WO1995013889A1 - Casting stainless steel strip on surface with specified roughness - Google Patents

Casting stainless steel strip on surface with specified roughness Download PDF

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Publication number
WO1995013889A1
WO1995013889A1 PCT/AU1994/000685 AU9400685W WO9513889A1 WO 1995013889 A1 WO1995013889 A1 WO 1995013889A1 AU 9400685 W AU9400685 W AU 9400685W WO 9513889 A1 WO9513889 A1 WO 9513889A1
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WO
WIPO (PCT)
Prior art keywords
casting
microns
range
rolls
metal
Prior art date
Application number
PCT/AU1994/000685
Other languages
French (fr)
Inventor
Rama Ballav Mahapatra
John Freeman
Lazar Strezov
Original Assignee
Bhp Steel (Jla) Pty Ltd
Ishikawajima-Harima Heavy Industries Company Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=3777367&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=WO1995013889(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Application filed by Bhp Steel (Jla) Pty Ltd, Ishikawajima-Harima Heavy Industries Company Limited filed Critical Bhp Steel (Jla) Pty Ltd
Priority to KR1019950701830A priority Critical patent/KR100305291B1/en
Priority to DE69419593T priority patent/DE69419593T3/en
Priority to AU81010/94A priority patent/AU676101B2/en
Priority to JP7514101A priority patent/JPH08505811A/en
Priority to EP95900015A priority patent/EP0679114B2/en
Priority to DK95900015T priority patent/DK0679114T4/en
Priority to FI951985A priority patent/FI101944B/en
Publication of WO1995013889A1 publication Critical patent/WO1995013889A1/en
Priority to GR990402313T priority patent/GR3031222T3/en

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/06Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
    • B22D11/0637Accessories therefor
    • B22D11/0665Accessories therefor for treating the casting surfaces, e.g. calibrating, cleaning, dressing, preheating
    • B22D11/0668Accessories therefor for treating the casting surfaces, e.g. calibrating, cleaning, dressing, preheating for dressing, coating or lubricating
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B22CASTING; POWDER METALLURGY
    • B22DCASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/06Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
    • B22D11/0637Accessories therefor
    • B22D11/0648Casting surfaces
    • B22D11/0651Casting wheels

