KR100544740B1 - Method for manufacturing grain oriented electrical steel sheet having low magnetostriction - Google Patents

Abstract

The present invention relates to a method for manufacturing low-temperature reheat oriented electrical steel sheet used as an iron core of an electrical device such as a transformer. The object of the present invention is to provide a magnetic field suitable for applied stress characteristics of low-temperature reheat oriented electrical steel sheet to minimize magnetic deformation. It is to provide a method for manufacturing a low-temperature reheat oriented electrical steel sheet.

The present invention for achieving the above object, in weight%, Si: 1.5 ~ 4.8%, Al: 0.012 ~ 0.050%, N: 0.0010 ~ 0.0120%, B: 0.0005 ~ 0.0080%, at least one selected from S and Se : 0.012% or less, Mn: 0.45% or less, Mn / (S + Se) ≥ 4.0 is satisfied, hot-rolled steel slab composed of remaining Fe and unavoidable impurities to a temperature of 1200 ° C or less, hot rolled, and 83% or more At least two cold rollings with one cold rolling or intermediate annealing at a rolling reduction rate, followed by decarbonization annealing at a temperature of 800-900 ° C. in a hydrogen / nitrogen mixed atmosphere having a dew point of 30 ° C. or higher, and annealing whose main component is MgO A process of applying a separator on the steel sheet, and then performing a final annealing followed by tension coating, and nitriding the steel sheet during the period from the end of the final cold rolling to the start of the secondary recrystallization in the final annealing. In the manufacturing method, under the tension coating In the cooling process for curing the coating layer, the magnetic field at 200 ° C or earlier while cooling at a rate of 120 ° C / sec or less by starting the application of any magnetic field of the pulse magnetic field or direct current magnetic field in the width direction of the steel plate between 720 ~ 400 ° C The technical gist of the present invention relates to a method for manufacturing a low-temperature reheating oriented electrical steel sheet having low magnetic deformation, which includes a magnetic field heat treatment step of terminating the application and is applied by applying a stress of -5.5 Mpa to +4 Mpa.

Low temperature reheating, directional electrical steel, magnetic field heat treatment, vertical magnetic field, pulse, bias magnetic field

Description

Method for manufacturing grain oriented electrical steel sheet having low magnetostriction}

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 ..... Pulsed power supply 35 ..... DC power supply

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

The present invention relates to a method for manufacturing a low-temperature reheat oriented electrical steel sheet used as an iron core of an electric device such as a transformer. More specifically, it is possible to minimize magnetostriction by providing a suitable magnetic field in accordance with the applied stress characteristics of a low-temperature reheat oriented electrical steel sheet. It relates to a method for manufacturing a low-temperature reheat 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.

Representative manufacturing technology of the grain-oriented electrical steel sheet is a method for manufacturing a low-temperature reheating grain-oriented electrical steel sheet proposed in Korean Laid-Open Patent Publication No. 1989-8334. This production method is Si: 1.5 to 4.8%, Al: 0.012 to 0.050%, N: 0.0010 to 0.0120%, B: 0.0005 to 0.0080%, at least one selected from S and Se: 0.012% or less, Mn: 0.45% or less, the Mn / (S + Se) ≥ 4.0 is satisfied, Ti: 0.002 ~ 0.012% is added if necessary, the steel slab consisting of the remaining Fe and unavoidable impurities is heated to a temperature of 1200 ℃ or less Hot-rolled, one cold-rolled at a rolling reduction of 83% or more, or at least two cold-rolleds with an intermediate annealing in between, and decarbonized annealing at a temperature of 800-900 ° C. in a hydrogen / nitrogen mixed atmosphere having a dew point of 30 ° C. or higher. And a step of applying an annealing separator whose main component is MgO on the steel sheet, followed by final annealing and tension coating, and nitriding the steel sheet during the period from the end of the final cold rolling to the start of the second recrystallization in the final annealing. Do it.

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. If the magnetic field heat treatment is applied to reduce the magnetostriction, it will be applied to the cooling process after the hardening treatment. However, it has not been reported that the magnetic field heat treatment is applied to low-temperature reheat oriented electrical steel sheet, it is known to produce without the actual magnetic field heat treatment. It is known that magnetic field heat treatment does not help to reduce magnetostriction because magnetic field heat treatment does not help.

