JP5942712B2 - Scum weir, thin slab manufacturing method, thin slab manufacturing equipment - Google Patents

Description

The present invention provides a scum weir used in a method for producing a thin slab by supplying molten steel to a molten steel reservoir formed by a pair of cooling drums and a pair of side weirs via an immersion nozzle to produce a thin slab, method for producing a thin cast strip using the scum dams are those concerning the manufacturing equipment of the thin cast strip.

  As described above, as a method for manufacturing a thin metal slab, for example, as shown in Patent Documents 1 and 2, a pair of cooling drums and a pair of side weirs provided with a cooling drum having a water cooling structure therein are provided. The molten steel is supplied to the molten steel reservoir formed by the above-described methods, solidified shells are formed and grown on the peripheral surface of the cooling drum, and the solidified shells formed on the pair of cooling drums are pressure-bonded to each other at a drum kiss point. A twin-drum continuous casting method for producing a thin slab of thickness is provided.

Here, in the above-mentioned molten steel pool part, it is known that an oxide etc. will float on the molten steel surface, and what is called a scum will generate | occur | produce. When this scum reaches the solidification start point of the cooling drum, it is caught between the cooling drum and the solidified shell as the cooling drum rotates, resulting in non-uniform solidification, resulting in surface defects of thin-walled slabs, etc. Resulting in. Further, when the molten steel surface fluctuates at the solidification start point of the cooling drum, solidification may not be stable.
Therefore, as disclosed in Patent Documents 3 and 4, a technique has been proposed in which a scum weir is disposed in the molten steel pool portion to suppress scum entrainment and fluctuation of the molten steel surface at the solidification start point.

Here, since the scum weir is disposed between the pair of cooling drums, it is difficult to sufficiently perform preheating. And since molten steel over 1500 degreeC is supplied to a molten steel pool part and a scum weir is immersed and used for this molten steel, the outstanding heat resistance and thermal shock resistance are requested | required of a scum weir. Therefore, BN (boron nitride) is generally used for conventional scum weirs.
As disclosed in Patent Document 3, the scum weir is also required to have characteristics such as corrosion resistance, particle size, strength, and volume stability (low thermal deformation). Therefore, Patent Document 3 proposes a scum weir made of graphite and metal oxide.

Japanese Patent Laid-Open No. 04-300049 JP 2002-113555 A JP 2003-039139 A JP 2003-266154 A

  By the way, in the above-mentioned twin-drum type continuous casting method, a thin cast piece having a thickness of several millimeters can be produced directly from molten steel, so that it is possible to omit steps such as hot rolling. Therefore, for example, Cu-containing steel (˜2 mass% Cu), Al-containing steel (0.1-4 mass% Al), P-containing steel (˜0.15 mass% P), Si-containing steel (˜4 mass% Si), etc. It is particularly suitable for the production of brittle materials and hard-to-heat rolled materials.

Here, in the above-described twin-drum type continuous casting method, since no mold flux or the like is interposed between the cooling drum and the molten steel, the molten steel has a high cooling rate, and the produced thin cast slab has columnar crystals. The organization tends to develop easily.
In a thin cast slab with a developed columnar crystal structure, cracks are likely to occur at the grain boundaries of columnar crystals when bending stress acts. For this reason, there is a possibility that cracks and breaks may occur during the conveyance and winding of thin cast pieces, and edge cracks and breaks may occur during cold rolling. This tendency is particularly remarkable in the above-described brittle materials and heat-resistant rolled materials. For this reason, although hot rolling was abbreviate | omitted by manufacturing a thin-walled slab, it was cracked by the subsequent process etc. and the manufacturing yield could not be improved.

The present invention has been made in view of the above-described situation, and is a scum weir capable of producing a thin cast slab that has a high ratio of equiaxed crystals and is not easily cracked by bending or the like. manufacturing method, and an object thereof is to provide a manufacturing equipment of the thin cast strip.

In order to solve the above problems, a scum weir according to the present invention supplies molten steel to a molten steel reservoir formed by a pair of rotating cooling drums and a pair of side weirs via an immersion nozzle, and to form and grow a solidified shell on the peripheral surface a scum dams used in the method for producing a thin cast strip for producing a thin cast strip, the carbon content is less 3 mass% or more 15 mass%, the ferrite iron The total content of one or more solidification nucleation promoting substances having a lattice matching degree of 6% or less is 5 mass % or more and 97 mass% or less , and the total content of one or more metal oxides is 55 mass%. it is equal to or less than than 95 mass%.

