JP4216636B2 - Continuous casting method and continuous casting apparatus - Google Patents

Description

【００４７】
【発明の効果】
本発明により、鋳片の表層部の溶質元素濃度が内部に比べて高い鋳片を鋳造する際に、添加する合金元素の添加量等を制限することなく、また複数の元素の濃度を同時に高くしながら、鋳片内部に比べて表層濃度が高い鋳片を鋳造することができる。
【００４８】
また、鋳片の表層厚みについても、変更できる自由度が大きいため、様々な目的に対して本発明を適用することができる。
【００４９】
加えて、本発明は鋳片断面形状に何ら制約はなく、スラブ、ブルーム、ビレット鋳造に適用することができる。
【図面の簡単な説明】
【図１】本発明の構成を模式的に示した図である。
【図２】本発明の方法を用いて鋳造した結果の一例で、(a)は鋳片内でのＣ濃度の分布を調査した結果を示した図、(b)は鋳片厚み方向でのＣ濃度の分布を示した図である。
【図３】本発明の方法を用いて鋳造した結果の一例で、凝固組織から表層厚みを求め、その鋳片幅方向の分布を示した図である。
【符号の説明】
１…誘導加熱コイル
２…耐火物製容器
３…セラミック
４…直流磁場コイル
５…水冷鋳型
６…合金添加
７…上部プール
８…下部プール
９…上部プールで形成した凝固シェル（表層）
１０…直流磁場印加領域で形成した凝固シェル（遷移領域）
１１…下部プールで形成した凝固シェル（内層）
１２…浸漬ノズル[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of casting a slab having a higher concentration of the slab surface layer than the inside, a device therefor, and a slab cast in this way.
[0002]
[Prior art]
As a method for manufacturing a slab having a different concentration from the surface layer of the slab, for example, in Patent Document 1, a DC magnetic field having a substantially uniform magnetic flux density in the mold width direction is applied in the pool thickness direction to move the strand pool up and down. The surface layer and inner layer components are supplied by supplying molten steel with different component compositions from two immersion nozzles with different lengths installed at different positions above and below the strand pool across the DC magnetic field application region. Different slab manufacturing methods are disclosed.
[0003]
In addition, as a method of manufacturing a slab having a different concentration from the surface layer, the DC magnetic field having a substantially uniform magnetic flux density distribution in the mold width direction is applied in the thickness direction, and the DC magnetic field is applied. A method of casting while adding an alloy element with a wire to the upper pool is described in Patent Document 2, and a method of casting while supplying an alloy element in a powder used as a lubricant and supplying it in a mold. Patent Document 3 discloses the above.
[0004]
[Patent Document 1]
Japanese Patent Publication No. 61-252898 [Patent Document 2]
JP-A-3-243245 [Patent Document 3]
Japanese Patent Laid-Open No. 8-290236
[Problems to be solved by the invention]
However, in the method of Patent Document 1, although it is possible to produce slabs having completely different compositions of the surface layer and the inner layer, it is necessary to prepare two molten steel, ladle, tundish, and immersion nozzle. In addition to the cost, it is necessary to accurately control the amount of pouring of each of the surface layer molten steel and the inner layer molten steel.
[0006]
Moreover, in any of the wire addition method which makes the density | concentration of the surface layer part of slab high like patent document 2, and the addition method of the solute element from a powder layer like patent document 3 Since the solute element is added through the powder layer, the influence of powder entrainment is inevitable, and the amount of solute element to be added is limited because melting is performed using the degree of superheat of the molten steel in the molten steel pool in the mold. In addition, since powder lubrication is used, there are problems such as limitations on the types of solute elements to be added.
[0007]
The present invention provides a method and apparatus for casting a slab having a higher surface layer concentration than the inside of a slab, and its slab, without limiting the type and amount of solute element to be added. Objective.
[0008]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and the gist thereof is as follows.
(1) A DC magnetic field having a substantially uniform magnetic flux density distribution in the mold width direction below the solidification start point is applied in the thickness direction, and in the molten steel pool above the region to which the DC magnetic field is applied In a continuous casting method in which molten steel is supplied below the DC magnetic field application region while adding the solute element, the molten steel in the upper pool is heated from the region where the DC magnetic field is applied to dissolve the added solute element. The continuous casting method is characterized in that a solidification start point is set below the molten metal surface and a slab having a surface layer different from the inner layer is cast.
(2) The continuous casting method according to (1), wherein the surface layer thickness of the slab and the concentration of the solute element added to the surface part of the slab are adjusted using the following relational expression.
