KR20030053793A - Method for magnetic annealing non- oriented electrical steel sheet to improve magnetic properties and magnetic annealing apparatus used therein - Google Patents

Abstract

PURPOSE: A method for magnetic annealing non-oriented magnetic steel sheet to improve magnetic properties is provided to increase magnetic permeability as lowering watt loss by impressing horizontal magnetic field and vertical magnetic field sequentially, and a magnetic annealing apparatus used therefor is provided. CONSTITUTION: The method comprises a step of heating non-oriented magnetic steel sheet to a temperature of 200 deg.C or more; and sequentially impressing horizontal magnetic field and vertical magnetic field to the heated non-oriented magnetic steel sheet at Curie temperature or less. The magnetic annealing apparatus includes a heat treatment furnace(2) for heating a strip continuously transferred; a horizontal magnetic field generating means installed at the rear side of the heat treatment furnace to impress a magnetic field to a length direction of the strip heated by continuously passing through the heat treatment furnace; a vertical magnetic field generating means installed adjacently to the side surface of the transferred strip in rear of front of the horizontal magnetic field generating means to impress a magnetic field to a width direction of the strip; a power supply(40) for supplying current to the horizontal magnetic field generating means and vertical magnetic field generating means; a power switching means for switching current supplied to the magnetic field generating means from the power supply(40); and a control part(50) for controlling the power switching means.

Description

Method for magnetic annealing non-oriented electrical steel sheet to improve magnetic properties and magnetic annealing apparatus used therein

The present invention relates to a method for manufacturing a non-oriented electrical steel sheet used as an iron core of an electric device such as a motor, and more particularly to a magnetic field heat treatment method that can increase the magnetic permeability while lowering iron loss by applying horizontal and vertical magnetic fields in sequence. It is about. It also relates to a magnetic field heat treatment apparatus used therefor.

Non-oriented electrical steel sheets used as iron cores in electric devices such as motors and transformers are the most energy-loss parts when electrical energy is converted into mechanical energy. Therefore, the use of low iron loss electrical steel sheet can reduce the energy loss by that much. Recently, the use of low-loss materials due to environmental problems, besides energy loss, can reduce the amount of power generation, and interest in low-loss materials is increasing in terms of suppressing power plant construction. If the power loss can be reduced by 10%, it is calculated that 20 power plants can be reduced based on 200 domestic power plants.

Magnetic properties in non-oriented electrical steel sheets include magnetic flux density, iron loss, permeability, and magnetostriction. Higher magnetic flux density and permeability are better, and lower iron loss and magnetostriction are better products. If the magnetic flux density and permeability are good, the torque (rotational power) of the motor will increase, which will bring it to a relatively small size, and the amount of copper wire wound on the iron core can be reduced, thereby reducing the copper wire. In order to increase the magnetic flux density and permeability, many researchers have been studying the aggregate structure according to the change of component design and processing conditions.

Iron loss in non-oriented electrical steel sheet has hysteresis loss and eddy current loss. Hysteresis losses are largely affected by grain size and steel cleanliness. Vortex losses are mainly affected by the resistivity, thickness and grain size of the steel sheet. In order to reduce the iron loss, the researchers have mainly attempted to increase the specific resistance by adding Si and Al in steelmaking or to reduce the thickness through cold rolling. However, in general, the method of adding Si or Al is accompanied with the effect of lowering the magnetic flux density but lowering the iron loss. Lowering iron loss while increasing the magnetic flux density is very difficult because the two properties are mutually opposite. To this end, there is a technique for reducing the thickness of the non-oriented electrical steel sheet. If the thickness of the steel sheet is taken thin, the vortex loss is reduced in proportion to the iron loss, and the magnetic flux density is affected by the components, and thus the magnetic flux density and the iron loss can be obtained at the same time. However, thinning the steel sheet has a great influence on the production volume for the steel sheet manufacturer. The thinner the thickness, the lower the reduction ratio, the harder the material, so it is not easy to make. In addition, in order to make the thickness thinner, the number of rolls increases, which inevitably decreases the yield.

Therefore, the technology for improving the iron loss and the magnetic flux density at the same time while reducing the thickness of the steel sheet is not very positive, and the introduction of a new technology is required.

