Ferry M. Direct Stripcasting of Metals and Alloys: Processing, Microstructure and Properties
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List of
abbreviations
xi
LIST
OF
ABBREVIATIONS
AA
ACB
AISI
ASTM
bcc
CAFE
CBMS
CCC
CCT
CD
CRA
CSIRO
CSP
DCAP
DCC
DSC
EBSD
fcc
hcp
HRA
ISP
LDR
ND
NNSC
ODF
PFC
RD
SDAS
SEM
SFE
TD
TEM
TMP
TRC
TSC
TIT
UNS
XRD
Aluminium
Association Inc.
Articulated chill block (caster)
American Iron
and
Steel Institute
American
Society of Testing Materials
Body centred cubic
Cellular automata-finite element (modelling)
Chill block melt spinning
Conventional continuous casting
Continuous cooling transformation (diagram)
Casting direction
Cold rolling
and
annealing
Commonwealth Scientific
and
Industrial Research Organisation
Compact strip
production
Dissimilar channel angle pressing
Direct chill casting
Direct strip casting
Electron backscatter diffraction
Face centred cubic
Hexagonal close packed
Hot
rolling
and
annealing
In-line strip production
Limiting
drawing
ratio
Normal direction
Near
net
shape casting
Orientation distribution function
Planar flow casting
Rolling direction
Secondary dendrite
arm
spacing
Scanning electron microscope/microscopy
Stacking fault energy
Transverse direction
Transmission electron microscope/microscopy
Thermomechanical processing
Twin roll casting
Thin slab casting
Time-temperature-transformation (diagram)
Unified
numbering
system
X-ray diffraction
xii List of
Symbols
LIST OF SYMBOLS
a,A,b
A
ASL
ASM
Ac
Av
B
C
lI
c
2
C
C
E
C
Fe
-
X
C
g
C
L
Co
C
s
C
p
C~
C~
Cr
eq
d
t
d
T
D
D
DLM
DL
Do
Ds
DT
fL
fs
f(B)
Fe
FG
g
G
G
G;
G
L
G
min
G
s
G
h
Constants
Metal/mould interfacial area
Surface area of solid-liquid interface
Surface area of solid-mould interface
Metal-mould contact interfacial area
Metal-mould void interfacial area
Kinetic function in JMAK equation
Constants
Concentration/composition
Eutectic composition
Concentration of X in equilibrium with ferrite
or
austenite
Dissolved gas concentration in the liquid
or
solid state
Composition of the liquid within the two phase
(S+L)
region
Average composition of an alloy
Composition of the solid within the two phase
(S+L)
region
Heat capacity
Maximum concentration between adjacent dendrites
Minimum concentration between adjacent dendrites
Chromium equivalent
Thickness of a solidified shell
in
strip casting
Strip/plate/slab thickness
on
leaving the continuous caster
Diameter of a circular channel
Roll diameter of a twin roll caster
Liquid diffusion coefficient at the melting point
Liquid diffusion coefficient
Frequency factor in solid-state diffusion
Solid-state diffusion coefficient
Strip thickness
on
leaving the nozzle of a twin roll caster
Liquid volume fraction
Solid volume fraction
Shape factor
Emissivity function
Geometric view factor
Mould-nozzle gap height in planar flow casting
Temperature gradient
Conductivity-weighted temperature gradient
Concentration gradient
in
the liquid
Temperature gradient in the liquid
Minimum growth velocity for interface instability
Temperature gradient in the solid
Growth rate of recrystallizing grains
Heat transfer coefficient
h
HL
Hs
k
k
k
kg
kL
k
m
kM
k,
kll
k2
etc
K
K
L
L
f
m
L
M
n
n
n
.
n
i
no
nr
N
N
het
N
hom
Nieq
p
p
p
q
"if
qmax
if
Q,
r
r
r
r*
r
R
R
R
R
Average heat transfer coefficient
Enthalpy of liquid phase
Enthalpy of solid phase
Equilibrium partition coefficient
Thermal conductivity
Boltzmann constant
List
of
Symbols
xiii
Thermal conductivity of gas layer between mould and metal
Thermal conductivity of liquid
Thermal conductivity of metal
Thermal conductivity of mould
Thermal conductivity of solid
Constants
Solidification rate constant
Strength coefficient
Fluidity of the melt
Latent heat of fusion
Gradient of liquidus
Function
in
the
SDAS
equation
Dendrite arm spacing exponent
JMAK exponent
Strain hardening exponent
Number of clusters of critical radius in a volume of liquid
Total number of atoms in a volume of liquid
Number of clusters of atoms of a given radius
Rate of nucleation per
unit
volume
Rate of heterogeneous nucleation
per
unit volume
Rate of homogeneous nucleation per unit volume
Nickel equivalent
Constant
Contact pressure between metal casting and mould
Melt ejection pressure in planar flow casting
Heat flux
Average (interfacial) heat flux
Maximum (interfacial) heat flux
Energy generated per unit volume
Activation energy of solid-state bulk diffusion of solute atoms
Normal plastic anisotropy
Radial position within the roll of a twin roll caster
.