Since the scum weir with this structure contains a solidification nucleation promoting substance having a lattice matching degree of 6% or less with ferritic iron, the scum weir is in contact with the molten steel for the first time on the surface of the scum weir. Solidification nuclei of ferritic iron are formed. The solidification nuclei are dispersed in the molten steel by the flow of the molten steel, so that equiaxed crystals develop, and it is possible to manufacture a thin cast slab having a high equiaxed crystal ratio. Therefore, it is possible to manufacture a thin cast slab that is not easily cracked by bending or the like.
Here, when the total content of one or more of the solidification nucleation promoting substances is less than 5 mass %, the solidification nucleation promoting substance is not sufficiently exposed on the surface of the scum weir, and solidification nucleation is generated. May not be promoted. For this reason, the total content of one kind or two or more kinds of solidification nucleation promoting substances is set to 5 mass % or more.

Also, with this in scum dams configuration, since the content in one or range of 55 mass% or more 95 mass% of two or more metal oxides, it is possible to ensure the melting loss resistance, thermal shock resistance Sex can be secured. In addition, when a metal oxide is included as the above-mentioned solidification nucleation promoting substance, the total content of the metal oxide including the metal oxide that is a solidification nucleation promoting substance and other metal oxides is 55 mass% or more and 95 mass%. % May be within the range.
Furthermore, since carbon is contained within the range of 3 mass% or more and 15 mass% or less, the thermal shock resistance can be secured, and the strength and the erosion resistance can be secured.

Here, the solidification nucleation promoting substance preferably contains one or more selected from TiN, TiC, β-type SiC, MgO.Al ₂ O ₃ , MgO, and Rem ₂ O ₃ .
Since these substances have a lattice matching degree of 6% or less with ferritic iron, the formation of solidification nuclei can be surely promoted, and the ratio of equiaxed crystals in the thin cast slab can be increased. Specifically, the lattice matching with ferritic iron is 3.9% for TiN, 5.9% for TiC, 6.0% for β-type SiC, 1.4% for MgO.Al ₂ O ₃ , MgO Is 2.8%, and Rem ₂ O ₃ is 5.0%. Note that β-type SiC has a crystal structure different from that of general α-type SiC manufactured by a direct energization method (Acheson method).

Further, as the coagulation nucleation-promoting substances, TiN, and one or more selected from _{TiC, MgO · Al 2 O 3} , MgO, 1 or two or more selected from _Rem 2 _{O 3} and, It is preferable to contain together.
In this case, since the formation of solidification nuclei is further promoted, the ratio of equiaxed crystals in the thin cast slab can be further increased.

The maximum particle size of the solidification nucleation promoting substance and the metal oxide is preferably 100 μm or less and the average particle size is 50 μm or less.
In this case, even when the solidification nucleation promoting substance and the metal oxide drop off from the scum weir and are caught in the thin cast piece, it is possible to suppress the surface defect of the thin cast piece. Therefore, casting can be carried out stably for a long time.

  The method for producing a thin slab according to the present invention includes supplying molten steel to a molten steel pool formed by a pair of rotating cooling drums and a pair of side weirs via an immersion nozzle, and solidifying shells on the peripheral surface of the cooling drum. The thin slab is manufactured by forming and growing a thin slab, wherein the scum weir is disposed in the molten steel reservoir, and is measured between the immersion nozzle and the scum weir. The superheat degree of the molten steel is set within a range of 3 ° C. or more and 30 ° C. or less, and the flow rate of the molten steel on the surface of the scum weir is set to 10 cm / sec or more.

According to the method for producing a thin cast slab of this configuration, a scum weir composed of a material containing 5 mass% or more of a solidification nucleation promoting substance having a lattice matching degree with ferrite iron of 6% or less is used. Since the flow rate of the molten steel on the surface of the scum weir is 10 cm / sec or more, the solidified nuclei generated on the surface of the scum weir can be dispersed in the molten steel, and the ratio of equiaxed crystals in the thin wall slab is increased. It becomes possible to do.
In addition, although a side dam, an immersion nozzle, etc. will be arrange | positioned in a molten steel pool part, it is difficult to ensure the flow velocity of molten steel in these surfaces. When solidification nuclei are generated at a site where the molten steel flow velocity on the surface is low in this way, the solidification nuclei grow on the surface and become bullion, and they are caught in thin-walled slabs, resulting in defects or casting troubles. There is a risk. For this reason, in this invention, it is comprised so that the production | generation of a solidification nucleus may be accelerated | stimulated in the surface of the scum weir which can ensure the flow velocity of molten steel.
Further, by reducing the degree of superheating to 3 ° C. or higher and 30 ° C. or lower, equiaxed crystallization is promoted, and the ratio of equiaxed crystals in the thin cast slab can be further increased. The degree of superheat can be measured by, for example, a radiation thermometer or a thermocouple. It is also possible to grasp the amount of temperature drop in the molten steel pool and manage it at the molten steel temperature of a tundish or the like that supplies the molten steel to the immersion nozzle.

Here, it is preferable that the atmosphere between the scum weir and the cooling drum is Ar.
Ar gas has a lower thermal conductivity than other inert gases such as nitrogen and He. Therefore, by interposing Ar gas having a low thermal conductivity in the gap between the cooling drum and the solidified shell, it is possible to suppress heat removal by the cooling drum and to suppress the development of columnar crystals.

