Grain-oriented electrical steel sheet, method for manufacturing the same, and transformer core

Abstract

To provide grain-oriented electrical steel sheets that can improve both transformer losses and noise. [Solution] A grain-oriented electrical steel sheet having an insulating coating on its surface, wherein the insulating coating contains 0.10 to 20% by mass of a ferromagnetic component relative to the insulating coating, and the ferromagnetic component is oriented at an angle of 20° or less along the rolling surface with respect to the rolling direction of the steel sheet, and at an angle of 1.0 to 20° in the thickness direction with respect to the rolling surface.

Description

[Technical Field]

[0001] This invention relates to grain-oriented electrical steel sheets and methods for manufacturing grain-oriented electrical steel sheets. Furthermore, this invention relates to a transformer core made using such grain-oriented electrical steel sheets. [Background technology]

[0002] The easy magnetization axis of iron. <001> Grain-oriented electrical steel sheets, which have a crystalline structure in which the orientation is highly aligned with the rolling direction of the steel sheet, are particularly used as core materials for power transformers. Generally, transformers are broadly classified into wound-core transformers and stacked-core transformers based on their core structure. A wound-core transformer is a transformer with a core formed by winding steel plates together. On the other hand, a stacked-core transformer is a transformer with a core formed by stacking steel plates cut into predetermined shapes. There are various characteristics required for transformer cores and the grain-oriented electrical steel sheets that constitute them, but particularly important characteristics are low transformer noise and low transformer losses due to iron loss in the steel sheets.

[0003] One of the causes of noise in transformers using stacked cores (also called laminated cores) is the natural vibration of the core. Natural vibration of a core refers to the vibration of a stacked core, which has been subjected to beveling or other processing, as a single structure at a specific frequency depending on the material and shape. Based on an understanding of the factors that increase such noise, the following measures have been proposed to reduce noise in transformers.

[0004] Patent Document 1 discloses that by providing protrusions on the surface of a steel plate to improve the rigidity of the steel plate, the natural frequency can be increased and excellent noise characteristics can be obtained. Patent Document 2 discloses a technology for reducing transformer noise by preventing an increase in magnetostriction by setting the crystallinity of the insulating coating to 20% or more and the minimum tension applied to the insulating coating on the steel plate at 100°C to 200°C to 10 MPa. Patent Document 3 discloses a technique for suppressing vibrations of an iron core by laminating electromagnetic steel sheets, each having mechanical grooves extending to the end faces, so that at least the sides without grooves do not overlap, fastening and fixing them with fasteners, and then applying an adhesive such as resin to the end faces of the laminated sheets, thereby fixing them to the inside of the iron core via the grooves. Furthermore, Patent Document 4 discloses a wound core in which noise is reduced by reducing the gap in the bent portion of the electromagnetic steel sheet in the wound core and increasing the packing ratio of the electromagnetic steel sheet in the bent portion. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2002-164230 [Patent Document 2] International Publication No. 2018 / 123339 [Patent Document 3] Japanese Patent Publication No. 2003-77747 [Patent Document 4] Patent No. 7288213 [Patent Document 5] Patent Application No. 2020-555935 [Overview of the project] [Problems that the invention aims to solve]

[0006] The technologies described in Patent Documents 1 to 4 are thought to have some effect in reducing transformer noise, but they had the following problems. The technology proposed in Patent Document 1 reduces the space factor of the steel plates in the core, leading to increased transformer losses. Furthermore, the increased size of the core also leads to increased costs. While the technology proposed in Patent Document 2 does reduce transformer noise, it does not sufficiently improve transformer losses, which are another important characteristic for transformers. Even when bonding steel plates together according to the technique proposed in Patent Document 3, the packing ratio of the steel plates in the iron core decreases, which may lead to increased losses in the transformer. Furthermore, there are concerns about uneven stress being applied between the steel plates, as well as the time required for bonding. The technology proposed in Patent Document 4 has some effect in reducing noise in wound cores, but it does not take into account transformer losses. Thus, in all of the Patent Documents 1 to 4, the improvement in transformer characteristics was limited to noise only, and neither the transformer losses nor the iron losses of the steel plates were considered, resulting in a limited improvement effect.

[0007] On the other hand, Patent Document 5 discloses a technique for improving iron loss by adding a crystalline fibrous material with anisotropic linear thermal expansion coefficient to the insulating coating, thereby increasing the anisotropy of the tension applied to the insulating coating. However, Patent Document 5 does not consider transformer noise, and its improvement effect was limited.

[0008] Therefore, in view of the above problems, the present invention aims to provide a transformer core that can provide a transformer that reduces both noise and losses. Furthermore, the present invention aims to provide grain-oriented electrical steel sheets and a method for manufacturing the same, which can be used for iron cores that reduce both noise and losses in transformers. [Means for solving the problem]

[0009] Inside a transformer is a core made of laminated grain-oriented electrical steel sheets. As an example of a typical laminated core, Figure 1 shows a schematic diagram of the core of a laminated core transformer with beveled edges. To form the core using Figure 1 as an example, first, each polygonal part (beveled section) enclosed by the solid line is beveled on the grain-oriented electrical steel sheets that will be the constituent material. Next, in the example of Figure 1, the five beveled sections are butted together at the joints formed by the beveled edges to form a single core as shown on the outermost surface of Figure 1, creating a beveled member. Then, by laminating these beveled members in the lamination direction (the direction towards the viewer in Figure 1), a laminated core is manufactured. The stacked core may be constructed using a step-lap stacking method, where, for example, the vertices of each convex part (thick solid line in Figure 1) of the hexagonal bevel section that mainly constitutes the central leg of the five bevel sections shown in Figure 1 are offset by an arbitrary lap length parallel to the upper and lower sides of the yoke section (parallel to the dotted line in Figure 1), and these bevel members are stacked in the aforementioned stacking direction. In this case, the actual stacked core will differ from Figure 1 in that each bevel member is stacked with an offset of the lap length.

[0010] A stacked iron core is typically constructed by laminating steel plates with their surfaces facing the floor, that is, with the surfaces of the steel plates parallel to the floor. Therefore, after lamination, it is necessary to stand the stacked iron core upright in order to wind the coil around it. However, since the stacked iron core is simply made by butting the joints of the steel plates together, it is necessary to fix the stacked iron core in order to maintain its upright position. At this time, the yoke section is firmly fixed, but the leg section is not firmly fixed because it is necessary to wind the coil around it.

[0011] Here, the natural vibration of the iron core, which is one of the causes of transformer noise, can be suppressed by improving the rigidity of the iron core. As mentioned above, the laminated iron core is composed of a laminate of steel plates. Because the laminated steel plates are prone to slippage, the rigidity of the iron core is significantly lower than that of the steel plates themselves. To improve the rigidity of the iron core, one might consider pressing down strongly on both the yoke and the legs. However, pressing down too hard makes it difficult to wind the coil, and also puts strong stress on the steel plates, introducing strain into the steel plates and causing them to deform. As a result, there is a problem of increased transformer losses (iron loss of the steel plates).

