JPS6324046B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a unidirectional electrical steel sheet, and in particular, the present invention relates to a ceramic film mainly composed of forsterite (Mg ₂ SiO ₄ ) having properties different from those of the past on the surface of the steel sheet. The present invention relates to a grain-oriented electrical steel sheet having a high magnetic flux density and a lower core loss than conventional ones. <Prior Art> Unidirectional electrical steel sheets are functional materials used in transformer cores, and the most strongly desired property is low iron loss. From the viewpoint of the material, this material has an axis of easy magnetization aligned in the rolling direction (110)
[001] A composite with crystal grains covering the plate surface and a ceramic film mainly composed of forsterite (Mg ₂ SiO ₄ ) and a secondary film mainly composed of colloidal silica and various acid salts on the surface for insulation purposes etc. It is the material. Now, due to the energy situation in recent years, great efforts are being made to reduce the amount of electricity that is meaninglessly consumed as iron loss. Iron loss is often separated into eddy flow loss, hysteresis loss, and abnormal loss, which is the difference between the theoretical sum of these two and the actual total iron loss. Eddy current loss is an iron loss caused by the induced current inside the sample that occurs as the domain wall moves, which is the main part of the magnetization mechanism, and is consumed as Joule heat. To reduce this kind of iron loss, it is effective to increase the specific resistance of the material by increasing Si, etc., reduce the plate thickness, and narrow the magnetic domain width. That is, since the Joule heat generated is proportional to the square of the moving speed of the domain wall, narrowing the magnetic domain width reduces the moving speed of the domain wall and reduces the amount of induced current. On the other hand, hysteresis loss is caused by the inhibition of domain wall movement and is greatly affected by the unevenness of the sample surface and the presence of internal inclusions. In the production of grain-oriented electrical steel sheets, this kind of core loss deterioration can be avoided by completely removing C, N, S, etc. from the steel, minimizing the formation of precipitates, and removing the carbon under the forsterite film on the surface. This has been prevented by lowering the amount of oxides present. To summarize the above, it can be understood that the reduction in iron loss has been achieved by narrowing the magnetic domain width and increasing the mobility of the domain walls that constitute the magnetic domains. Conventional techniques related to these two points will be described next. The basic idea regarding magnetic domain subdivision can be broadly divided into two methods. The first method takes into account the magnetostatic energy of the system. When the axis of easy magnetization of crystal grains is tilted several degrees with respect to the rolling surface, magnetic poles are generated on the surface of the steel sheet, and the magnetostatic energy of the system increases. It is theoretical that the domain wall spacing should be narrowed to minimize this increase in magnetostatic energy (C. Kittel, Rev.
Mod.Phys 21 , 541 (1949)) and experimentally (JW
Shilling S, IEEE Trans.Mag.MAG―14 104
(1978), T. Nozawa et al., same magazine MAG-14 252
(1978)), and by applying this principle, magnetic domains can be subdivided. In addition, reflux magnetic domains are also generated to lower the static magnetic energy due to the surface magnetic poles, but reflux magnetic domains tend to convert into 180° magnetic domains or disappear due to tension applied in the rolling direction, so adding tension reduces iron loss. It is effective for The second method is to apply strain to a steel plate to artificially generate a reflux magnetic domain, and then apply tension in the rolling direction. In this method, it is thought that reflux domains are likely to occur due to the demagnetizing field due to the magnetic pole near the strain line and local internal strain, and the 180° magnetic domain in the demagnetized state becomes fragmented. When tension is applied, the reflux magnetic domain existing near the strain line becomes the starting point of a new magnetic domain, and the width of the magnetic domain becomes even narrower. Most of the conventional techniques related to magnetic domain subdivision can be considered to belong to this category. First, the deviation angle β (closest to the grain rolling direction [001]
Japanese Patent Publication No. 57-61102 and Japanese Patent Publication No. 58-5969 are examples of methods in which the angle between the shaft and the rolling surface is within a range of 4°. These methods obtain a desired deviation angle β by shaping the steel plate into a waveform before final annealing and correcting and removing the waveform after secondary recrystallization. Laser,
Various methods such as scribing can be considered. Various applied technologies using lasers have been published, including Japanese Patent Publication No. 57-2252. Furthermore, Japanese Patent Publication No. 58-5968 is cited as an example of applying a minute strain using a ball point or the like. In addition, Tokko Akira
No. 58-747 discloses a method of subdividing magnetic domains using a combination of deviation angle β and minute strain. These means usually provide external tension as disclosed in Japanese Patent Publication No. 53-28375.
