KR20030053795A - Method for Magnetic annealing high permeability grain oriented electrical steel with low magnetostriction - Google Patents

Abstract

PURPOSE: A method for magnetic-annealing high flux density grain-oriented electrical steel sheet is provided to minimize magnetostriction by giving a proper magnetic field correspondingly to application stress characteristics of the high flux density grain-oriented electrical steel sheet. CONSTITUTION: In a method for manufacturing high flux density grain-oriented electrical steel sheet comprising a process of hot rolling the steel slab by reheating a steel slab comprising 0.02 to 0.1 wt.% of C, 1.0 to 4.8 wt.% of Si, 0.006 wt.% or less of S, 0.01 to 0.05 wt.% of acid soluble Al, 0.05 to 0.2 wt.% of Mn, 0.010 wt.% or less of N, 0.001 to 0.012 wt.% of B and a balance of Fe and other inevitable impurities in the temperature range of 1,200 to 1,300 deg.C; a process of hot annealing the hot rolled steel slab in the temperature range satisfying the following expression: 1,360-11,111x£sol. Al(wt.%)|±100 deg.C; a process of cold rolling the hot annealed steel slab; a process of forming AlN by performing decarburization and nitriding annealing simultaneously or sequentially; and a process of performing tension coating on the annealed strip after final finish annealing the resulting strip, the method for magnetic annealing the high flux density grain-oriented electrical steel sheet comprises magnetic annealing step of finishing impressing of magnetic field before 200 deg.C as cooling the strip to a temperature of 720 to 350 deg.C at a cooling rate of 120 deg.C/sec or less by starting impressing a pulse magnetic field having pulse width of 10 to 40 ms and frequency of 1 to 8 Hz in a width direction of the strip in an intensity of 400 to 700 Oe; and a step of performing simultaneous decarburization-nitriding annealing by applying stress of -5 MPa to +4 MPa in the process of cooling the strip for hardening coating layer after completing tension coating.

Description

Method for magnetic annealing high permeability grain oriented electrical steel with low magnetostriction}

The present invention relates to a method of manufacturing a high magnetic flux density oriented electrical steel sheet used as an iron core of an electrical device such as a transformer, and more particularly, by minimizing magnetic deformation by applying a magnetic field suitable for the applied stress characteristics of the high magnetic flux density oriented electrical steel sheet. It relates to a magnetic field heat treatment method for high magnetic flux density oriented electrical steel sheet.

The grain-oriented electrical steel sheet has an aggregate structure of {110} <001> direction in the rolling direction, and since many methods have been invented by many researchers since the manufacturing method was first proposed by NP Goss in US Pat. No. 1,965,559, Characteristics have been improved. Magnetic properties of oriented electrical steel sheets include magnetic flux density, iron loss, permeability, and magnetostriction.

Applicant has proposed a technology for manufacturing high magnetic flux density oriented electrical steel sheet in Korean Patent Application No. 2000-72745. The manufacturing technique is, in weight%, C: 0.02 to 0.1%, Si: 1.0 to 4.8%, S: 0.006% or less, acid soluble Al: 0.01 to 0.05%, Mn: 0.05 to 0.2%, N: 0.010% or less , B: 0.001-0.012%, steel slab consisting of the remaining Fe and other unavoidable impurities, after reheating and hot-rolled at 1200 ~ 1300 ℃, the following conditions, 1360-11,111 x [Sol. Al (wt%)] in the temperature range satisfying ± 100 ° C, followed by cold rolling, followed by decarburization and nitride annealing at the same time or in succession to form AlN, followed by final annealing.

Thus, the final annealed steel sheet is usually tension coated to prevent corrosion and eddy current loss to minimize the power loss and to give tension to the surface of the steel sheet. In tension coating, an inorganic, organic, or mixed solution of inorganic and organic is coated on the surface of a steel sheet and then cured in a curing furnace at about 800 ° C. to form an insulating coating. And, if the magnetic field heat treatment to reduce the magnetostriction is applied to the cooling process after the curing treatment.