  The apparatus for producing a thin slab according to the present invention supplies molten steel to a molten steel reservoir formed by a pair of rotating cooling drums and a pair of side weirs via an immersion nozzle, and solidifies the peripheral surface of the cooling drum. An apparatus for manufacturing a thin-walled slab that forms and grows a shell to manufacture a thin-walled slab, wherein the above-described scum weir is disposed in the molten steel reservoir.

  According to the thin-walled slab manufacturing apparatus having this configuration, a scum weir composed of a material containing 5 mass% or more of a solidification nucleation promoting substance having a lattice matching degree with ferritic iron of 6% or less is provided in the molten steel pool. Since it is disposed, solidification nuclei generated on the surface of the scum weir can be dispersed in the molten steel, and the ratio of equiaxed crystals in the thin cast slab can be increased.

  As described above, according to the present invention, it is possible to manufacture a thin cast slab having a high ratio of equiaxed crystals and being less likely to be cracked by bending or the like.

It is explanatory drawing which shows the manufacturing apparatus of the thin cast slab provided with the scum weir which is embodiment of this invention. FIG. 2 is an enlarged explanatory view of a molten steel pool portion in FIG. 1.

  Hereinafter, a scum weir which is an embodiment of the present invention, a method for manufacturing a thin cast piece using the scum weir, a manufacturing apparatus for a thin cast piece, and a thin cast piece manufactured using the thin cast piece manufacturing apparatus A description will be given with reference to the attached drawings.

First, the thin cast piece 1 which is this embodiment is demonstrated. The thin cast piece 1 according to the present embodiment is made of a steel material whose primary crystal upon solidification is ferritic iron, and the thickness ratio of the equiaxed crystal to the cast piece thickness is 25% or more.
Specifically, the thin cast slab 1 according to the present embodiment has C: 0.001 mass% to 0.055 mass%, Si: 0.10 mass% to 4.15 mass%, Mn: 0.07 mass% to 0 .60 mass% or less, P; 0.15 mass% or less, S; 0.01 mass% or less, Al; 0.02 mass% or more and 4.0 mass% or less, Ti; 0.20 mass% or less, Cu; 3.0 mass% or less, It is comprised with the steel material containing. Hereinafter, the reason why each element is defined as described above will be described.

(C)
C is an element having an effect of improving the strength of the steel material. Here, it is not preferable that the C content is less than 0.001 mass% because the refining cost is significantly increased. On the other hand, if the C content exceeds 0.055 mass%, the workability deteriorates, which is not preferable. Therefore, the C content is set in the range of 0.001 mass% to 0.055 mass%.

(Si)
Si is an element that acts as a deoxidizer, and is particularly added as a preliminary deoxidation before the addition of Al. Moreover, it is added as a main component of electromagnetic steel. Here, if content of Si is less than 0.10 mass%, the deoxidation effect cannot fully be achieved. On the other hand, when the content of Si exceeds 4.15 mass%, the toughness is lowered, and there is a possibility that a lateral crack or the like of the slab is generated. Therefore, the Si content is set within a range of 0.1 mass% to 4.15 mass%.

(Mn)
Mn is an element having an effect of improving strength. Here, if the Mn content is less than 0.07 mass%, the strength cannot be sufficiently improved. On the other hand, if the Mn content exceeds 0.60 mass%, the toughness decreases, which is not preferable. Therefore, the Mn content is set within a range of 0.07 mass% to 0.60 mass%.

(P)
P is a so-called solid solution strengthening element and has an effect of improving the strength of steel. Here, when the content of P exceeds 0.15 mass%, it is not preferable because cracking of a cast piece is likely to occur at a segregated portion. Therefore, the P content is set to 0.15 mass% or less. The lower limit is not particularly defined, but is preferably 0.002 mass% or more in consideration of reasonable cost.

(S)
S is a harmful element that decreases workability and toughness. Therefore, the upper limit is limited to 0.01 mass% or less. In addition, although a minimum is not prescribed | regulated, it is preferable to set it as 0.001 mass% or more from balance with refining cost.

(Al)
Al is an element that acts as a deoxidizer. It also has the effect of reducing the specific gravity. Here, if the Al content is less than 0.02 mass%, the effect as a deoxidizer cannot be sufficiently achieved. On the other hand, if the Al content exceeds 4.0 mass%, the toughness decreases, which is not preferable. Therefore, the Al content is set within a range of 0.02 mass% to 4.0 mass%.

(Ti)
Ti is an element having an effect of improving the strength of steel. Here, when the Ti content exceeds 0.20 mass%, coarse TiN is generated, and the toughness is lowered. Therefore, the Ti content is set to 0.20 mass% or less. The lower limit is not particularly specified and may be 0 mass%. However, in order to ensure the effect of improving the strength, the content of Ti is preferably set to 0.01 mass% or more.