Used in combination with stress coating. The reason is as described above. On the other hand, the following ideas exist regarding increasing the mobility of domain walls by smoothing the surface of the material. The surface layer of unidirectional electrical steel sheets currently available on the market is formed by selective oxidation of the steel sheet.
_SiO2 and applied as an annealing separator on top of it
Forsterite (Mg ₂ SiO ₄ ) generated by a solid phase reaction with MgO during final annealing.
It has a membrane. Under this film, SiO ₂ and
In many cases, there are oxide grains with a diameter of 1 μm or less mainly composed of Mg ₂ SiO ₄ , and it is necessary to remove these oxides in order to reduce hysteresis loss. For this purpose, it is known that it is advantageous to add Sr, as disclosed in, for example, Japanese Patent Publication No. 57-32716, Japanese Patent Application Laid-open No. 55-89422, and Japanese Patent Application Laid-open No. 56-75577. However, in the case of unidirectional electrical steel sheets that assume the existence of a forsterite film, even if the internal oxides under the film could be completely removed, unevenness would still form at the interface between the film and the steel sheet during the forsterite formation stage. It is said that this is unavoidable and becomes a source of pinning due to domain wall movement, leading to an increase in hysteresis loss.
In order to avoid such negative effects and create an ideal interfacial condition, the forsterite film on the surface must be removed.
A smoother surface may be created; such a surface is usually referred to as a mirror-polished surface. In order to create this mirror-polished surface, the forsterite film may be removed by pickling, and then the surface may be made smooth by chemical polishing or the like.
Such methods are described in U.S. Pat. No. 3,125,473;
Disclosed in No. 3227589, No. 3263600, etc. Furthermore, Japanese Patent Publication No. 14851/1983 discloses a method in which the above-mentioned subdivision of magnetic domains by introducing minute strain is combined with a mirror-polished surface. By the way, with this method of obtaining a mirror-polished surface by chemical polishing or the like after removing the forsterite film once formed by pickling, the manufacturing cost inevitably increases, and the yield also decreases due to the elution of the iron source. Inevitable. In order to improve these problems, a method using inert Al ₂ O ₃ , which does not react with the steel sheet, as an annealing separator instead of MgO is disclosed in US Pat. No. 3,785,882.
It was disclosed in the same No. 3932235 and Japanese Unexamined Patent Publication No. 53-22113. Furthermore, according to Special Publication No. 58-44152,
Sr or Ba is added to the annealing separator mainly composed of Al ₂ O ₃ .
A method was disclosed to remove subsurface internal oxides by adding a source to obtain a smoother surface. In parallel with the advances in technology for reducing iron loss through magnetic domain refinement and improvement of domain wall mobility as described above, the forsterite film on the surface of unidirectional electrical steel sheets and the tension coating thereon have an effect on the magnetic domain structure of the material. The effect was fundamentally investigated for the purpose of reducing iron loss or from the viewpoint of magnetic properties. This type of research progressed rapidly with the establishment of a means to directly observe magnetic domains with the film attached. Irie was the first to report the magnetic domain structure of a grain-oriented electrical steel sheet with a coating using a scanning electron microscope.
Fukuda (AIP Conf.Proc.No.29P.574
(1975)). They discovered that the reflux magnetic domain disappeared when the film was attached, and the 180° magnetic domain was subdivided, and attributed this to the tension of the film.
Since then, many papers have been published on magnetic domain observation using scanning electron microscopy (for example, SDWashko
& E.G.Choby, IEEE Trans Mag MAG―15,
P1586 (1979), SDWDWashko, TSHhen W.
