JP2002273551A - Twin-roll type continuous casting method for continuously casting cast strip excellent in surface characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To continuously cast a cast strip excellent in the surface characteristic by restraining entrapment of deposited or floating scum on molten steel surface in a molten steel pool part between the peripheral surfaces of cooling rolls and solidified shells, in a twin-roll type continuous casting. SOLUTION: In the twin-roll type continuous casting method for continuously casting the cast strip while cooling and solidifying the molten steel on the peripheral surfaces of these cooling rolls by pouring the molten steel into the molten steel pool part formed with a pair of the cooling rolls having parallel axes and rotating to mutually reverse directions and side weirs, almost the whole range or a part of the molten steel surface in the molten steel pool part is covered with solid oxide. The solid oxide is made of solid phase of one or more of plate-like solid oxides or the scum. The solidification of the scum is made by blowing cooling gas to the scum and/or by adding a cooling- solidifying agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for injecting molten steel into a pool formed by a pair of cooling drums and side dams which rotate in opposite directions and are parallel to each other. The present invention relates to a twin-drum continuous casting method for continuously casting a ribbon slab having excellent surface properties while cooling and solidifying to form a solidified shell.

[0002]

2. Description of the Related Art In recent years, a technique for continuously casting thin strip slabs having excellent surface properties by twin-drum continuous casting has been established. By subjecting the strip slab to the required rolling, a product strip with excellent surface properties can be produced. However, there is a demand for the surface properties of product strips, especially for stainless steel product strips. There is a strict requirement, and in order to satisfy this requirement, it is necessary to produce a ribbon slab having better surface properties at the casting stage.

[0003] In the twin drum type continuous casting, in order to continuously cast a thin strip slab having excellent surface properties, a solidified shell pressed at a drum kiss point on the peripheral surfaces of a pair of cooling drums is stably provided. It is indispensable to grow the molten steel on the surface of the molten steel in the basin formed by the pair of cooling drums and side dams. It is inevitable that the scum (floating matter mainly composed of oxides) generated by the floating of the inclusions floats, and this scum flows along with the molten steel flowing with the rotation of the cooling drum, and flows around the cooling drum. Face to face,
When caught between the peripheral surface of the cooling drum and the solidified shell that is being formed, it causes surface defects such as surface roughness and cracks on the surface of the strip slab.

[0004] If the strip slab having the above-mentioned surface defects is rolled as it is, fatal defects (cracks, unevenness in gloss, etc.) will be induced as product ribbons. Many improvements and devices have been proposed to prevent the scum to be caught between the peripheral surface of the cooling drum and the solidified shell being formed. For example, Japanese Unexamined Patent Publication (Kokai) No. 61-162249 discloses that a casting surface (SiO ₂ , CaO, N
a ₂ O is covered with the main component), a continuous casting apparatus for casting a thin cast strip is disclosed while kept the surface of the molten steel. In this continuous casting apparatus, the molten steel surface is cut off from the surrounding atmosphere by the presence of the casting powder,
Although it is considered that the generation of scum due to the oxidation of the molten steel surface is suppressed to some extent, the casting powder does not prevent the scum from being caught between the peripheral surface of the cooling drum and the solidified shell being generated. .

Japanese Unexamined Patent Publication No. Hei 6-106304 discloses that a pair of scum floating in the axial direction of a cooling drum is provided in a basin to prevent scum floating on the surface of molten steel from being caught and caught in a solidified shell. A continuous casting apparatus for thin slabs in which the barrier is immersed and arranged apart from the cooling drum and the side weir is disclosed. In this continuous casting apparatus, the scum flows away from the cooling drum according to the flow of the molten steel discharged from the molten steel nozzle on the surface of the molten steel due to the existence of the above-mentioned “pair of barriers”. In the entire width region, the scum entrainment frequency is greatly reduced, but since the scum weir and cooling drum are far apart, scum often leaks from both ends of the barrier to the cooling drum side due to fluctuations in the molten metal flow. The effect of preventing entanglement cannot be obtained.

Japanese Unexamined Patent Publication No. 6-339754 also discloses that a side weir and a scum are provided on the molten steel surface of the pool in order to prevent the scum floating on the surface of the molten steel from being caught and caught in the solidified shell. We set up a space surrounded by weirs,
A continuous casting method in which a thin slab is cast by adding a flux that keeps the scum floating on the surface of molten steel in a molten state in the space is disclosed.

