UNIVERSITI TEKNIKAL MALAYSIA MELAKA

Faculty of Manufacturing Engineering

EFFECT OF HEAT TREATMENT ON LOW CARBON STEEL

CORROSION BEHAVIOR

Raed Abdulameer Mahmood

Master of Manufacturing Engineering

(Manufacturing System Engineering)

2013

EFFECT OF HEAT TREATMENT ON LOW CARBON STEEL CORROSION

BEHAVIOR

RAED ABDULAMEER MAHMOOD

A thesis submitted in fulfillment of the requirement for the degree of Master of

Manufacturing Engineering (Manufacturing System Engineering)

Faculty of Manufacturing Engineering

UNIVERSITI TEKNIKAL MALAYSIA MELAKA

2013

DECLARATION

I declare that this thesis entitle "EFFECT OF HEAT TREATMENT ON LOW CARBON

STEEL CORROSION BEHAVIOR" is the result of my own research except as cited in the

references. The thesis has not been accepted for any degree and is not concurrently submitted

in candidature of any other degree.

Signature

Name

Date

~-······························ Raed Abdulameer Mahmood

. fl::..?..:-:-: .2-dl:) ..

APPROVAL

This report submitted to the Faculty of Manufacturing Engineering of UTeM as apartial

fulfillment of the requirement for master of manufacturing engineering (manufacturing system

engineering). The member of supervisory committee is as follow:

Signature

Supervisor

Date

: PM. DR.MOHD WARIKH BIN ABD RASHID

4- 9. J.A/ 3. oii .. MOHD \NARl·Ki:i 8"1N ·Aa·o: "RASHID

Associate Professor Faculty of Manufacturing E~gineering

Universiti Teknikal Malaysia Melaka Hang Tuah Jaya

76100 Durian Tunggal, Melaka

ABSTRACT

This work was to investigating the corrosion behavior of low carbon steel in a salt

solution of 3.5wt% NaCl after undergoing two different types of heat treatment at 960 °C in a

furnace. The material of low carbon steel was cut into nine small pieces under three groups A,

B and C, without heated annealing and hardening heat treatment respectively. The heat

treatment was at temperature 960°C. The hardness of the sample as received will be 203

kg/mm2 while after hardening the hardness was increased. The sample was mounted using hot

and cold mounting. The microstructure and surface morphology was observed by using

Scanning Electron Microscope (SEM) and Optical Microscope (OM) after grinding, polishing

and etching on the sample. In group A cementite can be observed clearly on pearlite on the

surface before corrosion test. After four days soaking in 3.5 wt% NaCl solution was observed

all cementite and pearlite will be transformed to austenite with the remnants of cementite

make the surface unstable hence increases the initial corrosion. After four days soaking when

the cementite is oxidized and a thick film of corrosion product covers the material surface.

The formation of Martensite due to quenching and rapid cooling in group C sample increases

the corrosion rate from 0.072 mpy to 0.302 due to decreased of corrosion potential from -572

m V to -639 m V after four days soaking. The corrosion rate of each sample was measured by

using electrochemical polarization measurement and Tafel extrapolation technique. From

previous result, it was observed that samples which had undergone annealing mode of heat

treatment turned out to be the ones with the best corrosion resistance.

ABSTRAK

Projek ini adalah untuk mengkaji kelakuan terhadap kakisan keluli karbon yang

rendah dalam larutan garam 3.5wt% NaCl selepas menjalani duajenis rawatan haba iaitu pada

960 ° C dalam relau. Bahan keluli karbon rendah telah dipotong sembilan keping kecil di

bawah tiga kumpulan A, B dan C, masing-masing tanpa rawat dan dipenyepuhlindapan dan

dirawat haba pengerasan. Rawatan haba adalah pada suhu 960 ° C. Kekerasan sampel yang

diterima terjadi 203 kg/mm2 dan diperhatikan ia akan menjadi bacaan tertinggi selepas

rawatan pengerusm keras. Sampel telah dipasang menggunakan pelekap panas dan sejuk.

