ FeSn2

2320

FIGURE 1: EQUILIBRIUM DIAGRAMS OF TIN COPPER RICHALLOYS AFTER SOLDERING OPERATION(Higgins, 1977)

15

Soldering fluxes:

The following are properties of soldering fluxes:

i. it should be fluid at the soldering temperature and should also

either have a solvent action on the oxide film or combine with it to

form slag;

ii. it must protect the metal surface from re-oxidation; and

iii. it must be of such nature that it can be displaced from the

surface being soldered by molten solder (Mckeown, 1973, Manko,

1968 and Andrew, 1978).

2.2 Welding process

Welding, or more specifically fusion welding, may be defined as a

group of processes in which metals are joined by bringing abutting

surfaces to a molten state. Welding may be performed with or

without the application of pressure and with or without the use of a

filler metal (Davies, 1993). Heat may be provided by an electronic

arc, a gas flame, a chemical reaction or the electrical resistance of

the metals being joined by current passed through the joint.

Welding offers many advantages. It lends flexibility to machine

designs. It facilitates light weight construction and permits the use of

standard rolled shapes. Standard shapes may be rolled or formed

and joined by welding to cut costs through reducing materials,

machining, and finishing (Davies, 1993). As a joining process, it is

used not only

16

For fabrication, but also for the repair and maintenance of broken

and worn parts. It requires relatively low capital investment costs.

Welding processes may be classified into:

i. gas welding;

ii. resistance welding; and

iii. arc welding.

2.2.1 Gas welding

In gas welding processes, the heat necessary to produce fusion

of the metal to be welded is obtained by burning some gas issuing

from the nozzle of a blow pipe or torch. The gas issuing from the

nozzle is already mixed with the appropriate amount of oxygen

required to produce a flame, which may be chemically oxidizing,

neutral or reducing. The chemical nature of the flame can thus be

altered to suite the type of metal or alloy being welded. It remains

an important process for welding steel sheet since the equipment is

relatively cheap (Higgins, 1994).

The oxyacetylene process is quite widely used as an auxiliary tool for

heating metals and for brazing jobs. As with arc welding, the

processes may be autogenous or a filler rod may be used. Automatic

oxyacetylene welding is useful for joining sheet metal components in

which edge joints are involved. The use of a filler rod is then

necessary (Choudhury, 1982).

17

Advantages of gas welding are as follows:

i. it is a very versatile process, (the chemical nature of the flame

can be altered to suite the metal or alloy being welded;

ii. it is used for welding sheet metal, copper-aluminum,

hardsurfacing and bronze;

iii. both oxygen and acetylene can be stored conveniently in

cylinders;

iv. it is used for maintenance and repair works;

v. it is used for brazing, soldering and cutting;

vi. it is used for root run of pipelines; and

vii. equipment is relatively cheap (Agarwel and Manghnani, 1985).

Disadvantages of gas welding are as follows:

i. the filler metal permits oxidization of the weld metal;

ii. there is extension of the heat affected zone; and

iii. there is greater distortion of heat spread because of extension

of heat affected zone (Carmichael, 1976, Higgins, 1994, and Schell,

1997 and 1978).

2.2.2 Resistance welding

In resistance welding, coalescence is produced by the heat obtained

from the resistance offered by the work to the flow of electric

current in a circuit of which the work is a part, and by the application

of pressure (Agarwel and Manghnani, 1985). The parts to be joined

are heated by an electric current which passes through them. With

such a method of heating, temperature can be strictly controlled, so

that

18

Welds with consistent properties can be produced, making the

process very suitable for joining light-gauged materials which are

generally joined fusion welding process (Philips, 1974).

The specific process as review by (Romans and Simons, 1974,

Richard, 1973, Philips, 1968, Higgins, 1994, Jeffus, 1984, Rossi, 1968

and Patton, 1967) are spot welding, projection welding and seam

welding.

Advantages of resistance welding are as follows:

i. heating temperature is easily controlled;

ii. multiple welds can be made;

iii. it is used for mass production;

iv. it is suitable for light-gauge materials;

v. it is widely used than any other pressure welding process; and

vi. formation of cracks and porosity are reduced during re-

crystallization resulting to fine-grain structure in the weld (Richard,

1973 and Jeffus, 1984).

Disadvantages of resistance welding are as follows:

i. only a fraction of the actual heat generated at the joint is used in

raising the metal to welding temperature;

19

ii. much heat is lost by conduction to the adjacent metal and to the

electrodes; and

iii. so much pressure is required to be applied to the electrodes

before the current begins to flow (Jeffus, 1984 and Schwarts, 1979).

2.2.3 Arc welding process

In the electric-arc welding process, the arc is used as the

source of heat, which is transferred to the weld metal partly by

direct radiation and partly the gas or irons in the arc stream (Jeffus,

1984 and Houldcroft, 1967).

Lancaster (1993) defined arc welding as a process whereby the

heat generated by an electric arc is maintained in most cases

between the electrode (rod) and the work piece. The arc furnishes

sufficient heat to melt the base metal in the vicinity of the arc and

usually the electrode. Such metals of welding may be autogenous,

that is, the weld metal is derived from the two work pieces being

joined, but in most cases welds metal supplied from an external

source to the joint.

In arc welding, some of the processes utilize consumable

electrodes which are used to strike an arc on the work pieces, and

which themselves melt to provide the weld metal. Others make use

of non-consumable tungsten electrodes, whereby the weld metal is

obtained from a separate filler rod.

20

The following are some common processes and methods of arc

welding as reviewed by (Higgins, 1994, Patton, 1967 and 1972,

Moses, 1967, Agarwel and Manghnani, 1985, Davies, 1993 and

Giachino et al. 1980).

i. Carbon-arc welding/carbon dioxide shielded;

ii. Submerged arc welding;

iii. Atomic hydrogen welding;

iv. Shielded metal arc welding;

v. Gas metal welding/metal insert gas;

vi. Gas tungsten arc welding/tungsten insert gas;

vii. Plasma arc welding;

viii. Electro slag welding;

ix. Electrogas welding; and

x. Metallic-arc welding.

Advantages of arc welding processes are as follows:

i. It is the most widely used fusion-welding process;

ii. It produces smooth weld surface;

iii. Both alternating and direct current are used;

iv. The weld metal is completely protected from the atmosphere

so that oxidation is at a minimum;

v. The arc is very quiet and there is no discomfort from the glare

or fumes;

vi. The process is widely used for welding low and medium carbon

steels and low-alloy steels;

21

vii. It is applied in fabrication of pressure vessels, boilers and pipes

and in shipbuilding and structural engineering;

viii. The weld produced is autogenous weld metal and is derived

from the two work pieces being joined; and

ix. It is adapted to intermittent process and continuous operation.

Disadvantages of arc welding processes are as follows:

i. The pressure produced by the stream of irons flowing from the

electrode causes a crater to form in the molten metal of the work

piece; and

ii. Very high currents are required for welding operations

(Higgins,1994 and Agrawel and Manghnani,1985).

2.2.4 Metallic arc welding

Metallic-arc welding using manually operated equipment is by

far the most widely used fusion welding process in Nigeria. In this

process the metal electrode, which is used, serves both to carry the

arc and to act as a filler rod, which deposits molten metal into the

joint. The use of a base electrode permits considerable oxidation of

the weld metal and this is not satisfactory when a weld of high

strength is required (Jeffus, 1984).

Consequently coated electrodes are invariably used resulting in

the formation of a layer of slag at the surface of the weld, whilst

combustible materials in the coating generate gases which form a

22

Protective blanket over the metal in the region of the weld. Either

alternating or direct current may be used for metallic arc welding.

When alternating current may be used for metallic arc welding.

When alternating current is used, the arc must re-ignite at each half-

circle as the polarity is reversed. This causes some instability of the

arc, which however can be overcome by the use of arc stabilizing

agents in the flux coating of coated electrodes (Jeffus, 1984 and

Niebel et al, 1989).

2.3 Consideration for selection of a joining process

In selecting a joining process the following factors should be

considered:

i. Strength required: the stronger the joint the higher the load.

ii. Ease of repairs: access to joint and costs of repairs should be

low.

iii. Reliability: the joint should serve without premature failure

iv. Ease of visual inspection: failure of joint should be noticed

by physical observation.

v. Appearance: the joint should be smooth and neat.

2.4 Electrodes

Electrodes are the elements of an arc lamp or furnace between

which an electric arc is struck. Electrodes are filler materials that a

joining engineer should be able to match with the parent material to

avoid failure (Davies, 1993). Electrodes are coated or uncoated. If an

uncoated electrode is used, the weld is surrounded with an

atmosphere containing oxygen and nitrogen and both oxides and

nitrides may

23

therefore form in the weld metal. This causes the impairment of

ductility and impact toughness in the weld. Coated electrodes

overcome the difficulties mentioned above. Coated electrodes

contain both slag forming ingredients such as iron powder, sodium,

cellulose and potassium silicate which produce a fluid coating, over

the weld as is cools, and gas forming materials, which generate an

atmosphere of carbon monoxide, carbon dioxide and hydrogen

around the arc (Higgins, 1994).

The essence of the coated electrode is stabilization of the arc,

which is achieved by including materials which would produce

ionization and consequently may be welded by the metallic arc

process. In welding carbon and low alloy steels the coated

electrodes, usually of low-carbon steel, are used. For welding those

alloy steels, in which martensite is likely to form on cooling, and

which are also prone to the formation of hydrogen forming cellulose

(Higgins, 1977).

2.4.1 American Welding Society (AWS) Specification for Filler

Materials Electrodes

Specification code numbers are given for each group of filler

materials. For example, all mild steel covered electrodes are listed as

A5.1XX.The A5 is used for all filler materials.