There is not much interest in magnetostriction because there is much room for improvement of magnetic flux density, iron loss and permeability in magnetic properties of non-oriented electrical steel sheet. Magnetostriction causes noise generated when the steel sheet is processed with iron cores and used in applications such as motors. That is, the change of the magnetic core in the iron core in the length of the iron core causes a noise, which is called magnetostriction. Magnetostriction is known to be caused by the change of the length of the material as the distance between atoms is changed by the rotation of the magnetic domain in the material.

For a long time, many researchers have used magnetic field heat treatment to control the magnetic domains present in the material. Magnetic field heat treatment has been applied to a variety of materials since it was discovered by Pender and Jones in 1913. This is to change the magnetization curve by rearranging the magnetic domain of the material by imparting a magnetic field while cooling to room temperature below the Curie temperature. Magnetic field heat treatment is mainly used to improve magnetic properties in materials with low magnetic anisotropy energy. In the Physics of Ferromagnetism (S. Chikazumi. Oxford Press, NY, 1997) and Introduction to Magnetic Materials (B.Cullity. A. Wesley Publ., London, 1972) The heat treatment while applying in the axial direction, that is, the rolling direction, has been explained by the magnetic field heat treatment.

However, this magnetic field heat treatment technology has been mainly applied to oriented electrical steel sheet. 1964 V.A. ZAYKOVA et al. (Fiz. Metal. Metalloved. 18, 349 (1964)) was actively studied at that time. However, it was found that it is not easy to change the magnetic properties of the steel sheet by magnetic field heat treatment because the crystal magnetic anisotropy energy of the grain-oriented electrical steel sheet is too large.

Specific techniques for applying magnetic field heat treatment to a grain-oriented electrical steel sheet include (1) Japanese Patent Application Laid-open No. Hei 8-134543, (2) Hei 8-134551, and (3) Hei 7-197132.

(1) Japanese Patent Application Laid-Open No. 8-134543 shows a magnetic strain reduction effect according to the proper temperature and cooling rate of magnetic field heat treatment using a material having a magnetic flux density of 1.93 to 1.94 Tesla at 800 A / m (B ₈ ). Giving. In this case, the oriented electrical steel sheet is subjected to secondary recrystallization annealing, followed by coating and flattening. It is characterized by.

(2) In Japanese Patent Laid-Open No. 8-134551, a temperature gradient of 1.5 ° C in the width direction of the steel sheet from 700 ° C to 400 ° C was obtained using a material having a magnetic flux density of 800 A / m (B ₈ ) of 1.94 Tesla. At the same time, the tensile stress of the steel sheet is 0.30% or more, or 0.15% or less, and the DC magnetic field is applied to 50 Eersted or more, thereby reducing the iron loss and the magnetic flux density.

(3) Japanese Patent Application Laid-Open No. 7-197132 shows an alternating magnetic field of more than 40 A / m in an effective magnetic field (sine wave, triangular wave and square wave magnetic fields) in a silicon steel sheet containing Si: 1 to 10% by weight in the region below the Curie temperature. A method for producing a grain-oriented electrical steel sheet is disclosed, which is cooled to 400 ° C. or lower in this magnetic field.

In the above prior arts, high magnetic flux density oriented electrical steel sheets (magnetic flux density of 1.90 Tesla or more at 800 A / m) or substantially high silicon (silicon content of 4% or more) steel sheets are used. Further, in the prior art of (1) (2) (3), the magnetic field heat treatment technique of applying the magnetic field in the biaxial direction for magnetization (to impart the magnetic field in the rolling direction of the steel sheet), and in (1) (2), the direct current magnetic field ( In 3), exchange magnetic field is given. In the case of the DC magnetic field, a lot of power is required according to the magnetic field strength, so it is very difficult to obtain a high magnetic field strength, and it is very inefficient because the magnetic field is not high compared to the power input. In addition, the alternating magnetic field has a good effect of reducing the magnetostriction according to the magnetic field strength, and has a better effect than the direct current magnetic field, but it also requires a lot of power to obtain a high magnetic field.