Magnetostriction is a cause of noise generated when the directional electrical steel sheet is used as the iron core of a transformer, so it is required to reduce the magnetic field through heat treatment. In other words, the grain-oriented electrical steel sheet is processed into a certain shape and enters the inside of the transformer with iron cores stacked from tens to hundreds of sheets, and the coil is wrapped around the iron core. When the iron core is operated by applying current to the coil, the length of the iron core is changed by the change of magnetic flux direction inside the iron core. This phenomenon is called magnetostriction. The change in length of the iron core occurs in multiples of the frequency of the supplied voltage or current. The change in length causes the ends of the iron core to hit the air, which is loud enough to be heard by human ears. The magnetostriction of a grain-oriented electrical steel sheet is expressed as "length variation ÷ original specimen length", and about 1.5x10 ^-6 at 1.7 Tesla for a general general grain-oriented electrical steel sheet. In other words, each time the direction of the magnetic flux changes, it increases and decreases by this ratio with respect to the original length.

The value of magnetostriction varies greatly depending on the stress applied to the steel sheet. In particular, the magnetostriction is significantly different with respect to the compressive stress rather than the tensile stress in the rolling direction of the steel sheet. In fact, when the steel core is laminated to make the iron core of the transformer, compressive stress is applied to the steel sheet by tightening or welding bolts to eliminate the gap between the steel sheets. In consideration of this, if the magnetic strain is measured by intentionally applying compressive stress to the sheet of steel sheet, a higher magnetostriction value appears than when no stress is applied. For example, in the case of oriented electrical steel sheet, the magnetostriction is generally about 1.5x10 ^-6 at 1.7Tesla, and the magnetostriction increases rapidly when compressive stress is applied to the longitudinal direction in consideration of the stress of the transformer. In other words, the compressive stress of 2MPa is about 4.2x10 ^-6 . Noise problems are serious in the case of transformers made of directional electrical steel sheets of this magnitude. Therefore, directional electrical steel is used at the lowest magnetic flux density in order to reduce the magnetostriction as much as possible to reduce noise. In view of this, conventional transformers are designed with magnetic flux densities of 1.65 to 1.75 Tesla. Therefore, if the transformer's efficiency is inevitably reduced, if the magnetostriction of the oriented electrical steel sheet is lowered as much as possible, the transformer can be used at a higher magnetic flux density, thereby increasing the efficiency or reducing the size of the transformer. The need for steel sheet is growing that much.

The grains inside the grain-oriented electrical steel sheet each do not ideally have a perfect goth orientation 110 <001> and have some deviation. Due to this, the main and secondary spheres are formed in the material. The main magnetic domain is in the direction of the <001> magnetic domain is to obtain an electrical steel sheet having excellent directionality in how it coincides with the rolling direction. Assistive devices provide the main reason for the change of the length of the material when applying magnetic field to the material. The generation of the auxiliary magnetic domain increases as the difference between the angle between the (110) plane of the crystal grains in the material and the rolled surface of the material increases, and also occurs due to residual stress or surface defects. When the magnetic field is applied to the material, the rotation of the assisting magnet causes a change in the distance between atoms and the overall length of 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.

The application of magnetic field heat treatment to oriented electrical steel sheets was carried out in 1964 by V.A. ZAYKOVA et al. (Fiz. Metal. Metalloved. 18, 349 (1964)) was actively studied at that time. However, it is difficult 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.

Magnetic field heat treatment is applied to a grain-oriented electrical steel sheet (1) Japanese Patent Laid-Open Nos. 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 ersted 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 prior art of (1) (2) (3), as a magnetic field heat treatment technology for applying a magnetic field in the biaxial direction for magnetization (to give a magnetic field in the rolling direction of the steel sheet), the magnetic field heat treatment of the high magnetic flux density oriented electrical steel sheet proposed by the present applicant This magnetic field heat treatment technology can also be applied. However, the application of these techniques did not help to reduce the magnetostriction at stresses above -5 ~ + 4Mpa.

In the prior arts (1) and (2), a direct current magnetic field is given in (3). 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.

The present invention provides a magnetic field heat treatment method capable of lowering the magnetostriction of a high magnetic flux density oriented electrical steel sheet to which a stress of -5 to 4 Mpa or more is applied.