The 1 designates mild steel covered electrodes and the XX, when

used is fir the year the specification was last updated.

Table 1.0 shows the AWS filler metal specifications.

24

TABLE 1:AMERICAN WELDING SOCIETY (AWS) FILLER METAL

SPECIFITION

AWS

DESIGNATION

1. Mild steel covered arc welding electrode

A5.1

2. Iron and steel gas welding rods A5.2

3. Aluminum and aluminum alloys arc welding

A5.3

4. Corrosion resisting chromium and chromium nickel,

steel covered arc welding electrodes

A5.4

5. Low alloy steel welding electrode

A5.5

6. Copper and copper alloy arc welding electrodes

A5.6

7. Copper and copper alloy welding rods

A5.7

8. Brazing filler metal A5.8

Source: (Lancaster, 1970)

25

2.4.2 MILD STEEL COVERED ELECTRODES

The AWS classification of mild steel electrodes is printed on the

coating near the bare end of each electrode.

It has a letter followed by four digits, E6010, (Albery, 1975 and

Callister Jr., 1996).

Where

E=electrode

60-minimum tensile strength in 1000 psi (6.89MPa) of deposited

weld metal in the as weld condition.

1-recommended position for specific electrodes to make a

satisfactory weld.

1. All position (flat, horizontal, vertical and over head)

2. Limited to flat position or horizontal fillers only

3. Flat or down head position only.

4. the fourth digit has meaning only in terms of the third. Tables 2, 3

and 4 show characteristics of mild steel covered electrodes,

descriptions and their applications respectively.

26

TABLE 2: CHARACTERISTICS OF MILD STEEL COVERED ELECTRODES

DESIGNATION CURRENT COVERING TYPE

EXX 10 DCRP Only Organic

EXX11 Ac or DCSP Organic

EXX12 Ac or DCSP Rutile

EXX13 Ac or DCSP/RP Rutile

EXX14 Ac or DCSP/RP Rutile,

iron powder

EXX15 DC RP only Low

hydrogen

EXX16 Ac or DCRP Low

hydrogen

EXX18 Ac or DCRP Low

hydrogen,

EXX20 AC OR DCRP/SP Low

hydrogen, iron powder

EXX24 AC or DCSP/RP Rutile, iron, powder

EXX28 AC or DCRP Low hydrogen, iron

powder

Source: (Davies, 1994).

27

TABLES 3: ELECTRONICS DESCRIPTION AND RODS

CHARACTERISTICS

CLASSIFICATION COATING WELD CURRENT

(AWS) POSITION

E60 10 High cellulose All positions DC RP

E60 11 High cellulose All positions AC/DCRP

Potassium

E60 12 High titanium All positions DCSP,

DCRP

E60 13 Rutile and other All positions AC/DC

Easily ionized

Materials

E70 14 Same as E6012 and All positions AC/ DC

E7013 plus iron powder

E70 15 Limestone All positions DC RP

E70 16 Same as E7015 plus All positions AC/DC RP

Potassium, silicate or

Other potassium salts

E70 18 Same as E70 16, plus All positions AC/DC RP

Iron powder 25% to

40% by weight

E60 20 High iron oxide, Horizontal filter AC/DC

Sodium type

E70 24 Same E6012 and Horizontal and flat AC/DC

E6013 PLUS 50% of position fillets

coating weight of iron

powder.

E7027 Same E6020 plus Fillet and

groove weld in

flat and AC/DC

50% by weight of

iron in welds in flat

and Coating. Horizontal positions

Source: (Davies, 1994)

28

TABLE 4: ELECTRODES CHARACTERISTICS AND THEIR APPLICATIONS

CHARACTERISTICS APPLICATIONS

1. Deep penetrating spray type arc, Ship building, bridges, buildings and

Thin friable slag. Similar to those of pressure vessels. Same as those for

E6010 E6010

2. Medium penetration, quiet type where poor fitup exists sheet metal.

Arc, single pass, high speed, shallow

Penetration, excellent radiographic

Quality.

3. Medium rate of deposition, medium Mild steel and low alloy steel.

Penetration similar to the E6012

4. Low hydrogen, moderate penetration High strength high carbon alloy

steels ,

Heavy friable slag high sulphur steels, malleable iron, spring

Steel and blenium and steels

5. High lineal speeds, low penetration High strength high carbon alloy steel

Low splatter, smooth quite arc, and

Globular type transfer.

6. Spray type arc, heavy slag, medium

To high deposition rates, excellent

Radiographic properties Pressure vessel, heavy machine

bases, structural

parts, specialized procedures

7. smooth quiet arc, spatter low fillet welds on low, medium

and high carbon steels,

Penetration, used at high lineal speed. And low alloy steels.

8. Spray type transfer High strength high carbon or alloy

steel

9. Spray type metal transfer, high Heavy section

deposition rates at high lineal speeds,

medium penetration, low spatter losses,

and heavy friable slag.

Sources: (Davies, 1994)

29

2.5 The weld

The term weld is, unfortunately, ambiguous because it is used

in so many ways. Technically, it refers to the area of coalesce

produced by the welding process. In describing a weld, it is helpful to

be to be more specific, and thus the term used here, and the one

most often when a weld is mentioned is a welded joint, which

includes not only the melted or coalesced zone but also the region

around it. Another term often used is weldment. This term normally

means an assembly, large or small, which contains one or more

welded joints (Linnert, 1975).

The welded joint is a composite of all the parts involved in the

welding and comprises the weld metal, the heat affected zone and

the unaffected base metal. The metallurgy of a weld area is

intimately related to the materials as well as the welding process

and procedure. The weld metal, the region which has been melted

during welding, is the first of the three parts. Some welds are

autogenous that is such weld metal is composed of only remelted

base metal and does not contain any filler metal. The second region

of the welded joint, the ``heat affected zone’’ is the part of the base

metal which, because of its proximity to the metal, has been

affected by the heat generated in the welding process. The thermal

cycle of welding normally brings the metal nugget to its melting

temperature, although its condition may be very local, as in a flash

weld, or perhaps may even fall short of full melting, as in an

ultrasonic or a forge weld. Heat affected zones are

30

Often defined by the response of the welded joint to hardness or

etching effect tests. Thus changes in micro-structure, produced by

welding heat, which are seen in etching or in hardness profiles, may

be used to define the heat affected zone with compatible properties.

When the base metals are strengthened by complex heat treatments

or mechanical deformation, it may be difficult to produce completely

compatible weldments.

The production of a sound weld joint requires a thorough

understanding of all metallurgical factors that are involved. From the

control of the chemical composition and heat treatment of the base

metal, through the selection of the proper process and procedure, to

the utilization of the proper filler metal, the welded joints

requirement with the available materials to produce a satisfactory

joint (Lancaster, 1970 and Petershagen, 1993).

31

2.6 Development of a weld in Arc welding

A fusion weld is most readily made when the plate lies in a

horizontal plane and the welding is carried out from the topside. This

process is down hand welding. Quite frequently however, it is

necessary to make the joints when two members are setup vertically

or at a horizontal angle, or it may be required to weld horizontal

plates from the underside. This operation is known as positional

welding (Linnert, 1975).

The formation of a fusion welded joint is a complex process, as

a number of factors are considered in the development of a weld

pool.

The most important of these factors are;

i. the nature of the heat source;

ii. the manner in which the metal is deposited in the weld pool; in

the case of ace welding with consumable electrode;

iii. the type of metal transfer;

iv. the character of heat flow in the joints, which in turn governs

the thermal cycle to which the weld metal and heat affected zone

are subjected;

v. metallurgical reactions in the weld pool, particularly gas-metal

and slag-metal reactions; and

vi. contraction of the weld pool which may cause cracking of hot

short alloys and give rise to residual stress in and near the fused

zone.

32

2.6.1 Heat sources

It will be necessary to review the properties of heat sources

used to generate a molten pool in the welding arc, since the nature

of the melting process can have potent effect on the metallurgical

quality of the welded joint. To be effective, a welding heat source

must emit sufficient heat to maintain a weld pool of the required

size while moving along the joint, and must be sufficiently

concentrated (Lancaster, 1970)

It is desirable for economy to avoid excessive heating of the

surrounding metal, that a high proportion of the heat input be

librated within the area of the weld pool itself.

There are a number of types of heat sources used in fusion

welding out of which the electric arc is the most common (Lancaster

1970).

The welding arc: The electric arc that is used in welding is a high-

current, low-voltage discharge, operating generally in the range 10-

2,000 amperes and at 10-50 volts.

The arc constitutes a mechanism whereby electrons are evaporated

from the cathode, transferred through a region of hot,, ionized gas

to the anode and then condensed.

Structurally the arc may be divided into five parts as follows

(Lancaster, 1970)

33

i. The cathode spot, which is that part of the negative electrode

from which the electrons are emitted;

ii. The cathode drop zone which is the gaseous region

immediately adjacent to the cathode in which a sharp drop of

potential occurs;

iii. The arc column which is the bright visible portion of the arc,

characterized by high temperature and low potential gradient;

iv. The anode drop zone which is the gaseous region immediately

adjacent to the anode in which a further sharp drop of potential

takes place; and

v. The anode spot which is the portion of the positive electrode in

which the electrons are absorbed. The arc appearance and structure

as explained in i-v are shown in figure 2.

34

Potential

Cathode drop zone

ColumnPositive

Anode dropZone

~10 to 15cm-2 3

~10cm-3

(b) Structure

Column+Positive

spot-Cathodeinert

Tungsten

gas

+Anode spot

(a) Appearance

FIGURE 2: ARC APPEARANCE AND STRUCTURE (Lancaster, 1970)

35

Electrical characteristics of the arc: The relationship between the arc

voltage and arc current is known as the arc characteristic (Lancaster,

1970). Figure 3 illustrates the relationship for various welding

processes. In manual welding, irregular changes in the arc length are

inevitable and lead to changes in welding current as shown in figure

3.