As described above, the prior art related to the technique of improving the magnetic properties through magnetic field heat treatment for the non-oriented electrical steel sheet is difficult to find, because the magnetic field heat treatment until now is recognized as a technique for arranging magnetic domains in one direction. The application of non-oriented electrical steel sheets having different orientations was not considered at all.

The present invention provides a magnetic field heat treatment method capable of reducing magnetic strain while reducing iron loss through magnetic field heat treatment using non-oriented electrical steel sheet, and increasing magnetic flux density.

Furthermore, an object of the present invention is to provide a magnetic field heat treatment apparatus that can be used for magnetic field heat treatment of non-oriented electrical steel sheet. This magnetic field heat treatment apparatus can apply a magnetic field in a desired direction.

1 is a schematic view of a magnetic field heat treatment apparatus

2 is a schematic diagram of a magnetic field heat treatment in a magnetic field direction;

Fig. 2 (a) is a schematic diagram of magnetic field heat treatment (LDMA) for magnetically applying in the longitudinal direction (rolling direction) of the steel sheet;

Fig. 2 (b) is a schematic diagram of magnetic field heat treatment (TDMA) for magnetically imparting in the width direction (vertical direction to the rolling direction of the steel sheet) of the steel sheet;

3 is a graph showing the change in iron loss and permeability according to the magnetic field strength

4 is a graph showing changes in iron loss and permeability with frequency

5 is a graph showing the change in iron loss and permeability according to the pulse width

6 is a graph showing the magnetostriction before and after magnetic field heat treatment.

* Description of the symbols for the main parts of the drawings *

1 .. electrical steel sheet 2.. Heat treatment furnace

20 .. Horizontal magnetic field generating means 30. Vertical magnetic field generating means

40. Power supply 50. Control unit

52. Power switching means 60. Oscilloscope

Non-oriented magnetic field heat treatment method of the present invention for achieving the above object, the step of heating the non-oriented electrical steel sheet to a temperature of 200 ℃ or more,

And sequentially applying a horizontal magnetic field and a vertical magnetic field below a Curie temperature of the heated non-oriented electrical steel sheet.

In addition, the magnetic field heat treatment apparatus of the present invention, as one example thereof is shown in FIG.

A heat treatment furnace (2) for heating the steel sheet continuously transferred,

Horizontal magnetic field generating means 20 which is installed at the rear of the heat treatment furnace for applying a magnetic field in the longitudinal direction of the heated steel sheet continuously passing through the inside,

Vertical magnetic field generating means 30 is installed in close proximity to the side of the conveying steel sheet in the rear or front of the horizontal magnetic field generating means for applying a magnetic field in the width direction of the steel sheet,

A power supply 40 for supplying current to the horizontal magnetic field generating means 20 and the vertical magnetic field generating means 30,

Power switching means 52 for switching the current supplied to each of the magnetic field generating means 20, 30 in the power supply 40

It is configured to include a control unit 50 for controlling the power switching means 52.

Hereinafter, the present invention will be described in detail.

There are many grains in the non-oriented electrical steel sheet, and each grain has different orientations, so the domains formed therein also face different directions. When the motor rotates, the magnetic domain at any point inside the iron core rotates or moves the wall according to the magnetic field given from the outside at the same time. At this time, the better the movement of the magnetic wall is less iron loss. The magnetic anisotropy energy must be low in order for the movement of the magnetic wall to move easily according to the external magnetic field.

Therefore, the present inventors realized that lowering the magnetic anisotropy energy could easily rotate the magnetic domains arranged in different directions or move the magnetic walls to lower the iron loss, thereby reducing the magnetic anisotropy energy in the oriented electrical steel sheet. An experiment was introduced to introduce the technology. However, as a result of applying the horizontal magnetic field (FIG. 2a) applying the magnetic field in the longitudinal direction of the steel sheet, which is a biaxial axis for magnetization, there was no effect. In the ongoing research, the vertical magnetic field and the horizontal magnetic field were sequentially applied along with the vertical magnetic field (FIG. 2b) to apply the magnetic field in the width direction of the steel sheet. As a result, the magnetic anisotropy energy was significantly reduced.

