JP2017039165A - Casting mold for continuous casting and continuous casting method of steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent surface cracking due to uneven cooling of solidified shell on an initial solidification stage and surface cracking due to unevenness of solidified shell thickness caused by transformation from δ iron to γ iron in medium carbon steel.SOLUTION: A casting mold for continuous casting according to the present invention includes, in a prescribed range of an inner wall surface of a water-cooled copper alloy casting mold, a dissimilar substance-filled part in which metal or nonmetal having a thermal conductivity different from a thermal conductivity of casting mold copper plate is filled 1. Heat resistance R(m×K/W) between a casting mold copper plate surface and a slit of the casting mold copper plate as a flow channel of casting mold cooling water on an installation position of the dissimilar substance filled part falls into the range of the following relation (1) and the ratio (λ/λ) of thermal conductivity λof the casting mold copper plate to thermal conductivity λma of the metal or nonmetal is larger than 0.2 and is less than 20.0 (however, such a case that λ=λis excluded):1.0×10<R<6.0×10...(1).SELECTED DRAWING: Figure 4

Description

  The present invention relates to a continuous casting mold capable of continuously casting molten steel while suppressing slab surface cracking due to non-uniform cooling of the solidified shell in the mold, and a continuous casting method of steel using this mold. About.

  In continuous casting of steel, molten steel poured into a mold is cooled by a water-cooled mold, and the molten steel is solidified at a contact surface with the mold to generate a solidified layer (referred to as “solidified shell”). The slab having the solidified shell as an outer shell and the inside as an unsolidified layer is continuously drawn below the mold while being cooled by a water spray or an air / water spray installed on the downstream side of the mold. The slab is solidified to the center by cooling with water spray or air-water spray, and then cut by a gas cutter or the like to produce a slab of a predetermined length.

  If the cooling in the mold becomes non-uniform, the thickness of the solidified shell becomes non-uniform in the casting direction of the slab and in the mold width direction. A stress caused by the shrinkage or deformation of the solidified shell acts on the solidified shell, and in the initial stage of solidification, this stress is concentrated on the thin portion of the solidified shell, and the stress causes cracks on the surface of the solidified shell. This crack expands due to subsequent external stresses such as thermal stress, bending stress due to the roll of a continuous casting machine, and straightening stress, resulting in a large surface crack. When the non-uniformity of the solidified shell thickness is large, a vertical crack is generated in the mold, and a breakout in which the molten steel flows out from the vertical crack may occur. Since the cracks present in the slab become surface defects in the subsequent rolling process, it is necessary to care for the surface of the slab and remove the surface cracks at the stage of the cast slab after casting.

  Inhomogeneous solidification in the mold is likely to occur particularly in steel (referred to as medium carbon steel) having a carbon content of 0.08 to 0.17% by mass. In a steel having a carbon content of 0.08 to 0.17% by mass, a peritectic reaction occurs during solidification, and the non-uniform solidification in the mold is caused by the peritectic reaction from δ iron (ferrite) to γ iron (austenite). It is thought to be caused by transformation stress due to volume shrinkage during transformation. That is, the solidified shell is deformed by the strain caused by the transformation stress, and the solidified shell is separated from the inner wall surface of the mold by this deformation. Cooling by the mold is reduced at the part away from the inner wall surface of the mold, and the solidified shell thickness of the part away from the inner wall surface of the mold (the part away from the inner wall surface of the mold is referred to as “depression”) is reduced. It is considered that the above stress concentrates on this portion and the surface crack occurs due to the thinning.

  In particular, when the slab drawing speed is increased, the average heat flux from the solidified shell to the mold cooling water increases (the solidified shell is rapidly cooled), and the heat flux distribution is irregular and irregular. Since it becomes uniform, the occurrence of slab surface cracks tends to increase. Specifically, in a slab continuous casting machine having a slab thickness of 200 mm or more, surface cracks are likely to occur when the slab drawing speed is 1.5 m / min or more.

  Therefore, conventionally, various means have been proposed in order to suppress surface cracks (particularly longitudinal cracks) of the steel types that are likely to cause surface cracks that accompany the peritectic reaction.

  For example, Patent Document 1 proposes using mold powder having a composition that is easily crystallized, and increasing the thermal resistance of the mold powder layer to slowly cool the solidified shell. This is a technique of suppressing surface cracking by reducing the stress acting on the solidified shell by slow cooling. However, only the slow cooling effect by the mold powder has not sufficiently improved the non-uniform solidification, especially in medium carbon steel where transformation occurs due to a slight temperature drop accompanying solidification, preventing the occurrence of surface cracks. The fact is that you can't.

  In Patent Document 2, a vertical groove and a horizontal groove are provided on the inner wall surface of the mold, and mold powder is allowed to flow into the vertical groove and the horizontal groove, thereby slowing down the cooling of the mold and at the same time uniforming in the mold width direction. A technique for preventing vertical cracking of a slab has been proposed. However, when the inner wall surface of the mold is worn due to contact with the slab, and the groove provided on the inner wall surface of the mold becomes shallow, the amount of mold powder flowing in decreases and the slow cooling effect is reduced. There is a problem of not persisting. In addition, when molten steel is poured into an empty mold space at the start of casting, the injected molten steel penetrates into the groove provided on the inner wall surface of the mold and solidifies, and the mold copper plate and the solidified shell adhere to each other, thereby solidifying the shell. There is also a problem in that it becomes impossible to pull out the wire and a constraining breakout may occur.

Patent Document 3 proposes a mold in which a lattice-shaped groove is provided on the inner wall surface of the mold, and a mold in which the lattice-shaped groove is filled with a different metal (Ni, Cr) or ceramics (BN, AlN, ZrO ₂ ). Has been. This technology creates a difference in the amount of heat removal between the groove and the portion other than the groove, and suppresses vertical cracking of the slab by dispersing the stress due to transformation and thermal shrinkage accompanying solidification in the low heat removal region. Technology. However, the grooves are in a lattice shape, and in the lattice groove shape, the boundary between the groove portion of the inner wall surface of the mold and the mold copper plate (copper or copper alloy) is a straight line, and the boundary surface is cracked due to the difference in thermal expansion. In addition, there is a problem that propagation is easy and the mold life is reduced.

Patent Document 4 discloses a mold in which a vertical groove parallel to the casting direction is provided on the inner wall surface of the mold, and a mold in which the vertical groove is filled with a different metal (Ni, Cr) or ceramics (BN, AlN, ZrO ₂ ). There has been proposed a continuous casting method that uses a slab drawing speed and a mold vibration cycle within a predetermined range. According to Patent Document 4, by optimizing the mold vibration period in accordance with the slab drawing speed, the oscillation mark formed on the slab works as if a lateral groove was provided. It is said that the same effect of reducing surface cracks is observed. However, as in Patent Document 3, the boundary between the groove on the inner wall surface of the mold and the mold copper plate (copper or copper alloy) is a straight line, and the boundary surface is easily cracked and propagated due to the difference in thermal expansion. There is a problem that the mold life is reduced.

