Direct strip casting of metals and alloys

295 Pages·2006·68.06 MB·English

by  Michael Ferry

Direct strip casting of metals and alloys
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Direct strip casting of
metals and alloys
Processing, microstructure
and properties
Michael Ferry
School of Materials Science and Engineering
University of New South Wales
Woodhead Publishing and Maney Publishing
on behalf of
The Institute of Materials, Minerals & Mining
CRCPress
Boca Raton Boston New York Washington, DC
WOODHEAD PUBLISHING LIMITED
Cambridge England
Woodhead Publishing Limited and Maney Publishing Limited on behalf of
The Institute of Materials, Minerals & Mining
Woodhead Publishing Limited, Abington Hall, Abington, Cambridge CB I 6AH,
England
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Published in North America by CRC Press LLC, 6000 Broken Sound Parkway, NW,
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First published 2006, Woodhead Publishing Limited and CRC Press LLC
© 2006, Woodhead Publishing Limited
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Woodhead Publishing ISBN-13: 978-1-84569-049-6 (book)
Woodhead Publishing ISBN-l 0: 1-84569-049-4 (book)
Woodhead Publishing ISBN-13: 978-1-84569-166-0 (e-book)
Woodhead Publishing ISBN -1 0: 1-84569-166-0 (e-book)
CRC Press ISBN-lO: 0-8493-7600-9
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Contents
List of abbreviations xi
List of symbols xii
Preface xvii
CHAPTER 1 1
Metallurgy of Alloys Suitable for Direct Strip Casting
1.1 Introduction 1
1.2 Metallurgy of ferrous alloys 1
1.2.1 Phase stability 2
1.2.2 Alloying elements in iron 4
1.2.3 Phase transformations and key DSC steel grades 8
1.2.3.1 Carbon steel 8
1.2.3.2 Stainless steel 9
1.2.3.3 Silicon iron 12
1.3 Metallurgy of non-ferrous alloys 13
1.3.1 Aluminium alloys 13
1.3.1.1 Alloying elements in aluminium 14
1.3.1.2 Classification and key aluminium grades 14
1.3.1.3 Alloys amenable to direct strip casting 16
1.3.2 Magnesium alloys 17
1.3.2.1 Alloying elements in magnesium 18
1.3.2.2 Classification and key magnesium grades 19
1.3.2.3 Alloys amenable to direct strip casting 20
1.3.3 Titanium alloys 20
1.3.3.1 Alloying elements and phase stability 21
1.3.3.2 Alloy types and phase transformations 22
1.3.3.3 Alloys amenable to direct strip casting 23
v
vi Contents
1.3.4 Copper alloys 24
1.3.5 Other non-ferrous alloys 24
CHAPTER 2 25
Overview of Solidification Processing
2.1 Introduction 25
2.2 Development of solidification microstructure 25
2.2.1 Nucleation from the melt 25
2.2.1.1 Homogeneous nucleation 27
2.2.1.2 Heterogeneous nucleation 31
2.2.1.3 Factors affecting nucleation 34
2.2.2 Crystal growth beyond the nucleation stage 36
2.2.2.1 Morphology of the solid-liquid interface 36
2.2.2.2 Interface growth kinetics 36
2.2.2.3 Interface stability in pure materials 37
2.2.2.4 Interface stability in impure materials 38
2.2.2.5 Morphology of cellular and dendritic growth 45
2.2.2.6 Growth selection of dendrites during solidification 46
2.3 Effect of processing variables on cast structure 49
2.3.1 Possible grain structures 49
2.3.2 Mould properties, melt superheat and cooling rate 50
2.3.2.1 Dendrite arm spacing 51
2.3.3 Fluid flow during casting 53
2.3.3.1 Fluidity of the melt 53
2.3.3.2 Growth behaviour of dendrites 53
2.4 Typical casting defects 54
2.4.1 Segregation of alloying elements 54
2.4.1.1 Macrosegregation 55
2.4.1.2 Microsegregation 56
2.4.1.3 Removal of micro segregation - homogenisation 57
2.4.2 Other casting defects 59
2.4.2.1 Porosity 59
2.4.2.2 Inclusions 59
2.5 Macroscopic heat flow in solidification 60
CHAPTER 3 63
Continuous Casting Processes and the Emergence of DSC
3.1 Introduction 63
3.2 Types of contin uous casting processes 65
3.2.1 Casting of ingots, billets and slabs 65
3.2.1.1 Semicontinuous casting processes 65
3.2.1.2 Genuine continuous casting processes 70
3.2.2 Thin slab casting 72
Contents vii
3.2.3 Direct strip casting 76
3.2.4 Melt quenching processes 81
3.3 The emergence of direct strip casting 83
3.3.1 General evolution of the process 83
3.3.2 The revival of strip casting of iron alloys 85
3.3.3 Current status of direct strip casting 88
3.4 Comparison between DSC and other continuous casting processes 92
3.4.1 Process characteristics and advantages of strip casting 92
3.4.2 Economic viability of strip casting 95
3.4.3 Energy and environmental considerations 98
CHAPTER 4 101
DSC Process Variables and Cast Strip Quality
4.1 Introduction 101
4.2 Overview of process control in strip casting 101
4.3 Important process variables in DSC 105
4.3.1 Melt management 105
4.3.1.1 Mould level control and melt quality 105
