EP3795274B1 - Moule de moulage continu et procédé de moulage continu d'acier - Google Patents

Moule de moulage continu et procédé de moulage continu d'acier Download PDF

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Publication number
EP3795274B1
EP3795274B1 EP20206258.4A EP20206258A EP3795274B1 EP 3795274 B1 EP3795274 B1 EP 3795274B1 EP 20206258 A EP20206258 A EP 20206258A EP 3795274 B1 EP3795274 B1 EP 3795274B1
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European Patent Office
Prior art keywords
thermal conductivity
metal
mold
low thermal
filled
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EP20206258.4A
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German (de)
English (en)
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EP3795274A1 (fr
Inventor
Naomichi IWATA
Norichika ARAMAKI
Seiji Nabeshima
Yuji Miki
Kohei FURUMAI
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JFE Steel Corp
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JFE Steel Corp
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Priority claimed from JP2016143909A external-priority patent/JP6428721B2/ja
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    • 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
    • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
    • B22D11/055—Cooling the moulds
    • 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
    • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
    • 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
    • B22D11/04—Continuous casting of metals, i.e. casting in indefinite lengths into open-ended moulds
    • B22D11/059—Mould materials or platings
    • 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
    • B22D11/10—Supplying or treating molten metal
    • B22D11/108—Feeding additives, powders, or the like
    • 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
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/20—Controlling or regulating processes or operations for removing cast stock

Definitions

  • the present invention relates to a continuous casting mold with which continuous casting can be performed on molten steel while inhibiting a surface crack from occurring in a cast piece caused by inhomogeneous cooling of a solidified shell in the mold, and to a method for continuous casting of steel by this mold.
  • a solidified shell (also referred to as a "solidified layer") is formed as a result of the surface portion of the molten steel which is in contact with the mold being solidified.
  • a cast piece having the solidified shell as an outer shell and a non-solidified layer inside the shell is continuously drawn in a downward direction through the mold while the cast piece is cooled by water sprays or air-water sprays which are installed on the downstream side of the mold.
  • the central portion in the thickness direction of the cast piece is solidified as a result of being cooled by the water sprays or the air-water sprays, and then the cast piece is cut into cast pieces having a predetermined length by a gas cutting machine, for example.
  • Inhomogeneous solidification in the mold tends to occur, in particular, in the case of steel (referred to as "medium-carbon steel") having a carbon content of 0.08 mass% to 0.17 mass%.
  • a peritectic reaction occurs at the time of solidification. It is considered that inhomogeneous solidification in the mold is caused by transformation stress due to a decrease in volume which occurs when transformation from ⁇ iron (ferrite phase) to ⁇ iron (austenite phase) occurs due to this peritectic reaction. That is, the solidified shell is deformed due to strain caused by this transformation stress, and the solidified shell is detached from the inner wall surface of the mold due to this deformation.
  • this portion which has been detached from the inner wall surface of the mold becomes less likely to be cooled through the mold, there is a decrease in the thickness of the solidified shell of this portion which has been detached from the inner wall surface of the mold (this portion which is detached from the inner wall surface of the mold is referred to as a "depression"). It is considered that, since there is a decrease in the thickness of the solidified shell, a surface crack occurs due to the stress described above being concentrated in this portion.
  • Patent Literature 1 proposes a technique in which mold powder having a chemical composition which tends to cause crystallization is used to increase the thermal resistance of a mold powder layer, so that a solidified shell is slowly cooled. This is a technique for inhibiting a surface crack from occurring by decreasing stress applied to the solidified shell as a result of slow cooling.
  • slow cooling utilizing mold powder since there is an insufficient improvement in inhomogeneous solidification, it is not possible to sufficiently inhibit a surface crack from occurring, in particular, in the case of medium-carbon steel in which transformation from ⁇ iron to ⁇ iron occurs due to a small decrease in temperature when solidification occurs.
  • Patent Literature 2 proposes a technique in which a longitudinal crack is inhibited from occurring in a cast piece by making mold powder flow into vertical grooves and horizontal grooves formed on the inner wall surface of a mold to slowly decrease the cooling rate of the mold and to homogenize the cooling rate in the width direction of the mold.
  • Patent Literature 2 proposes a technique in which a longitudinal crack is inhibited from occurring in a cast piece by making mold powder flow into vertical grooves and horizontal grooves formed on the inner wall surface of a mold to slowly decrease the cooling rate of the mold and to homogenize the cooling rate in the width direction of the mold.
  • Patent Literature 3 proposes a technique in which a longitudinal crack is inhibited from occurring in a cast piece by forming vertical grooves parallel to the casting direction or grid grooves in the central portion in the width direction of the inner wall surface of a mold with the width and depth of the grooves being controlled in accordance with the viscosity of mold powder, so that gaps for letting air flow thereinto are formed in the grooves without filling the grooves with the mold powder to slowly decrease the cooling rate of the mold and to homogenize the cooling rate in the width direction of the mold.
  • Patent Literature 4 proposes a mold in which grid grooves are formed on an inner wall surface thereof and a mold in which the grid grooves are filled with a foreign metal (such as Ni or Cr) or a ceramic (BN, AlN, or ZrO 2 ).