[0012] On the other hand, an insulating coating is formed on the surface of grain-oriented electrical steel sheets to prevent electrical conductivity when the steel sheets are laminated. This insulating coating also plays a role in reducing iron loss by applying tension in the rolling direction of the grain-oriented electrical steel sheet. As a means of improving the tension applied by the insulating coating, it is well known to increase the thickness of the coating and to impart anisotropy to it. However, when implementing a thick coating, the area occupied by the coating in the cross-sectional area of the steel sheet increases, which can also cause deterioration of the iron loss when assembled into a transformer core. Regarding the imparting of anisotropy, the glass coating generally used as an insulating coating for grain-oriented electrical steel sheets has poor crystallinity and is an isotropic coating without anisotropy in its structure. Therefore, it is necessary to develop a coating with a new composition. In this case, there is a risk of cost increase due to the need to update existing equipment or an increase in raw material costs depending on the composition.

[0013] Here, the inventors turned to Patent Document 5, which adds crystals with anisotropy to the insulating coating in order to improve the composition of the insulating coating. However, when the inventors reproduced Patent Document 5 and further investigated the orientation state of the crystals in the insulating coating in particular, it was found that the crystals may be randomly present. Therefore, by further enhancing the orientation of the crystals, improvements in properties, such as loss reduction and iron loss reduction, can be expected. However, it is difficult to orient the crystalline substances contained in the insulating coating solution.

[0014] Based on such a background, as a result of intensive studies by the inventors to solve the above problems, new findings were obtained regarding a technique that can reduce transformer noise while improving transformer losses, as follows. That is, first, the idea was conceived to include a ferromagnetic component, which is a magnetic material, in the coating solution for the insulating coating. Next, after applying this coating solution to the surface of the steel sheet, the idea was conceived to orient the ferromagnetic component in the insulating coating by applying a magnetic field to the steel sheet before baking. Furthermore, the idea was conceived to control the direction of applying the magnetic field in two directions: the in-plane rolling direction and the direction perpendicular to the in-plane direction. And it was found that by highly controlling the orientation of the composition of the insulating coating in this way, an improvement in the iron loss of the steel sheet is recognized, and an improvement in the transformer noise when a core is manufactured using the steel sheet is also recognized.

[0015] The gist configuration of the present invention completed based on the above findings is as follows. [1] A grain-oriented electrical steel sheet having a glassy insulating coating on the surface of the steel sheet, The insulating film contains a ferromagnetic component in an amount of 0.10% by mass or more and 20% by mass or less relative to the insulating film. A grain-oriented electrical steel sheet characterized in that the ferromagnetic component is oriented at an angle of 20° or less along the rolling surface with respect to the rolling direction of the grain-oriented electrical steel sheet, and at an angle of 1.0° or more and 20° or less in the thickness direction with respect to the rolling surface.

[0016] Here, the predetermined angle "along the rolling plane with respect to the rolling direction" is, for example, the angle shown by the solid arrow in Figure 2(a), and both the angle directed upwards and downwards with respect to the rolling direction in Figure 2(a) are positive absolute values. In this specification, this angle is also referred to as angle A. Furthermore, the predetermined angle "in the thickness direction relative to the rolling surface" is, for example, the angle indicated by the solid arrow in Figure 2(b), and both the angle directed upwards and downwards relative to the rolling direction in Figure 2(b) are positive absolute values. In this specification, this angle is also referred to as angle B. Note that in Figure 2(b), the steel plate (base metal and undercoat) that forms the base of the insulating coating is not shown.

[0017] Furthermore, in calculating the angle at which the ferromagnetic components are oriented, we also refer to Figure 3. In the observed image, adjacent ferromagnetic components are considered as a single ferromagnetic component grain if they are located at a distance equal to or less than the particle diameter of the component that is smaller than or equal to the particle diameter of the component. The orientation direction of the ferromagnetic component is defined as the direction along the longer side of the rectangle with the smallest area that is inscribed within this single ferromagnetic component grain. The orientation direction of the ferromagnetic component can be measured according to the experimental method described later.

[0018] [2] The grain-oriented electrical steel sheet according to [1] above, wherein the ferromagnetic component contains at least one of iron, cobalt, nickel, magnetite, and ferrite, and the average particle size of the ferromagnetic component is 1.5 μm or less.

[0019] Here, the "average particle size of the ferromagnetic component" can be measured according to the method described later.

[0020] [3] A transformer core made of the grain-oriented electrical steel sheet described in [1] or [2] above.

[0021] [4] A method for manufacturing grain-oriented electrical steel sheets, comprising: hot rolling a steel slab to obtain a hot-rolled sheet; cold rolling the hot-rolled sheet to obtain a cold-rolled sheet; recrystallization annealing and decarburization annealing the cold-rolled sheet to obtain a decarburized annealed sheet; applying an annealing release agent to the decarburized annealed sheet and then performing finish annealing to obtain a steel sheet; and then applying a coating liquid to the surface of the steel sheet and baking it to form a glassy insulating film, The coating liquid contains a ferromagnetic component in an amount of 0.10% by mass or more and 20% by mass or less on a solid content basis. After the application of the coating liquid and before the baking, a magnetic field is applied to the steel sheet at an angle of 20° or less along the rolling surface with respect to the rolling direction of the steel sheet, and at an angle of 1.0° or more and 20° or less in the thickness direction with respect to the rolling surface. A method for manufacturing grain-oriented electrical steel sheets, characterized in that the baking temperature is 800°C or higher and 1000°C or lower.

[0022] [5] The method for producing grain-oriented electrical steel sheets according to [4] above, wherein the ferromagnetic component contains at least one of iron, cobalt, nickel, magnetite, and ferrite, and the average particle size of the ferromagnetic component is 1.5 μm or less. [Effects of the Invention]

[0023] According to the grain-oriented electrical steel sheet of the present invention, when the steel sheet is used as a core for a transformer, it is possible to achieve both improvement in transformer losses and improvement in transformer noise. Specifically, it is possible to achieve both a reduction in the iron loss of the steel sheet constituting the transformer and a reduction in transformer noise. Furthermore, the present invention provides a method for manufacturing grain-oriented electrical steel sheets that can achieve both improved transformer losses and reduced transformer noise. Specifically, it can achieve both a reduction in iron loss of the steel sheets constituting the transformer and a reduction in transformer noise. Furthermore, the transformer core of the present invention makes it possible to achieve both improved transformer losses and reduced transformer noise. Specifically, it is possible to reduce the iron loss of the steel plates constituting the core and reduce the noise of the transformer. These effects can be achieved without increasing the thickness of the insulating coating on the grain-oriented electrical steel sheets, that is, without reducing the space factor of the steel sheets when they are laminated as a transformer core. [Brief explanation of the drawing]

[0024] [Figure 1] This is a schematic diagram showing a typical stacked iron core. [Figure 2] This is a schematic diagram illustrating the angles formed by ferromagnetic components, with (a) a plan view of the insulating coating seen from above, and (b) a perspective view of the insulating coating seen from the upper side. [Figure 3] This is a schematic diagram showing the orientation direction of the ferromagnetic component. [Figure 4] This is a schematic diagram of a transformer core according to one embodiment of the present invention. [Figure 5] These graphs show the relationship between angle A and iron loss (a) and the relationship between angle A and noise (b) in Experiment 1. [Figure 6] These graphs show the relationship between angle B and iron loss (a) and the relationship between angle B and noise (b) in Experiment 2. [Figure 7] This graph shows the relationship between the ferromagnetic component content and iron loss (a) and the relationship between the ferromagnetic component content and noise (b) in Experiment 3. [Figure 8] This graph shows the relationship between firing temperature and iron loss (a) and the relationship between firing temperature and noise (b) in Experiment 4. [Figure 9] This is a schematic diagram of a transformer core according to another embodiment of the present invention. [Modes for carrying out the invention]

[0025] The present invention will be described in detail below. The following description is an example of a preferred embodiment of the present invention, and the present invention is not limited to the embodiments described below. <Grain-oriented electrical steel sheet> The grain-oriented electrical steel sheet of the present invention has a specific insulating coating on its surface, and the component composition of the steel sheet (so-called base steel) is not particularly limited. The grain-oriented electrical steel sheet of the present invention can be suitably obtained by a manufacturing method according to one embodiment of the present invention. Furthermore, the grain-oriented electrical steel sheet of the present invention can be suitably used in a transformer core according to one embodiment of the present invention. Furthermore, the grain-oriented electrical steel sheet of the present invention is particularly useful for use as the core of a stacked core transformer.

