JP2019137874A - Oriented electrical steel sheet and manufacturing method thereof - Google Patents

Abstract

To provide an oriented electrical steel sheet having, on the outermost surface, an aluminum borate coating, excellent in water resistance, and capable of imparting a larger tension than hitherto to the steel sheet, having a small iron loss, and excellent in rust resistance.SOLUTION: In an oriented electrical steel sheet having insulation coating comprising an oxide containing aluminum and boron as components, a mass of a water-soluble component per unit area of the steel sheet: A, and a mass of the coating per unit area of the steel sheet: C satisfy inequalities; 0.05≤A/C≤0.15.SELECTED DRAWING: None

Description

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

  Oriented electrical steel sheets have a crystal structure with {110} <001> as the main orientation and are frequently used as iron core materials for transformers. In particular, materials with low iron loss are required to reduce energy loss. ing.

  Patent Document 1 discloses a method for applying a local distortion by irradiating a surface of a steel sheet after finish annealing with a laser beam as a means for reducing iron loss of a grain-oriented electrical steel sheet, thereby subdividing a magnetic domain. ing.

  Patent Document 2 discloses a magnetic domain subdividing means that does not lose its effect even after performing stress relief annealing (stress removal annealing) after iron core processing.

  On the other hand, since an iron alloy containing iron and silicon has a large magnetocrystalline anisotropy, when an external tension is applied, magnetic domains are subdivided, and eddy current loss, which is a main element of iron loss, can be reduced. In particular, it is known that applying tension to a steel sheet is effective for reducing the iron loss of a grain-oriented electrical steel sheet containing 5% or less of silicon. This tension is applied by the coating formed on the surface.

The grain-oriented electrical steel sheet includes a primary coating mainly composed of forsterite formed by a reaction between an oxide on the surface of the steel sheet and an annealing separator in the finish annealing process, and colloidal silica and phosphorus disclosed in Patent Document 3 and the like. Due to the two-layered film of an amorphous secondary film produced by baking a coating liquid mainly composed of an acid salt, a tension of about 1.0 kgf / mm ^{2 is obtained} when the plate thickness is 0.23 mm. Has been granted.

  In the case of the conventional coating as described above, even greater tension can be applied by increasing the coating amount, and although there is still a possibility of iron loss improvement by improving the tension, it is more than the current coating to improve the applied tension. Increasing the thickness is not preferable because it reduces the space factor. For this reason, the coating film which is excellent in adhesiveness without causing a space factor fall, and is thin and can give a big tension | tensile_strength to a steel plate is desired.

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

  In order for a film to become a high-tensile film, it is required that the film has a high Young's modulus and a low coefficient of thermal expansion. In general, crystals have a higher Young's modulus than amorphous. A film made of aluminum borate has a Young's modulus higher than that of a conventional amorphous film made of silica and phosphate because the main constituent is a crystal. Since the thermal expansion coefficient is also sufficiently low, it is possible to obtain a higher tension than that of the coating disclosed in Patent Document 3, coupled with the effect of Young's modulus.

  On the other hand, in an aluminum borate film, a certain amount of amorphous component is necessary to ensure film adhesion. On the other hand, the presence of this amorphous material is caused by a decrease in tension or rusting of the steel sheet in a wet atmosphere. It has been pointed out to cause problems. Since amorphous material has a lower Young's modulus than crystalline material, if a large amount of amorphous material is present, the tension is lower than that of a film with 100% crystalline material, and it is difficult to obtain low iron loss.

  In addition, when a component that is easily dissolved in water is present in the coating, rust is likely to be generated on the steel sheet in a wet atmosphere. Since aluminum borate crystals are considered to be insoluble in water, the components that are easily dissolved in water in the coating are considered to be amorphous other than aluminum borate crystals.

  In patent document 5, in order to solve the above problems, the method of containing an alkali component in a film is disclosed. According to this method, the problem of rust is solved, but there is a problem that the film adhesion may not be sufficient. That is, there is still a need for development of means for solving problems such as rust resistance which is a drawback of the aluminum borate coating.

JP 58-26405 A JP-A-62-86175 JP 48-39338 A JP-A-6-65754 JP-A-8-325745

  The present invention solves these problems in the prior art, and achieves low iron loss by having an aluminum borate coating on the outermost surface that is excellent in water resistance and capable of imparting a larger tension to the steel sheet than before. And it aims at providing the directionality electromagnetic steel excellent in rust resistance.