(Cu)
Cu is an element having an effect of improving the strength of steel. Here, when the content of Cu exceeds 3.0 mass%, the toughness is lowered, and there is a possibility that a lateral crack of the slab occurs. Therefore, the Cu content is set to 3.0 mass% or less. The lower limit is not particularly defined and may be 0 mass%.

  Here, the steel material having the composition range described above is susceptible to cracking and difficult to hot-roll, so that, for example, the thickness is 0.8 mm to 5 mm according to the method for manufacturing a thin cast slab according to this embodiment. It is manufactured as a thin cast slab 1 within a range of 2 mm.

Next, a scum weir 20 according to this embodiment and a thin cast slab manufacturing apparatus 10 including the scum weir 20 will be described with reference to FIGS. 1 and 2.
As shown in FIG. 1, the thin-walled slab manufacturing apparatus 10 according to the present embodiment supports a pair of cooling drums 11 and 11, bender rolls 12 and 12 that bend the thin-walled slab 1, and the thin-walled slab 1. Pinch rolls 13, a pair of cooling drums 11, a side weir 15 disposed at an end in the width direction, and a molten steel pool portion defined by the pair of cooling drums 11, 11 and the side weir 15 A tundish 18 for supplying the molten steel 3 to the nozzle 16 and an immersion nozzle 19 are provided.
The molten steel reservoir 16 is provided with a scum weir 20 according to this embodiment. More specifically, as shown in FIG. 2, the scum weir 20 is disposed between the immersion nozzle 19 and the cooling drums 11 and 11, and a part thereof is immersed in the molten steel 3. In the present embodiment, the scum weir 20 has a rectangular flat plate shape, and the immersion depth D in the molten steel 3 is 5 mm or more.

  The scum weir 20 is made of 3 mass% or more and 15 mass% or less of carbon, 5 mass% or more of a solidification nucleation promoting substance having a lattice matching with ferrite iron of 6% or less, and a metal oxide containing the solidification nucleation promoting substance. It is comprised with the material containing 55 mass% or more and 95 mass% or less. Below, the reason which prescribed | regulated each component as mentioned above is demonstrated.

(carbon)
If the carbon content is less than 3 mass%, the thermal shock resistance is insufficient, so that cracking may occur when the scum weir 20 is used, particularly at the start of casting. On the other hand, if the carbon content exceeds 15 mass%, the strength decreases and the amount of erosion increases, so the life of the scum weir 20 may be shortened. From the above, the carbon content is set in the range of 3 mass% to 15 mass%.

(Coagulation nucleation promoting substance)
The solidification nucleation promoting substance having a lattice matching degree with ferrite iron of 6% or less generates solidification nuclei of primary ferrite iron on the surface of the scum weir 20 at the portion where the scum weir 20 and the molten steel 3 are in contact with each other. The equiaxed crystal ratio in the thin cast slab 1 is improved. When the content of the solidification nucleation promoting substance is less than 5 mass%, the solidification nucleation promoting substance is not sufficiently exposed on the surface of the scum weir 20 and the formation of solidification nuclei may not be promoted. From the above, the content of the solidification nucleation promoting substance is set to 5 mass% or more. As described above, since 3 mass% of carbon is contained, the upper limit of the content of the solidification nucleation promoting substance is 97 mass%.

(Metal oxide)
Further, when the content of the metal oxide containing the solidification nucleation promoting substance is less than 55 mass%, the resistance to melting loss is lowered, and the scum weir 20 may be deteriorated early. Moreover, when content of a metal oxide exceeds 95 mass%, a thermal shock resistance falls and there exists a possibility that the scum weir 20 may crack. From the above, the content of the metal oxide containing the solidification nucleation promoting substance is set in the range of 55 mass% or more and 95 mass% or less.

Here, as the solidification nucleation promoting substance, it is preferable to contain one or more selected from TiN, TiC, β-type SiC, MgO · Al ₂ O ₃ , MgO, and Rem ₂ O ₃ .
Further, as the coagulation nucleation promoting substances described above, TiN, and one or more selected from _{TiC, MgO · Al 2 O 3} , MgO, 1 or two or more selected from _Rem 2 _{O 3} and It is more preferable to contain these together.

  In the scum weir 20, the maximum particle size of the solidification nucleation promoting substance and the metal oxide is 100 μm or less, the average particle size is 50 μm or less, and the maximum particle size of carbon particles is 300 μm or less. The particle size is 100 μm or less.

Next, the manufacturing method of the thin cast piece by the thin cast piece manufacturing apparatus 10 provided with the scum weir 20 which is this embodiment is demonstrated.
Each of the pair of cooling drums 11 and 11 is directed in the rotation direction R, that is, the region where the pair of cooling drums 11 and 11 are close to each other is directed in the drawing direction of the slab (downward in FIG. 1). The cooling drums 11 and 11 are rotated.