JP 2005-297001 A Japanese Patent Laid-Open No. 9-276994 JP-A-1-289542 Japanese Patent Laid-Open No. 2-6037

  The present invention has been made in view of the above circumstances, and the object of the present invention is to generate a constraining breakout at the start of casting and to reduce the mold life due to cracks on the surface of the mold copper plate, and at the initial stage of solidification. Surface cracks due to non-uniform cooling of solidified shells and surface cracks due to non-uniform solidified shell thickness due to transformation from δ iron to γ iron in medium carbon steel with peritectic reaction can be suppressed over a long period of time. It is to provide a continuous casting mold, and to provide a continuous casting method of steel using the continuous casting mold.

The gist of the present invention for solving the above problems is as follows.
[1] The recess of the inner wall surface of the copper alloy mold copper plate in the region including at least the meniscus of the inner wall surface of the water-cooled copper alloy mold is filled with a metal or non-metal having a thermal conductivity different from that of the mold copper plate. A continuous casting mold having a plurality of dissimilar substance filling portions, wherein a thermal resistance between a surface of the mold copper plate at a position where the dissimilar substance filling portion is installed and a slit of the mold copper plate which is a flow path of the mold cooling water is The range of the following formula (1), and the ratio of the thermal conductivity of the mold copper plate to the thermal conductivity of the metal or nonmetal filled in the inner wall surface of the copper alloy mold copper plate is the following formula (2) Or a casting mold for continuous casting, characterized by having a foreign substance filling portion within the range of the formula (3).
1.0 × 10 ⁻⁵ <R <6.0 × 10 ⁻⁴ (1)
0.2 <λ _Cu / λ _ma <1.0 (2)
_{1.0 <λ Cu / λ ma <} 20.0 ··· (3)
However, in the formula (1), R is the thermal resistance (m ² × K / W) between the surface of the mold copper plate and the slit of the mold copper plate, and in the formulas (2) and (3), λ _Cu Is the thermal conductivity (W / (m × K)) of the mold copper plate, and λ _ma is the thermal conductivity (W / (m × K)) of the metal or non-metal filled in the inner wall surface of the copper alloy mold copper plate. is there.
[2] The continuous casting mold has a periodically increasing / decreasing heat formed by the plurality of different material filling portions in the range of the inner wall surface of the copper alloy mold copper plate provided with the plurality of different material filling portions. The mold for continuous casting according to [1], which has a resistance distribution or a heat flux distribution.
[3] The continuous casting mold according to [1] or [2], wherein the concave portion of the inner wall surface is a circular concave groove or a pseudo-circular concave groove.
[4] The continuous casting mold according to any one of [1] to [3], wherein the plurality of different substance filling portions are independent of each other.
[5] On the inner wall surface of the mold copper plate, the thermal conductivity of the plating layer satisfies the following formula (4) with respect to the thermal conductivity of the mold copper plate, and the thickness of the plating layer is equal to the thickness of the mold copper plate. On the other hand, any one of [1] to [4] is characterized in that a plating layer satisfying the following formula (5) is formed, and the dissimilar substance filling portion is covered with the plating layer. Continuous casting mold described in 1.
0.5 <λ _Cu / λ _coating <15.0 (4)
4.0 <T _Cu / T _coating <250.0 (5)
However, in Formula (4), λ _Cu is the thermal conductivity (W / (m × K)) of the mold copper plate, λ _coating is the thermal conductivity of the plating layer (W / (m × K)), and In Equation (5), T _Cu is the thickness of the mold copper plate, specifically, the distance (m) between the surface of the mold copper plate and the bottom of the slit of the mold copper plate, and T _coating is the thickness of the plating layer (m). It is.
[6] Using the continuous casting mold according to any one of [1] to [5], the thermal conductivity of the mold copper plate, the thermal conductivity of the dissimilar material filling portion, and the total sectional area of the slits of the mold copper plate Accordingly, the continuous casting of the steel is characterized in that the molten steel is continuously cast by controlling the flow rate of the mold cooling water so that the flow rate of the mold cooling water satisfies the following formula (6) or (7): Casting method.
3 <(Q / S) × (λ _Cu / λ _ma ) <150 (provided that λ _Cu > λ _ma ) (6)
3 <(Q / S) × (λ _ma / λ _Cu ) <120 (provided that λ _Cu <λ _ma ) (7)
However, in the formulas (6) and (7), Q is the flow rate (m ³ / sec) of the mold cooling water, S is the total sectional area (m ² ) of the slits of the mold copper plate, and λ _Cu is the heat conduction of the mold copper plate. Rate (W / (m × K)),
λ _ma is the thermal conductivity (W / (m × K)) of the dissimilar substance filling portion.

  According to the present invention, a metal or a non-metal having a ratio with respect to the thermal conductivity of the mold copper plate within a predetermined range is used as a substance forming the foreign substance filling portion, and the mold copper plate surface at the installation position of the foreign substance filling portion A plurality of dissimilar substance filling portions having a predetermined value of thermal resistance between the slits of the mold copper plate, which is the flow path of the mold cooling water, include the meniscus position and the width direction of the continuous casting mold in the vicinity of the meniscus and casting. Since the thermal resistance of the continuous casting mold in the mold width direction and casting direction near the meniscus increases or decreases, the heat flux from the solidified shell near the meniscus, that is, in the initial stage of solidification, to the continuous casting mold. Increases or decreases. By increasing or decreasing this heat flux, the stress and thermal stress due to transformation from δ iron to γ iron are reduced, the deformation of the solidified shell caused by these stresses is reduced, and the deformation of the solidified shell is reduced, so that The non-uniform heat flux distribution resulting from the deformation is made uniform, and the generated stress is dispersed to reduce the amount of individual strain. As a result, the occurrence of cracks on the surface of the solidified shell is suppressed.

