JP7389341B2 - Method for producing thin slabs - Google Patents

Description

The present invention supplies molten metal to a molten metal pool formed by a pair of rotating cooling drums and a pair of side weirs, and forms and grows a solidified shell on the circumferential surface of the cooling drums to produce thin slabs. The present invention also relates to a method for manufacturing a thin cast slab, in which the thin cast slab is conveyed by a conveyance unit equipped with pinch rolls that clamp the thin cast slab.

As a method for producing thin metal slabs, a cooling drum having an internal water cooling structure is provided, molten metal is supplied to a molten metal pool formed between a pair of rotating cooling drums, and the peripheral surface of the cooling drum is A twin-drum continuous casting method in which a solidified shell is formed and grown on the outer peripheral surfaces of a pair of cooling drums, and the solidified shells formed on the outer peripheral surfaces of a pair of cooling drums are joined at the drum kiss point and rolled down to produce a thin slab of a predetermined thickness. Equipment is provided.
The thin slab produced downward from between the cooling drums is bent at the curved section, and is conveyed in a substantially horizontal direction by a conveyor section having pinch rolls that vertically pinch the thin slab, and is transferred to an in-line mill as necessary. It is rolled by a coiler and wound by a coiler.

When starting casting in the above-mentioned twin-drum continuous casting apparatus, one end of the dummy sheet placed in the conveyance section is sandwiched between the cooling drums, as shown in Patent Documents 1 and 2, for example. The cooling drum is rotated while supplying molten metal to the molten metal pool formed by the drum and a pair of side weirs to form a thin slab so as to be connected to the dummy sheet, and the dummy sheet and this slab are poured from between the cooling drums. The thin cast slab connected to the dummy sheet is pulled out, the thin cast slab is conveyed by the conveyance section, and is wound up by the coiler.

By the way, when a dummy sheet is used as described above, it is necessary to place the dummy sheet in the conveying section and coiler before starting casting, and also to place one end of the dummy sheet between the cooling drums, which increases the work load. growing.
In addition, since the casting conditions are not stable at the beginning of casting, the strength of the thin slab formed to connect to the dummy sheet is insufficient, and the thin slab may break when the dummy sheet is pulled out. There were times when a problem occurred and casting could not be started.
Furthermore, if a trouble occurs in a conveying section or the like during casting, the casting cannot be restarted after being temporarily interrupted, and the casting itself has to be stopped.

Therefore, there is a need for a method for manufacturing thin slabs that can start casting without using a dummy sheet.
Here, in order to start casting without using a dummy sheet, it is necessary to feed the thin slab drawn out from between the cooling drums directly to the conveying section. However, since the casting conditions are not stable at the start of casting, an unsteady portion is formed in the thin slab. In this unsteady part, there are burrs on the edges and unevenness on the surface, so it is very difficult to send the material as it is to the conveying part.

Therefore, it is required to cut the thin slab directly below the cooling drum and remove the unsteady portion.
Normally, cutting devices such as shears are used to cut thin plates, but thin slabs directly under the cooling drum are fragile at high temperatures, and furthermore, because no tension is applied, existing cutting devices cannot cut thin sheets. It was not possible to stably cut the thin slab, and it was not possible to form a straight cut end extending in the width direction of the thin slab.

Therefore, for example, Patent Document 3 discloses that by instantly opening the gap between the cooling drums at the start of casting, the pressure bonding of the solidified shells is locally weakened by a length of about 20 to 30 mm in the casting direction. There is a method of sandwiching molten metal to form a bulge-like thin slab, using the sensible heat of the molten metal to raise the temperature of the bulge, weakening the strength, and cutting the thin slab using its own weight. Proposed.

Japanese Patent Application Publication No. 57-058957 Japanese Unexamined Patent Publication No. 63-224847 Patent No. 3007941

By the way, as described in Patent Document 3, when adjusting the interval between cooling drums to form a bulge at the start of casting, it is necessary to move the cooling drum with a large inertial mass at a relatively high speed. In addition, the driving device for the cooling drum becomes complicated, and in order to precisely control the operation of the cooling drum, high rigidity of the mechanical system and precise sensors and control devices are required, which increases equipment costs. there were. Moreover, since the drum interval is changed rapidly, it is difficult to maintain the drum reaction force (slab rolling force) appropriately, and there is a fear that stable casting cannot be performed.