Mikrostruktur diperhatikan dengan menggunakan Mikroskop Imbasan Elektron (SEM) dan

Mikroskop optik (OM) selepas pembersihan sampel. Ini kerana, kumpulan simentit boleh

menjadi jelas dalam pearlit di permukaan sebelum kakisan, (selepas empat hari direndam di

dalam 3.5 wt% larutan NaCl). Kadar hakisan sampel telah ditentukan dengan menggunakan

kaedan elektrokirnia polarisasi dan ekstrapolasi Tafel teknik. Permukaan morfologi

diperhatikan dengan menggunakan Mikroskop imbusan Elektron (SEM) dan didapati

pertumbuhan karat pada pearlit, di masa sama JUga ada meningkatkan hakisan dengan

peningkatan masa rendaman. Sebaliknya dikumpulan B penyepuhlindapan rawatan haba

menukarkan semua simentit dan pearlit lcepada austenit dengan sisa simentit yang menjadikan

punca permukaan tidak stabil dan meninglcatken kader kalaisan kadar kaksin akan meningiear

selama empat hair redam dan selepas sepuluh hair rendaman benkatan berikatan pening kecton

kaksisan.Sample Kumpulan C menerusi proses haba pengerasan dan dimana mengubah

11

struktur mikroskopik komposisi kepads lapisan logam Martensit. Proses pelindapkejutan dan

penyejukan yang pantas menyebabkan peningkatkan kadar hakisan dari 0.072 mpy kepada

0.302 mpy dan menurun potensi kakisan dari -572 mV kepada -639 mV. Dari hasil kajian

sebelumnya, didapati bahawa sampel yang telah menjalani mod penyepuhlindapan rawatan

haba temyata mempunyai rintangan kakisan yang terbaik .

111

DEDICATION

I would like to present my work to those who did not stop their daily support since I

was born, my dear mother, my kind father, my wife and my daughter "Shaghaf'. They never

hesitate to provide me all the support to push me foreword as much as they can. This work is a

simple and humble reply to their much goodness I have taken over during that time. I don't

forget my brothers, sisters, and all my friends from Iraq and Malaysia.

<i«utf fl_6tfufameer 9J.ali.mootf

IV

ACKNOWLEDGEMENT

J LJ

~I .:ful

First and foremost, praise is to Allah, for giving me this opportunity, the strength and

the patience to complete my thesis finally, after all the challenges and difficulties. I would like

to thank my supervisor, Assoc. Prof. Dr. Mohd Warikh Bin Abd Rashid for his high

motivation and most significant contribution in this thesis, to the Dean of Faculty of

manufacturing engineering Assoc. Prof. Dr. Mohd Rizal Bin Salleh

I would also like to thank the Ministry of Higher Education and Scientific Research of IRAQ,

Furthermore, I want to thank my friends who have helped and motivated me throughout. May