It is the schematic side view which looked at the long side copper plate which comprises a part of mold for continuous casting concerning this embodiment from the inner wall surface side. It is X-X 'sectional drawing of the casting_mold | template long side copper plate shown in FIG. The thermal resistance at three positions of the long-side copper plate of the mold having a different material filling portion formed by filling a material having a lower thermal conductivity than the mold copper plate is conceptually corresponding to the position of the different material filling portion. FIG. It is a figure which shows the result of having investigated the influence which the thermal resistance between the casting_mold | template copper plate surface and slit in the installation position of a dissimilar substance filling part has on a slab surface crack. Is a graph showing a result of the ratio of the thermal conductivity lambda _ma metal or nonmetal which is filled with thermal conductivity lambda _Cu of mold copper plate (λ _{Cu /} λ _ma) was investigated the effect on the cast slab surface cracks. It is the schematic which shows the example which provided the plating layer for protection of a mold surface on the inner wall surface of a mold long side copper plate. Is a graph showing a result of the ratio of the thermal conductivity lambda _coating of thermal conductivity lambda _Cu and plating layer of mold copper plate (λ _Cu / λ _coating) was investigated the effect on the cast slab surface cracks. It is a graph showing a result of the ratio of the mold copper plate thickness _{T Cu} and plating layer thickness _{T coating (T Cu / T coating} ) was investigated the effect on the cast slab surface cracks. Under the condition that the thermal conductivity λ _Cu of the mold copper plate is larger than the thermal conductivity λ _ma of the filled metal or non-filled metal, the value of “(Q / S) × (λ _Cu / λ _ma )” is the slab surface crack It is a figure which shows the result of having investigated the influence which acts on. Under the condition that the thermal conductivity λ _Cu of the mold copper plate is smaller than the thermal conductivity λ _ma of the filled metal or the filled nonmetal, the value of “(Q / S) × (λ _ma / λ _Cu )” is the surface crack of the slab It is a figure which shows the result of having investigated the influence which acts on. It is a figure which compares and shows the surface crack number density of a slab cast piece by the example of this invention, a comparative example, and a prior art example.

  Hereinafter, the present invention will be specifically described through embodiments of the invention. FIG. 1 is a mold long side copper plate constituting a part of a continuous casting mold according to the present embodiment, and a mold long side copper plate in which a different substance filling portion is formed on the inner wall surface side is viewed from the inner wall surface side. FIG. 2 is a schematic side view, and FIG. 2 is a cross-sectional view taken along the line XX ′ of the long-side copper plate shown in FIG.

  The continuous casting mold shown in FIG. 1 is an example of a continuous casting mold for casting a slab slab. A continuous casting mold for a slab slab is configured by combining a pair of copper alloy long mold copper plates and a pair of copper alloy short mold copper plates, and FIG. Is shown. Similarly to the long-side copper plate 1, the short-side copper plate is formed with the different material filling portion 3 on the inner wall surface side, and the description of the short-side copper plate is omitted here. However, in slab slabs, stress concentration is likely to occur in the solidified shell on the long side of the slab due to the shape of the slab width being extremely large relative to the slab thickness, and surface cracks occur on the long side of the slab It's easy to do. Therefore, the dissimilar substance filling part does not have to be installed on the short side copper plate of the continuous casting mold for the slab slab.

As shown in FIG. 1, from the upper position away from the meniscus by a length L ₁ (the length L ₁ is an arbitrary value equal to or greater than zero) from the position of the meniscus at the time of steady casting in the long copper plate 1 of the mold. The inner wall surface of the mold long side copper plate 1 up to a position below the length L ₂ was filled with a metal or a nonmetal having a diameter d and a thermal conductivity different from that of the mold long side copper plate 1. A plurality of different substance filling portions 3 are set with P being the interval between the different substance filling portions. Here, “meniscus” is “molten steel surface in mold” and its position is not clear during non-casting, but in the normal continuous casting operation of steel, the meniscus position is 50 mm to 200 mm from the upper end of the mold copper plate. The position is about below. Therefore, even if the meniscus position is 50 mm below the upper end of the long copper plate 1 and 200 mm below the upper end, the length L ₁ and the length L ₂ will be described below. What is necessary is just to arrange | position the dissimilar substance filling part 3 so that conditions may be satisfied.

That is, considering the influence of the solidified shell on the initial solidification, the disposition position of the different substance filling portion 3 is a length calculated from the following equation (8) according to the slab drawing speed V _c during steady casting. it is necessary to up position below the L ₀ or meniscus. That is shown in FIG. 1, the length L ₂ from the meniscus position is required to be a length L ₀ greater.

L ₀ = 2 × V _c × 1000/60 (8)
However, in the equation (8), L ₀ is the length (mm), and V _c is the slab drawing speed (m / min) during steady casting.

The length L ₀ is related to the time during which the slab after the start of solidification passes through the range where the foreign substance filling portion 3 is installed. The inventors have confirmed that it is necessary for the slab to stay in the range where the foreign substance filling portion 3 is installed for at least 2 seconds. In order for the slab to be present in the range where the foreign substance filling portion 3 is installed for at least 2 seconds after the start of solidification, the length L ₀ needs to satisfy the equation (8).

  By securing the time for the slab after the start of solidification to stay in the range where the foreign material filling unit 3 is installed for 2 seconds or more, the effect of periodic fluctuation of the heat flux by the foreign material filling unit 3 is sufficiently obtained. Thus, the effect of suppressing the surface cracking of the slab can be obtained at the time of high-speed casting in which surface cracks are likely to occur or during the casting of medium carbon steel. In order to stably obtain the effect of the periodic fluctuation of the heat flux by the foreign material filling section 3, it is more preferable to secure a time for the slab to pass through the range where the foreign material filling section 3 is installed for 4 seconds or more. .

Specific lengths of _{L 2} are slab drawing speed _{V c} thickness of 200mm or more slab continuous casting machine, since the order of 3.0 m / min is at an upper limit, the length _{L 2} is 100mm or more, What is necessary is just to install the dissimilar substance filling part 3 according to a meniscus position so that it may become 200 mm or more desirably. May not set the upper limit of the length L _2, the different materials filling unit 3 may be installed to the mold bottom.

On the other hand, the position of the upper end portion of the heterologous material filling unit 3 may be anywhere in the location if above a than meniscus and the same position or the meniscus position, therefore, the length L ₁ shown in FIG. 1, or zero Any value can be used. However, the meniscus needs to exist in the installation region of the foreign material filling portion 3 during casting, and the meniscus fluctuates in the vertical direction during casting, so that the upper end portion of the foreign material filling portion 3 is always higher than the meniscus. It is preferable that the upper end portion of the different material filling portion 3 is positioned about 10 mm above the assumed meniscus position so that the upper position is 20 mm from the assumed meniscus position. More preferably, the upper position is about 50 mm.

  As shown in FIG. 2, the dissimilar substance filling portion 3 has a thermal conductivity of the copper alloy constituting the long copper plate 1 in the circular groove 2 processed on the inner wall surface side of the long copper plate 1. It is formed by being filled with a metal or non-metal having a different thermal conductivity. In addition, it is more preferable to process the circular groove 2 so that the different-material filling portions 3 are independent from each other.

