JP7356017B2 - Grain-oriented electrical steel sheet and method for producing grain-oriented electrical steel sheet - Google Patents

Description

The present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing a grain-oriented electrical steel sheet.

Grain-oriented electrical steel sheets have a crystal structure with {110}<001> as the main orientation, and are often used as core materials for transformers. Grain-oriented electrical steel sheets are required to be materials with low iron loss, especially in order to reduce energy loss.

Patent Document 1 describes a method of irradiating a laser beam onto the surface of a steel sheet after final annealing to give local strain, thereby subdividing magnetic domains, as a means of reducing iron loss in a grain-oriented electrical steel sheet. ing.

Patent Document 2 describes a magnetic domain refining means that does not lose its effect even after applying strain relief annealing (stress relief annealing) after core processing.

On the other hand, iron alloys containing iron and silicon have large magnetocrystalline anisotropy, so when external tension is applied, magnetic domains become fragmented, which can reduce eddy current loss, which is the main element of iron loss. . In particular, it is known that applying tension to the steel sheet is effective in reducing iron loss in grain-oriented electrical steel sheets containing 5% or less silicon. This tension is provided by a coating formed on the surface.

Grain-oriented electrical steel sheets include a primary film mainly composed of forsterite, which is produced by the reaction between oxides on the surface of the steel sheet and an annealing separator in the final annealing process, and colloidal silica and phosphorus described in Patent Document 3. A tension of about 10 MPa is applied to a plate with a thickness of 0.23 mm by the two-layer coating consisting of a secondary coating mainly made of amorphous material produced by baking a coating liquid mainly composed of acid salts. There is. In order to effectively apply tension to a steel plate with such a coating, the mechanical properties of the coating itself must be appropriate, such as a low thermal expansion coefficient and high rigidity of the entire coating, and the coating must have appropriate mechanical properties. It is necessary to satisfy two conditions: the adhesion of the steel plate is good.

Regarding the mechanical properties of the coating, Patent Document 4 proposes a grain-oriented electrical steel sheet having a coating mainly composed of aluminum borate crystals on its surface.

Japanese Unexamined Patent Publication No. 55-018566 Japanese Unexamined Patent Publication No. 62-86175 Japanese Unexamined Patent Publication No. 48-39338 Japanese Patent Application Publication No. 6-65754

In the case of a conventional coating as described in Patent Document 3, increasing the amount of coating increases the rigidity of the entire coating, so it is possible to apply even greater tension, and there is a possibility of improving iron loss by increasing the tension. is left behind. However, it is not preferable to make the coating thicker than the current thickness in order to improve the applied tension because this will result in a decrease in the space factor. For this reason, there is a need for a coating that has excellent adhesion without causing a decrease in space factor, and is capable of imparting large tension to a steel plate even if it is thin.

In order for a certain coating to have a high tensile strength without increasing the coating thickness, it is required that the Young's modulus of the coating be increased or that the thermal expansion be low, or that both be achieved at the same time. Generally, a crystalline material has a higher Young's modulus than an amorphous material, so a method of forming a crystalline coating may be considered in order to increase the Young's modulus. The film made of aluminum borate developed based on these guidelines and described in Patent Document 4 is mainly composed of crystals, so it is different from the conventional film made of silica and phosphate as described in Patent Document 3. Young's modulus is higher than that of an amorphous film. Aluminum borate crystals also have a sufficiently low coefficient of thermal expansion, so combined with the effect of Young's modulus, it is possible to obtain higher tension than the coating described in Patent Document 3.

On the other hand, even if the coating itself has high rigidity and low thermal expansion, if the adhesion between the coating and the steel plate is not good, the coating will peel off and no tension can be applied. In particular, since the aluminum borate coating has a high ability to impart tension, a large tension can be obtained by coating it thickly. However, when the tension is increased, adhesion may become a problem, but it has not always been clear how to easily obtain sufficient adhesion.

An object of the present invention is to provide a grain-oriented electrical steel sheet and a method for manufacturing the grain-oriented electrical steel sheet, which have an insulating film that can be applied with a larger tension than before.