G. Morris J. Appl. Phys. 53, P8296 (1982)). At present, the effects of the forsterite film and the tension coating thereon on the magnetic domain structure and core loss of unidirectional electrical steel sheets can be summarized as follows, for example. 1. If the [001] axis of the crystal grain has a deviation angle β of several degrees from the rolling surface, the magnetic domain width will be reduced by the addition of a forsterite film. This is thought to be due to the increase in static magnetic energy on the surface of the steel sheet due to the surface roughness that occurs with the addition of the film. 2 However, despite this subdivision of magnetic domains, the core loss values obtained at 1.7T excitation are worse than those of mirror-polished materials. This is thought to be due to the pinning of the domain wall due to the unevenness of the steel sheet surface that occurs when the film is added. 3. The tension coating added on top of the forsterite film reduces the iron loss value. The reason for this is thought to be that the generation of refluxing magnetic domains during the magnetization process is suppressed by the tension effect, rather than the subdivision of the magnetic domain width. <Problems to be Solved by the Invention> As described above, in order to reduce iron loss, it is important to reduce the magnetic domain width and increase the mobility of the domain wall. However, the conventional techniques have several problems as described below. First, the method of subdividing magnetic domains by introducing a laser or minute strain has the disadvantage that the introduced strain disappears during annealing when assembling the transformer, and the effect is lost. The method of shaping a steel plate into a corrugated shape before final annealing also has problems with shape correction after annealing. Regarding the method of smoothing the surface, the method of pickling is not profitable in terms of equipment and cost, and the method of using Al ₂ O ₃ as an annealing separation material has problems such as subsequent insulation coating, so it is not practical. It has not yet come to fruition. In addition, although the forsterite films obtained to date have a magnetic domain refining effect, the iron loss value obtained due to the pinning effect on the domain wall is poor.
Tension coating is required. <Means for Solving the Problems> An object of the present invention is to eliminate and improve these problems seen in the prior art and to provide a forsterite film that significantly reduces the iron loss value. The forsterite film is produced by a solid phase reaction between SiO ₂ in the oxide film formed during decarburization annealing and MgO applied afterwards during final finish annealing. This MgO--SiO ₂ solid phase reaction, like reactions between oxides in general, is greatly affected by the atmosphere during the reaction, the components in the steel, or the trace additives present there. Therefore, by using these conditions as parameters, it is possible to obtain forsterite films having various different properties. For example, the addition of Sr to powder as seen in the above-mentioned Japanese Patent Publication No. 57-32716, Mn in steel as seen in Japanese Patent Application No. 59-53819 by the present inventors.
Such techniques include the regulation of activity and oxygen partial pressure during final annealing. After forming forsterite films with different properties on unidirectional electrical steel sheets in this way, the present inventors investigated the advantages and disadvantages of these films from the perspective of subdivision of magnetic domains and mobility of domain walls. Through investigation, we obtained a forsterite coating that has a superior effect on reducing iron loss. The characteristics of the present invention are weight %, C≦0.085%, Si: 2.5 to 4.5
%, acid soluble Al: 0.010~0.050%, N: 0.0045~
A silicon steel slab containing 0.012% and S, Se, and Mn with the following relationship: S+0.405Se≦0.010, and 0.8≧Mn≧0.05+7 (S+0.405Se), and the remainder being substantially Fe, is heated. After rolling, precipitation annealing, cold rolling with a final cold rolling reduction of 81% or more, decarburizing annealing, and finishing annealing after applying an annealing separator, under oxygen partial pressure PO in a temperature range of 850 to 1100°C. ₂ in the area surrounded by A, B, C, D, and E in Figure 11 for Mn-1.719 (V + 0.405 Se). Saga is 1.5~ in JIS (B0601)
Forstellite (Mg ₂ SiO ₄ ) on the surface of a unidirectional electrical steel sheet whose diameter is 4.0 μm and whose primary insulation film exerts a tension of 550 g/mm ² or more (value converted to a product sheet thickness of 0.30 mm). with B ₈ ≧1.9
The present invention provides a method for manufacturing a unidirectional electrical steel sheet having excellent magnetic properties and having a magnetic flux density of (T). Next, the present invention will be explained in detail. FIG. 1 shows a cross-sectional photograph of the forsterite film of the present invention together with a comparative example. The film tension that these films give to a product with a plate thickness of 0.30 mm is 610, respectively.
g/mm ² , 380 g/mm ² . The film tension was measured using the usual deflection method (A.Brenner & S.Sendexott J.Res.
