Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF PROVIDING STEEL STRIP TO ORDER
Field Of The Invention:
The present invention relates generally to systems and methods for providing
steel strip to order, and more specifically to systems and methods for
converting
customer-specified steel strip requirements to process operating parameters
for
controlling a continuous strip casting process operable to produce the
customer-
specified steel strip product.
BACKGROUND OF THE INVENTION
The conventional steel industry process for fulfilling a customer's order for
a
steel product with particular mechanical and dimensional properties is
complicated
3o and time-consuming, and may typically require 10 or more weeks to
accomplish.
Referring to FIG. 1, for example, a flowchart is shown illustrating a flow of
one
conventional process 10 for producing a customer-ordered steel strip product,
wherein the term "strip" as used herein is to be understood to mean a product
of 5mm
thickness or less.
Process 10 begins at step 12 where the steel manufacturer receives the
customer order, typically set forth in terms of mechanical and dimensional
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requirements for the steel strip product as well as a desired quantity.
Thereafter at
step 14, the steel manufacturer determines from the customer order the
particular
steel chemistry requirements for achieving the product's broad properties. The
chemistry requirements are selected from a large recipe list of steel
chemistries that
is available (and in many cases dates back to ingot casting/hot rolling
technology
where chemistry was the prime determinant of properties). Thereafter at step
16, the
steel manufacturer determines casting parameters corresponding to operating
parameters and/or set points for a steel casting process that will be used to
produce
steel slabs from molten steel formed in accordance with the steel chemistry
1o requirements. At step 18, the steel manufacturer determines downstream slab
processing requirements, initially focusing on achieving the customer's
dimensional
requirements such as thickness etc and then working through additional
downstream
processing steps that may be required to achieve the final product properties.
Such
downstream slab processing requirements may include, for example, any one or
combination of (a) slab reheat parameters corresponding to hot mill furnace
operating
parameters and/or set points for a hot strip mill processing apparatus, (b)
hot rolling
parameters corresponding to mill rolling operating parameters and/or set
points for
the hot strip mill processing apparatus, (c) cold rolling parameters
corresponding to
pickling and cold rolling operating parameters and/or set points for a cold
mill
zo processing apparatus, and (d) heat treatment parameters corresponding to
heat
treatment operating parameters and/or set points for a heat treatment
apparatus.
From step 18, process 10 advances to step 20 where the steel manufacturer
produces a batch of molten steel in accordance with the chemistry requirements
for
the specified steel product and casts the steel product into slab stock in
accordance
with the casting parameters established at step 16. Oftentimes, customer's
orders
(which can be as small as 5 tonnes) are batched until there are sufficient
orders to fill
one steelmaking heat - typically 100 to 300 tonnes depending on the specific
steel
plant design. This adds further delay to the time that a particular customer's
order
can be filled, thereby extending the total time for production well in excess
of 10
weeks. In any case, process 10 advances from step 20 to step 22 where the slab
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stock is reheated and hot rolled at a hot strip mill apparatus, in accordance
with the
slab reheat and hot rolling parameters established at step 18, to produce
steel coil
stock of a predefined thickness. Thereafter at step 24, the coil stock is
pickled and
cold rolled at a cold mill in accordance with any pickling and cold rolling
parameters
established at step 18 to reduce the thickness of the coil stock to a customer-
specified thickness. Finally, at step 26 the coil stock is heat treated at a
heat
treatment apparatus in accordance with any heat treatment parameters
established at
step 18 to anneal the coil stock such that it meets the requirements of the
customer's
order.
Conventional steel strip production of the type just described necessitates
the
production of many different steel grades (typically, in excess of 50) that
are first cast
into slabs and then processed through complex hot rolling schedules in hot
strip mills
that produce product in thicknesses as low as 1.5mm with yield strengths in
the range
300 to 45OMPa. If the customer requires thinner material or properties outside
this
range, subsequent processing involving pickle lines, cold reduction mills and
annealing
furnaces is required.
A primary drawback associated with the conventional steel strip production
process just described is the lengthy time period; typically 10 or more weeks,
required
to produce the steel product that satisfies the customer order. What is
therefore
needed is an improved steel strip production process that is more responsive
to
customer needs by greatly reducing the time required to produce customer-
specified
steel strip product.