36

0 100 200 300 400 500 600 700

10

20

30

40

50

Arc

vol

tage

(vo

lts)

Welding current (AMP)

CoatedElectrodes

AWS type E6010

d.c.submerged arc

Metal Inert Gas Aluminum

Tungsten Inert Gas

FIGURE 3: TYPICAL VOLTAGE-CURRENT CHARACTERISTICS FORVARIOUS PROCESSESS WITH ARC LENGTH 6MM IN EACH CASE (Lancaster, 1970).

37

2.6.2 Metal Transfer

The manner in which liquid is transferred from the consumable

electrode to the weld pool may have an important effect upon the

usefulness of the welding process,. Control of metal transfer, where

this is possible, maybe one means of extending the range of plate

thickness for which a given welding process can be used.

The forces which can cause the transfer of metal from a fusible

electrode are:

i. Surface tension;

ii. Gravity;

iii. Electromagnetic force; and

iv. Hydrodynamic forces due t gas flow.

Surface tension leads to retain in position the drop that forms at the

tip of the electrode.

Gravity is a detaching force, Fg, when the electrodes is pointed

downwards, and retaining force when it is pointed upwards and is

equal to,

Fg=gρv, -----------------------------------------------------------------2.1

Where

g= acceleration due to gravity, m/s₂

ρ= density, km/m3 and

V= Volume of liquid, m3 (Lancaster, 1970).

The electromagnetic force sometimes designated as the Lorentz

force is due to the interactions of the electrode current with its own

magnetic

38

field. For a solid conductor with constant current density, j, across its

section, the magnetic force pre unit area is given as

F=Ij (1-r²)

100 R² -----------------------------------------------2.2

Where

F=Force, (N);

I=Current, (A);

r= radius at any point, (cm); and

R=radius of conductor, cm, (Lancaster, 1970).

In a solid, this force is balanced at energy point by an equal

compressive stress and in a non flowing liquid by an equal pressure

(Lancaster, 1993).

The transfer of metal when welding with coated electrodes is

categorized into two main classes thus; free flight and short

circuiting transfer (Lancaster, 1970). The free flight is sub divided

into three categories- gravitational, projected and propelled transfer

(Lancaster, 1970 and 1993). Table 5 shows the different types of

metal transfer.

39

TABLE 5: METAL TRANSFER TYPES

PROCESS CURRENT ARC TRANSFER

DENSITY LENGTH TYPES

Coated electrode

Iron Oxide Normal Normal Free flight

Coated electrode

Cellulose, Rutile or Normal Normal Short circuiting

basic

Metal Inert gas

(argon or argon Low Long Gravitational

Oxygen shielding) Short Short circuiting

Electrode positive High Normal Projected

Carbon dioxide All Long Repelled

Short Short circuiting

Source: (Lancaster, 1970).

40

2.6.3 Heat flow

Heat flow and its understanding is essential for the proper

appreciation of the heat effect of fusion welding. Heat flow theory

indicate the minimum heat input rate to form a weld of any given

width, and the essential variables which govern the heating rate and

cooling rate in the heat affected zone and in the weld metal (Linnert,

1975). The type of thermal cycle in the weld metal and heat affected

zones has important effect on the properties of certain alloys

particularly hardenable alloy steels.

There are two essentially different types of heat sources used in

welding and cutting metals.They surface and penetrating heat

sources.

Surface heat sources: the surface heat source is the familiar arc or

flame which librates heat over a small area on the metal surface.

Penetrating heat source: the penetrating heat source develops heat

at such an intensity to evaporate or otherwise remove metal below

the point of application and thus penetrate it. Such sources are used

primarily for cutting.

The surface heat source which of course is the normal; type of

welding heat source, in spot welding is stationary.

In most fusion welding a continuous moving source of heat with

a special characteristic is used.

Once steady conditions have been achieved, the temperature

distribution relative to the heat source is stationary.

41

The equation for the conduction of heat in a homogenous isotropic

solid in terms of rectangular co-ordinates (X, y, z) is

∂²T/dx²+∂²T/dy²+∂²T/dz²-(1/α) (dT/dt )=0 ………………………………..2.3

Where

T=temperature in excess of the initial temperature of the solid (For

welding this is for room temperature or, when the metal is pre

heated, the preheat temperature);

t= time; and

α= thermal diffusivity (thermal conductivity k divided by the product

of specific heat c and density (ρ) of the solids (Lancaster, 1993).

The solutions of equation 2.3 are appropriate to fusion welding arc,

which have been obtained using the mathematical concept of heat

source, that is, a point line or plane, which emits heat. The heat may

be librated instantaneously from an instantaneous source, of at a

steady rate from a continuous source. The fundamental solution is

that the temperature distribution in a body of infinite extent after a

quantity of heat, Q, has been librated instantaneously at a point, is

here assumed to be the origin. The temperature in excess above

surrounding is reduced to temperature distributed in the parent

material during welding and is given by (Lancaster, 1970) as:

Q

___________ e-r ²/⁴αt ……………………………………2.4

T= 8ρc (παt)³/²

Where r²=x²+y²+z²,

42

Q= total quantity of heat librated,

Ρ=density,

C=specific heat, and

α=k/ρc=thermal diffusivity.

r= (x²+y²+z²)½

T=Temperature in excess above surroundings

t= time

k=modified Bessel function of the same kind of zero order

z= distance from source at right angles to plate

x= distance from source along line of travel (positive in wake of

source).

2.6.4 The Weld Metal

Gas-metal reactions: the first, and in some cases the most

important, metallurgical changes which take place as a result of the

formation of a weld pool is the absorption of gas from the arc or

flame atmosphere and its subsequent reaction with the liquid metal

and with other gases therein. This is common in arc welding, in

which both gas and metal temperatures are high compared with

other melting processes. The gas-metal interaction may take the

form of exothermic or endothermic reaction to form a stable

chemical compound (Lancaster, 1970).

43

An endothermic solution does not inhibit fusion but can result in

porosity, either due to super saturation of the weld pool with a

particular gas, or by reaction between two gases.

It may also in a special case result in embrittlement of the heat

affected zone. The mechanism of the endothermic solution is of

particular importance in welding and can be discussed under

absorption, reaction and evolution (Lancaster, 1993).

2.7 Weld pool solidification and contraction

The macrostructure of the weld is determined by the welding

speed and by the shape and size of the weld pool. The crystal axes

are a quarter circles that terminate along the center line of the weld.

More commonly, the weld pool is elongated and with higher welding

speeds, kite shaped, when the crystal are almost straight sided

(Figure 4).

44

Low Speed

High Speed

FIGURE 4: WELD MACROSTRUCTURE AS AFUNCTIONOF WELD POOL SHAPE (Lancaster, 1970).

45

The larger the weld pool, the coarser the grains. Grains re

finement may be achieved in certain cases by suitable additives,

such as titanium in the case of aluminum and its alloys.

A significant amount of grain coarsening also occurs in the heat

affected zone of welds resulting from processes that give low cooling

rates, particularly electro slag and oxy-acetylene welding (Lancaster,

1993).

2.8 Weld cracking

The contraction of a weld during sets up tensile stresses in the

joints resulting to cracking which is one of the most serious weld

defects. Cracking may occur in the deposit, in the heat affected zone,

or in both regions. It is either of gross type, which is visible to the

naked eye-macro cracking or micro fissuring (Lancaster, 1970).

2.8.1 Measurement of crack sensitivity

Tests for determining the susceptibility of a material to weld

cracking are numerous. They may be divided into two main classes.

Tensile tests carried out at the known cracking temperature in order

to determine strength and ductility, and welding tests which are

made with the object of measuring the amount of cracking as a

function of welding variables (Lancaster, 1994).

46

2.9 Ductility and uniformity of the weld Deposit

In most instances filler metal is added to fusion-weld joints and

the weld deposit therefore consist of a mixture of parent metal and

filler metal. When parent metal and filler metal have the same

composition, it is of no consequence, but where they differ,, suitable

measure must be taken to ensure that the completed weld has the

desired composition (Raghavan, 1990).

The degree of the dilution depends on the type of joint, the

edge preparation and the process used.

Dilution (expressed as a percentage) may be defined as:

Weight of parent metal melted

D= __________________________

Total weight of fused metal -----------------2.5

Dilution is of particular importance in the case of dissimilar metal

joints and in the welding of clad materials. In most metals and alloys,

the boundary between the fusion zone and the unmelted part of a

welded joint is quite sharp (Lancaster, 1993).

2.10 Weld Quality and Weldability

2.10.1 Weld quality

Fusion welding is a melting process and must be controlled

accordingly. Unwanted reactions with the atmosphere are

prevented by sealing of the melt zone with a vacuum, a protective

(inert) atmosphere, or a slag (which is chosen and is, therefore called

a flux) (Giachino et al, 1980). Surface films, especially ones that could

47

prevent bonding or would lead to gas porosity,, are kept out by

chemical or mechanical preparation of the surfaces.

The properties of a pure metal can be improved only by strain

hardening, induced by hammering (peening) or rolling of the weld

bead. Welds in solid-solution alloy show the effects of non

equilibrium solidification. Coring in itself is harmless but a low

melting grain boundary eutectic could result in cracking the joint on

cooling (hot shortness). While intermetallic compounds would make

the compound brittle, preheating minimizes internal stresses, but

even then, it may be necessary to use a low alloy, more ductile filler

materials that reduce hot shortness. Residual stresses and their

harmful effects can be reduced at the same time, more

homogenous structure can be obtained by ``post welding stress-

relief heat treatment or even homogenization of the entire welded

structure (Agarwel and Manghnani, 1985).