The present invention has been made in view of the above-mentioned situation, and uses a relatively simple structure without using a complicated mechanism to cut a thin cast slab directly below a cooling drum, and cut a thin slab in a straight line extending in the width direction. It is an object of the present invention to provide a method for producing a thin cast slab in which a thin cast slab in a stationary section having a cut end formed therein can be sent to a conveying section, and casting can be carried out stably.

In order to solve the above problems, a method for manufacturing a thin slab according to the present invention supplies molten metal to a molten metal pool portion formed by a pair of rotating cooling drums and a pair of side weirs, and A method for manufacturing a thin slab, in which a thin slab is manufactured by forming and growing a solidified shell on the peripheral surface, and the thin slab is transported by a conveying unit equipped with pinch rolls that pinch the thin slab , the method comprising: A dummy sheet is not disposed between the cooling drums, and when the thin slab cast at the start of casting is cut, a base metal is generated in the molten metal pool, and this base metal is passed between the pair of cooling drums. By winding the cooling drums between them, the cooling drums are temporarily spaced apart, thereby forming an enlarged plate thickness part in the thin slab, and the self-weight of the thin slab is formed on the lower side of the pair of cooling drums. The thin slab is cut at the thickened section, and the thin slab cast after cutting is conveyed while being held between the pinch rolls.

According to the method for manufacturing a thin slab having this configuration, a base metal is generated in the molten metal pool portion, and the base metal is rolled up between the pair of cooling drums, thereby temporarily separating the gap between the pair of cooling drums. As a result, an enlarged plate thickness portion extending in the width direction is formed in the thin slab, and the strength of the region where the thickened plate portion is formed is locally reduced. Therefore, due to the weight of the portion of the thin slab located below the thickened section, the thin slab can be cut along the thickened section, and a straight line extending in the width direction can be cut. A sharp cut edge can be formed.
Thereby, the thin slab from which the unsteady portions have been removed can be sent to the conveyance section, and it becomes possible to stably perform casting.
In addition, since the cooling drum interval is temporarily separated by rolling in the bare metal, by controlling the normal drum reaction force, it is possible to stably form thickened parts and cast steady parts. equipment costs will not increase significantly.

Here, in the method for manufacturing a thin slab of the present invention, it is preferable that the base metal is generated in a region within 30 mm from the widthwise end of the molten metal pool portion.
The area near the surface of the molten metal at the widthwise end of the molten metal pool is an area where the temperature tends to drop as heat is radiated to the cooling drum, side weir, and outside air, so it is relatively easy to generate bullion. , it becomes possible to form thickened parts with good responsiveness.

Moreover, in the method for manufacturing a thin slab of the present invention, a structure may be adopted in which a base metal is generated by introducing a base metal generating material into the molten metal pool.
In this case, by putting the bullion generating material into the molten metal pool, bullion can be reliably generated.

Furthermore, in the method for manufacturing a thin slab of the present invention, the metal generating material may be a metal material having the same composition as the thin slab.
In this case, by charging a metal material having the same composition as the thin slab into the molten metal pool, the temperature of the molten metal can be locally lowered and bare metal can be generated. Since the metal material has the same composition as the thin slab, it does not affect the composition of the thin slab.

Further, in the method for manufacturing a thin slab of the present invention, the molten metal in the molten metal pool may be locally cooled to generate a base metal.
In this case, by locally cooling the molten metal in the molten metal pool, metal can be reliably generated.

Further, in the method for manufacturing a thin slab of the present invention, the molten metal in the molten metal pool may be cooled by liquefied gas.
In this case, by dropping the liquefied gas into the molten metal pool, it is possible to locally cool the molten metal and reliably generate metal.