Nat. Bur. Stand 42 105 1949).
In addition, as can be seen from this photo, the film of the present invention has significant unevenness, with a difference of approximately 5 μm between the highest and lowest points, which is in accordance with the JIS standard (JIS B
The average roughness defined by 0601), Ra, is 3 μm.
In contrast, the average roughness of the comparative material is 1 μm. These two types of coatings were added to steel sheets that had already undergone secondary recrystallization, and the iron loss values at 1.7T and 50Hz were compared. The results are shown in FIG. When the film of the present invention is added, the iron loss value is 0.05 to 0.05 compared to comparative materials.
About 0.10watts/Kg is low. In order to clarify that these differences are due to the film, the added forsterite film was removed by pickling, and 10%
After mirror polishing using hydrogen peroxide solution containing hydrofluoric acid, measure the iron loss again, subtract this value from the iron loss value before removing the film (Figure 2), and calculate this difference ΔW for the material with the forsterite film. Plotted against _B8 .
The results are shown in FIG. The following can be seen from this figure. In the case of ordinary materials, the iron loss deteriorates due to the addition of a forsterite film, as has been said in the past. On the other hand, when the film of the present invention is added, the amount of deterioration may be small, or conversely, the iron loss may be improved by adding the film. As described above, it was experimentally confirmed that the iron loss of the steel sheet having the coating of the present invention is lower than that of the conventional steel sheet. However, the fact that the iron loss value decreases due to the addition of an uneven film is contrary to conventional knowledge. Although the reason for this is not necessarily clear, the inventors conducted experiments centered on magnetic domain observation as described below and proceeded with the study. First, we observed the magnetic domains of the static magnetic field using the usual Bitter method. FIG. 4 shows the magnetic domain structure in a demagnetized state with a film attached. The figure also shows the distribution of the deviation angle β of each crystal grain existing in the same area as the photograph. As can be seen from these drawings, in the material of the present invention, even if the crystal grains of the material are relatively large, the magnetic domain width is uniformly narrow. Next, the magnetization process was investigated using a BH curve and SEM to see changes in the magnetization mechanism due to the addition of a film. Figure 5 shows B- of the material coated with the film of the present invention.
The H curve is shown together with the results of comparative materials. The same figure also shows the BH curve of the material from which the film was removed and mirror-polished in order to clarify the effect of the film. Fifth
As shown in Figure a, the addition of the coating of the present invention results in a constricted BH curve with low initial permeability and low residual magnetic flux density. There was no increase in hysteresis loss due to the appearance of this snake-shaped curve. However, the appearance of such a snake-shaped curve suggests a change in the magnetization mechanism of the material, and the present inventors continued to observe magnetic domains along this BH curve. Figure 6 shows photographs of a series of magnetic domains along the BH curve, together with comparative materials. The observations can be summarized as follows. 1. The film of the present invention tends to drag the movement of the 180° domain wall and has a low initial magnetic permeability. 2 Once a reflux magnetic domain is formed, its contraction is smooth. Therefore, the magnetization of the material at this stage is fast. 3. Even when the magnetic field is reversed, a series of refluxing magnetic domains coalesce, and the process of forming 180° magnetic domains occurs faster and more uniformly than in normal materials. 4 The width of the formed 180° magnetic domain is somewhat wide, which corresponds to a relatively low residual magnetic flux density, Br. 5. The width of the magnetic domain narrows due to the movement of the 180° domain wall until a refluxing domain in the opposite direction is generated, but this process is slow and the coercive force is not much different from that of a normal material. 6. The above changes occur when the coating of the present invention is applied. As known (e.g. JWShilling IEEE
Trans Mag MAG-14, 104, 1978) When the deviation angle β is several degrees, the dominant magnetization mechanism in the relatively high excitation region of about 1.7 (T) is not the movement of the 180° domain wall, but the growth and coalescence of the refluxing domain. It's a process. It is observed that the film of the present invention not only does not act as a barrier to the movement of the refluxing magnetic domain, but also increases its mobility. It is thought that the difference in the effect of the film on the movement of the reflux magnetic domain causes the difference in the iron loss value of the materials. Adding a tension coating to a material that has a forsterite film with a normal tension of about 350 g/mm ² causes a decrease in iron loss, but there is a large change in the magnetization process as seen in the occurrence of a snake-shaped hysteresis curve. doesn't happen. The reduction in iron loss due to tension coating is thought to be due to the effect of suppressing the generation of reflux magnetic domains that occur in the main magnetic domain during the magnetization process (SDWashko & W.G.