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SUMMARY OF THE INVENTION
The foregoing shortcomings of the prior art are addressed by the present
invention. In accordance with one aspect of the present invention, a method of
controlling a continuous strip steel .casting process to produce a customer-
specified
steel product includes receiving an order for a steel product including
customer-
specified requirements relating to said product, mapping said customer-
specified
requirements to a number of process parameters for controlling a continuous
strip steel
casting process to produce said steel product, and displaying said number of
process
parameters on a process change report to an operator of said continuous strip
steel
casting process.
In accordance with another aspect of the present invention, a method of
controlling a continuous strip steel casting process to produce a customer-
specified
steel product includes receiving an order for a steel product including
customer-
specified requirements relating to said product, mapping said customer-
specified
requirements to a number of process parameters for controlling a continuous
strip steel
casting process to produce said steel product, and controlling said continuous
strip
steel casting process based on said process parameters to produce said steel
product.
In accordance with yet another aspect of the present invention, a method for
controlling a continuous strip steel casting process to produce a customer-
specified
steel product includes controlling a continuous strip steel casting process
based on a
set of predefined process parameters to produce a first steel product,
receiving an
order for a second steel product including customer-specified requirements
relating to
said second steel product, mapping said customer-specified requirements to a
set of
new process parameters for controlling said continuous strip steel casting
process to
produce said second steel product, and substituting said set of new process
parameters for said set of predefined process parameters without interrupting
said
continuous strip steel casting process such that said continuous strip steel
casting
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process immediately switches from producing said first steel product to
producing said
second steel product.
In accordance with yet another aspect of the present invention a method of-
providing custom-specified steel strip includes processing orders for steel
strip of
5 customer-specified requirements into a schedule for producing the ordered
steel strip in
a production run of a continuous strip caster casting steel strip of a single
steel
chemistry, operating the continuous strip caster during the production run to
produce
cast strip of the single steel chemistry, cooling the strip through the
austenite to ferrite
transformation temperature range, and selectively controlling the process
parameters
io to produce strip having the customer-specified requirements.
Preferably the method further includes in-line hot rolling the cast strip
prior to
cooling the strip through the austenite to ferrite transformation temperature
range.
In each of the foregoing methods according to the present invention, the
customer-specified requirements may include a specified steel grade and/or a
specified
strip thickness, and the process parameters to produce the customer-specified
steel
product may include any one or combination of casting speed of the continuous
strip
casting process, as-cast steel thickness of the steel product, percentage of
hot
reduction of the steel product, cooling rate of the steel product, coiling
temperature of
the steel product, percentage of cold reduction of said steel product,
annealing cycle
type and annealing temperature.
One object of the present invention is to provide an improved method of
providing steel strip to meet customer's orders.
Another object of the present invention is to minimize the turnaround time
between receipt of a customer order for steel strip product and actual
production of the
steel strip product.
These and other objects of the present invention will become more apparent
from the following description of the preferred embodiment.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flowchart illustrating a conventional steel strip production
process.
FIG. 2 is a diagrammatic illustration of one preferred embodiment of a
continuous steel strip casting apparatus, in accordance with the present
invention.
FIG. 3 is a diagrammatic illustration showing some of the details of the twin
roll
strip caster of the apparatus of FIG. 2.
FIG. 4 is a block diagram illustration' of a general purpose computer system
operable to convert customer-specified steel strip requirements to process
parameters
io for controlling the continuous steel strip casting apparatus of FIGS. 2 and
3.
FIG. 5 is a flowchart illustrating one preferred embodiment of a process flow
for
controlling the continuous steel strip casting apparatus of FIGS. 2 and 3
using the
general purpose computer of FIG. 4.
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DESCRIPTION OF THE PREFERRED EMBODIMENT
For the purposes of promoting an understanding of the principles of the
invention, reference will now be made to a preferred embodiment illustrated in
the
drawings and specific language will be used to describe the same. It will
nevertheless
be understood that no limitation of the scope of the invention is thereby
intended, such
alterations and further modifications in the illustrated embodiment, and such
further
applications of the principles of the invention as illustrated therein being
contemplated
as would normally occur to one skilled in the art to which the invention
relates.