[0026] [Composition of steel sheets] The component composition of the steel plate (base metal) can be within the following range as an example. Furthermore, it is preferable that the component composition induces secondary recrystallization, without any particular limitations. If an inhibitor is used to grow the secondary recrystallized grains, AlN-based inhibitors, MnSe-based inhibitors, or inhibitors of other systems can be used. Inhibitors may not be used at all. In this specification, "%" represents "mass%" unless otherwise specified. Furthermore, any numerical range expressed using "~" in this specification includes the numbers before and after the "~" as the lower and upper limits, respectively. In addition, if a unit is attached to only one of the numbers before or after the "~", the same unit shall be attached to the other number unless otherwise specified.

[0027] The composition of the steel sheet may be an alloy steel with iron (Fe) as the main component, and any trace amounts of any element such as C, Si, Mn, Al, N, S, Se, Ni, Cr, P, Mo, Sb, Sn, O added. C: 0.001 to 0.20% can be suitably added. C is useful for the generation of Goss-oriented crystal grains. For this effect to be effectively exerted, a C content of 0.001% or more is preferable. On the other hand, if the C content exceeds 0.20%, decarburization failure may occur during decarburization annealing. Therefore, a C content of 0.20% or less is preferable.

[0028] Si can be suitably added in an amount of 1.0 to 5.0%. Si is useful for increasing electrical resistance and reducing iron loss, as well as stabilizing the BCC structure of iron, enabling high-temperature heat treatment. For these effects to be effectively exerted, a Si content of 1.0% or more is preferable. On the other hand, if the Si content exceeds 5.0%, normal cold rolling may become difficult. Therefore, a Si content of 5.0% or less is preferable.

[0029] Mn can be suitably added in amounts of 0.01 to 1.0%. Mn effectively contributes to improving the hot brittleness of steel. Furthermore, when S and Se are present, Mn forms precipitates such as MnS and MnSe, and functions as a grain growth inhibitor. For this effect to be effectively exerted, a Mn content of 0.01% or more is preferable. On the other hand, if the Mn content exceeds 1.0%, the grain size of precipitates such as MnSe may become coarser, and the inhibitory effect may be lost. Therefore, a Mn content of 1.0% or less is preferable.

[0030] Al can be suitably added in an amount of 0.003 to 0.050%. Al forms AlN in the steel and acts as an inhibitor as a dispersed second phase. For this effect to be effectively exerted, the Al content is preferably 0.003% or more as sol.Al. On the other hand, if the Al content exceeds 0.050%, AlN may precipitate coarsely, and the inhibitory effect may be lost. Therefore, the Al content is preferably 0.050% or less as sol.Al.

[0031] N can be preferably added in an amount of 0.001 to 0.020%. Like Al, N forms AlN. For this effect to be effectively exerted, an N content of 0.001% or more is preferable. On the other hand, if the N content exceeds 0.020%, blistering may occur during slab heating. Therefore, an N content of 0.020% or less is preferable.

[0032] A total of 0.001-0.05% of one or two selected from S and Se can be preferably added. S and Se combine with Mn or Cu to form MnS, MnSe, and Cu. 2-x S, Cu 2-x Se forms and acts as an inhibitor as a dispersed second phase in the steel. For this effect to be effectively exerted, it is preferable that the total content of S and Se be 0.001% or more. On the other hand, if the total content of S and Se exceeds 0.05%, solid solution may be incomplete when the slab is heated, or defects may occur on the product surface. Therefore, in both cases where one of S or Se is present, or where both S and Se are present, it is preferable that the total content of S and Se be 0.05% or less.

[0033] Furthermore, for example, it may contain one or more elements selected from Ni: 0.005-0.5%, Cr: 0.005-0.5%, P: 0.005-0.1%, Mo: 0.0005-0.5%, Sb: 0.01-0.1%, Sn: 0.0005-0.5%, and O: 0.0005-0.1%. These elements are expected to act as auxiliary inhibitors.

[0034] It is preferable to use the above as the basic components of steel. Alternatively, alloy steels may be made by adding any other elements in any amount. Examples of other elements include Cu, Bi, B, Ge, As, Te, Nb, Ti, V, and REM (rare earth metals, a collective term for 17 elements including the 15 lanthanides plus Y and Sc). The remaining portion, other than those mentioned above, can consist of Fe and unavoidable impurities.

[0035] [Insulating coating] A grain-oriented electrical steel sheet according to one embodiment of the present invention has a glassy insulating coating on one or both of its surfaces. Furthermore, this insulating coating is characterized by containing a specific amount of ferromagnetic components oriented at a specific angle.

[0036] [[Ferromagnetic component]] The ferromagnetic component in the insulating coating must have an angle A (see Figure 2(a)) of 20° or less along the rolling surface with respect to the rolling direction of the grain-oriented electrical steel sheet. In other words, the deviation within the rolling surface from the rolling direction must be within 20 degrees. Furthermore, the ferromagnetic component in the insulating coating must have an angle B (see Figure 2(b)) of 1.0° or more and 20° or less in the thickness direction with respect to the rolling surface of the grain-oriented electrical steel sheet. In other words, the deviation (elevation or depression angle) perpendicular to the rolling surface must be within the range of 1.0° to 20°. It is crucial that the ferromagnetic component in the insulating coating is oriented in a way that satisfies both of the above conditions for angles A and B. The following describes in detail the experiments that led to the identification of the orientation conditions for this ferromagnetic component.

[0037] Experiment 1: [[Effect of angle A on ferromagnetic components]] A steel slab containing the components shown in Table 1, with the remainder being Fe and unavoidable impurities, was used. This steel slab was heated at 1420°C and then hot-rolled to a thickness of 2.3 mm to obtain a hot-rolled sheet. This hot-rolled sheet was then cold-rolled once to obtain a cold-rolled sheet with a final thickness of 0.22 mm. This cold-rolled sheet was subjected to decarburization annealing, which also served as primary recrystallization annealing, at an oxidation state of PH2O / PH2 = 0.32 and a temperature of 850°C for 120 seconds, thereby creating the primary recrystallized structure necessary for secondary recrystallization grain growth, and thus obtaining a decarburized annealed sheet. The number of cold-rolling cycles, the number of additional annealing cycles, and other conditions should be adjusted as appropriate to achieve the desired final product thickness in order to create this primary recrystallized structure. Next, an annealing separator mainly composed of MgO was applied to the decarburized annealed sheet, and a finish annealing was performed at 1200°C for 10 hours under a nitrogen atmosphere to induce secondary recrystallization and obtain a steel sheet as the base metal. Regarding the application of the annealing separator, it is preferable that the composition and amount applied do not inhibit secondary recrystallization. Depending on the composition of the annealing separator, a base film may form on the surface of the steel sheet after finish annealing, but the presence or absence of this base film is not limited. After finish annealing, the residue of the annealing separator adhering to the surface of the steel sheet was removed by means of pickling and brushing.