Then, the molten steel 3 is supplied from the tundish 18 through the immersion nozzle 19 to the molten steel pool 16 defined by the pair of cooling drums 11 and 11 and the side weir 15.
In addition, the discharge flow from the immersion nozzle 19 is arranged so as to be directed to the immersed scum weir 20. Thereby, the flow velocity of the molten steel 3 on the surface of the scum weir 20 is set to 10 cm / sec or more.
Further, the atmosphere between the scum weir 20 and the cooling drum 11 is an Ar gas atmosphere, and Ar gas is interposed between the cooling drum 11 and the solidified shell 5.
Furthermore, the superheat degree of the molten steel 3 measured between the immersion nozzle 19 and the scum weir 20 is set within a range of 3 ° C. or higher and 30 ° C. or lower.

When the molten steel 3 comes into contact with the rotating cooling drum 11 and is cooled, the solidified shell 5 grows on the peripheral surface of the cooling drum 11, and the solidified shell 5 formed on the pair of cooling drums 11, 11, respectively. The thin cast piece 1 having a predetermined thickness is cast by pressing the five members together at the drum kiss point.
At this time, the scum weir 20 immersed in the molten steel pool portion 16 prevents inclusions (scum) floating above the molten steel 3 stored in the molten steel pool portion 16 from entering the cooling drum 11 side, Involvement of the scum into the thin cast slab 1 is suppressed. Further, the scum weir 20 suppresses the fluctuation of the molten steel surface at the solidification start point of the cooling drum 11.

  According to the scum weir 20, the thin cast slab casting method, and the thin cast slab casting apparatus of the present embodiment configured as described above, the scum weir 20 is composed of a material containing 5 mass% or more of a solidification nucleation promoting substance. Therefore, the generation of solidification nuclei of primary ferrite iron is promoted on the surface of the scum weir 20. The solidification nuclei are dispersed in the molten steel 3 by the molten steel flow from the immersion nozzle 19, and equiaxed crystals develop. Therefore, it is possible to manufacture the thin cast slab 1 that has a high ratio of equiaxed crystals and is not easily cracked by bending or the like. Specifically, the thin-walled slab 1 in which the thickness ratio of the equiaxed crystal to the slab thickness is 25% or more can be manufactured.

  Further, in the scum weir 20 according to the present embodiment, the metal oxide containing the solidification nucleation promoting substance is contained in the range of 55 mass% or more and 95 mass% or less. At the same time, thermal shock resistance can be ensured. Furthermore, since the scum weir 20 according to the present embodiment contains carbon in the range of 3 mass% to 15 mass%, it is possible to ensure thermal shock resistance and to ensure strength and erosion resistance. .

In the present embodiment, the solidification nucleation promoting substance is selected from TiN, TiC, β-type SiC, MgO.Al ₂ O ₃ , MgO, and Rem ₂ O ₃ having a lattice matching with ferrite iron of 6% or less. Since it contains 1 type or 2 types or more, it becomes possible to accelerate | stimulate the production | generation of a solidification nucleus reliably.
Furthermore, the coagulation nucleation-promoting substances, TiN, and one or more selected from _{TiC, MgO · Al 2 O 3} , MgO, and one or more selected from _Rem 2 _{O 3,} the Since it contains together, the production | generation of a solidification nucleus is further accelerated | stimulated and it becomes possible to make the ratio of the equiaxed crystal in the thin cast slab 1 high reliably.

  In this embodiment, the solidification nucleation promoting substance and the metal oxide have a maximum particle size of 100 μm or less and an average particle size of 50 μm or less. Even if it is a case where it falls off and is wound around the thin cast slab 1, it is possible to suppress the surface defect of the thin cast slab 1. Furthermore, in this embodiment, since the maximum particle diameter of the carbon particles is 300 μm or less and the average particle diameter is 100 μm or less, even when the carbon particles fall off, it can be suppressed that the surface defects of the thin cast slab 1 occur. . Since the solidification nucleation promoting substance and the metal oxide are harder than the carbon particles, the particle size is set smaller than that of the carbon particles.

  In the present embodiment, the discharge flow from the immersion nozzle 19 is arranged so as to face the immersed scum weir 20, and the flow rate of the molten steel 3 on the surface of the scum weir 20 is 10 cm / sec or more. The solidified nuclei generated on the surface of the scum weir 20 can be dispersed in the molten steel 3, and the ratio of equiaxed crystals in the thin cast slab 1 can be increased.

Furthermore, in this embodiment, the atmosphere between the scum weir 20 and the cooling drum 11 is an Ar gas atmosphere, and Ar gas having a relatively low thermal conductivity is interposed between the cooling drum 11 and the solidified shell 5. Therefore, heat removal from the cooling drum 11 is suppressed, the development of columnar crystals can be suppressed, and the ratio of equiaxed crystals can be increased.
Moreover, in this embodiment, since the superheat degree of the molten steel 3 measured between the immersion nozzle 19 and the scum weir 20 is set within a range of 3 ° C. or more and 30 ° C. or less, equiaxed crystallization is promoted. Thus, the ratio of equiaxed crystals in the thin cast slab 1 can be further increased.