The present invention is based on producing steel strip in a continuous strip
caster. Applicants have carried out extensive research and development work in
the
field of casting steel strip in a continuous strip caster in the form of a
twin roll caster. In
general terms, casting steel strip continuously in a twin roll caster involves
introducing
molten steel between a pair of contra-rotated horizontal casting rolls which
are
internally water-cooled so that metal shells solidify on the moving rolls
surfaces and are
brought together at the nip between them to produce a solidified strip
delivered
downwardly from the nip between the rolls, the term "nip" being used to refer
to the
general region at which the rolls are closest together. The molten metal may
be poured
from a ladle into a smaller vessel from which it flows through a metal
delivery nozzle
located above the nip so as to direct it into the nip between the rolls, so
forming a
casting pool of molten metal supported on the casting surfaces of the rolls
immediately
above the nip and extending along the length of the nip. This casting pool is
usually
confined between side plates or dams held in sliding engagement with end
surfaces of
the rolls so as to dam the two ends of the casting pool against outflow,
although
alternative means such as electromagnetic barriers have also been proposed.
The
casting of steel strip in twin roll casters of this kind is for example
described in U.S.
Patent Nos. 5,184,668, 5,277,243 and 5,934,359,
Applicants have determined that it is possible to produce steel strip of a
given
composition that has a wide range of microstructures, and therefore a wide
range of
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mechanical properties, by continuously casting the strip and thereafter
selectively
varying downstream strip processing parameters. For example, applicants have
determined from work carried out on plain carbon steel, including plain carbon
steel
that has been silicon/manganese killed, that selecting cooling rates in the
range of
0.1 C/s to greater than 100 C/s through the austenite to ferrite
transformation
temperature range can produce steel strip that has yield strengths that range
from
200MPa to greater than 550MPa. One example of the flexibility of continuous
strip
casting that has thus been recognized by applicants is that a production run
of a
continuous strip caster that is casting steel strip of a given composition can
be
1o controlled such that the cast strip can be selectively subjected to
different cooling rates
through the austenite to ferrite transformation temperature range, with the
result that
the strip can be produced so as to have any selection of a range of different
microstructures and therefore mechanical properties.
Applicants have discovered, generally, that by selectively varying downstream
strip processing parameters in a continuous strip steel casting process,
considerable
flexibility in terms of operating a continuous strip caster to meet production
(i.e.
customer) requirements can be realized. This means that orders placed by
customers
for steel strip of a given dimensional specification and a range of different
mechanical
properties can be produced from a single steel chemistry in a single
production run. In
?o . addition, this means that adjustments to a production run can be made
while the
production run is underway. This has been recognized by applicants as being an
important advantage of continuous strip casting in terms of meeting customer
demands
for urgent orders.
The following description of the preferred embodiment of the present invention
is
as in the context of continuous casting steel strip using a twin roll caster.
The present
invention is not limited to the use of twin roll casters, however, and extends
to other
types of continuous strip casters.
Referring to FIG. 2, a continuous strip steel casting apparatus/process 50
is illustrated as successive parts of a production line whereby steel strip
can be
3o produced in accordance with the present invention. FIGS. 2 and 3 illustrate
a twin roll
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caster denoted generally as 54 which produces a cast steel strip 56 that
passes in .a
transit path 52 across a guide table 58 to a pinch roll stand 60 comprising
pinch rolls
60A. Immediately after exiting the pinch roll stand 60, the strip passes into
a hot rolling
mill 62 comprising a pair of reduction rolls 62A and backing rolls 62B by in
which it is
hot rolled to reduce its thickness. The rolled strip passes onto a run-out
table 64 on
which it may be force cooled by water jets 66 and through a pinch roll stand
70
comprising a pair of pinch rolls 70A and 70B, and thence to a coiler 68.
