JPH0763725B2 - Series of continuous hot rolling equipment for unidirectional electrical steel sheets - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an equipment train for continuously hot rolling a continuously cast slab in a process for producing a steel sheet, and more particularly to a hot rolling method for a slab for unidirectional electrical steel which is heated at a high temperature. The present invention relates to a continuous hot rolling equipment train capable of being applied to obtain a unidirectional electrical steel sheet excellent in productivity and magnetic properties while improving the surface defects of the product.

[0002]

2. Description of the Related Art As is well known, grain-oriented electrical steel sheets are widely used as iron core materials for transformers and the like due to their excellent magnetic characteristics such as high magnetic flux density and low iron loss. As a characteristic of the manufacturing method, in order to obtain secondary recrystallized grains in which the so-called Goss orientation of [110] <001> is highly integrated, Mn
Inhibitor elements such as S and AlN that control the grain orientation are used. In order for this inhibitor element to appropriately bring about the intended action, after sufficiently dissociating and forming a solid solution (hereinafter referred to as solution heat treatment) during slab heating prior to hot rolling, hot rolling is performed under appropriate conditions. It is very important to precipitate finely and uniformly dispersed by cooling,
For solution treatment of such an inhibitor, for example, high temperature heating of the slab at 1300 ° C. or higher is performed.

When a gas combustion type heating furnace is used as a method for performing the high temperature heating of the slab, a large amount of molten scale is generated in the heating furnace, which not only deteriorates the yield but also
Not only does this impair the stable operability of the heating furnace, but it also causes defects in the surface of the product and so-called edge cracking defects at the ends in the width direction.
In addition, since it takes an extremely long time to reach the target temperature in this type of heating furnace, coarsening of the slab structure occurs in the meantime, and a huge stretched grain is expressed in the subsequent rolling, As a result, it also causes instability in the magnetic properties of the product.

In order to solve the above problems, Japanese Patent Laid-Open No. 61-69
In Japanese Patent Laid-Open No. 924 and Japanese Patent Laid-Open No. 61-69927,
It has been proposed that the slab is preheated to about 1250 ° C. in a gas combustion type heating furnace, and then the high temperature heating is performed for a short time in an induction heating furnace controlled to an inert atmosphere. Furthermore,
JP-A-63-109115 and JP-A-1-162.
In Japanese Patent No. 725, etc., it is described that similar high temperature heating is performed for a short time in an induction heating furnace controlled to an inert atmosphere, and there are many disclosures regarding such high temperature induction heating.

However, according to these methods, although the yield and operability in the hot rolling stage can be improved, in the high temperature rapid heating using the internal heating type induction heating furnace,
Unlike the conventional gas heating method, the temperature pattern at the time of furnace extraction is the coldest point on the surface, so in the subsequent hot rolling treatment, the edge temperature in the width direction of the hot rolled sheet is extremely likely to decrease, As a result, secondary recrystallization failure due to inhibitor aggregation may occur, resulting in deterioration of magnetic properties. For this reason, it is of course necessary to take measures against heating the slab edge portion, but the hot rolling process must be started immediately after the induction heating furnace is extracted.

[0006]

Although the above-mentioned publications relating to the induction heating describe the relation with the gas heating of the slab which is carried out before the induction heating, regarding the cooling of the slab after the induction heating. No problem has been raised. The slab heated to a high temperature in the induction heating furnace is exposed to the atmosphere after being extracted from the furnace and rapidly cooled. Especially at the edge, the temperature tends to drop, and it is inevitable that the amount of drop will increase as the distance from the heating furnace to the rolling mill (rough) increases.
This causes a problem that the magnetic characteristics are deteriorated as described above.

On the other hand, since this type of induction heating furnace is a type in which the slab is vertically inserted, installing this on an online roller table will complicate the installation of the handling device and equipment maintenance. When other steel types that do not perform induction heating are processed through the line, the stripability may be impaired, resulting in a decrease in productivity.

The present invention is intended to prevent the occurrence of such a problem and the internal heating type vertical electric slab heating device (hereinafter referred to as an induction heating furnace) is installed at a position as rough as possible outside the roller table. An object of the present invention is to provide a continuous hot rolling equipment train having a high productivity by preventing the temperature drop of the slab as much as possible and by bringing it close to the rolling mill.