In the present invention, while introducing a new magnetic field heat treatment technology to the non-oriented electrical steel sheet, there is a feature to apply the horizontal magnetic field and vertical magnetic field in sequence, and also to propose a magnetic field heat treatment apparatus used here. Therefore, the present invention will be described by dividing it into [1] object steel plate, [2] magnetic field heat treatment method, and [3] magnetic field heat treatment apparatus.

[1] sheet steels

The present invention is a non-oriented electrical steel sheet as a target steel. Non-oriented electrical steel sheet is produced by reheating a steel slab, hot rolling, winding, pickling and cold rolling, and final annealing of the cold rolled steel sheet. The final annealed cold rolled sheet may be insulated coated.

Therefore, in the present invention, magnetic field heat treatment is performed on the final annealed cold rolled steel sheet or insulation coated cold rolled steel sheet. Various kinds of components of non-oriented electrical steel sheet are suggested by manufacturers, and most steel grades contain Si of 4.5 wt% or less. In addition, it contains alloying elements such as Al, Mn, P, B, Sb, Cu, Ni and Cr for improving magnetic properties and processability.

[2] magnetic field heat treatment

In the present invention, the magnetic field heat treatment is performed on the final annealing material or the insulating coating material after the final annealing and the insulating coating. Therefore, these steel sheets may be heated and subjected to magnetic field heat treatment, or the magnetic field may be subjected to magnetic field heat treatment in the cooling process after the final annealing or in the cooling process after the curing of the insulating coating. Magnetic field heat treatment greatly improves iron loss, magnetic flux density, and magnetostriction by lowering magnetic anisotropy energy by optimizing the conditions of temperature, magnetic field application pattern and applied magnetic field.

Magnetic field, the heat treatment temperature conditions

The magnetic anisotropy energy of non-oriented electrical steel sheet is rapidly lowered at higher temperature, so it is better to apply magnetic field at high temperature. However, as the magnetic field heat treatment temperature approaches the magnetic transformation point (Curie temperature, about 720 ° C) of the steel sheet, the magnetic permeability of the non-oriented electrical steel sheet decreases, so that the magnetic flux is weakened. Do. In addition, when the magnetic field heat treatment temperature is less than 200 ° C., the magnetic field heat treatment effect is insignificant due to the high crystal magnetic anisotropy energy of the non-oriented electrical steel sheet. Therefore, the magnetic field heat treatment is preferably carried out at a temperature range of 200 ~ 720 ℃.

· Magnetic field-applied pattern

In the non-oriented electrical steel sheet, spontaneous spheres are formed according to the texture of grains during recrystallization through processing and heat treatment. As a way to lower the magnetic anisotropy energy of the spontaneous sphere formed as described above, the vertical magnetic field and the horizontal magnetic field are sequentially applied. A method of sequentially applying a magnetic field will be described with reference to FIG. 1.

The horizontal magnetic field is first applied to the heating steel sheet drawn out by the heat treatment through the first horizontal magnetic field applying means 20a. Then, immediately after the application of the horizontal magnetic field is applied, the vertical magnetic field is applied from the right side to the left side of the steel sheet in the conveying direction of the steel sheet through the first vertical magnetic field applying means 30a. Then, immediately after the application of the vertical magnetic field through the first vertical magnetic field applying means 30a, the horizontal magnetic field is applied in the reverse direction of the conveying direction of the steel sheet through the second horizontal magnetic field applying means 20b. Subsequently, the application of the horizontal magnetic field is terminated, and then the vertical magnetic field is applied from the left to the right through the second vertical magnetic field generating means 30b in the conveying direction of the steel sheet. In this pattern, horizontal and vertical magnetic fields are applied successively. Of course, this sequential application direction may be reversed. The application pattern may be any of various other methods. The possible method is expressed as the power supply method of the magnetic field generating means 20, 30 as follows.