Referring now to FIG. 3, twin roll caster 54 comprises a main machine frame 72
which supports a pair of parallel casting rolls 74 having a casting surfaces
74A and
748. Molten metal is supplied during a casting operation from a ladle (not
shown) to a
tundish 80, through a refractory shroud 82 to a distributor 84 and thence
through a
metal delivery nozzle 86 into the nip 88 between the casting rolls 74. Molten
metal thus
delivered to the nip 88 forms a pool 92 above the nip 88 and this pool 92 is
confined at
the ends of the rolls by a pair of side closure dams or plates 90 which are
applied to the
is ends of the rolls by a pair of thrusters (not shown) comprising hydraulic
cylinder units
connected to the side plate holders. The upper surface of pool 92 (generally
referred
to as the "meniscus" level) may rise above the lower end of the delivery
nozzle 86 so
that the lower end of the delivery nozzle 86 Is Immersed within this pool 92.
Casting rolls 74 are water cooled so that shells solidify on the moving roll
?o surfaces and are brought together at the nip 88 between them to produce the
solidified
strip 56 which is delivered downwardly from the nip 88 between the rolls 74.
The twin
roll caster 54 may be of the kind which Is illustrated and described in some
detail in
U.S. Patent Nos. 5,184,668 and 5,277,243 or U.S. Patent No. 5,488,988.
In accordance with the present invention, customer orders for steel strip are
entered into a general purpose computer system, such as computer system 150 of
FIG.
4, and processed in a manner to be more fully described hereinafter to
determine
process parameters and/or process set points for controlling a continuous
steel strip
casting process such as continuous steel strip casting process 50 just
described with
30 respect to FIGS. 2 and 3 to thereby satisfy the customer's order. Referring
to FIG. 4,
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general purpose computer system 150 includes a general purpose computer 152
that
may be a conventional desktop personal computer (PC), laptop or notebook
computer,
or other known general purposed computer configured to operate in a manner to
be
described subsequently. Computer system 150 includes a conventional keyboard
154
5 electrically connected to computer 152 for entering information relating to
the
customer's order therein, and may include any one or combination of output
devices.
For example, computer 152 may be electrically connected to a printer 156,
wherein
computer 152 may be configured to print a set of process parameters in the
form of a
process change report or similar report, wherein the process change report
sets forth
1o the process parameters and/or set points for controlling a continuous steel
strip casting
process, such as continuous steel strip casting process 50 illustrated in
FIGS. 2 and 3,
in a manner to produce the customer ordered steel strip product. In one
embodiment of
the present invention, an operator of the continuous steel strip casting
process, such as
process 50, views the process change report and makes corresponding physical
changes to the continuous steel strip casting process to thereby produce the
customer
ordered steel strip product.
Computer 152 may alternatively or additionally be electrically connected to a
conventional monitor 158, wherein computer 152 may be configured to display a
set of
process parameters in the form of a process change report or'similar report,
wherein
the process change report sets forth the process parameters and/or set points
for
controlling a continuous steel strip casting process, such as continuous steel
strip
casting process 50 illustrated in FIGS. 2 and 3, in a manner to produce the
customer
ordered steel strip product. An operator of the continuous steel strip casting
process,
such as process 50, may view the process change report displayed on the
monitor 158,
in addition to or in place of a printed report, and make corresponding
physical changes
to the continuous steel strip casting process to thereby produce the customer
ordered
steel strip product.
Computer 152 is also electrically connected to a conventional storage media
unit
160, wherein computer 152 is configured to store information to, and retrieve
3o information from, storage unit 160 in a known manner. In one embodiment of
the
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present invention, computer 152 is configured to download a set of process
parameters
in the form of a process change report or similar report to a storage media
162 via
storage unit 160, wherein the process change report sets forth the process
parameters
and/or set points for controlling a continuous steel strip casting process,
such as
continuous steel strip casting process 50 illustrated in FIGS. 2 and 3, in a
manner to
produce the customer ordered steel strip product. An operator of the
continuous steel
strip casting process, such as process 50, may then access the contents of the
storage
media via conventional techniques to view the process change report and make
corresponding physical changes to the continuous steel strip casting process
to
thereby produce the customer ordered steel strip product. Storage media unit
160 and
storage media 162 may be implemented as any known storage media unit and
storage
media combination. Examples include, but are not limited to, a magnetic disk
read/write unit 160 and magnetic diskette 162, CD ROM read/write unit 160
and.CD
ROM disk 162, and the like.