[0009]

In order to achieve the above object, the present invention has the following structures. That is, a gas type slab heating furnace, a vertical rough rolling mill for width reduction, a rough rolling mill and a bar heating device or an edge heating device as required, and then a continuous finishing rolling device are sequentially arranged, which are roller tables. In the connected hot rolling equipment line, there is a slab transfer device near the rough rolling mill, and
Oriented electrical steel which is characterized in that a vertical-type electric slab heating apparatus for heating a blanking the 1,300-1,450 ° C.
It is a series of continuous hot rolling equipment for strips . This hot rolling equipment
In備列, placing a vertical-type electric slab heating device outside of the roller table line the rough rolling mill vicinity, And
This vertical electric slab heating device has a roller
Stand under the bull and place the slab and rotate upward
It is preferable that the slab transfer device has a supporting arm to be provided .

Further, if necessary, a semi-finished product processing device may be installed after the rough rolling mill or a preliminary rolling mill may be installed after the vertical rough rolling mill for width reduction. By doing so, according to the present invention, the slab can be hot-rolled at a temperature as high as possible, and it is possible to prevent the occurrence of edge cracks due to the temperature decrease and the desired property deterioration such as magnetic properties.

[0011]

The present invention will be described in detail below. FIG. 1 is an explanatory diagram showing an example of an outline of a continuous hot rolling equipment line of the present invention, in which 1 is a gas type slab heating furnace, 2 is a vertical rough rolling mill for width reduction, and 3 is from one or several stands. Rough rolling mill and 4
Is a continuous finishing mill, these are roller tables 5
It is continuous with. In the figure, 6 is a bar heating device and 7 is an edge heating device, which is provided between the rough rolling mill 3 and the finish rolling mill 4 to perform heat retention of the roughly rolled sheet bar and heat retention or heating of the edge portion. Reference numeral 8 is a semi-finished product processing device that is provided after the rough rolling mill and cuts crops, and 9 is a preliminary rolling device that is provided after the vertical reduction rough rolling mill 2 for width reduction, and is a vertical rough rolling for width reduction. It is specially provided for straightening a slab formed into a dogbone shape by width reduction by the machine 2 or for further correcting the shape by further reducing the slab. 6 to 9 above
Is equipment installed if necessary. Although not shown, there is a winding device after the finish rolling.

Reference numeral 10 denotes an induction heating device (furnace), which is a characteristic part of the present invention, and is installed close to the rough rolling mill 3 and, in the illustrated example, is installed outside the roller table 5. Induction heating furnace 10
Then, the hot slab treated in the previous step (gas heating, wide reduction, preliminary (straightening) rolling) is vertically charged, and by induction heating, for example, by heating and holding at 1300 ° C. or higher for a short time,
The solution is extracted from the furnace after sufficient solution heat treatment, but the extracted slab must be quickly bitten into the rough rolling mill so as not to give time for the temperature to drop as much as possible. Therefore, the induction heating furnace 10 is installed at a position where the slab transfer from the furnace 10 to the rough rolling mill 3 can be performed in the shortest possible time within a range that does not hinder rolling and equipment operation. In the present invention, "nearby" or "nearby" is used in this sense. Further, it may be on either side (drive or work side) of the slab transfer line.

The induction heating furnace 10 includes a slab transfer device 11
Attach. One example (Overview) As shown in FIG. 2, the apparatus 11 to support shaft 14 which is rotatably supported Seung to the substrate 13, made by connecting the supporting arms 15 for mounting the slab 12, the slab 12 When being conveyed to the front surface of the induction heating furnace 10 by the roller table 5, the support arm 15 standing by at a position lower than the upper surface of the table between the roller tables 5 rotates upward in conjunction with the operation of the support shaft 14. Then, the slab 12 on the table 5 is placed and transferred to the lower part of the induction heating furnace body 10a. At the bottom of the main body 10a, there is a stand 17 connected to the lift 16,
The slab 12 received from the support arm 15 is stored in the induction heating furnace 10a by the lift 16 while being placed on the pedestal 17. When some distance is provided between the roller table 5 and the induction heating furnace 10, a horizontal conveying means for the slab is installed.

In the equipment row in the present invention, the continuously cast slab for unidirectional electrical steel sheets is first preheated in the gas slab heating furnace 1. Since this heating is performed at a relatively low temperature of 900 to 1250 ° C., the generation of molten slag is small, and the existing heating furnace can be used for efficient operation. or,
It also secures the temperature of preliminary rolling in the subsequent process.

