corrosion behaviour of ductile cast iron mohamed

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  • i

    CORROSION BEHAVIOUR OF DUCTILE CAST IRON

    MOHAMED ASSNOUSI ALI

    A Project report submited in partial fulfilment of the requirements for the award of the

    degree of Master of Engineering ( Mechanical Material )

    Faculty of Mechanical EngineeringUniversiti Teknologi Malaysia

    MAY 2009

  • iii

    To my late mother, my late father, my brothers and sisters

    for their support and care

  • iv

    ACKNOWLEDGEMENT

    First of all, Praise to Allah, the Most Gracious and Most Merciful, Who has

    created the mankind with knowledge, wisdom and power.

    I would like to express my utmost gratiude to my supervisor, Dr Astuty Amrine

    and AssociateProfessor Dr Ali Ourdjini for benig a dedixated mentor as well as for his

    valuable and valuable and constructive suggestions that enabled this project to run

    smoothly.

    Also,not forgetting my friends and classmates, I convey my full appreciation for

    his valuable and contributions toward this project , whether directly or indirectly.

    Last but not least, I am forever indebted to all my family member for their

    constant support throughout the entire duration of this project . their words of

    encouragement never failed to keep me going even through the hardest of times and it is

    here that I express my sincerest gratitude to them.

  • v

    ABSTRACT

    In this investigation the corrosion behavior of ductile cast iron as function of the

    microstructure and electrolyte solution has been conducted. The change in

    microstructure of the ductile cast iron is obtained by austenetising at different

    temperatures of 850C, 900C,950C and 1000C for 90 minutes followed by water

    quench. Corrosion tests included both immersion tests and electrochemical test.

    Corrosion rates measured from the immersion test using the weight loss method

    revealed that the cast iron investigated suffer less corrosion when exposed to sodium

    hydroxide compared to sodium chloride and that the corrosion rates are not significantly

    affected by the microstructure of the material. Observation of the corrosion attack also

    showed that the type of corrosion is that of uniform instead of localized. The low

    corrosion rates of the ductile iron are probably the results of the high Si content in the

    ductile iron, which provide a thin and protective hydrate layer. This observation is

    reconciled with previous research which investigated high Si containing ductile cast

    irons.

  • vi

    ABSTRAK

    Dalam kajian ini, ciri- ciri kakisan besi tuang mudah tempa sebagai fungsi

    terhadap mikrostruktur dan larutan elektrolit telah dijalankan. Perubahan mikrostruktur

    besi tuang mudah tempa didapati dengan proses austenising pada suhu yang berbeza

    iaitu 850C, 950C dan 1000C untuk 90 minit, diikuti dengan lindap kejut di dalam air.

    Ujian kakisan termasuklah ujian rendaman dan elektrokimia. Kadar kakisan diukur

    melalui ujian rendaman menggunakan teknik kehilangan jisim. Ini telah menunjukkan,

    besi tuang mudah tempa mengalami kakisan yang sedikit apabila didedahkan kepada

    Sodium Hidrokside berbanding Sodium Kloride dan kadar kakisan tidak dipengaruhi

    secara jelas oleh mikrostruktur bahan. Pemerhatian terhadap serangan kakisan juga

    telah menunjukkan bahawa jenis kakisan adalah secara menyeluruh dan bukan secara

    tertumpu. Kadar kakisan besi tuang mudah tempa yang rendah, mungkin disebabkan

    oleh kandungan Silikon yang tinggi di dalam bahan, yang mana ia menghasilkan

    lapisan pelindung hydrate yang nipis. Secara keseluruhannya, kajian ini disokong oleh

    kajian sebelum ini berkenaan kandungan Silikon yang tinggi dalam besi tuang mudah

    tempa.