  • This technique is a technique in which a longitudinal crack is inhibited from occurring in a cast piece by providing a periodic variation in the amount of heat removed through the grooves and the portions other than the grooves to disperse stress caused by transformation from ⁇ iron to ⁇ iron or thermal shrinkage of a solidified shell in the regions where the removed amount of heat is small.
  • Patent Literature 5 proposes a continuous casting method in which a mold in which vertical grooves parallel to the casting direction are formed on an inner wall surface thereof, or a mold in which the vertical grooves are filled with a foreign metal (such as Ni or Cr) or a ceramic (BN, AlN, or ZrO 2 ) is used with a cast piece drawing speed and a mold oscillation period being specified to be within predetermined ranges.
  • a mold oscillation period in accordance with the cast piece drawing speed, since oscillation marks formed on the cast piece have a function of horizontal grooves, the effect of inhibiting a surface crack from occurring is realized as in the case of Patent Literature 4 by forming only vertical grooves.
  • Patent Literature 6 proposes a mold in which concave grooves having a diameter of 2 mm to 10 mm are formed in a part of an inner wall surface of the mold in the vicinity of the upper surface of molten steel in the mold (hereinafter, also referred to as a "meniscus") and filled with a foreign metal (such as Ni or stainless steel) or a ceramic (such as BN, AlN, or ZrO 2 ) with the distance between the grooves being 5 mm to 20 mm.
  • This technique is also a technique in which, as in the cases of Patent Literature 4 and Patent Literature 5, by providing a periodic distribution of thermal conduction to inhibit inhomogeneous solidification, a vertical crack is inhibited from occurring in a cast piece.
  • Patent Literature 6 since the groove openings are formed by a drill on the surface of a mold copper plate, and since the grooves are filled with the foreign metal or the ceramic formed into the shape of the grooves, the conditions of contact between the back surfaces of filling pieces of the metal or the ceramic and the mold copper plate are not constant, which increase a risk of gaps being formed in the contact parts. In the case where such gaps are formed, there is a large variation in the amount of heat removed among the concave grooves depending on such gaps, which results in a problem in that it is not possible to appropriately control the cooling of a solidified shell. In addition, there is also a problem in that the filling pieces of the foreign metal or the ceramic tend to be separated from the mold copper plate.
  • an object of the present invention is to provide a continuous casting mold with which it is possible to inhibit, for a long period of time, a surface crack from occurring in a cast piece due to the inhomogeneous cooling of a solidified shell in the early solidification stage and a surface crack from occurring in a cast piece due to a variation in the thickness of a solidified shell caused by transformation from ⁇ iron to ⁇ iron accompanied by a peritectic reaction in medium-carbon steel without a constrained breakout occurring at the start of casting or a decrease in the life of the mold due to a surface crack occurring in a mold copper plate, and to provide a continuous casting method for steel utilizing this continuous casting mold.
  • plural portions filled with a metal of low thermal conductivity which are formed by filling the portions with a metal of low thermal conductivity having a thermal resistance ratio R, that is, the thermal resistance ratio of the portions filled with a metal of low thermal conductivity to the mold copper plate, of 5% or more and thermal conductivity which is 80% or less of the thermal conductivity of the mold copper plate, are disposed in the width direction and casting direction of a continuous casting mold in a region including a meniscus position in the vicinity of the meniscus.
  • the thermal resistance of the continuous casting mold periodically increases and decreases in the width direction and casting direction of the continuously casting mold in the vicinity of the meniscus
  • the thermal flux from a solidified shell to the continuous casting mold periodically increases and decreases in the vicinity of the meniscus, that is, in the early solidification stage.
  • there is a decrease in stress due to transformation from ⁇ iron to ⁇ iron and in thermal stress there is a decrease in the amount of deformation of the solidified shell caused by these stresses.
  • Fig. 1 is a schematic side view of a mold copper plate 1 on the long side of a mold constituting a part of the water-cooled continuous casting mold according to the present embodiments, that is, the mold copper plate 1 on the long side of the mold having portions 3 filled with a metal of low thermal conductivity formed on an inner wall surface side thereof, viewed from the inner wall surface side.
  • Fig. 2 is an X-X' cross-sectional view of the mold copper plate 1 on the long side of a mold in Fig. 1 .
  • the continuous casting mold in Fig. 1 is an example of a continuous casting mold used for casting a cast slab.
  • a water-cooled continuous casting mold made of a copper alloy for a cast slab consists of a combination of a pair of mold copper plates made of a copper alloy on the long side of the mold and a pair of mold copper plates made of a copper alloy on the short side of the mold. Of such mold copper plates, a mold copper plate 1 on the long side of the mold is illustrated in Fig. 1 .
  • plural portions 3 having a diameter d and filled with a metal of low thermal conductivity are formed with the distance P between the portions filled with a metal of low thermal conductivity in a region, on the inner wall surface of the mold copper plate 1 on the long side of the mold, from a position located above the position of a meniscus when stationary casting is performed on the mold copper plate 1 on the long side of the mold and at a distance equal to a length Q (length Q is assigned a value larger than 0) from the meniscus to a position located below the meniscus and at a distance equal to a length L from the meniscus.