The present inventor believes that in order to impart high tension to a steel plate with an insulating film such as an aluminum borate film, the adhesion of the interface between the aluminum borate film located at the outermost layer and the primary film located below it is important. We considered ways to improve the adhesion of this interface. As a result, it was found that adhesion can be improved by keeping the roughness of this interface constant.

The present invention has been made based on the above findings, and the gist thereof is as follows.

(1) The outermost layer of the steel plate has an insulating coating made of oxide crystal containing aluminum and boron and having a mass ratio of 1.80 to 2.60 in terms of Al ₂ O ₃ /B ₂ O ₃ . death,
There is an intermediate layer made of forsterite between the insulating coating and the steel plate, and the tension of the insulating coating is 4.0 MPa/g/m ² or more per amount of the insulating coating deposited on one side of the steel plate,
The arithmetic mean roughness Ra of the roughness curve of the interface between the insulating coating and the intermediate layer is 0.35 μm or more and 0.85 μm or less, and the average length RSm of the elements in the roughness curve of the interface is 20 μm or more. A grain-oriented electrical steel sheet characterized by having a thickness of 100 μm or less.
(2) Applying a coating solution containing a boron source and an aluminum source with a mass ratio of 1.80 to 2.60 in terms of Al ₂ O ₃ /B ₂ O ₃ to the surface of a steel plate having a primary coating made of forsterite. and the step of
Heating the steel plate in an inert gas atmosphere having a dew point of 0 to 40°C and containing 0 to 25% by volume of hydrogen such that the average temperature increase rate is 2 to 5°C/sec to reach a temperature of 600°C or less. After that, cooling to 200°C or less at an average cooling rate of 5°C/second or more and less than 10°C/second,
heating the steel plate at an average temperature increase rate of 10 to 100°C/sec to 750°C, and heat-treating the steel plate in a temperature range of 750 to 1000°C for 20 to 120 seconds. manufacturing method of magnetic steel sheet.

According to the present invention, by controlling the roughness of the interface between the insulating coating and the intermediate layer made of forsterite, it is possible to obtain a grain-oriented electrical steel sheet having an insulating coating that can be applied with greater tension than before. can.

<1. Grain-oriented electrical steel sheet＞
The grain-oriented electrical steel sheet according to this embodiment will be described below. The grain-oriented electrical steel sheet according to the present embodiment includes a steel plate (base steel plate), an intermediate layer made of forsterite provided on the steel plate , and aluminum and boron further formed on the intermediate layer. and an insulating coating made of an oxide crystalline material having a mass ratio in terms of Al ₂ O ₃ /B ₂ O ₃ of 1.80 to 2.60.

There are no particular restrictions on the steel plate (base steel plate) that can be used in this embodiment as long as it has undergone secondary recrystallization. A steel plate generally used as a base material steel plate is, for example, a steel plate having a forsterite primary coating formed during finish annealing (secondary recrystallization annealing).

As described above, an insulating film made of an oxide containing aluminum and boron and an intermediate layer made of forsterite are provided on the surface of the steel plate.

The present inventor investigated and studied conditions for realizing improved adhesion of an insulating coating. As a result, by controlling the roughness of the interface between the insulating coating (aluminum borate coating) and the intermediate layer made of forsterite, grain-oriented electrical steel sheets with coatings with good adhesion and high tensile ability were created. I found out what I can get. Specifically, when the arithmetic mean roughness Ra of the interface is 0.35 μm or more and 0.85 μm or less and the average length RSm of the elements in the interface roughness curve is 20 μm or more and 100 μm or less, good adhesion and high tension are achieved. It has been found that a grain-oriented electrical steel sheet can be obtained that has a coating that has the ability to provide a coating.
Furthermore, since it is necessary to ensure tension, it is necessary that the tension of the insulating coating is 4.0 MPa/g/m ² or more per amount of the insulating coating deposited on one side of the steel plate.

There are various methods for measuring surface roughness, but a method using a stylus roughness meter or a measuring device using a laser beam is simple, and in the case of the present invention, a method using a measuring device using a laser beam is particularly convenient. Ra and RSm are measured in accordance with JIS B601:2001.

