JPH0551639A - Method for heating grain oriented silicon steel slab - Google Patents

Abstract

PURPOSE:To provide a method for heating a grain oriented silicon steel slab capable of heating even a slab fairy shorter than the length of a furnace at high product yield by a simple equipment. CONSTITUTION:In the method of subjecting a silicon steel slab to preliminary heating by a gas fired heating furnace, next subjecting it to high temp. heating by an induction heating furnace in a nonoxidizing gas atmosphere and holding it for soaking for prescribed time, at the time of subjecting a slab 3 fairy shorter than the furnace length of an induction heating furnace 13 to high temp. heating, as for the longitudinal direction of the slab, the slab 3 is put aside on the side of either furnace wall 15a and is charged to the induction heating furnace 13. The edge part of the slab in close vicinity to the furnace wall face 15a has small thermal radiation and is heated to a prescribed temp. in the similar way to the central part of the slab. Thus, at least either edge part of the slab can be done without being made scraps.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for heating a grain-oriented electrical steel slab in a hot rolling line.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets have excellent magnetic properties such as high magnetic flux density and low iron loss, and are widely used as core materials for transformers and the like. In the manufacturing process, an inhibitor such as MnS or AlN that controls the crystal grain direction is used in order to obtain secondary recrystallization highly integrated in the [110] <001> orientation. In order for this inhibitor to properly produce the intended action, it is necessary to sufficiently dissociate and solidify the inhibitor during slab heating prior to hot rolling. Further, it is important that the slab is hot-rolled under appropriate conditions and cooled to disperse and precipitate the inhibitor finely and uniformly. The slab is heated at a high temperature of, for example, 1200 ° C. or higher to dissociate and solidify the inhibitor.

The high temperature heating is disclosed in, for example, Japanese Patent Laid-Open Nos. 61-6994 and 61-69927. In the high temperature heating methods disclosed in these publications, the slab is preheated to about 1250 ° C. in a gas combustion type heating furnace, and the subsequent high temperature heating is performed in a short time in an induction heating furnace controlled to an inert atmosphere. The induction heating furnace that performs high-temperature heating is provided along the hot rolling line. Also, the slab is transported in its longitudinal direction,
It is picked up from the hot rolling line by the vertically movable hearth and charged into the induction heating furnace. The slab charged in the furnace has its lower side surface supported by the hearth from below, and is heated in a posture in which the upper and lower surfaces of the slab are vertical.

By the way, depending on the work schedule, it is considerably shorter than the length of the induction heating furnace, for example, 1/2 of the furnace length.
Slabs of moderate length may have to be heated to high temperatures. On the other hand, since the slab itself generates heat by electromagnetic induction to raise its temperature, the surface temperature of the slab becomes higher than the surface temperature of the furnace wall of the induction heating furnace. For this reason, the slab surface radiates heat toward the furnace wall. As the front and rear end surfaces of the slab move away from the furnace wall surface of the front and rear ends of the induction heating furnace, the ratio of the furnace wall radiation surface to the radiation surface of the slab front and rear ends increases. Conventionally, even if the slab is considerably shorter than the furnace length, the slab is placed in the center of the furnace length and heated. Therefore, in such a case, the distance between the slab front-rear end and the furnace wall surface was large, and the slab front-rear end was at a low temperature. At the front and rear ends where the temperature becomes low, the inhibitor may not be sufficiently dissociated and solid-dissolved. The front and rear end portions of the electromagnetic steel sheet manufactured with such a slab have lower magnetic flux density and higher iron loss than other portions. Therefore, the front and rear ends of the electromagnetic steel sheet are scrapped, resulting in a decrease in product yield. Note that it is conceivable to heat the front and rear end portions of the slab, which have become low temperature, to a predetermined temperature, but this causes additional heating of other portions of the slab, and wastes energy.