  The thermal conductivity of metal or nonmetal filled in the circular concave groove 2 is generally lower than the thermal conductivity of the copper alloy constituting the mold long-side copper plate 1, but for example, the mold long-side copper plate When a copper alloy having a low thermal conductivity is used as the copper alloy constituting 1, the thermal conductivity of the filled metal or nonmetal may be higher. When the material to be filled is metal, it is filled by plating or thermal spraying. When the material to be filled is non-metal, a non-metal processed according to the shape of the circular groove 2 is fitted into the circular groove 2. Fill and fill. Here, reference numeral 4 in FIG. 2 is a slit installed on the back side of the mold long-side copper plate 1 constituting the flow path of the mold cooling water, reference numeral 4a is the bottom of the slit, and reference numeral 5 is the long-side copper plate 1 of the mold. The long side copper plate 1 is cooled by the mold cooling water passing through the slit 4.

  In this embodiment, as a copper alloy used as a mold copper plate, a copper alloy to which chromium (Cr), zirconium (Zr), or the like, which is generally used as a mold copper plate for continuous casting, is added may be used. In recent years, an electromagnetic stirrer for stirring the molten steel in the mold is generally installed in order to make the solidification in the mold uniform or prevent the inclusions in the molten steel from being trapped in the solidified shell. In order to suppress the attenuation of the magnetic field strength from the coil to the molten steel, a copper alloy with reduced conductivity is used. In this case, the thermal conductivity is reduced according to the decrease in conductivity, and a copper alloy mold copper plate having a thermal conductivity of about 1/2 that of pure copper (thermal conductivity: about 400 W / (mxK)) is also used. Sometimes. In addition, the copper alloy used as a mold copper plate generally has a lower thermal conductivity than pure copper.

  FIG. 3 shows the thermal resistance at three positions of the long copper plate 1 having a different material filling portion 3 formed by filling a material having a lower thermal conductivity than that of the mold copper plate. Conceptually corresponding to In this case, the thermal resistance is relatively high at the installation position of the foreign substance filling unit 3.

  A plurality of different substance filling portions 3 are installed in the width direction and casting direction of the continuous casting mold near the meniscus including the meniscus position, and as shown in FIG. 3, continuous in the mold width direction and casting direction near the meniscus. It is preferable to form a thermal resistance distribution in which the thermal resistance of the casting mold periodically increases and decreases. As a result, a heat flux distribution is formed in which the heat flux in the vicinity of the meniscus, that is, in the initial stage of solidification, from the solidified shell to the continuous casting mold is periodically increased or decreased.

  In addition, when the different material filling portion 3 is formed by filling a material having higher thermal conductivity than the mold copper plate, unlike FIG. 3, the thermal resistance is relatively low at the installation position of the different material filling portion 3. However, in this case as well, the thermal resistance of the continuous casting mold in the mold width direction and the casting direction in the vicinity of the meniscus periodically increases and decreases.

  Due to the periodic increase and decrease of the heat flux, stress and thermal stress generated by transformation from δ iron to γ iron (hereinafter referred to as “δ / γ transformation”) are reduced, and deformation of the solidified shell caused by these stresses is reduced. Get smaller. By reducing the deformation of the solidified shell, the non-uniform heat flux distribution resulting from the deformation of the solidified shell is made uniform, and the generated stress is dispersed to reduce the amount of individual strain. As a result, the occurrence of surface cracks on the surface of the solidified shell is suppressed.

  However, in order to stably suppress the occurrence of surface cracks on the surface of the solidified shell, it is necessary to appropriately increase or decrease the heat flux due to the dissimilar substance filling portion 3 being installed. That is, if the difference in the increase and decrease in the heat flux is too small, the effect of installing the dissimilar substance filling unit 3 cannot be obtained. Conversely, if the difference in the increase and decrease in the heat flux is too large, the stress generated due to this is increased. The surface becomes cracked by this stress. The difference in increase / decrease in the heat flux due to the dissimilar material filling unit 3 depends on the thermal resistance at the installation position of the dissimilar material filling unit 3 and the thermal conductivity of the metal or non-metal filled in the dissimilar material filling unit 3.

Therefore, the inventors of the present invention have the effect that the thermal resistance between the mold copper plate surface and the slit 4 of the mold copper plate at the installation position of the foreign material filling portion 3 has an effect on the slab surface crack, and the foreign material filling portion 3 The effect of the thermal conductivity of the metal or nonmetal to be filled on the slab surface crack was investigated. The investigation method is to produce the continuous casting mold shown in FIG. 1 by variously changing the metal d or non-metal forming the foreign material filling portion 3 and the diameter d, interval P or filling thickness H of the foreign material filling portion 3. Then, continuous casting of medium carbon steel was performed using this continuous casting mold, and the occurrence of surface cracks in the slab slab after the casting was investigated. The surface cracks of the slab are examined by inspecting the surface of a slab having an area of 21 m ² or more by dye penetration inspection, measuring the number of detected vertical cracks having a length of 1.0 mm or more, and measuring this number of slabs. The product divided by the measurement area was defined as the slab surface crack number density, and this slab surface crack number density was evaluated.

  In FIG. 4, the result of investigating the influence which the thermal resistance R between the casting_mold | template copper plate surface and the slit 4 in the installation position of the dissimilar substance filling part 3 has on a slab surface crack is shown.

As shown in FIG. 4, when the thermal resistance R is in a range larger than 1.0 × 10 ⁻⁵ m ² × K / W and smaller than 6.0 × 10 ⁻⁴ m ² × K / W, It was found that the number density of cracks on the slab surface was stably 0.40 or less. That is, the thermal resistance R (m ² × K / W) between the surface of the mold copper plate at the installation position of the dissimilar substance filling unit 3 and the slit 4 of the mold copper plate which is the flow path of the mold cooling water is expressed by the following (1) It turns out that the range of the formula needs to be satisfied.

1.0 × 10 ⁻⁵ <R <6.0 × 10 ⁻⁴ (1)
This is because when the thermal resistance R is 1.0 × 10 ⁻⁵ m ² × K / W or less, the amount of heat removed in the mold is increased, and surface cracks are likely to occur in the slab. On the other hand, when the thermal resistance R is 6.0 × 10 ⁻⁴ m ² × K / W or more, the amount of heat removal in the mold is insufficient, and the effect of installing the dissimilar substance filling portion 3 is reduced, and the surface of the slab Not only is cracking likely to occur, but the surface temperature of the mold copper plate becomes too high, the thickness of the solidified shell is insufficient, and there is a concern about the occurrence of breakout due to this.