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 sheets, 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 stresses in the actual transformer manufacturing. . 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 formed by the (110) plane of the crystal grains in the material and the rolling plane 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), the magnetic field heat treatment technique is applied to the magnetic axis in the biaxial direction for magnetization (a magnetic field is applied toward the rolling direction of the steel sheet), and this magnetic field heat treatment is also applied to the magnetic field heat treatment of low-temperature reheated oriented electrical steel sheet. The technique can be applied. In (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 manufacturing method that can lower the magnetostriction as much as possible by optimizing the magnetic field heat treatment conditions of the low-temperature reheating oriented electrical steel sheet, an object thereof.

Production method of the present invention for achieving the above object, in weight%, Si: 1.5 ~ 4.8%, Al: 0.012 ~ 0.050%, N: 0.0010 ~ 0.0120%, B: 0.0005 ~ 0.0080%, selected from S and Se At least one species: 0.012% or less, Mn: 0.45% or less, Mn / (S + Se) ≥ 4.0, and hot rolled by heating the steel slab made of the remaining Fe and unavoidable impurities to a temperature of 1200 ° C or less, At least two cold rollings with one cold rolling or intermediate annealing at a rolling reduction rate of 83% or more, decarbonization annealing at a temperature of 800-900 ° C. in a hydrogen / nitrogen mixture atmosphere having a dew point of 30 ° C. or higher, A method of applying a MgO phosphorus annealing separator to a steel sheet, followed by final annealing, followed by tension coating, and the nitriding of the steel sheet is carried out for a period from the end of the final cold rolling to the start of the secondary recrystallization in the final annealing. In the manufacturing method of the electrical steel sheet, In the process of tension coating and cooling for curing the coating layer,

A magnetic field heat treatment step of starting one of the magnetic field of the pulse magnetic field or the direct current magnetic field in the width direction of the steel plate between 720 and 400 ° C, and ending the application of the magnetic field before 200 ° C while cooling at a rate of 120 ° C / sec or less. It is composed. The low-temperature reheating oriented electrical steel sheet subjected to the magnetic field heat treatment is used by applying a stress of -5.5Mpa ~ + 4Mpa.

Hereinafter, the present invention will be described in detail.

The present invention is characterized in that the magnetic field heat treatment is applied to the method for manufacturing a low-temperature reheat oriented electrical steel sheet proposed in Korean Laid-Open Patent Publication No. 1989-8334. This production method is Si: 1.5 to 4.8%, Al: 0.012 to 0.050%, N: 0.0010 to 0.0120%, B: 0.0005 to 0.0080%, at least one selected from S and Se: 0.012% or less, Mn: 0.45% or less, the Mn / (S + Se) ≥ 4.0 is satisfied, Ti: 0.002 ~ 0.012% is added if necessary, the steel slab consisting of the remaining Fe and unavoidable impurities is heated to a temperature of 1200 ℃ or less Hot-rolled, one cold-rolled at a rolling reduction of 83% or more, or at least two cold-rolleds with an intermediate annealing in between, and decarbonized annealing at a temperature of 800-900 ° C. in a hydrogen / nitrogen mixed atmosphere having a dew point of 30 ° C. or higher. And a step of applying an annealing separator whose main component is MgO on the steel sheet, followed by a final annealing and a tension coating, wherein the nitriding treatment of the steel sheet from the end point of the final cold rolling to the start point of the secondary recrystallization in the final annealing Do it for a while.

As a method of nitriding treatment in the above-mentioned Korea Patent Publication No. 1989-8334

(a) applying an annealing separator containing a compound having nitriding capacity onto a steel sheet,

(b) incorporating an atmosphere into the gas with a nitriding gas during the elevated temperature in the finishing annealing process, and

(c) It is disclosed that at least one selected from nitriding steel sheets in an atmosphere of nitriding gas after cracking in a decarbonization annealing process is applied.

In the manufacturing technology of such low-temperature reheat 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 Laid-Open Patent Publication No. 1989-8334, and the description thereof is omitted here to avoid duplication. In order to improve the characteristics of the low-temperature reheat oriented electrical steel sheet, various techniques have been proposed, such as adding other components or changing manufacturing conditions, and the technical contents are readily available. In the present invention, based on the technical contents proposed in Korean Laid-Open Patent Publication No. 1989-8334, the techniques for changing manufacturing conditions before tension coating are also included in the target category.

