Grain-oriented electrical steel sheet and method of manufacturing the same

Abstract

This oriented electrical steel sheet is an oriented electrical steel sheet having a base steel sheet and an insulating film containing a metal phosphate formed on the surface of the base steel sheet, wherein the base steel sheet has an oxide layer containing an oxide of Si in a region in contact with the interface between the base steel sheet and the insulating film, and the average thickness of the oxide layer from the interface is 0.5 to 2.5 μm.

Description

Technology Field

[0001] The present invention relates to a oriented electrical steel sheet and a method for manufacturing the same.

[0002] The present application claims priority based on patent application No. 2024-018850 filed in Japan on February 9, 2024, and incorporates the contents thereof herein. Background Technology

[0003] Grain-oriented electrical steel sheets are primarily used in transformers. Transformers are continuously energized over a long period from installation to decommissioning, resulting in continuous energy loss. Therefore, energy loss when magnetized by alternating current—that is, iron loss—becomes a major indicator determining the performance of a transformer.

[0004] To reduce iron loss in oriented electrical steel sheets, (a) {110} <001> Many technologies have been developed to date from the perspective of increasing the integration into orientation (GOS orientation), (b) increasing the electrical resistance of the steel sheet by increasing the content of solid solution elements such as Si, or (c) reducing the thickness of the electrical steel sheet.

[0005] In addition, applying tension to the steel plate is effective for reducing iron loss. Forming a film of a material with a coefficient of thermal expansion smaller than that of the steel plate on the surface of the steel plate at high temperature is an effective means for reducing iron loss. In the finishing annealing process of electrical steel sheets, a forsterite-based film (inorganic film) with excellent film adhesion, which is produced by the reaction of oxides on the surface of the steel plate with an annealing separator, is a film that can apply tension to the steel plate.

[0006] For example, the method disclosed in Patent Document 1, which forms an insulating film by baking a coating solution mainly composed of colloidal silica and phosphate onto the surface of a steel sheet, is effective for reducing iron loss because it has a large effect of imparting tension to the steel sheet. Therefore, leaving the forsterite-based film generated in the finishing annealing process and applying an insulating coating mainly composed of phosphate thereon is a general method for manufacturing oriented electrical steel sheets.

[0007] However, recently, there has been an increasing demand for miniaturization and high performance of transformers. To achieve this miniaturization, oriented electrical steel sheets are required to have excellent high-field iron loss, which is good even at high magnetic flux densities. At the same time, it has recently been discovered that forsterite-based films hinder the movement of magnetic domain walls, thereby adversely affecting iron loss. In oriented electrical steel sheets, magnetic domains change as magnetic domain walls move under an alternating magnetic field. While smooth and rapid movement of these magnetic domain walls is effective for reducing iron loss, forsterite-based films (also called glass films or primary films) are non-magnetic themselves and have an uneven structure at the interface between the steel sheet and the film. Since this uneven structure hinders the movement of magnetic domain walls, it is believed to have an adverse effect on iron loss.

[0008] For this reason, as a means to improve high magnetic field iron loss, methods are being researched to remove forsterite-based films using mechanical means such as grinding or chemical means such as pickling, or to prevent the formation of forsterite-based films during high-temperature finish annealing, thereby producing oriented electrical steel sheets without forsterite-based films, or to make the steel sheet surface mirror-like (in other words, a technology to magnetically smooth the steel sheet surface).

[0009] As a technique for preventing the formation of forsterite-based films, for example, Patent Document 2 discloses a technique in which, after conventional finish annealing, the surface formed material is removed by pickling, and then the steel sheet surface is polished to a mirror-like state by chemical polishing or electrolytic polishing. It has been found that by forming a tension-imparting insulating film on the surface of an oriented electrical steel sheet that does not have a forsterite-based film obtained by such known methods, an even better iron loss improvement effect is obtained. Furthermore, according to the tension-imparting insulating film, various properties such as corrosion resistance, heat resistance, and slipperiness can be imparted in addition to iron loss improvement.

[0010] However, forsterite-based films have the effect of exhibiting insulating properties, as well as serving as an intermediate layer that ensures adhesion when forming a tension film (tension-applying insulating film). That is, since forsterite-based films are formed by penetrating deeply into the steel sheet, they have excellent adhesion to the metal steel sheet. Therefore, when a tension-applying film (tension film) with colloidal silica or phosphate as the main component is formed on the surface of a forsterite-based film, the film adhesion is excellent. On the other hand, since the bonding between metal and oxide is generally difficult, it was difficult to ensure sufficient adhesion between the tension film and the steel sheet surface when a forsterite-based film was not present.

[0011] For this reason, for oriented electrical steel sheets that do not have a forsterite-based film, when a tension film is formed, it is being considered to provide a layer that replaces the role of an intermediate layer of the forsterite-based film.

[0012] Patent Document 3 discloses a technique for ensuring the adhesion of a tension-applying insulating film by applying a coating that serves as an intermediate layer in advance when forming a tension-applying coating.

[0013] However, in the technology disclosed in Patent Document 3, there is a problem in that a tension-applying insulating film having a large tension cannot be maintained with good adhesion.

[0014] In addition, for example, Patent Document 4 discloses a oriented electrical steel sheet having a base steel sheet and an insulating film formed on the surface of the base steel sheet, wherein the insulating film is formed on the side of the base steel sheet and has an intermediate layer comprising a crystalline metal phosphate salt and a tension film layer formed on the surface side of the insulating film. In Patent Document 4, it is disclosed that the oriented electrical steel sheet does not have a forsterite-based film, has excellent film adhesion, excellent film tension, and also has excellent magnetic properties.

[0015] However, depending on the application, grain-oriented electrical steel sheets may be processed into a predetermined shape and then subjected to stress-relief annealing. As a result of the inventors' investigation, it was found that in grain-oriented electrical steel sheets to which the technology of Patent Document 4 is applied, stress-relief annealing is not conceived, and that when stress-relief annealing is performed, the adhesion of the film may be reduced. Prior art literature

[0016] Japanese Patent Publication No. Sho 48-39338, Japanese Patent Publication No. Sho 49-96920, Japanese Patent Publication No. Hei 5-279747, International Publication No. 2022 / 215709 The problem to be solved

[0017] As described above, Patent Documents 1 to 4 did not disclose a oriented electrical steel sheet having excellent film adhesion even after stress relief annealing was performed (after stress relief annealing) in a oriented electrical steel sheet that does not have a forsterite-based film.

[0018] Accordingly, the present invention aims to provide a oriented electrical steel sheet and a method for manufacturing the same, wherein, based on the premise of an oriented electrical steel sheet without a forsterite-based film, film tension, corrosion resistance, phosphorus leaching resistance from the film, packing ratio when used as a core, and iron loss are secured to be equal to or greater than those of the conventional steel, while excellent film adhesion is obtained even after stress relief annealing. means of solving the problem

[0019] The inventors examined the effect of stress relief annealing on the adhesion of the insulating film.