In an alternative embodiment, the continuous steel strip casting process, such
as
continuous steel strip casting process 50 illustrated in FIGS. 2 and 3, is a
computer-
controlled process, and in this case computer system 150 may be configured to
provide
the process change report directly (electronically) to process 50 via a
suitable
communication link 164 as shown in phantom, in FIG. 4. Alternatively still,
computer
152 may be configured in such an embodiment to download the process change
report
to storage media 162, wherein an operator loads the storage media 162
containing the
process change report into a storage media unit (not shown) similar to.
storage media
unit 160 resident within process 50 as illustrated in FIG. 4 by dashed line
166. In either
case, the continuous steel strip casting process, such as process 50, is
responsive to
the process change report to automatically make corresponding process changes
and/or apparatus set point changes. It is to be understood, however, that
regardless of
how process and/or set point changes are made to the continuous steel strip
casting
process, the strip casting process apparatus is responsive to such changes to
immediately switch from producing the steel strip product that it is currently
producing
to producing steel strip product according to the new process
parameter/process set
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point information.
Referring now to FIG. 5, a flowchart is shown illustrating one preferred
embodiment of a process 200 for controlling a continuous strip steel casting
process,
such as process 50 illustrated and described with respect to FIGS. 2 and 3, to
produce
a customer-specified steel product. Process 200 begins with an initial step
202 of
receiving a customer order for a steel strip product having specified
mechanical
properties or product specifications. In one embodiment, the product
specifications
include a desired grade of the steel product, a desired strip thickness and
total strip
quantity, although the present invention contemplates requiring additional or
alternative
1o information relating to the customer ordered product. Thereafter at step
204, the
product specifications are entered into computer 152 via any known mechanism
therefore. For example, an operator may key the information into computer 152
via
keyboard 154, or if the information is provided by the customer on a storage
media
such as a diskette, an operator may simply upload the information into the
computer via
storage media unit 160. Alternatively, the present invention contemplates
entering the
product specifications into computer 152 in accordance with other known
techniques
not detailed in the attached drawings, wherein such other known techniques may
include, but are not limited to, transferal of the product specifications via
a telephone
modem connection between computer 152 and a customer computer, transferal of
the
product specifications via an internet connection, or the like.
In any case, process 200 advances from step 204 to step 206 where computer
152 is operable to compute the process parameters and/or process set points
for
controlling a continuous steel strip casting process, such as process 50, in a
manner to
produce the customer ordered steel product, based on the product
specifications
entered into computer 152 at step 204. In accordance with the present
invention,
computer 152 is programmed with one or more sets of rules relating the product
specifications entered into computer 152 at step 204 to a set of process
parameters/set
points for controlling the continuous steel strip casting process in a manner
to produce
the customer ordered steel product. The one or more sets of rules may be
implemented as any one or combination of one or more tables, one or more
graphs,
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one or more equations, and the like. An example of one illustrative set of
rules is set
forth below in Tables I, II and III.
Table I details a set of rules mapping product specifications relating to
steel
products that may be ordered by any customer to hot brand product processing
parameters/set points for the continuous steel strip casting process 50 shown
and
described herein. As they relate to table I, ASTM-specified steel grades for
hot brand
products are associated with the following yield strengths (YS) and percent
elongations
(% Elong):
ASTM Grade YS (ksi) % Elona
Grade 33 33 to 43 30 to 35
Grade 40 40 to 50 25 to 30
Grade 50 50 to 60 20 to 25
Grade 65 65 to 75 15 to 20
Grade 80 80 to 90 10 to 15,
And the residual level indicators L, M and H are defined by the relationships
Low (L) <
0.35 %, Med (M) = 0.8 %, and High (H) =1.2 %.