[0009]
d = K × (L / Vc) ⁿ
q = {W × T− (W−2 × d) × (T−2 × d)} × ρ × Vc
Q = α × q × ΔC / 100
W: Mold width T: Mold thickness K, n: Solidification shell growth rate coefficient ρ: Molten steel density Vc: Casting speed Q: Addition rate of solute element ΔC: Concentration of solute element added to slab surface layer q: Upper part Surface mass formed per unit time in the pool d: Surface thickness of the slab L: Distance from the solidification start point to the DC magnetic field application region α: Coefficient due to the difference in yield depending on the additive element (3) Solidification start point The continuous casting method according to (1) or (2), wherein the surface layer thickness of the slab is adjusted by either one or both of the distance from the DC magnetic field application region and the casting speed.
(4) The solute element addition rate is adjusted according to the concentration of the solute element in the molten steel pool above the region to which the DC magnetic field is applied. The continuous casting method described.
(5) The continuous casting method according to any one of (1) to (4), wherein an induction heating coil is used as means for heating the molten steel pool above the region to which a DC magnetic field is applied.
(6) The continuous casting method according to any one of (1) to (5), wherein an apparatus having a different cross-sectional shape on the molten metal surface and a cross-sectional shape of the slab is used.
(7) A DC magnetic field coil having a function of applying a DC magnetic field having a substantially uniform magnetic flux density distribution in the mold width direction in the water-cooled mold in the thickness direction, and a tip of an immersion nozzle for injecting molten steel into the mold In a continuous casting apparatus in which an immersion nozzle below the DC magnetic field coil and a device capable of adding a solute element above the DC magnetic field coil are installed, heating above the DC magnetic field coil is added. A continuous casting apparatus having a function of dissolving the solute element and lowering the solidification start point below the molten metal surface.
(8) The continuous casting apparatus according to (7), wherein an induction heating coil is installed on an outer periphery of the refractory container as a function of heating the portion above the DC magnetic field coil.
(9) The continuous casting apparatus according to (7) or (8), wherein the application position of the DC magnetic field coil can be adjusted in the water-cooled mold.
(10) The continuous casting apparatus according to (8) or (9), wherein the cross-sectional shape of the refractory container and the cross-sectional shape of the water-cooled mold are different.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
The configuration of the present invention will be described in detail below with reference to FIG.
[0011]
First, a DC magnetic field having a substantially uniform magnetic flux density distribution in the width direction is applied in the thickness direction by the DC magnetic field coil 4. In addition, the position of the tip of the immersion nozzle 12 for injecting the molten steel into the mold 5 is set below the region where the DC magnetic field is applied, and the molten steel having the component composition in the tundish which is the previous process is supplied to this region. To do. Further, a solute element is added to the upper pool 7 divided by the DC magnetic field, and the concentration of the upper pool 7 is made higher than the concentration of the lower pool 8. Here, the solute element means various alloy elements.
[0012]
With such a configuration, the composition inside the slab can be made substantially equal to the composition in the tundish, and a solute element can be added to the upper pool 7.
[0013]
Up to this point, the conventional method has been proposed so far, but the added solute element is added to dissolve the added solute element by utilizing a part of the sensible heat of the cooled molten steel pool in the mold. If the amount is excessive, solidification may proceed while the various solute elements added are not sufficiently dissolved in the upper molten steel pool. Therefore, there is a limit to the amount of solute element to be added. In addition, when casting using powder, which is a lubricant between the mold and the solidified shell, the powder changes in quality when the added solute element reacts with the powder. Limitations are naturally added to the types of solute elements to be added, such as the addition of elements that are likely to react to form oxides.
[0014]
Therefore, in the present invention, by heating the upper pool 7, the added solute element can be sufficiently dissolved, and the outer layer has a slab whose component is different from the inside without limiting the amount and type of the added solute element. I found out that I could do it.
[0015]
By heating the molten steel in the upper pool 7 to a temperature higher than the liquidus temperature, the solidification start point can be positioned below the molten metal surface, so that solidification does not occur in the heated region of the upper molten steel pool. Therefore, in the heated region in the upper molten steel pool, it is possible to reliably prevent molten steel in a process in which the added solute element is melted, that is, a state where the solute element is partially undissolved.
[0016]
Here, the upper molten steel pool means a pool above the area where the DC magnetic field is applied, but the heating area is from the molten metal surface until reaching the area where the DC magnetic field is applied. This region may be set as appropriate as long as the added solute element can be sufficiently dissolved.
