JPH07100587A - Method for producing difficult-to-separate multi-layer cast slab - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a casting method for continuously producing a difficult-to-separate multi-layer cast slab comprising an inner layer and a surface layer having different densities. [Structure] In a combination of steel types in which the density of the molten steel for the surface layer is higher than that of the molten steel for the inner layer, the size of the mold is specified so that the cross-sectional area of the molten pool at the position separated by the static magnetic field falls within the range of the following formula. Further, it is a casting method for a difficult-to-separate multi-layer cast piece, in which the discharge depth of the nozzle for supplying the molten metal for the surface layer is set within 200 mm from the meniscus portion for casting. Δρ × (W-2d) × (T-2d) ≦ 0.05 Δρ: Molten steel density difference, W: Mold width, T: Mold thickness, d: Solidified shell thickness at the center of the magnetic pole [Effect] Components in the surface layer It is possible to eliminate the non-uniformity and to continuously manufacture a multi-layer cast product in which the surface layer and the inner layer are not mixed, at low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method for continuously producing inseparable multi-layer cast slabs having different compositions in the inner layer and the surface layer from a molten state.

[0002]

2. Description of the Related Art As a method for producing a composite steel material by continuous casting, two immersion nozzles having different lengths are inserted into a pool of molten metal in a mold, and the discharge ports of the respective nozzles are located at different depths. Japanese Patent Publication No. 44-27361 discloses a technique for injecting different kinds of molten metal in the above.

Japanese Patent Publication No. 49-44859 discloses that
A technique is disclosed in which partition walls made of a refractory are provided between different kinds of molten metals injected into a mold, and continuous casting is performed while preventing different kinds of metals from mixing with each other.

Further, in Japanese Patent Publication No. 63-108947, as shown in FIGS. 2 (a) and 2 (b), between different kinds of molten metals injected into a mold 1 through immersion nozzles 2 and 3,
It is disclosed that a static magnetic field 6 is used to produce a multilayer slab while preventing both metals from mixing.

This forms a static magnetic field 6 having magnetic lines of force over the entire width of the slab in a certain length region in the casting direction,
With the static magnetic field 6 as a boundary, different kinds of molten metals 4, 5 are supplied above and below the boundary. As a result, it is possible to minimize the mixing of the upper and lower layers at the position where the upper and lower layers are in contact with each other.

[0006]

Conventionally, in continuous casting, a single-density metal has been supplied into the mold. Therefore, the change in the density of the molten metal did not affect the properties of the slab.

On the other hand, in the technique for producing a multi-layer cast product by simultaneously injecting two kinds of metals into the mold, the density of the molten metal for the surface layer located above the static magnetic field 6 depends on the combination of the metals used. It also occurs when the density is higher than the density of the molten metal for the inner layer located at the bottom.

In this case, as shown in FIG. 2 (a), the high-density surface layer molten metal flows into the low-density inner layer metal portion through the place where the static magnetic field 6 is used. As a result, the cast piece to be cast becomes an incomplete cast piece in which the surface layer molten metal 4 and the inner layer molten metal 5 are mixed.

Further, since the above-mentioned effect of mixing appears largely in the surface layer pool in which the pouring amount is a fraction of that of the inner layer, the composition for the slab surface layer is kept within the target range in the molten steel for the surface layer. Casting is performed by increasing the alloy amount of No. 3, but in that case, the difference in density between the molten steel in the surface layer and that in the inner layer further increases. In that case, since the molten steel in the pool for the surface layer in the mold is poorly mixed, a molten steel region zone 10 having an extremely high molten steel density is generated in the upper part of the static magnetic field as shown in FIG. 2B.

When the casting is further continued in this state, and the height of the molten steel zone having an extremely high molten steel density reaches a certain level or higher, it cannot be supported by the static magnetic field and the molten steel for the surface layer and the inner layer is mixed. Since this state is repeated, a steady cast piece cannot be obtained.

The present invention solves the above-mentioned problems, and particularly provides a method for producing a difficult-to-separate multi-layer slab that continuously casts a multi-layer slab with a combination in which the surface layer density is higher than the inner layer density.