Table I
Hot band product Caster process set points
specifications
CUSTOMER ORDER
Thickness ASTM Level of Casting As-cast % hot ROT cooling
(mm) grade residuals Speed thickness reduction curve
(Cu+Sn+ (m/min) (mm)
Mo+Ni+ Cooling Coiling
Cr) Rate* Temp
C/s C
0.04" Grade 33 Cannot be produced with the current chemistry
(1.0 mm)
0.04" Grade 40 = L 80 1.6 38 700
(1.0 mm)
0.04" Grade 50 L 80 1.6 38 150
(1.0 mm) M 80 1.6 38 700
0.04" Grade 65 L 80 1.6 38 200
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(1.0 mm) M 80 1.6 38 150
H 80 1.6 38 650
0.04" Grade 80 M 80 1.6 38 200
(1.0 mm) L 80 1.6 38 250
0.047" Grade 33 Cannot be produced with the current chemistry
(1.2 mm)
0.047" Grade 40 L 80 1.6 25.0 700
(1.2 mm)
0.047" Grade 50 L 80 1.6 25.0 150
(1.2 mm) M 80 1.6 25.0 700
L 45 1.9 37 650
0.047" Grade 65 L 80 1.6 25.0 200
(1.2 mm) M 80 1.6 25.0 150
H 80 1.6 25.0 650
0.047" Grade 80 H 80 1.6 25.0 200
(1.2 mm) M 80 1.6 25.0 250
0.055" Grade Cannot be produced with the current chemistry
(1.411) 33
0.055" Grade 40 L 80 1.6 12.5 700
(1.4mm)
0.055" Grade 50 L 80 1.6 12.5 60
(1.4mm) M 80 1.6 12.5 650
L 45 1.9 26.0 650
0.055" Grade 65 L 80 1.6 12.5 100
(1.4mm)
0.055" Grade 80 L 80 1.6 12.5 150
(1.4mm) H 80 1.6 12.5 650
0.063" Grade 33 Cannot be produced with the current chemistry
(1.6 mm)
0.063" Grade 40 L 80 1.6 0.0 700
(1.6 mm)
0.063" Grade 50 L 80 1.6 0.0 60
(1.6 mm) M 80. 1.6 0.0 650
0.063" Grade 65 L 80 1.6 0.0 100
1.6 mm
0.063" Grade 80 L 80 1.6 0.0 150
1.6 mm) H 80 1.6 0.0 650
0.075" Grade 33 Cannot be produced with the current chemistry
(1.9 mm
0.075" Grade 40 L 45 1.9 0.0 700
(1.9 mm)
0.075" Grade 50 M 45 1.9 0.0 650
(1.9 mm)
0.075" Grade 65 H 45 1.9 0.0 650
(1.9-mm)
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0.075" Grade 80 Unlikely to produce as the transformation will occur before
(1.9 mm) the ROT
* - cooling rate in the 800 - 5000 C temperature range
A general set of rules for hot band products used to generate the Table I
values
5 are summarized in Table II below, wherein the term "chemistry" refers to the
level of
residuals in the steel product, and wherein the Low, Med and High levels are
summarized above.
Table II
Chemistry %HR Cooling rate Yield strength
MPa
Low <15 150 550
Low 25-40 250 550
Med 25-40 200 550
High 0-50 30* 550
Low <15 100 475
Low 25-40 200 475
Med 25-40 150 475
High 0-50 30* 475
Low <15 60 400
Low 25-40 150 400
Med 25-40 30* 400
Low 0-50 30* 350
* - standard cooling rate to achieve coiling temperatures around 650 - 700 C
From data gathered from actual runs, it was determined that 1.2% of residuals
resulted in an increase in yield strength of approximately 120 Mpa, and it is
therefore
assumed that a 0.1 % increase in residuals results in a corresponding 10 Mpa
increase
in yield strength.
From Table I, it should now be apparent that the process parameters required
to
produce a customer-specified hot band steel product may include any one or
combination of casting speed of the continuous strip casting process, as-cast
steel
thickness of the steel product, percentage of hot reduction of the steel
product, cooling
rate of the steel product and coiling temperature of the steel product.
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Table III details a set of rules mapping product specifications relating to
steel
products that may be ordered by any customer to cold rolled product processing
parameters/set points for the continuous steel strip casting process 50 shown
and
described herein. As they relate to table III, the ASTM-specified steel grades
for cold
rolled products are associated with the following yield strengths (YS) and
percent
elongations (% Elong):
ASTM Grade YS (ksi) % Elong
Grade 33 33 to 43 30 to 35
Grade 40 40 to 50 30 to 35
Grade 50 50 to 60 25 to 30
Grade 65 65 to 75 10 to 15
Grade 80 80 to 90 2 min.