FIG. 5 shows the thermal conductivity λ _Cu (W / (W / () of the mold copper plate as an index of the thermal conductivity λ _ma (W / ( _mxK )) of the metal or nonmetal filled in the circular concave groove. m × K)) and the ratio (λ _Cu / λ _ma ) of the thermal conductivity λ _ma (W / (m × K)) of the metal or non-metal to be filled, and this ratio (λ _Cu / λ _ma ) The result of investigating the influence which has on the slab surface crack is shown.

As shown in FIG. 5, when the ratio (λ _Cu / λ _ma ) satisfies the following formula (2) or (3), the slab surface crack number density is stably reduced to 0.40 or less. I found out that

0.2 <λ _Cu / λ _ma <1.0 (2)
1.0 <λ _Cu / λ _ma <20.0 (3)
Formula (2) is a case where the thermal conductivity λ _ma of the metal or nonmetal filled in the circular concave groove is larger than the thermal conductivity λ _Cu of the mold copper plate, and the formula (3) is the thermal conductivity. This is a case where λ _Cu is larger than the thermal conductivity λ _ma .

When the ratio (λ _Cu / λ _ma ) is 0.2 or less, the heat flux at the place where the different-material filling part 3 is installed becomes large, the heat removal amount of the solidified shell becomes excessive, and surface cracks occur in the slab. There is a risk. On the other hand, when the ratio (λ _Cu / λ _ma ) is 20.0 or more, as a result of the slow cooling of the solidified shell being promoted too much, the effect of installing the dissimilar material filling portion 3 is reduced and the slab surface cracks In addition to being easily generated, there is a concern about breakout due to insufficient thickness of the solidified shell.

As described above, in the continuous casting mold according to the present embodiment, the thermal resistance between the surface of the mold copper plate at the position where the dissimilar substance filling portion 3 is installed and the slit 4 of the mold copper plate that is the flow path of the mold cooling water. The ratio of the thermal conductivity λ _Cu of the mold copper plate to the thermal conductivity λ _ma of the metal or non-metal filled in the circular concave groove (λ _Cu / Λ _ma ) needs to be in the range of the above formula (2) or (3).

  In the continuous casting mold according to the present embodiment, as long as the above formulas (1) to (3) are satisfied, the metal used for filling the circular groove (hereinafter also referred to as “filling metal”) and the circular groove are used. The type of nonmetal used for filling (hereinafter also referred to as “filling nonmetal”) need not be specified. However, for reference, examples of metals that can be used as filler metals include nickel (Ni, thermal conductivity: 90 W / (m × K)), chromium (Cr, thermal conductivity: 67 W / (m × K). ), Cobalt (Co, thermal conductivity; 70 W / (mxK)), alloys containing these metals, and the like are suitable. These metals and alloys have lower thermal conductivity than copper alloys, and can be easily filled into circular grooves by plating or thermal spraying. Further, pure copper having a higher thermal conductivity than that of a copper alloy can be used as a metal used for filling circular concave grooves. When pure copper is filled, the thermal resistance of the part where the foreign substance filling part 3 is installed is smaller than the part of the mold copper plate.

Moreover, ceramics such as BN, AlN, and ZrO ₂ are suitable as the filling nonmetal used for filling the circular concave grooves. Since these have low thermal conductivity, they are suitable as filled nonmetals.

  1 and 2 show an example in which the shape of the inner wall surface of the long-side copper plate 1 of the mold of the foreign substance filling portion 3 is circular, but the shape is not limited to a circle. For example, any shape may be used as long as it does not have a so-called “corner” such as an ellipse and has a shape close to a circle. Hereinafter, a shape close to a circle is referred to as a “pseudo circle”. In the case where the shape of the foreign substance filling portion 3 is a pseudo circle, the groove processed on the inner wall surface of the long copper plate 1 in order to form the foreign substance filling portion 3 is referred to as a “pseudo circular groove”.

  The pseudo circle is, for example, an ellipse or a shape having no corners such as a rectangle whose corners are circles or ellipses, and may be a petal pattern. The size of the pseudo circle is evaluated by an equivalent circle diameter obtained from the area of the pseudo circle. The pseudo circular equivalent circle diameter d is calculated by the following equation (9).

Equivalent circle diameter d = (4 × S _ma / π) ^1/2 (9)
However, in the formula (9), S _ma is the area (mm ² ) of the foreign substance filling portion 3.

  When a longitudinal groove or a lattice groove is provided as in Patent Document 3 and Patent Document 4 and a filling metal or a filling nonmetal is disposed in the groove, a boundary surface and a lattice between the filling metal or the filling nonmetal and the mold copper plate In the orthogonal part of the part, the stress due to the thermal strain difference between the filled metal or filled nonmetal and copper concentrates, causing a problem that cracks occur on the surface of the mold copper plate. On the other hand, in the continuous casting mold according to the present embodiment, the shape of the dissimilar substance filling portion 3 is circular or pseudo-circular. As a result, the boundary surface between the filled metal or filled nonmetal and copper has a curved surface, so that the stress is less likely to concentrate on the boundary surface and the advantage that cracks are less likely to occur on the surface of the mold copper plate.

  It is preferable that the diameter d and the equivalent circle diameter d of the foreign substance filling portion 3 are 2 to 20 mm. By setting the diameter d and equivalent circle diameter d of the foreign material filling portion 3 to 2 mm or more, the heat flux in the foreign material filling portion 3 is sufficiently lowered, and the effect of suppressing the surface cracking of the slab can be obtained. Moreover, by setting it as 2 mm or more, it becomes easy to fill a filling metal into the inside of the circular ditch | groove 2 or a pseudo-circular ditch | groove (not shown) by a plating process or a thermal spraying process. On the other hand, by setting the diameter and equivalent circle diameter of the foreign material filling portion 3 to 20 mm or less, a decrease in heat flux in the foreign material filling portion 3 is suppressed, that is, a solidification delay in the foreign material filling portion 3 is suppressed. The concentration of stress on the solidified shell at that position is prevented, and the occurrence of surface cracks in the solidified shell can be suppressed. That is, if the diameter and the equivalent circle diameter exceed 20 mm, surface cracks may increase. Therefore, the diameter and equivalent circle diameter of the dissimilar substance filling portion 3 are preferably 20 mm or less.

  The filling thickness H of the foreign substance filling portion 3 is preferably 0.5 mm or more. By setting the filling thickness H to 0.5 mm or more, the heat flux in the foreign substance filling portion 3 is sufficiently lowered, and the effect of suppressing the surface cracking of the slab can be obtained.

