Grain-oriented electrical steel sheets and wound cores

Abstract

The steel sheet has a composition containing C: 0.0050 mass% or less, Si: 2.0 to 8.0 mass%, and Mn: 0.02 to 1.0 mass%, with the balance being Fe and unavoidable impurities, has a base coating mainly made of forsterite on the surface of the base steel sheet, and has a number density of inclusions having a diameter of 0.5 μm or more and 3.0 μm or less present inside the base steel sheet of 1.0 pieces / mm 2 More than 20.0 pieces / mm 2 The present invention provides a grain-oriented electrical steel sheet having excellent magnetic properties and excellent bending processing accuracy, and a wound core using the grain-oriented electrical steel sheet, as described below.

Description

[Technical field]

[0001] The present invention relates to a grain-oriented electrical steel sheet suitable for use as a transformer core material, and a wound core manufactured using the steel sheet. [Background technology]

[0002] Grain-oriented electrical steel is a soft magnetic material that is mainly used as the iron core material for transformers and large generators. It has a crystal orientation that is the easy axis of magnetization of iron. <001> The texture is characterized by a highly aligned axis in the rolling direction of the steel sheet. This texture is characterized by a secondary recrystallization that results in a Goss orientation {110} <001> This can be achieved by preferentially growing crystal grains of the desired orientation.

[0003] In grain-oriented electrical steel sheets, the iron loss characteristics are of utmost importance in terms of their applications. Iron loss indicates the amount of energy lost, mainly as heat, when the steel sheet is excited; the lower the value, the less loss there is, and the better the material is considered to be. Known methods for reducing the above-mentioned iron loss include reducing the variation in the Goss orientation to approach the ideal Goss orientation, and applying a special process called magnetic domain refining. In addition, grain-oriented electrical steel sheets are generally used in layers, so an insulating coating is formed on the surface of the steel sheet. Iron loss can also be reduced by applying tensile tension to the surface of the steel sheet through this coating.

[0004] Transformer cores using grain-oriented electromagnetic steel sheets are roughly divided into wound cores and stacked cores. Wound cores are a type in which steel sheets are wound and stacked, and are applied to relatively small transformers. For example, Patent Document 1 discloses a method for making a three-phase three-legged transformer with a wound core. Patent Document 2 discloses a manufacturing method for a wound core that can obtain low iron loss. Patent Document 3 describes a technology for extending the tool life during slitting by applying an organic substance to the surface of grain-oriented electromagnetic steel sheets for wound cores. On the other hand, stacked cores are a type in which cut sheets cut into rectangular or trapezoidal shapes are stacked, and are often applied to relatively large transformers. For example, Patent Document 4 and Patent Document 5 disclose technologies related to reducing iron loss in three-phase stacked transformers. Patent Document 6 describes a manufacturing technology for a three-phase stacked transformer that achieves low iron loss and low noise. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 05-101943 [Patent Document 2] Japanese Patent Application Publication No. 15309 / 1983 [Patent Document 3] Japanese Patent Publication No. 14405 / 1983 [Patent Document 4] Japanese Patent Application Publication No. 06-251966 [Patent Document 5] Japanese Patent Application Publication No. 10-261536 [Patent Document 6] JP 2000-114064 A Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, wound cores have been attracting attention, and in particular, there is an increasing demand for the so-called "Unicore" type of wound core, which is a rectangular wound core made by individually bending steel sheets and laminating these individually processed steel sheets in multiple layers. Conventionally, wound cores are assembled by preparing a mold for winding electromagnetic steel sheets and winding steel sheets around it. However, this Unicore type wound core does not require a mold, and is easy to assemble and modify, so it is expected to reduce costs and improve manufacturability. In addition, conventional wound cores have a problem in that strain is introduced into the steel sheet when it is wound around the mold, causing a significant deterioration in iron loss characteristics. However, with Unicore, the strain introduction portion due to core processing is limited to the bent portion, so there is little iron loss deterioration and, in some cases, there is also the advantage that strain relief annealing can be omitted.

[0007] The grain-oriented electrical steel sheets used in the above-mentioned wound cores are folded during the manufacturing process, but the poor accuracy of this folding process has become a problem. For example, the steel sheets used in Unicore are slit to a specified width and then folded in several places, as shown in Figure 1. However, as shown in Figure 2, after the folding process, there are many cases where the two sides of the butted steel sheet ends are not parallel. This makes it difficult to stack the steel sheets, which creates the problem of not being able to form the core.

[0008] The present invention has been made in consideration of the above-mentioned problems associated with the conventional technology, and has an object to provide a grain-oriented electrical steel sheet that is excellent in bending accuracy without incurring deterioration of magnetic properties, and a wound core manufactured using the above-mentioned steel sheet. [Means for solving the problem]

[0009] In order to achieve the above object, the inventors have conducted extensive research focusing on the effects of inclusions present inside a product sheet on magnetic properties and bending accuracy. As a result, they have discovered that in order to improve bending accuracy without deteriorating magnetic properties, it is important to have fine inclusions present inside a steel sheet and to optimize their number density, which led to the development of the present invention.