Definitions

  • This invention relates to the casting of steel strip. It has particular but not exclusive application to continuous casting of stainless steel strip in a twin roll caster.
  • molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls.
  • the term "nip" is used herein 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. This casting pool may be confined between side plates or dams held in sliding engagement with the ends of the rolls.
  • Twin roll casting has been applied with some success to non-ferrous metals which solidify rapidly on cooling, for example aluminium.
  • Our Australian Patent No 631728 discloses a method and apparatus which enables continuous casting of ferrous strip within 0.5 mm to 5 mm and apparatus of this type has been developed to the stage where it is possible to consistently produce good quality mild steel strip.
  • there have been particular problems in casting austenitic stainless steel strip because of the marked tendency for such steel to suffer from cracking and repetitive surface depressions appearing as a surface defect generally known as "crocodile skin".
  • the Arithmetic Mean Roughness Value which is generally indicated by the symbol R a .
  • This value is defined as the arithmetical average value of all absolute distances of the roughness profile from the centre line of the profile within the measuring length l m .
  • the centre line of the profile is the line about which roughness is measured and is a line parallel to the general direction of the profile within the limits of the roughness-width cut-off such that sums of the areas contained between it and those parts of the profile which lie on either side of it are equal.
  • the Arithmetic Mean Roughness Value may be defined as
  • a method of continuously casting metal strip of the kind in which a casting pool of molten metal is formed in contact with a moving casting surface such that metal solidifies from the pool onto the moving casting surface, wherein the metal is an austenitic stainless steel containing chromium and nickel in a ratio (Cr/Ni)-.-- of less than 1.60 and the casting surface has an Arithmetical Mean Roughness Value (R a ) of more than 2.5 microns. More particularly the Arithmetic Mean Roughness Value R a of the casting surface may be in the range 2.5 to 15 microns. The surface of this texture may be produced by the machining of regular ridges in the surface.
  • the chromium to nickel ratio is no greater than 1.55. More specifically the invention provides a method of continuously casting metal strip of the kind in which molten metal is introduced into the nip between a pair of casting rollers via metal delivery nozzle disposed above the nip to create a casting pool of molten metal supported on casting surfaces of the rolls immediately above the nip and the casting rolls are rotated to deliver a solidified metal strip downwardly from the nip, wherein the metal is an austenitic stainless steel containing chromium and nickel in a ratio (Cr/Ni) of less than 1.60 and the casting surfaces of the rolls have an Arithmetical Mean Roughness Value (R a ) of greater than 2.5 microns.
  • the metal is an austenitic stainless steel containing chromium and nickel in a ratio (Cr/Ni) of less than 1.60 and the casting surfaces of the rolls have an Arithmetical Mean Roughness Value (R a ) of greater than 2.5 microns.
  • the casting surfaces of the rolls may have a texture of regular circumferential grooves with a texture depth in the range 10 microns to 60 microns and a groove pitch in the range 100 microns to 200 microns.
  • the roll may have a texture of regularly spaced projections, which may take the form of pyramids or cones with pitch spacing in the range 100 to 200 microns and depth in the range 10 to 60 microns.
  • the carbon, chromium and nickel contents of the steel be in the following ranges: Carbon - 0.04 - 0.06 % by weight Chromium - 17.5 - 19.5 % by weight Nickel - 8.0 - 10.0 % by weight.
  • Figure 1 is a plan view of a twin roll continuous strip caster which may be operated in accordance with the present invention
  • Figure 2 is a side elevation of the strip caster shown in Figure 1;
  • Figure 3 is a vertical cross-section on the line 3-3 in Figure 1 ;
  • Figure 4 is a vertical cross section on the line 4-4 in Figure 1;
  • Figure 5 is a vertical cross-section on the line 5-5 of Figure 1;
  • Figure 6 illustrates the textured surface of a casting surface used in a series of trial casts
  • Figures 7 to 9 illustrate the results of the trial casts using steels of varying compositions.
  • the illustrated caster comprises a main machine frame 11 which stands up from the factory floor 12.
  • Frame 11 supports a casting roll carriage 13 which is horizontally movable between an assembly station 14 and a casting station 15,
  • Carriage 13 carries a pair of parallel casting rolls 16 to which molten metal is supplied during a casting operation from a ladle 17 via a tundish 18 and delivery nozzle 19.
  • Casting rolls 16 are water cooled so that shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product 20 at the roll outlet.
  • This product is fed to a standard coiler 21 and may subsequently be transferred to a second coiler 22.
  • a receptacle 23 is mounted on the machine frame adjacent the casting station and molten metal can be diverted into this receptacle via an overflow spout 24 on the tundish or by withdrawal of an emergency plug 25 at one side of the tundish if there is a severe malformation of product or other severe malfunction during a casting operation.
  • Roll carriage 13 comprises a carriage frame 31 mounted by wheels 32 on rails 33 extending along part of the main machine frame 11 whereby roll carriage 13 as a whole is mounted for movement along the rails 33.
  • Carriage frame 31 carries a pair of roll cradles 34 in which the rolls 16 are rotatably mounted.
  • Roll cradles 34 are mounted on the carriage frame 31 by interengaging complementary slide members 35, 36 to allow the cradles to be moved on the carriage under the influence of hydraulic cylinder units 37, 38 to adjust the nip between the casting rolls 16.
  • the carriage is movable as a whole along the rails 33 by actuation of a double acting hydraulic piston and cylinder unit 39, connected between a drive bracket 40 on the roll carriage and the main machine frame so as to be actuable to move the roll carriage between the assembly station 14 and casting station 15 and vice versa.
  • Casting rolls 16 are contra rotated through drive shafts 41 from an electric motor and transmission mounted on carriage frame 31.
  • Rolls 16 have copper peripheral walls formed with a series of longitudinally extending and circumferentially spaced water cooling passages supplied with cooling water through the roll ends from water supply ducts in the roll drive shafts 41 which are connected to water supply hoses 42 through rotary glands 43.
  • the rolls may typically be about 500 mm diameter and up to 1300 mm long in order to produce 1300 mm wide strip product.
  • Ladle 17 is of entirely conventional construction and is supported via a yoke 45 on an overhead crane whence it can be brought into position from a hot metal receiving station.
  • the ladle is fitted with a stopper rod 46 actuable by a servo cylinder to allow molten metal to flow from the ladle through an outlet nozzle 47 and refractory shroud 48 into tundish 18.
  • Tundish 18 is also of conventional construction. It is formed as a wide dish made of a refractory material such as magnesium oxide (MgO) .
  • MgO magnesium oxide
  • One side of the tundish receives molten metal from the ladle and is provided with the aforesaid overflow 24 and emergency plug 25.
  • the other side of the tundish is provided with a series of longitudinally spaced metal outlet openings 52.
  • the lower part of the tundish carries mounting brackets 53 for mounting the tundish onto the roll carriage frame 31 and provided with apertures to receive indexing pegs 54 on the carriage frame so as to accurately locate the tundish.
  • Delivery nozzle 19 is formed as an elongate body made of a refractory material such as alumina graphite. Its lower part is tapered so as to converge inwardly and downwardly so that it can project into the nip between casting rolls 16. It is provided with a mounting bracket 60 whereby to support it on the roll carriage frame and its upper part is formed with outwardly projecting side flanges 55 which locate on the mounting bracket.
  • a refractory material such as alumina graphite.
  • Nozzle 19 may have a series of horizontally spaced generally vertically extending flow passages to produce a suitably low velocity discharge of metal throughout the width of the rolls and to deliver the molten metal into the nip between the rolls without direct impingement on the roll surfaces at which initial solidification occurs.
  • the nozzle may have a single continuous slot outlet to deliver a low velocity curtain of molten metal directly into the nip between the rolls and/or it may be immersed in the molten metal pool.
  • the pool is confined at the ends of the rolls by a pair of side closure plates 56 which are held against stepped ends 57 of the rolls when the roll carriage is at the casting station.
  • Side closure plates 56 are made of a strong refractory material, for example boron nitride, and have scalloped side edges 81 to match the curvature of the stepped ends 57 of the rolls.
  • the side plates can be mounted in plate holders 82 which are movable at the casting station by actuation of a pair of hydraulic cylinder units 83 to bring the side plates into engagement with the stepped ends of the casting rolls to form end closures for the molten pool of metal formed on the casting rolls during a casting operation.
  • the ladle stopper rod 46 is actuated to allow molten metal to pour from the ladle to the tundish through the metal delivery nozzle whence it flows to the casting rolls.
  • the clean head end of the strip product 20 is guided by actuation of an apron table
  • Apron table 96 hangs from pivot mountings 97 on the main frame and can be swung toward the coiler by actuation of an hydraulic cylinder unit 98 after the clean head end has been formed.
  • Table 96 may operate against an upper strip guide flap 99 actuated by a piston and a cylinder unit 101 and the strip product 20 may be confined between a pair of vertical side rollers 102.
  • the coiler is rotated to coil the strip product 20 and the apron table is allowed to swing back to its inoperative position where it simply hangs from the machine frame clear of the product which is taken directly onto the coiler 21.
  • the resulting strip product 20 may be subsequently transferred to coiler 22 to produce a final coil for transport away from the caster.
  • Ni ⁇ rent Ni + 0.31 Mn + 22.0 C + 14.2 N + Cu (2)
  • Figure 8 reveals the influence of (Cr/Ni) eq ratio on heat transfer for a smooth substrate. It can be seen that the heat fluxes are relatively constant throughout solidification and most importantly, the magnitudes of the peak fluxes are much lower than those measured for a textured substrate ( Figure 7). This finding is in agreement with the observed solidification structure which is coarse at the surface. Although there are some variations in heat flux at different (Cr/Ni) eq ratios, there are no definite trends. However, with increasing time the heat fluxes approach similar values irrespective of (Cr/Ni) eq . This apparent lack of dependence of heat transfer on (Cr/Ni) eq ratio with a smooth substrate is in agreement with the observations of strip surface texture which was not influenced by (Cr/Ni) ⁇ q .