4.3.1.2 Melt atmosphere 105
4.3.1.3 Liquid metal containment in the mould 106
4.3.2 Mould characteristic and molten metal delivery 107
4.3.2.1 Style of mould and materials 107
4.3.2.2 Molten metal delivery 109
4.3.2.3 Mould integrity - wear, deformation and oxidation 112
4.3.3 Secondary processes and processing 115
4.4 Strip formation during DSC 115
4.4.1 Single roll/belt casters 115
4.4.2 Twin roll casters 116
4.4.3 Twin belt /block casters 121
4.4.4 Influence of casting speed on strip characteristics 122
4.4.4.1 Liquid sump profile 122
4.4.4.2 Exit temperature of as-cast strip 123
4.4.5 Some factors affecting as-cast strip thickness 125
4.5 Heat transfer in strip casting 128
4.5.1 Principal modes of heat transfer 128
4.5.2 Variation of heat transfer in strip casting 131
4.5.2.1 Transient heat flux 132
4.5.2.2 Heat flux and a moving mould 133
4.5.3 Factors influencing heat transfer in strip casting 135
4.5.3.1 Casting velocity 135
4.5.3.2 Structure and condition of the mould surface 136
4.5.3.3 Melt atmosphere 139
4.5.3.4 Melt composition 140
4.5.3.5 Melt superheat 141
4.5.3.6 Other variables 142
4.6 Cast strip quality 145
viii Contents
4.6.1 Control of internal defects 145
4.6.2 Surface condition of as-cast strip 146
4.6.3 Mechanical and other properties 150
CHAPTER 5 151
As-Cast Microstructure, Texture and Properties
5.1 Introduction 151
5.2 General features of strip-cast microstructures 151
5.2.1 Dendritic growth in a flowing melt 151
5.2.2 Secondary dendrite arm spacing 155
5.3 Strip-cast ferrous alloys 156
5.3.1 Low carbon steels 156
5.3.1.1 As-cast microstructure 156
5.3.1.2 As-cast texture 161
5.3.1.3 Methods of modifying as-cast microstructure 162
5.3.2 Austenitic stainless steels 164
5.3.2.1 As-cast microstructure 164
5.3.2.2 Phase formation during solidification 167
5.3.2.3 Segregation effects 169
5.3.2.4 As-cast textures 170
5.3.3 Ferritic stainless steels 172
5.3.3.1 Cast structure and texture 173
5.3.3.2 Texture enhancement during casting 174
5.3.3.3 Comparison of texture in strip-cast stainless steel 177
5.3.4 Other ferrous alloys 178
5.4 Strip-cast non-ferrous alloys 181
5.4.1 Aluminium alloys 181
5.4.1.1 General microstructure 182
5.4.1.2 Grain and particle morphology 184
5.4.1.3 Texture development 186
5.4.1.4 Segregation effects 189
5.4.2 Magnesium alloys 189
5.4.2.1 Cast structure and texture 190
5.4.2.2 Potential for downstream processing 191
5.4.3 Copper alloys 192
5.4.4 Other non-ferrous alloys 193
CHAPTER 6 195
Secondary Processing and Fabrication
6.1 Introduction 195
6.2 Scope of secondary processing 195
6.3 Control of thermal path after strip casting 196
Contents ix
6.3.1 Direct cooling and coiling 196
6.3.2 Direct heat treatment processes 199
6.3.2.1 Austenitisation treatments 199
6.3.2.1 Homogenisation and other treatments 200
6.4 Hot rolling processes 203
6.4.1 Conventional hot rolling 203
6.4.2 In-line rolling 204
6.4.3 Ferrite grain refinement by controlled rolling 206
6.5 Low temperature rolling processes 207
6.5.1 Microstructural development during cold rolling 207
6.5.2 Rolling textures 208
6.5.2.1 bcc metals 209
6.5.2.2 fcc metals 210
6.5.2.3 hcp metals 212
6.5.3 Warm rolling of strip-cast low carbon steel 212
6.5.3.1 Microstructural evolution 212
6.5.3.2 Warm rolling textures 213
6.6 Static annealing processes 214
6.6.1 Annealing methods 215
6.6.1.1 Batch annealing 215
6.6.1.2 Continuous annealing 215
6.6.2 Quantifying recrystallization 215
6.6.3 Recrystallization behaviour of strip-cast metals" 216
6.6.3.1 Low carbon steel 216
!
6.6.3.2 Stainless steel 220
6.6.3.3 Aluminium alloys 221
6.6.3.4 Other alloys 226
6.7 Final fabrication methods 227
6.7.1 Forming and formability 227
6.7.1.1 Forming processes 227
6.7.1.2 Factors affecting formability 227
6.7.1.3 Relationship between microstructure and formability 230
6.7.2 Surface treatments and coatings 235
APPENDIX A 237
Simulation and Modelling of Direct Strip Casting
A.l Introduction 237
A.2 Experimental techniques 237
A.2.1 Splat quenching 237
A.2.2 Substrate immersion 238
A.2.3 Laboratory-and pilot-scale strip casters 240
A.3 Mathematical techniques 241
A.3.1 Modelling of heat transfer 241
A.3.2 Modelling of fluid flow 244
A.3.3 Microstructural modelling 244
x Contents
APPENDIX B 245
Representation of Textures and Their Interpretation
B.1 Introduction 245
B.2 Measurement of textures 245
B.3 Representation of orientations and textures 247
B.3.1 Pole figures 247
B.3.2 Inverse pole figures 249
B.3.3 Orientation distribution function 250
B.4 Typical textures in metal strip 253
B.4.1 Solidification textures 253
B.4.2 Texture development during secondary processing 253
REFERENCES 255
INDEX 271