(1) First horizontal magnetic field generating means 20a → First vertical magnetic field generating means 30a → Second horizontal magnetic field generating means 20b → Second vertical magnetic field generating means 30b: Circulation

(2) First horizontal magnetic field generating means 20a → Second vertical magnetic field generating means 30b → Second horizontal magnetic field generating means 20b → First vertical magnetic field generating means 30a: Circulation

(3) First horizontal magnetic field generating means (20a) → First vertical magnetic field generating means (30a) → First horizontal magnetic field generating means (20a) → First vertical magnetic field generating means (30a): Circulation

(4) First horizontal magnetic field generating means (20a) → Second vertical magnetic field generating means (30b) → First horizontal magnetic field generating means (20a) → Second vertical magnetic field generating means (30b): Circulation

(5) Second horizontal magnetic field generating means 20b → First vertical magnetic field generating means 30a → Second horizontal magnetic field generating means 20b → First vertical magnetic field generating means 30a: Circulation

(6) First horizontal magnetic field generating means (20b) → Second vertical magnetic field generating means (30b) → First horizontal magnetic field generating means (20b) → Second vertical magnetic field generating means (30b): Circulation

The most preferable example in the above six application patterns is (1) (2). When the magnetic field is applied to the non-oriented electrical steel sheet along the application patterns (1) and (2), the magnetic domain at any point rotates in response to the magnetic field. And the traveling speed of the steel sheet needs to be adjusted so that any part of the steel sheet is in the region of the magnetic field circulating at least once. At this time, it is preferable that each magnetic field generating means applies a magnetic field in one direction as indicated by arrows in FIG. This is because it is very effective in rotating the magnetic domain inside the steel sheet.

· Conditions for magnetic field

In the present invention, the magnetic field to be applied may be any one of direct current, alternating current, and pulse, but it is preferable to use alternating current or pulse. More preferably, a pulse magnetic field capable of instantaneously applying a high magnetic field is preferable. Pulsed magnetic field means that the time for applying the magnetic field is very short compared to the direct or alternating magnetic field. The alternating magnetic field may be square, triangular, or reflected wave. The magnetic field application condition at this time is preferably a pulse width of 10 ms or more, a frequency of 1 Hz or more, and a pulse intensity of 100 0e or more.

That is, as shown in FIG. 3 (pulse width 35 ms, frequency 8 Hz), the magnetic field strength increases in proportion to the iron loss and permeability improvement rate when the magnetic field strength is 100 Oe or more, but the magnetic improvement effect is higher than that of 600 Oe at 700 Oe. Invisible Therefore, the most preferable pulse magnetic field strength is 100 to 700 Oe, but the present invention is not necessarily limited thereto.

As shown in FIG. 4 (pulse width 35 ms, magnetic field strength 300 Oe), the higher the frequency, the greater the iron loss and permeability improvement, but the magnetostriction improvement effect is larger when the frequency is greater than 1 Hz, and the increase is slowed down to 8 Hz or more.

As shown in FIG. 5 (frequency 8 Hz, pulse intensity 600 Oe), when the pulse width is set to 10 ms or more, the magnetic improvement effect starts to appear. As the pulse width approaches 40 ms, the improvement effect is not so large.

[3] magnetic field heat treating equipment

The magnetic field heat treatment apparatus of the present invention will be described with reference to FIG. 1 is not limited to the present invention, which is an example of a magnetic field heat treatment apparatus.

The magnetic field heat treatment apparatus of the present invention comprises a heat treatment furnace (2), a horizontal magnetic field applying means (20), a vertical magnetic field applying means (30), a power supply (40), a power switching means (52), and a controller (50).

, The heat treatment furnace (2)

The heat treatment furnace of the present invention is to heat the electrical steel sheet to the magnetic field heat treatment temperature, it can be replaced by the final annealing furnace of the non-oriented electrical steel sheet or the curing of the insulating coating.

And horizontal magnetic field applying means (20),

The horizontal magnetic field applying means is provided at the rear of the heat treatment as shown in FIG. 1, but may be disposed in whole or in part in the heat treatment furnace. The design can be changed according to the magnetic field application temperature. The steel sheet passes through the horizontal magnetic field applying means 20 and a horizontal magnetic field is applied in the longitudinal direction thereof. If the magnetic field application pattern selects (1) and (2) above, two of the first vertical magnetic field generating means 20a and the second vertical magnetic field generating means 20b are provided at a predetermined interval, and a vertical magnetic field is generated therebetween. Means 30 are installed.

