JP4311230B2 - Oriented electrical steel sheet - Google Patents

Description

  The present invention relates to grain-oriented electrical steel sheets used mainly for iron core materials such as transformers.

  In grain-oriented electrical steel sheets, low iron loss at a commercial frequency and high magnetic flux density in a low excitation field are extremely important characteristics for improving the efficiency and energy saving of a transformer. In recent years, there is an urgent need for further energy loss improvement, that is, lower iron loss, in order to save energy. To achieve low iron loss, {110} <001> orientation increases the degree of integration in the rolling direction (high orientation), increases the tensile stress in the rolling direction (high tensile stress of the coating), There are technologies such as "domain refinement" by local strain and groove processing on the steel sheet surface, "high Si" to increase electrical resistance, and "thinning" to suppress eddy currents. Are being studied and each is already reaching a very high level. Further, “surface smoothing” that suppresses unevenness on the surface of the steel sheet is effective in itself for reducing iron loss, and according to Non-Patent Document 1, it is shown that the tensile stress effect of the coating is changed. Yes.

Here, in order to obtain a low iron loss in a grain oriented electrical steel sheet that has been highly oriented, the surface of the steel sheet is irradiated with a laser (see Patent Document 1), a plasma flame (see Non-Patent Document 2), or the like. Alternatively, magnetic domain subdivision processing such as forming linear grooves on the steel sheet surface by a technique such as etching (see Patent Document 2) is an essential technique. In such domain refining alms steel sheet, the higher the magnetic flux density material (high B ₈ material), it is known that to obtain a low iron loss under the action of high tensile stress. Therefore, in order to reduce the iron loss by the tensile stress effect in the current high B ₈ material, a technique for adding a coating film having a high tensile stress is necessary.

However, since the tensile stress due to the coating is applied due to the difference in thermal expansion coefficient between the coating and the steel sheet, there is a problem that the coating with a higher tensile stress is more easily peeled off. Has become an obstacle.
In order to improve the peel resistance of the film, a film having a thermal expansion coefficient close to that of the steel sheet is formed, and instead, by using the relationship that the tensile stress due to the film is proportional to the film thickness, the film thickness is increased. A method for obtaining a high tensile stress is conceivable. However, this method causes a decrease in the space factor when used in a transformer, and greatly reduces its performance. On the contrary, in order to increase the space factor, it is necessary to form a film having a large tensile stress effect even if it is thin, in which case a film having a coefficient of thermal expansion greatly different from that of the steel sheet is formed. The anti-peeling properties will deteriorate, and eventually fall into a trade-off relationship.
Journal of Japan Society of Applied Magnetics, 17 (1993), 211. Japanese Patent Publication No.57-2252 B. Fukuda, K. Sato, T. Sugiyama, A. Honda and Y. Ito: Proc, of ASM Con. Of Hard and Soft Magnetic Materials, 8710-008, (USA), (1987) Japanese Patent Publication No. 8-6140

As described above, in order to obtain a further low iron loss, it is necessary to develop a film having a high tensile stress, but measures that do not cause deterioration of the peeling resistance characteristics of the film and the space factor of the product are also combined. Therefore, there are many technical problems, and the technology using a coating film having a high tensile stress has not been put into practical use yet.
Therefore, if there is a steel sheet that can achieve the same low iron loss as when a high tensile stress coating is added in the tensile stress range obtained with the coating currently used, or in the tensile stress range that can be applied relatively easily, It is extremely useful without worrying about the peeling resistance characteristics of the film and the deterioration of the space factor of the product. Furthermore, in a steel sheet that can realize low iron loss with such a low tensile stress, when a coating having high adhesion characteristics and a high tensile stress is developed, the thickness required for the coating can be reduced. Further improvement in the space factor is also expected.

  The present invention is relatively easy to obtain in the present coating technology, and within the range of low tensile stress that does not cause the problem of film peeling, specifically under the tension coating with a tensile stress of 12 MPa or less. The purpose is to propose a way to obtain iron loss equivalent to the case where a tensile coating with a tensile stress exceeding 15 MPa is applied to the steel sheet.

As described above, application of tensile stress to a steel sheet is known as means for improving the iron loss of grain-oriented electrical steel sheets. In general, the iron loss improvement effect due to the application of tensile stress, the Institute of Electrical Engineers of Japan Magnetics Society materials Mag, 86-170 p.62 Fig.2 as seen in (1986), ₈ value B is at a high grain-oriented electrical steel sheet, It is known that the effect is great. Increasing the B ₈ value can be realized by having a high accumulation rate in the rolling direction in the {110} <001> orientation, the so-called Goss orientation.