[0020] As a result, it was discovered that by forming a phosphate film that serves as an intermediate layer and an insulating film on the surface of a oriented electrical steel sheet that does not have a forsterite-based film formed by chemical treatment, and by fusing the intermediate layer and the insulating film during stress relief annealing, and by forming a layer containing an oxide of Si (oxide layer) immediately below the insulating film obtained by fusing, it is possible to suppress the decrease in adhesion of the insulating film without deteriorating magnetic properties or other film properties.

[0021] The present invention was made in consideration of the above findings.

[0022] The gist of the present invention is as follows.

[0023] [1] A oriented electrical steel sheet according to one embodiment of the present invention is a oriented electrical steel sheet having a base steel sheet and an insulating film comprising a metal phosphate formed on the surface of the base steel sheet, wherein the base steel sheet has an oxide layer comprising an oxide of Si in a region in contact with the interface between the base steel sheet and the insulating film, and the average thickness of the oxide layer from the interface is 0.5 to 2.5 μm.

[0024] [2] For the oriented electrical steel sheet described in [1], the ratio of the length of the interface between the oxide layer and the insulating film to the length of the interface between the base steel sheet and the insulating film may be 30% or more.

[0025] [3] The directional electrical steel sheet described in [1] or [2] has a void area ratio of 30% in the insulating film.

[0026] [4] A method for manufacturing a oriented electrical steel sheet according to another aspect of the present invention comprises: a finishing annealing process in which an annealing separator containing 10 to 100 mass% of Al2O3 is applied to a steel sheet, dried, and then a finishing annealing is performed; an annealing separator removal process in which excess annealing separator is removed from the steel sheet after the finishing annealing process; a light pickling process in which the steel sheet after the annealing separator removal process is pickled with 0.1 to 5.0 mass% of an inorganic acid for 10 to 60 seconds; a washing process in which the steel sheet after the light pickling process is washed with water and dried; and a first insulating film in which the steel sheet after the washing process is immersed for 5 to 150 seconds in a treatment solution having a liquid temperature of 30 to 85°C and a metal phosphate salt concentration of 1.0 to 10.0 mass%, and then the treatment solution is washed away and the steel sheet is dried. The method comprises a forming process, a second insulating film forming process in which a coating solution comprising a metal phosphate salt and colloidal silica is applied to the steel plate after the first insulating film forming process, wherein the content of the colloidal silica is 30 to 150 parts by mass relative to 100 parts by mass of the metal phosphate salt and the solid content concentration is 10 to 40 parts by mass, and after drying, the plate temperature is maintained at 700 to 950°C for 10 to 90 seconds, and the steel plate after the second insulating film forming process is heated to a temperature range of 700 to 900°C in an atmosphere having a dew point of 0 to 30°C, a nitrogen content of 50 to 100 volume%, and a hydrogen content of 0 to 50 volume%, and maintained at the temperature range for 10 to 180 minutes.

[0027] [5] The method for manufacturing a oriented electrical steel sheet described in [4] may include one or two types of annealing separator, which are MgO: 5 to 90 mass% and chloride: 0.5 to 10.0 mass%. Effects of the invention

[0028] According to the above embodiment of the present invention, a directional electrical steel sheet having excellent film adhesion even after stress relief annealing and a method for manufacturing the same can be provided. Brief explanation of the drawing

[0029] FIG. 1 is an example of a cross-sectional photograph of a oriented electrical steel sheet according to the present embodiment, including an insulating film and a base steel sheet. Specific details for implementing the invention

[0030] A oriented electrical steel sheet (oriented electrical steel sheet according to the present embodiment) and a method for manufacturing the same are described in accordance with one embodiment of the present invention.

[0031] Grain-oriented electrical steel sheets

[0032] As illustrated in FIG. 1, the directional electrical steel sheet according to the present embodiment has a base steel sheet (11) and an insulating film (21) containing a metal phosphate salt formed on the surface of the base steel sheet (11).

[0033] Each of these is explained below.

[0034] [Base material steel plate]

[0035] As illustrated in FIG. 1, the base steel plate (11) has an oxide layer (12) containing an oxide of Si in the region in contact with the interface (IF) between the base steel plate (11) and the insulating film (21). The portion other than the oxide layer (12) is made of steel plate.

[0036] (Oxide layer)

[0037] In the oriented electrical steel sheet according to the present embodiment, an oxide layer containing an oxide of Si is formed in the region of the base steel sheet that contacts the interface between the base steel sheet and the insulating film. This oxide layer contributes to improving the adhesion between the base steel sheet and the insulating film. If the oxide layer is not formed, sufficient adhesion cannot be secured.

[0038] When obtaining high adhesion improvement effects and magnetic properties, the average thickness of the oxide layer from the interface between the base steel sheet and the insulating film is 0.5 to 2.5 μm. If the average thickness is less than 0.5 μm, the effect of improving adhesion is reduced. On the other hand, if the average thickness exceeds 2.5 μm, the magnetic properties become inferior.

[0039] In addition, the adhesion (adhesion of the film) is improved by the oxide layer existing in the region in contact with the interface between the base steel sheet and the insulating film, that is, by forming an interface with the insulating film. To obtain a higher adhesion improvement effect, it is preferable that the ratio of the length of the interface between the oxide layer and the insulating film to the length of the interface between the base steel sheet and the insulating film (coverage rate) be 30% or more. The ratio of the length may be 100%.

[0040] The oxide layer mainly contains Si oxide, but the Si content in the Si oxide layer is preferably 60 to 70 mass%. The Si oxide includes Si-containing composite oxides such as SiO2 or FeSiO4. In addition to Si oxide, iron oxide, aluminum oxide, chromium oxide, etc. may be included. Furthermore, the P content of the oxide layer is 1.0 mass% or less, and it is clearly distinguishable from an insulating film.

[0041] In addition, the oxide layer of the oriented electrical steel sheet according to the present embodiment is formed as part of the base steel sheet, thereby having extremely high adhesion to the base steel sheet.

[0042] Whether an oxide layer is formed, the average thickness of the oxide layer, and the proportion occupied at the interface (coverage rate) can each be determined by the following methods.

[0043] A transmission electron microscope (TEM) is used on a cross-section of a steel plate including the surface layer to magnify it 30,000 times and photograph the area along the interface with a length of 10 μm or more.

[0044] It is possible to distinguish the base steel sheet and the insulating film from the captured images. This is because, while the base material consists almost entirely of iron atoms, phosphates, aggregated colloidal silica, and pores are observed in the insulating film.

[0045] Furthermore, although an oxide layer exists as an internal oxide layer on the base steel sheet, it is composed almost entirely of silica with a low phosphorus content and exists within the base material; therefore, the difference from the insulating film, which is primarily composed of phosphates, can be confirmed by performing elemental analysis. If the image resolution is low and a clear image cannot be obtained, it is also possible to clarify the image using an image processing device such as a Lujex.