  Moreover, it is preferable that the filling thickness H of the foreign substance filling portion 3 is not more than the diameter d of the foreign substance filling portion 3 and the equivalent circle diameter d or less. Since the filling thickness H is equal to or smaller than the diameter d and equivalent circle diameter d of the different substance filling portion 3, filling of the filling metal into the circular concave groove and the pseudo circular concave groove by plating or spraying is easy. In addition, there are no gaps or cracks between the filling metal and the mold copper plate. When a gap or crack occurs between the filling metal and the mold copper plate, the filling metal cracks or peels off, causing a reduction in mold life, cracking of the cast piece, and further a restrictive breakout.

  The distance P between the different substance filling portions is preferably 0.25 times or more the diameter d and equivalent circle diameter d of the different substance filling portion 3. Here, the interval P between the different substance filling parts is the shortest distance between the end parts of the adjacent different substance filling parts 3 as shown in FIG. By setting the interval P between the different substance filling portions to be “0.25 × d” or more, the interval is sufficiently large, and the heat flux and the copper alloy portion (the different substance filling portion 3 is formed in the different substance filling portion 3). The difference from the heat flux of the non-part) becomes large, and the effect of suppressing the surface cracking of the slab can be obtained. The upper limit value of the interval P between the different substance filling portions may not be determined. However, since the area ratio of the different substance filling portion 3 is reduced when the interval P is increased, it is preferably set to “2.0 × d” or less. .

Area ratio ε (ε) which is a ratio of the total area B (mm ² ) of all the different material filling portions 3 to the area A (mm ² ) of the inner wall surface of the mold copper plate in the region where the different material filling portions 3 are arranged. = (B / A) × 100) is preferably 10% or more. By securing an area ratio ε of 10% or more, the area occupied by the different material filling portion 3 having a small heat flux is ensured, and a heat flux difference is obtained between the different material filling portion 3 and the copper alloy portion. A crack suppressing effect can be obtained stably.

  The arrangement of the different substance filling portions 3 is preferably a zigzag arrangement as shown in FIG. 1, but is not limited to the zigzag arrangement and may be any arrangement as long as the arrangement satisfies the interval P between the different substance filling portions.

  In the continuous casting mold according to the present embodiment, as shown in FIG. 6, the inner wall surface of the mold copper plate on which the dissimilar substance filling portion 3 is formed suppresses the wear of the solidified shell and the crack of the mold surface due to the thermal history. For this purpose, the plating layer 6 is preferably provided. The plating layer 6 is obtained by plating a commonly used nickel or nickel-containing alloy such as a nickel-cobalt alloy (Ni-Co alloy) or a nickel-chromium alloy (Ni-Cr alloy). It is done.

In FIG. 7, when the plating layer 6 is formed on the entire inner surface of the mold copper plate, the copper alloy constituting the mold copper plate and the metal constituting the plating layer 6 are variously changed, and the thermal conductivity λ _Cu and the plating of the mold copper plate are changed. It shows the results of the ratio of the thermal conductivity lambda _coating layer (λ _Cu / λ _coating) was investigated the effect on the cast slab surface cracks. As shown in FIG. 7, when the ratio (λ _Cu / λ _coating ) is in the range of the following formula (4), it was found that the slab surface cracks were reduced.

0.5 <λ _Cu / λ _coating <15.0 (4)
When the ratio (λ _Cu / λ _coating ) is 0.5 or less, the thermal resistance is small, and surface cracking occurs in the slab, which is not preferable. On the other hand, if the ratio (λ _Cu / λ _coating ) is 15.0 or more, the thermal resistance of the plating layer is high, the temperature of the plating layer becomes too high during continuous casting, and there is a concern about peeling of the plating layer. Moreover, the thermal resistance of the plating layer is increased, the effect of disposing the different substance filling portion 3 is reduced, and cracks are generated on the surface of the slab.

FIG. 8 shows the results of investigating the influence of the ratio (T _Cu / T _coating ) between the mold copper plate thickness T _Cu and the plating layer thickness T _coating on the slab surface crack. Here, the mold copper plate thickness T _Cu is a distance from the surface of the mold copper plate to the bottom 4a of the slit 4 as shown in FIG. As shown in FIG. 8, it was found that when the ratio (T _Cu / T _coating ) is in the range of the following formula (5), the slab surface crack is reduced.

4.0 <T _Cu / T _coating <250.0 (5)
When the ratio (T _Cu / T _coating ) is 4.0 or less, the plating layer is relatively thick, the thermal resistance of the plating layer is increased, and the effect of installing the dissimilar substance filling portion 3 is reduced. Cracks are generated. Further, since the plating layer becomes relatively thick, the amount of heat removed from the solidified shell is insufficient, and there is a concern about breakout due to insufficient thickness of the solidified shell. On the other hand, when the ratio (T _Cu / T _coating ) is 250 or more, the thickness of the plating layer is thin, and peeling of the plating layer is a concern. Further, when the thickness of the plating layer is small, the thermal resistance of the entire mold becomes small, and thus surface cracks are likely to occur in the slab. As long as the plating layer thickness T _coating satisfies the relationship of the above formula (5), the plating layer 6 may have the same thickness from the upper end to the lower end of the mold or may have a different thickness from the upper end to the lower end.

  In continuous casting of a slab using the continuous casting mold configured as described above, a slab slab of medium carbon steel having particularly high surface cracking sensitivity and a carbon content of 0.08 to 0.17% by mass. (Thickness: 200 mm or more) is preferably used for continuous casting. Conventionally, when continuously casting a slab slab of medium carbon steel, it is common to reduce the slab drawing speed in order to suppress surface cracking of the slab, but the continuous casting according to this embodiment Since casting surface cracks can be prevented by applying molds for casting, continuous casting of slabs with no surface cracking or very little surface cracking is possible even at a slab drawing speed of 1.5 m / min or more. Is realized.

  However, at that time, the mold cooling depends on the thermal conductivity of the mold copper plate, the thermal conductivity of the metal or non-metal filled in the circular concave groove or the pseudo circular concave groove, and the total sectional area of the slit of the mold copper plate. It is necessary to continuously cast the molten steel by controlling the flow rate of the mold cooling water so that the water flow rate satisfies the following formula (6) or (7).

3 <(Q / S) × (λ _Cu / λ _ma ) <150 (provided that λ _Cu > λ _ma ) (6)
3 <(Q / S) × (λ _ma / λ _Cu ) <120 (provided that λ _Cu <λ _ma ) (7)
In the formulas (6) and (7), Q is the flow rate of the mold cooling water (m ³ / sec), S is the total cross-sectional area (m ² ) of the slit of the mold copper plate, and λ _Cu is the thermal conductivity of the mold copper plate ( W / (m × K)), λ _ma is the thermal conductivity (W / (m × K)) of the metal or non-metal filled in the circular or pseudo-circular groove.