To measure the roughness of the interface, remove the outermost insulating coating, the aluminum borate coating, expose the intermediate layer, the primary coating, measure the surface roughness of the intermediate layer, and calculate the surface roughness of the interface. Surface roughness. Removing the outermost insulating film to expose the intermediate layer can be easily achieved by removing the insulating film by immersing it in an aqueous sodium hydroxide solution.

The reason why the roughness of the interface between the aluminum borate film and the intermediate layer affects the adhesion of the aluminum borate film is that the adhesion of this interface depends on the strength of the mechanical bond. Conceivable. In other words, it is considered that the type of bonding force that influences the adhesion of this interface is not the bonding force between atoms or molecules, but the mechanical bonding force due to the so-called fitting structure has a large effect.

In order to obtain a strong fitted structure, it is considered important to control the depth of the fitting that penetrates into the mating layer and the period of the portion that penetrates. When expressed in terms of the roughness curve of the surface of the intermediate layer, it is thought that the depth of the fit corresponds to the arithmetic mean roughness Ra, and the period of the intruding portion corresponds to the average length RSm of the elements in the roughness curve.

Considering the above mechanism, it can be understood why the roughness of the interface between the aluminum borate film, which is an insulating film, and the intermediate layer affects the adhesion. Note that a fitting structure is developed at the interface between the intermediate layer and the steel plate, and sufficient adhesion is obtained at this interface.

There is a good range for Ra and RSm, and good adhesion cannot be obtained outside this range. Regarding Ra, if this value is too small, the adhesion will be insufficient. Further, if Ra is too large, the adhesion between the intermediate layer and the steel plate deteriorates, but the details of this reason are not clear, but the inventor estimates it as follows. It is presumed that if Ra is too large, the fitting structure will develop excessively, and the intermediate layer will no longer be able to maintain its membrane structure, making it impossible to maintain the strength of the intermediate layer itself, and peeling will occur between the intermediate layer and the steel plate. For the above reasons, the arithmetic mean roughness Ra needs to take a value of 0.35 μm or more and 0.85 μm or less.

There is also a good range for RSm, which needs to be 20 μm or more and 100 μm or less. Even if Ra is 0.35 μm or more and 0.85 μm or less, good adhesion cannot be obtained if RSm is too small or too large, and in either case, the interface between the aluminum borate film and the intermediate layer Peeling is more likely to occur. The reason for this is not clear, but the inventor estimates it as follows. In other words, if RSm is too small, the thickness of the parts that penetrate into each other's layers will become too thin, making it impossible to maintain the strength of the mating structure, and if RSm is too large, the parts that penetrate into each other's layers will have sufficient strength, but they will still penetrate. It is presumed that this is because the spacing between the parts is too wide, reducing the strength of the fitted structure.

<2. Manufacturing method of grain-oriented electrical steel sheet>
Next, a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment will be described. In the method for producing a grain-oriented electrical steel sheet according to the present embodiment, a coating solution containing a boron source and an aluminum source having a mass ratio of 1.80 to 2.60 in terms of Al ₂ O ₃ /B ₂ O ₃ is mixed with forsterite. The step of coating the surface of a steel sheet with a primary coating consisting of the following steps, and the average temperature increase of the steel sheet to an ultimate temperature of 600°C or less in an inert gas atmosphere with a dew point of 0 to 40°C and containing 0 to 25% by volume of hydrogen. After heating the steel plate at a rate of 2 to 5°C/sec, the steel plate is cooled to 200°C or less at an average cooling rate of 5°C/sec or more and less than 10°C/sec, and the steel plate is heated at an average heating rate of 750°C. and heat treatment in a temperature range of 750 to 1000°C for 20 to 120 seconds.

The present inventors have studied in detail the process conditions for achieving the above-mentioned interface roughness. As a result of process studies, in order to form an insulating film that satisfies the above conditions, the mass ratio of aluminum oxide to boron oxide, Al ₂ O ₃ /B ₂ O ₃ , in the base steel sheet of grain-oriented electrical steel sheet must be 1.80. It has become clear that after coating a coating solution with a coating temperature of ~2.60, it is advisable to limit the temperature and atmospheric conditions for post-coating drying and heat treatment, including baking temperature.

This process consists of the following (i) to (iii).
(i) Diffusion of boron during heating after drying of the coating solution and before crystallization of aluminum borate.
(ii) Reaction of excess boron with the intermediate layer and nucleation of aluminum borate crystals.
(iii) Crystal growth of aluminum borate.