Abstract

Method of continuously casting metal strip (20) from a casting pool of molten metal supported on chilled casting rolls (16) such that metal solidifies onto moving casting surfaces of the rolls. The metal is austenitic stainless steel containing chromium and nickel in a ratio (Cr/Ni)eq of less than 1.60 (preferably no greater than 1.55) and the casting surface of each roll has an Arithmetical Mean Roughness Value (Ra) of more than 2.5 microns (preferably in the range 2.5 to 15 microns).

Description

CASTINGSTAINLESS STEELSTRIPON SURFACEWITH SPECIFIEDROUGHNESS TECHNICAL FIELD
This invention relates to the casting of steel strip. It has particular but not exclusive application to continuous casting of stainless steel strip in a twin roll caster.
It is known to cast metal strip by continuous casting in a twin roll caster. Molten metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product delivered downwardly from the nip between the rolls. The term "nip" is used herein 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. This casting pool may be confined between side plates or dams held in sliding engagement with the ends of the rolls.
Twin roll casting has been applied with some success to non-ferrous metals which solidify rapidly on cooling, for example aluminium. Our Australian Patent No 631728 discloses a method and apparatus which enables continuous casting of ferrous strip within 0.5 mm to 5 mm and apparatus of this type has been developed to the stage where it is possible to consistently produce good quality mild steel strip. However there have been particular problems in casting austenitic stainless steel strip because of the marked tendency for such steel to suffer from cracking and repetitive surface depressions appearing as a surface defect generally known as "crocodile skin". We have undertaken extensive experimental work in which we have determined factors which make it possible consistently to cast austenitic stainless steel strip of good surface quality without significant cracking defects.
In the ensuing description it will be necessary to refer to a quantitative measure of the smoothness of casting surfaces. One specific measure used in our experimental work and helpful in defining the scope of the present invention is the standard measure known as the Arithmetic Mean Roughness Value which is generally indicated by the symbol Ra. This value is defined as the arithmetical average value of all absolute distances of the roughness profile from the centre line of the profile within the measuring length lm. The centre line of the profile is the line about which roughness is measured and is a line parallel to the general direction of the profile within the limits of the roughness-width cut-off such that sums of the areas contained between it and those parts of the profile which lie on either side of it are equal. The Arithmetic Mean Roughness Value may be defined as
X = 1„
Ra = dx
- / ι„ J x = 0
DISCLOSURE OF THE INVENTION
According to the invention there is provided a method of continuously casting metal strip of the kind in which a casting pool of molten metal is formed in contact with a moving casting surface such that metal solidifies from the pool onto the moving casting surface, wherein the metal is an austenitic stainless steel containing chromium and nickel in a ratio (Cr/Ni)-.-- of less than 1.60 and the casting surface has an Arithmetical Mean Roughness Value (Ra) of more than 2.5 microns. More particularly the Arithmetic Mean Roughness Value Ra of the casting surface may be in the range 2.5 to 15 microns. The surface of this texture may be produced by the machining of regular ridges in the surface.
Preferably the chromium to nickel ratio is no greater than 1.55. More specifically the invention provides a method of continuously casting metal strip of the kind in which molten metal is introduced into the nip between a pair of casting rollers via metal delivery nozzle disposed above the nip to create a casting pool of molten metal supported on casting surfaces of the rolls immediately above the nip and the casting rolls are rotated to deliver a solidified metal strip downwardly from the nip, wherein the metal is an austenitic stainless steel containing chromium and nickel in a ratio (Cr/Ni) of less than 1.60 and the casting surfaces of the rolls have an Arithmetical Mean Roughness Value (Ra) of greater than 2.5 microns.
The casting surfaces of the rolls may have a texture of regular circumferential grooves with a texture depth in the range 10 microns to 60 microns and a groove pitch in the range 100 microns to 200 microns.
In an alternative embodiment, the roll may have a texture of regularly spaced projections, which may take the form of pyramids or cones with pitch spacing in the range 100 to 200 microns and depth in the range 10 to 60 microns.
It is preferred that the carbon, chromium and nickel contents of the steel be in the following ranges: Carbon - 0.04 - 0.06 % by weight Chromium - 17.5 - 19.5 % by weight Nickel - 8.0 - 10.0 % by weight. BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more fully explained its application to the production of stainless steel strip in a twin roll continuous caster will be explained with reference to the accompanying drawings in which:
Figure 1 is a plan view of a twin roll continuous strip caster which may be operated in accordance with the present invention; Figure 2 is a side elevation of the strip caster shown in Figure 1;
Figure 3 is a vertical cross-section on the line 3-3 in Figure 1 ;
Figure 4 is a vertical cross section on the line 4-4 in Figure 1;
Figure 5 is a vertical cross-section on the line 5-5 of Figure 1;
Figure 6 illustrates the textured surface of a casting surface used in a series of trial casts; and