  Moreover, the thin cast 1 which is this embodiment is C; 0.001 mass% or more and 0.055 mass% or less, Si; 0.10 mass% or more and 4.15 mass% or less, Mn; 0.07 mass% or more and 0.60 mass% %: P: 0.15 mass% or less, S: 0.01 mass% or less, Al: 0.02 mass% or more and 4.0 mass% or less, Ti: 0.20 mass% or less, Cu: 3.0 mass% or less It is made of steel and has a composition that tends to cause cracks, but since the thickness ratio of equiaxed crystals to the slab thickness is 25% or more, cracks occur at the grain boundaries when bending stress is applied. This can be suppressed. Therefore, it is possible to suppress the occurrence of cracks and breaks during conveyance of the thin cast slab 1 to the coiler during casting, winding during winding, and edge cracks and breaking during cold rolling.

As described above, the scum weir, the method for producing a thin cast piece, the thin cast piece manufacturing apparatus, and the thin cast piece according to the embodiment of the present invention have been specifically described, but the present invention is not limited to this, Modifications can be made as appropriate without departing from the technical idea of the invention.
For example, in the present embodiment, the description has been made with the bender roll and the pinch roll provided, but the arrangement of these rolls and the like is not limited, and the design may be changed as appropriate. Further, the configuration of the tundish, the immersion nozzle, etc. is not limited to this embodiment, and the design may be changed as appropriate.

  In the present embodiment, C: 0.001 mass% or more and 0.055 mass% or less, Si: 0.10 mass% or more and 4.15 mass% or less, Mn: 0.07 mass% or more and 0.60 mass% or less, P: 0.15 mass% In the following, steels including S; 0.01 mass% or less, Al; 0.02 mass% to 4.0 mass%, Ti; 0.20 mass% or less, Cu; 3.0 mass% or less, were targeted. There is no limitation, and other steel materials may be targeted.

In the present embodiment, TiN, TiC, β-type SiC, MgO.Al ₂ O ₃ , MgO, and Rem ₂ O ₃ are exemplified as solidification nucleation promoting substances. However, the present invention is not limited to this, and ferrite Another substance having a lattice matching degree with iron of 6% or less may be used.
Although the explanation has been made assuming that the atmosphere between the scum weir and the cooling drum is Ar gas, the present invention is not limited to this, and another gas atmosphere may be used.

Below, in order to confirm the effect of this invention, the comparative experiment result implemented by changing the composition of the refractory material which comprises a scum weir is demonstrated.
Here, in all the refractory materials described later, the maximum particle size of carbon particles was 300 μm or less, the average particle size was 100 μm or less, and the maximum particle sizes of oxide, carbide, and nitride were 100 μm or less and the average particle size was 50 μm or less.

  In the apparatus for manufacturing a thin cast slab shown in FIGS. 1 and 2, C: 0.05 mass%, Si: 0.15 mass%, Mn: 0.6 mass% using a scum weir having the composition shown in Tables 1 and 2 P: 0.1 mass%, S: 0.007 mass%, Al: 0.038 mass%, Cu: A thin-walled slab made of steel containing 1.5 mass% was cast under the following conditions.

Diameter of cooling drum: 1200mm
Casting speed: Average 50m / min
Casting width: 1300mm
Scum weir immersion depth: 15 mm
Flow velocity between the scum weir / cooling drum: 20 cm / sec or more Flow velocity of molten steel facing the scum weir on the nozzle side: 15 cm / sec or more Superheat degree in the molten steel pool: 25 ° C target, within a range of 20-30 ° C Casting atmosphere: Ar
Casting thickness: Average 3.0mm
Casting amount: 10ton

Here, in Tables 3 and 4, the total mass% of the solidification nucleation promoting substances whose lattice matching with ferrite iron is 6% or less is indicated as p. In addition, p was calculated by the following formula.
p =% TiN +% TiC +% β-SiC +% MgO ・ Al ₂ O ₃ +% MgO +% Rem ₂ O ₃
Moreover, in Table 3 and Table 4, the total mass% of the metal oxide was displayed as q. In addition, q was computed with the following formula | equation.
q =% Al ₂ O ₃ +% SiO ₂ +% ZrO ₂ + (other oxides) +% MgO · Al ₂ O ₃ +% MgO +% Rem ₂ O ₃

(Ratio of equiaxed crystals in thin-walled slabs)
The ratio of equiaxed crystals of the obtained thin cast slab was measured. Observe the solidification structure of the slab 1/4 width, 1/2 width, and 3/4 width section, and calculate (equal axis thickness) / (total slab thickness) × 100 (%) at each position. The average value of three locations was used as a representative value. The evaluation results are shown in Tables 3 and 4.