[0010] The present invention based on the above findings provides a grain-oriented electrical steel sheet having a base coating mainly composed of forsterite on the surface of a base steel sheet, the base steel sheet having a composition containing C: 0.0050 mass% or less, Si: 2.0 to 8.0 mass%, Mn: 0.02 to 1.0 mass%, with the balance being Fe and unavoidable impurities, and the number density of inclusions having a diameter of 0.5 μm or more and 3.0 μm or less present inside the base steel sheet is 1.0 pieces / mm 2 More than 20.0 pieces / mm 2 The grain-oriented electrical steel sheet is characterized in that:

[0011] The grain-oriented electrical steel sheet of the present invention, with a base coating, contains S: 0.0005 to 0.0100 mass% and Se: 0.0005 to 0.0100 mass%, and when the concentration distributions of Se and S in the sheet thickness direction from the steel sheet surface are measured by glow discharge optical emission spectrometry, the peaks of the emission intensity profiles of Se and S are present at the interface between the base coating and the base steel sheet, and the Se emission intensity peak value I Se and the peak value of the emission intensity of S S is expressed as the following equation (1); I Se / I S ≦1.0 (1) The present invention is characterized in that:

[0012] In addition, the grain-oriented electrical steel sheet of the present invention has a number density of inclusions having a diameter of more than 5.0 μm present inside the base steel sheet of 2.0 pieces / mm 2 The present invention is characterized in that:

[0013] Furthermore, the base steel sheet in the grain-oriented electrical steel sheet of the present invention further contains, in addition to the above-mentioned components, Sn: 0.005 to 0.500 mass%, Cr: 0.005 to 0.500 mass%, Cu: 0.01 to 0.50 mass%, Ag: 0.001 to 0.050 mass%, Au: 0.001 to 0.050 mass%, Ni: 0.01 to 0.50 mass%, Bi: 0. 005~0.500mass%, P:0.005~0.50mass%, Sb:0.005~0.50mass%, Mo:0.005~0.50mass%, B:0.0000 1~0.00250mass%, Nb:0.001~0.020mass%, Ti:0.0005~0.0400mass%, V:0.001~0.020mass%, As:0 .0010~0.0200mass%, Zn:0.001~0.020mass%, Pb:0.0001~0.0100mass%, W:0.0010~0.0100mass %, Co:0.002~0.050mass%, Ga:0.0001~0.0050mass%, Ge:0.0001~0.0050mass%, Ca:0.001~0.020 mass%, Nd: 0.001 to 0.020 mass%, La: 0.001 to 0.020 mass%, Ce: 0.001 to 0.020 mass%, Pr: 0.001 to 0.020 mass%, Dy: 0.001 to 0.020 mass%, and Hf: 0.001 to 0.020 mass%.

[0014] The present invention also relates to a wound core made of any of the grain-oriented electrical steel sheets described above. Effect of the Invention

[0015] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet that not only has excellent magnetic properties but also has excellent bending accuracy, making it possible to manufacture wound cores with high efficiency. [Brief description of the drawings]

[0016] [Figure 1] FIG. 2 is a schematic diagram illustrating a bending process of a steel plate when manufacturing a Unicore. [Diagram 2] FIG. 2 is a schematic diagram illustrating defects in the bending process of a steel plate when manufacturing a Unicore. [Diagram 3] FIG. 1 is a diagram illustrating parameters θ and H for evaluating machining accuracy. [Figure 4] 1 is a graph showing the effect of the number density of inclusions having a diameter of 0.5 to 3.0 μm on the processing accuracy of bending and iron loss. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] First, the experiment that led to the development of the present invention will be described. <Experiment 1> The molten iron tapped from the blast furnace was subjected to primary refining in a converter in the steelmaking process, where it was decarburized, dephosphorized, and desulfurized, and then secondary refining in a vacuum degassing treatment device to produce steel with a composition containing C: 0.031-0.051 mass%, Si: 3.20-3.35 mass%, Mn: 0.07-0.11 mass%, Al: 0.005-0.011 mass%, N: 0.0011-0.0044 mass%, and S: 0.0008-0.0023 mass%, with the balance being Fe and unavoidable impurities. During this secondary refining, the amount and size of inclusions contained in the molten steel were variously changed by adjusting the nitrogen partial pressure and the treatment time. Furthermore, in order to change the state of the inclusions in the steel, the casting speed was changed in the range of 0.4-1.5 m / min when the molten steel was continuously cast to produce a slab. Next, the slab obtained as described above was reheated to a temperature of 1230°C, and then hot-rolled to a hot-rolled sheet having a thickness of 2.4 mm. The surface scale of the hot-rolled sheet was removed by pickling, and then cold-rolled to a cold-rolled sheet having a final thickness of 0.23 mm. Next, the cold-rolled sheet was subjected to decarburization annealing, which also served as primary recrystallization annealing, at 850°C for 200 s in an atmosphere of 60 vol% H2 + 40 vol% N2 with a dew point of 45°C to obtain a decarburized annealed sheet. Next, an annealing separator mainly composed of MgO was applied to the surface of the decarburized annealed sheet and dried. After completing the secondary recrystallization, the sheet was subjected to finish annealing in which the sheet was kept at a temperature of 1200°C for 5 hours in an H2 atmosphere for purification, to obtain a grain-oriented electrical steel sheet (product sheet) having a base coat mainly composed of forsterite.

[0018] For the product sheet obtained as described above, a composition analysis was performed on the base steel sheet after removing the base coating mainly composed of forsterite that had formed on the steel sheet surface. The composition was found to contain C: 0.0008-0.0021 mass%, Si: 3.20-3.35 mass%, Mn: 0.07-0.11 mass%, and the remainder being Fe and unavoidable impurities.

[0019] In addition, a test piece with a width of 100 mm and a length of 300 mm was taken from the above product plate, and the iron loss W was measured using the single plate magnetic property test method described in JIS C 2556. 17 / 50 In the present invention, the iron loss W 17 / 50 If the core loss is 0.85 W / kg or less, the core loss characteristics are evaluated as good.