[0012]

The first aspect of the present invention is to inject two kinds of molten metal having different densities into respective molds which are divided into upper and lower portions by a static magnetic field, and cool and solidify the molten metal. The density of the molten steel for the surface layer of the cast multi-layer slab to be cast is greater than the density of the molten steel for the inner layer, in the casting method of the multi-layer slab, the cross-sectional area of the molten pool at the position separated by the static magnetic field is A casting method for a difficult-to-separate multi-layer cast product, characterized in that the casting is performed by defining the size of the mold so as to fall within the range of the following formula (1).

[0013]

(3) Δρ × (W-2d) × (T-2d) ≦ 0.05 (1)

The second aspect of the present invention is that the molds divided into upper and lower parts by a static magnetic field have different densities.
In the casting method of a multi-layer cast product in which the density of the molten steel for the surface layer of the cast multi-layer cast product in which a molten metal of a type is injected, and the molten metal is cooled and solidified is higher than the density of the molten steel for the inner layer , The size of the mold is defined so that the cross-sectional area of the molten pool at the position separated by the static magnetic field falls within the range of the following formula (2), and the discharge depth of the nozzle for supplying the molten metal for the surface layer used during casting Is placed within 200 mm from the meniscus portion in the mold for casting, and is a method for casting a difficult-to-separate multi-layer cast slab.

[0015]

[Formula 4] Δρ × (W-2d) × (T-2d) ≦ 0.05 (2)

[0016] (1) and (2), [Delta] [rho] is the density of the surface layer molten steel ([rho ₁₎ - molten steel density difference represented by the density of the inner layer for the molten steel ([rho ₂₎ (g / cm ^2), W : Mold width (m), T: Mold thickness (m), d: Surface layer solidified shell thickness (m) at the center of the magnetic pole.

[0017]

FIG. 1 shows a static magnetic field and a nozzle in the case where a multi-layer slab of a combination of molten metals in which the density of the molten metal 4 for the surface layer is higher than that of the molten metal 5 for the inner layer is produced by continuous casting according to the present invention. It is a figure which shows the positional relationship with.

Reference numeral 1 is a mold, 2 and 3 are immersion nozzles for injecting respective molten metals, 6 is a static magnetic field, and 8 and 9 are multi-layers composed of a cast slab surface layer 8 and a cast slab inner layer 9. The cross section of a cast piece is shown.

FIG. 2 (a) shows the case where the molten metal for the surface layer is supplied and casting is performed so that the mass balance is perfectly achieved at the position of the static magnetic field, as used in the above-mentioned conventional process. Since the molten metal 5 for the inner layer having a low density floats and mixes into the molten metal 4 for the surface layer having a high density,
It is a figure showing the phenomenon that an inner layer element mixes in a cast slab surface layer part.

FIG. 2 (b) shows a case where casting is performed in the above-mentioned conventional process by increasing the alloy concentration in the molten steel for the surface layer in order to compensate for the decrease in the alloy concentration in the molten steel for the surface layer in the mold. 2 is a drawing showing a state in which concentrated molten steel stays above the static magnetic field to form a region zone 10 having a high molten steel density.

FIG. 3 shows that when casting is performed in the state shown in FIG. 2B, the composition of the surface layer near the surface of the slab is low at the surface and high near the magnetic pole. It is a drawing explaining that.

FIG. 4 is a diagram for explaining that the mixing of molten steel can be suppressed by changing the size of the ingot to be cast according to the density difference of the molten steel to be combined according to the present invention.

This is because when supplying the surface layer molten steel having a density higher than that of the inner layer molten steel to the upper part of the static magnetic field, the surface layer molten steel passes through the static magnetic field and flows into the inner layer molten steel. The extent depends on the area of the molten part of the pool in the mold separated by the static magnetic field. That is, when the area of the molten portion of the static magnetic field portion in the mold is increased, the molten steel is easily moved across the static magnetic field, so that the mixing amount is increased.

The influence of the molten steel density difference (Δρ) is as follows.
The mixing amount increases as the density difference increases. Therefore, the relationship shown in FIG. 4 is a summary of these effects. From Figure 4,
When the product of the difference in molten steel density and the molten region at the interface between the surface layer molten steel pool and the inner layer molten steel pool exceeds 0.05, the concentration of the cast slab surface layer sharply decreases. Therefore, in order to stably cast the multilayer slab while suppressing the mixing of molten steel, it is necessary to control these values to 0.05 or less.