2.10.2 Weldability

Weldability donates an extremely complex collection of

technological properties. These properties are melting temperature,

thermal conductivity, thermal expansion and metallurgical

transformation.

Melting temperature determines, together with specific heat and

latent heat fusion, requisite heat input.

48

High thermal conductivity allows the heat to dissipate and therefore

requires a high rate of inputs and leads to more rapid cooling.

High thermal expansion results in grater extortion, residual

stresses, and greater danger of cracking in a hot-short material.

Surface contaminants include oxides, oils, dirt, paints, metal plating

and coatings incompatible with the workpiece materials,

atmospheric contaminants etc all militate against the success of

welding as do gas forming reactions (Elnar and Ramstand, 1994).

Metallurgical transformations are of great importance,

especially if they results to brittle phases such as martensite. The

absolute and relative thickness of part to be joined and the design of

the joint have a decisive influence on heating, cooling and thus on

weldability.

Weldability of an alloy is its capability to undergo welding without

cracking or serious embrittlement.

In weld repairs, stresses are generated which can cause cracking,

distortion and reduction in strength. Stresses originate in different

expansion and contraction produced by excessive and intensive local

heating. Residual stress can be minimized by preheating either of the

entire weld or the heat affected zone only (Koenigsberger and Adair,

1968).

49

2.11 Some Mechanical Properties of Materials and Their Tests

The mechanical properties of materials relate to its response

when it is loaded or deformed. That is, when it is subjected to stress

or strain. The load may be constant in magnitude or fluctuating

continuously, and be applied for a fraction of a second or many

years (Vanvlack, 1982).

The mechanical properties of materials are ascertained by

performing carefully designed laboratory experiments that replicate

as nearly as possible the service conditions.

Factors to be considered include the nature of the applied load

and its duration, as well as load to be tensile, compressive, or shear,

and its magnitude may be constant with time, or it may fluctuate

continuously.

Materials are frequently chosen for structural applications

because they have desirable combinations of mechanical

characteristics (Callister Jr., 1996). These materials are also tested to

ascertain how they will perform their designed functions while in

service. The test could either be destructive or non destructive.

2.11.1 Tensile Strength

Most structures are designed to ensure that only elastic

deformation will result when a stress is applied. It is therefore

desirable to know the stress level at which the plastic deformation

begins or where the phenomenon of yielding occurs.

50

For metals, the point of yield may be determined at the initial

departure from linearity of the stress-strain curve.

Afire yielding, the stress necessary to continue plastic

deformation in metals increases to a maximum point, Min figure 5

and then decreases to eventual fracture point, F.

The tensile strength, TS (Mpa), is the stress at the maximum point in

the engineering stress-strain curve.

This corresponds to the maximum stress that can be applied and

maintained before fracture will result (Callister Jr., 1996).

51

Stress(o)

Strain(E)

MF

FIGURE 5: TYPICAL ENGINEERING STRESS - STRAIN

BEHAVIOUR TO FRACTURE (Charles and Crane, 1992)

52

2.11.2 TENSILE TEST

Tensile test is carried out in engineering materials to determine

the maximum strength (tensile) that the material will withstand

before fracturing.

Tensile testing machine (screw type) is used for either tension or

compression testing. The stress on the test piece is produced

through the movement of platforms by screws, which, depending on

the direction of turning, will either separate the platforms or draw

them towards each other. A compound lever system transmits the

platform force to a weighing beam kept in balance by moving the

poise.

Tensile testing machine (hydraulic type) is a direct acting

hydraulic tensile testing machine and has a head moved by hydraulic

pressure, intensity of which is read on a pressure gauge. The load on

the test piece is determined by multiplying the pressure reading by a

constant which depends on the area of cylinder (Wyatt, 1974).

2.11.3 Hardness

Hardness is a property which is not uniquely defined. Several

tests which claim to measure hardness are actually different

properties.

It is a measure of a material’s resistance to localized plastic

deformation (example, small dent or scratch).

The relative hardness of materials is obtained from different

textbooks on materials science and engineering (Shackelford, 1985).

53

2.11.4 Hardness Test

A hardness test is usually performed by pressing an indenter

into the surface of a specimen under the application of a known

load. The indenter is usually of a fixed and known geometry and the

load is applied to the specimen either directly or by way of a system

of levers.

The indentation produced in the surface of the specimen is

measured and either partial or the complete load has been

removed.

Thus elastic recovery is permitted, it should be known that

measurement of the indentation does not represent its actual size

under the applied load, but a measurement of the recovered

indentation.

Depending on the type of test employed, the hardness value is

expressed by a number, which is either proportional to the depth of

indentation for specific load or indenter or proportional to a mean

load over the area of indentation. For testing hard materials, a

diamond indenter is preferred, because it does not deform.

These are principally three different testing machines used in

testing for materials hardness. They are;

i. Brinell hardness;

ii. Rockwell hardness; and

iii Vickers pyramid hardness testing machines

Brinell hardness testing machine: This machine normally consists of

a hard operated hydraulic press which has been designed to force a

small hardened steel ball into the surface of the specimen under a

predetermined load. The diameter of the impression produced is

54

measured by using a microscope containing an ocular scale, which is

usually graduated in tenths of a millimeter.

The reading obtained from the test is converted to a Brinell

hardness number (BHN), which is the ratio of the load, in kilogram to

the area of impression in square millimeters (Callister Jr., 1996). That

is,

BHN = P

__________________ ------------------------------2.6

(πD/2[D-√D²-d²])

Where P= load applied in kilogram

D=the diameter of the ball in (mm); and

D= the diameter of impression in (mm)

Rockwell hardness testing machine: In the standard Rockwell test

the specimen is placed on surface uppermost on an anvil which is

slowly raised by a hand wheel until the surface of the specimen just

touches an intender.

The relevant number is read directly on the dial indicator,

having been derived from the measurement of the depth of the

impression by the formula,

HR= E-e ---------------------------------2.7

Where

e is the difference between the depth of penetration before and

after

55

The application of the major load. E is an arbitrary constant and HR is

an abbreviation for Rockwell hardness (Callister Jr., 1996).

Rockwell number is quoted with the range of load, that is Rc

and RB where C and B are the scales which is obtained from the dial

or scale on the machine during test.

The loads used in the Rockwell are in the range of;

A = 60 - 80kgf;

B = 100kgf; and

C = 150kgf and above.

Vickers Pyramid Hardness Testing Machine: The Vickers pyramid

hardness testing machine for measuring the hardness of all types of

materials, from thin sheet to very large section of metal or complete

components. The specimen should be placed on a table of the

machine, which may be raised by way of a hand-wheel, until the

surface of the specimen is just clear of the point of the indenter.

The impression on the surface of the specimen is measured by

either (a) swinging a microscope over, the specimen is measured

across the diagonal corners of the square impression, or (b) the

machine may be equipped with a sliding table, which may be moved

sideways into position under the microscope. The impression

produced by the indenter in the surface of the specimen may then

be observed through the microscope (Carmichael, 1976).

56

2.11.5 Fatigue Strength

The load on many structural components varies repeatedly

and this can lead to fracture, although the maximum yield stress is

less than the tensile strength and even below the nominal yield

stress. This type of failure is known as fatigue failure, it occurs in all

classes of materials except glasses and is easily the most common

cause of failure in engineering components while in service.

Fatigue strength is the resistance of a material to frequent

application or fluctuation of a load cycle. It may be specified as an

endurance limit or a fatigue relative to a specific kind of load cycle,

which could be any variety of combination of tension, compression

and shear (Charles and Crane, 1992).

The endurance is the number of cycles to failure under a

specified stress cycle at a specified stress level while the endurance

level limit is the maximum stress intensity as shown in figure 6.

57

0

S

0

S

Y

X

(a) (b)

NNo Failure

No. of cycle of stress

Range ofMaximumintensity of stresscycle

(a) Typical S/N curve ox = endurance limit for Y cycles below OY

(b) Fatigue limit. No. of failures F

FIGURE 6: GRAPHICAL RECORDING OF FATIGUE PROPERTIES(Charles and Crane, 1992)

58

2.11.6 Fatigue Test

In many types of service application, parts are required to

withstand repeated or cycle stressing. Such moving parts of

machinery are shafts, connecting rods, gears and contacts are tested

for fatigue materials that are subjected to repeated alternating

stresses may fail under considerably lower load than normal through

a process known as fatigue.

The Haigh machine is one of the commonest fatigue testing

machines. The machine is operated electro-magnetically; two

electromagnets are supplied with an alternating current. This

produces an alternating force on armature, supported between two

magnets, which is transmitted to the lower end of the specimen. The

upper end of the specimen is held in a “head” which is bolted to the

main frame of the machine.

The load is measured by the voltage which is reduced by the

secondary coils of the armatures, and the voltage reading is

calibrated by making a comparison with a measured deflection of a

weight bar, which is substituted in place of the test specimen (Paul

et al, 1988).

2.11.7 Toughness

Toughness is measured in terms of the amount of energy

required to fracture a standard test piece. Specimen geometry as

well as the manner of load application is important in toughness

determination.

59

In static situations, toughness may be ascertained from the result of

a tensile stress-strain test.

For a material to be tough, it must display both strength and

ductility and often ductile materials are tougher than brittle ones

(Benham and Crawford, 1988).

2.11.8 Impact Test

Since toughness of a material is measured in terms of the

amount of energy absorbed while in service. Impact testing

machines are used to test for toughness properties as discussed

below. Impact forces which occur from load which are transient with

time. The duration of the load application is of the same magnitude

as the natural period of variation of the specimen (Zbiguiew, 1977).