[0017]
Moreover, the addition of the alloy element to the upper pool 7 divided by the direct-current magnetic field can be added by a wire 6 or the like, and the alloy to be added may be any of granular or powdery metal and alloy powder or lump. .
[0018]
Next, specific parameters for adjusting the surface layer thickness of the slab whose surface layer is different from the inner layer and the concentration of the solute element in the slab surface layer portion will be described.
[0019]
In the present method, the desired surface thickness d of the slab formed by the upper pool divided by the DC magnetic field is defined as follows by the distance L from the solidification start point to the DC magnetic field application region and the casting speed Vc. The Here, K and n are growth rate coefficients of the solidified shell.
[0020]
d = K × (L / Vc) ⁿ
Further, the casting progresses while the molten steel in the upper pool is replaced by the surface layer mass q formed per unit time in the upper pool so that the surface layer thickness d of the slab is reached. That is, the relationship between the surface layer thickness d of the slab and the surface layer mass q formed per unit time in the upper pool is as follows. Here, W is the mold width, T is the mold thickness, and ρ is the molten steel density.
[0021]
q = {W × T− (W−2 × d) × (T−2 × d)} ρ × Vc
Next, regarding the concentration ΔC of the solute element added to the slab surface layer portion, the relationship with the addition rate Q of the solute element is as follows using the surface layer mass q formed per unit time in the above upper pool. become that way. Here, α is a coefficient due to the difference in yield depending on the solute element to be added.
[0022]
Q = α × q × ΔC / 100
Therefore, it is possible to adjust the slab surface layer to the desired thickness and the desired concentration of the solute element by adding the solute element to the upper pool divided by the DC magnetic field so as to satisfy the above relational expression. It becomes.
[0023]
In the DC magnetic field application region, the solute concentration continuously changes from the concentration in the upper pool 7 to the concentration in the lower pool 8. Therefore, in the DC magnetic field application region, a very thin solidified shell layer (solute concentration transition region layer). ) 10 is formed between the slab surface layer portion and the inner layer portion.
[0024]
As described above, the surface layer thickness d in the slab is defined by the distance L from the solidification start point to the DC magnetic field application position and the casting speed Vc. Therefore, by adjusting one or both of these, the surface layer in the slab The thickness d can be controlled.
[0025]
In particular, the adjustment of the distance L from the solidification start point to the DC magnetic field application position can be performed by allowing the DC magnetic field coil 4 to move up and down in the water-cooled mold 5.
[0026]
In addition, by grasping the concentration of the solute element in the molten steel pool above the region where the DC magnetic field is applied and adjusting the amount of solute element added according to the concentration, the surface layer portion of the slab during casting is adjusted. It is desirable because it can prevent solute element concentration fluctuations.
[0027]
As a method for grasping the concentration of the solute element in the upper molten steel pool, the molten steel is usually sampled during casting, and the concentration is measured by spark emission spectroscopic analysis: JIS G 1253 (1994) or fluorescent X-ray analysis: JIS G 1256 (1997) or the like. Thus, the fluctuation | variation of the component density | concentration of a slab surface layer part can be prevented by adjusting the addition speed | rate of a solute element as needed from the result which grasped | ascertained this molten steel component. The sampling frequency of molten steel is not particularly specified, and may be set as appropriate.
[0028]
Next, it is preferable to use the induction heating coil 1 as a means for melting the alloy element added to the upper molten steel pool. It is used for melting an alloy containing a solute element added with the amount of heat when the molten steel is heated using the induction heating coil 1 so that the solidification start point is below the molten metal surface, and the molten steel pool It is possible to mix the added solute elements by using the stirring flow induced by the electromagnetic force formed inside, and to dissolve the solute elements in the molten steel and to make the concentration in the pool more uniform. Because it can be done.
[0029]
Normally, when the induction heating coil 1 is used, the induction heating coil 1 is used to heat the outside from the refractory container 2 provided above the water-cooled mold 5.
[0030]
On the other hand, since the amount of heat removed from the area of the water-cooled mold 5 below the refractory container 2 rapidly increases, solidification starts from the molten steel that has reached the area of the water-cooled mold 5. Further, since the static pressure of the molten steel acts on the solidification start point, the solidified shell 9 grows uniformly.
[0031]
Since the refractory container 2 and the water-cooled mold 5 are in contact with each other, the solidification tends to proceed in the lower part of the refractory container 2 and the solidification start point may become unstable. Induction heating of the entire refractory container prevents solidification at the bottom of the refractory container.