  • the term "meniscus” refers to "the upper surface of molten steel in a mold", and, although its position is not clear when casting is not performed, the meniscus position is set to be about 50 mm to 200 mm lower than the upper edge of the mold copper plate in an ordinary continuous casting operation for steel. Therefore, even in the case where the meniscus position is 50 mm or 200 mm lower than the upper edge of the mold copper plate 1 on the long side of the mold, the portions 3 filled with a metal of low thermal conductivity may be disposed so that a length Q and a length L satisfy the conditions according to the present invention as described below.
  • the portions 3 filled with a metal of low thermal conductivity are formed on the inner wall surface of the mold copper plate 1 on the long side of the mold by filling separately formed circular concave grooves 2 having a diameter of d with a metal (hereinafter, referred to as a "metal of low thermal conductivity") having thermal conductivity ⁇ m , which is 80% or less of the thermal conductivity ⁇ c of the copper alloy used to construct the mold copper plate 1 on the long side of the mold through a plating treatment or a thermal spraying treatment.
  • the concave grooves 2 having a circular opening shape on the inner wall surface of the mold copper plate are referred to as "circular concave grooves".
  • reference 5 denotes a back plate which is in close contact with the back surface of the mold copper plate 1 on the long side of the mold.
  • Fig. 3 is a conceptual diagram illustrating the thermal resistance distributions in accordance with the positions where portions 3 filled with a metal of low thermal conductivity are formed at three positions on a mold copper plate 1 having portions 3 filled with a metal of low thermal conductivity on the long side of a mold. As illustrated in Fig. 3 , there is a relative increase in thermal resistance at the positions where portions 3 filled with a metal of low thermal conductivity are formed.
  • the ratio between the thermal conductivity ⁇ c of the copper alloy and the thermal conductivity ⁇ m of the metal of low thermal conductivity is defined as the ratio at room temperature (about 20°C).
  • the thermal conductivities of the copper alloy and the metal of low thermal conductivity generally decrease with an increase in temperature, in the case where the ratio of the thermal conductivity ⁇ m of the metal of low thermal conductivity to the thermal conductivity ⁇ c of the copper alloy is 80% or less at room temperature, it is possible to provide a difference in thermal resistance between the positions where the portions 3 filled with a metal of low thermal conductivity are formed and the positions where no such portion 3 filled with a metal of low thermal conductivity is formed even at a temperature (about 200°C to 350°C) at which the continuous casting mold is used.
  • the portions 3 filled with the metal of low thermal conductivity are formed in accordance with the shape of the mold copper plate so that the thermal resistance ratio R of the portions filled with a metal of low thermal conductivity to the mold copper plate, which is defined by expression (1) below, is 5% or more.
  • the thermal resistance ratio R is, as expressed in expression (1), defined by the distance T from the bottom surface 4a of a slit 4 of the mold copper plate, which is used as a flow channel of mold-cooling water, to the surface of the mold copper plate, the filling thickness H of the metal of low thermal conductivity in the portions 3 filled with a metal of low thermal conductivity, the thermal conductivity ⁇ c of the mold copper plate, and the thermal conductivity ⁇ m of the metal of low thermal conductivity.
  • R T ⁇ H / 1000 ⁇ ⁇ c + H / 1000 ⁇ ⁇ m ⁇ T / 1000 ⁇ ⁇ c / T / 1000 ⁇ ⁇ c ⁇ 100
  • R denotes the thermal resistance ratio (%) of the portions filled with a metal of low thermal conductivity to the mold copper plate
  • T denotes a distance (mm) from the bottom surface of a slit of the mold copper plate, which is used as a flow channel of mold-cooling water, to the surface of the mold copper plate
  • H denotes a filling thickness (mm) of the metal of low thermal conductivity
  • ⁇ c denotes the thermal conductivity (W/(m ⁇ K)) of the mold copper plate
  • ⁇ m denotes the thermal conductivity (W/(m ⁇ K)) of the metal of low thermal conductivity.
  • the thermal resistance ratio R is more than 100%, since there is a significant delay in solidification at the portions 3 filled with a metal of low thermal conductivity, inhomogeneous solidification is promoted, which increases a risk of a surface crack and a breakout occurring in a cast piece. Therefore, it is preferable that the thermal resistance ratio R be 100% or less.
  • the lower edge of a region where the portions 3 filled with a metal of low thermal conductivity be located below the meniscus and at a distance equal to or more than a length L 0 from the meniscus, where L 0 is calculated by expression (2) below from a cast piece drawing speed Vc when stationary casting is performed. That is, it is preferable that a length L from the meniscus in Fig. 1 be equal to or more than the length L 0 .
  • L 0 2 ⁇ Vc ⁇ 1000 / 60
  • L 0 denotes a length (mm)
  • Vc denotes a cast piece drawing speed (m/min).