It is preferable that the slab produced by continuous casting has a constant maximum width which is restricted by casting stability, and the slab is subjected to width reduction so as to obtain a desired product width. Help improve productivity.
That is, the preheated slab is sent to the roller table 5 and immediately conveyed to the vertical horizontal mill for width reduction 2 to perform width reduction rolling. Internal defects (segregation, cracks, etc.) peculiar to continuous casting are formed in the continuous casting slab, and when heated at high temperature,
This causes a surface defect in the hot-rolled steel sheet that follows. When the rolling mill 2 for width reduction performs a large width reduction with a large reduction amount, the surface defects are further promoted.
In order not to cause this, it is recommended that the widthwise reduction amount in one pass is 50 mm or less and the condition is three or more passes.

The slab after the width reduction rolling is normally induction heating furnace 10 through the front, is conveyed directly to rough rolling mill 3 consisting of one or more stand provided behind the vicinity of the induction furnace 10, wherein At a rolling reduction rate of 900 to 1250 ° C
Preliminary rolling of 0% or less is promptly performed in two or more passes. Thereby, the surface defects caused by the internal defects can be eliminated by carrying out the width reduction rolling under the above conditions. Further, in this pre-rolling, the dog bones formed by the wide-width reduction rolling are erased and formed into a shape with good heating efficiency, and the role of facilitating and stabilizing the charging into the induction heating furnace in the subsequent step is fulfilled.

As described above, this preliminary rolling may be carried out by installing the preliminary rolling mill 9 separately from the rough rolling mill 3 immediately after the vertical rolling rough rolling mill 2 for width reduction. .

The slab preliminarily rolled is prepared by the rough rolling machine 3
In the case of (1), the roller table 5 is returned to the reverse position, and the induction heating furnace 10 installed near the rough rolling mill is charged by the means as shown in the above-mentioned drawing. That is, N ₂ and A in the furnace
A non-oxidizing atmosphere such as r gas is used to prevent surface oxidation of the slab and a sufficient solid solution of MnS, AlN, etc. contained in the slab is achieved, and excellent magnetic properties are obtained in the final product after cold rolling, finish annealing, etc. A high temperature solution heat treatment for imparting the heat treatment is performed. The slab 12 that has already been preheated is heated and soaked in the induction heating furnace 10 within a temperature range of 1300 to 1450 ° C. in a short time.

The slab 1 heated to a high temperature in the induction heating furnace 10.
2 is extracted by the procedure reverse to the charging, is transferred to the roller table 5, is conveyed, is quickly bitten into the rough rolling mill 3, and thereafter is rolled by the rough rolling mill 3 and the finish rolling mill 4 in accordance with the usual method. It At this time, the sheet bar rolled by the rough rolling mill 3 is kept warm by the bar heating device 6 which is provided between the finishing rolling mill 4 and the edge rolling device by actively performing edge heating. The temperature drop can be prevented more effectively. The hot-rolled steel sheet on the exit side of the finish rolling mill 4 is approximately 1000 to 1
100 ° C. is obtained, and the temperature in the width direction is made uniform. As a result, it is possible to prevent the occurrence of edge cracks and fine grains due to the temperature drop in the width direction, which is seen in the conventional method. Incidentally sheet bars, crop is cut processed in the semi-finished product processing apparatus 8 provided in the finishing mill 4 front.

Then, it is wound around a coil to obtain a hot rolled steel sheet for unidirectional electromagnetic steel sheet. And this hot rolled steel sheet is cold rolled,
It is possible to stably obtain a final product having excellent surface properties and magnetic properties by treating it with a usual unidirectional electrical steel sheet manufacturing method such as annealing.

[0021]

Example: C: 0.078% by weight, Si: 3.2 by weight
5%, Mn: 0.079%, S: 0.026%, Sol
Al: 0.026%, N: 0.0083%, Sn: 0.
A continuous cast slab for unidirectional electrical steel sheet with a thickness of 250 mm consisting of 14%, Cu: 0.05% and the balance substantially Fe,
12 slabs were cut into pieces, 4 slabs of which were heated in a gas heating furnace at an average temperature of 1180 ° C. for 3 hours, then width-reduced to a slab width of 1010 mm by a vertical rough rolling mill, and further conveyed to a rough rolling mill. After pre-rolling to adjust to an appropriate slab size, heat in an induction heating furnace at 1335 ° C. for 50 minutes, extract from the furnace and quickly bite into a rough rolling mill, then hot-roll under the conditions shown in Table 1. Then, a hot coil having a thickness of 2.3 mm was obtained (Example of the present invention).

