KR100345695B1 - A manufacturing method of a grain oriented electrical steel having a low noise and a magnetic flux-heating treatment apparaturs used therein - Google Patents

Abstract

PURPOSE: A method of manufacturing grain oriented electrical steel having low noise and magnetic flux, and a heating treatment apparatus used therefor are provided. CONSTITUTION: In a method of manufacturing a grain oriented electrical steel where a steel slab comprising Si 0.4 to 4.8 wt.%, C 0.02 to 0.07 wt.%, Mn 0.05 to 0.2 wt.%, S 0.02 to 0.03 wt.%, Cu 0.05 to 0.3 wt.%, Ce, a balance of Fe and incidental impurities is subject to reheating at 1250 to 1400 deg.C, hot rolling, annealing, pickling, two times cold rolling including process annealing, decarburization annealing, final hot annealing and tension coating, the method is characterized in that Ce is added in the steel slab in an amount of 0.006 to 0.09 wt.%; the steel sheet after final hot annealing is magnetic heat-treated at 300 to 600°C for more than 10 sec, wherein the magnetic heat treatment is conducted at 400 to 550 deg.C for more than 2 min under direct current saturation magnetic field. The apparatus used for the manufacture of grain oriented electrical steel comprises a furnace(4) for heating a specimen(1); a solenoid(5) which is installed inside the furnace with spaced apart from the inner surface of the furnace in a fixed distance to excite the specimen; a steel strip(6) which is connected to both ends of a specimen and forms a closed circuit passing through the solenoid; and a power supply to impress voltage to the solenoid.

Description

A manufacturing method of a grain oriented electrical steel having a low noise and a magnetic flux-heating treatment apparaturs used therein}

The present invention relates to a method for manufacturing a low-noise oriented electrical steel sheet used as an iron core of an electrical apparatus such as a transformer and a magnetic flux heat treatment apparatus used therein.

A grain-oriented electrical steel sheet has an aggregate structure of (110) [001] orientation in the rolling direction, and since its manufacturing method was first proposed by NP Goss in US Patent 1,965,559, many researchers have proposed a new manufacturing method. Invention and property improvement have been made.

A method for producing conventional grain oriented sliicon steel, which is currently mainly used industrially, is disclosed in Japanese Patent Publication No. 30-5651 by M. F. Littmann. According to this method, the secondary recrystallized structure is obtained by using MnS as two cold rolling, de-carbon annealing, MgO coating and inhibitor including silicon steel hot rolling, pre-annealing, pickling, intermediate annealing. As described above, various types of working conditions have been changed for the improvement of characteristics of oriented electrical steel sheet manufactured by a series of processes, but the main one is used without change.

A grain-oriented electrical steel sheet is enclosed by tens to hundreds of iron cores stacked inside a transformer or current transformer to convert voltage and current into the desired amount or phase. The coil is wrapped around the core, and when the iron core is operated by applying current to the coil, the length of the core is caused by the change of magnetic flux direction inside the core.

This phenomenon is called magnetostriction, and the change in length occurs in multiples of the frequency of the supplied voltage or current. This change in length causes the ends of the iron core to hit the air, which is audible to the human ear.

In general, the magnetostrictive size of the steel sheet is expressed as "length variation ÷ original specimen length", and in the case of a general general oriented electrical steel sheet, about 1.7xes to 3x10 ^-6 . This amount is the magnetostrictive size without any stress applied to the specimen. If the specimen is subjected to compressive stress in the longitudinal direction of the steel sheet, this value will vary greatly.

In other words, when the actual electrical steel sheet is used as the iron core of the transformer, the compressive stress is applied to the steel sheet to increase the magnetostrictive size because the bolt is tightened or welded in order to laminate the steel sheets and eliminate the gap between the steel sheets.

In addition, the value for the magnetostriction size is slightly different depending on the shape of the measuring instrument and the specimen. This is because the magnetostrictive value is sensitive to the microscopic stress, and the amount is so small that the friction between the specimen and the magnetostrictive measuring device is different for each measuring device. For this reason, the magnetostrictive size differs between the measurements of the reported literature.

In the case of general oriented electrical steel sheet, the magnetostriction size is about 3x10 ^-6 at 1.7Tesla under no stress, and about 10x10 ^-6 under compressive stress of 3MPa.