  • the length L 0 relates to the time taken for a cast piece which has started being solidified to pass through the region where the portions 3 filled with a metal of low thermal conductivity are formed, and, to inhibit a surface crack from occurring in the cast piece, it is preferable that the cast piece stay in the region where the portions 3 filled with a metal of low thermal conductivity are formed at least 2 seconds after solidification has started. To ensure that a cast piece to stay in the region where the portions 3 filled with a metal of low thermal conductivity are formed at least 2 seconds after solidification has started, it is necessary that the length L 0 satisfy expression (2).
  • the time taken for a cast piece to pass through the region where the portions 3 filled with a metal of low thermal conductivity are formed is 4 seconds or more.
  • the length L be 5 times or less of the length L 0 from the viewpoint of decreasing costs for forming concave grooves and performing a plating treatment or a thermal spraying treatment on the surface of the mold copper plate to form the portions 3 filled with a metal of low thermal conductivity.
  • the upper edge of the region where the portions 3 filled with a metal of low thermal conductivity are formed may be located at any position as long as the position is above the meniscus, a length Q in Fig. 1 may take a value larger than 0.
  • the meniscus moves in an up and down direction when casting is performed, to ensure that the upper edge of the region where the portions 3 filled with a metal of low thermal conductivity are formed is always located at a position above the meniscus, it is preferable that the upper edge of the portions 3 filled with a metal of low thermal conductivity be located about 10 mm, or more preferably about 20 mm to 50 mm, higher than a set meniscus.
  • the opening shape of the portions 3 filled with a metal of low thermal conductivity on the inner wall surface of a mold copper plate 1 on the long side of a mold is circular, it is not necessary that the opening shape be circular. Any kind of shape may be used as long as the shape is one similar to a circle such as an ellipse which does not have a so-called "angulated corner".
  • a shape similar to a circle will be referred to as a "quasi-circle".
  • grooves 2 formed on the inner wall surface of the mold copper plate 1 on the long side of the mold to form the portions 3 filled with a metal of low thermal conductivity are referred to as "quasi-circle grooves".
  • Examples of a quasi-circle include an ellipse and a rectangle having corners having a shape of a circular arc or an elliptic arc which have no angulated corner, and, further, a shape such as a petal-shaped pattern may be used.
  • the size of a quasi-circle is measured in terms of circle-equivalent diameter, which is calculated from the area of the opening having a quasi-circular shape on the inner wall surface of the mold copper plate 1 on the long side of the mold.
  • Patent Literature 4 and Patent Literature 5 where vertical grooves or grid grooves are formed and the grooves are filled with a metal of low thermal conductivity, there is a problem in that, since stress caused by a difference in thermal strain between the metal of low thermal conductivity and copper is concentrated at the boundary surface between the metal of low thermal conductivity and copper and at the intersections of the grid portions, surface cracks occur in the mold copper plate.
  • the shape of the portions 3 filled with a metal of low thermal conductivity is set to be a circle or a quasi-circle. With this, since the boundary surface between the metal of low thermal conductivity and copper is a curved surface, stress is less likely to be concentrated at the boundary surface, which results in an advantage in that a surface crack is less likely to occur in a mold copper plate.
  • the portions 3 filled with a metal of low thermal conductivity have a diameter d or a circle-equivalent diameter d of 2 mm to 20 mm.
  • the diameter d or the circle-equivalent diameter d is controlled to be 2 mm or more, it is easy to fill circular concave grooves 2 or quasi-circular concave grooves 2 with the metal of low thermal conductivity by performing a plating treatment or a thermal spraying treatment.
  • the diameter d or circle-equivalent diameter d of the portions 3 filled with a metal of low thermal conductivity is controlled to be 20 mm or less, since a decrease in thermal flux in the portions 3 filled with a metal of low thermal conductivity is inhibited, that is, since solidification delay in the portions 3 filled with a metal of low thermal conductivity is inhibited, stress concentration in a solidified shell at positions corresponding to the portions 3 is prevented, which results in a surface crack being inhibited from occurring in the solidified shell.
  • the portions 3 filled with a metal of low thermal conductivity have a diameter d or a circle-equivalent diameter d of 20 mm or less.
  • the circle-equivalent diameter d of the quasi-circle is calculated by expression (5) below.
  • circle-equivalent diameter 4 ⁇ S / ⁇ 1 / 2
  • S denotes the area (mm 2 ) of the opening of the portions 3 filled with a metal of low thermal conductivity on the inner wall surface of the mold copper plate.
  • the ratio of the thermal conductivity ⁇ m of a metal of low thermal conductivity with which circular concave grooves or quasi-circular concave grooves are filled to the thermal conductivity ⁇ c of a copper alloy to be used to construct a mold copper plate be 80% or less.
  • Examples of the metal of low thermal conductivity used for the continuous casting mold according to the present embodiments include nickel (Ni, having a thermal conductivity of 90.5 W/(m ⁇ K)), a nickel-based alloy, chromium (Cr, having a thermal conductivity of 67 W/(m ⁇ K)), and cobalt (Co, having a thermal conductivity of 70 W/(m ⁇ K)), which are easy to use as filling materials in a plating treatment or a thermal spraying treatment.
  • the thermal conductivity described in the present description is that determined at room temperature (about 20°C) .
  • a copper alloy used for a mold copper plate a copper alloy to which, for example, minute amounts of chromium and zirconium (Zr) generally used for a continuous casting mold are added may be used.