Allah reward them all abundantly, Sincere thanks to all

~a fl.6aufameer 9'!.alimooa

v

ABSTRACT

ABSTRAK

DEDICATION

ACKNOWLEDGEMENT

TABLE OF CONTENT

LIST OF TABLES

LIST OF FIGURES

CHAPTER 1

INTRODUCTION

1.0 Background of Study

1.1 Problem Statement

1.2 Objectives

1.3 The Scope of Present Work

CHAPTER2

LITERATURE REVIEW

2.0 Introduction

TABLE OF CONTENT

2.1 Electrochemical Aspects of Corrosion

VI

11

IV

v

VI

x

XI

1

1

4

7

7

10

10

10

2.2 Corrosion Classifications

2.2.1 Dry Corrosion

2.2.2 Wet Corrosion

2.3 Forms of Corrosion Attack

2.3 .1 Uniform Corrosion

Galvanic Corrosion

Localized Corrosion

Pitting Corrosion

Selective Dissolution

2.3.2

2.3.3

2.3.4

2.3.5

2.3.6 Conjoint Action of Corrosion and a Mechanical Factor

2.4 Factors Effecting Corrosion Rate

2.4.1 Effect of pH

2.4.2

2.4.3

Effect of Temperature

Effect of Heat Treatment

2.5 Limiting Current Density

2.6 Polarization Concept

2. 7 Polarization Types

2.7.1

2.7.2

2.7.3

Activation Polarization

Concentration Polarization

Combined Polarization

CHAPTER3

METHODOLOGY

3.0 Introduction

3.1 Raw Materials

3.2 Sample preparation

3.3 Heat Treatment

Vll

12

12

13

13

13

15

16

17

17

17

17

17

19

20

24

25

25

26

27

28

30

30

30

32

35

3.3.1 Annealing

3.3.2 Hardened

3.4 Corrosion experiment

3.5 Method of experiment

3.6 Analyzing and testing

3.6.1 Etching process

3.6.2 Scanning Electron Microscope (SEM)

3.6.3 Optical Microscope (OM)

3.6.4 Polarization Measurements

CHAPTER4

RESULTS AND DISCUSSION

4.0 Introduction

4.1 Analysis of Raw Material

4.2 Effect of Heat treatment on mechanical properties

4.2.1 Hardness test

4.3 Physical properties

4.3.1 Surface color

Optical Microscope test 4.3.3

4.3.4 Scanning Electron Microscope (SEM) test

4.4 Corrosion test

4.4.1 Tafel Extrapolation

4.4.2 Surface morphology after corrosion

CHAPTERS

CONCLUSIONS AND RECOMMENDATION

5.0 Conclusion

Vlll

35

36

36

36

38

38

38

39

40

41

41

41

42

42

44

44

45

46

48

50

56

60

60

5 .1 Recommendation 61

REFERENCES 62

APPENDICES

Al Analysis Raw Material Samples 70

B XRD Analysis 72

Cl RWOOl Hardness Test 73

C2 RAOOl Hardness Test 74

C3 RHOOl Hardness Test 75

D Tafel Plot of group A 76

Dl Tafel Plot of group B 76

E Microstructure of Group A 77

El Microstructure of Group B 78

E2 Microstructure of Group C 79

F Ganti Chart of master project 1 80

Fl Ganti Chart of master project 2 81

IX

LIST OF TABLES

TABLE TITLE PAGE

2.1 Chemical composition of low carbon steel used for the experimentation 21

3.1 Classifying the samples according codes 34

4.1 Vickers hardness value of the sample before corrode 43

4.2 Corrosion rate of the group A (RWOOl, RW002 and, RW003) m 51

3.5wt%NaCl solution

4.3

4.4

Corrosion rate of Group B (RA001,RA002 and RA003) m

3.5wt%NaCl solution

Corrosion rate of Group C samples (RHOOl, RH002 and RH003) in 3.5

wt % NaCl solution

x

52

54

LIST OF FIGURES

FIGURE TITLE PAGE

1.1 Flowchart of research methodology 9

2.1 Electrochemical corrosion of metal 11

2.2 Uniform corrosion 14

2.3 Automobile door with significant corrosion 15

2.3 Effect of pH on Corrosion Rate of Iron 18

2.4 Weight losses against Time of Exposure 22

2.5 Corrosion Penetration Rate against Time of Exposure 22

2.6 The micrograph of the as-received low carbon steel 23

2.7 (a) Annealed Sample, un-corroded, 23

(b) Annealed Sample 9 days in corrosion fluid.

2.8 (a) Non-corroded hardened Sample, 23

(b) Hardened Sample 9 days in corrosion fluid.

3.1 Samples shape and dimension 31

3.2 Sample analysis by (OES) material analysis 31

3.3 X-Ray Diffraction (XRD) 32

Xl

3.4

3.5

3.6

3.7

3.8

3.9

3.10

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4.10

4.11

Sample inside the poured by hot mounting

Cold mounting

Schematic diagram of annealing process

Diagram of electrochemical measurement cell

A Scanning Electron Microscope (SEM) (oxford, model7636)