[0046] Alternatively, the interface between the insulating film and the base material may be designated as the point where the distribution of P element decreases sharply from the insulating film side. This is because the P element exists in the insulating film in the form of phosphoric acid or phosphorus oxide and hardly diffuses into the steel.

[0047] Likewise, the interface between the insulating film and the base material may be the location where Al, Mg, Mn, Zn, Ca, Cu, Co, and Li, which are presumed to exist as cations within the insulating film, decrease rapidly.

[0048] Based on the TEM images obtained at three or more locations as described above, the average thickness of the oxide layer is determined by averaging the thickness of the oxide layer measured at three locations (i.e., at a total of nine or more locations) within each image.

[0049] The ratio of the oxide layer to the interface is obtained by measuring the length of the interface between the oxide layer and the insulating film at three locations within each of the three or more TEM images above, with a width of 10 μm as the imageable width, calculating the ratio, and averaging the obtained results.

[0050] The Si content of the oxide layer is obtained by using an energy-dispersive X-ray analysis device attached to a transmission electron microscope to perform elemental analysis at three or more locations for each of the three fields of view and averaging the measurement results.

[0051] (Chemical composition)

[0052] Regarding the chemical composition of the portion other than the oxide layer (steel portion) of the base steel sheet of the oriented electrical steel sheet according to the present embodiment, it may be within a known range for oriented electrical steel sheets to obtain the characteristics generally required for oriented electrical steel sheets.

[0053] For example, as a chemical component constituting the chemical composition, it is preferable to include the following. In the present embodiment, the % of the chemical component is mass % unless otherwise specified.

[0054] C: 0.010% or less

[0055] Carbon (C) is an element effective for controlling the microstructure of steel sheets during the process up to the completion of the decarburization annealing process in the manufacturing process. However, if the C content exceeds 0.010%, the magnetic properties of the product sheet, the oriented electrical steel sheet, deteriorate. Therefore, in the base steel sheet of the oriented electrical steel sheet according to the present embodiment, it is preferable that the C content be 0.010% or less. More preferably, the C content is 0.005% or less. Although it is preferable for the C content to be low, even if the C content is reduced to less than 0.0001%, the effect of microstructure control becomes saturated and only the manufacturing cost increases. Therefore, the C content may be 0.0001% or more.

[0056] Si: 2.50 to 4.00%

[0057] Silicon (Si) is an element that increases the electrical resistance of grain-oriented electrical steel sheets and improves iron loss characteristics. If the Si content is less than 2.50%, a sufficient eddy current loss reduction effect is not obtained. Therefore, it is desirable to have a Si content of 2.50% or more. More preferably, the Si content is 2.70% or more, and even more preferably 3.00% or more.

[0058] Meanwhile, if the Si content exceeds 4.00%, the grain-oriented electrical steel sheet becomes embrittled, and its passability deteriorates significantly. In addition, the workability of the grain-oriented electrical steel sheet decreases, and the steel sheet may break during rolling. For this reason, it is desirable to keep the Si content at 4.00% or less. More preferably, the Si content is 3.80% or less, and even more preferably 3.70% or less.

[0059] Mn: 0.01 to 0.50%

[0060] Manganese (Mn) is an element that combines with S during the manufacturing process to form MnS. This precipitate functions as an inhibitor (an inhibitor of normal grain growth) and induces secondary recrystallization in steel. Mn is also an element that improves the hot workability of steel. If the Mn content is less than 0.01%, the above effects cannot be sufficiently obtained. Therefore, it is desirable to have a Mn content of 0.01% or more. More preferably, the Mn content is 0.02% or more.

[0061] Meanwhile, if the Mn content exceeds 0.50%, secondary recrystallization does not occur, and the magnetic properties of the steel deteriorate. Therefore, in the base steel sheet of the oriented electrical steel sheet according to the present embodiment, it is preferable that the Mn content be 0.50% or less. More preferably, the Mn content is 0.20% or less, and even more preferably 0.10% or less.

[0062] N: 0.010% or less

[0063] N (nitrogen) is an element that combines with Al during the manufacturing process to form AlN, which functions as an inhibitor. However, if an excess of inhibitors remains in the grain-oriented electrical steel sheet and the N content exceeds 0.010%, the magnetic properties deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to the present embodiment, it is preferable that the N content be 0.010% or less. More preferably, the N content is 0.008% or less.

[0064] Meanwhile, although the lower limit of the N content is not specifically stipulated, reducing it to less than 0.001% only increases manufacturing costs. Therefore, the N content may be 0.001% or more.

[0065] Sol. Al: 0.020% or less

[0066] Sol. Al (acid-soluble aluminum) is an element that combines with N during the manufacturing process of oriented electrical steel sheets to form AlN, which functions as an inhibitor. However, if an excess of inhibitors remains in the base steel sheet and the sol. Al content exceeds 0.020%, magnetic properties deteriorate. Therefore, in the base steel sheet of the oriented electrical steel sheet according to the present embodiment, it is preferable that the sol. Al content be 0.020% or less. More preferably, the sol. Al content is 0.010% or less, and even more preferably less than 0.001%. Although the lower limit of the sol. Al content is not specifically defined, reducing it to less than 0.0001% only increases manufacturing costs. Therefore, the sol. Al content may be 0.0001% or more.

[0067] S: 0.010% or less

[0068] Sulfur (S) is an element that combines with Mn during the manufacturing process to form MnS, which functions as an inhibitor. However, if the S content exceeds 0.010%, magnetic properties are degraded due to the remaining inhibitor. Therefore, in the base steel sheet of the oriented electrical steel according to the present embodiment, it is preferable that the S content be 0.010% or less. It is more preferable that the S content in the oriented electrical steel be as low as possible. For example, less than 0.001%. However, even if the S content in the base steel sheet of the oriented electrical steel is reduced to less than 0.0001%, the manufacturing cost only increases. Therefore, the S content in the base steel sheet of the oriented electrical steel may be 0.0001% or more.

[0069] Remainder: Fe and impurities

[0070] The chemical composition of the base steel sheet of the oriented electrical steel sheet according to the present embodiment may contain the elements described above, and the remainder may be Fe and impurities. However, for the purpose of improving magnetic properties, etc., Sn, Cu, Se, and Sb may also be contained in the ranges shown below. In addition, as for elements other than these, for example, one or two or more of W, Nb, Ti, Ni, Co, V, Cr, and Mo may be contained in a total of 1.0% or less, and this does not impair the effect of the oriented electrical steel sheet according to the present embodiment.

[0071] Here, impurities refer to elements that are incorporated from raw materials such as ore, scrap, or the manufacturing environment when the base steel sheet is manufactured industrially, and which are allowed to be contained in an amount that does not adversely affect the operation of the oriented electrical steel sheet according to the present embodiment.

