Grain-oriented electrical steel sheet

Abstract

A grain-oriented magnetic steel sheet having a base steel sheet, an oxide film, and a phosphoric acid-based coating film containing a first crystalline phosphoric acid compound having a crystal structure corresponding to Fe2P2O7 and a second crystalline phosphoric acid compound having a crystal structure corresponding to Fe7(P2O7)4, the second crystalline phosphoric acid compound containing at least one selected from the group consisting of V, W, Zr, Co, and Mo.

Description

Technical Field

[0001] This invention relates to directional electromagnetic steel sheets. In particular, this invention relates to directional electromagnetic steel sheets with excellent adhesion of the insulating coating even without a magnesium olivine coating.

[0002] This application claims priority based on Japanese Patent Application No. 2021-090213 filed on May 28, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Directional electromagnetic steel sheets are mainly used in transformers. Transformers are continuously energized over long periods of time, from installation to disposal, resulting in continuous energy loss. Therefore, the energy loss during magnetization via alternating current, i.e., iron loss, becomes the main indicator determining the performance of a transformer.

[0004] To reduce iron loss in directional electromagnetic steel sheets, many methods have been proposed to date. For example, regarding the steel sheet microstructure, there are methods to increase the aggregation towards the {110}<001> orientation, which is called Gaussian orientation; regarding the steel sheet itself, there are methods to increase the content of solid solution elements such as Si, which increase resistance, and methods to reduce the thickness of the steel sheet, etc.

[0005] Furthermore, it is known that applying tension to the steel sheet is an effective method for reducing iron loss. Therefore, a coating is usually formed on the surface of directional electromagnetic steel sheets to reduce iron loss. This coating reduces iron loss as a single sheet by applying tension to the directional electromagnetic steel sheet. The coating also ensures electrical insulation between the steel sheets when they are stacked, thereby reducing iron loss as the core.

[0006] As a type of directional electromagnetic steel sheet with a coating, it comprises: a magnesium olivine oxide coating containing Mg formed on the surface of a base steel sheet, and an insulating coating formed on the surface of the magnesium olivine coating. In other words, in this case, the coating on the base steel sheet includes both a magnesium olivine coating and an insulating coating. The magnesium olivine coating and the insulating coating respectively perform the functions of insulation and imparting tension to the base steel sheet.

[0007] The final annealing process, which causes secondary recrystallization of the steel plate, involves reacting an annealing separating agent, mainly composed of magnesium oxide (MgO), with silicon oxide (SiO2) formed on the base steel plate during decarburization annealing, at 900–1200°C for more than 30 hours to form a magnesium olivine coating.

[0008] The insulating coating is formed by the following process: applying a coating solution containing, for example, phosphoric acid or phosphate, colloidal silica, and chromic anhydride or chromate to the steel sheet after final annealing, baking at 300-950°C for more than 10 seconds, and drying.

[0009] These coatings require a high degree of adhesion between the coating and the base steel sheet to perform functions such as insulation and applying tension to the base steel sheet.

[0010] Previously, the aforementioned tightness was mainly ensured by the anchoring effect produced by the unevenness of the interface between the base steel plate and the forsterite coating. However, in recent years, it has been known that the unevenness of this interface hinders the movement of magnetic domain walls when the directional electromagnet is magnetized, becoming a major factor preventing low iron loss.

[0011] Therefore, in order to further reduce iron loss, for example, Patent Document 1 and Patent Document 2 propose the following technology: an insulating coating is formed on the base steel plate without magnesium olivine coating, while the surface of the base steel plate is made smooth.

[0012] In the manufacturing method of directional electromagnetic steel sheet disclosed in Patent Document 1, the forsterite coating is removed by pickling or the like, and the surface of the base steel sheet is smoothed by chemical polishing or electrolytic polishing. In the manufacturing method of directional electromagnetic steel sheet disclosed in Patent Document 2, an annealing separating agent containing alumina (Al2O3) is used during the final annealing to suppress the formation of the forsterite coating itself, thereby smoothing the surface of the base steel sheet.

[0013] However, in the manufacturing methods of Patent Document 1 and Patent Document 2, when an insulating coating is formed in contact with the surface of the base steel plate (directly on the surface of the base steel plate), there is a problem that the insulating coating does not adhere well to the surface of the base steel plate (insufficient adhesion is not achieved).

[0014] Therefore, in order to ensure the tightness of the coating, for example, patent documents 3 and 4 propose the following technology: by controlling the form of the insulating coating and the form of the intermediate layer disposed between the base steel plate and the insulating coating, the tightness of the insulating coating is improved.

[0015] In the directional electromagnetic steel sheet disclosed in Patent Document 3, the insulating coating has a crystalline phosphate layer containing crystalline phosphate. In the directional electromagnetic steel sheet disclosed in Patent Document 4, the intermediate layer has selective oxidation regions, and the thickness of the intermediate layer in the regions where the selective oxidation regions exist is 50 nm or more.

[0016] Existing technical documents

[0017] Patent documents

[0018] Patent Document 1: Japanese Patent Application Publication No. 49-096920

[0019] Patent Document 2: International Publication No. 2002 / 088403

[0020] Patent Document 3: International Publication No. 2019 / 013353

[0021] Patent Document 4: International Publication No. 2019 / 013350 Summary of the Invention

[0022] The problem that the invention aims to solve

[0023] As mentioned above, smoothing the surface of the base steel sheet of the directional electromagnetic steel sheet is effective in reducing iron loss. However, smoothing the surface of the base steel sheet reduces the adhesion of the insulating coating.

[0024] In the technologies disclosed in Patent Documents 1 and 2, the film adhesion is not considered sufficient. Furthermore, in the technologies disclosed in Patent Documents 3 and 4, the film adhesion is indeed improved, but further improvement in film adhesion would be preferred for directional electromagnetic steel sheets.

[0025] The present invention was made in view of the above-mentioned problems. The object of the present invention is to provide a directional electromagnetic steel sheet with excellent adhesion even in the absence of magnesium olivine coating and insulating coating.

[0026] Methods for solving problems

[0027] The main idea of ​​this invention is as follows.

[0028] (1) One aspect of the present invention relates to a directional electromagnetic steel plate comprising: a base steel plate as a silicon steel plate; an intermediate layer disposed in contact with the silicon steel plate; and an insulating coating disposed in contact with the intermediate layer.

[0029] The aforementioned intermediate layer is an oxide film that satisfies the following composition:

[0030] Si content: ≥20 atomic% and ≤70 atomic%;

[0031] O content: 30 atomic% or more and 80 atomic% or less;

[0032] Mg content: less than 20 atomic percent;

[0033] P content: less than 5 atomic percent;

[0034] Fe content: less than 20 atomic%.

[0035] Furthermore, the average thickness of the aforementioned oxide film is greater than 2 nm and less than 500 nm.

[0036] The above-mentioned insulating coating is a phosphoric acid-based coating that satisfies the following composition:

[0037] P content: 5 atomic% or more and 30 atomic% or less;

[0038] Si content: 5 atomic% or more and 30 atomic% or less;

[0039] O content: 30 atomic% or more and 80 atomic% or less;

[0040] Fe content: ≥1 atomic% and ≤25 atomic%;

[0041] Cr content: less than 1.0 atomic percent;

[0042] Al content: 0 atomic% or more and 10 atomic% or less;

[0043] Mg content: ≥0 atomic% and ≤10 atomic%;

[0044] Mn content: ≥0 atomic% and ≤10 atomic%;

[0045] Ni content: 0 atomic% or more and 10 atomic% or less;

[0046] Zn content: 0 atomic% or more and 10 atomic% or less;

[0047] The total content of Al+Mg+Mn+Ni+Zn is 0.1 atomic% or more and less than 10 atomic%;

[0048] V content: 0 atomic% or more and 10 atomic% or less;

[0049] W content: 0 atomic% or more and 10 atomic% or less;

[0050] Zr content: 0 atomic% or more and 10 atomic% or less;

[0051] Co content: 0 atomic% or more and 10 atomic% or less;

[0052] Mo content: 0 atomic% or more and 10 atomic% or less;

[0053] The total content of V+W+Zr+Co+Mo is ≥0.1 atomic% and ≤10 atomic%.

[0054] Furthermore, the average film thickness of the aforementioned phosphate-based coatings is 0.1 μm or more and 10 μm or less.

[0055] The aforementioned phosphoric acid coating contains a first crystalline phosphate (also known as a first crystalline phosphorus oxide) with a crystal structure corresponding to Fe2P2O7 and a second crystalline phosphate (also known as a second crystalline phosphorus oxide) with a crystal structure corresponding to Fe7(P2O7)4.

[0056] The aforementioned second crystalline phosphate contains at least one selected from the group consisting of V, W, Zr, Co, and Mo.

[0057] (2) According to the directional electromagnetic steel plate described in (1) above, when the phosphate coating is divided into an internal region that contacts the oxide film and a surface region that does not contact the oxide film on a cutting surface parallel to the plate thickness direction, the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the internal region may be greater than the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the surface region.

[0058] (3) According to the directional electromagnetic steel plate described in (1) or (2) above, the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the surface region may be 0% or more and 30% or less, and the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the internal region may be 3% or more and 50% or less.

[0059] (4) The directional electromagnetic steel sheet according to any one of (1) to (3) above, wherein, when the internal region is divided into a first internal region in contact with the oxide film and a second internal region not in contact with the oxide film along the thickness direction 2 on the cutting surface, and the percentage of the value obtained by dividing the area ratio of the second crystalline phosphate contained in the first internal region by the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the first internal region is used as the first area ratio, and the percentage of the value obtained by dividing the area ratio of the second crystalline phosphate contained in the second internal region by the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the second internal region is used as the second area ratio, the second area ratio may be larger than the first area ratio.

[0060] (5) The directional electromagnetic steel plate according to any one of (1) to (4) above, wherein the first area ratio may be 0% or more and 70% or less, and the second area ratio may be 50% or more and 100% or less.

[0061] (6) The directional electromagnetic steel sheet according to any one of (1) to (5) above, wherein the equivalent circle diameter of the second crystalline phosphate can also be 5 nm or more and 300 nm or less on average.