[0020] Similarly, a sample with a width of 150 mm and a length of 1000 mm was cut out from the above product plate, with the rolling direction as the length direction, and was bent at 45° at 8 locations in the length direction with a radius of curvature r: 3 mm, as shown in FIG. 1. Next, the processing accuracy of the ring-shaped sample after the above bending processing was evaluated using two parameters θ and H shown in FIG. 3. Here, θ is the angle between the two butted sides (A and B in FIG. 3), and H is the vertical deviation distance between the two butted sides A and B. When an ideal shape is obtained, θ: 0° and H: 0 mm, and the more deviated from these values, the worse the processing accuracy is. In this experiment, if each parameter was within the range of θ: 0 to 3.0° and H: 0 to 5.0 mm, respectively, the processing accuracy was judged to be acceptable, and if both parameters were acceptable, it was represented as ◯, if only one of them was acceptable, it was represented as △, and if both parameters were unacceptable, it was represented as ×.

[0021] In addition, to investigate the inclusions present in the steel plate, one side of the sample taken from the above product plate was pickled with hydrochloric acid and removed down to the center of the plate thickness to reveal a surface passing through the center of the plate thickness that is parallel to the rolling surface (steel plate surface). The size and number of inclusions present in the surface were then measured using a scanning electron microscope (Personal SEM: ASPEX Co.) equipped with an automatic particle measurement mechanism at a 50 mm 2 The measurements were carried out over a range of

[0022] Figure 4 shows the number density (number / mm2) of inclusions with diameters of 0.5 μm to 3.0 μm measured as described above. 2 ) and iron loss W 17 / 50 The figure shows the relationship between the number density of inclusions of the above size and the evaluation results of machining accuracy. 2 More than 20.0 pieces / mm 2 Iron loss W in the following range 17 / 50 It can be seen that both the diameter and processing accuracy are good. Here, the diameter of the above inclusions refers to the average value of the Feret diameter in the rolling direction and the plate width direction read from the SEM image.

[0023] The reason why the machining accuracy is good when the number density of the inclusions is in the above range has not yet been fully clarified at present, but the inventors believe it to be as follows. As mentioned above, grain-oriented electrical steel sheets are characterized by the crystal orientation of the base steel sheet being highly aligned in a specific direction and by the large crystal grains. Therefore, there are few places where stress concentrates when bending, and the starting point of the bending is uneven, which makes the deformation prone to be uneven. However, as obtained in this experiment, it was found that the presence of inclusions of a certain size in the steel sheet at a certain density causes stress to concentrate on the inclusions, which become the starting points of deformation, and that if the inclusions are uniformly distributed, the starting points of deformation will also be uniform, which is thought to improve the processing accuracy. However, if the size of the inclusions is less than 0.5 μm or the number density of the inclusions is less than 1.0 pieces / mm 2 On the other hand, if the number density is less than 20.0 pieces / mm 2If the density exceeds this range, the inclusions will hinder the domain wall movement, resulting in a deterioration in iron loss. The force that hinders the domain wall movement depends on the average grain size and the amount of inclusions present, but for a single inclusion, the larger the grain size, the greater the force, and when the grain size exceeds 3.0 μm, this force becomes particularly noticeable. Therefore, as revealed by this experiment, by having relatively small inclusions with an average grain size of about 0.5 to 3.0 μm present at the above density, it is possible to obtain a steel sheet with good processing accuracy without causing a deterioration in the magnetic properties. Based on this concept, the number of inclusions exceeding 5.0 μm, which have a particularly large force for hindering domain wall movement, is 2.0 pieces / mm 2 It is desirable that the following:

[0024] In addition, when bending is performed, there is a concern that the undercoat, which is mainly composed of forsterite and formed on the surface of the steel sheet, may peel off at the bent portion, exposing the base steel sheet and causing insulation failure. As a result of conducting separate experiments and examining measures to prevent this peeling, it became clear that it is preferable to have soft compounds such as sulfides and selenides present between the undercoat and the base steel sheet (at the interface). The present invention was developed based on the above novel findings.

[0025] Next, the chemical composition of the grain-oriented electrical steel sheet (product sheet) of the present invention will be described. C: 0.0050mass% or less If the C content in the product sheet exceeds 0.0050 mass%, magnetic aging occurs, leading to core loss deterioration, so the C content is limited to 0.0050 mass% or less, preferably 0.0030 mass% or less.

[0026] Si: 2.0~8.0mass% Silicon is an element necessary for increasing the resistivity of steel and reducing iron loss. However, if the Si content is less than 2.0 mass%, the above effects are not sufficiently obtained, while if the Si content exceeds 8.0 mass%, the workability of the steel decreases, making it difficult to slit and bend the steel sheet. Therefore, the Si content is set to the range of 2.0 to 8.0 mass%, and preferably to the range of 3.0 to 6.5 mass%.

[0027] Mn: 0.02~1.0mass% Mn is an element that is effective in improving hot workability and stabilizing secondary recrystallization. However, if the Mn content is less than 0.02 mass%, the above effects are poor, and a large cost is required to reduce the Mn content. On the other hand, if the Mn content exceeds 1.0 mass%, the magnetic flux density of the product sheet decreases. Therefore, the Mn content is set to a range of 0.02 to 1.0 mass%, and preferably to a range of 0.05 to 0.50 mass%.