  • vii

    TABLE OF CONTENTS

    CHAPTER TITLE PAGE

    DECLARATION ii

    DEDICATION iii

    ACKNOWLEDGEMENT iv

    ABSTRACT v

    ABSTRAK vi

    TABLE OF CONTENTS vii

    LIST OF TABLE x

    LIST OF FIGURES xii

    1 INTRODUCTION 1

    1.1 Background of the Research 1

    1.2 Problem Satement of Research 2

    1.3 Objectives of the Research 3

    1.4 Scopes of the Research 3

  • viii

    2 LITERATURE REVIEW 1

    2.1 General Review of Cast Iron 4

    2.2 Classification of Cats Iron 5

    2.2.1 White Cast Irons 6

    2.2.2 Gray Cast Irons 8

    2.2.3 Malleable Cast Irons 9

    2.2.4 Nodular Cast Irons 10

    2.2.5 Compacted Graphite Cast Irons 11

    2.3 Typically Microstructure of Cats Iron 12

    2.3.1 Ferrite (-Fe) 13

    2.3.2 Pearlite 13

    2.3.3 Cementite (Fe3C) 14

    2.3.4 Phosphide eutectic ( melting point about 930C ) 15

    2.3.5 Martensite 15

    2.3.6 Acicular or bainitic 16

    2.3.7 Austenite 17

    2.3.8 Graphite 17

    2.4 Properties of Cast Iron 18

    2.5 Ductile Cast iron 19

    2.5.1 Mechanical Properties 20

    2.5.2 Chemical Composition 21

    2.5.3 Grade of Ductile Cast Iron 21

    2.5.4 Hardness 23

    2.5.5 Tensile Properties 25

    2.6 Heat Treatment 25

    2.6.1 Austenitisation 26

    2.6.2 Cooling rate During Quenching 26

    2.7 Corrosion Of Metals 26

    2.8 Electrochemical Reactions 27

    2.9 Corrosion of Cast Iron 29

  • ix

    2.9.1.1 Effect Structure on Corrosion Resistance 30

    2.9.1.2 Effect Composition on Corrosion Resistance 30

    2.10 Corrosion of Cast Iron In Nature Environment 31

    2.10.1 Atmospheric Corrosion 31

    2.10.2 Corrosion by Waters of Cast Iron 31

    2.11 Soil Corrosion of Cast Iron 32

    2.12 Corrosion in industrial Environment of Aast Iron 32

    2.12.1 Corrosion by Acids 32

    2.12.2 Mineral Acids 33

    2.12.3 Organic Acids 33

    2.13 Corrosion by Alkalis

    2.13.1 Corrosion by Salt Solution Sf Cast Iron

    33

    2.14 Corrosion Under Stress 34

    2.15 Corrosion f Ttwo Types of Cast Iron 34

    2.15.1 high nickel Cast Iron 34

    2.15.1.1 Composition and Properties 35

    2.15.1.2 Aqueous Corrosion Behaviour 35

    2.15.1.3 Nature waters 35

    2.15.2 High Chromium Cast Iron 36

    2.15.2.1 Corrosion Resistance 36

    2.15.2.2 Atmopheric Corrosion 36

    2.15.2.3 Nature and Industrial Waters 37

    2.16 Corrosion of Ductile Cast Iron 37

    2.16.1 Cavitation Erosion of Ductile iron 38

    2.16.2 ErosionCorrosion of Ductile Cast Iron 39

    2.16.3 High Temperature Corrosion of Ductile Cast

    Irons40

    2.16.4 Corrosion fatigue of ductile iron 41

    2.16.4.1 Fatigue Behaviour In Various Environment 42

  • x

    3 METHODOLOGY 43

    3.1 Introduction 43

    3.2 Materials 44

    3.3 Samples Preparation 44

    3.4 Compositional Analysis 48

    3.5 Metallography Analysis 50

    3.6 Heat Treatment 51

    3.7 Hardness Measurement 52

    3.7 Microstructure Analysis 53

    3.8 Electrochemical Testing 53

    3.8.1 Principle of Measurement 53

    3.8.2 Preparation of Working Electrode 55

    3.9 Immersion Test 57

    4 RESULTS AND DISCUSSION 62

    4.1 Compositional Analysis 62

    4.2 Microstructural Examination of As-Received Sample 63

    4.3 Hardness Test 65

    4.4 Immersion Test 66

    4.5 Elechtrochemical ( Polraisation Results) 72

    4.6 Microstructure Analysis of Samples after Immersion Corrosion Test 79

  • xi

    5 CONCLUSIONS AND RECOMMENDATIONS

    5.1 Conclusions 92

    5.2 Recommendations for Future Work 93

    REFERENCES 94

  • xii

    LIST OF TABLES

    TABLE NO TITLE PAGE

    2.1 Grade of Ductile Cast Iron in ASTM A- 536-77 22

    2.2 Grade of Ductile Cast Iron in SAE specification No. J434c for

    Automotive Castings 23

    2.3 Typical Hardness Brinell for Ductile cast Iron 24

    3.1 Potentiodynamic Polarization Test Parameters 58

    3.2 Parameters for immersion test 61

    4.1 Chemical composition of as-received Ductile Cast Iron 63

    4.2 Analysis Hardness Rate for ductile Cast Iron 66

    4.3 Corrosion rate of specimens expressed in mm/yr after 1 day in

    ( NaCl ) 67

    4.4 Corrosion rate of specimens expressed in mm/yr after 7days in

    ( NaCl ) 68

    4.5 Corrosion rate of specimens expressed in mm/yr after 14 days

    in ( NaCl ) 68

    4.6 Corrosion rate of specimens expressed in mm/yr after 28days

    in ( NaCl) 69

    4.7 Corrosion rate of specimens expressed in mm/yr after 1

    day in ( NaOH ) 70

    4.8 Corrosion rate of specimens expressed in mm/yr after 7 days in

    ( NaOH ) 70

  • xiii

    4.9 Corrosion rate of specimens expressed in mm/yr after14 days

    in ( NaOH ) 71

    4.10 Corrosion rate of specimens expressed in mm/yr after 28 days

    in ( NaOH ) 73

  • xiv

    LIST OF FIGURES

    FIGURE NO TITLE PAGE

    2.1 Schematic of iron- iron carbide systems 6

    2.2 Microstructure of white cast iron Fe3.6C0.1Si, dentrites of

    pearlite 7

    2.3 Microstructure of Gray cast iron ( graphite flakes ) 8

    2.4 Microstructure of Malleable cast iron 9

    2.5 Microstructure of spheroidal graphite cast iron as cast

    Fe3.5C-2.5Si-0.5Mn-0.15Mo-0.31Cu-0.042Mg wt% 10

    2.6 Microstructure of spheroidal graphite cast iron as cast

    Fe3.2C-2.5Si-0.05Mg wt% 11

    2.7 Flowchart for Classification of Cast Iron 12

    2.8 Microstructure of cast iron under cooled graphite 13

    2.9 Microstructure of cast iron consist of alternate lamellae

    of ferrite and cimentite 14

    2.10 Microstructure of cast iron consist cementite 14

    2.11 Grey cast iron with a high phosphorus content 15

    2.12 Microstructure of cast iron with some retained austenite 16