[0038] [Table 1]

[0039] Next, an insulating coating solution was applied to both sides of the steel plate. The coating solution was prepared using 100 g of magnesium salt of phosphoric acid (based on solid content), 50 g of colloidal silica (based on SiO2 solid content), and 10 g of magnetite fine powder (average particle size: 1 μm) as a ferromagnetic component. The ferromagnetic component content in the coating solution (based on solid content) was 6.25% by mass. The coating solution was applied using a roll coater, but is not limited to this method. The amount of coating solution applied was 10 g / m² in total for both sides after the baking process described later, resulting in an insulating coating weight. 2 This was the amount that resulted in this. Here, the average particle size of the magnetite fine powder was measured according to the method described later.

[0040] After applying the coating solution, and before the curing process (60 seconds after application and 120 seconds before curing began), a 1.5T magnetic field was applied for 60 seconds along the rolling surface of each steel sheet, shifted at various angles A from 0° to 30° relative to the rolling direction. The angle B of the magnetic field applied in the thickness direction relative to the rolling surface was kept constant at 2° for all steel sheets.

[0041] After applying a magnetic field, the steel sheet was baked for 20 seconds at a temperature of 830°C in an atmosphere of 100% by volume of nitrogen to form an insulating coating on both surfaces of the steel sheet. Planar annealing combined with baking may also be performed during the baking process. In Experiment 1, the baking was carried out in two stages: pre-baking and final baking. The pre-baking conditions were annealing at 400°C for 20 seconds in air, and the final baking conditions were as described above. In this way, a grain-oriented electrical steel sheet with insulating coatings on both sides of the steel sheet was obtained.

[0042] Using the obtained grain-oriented electrical steel sheet, the orientation direction (angle A) of the ferromagnetic component in the insulating coating within the rolling surface was confirmed as follows. For each type of oriented electrical steel sheet with different magnetic field application directions (angle A), five fields of view were observed using a scanning electron microscope (SEM) in arbitrary 500 μm × 500 μm areas on the insulating coating surface. In the observed images, areas where Fe atoms, a constituent element of magnetite, were confirmed to be the main component were identified as ferromagnetic components (ferromagnetic powder) using energy-dispersive X-ray spectroscopy (EDS). After identifying the ferromagnetic components in the insulating film in this way, groups of ferromagnetic particles that are adjacent to each other at a distance less than or equal to the particle size of the smaller of the two components are considered as a single ferromagnetic particle, and the rectangle with the smallest area among the rectangles inscribed in this particle is drawn. As an example in Figure 3, a powder component with particle size d1 and a powder component with particle size d2 are adjacent to each other at a distance of d1 or less and therefore constitute a single particle (or part of a single particle). On the other hand, a powder component with particle size d2 and a powder component with particle size d3 are at a distance greater than d2 and therefore are considered separate particles. A single particle may be composed of one powder component or of two or more powder components. The above particle sizes and rectangles can be automatically calculated using the image analysis software provided by the SEM.

[0043] These rectangles were defined for all ferromagnetic components within a single field of view, and the direction parallel to the longer side of these rectangles was defined as the orientation direction of each ferromagnetic component grain. This orientation direction represents the in-plane component of each ferromagnetic component grain. The average value of the angle between the orientation direction and the rolling direction within a single field of view was then calculated. Furthermore, the same calculation was performed for five fields of view of the surface observation image, and the average value was calculated as angle A. Furthermore, when angle A was calculated using an electron beam microanalyzer (EPMA) instead of SEM and EDS, following the same method as described above, it was confirmed that the same results as those obtained using SEM and EDS were obtained. In EPMA, areas where iron was detected more strongly than the average iron detection level across the entire field of view were identified as ferromagnetic components (ferromagnetic powder). The orientation direction (angle B) of the ferromagnetic component in the thickness direction of the plate was confirmed to be 2° in all cases using the method detailed in Experiment 2.

[0044] Furthermore, the magnetic properties of the obtained grain-oriented electrical steel sheet were measured as follows. Under conditions of a frequency of 50 Hz and a maximum excitation magnetic flux density of 1.7 T, iron loss (W) was measured according to the single-disk magnetic properties measurement method of JIS C 2556. 17 / 50 The magnetic flux density (B8) of the grain-oriented electrical steel sheets used was 1.90 T in all cases. The relationship between the calculated angle A and iron loss is shown in Figure 5(a).

[0045] Next, the transformer core was assembled to the dimensions shown in Figure 4. In assembling the core, the grain-oriented electrical steel sheets obtained above were beveled to each part, and the resulting beveled sections were butted together to form beveled members. Although omitted in Figure 4, the beveled members had a lap length of 2 mm and were stacked in a step-lap construction with five layers of two sheets stacked on top of each other. This step-lap construction was further stacked 70 times to form the transformer core. When magnetic flux flows through the core, energy loss is less when it passes through the steel sheets stacked above and below rather than through the joints where the permeability is relatively low due to the influence of air, so the sheets were stacked with an offset equal to the aforementioned lap length. For the yoke section of the iron core, backing plates were placed on both the front and back surfaces, and clamps were used to tighten them so that a uniform pressure of 0.2 MPa was applied to the entire surface of the backing plates. For the legs, they were secured by wrapping them with glass tape so as not to interfere with the coils, and then one 50-turn primary coil and one 50-turn secondary coil were wound around each of the three legs to form a three-phase tripod iron core for a stacked iron core transformer.

[0046] Using the obtained iron core, the transformer noise was measured as follows. Three-phase excitation was performed under the conditions of a frequency of 50 Hz and a maximum excitation magnetic flux density of 1.7 T. During excitation, noise levels were measured at eight equally spaced points on the circumference surrounding the core, at a height of half the core height (midway between points a in Figure 4) and 30 cm horizontally from the core surface. The noise level was measured using a microphone attached to a sound level meter, and the average value was defined as the transformer noise level. Noise measurements were performed using a digital sound level meter (Lion Corporation, NL-62). The relationship between the calculated angle A and noise is shown in Figure 5(b).

[0047] As is clear from Figure 5(a), if the ferromagnetic component in the insulating film is oriented with a deviation of 20° or less along the rolling surface relative to the rolling direction (angle A ≤ 20°), then the iron loss W 17 / 50 This was kept below 0.88 W / kg. On the other hand, when the orientation was 25° with an angle A exceeding 20°, the iron loss W 17 / 50 It has increased significantly. Furthermore, as is clear from Figure 5(b), if the ferromagnetic component in the insulating film is oriented with a deviation of 20° or less relative to the rolling direction along the rolling surface (angle A ≤ 20°), the noise was suppressed to less than 56 dBA. On the other hand, if the orientation was with a deviation of 25°, exceeding 20°, the noise increased significantly. Surprisingly, by controlling the orientation angle A of the ferromagnetic component to 20° or less, we were able to improve both iron loss and noise.