Optical Microscope Devices

Classic Tafel extrapolation

Certificate of raw material test

X-ray diffraction (XRD) analysis of low carbon steel

Illustration hardness plot

Un-corroded samples surface

Microstructure of low carbon steel without heat treatment by

using OM of material

Microstructure of low carbon steel without heat treatment

(group A) by using SEM

Microstructure of low carbon steel after annealing heat

treatment (group B) by using SEM

Microstructure of low carbon steel after annealing heat

treatment (group C) by using SEM

Anodic and cathodic polarization curves recorded for (grope

C) low carbon steel after hardening in 3.5wt% NaCl solution

Tafel corrosion rate plot of group A in 3.5wt%NaCl solution

Tafels corrosion rate plot of group Bin 3.5wt%NaCl solution

Xll

33

34

35

37

38

39

40

41

42

43

44

45

46

47

48

49

51

53

3.4

3.5

3.6

3.7

3.8

3.9

3.10

4.1

4.2

4.3

4.4

4.5

4.6

4.7

4.8

4.9

4.10

4.11

Sample inside the poured by hot mounting

Cold mounting

Schematic diagram of annealing process

Diagram of electrochemical measurement cell

A Scanning Electron Microscope (SEM) (oxford, model7636)

Optical Microscope Devices

Classic Tafel extrapolation

Certificate of raw material test

X-ray diffraction (XRD) analysis of low carbon steel

Illustration hardness plot

Un-corroded samples surface

Microstructure of low carbon steel without heat treatment by

using OM of material

Microstructure of low carbon steel without heat treatment

(group A) by using SEM

Microstructure of low carbon steel after annealing heat

treatment (group B) by using SEM

Microstructure of low carbon steel after annealing heat

treatment (group C) by using SEM

Anodic and cathodic polarization curves recorded for (grope

C) low carbon steel after hardening in 3.5wt% NaCl solution

Tafel corrosion rate plot of group A in 3.5wt%NaCl solution

Tafels corrosion rate plot of group Bin 3.5wt%NaCl solution

Xll

33

34

35

37

38

39

40

41

42

43

44

45

46

47

48

49

51

53

4.12 Tafel corrosion rate plot of group C in 3.5wt%NaCl solution 54

4.13 Comparison between three group's corrosion rates after 96 55

hour soaking in 3.5wt%NaCl solution

4.14 Comparison between three group's corrosion rates after 240 55

hour in 3.5wt%NaCl solution

4.15 The SEM surface morphology of low carbon steel sample 56

without heat treatment after soaking in 3.5 wt% NaCl solution

(a) RW002 (b) RW003

4.16 The SEM surface morphology of low carbon steel samples 57

after annealing after soaking in 3.5 wt% NaCl solution (a)

RA002 (b) RA003

4.17 The SEM surface morphology of low carbon steel samples 58

after hardening after soaking in 3.5 wt% NaCl solution (a)

RH002 (b) RH003

4.18 Relationship of corrosion behavior between three groups after 59

soaking.

Xlll

CHAPTERl

INTRODUCTION

1.0 Background of Study

The mainly accepted definition for corrosion is the damage of material due to chemical

reaction of the material with its environment. Generally, this destruction takes place on its

surface in the form of material dissolution or redeposit ion in some other forms. Metallic

systems are the predominant materials of construction, and as a class, are generally

susceptible to corrosion. Therefore, the bulk of corrosion science focuses upon metals and

alloys (Guthrie and Gretchen, 2002). Usually it's beginning at the surface of the material

and occurs because of the natural tendency of the materials to return to their

thermodynamic stable state or to one of the forms in which they were originally found.

Metals are generally prone to corrosion because most of them occur naturally as ores,

which is the most stable state of low energy and there is a net decrease in free energy, ~G

from metallic to oxidized state (Ogunleye et al., 2011). The corrosion is happening

extensively in carbon steel because the resistance of its relatively limited, despite from this

most widely used engineering material, accounts for approximately 85% of the annual steel

production worldwide, carbon steel is used in large tonnages in marine applications,

chemical processing, petroleum production and refining, construction and metal processing

equipment (Fouda et al., 2011).

