WO2023140865A1 - Procédé de coulée continue - Google Patents

Procédé de coulée continue Download PDF

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Publication number
WO2023140865A1
WO2023140865A1 PCT/US2022/013455 US2022013455W WO2023140865A1 WO 2023140865 A1 WO2023140865 A1 WO 2023140865A1 US 2022013455 W US2022013455 W US 2022013455W WO 2023140865 A1 WO2023140865 A1 WO 2023140865A1
Authority
WO
WIPO (PCT)
Prior art keywords
strand
opposite sides
metal
center
solid
Prior art date
Application number
PCT/US2022/013455
Other languages
English (en)
Inventor
Nuredin Kapaj
Original Assignee
Primetals Technologies USA LLC
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.)
Filing date
Publication date
Application filed by Primetals Technologies USA LLC filed Critical Primetals Technologies USA LLC
Priority to PCT/US2022/013455 priority Critical patent/WO2023140865A1/fr
Publication of WO2023140865A1 publication Critical patent/WO2023140865A1/fr

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/12—Accessories for subsequent treating or working cast stock in situ
    • B22D11/1206—Accessories for subsequent treating or working cast stock in situ for plastic shaping of strands
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/12—Accessories for subsequent treating or working cast stock in situ
    • B22D11/1213—Accessories for subsequent treating or working cast stock in situ for heating or insulating strands