However, when the transformer is made of a general oriented electrical steel sheet having a magnetostriction size of this level, the noise problem due to the magnetostriction is seriously raised. Therefore, in order to reduce the magnetostriction size as much as possible to reduce the noise, it is used at the lowest magnetic flux density. In view of this, the conventional transformer is designed at 1.70-1.75 Tesla level.

However, this method has a problem of decreasing the efficiency of the transformer, so if a method can be used to reduce the magnetostriction of the oriented electrical steel sheet more than now, the transformer can be used at a higher magnetic flux density, and then the transformer in proportion In order to increase the efficiency or to reduce the size, the need for directional electrical steel sheet having a small magnetostrictive size is increasing.

Accordingly, the present invention has been made to meet the above requirements, to provide a method for producing a low distortion directional electrical steel sheet that can reduce the noise generated when the transformer or the current transformer operating as possible, the object thereof.

Furthermore, another object of the present invention is to provide a magnetic flux heat treatment apparatus that can effectively reduce magnetic distortion during magnetic flux heat treatment of a grain-oriented electrical steel sheet.

Figure 1 is a schematic diagram showing the structure of the magnetic flux heat treatment apparatus designed for the present invention

Figure 2 is a graph showing the change in magnetostrictive size according to the magnetic flux heat treatment temperature

3 is a graph showing a change in magnetostriction size according to magnetic flux heat treatment time.

* Description of the major symbols in the drawings *

1. Specimen 2. Heating element 3. Tube 4. Heating furnace 5. Solenoid 6. Steel strip

7. Roll 8. Magnetic flux detection coil 9. Detector

10.Voltage-to-current regulator to control waveform synthesis and input voltage-current

The present invention for achieving the above object, Si: 0.4-4.8%, C: 0.02-0.07%, Mn: 0.05-0.2%, S: 0.02-0.03%, Cu: 0.05-0.3%, and Ce by weight% Wherein the remainder is reheated to a steel slab consisting of Fe and unavoidable impurities at a temperature of 1250-1400 ° C., followed by hot rolling, and two cold rolling, annealing, annealing, annealing separators, including hot rolled sheet annealing, pickling and intermediate annealing. In the method for producing a grain-oriented electrical steel sheet, which is formed by applying, followed by final high temperature annealing for secondary recrystallization and purification of steel, and then tension coating,

0.006-0.09% of Ce is added to the steel slab, and the final high temperature annealed steel sheet or the tension-coated steel sheet is configured to include magnetic flux heat treatment at a temperature of 300-600 ° C.

The present invention for achieving the above another object is a heating furnace for enclosing the tube in which the specimen is embedded and heating the specimen,

Solenoids are installed at a certain distance from the heating to excite the position located therein,

A steel strip connected to both ends of the specimen in the heating furnace and passing through the solenoid to form a closed circuit;

It comprises a power supply for applying a current to the solenoid.

Hereinafter, the present invention will be described in detail.

In general, magnetostriction is determined by the spin-orbit coupling of the electrons surrounding the atoms in the material.

The present invention is to produce a slab by adding a small amount of Ce (Cerium, cerium) in the molten steel of the general grain-oriented electrical steel sheet in order to change the bond to secure the properties of the low distortion.

In addition, there is also a feature to provide a magnetic flux heat treatment apparatus for further reducing the magnetostriction of the steel sheet provided as described above.

First, the reason for limitation of the steel slab component manufactured according to the present invention will be described.

Si is an element in which steel increases resistivity and significantly improves iron loss characteristics. The amount of addition is determined by various limiting factors, and in the case of aromaticity, it actually contains about 2.95-3.5%, and in the case of non-orientation, which generally contains 0.4-3.5%, but it is industrially stable for cold rolling. The amount of addition is determined by whether it can be done. That is, it is known that the rolling of steel containing about 4.8% of Si is also possible in the special and strictly controlled rolling method, and the addition amount thereof is increasing. The present invention adds up to 4.8% in consideration of this point. If Si is 0.4% or less, the addition effect is insignificant and does not have a significant meaning. Therefore, the Si content is preferably set to 0.4-4.8%.

