Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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GLAD-1030 ~ PATENT
CONTINUOUS CASTING RO~.,S AND METHOD OF USING
s
1. Field of the Invention
This invention relates to. the field of conti uous casting, and in particular
to continuous
casting rolls that are used to guide a newly-form cast strand after it emerges
from a continuous
casting mold.
2. Description of the ~telated Technolo~r
Metals such as steel are continuously cast to strands by pouring hot, molten
metal into
the upper end of a mold and continuously withd ing a metal strand from the
mold's bottom.
As the molten metal passes through the mold, the aces of the metal that are
adjacent to the
mold walls are cooled, thus solidifying and hard ing the metal to form a
casting or shell of
solidified metal around the molten metal in the s d. After leaving the bottom
of the xnold, the
metal continues to cool and the casing or shell of olidified metal around the
molten core
thickens until the whole strand section is
The shell of solidified metal around the molten cone as the continuous casi
strand leaves
the mold is relatively thin and fragile and requir support. Such support, in
continuous casting
of metals, is customarily provided by "guide rolls ' or "caster rolls" which
engage and suppoxt
the opposite sides of the continuously cast strand. a supporting rolls
immediately below the
mold, where the shell of solidified metal is relativ ly thin, are usually of
relatively small
diameter and are longitudinally spaced closely to then. To assist cooling of
the slab and to
prevent the rolls and bearings from overheating, ese suppozting rolls may be
li9uid cooled.
2s Further away from the mold bottom, where the m tal has cooled and the shell
of solid metal has
thickened, rolls of larger diameter, spaced at great~z longitudinal distance,
are usually employed.
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To control the casting speed, certain of the supp rung and guiding rolls may
be driven.
Typically, of course, the supporting rolls arc ged about an arcuate path or
apron that defines
the path of the strand as it emerges vertically do wardly from the mold, then
gradually bends
about a 90 degree arc until it emerges as a fully lidified, horizontally
oriented casting. Space is
generally provided between the rolls for permit ' g introduction of spray
water to cool the cast
strand.
Caster rolls are required to operate in a s~vere hostile service cnvironrner~t
which subjects
the rolls to cyclic thermal shock, thermal and m ical bending stresses and
elevated
temperature abrasion. The temperature of the sol difying slab at the first
caster roll may exceed
1200 degrees C. Also, the solidifying slab is rapi ly quenched as it moves
between the caster
rolls, producing rapid thermal excursions in the lls and superheated steam.
All of these actions
are occurring while the roll is in a highly corrosi a aqueous environment of
the cooling water
which contains acids and/or bases from the flux d water treatment chemicals,
most notably
fluorine and fluoride solutions. Moreover, while a roll is in contact with the
solidifying slab,
the roll is elongating at that contact position such that the rolls are
continuously undergoing
tension-compression cycles.
To extend caster roll life in this severe s 'ce environment, the working
surface of caster
roil bodies are generally weld surfaced or cladd with alloys having superior
resistance to the
harmful effects of the service environment as co pared to the base alloy steel
roll material. Thus,
the roll is a composite or bimetallie structure. l~u~ to the narrow tolerances
required to control
slab thickness and solidification, the roll diamet must not vary (due to wear
or other factors)
more than about 0.040 in. When wear, thermal s ek or corrosion produces even a
small change
in the roll surface, the casting operation must shu down. The assembly of
rolls (typically 8 to 16
rolls in a segment) is then replaced and the affect rolls are re-machined
and/or rc-weld
surfaced.
Surfacing of caster rolls has been performed with nickel base, cobalt base,
iron base and
stainless steel type alloys. Most typically, the cla~ding is martensitic
stainless steel. As will be
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GLAD~X030 ~ PATENT
appreciated by those skilled in the art, the micro cture of stainless steel
alloys and other
materials is adversely affected by the heat input d cooling rate associated
with surface cladding
processes. This results in microstructure change, egregation and zones of
deposit non-
uniformity that affect service performance.
A need exists for an improved continuo casting roll that exhibits high
temperature
strength and stability, low thermal expansion , superior oxidation resistance
at temperatures
that are typical during operation in a continuous acting machine. A further
need exists for such
a roll to exhibit superior resistance to degradatio in high temperature
fluorine and fluoride
environments.
Accordingly, it is an object of the inventi n to provide an improved
continuous casting
roll that exhibits high temperature strength and s bility, low thermal
expansion, and superior
oxidation resistance at temperatures that are typi 1 during operation in a
continuous casting
machine.
It is further an object of the invention to p~ovide any improved continuous
castizrg roll that
exhibits superior resistance to degradation in high temperature fluorine and
fluoride
environments.