(Evaluation of scum weir resistance)
The scum weir after the completion of casting was collected, and the case where the maximum value of the erosion depth after casting on one side was 0.5 mm or more was rated as x, and the case where it was less than 0.5 mm was marked as ○. The evaluation results are shown in Tables 3 and 4.

(Evaluation of thermal shock resistance of scum weir)
The scum weir after the completion of casting was collected, and the case where a crack of 3 mm or more in length was seen on the surface of the scum weir was rated as x, and the case other than that was marked as ◯. In many cases, cracks often occur at the corner of the scum weir tip. The evaluation results are shown in Tables 3 and 4.

In Comparative Example 28 in which the carbon content was less than 3%, the thermal shock resistance was insufficient, and cracks occurred in the scum weir after casting.
In Comparative Example 29 in which the carbon content was more than 15%, decarburization progressed during casting, and the scum weir depth after casting was 0.5 mm or more.
In Comparative Examples 30 to 38 in which the total amount p of nucleation promoting substances was less than 5 mass%, the ratio of equiaxed crystals did not reach 25%.
In Comparative Example 39, in which the total amount q of the metal oxide was less than 55 mass%, the resistance to melting loss was insufficient.
In Comparative Example 40 in which the total amount q of the metal oxide was over 95 mass%, the thermal shock resistance was insufficient.

On the other hand, in the inventive examples 1 to 27, the ratio of equiaxed crystals was high, and the melt resistance and thermal shock resistance were excellent.
Inventive Examples 20 to 27 are selected from (a) one or more materials selected from TiN and TiC, and (b) MgO.Al ₂ O ₃ , MgO, and Rem ₂ O _3. A refractory to which one or more of the substances are added in combination is used.
Compared with the case where p (total mass% of coagulation nucleation promoting substances) is the same, compared to the case where only the substance selected from (a) above or only the substance selected from (b) above is added ( When the substances selected from a) and (b) are added together, it is confirmed that the ratio of equiaxed crystals is increased.

  Specifically, while the ratio of equiaxed crystals of Invention Examples 1, 5, 7, 11, 13, and 15 in which p = 5 mass% is less than 30%, Invention Examples 20, 21, The ratio of 25 equiaxed crystals is 36% or more. Further, the ratio of equiaxed crystals in Invention Example 18 in which p = 60 mass% is 67%, whereas the ratio of equiaxed crystals in Invention Examples 24 and 27 is 74% or more.

Next, the composition of the refractory material constituting the scum weir was fixed, and the effect on various steel types was evaluated.
The composition of the refractory constituting the scum weir includes C: 10 mass%, Al ₂ O ₃ ; 75 mass%, TiN: 11 mass%, TiO ₂ ; 4 mass% shown in Invention Example 2 of Example 1. did. The particle size of the raw material for the scum weir was defined as shown in Tables 5 and 6.

The composition of the steel type was specified as shown in Tables 5 and 6.
Invention Examples 101 to 104 are copper-containing high-phosphorus low-carbon steels, and the atmosphere and the molten steel pool superheat degree were changed.
Invention Examples 105 to 107 and Comparative Examples 120 and 121 are high Al steel, and the degree of superheat was changed.
Invention Examples 108 to 114 and Comparative Examples 122 to 124 are high Si steels, and the atmosphere, superheat, flow rate, and particle size of the refractory material powder were changed.
Invention Examples 115 to 119 and Comparative Examples 125 and 126 are highly fragile steel types containing high Si, high P, high Al, and high Cu, and the atmosphere and superheat degree were changed.
The casting conditions other than the conditions shown in Table 2 were the same as those in Example 1.

(Velocity of molten steel)
The flow rate of molten steel during casting was measured. In Tables 7 and 8, the flow velocity between the scum weir and the cooling drum or the flow velocity of the molten steel facing the immersion nozzle side of the scum weir is the lower one. In addition, it computed from the moving speed of the scum which floats on the molten steel surface in the molten metal surface monitor image.

(Evaluation of metal adhesion)
The scum weir after casting was observed, and the case where a metal bar with a maximum length of 5 mm or more was attached to the scum weir (both the surface on the immersion nozzle side and the surface on the cooling drum side) x 4 mm or less The case was marked with ○. The evaluation results are shown in Tables 7 and 8.

(Evaluation of operability)
When the metal core is wound between the cooling drums during casting and the space between the cooling drums is opened when passing through the drum kiss point, a local high-temperature slab part including an unsolidified part is generated. In the case, it was set as ○. The evaluation results are shown in Tables 7 and 8.

(Slab side crack)
After winding the coiler, it was cooled to room temperature, and then the slab was rewound to investigate the presence of transverse cracks. The case of 1 or more per 1 m of slab length was evaluated as x and the case of less than 1 was evaluated as ◯. The evaluation results are shown in Tables 7 and 8.