C is an element that is added to refine the hot rolled structure. After performing the function of hot rolling, it becomes an impurity and has to be removed because it adversely affects the magnetic properties. When 3% of Si is contained, when about 0.018% of C is contained, ferrite-austenite transformation may occur during hot rolling, thereby miniaturizing the hot rolled tissue. Therefore, when the amount of Si increases, a slightly higher amount of C is required, so the present invention adds 0.02% or more of C. On the other hand, C is an element that deteriorates the characteristics of the transformer by causing magnetic aging when it remains in the final product, so it is strictly managed to be less than 0.003% in the final product by decarbonization annealing. However, if the content is too large, it is difficult to remove even in the decarburization process, so the present invention is added in an amount of 0.07% or less in consideration of this.

Mn is an ingredient that increases the electrical resistance and lowers the iron loss. To secure the effect, Mn is added at 0.05% or more, but when the content is more than 0.2%, the Mn content is 0.05-0.2. It is preferable to select in%.

In the case of Cu, MnS precipitates, which are inhibitors, have an effect of making the fine and uniform particles, thereby increasing magnetism by increasing grain growth inhibition. If the content is less than 0.05%, the effect is insignificant, and if the content is more than 0.3%, an undesirable oxide is formed on the surface of the hot-rolled sheet, which is difficult to pickle, so it is preferable to select an appropriate amount of 0.05-0.3%.

S is formed as a precipitate by Cu or Mn, which acts as an inhibitor, but if it exceeds 0.03%, sufficient de-tutu is not made during final high-temperature annealing, resulting in deterioration of magnetic properties. It is not desirable to obtain an emulsion in the form of an emulsion.

Ce is an element specifically added in the present invention to reduce magnetostriction. The atomic number thereof is 58, and the arrangement of the outer electrons is 4f1, 5S2 5P6 5d1 6S2. When Ce having such an atomic arrangement and Fe having an atomic arrangement of 3d6 4S2 meet, the spin-orbital bond affecting magnetostriction is changed by changing the arrangement of electrons. If the content is less than 0.006%, the above-mentioned effect is insignificant, and if the content is more than 0.09%, the atomic radius is about 1.5 times that of Fe, which seriously affects the mechanical properties. Therefore, the Ce content is preferably set to 0.006-0.09%. .

As described above, Ce, which reduces the magnetostriction by changing the spin-orbital bond, has a small amount of addition and thus does not affect the secondary recrystallized structure formed through high temperature annealing. Therefore, the magnetic properties of the electrical steel sheet can effectively reduce the size of the magnetostriction while maintaining the same level.

The steel formed as described above may contain impurities inevitable to N2. The N2 content of the oriented electrical steel is usually controlled to 60 ppm or less in the steelmaking process, but this content does not have much effect.

Hereinafter, a method of manufacturing electrical steel sheet according to the present invention will be described.

The electrical steel sheet slab formed as described above is heated before hot rolling, and the heating temperature at this time is preferably set to 1250-1400 ° C. The reason for this is that when the heating temperature is 1250 ° C or lower, it is difficult to reinvent the inhibitor, and above 1400 ° C, the surface of the steel sheet melts so much that hot rolling becomes difficult. When the slab is reheated in this way, the inhibitor MnS is re-used and re-precipitated during the hot rolling process. At this time, the distribution of the inhibitor precipitated determines the magnetic properties of the final product.

The slab reheated as described above is hot rolled, followed by hot rolled sheet annealing in the range of 900-1150 ° C. for uniformity, control of precipitates and improvement of pickling properties, and cooling in air.

The plate annealed as above is pickled and cold rolled twice. Intermediate annealing is usually performed between these two cold rollings in the temperature range of 900-1000 ° C., which aims to give ductility for secondary rolling. In addition, it is possible to obtain a secondary recrystallization in which the reduction ratio during secondary rolling is usually 55-65%.

As described above, the cold rolled sheet having the final product thickness by cold rolling twice is annealed to form a decarburization and an internal oxide layer. At this time, the atmosphere of the annealing furnace is usually performed in a mixed atmosphere of wet hydrogen nitrogen. In this process, the carbon inside the steel sheet is removed, and an internal oxide layer is formed to form an excellent glass film during high temperature annealing. In this process, the amount of carbon is lowered below 20-30 ppm.