As described above, according to the present invention, a thin slab is cut directly below the cooling drum using a relatively simple configuration without using a complicated mechanism, and a straight cut end extending in the width direction is formed. It becomes possible to provide a method for manufacturing a thin-walled slab in which the thin-walled slab in the stationary section can be sent to the conveying section, and casting can be performed stably.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic explanatory drawing which shows an example of the twin drum type continuous casting apparatus in embodiment of this invention. FIG. 2 is an explanatory side view of the vicinity of a molten steel pool in the twin-drum continuous casting apparatus shown in FIG. 1. FIG. FIG. 2 is an explanatory top view of the vicinity of a molten steel pool in the twin-drum continuous casting apparatus shown in FIG. 1; FIG. 3 is an explanatory diagram showing a procedure for cutting a thin slab at the start of casting. FIG. 3 is an explanatory diagram showing a procedure for cutting a thin slab when restarting casting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a thin slab according to an embodiment of the present invention will be described below with reference to the attached drawings. Note that the present invention is not limited to the following embodiments.
Here, the thin slab 1 manufactured in this embodiment is made of steel of various compositions, for example, 0.001 to 0.01% C ultra low carbon steel, 0.02 to 0.05% C low carbon steel , 0.06~0.4% C medium carbon steel, 0.5~1.2% C high carbon steel, austenitic stainless steel represented by SUS304 steel, ferritic stainless steel represented by SUS430 steel, 3 Examples include .0 to 3.5% Si oriented electrical steel, 0.1 to 6.5% Si non-oriented electrical steel, etc. (% is mass %).
Further, in this embodiment, the width of the thin slab 1 to be manufactured is within the range of 500 mm or more and 2000 mm or less, and the thickness is within the range of 1 mm or more and 5 mm or less.

As shown in FIG. 1, the twin-drum continuous casting apparatus 10 of this embodiment includes a pair of cooling drums 11, and a thin slab 1 produced on the lower side of the cooling drum 11 whose traveling direction is approximately horizontal. It is provided with a curved part 17 that curves toward , and a conveying part 20 that conveys the thin slab 1 in a substantially horizontal direction.
In the present embodiment, the curved section 17 has a "curved shape" in which the thin slab 1 produced below the cooling drum 11 is directly curved and connected to the conveyance section 20 . Further, a slab guide portion 18 is provided in the curved portion 17 to guide the thin slab 1 to the conveyance device.

The conveyance unit 20 includes a pinch roll 21 that vertically pinches and conveys the thin slab 1, a conveyance roll 22, a looper 23, and a coiler 24 that winds up the thin slab 1.
Here, the pinch roll 21 is a drive roll that is driven to rotate, and the conveyance roll 22 is a driven roll that rotates as the thin slab 1 moves.

As shown in FIGS. 2 and 3, the twin-drum continuous casting apparatus 10 of this embodiment has side weirs 12, 12 disposed at the widthwise ends of a pair of cooling drums 11, 11. A molten steel pool portion 13 is formed by the pair of cooling drums 11, 11 and the side weirs 12, 12.
Further, above the pair of cooling drums 11, 11, there is a tundish 14 that holds molten steel 5 to be supplied to the molten steel pool section 13, and an immersion nozzle that supplies molten steel 5 from this tundish 14 to the molten steel pool section 13. 15 are arranged.
Note that a chamber 16 is provided above the pair of cooling drums 11, 11 so as to cover the surface of the molten steel pool portion 13.

Here, when the molten steel surface of the molten steel pool section 13 is viewed from vertically above, as shown in FIG. The immersion nozzle 15 is arranged in the center of the rectangular hot water surface.
As shown in FIG. 3, the molten steel 5 near the surface of the molten steel pool portion 13 flows from the immersion nozzle 15 toward the circumferential surface of the cooling drum 11, and flows along the circumferential surface of the cooling drum 11 through a pair of side weirs. Each flows to the 12th side. The contact point between the cooling drum 11 and the side weir 12 is a dead zone for the flow of the molten steel 5, and becomes an area (stagnation area) D where the molten steel 5 does not flow sufficiently and stagnates.

Next, a method for manufacturing thin slab 1 using the above-mentioned twin-drum continuous casting apparatus 10 will be described.