Izod machine: The Izod machine is used for testing a notched

specimen for energy absorption, the specimen is supported at its

lower end in a vertical position as a cantilever. The pendulum strikes

the specimen at a definite distance above the notch on the same

side of the notch. The energy used in breaking the specimen is the

product of the weight of the pendulum and the difference in its

height is expressed in kilogram/meter known as Izod value

(Zbiguiew, 1977).

Charpy pendulum machine: This machine is used for testing small

notched specimen for energy absorption. The specimen is placed

horizontally with the ends supported by an anvil. The hammer

strikes the specimen midway between the supports opposite the

notch. The energy expended in fracturing the specimen is the

product of the

60

Weight of the pendulum and the difference between its height of

fall and height of rise. The energy is expressed in kilogram/meter

(Charles and Crane, 1992).

2.11.9 Creep strength

It is the resistance of a material to conditions (usually at

elevated temperature) in which a steady load is strain likely to

induce continually increasing with time of application. It is said to be

the stress required to give a maximum tolerable total amount of

strain after a separate time at a specific temperature.

Creep is a time dependent strain, which sometimes follows the

instantaneous strain obtained on stressing a material (Seaward,

1998).

2.11.10 Creep Test

The creep test investigates metals bonded at elevated

temperatures. If a load is applied to a metal at various temperatures,

and is retained for a long period of time, the metal may show

evidence of having undergone gradual extension.

This phenomenon is known as creep, and by this process a

metal or component in service may fail under a particular stress

which is well below its ultimate tensile stress. The specimen used in

the creep test is similar to the tensile test specimen, but usually with

a much greater gauge length.

61

Measurement of the extension of the specimen may be made

by using extensometer of the optical type, which allows very

accurate measurements. This is done after the specimen has been

subjected to the appropriate temperatures (Higgins, 1985).

2.11.11 Ductility

(Paul et al, 1988) explains ductility as a desirable property of a

material to be used in engineering structure, for which the stress

level is predominantly in elastic stress concentration to flow

plastically rather than fracture. Ductility may be expressed

quantitatively as either percent elongation or percent area

reduction. The percent elongation %EL is the percentage of plastic

strain at fracture,

Or

Lf-Lo

% EL = __________ Х100 …………………. 2.8

Lo

Where, Lf is the fracture length and Lo is the original gauge length

(Callister Jr., 1996).

2.11.12 Torsion test

Torsion test is usually used for quality tests on metals for such

components as axles, shafts, twist, drills and on materials at elevated

temperatures to determine forgeability. The machine used to apply

the load consists basically of a rotating head, to which is attached

one end of the specimen gripped in a suitable chuck supplies the

necessary twisting motion by way of an electric motor. The other

end

62

of the specimen is also gripped in chuck, which has provisions for

carrying weights and for measuring the applied torque.

The angle of twist is measured directly on the turning head of

the machine. The angle through which the specimen twists is

recorded for each increment of torque until rupture occurs (Callister

Jr., 1996).

2.11.13 The simple bend test

The simple bend test may be performed on wire, tube of sheet to

determine ductility. The test usually consists of recording the

number of reverse bends thee metal will endure before fracturing

(Gourd, 1982).

2.11.14 Compression test

The compression test is not carried out as frequently as the

tensile test, but it still has a place in engineering service, since

compression properties of metals cannot always be deduced

accurately from a tensile test.

Therefore tensile testing machines usually have provisions for

suitable attachments to enable materials to be subjected to

compression loads (Zbiguiew, 1977).

2.12 Non Destructive Testing

Non destructive testing is descriptive of test and inspection

methods which, when applied to materials for purposes of detecting

mechanical defects, variations in metallurgical conditions, or

63

Compositions do not impair the usefulness of the materials or part

(Meyer and Selvadurai, 1996).

The following are some of the common types of nondestructive

tests as reviewed by (Hamer and George, 1964, Choudhury, 1982,

Foresten and Aaltio, 1982, Ormandy 1978, Paul and Adams, 1981,

and Carmichael, 1976).

i. Magnetic test;

ii. Fluorescent test;

iii. X-ray test;

iv. Ultra-sonic test; and

v. Deep penetrate test.

2.13 Engineering materials

In designing a machine member, the selection of materials and

the manufacturing process by which the part to be made should be

considered together. Based on the above assertion the mechanical

designer should be familiar with such inter dependent factor as the

adaptability of materials to the various processes, the effect of the

processes on the properties of materials, and the design details

involved in the process (Sundrarayamorthy, 1983 and Ullman, 1997).

The common materials, of which machine parts are made from

in engineering practice include cast iron, malleable iron, wrought

iron, wrought steel, brass and bronze, aluminum and aluminum

alloys,

64

Carbon steels, rubber and non metallic metals. These materials are

reviewed by (Choudhury, 1982 smith, 1990,Paul et al Jr., 1998,

Shackelford,1981, Oriovi, 1986, Paul and Adams, 1981, and Ashby

and Jones, 1986 ).

2.14 The Structure of Metals

The most important aspect of engineering material is its

structure, because its properties are closely related to their features.

Metallography is the study of the material structure in relation

to their properties (Reed-Hill, 1973). Metals are crystalline when in

solid form and are therefore polycrystalline. The crystals in these

materials are normally referred to as its grains. Because of their

small sizes, an optical microscope, operating at magnifications

between about 100 and 1000 times is usually required in other to

examine the structural features associated with the grains in a metal

(Reed-Hill, 1973).

Structure requiring this range of magnification for their examination

falls into the class known as microstructures. Others that have very

large crystals that are discernible to the naked eye or are easily

resolved under a low-power microscope are known as

microstructure (Reed-Hill, 1973). While the basic structure inside the

grains themselves, that is, the atomic arrangements inside the

crystal is called the crystal structure. The first stage in Metallography

is the production of a true undistorted structure on the surface of

the specimen to be examined. This usually involves mechanical or

65

electrolytic polishing, the principles of which are sufficiently

understood for reliable results to be obtained followed by etching

which is still very much a matter of using recipes (Gifkins, 1970).

The structure of the specimen or specimens will sometimes

have been developed on a previously polished surface by

deformation, or it may be the result of damage to a machine part, in

such cases the art is more in perseveration than in preparation of

the specimen (Gifkins, 1970). The majority of specimens require

examination of a magnified image of their structure before much

useful information about them can be obtained, and this generally

requires the use of a microscope (Higgins, 1994).

2.15 Summary of Findings

The literature available for this work revealed that much work

has been carried out on different joining processes and methods,

with less emphasis on the classes of steels in relation to their carbon

contents and how the mechanical properties are affected when the

joints are produced with certain categories of electrodes, hence the

need for further work to define the effect of electrodes on the

mechanical properties of welded steels.

66

MATERIALS AND METHODS

3.1 MATERIALS: The following materials were used in carrying out

the research work.

* Carbon steel (low and medium carbon steel)

* Electrodes (E6013-gauge 10, gauge 12) electrodes and stainless

steel electrodes.

* Metallic arc welding machine

* Extensometer

* Meter rule

* Venier caliper

* Lathe machine

* Grinding machine

* Izod testing machine

* Rockwell testing machine.

* Metallographic microscope

* Nital etchant

3.2 SPECIMEN PREPARATION AND TEST METHOD

3.2.1 Hardness Test

Preparation of specimen: Eight (8) pieces (Ø14.0Х120mm) each of

low and medium carbon steel were measured and cut. 6 pieces each

were then cut into 60mm and welded back with mild steel electrode

(E6013-gauge 10 and gauge 12) and stainless steel electrodes

respectively.

67

The joints of specimen were then properly ground to obtain a

smooth surface. Two (2) pieces each were tested without joint. A

total of 16 specimens of medium carbon steels were therefore

tested.

3.2.2 Test method

The testing equipment used was the Rockwell testing machine.

The specimen was placed with the surface on the anvil, which was

slowly raised by turning the hand wheel until the specimen touched

the intender.

The numbers were read directly from the dial indicator and

converted to the Rockwell number as shown in tables6 and 7.

3.3 IMPACT TEST

3.3.1 Specimen preparation

Eight (8) pieces (Ø14.0Х75m 35*m) each of low and medium

carbon steel were measured and cut. There were taken to a vice

where the v-shaped notch of 45⁰ was made as shown in figure 7.

Six (6) pieces of the notched specimen were then cut at the v-

notched point and welded back preparatory to testing. The joints

were made back using mild steel (E6013-gauge-10, gauge-12)

electrode and stainless steel electrode. The specimens were then

notched and ground to the appropriate shape.

68

0.25mm radiu s

450

8mm

75mm

14.0mm

22mm

28mm

strikingedge

FIGURE 7: STANDARD SPECIMEN FOR IZOD TEST FOR IMPACT PROPERTY

69

3.3.2 Test method

The specimen was clamped in a horizontal position with the

center of the notch in line with the upper face of the jaws. The load

weighed in the pendulum was raised from the test position and

allowed to strike the notched specimen held in the vice. The energy

absorbed to fracture the specimen was read and recorded from the

scale as indicated in Tables 8 and 9.

3.3 TENSILE TEST

3.3.1 Specimen preparation

Eight (8) pieces (Ø14.0Х165mm) each of low and medium

carbon steel were measured and cut. The pieces were taken to the

lathe machine and turned to the desired shape as shown in Figure 8.

6 pieces each of the turned pieces were cut to (82.5mm) and welded

back with mild steel electrode (E6013-gauge-10 and gauge-12) and

stainless steel electrode respectively.

The joints of each specimen were properly cleaned by grinding

obtain a smooth surface. Two (2) pieces each of the remaining

specimen were tested without joints.

70

FIGURE 8: STANDARD TENSILE SPECIMEN WITH

CIRCULAR CROSS SECTION

Reduced section

Guage length2"

21/4"

3/8" radius

1/4" diameter

71

3.4.2 Test Method

The tensile testing machine used in this test was the

extensometer. The extensometer was the hydraulic type. The

specimen was mounted on the head and the other side of the jaws.