  In order to solve the problem of the aluminum borate film, the present inventors considered that it is an essential problem to control the amount of the amorphous component in the film, that is, the water-soluble component. And, as a result of intensive studies, by setting the ratio of the water-insoluble component and the water-soluble component in the coating to an appropriate value, it is possible to obtain a grain-oriented electrical steel with low iron loss and excellent rust resistance. I found out. It has also been found that this can be realized by optimizing the ratio of Al and B in the coating solution and the baking condition of the coating.

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

  (1) It has an insulating coating composed of an oxide containing aluminum and boron as components, the mass of the water-soluble component per unit area of the steel sheet: A, the mass of the coating film per unit area of the steel sheet: C is 0.05 A grain-oriented electrical steel sheet satisfying ≦ A / C ≦ 0.15.

  (2) The method for producing a grain-oriented electrical steel sheet according to (1), wherein a compound containing aluminum and a compound containing boron have a molar ratio Al / B of aluminum to boron of 1.25 to 1.81. A suspension is prepared by dispersing in a dispersion medium, and the suspension is applied to a unidirectional silicon steel plate, and then the unidirectional silicon steel plate has a dew point of 0 to 40 ° C. and 0 to 25% by volume of hydrogen. In addition, in the atmosphere where the balance is nitrogen, the average temperature increase rate up to 500 ° C. is heated at 2 to 5 ° C./second, and then the temperature increase rate up to 750 ° C. is 10 ° C./second or more on average. And then heat-treating in a temperature range of 750 to 1000 ° C. for 20 to 120 seconds.

  According to the present invention, a grain-oriented electrical steel sheet having excellent iron loss and excellent adhesion and rust resistance can be realized by having a film having a large tension imparting effect.

  The present inventors investigated and examined the improvement of the film properties. As a result, it was found that a grain-oriented electrical steel sheet with low iron loss and no rust generation can be obtained by limiting the amount of water-soluble components in the aluminum borate coating. Specifically, when the mass of the water-soluble component per unit area of the steel sheet is A, the ratio to the mass C of the coating film per unit area of the steel sheet satisfies 0.05 ≦ A / C ≦ 0.15. It has been found that a grain-oriented electrical steel sheet with low iron loss and no rust can be obtained.

  In order to obtain the effects of the present invention, it is necessary to define water-soluble components. The aluminum borate film is made of an aluminum borate crystal and an amorphous material containing boric acid and aluminum. Furthermore, a trace amount of aluminum oxide crystal may be included. Since the aluminum borate crystal and the aluminum oxide crystal are considered to be insoluble in water, it is amorphous that contains boric acid and aluminum that is soluble in water in the coating.

  In the present invention, the amount of the water-soluble coating component relative to the mass of the coating per unit area of the steel sheet is specified, but among the coating components, the amount of coating per unit area of the water-soluble steel sheet is determined. For this, a steel plate having an aluminum borate film to be analyzed is boiled in boiling water, and the mass of the steel plate before and after boiling is measured. Specifically, the following method is used.

  First, a steel plate with a known coating amount per unit area is cut into a size of 5 cm on a side, and immersed in 150 cc boiling water for 10 minutes after mass measurement. Thereafter, the steel plate is pulled up and the mass of the steel plate is measured again. Next, the mass difference per unit area is calculated from the mass difference before and after immersion in boiling water. As described above, a water-soluble coating component per unit area of the steel sheet can be obtained.

In the present invention, in order to obtain a grain-oriented electrical steel sheet having an aluminum borate film excellent in water resistance, the coating amount per unit area is C (g / m ² ), soluble in water per unit area. The coating component amount is A (g / m ² ), and 0.05 ≦ A / C ≦ 0.15. When the adhesion amount of the aluminum borate coating is ^{2 to} 6 g / m ² per one surface of the steel sheet, good iron loss is easily obtained.

  It is considered that when there are many components that are easily soluble in water (when A / C> 0.15), moisture easily reaches the surface of the steel sheet in a wet atmosphere, causing rust. Since the aluminum borate crystals are considered insoluble in water, it is considered that the amorphous component in the film constitutes the water-soluble component of the film.

  The aluminum borate coating solution contains boron in excess of the stoichiometric composition of the aluminum borate crystals in order to promote film adhesion and promote the formation of aluminum borate crystals. This excess boron is one of the causes of amorphous formation. Therefore, in order to improve the rust resistance, it is necessary to suppress the amorphous amount in the film as much as possible. However, if it is excessively suppressed (when A / C <0.05), the film adhesion becomes inferior, and There arises a problem that it becomes difficult to form aluminum oxide crystals.