FIG. 9 shows the flow rate Q of the mold cooling water, the total cross-sectional area S of the slits of the mold copper plate, the mold, under the condition that the thermal conductivity λ _Cu of the mold copper plate is larger than the thermal conductivity λ _ma of the filled metal or non-filled metal. Effect of the value of “(Q / S) × (λ _Cu / λ _ma )” on the slab surface cracks by variously changing the thermal conductivity λ _{Cu of} the copper plate and the thermal conductivity λ _ma of the filled metal or non-filled metal The results of the investigation are shown. As shown in FIG. 9, under the condition where the thermal conductivity λ _Cu is larger than the thermal conductivity λ _ma , “(Q / S) × (λ _Cu / λ _ma )” is in the range of the above equation (6). In addition, it was confirmed that surface cracking of the slab was suppressed.

FIG. 10 shows that the value of “(Q / S) × (λ _ma / λ _Cu )” is obtained under the condition that the thermal conductivity λ _Cu of the mold copper plate is smaller than the thermal conductivity λ _ma of the filled metal or the filled nonmetal. It is a figure which shows the result of having investigated the influence which acts on a slab surface crack. As shown in FIG. 10, under the condition that the thermal conductivity λ _Cu is smaller than the thermal conductivity λ _ma , “(Q / S) × (λ _ma / λ _Cu )” is in the range of the above formula (7). In addition, it was confirmed that surface cracking of the slab was suppressed.

When “(Q / S) × (λ _Cu / λ _ma )” or “(Q / S) × (λ _ma / λ _Cu )” is 3 or less, the cooling in the mold becomes too weak, and the foreign substance The effect of installing the filling portion 3 is reduced, and cracks are generated on the surface of the slab. Moreover, there is a concern about breakout due to insufficient heat removal from the solidified shell and insufficient solidified shell thickness. On the other hand, when “(Q / S) × (λ _Cu / λ _ma )” is 150 or more, and when “(Q / S) × (λ _ma / λ _Cu )” is 120 or more, The cooling of the material becomes too strong, and the effect of the foreign substance filling portion 3 is diluted, and surface cracks are generated in the slab.

  As described above, the continuous casting mold according to the present embodiment uses a metal or a nonmetal having a ratio with respect to the thermal conductivity of the mold copper plate within a predetermined range as a material for forming the dissimilar material filling portion 3. A plurality of dissimilar substance filling portions 3 having a predetermined value of the thermal resistance R between the surface of the mold copper plate at the position where the material filling portion 3 is installed and the slit of the mold copper plate which is the flow path of the mold cooling water are arranged at the meniscus position Including in the width direction and casting direction of the continuous casting mold near the meniscus, the thermal resistance of the continuous casting mold in the mold width direction and casting direction near the meniscus periodically increases and decreases, thereby the vicinity of the meniscus, That is, the heat flux from the solidified shell to the continuous casting mold in the initial stage of solidification periodically increases and decreases. Due to the periodic increase / decrease of the heat flux, the stress and thermal stress due to the δ / γ transformation are reduced, the deformation of the solidified shell caused by these stresses is reduced, and the deformation of the solidified shell is reduced. The non-uniform heat flux distribution resulting from this is made uniform, and the generated stress is dispersed to reduce the amount of individual strain. As a result, the occurrence of cracks on the surface of the solidified shell is suppressed.

  In FIG. 1, an example is shown in which the same-shaped different substance filling portion 3 is installed in the casting direction or the mold width direction, but the different substance filling portion 3 may not have the same shape. However, it is preferable that the diameter d or the equivalent circle diameter d of any of the different substance filling portions 3 is 2 to 20 mm. Further, FIG. 2 shows an example in which the different substance filling portions 3 having the same filling thickness H are installed in the casting direction, but the filling thickness H may not be the same in the casting direction or the mold width direction. The filling thickness H may be different in the substance filling portion 3. However, the filling thickness H of any dissimilar substance filling portion 3 is also preferably 0.5 mm or more. Furthermore, although FIG. 1 shows an example in which the different substance filling portions 3 are installed at the same intervals in the casting direction or the mold width direction, the intervals at which the different substance filling portions 3 are installed may not be the same. However, also in this case, it is preferable that the distance P between the different material filling portions is 0.25 times or more the diameter d of the different material filling portion 3 and the equivalent circle diameter d.

  Moreover, although the said description was performed regarding the continuous casting of slab slab, the casting mold for continuous casting according to the present embodiment is not limited to continuous casting of slab slab, but continuous casting of bloom slab or billet slab. Can be applied along the above.

  Medium carbon steel (Chemical component, C: 0.08 to 0.17 mass%, Si: 0.10 to 0.30 mass%, Mn: 0.50 to 1.20 mass%, P: 0.010 to 0 0.030% by mass, S: 0.005 to 0.015% by mass, Al: 0.020 to 0.040% by mass), and a water-cooled copper alloy in which different-material-filled portions are installed on the inner wall surface under various conditions A continuous casting was performed using a mold or a water-cooled pure copper mold, and a test was conducted to investigate surface cracks in the slab slab after casting. The water-cooled copper alloy mold or the water-cooled pure copper mold used is a mold having an inner space size with a long side length of 1.8 m and a short side length of 0.22 m.

  The length from the upper end to the lower end of the water-cooled copper alloy mold or water-cooled pure copper mold used is 950 mm, and the position of the meniscus (molten steel surface in the mold) during steady casting is positioned 100 mm below the upper end of the mold. The dissimilar substance filling portion was arranged in a region from a position 60 mm below the upper end of the mold to a position 400 mm below the upper end of the mold.

  As the mold copper plate, pure copper or a copper alloy having a thermal conductivity of 70 to 380 W / (m × K) is used, and as the filling metal or the filling nonmetal of the dissimilar substance filling portion, pure nickel (thermal conductivity: 90 W / (MxK)), cobalt (thermal conductivity: 65 W / (mxK)), rhodium (thermal conductivity: 180 W / (mxK)), vanadium (thermal conductivity: 30 W / (mxK)) ), Palladium (thermal conductivity: 60 W / (mxK)), tantalum (thermal conductivity: 55 W / (mxK)), Ni-Co (thermal conductivity: 65 W / (mxK)), zirconium (Thermal conductivity: 15 W / (mxK)), antimony (thermal conductivity: 22 W / (mxK)), titanium (thermal conductivity: 20 W / (mxK)), and copper alloy (thermal Conductivity; 180, 360, 380 W / (m × K)) was used.