According to the magnetic field application technology, even if the low-temperature reheating oriented electrical steel sheet is magnetically heat treated, there is no positive side in reducing the magnetostriction. However, the inventors of the present invention, in the case of low-temperature reheating oriented electrical steel sheet, apply magnetic field in the width direction of the steel sheet, unlike the magnetic field heat treatment technology, under specific stress conditions applied when the product is applied as a product (iron core of a transformer). The present invention was found to be effective in reducing magnetostriction when heat-treated. The present invention optimizes the magnetic field heat treatment condition of the low-temperature reheat 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 grain-oriented electrical steel sheet of the low temperature reheating component system after the final annealing treatment 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 magnetostriction is more deteriorated than before the magnetic field heat treatment in the stress application section of -5.5Mpa ~ + 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 low temperature reheating oriented electrical steel sheet I learned.

Accordingly, the present inventors have applied the magnetic field in the width direction of the steel sheet as opposed to the horizontal magnetic field applying theory (FIG. 1A, LDMA: Longitudinal Direction Magnetic annealing), which applies the 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, TDMA: Transverse Diretion Magnetic annealing), the result of FIG. 2 was obtained. That is, in the case of low-temperature reheating 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. 3, 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. In the present invention, which applies the direction of the magnetic field to the width direction of the steel sheet, the effect is also applied to the direct current magnetic field or alternating magnetic field. In this case, the direct current saturation magnetic field is 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 a pulsed magnetic field is 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 5 to 40 ms, a frequency of 1 to 8 Hz, and a pulse intensity of 100 to 700 Oe.

As shown in FIG. 5 (frequency 3Hz, pulse intensity 520Oe), when the pulse width is 5 ms or more, the magnetostriction improvement effect starts to appear, and the effect becomes larger when the pulse width is longer than 30 ms, and the magnetostriction improvement effect is not so large even when larger than 50 ms. Can be. As shown in Fig. 6 (pulse width 20ms, magnetic field strength 520Oe), as the frequency increases, the magnetostriction improvement rate increases, but when the frequency is greater than 1 Hz, the magnetostriction improvement effect is greatly increased. To lose.

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 100Oe or more and exceeds 700 to 800Oe. Is not that big

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 "bias DC magnetic field" refers to a DC magnetic field that compensates 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 increased as the magnetic field application temperature 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 400 to 720 占 폚.

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 to about 120 ℃ / sec, the magnetostriction improvement rate was not significantly different compared with the case of slowing the cooling rate than this. Therefore, in the case of the cooling rate of 70 ~ 120 ℃ / sec, it was determined that the improvement rate of the magnetostriction can be increased while also securing 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

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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.

That is, by applying a tensile stress in the longitudinal direction of the steel sheet while applying a 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 provide a magnetic field in the width direction of the low-temperature reheat oriented electrical steel sheet. Could be actively introduced as a 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]

Slabs of silicon steel, consisting of C: 0.055%, Si: 3.50%, P: 0.031%, Al: 0.026%, N: 0.0077%, B: 0.0015 by weight Fe and other unavoidable elements, are heated at 1195 ° C. The hot rolled sheet was annealed at 1150 ° C. for 2 minutes, quenched in 100 ° C. boiling water, pickled and cold rolled to a thickness of 0.23 mm. Then, decarbonization annealing is carried out at a temperature of 830 ° C. for 2 minutes in a mixed atmosphere of 75% hydrogen and 25% nitrogen having a dew point of 55 ° C., and then annealing separator is added to the surface of the steel sheet with 4% by weight of fermanganese nitride. . The steel sheet was then heated to 1200 ° C. and maintained at 1200 ° C. for 20 hours at a temperature rising rate of 10 ° C./hr for secondary recrystallization and purification. The annealing atmosphere at this time was N2: H2 = 75%: 25% during the temperature raising process, and 100% H2 gas was used during the 1200 ° C cracking process.