Hereinafter, the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment will be explained in detail, referring to the correspondence with the above processes (i) to (iii).

First, prior to each step, a base steel plate on which an insulating coating will be formed is prepared. Specifically, as the base material steel plate, a steel plate that has been finish annealed, such as a steel plate on which a forsterite primary coating is formed by finish annealing by a conventionally known method, may be prepared. Since the present invention is a technology for controlling the roughness of the interface with the intermediate layer, a steel plate without a primary coating made of forsterite after secondary recrystallization is inappropriate.

Next, a coating liquid for forming an insulating film is applied to such a base steel plate. The coating liquid contains a boron source and an aluminum source having a mass ratio in terms of Al ₂ O ₃ /B ₂ O ₃ of 1.80 to 2.60.

As a boron source, orthoboric acid represented by H ₃ BO ₃ is most preferable from the viewpoint of workability, cost, etc., but metaboric acid represented by HBO ₂ , boron oxide represented by B ₂ O ₃ , or any of these may also be used. Mixtures of can also be used.

Examples of the aluminum source include aluminum oxide and aluminum oxide precursor compounds. Examples of aluminum oxide precursor compounds include hydrates of aluminum oxide expressed as Al ₂ O ₃ .mH ₂ O such as boehmite, aluminum hydroxide, and various other compounds including aluminum nitrate and aluminum chloride. Aluminum salts and the like are preferably used.

Further, the boron source and the aluminum source in the coating solution are contained so that the mass ratio in terms of Al ₂ O ₃ /B ₂ O ₃ is 1.80 to 2.60. Thereby, an insulating film can be formed with an appropriate composition ratio. On the other hand, if the above mass ratio is less than 1.80, the amount of boron in the insulating film becomes too large, resulting in too much boron being accumulated at the interface, and the presence of boron in the insulating film becomes uneven, resulting in In some parts of the coating, aluminum borate crystals may not be formed sufficiently, resulting in a decrease in coating tension. In addition, if the above mass ratio exceeds 2.60, the aluminum source becomes too large, and as a result, the amount of boron near the interface between the insulating coating and the base steel sheet is insufficient, resulting in fewer aluminum borate crystals being generated. , the coating tension does not increase.

The mass ratio is preferably 1.90 or more and 2.40 or less, more preferably 2.00 or more and 2.20 or less.

These raw materials are dispersed in a dispersion medium to prepare a slurry as a coating liquid. The best dispersion medium is water, but organic solvents or mixtures thereof can be used as long as they do not interfere with other steps. The solid content concentration of the slurry may be appropriately selected depending on the workability and the like, and is not particularly limited.

Furthermore, by using a fine particle dispersion system called a sol as the aluminum oxide precursor in this slurry, a thin, uniform, and highly adhesive insulating film may be obtained. This is particularly noticeable when there is no non-metallic substance on the surface of the steel plate and an insulating film is formed directly on the metal surface of the steel plate.

When a sol is used in the coating liquid, the above-mentioned boehmite sol and/or alumina sol are particularly suitable as aluminum oxide precursors from the viewpoint of workability, cost, etc.

In addition, the coating liquid may contain components other than those mentioned above within a range that does not inhibit the effects of the present invention.

The obtained slurry (coating liquid) is applied to the surface of a grain-oriented electrical steel sheet that has been finish-annealed using a coater such as a roll coater, a dipping method, spraying, electrophoresis, or the like.

Note that the coating liquid before application (coating) is preferably kept at a temperature of, for example, 20° C. or higher and 40° C. or lower in order to prevent precipitation of boric acid and excessive evaporation of water. If the temperature of the coating solution is too low, depending on the type and concentration of the boron source, boric acid may precipitate in the coating solution, and if the temperature is too high, the water content tends to decrease, making normal coating impossible. However, the desired coating may not be obtained.

Next, the steel plate was heated in an inert gas atmosphere with a dew point of 0 to 40°C and containing 0 to 25% by volume of hydrogen such that the average heating rate was 2 to 5°C/second to reach a temperature of 600°C or less. Heat. In such a temperature range from room temperature to an ultimate temperature of 600°C or less, the coating solution is heated, dried, and a film-like substance consisting of a mixture of boron compounds and aluminum compounds formed on the base steel plate after drying is completed. Heating takes place.