The corrosion of carbon steel in natural environments is of practical importance, therefore

it is considered by many studies. It is widely recognized that the corrosion of carbon steel

1

may be accounted for by the anodic reaction as in Equation 1.1 and cathodic reaction in the

presence of oxygen Equation 1.2,

Fe(s)"'illl,__-., .. Fe +2 + 2e- Material dissolution

Oxygen dissolution

(1.1)

(1.2)

In many corrosion problems, there is strong evidence that the rate of uniform corrosion is

controlled by mass transfer rate. This is true whether the corrosion fluid remains static or in

fast motion with respect to the metal surface. However, molecular diffusion is not the only

factor which influences the rate of corrosion. In addition, in turbulent fluids, the rate of

transport of eddy diffusion appears to participate in the control of the overall transfer rate

(Brodkey and Hershey, 1989). Seawater is one of the most corroded and most plentiful

naturally happening electrolytes. The corrosively of the seawater is reflected by the fact

that most of the common structural metals and alloys are attacked by this liquid or its

surrounding environments (Johnsirani et al., 2013)

The corrosion characteristic of low carbon steel in natural seawater is the formation and

growth of compact and thick layers composed of oxides, insoluble salts and organic

materials. The result of surrounding environmental conditions water oxygen supply; ionic

species; bacteria and organic matter, these layers are formed. The exchange of various

species (ions, molecules, gas) between seawater and the rust layers or the metal depends

both on the kinetics of the Faradaic reactions of the entities with either the oxides or the

metal, as well as on their transport properties through the different strata of the rust layers

(Memet et al., 2002).

Salts dissolved in water have a marked influence on the corrosivity of water. At extremely

low concentrations of dissolved salts, different anions and cations show various degrees of

influence on the corrosivity of the water. So there are many investigations for corrosion of

2

carbon steel in neutral aerated salt solutions, especially sodium chloride (NaCl) solution.

Some investigation has been found for corrosion of carbon steel in Na2S04 salt solution.

For example corrosion of turbine caused by a thin film deposit of fused salt (sodium

sulphate) on alloy surface (carbon steel) is an example of corrosion in sodium sulphate

(Bornstein and Decrescente, 1971; Goebel et. al., 1973). During combustion in the gas

turbine, sulfur from the fuel reacts with sodium chloride from the ingested air at elevated

temperatures to form sodium sulphate. The sodium sulphate then deposits in the hot­

section components, such as nozzle guide vanes and rotor blades, resulting in an

accelerated oxidation attack. This is commonly referred to as "hot corrosion" (Stringer,

2007). Generally, the corrosivity of waters containing dissolved salts increases with

increasing salt concentration until a maximum is reached, and then the corrosivity

decreases. This may be attributed to increased electro-conductivity because of the

increased salt content, until the salt concentration is great enough to cause an appreciable

decrease in the oxygen solubility, resulting in a decreased rate of depolarization (Revie and

Uhlig, 2008). It is accepted that the corrosion of mild steel in aerated water is controlled by

the rate of cathodic reduction of oxygen and hence by the oxygen transport from the

mainstream solution to the reacting surface, generally if a metal is corroding under

cathodic control it is apparent that the velocity of the solution will be more significant

when diffusion of the cathode reactant is rate controlling, although the temperature may

still have an effect. On the other hand if the cathodic process requires high activation

energy, temperature will have the most significant effect. The effects of concentration,

velocity and temperature are complex and it will become evident that these factors can

frequently outweigh the thermodynamic and kinetic considerations (Shreir et al., 2000).

Also the temperature representing one of the critical environmental parameters in corrosion

studies because of its severe effects on physicochemical and electrochemical reaction rates.

3

Accordingly, passive film stability and solubility, pitting and crevice corrosion behavior is

known to be closely related to temperature (Samuel et al., 2011).

1.1 Problem Statement

The use of carbon steel is indispensable to virtually all aspects of human endeavor. Our

human civilization cannot exist without metals and yet corrosion is their Achilles heel.

Failure of parts and components of engineering origin in different industries by corrosion

is one of the major problems. Corrosion is responsible for so many mishaps that have

occurred in the engineering history of man. The two particular reasons for the

extraordinary versatility of steel are heat treatment and alloying.

The usage of steel is well pronounced in various aspects of human life such as in

manufacturing, oil and gas, construction, medical, textile, transport and aviation industries

to mention a few. Low carbon steel is a type of metal that has an alloying element made up

of a relatively low amount of carbon. Typically, it has a carbon content that ranges

between 0.05% and 0.30% and a manganese content that falls between 0.40 and 1.5%.