The head was moved by hydraulic pressure. The intensity of the

hydraulic pressure was read on the pressure gauge. The load on the

test piece was then determined by multiplying the pressure reading

by the constant, which depends upon the area of the hydraulic

cylinder. The procedure was repeated on all the specimens and the

results were recorded as shown in Tables 10 and 11.

3.5 COMPRESSION TEST

3.5.1 Specimen preparation

Eight (8) pieces (Ø14.0Х25mm) each of low and medium carbon

steel were measured and cut.

6 pieces each were then cut into 12.5mm and welded back with

mild steel electrode (E6013-gauge-10 and gauge-12) stainless steel

electrode respectively. Figure 9 shows the compression test

specimen.

The joints of each specimen were properly ground to obtain a

smooth surface. The remaining two pieces were tested without

joints.

72

FIGURE 9: SPECIMEN FOR COMPRESSION TEST

250mm

14.0mm

73

3.5.2 Test Method

The compression test was carried out using the extensometer.

The different between the tensile test and the compression test

using same equipment for the test is in their method of loading

platform and hydraulic pressure was loaded from the top side of the

specimen. The reading was made from the pressure gauge and

converted to the different values as shown in tables 12 and 13.

3.6 Preparation of Specimens for Micrographs

3.6.1 Specimen preparation

Four (4) pieces of low and medium carbon steel welded with

electrodes gauge 10, 12 and stainless steel electrode respectively

were used in preparing the specimens, one (1) piece of the four

pieces of medium carbon steel were unwelded.

The eight specimens were then subjected to the same

procedure of preparation. The preparation was carried out in the

following steps:

Each of the specimens was put into a plastic disc with a simple

ring mold and liquid epoxy resin poured into the mold to fill it. The

epoxy hardens and makes it possible and convenient for holding the

specimens during the subsequent steps in surface preparation. They

were four basic steps for the operations, thus; fine grinding, rough

polishing, and final polishing and etching.

74

(i) Fine Grinding: In this step three grades of abrasive were used

they include 320 grit, 400 grit, and 600 grit with the corresponding

particle sizes of the silicon carbide of 33, 23, and 17 microns

respectively where one micron is 10-4cm.

In each of these fine grinding stages the specimens were moved over

the surface so that the scratches are formed in only one direction.

Grinding continued until the scratches from the preceding stages

disappeared.

(ii) Rough Polishing: At this stage the abrasive used for the rough

polishing operation was powdered diamond dust of about 6 microns.

This was placed on a nylon cloth covered surface of a rotating

polishing wheel. The specimens were pressed against the cloth of

the rotating wheel with considerable pressure. The specimens were

moved around the wheel in the direction opposite the rotation of

the wheel itself. This ensured a more uniformed polishing action.

The 6 micron diamond powder was used to facilitate the removal of

effects resulting from the silicon carbide abrasive.

(iii) Final Polishing: Here the fine scratches and very thin distorted

layers remaining from the rough polishing stage were removed. The

polishing compound used was alumina (Al₂O3) powder (gamma

form), with a particle size of 0.05 microns. This was also placed on a

cloth covered wheel, and distilled water was used as lubricant. After

this

75

Steps were successfully carried out, a scratch free with no detectable

layer of undistorted metal was obtained.

(iv) Etching: Etching was done on the specimens to make grain

boundaries to be visible for microscopic magnification to be

possible. The specimens of both low and medium carbon steels were

etched in natal (2% solution of nitric acid and alcohol). The polished

surfaces of each specimen was immersed in the etching solution for

30 seconds and removed. These procedural operations were

repeated in all the eight specimens.

3.6.2 Microscopy

The microscope that was used here was the table size

metallographic microscope. The specimens were successively placed

on the rotating stage of the metallographic microscope and the

image of the specimens captured at a magnification of 100 times.

The plates were then developed and printed as shown in plates 1-8

and labeled according to the electrodes used in preparing the joints.

3.7 SUMMARY OF SPECIMENS PREPARATION

Specimen’s preparation and test were carried out under the

following conditions:

* Welding current for E6013 (Ø250Х350, gauge 12 electrode) was

80-90 amperes

76

* Welding current for E6013 (Ø3.25Х350, gauge 10 electrode)

was 100-200 amperes.

* Welding current for stainless steel electrode was 240-260

amperes.

* All the joints produced were butt joints.

* The welding position was- flat

* The cooling mode was air cool.

* The metallic arc welding machine was used for the welding.

77

RESULTS

4.1 INTRODUCTION

This chapter deals with analysis of data collected from the

different mechanical tests that were carried out. They include;

hardness test, impact test, tensile and compression test the data are

presented as shown in Tables 6 to 13.

4.2 HARDNESS TEST

With the use of low and medium carbon steels and gauge-10, gauge-

12 and stainless steel electrodes, butt joints were produced as

specimens and tested.

The results were entered in the tables below.

Table six shows the average n hardness values of the low carbon as

unwelded region 56.72HRC, welding region with gauge-10 electrode

56. 80 HRC and welded region with gauge-12 electrode 55.86 HRC

and welding region with stainless steel electrode 58.34 HRC. This

test was performed on various parts of the welded carbon steel.

78

TABLE 6: HARDNESS OF LOW CARBON STEEL

S/N Specimens/ dimension I ii iii iv v

Average

1 LCS with unwelded 60 55.30 57.50 54.80

56.00 56.72

Region (HRC) 14.0

2 LCS with welded

Region (gauge 10

Electrode(HRC)14.0 58.80 57.00 54.00

56.20 58.00 56.80

3 LCS with welded

Region (gauge12

Electrode(HRC)14.0 55.60 55.20 54.00 56.60

58.00 55.86

4 LCS with welded

Region(stainless 59.20 56.50 58.00 56.00

62.00 58.34

Steel electrode)

(HRC)

14.0 represents diameter of specimen in mm

79

Table 7 shows the average hardness values of the medium carbon

steel as unwelded region 56.08 HRC, welded region with gauge -10

electrode 56.28 HRC, welded region with gauge-12 electrode 56.26

HRC and welded region with stainless steel electrode 57.56 HRC.

These tests were performed in the various parts of the welded

medium carbon steel specimens.

80

TABLE 7: HARDNESS OF MEDIUM CARBON STEEL

S/N Specimen i ii iii iv v

Average

1 MCS with

unwelded

region (HRC) 57.00 55.00 54.00

57.00 56.80 56.08

14.0

2 MCS with

welded region

gauge 10

electrode (HRC)

14.0 57.20 58.00 56.00 55.2

60.00 56.28

3 MCS with

welded region

gauge 10

electrode 53.50 57.00 57.20 55.50

57.50 56.26

(HRC) 14.0

4 MCS with

welded region

using stainless

steel electrode 58.80 58.20 55.5 56.80

58.50 57.56

14.0

14.0 represents diameter of specimen in mm

81

4.2 Impact test

The test specimens were prepared carefully using low carbon

and medium carbon steels, and gauge-10 gauge-12 and stainless

steel electrodes. Butt welds were then made after the v-notch were

produced on each specimen and were all tested. The results were

recorded in the tables below.

Each electrode was used to prepare two specimens and tested

for impact, the average value was recorded in table 8. The

discrepancy between gauge-10 and gauge-12 electrodes with

respect to their values in Table 8 is that the gauge-12 electrode has

increased the ductibility of the specimen produced with low carbon

steel.

This is as a result of the presence of a smaller quantity of

electrode materials compared to those of the gauge-10.

The electrodes materials include cellulose, high titanium

potassium and rutile.

The results show the maximum energies that were absorbed by

the low carbon steel specimens before fracture occurred. There

include: unwelded region with gauge-12 electrode 52.9] and welded

region with stainless steel electrode is 28.8J. These tests were not

repeated on each specimen because each of the energies recorded

fractured the specimen to failure.

82

TABLE 8: IMPACT STRENGTH FOR LOW CARBON STEEL

Energy Absorbed (J)

S/N Specimens i ii Average

1 LCS with unwelded 27.0 27.8

27.4

Region 14.0

2 LCS with welded

Region using gauge-10 29.0 29.6

27.3

Electrode 14.0

3 LCS with welded

Region using gauge-12 52.0 53.8

52.9

electrode 14.0

4 LCS with welded

Region using stainless 29.0 28.5

28.8

Steel electrodes 14.0

14.0 represents diameter of specimen in mm

83

Table 9 shows the average impact values of medium carbon steel as

unwelded region 15.0], welded region with gauge-10 electrode

10.5], welded region with gauge-12 electrode 16.5] and welded

region with stainless steel electrode is 13.0J. The averages show the

maximum energies absorbed by the medium carbon steel specimen

at fracture points.

84

TABLE 9; IMPACT STRENGTH FOR MEDIUM CARBON STEEL

Energy Absorbed (J)

S/N Specimens i ii Average

1 MCS with unwelded 15.0 15.0

15.0

region 14.0

2 MCS with welded

region using gauge 10.0 11.0

10.5

10 electrode 14.0

3 MCS with welded

region using gauge 17.0 16.0

16.5

12 electrode 14.0

4 MCS with welded

region using stainless 12.0 14.0

13.0

electrode 14.0

14.0 represents diameter of specimen in mm

85

4.4 Tensile test

The tensile test was carried out in a bar of uniform section,

circular in shape, in a tensile testing machine which indicated the

tensile load being applied. These were carried out on both low and

medium carbon steel specimens.

For every small strain (deformation) involved in the test the

elongation of the (gauge length) was recorded by an extensometer

as shown in tables 10 and 11.