After the final high temperature annealing, an inorganic glass film is formed on the surface of the steel sheet. However, a tension coating is applied for the purpose of improving the insulation and improving the iron loss by micronization. The tension coating material is a mixture of aluminum phosphate, chromic anhydride, and colloidal silica slurry. Tension coating is used to clean unreacted and leftovers of the annealing separator, which is the MgO main component, applied to the steel plate surface to form a glass coating during the secondary recrystallization process on the above-mentioned steel plate surface. Apply. Dry the coated liquid and perform curing at about 750 ~ 850 ℃ for 1 minute to generate tension in the steel sheet.

The magnetic properties of the grain-oriented electrical steel sheet thus prepared are magnetic flux density B10 = 1.93 Tesla, iron loss W17 / 50 = 1.05 watt / kg, and the magnetostriction values according to stress are shown in FIG. 10. However, when used in a product to which a stress of -5.5MPa ~ 4MPa is applied, it can be seen that the magnetostriction causes a lot of noise.

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: 520 Oe, pulse width: 16.4 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. 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.

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 5 ms at a frequency of 5 Hz in the width direction of the steel sheet (the angle formed with the rolling direction of the steel sheet within the range of 75 to 105 degrees). . After the magnetic field heat treatment, the magnetostriction is 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 of the specimen, and the results are shown in Table 1. It was.

Cooling rate (℃ / sec) Magnetostriction improvement rate (%) 60 43 80 41 100 26 120 13

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 -5.5Mpa ~ + 4Mpa is applied in the magnetic field heat treatment according to the invention it can be seen that the magnetostriction is reduced. Even when the magnetic field was applied up to 100 ° C., there was no difference in the improvement of the magnetostriction compared to the case where the magnetic field was applied at 200 ° C. This is also true of Fig. 9 (a).

As mentioned above, according to the present invention, there is a useful effect of providing a low temperature reheating oriented electrical steel sheet with little magnetostriction.

Claims (6)

By weight%, Si: 1.5 to 4.8%, Al: 0.012 to 0.050%, N: 0.0010 to 0.0120%, B: 0.0005 to 0.0080%, at least one selected from S and Se: 0.012% or less, Mn: 0.45% or less The steel slab satisfying the Mn / (S + Se) ≥ 4.0 and consisting of the remaining Fe and unavoidable impurities is hot-rolled by heating to a temperature of 1200 ° C. or lower, and once cold-rolled at a rolling reduction ratio of 83% or more. Cold rolling is carried out at least two times for intermediate annealing, decarbonization annealing at a temperature of 800 to 900 ° C. in a hydrogen / nitrogen mixed atmosphere having a dew point of 30 ° C. or more, and an annealing separator whose main component is MgO is applied onto the steel sheet, and the final annealing is performed. In the manufacturing method of the low-temperature reheat-oriented electrical steel sheet comprising a step of tension coating, and then nitriding the steel sheet during the period from the end of the final cold rolling to the start of the secondary recrystallization in the final annealing, the tension coating and coating layer Process for curing Standing, A magnetic field heat treatment step of starting one of the magnetic fields of the pulse magnetic field or the direct current magnetic field in the width direction of the steel plate between 720 and 400 ° C. and ending the application of the magnetic field before 200 ° C. while cooling at a rate of 120 ° C./sec or less; , Method for producing low-temperature reheating oriented electrical steel sheet with low magnetostriction applied by applying -5.5Mpa ~ + 4Mpa stress. The method of claim 1, wherein the steel slab contains 0.0020% to 0.012% Ti. The method according to claim 1, wherein the pulse magnetic field is applied to a pulse magnetic field of 5 to 40 ms in pulse width and a frequency of 1 to 8 Hz as an intensity of 100 to 700 Oe. 4. The method for manufacturing a low-temperature reheat oriented electrical steel sheet having low magnetostriction according to claim 3, wherein a bias DC magnetic field of 10Oe or more is applied in the width direction of the steel sheet together with the pulse magnetic field. The method of claim 1, wherein the cooling rate is 70 to 120 ° C./sec. The method of manufacturing a low-temperature reheat oriented electrical steel sheet having low magnetostriction according to claim 1, wherein the magnetic field heat treatment is performed while giving a tensile stress of 2 to 25 Mpa in the longitudinal direction of the tension coated steel sheet.

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