Low carbon steel is one of the most common types of steel used for general purposes, in

part because it is often less expensive than other types of steel. While the steel contains

properties that work well in manufacturing a variety of goods, it is most frequently made

into flat-rolled sheets or strips of steel.

Items made from low carbon steel compete with products that can be manufactured using

stainless steel and aluminum alloy metals. Low carbon steel can be used to manufacture a

wide range of manufactured goods - from home appliances and ship sides to low carbon

steel wire and tin plates. Since it has a low amount of carbon in it, the steel is typically

more malleable than other kinds of steel. As a result, it can be rolled thin into products like

car body panels. So the steel industry as profitable and important as one of the most

engineering-solution defying problems known to man, is it Corrosion (Kruger, 1986).

4

The cost of corrosion has been estimated at $300 billion per year in the United States

(Gerhardus et al., 2002). The corrosion-related cost to the transmission pipeline industry is

approximately $5.4 to $8.6 billion annually (David and James 2008). This can be divided

into the cost of failures, capital, and operations and maintenance (O&M) at 10, 38, and 52

percent, respectively (Gerhardus et al., 2002). Carbon steel and wide varieties of materials

of diverse properties are used in Multi Stage Flash evaporation MSF plants. Especially in

the Arabian Gulf Countries seawater that containing salts with different concentrations is

the prime source of fresh water supply by desalination plants. where A seawater

desalination plant offers numerous corrosion problems due to its process conditions,

including factors such as temperature and pH, and operation in relatively aggressive

environments consisting of deaerated seawater, seawater-air and salt-air aerosols, corrosive

gases, slow moving or stagnant liquids or deposit forming liquids to control the scale

formation, acid treatment and anti-scale additive are used in desalination plants. (lsmaeel

and Turgoose, 1999).

High temperature corrosion is a widespread problem in vanous industries, including;

establishing (oil pipelines), is an important element low carbon steel in especially at the

edges of the pipes that are linked through by welding that high temperature is effect on

microstructures of materials, so when are extended over long distances and sometimes

within the sea or be displayed to normal environment condition shall be more prone to

erosion.

Heat treatment is a heating and cooling operation applied to metals and alloys in solid

state to impact desirable properties to the metal or alloy. Heat treatment of metals is an

important operation in the final fabrication process of many engineering components.

Heat treatment is of various forms which include annealing, normalizing, tempering,

hardening and isothermal operations. Heat treatment improves the microstructure of the

5

metal, and this is what gives the metal desired properties for different service conditions.

The purpose of heat treatment of low carbon steel is to improve the ductility, toughness,

hardness tensile strength, and corrosion resistance.

Hardening and tempering process of metals offer enormous advantages to the

manufacturing industry because the heat treatment results can reveal optimum combination

of mechanical properties (Murugan, 2012). For example annealing process heated to

austenitic temperature of 960 °C and held for one hour to ensure complete homogenization,

without excessive grain growth and then cooled inside the furnace to room temperature an

initial corrosion rate of l 7.58x 10-5 cm/hr was observed after 72 hours. This corrosion rate

could be attributed to the larger portion of pearlite formed from cooling austenite. After 72

hours of soaking, corrosion rate reduction was observed, between the 144th hour and the

216th hour. The corrosion rate decreased due to the thicker corrosion products covering the

surface of the sample, thus it formed a kind of protective film on the surface which

retarded the corrosion rate. While the hardening process heated to austenitic temperature of

960 °C and held for one hour to ensure complete homogenization, without excessive grain

growth and then quenched in cold water to room temperature If referring to heat treating,

then the temperature in which the steel starts to tum to Austenite is 727 °C, and to be fully

austenitic that will depend on the carbon content. Low carbon could be around 900 °C,

medium around 850 °C and high carbon maybe below 800 °C. It can be observed the

greatest weight loss trends of all the heat treatment modes the initial corrosion rate notice

at 72nd hour was the highest after which it took a dive from the 72nd to the 216th hour. This

initial rise in corrosion rate could be because of the residual stresses in the steel which may

have arisen due to rapid cooling (Atanda et al., 2012).

In this research will study the effect of different heat treatment (annealing and hardening)

on low carbon in saline solution soaking time to 96-240 hours the initiated, finally

6