86

TABLES 10: RESULT OF TENSILE TEST FOR LOW CARBON STEEL

S/N Electrode

types and length of Final Elong Yield Yield

Ultimate Ultimate

diameter test piece length ation load stress

load stress

specimen (mm) (mm) (%) (N) (N/mm2)

(N) (N/mm2)

(mm)

1 Unwelded 170 185 8.82 64020 415.98

85945 538.78

14.0

2 Gauge 12

14.0 170 171 0.59 29100 189.05 43690

283.57

3 Gauge 10 170 171 0.59 32010 207.95 34920

226.86

14.0

4 Stainless

Stee 170 173 1.76 61110 397.00 66930

434.81

Electrode

14.0

14.0 represent the diameter of the specimen, gauge represent the

different classes of electrodes used in preparing the specimens.

87

Table 11 shows that the yield load for the un-welded specimen is

72750 N that of the specimen welded gauge-12 electrode has yield

load of 30555Nthe yield load of specimen welded with gauge-10

electrode is 32010N while the yield load of specimen welded with

stainless steel electrode is 43650N.

88

TABLES 11: RESULT OF TENSILE TEST FOR MEDIUM CARBON STEEL

S/N Electrode

types and length of Final Elong Yield Yield

Ultimate Ultimate

diameter test piece length ation load stress

load stress

specimen (mm) (mm) (%) (N) (N/mm2)

(N) (N/mm2)

(mm)

1 Un-welded

14.0 170 180 5.38 72750 472.6 87300

567.14

2 Gauge-12 170 171 0.59 30555 198.50

34928 226.91

14.0

3 Gauge-10

14.0 170 172 1.18 32010 207.95

37830 245.76

4 stainless

steel

electrode

14.0 170 172 1.18 43650 283.59 50925

330.83

14.0 represents the diameter of the specimens, gauge represents

the different classes of electrode used in preparing the specimens.

89

4.5 Compression test

Compression test was carried out on the two classes of carbon,

the low and medium carbon steel with the different electrodes or

filler materials.

The tensile testing machine was used since it has provision for

suitable attachments for compression test the result obtained are as

contained in tables 12 and 13.

90

TABLES 12: COMPRESSION STRENGTH FOR LOW CARBON STEEL

S/N Electrode

types and length of Final Strain Ultimate

Ultimate

diameter test piece length % load

stress

specimen (mm) (mm) (N) (N/mm2)

(mm)

1 Un-welded

14.0 25.0 23.2 7.40 101850 2026.24

2 Gauge-12

14.0 25.0 23.4 6.25 88755 1765.72

3 Gauge-10

14.0 25.0 23.4 6.25 19665 1823.62

4 Stainless

steel

electrode

14.0 25.0 23.0 8.00 93120

1852.56

14.0 represents the diameter of the specimen, gauge represent the

different classes of electrode used in preraring the specimen.

91

TABLES 13: COMPRESSION STRENGTH FOR MEDIUM CARBON STEELS

S/N Electrode

types and length of Final Strain Ultimate

Ultimate

diameter test piece length % load

stress

specimen (mm) (mm) (N) (N/mm2)

(mm)

1 Un-welded

14.0 25.0 23.3 6.67 101850 1296.79

2 Gauge-12

14.0 25.0 23.5 6.06 87300 1111.54

3 Gauge-10

14.0 25.0 24.2 3.13 93120 1185.64

4 Stainless

steel

electrode

14.0 25.0 22.8 8.8 93125 1185.70

14.0 represent the diameter of the specimen, gauge represent the

different classes of electrode used in preparing the specimen.

92

DISCUSSION

5.1 INTRODUCTION

The focus of this chapter is the discussion of the general results

of this work. This will be based on findings as they relate to

theoretical background of the study.

5.2 HARDNESS RESULTS

Hardness test was carried out in two phases with two different

properties of carbon: low and medium carbon steels welded with

different types of electrodes such as gauges-10, 12 and stainless

steel electrode.

5.2.1 Low carbon steel

Low carbon steel was welded with stainless steel electrode then

gauge-12 electrodes respectively. A hardness test was carried out

and the result is as presented in table 6.

The result shows that the weld with stainless steel electrode

has a hardness value of 58.84HRC on the average. This value is

comparable to the control specimen hardness value of steel of

56.72HRC.

This hardness has no significant difference when compared to

the value of low carbon steel with un-welded region. To specifically

determine the gauge of the electrode that would be more effective,

gauges-10 and 12 were also used and the result is as shown in table

6. Low carbon steel welded with gauge-10 electrodes recorded a

hardness value of 56.80HRC while that of gauge – 12 gave a

hardness of 55.86HRC both are about the controlled specimen value.

93

5.2.2 Medium carbon steel

The result of this test is assured in table 7. Medium carbon steel with

un-welded region was found to have a hardness of 56.08HRC

gauged-10 and 12 electrode welds were produced and tested and

have hardness values of 56.28HRC and 56.26HRC respectively.

The differences in hardness between the gauges for medium

carbon steel is not significant enough. This implies that the

electrodes contributes significantly to the hardness of the welded

region though not as much as that of low carbon steel welded with

the same electrodes as shown in tables 6 and 7.

Similarly medium carbon steel welded with stainless steel

electrodes adds to the hardness of welds significantly (Tables 7).

This shows that medium carbon steel welded with stainless

steel electrode can also be used in the absent of low carbon steel

when hardness is required in joints. These results agreed with

theoretical value and hardness in the scanty literature available in

this research work (Allen, 1979).

5.3 Impact results

When stress is applied to a bar it may either deform plastically

or may break in a brittle manner and the relationship between these

types of behavior determines whether brittle failure will occur or not

at the welded joint. In the specimens used in this research work for

impact test, there were notches produced and subjected to impact

test. The stresses on the specimens were below the elastic limit of

the main

94

section while at the root of the notches, plastic flow may have

occurred under a higher stress due to the reduced area.

This localized plastic flow at the notches may cause rapid strain

hardening which may lead to cracking at the root of the notches and

once this crack has began. There appeared a natural notch of

uniform size instead of variable size of machined notches. Before a

crack can be instead there must therefore be some de-formation.

When this stress exceeds the elastic limit the preparation of the

crack produced yields further and deforms plastically (Reed-Hill,

1973 and Ormandy, 1978).

The impact test result is contained in table 8 and 9. The test

was carried in two phases with respect to low and medium carbon

steel. The different carbon steel was welded with electrodes, gauge-

10, 12 and stainless steel electrode.

The low carbon steel welded with gauge-12 electrodes

indicated the highest impact value of 52.90J. The value is about

twice the controlled specimen value of 27.40J which implies that the

gauge-10 and stainless steel electrodes used in low carbon steels.

The gauge 12 electrodes indicated that when used in producing

welds, it will serve better in service.

The medium carbon steel result is shown in table 9. The

specimen welded with gauge-10 electrode shows the value of

energy absorption of 10.5J.The welds produced with gauge-12 and

95

Stainless steel electrode recorded the value of 16.5J and 13.0J

respectively.

From the above values it shows that the design for components

that requires welded joints for impact service will serve better if

gauge-12 and stainless steel electrodes are used. These values are

about the controlled specimen value of 15.0J. For specimens welded

with gauge-12 electrodes, the joints were stronger than the parent

material resulting from the fracture of the specimens away from the

joints.

5.4 Tensile Results

Tensile results is shown in tables 10 and 11, these results were

obtained by subjecting the different specimens to tensile test

using the extensometer. From the results, a tensile test on a

welded joint is not the same as the test on a homogenous bar.

he carbon steel weld metal may be strong, yet brittle and hard

when tested in machine, the specimen would most probably

break outside the weld in the parent material while in service,

due to its brittleness, failure might easily occur in the weld

itself. The result of this test gives the tensile strength of the

specimen.

If the weld metal is softer than the parent metal, the weld itself

yields and fracture will occur in the weld. The elongation of the

specimen will be small, since the parent material will have only

straightened a small amount and this will lead to the belief that the

metal has a little elasticity (Allen, 1979).

96

The yield load-which is the maximum load, required to cause the

joint in question to fail while in service was the concern of the

tensile test.

The specimens were tested in two phases though thus; the low

and medium carbon steel welded with the different type of electron

as shown in the tables. The low carbon steel results shown in table

10 indicates that the specimen welded with stainless steel electron

produce the highest value of 61110N relative to the control

specimen value of 64020N. The gauge-12 electrode yielded the load

of 29100N which is the least when compared with the different

specimen results.

Generally the results shows and satisfy the first theory of failure

also referred to as maximum principal stress theory or maximum

normal stress theory, which states that; failure can only occur

whenever the largest principal stress equal the strength of the

material (Shackelford, 1985 and Shigley, 1983). That the criterion

failure is:

σ₁ = Sy -------------------------------------------------------5.0

Where σ₁ =principal stress (N)

Sy = Yield or yield load (N)

To design for strength the most suitable electrode from the research

test is the stainless steel electrode.

The medium carbon steel result is represented in table 11. This

results show that the specimen welded with stainless steel electrode

produced a more significant result with a value of 43650N which is

97

within the controlled specimen value of 72750N. The gauges 12 and

10 electrodes have the values of 30555N and 32010N respectively.

These results are still within the theoretical values and satisfy

the first theory of failure as expressed in equation 5.0. When

compared with the yield load of low carbon steel there is a

significant increase in the maximum load that caused the yield.

This shows that increased carbon content in the medium

carbon steel have caused a corresponding increase in the strength.

Stainless steel electrode is still preferred for producing a good

weld when using a medium carbon steel as a raw material. The

result of this test gives the tensile strength of the specimens and

indicates that the welded joints are sound.

5.5 COMPRESSION RESULTS

The result for the compression test is shown in tables 12 and 13, the

tables show the ultimate that produced the strain in the specimens.