The molten steel 5 is supplied from the tundish 14 through the immersion nozzle 15 to the molten steel pool portion 13 formed by the pair of cooling drums 11, 11 and the side weirs 12, 12, and the pair of cooling drums 11, 11 are rotated in the rotation direction. The cooling drums 11, 11 are rotated in the direction R, that is, in such a manner that the area where the pair of cooling drums 11, 11 are close to each other is directed in the drawing direction of the thin slab 1 (downward in FIG. 2). .

Then, a solidified shell 7 is formed on the circumferential surface of the cooling drum 11. Then, the solidified shell 7 grows on the circumferential surface of the cooling drum 11, and the solidified shells 7, 7 formed on the pair of cooling drums 11, 11 are pressed together at the drum kiss point P, so that a predetermined thickness is achieved. A thin slab 1 is cast.

Here, at the start of casting, the molten steel 5 is supplied to the molten steel pool portion 13 without disposing a dummy sheet between the cooling drums 11, 11, and the rotation of the cooling drums 11, 11 is started. Note that the cooling drums 11, 11 may be activated at the same time as the start of supply of the molten steel 5, or at the time when the molten metal level in the molten steel pool portion 13 reaches an arbitrary height. The activation timing of the cooling drums 11, 11 is preferably set using a sensor that detects the molten steel 5, a timer, and the like.

As a result, the thin slab 1 that is cast at the start of casting has unstable casting conditions and becomes an unsteady part with burrs at the ends and unevenness on the surface. Then, when the molten steel level in the molten steel pool portion 13 reaches a certain level and the casting conditions become stable, a thin slab 1 of a steady portion with a stable shape is obtained.
Therefore, in this embodiment, the thin slab 1 is cut on the lower side of the cooling drums 11, 11 to eliminate the unsteady portion.

In this embodiment, when cutting the thin slab 1, a base metal is generated in the molten steel pool portion 13, and this base metal is rolled up between the pair of cooling drums 11, 11. Then, when the bare metal is rolled in, the gap between the cooling drums 11, 11 increases instantaneously, and a thickened section 3 (hereinafter referred to as an artificial hot band 3) is formed in the thin slab 1. Become. This artificial hot band 3 is a region where the temperature is high and the intensity is locally weak.
Then, as shown in FIG. 4(a), the thin slab 1 is cut at the artificial hot band 3 due to its own weight.

After removing the cut unsteady parts, as shown in FIG. Piece 1 (stationary part) is guided to pinch rolls 21, 21.
Then, as shown in FIG. 4(c), the thin slab 1 is conveyed while being held between pinch rolls 21, 21.

Further, during casting, if a trouble occurs, for example, in the conveying section 20, the casting is temporarily interrupted, the above-mentioned trouble is resolved, and then the casting is restarted.
In such a case, as shown in FIG. 5(a), first, when the casting is temporarily interrupted, metal is generated in the molten steel pool 13, and this metal is transferred to the pair of cooling drums 11, 11. An artificial hot band 3 is formed on the thin slab 1 by rolling it between the thin slabs 1 and the thin slab 1 is cut at the artificial hot band 3 by the weight of the thin slab 1.

Next, as shown in FIG. 5(b), after the trouble in the conveyance section 20 is resolved, the thin slab 1 located on the conveyance section 20 side is conveyed to the coiler 24 side.
Then, casting resumes. At this time, in order to cut and remove the unsteady part until the casting is stabilized, metal is generated in the molten steel pool part 13, and this metal is rolled up between the pair of cooling drums 11, 11. An artificial hot band 3 is formed on a thin slab 1, and the thin slab 1 is cut at the artificial hot band 3 by its own weight.

After removing the cut unsteady parts, as shown in FIG. The piece 1 (stationary part) is guided to the pinch rolls 21, 21, and the thin slab 1 is conveyed while being held between the pinch rolls 21, 21.