Table III
Cold rolled product Hot band Cold rolling/annealing parameters
specifications specifications
CUSTOMER ORDER
Cold Cold Hot band Hot band % cold Annealing Annealing
rolled rolled thickness ASTM reduction cycle temperature
Thickness ASTM (mm) grade ( F)
(mm) grade
0.008" Grade 33 1.0 -1.6 Grade 40 80-88 Batch Lab data* -
(0.2 mm) Annealing see
(BA) - footnote
0.008" Grade 40 1.0-1.6 Grade 40 80-88 Batch/Con 1250-1350
(0.2 mm) -tinuous
Annealing
(CA)
0.008" Grade 50 1.4-1.6 Grade 50 86-88 CA 1250-1350
0.2 mm)
0.008" Grade 65
(0.2 mm)
0.008" Grade 80 1.0-1.6** Grade 40 80-88 N/A N/A
(0.2 mm)
0.016" Grade 33 1.0-1.6 Grade 40 60-75 BA
0.4 mm
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0.016" Grade 40 1.0-1.6 Grade 40 60-75 BA/CA 1250-1350
(0.4 mm)
0.016" Grade 50 1.4-1.6 Grade 50 70-75 CA 1250-1350
(0.4 mm)
0.016" Grade 65
(0.4 mm)
0.016" Grade 80 1.0-1.6** Grade 40 60-75 N/A N/A
(0.4 mm)
0.024" Grade 33 1.4-1.6 Grade 40 57-63 BA
(0.6 mm)
0.024" Grade 40 1.4-1.6 Grade 40 57-63 CA 1250-1350
(0.6 mm)
0.024" Grade 50 1.6-1.9*** Grade 50 57-68 CA 1250-1350
(0.6 mm)
0.024" Grade 65
(0.6 mm)
0.024" Grade 80 1-1.6** Grade 40 40-63 N/A N/A
(0.6 mm)
0.032" Grade 33 1.4-1.6 Grade 40 43-50 BA
0.8 m m
0.032" Grade 40 1.6-1.9*** Grade 40 50-58 BA
0.8 m m
0.032" Grade 50
0.8mm
0.032" Grade 65 1.0 Grade 40 20 N/A N/A
(0.8mm)
0.032" Grade 80 1.2-1.6** Grade 40 33-50 N/A N/A
0.8 mm
0.040" Grade 33 1.9 Grade 40 47 BA
(1.0 mm)
0.040" Grade 40 1.9 Grade 40 47 BA
1.0 mm)
0.040" Grade 50
(1.0 mm)
0.040" Grade 65 1.3 Grade 40 23 N/A N/A
(1.0 mm)
0.040" Grade 80 1.6-1.9*** Grade 40 38-48 N/A N/A
1.0 mm)
* Lab data on batch annealing - slow heating to 1275 F (took around 33 hours)
followed by slow cooling from 1275 F to 750 F (took around 8 hours). Material
yield
strength after annealing was quite low (23 ksi), there accordingly exists an
opportunity
s to optimize batch annealing for Grade 33.
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18
** thinner gauge hot band preferred, as less cold reduction will give better
elongation.
*** thicker gauge hot band preferred to get higher yield strength with good
elongation
after annealing.
A general set of rules for cold rolled material used to generate the Table III
values are:
(i) need greater than 35-40 % CR to get Grade 80,
(ii) for continuous annealing, need at least 50% cold reduction, and
(iii) for batch annealing, need at least 40% cold reduction.
From Table III, it should now be apparent that the process parameters required
to produce a customer-specified cold rolled steel product may include any of
the hot
band process parameters for producing hot band products, and additionally one
any or
combination of percentage of cold reduction, annealing type; e.g., batch or
batch/continuous, and annealing temperature.