In the above continuous casting method, most of the molten steel surface is surrounded by the side weir and the scum weir, and the scum does not leak directly. However, since the scum is in the molten state, the surface flow of the molten steel is And get caught in the molten steel, resulting in leakage.
Japanese Patent Application Laid-Open No. 9-141397 discloses an apparatus for continuously casting thin cast slabs, which is provided with an absorbing plate for absorbing waving generated on the surface of molten steel in a basin and covers the entire surface of molten steel in the basin. A hot water surface protection cover is disclosed.

[0008] The above-mentioned molten metal surface protection cover also serves to block the molten steel surface from the surrounding atmosphere, and is considered to have an effect of suppressing the generation of scum due to oxidation of the molten steel surface to some extent. As with the casting powder described in Japanese Patent No. 162249, it does not prevent scum from being caught between the peripheral surface of the cooling drum and the solidified shell being formed.

Japanese Patent Application Laid-Open No. 2000-246402 discloses that even if a scum is caught between the peripheral surface of a cooling drum and a solidified shell being formed, the scum does not cause a surface defect. Having a solid fraction of 5 to 60
%, And a continuous casting method for casting a thin slab is disclosed. Although the adjustment of the scum composition described in the above publication has a remarkable effect in suppressing the occurrence of surface defects, it is assumed that the scum is caught between the peripheral surface of the cooling drum and the solidified shell being formed. When continuous casting is performed for a long time, the amount of scum increases.

As described above, in twin-drum continuous casting, there is still no sufficient measure to prevent scum from being caught between the peripheral surface of the cooling drum and the solidified shell being formed. It is. Furthermore, in recent years, twin-drum continuous casting tends to continue for a long time, but in continuous casting for a long time, scum is generated more than the conventional amount over time, and the molten steel surface It will accumulate and float on top. Therefore, there is a need for a measure for the scum more than ever so as to prevent the scum from being caught between the peripheral surface of the cooling drum and the solidified shell being formed.

[0011]

SUMMARY OF THE INVENTION In view of the above demand, the present invention is to inject molten steel into a basin formed by a pair of cooling drums and side weirs, whose shafts are parallel and rotate in opposite directions.
In the twin-drum continuous casting in which the molten steel is cooled and solidified on the peripheral surface of the cooling drum to continuously cast the thin strip while forming a solidified shell, scum deposited and suspended on the molten steel surface of the basin is More than ever, it is necessary to prevent entanglement between the peripheral surface of the cooling drum and the solidified shell being formed, to facilitate scum treatment, and to continuously cast thin strip slabs with excellent surface properties. Make it an issue.

[0012]

In order to solve the above-mentioned problems, the present inventor has set forth the relationship between the properties and form of scum deposited and floating on the surface of molten steel in a basin and defects appearing on the surface of a strip slab. We conducted an intensive investigation on As a result, it has been found that, when the scum is fixed, the defects appearing on the surface of the thin strip slab are reduced more than before, and the scum treatment becomes easier than before.

As a specific method of fixing the scum,
There are a method of attaching scum to some solid and a method of solidifying the scum itself, but in the present invention, either method is applicable. When scum is attached to some solid,
The scum need not necessarily be solid-phased. The solidification of part of the scum itself is described in JP-A-2000-2464.
As disclosed in Japanese Patent Application Publication No. 02-302, completely solidifying the scum may lower the temperature of the molten steel surface and promote the production of ingots. As, in particular, was not considered.

However, as a result of further investigation, the present inventor has found that if the scum is solidified in a partial region of the molten steel surface in the basin and / or the melting point of the scum is raised to a temperature equal to or higher than the molten steel temperature. It was found that the temperature of the molten steel surface did not drop so much and had no effect on continuous casting. The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) Molten steel is poured into a pool formed by a pair of cooling drums and side dams whose axes are parallel and rotate in opposite directions, and the molten steel is cooled and solidified on the peripheral surface of the cooling drum. A twin-drum continuous casting method for continuously casting a strip slab, wherein the molten steel surface in the basin is covered with a solid oxide, and the strip slab having excellent surface properties is continuously cast. Drum type continuous casting method.

(2) The twin-drum continuous casting method according to (1), wherein a part of the molten metal surface is covered with a solid oxide. (3) The twin-drum continuous casting method according to (2), wherein a part of the molten metal surface is a molten metal surface between two scum dams immersed and arranged in a basin portion. (4) The twin-drum continuous casting method according to (1), (2) or (3), wherein the solid oxide comprises one or more plate-like solid oxides.