[0072] Sn: 0 to 0.50%

[0073] Sn (tin) is an element that contributes to the improvement of magnetic properties through the control of the primary recrystallization structure. To obtain the effect of improving magnetic properties, it is desirable to have a Sn content of 0.01% or more. More preferably, the Sn content is 0.02% or more, and even more preferably 0.03% or more.

[0074] On the other hand, if the Sn content exceeds 0.50%, secondary recrystallization becomes unstable, and magnetic properties deteriorate. Therefore, it is desirable to keep the Sn content at 0.50% or less. More preferably, the Sn content is 0.30% or less, and even more preferably 0.10% or less.

[0075] Cu: 0 to 0.50%

[0076] Copper (Cu) is an element that contributes to an increase in the Goss orientation share in the secondary recrystallization structure. To obtain the above effect, it is desirable to have a Cu content of 0.01% or more. More preferably, the Cu content is 0.02% or more, and even more preferably 0.03% or more.

[0077] On the other hand, if the Cu content exceeds 0.50%, the steel sheet becomes embrittled during hot rolling. Therefore, in the base steel sheet of the oriented electrical steel sheet according to the present embodiment, it is preferable to keep the Cu content 0.50% or less. More preferably, the Cu content is 0.30% or less, and even more preferably 0.10% or less.

[0078] Se: 0 to 0.020%

[0079] Se (selenium) is an element that has a magnetic property improvement effect. When Se is included, it is desirable to have a Se content of 0.001% or more so that the magnetic property improvement effect is well exhibited. More preferably, the Se content is 0.003% or more, and even more preferably 0.006% or more.

[0080] Meanwhile, if the Se content exceeds 0.020%, the adhesion of the film deteriorates. Therefore, it is desirable to keep the Se content at 0.020% or less. More preferably, the Se content is 0.015% or less, and even more preferably 0.010% or less.

[0081] Sb: 0 to 0.50%

[0082] Sb (antimony) is an element that has a magnetic property improvement effect. When Sb is included, it is desirable to have an Sb content of 0.005% or more so that the magnetic property improvement effect is well exhibited. More preferably, the Sb content is 0.01% or more, and even more preferably 0.02% or more.

[0083] Meanwhile, if the Sb content exceeds 0.50%, the adhesion of the film deteriorates significantly. Therefore, it is desirable to keep the Sb content at 0.50% or less. More preferably, the Sb content is 0.30% or less, and even more preferably 0.10% or less.

[0084] As described above, in this embodiment, the chemical composition of the base steel sheet of the oriented electrical steel sheet is exemplified as containing the elements described above, with the remainder consisting of Fe and impurities.

[0085] The chemical composition of the base steel sheet of the oriented electrical steel sheet according to the present embodiment can be measured using a known ICP emission spectroscopy method. However, when measuring, if an insulating film is formed on the surface, it is peeled off before measurement. As a method for peeling, it is possible to peel off by immersing in a high-concentration alkaline solution (e.g., a 30% sodium hydroxide solution heated to 85°C) for 20 minutes or more. Whether peeling has been performed can be determined by visual inspection. In the case of small samples, peeling may be performed by surface grinding.

[0086] (Plate thickness)

[0087] The thickness of the base steel plate is not limited, but it is preferably 0.15 to 0.35 mm in terms of iron loss.

[0088] [Insulating film]

[0089] In the oriented electrical steel sheet according to the present embodiment, an insulating film is formed on the base steel sheet. That is, since a forsterite-based film is not formed, the insulating film is formed in direct contact with the base steel sheet.

[0090] The insulating film included in the oriented electrical steel sheet according to the present embodiment is a single layer formed by fusing a first insulating film and a second insulating film by heat treatment, as described below.

[0091] This insulating film contains metal phosphate salts. The metal phosphate salts are, for example, Al phosphate, Mg phosphate, Mn phosphate, Zn phosphate, Calcium phosphate, Fe phosphate, Cu phosphate, Co phosphate, and Li phosphate.

[0092] In addition, this insulating film contains Si derived from colloidal silica.

[0093] In the insulating film, it is preferable that the metal phosphate salt is 90 to 50 mass% and the Si content is 10 to 40 mass%.

[0094] The ratio of metal phosphate salt and Si content of the insulating film can be measured by SEM-EDS as described below.

[0095] (Void)

[0096] In an insulating film, it is preferable that the area ratio of voids be 30% or less. By reducing the area ratio of voids, the effect of further improving film tension is obtained.

[0097] The area ratio of voids in the insulating film is calculated using the following method.

[0098] Based on an image of a steel plate cross-section including the surface layer, magnified 30,000 times and with a length of 10 μm or more, taken using a transmission electron microscope (TEM), an insulating film mainly composed of phosphate and voids are identified by performing elemental analysis, and the void area is determined. The ratio of the void area to the total area of ​​the observation field is defined as the void area percentage (%). If the image resolution is low and a clear image cannot be obtained, it is also possible to clarify the image using an image processing device such as a LUZEX.

[0099] (thickness)

[0100] In the directional electrical steel sheet according to the present embodiment, the thickness of the insulating film (21) is preferably 1.0 to 10.0 μm in terms of the packing ratio.

[0101] The thickness of the insulating film is determined by the following method.

[0102] For the flat section, a square sample with sides of 10 mm (10 mm in the rolling direction and 10 mm in the direction perpendicular to the rolling direction) is taken, and a cross-section of the sample in the thickness direction perpendicular to the rolling direction is observed with a scanning electron microscope, and at least 5 thicknesses are measured and the average is taken as the thickness of the insulating film.

[0103] At that time, the P content is measured using an energy-dispersive elemental analyzer, and the location where the distribution of P element decreases sharply from the insulating film side (surface side) is defined as the interface between the insulating film and the base steel sheet. Additionally, the location where Al, Mg, Mn, Zn, Ca, Cu, Co, and Li, which are presumed to exist as cations within the insulating film, decrease sharply may also be defined as the interface between the insulating film and the base material.

[0104] In addition, the mass ratio of metal phosphate salts and the type of metal phosphate salts are determined by using a scanning electron microscope and an energy dispersive elemental analyzer. In addition, the Si content can also be measured by using a scanning electron microscope and an energy dispersive elemental analyzer. The mass ratio of metal phosphate salts and the Si content are measured at three locations and the average value is used.

[0105] Manufacturing Method

[0106] The oriented electrical steel sheet according to the present embodiment can be manufactured with the above-mentioned composition regardless of the manufacturing method, and the effect can be obtained, for example, by a manufacturing method including the following process.

[0107] (i) A hot rolling process in which a steel billet is heated and the steel billet is turned into a hot-rolled plate by hot rolling,

[0108] (ii) A hot-rolled plate annealing process for performing hot-rolled plate annealing on the above hot-rolled plate,

[0109] (iii) A pickling process for pickling the hot-rolled plate after the annealing process of the hot-rolled plate,

[0110] (iv) A cold rolling process in which the hot-rolled plate after the above pickling process is cold-rolled to form a steel plate (cold-rolled plate),

[0111] (v) A decarburization annealing process for performing decarburization annealing on the above steel plate,

[0112] (vi) A finishing annealing process in which an annealing separating agent containing 10 to 100 mass% of Al2O3 is applied to the steel plate after the decarburization annealing, dried, and then finishing annealing is performed.