Figures 7 to 9 illustrate the results of the trial casts using steels of varying compositions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The illustrated caster comprises a main machine frame 11 which stands up from the factory floor 12. Frame 11 supports a casting roll carriage 13 which is horizontally movable between an assembly station 14 and a casting station 15, Carriage 13 carries a pair of parallel casting rolls 16 to which molten metal is supplied during a casting operation from a ladle 17 via a tundish 18 and delivery nozzle 19. Casting rolls 16 are water cooled so that shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product 20 at the roll outlet. This product is fed to a standard coiler 21 and may subsequently be transferred to a second coiler 22. A receptacle 23 is mounted on the machine frame adjacent the casting station and molten metal can be diverted into this receptacle via an overflow spout 24 on the tundish or by withdrawal of an emergency plug 25 at one side of the tundish if there is a severe malformation of product or other severe malfunction during a casting operation. Roll carriage 13 comprises a carriage frame 31 mounted by wheels 32 on rails 33 extending along part of the main machine frame 11 whereby roll carriage 13 as a whole is mounted for movement along the rails 33. Carriage frame 31 carries a pair of roll cradles 34 in which the rolls 16 are rotatably mounted. Roll cradles 34 are mounted on the carriage frame 31 by interengaging complementary slide members 35, 36 to allow the cradles to be moved on the carriage under the influence of hydraulic cylinder units 37, 38 to adjust the nip between the casting rolls 16. The carriage is movable as a whole along the rails 33 by actuation of a double acting hydraulic piston and cylinder unit 39, connected between a drive bracket 40 on the roll carriage and the main machine frame so as to be actuable to move the roll carriage between the assembly station 14 and casting station 15 and vice versa.
Casting rolls 16 are contra rotated through drive shafts 41 from an electric motor and transmission mounted on carriage frame 31. Rolls 16 have copper peripheral walls formed with a series of longitudinally extending and circumferentially spaced water cooling passages supplied with cooling water through the roll ends from water supply ducts in the roll drive shafts 41 which are connected to water supply hoses 42 through rotary glands 43. The rolls may typically be about 500 mm diameter and up to 1300 mm long in order to produce 1300 mm wide strip product.
Ladle 17 is of entirely conventional construction and is supported via a yoke 45 on an overhead crane whence it can be brought into position from a hot metal receiving station. The ladle is fitted with a stopper rod 46 actuable by a servo cylinder to allow molten metal to flow from the ladle through an outlet nozzle 47 and refractory shroud 48 into tundish 18.
Tundish 18 is also of conventional construction. It is formed as a wide dish made of a refractory material such as magnesium oxide (MgO) . One side of the tundish receives molten metal from the ladle and is provided with the aforesaid overflow 24 and emergency plug 25. The other side of the tundish is provided with a series of longitudinally spaced metal outlet openings 52. The lower part of the tundish carries mounting brackets 53 for mounting the tundish onto the roll carriage frame 31 and provided with apertures to receive indexing pegs 54 on the carriage frame so as to accurately locate the tundish.
Delivery nozzle 19 is formed as an elongate body made of a refractory material such as alumina graphite. Its lower part is tapered so as to converge inwardly and downwardly so that it can project into the nip between casting rolls 16. It is provided with a mounting bracket 60 whereby to support it on the roll carriage frame and its upper part is formed with outwardly projecting side flanges 55 which locate on the mounting bracket.
Nozzle 19 may have a series of horizontally spaced generally vertically extending flow passages to produce a suitably low velocity discharge of metal throughout the width of the rolls and to deliver the molten metal into the nip between the rolls without direct impingement on the roll surfaces at which initial solidification occurs. Alternatively, the nozzle may have a single continuous slot outlet to deliver a low velocity curtain of molten metal directly into the nip between the rolls and/or it may be immersed in the molten metal pool.
The pool is confined at the ends of the rolls by a pair of side closure plates 56 which are held against stepped ends 57 of the rolls when the roll carriage is at the casting station. Side closure plates 56 are made of a strong refractory material, for example boron nitride, and have scalloped side edges 81 to match the curvature of the stepped ends 57 of the rolls. The side plates can be mounted in plate holders 82 which are movable at the casting station by actuation of a pair of hydraulic cylinder units 83 to bring the side plates into engagement with the stepped ends of the casting rolls to form end closures for the molten pool of metal formed on the casting rolls during a casting operation.
During a casting operation the ladle stopper rod 46 is actuated to allow molten metal to pour from the ladle to the tundish through the metal delivery nozzle whence it flows to the casting rolls. The clean head end of the strip product 20 is guided by actuation of an apron table
96 to the jaws of the coiler 21. Apron table 96 hangs from pivot mountings 97 on the main frame and can be swung toward the coiler by actuation of an hydraulic cylinder unit 98 after the clean head end has been formed. Table 96 may operate against an upper strip guide flap 99 actuated by a piston and a cylinder unit 101 and the strip product 20 may be confined between a pair of vertical side rollers 102. After the head end has been guided in to the jaws of the coiler, the coiler is rotated to coil the strip product 20 and the apron table is allowed to swing back to its inoperative position where it simply hangs from the machine frame clear of the product which is taken directly onto the coiler 21. The resulting strip product 20 may be subsequently transferred to coiler 22 to produce a final coil for transport away from the caster.