(5) The dual oxide as described in (1), (2), (3) or (4), wherein the solid oxide is a plate-shaped solid oxide having voids of a predetermined shape. Drum type continuous casting method. (6) The solid oxide according to (1), wherein the solid oxide is an oxide obtained by solidifying scum floating on the surface of molten metal.
The twin-drum continuous casting method according to (2) or (3).

(7) The solid oxide comprises at least one solid oxide,
And / or a plate-shaped solid oxide having voids of a predetermined shape and / or an oxide in which scum is solidified, and the twin drum according to (1), (2) or (3) above. Continuous casting method. (8) When the solid oxide is CaO and / or Mg
The twin-drum continuous according to the above (1), (2), (3), (4), (5), (6) or (7), which is a solid oxide containing O as a main component. Casting method.

(9) The twin-drum continuous casting method according to (6) or (7), wherein a cooling gas is blown to the scum to solidify the scum. (10) The above (6) or (7), wherein a cooling and solidifying agent is added to the scum to solidify the scum.
The twin-drum continuous casting method described. (11) The twin-drum continuous casting method according to (6) or (7), wherein the scum is solidified by blowing a cooling gas while adding a cooling solidifying agent to the scum.

(12) The cooling and solidifying agent is powdered Ca
The twin-drum continuous casting method according to the above (10) or (11), comprising O, powdery MgO, and / or a mixture thereof.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the drawings. FIGS. 1 (a) and 1 (b) show almost the entire surface of molten steel in a pool formed by a pair of cooling drums 1 and side weirs 2 whose axes are parallel and rotate in opposite directions.
An embodiment covered with one sheet of solid oxide 3 is shown. In the figure, reference numeral 9 denotes an immersion nozzle.

In the present invention, when the surface of the molten steel is covered with the solid oxide, a part of the surface of the molten steel, for example, only the central portion or only the peripheral portion may be covered. Whether to cover the entire surface or a part of the molten steel surface in the basin can be appropriately selected according to the atmosphere surrounding the basin, casting conditions, and the like. As shown in FIG.
The plate-like solid oxide 3 blocks the molten steel surface from the atmosphere surrounding the basin, prevents oxidation of the molten steel surface, and causes the inclusions 5 that float from the inside of the molten steel to the surface to become scum,
Can be captured on the lower surface of the solid oxide 3;
Depending on the state of heat transfer of the solid oxide, the inclusions 5 can be solidified. In this way, the inclusions and / or scum can be fixed.

The solid oxide used in the present invention may be, for example, a combination of four plate-like solid oxides as shown in FIGS. When a plurality of plate-shaped solid oxides are used in combination, the shape of each solid oxide is arbitrary, and covers a required range of the molten steel surface in consideration of the atmosphere surrounding the basin, casting conditions, and the like. Any combination may be used.

In the embodiment shown in FIG. 2, inclusions 5 are trapped on the lower surface of each plate-like solid oxide 3 and, depending on the heat transfer state of the solid oxide, the inclusions 5 are solid-phased. Further, the scum 6 generated by the inclusions 5 floating between the plate-like solid oxides 3 is trapped between the plate-like solid oxides 3, and the scum 6 may be solid-phased depending on the heat transfer condition of the plate. Can be

Further, the plate-like solid oxide used in the present invention may have voids 10 of a predetermined shape, for example, as shown in FIGS. 3 (a) and 3 (b). The shape of the gap 10 is arbitrary, and the shape of the gap may be determined in consideration of the atmosphere surrounding the basin section, casting conditions, and the like so that the required range of the molten steel surface can be covered. In the embodiment shown in FIG. 3, inclusions 5 can be captured on the lower surface of the plate-shaped solid oxide 3, and depending on the heat transfer state of the plate, the inclusions 5 can be solidified. The scum 6 generated by the inclusions 5 floating in the gap 10 is captured, and the scum 6 can be solidified depending on the heat transfer condition of the plate.

Further, in the present invention, a plurality of plate-like solid oxides having voids of a predetermined shape can be used in combination. Further, in the present invention, when the surface of the molten steel is covered with the solid oxide, when the scum weir is immersed and arranged in the basin, the scum weir may be covered between the scum weir. FIGS. 4A and 4B illustrate an embodiment in which the surface of molten steel between two scum weirs 4 is covered with a single plate-like solid oxide 3.