[0062] Invention Effects

[0063] According to the above-described solution of the present invention, it is possible to provide a directional electromagnetic steel sheet with excellent adhesion of the insulating coating even without the presence of a magnesium olivine coating. Attached Figure Description

[0064] Figure 1 This is a cross-sectional schematic diagram showing the layered structure of a directional electromagnetic steel plate according to one embodiment of the present invention.

[0065] Figure 2 This is a cross-sectional schematic diagram showing the layered structure of the directional electromagnetic steel plate according to a preferred embodiment of the present invention.

[0066] Figure 3 This is a flowchart illustrating a method for manufacturing a directional electromagnetic steel sheet according to one embodiment of the present invention. Detailed Implementation

[0067] The preferred embodiments of the present invention will now be described in detail. However, the present invention is not limited to the configuration disclosed in these embodiments, and various modifications can be made without departing from the spirit of the invention. Furthermore, regarding the numerical ranges shown in these embodiments, the lower and upper limits are included within these ranges. Values ​​expressed as "more than" or "less than" are not included in the numerical range. Regarding the "%" related to the content of each element, unless otherwise specified, it refers to "mass %" in the base steel sheet and "atomic %" in the intermediate layer and insulating coating.

[0068] Figure 1 This is a cross-sectional schematic diagram showing the layered structure of a directional electromagnetic steel plate according to one embodiment of the present invention. (See diagram below.) Figure 1 As shown, for the directional electromagnetic steel plate involved in this embodiment, when viewed on a cut surface parallel to the plate thickness direction, there is no magnesium olivine coating on the surface of the base steel plate 1, and there is an intermediate layer 2 with silicon oxide as the main body on the surface of the base steel plate 1, and an insulating coating 3 derived from phosphate and colloidal silicon dioxide on the intermediate layer 2.

[0069] Specifically, the directional electromagnetic steel plate according to this embodiment includes: a base steel plate as a silicon steel plate; an intermediate layer disposed in contact with the silicon steel plate; and an insulating coating disposed in contact with the intermediate layer.

[0070] The aforementioned intermediate layer is an oxide film that satisfies the following composition:

[0071] Si content: ≥20 atomic% and ≤70 atomic%;

[0072] O content: 30 atomic% or more and 80 atomic% or less;

[0073] Mg content: less than 20 atomic percent;

[0074] P content: less than 5 atomic percent;

[0075] Fe content: less than 20 atomic%.

[0076] Furthermore, the average thickness of the aforementioned oxide film is greater than 2 nm and less than 500 nm.

[0077] The above insulating coating satisfies the following composition of phosphoric acid-based coating:

[0078] P content: 5 atomic% or more and 30 atomic% or less;

[0079] Si content: 5 atomic% or more and 30 atomic% or less;

[0080] O content: 30 atomic% or more and 80 atomic% or less;

[0081] Fe content: ≥1 atomic% and ≤25 atomic%;

[0082] Cr content: less than 1.0 atomic percent;

[0083] Al content: 0 atomic% or more and 10 atomic% or less;

[0084] Mg content: ≥0 atomic% and ≤10 atomic%;

[0085] Mn content: ≥0 atomic% and ≤10 atomic%;

[0086] Ni content: 0 atomic% or more and 10 atomic% or less;

[0087] Zn content: 0 atomic% or more and 10 atomic% or less;

[0088] The total content of Al+Mg+Mn+Ni+Zn is 0.1 atomic% or more and less than 10 atomic%;

[0089] V content: 0 atomic% or more and 10 atomic% or less;

[0090] W content: 0 atomic% or more and 10 atomic% or less;

[0091] Zr content: 0 atomic% or more and 10 atomic% or less;

[0092] Co content: 0 atomic% or more and 10 atomic% or less;

[0093] Mo content: 0 atomic% or more and 10 atomic% or less;

[0094] The total content of V+W+Zr+Co+Mo is ≥0.1 atomic% and ≤10 atomic%.

[0095] Furthermore, the average film thickness of the aforementioned phosphate-based coatings is 0.1 μm or more and 10 μm or less.

[0096] The aforementioned phosphoric acid coating contains a first crystalline phosphate with a crystal structure corresponding to Fe2P2O7 and a second crystalline phosphate with a crystal structure corresponding to Fe7(P2O7)4.

[0097] The aforementioned second crystalline phosphate contains at least one selected from the group consisting of V, W, Zr, Co, and Mo.

[0098] As described above, the main technical feature of the directional electromagnetic steel plate involved in this embodiment is that the intermediate layer is not a magnesium olivine coating, but a Si-based oxide film, and the insulating coating is a phosphate-based coating, which contains a first crystalline phosphate and a second crystalline phosphate.

[0099] The features will be described in detail below. First, the phosphate coating on the directional electromagnetic steel sheet according to this embodiment will be described.

[0100] (Regarding phosphate-based coatings)

[0101] The phosphate coating is located on the outermost surface of the directional electromagnetic steel sheet's layered structure. This phosphate coating uses a material with a lower coefficient of thermal expansion than the base steel sheet and is formed on the base steel sheet at high temperatures. Therefore, a shrinkage difference occurs between the phosphate coating and the base steel sheet during cooling, resulting in the phosphate coating imposing tension on the base steel sheet. In directional electromagnetic steel sheets that impose tension on the base steel sheet, iron loss characteristics are preferably improved.

[0102] In order for the phosphate coating to impart tension to the base steel sheet, it is important to ensure a tight bond between the phosphate coating and the base steel sheet. In the directional electromagnetic steel sheet according to this embodiment, in order to improve the coating adhesion, the coating composition and thickness of the phosphate coating are controlled, and the phosphate coating contains a variety of crystalline phosphates.

[0103] First, the composition of the phosphate-based coating will be explained.

[0104] In the directional electromagnetic steel sheet according to this embodiment, a phosphate-based coating comprises basic elements as a coating component, and optional elements are included as needed. Furthermore, it is preferable that the remaining portions of the basic elements and optional elements contain impurities.

[0105] Specifically, phosphate-based coatings, as basic elements, only need to satisfy the following composition:

[0106] P content: 5 atomic% or more and 30 atomic% or less;

[0107] Si content: 5 atomic% or more and 30 atomic% or less;

[0108] O content: 30 atomic% or more and 80 atomic% or less; and

[0109] Fe content: ≥1 atomic% and ≤25 atomic%.

[0110] In addition, the phosphate coating is an optional element, and it only needs to meet the following composition:

[0111] Al content: 0 atomic% or more and 10 atomic% or less;

[0112] Mg content: ≥0 atomic% and ≤10 atomic%;

[0113] Mn content: ≥0 atomic% and ≤10 atomic%;

[0114] Ni content: 0 atomic% or more and 10 atomic% or less;

[0115] Zn content: 0 atomic% or more and 10 atomic% or less;

[0116] The total content of Al+Mg+Mn+Ni+Zn is 0.1 atomic% or more and less than 10 atomic%;

[0117] V content: 0 atomic% or more and 10 atomic% or less;

[0118] W content: 0 atomic% or more and 10 atomic% or less;

[0119] Zr content: 0 atomic% or more and 10 atomic% or less;

[0120] Co content: 0 atomic% or more and 10 atomic% or less;

[0121] Mo content: 0 atomic% or more and 10 atomic% or less;

[0122] The total content of V+W+Zr+Co+Mo is ≥0.1 atomic% and ≤10 atomic%.

[0123] In addition, the phosphate coating is an impurity and only needs to meet the requirement of Cr content: less than 1.0 atomic%.

[0124] Typically, the phosphate-based coating on directional electromagnetic steel sheets is formed by baking a coating solution containing phosphate, colloidal silica, and chromate. The chromate is added to improve corrosion resistance, enhance chemical resistance, and suppress porosity.

[0125] On the other hand, the phosphate-based coating of the directional electromagnetic steel sheet according to this embodiment is formed by baking a coating solution containing phosphate and colloidal silica but not chromate. Therefore, as described above, the Cr content in the phosphate-based coating of the directional electromagnetic steel sheet according to this embodiment is limited to less than 1.0 atomic%. The Cr content is preferably 0.8 atomic% or less, and more preferably 0.5 atomic% or less.

[0126] In the directional electromagnetic steel sheet according to this embodiment, limiting the Cr content of the phosphate coating to less than 1.0 atomic% is one of the control conditions for forming the first crystalline phosphate and the second crystalline phosphate described above in the phosphate coating. Details of the formation conditions of these crystalline phosphates will be described later.

[0127] The basic elements of the aforementioned phosphate-based coating, P, Si, O, and Fe, are derived from phosphates contained in the coating solution, colloidal silica, oxidation reactions during baking heat treatment, and elements diffused from the base steel sheet. Furthermore, the optional elements of the aforementioned phosphate-based coating, Al, Mg, Mn, Ni, Zn, V, W, Zr, Co, and Mo, are derived from phosphates contained in the coating solution. For example, at least one phosphate selected from Al, Mg, Mn, Ni, Zn, V, W, Zr, Co, and Mo may be used as the phosphate contained in the coating solution. Preferably, at least one phosphate selected from Al, Mg, Mn, Ni, and Zn is used as the phosphate contained in the coating solution, and the phosphate-based coating composition satisfies that the total content of Al+Mg+Mn+Ni+Zn is 0.1 atomic% or more and 10 atomic% or less. For example, aluminum phosphate can be used as the phosphate contained in the coating solution, and the phosphate-based coating can be composed of an Al content of 0.1 atomic% or more and 10 atomic% or less. Furthermore, at least one phosphate selected from Co, Mo, V, W, and Zr can be used as the phosphate contained in the coating solution, and the total content of V+W+Zr+Co+Mo in the coating can be 0.1 atomic% or more and 10 atomic% or less. In addition, the aforementioned Cr is an impurity in the phosphate-based coating, which originates from the raw materials used to form the phosphate-based coating, elements introduced from the manufacturing environment, or elements diffused from the base steel sheet. Furthermore, there is no particular limitation on the lower limit of the impurity content; the lower the content, the better, therefore, 0% is also acceptable.

[0128] In the directional electromagnetic steel sheet according to this embodiment, in order to improve the adhesion of the coating, the composition of the phosphate-based coating only needs to meet the above conditions. In particular, the Cr content of the phosphate-based coating is limited to less than 1.0 atomic%.