(Crack of cold-rolled sheet)
The part where there was no transverse crack was cold-rolled at a reduction rate of 67%, and the case where a transverse crack with a length of 100 mm or more occurred was marked as x, and the case where it did not occur was marked as ◯. The evaluation results are shown in Tables 7 and 8.

(Cold rolled sheet surface)
When the surface of the cold-rolled sheet is visually observed, when 3 or more surface wrinkles of 5 mm or more are generated per 1 m in length, × when 1 or more and less than 3 are generated, ○ when less than 1 evaluated. The evaluation results are shown in Tables 7 and 8.

In Comparative Example 122, since the flow rate of the molten steel facing the scum weir on the nozzle side was less than 10 cm / second, the metal was attached to the scum weir, peeled off during operation, and caught between the cooling drums. Part occurred.
In Comparative Examples 120 and 125, since the superheat degree of the molten steel pool exceeded 30 ° C, the ratio of equiaxed crystals was less than 25%. Therefore, the slab transverse crack and the cold rolled sheet crack occurred, Evaluation was also x.
In Comparative Examples 121 and 126, the degree of superheat of the molten steel pool portion was less than 3 ° C., so that the metal was attached to the surface of the scum weir, and the evaluation of metal adhesion was x. And since the local high temperature part including the non-solidified part generate | occur | produced by involving the bullion during operation, the operability was x.
In Comparative Examples 123 and 124, the particle diameter of the refractory raw material exceeds the specified range, and due to the coarse particles that fall off during casting and are wound into the slab, the length of the cold rolled sheet is 5 mm or more. Since surface flaws occurred, the cold-rolled plate surface flaws were x.

  On the other hand, in this invention example 101-119, there was no adhesion of a big metal, and operativity was also favorable. Further, the ratio of equiaxed crystals was high, and the evaluation of the lateral crack of the slab, the crack of the cold-rolled plate, and the surface defect of the cold-rolled plate was also good.

  From the above results, according to the scum weir, the method for producing a thin-walled slab and the apparatus for producing a thin-walled slab according to the present invention, the ratio of equiaxed crystals can be improved and the occurrence of cracks and the like can be suppressed. It was confirmed that a quality thin-walled slab could be produced.

DESCRIPTION OF SYMBOLS 1 Thin-walled slab 3 Molten steel 5 Solidified shell 10 Thin-walled slab manufacturing apparatus 11 Cooling drum 15 Side weir 16 Molten steel pool part 19 Immersion nozzle 20 Scum weir

Claims (7)

A molten steel is supplied to a molten steel reservoir formed by a pair of rotating cooling drums and a pair of side weirs through an immersion nozzle, and a solidified shell is formed and grown on the peripheral surface of the cooling drum to produce a thin cast slab. A scum weir used in a method for manufacturing a thin-walled slab,
The total content of one or more solidification nucleation promoting substances having a carbon content of 3 mass% or more and 15 mass% or less and a lattice matching degree with ferrite iron of 6% or less is 5 mass% or more and 97 mass% or less. The scum weir is characterized in that the total content of one or more metal oxides is 55 mass% or more and 95 mass% or less. 2. The solidification nucleation promoting substance contains one or more selected from TiN, TiC, β-type SiC, MgO.Al ₂ O ₃ , MgO, and Rem ₂ O _3. Scum weir as described in As the coagulation nucleation promoting substance, together TiN, and one or more selected from _{TiC, MgO · Al 2 O 3} , MgO, and one or more selected from _Rem 2 _{O 3,} the The scum weir according to claim 1, wherein the scum weir is contained.   2. The scum weir according to claim 1, wherein the solidification nucleation promoting substance and the metal oxide have a maximum particle size of 100 μm or less and an average particle size of 50 μm or less. A pair of rotating cooling drums is supplied to the molten steel pool formed by a pair of side weirs through an immersion nozzle, and a solidified shell is formed and grown on the peripheral surface of the cooling drum to produce a thin cast slab. A method for producing a thin slab comprising:
The scum weir according to any one of claims 1 to 4 is disposed in the molten steel pool portion,
While setting the superheat degree of the molten steel measured between the immersion nozzle and the scum weir within a range of 3 ° C. or more and 30 ° C. or less,
A method for producing a thin cast slab, wherein a flow rate of the molten steel on the surface of the scum weir is 10 cm / sec or more.   The method for producing a thin cast slab according to claim 5, wherein an atmosphere between the scum weir and the cooling drum is Ar. A molten steel is supplied to a molten steel reservoir formed by a pair of rotating cooling drums and a pair of side weirs through an immersion nozzle, and a solidified shell is formed and grown on the peripheral surface of the cooling drum to produce a thin cast slab. An apparatus for producing thin-walled slabs,
The scum weir according to any one of claims 1 to 4 is disposed in the molten steel pool part.

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