Definitions

  • the present invention relates to a method for continuous casting of a metal (for example, steel) product such as a billet or a bloom.
  • a metal billet or a metal bloom is an elongated metallic body, which can be produced by continuous casting.
  • Continuous casting is a method of making a metal product such as a billet, a bloom, or a slab for subsequent rolling in a finishing mill by solidifying a strand of metal from liquid metal to a solid, elongated metal body.
  • a continuous casting system typically includes a ladle having an outlet pipe, a casting distributor with a casting tube disposed below the ladle, and a plug or another closure disposed in the casting distributor.
  • a permanent mold may be disposed below the casting distributor to receive a lower end of the casting tube.
  • the mold may have cooled side plates.
  • the liquid metal from the casting distributor is directed by way of the casting tube into the permanent mold.
  • the mass flow of the liquid metal flowing into the permanent mold may be controlled with the plug or the closure.
  • the liquid metal 44 is partially solidified by being subjected to primary cooling by the cooled side plates of the permanent mold 42.
  • the partially solidified body that exits the permanent mold is a strand 30.
  • the cooling of the liquid steel 44 with the cooled side plates to form the strand 30 is controlled so that when the strand 30 exits, it has a solidified shell 48, typically several centimeters thick, while a majority of the cross section of the strand 30 is still liquid and contained within the solidified shell 48 of the strand 30.
  • a strand guiding system located below the permanent mold guides the strand in a line through a so-called casting bow disposed below the permanent mold, or downstream thereof. After exiting the casting bow the strand 30 is guided (for example, horizontally) onward supported by the strand guiding system support elements, namely pinch rollers 32, 34, and then is guided or transported away for further processing.
  • the strand may be subjected to a controlled secondary cooling by, for example, a liquid coolant (typically water), or a mixture of a liquid cooling medium and a gas (for example, "air mist” cooling, or spraying with air/water, respectively) after exiting the mold (downstream of the mold) and before being received by the strand guiding system (upstream of the strand guiding system).
  • a liquid coolant typically water
  • a gas for example, "air mist” cooling, or spraying with air/water, respectively
  • the coolant may be supplied from, for example, nozzles 46 arranged upstream of the strand guiding system and downstream of the mold 42.
  • the controlled primary cooling and the controlled secondary cooling cause the solidification of the liquid metal into a solid body in a controlled manner. Crystal formation takes place during the controlled solidification of liquid metal.
  • solidifying steel for example, dendrites, which are tree-like features, may form.
  • three morphological crystal zones (fine grained chilled zone 10 at the surface followed by a columnar zone 12 and a central equiaxed zone 14) are typically present in a continuously cast product 16.
  • the “chill zone” 10 lies in a narrow band following the contour of the mold and consists of small equiaxed crystals (dendrites), which usually have random orientations.
  • the central equiaxed zone 14 lies at the center of the product 16 and represents the last metal to solidify. In this zone, the crystals (grains) are again equiaxed and have random orientations.
  • microsegregation is a consequence of the rejection of certain elements from the solid into the interdendritic liquid 18.
  • Macrosegregation results from the movement of microsegregation regions over macroscopic distances due to the motion of the liquid and the free crystals.
  • the motion of impure interdendritic liquid 18 causes zones of positive macrosegregation; whereas, purer solid crystals yield negative macrosegregation.
  • the flow of interdendritic liquid 18 is primarily driven by natural convection due to the thermal and solutal buoyancy and partly forced convection due to the suction caused by shrinkage, which may cause cavity formation also.
  • Fluid flow during solidification is principally driven by the natural convection caused by the density gradient to thermal convection. Due to the rejection of solutes into the interdendritic liquid 18, concentration and consequent density gradients are set up in the liquid. This is known as solutal buoyancy, and the resulting convective flow as solutal convection. In most situations, both are significant, and the resulting convection has been termed thermo-solutal convection or double diffusive convection.
  • the strand 30 having a central mushy zone 24 may be squeezed by pinch rollers 32 in the caster to deform the solid metal surrounding the mushy zone 24 in order to compensate for the shrinkage. In this way, the deformation of the solid metal can counteract the density increase and thus avoid porosity formation without the need for liquid metal filling the voids caused by liquid to solid phase transformation.
  • the squeezing of the mushy zone 24 will also reduce macrosegregation by preventing the suction of the interdendritic liquid 18 having the segregated elements.
  • the strand 30 can be squeezed after it has fully solidified (i.e. it is entirely solid).
  • the fully solidified strand may be squeezed by pinch rollers 34 in the caster to reduce the central porosity caused by shrinkage, which is referred to as hard reduction.
  • the existing soft and hard reductions while efficient, have drawbacks. For example, the deformation during the squeezing is not concentrated toward the center of the strand 30 where the shrinkage is generated. Thus, as shown in FIG. 7, the deformation is extended from the surface of the strand 30 down to its center. This is due to the temperature distribution along the cross section of the strand. Specifically, referring to FIGs.
  • the lateral sides 36 of the strand 30 that are deformed by soft or hard reduction are at a relatively low temperature, and thus resist mechanical deformation under the squeezing force applied to the sides 38 transverse to the lateral sides 36, which results in the distortion of the shape of the strand 30 as seen in FIG. 7.
  • Macrosegregation and central porosity may be reduced by other methods, namely:
  • the electromagnetic stirring in the mold is common for quality grades. It is frequently used in combination with the final stirrer. The strand stirrer is rarely used.
  • a method for continuous casting of a metal product according to the present invention includes cooling liquid metal in a mold to form a metal strand having first opposite sides and second opposite sides; heating the first opposite sides of the strand to cause reduction of strength of the first opposite sides relative to the second opposite sides of the strand; and pressing the strand with heated first opposite sides from the second opposite sides to deform the strand.
  • the metal strand may have a solid external shell and a central zone that contains liquid metal
  • the method includes feeding the metal strand toward pinch rollers, and squeezing the strand between at least two opposing pinch rollers from the plurality of pinch rollers to deform the strand, whereby segregation and central porosity formation may be suppressed.
  • the metal strand is solid from side to side, and the method includes feeding the metal strand toward pinch rollers, and squeezing the strand between at least two opposing pinch rollers from the plurality of pinch rollers to deform the strand, whereby central porosity formation may be suppressed.
  • the second opposite sides may be transverse to the first opposite sides.
  • a temperature gradient from a center of the strand to a center of each side of the strand decreases at a same rate, and, after heating, on the transverse plane, a temperature gradient from the center of the strand to the center of each of the first opposite sides decreases at a rate lower than a temperature gradient from the center of the strand to the center of each of the second opposite sides.
  • the metal strand may have a square cross section.
  • the metal strand may have a rectangular cross section.
  • the metal strand may have a circular cross section.
  • the heating of the metal strand may be performed by induction heaters.
  • the heating of the metal strand may be performed by burners.
  • the product cast with a method according to the present invention may be a billet or a bloom.
  • FIG. 1 shows a cross-sectional view of a continuously cast billet or bloom having three crystal zones (on the right) and an enlarged view of a portion of the cross- sectional view (on the left).