1 is a schematic diagram of a magnetic field heat treatment according to a magnetic field direction;

Fig. 1 (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. 1 (b) is a schematic diagram of magnetic field heat treatment (TDMA) for magnetically applying in the width direction (vertical direction to the rolling direction of the steel sheet) of the steel sheet;

2 is a graph showing the effect of improving the magnetostriction according to the vertical magnetic field applying direction

3 is a graph showing the magnetostriction according to the angle of the vertical magnetic field and the steel sheet

4 is a graph showing the relationship between the field strength and the period according to the type of magnetic field

5 is a graph showing the magnetostriction according to the pulse width

6 is a graph showing magnetostriction with frequency

7 is a graph showing the magnetic strain according to the magnetic field strength

8 is a schematic diagram of a magnetic field shape in which a pulse magnetic field and a bias DC magnetic field are simultaneously applied.

9 is a graph showing the magnetostriction improvement rate according to the magnetic field start temperature and cooling rate

10 is a graph showing the magnetostriction by the conventional magnetic field heat treatment method

11 is an example of a magnetic field heat treatment apparatus used in the present invention;

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

1 ..... oriented electrical steel sheets 2, 4, 5 ..... solenoid

30 ..... Vertical magnetic field 32 ..... Magnetic field generating means

34 ..... pulse power supply 35 ..... dc power supply

36 ..... Pulse waveform controller 37 ..... DC waveform controller

Magnetic field heat treatment method of the present invention for achieving the above object, by weight%, C: 0.02 ~ 0.1%, Si: 1.0 ~ 4.8%, S: 0.006% or less, acid soluble Al: 0.01 ~ 0.05%, Mn: 0.05 ~ 0.2%, N: 0.010% or less, B: 0.001 ~ 0.012%, steel slab composed of remaining Fe and other unavoidable impurities, after reheating and hot rolling at 1200 ~ 1300 ° C, the following conditions, 1360-11,111 x [Sol . Al (wt%)] hot-rolled annealing at a temperature range that satisfies ± 100 ° C, cold rolling, followed by decarburization and nitriding annealing to form AlN, and final finishing annealing followed by tension coating. In the method of manufacturing a high magnetic flux density oriented electrical steel sheet, in the step of tension coating and cooling for curing the coating layer,

In the width direction of the steel sheet, the pulse width of 10 to 40 ms and the frequency of 1 to 8 Hz pulsed magnetic field of 400 ~ 700 Oe between the start of 720 ~ 350 ℃ to start at 200 ℃ while cooling at a rate of 120 ℃ / sec or less And a magnetic field heat treatment step of terminating the application of the magnetic field at.

The magnetic field heat-treated oriented electrical steel sheet according to the present invention is used by applying a stress of -5Mpa ~ + 4Mpa. Of course, if necessary it can be used by applying a stress of more than + 4Mpa.

Hereinafter, the present invention will be described in detail.

In the present invention, it is characterized by applying the magnetic field heat treatment to the manufacturing method of the high magnetic flux density oriented electrical steel sheet proposed by the applicant in Korean Patent Application No. 2000-72745. This manufacturing method is, in weight%, C: 0.02 to 0.1%, Si: 1.0 to 4.8%, S: 0.006% or less, acid-soluble Al: 0.01 to 0.05%, Mn: 0.05 to 0.2%, N: 0.010% or less , B: 0.001-0.012%, steel slab consisting of the remaining Fe and other unavoidable impurities, after reheating and hot-rolled at 1200 ~ 1300 ℃, the following conditions, 1360-11,111 x [Sol. Al (wt%)] in the temperature range satisfying ± 100 ° C, followed by cold rolling, followed by decarburization and nitride annealing at the same time or in succession to form AlN, followed by final annealing.

In the manufacturing technology of such high magnetic flux density oriented electrical steel sheet, the specific manufacturing conditions up to the reason for the limited composition range and the final annealing are described in detail in Korean Patent Application No. 2000-72745, and description thereof is omitted here to avoid duplication.

Until now, magnetic field heat treatment of high magnetic flux density oriented electrical steel sheets has not had any positive effect on the reduction of magnetostriction. Therefore, the present inventors apply magnetic field in the width direction of the steel sheet, unlike the magnetic field heat treatment technology, which has been applied to a high magnetic flux density oriented electrical steel sheet when applied to a product (iron core of a transformer). When the present invention was found to be effective in reducing magnetostriction, the present invention has been completed. The present invention optimizes the magnetic field heat treatment condition of the high magnetic flux density oriented electrical steel sheet by controlling various process conditions of the magnetic field heat treatment when the magnetic field is applied in the width direction of the steel sheet. That is, the unannealed and remaining annealing separator is washed off on the surface of the oriented electrical steel sheet of the high magnetic flux density component system subjected to the final annealing according to a conventional method, and a tension coating solution is applied. Magnetic field treatment conditions applied to the process of drying and applying the coating liquid to hardening and cooling in order to generate tension in the steel sheet, that is, [1] magnetic field application direction, [2] type of magnetic field applied, [3] heat treatment conditions, [ Tensile stress is to control. Hereinafter, the magnetic field heat treatment method for each specific condition will be described.