After decarbonization annealing as described above, an annealing separator containing MgO as a main component is applied to the surface of the steel sheet, followed by final high temperature annealing. In this case, the final high temperature annealing is composed of a temperature rising section for developing a secondary recrystallization structure and a quenching annealing section for removing impurities. The temperature rising rate of the temperature rising section is important because rearrangements of precipitates occur.

If the rate of temperature rises fast, the second recrystallization becomes unstable, while if the rate of temperature rises too slow, the annealing time is long, which is uneconomical. Therefore, the preferable temperature increase rate is 10-40 degreeC / hr. In addition, since the purified annealing is a process of removing harmful elements in the steel by maintaining in a reducing atmosphere, it is preferable to carry out in a 100% hydrogen atmosphere.

As described above, the final annealed electrical steel sheet has a stable secondary recrystallization, and has a magnetic flux density of 1.80 Tesla or more and an iron loss of 1.50 watt / kg or less.

After the final annealing or tension coating of the electrical steel sheet having such magnetic properties, the magnetic flux heat treatment is performed.

The magnetic flux heat treatment is performed to rearrange the magnetic domains in the steel sheet in a direction less magnetostrictive. In order to rearrange the magnetic domains, it is advantageous to lower the magnetic anisotropy energy in the crystal. The magnetic anisotropy energy of the electrical steel sheet is rapidly lowered as the temperature increases, so it is preferable to perform the magnetic flux heat treatment at a high temperature. However, as the magnetic flux heat treatment temperature approaches the magnetic transformation point (approximately 720 ° C.) of the electrical steel sheet, the magnetic permeability of the electrical steel sheet is lowered, so that the magnetic flux is weakened. In consideration of this, the present invention is preferably carried out in the range of 300-600 ° C. in which hypoallergenic distortion is ensured. The magnetostrictive reduction effect is small when the magnetic field heat treatment temperature is less than 300 ℃, and the magnetostrictive reduction effect is less even when the temperature exceeds 600 ℃. As the magnetic field heat treatment time can be seen in Figure 3, the longer the time, the greater the effect, the more than 10 seconds the magnetostrictive effect is significant. At this time, the more preferable magnetic flux heat treatment conditions, as shown in Figure 2 and 3, the temperature is performed for more than 2 minutes in the 400-550 ℃ range can significantly reduce the size of the magnetostrictive.

In the magnetic flux heat treatment, the magnetic field moment is aligned by aligning the magnetic field moment in one direction to reduce the magnetic distortion, and the magnetic flux heat treatment improves the magnetic field moment when the magnetic flux of the steel sheet is saturated. It is more preferable to heat-treat at the direct current saturation flux since the magnetostriction is further reduced because it is completely aligned in one direction.

On the other hand, the above-described magnetic flux heat treatment is useful to use the magnetic flux heat treatment apparatus designed according to the present invention as shown in Figure 1 can be strongly and easily control the amount of magnetic flux inside the material.

Specifically, the magnetic flux heat treatment apparatus of the present invention, as shown in Figure 1,

A heating furnace 4 is provided to surround the tube 3 in which the specimen 1 is embedded and to heat the specimen 1, wherein the heating element is provided with a heating element 2 like a normal heating furnace.

The solenoid 5 is configured to excite what is located therein and is installed at a predetermined distance from the heating furnace 4. In addition, the solenoid 5 is preferably connected to a voltage-current regulator 10 for regulating waveform synthesis, input voltage and current.

The steel strip 6 is connected to and connected to both ends of the specimen 1 in the heating furnace 4, and is configured to pass through the solenoid 5 to form a closed circuit, which is magnetized in the solenoid 5 so that the specimen 1 Magnetize At this time, if the roll 7 is provided so that the steel strip 6 has a constant tencene, the magnetic flux heat treatment effect of a test piece will be more favorable.

In addition, a power supply unit (not shown) for applying a current to the solenoid is provided.

In addition, between the heating furnace 4 and the solenoid 5, a coil 9 for detecting the magnetic flux of the steel strip 6 and a detector 9 having an oscilloscope for reading the detected magnetic flux density are included.