  • FIG. 2 schematically shows the continuous casting of a metal strand, for example, steel (shown in longitudinal section on the right), and an enlarged view of a portion of the cross-sectional view of the metal strand (on the left).
  • a metal strand for example, steel (shown in longitudinal section on the right), and an enlarged view of a portion of the cross-sectional view of the metal strand (on the left).
  • FIG. 3 A and FIG. 3B show longitudinal sections of a continuous cast billet or bloom with segregated lines (sulphur print samples in this case).
  • FIG. 4 schematically demonstrate the generation of the central porosity in the mushy zone of a strand as it is being continuously cast (on the right), and an enlarged portion of the strand (on the left).
  • FIG. 5 shows an example of a centrally located porosity along a longitudinal central section of a continuously cast billet.
  • FIG. 6A schematically shows casting of a metal strand (shown along a longitudinal cross section) in a continuous caster.
  • FIG. 6B shows a view of the pinch roll units of a continuous caster seen in the direction of the arrow pointing at the pinch roll units in the continuous caster shown in FIG. 6A.
  • FIG. 7 schematically shows the shape of a strand after squeezing (deformation).
  • FIG. 8A shows and example of the thermal distribution across the strand after soft reduction.
  • FIG. 8B shows an example of the thermal distribution across the strand after hard reduction.
  • FIG. 9A shows the position of heaters in the path of the strand in a continuous casting machine (a curve caster for casting a billet or a bloom) according to the first embodiment of the present invention.
  • FIG. 9B also shows the position of heaters relative to the strand in the continuous casting machine shown in FIG. 9A.
  • FIG. 9C shows examples of temperature values along the cross-section A-A of the strand in FIG. 9A before (upstream of) the heaters.
  • FIG. 9D shows examples of temperature values along the cross-section B-B of the strand in FIG. 9 A after (downstream of) the heaters.
  • FIG. 10A shows the position of heaters in the path of the strand in a continuous casting machine (a curve caster for casting a billet or a bloom) according to the second embodiment of the present invention.
  • FIG. 10B also shows the position of heaters relative to the strand in the continuous casting machine shown in FIG. 10 A.
  • FIG. 10C shows examples of temperature values along the cross-section A-A of the strand in FIG. 10A before (upstream of) the heaters.
  • FIG. 10D shows examples of temperature values along the cross-section B-B of the strand in FIG. 10A after (downstream of) the heaters.
  • FIG. 11 schematically shows the shape of the strand that has been heated according to the present invention after squeezing.
  • the application of the soft reduction and/or the hard reduction can be improved by modifying the temperature distribution across (along the thickness of) the strand.
  • the distribution of temperature across (along the thickness of) the strand is modified prior to soft reduction and/or prior to hard reduction to direct the deformation of the strand toward the center of the strand.
  • two first opposite sides of a soft strand are directly heated by heaters before the second opposite sides of the strand that are, for example, transverse to the first opposite sides are squeezed toward each other by, for example, pinch rollers to perform soft reduction.
  • the heating of the first opposite sides increases the temperature of the first opposite sides relative to the second opposite sides of the soft strand. Consequently, the first opposite sides that are heated to have the higher temperature become less resistant to deformation, thereby allowing the pinch roller to more efficiently direct deformation toward the center of the soft strand.
  • heaters 40 may be arranged opposite one another each toward a respective one of first opposite sides 36 of a soft strand 30 before the soft strand 30 is fed to pinch rollers 32 for soft reduction by squeezing the second opposite sides 38 of the soft strand 30 that are, in this example, transverse to the first opposite sides 36.
  • the temperature gradient from the center of the soft strand 30 to the center of each side 36, 38 located between the corners of the transverse plane of the soft strand 30 is essentially uniform meaning that the temperature decreases from the center of the soft strand 30 toward each center of each side 36, 38 at about the same rate.
  • the temperature gradient from the center of the soft strand 30 to the center of each first opposite side 36 decreases at a rate lower than the temperature gradient from the center of the soft strand 30 to the center of each of the second (in this example transverse) opposite sides 38.
  • the temperature at the center of the soft strand 30 is the same as the temperature of the center of each first opposite side 36 indicating a flat gradient. Consequently, the first opposite sides 36 of the soft strand 30 (i.e. the heated sides) exhibit less resistance to deformation when subjected to squeezing by the pinch rollers 32 during soft reduction.
  • two first opposite sides of a solid strand are directly heated by heaters before the second opposite sides of the solid strand that, for example, are transverse to the first opposite sides are squeezed toward each other by, for example, pinch rollers during hard reduction.
  • the heating of the first opposite sides increases the temperature of the first opposite sides relative to the second opposite sides of the solid strand. Consequently, the first opposite sides that are heated to have the higher temperature become less resistant to deformation, thereby allowing the pinch rollers to more efficiently direct deformation toward the center of the solid strand.
  • heaters 40 may be arranged opposite one another each toward a respective first opposite side 36 of a solid strand 30 before the solid strand 30 is fed to pinch rollers 34 for hard reduction by squeezing the second opposite sides 38 of the solid strand 30 that are, for example, transverse to the first opposite sides 36.
  • the temperature gradient from the center of the solid strand 30 to the center of each side 36, 38 located between the corners of the transverse plane of the solid strand 30 is essentially uniform meaning that the temperature decreases from the center of the solid strand 30 toward each center of each side 36, 38 at about the same rate.
  • the temperature gradient from the center of the solid strand 30 to the center of each first opposite side 36 decreases at a rate lower than the temperature gradient from the center of the solid strand 30 to the center of each of the second opposite sides 38.
  • the temperature at the center of the solid strand 30 is the same as the temperature of the center of each first opposite side 36 indicating a flat gradient. Consequently, the first opposite sides 36 of the solid strand exhibit a lesser resistance to deformation when subjected to squeezing by the pinch rollers 34 during hard reduction.
  • the first opposite sides 36 of the soft strand 30 are heated according to the first embodiment followed by soft reduction using at least two opposing pinch rollers 32, and then the first opposite sides 36 of the solid strand are heated according to the second embodiment followed by hard reduction using at least two other opposing pinch rollers 34.
  • a method according to the present invention will suppress the central porosity formation in the strand.
  • At least a method according to the first embodiment or the third embodiment may also suppress internal segregation in the strand.
  • induction heaters may be positioned to project energy toward the first opposite sides 36 for heating.
  • burners or other types of heaters may be used without deviating from the present invention.
  • the heating of the first opposite sides 36 will reduce their mechanical resistance during squeezing, whereby the deformation of the strand 30 will be concentrated only at the center.
  • the shape of the squeezed strand 30 will be quite regular as illustrated in FIG. 11.
  • the force for squeezing the strand 30 during the soft reduction or the hard reduction will be lower when compared to the current methods. Consequently, smaller pinch rollers may be used.
  • a method according to the present invention may permit the application of soft or hard reduction to larger blooms, which are difficult to process with the existing methods.
  • a method according to the present invention is not limited to a strand having a square cross section and can be applied to a strand having any cross section including a round or a rectangular cross section.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Metal Rolling (AREA)