[1] magnetic field direction

The inventors of the present invention show that the magnetic strain is degraded more than before the magnetic field heat treatment in the stress application section of -5Mpa ~ + 4Mpa as a result of heat treatment applying the magnetic field in the longitudinal direction of the steel sheet which is the biaxial direction for magnetization of high magnetic flux density oriented electrical steel sheet. I learned.

Accordingly, the inventors of the present invention have a vertical magnetic field imparting a magnetic field in the width direction of the steel sheet as opposed to a horizontal magnetic field applying theory (FIG. 1A, LDMA: Longitudinal Direction Magneticannealing) which applies a magnetic field in the longitudinal direction of the steel sheet, which has been accepted as the orthodoxy. As a result of magnetic field heat treatment while applying FIG. 1B and TDMA: Transverse Diretion Magnetic annealing, the results of FIG. 2 were obtained. That is, in the case of high magnetic flux density oriented electrical steel sheet, it can be seen that in the applied stress section of -5Mpa ~ 4Mpa, the magnetostriction can be reduced when the vertical magnetic field is applied.

At this time, when the magnetic field is applied in the width direction (the direction perpendicular to the rolling direction) of the steel sheet, it is most preferable to set the angle between the magnetic field and the steel sheet to 90 °, but a certain angle range is allowed. As shown in FIG. 4, when the angle between the steel sheet and the magnetic field is 40 ° or more (that is, 40 to 140 °), the magnetostriction is smaller than before the magnetic field heat treatment. The preferred allowable range is 80 to 100 °, and excellent magnetostriction improvement rate can be secured in this range.

And the direction of the magnetic field is good to take one direction from the beginning to the end. Instead of giving the N and S poles alternately, the same pole is maintained to form the magnetic field in the same direction in order to eliminate the disturbance of the magnetic field caused by the pole change.

[2] magnetic fields

As the magnetic field moment of the oriented electrical steel sheet is aligned in one direction, the magnetostriction decreases. However, when the magnetic anisotropy energy in the crystal is large, the rotation of the magnetic domain is difficult. Therefore, it is necessary to increase the strength of the magnetic field because a large amount of energy is required to change the direction of all of the magnetic domain in any one direction, which requires a lot of power. Until now, DC and AC magnetic fields are mainly applied.

The present inventors have concluded that for the rotation of magnetic domains facing different directions, a high magnetic field flows instantaneously in the crystal when pulsed magnetic fields are applied, which is more effective in changing the magnetic domain in any one direction.

That is, as shown in Figure 4 (a), in the case of the direct current (DC) magnetic field energy is proportional to the area of the H-T can not obtain a high H compared to the energy entering. In the case of the alternating current (AC) magnetic field in FIG. 4 (b), high H can be obtained as compared to DC with the same amount of energy. However, since the field flows toward the negative side, disturbance of the field may occur and there may be a problem in the arrangement of magnetic domains. have. On the other hand, in the case of the pulse magnetic field shown in Fig. 4 (c), very high H (about 10 times of AC) can be obtained compared to DC and AC with the same amount of energy, and since the field is given only in one direction, There is no disturbance. In pulses, the magnitude of the waveform varies with magnetic field strength, but the shape does not change.

The condition of the pulse magnetic field according to the present invention is that when the pulse magnetic field is applied, the most optimal condition is a pulse width of 10 to 40 ms, a frequency of 1 to 8 Hz, and a pulse intensity of 400 to 700 Oe.

As shown in FIG. 5 (frequency 3 Hz, pulse intensity 520Oe), when the pulse width is set to 10 ms or more, the magnetostriction improvement effect starts to appear, and the magnetostriction improvement effect is not so large even if it is larger than 40 ms.