[0048] Based on the above results, it is necessary to keep the orientation angle A of the ferromagnetic component below 20°. If the orientation angle A of the ferromagnetic component is not below 20°, it is not possible to achieve both a reduction in iron loss and a reduction in noise. If the orientation angle A of the ferromagnetic component is below 20°, the anisotropy of the tension imparted by the insulating coating can be increased to be parallel to or close to the rolling direction, which is thought to reduce iron loss. Furthermore, if the orientation angle A of the ferromagnetic component is below 20°, the lancet magnetic domains decrease due to the increase in coating tension in the rolling direction, and as a result of reduced magnetostrictive vibration during excitation, noise is also thought to have been reduced. The orientation angle A of the ferromagnetic component is preferably 10° or less, more preferably 5° or less, and can be 0° (parallel to the rolling direction).

[0049] Experiment 2: [[Effect of angle B on ferromagnetic components]] The magnetic field application conditions were shifted by various angles B, ranging from 0.5° to 25°, in the thickness direction relative to the rolling surface of each steel sheet. Except for keeping the angle A along the rolling surface relative to the rolling direction constant at 0°, grain-oriented electrical steel sheets were manufactured in the same manner as in Experiment 1.

[0050] For each grain-oriented electrical steel sheet with different magnetic field application directions (angle B), the cross-section of the insulating coating along the rolling direction was observed. Furthermore, the orientation direction (angle B) of the ferromagnetic components in the thickness direction was confirmed in the same manner as in Experiment 1, except that the longer side of the rectangle defined in this cross-sectional observation image was defined as the thickness-direction component of the orientation direction of each ferromagnetic component grain. The orientation direction (angle A) of the ferromagnetic component within the rolling plane was confirmed to be 0° in all cases, as per Experiment 1.

[0051] Furthermore, the magnetic properties were measured using the same method as in Experiment 1. The magnetic flux density B8 of all the grain-oriented electrical steel sheets used was 1.90 T. The relationship between the calculated angle B and iron loss is shown in Figure 6(a).

[0052] Next, transformer noise was measured using the same method as in Experiment 1. The relationship between the calculated angle B and noise is shown in Figure 6(b).

[0053] As is clear from Figure 6(a), if the ferromagnetic component in the insulating film is oriented with a deviation of 1.0° to 20° in the thickness direction relative to the rolling surface (1.0° ≤ angle B ≤ 20°), then iron loss W 17 / 50 This was kept below 0.93 W / kg. On the other hand, even if the orientation was with a deviation of 0.5°, which is less than 1.0°, or with a deviation of 25°, which is greater than 20°, the iron loss W 17 / 50 It has increased significantly. Furthermore, as is clear from Figure 6(b), noise levels were kept below 56 dBA when the ferromagnetic component in the insulating film was oriented with a deviation of 1.0° to 20° in the thickness direction relative to the rolling surface (1.0° ≤ angle B ≤ 20°). On the other hand, noise levels increased significantly when the orientation was with a deviation of 0.5° (angle B less than 1.0°) or when the orientation was with a deviation of 25° (angle B greater than 20°). Surprisingly, by controlling the orientation angle B of the ferromagnetic component to 1.0° to 20°, we were able to improve both iron loss and noise.

[0054] Based on the above results, it is necessary to set the orientation angle B of the ferromagnetic component to between 1.0° and 20°. If the orientation angle B of the ferromagnetic component is not within the range of 1.0 to 20°, it is not possible to achieve both reduction of iron loss and reduction of noise. By setting the orientation angle B of the ferromagnetic component to 1.0° or higher, orientation in the thickness direction can be imparted to the ferromagnetic component, creating appropriate irregularities on the coating surface and improving the frictional force of the steel plate. Therefore, when steel plates are stacked to create an iron core, it is thought that the rigidity of the iron core improved and noise was reduced. Furthermore, by setting the orientation angle B of the ferromagnetic component to 1.0° or higher, the magnetization strength in the thickness direction of the plate is reinforced, and it is thought that the number of magnetic poles within the plate surface increased. As a result, in order to mitigate the increased magnetostatic energy, the magnetic domains in the thickness direction of the plate were further subdivided, which is thought to have reduced even iron loss.

[0055] Furthermore, if the orientation angle B of the ferromagnetic component exceeds 20°, excessive irregularities will occur on the surface, increasing the gaps between stacked steel sheets, reducing rigidity, and potentially increasing noise. Also, if the orientation angle B of the ferromagnetic component exceeds 20°, the anisotropy of the tension applied to the insulating coating in the direction perpendicular to rolling (thickness direction) will increase. Grain-oriented electrical steel sheets are formed by accumulating the easy magnetization axes of the crystal grains within the steel sheet in the rolling direction, and a reduction in iron loss can be expected by aligning the direction of the easy magnetization axis and the tension. However, if the applied tension also has a large anisotropy in the perpendicular direction, the easy magnetization axis and the tension will not be aligned to that extent, and as a result, the iron loss is thought to have deteriorated. The orientation angle B of the ferromagnetic component is preferably 1.5° or greater, and more preferably 2.0° or greater. Furthermore, the orientation angle B of the ferromagnetic component is preferably 5.0° or less, and more preferably 3.0° or less.

[0056] Regarding these orientation angles A and B, the inventors further investigated the degree of variation in their orientation. From the SEM images of the magnetic field application direction observed in Experiments 1 and 2 described above, one condition (A=0°, B=1°) was read for each ferromagnetic orientation direction, and the standard deviation in each field of view was calculated. Then, as described above, the average of the standard deviations across the five fields of view was taken as the variation for each orientation angle. For comparison, a sample without applied magnetic field was also prepared. In this way, the variation in orientation of the ferromagnetic component with respect to angle A and the variation in orientation with respect to angle B were confirmed. As a result, the standard deviation for orientation angle A was 0 to 3°, indicating that the ferromagnetic component in the insulating film can be uniformly oriented in the direction of the rolling plane by applying a magnetic field at a predetermined angle in the direction of the rolling plane. Furthermore, the standard deviation for orientation angle B was 0 to 3°, indicating that the ferromagnetic component in the insulating film can also be uniformly oriented in the direction of the thickness by applying a magnetic field at a predetermined angle in the thickness direction.

[0057] On the other hand, even when ferromagnetic components were present, when no magnetic field was applied, both the standard deviation for orientation angle A and the standard deviation for orientation angle B exceeded 20°, indicating a large variation in the orientation direction of the ferromagnetic components and indicating a disordered orientation. Furthermore, in cases where the ferromagnetic components were randomly arranged in the insulating film and no orientation was observed, although a reduction in iron loss due to the introduction of crystalline material (magnetite fine powder) into the insulating film was sometimes observed, no reduction in transformer noise was observed. The standard deviation of orientation angle A is preferably 3° or less, more preferably 2° or less, even more preferably 1° or less, and most preferably 0°. Similarly, the standard deviation of orientation angle B is preferably 3° or less, more preferably 2° or less, even more preferably 1° or less, and most preferably 0°. It is believed that the more highly the ferromagnetic components are aligned in the desired direction within the insulating film, the greater the improvement effect on iron loss and noise described above.