Next, the influence of the immersion depth of the immersion nozzle for supplying molten steel for the surface layer is as follows:
The discharge flow of molten steel is not supplied to the meniscus portion in the mold but directly drops and flows into the static magnetic field portion. Therefore, to prevent this, it is necessary to improve the mixing in the pool for the surface layer in the mold.

Regarding this, from the experimental results of the immersion depth of the surface layer nozzle in the mold in FIG. 5 and the molten steel concentration at the two magnetic pole upper end portions of the meniscus in the mold, the immersion depth (nozzle discharge port When the position) is deeper than 200 mm, the concentrations of the meniscus portion and the upper end of the static magnetic field are different, and the mixing in the surface pool is reduced. Therefore, the discharge port position of the immersion nozzle is 200m from the meniscus.
It is necessary to make it shallower than m.

When the molten metal for the surface layer is supplied at an increased supply rate according to this method, the mixing of the above-mentioned difficult-to-separate materials can be suppressed to a minimum.

[0028]

EXAMPLE As Example 1, the horizontal cross section is 250 × 150.
Using a continuous casting mold with an internal space of 0 mm, aluminum-killed steel (ρ ₁ = 7.01 g / cm ³ ) was used for the surface layer and Si was used for the inner layer.
A multi-layer slab having the structure of steel containing 1% of (rho ₂ = 6.82 g / cm ³ ) was produced by a continuous casting method at a casting speed of 1 m / min. In this case, the thickness of the surface layer of the cast slab is 25 mm, and the difference in molten steel density is 0.21 g / cm ³ .

Initially, as shown in FIG. 2 of the conventional method, the molten metal for the surface layer was supplied so that the boundary between the two kinds of molten metal was located at the center of the static magnetic field, and casting was performed. However, since the density of [Si] is lower than that of iron, in the casting using the molten metal of this combination, the molten metal for the surface layer, which does not contain [Si] having a high density, is separated by the static magnetic field for mixture suppression. The molten metal for the inner layer containing the low density [Si] is supplied to the lower portion.

In this case, the inner layer molten metal having a low density is mixed with the surface molten metal by passing through the static magnetic field. Therefore, the slab produced in the case of such a combination of metals has become a slab in which the components of the surface layer and the inner layer are mixed.

Since the product of Δρ and the area of the fused portion of the static magnetic field portion at this time was 0.058, the thickness of the casting mold during casting was reduced to 200 mm as shown in FIG. Was reduced to about 0.04 and casting was performed. As a result, the produced slab became a multi-layer slab without mixing of the surface layer and the inner layer.

Here, the molten metal for the surface layer is mixed with the inner layer portion, but the mixing amount is small, and the components in the inner layer portion of the cast slab produced due to complete mixing under the static magnetic field are mixed. No heterogeneity occurred.

As a second embodiment, the horizontal cross section is 250 × 15.
Using a continuous casting mold with an internal space of 00 mm, steel containing 5% of [Ni] in the surface layer (ρ ₁ = 7.28 g / cm ³ ),
A multi-layer slab having an aluminum killed steel (ρ ₂ = 7.01 g / cm ³ ) structure in the inner layer was cast at a casting speed of 1 by continuous casting.
Produced at m / min. At this time, the discharge port of the surface layer nozzle is
Casting was performed at a position of 250 mm from the meniscus in the mold.

The thickness of the surface layer of the slab obtained by the main casting is 25
mm. With this combination, it was expected that the molten steel for the surface layer with a high density would be mixed into the molten steel for the inner layer with a low density, so the [Ni] concentration in the molten steel for the surface layer was adjusted from the required concentration of 4% to 5%. And added. Therefore, the difference in density during casting expanded to 0.28 g / cm ³ .

Initially, as shown in FIG. 2 of the conventional method, the molten metal for the surface layer was supplied so that the boundary between the two kinds of molten metal was located at the center of the static magnetic field, and casting was performed. However, in the casting using the molten metal of this combination, the molten metal for the surface layer with a high density in the upper part flows into the molten metal for the inner layer with a low density in the lower part by separating the static magnetic field for suppressing mixing, and therefore the casting As shown in FIG. 2 (a), the cast slab was an incomplete slab with a non-uniform concentration in the surface layer of the cast slab.