As shown in FIG. 6 (pulse width 20ms, magnetic field strength 520Oe), the higher the frequency, the greater the magnetostriction improvement. When the frequency is greater than 1 Hz, the magnetostriction improvement effect is large. There is no change.

As shown in FIG. 7 (pulse width 20 ms, frequency 5 Hz), the higher the magnetic field strength, the higher the magnetostriction improvement effect. The pulse intensity increases in proportion to the magnetostriction improvement rate from 200Oe or more and exceeds 700 Oe and the magnetostriction improvement effect is increased. It no longer appears. Therefore, in the present invention, a magnetic field of 400 to 700Oe having a pronounced magnetostriction improvement effect is applied.

By the way, in Figure 8 (a) showing such a pulse waveform in detail, it can be seen that the magnetic field strength of the pulse descends downward with a negative value at the end of the pulse, a slight disturbance occurs in this portion. This disturbance occurs inevitably in the pulse waveform, and it has been found to reduce the effect of reducing the magnetostriction. In order to reduce the magnetostriction, the magnetic domains should be rearranged in the direction of applying the magnetic field, because even if there is some disturbance in the magnetic field direction, the arrangement of the magnetic domains is disturbed and the degree of magnetic domain arrangement in the desired direction drops by that much.

Therefore, the present inventors sought to solve the problem by applying a DC magnetic field to the bias. That is, the bias DC magnetic field that does not change with time is applied in the same direction as the pulse magnetic field so that the intensity of the pulse magnetic field is all positive. In the present invention, the term "biased DC magnetic field" refers to a DC magnetic field that compensates for the minimum intensity of the pulse magnetic field to be 0 or more so that the pulse magnetic field is always directed in the same direction, which will be described with reference to FIG. 4.

In FIG. 8A, the minimum intensity of the pulsed magnetic field is −5Oe. Therefore, when the DC magnetic field of at least 5Oe or more, that is, 10Oe intensity, is biased together with the pulsed magnetic field as shown in FIG. 8 (b), the minimum intensity of the pulsed magnetic field becomes 5Oe of 0Oe or more as shown in FIG. Does not happen. In this way, even if disturbance occurs at the end of the pulse, if the bias DC field is applied in the same direction as the pulse magnetic field, which is larger than the disturbed magnetic field, the whole magnetic field is always directed in the same direction, and the magnetic field is not disturbed. The domains can be rearranged in the grant direction.

The bias DC magnetic field may be provided with a DC magnetic field larger than the magnitude of the disturbing magnetic field of the pulse magnetic field. Under the condition of the pulse magnetic field, a DC magnetic field of 10Oe or more is sufficient.

[3] heat treatment conditions

In the present invention, when the magnetic field is applied to the grain-oriented electrical steel sheet, the magnetostriction improvement rate according to the magnetic field application start temperature was examined. As a result, the magnetostriction improvement rate was increased as the magnetic field application temperature was increased. However, even when the magnetic field application start temperature was lowered to about 350 ° C., the difference in the magnetostriction improvement rate was not large (FIG. 9A). Therefore, it was found that the magnetic field heat treatment does not have to be magnetic field heat treatment at high temperature while consuming heat energy. Therefore, in consideration of productivity and magnetostriction, a preferable magnetic field application start temperature is 350 to 720 ° C.

In addition, as a result of checking the magnetostriction improvement rate with respect to the cooling rate of the steel sheet while applying a magnetic field, the slower the cooling rate is the better the magnetostriction improvement rate. However, even if the cooling rate is increased up to about 120 ℃ / min, there was no difference in the magnetostriction improvement rate compared with the case of slowing the cooling rate than this. Therefore, when the cooling rate of 50 ~ 120 ℃ / min it was determined that the improvement rate of the magnetostriction can be increased while ensuring the productivity.

Maintaining the magnetostriction at a certain level while lowering the magnetic field application start temperature and increasing the cooling rate is important in terms of industrial productivity.

[4] tensile stresses

The magnetic field heat treatment technology to impart a magnetic field in the width direction of the steel sheet has been studied at all by the stereotypical idea that imparting a magnetic field in a direction other than the biaxial direction for the magnetization (the longitudinal direction of the steel sheet) worsens the magnetic properties in the longitudinal direction. It hasn't been.