  • Zr zirconium
  • a continuous casting mold is generally provided with an electromagnetic stirring device, with which molten steel in a mold is stirred.
  • an electromagnetic stirring device with which molten steel in a mold is stirred.
  • a copper alloy whose electrical conductivity is decreased is used.
  • the filling thickness H of the portions 3 filled with a metal of low thermal conductivity be 0.5 mm or more.
  • the filling thickness H be 0.5 mm or more, since there is a sufficient decrease in thermal flux in the portions 3 filled with a metal of low thermal conductivity, it is possible to realize the effect of inhibiting a surface crack from occurring in a cast piece.
  • the filling thickness H of the portions 3 filled with a metal of low thermal conductivity be equal to or less than the diameter d or circle-equivalent diameter d of the portions 3 filled with a metal of low thermal conductivity. Since the filling thickness H is controlled to be equal to or less than the diameter d or circle-equivalent diameter d of the portions 3 filled with a metal of low thermal conductivity, it is easy to fill the concave grooves 2 with the metal of low thermal conductivity by performing a plating treatment or a thermal spraying treatment, and a gap or a crack does not occur between the filling pieces of metal of low thermal conductivity and the mold copper plate.
  • a distance P between the portions filled with a metal of low thermal conductivity is 0.25 times or more of the diameter d or circle-equivalent diameter d of the portions 3 filled with a metal of low thermal conductivity. That is, a distance P between the portions filled with a metal of low thermal conductivity satisfy the expression (3) below with respect to the diameter d or circle-equivalent diameter d of the portions 3 filled with a metal of low thermal conductivity. P ⁇ 0 .25 ⁇ d
  • P denotes the distance (mm) between the portions filled with a metal of low thermal conductivity and d denotes the diameter (mm) or circle-equivalent diameter (mm) of the portions filled with a metal of low thermal conductivity.
  • a distance P between the portions filled with a metal of low thermal conductivity refers to the shortest distance between the edges of the adjacent portions 3 filled with a metal of low thermal conductivity as illustrated in Fig. 1 .
  • the distance P there is no particular limitation on the upper limit of the distance P between the portions filled with a metal of low thermal conductivity, since there is a decrease in the area ratio of the portions 3 filled with a metal of low thermal conductivity in the case where the distance P is large, it is preferable that the distance P be equal to or less than "2.0 ⁇ d".
  • the arrangement pattern of the portions 3 filled with a metal of low thermal conductivity is not limited to a zigzag pattern, and any arrangement may be used as long as the distance P between the portions filled with a metal of low thermal conductivity satisfies expression (3) above.
  • the ratio ⁇ varies depending on the diameter d or circle-equivalent diameter d of portions 3 filled with a metal of low thermal conductivity and the number of portions 3 filled with a metal of low thermal conductivity.
  • the ratio ⁇ is less than 0.07, since the number of portions 3 filled with a metal of low thermal conductivity is small, stress caused by a decrease in volume when ⁇ / ⁇ transformation occurs or thermal shrinkage is less likely to be dispersed across a shell, which results in a decrease in the effect of inhibiting a surface crack from occurring in a cast piece.
  • the ratio ⁇ is more than 0.60, since the number of portions 3 filled with a metal of low thermal conductivity is excessively large, the amount of periodic increase and decrease in thermal flux does not reach a target level, which results in a decrease in the effect of inhibiting a surface crack from occurring in a cast piece.
  • the ratio ⁇ is more than 0.60, bulging occurred in a cast piece immediately below a mold.
  • the portions 3 filled with a metal of low thermal conductivity are basically formed on the mold copper plates on both of the long side and short side of the continuous casting mold, in the case of a cast slab where the ratio of the long side length of the cast piece to the short side length of the cast piece is significantly large, since a surface crack tends to occur on the long side of the cast piece, it is possible to realize the effect of inhibiting a surface crack from occurring in a cast piece even in the case where the portions 3 filled with a metal of low thermal conductivity are formed only on the mold copper plates on the long side of a mold.
  • a coating layer 6 be formed on the inner wall surface of a mold copper plate on which the portions 3 filled with a metal of low thermal conductivity is formed to prevent abrasion caused by a solidified shell and a surface crack occurring in the mold surface due to a thermal history. It is possible to form the coating layer 6 by performing a plating treatment utilizing commonly used nickel or a nickel-containing alloy such as a nickel-cobalt alloy (Ni-Co alloy) or a nickel-chromium alloy (Ni-Cr alloy). It is preferable that the thickness h of the coating layer 6 be 2.0 mm or less.
  • the thickness h of the coating layer 6 By controlling the thickness h of the coating layer 6 to be 2.0 mm or less, since there is a decrease in the influence of the coating layer 6 on thermal flux, it is possible to sufficiently realize the effect of a periodic variation in thermal flux caused by the portions 3 filled with a metal of low thermal conductivity. However, in the case where the thickness h of the coating layer 6 is larger than 0.5 times of the filling thickness H of the portions 3 filled with a metal of low thermal conductivity, a periodic variation in thermal flux caused by the portions 3 filled with a metal of low thermal conductivity is inhibited from being provided. Therefore, it is preferable that the thickness h of the coating layer 6 be 0.5 times or less of the filling thickness H of the portions 3 filled with a metal of low thermal conductivity.