[0058] Experiment 3: [[Effect of Ferromagnetic Component Content]] By varying the amount of magnetite fine powder added, the solid content of the ferromagnetic component in the coating solution was changed from 0.05% to 22% by mass. Furthermore, grain-oriented electrical steel sheets were manufactured in the same manner as in Experiment 1, except that the application angle A along the rolling surface relative to the rolling direction was kept constant at 0°, and the application angle B in the thickness direction relative to the rolling surface was kept constant at 2°. The orientation direction (angle A) of the ferromagnetic component within the rolling plane was confirmed to be 0° in all cases, according to Experiment 1. Furthermore, the orientation direction (angle B) of the ferromagnetic component in the thickness direction was confirmed to be 2° in all cases, according to Experiment 2.

[0059] The magnetic properties were measured using the same method as in Experiment 1. The magnetic flux density B8 of all the grain-oriented electrical steel sheets used was 1.90 T. Figure 7(a) shows the relationship between the ferromagnetic component content and iron loss.

[0060] Next, transformer noise was measured using the same method as in Experiment 1. The relationship between the content of the ferromagnetic component and the noise is shown in Fig. 7(b).

[0061] As is clear from Fig. 7(a), if the ferromagnetic component is contained in the insulating film at 0.10 to 20%, the iron loss W 17 / 50 was suppressed to less than 0.88 W / kg. On the other hand, even when the content of the ferromagnetic component in the insulating film was 0.05% less than 0.10% or 22% exceeding 20%, the iron loss W 17 / 50 significantly increased. Also, as is clear from Fig. 7(b), if the ferromagnetic component is contained in the insulating film at 0.10 to 20%, the noise was suppressed to less than 57 dBA. On the other hand, even when the content of the ferromagnetic component in the insulating film was 0.05% less than 0.10% or 22% exceeding 20%, the noise significantly increased. Surprisingly, by controlling the content of the ferromagnetic component in the insulating film to 0.10 to 20%, both the iron loss and the noise could be improved. In addition, the content of the ferromagnetic component in the formed insulating film can be measured by performing ICP emission analysis after separating only the base film by fluorescent X-ray analysis and chemical treatment.

[0062] From the above results, it is necessary to set the content of the ferromagnetic component with respect to the insulating film to 0.10 mass% or more and 20 mass% or less. If the content of the ferromagnetic component is not within the range of 0.10 to 20%, even if its orientation direction is controlled, both reduction of iron loss and reduction of noise cannot be achieved. By sufficiently containing the ferromagnetic component at 0.10% or more, it is considered that the effect of controlling its orientation direction as described above is sufficiently exerted. On the other hand, by setting the content of the ferromagnetic component to 20% or less, it is possible to prevent the ferromagnetic component from excessively occupying the insulating film. As a result, it is considered that excessive unevenness on the surface of the insulating film is not generated, and a decrease in rigidity due to the gap generated between the steel sheets when laminated is prevented, and the transformer noise is improved. Also, it is considered that the insulating property of the insulating film is not impaired and the above-described effect on the iron loss is also exhibited. The ferromagnetic component content is preferably 0.5% or more, more preferably 2% or more, and even more preferably 5% or more. Furthermore, the ferromagnetic component content is preferably 15% or less, and more preferably 10% or less.

[0063] The ferromagnetic component is not limited to any component that exhibits ferromagnetism. In particular, the ferromagnetic component preferably contains at least one of iron, cobalt, nickel, magnetite, and ferrite, and may be a single component or a combination of several different components. The ferromagnetic components exemplified above are industrially more suitable because they exhibit ferromagnetism at room temperature, are inexpensive, and their particle size can be adjusted relatively easily.

[0064] The ferromagnetic component is not limited in shape, but it is preferably a particulate ferromagnetic powder. When a ferromagnetic powder is used, the individual powder particles tend to align in the desired direction when a magnetic field is applied, and as a result, the particles of the ferromagnetic component described above can be highly oriented in the desired direction. In addition, using a ferromagnetic powder can prevent excessive irregularities from forming on the surface of the insulating coating. Here, the "ferromagnetic powder" can, for example, have an aspect ratio of less than 1.5, preferably 1.2 or less, when measured with a known image-analytical particle size distribution analyzer.

[0065] The ferromagnetic component preferably has an average particle size of 1.5 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less. If the average particle size of the ferromagnetic component is below the above upper limit, it is possible to prevent the ferromagnetic component from becoming larger than the thickness of the insulating film, or the ferromagnetic component from protruding from the surface of the insulating film and reducing the insulating properties of the steel plate. In addition, it is possible to obtain good noise characteristics without creating excessive irregularities on the surface. On the other hand, the average particle size of the ferromagnetic component can be 0.3 μm or more from the viewpoint of easily orienting it in a desired direction and giving anisotropy to the tension. The average particle size of the ferromagnetic component can be measured according to the particle size distribution measurement method using laser diffraction. If the ferromagnetic component is a combination of multiple components, the average value considering each component can be used.

[0066] [[Other ingredients]] The glassy insulating coating is not particularly limited except for the ferromagnetic component, but it can preferably be made of silicate glass. In addition to the ferromagnetic component, the silicate glass insulating coating can have as its basic components at least one selected from Mg, Al, Ca, Ba, Sr, Zn, Cr, and Mn salts of phosphoric acid and colloidal silica. When forming the insulating coating, any other additives may be added to the composition of the coating solution. For example, it is not limited to adding hexavalent chromic acid, titanium dioxide, vanadium oxide, etc., to improve the durability of the insulating coating. Whether or not the insulating coating is glassy, ​​and its composition, can be determined, for example, by XRD.

[0067] We also investigated various phosphate species that can constitute the insulating coating. The metal species of phosphate used in the preparation of the coating solution was determined to be Mg, Al, Ca, Ba, Sr, Zn, Cr, or Mn phosphate salts, respectively. Furthermore, the solid content of magnetite fine powder in the coating solution was kept constant at 5.0% by mass. The angle A when applying the magnetic field was kept constant at 0°, i.e., parallel to the rolling direction, and the angle B when applying the magnetic field was kept constant at 2°. The baking (final firing) temperature was kept constant at 840°C. Grain-oriented electrical steel sheets were manufactured in the same manner as in Experiment 1, except for the above. When the orientation of the ferromagnetic component was calculated for the obtained grain-oriented electrical steel sheets using the same method as in Experiments 1 and 2, it was confirmed that the magnetite was oriented at angles A: 0° and B: 2°. Furthermore, when the variation of each orientation angle was calculated using the same method as above, it was confirmed that the mean standard deviation of orientation angle A was 0° and the mean standard deviation of orientation angle B was 0°, indicating that the magnetite was highly uniformly oriented. Furthermore, in all cases where phosphates of the eight metal species are used, W 17 / 50 A good iron loss of 0.88 W / kg or less and a good transformer noise of 55.0 dBA or less were achieved.

[0068] For glassy insulating coatings, it is preferable to have few voids within the coating. Specifically, five cross-sectional SEM images are taken of the insulating coating, and the area of ​​voids in the insulating coating in each field of view is determined. It is preferable that the void ratio (area %), which is the ratio of the area of ​​the voids to the cross-sectional area of ​​the insulating coating, is 30% or less as an average value over the five fields of view. Voids in the insulating coating occur when water in the coating liquid vaporizes and escapes during the vitrification process in the insulating coating formation process. For example, if the baking temperature for forming the insulating coating exceeds 1000°C, the vaporization of water becomes more intense, and the rate of void formation in the coating also increases. If the insulating coating is of good quality with a void ratio below the above upper limit, sufficient tension can be applied to the steel plate, thereby better reducing iron loss in the steel plate. Furthermore, if sufficient tension can be applied to the steel plate by such a good glassy insulating coating, the effect of reducing lancet magnetic domains will be further enhanced, and it will be easier to reduce the magnetostriction of the steel plate and achieve lower noise.