The inventors of the present invention performed a magnetic field heat treatment to impart a magnetic field in the width direction of the steel sheet, but the magnetostriction was greatly improved, but a slight increase in iron loss was inevitable. Therefore, the magnetic field was heat treated while applying tensile stress to the steel sheet while finding a way to prevent the deterioration of iron loss while providing magnetic field improvement in the width direction, and confirmed that the iron loss was restored to its original state.

Magnetic field heat treatment for imparting a magnetic field in the width direction of the steel sheet due to the stereotype that the magnetic field is imparted in a direction other than the biaxial direction for the magnetization (longitudinal direction of the steel sheet) worsens the magnetic properties in the longitudinal direction (Fig. 1b, TDMA: Transverse Diretion Magnetic annealing (TDMA) technology has not been studied at all.

The inventors of the present invention performed a magnetic field heat treatment to impart a magnetic field in the width direction of the steel sheet, but the magnetostriction was greatly improved, but a slight increase in iron loss was inevitable. Therefore, the magnetic field was heat treated while applying tensile stress to the steel sheet while finding a way to prevent the deterioration of iron loss while providing magnetic field improvement in the width direction, and confirmed that the iron loss was restored to its original state.

In other words, when the tensile stress is applied in the longitudinal direction of the steel sheet while applying the magnetic field in the width direction of the steel sheet, it is possible to improve the magnetostriction and to prevent the deterioration of iron loss, and to give the magnetic field in the width direction of the high magnetic flux density oriented electrical steel sheet. The method could be actively introduced with magnetic field heat treatment technology.

At this time, the tensile portion can improve the iron loss when a tensile stress of about 2 ~ 25MPa is applied. If the tensile stress is lower than 2MPa or higher than 25MPa, the improvement of iron loss is not good. More preferably, the tensile stress is noticeable when the iron loss is in the range of 8 ~ 20Mpa.

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

[Prior example]

By weight% C: 0.035%, Si: 3.15%, Sol-Al: 0.027%, N: 0.0069%, Mn: 0.1%, S: 0.006%, B: 0.0065%, remaining Fe and other unavoidable impurities The silicon steel slab formed was heated at a temperature of 1250 ° C. for 2 hours, hot rolled to a thickness of 2.3 mm, hot rolled annealed at 1120 ° C. for 2 minutes, cooled, and cold rolled to 0.3 mm.

As described above, the cold rolled sheet having a final thickness is subjected to decarbonization annealing and nitride annealing simultaneously.

The process for simultaneous decarburization and sedimentation involves the cold rolled plate containing a mixed gas of 25% hydrogen + 75% nitrogen with a dew point of 48 ° C in a furnace maintained at 875 ° C in a humid atmosphere of ammonia + hydrogen + nitrogen mixed gas. Decarburization and nitriding were performed simultaneously for 155 seconds in the atmosphere.

5 minutes treatment. An annealing separator composed mainly of MgO was applied to the surface of the steel sheet, followed by finishing high temperature annealing. In this case, the high temperature annealing was performed by a heat treatment cycle of raising the temperature to 1200 ° C. at a temperature rising rate of 15 ° C./hr and cooling after cracking for 15 hours in order to cause secondary recrystallization. After heating up at 1200 degreeC, pure hydrogen gas was used. After cooling for 10 hours at 1200 ℃ was cooled by. After the final high temperature annealing, the unreacted and remaining ones of the annealing separator, which is the main component of MgO, applied to the surface of the steel sheet were washed out and tension coated on the surface of the steel sheet. The tension coating material is a mixture of aluminum phosphate, chromic anhydride, and colloidal silica slurry. The coating solution was dried and cured for about 1 minute at about 800 ° C. in order to generate tension in the steel sheet.

The magnetic properties of the grain-oriented electrical steel sheet thus prepared were magnetic flux density B10 = 1.92 Tesla, iron loss W17 / 50 = 1.06 watt / kg, and the magnetostriction according to stress is shown in FIG. 10. Magnetostriction was measured at 1.7 Tesla, 50 Hz. B10 is the magnetic flux density induced at an excitation force of 1000 A / m, and W17 / 50 is iron loss at 1.7 Tesla and 50 Hz.

As shown in Figure 10, when used in the product to which the stress of -5MPa ~ + 4MPa is applied to the magnetostriction can be seen that a lot of noise occurs.