Also in this case, as shown in FIG.
A plurality of plate-like solid oxides may be used in combination, or as shown in FIG. 3, a plate-like solid oxide having voids of a predetermined shape may be used. Furthermore, a plurality of plate-shaped solid oxides having voids of a predetermined shape may be combined to cover the surface of the molten steel between the two scum weirs 4.
In this case, combined with the effect of the scum weir, the inclusion 5 and the scum can be effectively captured and solidified.

As described above, the inclusions serving as scum are captured on the lower surface of the solid oxide and solidified and fixed depending on the heat transfer conditions of the solid oxide.
It is not caught between the peripheral surface of the cooling drum and the solidified shell, and further, the scum floating on the surface of the molten steel is also trapped between solid oxides or in voids, solidified depending on the heat transfer conditions, fixed. Similarly, it is not caught between the peripheral surface of the cooling drum and the solidified shell.

Further, when the solidified inclusions 5 are removed from the surface of the molten steel, the removal operation is easy. In the present invention, the solid oxide maintains a solid phase on the surface of the molten steel,
Any component can be used as long as it can cover at least a part of the surface, and its component composition is not particularly limited.
And / or a solid oxide containing MgO as a main component has a solid phase temperature much higher than the temperature of molten steel in the entire composition range, and a floating inclusion (CaO and / or MgO is mainly used). This is a preferred solid oxide because it has good wettability with the component (1), easily traps the inclusions, and can be easily solid-phased depending on heat transfer conditions.

As described above, in the present invention, the solid oxide may be any solid oxide as long as it can maintain a solid phase on the surface of the molten steel, and may be solid scum. In the present invention, in order to solidify the scum, a cooling gas is sprayed on the scum or a cooling solidifying agent is added. Further, the blowing of the cooling gas and the addition of the cooling solidifying agent may be used in combination.

FIGS. 5A and 5B show the cooling drum 1
An embodiment is shown in which a cooling gas 7 is blown between two scum weirs 4 to solidify and fix the scum 6 between the two scum weirs 4 in the basin formed by the side weirs 2. A liquid gas or a mixture of a solid phase and a liquid phase is deposited on a molten steel surface, and a cooling gas 7 is sprayed on the floating scum 6 to solidify the scum 6 between the scum weirs 4 and the scum is cooled. Avoid flowing to the drum side. As the cooling gas 7, a non-oxidizing gas is preferably used so as not to oxidize the molten steel.

6 (a) and 6 (b), a cooling and solidifying agent 8 is introduced between the two scum weirs 4 in the basin formed by the cooling drum 1 and the side weir 2, and the scum is formed. 6
An embodiment in which is immobilized by immobilizing is shown. The scum 6 is solidified by mixing the cooling and solidifying agent 8 with the scum 6 and adjusting the composition of the scum 6. The cooling and solidifying agent is powdered C
Preferably, it contains aO, powdered MgO, and / or a mixture thereof.

In the scum, powdered CaO, powdered MgO,
And / or by adding these mixtures to adjust the composition, the melting point is equal to or higher than the molten steel temperature, and the scum is solidified. The scum solidified in this manner functions as a solid oxide that covers the surface of the molten steel and captures the floating inclusions. The solidified scum, of course, has good wettability with the floating inclusions,
The inclusion can be easily captured.

Furthermore, in the present invention, one or more sheets
In the case where a plate-shaped solid oxide having voids of a predetermined shape is used (see FIGS. 2 and 3), blowing of a cooling gas and / or addition of a cooling solidifying agent may be used in combination. When a cooling gas is sprayed between the solid oxides or on the scum floating in the voids and / or a cooling solidifying agent is added to solidify the scum, the scum can be further fixed. it can.

As described above, various embodiments are possible in the present invention. Hereinafter, although an Example is described, the conditions concerning implementation of the present invention are not limited to the conditions described in an Example.

[0036]

EXAMPLE 1 When a SUS304 steel was continuously cast into a 4.0 mm-thick strip slab using a cooling drum having a width of 30 mm, the surface of the molten steel in the pool was mainly made of MgO (or CaO). Inclusions and scum were fixed by covering with a plate as a component. Further, a cooling gas was blown onto the molten steel surface of the basin in which the scum dam was immersed and arranged, or a cooling and solidifying agent was introduced to solidify and fix the scum.

Table 1 shows the surface properties of the obtained ribbon slab. Table 1 shows, as a comparative example, the surface properties of the strip slab in the case where the scum weir was immersed and arranged in the basin and continuous casting was performed, and in the case where the continuous casting was performed without using the scum weir. Show. From Table 1, it can be seen that in the invention examples, the surface properties of the thin strip slab were improved.