[0113] (vii) An annealing separator removal process for removing excess annealing separator for the steel plate after the above finishing annealing process,

[0114] (viii) a light pickling process in which the steel plate after the annealing separator removal process is pickled with 0.1 to 5.0 mass% of inorganic acid for 10 to 60 seconds,

[0115] (ix) a washing process for washing and drying the steel plate after the above acidity process, and

[0116] (x) A first insulating film forming process, wherein the steel plate after the above washing process is immersed for 5 to 150 seconds in a treatment solution having a liquid temperature of 30 to 85°C and a metal phosphate salt concentration of 1.0 to 10.0 mass%, and after washing away the treatment solution, the steel plate is dried to form a first insulating film,

[0117] (xi) A second insulating film forming process, wherein a coating solution comprising a metal phosphate salt and colloidal silica, wherein the content of the colloidal silica is 30 to 150 parts by mass relative to 100 parts by mass of the metal phosphate salt and the solid content concentration is 10 to 40 mass% is applied to the steel plate after the first insulating film forming process, and after drying, the second insulating film is formed by maintaining the plate temperature at 700 to 950°C for 10 to 90 seconds, and

[0118] (xii) A heat treatment process in which the steel plate after the second insulating film forming process is heated to a temperature range of 700 to 900°C in an atmosphere having a dew point of 0 to 30°C, a nitrogen content of 50 to 100 volume%, and a hydrogen content of 0 to 50 volume%, and maintained in the temperature range for 10 to 180 minutes to fuse the first insulating film and the second insulating film to form an insulating film, and at the same time form an oxide layer in the steel plate.

[0119] In the method for manufacturing a oriented electrical steel sheet according to the present embodiment, (vi) the finishing annealing process to (xii) the heat treatment process are characterized, and (i) the hot rolling process to (v) the decarburization annealing process are not particularly limited and known conditions may be applied.

[0120] [Hot Rolling Process]

[0121] In the hot rolling process, a steel billet, such as a slab having a predetermined chemical composition, is heated and then hot-rolled to obtain a hot-rolled plate. The heating temperature of the steel billet is preferably within the range of 1100 to 1450°C. More preferably, the heating temperature is 1300 to 1400°C.

[0122] The chemical composition of the steel billet can be changed according to the chemical composition of the base steel sheet of the oriented electrical steel sheet to be finally obtained, but for example, a chemical composition containing, in mass%, C: 0.01 to 0.20%, Si: 2.50 to 4.00%, sol. Al: 0.01 to 0.040%, Mn: 0.01 to 0.50%, N: 0.020% or less, S: 0.005 to 0.040%, Cu: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.50%, and the remainder being Fe and impurities can be exemplified.

[0123] Regarding the hot rolling conditions, they are not specifically limited and can be set appropriately based on the required characteristics. For example, the thickness of the hot-rolled plate is preferably within the range of 2.0 mm or more and 3.0 mm or less.

[0124] [Hot Rolled Plate Annealing Process]

[0125] In the hot-rolled sheet annealing process, the steel sheet (hot-rolled sheet) is annealed after the hot rolling process. By performing this annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to realize good magnetic properties.

[0126] In the hot-rolled sheet annealing process of the present embodiment, a hot-rolled sheet manufactured through a hot rolling process according to a known method may be annealed. The means for heating the hot-rolled sheet during annealing is not particularly limited, and known heating methods may be adopted. For example, so-called continuous annealing may be used, or batch annealing may be performed by forming the hot-rolled sheet into a coil shape. Furthermore, the annealing conditions are not particularly limited, but for example, annealing may be performed on the hot-rolled sheet for 10 seconds to 5 minutes in a temperature range of 900 to 1200°C. In addition, the atmosphere is not particularly limited, but it is preferable to suppress oxidation of the steel sheet, so it is preferable to perform the process in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen.

[0127] [Pickling Process]

[0128] In the pickling process, scale (oxide) formed on the surface of the steel sheet during hot rolling and hot-rolled sheet annealing is removed. In the pickling process of the present embodiment, a known method is used. As the pickling solution, known acids such as hydrochloric acid, sulfuric acid, or nitric acid are used. In addition, known pickling inhibitors or pickling accelerators may be added to the pickling solution as needed. Furthermore, before contacting the steel sheet with the pickling solution, it is also possible to perform physical treatment such as shot blasting on the steel sheet before pickling to improve pickling efficiency by allowing the pickling solution to penetrate the interface between the scale and the steel sheet.

[0129] [Cold Rolling Process]

[0130] In the cold rolling process, the steel sheet after the pickling process is cold rolled to form a cold-rolled sheet (a steel sheet having the same thickness as the base steel sheet of the oriented electrical steel sheet). The cold rolling may be a single cold rolling (a series without intermediate annealing), or the cold rolling may be stopped before the final pass of the cold rolling process and at least one or two intermediate annealings may be performed to carry out multiple cold rollings with intermediate annealings in between.

[0131] The conditions for cold rolling may be determined according to known methods. The cold rolling reduction rate in oriented electrical steel sheets significantly affects their magnetic properties. In particular, the final reduction rate has a significant influence, so the final reduction rate can be set to 80 to 95%. The final reduction rate is the cumulative reduction rate of cold rolling, and in the case of intermediate annealing, it is the cumulative reduction rate of cold rolling after the final intermediate annealing.

[0132] When performing intermediate annealing, for example, the temperature is maintained at 800 to 1200°C for 5 to 180 seconds. The annealing atmosphere is not particularly limited, but to prevent oxidation of the steel sheet, it is preferable to perform it in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen. Furthermore, regarding the annealing method, so-called continuous annealing or batch annealing in a coil shape may be used, or any other method may be used. Considering manufacturing costs, it is preferable to limit the number of intermediate annealing cycles to three or fewer.

[0133] [Decarburization Annealing Process]

[0134] In the decarburization annealing process, decarburization annealing is performed on the cold-rolled sheet after the grinding process. In this decarburization annealing, carbon that adversely affects magnetic properties is removed (decarburized) from the steel sheet, and the cold-rolled sheet is recrystallized for the first time.

[0135] The decarburization annealing conditions are not limited, but annealing is performed in an atmosphere in which the oxygen potential is increased by humidification and a nitrogen-hydrogen mixed atmosphere is used for decarburization. In addition, since it is necessary to form a primary recrystallization structure together, the humidification temperature (dew point) is determined in terms of the annealing temperature required for recrystallization and the oxygen potential at which decarburization is possible at said annealing temperature.

[0136] The annealing temperature is, for example, about 700 to 900°C, and since annealing is generally performed in a continuous annealing process, a crack is formed for 30 to 90 seconds.