Here, as shown in FIG. 1, the angle formed between the rolling direction and the Goss direction includes the neck angle (hereinafter referred to as α angle) of the <001> axis steel plate and the <001> axis steel plate. There is an elevation angle (hereinafter referred to as β angle) in the vertical direction with respect to the surface, and a high B ₈ value can be realized by reducing the α and β angles.
On the other hand, the mechanism of the effect of improving the iron loss due to the tensile stress of the coating is that the eddy current loss is reduced by the magnetic domain fragmentation caused by the addition of the tensile stress. The main factor for determining the magnetic domain width is the β angle described above, and it is not always necessary to control the α angle. Therefore, it is considered that there is a possibility that a large effect can be obtained with a low tensile stress by using a steel sheet in which the β angle is limited to an appropriate range rather than increasing the B ₈ value.

  Therefore, the inventors obtained a steel sheet having a β angle limited to a very narrow range by utilizing an annealing method for controlling the β angle when developing secondary recrystallization, The iron loss was measured in the state where the magnetic domain was further subdivided and various tensile stresses were applied. As a result of diligent examination of the effect of reducing the iron loss due to the various tensile stresses thus measured, the inventors have found a β-angle region where the iron loss improvement is particularly remarkable at a low tensile stress, and completed the present invention. Furthermore, it came to discover also about the thickness of a film required in order to obtain a required tensile stress.

That is, the gist configuration of the present invention is as follows.
(1) A polycrystalline grain-oriented electrical steel sheet having a tension-imparting coating on the surface of a steel sheet subjected to magnetic domain refinement treatment, the steel sheet being an angle formed with the rolling direction among three <001> axes The area of the region where the elevation angle of the <001> axis with respect to the steel sheet surface, which is the smallest, is 1 ° or less is 80% or more of the steel sheet surface area, and the tensile stress in the coating is 5 MPa or more and 12 MPa or less. Electrical steel sheet.

(2) the <001> oriented electrical steel sheet according area of the region elevation to the steel sheet surface of the shaft is 1 ° or less in the above (1) is 95% or more of the steel plate surface area.

(3) on the surface of the steel sheet, oriented electrical steel sheet towards according to (1) or (2) the film thickness has a TiN coating 0.3 to 2.0 .mu.m.

(4) The grain-oriented electrical steel sheet according to (1) or (2) , wherein the steel sheet has a coating film mainly composed of glass having a film thickness of 1.0 to 3.5 μm.

  According to the present invention, a sufficient iron loss reduction effect can be realized by the low tensile stress that can be easily obtained. Therefore, it is possible to avoid the problem of deterioration of the peeling characteristics of the high tensile stress film, and to suppress the increase in the film thickness necessary for obtaining the high tensile stress and to obtain a steel sheet having a high space factor. I can do it.

Next, the experimental results that led to the present invention will be described in detail.
Experiment 1
First, decarburization and primary recrystallization annealing were applied to a steel sheet containing Si: 3 mass%: 0.23 mm, followed by the application of an annealing separator mainly composed of MgO, followed by final finish annealing. . Next, the obtained forsterite-coated grain-oriented electrical steel sheet was subjected to magnetic domain subdivision treatment by a plasma jet method, and then crystal orientation analysis by X-ray Laue diffraction was performed at intervals of 5 mm to identify the crystal orientation. In order to eliminate the influence of the α angle, four types of test pieces with an α angle <1 ° and a measured value of the β angle within ± 0.1 ° from each of 0.3 °, 1.0 °, 1.4 ° and 2.7 ° Using a jig for cutting and applying a tensile stress, both ends of the steel plate were pulled in order in the rolling direction up to 15 MPa, and AC iron loss characteristics were measured in that state.

In addition, the magnetic domain subdivision process by the plasma jet method is a high-temperature plasma flame as described in Non-Patent Document 2 is irradiated at intervals of 5 mm in the direction perpendicular to the rolling direction of the steel sheet to give a linear thermal strain region. Is.
The crystal orientation analysis by Laue diffraction is a method of irradiating the steel plate surface with X-rays and measuring the crystal orientation from the reflected diffraction spot. This time, the steel plate surface is divided into meshes with intervals of 5 mm, and each mesh intersection part. Was measured and averaged to obtain the crystal orientation of each test piece.

FIG. 2 shows the results of examining the AC iron loss characteristics when a tensile stress is applied in the grain-oriented electrical steel sheet with the specified β angle thus obtained. Here, W _17/50 is the iron loss value when excited at 50 Hz and 1.7 T.