[0028] In the grain-oriented electrical steel sheet (product sheet) of the present invention, the remainder other than the above-mentioned C, Si, and Mn is substantially Fe and unavoidable impurities. However, for the purpose of improving the magnetic properties, the following elements may be added: Sn: 0.005 to 0.500 mass%, Cr: 0.005 to 0.500 mass%, Cu: 0.01 to 0.50 mass%, Ag: 0.001 to 0.050 mass%, Au: 0.001 to 0.050 mass%, Ni: 0.01 to 0.50 mass%, Bi: 0.005 to 0.500 mass% , P:0.005~0.50mass%, Sb:0.005~0.50mass%, Mo:0.005~0.50mass%, B:0.00001~0.00250ma ss%, Nb:0.001~0.020mass%, Ti:0.0005~0.0400mass%, V:0.001~0.020mass%, As:0.0010~0. 0200mass%, Zn:0.001~0.020mass%, Pb:0.0001~0.0100mass%, W:0.0010~0.0100mass%, Co: 0.002~0.050mass%, Ga:0.0001~0.0050mass%, Ge:0.0001~0.0050mass%, Ca:0.001~0.020m At least one selected from the group consisting of 0.001-0.020 mass%, Nd: 0.001-0.020 mass%, La: 0.001-0.020 mass%, Ce: 0.001-0.020 mass%, Pr: 0.001-0.020 mass%, Dy: 0.001-0.020 mass%, and Hf: 0.001-0.020 mass% may be appropriately contained. If the content of each element is less than the lower limit, the effect of improving the magnetic properties is not sufficiently obtained, and conversely, if the content exceeds the upper limit, the development of secondary recrystallized grains is inhibited, and the magnetic properties are deteriorated.

[0029] Next, the grain-oriented electrical steel sheet of the present invention will be described. The grain-oriented electrical steel sheet of the present invention has inclusions having a diameter of 0.5 μm or more and 3.0 μm or less inside the steel sheet (base steel sheet) after removing a base coating mainly composed of forsterite from the steel sheet surface, and the number density of the inclusions is 1.0 piece / mm 2 More than 20.0 pieces / mm 2The number density is a value measured in a plane parallel to the steel sheet surface including the center of the sheet thickness. 2 If it is less than 20.0 pieces / mm, the effect of improving the processing accuracy described above cannot be obtained sufficiently. 2 If it exceeds this limit, the iron loss will increase significantly. 2 More than 10.0 pieces / mm 2 The range is as follows:

[0030] In addition, in order to suppress the deterioration of iron loss due to inclusions, the number density of inclusions exceeding 5.0 μm in diameter, which are a major obstacle to the movement of the domain walls, must be kept at 2.0 pieces / mm 2 It is preferable that the number of particles is 1.0 or less per mm. 2 It is more preferable that:

[0031] Next, a method for producing the grain-oriented electrical steel sheet of the present invention will be described. The steel material (slab) used in the production of the grain-oriented electrical steel sheet of the present invention is produced by refining molten pig iron obtained by a blast furnace process or molten steel obtained by an electric furnace process using a conventionally known refining process, adjusting the components, and melting steel having the component composition described above, and then producing the molten steel using a continuous casting process or an ingot casting-slabbing rolling process, or the like.

[0032] The steel material preferably contains C in the range of 0.010 to 0.090 mass%. C is an element that is reduced to 0.0050 mass% or less in the decarburization annealing process so that the product sheet does not undergo magnetic aging, but if it exceeds 0.090 mass%, there is a risk that decarburization will be insufficient and the C in the product sheet will exceed 0.0050 mass%. On the other hand, C is an element that has the effect of strengthening the grain boundaries of the steel material and improving the texture via the α-γ transformation of the hot-rolled sheet, and in order to obtain such effects, it is preferable that the C content be 0.010 mass% or more.

[0033] In addition, when an inhibitor is used to induce secondary recrystallization in the finish annealing described later, the steel material preferably contains Al, N, S, and Se, which are inhibitor-forming components, in addition to the above-described composition. Specifically, when AlN is used as the inhibitor, it is preferable to contain Al in the range of 0.010 to 0.040 mass%, and N in the range of 0.005 to 0.020 mass%. In addition, when MnS and / or MnSe are used as the inhibitor, it is preferable to contain S in the range of 0.005 to 0.040 mass% and / or Se in the range of 0.005 to 0.040 mass%. The inhibitor-forming components are reduced to the impurity level by the purification treatment in the finish annealing described later. The inhibitors AlN and MnS and / or MnSe may be used alone or in combination.

[0034] On the other hand, when no inhibitor is used to induce secondary recrystallization, it is preferable to reduce the inhibitor-forming components Al, N, S, and Se as much as possible. Specifically, Al: less than 0.010 mass%, N: less than 0.005 mass%, S: less than 0.005 mass%, and Se: less than 0.005 mass%. As described later, the inhibitor-forming components S and Se are elements that contribute to improving the adhesion of the forsterite undercoat, so it is preferable to appropriately contain them within the above-mentioned ranges.

[0035] Of the above-mentioned components, C can be reduced in the decarburization annealing process, and N can be nitrogenated in the finish annealing process. However, since it is difficult to change the content of components other than C and N in processes after hot rolling, it is preferable to adjust the components at the stage of producing molten steel.

[0036] In the present invention, in addition to adjusting the steel composition to the above-mentioned composition range in the refining process, it is important to control the shape of inclusions present in the steel. In general, inclusions present in steel deteriorate the iron loss in grain-oriented electrical steel sheets, so it is considered desirable to reduce them as much as possible. However, in the present invention, in order to improve the processing accuracy of the bending process, it is necessary to have inclusions of a suitable size that do not adversely affect the magnetic properties in the steel at a suitable density.

[0037] As a method for controlling the shape of the inclusions, for example, a method for shortening the time during primary refining in a converter, a method for limiting the discharge of slag, a method for reducing the flow rate of blown gas during secondary refining, a method for shortening the blowing time, etc. can be used. However, in the present invention, the method is not particularly limited.

[0038] Next, the steel material (slab) in which the steel composition and inclusions have been appropriately controlled is heated to a predetermined temperature by a normal method and conditions, and then hot rolled to obtain a hot-rolled sheet of a predetermined thickness. When the slab contains an inhibitor-forming component, the slab is preferably heated to a temperature of 1350°C or higher before the hot rolling in order to completely dissolve the inhibitor. On the other hand, when the slab does not contain an inhibitor-forming component, the slab is preferably heated to a temperature of 1250°C or lower, which is higher than the temperature at which hot rolling is possible, in order to reduce thermal energy costs.