The magnetic flux heat treatment apparatus of the present invention has a small solenoid compared to a magnetic field heat treatment apparatus, but is installed outside the furnace without entering the heating furnace, and the amount of magnetic flux inside the actual material can be strongly and easily adjusted. It is very effective for magnetic flux heat treatment of electrical steel sheets.

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

Example 1

By weight% C: 0.048%, Si: 3.15%, Mn: 0.065, S: 0.024%, Cu: 0.17%, N ₂ : 0.0050%, Ce is as shown in Table 1 (a) 0.005, (b) 0.01% , (c) 0.03%, (d) 0.05%, (d) 0.1%, and the slab composed of the balance Fe and the unavoidable element is heated to 1350 ° C., followed by hot rolling to obtain a hot rolled sheet having a thickness of 2.0 mm. Got it. The hot rolled sheet was annealed at 950 ° C. for 5 minutes, cooled in air, first cold rolled to a thickness of 0.75 mm, annealed at 950 ° C. for 2 minutes, and subjected to secondary cold rolling to a thickness of 0.3 mm.

The cold rolled plate was decarburized for 2 minutes with a mixed gas of 25% H ₂ + 75N _{2 having} a dew point of 51 ° C. in a furnace maintained at 850 ° C. Next, MgO, an annealing separator, was applied to the surface of the steel sheet to perform final high temperature annealing. The high temperature annealing was heated to 1200 ° C. at an elevated temperature rate of 15 ° C./hr in an atmosphere of 25% H ₂ + 75N ₂ , and maintained at 100% H ₂ for 10 hours after reaching 1200 ° C.

As described above, a stable secondary recrystallized oriented electrical steel sheet was obtained.

The steel sheet was subjected to magnetic flux heat treatment at a temperature of 400 ° C. for 2 minutes with the apparatus shown in FIG. 1. At this time, the magnetic flux of the steel sheet was performed at almost saturation magnetic flux using a DC current, and then the magnetic and magnetostrictive properties were measured, and the results are shown in Table 1 below.

At this time, the magnetic properties measured the magnetic flux density (B ₁₀ ) and the iron loss (watt / kg) at 1.7 Tesla induced in the specimen under a magnetic field of 1000A / m. And, the magnetostriction is shown by comparing the magnetostriction according to the external stress applied to the specimen at 1.7Tesla with before and after the magnetic flux heat treatment.

At this time, in the artificial stress applied to the specimen, '-' represents the compressive stress and '+' represents the tensile stress.

Addition amount of Ce (%) B ₁₀ (Tesla) W _17/50 (watt / kg) Magnetostrictive size before magnetic flux heat treatment (x10 ^-6 ) Magnetostrictive magnitude after flux heat treatment (x10 ^-6 ) Remarks -4 MPa -3 MPa -1 MPa 0 MPa +3 MPa -4 MPa -3 MPa -1 MPa OMPa +3 MPa 0 1.853 1.21 22.0 15.5 8.0 2.5 0.5 18.2 11.3 6.0 2.0 0.4 Comparative material 0.005 1.853 1.21 21.5 15.3 8.0 2.5 0.5 18.0 11.1 5.9 2.1 0.4 Comparative material 0.01 1.861 1.20 21.0 15.3 7.9 2.4 0.5 8.5 5.2 2.7 1.2 0.2 Invention 0.03 1.862 1.23 21.3 15.2 7.8 2.4 0.6 8.3 4.8 2.1 1.0 0.2 Invention 0.05 1.863 1.22 21.3 17.1 7.8 2.5 0.5 7.9 5.0 2.5 1.2 0.3 Invention 0.08 1.860 1.19 22.2 16.8 9.1 2.9 0.6 14 8.5 5.1 1.9 0.4 Invention 0.1 1.810 1.25 22.2 19 11.1 4.2 0.7 20.1 12.1 8.9 2.3 0.7 Comparative material

As shown in Table 1 above, when the Ce-added steel sheet was subjected to magnetic flux heat treatment, it was found that a low-distortion, low-distortion electrical steel sheet could be obtained under compressive stress, and there was an appropriate range of Ce.