[0069] The grain-oriented electrical steel sheet in one embodiment of the present invention can be used regardless of the properties of the steel sheet, such as a magnetic flux density of B8. Furthermore, the grain-oriented electrical steel sheet in one embodiment of the present invention can also be made to be a so-called magnetic domain refined material, which is manufactured by forming grooves on the surface of the steel sheet (for example, a steel sheet made of base metal, or a steel sheet with an undercoat such as a forsterite coating formed on the surface of the base metal) using electrolytic etching, gear rolls, laser etching, etc. Moreover, the grain-oriented electrical steel sheet in one embodiment of the present invention can also be made to be a so-called non-heat-resistant magnetic domain refined material, which is made by introducing thermal strain by laser, electron beam, plasma jet, etc., to the steel sheet after secondary recrystallization.

[0070] <Transformer core> The transformer core of the present invention is made using grain-oriented electrical steel sheet according to the embodiment of the present invention described above. Therefore, the transformer core of the present invention provides the same effects as described above for grain-oriented electrical steel sheet. The transformer core of the present invention is particularly useful for stacked core transformers. The transformer core of the present invention can be applied as, for example, a single-phase core, a three-phase tripod core, or a three-phase quinod core, and its dimensions and the magnetization conditions under which it is used are not limited.

[0071] <Manufacturing method for grain-oriented electrical steel sheets> The present invention relates to a method for manufacturing grain-oriented electrical steel sheets, characterized in that, when hot rolling, cold rolling, recrystallization annealing and decarburization annealing, application of an annealing separating agent, finish annealing, application of a coating solution, and baking are performed sequentially on a steel slab, the coating solution is made of specific components; a magnetic field is applied in a specific direction after application of the coating solution and before baking; and the baking temperature is set to a specific temperature; other conditions are not particularly limited. The manufacturing method of the present invention may further include any other steps, such as performing annealing such as hot-rolled sheet annealing and intermediate annealing before and after cold rolling. According to the manufacturing method of the present invention, for example, the grain-oriented electrical steel sheet of the present invention can be obtained. Therefore, the manufacturing method of the present invention has the same effects as the grain-oriented electrical steel sheet of the present invention. The manufacturing method of the grain-oriented electrical steel sheet of the present invention is particularly useful for obtaining iron cores for stacked iron core transformers.

[0072] Specifically, the coating solution must contain a ferromagnetic component in an amount of 0.10% to 20% by mass, calculated on a solid content basis. Here, the ferromagnetic component and its preferred content are as described above for grain-oriented electrical steel sheets.

[0073] The application of a magnetic field to a steel sheet must be performed at an angle of 20° or less along the rolling surface with respect to the rolling direction of the steel sheet (angle A), and at an angle of 1.0° to 20° in the thickness direction with respect to the rolling surface (angle B). Here, the application angles A and B are as described above for grain-oriented electrical steel sheets, and in this invention, since the magnetic field is applied to the ferromagnetic component, the direction in which the magnetic field is applied and the direction in which the ferromagnetic component actually orients can usually be substantially the same. Thus, according to the manufacturing method of this invention, the ferromagnetic component in the insulating coating can be oriented to a high level in a desired direction and magnetized.

[0074] The curing temperature must be between 800°C and 1000°C. The following is a detailed explanation of the experiments that led to the determination of this curing temperature.

[0075] Experiment 4: [[Effect of baking temperature]] The magnetic field was applied with a constant angle A along the rolling surface relative to the rolling direction (0°) and a constant angle B in the thickness direction relative to the rolling surface (2°). Furthermore, grain-oriented electrical steel sheets were manufactured in the same manner as in Experiment 1, except that the baking (final firing) temperature was changed within the range of 780°C to 1020°C. The orientation direction (angle A) of the ferromagnetic component within the rolling plane was confirmed to be 0° in all cases, according to Experiment 1. Furthermore, the orientation direction (angle B) of the ferromagnetic component in the thickness direction was confirmed to be 2° in all cases, according to Experiment 2.

[0076] The magnetic properties were measured using the same method as in Experiment 1. The magnetic flux density B8 of all the grain-oriented electrical steel sheets used was 1.90 T. The relationship between the baking temperature and iron loss is shown in Figure 8(a).

[0077] Next, transformer noise was measured using the same method as in Experiment 1. Figure 8(b) shows the relationship between baking temperature and noise.

[0078] As is clear from Figure 8(a), if the baking temperature is 800-1000°C, the iron loss W 17 / 50 This was kept below 0.90 W / kg. On the other hand, even when the baking temperature was less than 800°C (780°C) and more than 1000°C (1020°C), the iron loss W was kept below 0.90 W / kg. 17 / 50 It has increased significantly. Furthermore, as is clear from Figure 8(b), when the curing temperature was between 800 and 1000°C, the noise level was kept below 57 dBA. On the other hand, when the curing temperature was below 800°C (780°C) and above 1000°C (1020°C), the noise level increased significantly. Surprisingly, by controlling the baking temperature to 800-1000°C, we were able to improve both iron loss and noise levels.

[0079] Based on the above results, it is necessary to set the curing temperature of the coating solution to between 800°C and 1000°C. If the curing temperature is not above 800°C, the curing of the insulating film will not proceed sufficiently, the glass transition temperature of the insulating film components will decrease, the vitrification of the insulating film will not proceed sufficiently, and sufficient tension will not be applied to the steel sheet. In this way, it will not be possible to form a good glassy insulating film itself. As a result, many lancet magnetic domains remain in the steel sheet, and the magnetostriction will also increase, which is thought to have led to a deterioration in noise. In order to form an insulating film even at low temperatures, it is conceivable to extend the curing (annealing) time, but extending the annealing time will reduce productivity and increase costs.

[0080] On the other hand, if the baking temperature exceeds 1000°C, the moisture in the applied coating evaporates rapidly, forming numerous cavities in the insulating coating and reducing its volume. As a result, the aforementioned good glassy insulating coating cannot be formed, and the tension from the insulating coating is not sufficiently applied to the steel plate, leading to a deterioration in iron loss. In addition, if an undercoat is formed beneath the insulating coating, the tension of the undercoat also decreases if the baking temperature exceeds 1000°C. Consequently, the steel plate becomes more prone to creep deformation and stretching, reducing the tension on the steel plate and further degrading iron loss. Furthermore, due to this low coating tension, the effect of the insulating coating on reducing lancet magnetic domains is reduced, and many lancet magnetic domains remain in the steel plate. As a result, it is thought that the increased magnetostriction also led to a deterioration in noise. The baking temperature is preferably 820°C or higher, and more preferably 850°C or higher. Furthermore, the baking temperature is preferably 950°C or lower, and more preferably 900°C or lower.

[0081] [[Indicated time of magnetic field]] The time for applying the magnetic field to the steel plate is preferably 5 seconds or more, more preferably 10 seconds or more, preferably 60 seconds or less, and more preferably 30 seconds or less. If the application time is too short, it is difficult to complete the control of the orientation direction of the ferromagnetic component. On the other hand, if the application time is too long, it leads to a decrease in productivity.