  • Fig. 4 is a schematic diagram illustrating an example in which a coating layer is formed on the inner wall surface of a mold copper plate on the long side of a mold to protect the surface of the mold.
  • the continuous casting mold which is configured as described above, be used when a cast slab (having a thickness of 200 mm or more) of medium-carbon steel having a carbon content of 0.08 mass% to 0.17 mass%, which has high surface crack sensitivity, is manufactured by performing continuous casting.
  • a cast slab of medium-carbon steel is manufactured by performing continuous casting, a cast piece drawing speed has been generally decreased to inhibit a surface crack from occurring in the cast piece.
  • the continuous casting mold which is configured as described above, since it is possible to inhibit a surface crack from occurring in a cast piece, it is possible to manufacture a cast piece with no surface crack or a significantly small number of surface cracks even by performing continuous casting at a cast piece drawing speed of 1.5 m/min or more.
  • plural portions 3 filled with a metal of low thermal conductivity and having a thermal resistance ratio R, which is defined by expression (1), of 5% or more are disposed in the width direction and casting direction of the continuous casting mold in a region including a meniscus position in the vicinity of the meniscus.
  • Fig. 1 an example in which identically shaped portions 3 filled with a metal of low thermal conductivity are disposed in the casting direction or the mold width direction is illustrated in Fig. 1 , it is not necessary that identically shaped portions 3 filled with a metal of low thermal conductivity be disposed.
  • the diameter d or circle-equivalent diameter d of the portions 3 filled with a metal of low thermal conductivity is within a range of 2 mm to 20 mm
  • portions 3 filled with a metal of low thermal conductivity and having various diameters may be disposed in the casting direction or the mold width direction.
  • the diameter or the circle-equivalent diameter d of the portions 3 filled with a metal of low thermal conductivity widely varies from place to place, since solidification delay occurs in a region where the area ratio of the portions 3 filled with a metal of low thermal conductivity is locally high, there is a risk of a surface crack occurring in the region of the cast piece. Therefore, it is preferable that the diameter or the circle-equivalent diameter of the portions be identical.
  • portions 3 filled with a metal of low thermal conductivity and having an identical filling thickness H are disposed in the casting direction of a mold.
  • the portions 3 filled with a metal of low thermal conductivity and disposed in the width direction of the mold or in the width direction of the cast piece have an identical filling thickness H, that is, the filling thicknesses H of portions 3 filled with a metal of low thermal conductivity may vary one portion to another.
  • portions 3 filled with a metal of low thermal conductivity are disposed at regular intervals in the casting direction or width direction of a mold
  • the portions 3 filled with a metal of low thermal conductivity it is not necessary the portions 3 filled with a metal of low thermal conductivity be disposed at regular intervals.
  • the continuous casting mold according to the present embodiments is not limited to a continuous casting mold for a cast slab, that is, it is possible to use the continuous casting mold described above for casting a bloom or a billet.
  • the length from the upper edge to the lower edge of the water-cooled copper-alloy continuous casting mold used for the test was 950 mm, and the position of the meniscus (the upper surface of the molten steel in the mold) when stationary casting is performed was set to be located at a position 100 mm lower than the upper edge of the mold.
  • Circular concave grooves were formed in a region, on the inner wall surface of the mold copper plate, from a position 60 mm lower than the upper edge of the mold to a position located below the set meniscus and at a distance equal to a length L (mm) from the meniscus, and the circular concave grooves were filled with a metal of low thermal conductivity by performing an electroplating treatment.
  • a mold copper plate two kinds of copper alloys having different thermal conductivities, that is, 298.5 W/(m ⁇ K) and 120.0 W/(m ⁇ K), were used.
  • a metal of low thermal conductivity for filling hereafter, also referred to as a "filling metal"
  • pure nickel having a thermal conductivity of 90.5 W/(m ⁇ K)
  • pure cobalt having a thermal conductivity of 70 W/(m ⁇ K)
  • pure chromium having a thermal conductivity of 67 W/(m ⁇ K)
  • pure copper having a thermal conductivity of 398 W/(m ⁇ K)
  • mold powder having a basicity ((mass%CaO)/(mass%SiO 2 )) of 1.0 to 1.5 and a viscosity at a temperature of 1300°C of 0.05 Pa ⁇ s to 0.20 Pa ⁇ s was used.
  • a dye penetrant inspection was performed to investigate a state in which surface cracks occurred in a cast piece.
  • Example 1 refers to a case where a water-cooled copper-alloy continuous casting mold within the scope of the present invention was used
  • Comparative Example refers to a case where a water-cooled copper-alloy continuous casting mold outside the scope of the present invention despite having portions filled with a metal of low thermal conductivity was used
  • Conventional Example refers to a case where a water-cooled copper-alloy continuous casting mold having no portion filled with a metal of low thermal conductivity was used.