Here, a method for generating metal in the molten steel pool portion 13 in order to form the artificial hot band 3 will be described.
As shown in FIG. 3, in the stagnation area D where the molten steel 5 does not flow sufficiently and stagnates in the molten steel pool section 13, heat is taken away from the cooling drum 11, the side weir 12, and the molten metal surface, so the temperature of the molten steel 5 decreases. It tends to drop and bullion is likely to occur.
For this reason, in this embodiment, it is preferable to generate metal in a region within 30 mm from the widthwise end of the molten steel pool portion 13, which is the stagnation region D.

One of the means for generating bullion is to introduce a metal generating material into the molten steel pool section 13.
As the metal generating material, metal materials having the same components as the thin slab 1, high melting point metals, refractories such as alumina wool, and composite materials thereof can be used. When these metal-generating materials are thrown into the molten steel pool section 13, the molten steel 5 in the charged portion solidifies on the circumferential surface of the metal-generating materials to generate bullion.

Here, in order to reliably form the artificial hot band 3 and perform casting stably, the size of the generated metal material is 0.5 mm or more and 5 mm or less in thickness, 5 mm or more and 30 mm or less in width, and length It is preferably 10 mm or more and 50 mm or less. This metal generating material is thrown into at least one or more locations of the molten pool portion 13 within 0.1 seconds.
In addition, it is preferable that the metal-generating material is introduced into an area within 30 mm from the end of the molten steel pool section 13 in the width direction.

Moreover, as another means for generating ingots, locally cooling the molten steel 5 in the molten steel pool portion 13 can be mentioned.
For example, by dropping liquefied gas or spraying cooling gas, it is possible to locally cool the molten steel 5 in the molten steel pool portion 13 and generate metal.

Here, in order to reliably form the artificial hot band 3 and perform casting stably, the amount of liquefied gas to be dropped is preferably 5 cc or more and 50 cc or less, and the amount of cooling gas is 0.5 Nl or more and 5 Nl or less. preferable. This amount is poured into at least one or more locations of the melt pool section 13 within 0.1 seconds.
Note that cooling of the molten steel 5 is preferably carried out in an area within 30 mm from the widthwise end of the molten steel pool portion 13.

Here, from the viewpoint of protecting the cooling drum 11 when bullion is rolled up, the situation of metal generation (metal generation It is preferable to adjust the input amount of materials and cooling conditions).
Note that the lower limit of the fluctuation value of the reaction force of the cooling drum 11 may be within a range in which the thin slab 1 can be reliably cut by the artificial hot band 3, and there is no particular lower limit, but it is usually 0.5 tonf. It is preferable that it is above.

According to the method for manufacturing the thin slab 1 of this embodiment configured as described above, a base metal is generated in the molten steel pool portion 13, and this base metal is rolled up between the pair of cooling drums 11, 11. By this, the pair of cooling drums 11, 11 are temporarily spaced apart, and an artificial hot band 3 extending in the width direction of the thin slab 1 is formed. Since the strength of the region where the artificial hot band 3 is formed is locally low, the thin slab 1 is formed into the artificial hot band 3 by the weight of the portion of the thin slab 1 located below the artificial hot band 3. It becomes possible to cut along the width direction, and a straight cut edge extending in the width direction can be formed.
Thereby, the thin slab 1 from which unsteady portions have been removed can be sent to the conveyance section 20, and stable casting can be performed.
In addition, since the interval between the pair of cooling drums 11, 11 is widened by involving the bare metal, the formation of the artificial hot band 3 and the casting of the stationary part can be stabilized by controlling the normal drum reaction force. can be done without significantly increasing equipment costs.

Here, in the method for manufacturing the thin slab 1 according to the present embodiment, when the bare metal is generated in an area within 30 mm from the widthwise end of the molten steel pool portion 13, the raw metal can be generated relatively easily. The artificial hot band 3 can be formed accurately, and the thin slab 1 can be precisely cut at a desired position.

In addition, in the method for manufacturing the thin-walled slab 1 according to the present embodiment, when a configuration is adopted in which the base metal is generated by introducing a base metal generating material into the molten steel pool portion 13, the base metal is generated reliably. The artificial hot band 3 can be formed accurately and the thin slab 1 can be cut by its own weight.

Here, when a metal material having the same composition as the thin slab 1 is used as the metal generating material, it is possible to reliably generate the metal and eliminate the influence on the composition of the thin slab 1. I can do it.