As can be seen in FIG. 2, the improvement behavior of iron loss is changed in a sample having β of 1 ° or less as compared with a sample having a larger β angle. In other words, the β> 1 ° sample shows a behavior as in the conventional knowledge in which the iron loss gradually improves with the addition of the tensile stress, but the β ≦ 1 ° sample shows a sharp increase in the low tensile stress region. It shows an improvement in iron loss, and then the iron loss takes a minimum value when the tension is around 10 MPa.
The behavior of iron loss improvement due to such tension is not considered to be a mechanism that the lancet magnetic domain disappears due to tension and magnetic domain fragmentation occurs and iron loss is improved as occurs in the high β angle region. . That is, in the region of β ≦ 1 °, which is a low β angle, the auxiliary magnetic domains that are inevitably generated when the magnetic domain subdivision processing is performed become extremely large, and the auxiliary magnetic domains are rapidly reduced by applying appropriate tension thereto. This is considered to be due to the fact that the magnetic domain fragmentation effect was sufficiently exhibited.

Experiment 2
Although the forsterite film is small, it has a tensile stress on the film, and is not suitable for limiting the value of the tensile stress applied to the steel sheet. Further, irregularities are generated on the surface, and the influence thereof is also included. Therefore, the grain-oriented electrical steel sheet with forsterite coating obtained by the same method as in Experiment 1 was pickled and chemically polished, and the surface shape without the forsterite coating was extremely smooth, and the thickness was 0.20 mm. This steel sheet was subjected to a magnetic domain fragmentation treatment by the plasma jet method in the same manner as in Experiment 1, and the experiment was performed again.
FIG. 3 shows the results of examining the AC iron loss characteristics when tensile stress is applied in the grain-oriented electrical steel sheet with the specified β angle thus obtained.

As can be seen in FIG. 3, in the sample with β of 1 ° or less, the iron loss improvement behavior is different from the sample with β angle larger than that in the sample of β ≦ 1 °. Shows a drastic improvement in iron loss due to low tensile stress, and then the iron loss was minimized when the tension was around 5 to 10 MPa.
In addition, the iron loss value when a low tensile stress of 12 MPa or less is applied to a sample with β ≦ 1 ° is the same as the forsterite coating material, and the sample near β = 2 ° is said to show the highest iron loss when a tensile stress is applied. In addition, a value equivalent to that obtained by applying a high tensile stress of 15 MPa was shown.
The present invention has been derived from the above experimental results.

Below, the reason for limitation of the requirements is explained about the electrical steel sheet of the present invention.
[An elevation angle β with respect to the steel plate surface of the <001> axis that is substantially parallel to the rolling direction is 1 ° or less.]
In the above experimental results, all the samples with β> 1 ° showed a behavior in which the iron loss was gradually improved as a high tensile stress was applied, although the iron loss was improved by the tensile stress. That is, high tension is required to improve the iron loss, and the peel resistance is deteriorated.
On the other hand, a sample with β ≦ 1 ° has a large iron loss improvement effect at a low tensile stress of 12 MPa or less, with a minimum of about 10 MPa, and can achieve both peeling resistance and iron loss characteristics.
From the above, the β angle is 1 ° or less.

[A region where β ≦ 1 ° is 80% or more (preferably 95% or more) of the steel plate surface area]
Ratio of β ≦ 1 ° to steel sheet, specifically, the measurement points where β angle obtained at the measurement point of 5mm interval by X-ray Laue diffraction experiment is 1 ° or less is less than 80% of all measurement points If this is the case, the iron loss improvement behavior is the same behavior as the sample of β> 1 ° shown in FIG. 2 or FIG. 3 in which the iron loss improvement gradually progresses due to the tensile stress, and the iron loss is minimal in the low tensile stress region. Since no value is taken, low iron loss cannot be obtained with low tensile stress. As a result, with a low tensile stress of 5 MPa or more, an iron loss value equivalent to an iron loss obtained by adding a high tensile stress of 15 MPa to a sample having a β angle of about 2 ° obtained at present can be obtained. Therefore, the region of β ≦ 1 ° needs to be 80% or more of the steel plate surface area.
Further, when the accumulation rate increases and the area ratio becomes 95% or more, the iron loss improvement behavior due to the tensile stress is completely the same as that of the sample in which the entire steel plate in FIG. 2 or FIG. 3 has β ≦ 1 °. become.

[Tensile stress in the coating is 5MPa or more and 12MPa or less]
From the above experimental results, it can be seen that even if the tensile stress applied to the steel sheet having a low β angle is a weak tensile stress of less than 5 MPa, a large iron loss improvement effect can be obtained as compared with the steel sheet having a high β angle. Furthermore, when the tensile stress is 5 MPa or more, an iron loss value comparable to the iron loss obtained by applying high tensile stress to a high β-angle steel sheet can be obtained.