Example 1

The magnetic field heat treatment experiment was carried out with the hardened specimen as described above. These steel sheets were heated again to 800 ° C. and subjected to a magnetic field in the range of 720 to 200 ° C. while cooling to 200 ° C. at 20 ° C./sec. The magnetic field forms a pulse magnetic field (maximum magnetic field strength: 500 Oe, pulse width: 30 ms, pulse frequency: 5 Hz) and a bias of about 10 Oe whose intensity is constant with time to prevent the disturbance of the magnetic field from changing the direction of the pole. I gave it a hush at the same time. An example of the magnetic field heat treatment apparatus used at this time is shown in FIG.

The magnetic strain value according to the stress measured at 1.7 Tesla and 50 Hz after the magnetic field heat treatment under the above conditions is shown in FIG. 2. In Figure 2 it can be seen that the magnetostriction is greatly reduced through the magnetic field heat treatment in the vertical direction.

Example 2

The hardened specimens were subjected to a magnetic field at 650 ° C. and the cooling rate was changed to 60, 80, 100 and 120 ° C. per second until the temperature of the steel sheet was 100 ° C., and the effects of the cooling rate on the magnetostriction were tested. The magnetic field heat treatment conditions were applied in such a manner that the pulse magnetic field had a maximum height of 600 Herstes (Oe) and a pulse width of 6 ms at a frequency of 6 Hz in the width direction of the steel sheet (the angle formed with the rolling direction of the steel sheet within 75 to 105 degrees). . After the magnetic field heat treatment, the magnetostriction was measured at a magnetic flux density of 1.7 Tesla, 50 Hz with -2 MPa (compressive stress), a stress applied to the core in the transformer in the longitudinal direction, and the results are shown in Table 1. It was.

Cooling rate (℃ / sec) Magnetostriction improvement rate (%) 60 50 80 47 100 34 120 12

As shown in the above table, as the cooling rate increases to 120 ° C./sec, the magnetostriction improvement rate gradually decreases, but the difference is not large.

Figure 2 also shows the magnetostriction before the magnetic field heat treatment of the conventional example 1. As can be seen in Figure 2, when the stress of -5Mpa ~ + 4Mpa is applied in the magnetic field heat treatment according to the invention it can be seen that the magnetostriction is reduced. On the other hand, even when the end of magnetic field application was 100 ° C, the change in magnetostriction was not large compared with the case where the field was terminated at 200 ° C.

As described above, according to the present invention, there is a useful effect that a high magnetic flux density oriented electrical steel sheet with little magnetism is provided.

Claims (4)

By weight%, C: 0.02 ~ 0.1%, Si: 1.0 ~ 4.8%, S: 0.006% or less, acid soluble Al: 0.01 ~ 0.05%, Mn: 0.05 ~ 0.2%, N: 0.010% or less, B: 0.001 ~ After reheating and hot rolling a steel slab consisting of 0.012%, the remaining Fe and other unavoidable impurities at 1200-1300 ° C., the following conditions, 1360-11,111 × [Sol. Al (wt%)] hot-rolled annealing at a temperature range that satisfies ± 100 ° C, cold rolling, followed by decarburization and nitriding annealing to form AlN, and final finishing annealing followed by tension coating. In the manufacturing method of high magnetic flux density oriented electrical steel sheet, In the process of cooling the tension coating and curing of the coating layer, In the width direction of the steel sheet, the pulse width of 10 to 40 ms and the frequency of 1 to 8 Hz pulsed magnetic field of 400 ~ 700 Oe between the start of 720 ~ 350 ℃ to start at 200 ℃ while cooling at a rate of 120 ℃ / sec or less The magnetic field heat treatment method of the high magnetic flux density oriented electrical steel sheet comprising a magnetic field heat treatment step of terminating the application of the magnetic field in use, applying a stress of -5Mpa ~ + 4Mpa. The magnetic field heat treatment method of a high magnetic flux density oriented electrical steel sheet according to claim 1, wherein a bias DC magnetic field of 10 Oe or more is applied in the width direction of the steel sheet together with the pulse magnetic field. The magnetic field heat treatment method of claim 1, wherein the cooling rate is 50 to 120 ° C./sec. The magnetic field heat treatment method of high magnetic flux density oriented electrical steel sheet according to claim 1, wherein the magnetic field heat treatment is performed while applying a tensile stress of 2 to 25 Mpa in the longitudinal direction of the tension coated steel sheet.