Example 2

Electrical steel slab containing C: 0.048%, Si: 3.15%, Mn: 0.065, S: 0.024%, Cu: 0.17%, N ₂ : 0.0050%, Ce: 0.03% by weight, balance Fe and inevitable elements Was heated to 1350 ° C. and then hot rolled to obtain a hot rolled sheet having a plate thickness of 2.0 mm. The hot rolled sheet was annealed at 950 ° C. for 5 minutes, cooled in air, first cold rolled to a thickness of 0.75 mm, annealed at 950 ° C. for 2 minutes, and subjected to secondary cold rolling to a thickness of 0.3 mm. The cold rolled plate was decarburized for 2 minutes with a mixed gas of 25% H ₂ + 75N ₂ , which is a dew point maintained at 850 ° C. Next, MgO, an annealing separator, was applied to the surface of the steel sheet to perform final high temperature annealing. The high temperature annealing was heated to 1200 ° C. at a temperature rising rate of 15 ° C./hr in an atmosphere of 25% H ₂ + 75N ₂ , and maintained at 100% H ₂ for 10 hours after reaching 1200 ° C. As described above, a stable grain-oriented electrical steel sheet was obtained.

After using the steel sheet to saturate the steel plate by using a direct current at an arbitrary temperature to rearrange the magnetic domains, the magnetostriction according to the magnetic flux heat treatment was measured under a compressive stress of 4 MPa, and the results are shown in FIG. 2.

As shown in Figure 2, the magnetic flux heat treatment temperature for reducing the magnetostriction is best 400-550 ℃. At temperatures below 400 ° C, the magnetic anisotropy is so large that rearrangement of the domains through magnetic flux heat treatment is not possible. Above 550 ° C, the heat energy inside the steel sheet is large and the magnetic permeability of the steel sheet becomes low, making the alignment of the domains difficult.

On the other hand, Figure 3 shows the result of measuring the magnetostriction according to the magnetic flux heat treatment time at a magnetic flux heat treatment temperature of 450 ℃ using a secondary recrystallized steel sheet under a compression stress of 4MPa. As shown in FIG. 3, as the magnetic flux heat treatment time for the magnetic domains is aligned, the magnetostrictive decrease becomes larger, but a very large effect can be obtained from 2 minutes or more and gradually decreases from 4 minutes or more.

As described above, when a small amount of Ce is added, it is possible to supply an electrical steel sheet having a low distortion property by changing the spin-orbit coupling of electrons while satisfying the magnetic characteristics of a general general oriented electrical steel sheet. When using the magnetic flux heat treatment apparatus provided in accordance with the present invention in the magnetic flux heat treatment, there is an effect that can produce a directional electrical steel sheet with low magnetostriction under compressive stress.

Claims (4)

% By weight Si: 0.4-4.8%, C: 0.02-0.07%, Mn: 0.05-0.2%, S: 0.02-0.03%, Cu: 0.05-0.3%, and Ce, the balance being Fe and unavoidable impurities After reheating the steel slab to a temperature of 1250-1400 ° C., it is hot rolled, and applied two times of cold rolling, including annealing, pickling, and annealing, followed by applying a cold-breaking, de-carbon annealing, and annealing separator. In the method of manufacturing a grain-oriented electrical steel sheet which is subjected to the final high temperature annealing for purification and then tension coated, 0.006-0.09% of Ce is added to the steel slab, and the final high temperature annealed steel sheet or the tension-coated steel sheet is characterized in that the magnetic flux heat treatment for 10 seconds or more at a temperature of 300-600 ° C. . The method of claim 1, wherein the magnetic flux heat treatment is performed at a temperature of 400-550 ° C. for at least 2 minutes in a direct current saturation flux. A heating furnace (4) surrounding the tube (3) in which the specimen (1) is embedded and heating the specimen (1); A solenoid (5) installed at a predetermined distance from the heating furnace (4) and excited to be located therein; A steel strip (6) connected to both ends of the specimen (1) in the heating furnace (4) and passing through the solenoid (5) to form a closed circuit; And A power supply unit for applying current to the solenoid; Magnetic flux heat treatment apparatus for producing a grain-oriented electrical steel sheet comprising a. 4. A detector (9) according to claim 3, characterized in that between the furnace (4) and the solenoid (5) a detector (9) is provided with a coil for detecting the magnetic flux of the steel strip (6) and an oscilloscope for reading the detected magnetic flux density. Magnetic flux heat treatment apparatus for producing oriented electrical steel sheet.

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