Morris, J.Nag.Mag.Mat.19 349 (1980)). It is thought that the film of the present invention has other effects on the magnetization process, and this is thought to be due to factors other than tension, that is, the unevenness of the film. In other words, the roughness of the film-steel plate interface contributes to the fragmentation of the magnetic domain of the static magnetic field and increases magnetization, either by increasing the overall magnetostatic energy of the system or by imparting local strain. This makes it easier for freewheeling magnetic domains to occur and disappear during the process, and is considered to be effective in reducing iron loss overall. The present inventors found that such an effect due to unevenness at the interface between the coating and the steel plate appears only when the coating has a strong tension of 550 g/mm ² or more against the steel plate, and furthermore, the B ₈ of the steel plate is 1.91 (T) or more. We have arrived at the present invention by discovering this phenomenon, which is remarkable for high-magnetic-flux-density grain-oriented electrical steel sheets. Next, the reasons for limiting the constituent factors of the present invention will be described. First, the roughness at the interface between the coating and the steel plate is necessary to bring about a change in the magnetization process of the material, which is represented by the snake-shaped hysteresis curve. However, if the roughness is too large, the iron loss value will deteriorate, which is thought to be caused by pinning due to domain wall movement, so the roughness of the film should be the average roughness (JIS standard B0601).
It needs to be in the range of 1.5 to 4.0 μm. Also, with such roughness alone, the iron loss value is poor and it is not practical, but if the forsterite film is 550g/mm ² (plate thickness 0.3
If the tension is greater than (in terms of mm, the same applies hereinafter), a large change occurs in the magnetization mechanism, resulting in a good iron loss value. The coating of the unidirectional electrical steel sheet of the present invention may be only a primary coating or may further include a secondary coating, and in this case, the tension will be the sum of the primary and secondary coatings. The tension of conventional forsterite film is at most 300 to 450
g/mm ² , and the strong tension of 550 g/mm ² or more, which is a feature of the present invention, can be achieved, for example, by the method proposed by the present inventors (Japanese Patent Application No. 59-53819).