Therefore, as shown in FIG. 1, the width of the mold during casting is reduced to 1000 mm and the thickness is reduced to 200 mm, and the position of the discharge port of the dipping nozzle for the surface layer is made shallower from the meniscus portion in the mold to 100 mm. Then, casting was performed. As a result, the produced slab became a multi-layer slab in which the non-uniformity of the components in the surface layer portion was eliminated and the surface layer and the inner layer were not mixed.

Further, in this case, the molten metal for the surface layer is mixed with the inner layer portion, but the mixing amount is small, and since it is completely mixed in the lower part of the static magnetic field, the inner layer portion of the manufactured slab is Inhomogeneity of the ingredients did not occur.

[0038]

As described above, according to the method for producing a multi-layer cast product of the present invention, even in the casting of the multi-layer cast product by the combination of metals whose surface layer density is higher than the inner layer density, The non-uniformity of the components is eliminated, and it becomes possible to continuously manufacture a multi-layer slab without mixing of the surface layer and the inner layer at low cost, and the quality and productivity of the multi-layer slab can be improved.

[Brief description of drawings]

FIG. 1 is a view showing an example of the present invention and showing a state in which a multi-layer cast product is manufactured by increasing a supply rate of molten steel metal for surface layer.

FIG. 2 (a) is a drawing showing, as a comparative example, a phenomenon in which molten metal for a surface layer having a high density is mixed with molten metal for an inner layer when a molten metal is supplied by a conventional method, (b).
The figure is a view for explaining a state in which a heterogeneous layer of components is generated in the surface layer molten steel pool when the density difference between the surface layer molten steel and the inner layer molten steel is further large.

FIG. 3 shows a comparison of the analysis results of the components in the inward direction from the surface of the slab of the conventional example and the example of the present invention, and explains that the nonuniformity of the components in the surface layer portion is eliminated by casting according to the present invention. It is a drawing.

FIG. 4 is a diagram illustrating that mixing is prevented by controlling the product of the density difference of molten steel and the molten region of the static magnetic field use region in the case of casting according to the present invention.

FIG. 5 is a diagram for explaining that by making the discharge position of the immersion nozzle for the surface layer shallow, the uniformity of molten steel is improved and a slab with a uniform concentration can be cast.

[Explanation of symbols]

 1 Mold 2, 3 Immersion Nozzle 4 Molten Metal for Surface Layer 5 Molten Metal for Inner Layer 6 Static Magnetic Field 7 Multi-layer Cast Piece 8 Cast Piece Surface Layer 9 Cast Piece Inner Layer 10 Concentrated Molten Steel Region in Upper Static Magnetic Field in Mold

Claims (2)

[Claims] 1. A molten steel for a surface layer of a cast multi-layer cast slab for injecting two kinds of molten metals having different densities into respective molds divided into upper and lower parts by a static magnetic field, and cooling and solidifying the molten metals. In the casting method of a multi-layer cast product in which the density is a combination of steel types having a density higher than that of the molten steel for the inner layer, the mold size is set so that the cross-sectional area of the molten pool at the position separated by the static magnetic field is in the range of A method for casting a difficult-to-separate multi-layer slab, characterized by: [Formula 1] Δρ × (W-2d) × (T-2d) ≦ 0.05 where Δρ is the molten steel represented by the density (ρ ₁ ) of the surface layer molten steel-the density of the inner layer molten steel (ρ ₂ ). Density difference, W: mold width (m), T: mold thickness (m), d: solidified shell thickness (m) at the center of the magnetic pole. 2. A molten steel for a surface layer of a cast multi-layer cast product, which comprises injecting two kinds of molten metals having different densities into respective upper and lower molds divided by a static magnetic field and cooling and solidifying the molten metals. In the casting method of a multi-layer cast product in which the density is a combination of steel types having a density higher than that of the molten steel for the inner layer, the mold size is set so that the cross-sectional area of the molten pool at the position separated by the static magnetic field is in the range of several 2. In addition, the casting is performed by setting the discharge depth of the nozzle for supplying the molten metal for the surface layer used during casting within 200 mm from the meniscus portion in the mold for casting. Method. [Formula 2] Δρ × (W-2d) × (T-2d) ≦ 0.05 Here, Δρ is the molten steel represented by the density of the molten steel for the surface layer (ρ ₁ ) −the density of the molten steel for the inner layer (ρ ₂ ). Density difference (g / cm ² ),
W: mold width (m), T: mold thickness (m), d: solidified shell thickness (m) at the center of the magnetic pole.