In the present invention, the magnetic field generating means may be applied to a solenoid, a Helmholtz coil, an electromagnet, etc., and a Helmholtz coil is most preferable for applying a magnetic field in a wide space. When a Helmholtz coil is used, when the distance L between the first horizontal magnetic field generating means 20a and the second horizontal magnetic field generating means 20b satisfies the diameter D of the coil and the following relationship, D≥L It is preferable at the point of forming a uniform magnetic field. However, since the first horizontal magnetic field generating means 20a and the second horizontal magnetic field generating means 20b independently apply the magnetic field sequentially, it is not necessary to limit the diameter of the coil and the distance between the coils.

Means 30 generate a vertical magnetic field,

In FIG. 1, a first vertical magnetic field generating means 30a is provided immediately behind the first horizontal magnetic field generating means 20a. In this case, it is the case of the magnetic field applying pattern (1) (2) (3) (4). If the application patterns 5 and 6 are selected, the first vertical magnetic field generating means 30a may be provided immediately after the heat treatment. In the case of selecting the magnetic field applying patterns 3, 4, 5 and 6, only one vertical magnetic field generating means is provided.

In the case of implementing the application pattern (1) (2), as shown in FIG. 1, the first vertical magnetic field generating means 30a and the second vertical magnetic field generating means 30b are used to form the two horizontal magnetic field generating means 20. It is provided in close proximity to both sides of the steel sheet in between.

At this time, the vertical magnetic field generating means 30 and the horizontal magnetic field generating means 20 are independent of each other since the magnetic field is sequentially applied. Therefore, their placement and spacing have no effect on the magnetic field.

A vertical magnetic field generating means may also be applied to a solenoid, a Helmholtz coil, an electromagnet, etc., and a Helmholtz coil is most preferable for applying a magnetic field in a large space. When a Helmholtz coil is used, the distance L between the first vertical magnetic field generating means 30a and the second vertical magnetic field generating means 30b satisfies the diameter D of the coil and the following relationship, D≥L. It is preferable at the point of forming a uniform magnetic field. However, since the first vertical magnetic field generating means 30a and the second vertical magnetic field generating means 30b independently apply the magnetic field, it is not necessary to necessarily limit the diameter of the coil and the distance between the coils.

· Power supply (40)

A power supply 40 for supplying current to the magnetic field generating means is provided. Select a power source from the group of DC, AC and pulse. The power supply is preferably provided with a waveform controller (not shown) to adjust the frequency, width, and intensity. In FIG. 1, a single power supply is used to supply current to all magnetic field generating means. Of course, it can be configured to supply individually, but this is inefficient.

, Power switching means 52,

It is provided with a power switching means 52 so that the current supplied from the power supply 40 is sequentially transmitted to the magnetic field generating means. The application pattern of (1) to (6) is implemented by opening and shutting off the power by the power switching means. Of course, instead of applying a sequential magnetic field, a vertical magnetic field or a horizontal magnetic field can be given as necessary. In FIG. 1, four power switching means 52 are provided to sequentially supply current to four magnetic field generating means 20a, 20b, 30a, 30b.

, The controller 50

The controller 50 controls the power switching means 52 to implement the application patterns 1 to 6 or various application patterns as necessary. The operation of the controller will be described taking the application pattern 1 as an example. Control first,

Opening the first power source switching means 52a and blocking the remaining power source switching means 52b, 52c, 52d to supply current to the first horizontal field applying means 20a;

Then, the second power source switching means 52b is opened, and the remaining power source switching means 52a, 52c, 52d are blocked to apply current to the first vertical magnetic field applying means 30a,

Then, the third power source switching means 52c is opened and the remaining power source switching means 52a, 52b, 52d are

Supplying a current to the second horizontal magnetic field applying means (20b) by blocking;

Subsequently, the fourth power source switching means 52d is opened and the remaining power source switching means 52a, 52b, 52c are cut off to sequentially supply current to the second vertical magnetic field applying means 30b. The horizontal and vertical magnetic fields are sequentially applied to the non-oriented electrical steel sheet.