On the other hand, the other 4 slabs were treated in the same manner as in the example of the present invention until induction heating, 120 seconds after the induction heating furnace was extracted, and then the rough rolling mill was engaged, and then the conditions shown in Table 1 were used. Hot-rolling was performed to obtain a hot coil having a thickness of 2.3 mm (comparative example).

Further, the remaining 4 slabs are directly 1380
After heating for 7 hours in a gas heating furnace at ℃, after the extraction, the vertical width of the slab is reduced to 1010 mm by a vertical roughing mill, and then the slab is conveyed to a roughing mill and subjected to preliminary rolling to adjust to an appropriate slab size. Then, hot rolling was performed under the conditions shown in Table 1 to obtain a hot coil having a thickness of 2.3 mm (conventional example).

[0024]

[Table 1]

Ten hot-rolled sheets having different slab heating conditions were treated in the same process. That is, a cold-rolled steel sheet with a reduction rate of 33% is heated at 1120 ° C. for 30 seconds and then 900 ° C.
× Two-stage intermediate annealing with soaking for 60 seconds, reduction rate 85%
Final cold-rolling was finished to 0.23 mm.

Thereafter, this cold-rolled steel sheet was subjected to decarburization annealing at 840 ° C. for 30 minutes in an atmosphere of hydrogen 20%, nitrogen 80%, dew point 40 ° C., an annealing separator was applied, and then 1200 ° C. × 2.
A product was obtained by performing a finish annealing for 0 hours and then applying a final coating. The magnetic properties of the product thus obtained and the degree of occurrence of edge cracks in the hot-rolled steel sheet are as shown in Table 1. In the present invention example, iron loss W17 / 50 was 0.83 W /
It is possible to obtain a stable weight of less than kg, and ear cracking is 10 mm.
It turns out that the following subsides. That is, it is possible to obtain good magnetic properties and hot rolled sheets as compared with the comparative example.

Although the above description is mainly applied to the production of the grain-oriented electrical steel sheet, the present invention is not limited to this and can be sufficiently applied to other steel types.

[0028]

As described above, the induction heating furnace of the present invention is installed as close to the rough rolling mill as possible, so that the temperature drop of the slab can be prevented as much as possible, and the excellent magnetic characteristics can be obtained. The product can be obtained stably, the degree of edge cracking of the hot rolled steel sheet is extremely reduced, and the productivity is improved.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an outline of a continuous hot rolling equipment line of the present invention.

FIG. 2 is an explanatory diagram showing an example of an outline of an induction heating furnace 10 of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Kiyoichi Ichimura, 1 Fuji-machi, Hirohata-ku, Himeji-shi, Hyogo Shin Nippon Steel Co., Ltd. Inside Hirohata Works (56) Reference JP-A-3-47601 (JP, A) JP-A-1-162725 (JP, A) JP-A-63-109115 (JP, A) Actually developed Shou 62-44059 (JP, U)

Claims (4)

[Claims] 1. A gas type slab heating furnace, a vertical rough rolling mill for width reduction, a rough rolling mill and, if necessary, a bar heating device and an edge heating device are provided, and then a continuous finishing rolling device is sequentially arranged. In the hot rolling equipment row connected by the roller table, the slab which has a slab transportation device near the rough rolling mill and is transported to 1300 to 1450 ° C.
A continuous hot rolling equipment line for unidirectional electrical steel sheets, which is equipped with a vertical electric slab heating device for heating. 2. A gas type slab heating furnace, vertical type rough pressure for width reduction.
Rolling machine, rough rolling mill and bar heating equipment and
A heating device is installed, followed by a continuous finishing mill.
And hot rolling these are connected by roller table
In facilities column, place a vertical type electric slab heating device outside of the roller table line the rough rolling mill near the vertical
Type electric slab heating device, wait under the roller table.
Support arm for moving the machine and placing the slab and rotating it upward
A series of hot rolling equipment series for unidirectional electrical steel sheets, which is equipped with a slab transfer device. 3. The continuous hot rolling facility train for unidirectional electrical steel sheet according to claim 1, wherein a semi-finished product processing device is installed after the rough rolling mill. 4. A continuous hot rolling facility train for unidirectional electrical steel sheet according to claim 1 or 2, wherein a preliminary rolling mill is installed after the vertical rough rolling mill for width reduction.