Furthermore, in the method for manufacturing thin slab 1 according to the present embodiment, if the molten steel 5 in the molten steel pool 12 is locally cooled to generate metal, the metal can be reliably generated. The artificial hot band 3 can be formed accurately and the thin slab 1 can be cut by its own weight.
Here, if the molten steel 5 in the molten steel pool portion 13 is cooled by liquefied gas, it is possible to reliably generate metal.

Although the method for manufacturing the thin slab 1 which is an embodiment of the present invention has been specifically described above, the present invention is not limited to this and can be modified as appropriate without departing from the technical idea of the invention. It is.

Below, the results of experiments conducted to confirm the effects of the present invention will be explained.

Using the apparatus for manufacturing a thin slab described in the embodiment, a cast slab containing 0.05 mass% of C, 0.6 mass% of Si, 1.5 mass% of Mn, and 0.03 mass% of Al, with the balance being Fe and unavoidable A thin slab made of steel with a composition containing impurities was cast under the following conditions.

(Casting conditions)
Cooling drum diameter: 800mm
Cooling drum width: 1000mm
Thickness of thin slab: 2.5mm
Casting speed: 50mpm

<Example 1>
As a metal generating material, low carbon steel hoops with a width of 20 mm, a thickness of 0.7 mm, and a length of 30 mm are simultaneously added to positions 25 mm from both ends of one of the cooling drums to generate metal. An artificial hot band was formed by rolling it between cooling drums.
As a result, the thin slab was cut under its own weight under the cooling drum. The cut surface was straight along the width direction of the thin slab.

<Example 2>
By dropping 20cc of liquid Ar onto the molten steel surface (4 corners) within 30mm from the contact point between the cooling drum and side weir, a base metal is generated, and this base metal is rolled up between the cooling drums to create an artificial hot band. was formed.
As a result, the thin slab was cut under its own weight under the cooling drum. The cut surface was straight along the width direction of the thin slab.

From the above, according to the present invention, a thin slab is cut directly below the cooling drum using a relatively simple configuration without using a complicated mechanism, and a straight cut end extending in the width direction is formed. It has been confirmed that it is possible to provide a method for manufacturing a thin-walled slab in which the thin-walled slab in the stationary section can be sent to the conveying section and casting can be performed stably.

1 Thin slab 3 Artificial hot band 5 Molten steel (molten metal)
11 Cooling drum 12 Molten steel pool section (molten metal pool section)
20 Transport section

Claims (6)

Molten metal is supplied to a molten metal pool formed by a pair of rotating cooling drums and a pair of side weirs, and a solidified shell is formed and grown on the circumferential surface of the cooling drum to produce a thin slab. A method for manufacturing a thin slab, the method comprising: transporting a thin slab by a conveying unit equipped with pinch rolls that sandwich the slab;
At the start of casting, no dummy sheet is placed between the cooling drums,
When cutting the thin slab cast at the start of casting , a base metal is generated in the molten metal pool, and this base metal is rolled up between a pair of cooling drums, thereby temporarily reducing the distance between the cooling drums. forming an enlarged plate thickness part in the thin slab by separating the thin slab, and cutting the thin slab at the thickened part by the weight of the thin slab below the pair of cooling drums;
A method for manufacturing a thin cast slab, characterized in that the thin cast slab cast after cutting is conveyed while being held between the pinch rolls. 2. The method for manufacturing a thin slab according to claim 1, wherein the base metal is generated in a region within 30 mm from an end in the width direction of the molten metal pool. 3. The method for manufacturing a thin slab according to claim 1, wherein the metal is generated by introducing a metal generating material into the molten metal pool. 4. The method for manufacturing a thin slab according to claim 3, wherein the metal-generating material is a metal material having the same composition as the thin slab. 3. The method for producing a thin slab according to claim 1, wherein the molten metal in the molten metal pool is locally cooled to generate base metal. 6. The method for manufacturing a thin slab according to claim 5, wherein the molten metal in the molten metal pool is cooled by liquefied gas.

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