[0129] Furthermore, in the directional electromagnetic steel sheet involved in this embodiment, the coating composition (average coating composition) of the phosphate-based coating preferably has the following characteristics: P content is more than 8 atomic%, and more than 17 atomic%; Si content is preferably more than 7 atomic%, and more than 19 atomic%; O content is preferably more than 58 atomic%, and more than 66 atomic%; Fe content is preferably more than 1 atomic%, and more than 20 atomic%; Cr content is preferably less than 0.2 atomic%; Al content is preferably less than 10 atomic%, and more than 3 atomic%; Mg content is preferably less than 10 atomic%, and more than 3 atomic%; Mn content is preferably less than 10 atomic%, and more than 3 atomic%; Ni content is preferably less than 10 atomic%, and more than 3 atomic%; Zn content is preferably less than 10 atomic%. The total content of Al+Mg+Mn+Ni+Zn is preferably 0.1 atomic% or more, preferably more than 1 atomic%, and preferably less than 10 atomic%, preferably less than 3 atomic%, the V content is preferably less than 3.0 atomic%, preferably less than 2 atomic%, the W content is preferably less than 3.0 atomic%, preferably less than 2 atomic%, the Zr content is preferably less than 3.0 atomic%, preferably less than 2 atomic%, the Co content is preferably less than 3.0 atomic%, preferably less than 2 atomic%, and the Mo content is preferably less than 3.0 atomic%, preferably less than 2 atomic%, or the total content of V+W+Zr+Co+Mo is preferably 0.1 atomic% or more, preferably 0.2 atomic% or more, preferably less than 3.0 atomic%, preferably less than 2 atomic%.

[0130] The composition of phosphate-based coatings can be analyzed by examining the cross-section using SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) or TEM-EDS (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy). Details of the methods for determining the coating composition will be described later.

[0131] Next, the film thickness of the phosphate-based coating will be explained.

[0132] In the directional electromagnetic steel sheet of this embodiment, when viewed on a cut surface parallel to the thickness direction, the average thickness of the phosphate coating is 0.1 μm or more and 10 μm or less.

[0133] If the average film thickness of the phosphate coating is less than 0.1 μm, it is difficult to impart the required tension to the base steel sheet. Therefore, the average film thickness is preferably 0.1 μm or more, and more preferably 0.5 μm or more.

[0134] On the other hand, if the average thickness of the phosphate coating exceeds 10 μm, cracks may occur in the phosphate coating during the formation stage. Therefore, the average thickness is preferably 10 μm or less, and more preferably 5 μm or less.

[0135] The average thickness of phosphate-based coatings can be determined by line analysis of the cross-section using SEM-EDS or TEM-EDS. Details of the method for determining the average film thickness will be described later.

[0136] Next, the crystalline phosphates contained in the phosphate coating will be explained.

[0137] In the directional electromagnetic steel sheet involved in this embodiment, the phosphate coating contains a first crystalline phosphate with a crystal structure corresponding to Fe2P2O7 and a second crystalline phosphate with a crystal structure corresponding to Fe7(P2O7)4.

[0138] The inclusion of a first crystalline phosphate and a second crystalline phosphate in the phosphate coating improves the coating's adhesion. While the exact reasons for this are not yet clear, the following effects are considered: The presence of crystalline phosphate in an amorphous phosphate coating increases the overall elasticity of the coating. Even under bending stress, the stress accumulated in the phosphate coating and the oxide film as an intermediate layer is not locally concentrated but rather mitigated. As a result, the phosphate coating is believed to be difficult to peel off. In particular, the second crystalline phosphate is believed to significantly contribute to this effect.

[0139] In order to form the first crystalline phosphate and the second crystalline phosphate in the phosphate-based coating, the following three conditions need to be met.

[0140] (I) The intermediate layer is not a magnesium olivine coating, but a Si-based oxide film.

[0141] (II) Phosphate-based coatings, as a component of the coating, satisfy the requirement of Cr content: less than 1.0 atomic%.

[0142] (III) Control the formation conditions during the formation of the phosphate coating.

[0143] Only when all three conditions are met will the first crystalline phosphate and the second crystalline phosphate be formed in the phosphate coating.

[0144] First, as a condition (I), it is important that the intermediate layer is not a forsterite coating but a Si-based oxide film. If the intermediate layer is a forsterite coating, not only will there be no issue of coating adhesion, but crystalline phosphates will not form in phosphate-based coatings.

[0145] While the exact reasons why crystalline phosphates do not form in phosphate-based coatings when the intermediate layer is a forsterite coating are not yet fully understood, the following factors are considered. For example, if the intermediate layer is a forsterite coating, the Fe content in the phosphate-based coating is reduced and the hydrogen content in the baking heat treatment atmosphere is low. Therefore, Fe remains in a solid dissolved state in the phosphate-based coating, and as a result, it is believed that crystalline phosphates will not form in the phosphate-based coating.

[0146] Next, as condition (II), it is important that the Cr content of the phosphate coating is less than 1.0 atomic%. If the Cr content of the phosphate coating is 1.0 atomic% or more, then even if the first crystalline phosphate sometimes forms in the phosphate coating, the second crystalline phosphate will not form.

[0147] While the exact reasons why a second crystalline phosphate will not form in a phosphate-based coating when the Cr content is 1.0 atomic% or higher are currently unclear, the following reasons are considered: If the Cr content in the phosphate-based coating is 1.0 atomic% or higher, (Fe,Cr)₂P₂O₇ will form in the phosphate-based coating. This (Fe,Cr)₂P₂O₇ tends to form preferentially. Therefore, under the condition that (Fe,Cr)₂P₂O₇ forms in the phosphate-based coating, the formation of (Fe,Cr)₂P₂O₇ becomes preferential, and the formation of crystalline phosphates with the Fe₇(P₂O₇)₄ structure becomes less likely.

[0148] On the other hand, if the Cr content of the phosphate coating is less than 1.0 atomic%, (Fe,Cr)₂P₂O₇ will not form in the phosphate coating; instead, Fe₂P₂O₇ will form. However, this Fe₂P₂O₇ will not form preferentially. Therefore, under the conditions of Fe₂P₂O₇ formation in the phosphate coating, crystalline phosphates with the Fe₂P₂O₇ structure will form, and crystalline phosphates with the Fe₇(P₂O₇)₄ structure will also form together.

[0149] Finally, as condition (III), it is important to control the formation conditions during the formation of the phosphate coating. Even if conditions (I) and (II) are met, if the formation conditions are not properly controlled during the formation of the phosphate coating, crystalline phosphates, especially second crystalline phosphates, will not form in the phosphate coating.

[0150] Specifically, in the formation of phosphate-based coatings, it is important to control the atmosphere and oxygen potential during the baking heat treatment, and to control the atmosphere, oxygen potential, and cooling rate during the cooling process after the baking heat treatment. Details of these manufacturing methods will be described later.

[0151] The presence of the first and second crystalline phosphates can be confirmed using TEM. For example, electron beam diffraction is performed on a phosphate-based coating, and the crystal structure of the crystalline phase contained in the electron beam-irradiated region is identified based on the electron beam diffraction pattern. This confirms the presence of the first crystalline phosphate with a crystal structure corresponding to Fe2P2O7 and the second crystalline phosphate with a crystal structure corresponding to Fe7(P2O7)4. Details of the identification method for crystalline phosphates will be described later.

[0152] Furthermore, in the directional electromagnetic steel sheet according to this embodiment, if the phosphate coating includes both a first crystalline phosphate and a second crystalline phosphate, the coating adhesion is improved. Therefore, the composition, form, and size of the crystalline phosphate are not particularly limited. However, in order to preferably improve the coating adhesion, the composition, form, and size of the crystalline phosphate preferably have the following characteristics.

[0153] In the directional electromagnetic steel sheet of this embodiment, it is preferable that the phosphate coating as a component satisfies the following total content of V+W+Zr+Co+Mo: 0.1 atomic% or more and 10 atomic% or less, and the second crystalline phosphate contains at least one selected from the group consisting of V, W, Zr, Co and Mo.

[0154] When a phosphate-based coating, as a coating component, satisfies the following conditions: the total content of V+W+Zr+Co+Mo is 0.1 atomic% or more and 10 atomic% or less, and conditions (I) to (III) above are also satisfied, it becomes easier to form (Fe,M)7(P2O7)4 as a second crystalline phosphate with the Fe7(P2O7)4 structure. Here, M is selected from at least one of the group consisting of V, W, Zr, Co, and Mo.

[0155] If (Fe,M)7(P2O7)4 is formed, then regarding the phosphate-based coating, V, W, Zr, Co, or Mo contained as a component of the coating, for example, in the case of elemental analysis performed by irradiating the precipitate with an electron beam, it is detected as a peak corresponding to that element in the EDS spectrum. Therefore, it is presumed that it is contained in the precipitate as M of (Fe,M)7(P2O7)4. At this time, the number of second crystalline phosphates formed increases, and the influence of each formed second crystalline phosphate on the coating adhesion is also preferably increased. As a result, the coating adhesion is preferably improved.

[0156] Furthermore, in the directional electromagnetic steel sheet involved in this embodiment, it is preferable that, when viewed on a cut surface parallel to the thickness direction, when the phosphate coating 2 is divided into an internal region in contact with the oxide film and a surface region not in contact with the oxide film, the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the internal region is greater than the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the surface region.

[0157] If the phosphoric acid coating contains more first-crystal phosphate and second-crystal phosphate in the inner region compared to the surface region, the overall elasticity of the phosphoric acid coating is preferably increased, and the stress under bending stress is preferably mitigated. As a result, the phosphoric acid coating is considered to be difficult to peel off.

[0158] For example, preferably, the combined area percentage of the first crystalline phosphate and the second crystalline phosphate contained in the surface region is 0% or more and 30% or less, and the combined area percentage of the first crystalline phosphate and the second crystalline phosphate contained in the interior region is 3% or more and 50% or less.

[0159] When the phosphoric acid coating contains more first crystalline phosphate and second crystalline phosphate in the inner region compared to the surface region, and the total area ratio of the first crystalline phosphate and second crystalline phosphate is within the above range, the overall elasticity of the phosphoric acid coating is further preferably increased, and the coating adhesion is further preferably improved.