[0039] Next, the steel sheet (hot-rolled sheet) after the hot rolling may be subjected to hot-rolled sheet annealing depending on the required properties. In order to obtain good magnetic properties, the annealing temperature is preferably in the range of 800°C to 1150°C. If the hot-rolled sheet annealing temperature is less than 800°C, the band structure formed by hot rolling remains, making it difficult to obtain a uniform primary recrystallized structure, and there is a risk that the development of secondary recrystallized grains is hindered. On the other hand, if the hot-rolled sheet annealing temperature exceeds 1150°C, the grain size after the hot-rolled sheet annealing becomes too coarse, and it is also difficult to obtain a uniform primary recrystallized structure.

[0040] Next, the hot-rolled sheet or the hot-rolled sheet after the hot-rolled sheet annealing is cold-rolled once or cold-rolled twice or more with intermediate annealing in between to obtain a cold-rolled sheet of the final thickness (product thickness). When intermediate annealing is performed, the annealing temperature is preferably set to a range of 900°C to 1200°C. If the annealing temperature is less than 900°C, the recrystallized grains become fine, and the Goss nuclei in the primary recrystallized structure are reduced, which may deteriorate the magnetic properties. On the other hand, if the annealing temperature exceeds 1200°C, the grain size becomes too coarse, as in the case of hot-rolled sheet annealing, making it difficult to obtain a uniform primary recrystallized structure.

[0041] In the final cold rolling to obtain the final sheet thickness, it is preferable to employ warm rolling in which the steel sheet temperature during cold rolling is increased to 100°C to 300°C, or interpass aging in which aging is performed between rolling passes, which can improve the recrystallized texture and enhance the magnetic properties.

[0042] Next, the cold-rolled sheet having the final thickness is subjected to decarburization annealing, which also serves as primary recrystallization annealing. In order to ensure sufficient decarburization, the decarburization annealing is preferably performed at an annealing temperature in the range of 800°C to 900°C, and in a moist atmosphere with a dew point of 30°C or higher. Similarly, in order to promote decarburization, the atmosphere preferably contains H2 in the range of 5 vol% to 70 vol%. Furthermore, in order to improve the iron loss characteristics, the heating rate up to the annealing temperature is preferably 100°C / s or higher. However, the higher the heating rate, the more expensive the equipment required to achieve it, so the upper limit is preferably about 2000°C / s.

[0043] Next, the steel sheet after the decarburization annealing is coated with an annealing separator on the surface of the steel sheet, dried, wound into a coil, and subjected to finish annealing. By using an annealing separator containing MgO as the main component, it is possible to prevent the steel sheets from fusing together during annealing and to form an undercoat film mainly composed of forsterite on the steel sheet surface. Here, "containing MgO as the main component" means that the annealing separator contains 75 mass% or more of MgO. Also, "containing forsterite as the main component" means that the undercoat film contains 80 mass% or more of forsterite.

[0044] The above-mentioned finish annealing is preferably carried out at 800°C or higher in order to induce secondary recrystallization, and is preferably held at a temperature of 800°C or higher for 20 hours or more in order to complete secondary recrystallization. Furthermore, in order to purify impurities in the steel and form a forsterite film, it is preferable to heat the steel to a high temperature of about 1200°C in an H2-containing atmosphere after completing secondary recrystallization. Furthermore, in order to further promote the purification of impurities, it is preferable to hold the steel at a temperature of 1180°C or higher for 3 hours or more in an H2 atmosphere.

[0045] Next, the steel sheet after the above-mentioned finish annealing is preferably subjected to flattening annealing in order to remove unreacted annealing separator by water washing, brushing, pickling, or the like, and then to correct the shape of the steel sheet and improve the iron loss characteristics.

[0046] In addition, when product sheets are used in a laminated state, it is preferable to form an insulating coating on the surface of the steel sheet during flattening annealing or during a process before or after the flattening annealing in order to further improve iron loss. From the viewpoint of enhancing the iron loss reduction effect, it is preferable to apply a tension-imparting type insulating coating capable of imparting tensile tension to the steel sheet. In addition, by adopting a method of forming a tension coating via a binder or forming an inorganic coating on the surface layer of the steel sheet by physical vapor deposition or chemical vapor deposition, a coating with excellent adhesion can be obtained and a large iron loss reduction effect can be obtained.

[0047] Incidentally, there is a method for evaluating the adhesion strength of the coating of grain-oriented electrical steel sheets by measuring the bending peeling diameter. In this method, small pieces taken from the grain-oriented electrical steel sheets are wrapped around the surfaces of several round bars with different diameters to determine the limit value (bending peeling diameter) of the round bar diameter at which defects and peeling occur in the coating, and it is evaluated that the smaller the bending peeling diameter, the better the peeling resistance. However, since the Unicore type wound core is made by bending the steel sheet at several points, the curvature radius of each bending part may be 10 mm or less. In the part that is bent with such a small curvature radius, the forsterite base coating formed on the steel sheet surface is subjected to large strain, so there is a problem that even if the above-mentioned evaluation test for determining the bending peeling diameter is good, the coating is likely to peel off.

[0048] In order to make such peeling of the undercoat less likely to occur, it is effective to have soft sulfides or selenides present at the interface between the base steel sheet and the undercoat. Means for having sulfides or selenides present at the interface include, for example, a method of including S or Se as a steel material component, or a method of using an annealing separator to which a compound containing S or Se has been added as described in the Examples, with the latter method being preferred from the viewpoint of flexibility in implementation.