Therefore, the present inventors examined the optimum value of the amount of amorphous component in the film, that is, the water-soluble component. As a result, the coating amount per unit area is C (g / m ² ), the amount of coating component soluble in water per unit area is A (g / m ² ), and 0.05 ≦ A / C ≦ 0. .15. As a means for realizing such a film, there is a method using an additive or the like. In this study, an attempt was made to solve the problem by examining process conditions.

  As a result of the process study, in order to form an ideal film that satisfies the above conditions, the molar ratio Al / B ratio of aluminum to boron is 1.25 to 1.81 on the base steel sheet of the grain-oriented electrical steel sheet. After applying the coating solution, it became clear that the temperature and atmospheric conditions of the heat treatment including the drying and baking temperature after coating should be limited. This process includes (1) suppression of bumping during drying of the coating solution, (2) diffusion of boron during temperature rise after drying and before crystallization of aluminum borate, (3) suppression of transpiration of boron before crystallization, (4) Promotion of crystallization at an aluminum borate crystallization temperature or higher. Specifically, the object can be achieved under the following production conditions.

  A coating solution having the above composition is applied to a steel sheet, heated to an average of 2 to 5 ° C./second up to 500 ° C., heated at an average of 10 ° C./second or more between 500 to 750 ° C., and then 750 to 750 ° C. Heat-treat at 1000 ° C. for 20 seconds or longer. In the temperature range from room temperature to 500 ° C., heating of the applied liquid, drying, and heating of the film-like substance made of a mixture of a boron compound and an aluminum compound formed on the steel plate after completion of drying are performed.

  The coating solution before coating is preferably maintained at a temperature of 20 ° C. or higher and 40 ° C. or lower in order to prevent precipitation of boric acid and excessive evaporation of moisture. If the temperature of the coating solution is too low, precipitation of boric acid occurs in the coating solution, and if the temperature is too high, moisture tends to decrease and normal coating cannot be performed, and in any case, the desired film cannot be obtained.

  The reason for limiting the temperature rising rate up to 500 ° C. to 2 to 5 ° C./second is to sufficiently diffuse boron, which is the process (2). If the rate of temperature rise is too high, the diffusion of boron will not be sufficient, the target composition and amount of the water-soluble component will not be obtained, and film defects due to bumping will easily occur when the coating solution is dried. On the other hand, if the film is too slow, the transpiration of boron will proceed and a film having the targeted composition cannot be obtained.

  The reason for setting the temperature rising rate of 500 to 750 ° C. to 10 ° C./second or more is that, with regard to the above (3), in the temperature range of 500 ° C. or more, transpiration of boron easily proceeds. If the rate of temperature rise is slow, the transpiration of boron proceeds and a film having the targeted composition cannot be obtained. A particularly good result is obtained when the heating rate is 50 ° C./second or more, which is preferable. There is no problem even if the rate of temperature increase is high, but since the effect does not increase even if it exceeds 100 ° C./second, the substantial upper limit is 100 ° C./second.

  The reason why it is necessary to perform the heat treatment at 750 to 1000 ° C. for 20 seconds or more is that crystallization of aluminum borate proceeds at 750 ° C. or more with respect to the above (4). If the temperature and time are not within the above ranges, the crystallization of aluminum borate does not proceed sufficiently, the amount of water-soluble components increases, and as a result, good iron loss cannot be obtained and rust resistance deteriorates. To do. If the temperature and the heat treatment time exceed this, the adhesion is not sufficient. For this reason, the upper limits of temperature and heat treatment time are 1000 ° C. and 120 seconds. The reason for this upper limit is considered to be that the amorphous phase is reduced when the temperature is too high or the heat treatment time is too long.

  The grain-oriented electrical steel sheet of the present invention has the above-mentioned coating on the outermost surface of the steel sheet, but the base steel sheet is not particularly limited as long as the secondary rebonding product has been completed. Usually, the steel sheet generally used as a base material is a steel sheet having a forsterite primary coating formed during finish annealing (secondary re-annealing annealing), and the primary coating is removed by a method such as pickling. A steel plate with a metal surface exposed, or a steel plate whose surface has been flattened by polishing, etc., a steel plate with a metal film exposed by finish annealing (secondary recrystallization annealing) under conditions where no primary coating is formed, Or the steel plate etc. which further planarized the surface.

  When the coating of the grain-oriented electrical steel sheet of the present invention is too thick, the space factor decreases, so that it should be as thin as possible depending on the purpose, and the thickness is preferably 5% or less with respect to the steel sheet thickness. More preferably, 2 is% or less. Further, from the viewpoint of imparting tension, if it is extremely thin, a sufficient effect cannot be obtained, and 0.1 μm or more is preferable.