[0160] Furthermore, in the directional electromagnetic steel sheet according to this embodiment, it is preferable that, when viewed on a cut surface parallel to the thickness direction, the first area ratio is larger than the first area ratio when the aforementioned internal region 2 is divided into a first internal region in contact with the oxide film and a second internal region not in contact with the oxide film, and the percentage obtained by dividing the area ratio of the second crystalline phosphate contained in the first internal region by the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the first internal region is used as the first area ratio, and the percentage obtained by dividing the area ratio of the second crystalline phosphate contained in the second internal region by the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the second internal region is used as the second area ratio.

[0161] If the second inner region contains more second-crystal phosphates than the first inner region, the overall elasticity of the phosphate coating is preferably increased, and the stress under bending stress is preferably mitigated. As a result, the phosphate coating is believed to become more difficult to peel off.

[0162] For example, preferably, the first area ratio is 0% or more and 70% or less, and the second area ratio is 50% or more and 100% or less.

[0163] When the second internal region contains more second crystalline phosphates than the first internal region and the second area ratio is within the range described above, the overall elasticity of the phosphate coating is further preferably increased, and the coating adhesion is further preferably improved.

[0164] Figure 2 This is a cross-sectional schematic diagram showing the layered structure of the directional electromagnetic steel plate according to a preferred embodiment of the present invention. Figure 2 Examples include the surface region 32, the interior region 31, the first interior region 31a, and the second interior region 31b of the phosphate-based coating 3 (insulating coating 3).

[0165] Furthermore, in the directional electromagnetic steel sheet involved in this embodiment, it is preferable that the average equivalent circle diameter of the second crystalline phosphate is 5 nm or more and 300 nm or less.

[0166] When the equivalent circle diameter of the second crystalline phosphate is within the above-mentioned range, the effect of the second crystalline phosphate on the film adhesion is preferably increased. As a result, the film adhesion is preferably improved. The equivalent circle diameter of the second crystalline phosphate is preferably 20 nm or more, and preferably 220 nm or less.

[0167] The presence or absence of V, W, Zr, Co, or Mo in the aforementioned crystalline phosphates, the location and area fraction of the crystalline phosphates, and the equivalent circle diameter of the crystalline phosphates can be determined using SEM-EDS or TEM-EDS. Details of their determination methods will be described later.

[0168] Next, the intermediate layer, namely the oxide film, of the directional electromagnetic steel plate involved in this embodiment will be described.

[0169] (Regarding oxide films)

[0170] In the layered structure of directional electromagnetic steel sheets, the oxide film is located between the phosphate-based coating and the base steel sheet. This oxide film is not a magnesium olivine coating, but a Si-based oxide film, which has the function of ensuring a tight bond between the phosphate-based coating and the base steel sheet.

[0171] First, the composition of the oxide film coating will be explained.

[0172] In the directional electromagnetic steel sheet according to this embodiment, the oxide film comprises the basic elements as a coating component. Furthermore, optional elements may be included in addition to the basic elements as needed. Moreover, it is preferable that the remaining portions of the basic elements and optional elements contain impurities.

[0173] Specifically, the oxide film, as a basic element, only needs to meet the following requirements: Si content: above 20 atomic% and below 70 atomic% and O content: above 30 atomic% and below 80 atomic%.

[0174] In addition, the oxide film can be included as an optional element of the constituent elements of the base steel plate, and its total content can meet the requirement of more than 0.1 atomic% and less than 20 atomic%.

[0175] In addition, the oxide film, as an impurity, only needs to meet the following requirements: Mg content: less than 20 atomic%; P content: less than 5 atomic%; and Fe content: less than 20 atomic%.

[0176] Typically, in directional electromagnetic steel sheets, a magnesium olivine coating (a coating mainly composed of Mg2SiO4) is formed by coating a decarburized annealed sheet with an annealing separating agent with MgO as the main component for final annealing, thereby serving as an intermediate layer.

[0177] If the forsterite coating is formed, the adhesion of the coating is ensured by the anchoring effect created by the unevenness of the interface between the forsterite coating and the base steel plate. However, the unevenness of this interface becomes an obstacle to the movement of magnetic domain walls when the directional electromagnet is magnetized, negatively affecting the iron loss characteristics.

[0178] In the directional electromagnetic steel sheet according to this embodiment, the aim is to avoid the presence of a forsterite coating, thereby smoothing the interface between the intermediate layer and the base steel sheet. Furthermore, to improve the adhesion of the coating while ensuring a smooth interface, conditions (I) to (III) are satisfied to form a first crystalline phosphate and a second crystalline phosphate in the phosphate-based coating. As shown in condition (I), the intermediate layer is not a forsterite coating and needs to be controlled to be a Si-based oxide film.

[0179] Therefore, as described above, the Mg content in the oxide film (intermediate layer) of the directional electromagnetic steel sheet according to this embodiment is limited to less than 20 atomic percent. The Mg content is preferably 15 atomic percent or less, and more preferably 10 atomic percent or less. Furthermore, details regarding the control conditions for forming the oxide film (intermediate layer) without forming a magnesium olivine coating will be described later.

[0180] The Si and O elements, which are the basic elements of the oxide film, originate from the constituent elements of the base steel sheet and the oxidation reaction during oxide film formation. Furthermore, Mg, P, and Fe are impurities in the oxide film, originating from raw materials, elements introduced from the manufacturing environment, or elements diffused from the base steel sheet or phosphate-based coatings. There is no particular limitation on the lower limit of impurity content; lower is preferred, therefore, 0% is also acceptable.

[0181] Furthermore, for the directional electromagnetic steel sheet involved in this embodiment, as the coating composition (average coating composition) of the oxide film, the Si content is preferably more than 26 atoms, preferably less than 44 atoms, the O content is preferably more than 38 atoms, preferably less than 68 atoms, the Mg content is preferably less than 20 atoms, the P content is preferably less than 5 atoms, or the Fe content is preferably less than 20 atoms.

[0182] Similar to the composition of phosphate-based coatings, the composition of oxide coatings can be analyzed by examining the cross-section using SEM-EDS or TEM-EDS. Details of the methods for determining the coating composition will be described later.

[0183] Next, the thickness of the oxide film will be explained.

[0184] In the directional electromagnetic steel sheet of this embodiment, when viewed on a cut surface parallel to the thickness direction, the average thickness of the oxide film is 2 nm or more and 500 nm or less.

[0185] If the average thickness of the oxide film is less than 2 nm, the thermal stress mitigation effect is not fully realized. Therefore, the average thickness is preferably 2 nm or more, and more preferably 5 nm or more.

[0186] On the other hand, if the average thickness of the oxide film exceeds 500 nm, the thickness becomes uneven, and defects such as voids and cracks are generated within the layer. Therefore, the average thickness is preferably 500 nm or less, and more preferably 400 nm or less.

[0187] Similar to the coating composition of phosphate-based coatings, the average film thickness of oxide films can be determined by line analysis of the cross-section using SEM-EDS or TEM-EDS. Details of the method for determining the average film thickness will be described later.

[0188] Next, the base steel plate of the directional electromagnetic steel plate involved in this embodiment will be described.

[0189] (Regarding the base material, steel plate)

[0190] The base material steel plate is the substrate of directional electromagnetic steel plate, which is silicon steel plate. For this silicon steel plate, the Si content is above 0.8% by mass and below 7.0% by mass, and the crystal orientation is controlled to be {110}<001> orientation (Gaussian orientation).

[0191] Here, the {110}<001> orientation means that the {110} plane of the crystal is arranged parallel to the rolling plane, and the <001> axis of the crystal is arranged parallel to the rolling direction.

[0192] First, the steel composition of silicon steel sheets will be explained.

[0193] The steel composition of the silicon steel sheet is not directly related to the presence of the first and second crystalline phosphates in the phosphate-based coating. Therefore, the steel composition of the silicon steel sheet in the directional electromagnetic steel sheet according to this embodiment is not particularly limited. However, the preferred steel composition of the silicon steel sheet as a directional electromagnetic steel sheet will be described below. Hereinafter, the percentages in the steel composition of the silicon steel sheet refer to mass percentages.

[0194] Preferably, the silicon steel sheet contains basic elements as its chemical composition, and optionally contains optional elements as needed, with the remainder containing Fe and impurities.

[0195] Specifically, silicon steel sheets contain, by mass percent, the following chemical composition:

[0196] Si: 0.8% or more and 7.0% or less;

[0197] Mn: 0 or more and less than 1.00%;

[0198] Cr: 0% or more and 0.30% or less;

[0199] Cu: 0% or more and 0.40% or less;

[0200] P: Above 0 and below 0.50%;

[0201] Sn: 0% or more and 0.30% or less;

[0202] Sb: 0 or more and less than 0.30%;

[0203] Ni: 0% or more and 1.00% or less;

[0204] B: 0 or higher and less than 0.008%;

[0205] V: 0 or higher and 0.15% or lower;

[0206] Nb: 0% or more and 0.2% or less;

[0207] Mo: above 0 and below 0.10%;

[0208] Ti: 0 or higher and less than 0.015%;

[0209] Bi: 0 or more and less than 0.010%;

[0210] Al: 0 or more and less than 0.005%;

[0211] C: 0 or higher and less than 0.005%;

[0212] N: 0 or more and less than 0.005%;

[0213] S: 0 or higher and less than 0.005%;

[0214] Se: 0 or more and less than 0.005%,

[0215] The remaining portion should contain Fe and impurities.

[0216] In this embodiment, silicon steel sheet can be used as a basic element (main alloying element) containing Si.

[0217] Si: 0.8% or more and 7.0% or less

[0218] Silicon (Si) is an element that, as a chemical component of silicon steel sheets, is effective in increasing electrical resistance and reducing iron loss. If the Si content exceeds 7.0%, the material may become prone to cracking during cold rolling, making it difficult to roll. On the other hand, if the Si content is below 0.8%, the electrical resistance may decrease, leading to increased iron loss in the finished product. Therefore, Si can be present in a range of 0.8% to 7.0%. The lower limit of the Si content is preferably 2.0%, more preferably 2.5%, and even more preferably 2.8%. The upper limit of the Si content is preferably 5.0%, more preferably 3.5%.

[0219] In this embodiment, the silicon steel sheet may also contain impurities. Furthermore, "impurities" refers to substances that are introduced into the steel during industrial manufacturing from raw materials such as ore, waste, or from the manufacturing environment.