It has been found in the operation of the above described apparatus that it is possible to consistently produce good austenitic stainless steel strip by careful adjustment of the steel chemistry in combination with the use of rolls having textured surfaces to minimise segregation through initial rapid cooling rates. n austenitic stainless steel strip casting, solidification mode can play an important part in determining strip surface quality. Primary austenitic solidification mode which occurs when the Cr/Ni ratio is less than about 1.60 is not usually recommended as segregation is enhanced leading to an increase in cracking tendency. It has previously been thought necessary to ensure a Cr/Ni ratio within the range 1.7 to 1.9 in order to minimise cracks due to a reduction in segregation severity and to provide tortuous paths making crack propagation difficult. However our experimental work has shown that continuous strip casting with steel of this composition is very prone to produce strips with "crocodile skin" depressions and the depression severity may be so high as to cause cracking. Steel with Cr/Ni ratio less than 1.55 is most prone to segregation and can thus increase cracking. If solidification occurs on a smooth substrate initial heat transfer rates are low and the solidification structure is coarse resulting in segregation and cracking. However we have determined that this tendency to segregation and cracking can be overcome by ensuring a high initial heat transfer rate and this can most readily be achieved by using a textured substrate, for example by the machining of ridges in the substrate surface.
Initial experimental work was carried out in a metal solidification test rig in which a 40 mm x 40 mm chilled block is plunged into a bath of molten steel at such a speed as to closely simulate the conditions at the casting surfaces of a twin roll caster. Steel solidifies onto the chilled block as it moves through the molten bath to produce a layer of solidified steel on the surface of the block. The thickness of this layer can be measured at points throughout its area to map variations in the solidification rate and therefore the effective rate of heat transfer at the various locations. It is thus possible to produce an overall solidification constant, generally indicated by the symbol K, as well as a map of individual values throughout the solidified strip. It is also possible to examine the micro structure of the strip surface to correlate changes in the solidification micro structure with the changes in the observed heat transfer values.
The nature of the experimental work and the results obtained will now be described.
EXPERIMENTAL CONDITIONS Tests were conducted on three copper substrates with different surface characteristics; a smooth and a textured copper surface and a Cr coated (100 μm in thickness), ground surface. Texture was imparted to the copper block by machining longitudinal grooves and ridges with geometry shown schematically in Figure 6. Each of these blocks was instrumented with thermocouples to characterise the heat transfer rates prevailing during solidification. In order to maintain consistent casting conditions throughout the experiments, variables such as melt superheat and block temperature were kept constant within reasonable limits. The melt temperature was aimed at about 1525°C corresponding to a superheat of 75°C. Argon gas introduced into the furnace was quite effective in preventing chemical interaction of the melt with the surrounding atmosphere. The melt chemistry was adjusted to achieve the desired (Cr/Ni)eq ratios, primarily through additions of Cr, Ni, C and N2. The following expressions were used to determine Creq and Niβq:
Creq = Cr + 1.37 Mo + 1.50 Si + 2.0 Nb + 3.0 Ti (1)
Niβ„ = Ni + 0.31 Mn + 22.0 C + 14.2 N + Cu (2)
A summary of the test conditions is contained in Table 1. The entire experimental program comprised approximately 45 tests with (Cr/Ni)eq ratios varying between 1.55 and 1.74. Salient features of various tests are summarised in Table 2.
Figure imgf000012_0001
Table 1: Experimental conditions
Substrate surface Smooth copper
Cr plated (ground) copper
Textured copper (150μm pitch, 20μm depth)
Substrate cleaning procedure Bristle brush and air blowing
Melt temperature 1525°C
Block temperature 125°C
Table 2: Details of the various tests
O
Figure imgf000012_0002
RESULTS Effect of (Cr/Ni)βq ratio on strip surface quality
Visual examination of the samples revealed that (Cr/Ni)βq ratio has a direct influence on the surface quality of the strip obtained with a textured substrate, however, no noticeable effect could be seen with the smooth substrates. Samples cast at varying (Cr/Ni)βq ratio, reveal a gradual progression from a severe crocodile skin type texture to a smooth surface texture with decreasing (Cr/Ni)βq ratio. The effect of (Cr/Ni)βq ratio on crocodile skin severity, shown in Figure 9, suggests that substantial improvements in strip surface quality can be achieved by keeping the (Cr/Ni)βq ratio less than 1.60.
Effect of (Cr/Ni)eq ratio on heat transfer during solidification i) Textured substrate Heat transfer rates from the strip surface to the substrate were determined from the measured substrate temperatures. Figure 7 shows the influence of melt (Cr/Ni)eq ratio on heat fluxes for a textured substrate. It can be seen that the profiles are characterised by an early peak in the heat flux followed by rapid reduction of this peak and with increasing time, heat flux approaches a constant value. Higher heat transfer rates (about 30 MW/m2) encountered in the early stages of solidification can be attributed to the intimate contact. The experimental program determined that the
(Cr/Ni)βq ratio found to producing the best surface texture (on a textured substrate) is less than 1.60. ii) Smooth substrate
Figure 8 reveals the influence of (Cr/Ni)eq ratio on heat transfer for a smooth substrate. It can be seen that the heat fluxes are relatively constant throughout solidification and most importantly, the magnitudes of the peak fluxes are much lower than those measured for a textured substrate (Figure 7). This finding is in agreement with the observed solidification structure which is coarse at the surface. Although there are some variations in heat flux at different (Cr/Ni)eq ratios, there are no definite trends. However, with increasing time the heat fluxes approach similar values irrespective of (Cr/Ni)eq. This apparent lack of dependence of heat transfer on (Cr/Ni)eq ratio with a smooth substrate is in agreement with the observations of strip surface texture which was not influenced by (Cr/Ni)βq.
The experimental program demonstrated that the normal operating window for (Cr/Ni)βq ratios of 1.7-1.9 is not the optimum in terms of strip surface texture. Using a (Cr/Ni)βq ratio less than 1.60 produces better surface quality.