The reason why the average temperature increase rate is limited to 2 to 5° C./sec is to ensure sufficient diffusion of boron in the above process (i). If the average temperature increase rate is too fast, boron will not diffuse sufficiently, making it impossible to obtain the desired composition and amount of aluminum borate crystalline components, and also causing film defects due to bumping when the coating solution dries. Become. On the other hand, if the average temperature increase rate is too slow, boron evaporates too much, making it impossible to obtain an insulating film with the desired composition. That is, if the average temperature increase rate is outside the range of 2 to 5° C./sec, high tension cannot be obtained.

The temperature reached in heating the steel plate may be higher than 450°C and lower than 600°C, but preferably higher than 480°C and lower than 530°C. This makes it possible to sufficiently diffuse boron while suppressing evaporation of boron, and to suppress the formation of unnecessary crystals.

Furthermore, examples of the inert gas in the atmosphere during heating include nitrogen, and rare gases such as helium, argon, and xenon. Among these, nitrogen is preferable also in order to suppress costs.

Further, the atmosphere during heating contains hydrogen in an amount of 0 to 25% by volume, preferably more than 0 to 25% by volume. Thereby, oxidation between the steel plate and the insulating coating can be suppressed and adhesion can be ensured. Even if the hydrogen content in the atmosphere exceeds 25% by volume, there is no particular problem, but it is not preferable from the viewpoint of excessive cost.

Further, the dew point of the atmosphere during heating is 0° C. or higher and 40° C. or lower. When the dew point is less than 0°C, sufficient tension of the insulating coating cannot be ensured. Further, when the dew point exceeds 40° C., oxidation tends to occur at the interface between the steel plate and the insulating coating, resulting in a problem that adhesion may deteriorate. The dew point of the atmosphere during heating is preferably 10°C or more and 30°C or less.

Next, the steel plate is heated to the final temperature at the above-mentioned average heating rate, and then cooled to 200° C. or lower at a cooling rate of 5° C./second or more and less than 10° C./second. Although the reason for the effect of this process is not clear, regarding process (ii) above, such cooling treatment not only promotes nucleation of aluminum borate crystals, but also causes excess boron to interact with forsterite in the intermediate layer. It is believed to react and form a precursor stage structure for forming a mating structure. After this structure, it is thought that the fitting structure is completed in the next heating process of heating the steel plate to 750° C. or higher. By realizing such a fitting structure, adhesion is improved. By improving adhesion, high tension can be applied to the steel plate when a film with high tension application ability is formed. Conversely, even if a coating with high tension imparting ability is formed, if the adhesion is not sufficient, high tension cannot be applied to the steel plate, and as a result, a high tension coating cannot be realized. If the temperature reached by cooling is not 200° C. or less, or if the average cooling rate is less than 5° C./second or more than 10° C./second, sufficient adhesion cannot be obtained. In other words, under these conditions, the adhesion of the film is not sufficient, so it is not possible to obtain the high tension effect as in this case. The temperature reached by cooling may be 200°C or less, but from the viewpoint of cost and required time, it is not preferable to set the temperature to an excessively low temperature, and preferably 100°C or more and 200°C or less.

Next, the steel plate is heated so that the average temperature increase rate up to 750°C is 10 to 100°C/sec, and heat treated in a temperature range of 750 to 1000°C for 20 to 120 seconds. After drying the coated steel plate as described above, it is baked at 750° C. or higher to form an oxide film as an insulating film on the surface.

As described above, by heating the steel plate to 750° C. at an average heating rate of 10 to 100° C./sec, boron evaporation can be suppressed in the process (i) described above. That is, in a temperature range of 600° C. or higher, evaporation of boron is particularly likely to proceed, so the temperature of the steel plate is raised at a relatively fast rate as described above. If the average heating rate is slow, evaporation of boron will proceed, making it impossible to obtain an insulating film with the desired composition. There is no problem even if the average heating rate is fast, but if it exceeds 100°C/sec, no improvement will be seen compared to a lower average heating rate, and rapid heating The practical upper limit of the average temperature increase rate is 100° C./sec, since this can be a factor that increases equipment costs. The average temperature increase rate is preferably 50°C/second or more and 80°C/second or less.