[0082] [[Conditions for pre-baking]] When pre-baking is performed during the curing process, it is preferable to pre-bake in air at a temperature of 300°C or higher, more preferably 350°C or higher, 500°C or lower, and more preferably 450°C or lower. Pre-baking at low temperatures results in insufficient drying of moisture, and a large amount of moisture tends to remain on the steel plate. This remaining moisture then volatilizes during the final curing process and escapes from the coating film, resulting in a sparse insulating film and a decrease in the insulating properties and tension of the insulating film. On the other hand, pre-baking at too high a temperature tends to lead to excessive polymerization of the gel in the coating film during pre-baking. This also tends to reduce the tension of the insulating film formed after the final curing. Furthermore, the pre-baking time is preferably 10 seconds or more, more preferably 15 seconds or more, preferably 30 seconds or less, and more preferably 25 seconds or less. If the pre-baking time is too short, the moisture will not dry sufficiently, and the insulating properties and tension of the insulating coating will tend to decrease. On the other hand, if the pre-baking time is too long, it will lead to a decrease in productivity. [Examples]

[0083] The following embodiments illustrate preferred examples of the present invention, and the present invention is not limited in any way by these embodiments. Embodiments of the present invention can be modified as appropriate within the scope of the spirit of the present invention, and all such modifications fall within the technical scope of the present invention. Steel slabs containing the component composition shown in Table 2, with the remainder being Fe and unavoidable impurities, were manufactured by continuous casting. After heating these steel slabs at 1420°C, they were hot-rolled to a thickness of 2.3 mm. These hot-rolled sheets were then annealed at 900°C for 10 seconds. Next, the hot-rolled sheets were cold-rolled to an intermediate thickness of 1.1 mm and subjected to intermediate annealing at 1070°C for 30 seconds with an oxidation state of PH2O / PH2 = 0.32. The hot-rolled sheets were cold-rolled again to a thickness of 0.22 mm. Subsequently, these cold-rolled sheets were subjected to primary recrystallization annealing and decarburization annealing at 850°C for 120 seconds with an oxidation state of PH2O / PH2 = 0.32 to obtain decarburized annealed sheets. An annealing separation agent mainly composed of MgO was applied to the surface of these decarburized annealed sheets. Next, secondary recrystallization was performed, and finish annealing was carried out with the aim of forming a forsterite coating as an undercoat, thereby obtaining a steel sheet with an undercoat formed on the base metal. Finish annealing was carried out by heating to 1200°C at a rate of 20°C per hour under a nitrogen atmosphere, holding at 1200°C for 10 hours, and then cooling to room temperature at a rate of 20°C per hour.

[0084] [Table 2]

[0085] After finish annealing, an insulating coating solution was applied to both sides of the steel sheet. The coating solution was prepared using the formulations shown in Table 3, consisting of various metal phosphate salts, colloidal silica, and various ferromagnetic components (average particle size: 1.0 μm under all conditions). The coating solution was applied using a roll coater. The amount of coating solution applied was 10 g / m² in total for both sides, resulting in an insulating coating weight after baking. 2 This was the amount that resulted in this. Thirty seconds after the coating solution was applied, the angle A along the rolling surface with respect to the rolling direction and the angle B in the thickness direction with respect to the rolling surface were changed for each steel sheet as shown in Table 3, and a magnetic field with a magnetic flux density of 1.5T was applied for 15 seconds. Subsequently, the steel sheets were pre-baked in air at 400°C for 20 seconds, and then fully baked for 15 seconds at various baking temperatures shown in Table 3 under a 100% volume nitrogen atmosphere to obtain grain-oriented electrical steel sheets.

[0086] The magnetic properties (iron loss) of the obtained grain-oriented electrical steel sheet were measured using the same method as in Experiment 1. Furthermore, the insulating coatings of the grain-oriented electrical steel sheets were evaluated to determine whether they were good glassy insulating coatings using XRD and the void ratio measurement method described above. The evaluation criteria were that an insulating coating was good (Yes in Table 3) if it was glassy with a void ratio of 30% or less, and poor (No in Table 3) if it did not meet this void ratio or was not glassy.

[0087] Furthermore, the transformer core was assembled to the dimensions shown in Figure 9. For the core assembly, the obtained grain-oriented electrical steel sheets were used, and a stacked core was fabricated by stacking 10 layers with a lap length of 2 mm. After this, materials were applied to the front and back surfaces of the yoke section of the core and pressed down to 0.3 MPa. The legs of the core were wrapped with glass tape, and then 40 turns of primary and secondary coils were wound around each of the three legs. Then, using the same method as in Experiment 1, the transformed noise was measured using the obtained iron core. The results are shown in Table 3. From Table 3, it can be seen that by satisfying the conditions of the present invention, both iron loss and noise can be reduced, and grain-oriented electrical steel sheets and transformer cores with superior properties can be provided.

[0088] [Table 3] TIFF2026061672000005.tif255149TIFF2026061672000006.tif255148TIFF2026061672000007.tif255127 [Industrial applicability]

[0089] The grain-oriented electrical steel sheet, its manufacturing method, and transformer core of the present invention can be used to realize transformers that are excellent in both loss and noise.

Claims

1. A grain-oriented electrical steel sheet having a glassy insulating coating on the surface of the steel sheet, The insulating film contains 0.10% by mass or more and 20% by mass or less of a ferromagnetic component relative to the insulating film. A grain-oriented electrical steel sheet characterized in that the ferromagnetic component is oriented at an angle of 20° or less along the rolling surface with respect to the rolling direction of the grain-oriented electrical steel sheet, and at an angle of 1.0° or more and 20° or less in the thickness direction with respect to the rolling surface.

2. The grain-oriented electrical steel sheet according to claim 1, wherein the ferromagnetic component contains at least one of iron, cobalt, nickel, magnetite, and ferrite, and the average particle size of the ferromagnetic component is 1.5 μm or less.

3. A transformer core made using grain-oriented electrical steel sheet according to claim 1 or 2.

4. A method for manufacturing grain-oriented electrical steel sheets, comprising: hot rolling a steel slab to obtain a hot-rolled sheet; cold rolling the hot-rolled sheet to obtain a cold-rolled sheet; recrystallization annealing and decarburization annealing the cold-rolled sheet to obtain a decarburized annealed sheet; applying an annealing release agent to the decarburized annealed sheet and then performing finish annealing to obtain a steel sheet; and then applying a coating liquid to the surface of the steel sheet and baking it to form a glassy insulating film, The coating liquid contains a ferromagnetic component in an amount of 0.10% by mass or more and 20% by mass or less on a solid content basis. After the application of the coating liquid and before the baking, a magnetic field is applied to the steel sheet at an angle of 20° or less along the rolling surface with respect to the rolling direction of the steel sheet, and at an angle of 1.0° or more and 20° or less in the thickness direction with respect to the rolling surface. A method for manufacturing grain-oriented electrical steel sheets, characterized in that the baking temperature is 800°C or higher and 1000°C or lower.

5. The method for producing a grain-oriented electrical steel sheet according to claim 4, wherein the ferromagnetic component contains at least one of iron, cobalt, nickel, magnetite, and ferrite, and the average particle size of the ferromagnetic component is 1.5 μm or less.

Images