  Below, the method to manufacture suitably the grain-oriented electrical steel sheet of this invention is described.

First, a suspension (slurry) containing boric acid, aluminum oxide, or an aluminum oxide precursor compound is prepared. As the boric acid, 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 a mixture thereof. Can also be used.

Aluminum oxide precursor compounds, aluminum oxide as well, refer to hydrates of aluminum oxide represented by Al 2 _{O 3} · _mH 2 _O, such as boehmite, aluminum hydroxide and the like. Various aluminum salts including aluminum nitrate and aluminum chloride are also preferably used.

  These raw materials are dispersed in a dispersion medium to prepare a slurry. The dispersion medium is best water, but an organic solvent or a mixture thereof can be used if there is no particular problem in other processes. By using a fine particle dispersion called so-called sol as the aluminum oxide precursor in the slurry, a thin, uniform and good adhesive film may be obtained. This is particularly noticeable when a non-metallic substance is not present on the surface and a film is formed directly on the metal surface.

  In the case where a sol is used as the coating solution, the above-described boehmite sol and / or alumina sol as the aluminum oxide precursor is particularly suitable from the viewpoint of workability or cost.

  The obtained slurry is applied to the surface of the grain-oriented electrical steel sheet on which finish annealing has been completed by a conventionally known method such as a coater such as a roll coater, dip method, spray spraying or electrophoresis.

  The steel sheet that has been subjected to finish annealing here is (1) a steel sheet that has been subjected to finish annealing by a conventionally known method to form a forsterite primary coating on the surface, and (2) a primary coating and incidentally generated. Steel plate with internal oxide layer removed by dipping in acid, (3) Steel plate obtained in (2) above, subjected to planarization annealing in a hydrogen-containing atmosphere, or polishing such as chemical polishing or electrolytic polishing (4) Applying a conventionally known annealing separator added with trace amounts of additives such as alumina powder, which is inactive for film formation, or chloride, under conditions that do not produce a primary film This refers to steel sheets that have undergone finish annealing.

  The coated steel sheet is dried and then baked at 750 ° C. or higher to form an oxide film on the surface. The atmosphere during baking is preferably an inert gas atmosphere such as nitrogen or a reducing atmosphere such as a nitrogen-hydrogen mixed atmosphere, and an atmosphere containing air or oxygen is not preferable because it may oxidize the steel sheet.

  As for the dew point of the atmospheric gas, good results are obtained at 0 to 40 ° C. When the baking temperature is less than 750 ° C., the applied precursor may not be an oxide, and since the baking temperature is low, sufficient tension is not exhibited, which is not preferable. On the other hand, when the temperature exceeds 1000 ° C., inconvenience occurs as described above.

  Hereinafter, the present invention will be described based on examples, but the present invention is not limited to such examples.

[Example 1]
A commercially available boric acid (H ₃ BO ₃ ) reagent and aluminum oxide (Al ₂ O ₃ ) powder (average particle size: 0.4 μm) are mixed in the ratio shown in Table 1, and distilled water is added thereto to produce a slurry. did. This is 4.5 g / m ² in terms of the coating mass after baking onto a unidirectional silicon steel sheet (with a forsterite primary coating) having a final annealing of 0.23 mm thickness containing 3.2% Si. It applied so that it might become. Then, after drying under the conditions shown in Table 1, the temperature was raised to 750 ° C., and baking was performed at this temperature for a soaking time of 100 seconds. The atmosphere during drying, heating, and baking was a nitrogen atmosphere containing 10% hydrogen, and the dew point was 30 ° C.

  The steel sheet on which the film was formed was immersed in 150 cc boiling distilled water as it was for 10 minutes, and the ratio of the water-soluble component in the film per unit area of the steel sheet to the amount of film per unit area of the steel sheet from the mass change of the steel sheet A / C was obtained.

  As for the adhesion of the coating, a steel plate was wound around a cylinder having a diameter of 20 mm, and the peeling area of the coating was less than 5%.

  Rust resistance is good when rust is confirmed when the steel sheet is kept in an atmosphere of 50 ° C. and 91% RH for 1 week, and the surface condition is observed visually. Was evaluated as inferior.

  The iron loss is a single-plate magnetometer, and shows a value when excited at a magnetic flux density of 1.7 T and 50 Hz, and less than 0.85 W / kg was evaluated as a good iron loss.

  As can be seen from the results in Table 1, in the examples of the present invention, unidirectional silicon steel sheets having excellent film adhesion and rust resistance and low iron loss were obtained.