[0220] Furthermore, in this embodiment, the silicon steel sheet may contain optional elements in addition to the basic elements and impurities described above. For example, instead of Fe, which is part of the remaining portion described above, Mn, Cr, Cu, P, Sn, Sb, Ni, B, V, Nb, Mo, Ti, Bi, Al, C, N, S, and Se may be included as optional elements. These optional elements can be included according to their purpose. Therefore, there is no need to limit the lower limit value of these optional elements, and the lower limit value can also be 0%. Moreover, even if these optional elements are included as impurities, the above-mentioned effects will not be impaired.

[0221] Mn: 0 or more and less than 1.00%

[0222] Similar to Si, Mn (manganese) is an effective element for increasing electrical resistance and reducing iron loss. Furthermore, it functions as an inhibitor when combined with S or Se. Therefore, Mn can be present in the range of 1.00% or less. The lower limit of Mn content is preferably 0.05%, more preferably 0.08%, and even more preferably 0.09%. The upper limit of Mn content is preferably 0.50%, more preferably 0.20%.

[0223] Cr: 0% or more and less than 0.30%

[0224] Similar to Si, Cr (chromium) is an effective element for increasing electrical resistance and reducing iron loss. Therefore, Cr can be present in the range of 0.30% or less. The lower limit of Cr content is preferably 0.02%, more preferably 0.05%. The upper limit of Cr content is preferably 0.20%, more preferably 0.12%.

[0225] Cu: 0% or more and 0.40% or less

[0226] Copper (Cu) is also an effective element for increasing electrical resistance and reducing iron loss. Therefore, Cu can be contained in the range of 0.40% or less. If the Cu content exceeds 0.40%, it can sometimes lead to saturation of the iron loss reduction effect and become a cause of surface defects such as "copper scars" during hot rolling. The lower limit of Cu content is preferably 0.05%, more preferably 0.10%. The upper limit of Cu content is preferably 0.30%, more preferably 0.20%.

[0227] P: Above 0 and below 0.50%

[0228] Phosphorus (P) is also an effective element for increasing electrical resistance and reducing iron loss. Therefore, it can be present in the range of 0.50% or less. If the P content exceeds 0.50%, the rollability of silicon steel sheets may sometimes become problematic. The lower limit of the P content is preferably 0.005%, more preferably 0.01%. The upper limit of the P content is preferably 0.20%, more preferably 0.15%.

[0229] Sn: 0 or more and less than 0.30%

[0230] Sb: 0 or higher and 0.30% or lower

[0231] Sn (tin) and Sb (antimony) are effective elements for stabilizing secondary recrystallization and developing the {110}<001> orientation. Therefore, Sn and Sb can be contained in the range of less than 0.30%. If the content of Sn or Sb exceeds 0.30%, it may have a negative impact on the magnetic properties.

[0232] The lower limit of the Sn content is preferably 0.02%, more preferably 0.05%. The upper limit of the Sn content is preferably 0.15%, more preferably 0.10%.

[0233] The lower limit of Sb content is preferably 0.01%, more preferably 0.03%. The upper limit of Sb content is preferably 0.15%, more preferably 0.10%.

[0234] Ni: 0 or more and less than 1.00%

[0235] Ni (Ni) is also an effective element for increasing electrical resistance and reducing iron loss. Furthermore, Ni is effective in improving magnetic properties by controlling the microstructure of hot-rolled sheets. Therefore, Ni can be contained in the range of 1.00% or less. If the Ni content exceeds 1.00%, secondary recrystallization may become unstable. The lower limit of Ni content is preferably 0.01%, more preferably 0.02%. The upper limit of Ni content is preferably 0.20%, more preferably 0.10%.

[0236] B: 0 or higher and less than 0.008%

[0237] Boron (B) is an element effective as an inhibitor of boron (BN). Therefore, it can be present in amounts up to 0.008%. If the B content exceeds 0.008%, it may negatively affect the magnetic properties. The lower limit of the B content is preferably 0.0005%, more preferably 0.001%. The upper limit of the B content is preferably 0.005%, more preferably 0.003%.

[0238] V: 0 or higher and below 0.15%

[0239] Nb: 0% or higher and 0.2% or lower

[0240] Ti: 0 or higher and less than 0.015%

[0241] Vanadium (V), niobium (Nb), and titanium (Ti) are elements that function effectively as inhibitors when combining with nitrogen (N) and carbon (C). Therefore, V can be present in amounts below 0.15%, Nb in amounts below 0.2%, and Ti in amounts below 0.015%. If these elements remain in the final product (electromagnetic steel sheet), and the V content exceeds 0.15%, the Nb content exceeds 0.2%, or the Ti content exceeds 0.015%, the magnetic properties may be reduced.

[0242] The lower limit of the V content is preferably 0.002%, more preferably 0.01%. The upper limit of the V content is preferably 0.10% or less, more preferably 0.05%.

[0243] The lower limit of Nb content is preferably 0.005%, more preferably 0.02%. The upper limit of Nb content is preferably 0.1%, more preferably 0.08%.

[0244] The lower limit of the Ti content is preferably 0.002%, more preferably 0.004%. The upper limit of the Ti content is preferably 0.010%, more preferably 0.008%.

[0245] Mo: above 0 and below 0.10%

[0246] Mo (molybdenum) is also an effective element for increasing electrical resistance and reducing iron loss. Therefore, it can be contained in the range of 0.10% or less. If the Mo content exceeds 0.10%, the rollability of the steel sheet may sometimes be problematic. The lower limit of the Mo content is preferably 0.005%, more preferably 0.01%. The upper limit of the Mo content is preferably 0.08%, more preferably 0.05%.

[0247] Bi: 0 or more and less than 0.010%

[0248] Bismuth (Bi) is an element effective in stabilizing precipitates such as sulfides and enhancing its function as an inhibitor. Therefore, it can be contained in the range of 0.010% or less. If the Bi content exceeds 0.010%, it may sometimes have a negative impact on magnetic properties. The lower limit of Bi content is preferably 0.001%, more preferably 0.002%. The upper limit of Bi content is preferably 0.008%, more preferably 0.006%.

[0249] Al: 0 or higher and less than 0.005%

[0250] Al (aluminum) is an element effective at inhibiting the combination with nitrogen (N). Therefore, it can be included in the final product, for example, during the slab stage, in the range of 0.01 to 0.065%. However, if Al remains as an impurity in the final product (electromagnetic steel sheet), and the Al content exceeds 0.005%, it can sometimes negatively affect the magnetic properties. Therefore, the Al content in the final product is preferably 0.005% or less. The upper limit of the Al content in the final product is preferably 0.004%, more preferably 0.003%. Furthermore, since the Al content in the final product is an impurity, there is no particular limitation on the lower limit, but the lower the better. However, it is not easy to achieve 0% Al content in the final product industrially; therefore, the lower limit of Al content in the final product can also exceed 0%, or can be 0.0005%. In addition, the Al content indicates the content of acid-soluble Al.

[0251] C: 0 or higher and less than 0.005%

[0252] N: 0 or more and less than 0.005%

[0253] Carbon (C) is an effective element for improving magnetic properties by adjusting the texture of primary recrystallization. Nitrogen (N) is an effective element for inhibiting the binding of elements such as Al and B. Therefore, C may be present in the form of 0.02 to 0.10% before decarburization annealing, for example, during the slab stage. Furthermore, N may be present in the form of 0.01 to 0.05% before final annealing, for example, after nitriding annealing. However, if these elements remain as impurities in the final product, with C and N each exceeding 0.005%, it can sometimes negatively impact magnetic properties. Therefore, the C and N content in the final product is preferably 0.005% or less. The C and N content in the final product is preferably 0.004% or less, more preferably 0.003% or less. Furthermore, the total C and N content in the final product is preferably 0.005% or less. Additionally, since C and N in the final product are impurities, their content is not particularly limited, but lower levels are preferred. However, it is not easy to achieve 0% C and N content in the final product in industrial applications. Therefore, the C and N content in the final product can also exceed 0% or be above 0.0005%.

[0254] S: 0 or higher and less than 0.005%

[0255] Se: 0 or more and less than 0.005%

[0256] Sulfur (S) and selenium (Se) are effective elements in inhibiting the formation of Mn and other elements. Therefore, S and Se can be present in the final product, for example, at a concentration of 0.005% to 0.050%, before final annealing. However, if these elements remain as impurities in the final product, with S and Se each exceeding 0.005%, it can sometimes negatively impact magnetic properties. Therefore, the final product preferably contains 0.005% or less of S and Se. More preferably, the final product contains 0.004% or less of S and Se, and more preferably 0.003% or less. Furthermore, the total content of S and Se in the final product is preferably 0.005% or less. Additionally, since S and Se in the final product are impurities, their content is not particularly limited, but lower levels are preferred. However, achieving 0% S and Se content in the final product is not industrially feasible; therefore, the content of S and Se in the final product can exceed 0% or be 0.0005% or more.

[0257] In this embodiment, the silicon steel sheet may also contain, by mass percent, the following elements: Mn: 0.05% or more and 1.00% or less; Cr: 0.02% or more and 0.30% or less; Cu: 0.05% or more and 0.40% or less; P: 0.005% or more and 0.50% or less; Sn: 0.02% or more and 0.30% or less; Sb: 0.01% or more and 0.30% or less; Ni: At least one of the following groups: 0.01% or more and 1.00% or less; B: 0.0005% or more and 0.008% or less; V: 0.002% or more and 0.15% or less; Nb: 0.005% or more and 0.2% or less; Mo: 0.005% or more and 0.10% or less; Ti: 0.002% or more and 0.015% or less; and Bi: 0.001% or more and 0.010% or less.

[0258] The chemical composition of silicon steel sheets can be determined using conventional analytical methods. Details of the methods for determining the steel composition will be described later.

[0259] Next, we will describe the other characteristics of silicon steel sheets.

[0260] In the directional electromagnetic steel sheet of this embodiment, the silicon steel sheet preferably has a texture developed in the {110}<001> orientation. By controlling the silicon steel sheet to have a Gaussian orientation, the magnetic properties are preferably improved.

[0261] Furthermore, there are no particular restrictions on the thickness of the silicon steel sheet, but to further reduce iron loss, the average thickness is preferably 0.35 mm or less, and more preferably 0.30 mm or less. Additionally, there are no particular restrictions on the lower limit of the silicon steel sheet thickness, but from the viewpoint of manufacturing equipment and cost, 0.10 mm is also acceptable.