Claims

CLAIMS :
1. A method of continuously casting metal strip of the kind in which a casting pool of molten metal is formed in contact with a moving casting surface such that metal solidifies from the pool onto the moving casting surface, wherein the metal is an austenitic stainless steel containing chromium and nickel in a ratio (Cr/Ni)eq of less than 1.60 and the casting surface has an Arithmetical Mean Roughness Value (Ra) of more than 2.5 microns.
2. A method as claimed in claim 1, wherein the
Arithmetical Mean Roughness Value (Ra) of the casting surface is in the range 2.5 to 15 microns.
3. A method as claimed in claim 2, wherein the casting surface has a texture of regular grooves and ridges.
4. A method as claimed in claim 3, wherein the texture depth is in the range 10 microns to 60 microns and the groove pitch is in the range 100 microns to 200 microns.
5. A method as claimed in claim 3, wherein the casting surface has a texture of regularly spaced discrete projections at a pitch spacing in the range 100 to 200 microns and a texture depth in the range 10 to 60 microns.
6. A method as claimed in any one of the preceding claims, wherein the chromium to nickel ratio is no greater than 1.55.
7. A method as claimed in any one of the preceding claims wherein the carbon, chromium and nickel contents of the steel are in the following ranges: Carbon - 0.04 - 0.06 % by weight
Chromium - 17.5 - 19.5 % by weight Nickel - 8.0 - 10.0 % by weight.
8. A method of continuously casting metal strip of the kind in which molten metal is introduced into the nip between a pair of casting rollers via metal delivery nozzle disposed above the nip to create a casting pool of molten metal supported on casting surfaces of the rolls immediately above the nip and the casting rolls are rotated to deliver a solidified metal strip downwardly from the nip, wherein the metal is an austenitic stainless steel containing chromium and nickel in a ratio (Cr/Ni) of less than 1.60 and the casting surfaces of the rolls have an Arithmetical Mean Roughness Value (Ra) of greater than 2.5 microns.
9. A method as claimed in claim 8, wherein the Arithmetical Mean Roughness Value (Ra) of the casting surfaces of the rolls is in the range 2.5 to 15 microns.
10. A method as claimed in claim 9, wherein the casting surfaces of the rolls have a texture of regular circumferential grooves with a texture depth in the range 10 microns to 60 microns and a groove pitch in the range 100 microns to 200 microns.
11. A method as claimed in claim 9, wherein the rolls have a texture of regularly spaced discrete projections at a pitch spacing in the range 100 to 200 microns and a depth in the range 10 to 60 microns.
12. A method as claimed in any one of claims 8 to 11, wherein the chromium to nickel ratio is no greater than 1.55.
13. A method as claimed in any one of claims 8 to 12, wherein the carbon, chromium and nickel content of the steel are in the following ranges:
Carbon - 0.04 - 0.06 % by weight Chromium - 17.5 - 19.5 % by weight
Nickel - 8.0 - 10.0 % by weight.
PCT/AU1994/000685 1993-11-18 1994-11-09 Casting stainless steel strip on surface with specified roughness WO1995013889A1 (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
KR1019950701830A KR100305291B1 (en) 1993-11-18 1994-11-09 How to cast steel strip
DE69419593T DE69419593T3 (en) 1993-11-18 1994-11-09 MOLDING A CONTINUOUS STEEL STRIP TO A SURFACE OF SPECIFIC ROUGHNESS
AU81010/94A AU676101B2 (en) 1993-11-18 1994-11-09 Casting stainless steel strip on surface with specified roughness
JP7514101A JPH08505811A (en) 1993-11-18 1994-11-09 Steel strip casting
EP95900015A EP0679114B2 (en) 1993-11-18 1994-11-09 Casting stainless steel strip on surface with specified roughness
DK95900015T DK0679114T4 (en) 1993-11-18 1994-11-09 Casting of stainless steel strips on surface with specified roughness
FI951985A FI101944B (en) 1993-11-18 1995-04-26 Casting of steel strips
GR990402313T GR3031222T3 (en) 1993-11-18 1999-09-16 Casting stainless steel strip on surface with specified roughness.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPM253993 1993-11-18
AUPM2539 1993-11-18