On the other hand, oscilloscope 60 is shown in FIG. In the lower part of FIG. 1, which is an enlarged view of the oscilloscope, pulses may be sequentially applied.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

In the embodiment of the present invention, the target steel used non-oriented electrical steel sheet manufactured by the following process. That is, by weight percent, a directional electricity consisting of C: 0.002%, Si: 1.05%, Mn: 0.27%, P: 0.013, S: 0.0024%, Al: 0.34%, N: 0.0020%, remaining Fe and other unavoidable impurities The steel slab was heated to 1150 ° C. for 2 hours, and then hot rolled to obtain a hot rolled sheet having a plate thickness of 2.0 mm. The hot rolled sheet was wound in air at 700 ° C. and cooled. The cooled hot rolled sheet was cold rolled to a thickness of 0.50 mm after pickling the surface. The cold rolled plate was annealed for 2 minutes in a mixed gas of 20% H ₂ + 80% N ₂ in a furnace kept at 1000 ° C.

A magnetic field was applied to the steel sheet drawn out from the final annealing furnace 2 of FIG. As the magnetic field applying pattern, the magnetic field was sequentially applied by adopting the above (1). That is, the first horizontal magnetic field generating solenoid (20a) → the first vertical magnetic field generating solenoid (30a) → the second horizontal magnetic field generating solenoid (20b) → the second vertical magnetic field generating solenoid (30b): circulation

The temperature at which the steel sheet exits the final annealing furnace and enters the magnetic field applying solenoid is 720 ° C, where the steel plate receives the magnetic field generated sequentially from the solenoid, and 200 ° C when exiting after the second horizontal magnetic field generating solenoid 20b. The effect is shown in Table 1 below.

Condition Magnetic field (Oe) Frequency (Hz) Pulse width (ms) _Iron loss (W _17/50 ) Permeability (μ ₁₅ ) Comparative material - - - 3.85 3100 Comparative material 100 8 35 3.80 3300 Invention 200 8 35 3.55 3900 Invention 400 8 35 3.36 4200 Invention 600 8 35 3.25 4300 Invention 700 8 35 3.25 4300 Invention 300 6 35 3.51 4000 Invention 300 4 35 3.58 3800 Invention 300 2 35 3.77 3400 Comparative material 300 One 35 3.83 3200 Invention 600 8 30 3.25 4300 Invention 600 8 25 3.28 4200 Invention 600 8 20 3.34 4100 Invention 600 8 15 3.65 3600 Comparative material 600 8 10 3.80 3300

In the above table, the magnetic field heat treatment conditions have a magnetic field strength of 150 Oe to 600 Oe, a frequency range of 2 Hz or more, and a pulse width of 15 ms or more.

Example 2

The magnetostriction before and after the magnetic field heat treatment was measured using the steel sheet tested in the above example, and is shown in FIGS. 6 (a) and 6 (b). FIG. 6 (a) shows magnetostriction in the rolling direction of the steel sheet, and FIG. 6 (b) shows magnetostriction in the rolling vertical direction. The magnetic field heat treatment conditions were that the magnetic field strength was 500 Oe, the frequency was 6 Hz, and the pulse width was 25 ms. Magnetic strain according to stress was measured at a magnetic flux density of 1.3 Tesla, 50Hz. The stress is given in the longitudinal direction of the steel plate, the-sign means compressive stress, otherwise it means tensile stress.

In Figure 6 it can be seen that the magnetic field heat treatment reduces the magnetostriction.

As described above, according to the present invention, there is a useful effect that a non-oriented electrical steel sheet having low iron loss and high magnetic permeability and small magnetic strain is provided.