[0262] Furthermore, the surface roughness (roughness of the interface between the intermediate layer and the base steel sheet) of the silicon steel sheet is preferably smooth. For example, the surface roughness of the silicon steel sheet, expressed as an arithmetic mean roughness (Ra), is preferably 0.5 μm or less, more preferably 0.3 μm or less. Additionally, there is no particular limitation on the lower limit of the arithmetic mean roughness (Ra) of the base steel sheet, but if it is 0.1 μm or less, the iron loss improvement effect saturates; therefore, a lower limit of 0.1 μm is also acceptable.

[0263] In the directional electromagnetic steel sheet according to this embodiment, due to the above-described characteristics, the coating adhesion is excellent even without a forsterite coating. Therefore, the iron loss characteristics are preferably improved.

[0264] The following describes in detail the methods for measuring the various characteristics of the aforementioned directional electromagnetic steel sheet.

[0265] (Methods for determining technical characteristics)

[0266] First, the layer structure of the aforementioned directional electromagnetic steel sheet can be determined, for example, by the following method.

[0267] Test pieces are cut from directional electromagnetic steel sheets, and their layer structure is observed using scanning electron microscopy (SEM) or transmission electron microscopy (TEM). For example, layers with a thickness greater than 300 nm are observed using SEM, and layers with a thickness less than 300 nm are observed using TEM.

[0268] Specifically, firstly, a test piece is cut with the cutting direction parallel to the plate thickness direction (more specifically, the test piece is cut with the cutting surface parallel to the plate thickness direction and perpendicular to the rolling direction). The cross-sectional structure of this cut surface is observed using SEM at the magnification of each layer entering the field of view. For example, if observed using a composite electron image (COMPO image), the types of layers constituting the cross-sectional structure can be deduced. For example, in a COMPO image, it can be determined that the base steel plate is light-colored, the intermediate layer is dark-colored, and the insulating coating is intermediate-colored.

[0269] To determine the layers in the cross-sectional structure, SEM-EDS was used for linear analysis along the thickness direction to quantitatively analyze the chemical composition of each layer. For example, the elements to be quantitatively analyzed were set to five: Fe, P, Si, O, and Mg. The apparatus used was not particularly limited; for example, an SEM (Hitachi High Technologies NB5000), an EDS (Bruker AXS XFlash(r)6│30), and EDS analysis software (Bruker AXS ESPRIT 1.9) were all acceptable.

[0270] Based on the observation results obtained from COMPO images and the quantitative analysis results from SEM-EDS, if a layered region exists at the deepest position in the thickness direction and has an Fe content of 80 atomic% or more and an O content of less than 30 atomic% (excluding measurement noise), and the line segment (thickness) on the scan line corresponding to this region is 300 nm or more, then this region is identified as the base steel plate, and the regions other than the base steel plate are identified as the intermediate layer and the insulating coating.

[0271] Regarding the areas identified above, excluding the base steel plate, based on observations from COMPO images and quantitative analysis results from SEM-EDS, if an area has an Fe content of less than 80 atomic% (excluding measurement noise), a P content of 5 atomic% or more, a Si content of 5 atomic% or more, and an O content of 30 atomic% or more, and the line segment (thickness) on the scan line corresponding to that area is 300 nm or more, then that area is identified as a phosphate-based coating. In addition to the four elements mentioned above used to determine phosphate-based coatings, the phosphate-based coating may also contain optional elements derived from phosphates, such as aluminum, magnesium, nickel, and manganese.

[0272] When determining the regions that constitute phosphate-based coatings, precipitates, inclusions, and pores within the coating are not considered. Instead, regions that meet the quantitative analysis results as the parent phase are identified as phosphate-based coatings. For example, if precipitates, inclusions, and pores are confirmed to exist on the scan lines of the online analysis based on COMPO images and line analysis results, these regions are not considered, and the determination is made based on the quantitative analysis results as the parent phase. Furthermore, precipitates, inclusions, and pores can be distinguished from the parent phase in COMPO images by contrast, and in terms of quantitative analysis results, they can be distinguished from the parent phase by the amount of constituent elements present. Additionally, when determining phosphate-based coatings, it is preferable to determine them by the locations on the scan lines of the online analysis that do not contain precipitates, inclusions, or pores.

[0273] If the region is other than the base steel plate and phosphate coating identified above, and the line segment (thickness) on the scan line corresponding to the region is 300 nm or more, then the region is identified as the intermediate layer.

[0274] The intermediate layer should meet the following requirements: Fe content less than 80 atomic%, P content less than 5 atomic%, Si content more than 20 atomic%, and O content more than 30 atomic%. Furthermore, if the intermediate layer is not a forsterite coating but an oxide film mainly composed of silicon oxide, then the Mg content of the intermediate layer should be less than 20 atomic%. Additionally, the quantitative analysis results of the intermediate layer are the quantitative analysis results of the parent phase, excluding the analysis results of precipitates, inclusions, and pores contained in the intermediate layer. Preferably, the intermediate layer is determined by the location on the online analysis scan line that does not contain precipitates, inclusions, and pores.

[0275] By changing the observation field, the determination and thickness of each layer were carried out at more than 5 locations using the aforementioned COMPO image observation and SEM-EDS quantitative analysis. For the thickness of each layer determined at more than 5 locations, the average value was calculated from the values ​​excluding the maximum and minimum values, and this average value was taken as the average film thickness of each layer.

[0276] In addition, if there is a layer with a line segment (thickness) of less than 300 nm on the scan line of the line analysis in at least one of the above 5 or more observation fields, the corresponding layer is observed in detail by TEM, and the corresponding layer is identified and its thickness is measured by TEM.

[0277] A test piece containing the layers that should be observed in detail using TEM is cut using FIB (Focused Ion Beam) with the cutting direction parallel to the thickness direction of the plate (specifically, the test piece is cut with the cutting surface parallel to the thickness direction and perpendicular to the rolling direction). The cross-sectional structure of the cut surface is observed using STEM (Scanning-TEM) at the magnification of the corresponding layers entering the observation field of view (bright-field image). When no layers enter the observation field of view, the cross-sectional structure is observed in multiple successive fields of view.

[0278] To determine the layers in the cross-sectional structure, TEM-EDS was used for line analysis along the thickness direction to quantitatively analyze the chemical composition of each layer. The five elements selected for quantitative analysis were Fe, P, Si, O, and Mg. The apparatus used was not particularly limited; for example, a TEM (JEM-2100F manufactured by JEOL Ltd.), an EDS (JED-2300T manufactured by JEOL Ltd.), and EDS analysis software (Analysis Station manufactured by JEOL Ltd.) could be used.

[0279] Based on the bright-field image observation results obtained by TEM and the quantitative analysis results of TEM-EDS, each layer was identified, and the average film thickness of each layer was measured. The method for identifying each layer using TEM and the method for measuring the average film thickness of each layer can be performed according to the method for using SEM described above.

[0280] Furthermore, when the thickness of each layer determined by TEM is 5 nm or less, a TEM with spherical aberration correction is preferred from the viewpoint of spatial resolution. Alternatively, when the thickness of each layer is 5 nm or less, point analysis can be performed along the thickness direction at intervals of, for example, 2 nm or less, to measure the line segment (film thickness) of each layer, and this line segment can be used as the film thickness of each layer. For example, if a TEM with spherical aberration correction is used, EDS analysis can be performed with a spatial resolution of approximately 0.2 nm.

[0281] Furthermore, in the directional electromagnetic steel sheet involved in this embodiment, there is an oxide film in contact with the base steel sheet, and a phosphate coating in contact with the oxide film. Therefore, when each layer is determined by the above-mentioned judgment criteria, there are no layers other than the base steel sheet, the oxide film, and the phosphate coating.

[0282] For the composition of phosphate-based coatings and oxide films, detailed quantitative analysis can be performed using SEM-EDS or TEM-EDS within the regions defined above. This quantitative analysis can be conducted at multiple locations within the target region using line or point analysis. Furthermore, when quantitatively analyzing the coating composition, the elements to be analyzed can be set not only to Fe, P, Si, O, and Mg, but to all elements to be quantitatively analyzed. Additionally, the average composition of the phosphate-based coatings and oxide films can be calculated separately within the defined regions defined above.

[0283] Next, whether the phosphoric acid coating identified above contains the first crystalline phosphate corresponding to the crystal structure of Fe2P2O7 and the second crystalline phosphate corresponding to the crystal structure of Fe7(P2O7)4 can be determined by the following method.

[0284] Based on the above determination of the phosphate coating, a test piece containing the phosphate coating was cut by FIB processing in such a way that the cutting direction was parallel to the plate thickness direction (more specifically, the test piece was cut in such a way that the cutting surface was parallel to the plate thickness direction and perpendicular to the rolling direction). The cross-sectional structure of the cut surface was observed by TEM at a magnification that brought the phosphate coating into the field of view.

[0285] For observing phosphate coatings in the field of view, a wide-area electron beam diffraction is performed with the electron beam diameter set to the smaller of 1 / 10 or 200 nm of the phosphate coating. The presence of a certain crystalline phase in the electron beam irradiation area is then confirmed based on the electron beam diffraction pattern.

[0286] If the presence of a crystalline phase in the aforementioned electron beam diffraction pattern can be confirmed, the crystalline phase of the target is identified by bright-field imaging, and point analysis is performed on the crystalline phase using TEM-EDS. As a result of the point analysis performed by TEM-EDS, if the chemical composition of the target crystalline phase is set to a total content of Fe, P, and O of 70 atomic% or more and 100 atomic% or less, and Si of 10 atomic% or less, then it can be determined to be a crystalline phase and a phosphorus-containing phase. Therefore, the crystalline phase is determined to be a crystalline phosphate.

[0287] Furthermore, as needed, for the crystalline phase that is the object described above, electron beam diffraction is performed by focusing the electron beam in a manner that allows obtaining information solely from the crystalline phase of the object, and the crystal structure of the crystalline phase that is the object is identified based on the electron beam diffraction pattern. This identification can be performed using a PDF (Powder Diffraction File) from ICDD (International Centre for Diffraction Data).

[0288] Based on the above TEM-EDS spot analysis results and electron beam diffraction results, it can be determined whether the crystalline phase is the first crystalline phosphate of Fe2P2O7 structure or the second crystalline phosphate of Fe7(P2O7)4 structure.