The reason why heat treatment is required at 750 to 1000°C for 20 to 120 seconds is because crystal growth of aluminum borate occurs at 750°C or higher and crystallization progresses in the above-mentioned process (iii). If the temperature and time are less than the above ranges, crystallization of aluminum borate will not proceed sufficiently and sufficient tension will not be obtained. Furthermore, if the baking temperature (heat treatment temperature) is less than 750° C., the applied precursor may not become an oxide, and sufficient tension will not be developed due to the low baking temperature, which is not preferable.

Although there is no problem if the heat treatment temperature (soaking temperature) or heat treatment time exceeds this range, the effect of increasing the temperature or increasing the time will not be obtained.

The heat treatment temperature may be within the above-mentioned range, but is preferably 800° C. or higher and 950° C. or lower from the viewpoint of the balance between the effect on tension improvement and cost. Further, the heat treatment time may be within the above-mentioned range, but is preferably 50 seconds or more and 90 seconds or less.

Note that when the temperature is raised above 750°C, the time from when the temperature exceeds 750°C until the temperature becomes below 750°C is defined as the heat treatment time.

The atmosphere during baking (temperature raising and heat treatment) is preferably a reducing atmosphere such as an inert gas atmosphere such as nitrogen or a nitrogen-hydrogen mixed atmosphere. Air or an atmosphere containing oxygen may oxidize the steel plate and is therefore undesirable.

As for the dew point of the atmospheric gas, good results can be obtained at 0 to 40°C. Alternatively, the atmosphere during baking may be the same as the atmosphere during drying of the coating liquid.

In the manner described above, a grain-oriented electrical steel sheet having a high tensile strength and having an insulating coating as described above is obtained.

The present invention will be described in more detail below based on Examples, but the Examples shown below are merely examples of the present invention, and the present invention is not limited only to these Examples.

(Experiment example 1)
A commercially available boric acid reagent and aluminum oxide (Al ₂ O ₃ ) powder (average particle size: 0.4 μm) were mixed in the proportions shown in Table 1. Note that boric acid was weighed in terms of boron oxide (B ₂ O ₃ ) equivalent. Distilled water was added to this to prepare a slurry.

The obtained slurry was applied to a unidirectional silicon steel plate (with a forsterite primary coating) containing 3.2% Si, having a thickness of 0.23 mm, and which had been finish annealed. The coating was applied so that the weight was 4.5 g/m ² per side of the steel plate. Thereafter, after drying and cooling under the conditions shown in Table 1, the temperature was raised to 750°C, and baking (heat treatment) was performed at this temperature with a soaking time of 100 seconds to form an insulating coating. The temperature reached by the steel plate during drying was 500°C. The atmosphere during drying, cooling, heating, and baking was a nitrogen atmosphere containing 10% hydrogen, and the dew point was 30°C.

The sample on which the insulating coating was formed was measured by X-ray diffraction, and the presence of crystalline aluminum borate in the insulating coating was confirmed from the diffraction lines.

Next, a test piece of 80 mm x 80 mm was cut out from the grain-oriented electrical steel sheet on which the insulating film had been formed, wrapped around a round bar with a diameter of 20 mm, and then flattened to measure the area of the insulating film that had not peeled off from the electrical steel sheet. The remaining area ratio of the film was measured, and the adhesion of the insulating film was evaluated. "Good" means that the remaining area ratio of the film is 90% or more. "Poor" means that the remaining area ratio of the film is less than 90%.

Furthermore, the coating on one side of the steel plate on which the insulating coating was formed was removed, and the coating tension was calculated from the bending of the steel plate. This tension is the tension of only the aluminum borate film (insulating film), which does not include the forsterite layer. A sodium hydroxide aqueous solution was used to remove the insulating film. Specifically, the steel plate is immersed in a 20% aqueous sodium hydroxide solution at 80° C. for about 10 minutes. To remove only one side, protect the side that is not to be removed with tape or the like. The tension was defined as high tension when the tension per amount of insulating coating deposited on one side of the steel plate was 4.0 MPa/g/m ² or more.