Referring again to FIG. 5, process 200 advances from step 206 to step 208
where computer 152 is operable in one embodiment of the present invention to
display
the process parameters on a process change report to a continuous strip
casting
operator. It will be appreciated that step 208 is typically included only when
computer
152 is not operable to automatically control the continuous steel strip
casting process
50 as described hereinabove, and may otherwise be omitted from process 200. If
included, computer 152 may be configured to display the process change report
via
any one or more of the output devices described hereinabove with respect to
FIG. 4. In
this embodiment, dashed-line box 210 outlines the steps of process 200 that
are
executed by computer 152. Additionally, as described hereinabove, the present
invention contemplates embodiments wherein computer 152 is operable to receive
the
customer order electronically, and dashed-line box 210 may be extended in such
embodiments to include step 202.
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19
Following step,208, process 200 advances to step 212 where the continuous
strip casting process, such as continuous strip casting process 50 illustrated
and
described with respect to FIGS. 2 and 3, is controlled as a function of the
process-
parameters computed at step 206 to thereby produce the customer-specified
steel
product. In embodiments of process including step 208, step 212 is generally
not
executed by computer 152 but is instead carried out by an operator of the
continuous
steel strip casting process. The operator executes step 212 in such
embodiments by
physically implementing the process parameters/set points set forth in the
process
change report. In embodiments wherein computer 152 is configured to provide
the
1o process parameters/set points directly (electronically) to the continuous
steel strip
casting process, step 208 may be omitted an step 206 may advance directly to
step
212. In such embodiments, computer 152 may be configured to automatically
implement the process parameters/set points computed at step 206 in the
continuous
steel strip casting process, and these cases dashed-line box 210 extends to
include
step 212.
In accordance with the present invention, computer system 150 is operable to
map the customer-specified product specifications to a production run schedule
for a
steel of a selected composition. Typically, a production run schedule for a
given steel
chemistry may extend for at least several days during which steel strip'is
continuously
cast by the twin roll caster 54. Depending upon the number of orders and
ordered
quantities, an entire production run may be concerned with producing steel
strip having
one particular set of mechanical properties or for producing steel strip of
different
selected mechanical properties along the length of the strip.
The production run schedule takes into account parameters such as casting
speed, hot rolling temperature range, amount of hot reduction, and cooling
rates
through the austenite to ferrite transformation temperature range (typically
900 to
550 C) to produce final microstructures in the cast strip that provide the
strip with the
required mechanical properties and the consequential materials handling issues
associated with changing the cooling rates of the strip.
By adjusting the cooling rate within the range of 0.1 C/s and in excess of
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100 C/s it is possible to produce cast having microstructures including:
(i) predominantly polygonal ferrite;
(ii) a mixture of polygonal ferrite and low temperature transformation
products,-such
as a acicular ferrite, Widmanstatten ferrite, and bainite; and
s (iii) predominantly low temperature transformation products.
In the case of plain carbon steels, such a range of microstructures can
produce
yield strengths in the range of 200MPa to in excess of 700MPa. After the
production
run schedule has been established, the twin roll caster 54 can be operated to
produce
10 cast strip in accordance with the production schedule and the strip can be
delivered to
customers as required.
One advantageous feature of the method of the present invention is that it is
possible to adjust a production run schedule during the course of a production
run to
accommodate production on an urgent basis of a strip order of required
mechanical
15 properties. Thus, in the method of the present invention: a single steel
chemistry is
used to produce a wide range of mechanical properties - thus customer's orders
no
longer need to be delayed until a heat/batch is assembled; strip casting in
conjunction
with control of rolling temperature, degree of hot reduction and the final
product cooling
rate can enable the achievement of the customer's dimensional specification
and
zo required mechanical properties simultaneously within one production line
typically less
than 70 meters in length; properties can be changed in real time by modifying
appropriate set points on key process control loops in a central control
computer and
thus the time from receipt of customer order to product dispatch can be as
little as 8
hours as opposed to conventional steel production method that takes 14 to 30
days;
as and the very short order to delivery time enables the concept of a "virtual
warehouse "
via the application of e-commerce.
While the invention has been illustrated and described in detail in the
foregoing
drawings and description, the same is to be considered as illustrative and not
restrictive
in character, it being understood that only preferred embodiments thereof have
been
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21
shown and described and that all changes and modifications that come within
the spirit
of the invention are desired to be protected.