  • test Nos. 1 through 8 the influence of the ratio of the thermal conductivity ⁇ m of the filling metal to the thermal conductivity ⁇ c of the mold copper plate on a surface crack occurring in a cast piece was investigated. From the results of test Nos. 1 through 8 illustrated in Fig. 5 , it is clarified that it was possible to inhibit a surface crack from occurring in a cast piece in the case where the ratio of the thermal conductivity ⁇ m of the filling metal to the thermal conductivity ⁇ c of the mold copper plate was 80% or less.
  • test Nos. 9 through 19 the influence of the thermal resistance ratio R of the portions filled with the metal of low thermal conductivity to the mold copper plate on a surface crack occurring in a cast piece was investigated. From the results of test Nos. 9 through 19 illustrated in Fig. 6 , it is clarified that it was possible to inhibit a surface crack from occurring in a cast piece in the case where the thermal resistance ratio R was 5% or more. However, it is clarified that there was a decrease in the effect of inhibiting a surface crack in the case where the thermal resistance ratio R was more than 100%.
  • test Nos. 20 through 26 the influence of the ratio of a total area B (mm 2 ) of all the portions filled with the metal of low thermal conductivity to an area A (mm 2 ) of the region, on the inner wall surface of the mold copper plate, where the portions filled with the metal of low thermal conductivity are formed, that is, an area ratio S on a surface crack occurring in a cast piece, and the influence of the ratio of a total length C (mm) of boundaries between all the portions filled with the metal of low thermal conductivity and the mold copper plate to the area A (mm 2 ), that is, a ratio ⁇ on a surface crack occurring in a cast piece were investigated. From the results of test Nos. 20 through 26 illustrated in Fig.
  • test Nos. 27 through 32 the influence of the diameter d of portions filled with a metal of low thermal conductivity on a surface crack occurring in a cast piece was investigated. From the results of test Nos. 27 through 32 illustrated in Fig. 8 , it is clarified that it was possible to inhibit a surface crack from occurring in a cast piece in the case where the diameter d of portions filled with a metal of low thermal conductivity was 2 mm to 20 mm.
  • water-cooled copper-alloy continuous casting molds in which plural portions filled with a metal of low thermal conductivity were formed on the inner wall surfaces of copper-alloy mold copper plates on the long sides of the molds and inner wall surfaces of copper-alloy plates on the short sides of the molds so that the portions were combined with each other, that is, water-cooled copper-alloy continuous casting molds, in which portions filled with a metal of low thermal conductivity were not separated, were used.
  • test Nos. 40 through 44 as illustrated in Fig. 9 , the combined portions filled with a metal of low thermal conductivity which were formed by combining three portions filled with a metal of low thermal conductivity having a diameter of 3 mm were disposed with various distances P between the combined portions filled with a metal of low thermal conductivity. Also, in test Nos.
  • Fig. 10-(A) and Fig. 11-(A) are schematic side views of a mold copper plate on the long side of a mold on which portions filled with a metal of low thermal conductivity are formed as viewed from the inner wall surface side.
  • FIG. 10-(B) is the Y-Y' cross-sectional view of the mold copper plate on the long side of a mold illustrated in Fig. 10-(A)
  • Fig. 11-(B) is the Y-Y' cross-sectional view of the mold copper plate on the long side of a mold illustrated in Fig. 11-(A) .
  • test No. 46 it is considered that, since all the portions filled with a metal of low thermal conductivity are combined, solidification delay always occurred at the same position in the solidified shell when continuous casting was performed, which results in stress caused by ⁇ / ⁇ transformation or thermal stress being concentrated at such a position and then a slight surface crack being occurred.
  • test Nos. 47 and 48 conventional continuous casting molds in which no portion filled with a metal of low thermal conductivity was formed were used. In test Nos. 47 and 48, many surface cracks occurred in the cast pieces.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Continuous Casting (AREA)

Claims (5)

  1. Moule de fonderie continue, le moule étant un moule de fonderie continue refroidi par eau, comprenant :
    des parties (3) remplies d'un métal de faible conductivité thermique formé en remplissant une pluralité de rainures concaves (2) avec le métal de faible conductivité thermique dans une zone, sur une surface de paroi interne d'une plaque de cuivre de moulage (1) qui est constituée d'un alliage de cuivre et qui constitue le moule, depuis une position située au-dessus d'un ménisque jusqu'à une position située en dessous du ménisque, où :
    le rapport de la conductivité thermique λm (en W/m × K) du métal de faible conductivité thermique sur la conductivité thermique λc (en W/m × K) de la plaque de cuivre de moulage (1) vaut 80 % ou moins, et
    le rapport de résistances thermiques R défini par l'expression (1) ci-dessous vaut 5 % ou plus : R = T − H / 1000 × λ c + H/ 1000 × λ m − T/ 1000 × λ c / T/ 1000 × λ c × 100
    Figure imgb0014
     où