Publications (1)

Publication Number Publication Date
WO1995013889A1 true WO1995013889A1 (en) 1995-05-26

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PCT/AU1994/000685 WO1995013889A1 (en) 1993-11-18 1994-11-09 Casting stainless steel strip on surface with specified roughness

Country Status (12)

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EP (1) EP0679114B2 (en)
JP (1) JPH08505811A (en)
KR (1) KR100305291B1 (en)
AT (1) ATE182284T1 (en)
DE (1) DE69419593T3 (en)
DK (1) DK0679114T4 (en)
ES (1) ES2134427T5 (en)
FI (1) FI101944B (en)
GR (1) GR3031222T3 (en)
TW (1) TW276200B (en)
WO (1) WO1995013889A1 (en)
ZA (1) ZA949134B (en)

Cited By (17)

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Publication number Priority date Publication date Assignee Title
EP0740972A1 (en) * 1995-05-05 1996-11-06 Ishikawajima-Harima Heavy Industries Co., Ltd. Casting steel strip
EP0796685A1 (en) 1996-03-22 1997-09-24 Usinor Sacilor Process and apparatus for continuously casting a strand of inoxidable austenitic steel on a moving wall or in between two moving walls whose surfaces are grooved
WO1998055251A1 (en) * 1997-06-02 1998-12-10 Ishikawajima-Harima Heavy Industries Company Limited Amorphous or glassy alloy surfaced rolls for the continuous casting of metal strip
WO2000007753A1 (en) * 1998-08-07 2000-02-17 Ishikawajima-Harima Heavy Industries Company Limited Casting steel strip
FR2792560A1 (en) * 1999-04-22 2000-10-27 Usinor Continuous casting of stainless austenitic steel strips between rolls involves using rolls having surface comprising contacting circular or elliptical pits and inert gas soluble in steel around meniscus of molten metal
US6679313B2 (en) * 1999-03-26 2004-01-20 Sollac Process for manufacturing carbon-steel strip by twin-roll continuous casting, product produced and apparatus
WO2004035247A1 (en) * 2002-10-15 2004-04-29 Voest-Alpine Industrieanlagenbau Gmbh & Co Method for continuously producing a thin steel strip
US6942013B2 (en) 1998-08-07 2005-09-13 Lazar Strezov Casting steel strip
US7073565B2 (en) 1999-02-05 2006-07-11 Castrip, Llc Casting steel strip
KR100650967B1 (en) * 1996-03-22 2007-01-31 티쎈 스탈 아게 Process for the continuous casting of an austenitic stainless steel strip onto one or between two moving walls with dimpled surfaces, and casting plant for its implementation
US7281569B2 (en) 2003-01-24 2007-10-16 Nucor Corporation Casting steel strip with low surface roughness and low porosity
US7484550B2 (en) 2003-01-24 2009-02-03 Nucor Corporation Casting steel strip
US8122937B2 (en) 2007-10-12 2012-02-28 Nucor Corporation Method of forming textured casting rolls with diamond engraving
US9149868B2 (en) 2005-10-20 2015-10-06 Nucor Corporation Thin cast strip product with microalloy additions, and method for making the same
US9999918B2 (en) 2005-10-20 2018-06-19 Nucor Corporation Thin cast strip product with microalloy additions, and method for making the same
US10071416B2 (en) 2005-10-20 2018-09-11 Nucor Corporation High strength thin cast strip product and method for making the same
US11193188B2 (en) 2009-02-20 2021-12-07 Nucor Corporation Nitriding of niobium steel and product made thereby

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CH691575A5 (en) * 1999-10-08 2001-08-31 Main Man Inspiration Ag The strip casting machine for producing a metal strip, and method for operating same.

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AU2992992A (en) * 1991-12-11 1993-06-17 Thyssen Stahl Aktiengesellschaft Roll for a machine for the continuous casting of metal strips, corresponding continuous casting machine and method for producing said roll

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US5082046A (en) * 1989-12-20 1992-01-21 Usinor Sacilor Device for casting thin strips of metal between
WO1993008941A1 (en) * 1991-11-06 1993-05-13 Davy Mckee (Poole) Limited A roll for a twin roll caster
AU2992992A (en) * 1991-12-11 1993-06-17 Thyssen Stahl Aktiengesellschaft Roll for a machine for the continuous casting of metal strips, corresponding continuous casting machine and method for producing said roll