Particle/embryo radius
Critical embryo radius for nucleation
Normal plastic anisotropy (average)
Billet radius
Roll radius of a twin roll caster
Solid-liquid interface velocity
Universal gas constant
xiv List of
Symbols
R.
R;
SL
Ss
t
t
f
tN
to
ts
T
TE
Tm
Tm
TL
TL(x)
TM
To
t
Tl
T2
v
F
V
z
v,
V,
Vca,t
V,
W
x,y,z
Xv
a
a
a
a
L
as
a<uvw>
Arithmetic average roughness
of
a substrate surface
Average interface contact resistance
Entropy
of liquid
phase
Entropy
of solid
phase
Time
Local solidification time
Time
required
for nucleation of crystallization
Incubation
period
for nucleation of recrystallization
Contact time
between
the
melt
and
mould
wall
Absolute
temperature
Temperature
of the eutectic isotherm
Equilibrium melting
temperature
(pure
metal
or
alloy)
Metal
temperature
(at
the
metal/mould
interface)
Temperature
of metal
being
cast
Temperature
of liquidus
ahead
of
the
solid-liquid interface
Mould
temperature
(at
the
metal/mould
interface)
Ambient
(or
mould)
temperature
Cooling rate
Liquid
temperature
of average composition
Co
Liquid
temperature
at
the
solid-liquid interface
Liquid flow velocity
Casting velocity
in
the
vertical direction
Substrate
moving
velocity
Volume of solid forming
in
the liquid
Casting velocity
in
direct chill casting
Volume of a solid spherical cap
on
a
mould
wall
Width
of
the
orifice slot
in
planar
flow casting
Directions
Fraction recrystallized (transformed)
Dimensionless
number
(=
D,t /
e)
Metal/mould contact length
in
a
twin
roll caster
Thermal diffusivity
Liquid
thermal
diffusivity
Solid
thermal
diffusivity
Angular
deviation of grains
about
<uvw>
Sump
depth
in
continuous casting
Mould-liquid interfacial
energy
Solid-liquid interfacial
energy
Solid-mould interfacial
energy
Planar
lattice disregistry
between
adjacent
phases
Width
of
liquid
diffusional
boundary
layer
Amplitude
of a
perturbation
on
a solid-liquid interface
Time
dependence
of
the
amplitude
of
an
interfacial
perturbation
Interfacial gas film thickness
True
strain
£
("10)
()
()
1J
A.
A.
i
VLS
~
P
P
s
a
a
¢
0)*
r
L'lG
L'lG
r
L'lG
hom
L'lG
het
L'lG~et
L'lG~om
L'lh
L'lP
L'lr
L'lS
L'lT
L'lT
L'lTi
L'lTk
L'lTo
L'lTN
L'lTs
<l>,
CfJI'
CfJ2
List of
Symbols
xv
Degree of
hot
rolling
Dendrite
growth
angle from the
heat
flow direction
Wetting angle
Average misorientation of
an
aggregate of crystallites/grains
Wavelength of a perturbation
on
a solid-liquid interface
Dendrite
arm
spacing:
primary
(i
= 1); secondary
(i
= 2 ) etc.