  After installing the dissimilar material filling part, Ni—Co alloy (thermal conductivity: 65, 67 W / (m × K)), tungsten (thermal conductivity: 90 W / (m × K)) is formed on the entire inner wall surface of the mold copper plate. , Titanium (thermal conductivity: 20 W / (m × K)), Ni—Zn alloy (thermal conductivity: 30 W / (m × K)), tungsten (thermal conductivity: 260 W / (m × K)), Ni -Cr alloy (thermal conductivity: 10 W / (mxK)), gold (thermal conductivity: 300 W / (mxK)), Ag-Cu (thermal conductivity: 360 W / (mxK)), zirconium (Thermal conductivity: 16 W / (m × K)) and niobium (thermal conductivity: 50 W / (m × K)) were plated, and a plated layer was constructed.

After completion of continuous casting, the surface area of 21 m ² or more on the surface of the slab is inspected by dye penetration inspection, the number of surface cracks with a length of 1.0 mm or more is measured, and the sum is divided by the slab measurement area. The state of occurrence of surface cracks was evaluated using the obtained slab surface crack number density.

Table 1 shows the thermal conductivity of the mold copper plate, the thermal conductivity of the filled metal or the filled nonmetal, the thermal conductivity and the thickness of the plated layer in the continuous casting molds of Invention Examples 1 to 11, Comparative Examples 1 to 6, and the conventional example. The flow rate of mold cooling water, the total cross-sectional area of the slit, etc. are shown. The comparative example is a water-cooled copper alloy mold having a foreign material filling portion, but for continuous casting having a foreign material filling portion under conditions that do not satisfy the ranges of the thermal resistance R and the ratio (λ _Cu / λ _ma ). The test cast with a mold, the conventional example, is a test cast using a water-cooled copper alloy mold that does not have a foreign substance filling portion.

  Moreover, in FIG. 11, the slab surface crack number density of the slab slab in this invention examples 1-11, comparative examples 1-6, and a prior art example is compared and shown.

As is clear from FIG. 11, in Examples 1 to 11 of the present invention, the number density of slab surface cracks is 0.4 pieces / m ² or less, and it can be confirmed that surface cracks of the slab are suppressed. It was. In particular, the present invention is such that the ratio (λ _Cu / λ _coating ) and the ratio (T _Cu / T _coating ) are in a suitable range, and the flow rate of the mold cooling water satisfies the above expression (6) or (7). In Examples 1 to 4, it was confirmed that surface cracking of the slab was suppressed.

  On the other hand, in Comparative Examples 1 to 6, although the surface cracks of the slab were reduced as compared with the conventional examples, the slab surface cracks occurred frequently as compared with Examples 1 to 11 of the present invention.

DESCRIPTION OF SYMBOLS 1 Mold long side copper plate 2 Circular groove 3 Dissimilar substance filling part 4 Slit 5 Back plate 6 Sheet metal layer

Claims (6)

Plural in which recesses on the inner wall surface of the copper alloy mold copper plate in the area including at least the meniscus of the inner wall surface of the water-cooled copper alloy mold are filled with a metal or non-metal having a thermal conductivity different from the thermal conductivity of the mold copper plate A mold for continuous casting having a different substance filling portion of
The thermal resistance between the surface of the mold copper plate at the position where the dissimilar substance filling portion is installed and the slit of the mold copper plate which is the flow path of the mold cooling water is in the range of the following formula (1), and the heat conduction of the mold copper plate The ratio of the thermal conductivity of metal or non-metal filled in the inner wall surface of the copper alloy mold copper plate has a dissimilar substance filling portion in the range of the following formula (2) or (3) A casting mold for continuous casting.
1.0 × 10 ⁻⁵ <R <6.0 × 10 ⁻⁴ (1)
0.2 <λ _Cu / λ _ma <1.0 (2)
1.0 <λ _Cu / λ _ma <20.0 (3)
However, in the formula (1), R is the thermal resistance (m ² × K / W) between the surface of the mold copper plate and the slit of the mold copper plate, and in the formulas (2) and (3), λ _Cu Is the thermal conductivity (W / (m × K)) of the mold copper plate, and λ _ma is the thermal conductivity (W / (m × K)) of the metal or non-metal filled in the inner wall surface of the copper alloy mold copper plate. is there.   In the range of the inner wall surface of the copper alloy mold copper plate provided with the plurality of different material filling portions, the continuous casting mold has a thermal resistance distribution that increases or decreases periodically formed by the plurality of different material filling portions or The continuous casting mold according to claim 1, wherein the casting mold has a heat flux distribution.   The continuous casting mold according to claim 1, wherein the concave portion of the inner wall surface is a circular concave groove or a pseudo-circular concave groove.   The continuous casting mold according to any one of claims 1 to 3, wherein the plurality of different substance filling portions are independent of each other. On the inner wall surface of the mold copper plate, the thermal conductivity of the plating layer satisfies the following formula (4) with respect to the thermal conductivity of the mold copper plate, and the thickness of the plating layer is as follows with respect to the thickness of the mold copper plate: 5. The plating layer satisfying the formula (5) is formed, and the different substance filling portion is covered with the plating layer. 5. Mold for continuous casting.
0.5 <λ _Cu / λ _coating <15.0 (4)
4.0 <T _Cu / T _coating <250.0 (5)
However, in Formula (4), λ _Cu is the thermal conductivity (W / (m × K)) of the mold copper plate, λ _coating is the thermal conductivity of the plating layer (W / (m × K)), and In Equation (5), T _Cu is the thickness of the mold copper plate, specifically, the distance (m) between the surface of the mold copper plate and the bottom of the slit of the mold copper plate, and T _coating is the thickness of the plating layer (m). It is. Using the continuous casting mold according to any one of claims 1 to 5, depending on the thermal conductivity of the mold copper plate, the thermal conductivity of the dissimilar material filling portion, and the total cross-sectional area of the slit of the mold copper plate. A continuous casting method for steel, wherein the molten steel is continuously cast by controlling the flow rate of the mold cooling water so that the flow rate of the mold cooling water satisfies the following formula (6) or (7).
3 <(Q / S) × (λ _Cu / λ _ma ) <150 (provided that λ _Cu > λ _ma ) (6)
3 <(Q / S) × (λ _ma / λ _Cu ) <120 (provided that λ _Cu <λ _ma ) (7)
However, in the formulas (6) and (7), Q is the flow rate (m ³ / sec) of the mold cooling water, S is the total sectional area (m ² ) of the slits of the mold copper plate, and λ _Cu is the heat conduction of the mold copper plate. Rate (W / (m × K)),
λ _ma is the thermal conductivity (W / (m × K)) of the dissimilar substance filling portion.