[0049] Here, in order to reliably obtain the above-mentioned coating peeling prevention effect, when the composition of the entire steel sheet including the base coating is analyzed, the S content is within the range of 0.0005 to 0.0100 mass%, and the Se content is within the range of 0.0005 to 0.0100 mass%, and when the concentration distributions of Se and S in the sheet thickness direction from the steel sheet surface are measured by glow discharge optical emission spectrometry, the peaks of the emission intensity profiles of Se and S are present at the interface between the base coating and the base steel sheet, and further, the peak value I of the emission intensity of Se is greater than or equal to 0.0005 to 0.0100 mass%, and the concentration distributions of Se and S in the sheet thickness direction from the steel sheet surface are measured by glow discharge optical emission spectrometry. Se and the peak value of the emission intensity of S S Comparison with I Se / I S More preferably, the S content is in the range of 0.0020 to 0.0090 mass%, the Se content is in the range of 0.0030 to 0.0090 mass%, and the ratio I Se / I Sis less than 0.8.

[0050] The above ratio I Se / I S The reason why it is preferable that the ratio is 1.0 or less is that sulfides are softer than selenides and have a higher effect of suppressing peeling, and therefore it is preferable to have a large amount of sulfides present.

[0051] Furthermore, in order to obtain lower iron loss, the grain-oriented electrical steel sheet of the present invention may be subjected to a magnetic domain refinement treatment, which has a large effect of reducing iron loss. Wound cores are generally subjected to stress relief annealing, but in the case of unicore types, stress relief annealing may not be performed. Therefore, as a method for the magnetic domain refinement, in addition to a heat-resistant magnetic domain refinement treatment such as providing grooves on the steel sheet surface, a non-heat-resistant magnetic domain refinement treatment in which a laser or electron beam is irradiated onto the steel sheet surface may also be applied.

[0052] The grain-oriented electrical steel sheet of the present invention manufactured to satisfy the above conditions not only has excellent magnetic properties, but also has excellent processing accuracy when folded, and is therefore preferably used for wound cores. In particular, the grain-oriented electrical steel sheet of the present invention, which has appropriate amounts of S and Se present at the interface between the undercoat and the base steel sheet, also has excellent coating peeling resistance, and is therefore preferably used for "Unicore" type wound cores having folded parts with a small radius of curvature. EXAMPLES

[0053] The molten steel, which was first refined in an electric furnace, was secondarily refined by ladle refining (LF) to produce steel with the composition of C: 0.034-0.085 mass%, Si: 3.11-3.40 mass%, Mn: 0.07-0.12 mass%, Al: 0.004-0.007 mass%, N: 0.003-0.004 mass%, S: 0-0.022 mass%, Se: 0-0.007 mass%, Sb: 0.022-0.031 mass%, Sn: 0.045-0.055 mass%, and the balance being Fe and unavoidable impurities. The amount and grain size of inclusions in the steel were adjusted by changing the amount of Ar gas blown from the bottom of the furnace and the refining time. Next, when the molten steel after the above-mentioned composition adjustment was made into a slab by a continuous casting method, the casting speed was changed in the range of 0.6 to 1.6 m / min in order to further change the state of the inclusions in the steel. Next, the slab obtained as described above was reheated to a temperature of 1200 ° C, and then hot-rolled to a hot-rolled sheet with a thickness of 2.4 mm. The scale on the surface of the hot-rolled sheet was removed by pickling, and then cold-rolled to a cold-rolled sheet with a final thickness of 0.23 mm. Next, the above-mentioned cold-rolled sheet was subjected to decarburization annealing, which also served as primary recrystallization annealing, at 840 ° C × 100 s in an atmosphere of 60 vol% H2 + 40 vol% N2, dew point 60 ° C, to obtain a decarburized annealed sheet. Next, an annealing separator mainly composed of MgO was applied to the surface of the above-mentioned decarburized annealed sheet, and dried. Next, after completing the secondary recrystallization, the steel was subjected to a final annealing in which the steel was purified by holding it at 1200°C for 5 hours in a H2 atmosphere to produce a grain-oriented electrical steel sheet (product sheet) having a base coating mainly composed of forsterite.

[0054] A compositional analysis was performed on the steel sheets (base steel sheets) obtained from the product sheets thus obtained after removing the base coating. All of the steel sheets had a composition containing C: 0.0008-0.0015 mass%, Si: 3.11-3.40 mass%, Mn: 0.07-0.12 mass%, Sb: 0.022-0.031 mass% and Sn: 0.045-0.055 mass%, with the remainder being Fe and unavoidable impurities.

[0055] Next, a test piece with a width of 100 mm and a length of 300 mm was taken from the product plate, and the iron loss W was measured using the single plate magnetic property test method described in JIS C 2556. 17 / 50 was measured. Furthermore, a sample with a width of 150 mm and a length of 1000 mm was cut out from the above product plate, with the rolling direction as the length direction, and was bent at 45° at eight points in the length direction with a curvature radius r of 3 mm, as shown in Figure 1. In order to evaluate the processing accuracy of the obtained ring-shaped sample after bending, the two parameters θ and H shown in Figure 3 were measured, and if θ was within the range of 0 to 3.0° and H was within the range of 0 to 5.0 mm, the product plate was evaluated as having good processing accuracy (passed). Furthermore, to evaluate the inclusions in the product plate, a test piece was taken from the product plate, one side of which was pickled with hydrochloric acid to expose a surface parallel to the steel plate surface including the center of the plate thickness of the steel plate, and then a 50 mm 2 The number density (pieces / mm 2 ) was measured.

[0056] The results of the above measurements are shown in Table 1. It can be seen from the table that when the number density of inclusions with diameters of 0.5 μm or more and 3.0 μm or less is within the range satisfying the conditions of the present invention, both the magnetic properties and the processing accuracy are excellent.