Frequency
at
which atoms
jump
across a liquid-solid interface
Dimensionless instability function
Density
Density of a solid
Stefan-Boltzmann constant
True stress
Dendrite deflection angle in a flowing melt
Number
of atoms
surrounding
a critical-sized embryo
Gibbs-Thompson coefficient
Free energy change associated
with
a
phase
transformation
Excess free energy associated
with
a spherical cluster of atoms
Free energy change
in
homogeneous nucleation
Free energy change in heterogeneous nucleation
Free energy barrier to heterogeneous nucleation
Free energy barrier to homogeneous nucleation
Change
in
height of the melt
in
continuous casting
Change
in
metallostatic pressure of the melt
in
continuous casting
Planar anisotropy
Entropy of fusion
Thermal driving force in
heat
transfer
Undercooling (Supercooling)
Temperature difference across a metal/mould interface
Kinetic undercooling
Temperature range
in
the two-phase
(L+S)
region of
an
alloy
Maximum
undercooling (homogeneous nucleation)
Melt
superheat
Euler angles
Preface
Direct strip casting
(DSC)
is a continuous casting technique for producing
metallic sheet directly from the molten state that minimises the need for
substantial secondary processing. The process has come a long
way
since Sir
Henry Bessemer's first attempt
at
twin roll casting of lead
and
tin strip in 1846
and
it
is
now
possible to cast a range of ferrous
and
non-ferrous alloys into both
thick- and thin-gauge strip.
Over the
past
few decades, substantial progress in
process control together
with
a better understanding of various phenomena
associated
with
high speed casting has enabled DSC to compete with,
and
often
surpass, more conventional continuous casting processes. The process already
offers a
number
of significant advantages over conventional casting such as
an
increased cost effectiveness, energy efficiency and environmental sustainability.
If
the various metallurgical
and
technological challenges to produce high
quality as-strip-cast strip can be overcome,
it
is likely
that
DSC will make a
profound impact
on
the manufacturing landscape of the 21st century.
The book originated from the desire to provide
an
up-to-date account of the
influence of processing parameters
on
microstructure
and
properties of
both
ferrous
and
non-ferrous alloys produced
by
strip casting.
It
was
written for
senior
undergraduate
and
postgraduate students majoring in metallurgy,
materials science
or
mechanical engineering
but
is also suitable as a reference
text for practicing engineers involved in
high
speed continuous casting.
It
is
pertinent to note
that
the book is
not
intended to provide a detailed account of
machine dynamics
and
process control in DSC
but
interested readers can refer
to these aspects of the process in the various publications provided in the
reference list.
xvii
xviii
Preface
The book is divided into six chapters
with
the first two providing background
information
on
the metallurgical principles of metals
and
alloys in relation to
strip casting. Chapter 1 describes the physical metallurgy of alloys already
produced commercially
by
DSC
and those that are possible candidates. Since
solidification is fundamental to casting performance
and
the production of high
quality strip, Chapter 2 describes the more important theoretical
and
practical
aspects of solidification phenomena. Chapter 3 begins
with
a discussion of
various continuous casting processes for producing metallic sheet
and
follows
with
a discussion
on
the emergence of DSC. The chapter also compares these
continuous casting processes, with particular reference to the effect of economic
and
environmental constraints
on
the commercial viability of DSC. Chapter 4
provides a technical account of some of the important process variables
affecting the performance of a strip caster
and
factors influencing the quality of
the as-cast strip.
It
also covers heat flow during
high
speed continuous casting
and
the variables affecting solidification behaviour.
An
important metallurgical challenge associated
with
the development of strip
casting is the need to understand the relationship between casting variables
and
microstructure
and
properties.
Due
to the caster design
and
high
solidification
rates associated
with
DSC, the process is capable of producing thin-gauge strip
exhibiting far-from-equilibrium microstructures. The final two chapters deal
with
microstructural evolution in a range of commercially-significant ferrous
and
non-ferrous alloys
both
during casting
and
further downstream processing.
Chapter 5 focuses
on
some key casting variables affecting the development of
microstructure, texture
and
properties of as-cast strip
with
Chapter 6 providing
an
account of possible secondary processing strategies for structural/surface
modification of as-cast strip for enhancing the final properties of the material.
I
am
indebted to a
number
of students, friends
and
colleagues for stimulating
discussions
on
near-net-shape continuous casting over the
past
few years. In
particular, I
would
like to acknowledge
my
friends
and
colleagues
at
Bluescope
Steel (formerly BHP Steel) for introducing
me
to the fascinating field of direct
strip casting. I would especially like to thank Les Strezov, Kannappar
Mukunthan, Joe Herbertson
and
Rama Mahapatra.
On
a
more
personal level, I
am
sincerely grateful to Max Hatherly
and
Peter Krauklis for critically
reviewing the manuscript
and
providing
many
useful comments
and
suggestions. Finally, I
must
acknowledge the patience
and
understanding of
my
wife Debbie
and
our
children Matt
and
Meg during the writing of the book.
I thank them for the encouragement
and
support.
Michael Ferry
Sydney, Australia