Claims (11)

Heating the non-oriented electrical steel sheet to a temperature of 200 ° C. or higher, The magnetic field heat treatment method of the non-oriented electrical steel sheet for improving the magnetic characteristics comprising the step of sequentially applying a horizontal magnetic field and a vertical magnetic field below the Curie temperature of the heated non-oriented electrical steel sheet. The magnetic field heat treatment method of claim 1, wherein the heating is a final annealing process of the non-oriented electrical steel sheet or a curing heat treatment process of the insulation coating. The magnetic field heat treatment method of claim 1, wherein the applied magnetic field is one of an alternating magnetic field or a pulsed magnetic field selected from a group of square waves, triangle waves, and reflected waves. 4. The method of claim 3, wherein the alternating magnetic field and the pulse magnetic field have a pulse width of 10 ms or more, a frequency of 1 Hz or more, and a magnetic field strength of 100 to 700 Oe. The method of claim 1, wherein the sequential application of the horizontal and vertical magnetic fields, A first horizontal magnetic field applying step of applying a horizontal magnetic field in a conveying direction of the steel sheet, Terminating the application of the first horizontal magnetic field, and then applying a vertical magnetic field from the right side to the left side of the steel sheet in the conveying direction of the steel sheet; Terminating the application of the first vertical magnetic field, and then applying a second horizontal magnetic field to apply a horizontal magnetic field in a direction opposite to the conveying direction of the steel sheet; Terminating the application of the second horizontal magnetic field, and subsequently performing a second vertical magnetic field applying step of applying a vertical magnetic field from the left side to the right side of the steel sheet as viewed in the conveying direction of the steel sheet. . A heat treatment furnace (2) for heating the steel sheet continuously transferred, Horizontal magnetic field generating means 20 which is installed at the rear of the heat treatment furnace for applying a magnetic field in the longitudinal direction of the heated steel sheet continuously passing through the inside, Vertical magnetic field generating means 30 is installed in close proximity to the side of the conveying steel sheet in the rear or front of the horizontal magnetic field generating means for applying a magnetic field in the width direction of the steel sheet, A power supply 40 for supplying current to the horizontal magnetic field generating means 20 and the vertical magnetic field generating means 30, Power switching means 52 for switching the current supplied to each of the magnetic field generating means 20, 30 in the power supply 40 Magnetic field heat treatment apparatus comprising a control unit 50 for controlling the power switching means (52). The horizontal magnetic field generating means (20) is provided with a first horizontal magnetic field generating means (20a) and a second horizontal magnetic field generating means (20b) spaced apart at regular intervals, and the conveying steel sheet is continuously connected to the first vertical. The magnetic field heat treatment apparatus, characterized by continuously passing through the interior of the magnetic field generating means (20a) and the second vertical generating means (20b). 8. The magnetic field generating means (30) of claim 7, wherein the vertical magnetic field generating means (30) comprises a first vertical magnetic field generating means (30a) and a second vertical magnetic field generating means (30b) between the two horizontal magnetic field generating means (20). Magnetic field heat treatment apparatus, characterized in that installed in close proximity to each side of the steel plate. 8. The method of claim 7, wherein the horizontal magnetic field generating means (20a, 20b) is a Helmholtz coil, the distance (L) between the first horizontal magnetic field generating means (20a) and the second horizontal magnetic field generating means (20b) is A magnetic field heat treatment apparatus characterized by satisfying a diameter (D) and the following relationship, D≥L. The method of claim 8, wherein the vertical magnetic field generating means (30a, 30b) is a Helmholtz coil, the distance (L) between the first vertical magnetic field generating means (30a) and the second vertical magnetic field generating means (30b) is A magnetic field heat treatment apparatus characterized by satisfying a diameter (D) and the following relationship, D≥L. The method of claim 6 to 10, wherein the control unit 50, Opening the first power source switching means 52a and blocking the remaining power source switching means 52b, 52c, 52d to supply current to the first horizontal field applying means 20a; Then, the second power source switching means 52b is opened, and the remaining power source switching means 52a, 52c, 52d are blocked to apply current to the first vertical magnetic field applying means 30a, Then, the third power source switching means 52c is opened and the remaining power source switching means 52a, 52b, 52d are Supplying a current to the second horizontal magnetic field applying means (20b) by blocking; Subsequently, the fourth power source switching means 52d is opened and the remaining power source switching means 52a, 52b, 52c are cut off to sequentially supply current to the second vertical magnetic field applying means 30b. Magnetic field heat treatment apparatus characterized in that to sequentially apply a horizontal magnetic field and a vertical magnetic field to the non-oriented electrical steel sheet.