The surface roughness of the interface was determined by measuring the surface roughness of the intermediate layer in accordance with JIS B601:2001 using a laser beam measurement device on a steel plate with the insulation coating removed to expose the intermediate layer. is the roughness of the interface.

From the results in Table 1, it can be seen that in Examples of test numbers 1 to 3, 9 to 11, 17, 18, 21, and 22, insulating coatings with excellent adhesion and high tension were obtained.

(Experiment example 2)
To 100 g of commercially available aluminum oxide (Al ₂ O ₃ ) powder (average particle size: 0.4 μm), 45.3 g of boric acid reagent (equivalent to boron oxide (B ₂ O ₃ )) was added, and distilled water was added to this. A slurry was prepared. Al ₂ O ₃ /B ₂ O ₃ is 2.2.

This slurry was baked onto a unidirectional silicon steel plate (with a forsterite primary coating) containing 3.2% Si, having a thickness of 0.23 mm, and which had been finish annealed. It was applied at a concentration of 4.5 g/m ² per side. After that, the temperature was raised to 500°C at an average temperature increase rate of 3°C/sec in a nitrogen atmosphere containing 10% by volume of hydrogen with a dew point of 30°C, and then cooled to 200°C at an average cooling rate of 8°C/sec. The temperature was increased at an average temperature of 50° C./sec until the temperature reached 50° C., and baking (heat treatment) was performed under the conditions shown in Table 2 to form an insulating film.

The sample on which the insulating coating was formed was measured by X-ray diffraction, and the presence of crystalline aluminum borate in the insulating coating was confirmed from the diffraction lines.

In addition, in the same manner as in Experimental Example 1, the remaining area ratio of the insulating coating was calculated, and the adhesion of the insulating coating was evaluated. "Good" means that the remaining area ratio of the film is 90% or more. "Poor" means that the remaining area ratio of the film is less than 90%.

As in Example 1, the coating on one side of the steel plate on which the insulating coating was formed was removed, and the coating tension was calculated from the bending of the steel plate. This tension is the tension of only the aluminum borate film (insulating film), which does not include the forsterite layer. A sodium hydroxide aqueous solution was used to remove the insulating film. A tension of 18 MPa or more was defined as high tension.

The surface roughness of the interface was determined by measuring the surface roughness of the intermediate layer in accordance with JIS B601:2001 using a laser beam measurement device on a steel plate with the insulation coating removed to expose the intermediate layer. is the roughness of the interface.

From the results in Table 2, it can be seen that Examples with test numbers 24 to 30 had excellent adhesion and high film tension.

Claims (2)

The outermost layer of the steel plate has an insulating coating made of an oxide crystalline material containing aluminum and boron and having a mass ratio of 1.80 to 2.60 in terms of Al ₂ O ₃ /B ₂ O ₃ ,
There is an intermediate layer made of forsterite between the insulating coating and the steel plate, and the tension of the insulating coating is 4.0 MPa/g/m ² or more per amount of the insulating coating deposited on one side of the steel plate,
The arithmetic mean roughness Ra of the roughness curve of the interface between the insulating coating and the intermediate layer is 0.35 μm or more and 0.85 μm or less, and the average length RSm of the elements in the roughness curve of the interface is 20 μm or more. A grain-oriented electrical steel sheet characterized by having a thickness of 100 μm or less. applying a coating solution containing a boron source and an aluminum source with a mass ratio of 1.80 to 2.60 in terms of Al ₂ O ₃ /B ₂ O ₃ to the surface of a steel plate having a primary coating made of forsterite; ,
Heating the steel plate in an inert gas atmosphere having a dew point of 0 to 40°C and containing 0 to 25% by volume of hydrogen such that the average temperature increase rate is 2 to 5°C/sec to reach a temperature of 600°C or less. After that, cooling to 200°C or less at an average cooling rate of 5°C/second or more and less than 10°C/second,
heating the steel plate at an average temperature increase rate of 10 to 100°C/sec to 750°C, and heat-treating the steel plate in a temperature range of 750 to 1000°C for 20 to 120 seconds. manufacturing method of magnetic steel sheet.