    R indique un rapport de résistances thermiques (%) des parties remplies par le métal de faible conductivité thermique sur la plaque de cuivre de moulage (1),
    T indique la distance (mm) de la surface de fond d'une fente (4) de la plaque de cuivre de moulage (1), qui est utilisée comme canal d'écoulement de l'eau de refroidissement du moule, sur la surface de la plaque de cuivre de moulage (1), et
    H indique l'épaisseur de remplissage (mm) du métal de faible conductivité thermique,
    où plusieurs parties remplies d'un métal de faible conductivité thermique sont formées sur les surfaces de parois internes de plaques de cuivre de moulage en alliage de cuivre sur les côtés longs des moules et sur les surfaces de parois internes de plaques en alliage de cuivre sur les côtés courts des moules de sorte à ce que les parties soient combinées les unes avec les autres,
    où les parties remplies d'un métal de faible conductivité thermique n'ont pas été séparées,
    où les parties combinées remplies d'un métal de faible conductivité thermique, qui sont formées en combinant trois parties remplies d'un métal de faible conductivité thermique présentant un diamètre de 3 mm sont disposées à des distances variables (P) entre les parties combinées remplies d'un métal de faible conductivité thermique, où
    les rainures concaves (2) sont formées à une distance supérieure ou égale à la longueur L0 (mm) à partir du ménisque, L0 étant calculée par l'expression (2) ci-dessous à partir d'une vitesse d'étirage de pièces de moulage Vc (m/min) de 1,5 m/min ou plus : L 0 = 2 × Vc × 1000/60
    Figure imgb0015
     où
    les ouvertures des rainures concaves (2) sur la surface de paroi interne de la plaque de cuivre de moulage (1) présentent une forme circulaire ou quasi circulaire, et
    la forme circulaire présente un diamètre de 2 mm à 20 mm et la forme quasi circulaire présente un diamètre équivalent au cercle de 2 mm à 20 mm, où
    la distance entre les parties (3) remplies de métal de faible conductivité thermique satisfait à l'expression (3) ci-dessous par rapport au diamètre ou au diamètre équivalent des parties (3) remplies du métal de faible conductivité thermique : P ≥ 0 ,25 × d
    Figure imgb0016
     où
    P indique la distance (mm) entre les parties (3) remplies de métal de faible conductivité thermique, et
    d indique le diamètre (mm) ou le diamètre équivalent (mm) des parties (3) remplies de métal de faible conductivité thermique, et où
    le rapport de la surface totale B (mm2) de toutes les parties (3) remplies de métal de faible conductivité thermique sur la surface A (mm2) de la zone, sur la surface de paroi interne de la plaque de cuivre de moulage (1), où sont formées les parties (3) remplies de métal de faible conductivité thermique, c'est-à-dire le rapport de surfaces S (S = (B/A) × 100), vaut 10 % ou plus, et
    le rapport de la longueur totale C (mm) des limites entre toutes les parties (3) remplies de métal de faible conductivité thermique et la plaque de cuivre de moulage (1) sur la surface A (mm2) , c'est-à-dire le rapport ε (ε = C/A) , satisfait à l'expression (4) ci-dessous : 0,07 ≤ ε ≤ 0,60
    Figure imgb0017
  2. Moule de fonderie continue selon la revendication 1, présentant une répartition de résistances thermiques périodique ou une répartition de flux thermiques périodiques dans la zone, sur la surface de paroi interne de la plaque de cuivre de moulage (1), où sont formées les parties (3) remplies de métal de faible conductivité thermique.
  3. Moule de fonderie continue selon la revendication 1 ou la revendication 2, dans lequel les rainures concaves (2) sont remplies du métal à faible conductivité thermique grâce à un traitement de placage ou à un traitement de diffusion thermique.
  4. Moule de fonderie continue selon l'une quelconque des revendications 1 à 3, dans lequel :
    une couche de revêtement (6), présentant une épaisseur de 2,0 mm ou moins et contenant du nickel ou un alliage contenant du nickel, est formée sur la surface de paroi interne de la plaque de cuivre de moulage (1), et
    les parties (3) remplies de métal de faible conductivité thermique sont recouvertes de la couche de revêtement.
  5. Procédé de moulage continu d'acier, utilisant le moule de fonderie continue conforme à l'une quelconque des revendications 1 à 4, le procédé comprenant les étapes suivantes :
    l'injection d'acier à teneur moyenne en carbone présentant une teneur en carbone de 0,08 % en masse à 0,17 % en masse dans le moule, et
    l'étirage de l'acier à teneur moyenne en carbone depuis le moule sous la forme d'un lingot de fonderie présentant une épaisseur de 200 mm ou plus à une vitesse d'étirage de pièces de fonderie de 1,5 m/min ou plus.
EP20206258.4A 2015-07-22 2017-01-16 Moule de moulage continu et procédé de moulage continu d'acier Active EP3795274B1 (fr)

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JP2016143909A JP6428721B2 (ja) 2015-07-22 2016-07-22 連続鋳造用鋳型及び鋼の連続鋳造方法
EP17830623.9A EP3488946A4 (fr) 2015-07-22 2017-01-16 Moule de coulée continue et procédé de coulée continue d'acier
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US6024162A (en) * 1994-12-28 2000-02-15 Nippon Steel Corporation Continuous casting method for billet
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JPH1029043A (ja) * 1996-07-15 1998-02-03 Nkk Corp 鋼の連続鋳造方法及び連続鋳造用鋳型
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CN109475930A (zh) 2019-03-15
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