[0038]

[Table 1]

[0039]

According to the present invention, inclusions floating on the surface of molten steel in the basin and scum deposited and floating on the surface are captured, and in some cases, solidified and fixed, so that the scum is fixed. Is prevented from being caught between the peripheral surface of the cooling drum and the solidified shell, and a thin strip having excellent surface properties can be continuously cast for a long time.

Further, since the scum is solidified, the operation of removing the scum deposited and floating on the surface of the molten steel is facilitated.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment in which the surface of molten steel in a basin is covered with a single plate-like solid oxide. (A) is a figure which shows the cross section of a basin part, (b) is a figure which shows the molten steel surface of a basin part.

FIG. 2 is a view showing an embodiment in which the surface of molten steel in a basin is covered with a plurality of plate-like solid oxides. (A) is a figure which shows the cross section of a basin part, (b) is a figure which shows the molten steel surface of a basin part.

FIG. 3 is a view showing an embodiment in which the surface of molten steel in a basin is covered with a single plate-shaped solid oxide having a gap of a predetermined shape. (A) is a figure which shows the cross section of a basin part,
(B) is a figure which shows the molten steel surface of a basin part.

FIG. 4 is a view showing an embodiment in which a molten steel surface between two scum weirs is covered with a single plate-like solid oxide in a basin section. (A) is a figure which shows the cross section of a basin part, (b) is a figure which shows the molten steel surface of a basin part.

FIG. 5 is a view showing an embodiment in which a cooling gas is blown between two scum weirs to solidify the scum in the basin section. (A) is a figure which shows the cross section of a basin part, (b)
FIG. 4 is a view showing the surface of molten steel in a basin.

FIG. 6 is a view showing an embodiment in which a cooling and solidifying agent is charged between two scum weirs in a basin to solidify scum. (A) is a figure which shows the cross section of a basin part, (b)
FIG. 4 is a view showing the surface of molten steel in a basin.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Cooling drum 2 ... Side weir 3 ... Plate-shaped solid oxide 4 ... Scum weir 5 ... Inclusion 6 ... Scum 7 ... Cooling gas 8 ... Cooling and solidifying agent 9 ... Immersion nozzle 10 ... Void

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hideaki Kobayashi 3434 Shimada, Hikari-shi, Yamaguchi Prefecture Nippon Steel Corporation Hikari Works F-term (reference) 4E004 DA13 HA03 NB07 SB10

Claims (12)

[Claims] 1. A molten steel is poured into a basin formed by a pair of cooling drums and side dams whose axes are parallel to each other and rotate in opposite directions, and the molten steel is thinned while cooling and solidifying on the peripheral surface of the cooling drum. A twin-drum type continuous casting method for continuously casting a strip slab, wherein a molten steel surface in a basin is covered with a solid oxide, and a thin strip slab having excellent surface properties is continuously cast. Continuous casting method. 2. The twin-drum continuous casting method according to claim 1, wherein a part of the molten metal surface is covered with a solid oxide. 3. The twin-drum continuous casting method according to claim 2, wherein a part of the molten metal surface is a molten metal surface between two scum dams immersed and arranged in a basin portion. 4. The twin-drum continuous casting method according to claim 1, wherein the solid oxide comprises one or more plate-like solid oxides. 5. The twin-drum continuous casting method according to claim 1, wherein the solid oxide is a plate-shaped solid oxide having a void having a predetermined shape. 6. The twin-drum continuous casting method according to claim 1, wherein the solid oxide is an oxide obtained by solidifying scum floating on the surface of molten metal. 7. The solid oxide comprising one or more and / or plate-shaped solid oxides having voids of a predetermined shape,
4. The twin-drum continuous casting method according to claim 1, wherein the scum is made of solid-phased oxide. 8. The twin drum according to claim 1, wherein the solid oxide is a solid oxide containing CaO and / or MgO as a main component. Continuous casting method. 9. The twin-drum continuous casting method according to claim 6, wherein the scum is solidified by blowing a cooling gas onto the scum. 10. A cooling solidifying agent is added to the scum,
The scum is solid-phased.
The twin-drum continuous casting method described. 11. The twin-drum continuous casting method according to claim 6, wherein a cooling gas is blown onto the scum while a cooling solidifying agent is added thereto to solidify the scum. 12. The twin-drum continuous casting method according to claim 10, wherein the cooling and solidifying agent contains powdered CaO, powdered MgO, and / or a mixture thereof.