  Here, as described above, a coating film that generates a high tensile stress has poor peeling characteristics. Therefore, after depositing the tensile coating, the steel sheet is bent along a 70mmφ to 10mmφ cylinder at room temperature (25 °), and the peeling resistance of the coating is verified by the diameter of the cylinder where peeling occurs. did. The result is shown in FIG.

  As is clear from FIG. 4, the peel resistance starts to deteriorate at about 13 MPa. Therefore, in order to improve the peeling characteristics, it is necessary to set it to at least 13 MPa or less. As described above, by setting the tensile stress to 12 MPa or less, it is possible to achieve both iron loss characteristics and peeling resistance characteristics.

[Film mainly composed of TiN film with a film thickness of 0.3 to 2.0 μm or glass with a film thickness of 1.0 to 3.5 μm]
As the coating, a TiN coating and a coating mainly composed of glass can be used, and each coating uses a method by chemical vapor deposition or vacuum deposition, or a method in which a main component is applied to a steel plate and then deposited by baking. To form a film. Since the tensile stress obtained by these films depends on the thermal expansion coefficient, the magnitude of the film tensile stress varies depending on the temperature at the time of film formation even if the films have the same component. Therefore, for the TiN film and the film mainly composed of glass, the film thickness required to obtain a tensile stress of 5 to 12 MPa was determined.

  When the β angle is controlled to form a film only on one side of a steel sheet having a tensile stress effect, the steel sheet is warped as a result of applying a tensile stress only to the formed side. From the relationship between the warpage of the steel sheet and the Young's modulus of the steel sheet at room temperature (25 °), the tensile stress applied to the steel sheet is calculated, and it is necessary to obtain a tensile stress of 5 to 12 MPa from this result. As a result, the film thickness of the TiN film was 0.3 to 2.0 μm, and the film thickness of the film mainly composed of glass was 1.0 to 3.5 μm.

As shown in FIG. 5, the tensile stress is calculated by measuring L and X as warpage when a film is formed on one surface of a steel plate (ground iron), and the following two formulas L = 2Rsin (θ / 2) )
X = R {1-cos (θ / 2)}
Therefore, the radius of curvature R is R = (L ² + 4X ² ) / 8X
Therefore, the curvature radius R is calculated by substituting L and X into this equation. Next, if the calculated radius of curvature R is substituted into the following equation, the tensile stress σ on the surface of the ground iron can be obtained.
σ = E · ε = E · (d / 2R)
Where ε: Strain at the interface between iron and steel (ε = 0 at the center of the plate thickness)
d: Plate thickness
E: Young's modulus (E ₁₀₀ = 1.4 MPa)

Next, the manufacturing method shown below can be considered for the electrical steel sheet of the present invention.
Normally, according to the final finish annealing performed in a coil shape, even if secondary recrystallized grains of approximately β = 0 ° are generated, the growth is performed along the coil. Then, a variation of ± 2.0 ° occurs. Therefore, it is extremely difficult to obtain a steel sheet having a β angle within 1 ° at 80% or more of the steel sheet surface area. However, if the grain growth is controlled so that the secondary recrystallized grains become fine, fluctuations in the crystal orientation along the coil can be suppressed, so that β ≦ 1 ° can be controlled.

For this purpose, addition of elements such as Sn and Sb, which are elements that make secondary recrystallized grains fine, is effective. Or, in order to eliminate variations due to coil annealing, or continuous annealing in sheet form without a coil shape may be performed an annealing or changing the annealing by a very large diameter coil. Furthermore, it is conceivable to actively control the crystal orientation by annealing in a magnetic field.

  In addition, what is necessary is just to follow other general manufacturing conditions of a grain-oriented electrical steel sheet.

  The steel sheet thus obtained is further subjected to magnetic domain refinement treatment. As this magnetic domain subdivision treatment, linear grooves are formed on the surface of the steel sheet by a technique such as irradiation with laser or plasma flame or etching. Alternatively, a process such as mechanically giving a linear or point-like distortion is suitable.

  Next, in order to improve iron loss on the surface of the steel sheet after the magnetic domain refinement treatment, a film having a tensile stress is generated. For this purpose, a multilayer film structure composed of two or more kinds of films may be used. Moreover, you may give the coating which mixed resin etc. according to a use. Further, in the grain-oriented electrical steel sheet of the present invention, low iron loss can be obtained by low tensile stress. Therefore, colloidal silica, phosphate and the like described in JP-B-59-17521, JP-A-53-28043, and the like. Use of glassy coating made of chromic anhydride, etc., tensile stress film mainly composed of aluminum borate, as disclosed in JP-A-6-65755, etc., and ceramic film formed by TiN using CVD or PVD method (See, for example, Japanese Patent Publication No. 63-54767).