As a method for solving the above problems, a plurality of partition walls are provided in the furnace along the longitudinal direction, an inert gas is blown into each of the partition walls, and the gas blowing amount is adjusted to adjust the amount of material to be heated. A method of controlling the temperature distribution in the longitudinal direction can be considered. (See Japanese Patent Laid-Open No. 11717/1990)

[0006]

The method of controlling the temperature distribution in the longitudinal direction of the material to be heated by providing a plurality of partition walls, injecting an inert gas into each partition wall, and adjusting the gas injection amount, is aimed at. In order to achieve the above, the partition wall and the material to be heated must be brought into contact with each other, or the partition wall and the material to be heated must be sufficiently close to each other so that an inert gas does not pass therethrough. In this way, it is possible to adjust the temperature distribution in the longitudinal direction of the heated material by adjusting the gas injection amount,
It is not possible to expect an improvement in product yield due to heat removal from the heated material to the partition wall and local temperature deviation. Further, the structure of the furnace body becomes complicated, and in addition, a device for blowing an inert gas and a device for adjusting the blowing amount are required, and the structure of the entire heating equipment becomes complicated. Therefore, equipment,
Operating and maintenance costs will increase.

The present invention aims to provide a method for heating a grain-oriented electrical steel slab capable of heating a slab considerably shorter than the furnace length with a high product yield by simple equipment.

[0008]

A method for heating a grain-oriented electrical steel slab according to the present invention is to preheat an electrical steel slab in a gas combustion type heating furnace and then heat it in an induction heating furnace in a non-oxidizing gas atmosphere to high temperature. However, in the method of soaking for a predetermined time, when heating a slab that is considerably shorter than the furnace length of the induction heating furnace at a high temperature, the slab is offset to one furnace wall side in the longitudinal direction of the slab and placed in the induction heating furnace. Charge.

FIG. 1 shows a state in which a slab 3 having a slab length which is about ½ of a standard slab length is charged in an induction heating furnace 13. The slab 3 is biased and loaded into the furnace so that the slab front end surface 4 is close to the front end side inner surface or the rear end side inner surface 15a of the furnace wall 15. When the slab 3 is loaded into the furnace so as to be bilaterally symmetrical with respect to the center of the furnace in the longitudinal direction of the slab, if the slab front and rear ends are not heated to a predetermined temperature, they are biased and loaded into the furnace. The length of the slab that must be loaded into the furnace after being pushed to one side is 2 /
It is about 3 or less. When the slab 3 is conveyed to the induction heating furnace 13 from the gas combustion type heating furnace along the rolling line in order to load the slab 3 into the furnace, the slab front end or rear end is heated by induction heating. When the inner surface of the furnace wall 15 near the front end or the rear end 15a is reached, the slab 3 is stopped and charged into the furnace.

The slab which is loaded into the furnace while being biased is heated by an induction coil 17 arranged along the outer peripheral surface of the furnace wall 15, like a slab having a standard length.

It is desirable that the tip side of the slab be offset, and the reason is as follows. When the slab is extracted from the induction heating furnace, rough-rolled, and then rolled by the finishing rolling mill group, the most unstable rolling phenomenon occurs when the slab is threaded (biting the rolled material into the roll). .. Therefore, when the rear end side of the slab is offset, a temperature deviation occurs at the front end and the deformation resistance of the material to be rolled changes abruptly, amplifying the instability of the above rolling phenomenon, and in some cases rolling due to defective biting. The equipment will have to be stopped urgently.

[0012]

Since the slabs are loaded into the furnace while being biased, one end of the slab is close to the wall surface of the furnace and the other is away from the wall surface of the furnace. The ratio of the radiating surface of the furnace wall to the radiating surface of the slab end near the furnace wall is small. Therefore, the end portion of the slab that is close to the wall surface of the slab emits little heat, and is heated to a predetermined temperature like the central portion of the slab. On the contrary, the end portion of the slab, which is separated from the wall surface of the furnace, has large heat radiation, and may not be heated to a predetermined temperature. As a result, at least one slab end does not have to be scrapped.

