Ferry M. Direct Stripcasting of Metals and Alloys: Processing, Microstructure and Properties
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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
www.woodheadpublishing.com
Published in North America by CRC
Press LLC, 6000 Broken Sound Parkway, NW,
Suite
300, Boca Raton,
FL
33487, USA
First published 2006, Woodhead Publishing Limited and CRC Press LLC
© 2006, Woodhead Publishing Limited
The author has asserted his moral rights.
This book contains information obtained from authentic and highly regarded sources.
Reprinted material
is
quoted with permission, and sources are indicated. Reasonable
efforts have been made to publish reliable data and information, but the author and the
publishers cannot assume responsibility for the validity
of
all materials. Neither the
author nor the publishers, nor anyone else associated with this publication, shall be liable
for any loss, damage or liability directly or indirectly caused or alleged to be caused by
this book.
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British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library.
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of
Congress Cataloging in Publication Data
A catalog record for this book is available from the Library
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Congress.
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
CRC Press order number: WP7600
The publishers' policy is to use permanent paper from mills that operate a sustainable
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Printed by
TJ
International Ltd, Padstow, Cornwall, England
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