[0032]
Furthermore, in order to more reliably prevent solidification at the lower part of the refractory container, it is preferable to insert the ceramic 3 between the refractory container 2 and the water-cooled mold 5 to keep the solidification start point constant.
[0033]
Further, in order to ensure lubrication of the water-cooled mold 5 and the solidified shells 9 and 11, by injecting oil from a part of the water-cooled mold 5, it is possible to avoid the restriction of the solidified shell by oil lubrication.
[0034]
Furthermore, in this method, you may use the apparatus from which the cross-sectional shape in a molten metal surface differs from slab cross-sectional shape. This is because solidification does not proceed in the area where the upper molten steel pool is heated. For example, the thickness of the slab can be increased by increasing the cross-sectional area of the molten metal surface by increasing the area where the upper molten steel pool is heated. Even when it is thin (ie, when the mold short side width is narrow), the addition of solute elements can be facilitated, and the volume of the upper pool can be secured sufficiently to facilitate the dissolution and mixing of the added solute elements. You can enjoy it.
[0035]
Next, the apparatus of the present invention will be described.
[0036]
The DC magnetic field coil 4 having a function of applying a DC magnetic field having a substantially uniform magnetic flux density distribution in the mold width direction in the water-cooled mold in the thickness direction, and the tip of an immersion nozzle for injecting molten steel into the mold are the DC In the continuous casting apparatus in which the immersion nozzle 12 below the magnetic field coil and the apparatus capable of adding a solute element above the DC magnetic field coil 4 are installed, the function of heating the upper part than the DC magnetic field coil 4 is provided. It is a device that has.
[0037]
As the function of heating above the DC magnetic field coil 4, in particular, if the induction heating coil 1 is installed on the outer periphery via the refractory container 2, it is preferable for the reason described above.
[0038]
Here, as the material of the refractory container, MgO—C, MgO—Cr ₂ O ₃ , Al ₂ O ₃ —C, ZrO ₂ —C refractories, etc., melting furnace bricks, crucibles, immersion It is preferable to use a refractory material used as a nozzle.
[0039]
In addition, for an apparatus in which the application position of the DC magnetic field coil 4 can be adjusted in the water-cooled mold 5, the application position of the DC magnetic field coil is adjusted by installing the DC magnetic field coil on an apparatus that can be moved up and down by a hydraulic cylinder, for example. it can.
[0040]
Furthermore, as an apparatus in which the cross-sectional shape of the refractory container 2 and the cross-sectional shape of the water-cooled mold 5 are different, for example, by making the refractory container installed on the water-cooled mold upwardly spread, Thus, the volume of the upper pool can be increased, facilitating the addition of the solute element and the dissolution and mixing of the added solute element in the upper pool.
[0041]
The slab obtained by the continuous casting method of the present invention is inserted into a heating furnace in the next step to form a scale (iron oxide). Since the thickness is less than 1 mm in terms of iron mass, the minimum value of the surface layer thickness in the slab must be 1 mm or more.
[0042]
On the other hand, even when the slab of the component composition different from the surface layer and the inner layer is rolled and processed into a thin plate, about 20% of the slab thickness is sufficient to satisfy the function as the surface layer, The upper limit is 20% of the slab thickness. The reason why the upper limit value of the surface layer thickness is not defined as an absolute value is that the required surface layer thickness differs depending on the slab thickness.
[0043]
【Example】
Inventors performed casting on the conditions shown in Table 1, and confirmed the principle of this method. Fig. 2 shows the result of examining the solute element concentration distribution in the slab cut out of the slab obtained by casting, and the result of measuring the solute element concentration distribution in the width direction of the surface layer thickness from the solidified structure of the slab. As shown in FIG.
[0044]
It was found that by using the method described in the present invention, a slab having a solute element concentration in the surface layer portion of the slab higher than that in the interior and a uniform surface layer thickness in the circumferential direction can be produced. The same experiment was conducted under the conditions that the solute elements to be added were Al, Ti, Nb, Si, Mn, Ni, Cr, Cu, P, S, Mo, V, and W. Similar results could be obtained.
[0045]
In addition, in the present invention, since the application position of the DC magnetic field and the casting speed can be adjusted together, the thickness of the slab is changed from 1 mm to 50 mm without any operation trouble under the condition that the slab thickness is 250 mm. I was able to. Furthermore, when casting using a mold of approximately the same size for casting a slab of 50 mm × 1200 mm in slab size, the refractory container set on the top is expanded to 100 mm while maintaining the width of 1200 mm. The solute element can be easily added, the upper pool can be secured sufficiently, and the added solute element can be easily mixed and dissolved.