[0057] [Table 1] EXAMPLES

[0058] The molten iron tapped from the blast furnace is first refined in a converter to decarburize, dephosphorize, and desulfurize it, and then second refined and final component adjustment is performed in a vacuum degassing process to obtain the following contents: C: 0.006-0.153 mass%, Si: 1.1-8.5 mass%, Mn: 0.01-1.5 mass%, Al: 0-0.032 mass%, N: 0.0005-0.0112 mass%, S: 0-0.012 mass%, and Se: 0-0.021 mass%. s% or further, as other components, as shown in Table 2, at least one component selected from Sn, Cr, Cu, Ag, Au, Ni, Bi, P, Sb, Mo, B, Nb, Ti, V, As, Zn, Pb, W, Co, Ga, Ge, Ca, Nd, La, Ce, Pr, Dy and Hf was appropriately contained, and the balance was Fe and unavoidable impurities. In this case, the amount of slag discharged in the primary refining was changed, and the processing time in the secondary refining was adjusted to adjust the amount and particle size of inclusions contained in the steel to be within the range of the present invention. Next, the above molten steel was made into a steel material (slab) by a continuous casting method. Next, the above slab was reheated to a temperature of 1230 ° C. and then hot rolled to make a hot-rolled sheet with a plate thickness of 2.7 mm. Next, the scale on the surface of the hot-rolled sheet was removed by pickling, and then the sheet was cold-rolled to an intermediate thickness of 1.6 mm, and then intermediate annealed at 1000°C for 100 s, followed by a second cold rolling to obtain a cold-rolled sheet with a final thickness of 0.23 mm. Next, the cold-rolled sheet was subjected to decarburization annealing, which also served as primary recrystallization annealing, at 850°C for 200 s in an atmosphere of 60 vol% H2 + 40 vol% N2 with a dew point of 45°C, to obtain a decarburized annealed sheet. Next, an annealing separator mainly composed of MgO was applied to the surface of the decarburized annealed sheet and dried. After completing the secondary recrystallization, the sheet was subjected to finish annealing in which the sheet was kept at a temperature of 1200°C for 5 hours in an H2 atmosphere for purification, to obtain a grain-oriented electrical steel sheet (product sheet) having a forsterite coating.

[0059] For the product sheets thus obtained, the undercoat was removed and the components of the base steel sheet were analyzed. Further, test pieces with a width of 100 mm and a length of 300 mm, with the rolling direction as the length direction, were taken, and the magnetic properties were measured by the single sheet magnetic property test method described in JIS C 2556. In addition, to evaluate the processing accuracy, a sample with a width of 150 mm and a length of 1000 mm was cut out from the above product plate, with the rolling direction as the length direction, and was bent at 45° at eight points in the length direction with a curvature radius r of 3 mm, as shown in Figure 1. For the ring-shaped sample obtained after bending, the two parameters θ and H shown in Figure 3 were measured, and it was evaluated that the processing accuracy was good (passed) if θ was within the range of 0 to 3.0° and H was within the range of 0 to 5.0 mm. Furthermore, to evaluate the inclusions in the product plate, a test piece was taken from the product plate, and one side was pickled with a mixed solution of hydrofluoric acid and hydrogen peroxide to reveal a surface parallel to the steel plate surface including the center of the plate thickness. Then, a scanning electron microscope equipped with an automatic particle measuring mechanism was used to measure the inclusions in the product plate within 50 mm of the surface. 2 The number density (pieces / mm 2 ) was measured.

[0060] The results of the above measurements are shown in Table 2. From this table, it can be seen that the steel sheets satisfying the conditions of the present invention have good magnetic properties and processing accuracy. Steel sheet No. 4 is an example in which the C content of the slab was too high, resulting in insufficient decarburization during decarburization annealing. Steel sheet No. 9 is an example of the present invention, but it has many inclusions with a diameter of over 5.0 μm, which slightly deteriorates the magnetic properties, and it can be seen that the fewer the large inclusions, the better for the magnetic properties. The contents of the inhibitor-forming elements Al, N, S, and Se in the base steel sheet are not shown in Table 2, but in all steel sheets, the contents were reduced to the level of unavoidable impurities.

[0061] [Table 2] EXAMPLES

[0062] The steel sheet No. 1 after decarburization annealing produced in Example 2 was used as a material, and an annealing separator mainly composed of MgO was applied to the surface of the steel sheet and dried. The steel material of the steel sheet No. 1 contained 0.0050 mass% S and 0.0040 mass% Se. In this case, five kinds of annealing separators were applied: one with no magnesium sulfate or sodium selenate added to 100 parts by mass of MgO (No.1-1), one with 3 parts by mass of magnesium sulfate added to 100 parts by mass of MgO (No.1-2), one with 4 parts by mass of sodium selenate added to 100 parts by mass of MgO (No.1-3), one with 3 parts by mass of magnesium sulfate and 5 parts by mass of sodium selenate added to 100 parts by mass of MgO (No.1-4), and one with 2 parts by mass of magnesium sulfate and 6 parts by mass of sodium selenate added to 100 parts by mass of MgO (No.1-5). Next, the steel sheet was subjected to finish annealing in which it was purified by holding it at a temperature of 1200°C for 5 hours in an H2 atmosphere after completing secondary recrystallization, to obtain a grain-oriented electrical steel sheet (product sheet) having a forsterite coating.