[0289] Furthermore, the determination of whether the crystalline phase has an Fe2P2O7 structure can be performed based on PDF: No. 01-072-1516. Additionally, the determination of whether the crystalline phase has an Fe7(P2O7)4 structure can be performed based on PDF: No. 01-079-2259. Furthermore, when determining the crystalline phase based on the aforementioned PDFs, the allowable error for the interplanar spacing should be ±5%, and the allowable error for the interplanar angle should be ±3°.

[0290] Along the thickness direction of the plate, from the interface between the phosphate-based coating and the oxide film toward the outermost surface, the presence of a certain crystalline phase in the electron beam irradiation region is confirmed sequentially in a manner that does not create gaps (wide-area electron beam irradiation). The electron beam diffraction pattern is repeatedly confirmed until it is confirmed that there is no crystalline phase in the electron beam irradiation region.

[0291] By repeatedly irradiating the film with an electron beam along its thickness, it is possible to determine whether crystalline phosphates are present in the phosphate-based coating, and to identify the regions in which crystalline phosphates are present. For example, it is possible to determine whether crystalline phosphates are present in either the internal or surface regions of the phosphate-based coating.

[0292] The area ratio of crystalline phosphates can be calculated as follows. For example, by identifying the first and second crystalline phosphates using the method described above, the identified crystalline phosphates and the parent phase are binarized, and the area ratio of the crystalline phosphates is calculated using image analysis. For example, the area ratio of the first crystalline phosphates contained in the surface region is the percentage obtained by dividing the total area of ​​the first crystalline phosphates by the total area of ​​the surface region. Alternatively, the binarization of the image used for image analysis can also be based on the identification results of the crystalline phosphates described above, and the image can be binarized by manually coloring the tissue photograph with crystalline phosphates.

[0293] Furthermore, crystalline phosphates were observed as black precipitates. Therefore, the black precipitates and the parent phase can be binarized, and the area ratio of the crystalline phosphates can be determined through image analysis. This area ratio becomes the combined area ratio of the first and second crystalline phosphates contained in the field of view. Therefore, the ratio of the presence of the first to the second crystalline phosphates (area ratio) can be predetermined, and the area ratios of the first and second crystalline phosphates can be determined based on this ratio and the aforementioned combined area ratio.

[0294] Furthermore, in phosphoric acid-based coatings, whether V, W, Zr, Co, or Mo is contained in the second crystalline phosphate can be confirmed as follows. For example, the elements contained in the second crystalline phosphate with the Fe7(P2O7)4 structure identified above can be qualitatively analyzed using TEM-EDS. Since the second crystalline phosphate is thermally unstable as a precipitate, quantitative analysis is difficult; however, the qualitative analysis described above can confirm whether the second crystalline phosphate contains V, W, Zr, Co, or Mo.

[0295] Furthermore, the equivalent circle diameter of the second crystalline phosphate can be determined as follows. For example, in each of five or more observation fields, at least five equivalent circle diameters of the crystalline phosphate are determined through image analysis. The maximum and minimum values ​​are removed from the determined equivalent circle diameters, and the average value is calculated. This average value is used as the average equivalent circle diameter of the crystalline phosphate. Alternatively, the binarization of the image used for image analysis can also be based on the identification results of the crystalline phosphate described above, and the image can be binarized by manually coloring the tissue photograph with the crystalline phosphate.

[0296] Next, for example, the steel composition of the silicon steel sheet described above can be observed using the following method.

[0297] For example, the steel composition can be determined using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Additionally, C and S can be determined using combustion-infrared absorption spectroscopy, N using inert gas melting-thermal conductivity spectroscopy, and O using inert gas melting-non-dispersive infrared absorption spectroscopy.

[0298] In addition, when the directional electromagnetic steel plate used as the test sample has an oxide film or a phosphate coating on its surface, the steel composition is measured after removing these coatings by the following method.

[0299] For example, a coated directional electromagnetic steel sheet can be immersed in a high-temperature alkaline solution. Specifically, after immersion in a sodium hydroxide aqueous solution of 20% by mass NaOH + 80% by mass H2O at 80°C for 20 minutes, it is washed with water and dried to remove the coating (oxide film, phosphate coating) from the silicon steel sheet. Furthermore, the immersion time in the aforementioned sodium hydroxide aqueous solution can be adjusted according to the thickness of the coating on the silicon steel sheet.

[0300] The texture of silicon steel sheets can be determined using conventional analytical methods. For example, it can be determined using X-ray diffraction (Laué method). The Laue method involves irradiating the steel sheet with an X-ray beam perpendicularly and analyzing the transmitted or reflected diffraction spots. By analyzing the diffraction spots, the crystal orientation of the irradiated areas can be identified. By changing the irradiation position and analyzing the diffraction spots at multiple locations, the crystal orientation distribution at each irradiation location can be determined. The Laue method is suitable for determining the crystal orientation of metal structures with coarse grains.

[0301] The surface roughness of silicon steel sheets (the roughness of the interface between the intermediate layer and the base steel sheet) can be measured using a contact surface roughness meter or a non-contact laser surface roughness meter. When the surface of the silicon steel sheet has an oxide film or a phosphate coating, the surface roughness is measured after removing these coatings using the methods described above.

[0302] Next, the method for manufacturing the directional electromagnetic steel sheet involved in this embodiment will be described.

[0303] (Regarding the manufacturing method)

[0304] Figure 3 This is a flowchart illustrating a method for manufacturing a directional electromagnetic steel sheet according to one embodiment of the present invention. Figure 3 In the diagram, the steps enclosed by solid lines are required steps, while the steps enclosed by dashed lines are optional steps.

[0305] Furthermore, the method for manufacturing the directional electromagnetic steel sheet according to this embodiment is not limited to the method described below. The following manufacturing method is an example for manufacturing the directional electromagnetic steel sheet according to this embodiment.

[0306] The method for manufacturing directional electromagnetic steel plates according to this embodiment is a method for manufacturing directional electromagnetic steel plates without magnesium olivine coating, which includes the following steps.

[0307] (i) A hot rolling process in which a steel billet having a specified chemical composition is hot rolled to obtain a hot-rolled steel sheet.

[0308] (ii) A cold rolling process in which the above-mentioned hot-rolled steel sheet is subjected to one cold rolling or two or more cold rolling processes with intermediate annealing to obtain a cold-rolled steel sheet.

[0309] (iii) The decarburization annealing process of the above-mentioned cold-rolled steel sheet to obtain a decarburized annealed sheet.

[0310] (iv) The annealing separating agent coating process of applying an annealing separating agent containing Al2O3 and MgO to the above-mentioned decarburized annealed plate and drying it.

[0311] (v) The above-mentioned decarburized annealed plate coated with annealing separating agent is subjected to final annealing to obtain the final annealed plate.

[0312] (vi) Annealing separator removal process: removing excess annealing separator from the surface of the final annealed plate by means of one or both of water washing or acid washing.

[0313] (vii) Insulation film forming process for forming an insulating film on the surface of the final annealed plate.

[0314] Furthermore, the manufacturing method of the directional electromagnetic steel plate involved in this embodiment may also include the following steps.

[0315] (a) Annealing process of hot-rolled steel sheet

[0316] (b) Pickling process for hot-rolled steel sheets

[0317] (c) Domain control process for performing domain control processing

[0318] The following is a detailed explanation of each process.

[0319] <Hot Rolling Process>

[0320] In the hot rolling process, the following steel billet is hot-rolled to obtain a hot-rolled steel sheet, the steel billet containing, in terms of chemical composition by mass%, the following:

[0321] C: Above 0.020% and below 0.10%;

[0322] Si: 0.80% or more and 7.0% or less;

[0323] Mn: ≥0.05% and ≤1.0%;

[0324] The total of S+Se is between 0 and 0.050%.

[0325] Acid-soluble Al: ≥0.010% and ≤0.065%;

[0326] N: ≥0.004% and ≤0.012%;

[0327] Cr: 0% or more and 0.30% or less;

[0328] Cu: 0% or more and 0.40% or less;

[0329] P: Above 0 and below 0.50%;

[0330] Sn: 0% or more and 0.30% or less;

[0331] Sb: 0 or more and less than 0.30%;

[0332] Ni: 0% or more and 1.0% or less;

[0333] B: 0 or higher and less than 0.008%;

[0334] V: 0 or higher and 0.15% or lower;

[0335] Nb: 0 or more and less than 0.20%;

[0336] Mo: above 0 and below 0.10%;

[0337] Ti: 0 or higher and less than 0.015%;

[0338] Bi: 0 or more, less than 0.010%

[0339] The remaining portion contains Fe and impurities.

[0340] In this embodiment, the steel plate after the hot rolling process is referred to as hot-rolled steel plate.

[0341] There are no restrictions on the manufacturing method of steel billets (slabs) used in the hot rolling process. For example, molten steel with a specified chemical composition can be melted and used to manufacture slabs. Slabs can also be manufactured by continuous casting, or by using molten steel to manufacture steel ingots and then cutting the ingots into slabs. In addition, other methods can also be used to manufacture slabs.

[0342] The thickness of the slab is not particularly limited, but is, for example, 150–350 mm. The preferred thickness of the slab is 220–280 mm. Thin slabs with a thickness of 10–70 mm can also be used as slabs.

[0343] First, the rationale for defining the chemical composition of the steel billet will be explained. Hereafter, all percentages related to chemical composition refer to mass percentages.

[0344] C: Above 0.020% and below 0.10%

[0345] Carbon (C) is an element effective in controlling the primary recrystallization structure, but because it negatively affects magnetic properties, it is removed by decarburization annealing before final annealing. If the C content of the billet exceeds 0.10%, the decarburization annealing time becomes longer, and productivity decreases. Therefore, the C content is set to 0.10% or less. Preferably, it is 0.085% or less, and more preferably 0.070% or less.

[0346] The C content is preferred, but considering the productivity in industrial production and the magnetic properties of the product, the practical lower limit of the C content is 0.020%.

[0347] Si: 0.80% or more and 7.0% or less

[0348] Silicon (Si) increases the resistivity of directional electromagnetic steel sheets, thereby reducing iron losses. If the Si content is less than 0.80%, a γ-phase transformation occurs during final annealing, which damages the crystal orientation of the directional electromagnetic steel sheet. Therefore, the Si content is 0.80% or more. The Si content is preferably 2.0% or more, and more preferably 2.50% or more.