That is, when forming a forsterite film on a normal unidirectional silicon steel sheet, S, Se, and Mn in the steel are
The amount is S+0.405Se0.010 and 0.8Mn0.05+7 (S+0.405Se) in weight%, and the oxygen partial pressure PO ₂ in the temperature range of 850℃ to 1100℃ during final annealing is Mn-1.719 (S+0.405Se). ) is a method in which finish annealing is carried out while maintaining the temperature within a predetermined range. That is, this is a method of annealing while maintaining the range surrounded by A, B, C, D, and E shown in FIG. Furthermore, it has been confirmed that the above method can also be used to set the average roughness of the interface between the primary insulating film and the base metal to 1.5 to 4.0 μm. When such tension and roughness are combined, a desired iron loss value can be obtained.Next, the present invention will be explained based on specific examples. FIG. 7 shows the relationship between the tension (0.30 mm plate thickness conversion value) exerted by the coating on the steel plate and the average roughness of the interface between the coating and the steel plate. The manufacturing method for such a steel plate is as follows. C: 0.060%, Si: 3.25%, P: 0.020%, S:
0.008%, acid-soluble Al: 0.025%, N: 0.0075%,
Adding Mn to molten steel containing Cr: 0.10% (a) 0.075%, (b)
Ingots were prepared by adding 0.12%, (c) 0.18%, and (d) 0.24%. These ingots were heated at 1200°C and hot-rolled to produce hot-rolled sheets of 2.0 mm. This hot rolled sheet was annealed at 1150° C. for 2 minutes and then cold rolled to a thickness of 0.23 mm. After annealing in a humid atmosphere at 820° C. for 120 seconds, magnesia containing 3% TiO ₂ and 4% Mn _0.75 F _0.25 N _0.25 was applied and finish annealing was performed. The atmosphere at this time was 75% N ₂ , 25% H ₂ , dew point (a) 0℃, (b) −20
℃, (c) -50℃, and the temperature increase rate from 600 to 1200℃ was 10℃/hr. Magnetic flux density (B ₈ ) is obtained from a large number of unidirectional electrical steel sheets created in this way.
of 19.4 to 1.95 (T) was selected, and the average roughness of the forsterite film-steel plate interface and the tension exerted by the film on the steel plate were investigated, and the iron loss W _17/50 was measured. The iron loss values obtained in this way are plotted in FIG. 7, and each symbol in the diagram corresponds to a combination of Mn content and dew point as shown in the table below.

[Table] Based on the above, if the above tension is 550 g/mm2 ^or more and the above average roughness is in the range of 1.5 to 4.0 μm, iron loss
W _17/50 can achieve extremely low values of less than 0.9watts/Kg. In addition, in the above example, the magnetic flux density (B ₈ ) is 1.94 to 1.95.
The iron loss value was determined for the range of (T), but the reduction in iron loss due to the addition of such a forsterite film is the higher the orientation of the Goss-oriented grains of the material, that is, the higher the iron loss is for material B ₈ . Therefore, in the present invention, the magnetic flux density (B ₈ ) is specified to be 1.91 (T) or more. <Example> Example 1 C: 0.055%, Mn: 0.20%, P: 0.030%, S:
A slab containing 0.006% acid-soluble Al: 0.030% and N: 0.0078% was heated to 1150°C and then hot rolled to a thickness of 2.3 mm. After hot-rolled sheet annealing at 1120°C for 2 minutes, it was cold-rolled to 0.30mm. In this way 300
Approximately 80 cold-rolled plates measuring mm x 60 mm were obtained. These cold-rolled sheets were subjected to decarburization annealing at 830° C. for 2 minutes in wet hydrogen, and subsequently coated with magnesia containing 5% TiO ₂ . Approximately 40 of these boards were heated at 25% _N2 ,
H ₂ 75%, DP + 10℃ (invention material), N ₂ 25%,
700 in an atmosphere of H ₂ 75%, DP -40℃ (comparative material)
Annealing was performed at a heating rate of 8°C/hr to ~1200°C. Table 2 shows the average roughness of the forsterite film-steel plate interface of the obtained product and the tension exerted by the film on the steel plate. Magnetic flux density, B ₈ and iron loss W _17/50 were measured with the film thus prepared attached. Material B ₈
was distributed in the range of 1.90 to 1.95 (T). Thereafter, the film was removed by pickling, and after mirror polishing with hydrogen peroxide + 5% hydrofluoric acid solution, the iron loss W _17/50 was measured again. FIG. 8 shows a plot of these iron loss values. Thus, it can be seen that the iron loss value of the material of the present invention is as good as that of a mirror-polished material. Further, for the material with the film in FIG. 9, the DC hysteresis curves of the same material are shown in A and B in the figure.

[Table] Example 2 In order to confirm the effect of reducing the iron loss value due to the film, the forsterite film was removed from the product,
We conducted an experiment in which we added a film with different properties. First, plate thickness 0.18mm, Si3.3%, Mn0.18
300mm x 60 unidirectional electrical steel sheet products containing
After cutting into pieces of mm size, the forsterite film was removed by pickling. The average grain size of the material is approximately 2cm.
