CA2306571A1 - Continuous casting rolls and method of using - Google Patents

Abstract

A roll for use in a continuous casting machine includes a roll body that is constructed and arranged to be mounted for rotation in a guide segment area of a continuous casting machine, and a generally cylindrical outer surface on the roll body. Preferably, the outer surface is fabricated at least in part from an age-hardenable nickel-based alloy that includes, in weight percent, up to 0.3% carbon, about 5% to about 12% chromium, and about 10% to about 30%
molybdenum.
The roll exhibits superior high temperature strength and stability, low thermal expansion, and superior oxidation resistance at temperatures that are typical during operation in a continuous casting machine. A process of making a metal casting using such a roll is also disclosed.

Description

Apr~24. 2000 12:34PM KNOBLE & YOSHIDA LLC215-599-0601 No.8521 P. 3 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.

Avr.24. 2000 12:35PM KNOBLE & YOSHIDA LLC215-599-0601 No.8527 P. 4 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 Apr.24. 2000 12:35PM KNOBLE & YOSHIDA LLC215-599-0601 No.8527 P. 5 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) Apr.24. 2000 12:36PM KNOBLE & YOSNIDA LLC215-599-0601 No.8527 P. 6 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 Apr.24. 2000 12:36PM KNOBLr & YOSNIDA LLC215-699-0601 No.8527 P. 7 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.

Avr.24. 2000 12:31PM KNOBLE & YOSN1DA LLC215-599-0601 No.8527 P. 8 GLAD-1030 ~ PATEN'Y' It is anticipated that the material en 27 will be applied to roll body 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 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.

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 Apr.24. 2000 12:37PM KNOBLE & YOSNIDA LLC215-599-0601 No.8521 P. 9 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.

Mn 2 MA

Apr.24. 2000 12:38PM KNOBLE & YOSHfDA LLC215-599-0601 No.8527 P. 10 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.

Claims (17)

1. A roll for use in a continuous casting machine, comprising:
a roll body that is constructed and arranged to be mounted for rotation; and a generally cylindrical outer surface on said roll body, said outer surface comprising an age-hardenable nickel-based alloy comprising, in weight percent, up to 0.3% carbon, about 5% to about 12% chromium, and about 10% to about 30% molybdenum.

2. A roll according to claim 1, wherein said nickel based alloy comprises about 7% to about 9%
chromium.

3. A roll according to claim 1, wherein said nickel based alloy comprises about 10% to about 26% molybdenum.

4. A roll according to claim 1, wherein said nickel-based alloy consists essentially of up to 0.3%
carbon, 5% to 12% chromium, 10% to 30% molyodenum, 22% to 40% molybdenum plus tungsten, 1% maximum aluminum, trace to 0.015% boron, 5% maximum iron, 2%
maximum manganese, 1.2% maximum silicon, 0,1% maximum rare earth metals, balance nickel plus normal impurities wherein the ratio of Mo+W:Cris between 2:1 and 7:1 to provide a favorable combination of properties and wherein the chromium plus molybdenum content exceeds 3:1 to obtain optimum ordering characteristics.

5. A roll according to claim 1, wherein said roll body comprises a sleeve, and said outer surface is defined on said sleeve.

6. A roll according to claim 1, wherein said nicked-based alloy is deposited on said outer surface by a cladding process.

7. A process of making a metal casting, comprising steps of:
(a) introducing molten metal into a first end of continuous casting mold;
(b) withdrawing a newly-formed casting from a second end of the continuous casting mold; and (c) guiding the newly formed casting with a plurality of continuous casting rolls, and wherein at least one of the rolls has an outer surface that includes an age-hardenable nickel-based alloy comprising, in weight percent, up to 0.3% carbon, about 5% to about 12%
chromium, and about 10% to about 30% molybdenum.

8. A process according to claim 7, wherein step (c) is performed with a nickel based alloy that comprises about 7% to about 9% chromium.

9. A process according to claim 7, whereon step (c) is performed with a nickel based alloy that comprises about 10% to about 26% molybdenum.

10. A process according to claim 7, wherein step (c) is performed with roll with a nickel-based alloy that consists essentially of up to 0.3% carbon, 5% to 12% chromium, 10%
to 30%
molybdenum, 22% to 40% molybdenum plus tungsten, 1% maximum aluminum, trace to 0.015% boron, 5% maximum iron, 2% maximum manganese, 1.2% maximum silicon, 0.1%
maximum rare earth metals, balance nickel plus normal impurities wherein the ratio of Mo+W:Cr is between 2:1 and 7:1 to provide a favorable combination of properties and wherein the chromium plus molybdenum content exceeds 3:1 to obtain optimum ordering characteristics,

11. A roll for use in a continuous casting machine comprising:
a roll body that is constructed and arrange to be mounted for rotation; and a generally cylindrical outer surface on said roll body, said outer surface comprising an age-hardenable Ni-Mo-Cr alloy in which the weight percent of Mo is greater than the weight percent of Cr.

12. A roll according to claim 11, wherein said roll body comprises a sleeve, and said outer surface is defined on said sleeve.

13. A roll according to claim 11, wherein said age-hardenable Ni-Mo-Cr alloy is deposited on said outer surface by a cladding process.

14. A process of reconditioning a roll for a continuous casting machine, comprising steps of:
(a) removing a continuous casting roll from a continuous casting machine;
(b) stripping degraded material from a surface of the roll;
(c) applying a new outer surface to the roll, said outer surface comprising an age-hardenable Ni-Mo-Cr alloy in which the weight percent of Mo is greater than the weight percent of Cr; and (d) installing the roll into a continuous casting machine.

15. A process according to claim 14, wherein step (c) comprises applying the alloy by cladding.

16. A process according to claim 14, wherein step (c) comprises applying the alloy by securing a sleeve to the roll.

17. A process according to claim 14, wherein step (c) comprises applying the alloy by thermal spray deposition.