[0046]
[Table 1]

[0047]
【The invention's effect】
According to the present invention, when casting a slab in which the solute element concentration in the surface layer portion of the slab is higher than the inside, the concentration of the plurality of elements is simultaneously increased without limiting the amount of alloy elements to be added. However, it is possible to cast a slab having a higher surface layer concentration than the inside of the slab.
[0048]
Moreover, since the surface layer thickness of the slab has a large degree of freedom to be changed, the present invention can be applied to various purposes.
[0049]
In addition, the present invention has no restrictions on the cross-sectional shape of the slab, and can be applied to slab, bloom, and billet casting.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing the configuration of the present invention.
FIG. 2 is an example of the result of casting using the method of the present invention, where (a) shows the result of investigating the distribution of C concentration in the slab, and (b) shows the result in the thickness direction of the slab. It is the figure which showed distribution of C density | concentration.
FIG. 3 is an example of the result of casting using the method of the present invention, and is a diagram showing the distribution in the width direction of a slab obtained by determining the surface layer thickness from the solidified structure.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Induction heating coil 2 ... Refractory container 3 ... Ceramic 4 ... DC magnetic field coil 5 ... Water cooling mold 6 ... Alloy addition 7 ... Upper pool 8 ... Lower pool 9 ... Solidified shell (surface layer) formed by the upper pool
10: Solidified shell (transition region) formed in the DC magnetic field application region
11 ... Solidified shell (inner layer) formed by the lower pool
12 ... Immersion nozzle

Claims (10)

A DC magnetic field having a substantially uniform magnetic flux density distribution in the mold width direction below the solidification start point is applied in the thickness direction, and the solute element is placed in the molten steel pool above the region where the DC magnetic field is applied. In a continuous casting method in which molten steel is supplied below the DC magnetic field application area while adding, the molten steel in the upper pool is heated from the area where the DC magnetic field is applied to melt the added solute element and start solidification A continuous casting method characterized by casting a slab having a point lower than the molten metal surface and having a surface layer different from the inner layer. 2. The continuous casting method according to claim 1, wherein the surface thickness of the slab and the concentration of the solute element added to the surface portion of the slab are adjusted using the following relational expression.
d = K × (L / Vc) ⁿ
q = {W × T− (W−2 × d) × (T−2 × d)} × ρ × Vc
Q = α × q × ΔC / 100
W: Mold width T: Mold thickness K, n: Solidification shell growth rate coefficient ρ: Molten steel density Vc: Casting speed Q: Addition rate of solute element ΔC: Concentration of solute element added to slab surface layer q: Upper part Surface layer mass formed per unit time in the pool d: Surface layer thickness of the slab L: Distance from the solidification start point to the DC magnetic field application region α: Coefficient due to the difference in yield depending on the additive element   The continuous casting method according to claim 1 or 2, wherein the surface layer thickness of the slab is adjusted by one or both of the distance from the solidification start point to the DC magnetic field application region and the casting speed.   The continuous casting method according to any one of claims 1 to 3, wherein the addition rate of the solute element is adjusted according to the concentration of the solute element in the molten steel pool above the region to which the DC magnetic field is applied. .   The continuous casting method according to any one of claims 1 to 4, wherein an induction heating coil is used as means for heating the molten steel pool above a region to which a DC magnetic field is applied.   The continuous casting method according to any one of claims 1 to 5, wherein an apparatus having a different cross-sectional shape on the molten metal surface and a cross-sectional shape of the slab is used. A DC magnetic field coil having a function of applying a DC magnetic field having a substantially uniform magnetic flux density distribution in the mold width direction in the water-cooled mold and a tip of an immersion nozzle for injecting molten steel into the mold is the DC magnetic field. In a continuous casting apparatus provided with an immersion nozzle below the coil and a device capable of adding a solute element above the DC magnetic field coil , the solute element added by heating above the DC magnetic field coil is heated. A continuous casting apparatus characterized by having a function of dissolving the solidification start point below the molten metal surface.   The continuous casting apparatus according to claim 7, wherein an induction heating coil is installed on an outer periphery of the refractory container as a function of heating the portion above the DC magnetic field coil.   The continuous casting apparatus according to claim 7 or 8, wherein the application position of the DC magnetic field coil is adjustable in the water-cooled mold.   The continuous casting apparatus according to claim 8 or 9, wherein the cross-sectional shape of the refractory container is different from the cross-sectional shape of the water-cooled mold.

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