[0137] [Nitriding Process]

[0138] Nitriding treatment may be performed between the decarburization annealing process and the finishing annealing process described later.

[0139] In the nitriding process, for example, a decarburized annealed steel sheet is nitrided by maintaining it at approximately 700 to 850°C in a nitriding atmosphere (an atmosphere containing gases capable of nitriding, such as hydrogen, nitrogen, and ammonia). When AlN is used as an inhibitor, it is desirable to increase the nitrogen concentration of the steel sheet to 40 ppm (0.0040 mass%) or higher through the nitriding process. On the other hand, if the nitrogen concentration of the steel sheet exceeds 1000 ppm (0.1000 mass%), an excess of AlN remains in the steel sheet even after the secondary recrystallization is completed during the final annealing. This AlN causes iron loss deterioration. Therefore, it is desirable to keep the nitrogen concentration of the steel sheet after the nitriding process at 1000 ppm or less.

[0140] [Final Annealing Process]

[0141] In the finishing annealing process, an annealing separator containing 10 to 100 mass% of Al2O3 is applied to a steel plate after the decarburization annealing process (or after the nitriding treatment process), dried, and then the finishing annealing is performed.

[0142] In a conventional method for manufacturing oriented electrical steel sheets, a forsterite-based film was formed on the surface of a steel sheet (cold-rolled sheet) by applying an annealing separator mainly composed of MgO and performing a finishing annealing. In contrast, in the method for manufacturing oriented electrical steel sheets according to the present embodiment, an annealing separator containing 10 mass% or more of Al2O3 is used so as not to form a forsterite-based film. It is preferable that the content of Al2O3 be 40 mass% or more.

[0143] Meanwhile, although the proportion of Al2O3 may be 100 mass%, in order to prevent Al2O3 from being deposited on the surface of the steel sheet, it is preferable that the annealing separator include MgO in the method for manufacturing a oriented electrical steel sheet according to the present embodiment. Although MgO may be 0%, it is preferable that the proportion of MgO be 5 mass% or more to obtain the above effect. When MgO is included, the proportion of MgO is set to 90 mass% or less in order to secure 10 mass% or more of Al2O3. The proportion of MgO is preferably 50 mass% or less. With respect to the annealing separator, the sum of Al2O3 and MgO must exceed 50 mass% in terms of solid content.

[0144] In addition, in the method for manufacturing a oriented electrical steel sheet according to the present embodiment, the annealing separator may also contain chloride. By including chloride in the annealing separator, the effect of making it more difficult to form a forsterite-based film is obtained. The chloride content is not particularly limited and may be 0%, but 0.5 to 10.0 mass% is preferred to obtain the above effect. Examples of effective chlorides include bismuth chloride, calcium chloride, cobalt chloride, iron chloride, nickel chloride, etc.

[0145] The finishing annealing conditions are not limited, but for example, conditions of maintaining at a temperature of 1150 to 1250°C for 10 to 60 hours may be adopted.

[0146] [Annealing Separator Removal Process]

[0147] In the annealing separator removal process, excess annealing separator is removed from the steel sheet after the finishing annealing process. For example, excess annealing separator can be removed by washing with water.

[0148] [Gyeongsan Tax Process]

[0149] In the light acid pickling process, the steel plate after the annealing separator removal process is pickled with 0.1 to 5.0 mass% of inorganic acid for 10 to 60 seconds.

[0150] If the conditions of the acidity treatment are undesirable, problems such as excess annealing separator remaining on the steel sheet surface, increasing surface roughness and reducing the packing efficiency, or if the acid is too strong, etching the steel sheet surface and degrading magnetic properties occur.

[0151] [Washing Process]

[0152] In the washing process, the steel plate after the light acidity process is washed and dried.

[0153] As a result, the pickling solution is removed, making it possible to suppress rust formation.

[0154] The conditions for washing and drying are not limited.

[0155] [First Insulating Film Formation Process]

[0156] In the first insulating film forming process, the steel plate after the water washing process is immersed in a treatment solution having a liquid temperature of 30 to 85°C and a metal phosphate salt concentration of 1.0 to 10.0 mass% for 5 to 150 seconds, and after washing away the treatment solution, the steel plate is dried to form a first insulating film on the surface of the steel plate.

[0157] When the liquid temperature of the treatment solution is below 30°C, the amount of the first insulating film formed is too small, resulting in a partial decrease in the adhesion of the insulating film. On the other hand, when the liquid temperature exceeds 85°C, the first insulating film becomes too thick in some parts, resulting in a final increase in surface roughness and a decrease in the packing efficiency.

[0158] In addition, if the metal phosphate salt concentration (concentration of metal phosphate salt) is less than 1.0 mass%, it takes too long to form the first insulating film, making it cost-ineffective. On the other hand, if the metal phosphate salt concentration exceeds 10.0 mass%, the formation of the first insulating film becomes partially thick, resulting in a non-uniform insulating film.

[0159] In addition, if the processing time is less than 5 seconds, the amount of the first insulating film formed is too small, resulting in a partial decrease in the adhesion of the insulating film. On the other hand, if it exceeds 150 seconds, it takes too long and becomes disadvantageous in terms of cost.

[0160] [Second Insulation Film Formation Process]

[0161] In the second insulating film forming process, a coating solution (insulating film forming solution) comprising a metal phosphate salt and colloidal silica, wherein the content of colloidal silica is 30 to 150 parts by mass relative to 100 parts by mass of the metal phosphate salt and the solid content concentration is 10 to 40 mass% is applied to the steel plate after the first insulating film forming process, and after drying, the plate temperature is maintained at 700 to 950°C for 10 to 90 seconds to form a second insulating film on the first insulating film.

[0162] If the plate temperature is below 700°C, the storage capacity decreases, and the magnetic properties become inferior. Therefore, it is desirable to keep the plate temperature at 700°C or higher. On the other hand, if the plate temperature exceeds 950°C, the rigidity of the steel plate decreases, making it prone to deformation. In this case, deformation may occur in the steel plate due to transport, etc., resulting in inferior magnetic properties. Therefore, it is desirable to keep the plate temperature at 950°C or lower.

[0163] In addition, if the holding time is less than 10 seconds, the liquidity becomes inferior. Therefore, the holding time should be 10 seconds or more. On the other hand, if the holding time exceeds 90 seconds, adhesion decreases, or if one attempts to avoid the decrease in adhesion, productivity becomes inferior. Therefore, it is desirable for the holding time to be 90 seconds or less.

[0164] The coating solution contains a metal phosphate salt and colloidal silica in an amount of 30 to 150 parts by mass of colloidal silica per 100 parts by mass of metal phosphate salt. The solid content concentration of the coating solution is 10 to 40 mass%, and it is preferable that the total amount of the metal phosphate salt and colloidal silica in the coating solution exceeds 50 mass% in terms of solid content. As the metal phosphate salt, for example, one or a mixture of two or more selected from aluminum phosphate, zinc phosphate, magnesium phosphate, nickel phosphate, copper phosphate, lithium phosphate, cobalt phosphate, etc. may be used.