It was hot. These materials in a humid hydrogen atmosphere
It was annealed at 850°C for 60 seconds, coated with magnesia containing 3% TiO ₂ , and finished annealed. The atmosphere at this time
N ₂ 25%, H ₂ 75% dew point + 5°C (equivalent to the material of the present invention),
N ₂ 25%, H ₂ 75% dew point -40°C (comparison material). Through such processing, 2 as shown in Table 3
A seed forsterite film was obtained. B ₈ and W _17/50 of these samples were measured, and the results shown in FIG. 10 were obtained. It can be seen that the iron loss value is low when the film featured in the present invention is added, and this effect is large when the _B8 of the material is high.

[Table] <Effects of the Invention> The electrical steel sheet of the present invention has an iron loss value equivalent to or close to that obtained by magnetic domain refining technology. In addition, it has a good iron loss value comparable to mirror polishing material in the high magnetic field region of about 1.7 (T). Therefore, the effect of improving iron loss in the electrical steel sheet of the present invention is significant.
Furthermore, the industrial effect of contributing to the advancement of the manufacturing process by providing a magnetic property improvement technology that does not require magnetic domain refining technology or tension coating technology on forsterite film is also significant.

[Brief explanation of drawings]

Figure 1 is a cross-sectional photograph of the forsterite film claimed in the present invention. Figure 2 shows B ₈ of the invention material and comparative material.
It is a figure showing the relationship between and W _17/50 . Figure 3 is a diagram in which ΔW _17/50 , which is the value obtained by subtracting the iron loss value of the mirror-polished material from the iron loss value of the material with a forsterite film, is plotted against B ₈ of the material with a forsterite film. . FIG. 4 is a photograph of the magnetic domain of a material with forsterite observed by the Bitter method, a metallographic photograph showing the distribution of crystal grains present in the observed region, and a diagram showing the misorientation angle of each crystal grain. FIG. 5 shows DC hysteresis curves of the present invention and comparative materials at 1.5 (T) excitation before and after film removal. Figure 6 is a metallographic photograph (SEM photograph) and hysteresis showing changes in the magnetic domain structure along the DC hysteresis curve of a material with forsterite attached. FIG. 7 is a diagram showing the iron loss value (W _17/50 ) in relation to the film tension and the average roughness of the film. FIG. 8 is a diagram comparing the iron loss of the mirror-polished material and the forsterite film material in Example 1. FIG. 9 shows the DC hysteresis curves of the present invention material and the comparative material shown in FIG. 8 at 1.5 (T) excitation. FIG. 10 is a diagram showing the relationship between B ₈ and W _17/50 of the material shown in Example 2.
FIG. 11 is a diagram showing the relationship between oxygen partial pressure and Mn, S, and Se according to the present invention.

Claims (1)

[Claims] 1% by weight, C≦0.085%, Si: 2.5-4.5%, acid-soluble Al: 0.010-0.050%, N: 0.0045-0.012%
A silicon steel slab containing S, Se, and Mn in such a manner that S+0.405Se≦0.010 and 0.8≧Mn≧0.05+7 (S+0.405Se), the remainder being substantially Fe, is hot-rolled. Then, precipitation annealing is performed, followed by cold rolling with a final cold rolling ratio of 81% or more, followed by decarburization annealing, finishing annealing after applying an annealing separator, and oxygen partial pressure PO ₂ in a temperature range of 850 to 1100°C. The average roughness of the interface between the primary insulating film and the steel plate is , 1.5 to JIS (B0601)
Forsterite (Mg ₂ SiO ₄ ) on the surface of a unidirectional electrical steel sheet with a diameter of 4.0 μm and a tension applied to the steel sheet by the primary insulation film of 550 g/mm ² or more (value converted to a product sheet thickness of 0.30 mm). and B ₈ ≧
A method for producing a unidirectional electrical steel sheet with excellent magnetic properties, characterized by having a magnetic flux density of 1.9 (T).