The interest of this research in compression test is the strain or

percentage strain as represented in tables 121 and 13. The strain is

the ratio of extension to the original length of the specimen (Ashby

and Jones, 1993 and Callister Jr., 1996).

Expressed as follows:

Strain (ε) = ΔL = Extension Х 100 -----------------5.1

Lo Original length

98

Where

ΔL = change in length, (mm)

Lo = original length, (mm)

The compression test was carried out in two phases, the low

and medium carbon steels. The low carbon steel result as contained

in table 12 shows that the gauge-10 and 12 electrodes have strain

percentages of 6.45 and 6.25 respectively.

It also shows stainless steel electrode specimen having the

highest strain value of 8.00%. These strain values also have their

respective ultimate values as contained in the tables. The strain

percent values are above the theoretical values except for the

stainless steel electrode with a very negligible difference of 0.06%.

The result of the compression agrees with the third failure law

of maximum principal strain theory, which states that; failure occurs

whenever the maximum strain in a complex stress system equals

that of the yield point in a tensile test (Muvdi and McNabb, 1990 and

Shigley, 1983).

The criterion for failure is,

_ I_ (σ₁-Vσ₂–Vσ₃) = Sy ----------------------5.2

E ε

Where E = Modulus of elasticity

σ₁, σ₂, and σ₃, = Stress (Complex stresses)

V = Poisson ratio

99

Sy = Yield strength

ε = Strain.

The medium carbon steel result shows that gauge-12 electrode

produced the joint with the highest resistance to buckling. This is

represented in table 13 as 6.06% recorded during the test. This value

is about the theoretical value of 6.67 % while gauge 10 and stainless

steel electrode produced 3.13% and 3.64% respectively.

These values generally are within the theoretical value and also

fulfill one of the theory failure which states that failure can occur

whenever the maximum strain in a complex stress system equals

that at the yield point in a tensile test as shown in equation 5.2.

From the medium carbon steel result presented in table 13, the

gauge 10 electrode is about the best electrode when designing for

compression using the medium carbon steel as the raw material.

5.6 Micrography

Introduction: Welding processes involves the use of high

temperature so that the region containing the weld will be relatively

coarse grained in contrast to the remaining work piece, which will

generally be of a wrought, and consequently, fine grained structure.

In the fusion method of welding the weld metal itself shows a coarse

as-cast type of structure. The crystals are large and there is coring

and segregation of impurities at crystal boundaries.

100

These features give rise to brittleness which results from

weakness at crystal boundaries. The features are normally made

visible to the naked eye after they have been captured, magnified

and printed.

Plates 1-8 show the micrographs of joints produced with the

different electrodes on low and medium carbon steels.

Plate 1 shows the micrograph of unwelded low carbon steel.

The plate also shows the white crystals of ferrite with crystal

boundaries and also with dark areas indicating the carbon contents

in the steel. The ferrite iron is also known as the alpha (α) iron with

the body cubic center (BCC) structure. The presence of ferrite or

alpha iron in this steel with a carbon content of 0-0.3% makes it very

ductile with a good impact value and large value and a large value of

tensile strength (Tables 8 and 10).

101

Plate 1: Unwelded low carbon steel, × 100

102

Plate 2 displays low carbon steel welded with gauge 10

electrode showing the presence of ferrite (white) with pearlite

(dark).

During welding, the weld region and the heat affected zone have

their temperature raised towards the parent metal resulting in the

grain growth in the parent metal as shown in plate 2. The effect of

the increase in temperature is the hardness and brittleness of the

joint. Other improved mechanical properties are impact strength

(table 8) and hardness value (table 6).

103

Plate 2: Low carbon steel welded with gauge 10 electrode etched in 2% natal, × 100

104

Plate 3 shows low carbon steel welded with stainless steel electrode

etched in a 2% natal. The light spots indicate ferrite iron while the

black spots show the free carbon also known as graphite. The

graphite was introduced at the wake of the temperature generated

to melt the stainless steel electrode during the arc welding process.

The increased carbon content in the steel improved the mechanical

properties such as: hardness in table, impact strength in table 8,

tensile strength in table 10 and compression strength in table 12.

105

Plate 3: (a) Low carbon steel welded with stainless steel electrode etched in 2% natal, × 100

106

Plate 4 displays low carbon steel welded with gauge 12 electrode

etched in a 2% natal. The grain structure and grain sizes are finer

than the normal or unwelded low carbon steel, this is as a result f re-

crystallization of the grains of the steel resulting from the heating up

of the steel during the welding process. This accounts for the low

compression value (table12) and high impact strength value (table

8).

Re-crystallization is a process whereby a metal is heated up causing

distortion in the metal structure. The distortions attain a point

where new crystals begin to grow from nuclei initiate within the

most heavily deformed regions. The new crystals grow steadily until

it absorbs the whole of the distorted structure.

107

Plate 4: Low carbon steel welded with gauge 12 electrode etched in 2% natal, × 100

108

Plate 5 shows an unwelded medium carbon steel (0.3-0.45%C), with

re-crystallized pearlite iron and dark spot to form a very fine grain

austenite-alpha iron which finally changes to gamma iron. The

austenite is a solid solution of carbon in a face cubic center (FCC)

gamma iron. The grain sizes of the pearlite and gamma iron in the

medium carbon steel account for high tensile strength values (table

11), low impact strength (table 9) and low compression strength

values (table 13).

109

Plate 5: Unwelded Medium carbon steel, × 100

110

Plate 6 shows a medium carbon steel (0.30.4%C) welded with gauge

10 electrode (mild steel electrode).

The structure of the above micrograph is similar to the grain

structure of hypoeutectic carbon (Allen, 1979) containing less than

0.8% carbon (Higgins, 1997). The steel contains a pearlite and

cementite. During the arc welding process there was grain growth

when he steel was heated above re-crystallization temperature

resulting to reduction in impact strength and ductility (table9).

Conversely, hardness of the steel was increased (Table 11).

111

Plate 6: Medium carbon steel welded with gauge 10 electrode etched in 2% natal, × 100

112

Plate 7 shows a medium carbon steel (0.3-0.45%C) welded with

gauge 12 electrode and the junction between the weld metal and

the parent metal. The light part is the ferrite and the dark part is the

pearlite. Droplet of carbon and nitrogen absorbed into the weld

from the steel and electrode are also shown in the plate. The

impurities increased the grain size and introduce blow holes which

reduced the tensile strength of the medium carbon

113

Plate: Medium carbon steel welded with gauge 12 electrode etched in 2% natal, × 100

114

Plate 8 displays a medium carbon steel (0.3-0.45%C) welded with a

stainless steel electrode showing dendritic re-crystallization. The

heat condition favored uniform crystal growth, which is long and

narrow (columnar crystals).

The structure improved the mechanical properties of the medium

carbon steel welded with stainless steel electrode such as hardness

(table 11) and compression strength (table 13)

115

Plate8: Medium carbon steel welded with stainless steel electrode etched in 2% natal, × 100

116

6.0 CONCUSION AND RECOMMENDATIONS

6.1 CONCLUSION

The conclusion of this research work shall be considered on the basis

of the three different mechanical properties tested upon, n relation

to the different electrodes used in producing the specimens of low

and medium carbon steel composition . The mechanical properties

tested upon include; hardness, impact tensile and compression.

6.1.1 Hardness test: This work shows that the specimen of low

carbon steel welded with stainless steel electrode has the highest

value against that welded with gauge 12 with the lowest value on

the average. It is therefore concluded that stainless steel electrode

is he for producing joints of low carbon steel parent materials. Also

in the case of medium carbon steel specimens stainless steel

electrode is the best for highest hardness.

6.1.2 Impact test: The gauge 12 electrode weldment made on low

carbon steel absorbed the highest value of energy against the

stainless steel electrode with the lowest value. Consequent upon

this observation it is concluded that gauge 12 electrode is better for

impact strength. For medium carbon steel the energy absorption

level is higher in gauge 12 electrode and the least in gauge 10

specimens hence impact strength for medium carbon steel should

be made with gauge 12 electrode.

117

6.1.3 Tensile test: The stainless steel electrode showed a higher load

to fracture against the gauge 12 electrode with the least value

on low carbon steel specimens. Hence stainless steel electrodes

are preferred for filler metal for low carbon steel materials. This

is also applicable to the medium carbon steel specimen.

6.1.4 Compression test: The stainless steel electrode has a higher

strain percent for low carbon steel against the gauge 12 with the

least value. It is concluded that stainless steel electrode should be

used when producing joint compression purpose. The stainless steel

electrode can also be used when the parent material is medium

carbon steel composition.

118

6.0 RECOMMENDATIONS

From the findings of this research work, it is hereby recommended

as follows:

1. When designing a joint for hardness purpose using low carbon

steel as the raw material, stainless steel electrodes and gauge

10 electrodes should be used. If the raw material is the medium

carbon steel, stainless steel and gauge 10 electrode are also

recommended.

2. Impact joints should be produced using gauge 10 and gauge 12

electrodes for low carbon steel and gauge 12 electrode and

stainless steel electrode when the raw material is medium

carbon steel.

3. When designing for a higher yield load that is, for tensile

strength using low carbon steel, the recommended electrodes

are the stainless steel and gauge 10 electrodes for medium

carbon steel materials the stainless steel and gauge 10

electrodes also recommended for use by the designer.

4. The compression property if required I service will e better if

gauge 12 and gauge 10 and stainless steel electrode are

recommended as the filer metals if the parent material is

medium carbon steel.

5. It is pertinent that more work should be done on the

microstructure of the weldments to determine the grain

structures and sizes.

6. Further research work should be carried out on the corrosive

effect o these welds with different electrodes

119

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