[0165] The coating solution may include vanadium, tungsten, molybdenum, zirconium, etc. as additional elements.

[0166] Colloidal silica can be of type S or type C. Type S refers to colloidal silica where the silica solution is alkaline, while type C refers to silica where the silica particle surface has been treated with aluminum, resulting in a silica solution that is alkaline to neutral. Type S colloidal silica is widely used and is relatively inexpensive, but caution is required as there is a risk of aggregation and precipitation when mixed with acidic metal phosphate solutions. Type C colloidal silica is stable even when mixed with metal phosphate solutions and there is no risk of precipitation, but it is relatively expensive due to the higher processing steps required. It is advisable to select and use the appropriate type based on the stability requirements of the coating solution being prepared.

[0167] [Self-detailed process]

[0168] In the magnetic domain segmentation process, energy lines may be irradiated onto the surface of the insulating film (the surface of the insulating film of the base steel sheet and the oriented electrical steel sheet having the insulating film) to perform 180° magnetic domain segmentation. By performing magnetic domain segmentation, the iron loss of the oriented electrical steel sheet can be further reduced.

[0169] Any known method may be used for the process of subdividing the magnetic domain. For example, there is a method of narrowing the width of the 180° magnetic domain (subdividing the 180° magnetic domain) by forming linear or dot-shaped grooves extending in a direction intersecting the rolling direction at predetermined intervals along the rolling direction.

[0170] When forming a groove, mechanical groove forming methods using gears, chemical groove forming methods using electrolytic etching, and thermal groove forming methods using laser irradiation may be applied.

[0171] If the insulating film is damaged due to the formation of stress deformation areas or grooves, causing properties such as insulation to deteriorate, the damage may be repaired by forming a new insulating film.

[0172] [Heat Treatment Process]

[0173] In the heat treatment process, the steel plate after the second insulating film formation process is heated to a temperature range of 700 to 900°C in an atmosphere having a dew point of 0 to 30°C, a nitrogen content of 50 to 100 volume%, and a hydrogen content of 0 to 50 volume%, and maintained in this temperature range for 10 to 180 minutes, thereby fusing the first insulating film and the second insulating film to form an insulating film, and forming an oxide layer in the steel plate.

[0174] In addition, this heat treatment process may also serve as stress relief annealing. If the heat treatment process includes stress relief annealing, processing may be performed prior to the heat treatment process to change the shape of the steel plate to a predetermined shape (e.g., a core shape).

[0175] If the dew point is below 0°C, the oxide layer is not sufficiently formed. On the other hand, if the dew point exceeds 30°C, the average thickness of the oxide layer becomes excessive.

[0176] If the hydrogen content in the atmosphere exceeds 50 volume%, there is a concern that the oxide layer may not be sufficiently formed.

[0177] If the heat treatment temperature is below 700℃, the rate of oxide layer formation is slow, so the oxide is not sufficiently formed. On the other hand, if it exceeds 900℃, the rate of oxide formation becomes too fast, causing large fluctuations and an excessive thickness of the oxide layer.

[0178] In addition, if the holding time is less than 10 minutes, the formation of oxide is insufficient and fluctuations increase, resulting in an excessive thickness of the oxide layer. On the other hand, if it exceeds 180 minutes, the amount of oxidation becomes excessive, resulting in an excessive thickness of the oxide layer.

[0179] In the present invention, additional annealing may be performed in accordance with the formation of the oxide layer. For example, heating may be performed for 10 minutes in an atmosphere with a dew point of 20°C, and then annealing may be performed for 120 minutes in an atmosphere with 100% nitrogen and a dew point of -20°C.

[0180] Examples

[0181] A slab containing, in mass %, C: 0.08%, Si: 3.31%, Mn: 0.07%, sol. Al: 0.028%, N: 0.008%, with the remainder being Fe and impurities, was cast, and after heating the slab, it was hot-rolled to make a 2.2mm hot-rolled plate.

[0182] This hot-rolled plate was subjected to annealing by holding it at 1100°C for 10 seconds.

[0183] After that, a steel sheet (cold-rolled sheet) was obtained by pickling under announced conditions and then cold-rolling it to 0.22 mm by continuous cold rolling without intermediate annealing.

[0184] On this steel plate, decarburization annealing was performed by holding at 830°C for 3 minutes.

[0185] After decarburization annealing, an annealing separator containing MgO: 48 mass%, Al2O3: 48 mass%, and BiCl3: 4 mass% was applied and dried, then heated to 1200°C and maintained for 20 hours to perform finishing annealing.

[0186] After finishing annealing, the excess annealing separator was removed by rinsing, and no forsterite-based film was formed on the surface of the steel plate.

[0187] For this steel plate, light acidity was performed under the conditions shown in Table 1.

[0188] After that, the steel plate was washed and dried.

[0189] This steel plate was immersed in a treatment solution mixed with metal phosphate salts shown in Table 1 and additives such as preservatives or viscosity modifiers, and after washing off the treatment solution, the steel plate was dried to form a first insulating film.

[0190] After that, a coating solution containing metal phosphate salts and colloidal silica as shown in Table 2 in the ratios shown in Table 2 was applied and dried to form a second insulating film.

[0191] After that, grooves with a depth of 20㎛ and a width of 50㎛ were formed on the surface of the steel plate in a sawtooth shape at intervals of 6mm in a direction inclined 80° from the rolling direction.

[0192] After that, heat treatment was performed under the conditions shown in Table 3 to obtain a oriented electrical steel sheet.

[0193] For the obtained oriented electrical steel sheets, the presence or absence of an oxide layer, the average thickness of the oxide layer, and the coverage rate of the oxide layer were measured.

[0194] In addition, the composition and thickness of the insulating film were measured. The results are shown in Table 4.

[0195] Also, although not shown in the table, the chemical composition of the base steel sheet (excluding the oxide layer) was Si: 3.30 mass%, C: 0.0018 mass%, Mn: 0.06 mass%, sol. Al: 0.002 mass%, and the remainder being Fe and impurities.

[0196] In addition, for the obtained oriented electrical steel sheet, film adhesion, film tension, corrosion resistance, water resistance, fill factor, and iron loss were measured according to the following method. The results are shown in Table 5.

[0197] [Film Adhesion]

[0198] The adhesion of the film was evaluated by the degree of peeling (area ratio) of the film after performing a bending adhesion test in which a sample with a width of 30 mm and a length of 300 mm was taken from a steel plate, the sample was wrapped around a cylinder of 10 mmφ, and then unwound.

[0199] The evaluation criteria were set as follows, and in the case of Ex, G, and F, it was determined that the film adhesion was excellent.