[0063] Samples were taken from the product sheets thus obtained, and the C, Si and Mn contents of the base steel sheet from which the forsterite-based undercoating had been removed, and the S and Se contents of the steel sheet including the undercoating were analyzed. In addition, the concentration distribution of Se and S from the steel sheet surface to the sheet thickness direction of the above samples was measured by glow discharge optical emission spectrometry, and it was confirmed that the peaks of the emission intensity profiles of Se and S existed at the interface between the undercoat and the base steel sheet. Se , I S Ratio I Se / I S asked for. In addition, test pieces with a width of 100 mm and a length of 300 mm, with the rolling direction as the length direction, were taken from the above product sheets, and the magnetic properties were measured using the single sheet magnetic property test method specified in JIS C 2556. To evaluate the processing accuracy, a sample with a width of 150 mm and a length of 1000 mm was cut out from the product plate, with the rolling direction as the length direction, and was bent at 45° at eight points in the length direction with a curvature radius r of 3 mm, as shown in Figure 1. The two parameters θ and H shown in Figure 3 were measured for the ring-shaped sample obtained after bending, and it was evaluated that the processing accuracy was good (passed) if θ was within the range of 0 to 3.0° and H was within the range of 0 to 5.0 mm. At this time, the surface of the bent portion was visually observed to check whether or not the undercoat had peeled off. In addition, a hoop-shaped coil with a width of 150 mm and a length of 100 m was made from the above product plate, and 100 ring-shaped samples were folded using a steel plate bending and cutting machine for Unicore. These were then stacked to produce a Unicore with an outer diameter of long side: 300 mm × short side: 200 mm. The iron loss W 17 / 50 In the present invention, the iron loss W of the Unicore using a steel plate with a thickness of 0.23 mm was measured. 17 / 50 is rated as good if it is 1.00 W / kg or less. Furthermore, to evaluate the inclusions in the product plate, a test piece was taken from the product plate, one side of which was pickled with a mixed solution of hydrofluoric acid and hydrogen peroxide to expose a plane parallel to the steel plate surface including the center of the plate thickness. Then, a scanning electron microscope equipped with an automatic particle measuring mechanism was used to measure the inclusions in a 50 mm area of ​​the surface. 2 The number density (pieces / mm 2 ) was measured.

[0064] The results of the above measurements are shown in Table 3. From this table, it can be seen that the steel sheet satisfying the conditions of the present invention has good magnetic properties and processing accuracy. In addition, the peak intensity ratio I of Se and S at the interface between the undercoat and the base steel sheet is Se / I S It can be seen that steel sheets with a coefficient of friction of 1.0 or less also have excellent resistance to peeling of the coating in the bent section. Incidentally, in a "coating peeling test" in which the steel sheets are wrapped around a round bar with a diameter of 20 mm, it was confirmed that no peeling occurred in any of the steel sheets.

[0065] [Table 3]

Claims

1. In a grain-oriented electrical steel sheet having a base coating mainly made of forsterite on the surface of a base steel sheet, The base steel sheet has a composition containing C: 0.0050 mass% or less, Si: 2.0 to 8.0 mass%, and Mn: 0.02 to 1.0 mass%, with the balance being Fe and unavoidable impurities; The number density of inclusions having a diameter of 0.5 μm or more and 3.0 μm or less present inside the base steel sheet is 1.0 pieces / mm ２ 20.0 pieces / mm or more ２ A grain-oriented electrical steel sheet characterized in that:

2. The grain-oriented electrical steel sheet contains S: 0.0005 to 0.0100 mass% and Se: 0.0005 to 0.0100 mass% with a base coating, When the concentration distributions of Se and S in the thickness direction from the surface of the steel sheet are measured by glow discharge optical emission spectrometry, the peaks of the emission intensity profiles of Se and S are present at the interface between the base coating and the base steel sheet, and the peak value I of the emission intensity of Se is Ｓｅ and the peak value of the emission intensity of S I Ｓ The grain-oriented electrical steel sheet according to claim 1, characterized in that the following formula (1) is satisfied: Note I Ｓｅ / I Ｓ ≦1.0 ・・・(1)

3. The number density of inclusions having a diameter of more than 5.0 μm present inside the base steel sheet is 2.0 pieces / mm ２ 2. The grain-oriented electrical steel sheet according to claim 1, wherein:

4. The grain-oriented electromagnetic steel sheet according to claim 2, characterized in that the number density of inclusions having a diameter of more than 5.0 μm present inside the base steel sheet is 2.0 pieces / mm 2 or less.

5. In addition to the above components, the base steel sheet further contains Sn: 0.005 to 0.500 mass%, Cr: 0.005 to 0.500 mass%, Cu: 0.01 to 0.50 mass%, Ag: 0.001 to 0.050 mass%, Au: 0.001 to 0.050 mass%, Ni: 0.01 to 0.50 mass%, Bi: 0.005 to 0.500 mass%, P:

0. 005 to 0.50 mass%, Sb: 0.005 to 0.50 mass%, Mo: 0.005 to 0.50 mass%, B: 0.00001 to 0.00250 mass%, Nb:

0. 001 to 0.020 mass%, Ti: 0.0005 to 0.0400 mass%, V: 0.001 to 0.020 mass%, As: 0.0010 to 0.0200 mass%, Zn: 0.001 to 0.020 mass%, Pb: 0.0001 to 0.0100 mass%, W: 0.0010 to 0.0100 mass%, Co: 0.002 to 0.050 mass%, Ga: 0.0001 to 0.0050 mass%, Ge: 0.0001 to 0.0050 mass%, Ca: 0.001 to 0.020 mass%, Nd: 0.001 to 0.020 mass% 5. The grain-oriented electrical steel sheet according to claim 1, further comprising at least one component selected from the group consisting of 0.001 to 0.020 mass% of Al, 0.001 to 0.020 mass% of La, 0.001 to 0.020 mass% of Ce, 0.001 to 0.020 mass% of Pr, 0.001 to 0.020 mass% of Dy, and 0.001 to 0.020 mass% of Hf.

6. A wound core made of the grain-oriented electrical steel sheet according to any one of claims 1 to 4.

7. A wound core made of the directional electromagnetic steel sheet described in claim 5.

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