In order to achieve the above and other ob ects of the invention, a roll for
use in a
continuous casting machine includes, according a first aspect of the
invention, a roll body that
is constructed and arranged to be mounted for ro tion; and a generally
cylindrical outer surface
on the roll body, the outer surface comprising an ge-hardenable nickel-based
alloy that includes,
in weight percent, up to 0.3% carbon, about 5% t about 12% chromium, attd
about 10% to about
30% molybdenum.
According to a second aspect of the inve an, a process of making a metal
casting
includes steps of (a) introducing molten metal int a first end of continuous
casting mold; (b)
withdrawing a newly-formed casting from a seco end of the continuous casting
mold; and (c)
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GLAD-1030 ~ PATENT
guiding the newly formed casting with a pluralit of continuous casting rolls,
and wherein at
least one of the rolls has an outer surface compri ing an age-hardenable
nickel-based alloy that
includes, in weight percent, up to 0.3% carbon, ut 5% to about 12% chromium,
and about
10% to about 30% molybdenum.
According to a third aspect of the inventi n, a roll for use in a continuous
casting
machine includes a roll body that is constructed d arranged to be mounted for
rotation; and
a generally cylindrical outer surface on the roll b dy, the outer surface
including an age-
hardenable Ni-Mo-Cr alloy in which the weight ercent of Mo is greater than the
weight percent
of Cr.
According to a fourth aspect of 'on, a process of reconditioning
the irnven a roll for a
continuous casting machine includes removing a continuous casting
steps of (a roll from a
continuous casting machine; (b) strippinged material from a surface of
degra the roll; (e)
applying a new outer surface to the surface comprising an age-hardenable
roll, said out Ni-Mo-
Cr alloy in which the weight percentter than the weight percent
of Mo is gr of Cr; and (d)
installing the roll into a continuouse.
casting mach
These and various other advantages lures of novelty that characterize
and the invention
are pointed out with particularity exed hereto and forming a part
in the claims hereof.
However, for a better understanding on, its advantages, and the
of the inven objects obtained by
its use, reference should be made which form a further part hereof,
to the drawings and to the
accompanying descriptive matter, s illustrated and described
in which there a preferred
embodiment of the invention.
FIGURE 1 is a diagrammatical view of ~ conixnuous casting machine according to
a
prefernd embodiment of the invention;
FIGURE 2 is a diagarnmatical longitud cross-sectional depiction of a roll in a
Continuous casting machine as shown in FIGURl~ t; and
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GLAD-1030 I PATENT
FIGURES 3A and 3B are diagxamznati~al depictions of a fabrication of a roll as
is
shown in FIGURE 2 according to a preferrod prc~eess of the invention.
Referring now to the drawings, wh like reference numerals designate
corresponding structure throughout the views, xefeiring in particular to
FIGURE 1, a
continuous casting machine 10 according to a p farted embodiment of the
invention includes a
continuous casting mold 12 and a segment supp section 14, as is typical in
continuous casting
machines. As is depicted in FIGURE 1, continu us casting mold 12 has a first
end 16 into which
I O molten metal 19 is introduced during operation, d a second end 18 through
which the thin-
walled, newly formed casting or strand 20 emer as the continuous casting
machine 10
opexates.
As is further shown in FIGURE I, the se ant support section 14 includes, as is
typical,
a plurality of support rolls 22. As is better sho in FIGURE 2, at least one of
the rolls 22, and
preferably most or all of the rolls 22 include a ro body 23 that may have
journals 24 or other
bearing elements thereon to support the roll 22 f rotation within the segment
support I4, and a
sleeve 26, which forms a protective layer about a base of the roll body 23 and
defines an outer
surface 28, which, according to one particularly vantageous aspect of the
invention, is
fabricated from an age-hardenable nickel-based loy comprising, in weight
percent, up to 0.3%
carbon, about 5% to about 12% chromium, and a out 10% to about 30% molybdenum.
In the
embodiment shown in FIGURE 2, the age-hard ble material is a sleeve, but it
could
alternatively be applied in one of many conventi cladding processes, including
welding, as is
shown schematically in FIGURES 3A and 3B. this type of process, the material
27 is applied,
usually helically, about the roll body 23 until the mire outer surface that is
designed for contact
with the hot casting is formed together with roll dy 23 into a completed roll
30. Alternatively,
the material 27 could be applied by other known eposition techniques,
including, without
limitation, thermal spray techniques.
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GLAD-1030 ~ PATEN'Y'
It is anticipated that the material en
27 will be
applied
to
roll
body
23
iz~
a
reconditioning process wherein degradedis
materi first
stripped
from
the
roll
body,
and
then
one of the techniques discussed aboveto
will be re-apply
a
new
outer
surface
to
the
roll.