[0200] Ex: Peeling area rate 0 to 0.5%

[0201] G: Delamination area ratio greater than 0.5% and less than or equal to 5.0%

[0202] F: Peeling area ratio greater than 5.0% and less than or equal to 20%

[0203] P: Delamination area ratio exceeding 20% ​​and 50% or less

[0204] B: Delamination area rate exceeding 50%

[0205] [Film Tension]

[0206] The film tension was calculated by back-calculating from the curvature condition when one side of the insulating film was peeled off. It was determined that the film tension was sufficient when the obtained film tension was 4.0 MPa or higher.

[0207] [Corrosion Resistance]

[0208] Corrosion resistance was tested by naturally dropping a 5% NaCl aqueous solution onto a sample for 7 hours in an atmosphere of 35°C, in accordance with the salt spray test of the JIS method (JIS Z2371:2015).

[0209] Afterwards, the rust area was evaluated on a 10-point scale. The evaluation criteria are as follows. If the score is 5 or higher, it was determined that the corrosion resistance is excellent.

[0210] 10: No rust occurred

[0211] 9: Very small amount of rust (Area ratio: 0.10% or less)

[0212] 8: Rust-covered area ratio = greater than 0.10% and less than or equal to 0.25%

[0213] 7: Rust-covered area ratio = greater than 0.25% and less than or equal to 0.50%

[0214] 6: Area ratio with rust = greater than 0.50% and less than or equal to 1.0%

[0215] 5: Rust-covered area ratio = greater than 1.0% and less than or equal to 2.5%

[0216] 4: Rust-covered area ratio = greater than 2.5% and less than or equal to 5.0%

[0217] 3: Rust-covered area ratio = greater than 5.0% and less than or equal to 10%

[0218] 2: Rust-covered area ratio = greater than 10% and less than or equal to 25%

[0219] 1: Percentage of rusted area = Over 25% and up to 50%

[0220] [Content Source]

[0221] Release capability was evaluated based on whether it could inhibit the leaching of phosphoric acid from the sample.

[0222] The method for measuring the amount of leaching was performed by boiling the sample in boiling pure water for 10 minutes, measuring the amount of phosphoric acid leached into the pure water, and dividing the amount of phosphoric acid by the area of ​​the insulating film of the boiled oriented electrical steel sheet. The amount of phosphoric acid leached into the pure water was calculated by cooling the pure water (solution) from which phosphoric acid was leached, and measuring the phosphoric acid concentration of the sample diluted with pure water after cooling using ICP-AES.

[0223] The dissolution amount is 40 mg / m² 2 It was stated that if it is less than that, the content output is excellent.

[0224] [Points per liter]

[0225] The packing density was measured according to the method in accordance with JIS C 2550-5 (2020). Thirty test specimens with a width of 30 mm and a length of 320 mm were used. After measuring the total mass of the samples, the density was calculated by measuring the distance between the upper and lower butt plates with the laminated structure in between while under pressure of 1 MPa.

[0226] If the fill rate is 96.0% or higher, it was determined that a high fill rate is being secured.

[0227] [Iron Hand]

[0228] For the obtained steel sheet (oriented electrical steel sheet), B8 (magnetic flux density at a magnetizing force of 800 A / m) and W17 / 50 (iron loss per mass at a magnetic flux density amplitude of 1.7 T and 50 Hz) were measured.

[0229] These characteristic values ​​were measured by a Single Sheet Tester (SST) in accordance with JIS C2556 (2015).

[0230] It was determined that the magnetic properties are excellent if the iron loss is 0.74 W / kg or less.

[0231]

[0232]

[0233]

[0234]

[0235]

[0236] As can be seen from Tables 1 to 5, in the oriented electrical steel sheet corresponding to the invention example obtained by a preferred manufacturing method, the base steel sheet and an insulating film containing a metal phosphate formed on the surface of the base steel sheet are provided, and the base steel sheet has an oxide layer containing an oxide of Si in the region in contact with the interface between the base steel sheet and the insulating film, and the average thickness of the oxide layer from the interface is 0.5 to 2.5 μm, so that the film adhesion, film tension, corrosion resistance, water resistance, fill factor, and iron loss are all excellent.

[0237] In contrast, in the oriented electrical steel sheet of the comparative example, since one or more conditions among the first film formation process, the second film formation process, and the heat treatment process fell outside the scope of the present invention, a predetermined oxide layer was not formed, and one or more of the film adhesion, film tension, corrosion resistance, liquid leaching resistance, fill factor, and iron loss fell below the target. Explanation of the symbols

[0238] 11: Base steel plate 12: Oxide layer 21: Insulating film

Claims

Claim 1 A oriented electrical steel sheet having a base steel sheet and an insulating film comprising a metal phosphate salt formed on the surface of the base steel sheet, wherein the base steel sheet has an oxide layer comprising an oxide of Si in a region in contact with the interface between the base steel sheet and the insulating film, and the average thickness of the oxide layer from the interface is 0.5 to 2.5 μm. Claim 2 A oriented electrical steel sheet according to claim 1, characterized in that the ratio of the length of the interface between the oxide layer and the insulating film to the length of the interface between the base steel sheet and the insulating film is 30% or more. Claim 3 A oriented electrical steel sheet according to claim 1 or 2, characterized in that the area ratio of voids in the insulating film is 30% or less. Claim 4 A finishing annealing process in which an annealing separator containing 10 to 100 mass% of Al2O3 is applied to a steel plate, dried, and then finishing annealing is performed; an annealing separator removal process in which excess annealing separator is removed from the steel plate after the finishing annealing process; a light pickling process in which the steel plate after the annealing separator removal process is pickled with 0.1 to 5.0 mass% of an inorganic acid for 10 to 60 seconds; a washing process in which the steel plate after the light pickling process is washed with water and dried; a first insulating film forming process in which the steel plate after the washing process is immersed for 5 to 150 seconds in a treatment solution having a liquid temperature of 30 to 85°C and a metal phosphate salt concentration of 1.0 to 10.0 mass%, and then the treatment solution is washed away and the steel plate is dried; and on the steel plate after the first insulating film forming process, A method for manufacturing a oriented electrical steel sheet, characterized by comprising: a second insulating film forming process in which a coating solution containing a metal phosphate salt and colloidal silica is applied, wherein the content of the colloidal silica is 30 to 150 parts by mass relative to 100 parts by mass of the metal phosphate salt and the solid content concentration is 10 to 40 mass%, and after drying, the sheet is maintained at a temperature of 700 to 950°C for 10 to 90 seconds; and a heat treatment process in which the steel sheet after the second insulating film forming process is heated to a temperature range of 700 to 900°C in an atmosphere having a dew point of 0 to 30°C, a nitrogen content of 50 to 100 volume%, and a hydrogen content of 0 to 50 volume%, and maintained at the temperature range for 10 to 180 minutes. Claim 5 A method for manufacturing a oriented electrical steel sheet according to claim 4, wherein the annealing separator further comprises one or two types of MgO: 5 to 90 mass% and chloride: 0.5 to 10.0 mass%.

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