Cited By (32)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0740972A1 (en) * 1995-05-05 1996-11-06 Ishikawajima-Harima Heavy Industries Co., Ltd. Casting steel strip
CN1067306C (en) * 1996-03-22 2001-06-20 犹齐诺-萨西洛公司 Process for continuous casting of austenitic stainless steel strip onto one or between two moving walls with dimpled surfaces, and casting plant for its implementation
EP0796685A1 (en) 1996-03-22 1997-09-24 Usinor Sacilor Process and apparatus for continuously casting a strand of inoxidable austenitic steel on a moving wall or in between two moving walls whose surfaces are grooved
US5807444A (en) * 1996-03-22 1998-09-15 Usinor Sacilor Process for the continuous casting of an austenitic stainless steel strip onto one or between two moving walls with dimpled surfaces, and casting plant for its implementation
KR100650967B1 (en) * 1996-03-22 2007-01-31 티쎈 스탈 아게 Process for the continuous casting of an austenitic stainless steel strip onto one or between two moving walls with dimpled surfaces, and casting plant for its implementation
AU706394B2 (en) * 1996-03-22 1999-06-17 Thyssen Stahl Aktiengesellschaft Process for the continuous casting of an austenitic stainless steel strip onto one or between two moving walls with dimpled surfaces, and casting plant for its implementation
FR2746333A1 (en) * 1996-03-22 1997-09-26 Usinor Sacilor CONTINUOUS CASTING PROCESS OF AN AUSTENITIC STAINLESS STEEL STRIP ON ONE OR BETWEEN TWO MOVABLE WALLS WHOSE SURFACES ARE PROVIDED WITH DIMENSIONS, AND CASTING PLANT FOR ITS IMPLEMENTATION
CN1096900C (en) * 1997-06-02 2002-12-25 卡斯特里普公司 Amorphous or glassy alloy surfaced rolls for continuous casting of metal strip
WO1998055251A1 (en) * 1997-06-02 1998-12-10 Ishikawajima-Harima Heavy Industries Company Limited Amorphous or glassy alloy surfaced rolls for the continuous casting of metal strip
WO2000007753A1 (en) * 1998-08-07 2000-02-17 Ishikawajima-Harima Heavy Industries Company Limited Casting steel strip
KR100621084B1 (en) * 1998-08-07 2006-09-07 카스트립 엘엘씨. Casting steel strip
US6942013B2 (en) 1998-08-07 2005-09-13 Lazar Strezov Casting steel strip
US7604039B2 (en) 1999-02-05 2009-10-20 Castrip, Llc Casting steel strip
US7073565B2 (en) 1999-02-05 2006-07-11 Castrip, Llc Casting steel strip
US6679313B2 (en) * 1999-03-26 2004-01-20 Sollac Process for manufacturing carbon-steel strip by twin-roll continuous casting, product produced and apparatus
WO2000064612A1 (en) * 1999-04-22 2000-11-02 Usinor Method for continuously casting between two rolls austenitic stainless steel strips with excellent surface quality and resulting strips
AU767990B2 (en) * 1999-04-22 2003-11-27 Usinor Method for continuously casting between two rolls austenitic stainless steel strips with excellent surface quality and resulting strips
FR2792560A1 (en) * 1999-04-22 2000-10-27 Usinor Continuous casting of stainless austenitic steel strips between rolls involves using rolls having surface comprising contacting circular or elliptical pits and inert gas soluble in steel around meniscus of molten metal
US7328737B2 (en) 2002-10-15 2008-02-12 Voest-Alpine Industrieanlagenbau Gmbh & Co. Installation for continuously producing a thin steel strip
US7156152B2 (en) 2002-10-15 2007-01-02 Voest-Alpine Industrieanlagenbau Gmbh & Co. Process for the continuous production of a think steel strip
WO2004035247A1 (en) * 2002-10-15 2004-04-29 Voest-Alpine Industrieanlagenbau Gmbh & Co Method for continuously producing a thin steel strip
US7594533B2 (en) 2003-01-24 2009-09-29 Nucor Corporation Casting steel strip
US7367378B2 (en) 2003-01-24 2008-05-06 Nucor Corporation Casting steel strip with low surface roughness and low porosity
US7484550B2 (en) 2003-01-24 2009-02-03 Nucor Corporation Casting steel strip
US7299856B2 (en) 2003-01-24 2007-11-27 Nucor Corporation Casting steel strip with low surface roughness and low porosity
US7281569B2 (en) 2003-01-24 2007-10-16 Nucor Corporation Casting steel strip with low surface roughness and low porosity
US8016021B2 (en) 2003-01-24 2011-09-13 Nucor Corporation Casting steel strip with low surface roughness and low porosity
US9149868B2 (en) 2005-10-20 2015-10-06 Nucor Corporation Thin cast strip product with microalloy additions, and method for making the same
US9999918B2 (en) 2005-10-20 2018-06-19 Nucor Corporation Thin cast strip product with microalloy additions, and method for making the same
US10071416B2 (en) 2005-10-20 2018-09-11 Nucor Corporation High strength thin cast strip product and method for making the same
US8122937B2 (en) 2007-10-12 2012-02-28 Nucor Corporation Method of forming textured casting rolls with diamond engraving
US11193188B2 (en) 2009-02-20 2021-12-07 Nucor Corporation Nitriding of niobium steel and product made thereby

Also Published As

Publication number Publication date
JPH08505811A (en) 1996-06-25
DE69419593D1 (en) 1999-08-26
EP0679114A4 (en) 1997-03-19
DE69419593T3 (en) 2005-06-09
FI951985A (en) 1995-05-19
GR3031222T3 (en) 1999-12-31
KR950704070A (en) 1995-11-17
DK0679114T4 (en) 2004-12-13
ES2134427T3 (en) 1999-10-01
EP0679114B1 (en) 1999-07-21
TW276200B (en) 1996-05-21
FI951985A0 (en) 1995-04-26
KR100305291B1 (en) 2001-11-22
ATE182284T1 (en) 1999-08-15
DE69419593T2 (en) 1999-11-18
FI101944B1 (en) 1998-09-30
EP0679114B2 (en) 2004-11-03
DK0679114T3 (en) 2000-02-07
FI101944B (en) 1998-09-30
ZA949134B (en) 1995-07-24
EP0679114A1 (en) 1995-11-02
ES2134427T5 (en) 2005-05-16

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