It has been found that this materiala
gives roll
22
high
temperature
strength
and
stability, Ivw thermal expansion, dation
and superior o resistance
at
temperatures
that
are
typical during operation in a continuoushire.
casting
The alloy has unique long-range orderingaracteristics.
It
has
excellent
ordering
characteristics after an aging time .
of only 24 ho The
alloy
has
low
thermal
expansion
characteristics with high impact -term
strength after to aging.
The
alloy
is
not
notch
sensitive
in notched rupture tests. The a
alloy does not req a
coating
to
resist
long-term
thermal
damage,
i.e., oxidation. The excellent engineeringof
propert' the
alloy
are
provided
by
the
close
control
of compositions and especially the um
critical molyb plus
tungsten
to
chromium
ratio.
As
indicated in Table I, the ratio of a
Ma+W:Cr must between
2:1
and
7:1,
or
preferably
between
2:1 and 6:1. In this invention theretion of chromium to a nickel-molybdenum
is a minor ad '
base.
TABLE 1
PREFERRE ALLOY
COMPOSITION $ROAD NARROW
WEIGHT PERCENT RANGE RANGE TYPICAL
C UP TO .3 0.02-0.06 ABOUT 0.04
Cr 5-12 7-9 ABOUT 8
Mo 10-30 24-26 ABOUT 25
My + W 22-40 22-40 ABOUT 25
AI 1.0 MAX 0.5 MAX ABOUT 0.2
B TRACE TO .015 .002-.006 ABOUT .003
Fe 5 MAX 2.0 MAX ABOUT i.0
Mn 2 MAC 0.8 MAX ABOUT 0.5
Si I.2 MAX 0.8 MAX ABOUT 0.4
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GLAD-1030 ~ PATENT
Re 0.1 MAX 0.07 MAX ABOUT 0.03
Ni BALANCE HALANCE BALANCE
RATIO (Mo +'~ Cr 2-7.0 to one 2-6 to one ABOUT 3 to vne
It is well known in the art that molybden and tungsten are interchangeable in
many
alloy systems. In the alloy of this invention, thcs elements may be
interchanged. Because of the
lower cost of molybdenum and the high weight d metal working characteristics
of tungsten,
molybdenum is pzeferred. Thus, molybdenum m y be present in the alloy of this
invention at
not less than 10% for optimum economic and 'caI benefits. It is well known in
tlxe art that a .
composition adjustment must be made because o the difference in the atomic
weights of these
elements, defmcd as about Mo=1/2W. For exam e, to obtain the equivalent of 25%
molybdenum, it is necessary to have 10% molt' enum and 30% tungsten. Because
of the
possible interchange, molybdenum plus tungsten ay total 22 to 40% in the alloy
of this
itnvention.
Boron may be present in the alloy of this vention in a small, but effective
trace content
up to about 0.015% to obtain certain benefits as i known in the art. Other
elements may be
present in the alloy of this invention as adventitio s impurities or
deliberate additions for certain
benefits Imvwn in the art.
Some of the "impurities" may be present residual elements resulting from
certain
processing steps, or be adventitiously present in a charge materials; for
example, calcium,
magnesium, vanadium, zirconium and the Iike. In actual practice, certain
impurity elements are
kepi within established limits with a maximum or minimum to obtain uniform
products as is
well-ls~,own in the art and skill of melting and pro essing these alloys.
Sulfur, phosphorous and
zinc must generally be kept at low levels. Thus, alloys of this invention may
contain these
and other impurities within the limits usually asso fated with alloys of this
class, and as recited
nn commercial specifications.
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Mn 2 MA
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GLAD-1030 ~ PATENT
An alloy as described above is commerci ly available from I-Iaynes
International of
ICokomo, Indiana as Haynes Alloy 242, and is d scribed in U.S. latent
4,818,486, the disclosure
of which is hereby incorporated by reference as ' set forth fully herein.
In operation, molten metal 19 is introduc into the $rst end 16 of continuous
casting
mold 12, and, as a result of the cooling that is ed by the mold, a casting or
stnand ZO is
form~i. The strand is withdrawn from the seen end 18 of the mold, and is then
guided by the
rolls 22 as it moves away from the mold 12.
It is to be understood, however, that ev though numerous characteristics and
advantages of the present invention have been se forth in the foregoing
description, together
I O with details of the structure and function of the i ention, the disclosure
is illustrative only, and
clxenges may be made in detail, especially in m ers of shape, sine and
arrangement of parts
within the principles of the invention to the full tent indicated by the broad
general meaning of
the terms in which the appended claims are expr sed.
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