Abstract

L'invention concerne un procédé de coulée continue d'un produit métallique qui comprend la formation d'un brin à partir de métal liquide, le brin ayant des premiers côtés opposés et des seconds côtés opposés, le chauffage des premiers côtés opposés à une résistance inférieure des premiers côtés opposés à une déformation, et la déformation du brin par pression des seconds côtés opposés l'un vers l'autre.
PCT/US2022/013455 2022-01-24 2022-01-24 Procédé de coulée continue WO2023140865A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/US2022/013455 WO2023140865A1 (fr) 2022-01-24 2022-01-24 Procédé de coulée continue

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US2022/013455 WO2023140865A1 (fr) 2022-01-24 2022-01-24 Procédé de coulée continue

Publications (1)

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WO2023140865A1 true WO2023140865A1 (fr) 2023-07-27

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PCT/US2022/013455 WO2023140865A1 (fr) 2022-01-24 2022-01-24 Procédé de coulée continue

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS62197254A (ja) * 1986-02-25 1987-08-31 Nippon Steel Corp 連続鋳造鋳片のエツジ加熱装置
EP0391823A1 (fr) * 1989-04-06 1990-10-10 Techmetal Promotion Procédé et dispositif de coulée continue de produits métalliques minces
WO2008113848A1 (fr) * 2007-03-21 2008-09-25 Danieli & C. Officine Meccaniche S.P.A. Procédé et usine pour la production de bandes de métal

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS62197254A (ja) * 1986-02-25 1987-08-31 Nippon Steel Corp 連続鋳造鋳片のエツジ加熱装置
EP0391823A1 (fr) * 1989-04-06 1990-10-10 Techmetal Promotion Procédé et dispositif de coulée continue de produits métalliques minces
WO2008113848A1 (fr) * 2007-03-21 2008-09-25 Danieli & C. Officine Meccaniche S.P.A. Procédé et usine pour la production de bandes de métal

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