[0013]

EXAMPLE FIG. 2 schematically shows a structural example of a hot rolling facility for carrying out the method of the present invention. Slab 1 in the figure
Is a standard length slab and slab 3 is a short slab. As shown in the drawing, the hot rolling equipment is a gas combustion type heating furnace 11 arranged in sequence along a hot rolling line L,
Induction heating furnace 13, rough rolling mill 31, and finishing rolling mill train 32
Has become. In the induction heating furnace 13, the furnace body 14 is opened downward, and the heating coil 1 is provided on the outer periphery of the furnace wall 15.
7 is attached. The induction heating furnace 13 includes a slab turning device 21 that turns the slabs 1 and 3 from the horizontal position to the vertical position by 90 degrees and turns the slabs 1 and 3 inside the furnace.
A hearth 25 for supporting the furnace 3 in a vertical posture and an electric winch 27 for raising and lowering the hearth 25 are provided. Slab turning device 2
1 is a claw 22 on which the slabs 1 and 3 are placed, an arm (not shown) connected to the claw 22, and the claw 22 via the arm.
Is composed of a hydraulic cylinder 23 that turns 90 degrees. Further, the induction heating furnace 13 includes a support shaft 28 that supports the slabs 1 and 3 by pressing them from above. The support shaft 28 is moved up and down by an air cylinder 29. In this example,
There are four support shafts 28, and the required support shafts 28 hold down the slabs 1 and 3 according to the slab length. In the example of FIG. 2, 2
The short slab 3 is held by the book support shaft 28. A roller table 34 is provided along the rolling line L. The roller table 34 is rotated by a drive motor 35 and conveys the slabs 1 and 3 in the longitudinal direction thereof. The control device 39 controls the drive motor 35 to control the slabs 1, 3
Is stopped at a predetermined position. The control device 39 determines the slab stop position based on the slab size and a signal from the slab detector 37 which are input in advance from a host computer (not shown).

Here, an example in which the electromagnetic steel slab manufactured by the continuous casting method is heated by the hot rolling equipment configured as described above will be described.

The slab 3 is heated by the gas combustion type heating furnace 11
Preheating was performed up to 150 ° C. at a relatively low heating rate. The dimensions of the slab are 5500 mm in length, 1000 mm in width, and 25 in thickness.
It is 0 mm (standard length is 11000 mm). The slab 3 was loaded into the furnace with the slab tip 4 being close to the tip side furnace wall surface 15a. The distance D ₁ between the furnace wall surfaces of the slab tip 4 is 200
mm, and the distance D ₂ between the furnace wall surfaces of the rear end portion 5 was 5700 mm. Slab 3 was rapidly heated to 1350 ° C. and soaked for 15 minutes before extraction from the furnace. As a result of measuring the surface temperature of the slab 3 after the uniform heating with a radiation thermometer, the temperature of the slab front end is 1345 ° C and the temperature of the rear end is 1310 ° C.
Met.

The magnetic properties of the grain-oriented electrical steel sheet obtained by finish rolling the slab 3 heated at high temperature and subjecting it to a predetermined heat treatment were measured. As a result, the slab tip had the same value as the center, the _iron loss value W _17/50 was 0.810 W / kg on average, and the magnetic flux density B ₆ was 1.930 Wb / m ² on average. The iron loss value W _{17/50 at the} rear end of the slab is 0.850 W / kg on average,
The average magnetic flux density B ₆ was 1.915 Wb / m ² .

[0017]

According to the present invention, at least one end of the slab is heated to a predetermined temperature and the magnetic characteristics are not deteriorated. Therefore, both ends of the slab do not have to be scraped, and the yield of products can be improved. Further, since the slab may be loaded at a predetermined position in the induction heating furnace, the slab can be heated by the heating equipment having a simple structure.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an induction heating furnace with a slab charged therein.

FIG. 2 is a drawing schematically showing a configuration example of hot rolling equipment for carrying out the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 slab 3 slab 4 slab front end 5 slab rear end 11 gas combustion type heating furnace 13 induction heating furnace 15 furnace wall 17 heating coil 21 slab turning device 25 mount 28 support shaft 31 rough rolling mill 32 finishing rolling mill row 34 roller table 35 Drive Motor 39 Control Device

Claims (1)

[Claims] 1. A method of preheating an electromagnetic steel slab in a gas combustion type heating furnace, then heating it to a high temperature in an induction heating furnace in a non-oxidizing gas atmosphere, and holding the soaking for a predetermined time, the furnace of the induction heating furnace. A method for heating a grain-oriented electrical steel slab, characterized in that, when heating a slab much shorter than its length at a high temperature, the slab is biased toward one furnace wall surface side in the longitudinal direction of the slab and charged into an induction heating furnace.