  C: Steel slabs containing 0.01 mass% and Si: 3.4 mass% as basic components and containing Sn, the secondary grain refining element, in various amounts up to 0.15% are manufactured by continuous casting, and then heated. Thereafter, a hot-rolled sheet having a thickness of 2.2 mm was formed by hot rolling. Next, hot-rolled sheet annealing was performed at 900 ° C. for 3 minutes, and finished to a thickness of 0.80 mm by rolling. Thereafter, recrystallization annealing was performed at 910 ° C. for 3 minutes, and rolling was performed to a final thickness of 0.27 mm. The obtained steel sheet was decarburized and annealed at 820 ° C. for 3 minutes to reduce C in the steel to 0.0020 mass%, and then an annealing separator containing MgO as a main component was applied, followed by final finish annealing. Final finish annealing is performed in both coil shape and sheet shape, heated to 850 ° C in nitrogen atmosphere, then heated to 1100 ° C in hydrogen and nitrogen mixed atmosphere, then switched to hydrogen atmosphere at a high temperature of 1180 ° C or higher Annealing was performed.

  Next, the obtained steel plate was sheared to 100 mm × 300 mm, X-ray Laue diffraction was performed at 5 mm intervals on the surface, and the β angle of the steel plate was measured. Furthermore, from the measurement results, various test plates were determined in which the area satisfying β ≦ 1 ° was determined. These test plates were subjected to magnetic domain fragmentation by the plasma jet method. In addition, the test plate prepared both the steel plate which has a forsterite film, and the steel plate which smooth | blunted the surface by chemical polishing. Then, comparison was made with respect to samples in which the iron loss at the time of no tensile stress was almost the same and only the area ratio for which β ≦ 1 ° was different. Furthermore, the tensile stress was applied by forming a TiN film on the surface of the steel plate by the CVD method. And the tensile stress was changed by changing the film thickness.

The steel sheet thus obtained was _examined for iron loss W _17/50 and peel resistance of the coating. As shown in Table 1, the invention material (without forsterite coating) has achieved an improvement of about 0.1 W / kg with the addition of 5 MPa tensile stress, resulting in an extremely low iron loss of about 0.6 W / kg. Show.
Furthermore, the invention material (with forsterite coating) has improved by about 0.08 W / kg with the addition of 5 MPa tensile stress, indicating a low iron loss of less than 0.7 W / kg.

  In conventional grain-oriented electrical steel sheets, the iron loss deteriorates when compression force is applied to counteract the tensile stress of the tensile stress coating due to processing, etc., and the characteristics after product processing become worse than those expected from the material characteristics. There was a problem. However, in the present invention, since the iron loss value is almost constant at 5 MPa to 12 MPa, if a film having a tensile stress of 10 MPa is applied, the iron loss characteristics do not change even with a compressive force of about 5 MPa, that is, strain It is also very useful in that the sensitivity is very small and the final product characteristics are easy to predict.

It is a schematic diagram explaining the deviation angle between the Goth direction ({110} <001>) and the rolling direction. It is a figure which shows the iron loss improvement behavior at the time of the tensile stress addition in a forsterite coating material. It is a figure which shows the iron loss improvement behavior at the time of the tensile stress addition in a chemical abrasive. It is a figure which shows the peeling characteristic of a tensile stress film. It is a figure which shows the film tensile stress evaluation method.

Claims (4)

A polycrystalline grain-oriented electrical steel sheet having a tension-applying coating on the surface of a steel sheet subjected to magnetic domain refinement, the steel sheet having the smallest angle with the rolling direction among the <001> axes in three directions A grain-oriented electrical steel sheet characterized in that the area of an elevation angle of the <001> axis with respect to the steel sheet surface is 1 ° or less is 80% or more of the steel sheet surface area, and the tensile stress in the coating is 5 MPa or more and 12 MPa or less. The grain-oriented electrical steel sheet according to claim 1, wherein the area of the region where the elevation angle of the <001> axis to the steel sheet surface is 1 ° or less is 95% or more of the surface area of the steel sheet.   The grain-oriented electrical steel sheet according to claim 1 or 2, having a TiN film having a film thickness of 0.3 to 2.0 µm on the steel sheet surface.   The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the steel sheet has a coating mainly composed of glass having a film thickness of 1.0 to 3.5 µm.

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