[Example 2]
A slurry was prepared by adding 60.6 g of boric acid (H ₃ BO ₃ ) reagent and distilled water to 100 g of commercially available aluminum oxide (Al ₂ O ₃ ) powder (average particle size: 0.4 μm). The molar ratio of Al / B is 1.63.

This is 4.5 g / m ² in terms of the coating mass after baking onto a unidirectional silicon steel sheet (with a forsterite primary coating) having a final annealing of 0.23 mm thickness containing 3.2% Si. It applied so that it might become. Thereafter, in a nitrogen atmosphere containing 10% by volume of hydrogen at a dew point of 30 ° C., the temperature was raised to 500 ° C. at 3 ° C. per second, then raised to a soaking temperature at 50 ° C. per second, and baked under the conditions shown in Table 2.

  The steel sheet on which the film was formed was immersed in 150 cc boiling distilled water as it was for 10 minutes, and the ratio of the water-soluble component in the film per unit area of the steel sheet to the amount of film per unit area of the steel sheet from the mass change of the steel sheet A / C was obtained.

  As for the adhesion of the coating, a steel plate was wound around a cylinder having a diameter of 20 mm, and the peeling area of the coating was less than 5%.

  As for rust resistance, the steel sheet is kept in an atmosphere of 50 ° C. and 91% RH for one week, and the surface condition at that time is visually observed. Rated as inferior.

  The iron loss is a single-plate magnetometer, and shows a value when excited at a magnetic flux density of 1.7 T and 50 Hz, and less than 0.85 W / kg was evaluated as a good iron loss.

  As can be seen from the results in Table 2, in the examples of the present invention, unidirectional silicon steel sheets having excellent film adhesion and rust resistance and low iron loss were obtained.

[Example 3]
A slurry was prepared by adding 60.6 g of boric acid (H ₃ BO ₃ ) reagent and distilled water to 100 g of commercially available aluminum oxide (Al ₂ O ₃ ) powder (average particle size: 0.4 μm). The molar ratio of Al / B is 1.63.

This is 4.5 g / m ² in terms of the coating mass after baking onto a unidirectional silicon steel sheet (with a forsterite primary coating) having a final annealing of 0.23 mm thickness containing 3.2% Si. It applied so that it might become. Thereafter, the temperature was raised to 500 ° C. at 3 ° C. per second, and then the temperature was raised to a soaking temperature at 50 ° C. per second. Table 3 shows the atmosphere from the temperature rise to the end of baking.

  The steel sheet on which the film was formed was immersed in 150 cc boiling distilled water as it was for 10 minutes, and the ratio of the water-soluble component in the film per unit area of the steel sheet to the amount of film per unit area of the steel sheet from the mass change of the steel sheet A / C was obtained.

  As for the adhesion of the coating, a steel plate was wound around a cylinder having a diameter of 20 mm, and the peeling area of the coating was less than 5%.

  As for rust resistance, the steel sheet is kept in an atmosphere of 50 ° C. and 91% RH for one week, and the surface condition at that time is visually observed. Rated as inferior.

  The iron loss is a single-plate magnetometer, and shows a value when excited at a magnetic flux density of 1.7 T and 50 Hz, and less than 0.85 W / kg was evaluated as a good iron loss.

  As can be seen from the results in Table 3, in the examples of the present invention, unidirectional silicon steel sheets having excellent film adhesion and rust resistance and low iron loss were obtained.

Claims (2)

Having an insulating coating made of an oxide containing aluminum and boron as components;
About the water-soluble component in the insulating coating,
A grain-oriented electrical steel sheet characterized in that the mass of a water-soluble component per unit area of the steel sheet: A and the mass of the coating film per unit area of the steel sheet: C satisfy 0.05 ≦ A / C ≦ 0.15. It is a manufacturing method of the grain-oriented electrical steel sheet according to claim 1,
A suspension is prepared by dispersing a compound containing aluminum and a compound containing boron in a dispersion medium so that the molar ratio Al / B of aluminum to boron is 1.25 to 1.81.
After applying the suspension to a unidirectional silicon steel plate,
In the above-mentioned unidirectional silicon steel sheet, an average temperature increase rate of up to 500 ° C. is 2 to 5 ° C./second in an atmosphere in which the dew point is 0 to 40 ° C., hydrogen is 0 to 25% by volume, and the balance is nitrogen. Followed by heating with
The temperature is increased to 750 ° C. at an average rate of 10 ° C./second or more, and then
A method for producing a grain-oriented electrical steel sheet, wherein the heat treatment is performed in a temperature range of 750 to 1000 ° C. for 20 to 120 seconds.