[0349] On the other hand, if the Si content exceeds 7.0%, the cold workability decreases, and cracking is more likely to occur during cold rolling. Therefore, the Si content is 7.0% or less. The Si content is preferably 5.0% or less, and more preferably 3.5% or less.

[0350] Mn: ≥0.05% and ≤1.0%

[0351] Manganese (Mn) increases the resistance of directional electromagnetic steel sheets, thereby reducing iron losses. Furthermore, Mn combines with S or Se to form MnS or MnSe, acting as an inhibitor. Secondary recrystallization is stable when the Mn content is in the range of 0.05% to 1.0%. Therefore, the Mn content is 0.05% to 1.0%. The preferred lower limit for the Mn content is 0.08%, more preferably 0.09%. The preferred upper limit for the Mn content is 0.50%, more preferably 0.20%.

[0352] The sum of either or both of S and Se: greater than 0 and less than 0.050%

[0353] S (sulfur) and Se (selenium) are elements that combine with Mn to form MnS or MnSe, which function as inhibitors.

[0354] If either S or Se, or the total of both (S+Se), exceeds 0.050%, the precipitation and dispersion of MnS and MnSe after hot rolling becomes uneven. In this case, the desired secondary recrystallization structure cannot be obtained, the magnetic flux density decreases, or purified MnS remains in the steel, deteriorating hysteresis losses. Therefore, the total content of S and Se should be kept below 0.050%.

[0355] There is no particular limitation on the lower limit of the total content of S and Se; 0% is acceptable. This lower limit can also be 0.003% or 0.005%. When used as an inhibitor, 0.015% or more is preferred.

[0356] Acid-soluble Al (Sol.Al): ≥0.010% and ≤0.065%

[0357] Acid-soluble Al (Sol.Al) is an element that combines with N to form AlN and (Al,Si)N, which function as inhibitors. If the acid-soluble Al content is less than 0.010%, the effect is not fully manifested, and secondary recrystallization is not sufficiently achieved. Therefore, the acid-soluble Al content is 0.010% or more. The acid-soluble Al content is preferably 0.015% or more, and more preferably 0.020% or more.

[0358] On the other hand, if the acid-soluble Al content exceeds 0.065%, the precipitation and dispersion of AlN and (Al, Si)N become uneven, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the acid-soluble Al (Sol.Al) content is kept to be 0.065% or less. The acid-soluble Al content is preferably 0.055% or less, and more preferably 0.050% or less.

[0359] N: ≥0.004% and ≤0.012%

[0360] Nitrogen (N) is an element that combines with Al to form AlN and (Al, Si)N, which function as inhibitors. If the N content is less than 0.004%, the formation of AlN and (Al, Si)N is insufficient; therefore, the N content is 0.004% or more. Preferably, it is 0.006% or more, and more preferably 0.007% or more.

[0361] On the other hand, if the nitrogen content exceeds 0.012%, bubbles (pores) may form in the steel plate. Therefore, the nitrogen content should be kept below 0.012%.

[0362] The chemical composition of the steel billet described above includes the aforementioned elements, with the remainder containing Fe and impurities. However, considering the enhancement of inhibitory function and the influence of compound formation on magnetic properties, one or more optional elements may be included within the following ranges, replacing a portion of the Fe. Examples of optional elements included as replacements for Fe include Cr, Cu, P, Sn, Sb, Ni, B, V, Nb, Mo, Ti, and Bi. However, optional elements may not be included, therefore, the lower limit is 0%. Furthermore, even if these optional elements are included as impurities, the aforementioned effects will not be impaired. Additionally, "impurities" refers to substances that are introduced during the industrial manufacture of steel from the ore used as raw material, waste, or from the manufacturing environment.

[0363] Cr: 0% or more and 0.30% or less

[0364] Cu: 0% or more and 0.40% or less

[0365] P: Above 0 and below 0.50%

[0366] Sn: 0% or more and 0.30% or less

[0367] Sb: 0 or higher and 0.30% or lower

[0368] Ni: 0 or more and less than 1.00%

[0369] B: 0 or higher and less than 0.008%

[0370] V: 0 or higher and less than 0.15%

[0371] Nb: 0% or higher and 0.2% or lower

[0372] Mo: above 0 and below 0.10%

[0373] Ti: 0 or higher and less than 0.015%

[0374] Bi: 0 or more and less than 0.010%,

[0375] These optional elements may be included for a known purpose. There is no need to set a lower limit for the content of these optional elements; the lower limit can be 0%.

[0376] Next, the conditions for hot rolling the above-mentioned steel billets will be explained.

[0377] There are no specific restrictions on the hot rolling conditions. For example, the following conditions may apply.

[0378] The slab is heated before hot rolling. The slab is placed in a known heating furnace or a known soaking furnace for heating. One method is to heat the slab to below 1280°C. By keeping the slab heating temperature below 1280°C, various problems associated with heating at temperatures higher than 1280°C (such as the need for a dedicated heating furnace and a large amount of molten oxide scale) can be avoided. There is no particular limitation on the lower limit of the slab heating temperature. If the heating temperature is too low, hot rolling may become difficult, reducing productivity. Therefore, considering productivity, the heating temperature can be set within a range below 1280°C. A preferred lower limit for the slab heating temperature is 1100°C. A preferred upper limit for the slab heating temperature is 1250°C.

[0379] In addition, as another method, the slab is heated to a high temperature of 1320°C or higher. By heating to a high temperature of 1320°C or higher, AlN and Mn (S, Se) are dissolved and finely precipitated in subsequent processes, thereby enabling stable secondary recrystallization.

[0380] It is also possible to omit the slab heating process itself and start hot rolling after casting and before the slab temperature drops.

[0381] Next, the heated slab is hot-rolled using a hot rolling mill to produce hot-rolled steel sheet. A hot rolling mill may include a roughing mill and a finishing mill located downstream of the roughing mill. The roughing mill has roughing stands arranged in a row. Each roughing stand contains multiple rolls arranged vertically. The finishing mill also has finishing stands arranged in a row. Each finishing stand contains multiple rolls arranged vertically. After the heated steel is rolled in the roughing mill, it is then rolled in the finishing mill to produce hot-rolled steel sheet.

[0382] The finishing temperature in the hot rolling process (the temperature of the steel plate on the exit side of the finishing mill stand where the steel plate is finally pressed down) is, for example, 700–1150°C. Hot-rolled steel plates are manufactured through the above hot rolling process.

[0383] <Hot-rolled sheet annealing process>

[0384] In the hot-rolled steel sheet annealing process, the hot-rolled steel sheet obtained through the hot rolling process is annealed (hot-rolled steel sheet annealing) as needed to obtain a hot-rolled annealed sheet. In this embodiment, the steel sheet after the hot-rolled steel sheet annealing process is referred to as a hot-rolled annealed sheet.

[0385] The purpose of annealing hot-rolled steel sheets is to homogenize the non-uniform microstructure generated during hot rolling as much as possible, control the precipitation (fine precipitation) of AlN as an inhibitor, and control the second phase / solid carbon, etc. The annealing conditions can be selected from known conditions depending on the objective. For example, to homogenize the non-uniform microstructure generated during hot rolling, the hot-rolled steel sheet is held at an annealing temperature (furnace temperature in the hot-rolled steel sheet annealing furnace) of 750–1200°C for 30–600 seconds.

[0386] Annealing of hot-rolled steel sheets is not always necessary. Whether or not to perform the annealing process depends on the required characteristics of the final directional electromagnetic steel sheet and the manufacturing cost.

[0387] <Hot-rolled plate pickling process>

[0388] In the pickling process of hot-rolled steel sheets, pickling is performed on hot-rolled steel sheets after the hot-rolling process, or on hot-rolled annealed sheets after the hot-rolling annealing process, to remove the oxide scale generated on the surface as needed. There are no particular limitations on the pickling conditions; any known conditions may be used.

[0389] <Cold rolling process>

[0390] In the cold rolling process, hot-rolled steel sheets or hot-rolled annealed sheets that have undergone hot rolling, hot-rolled plate annealing, or hot-rolled plate pickling processes are cold-rolled in one or more cold rolling processes, including intermediate annealing, to produce cold-rolled steel sheets. In this embodiment, the steel sheet after the cold rolling process is referred to as a cold-rolled steel sheet.

[0391] The preferred cold rolling ratio in the final cold rolling (the cumulative cold rolling ratio without intermediate annealing or the cumulative cold rolling ratio after intermediate annealing) is preferably 80% or more, more preferably 90% or more. The preferred upper limit for the final cold rolling ratio is 95%.

[0392] Here, the final cold rolling yield (%) is defined as follows.

[0393] Final cold rolling yield (%) = (1 - final thickness of the cold-rolled steel sheet / final thickness of the steel sheet before cold rolling) × 100

[0394] <Decarburization Annealing Process>

[0395] In the decarburizing annealing process, cold-rolled steel sheets manufactured through the cold rolling process are subjected to magnetic domain control treatment as needed, followed by decarburizing annealing to achieve primary recrystallization. Furthermore, in decarburizing annealing, carbon (C) that negatively affects magnetic properties is removed from the steel sheet. In this embodiment, the steel sheet after the decarburizing annealing process is referred to as a decarburized annealed sheet.

[0396] To achieve the above objectives, during decarburization annealing, the oxidation degree (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) is maintained at 0.01–0.15 for 10–600 seconds at an annealing temperature of 750–900°C. Furthermore, the oxidation degree PH2O / PH2 can be defined as the ratio of the partial pressure of water vapor PH2O (atm) to the partial pressure of hydrogen PH2 (atm) in the atmosphere.

[0397] If the oxidation degree (PH2O / PH2) is below 0.01, the decarburization rate slows down, resulting not only in reduced productivity but also in poor decarburization, leading to deterioration of the magnetic properties after final annealing. On the other hand, if it exceeds 0.15, Fe-based oxides are formed, making it difficult to smooth the interface after final annealing.

[0398] Furthermore, if the annealing temperature is below 750°C, the decarburization rate slows down, resulting not only in reduced productivity but also in poor decarburization, leading to magnetic degradation after final annealing. On the other hand, if the annealing temperature exceeds 900°C, the primary recrystallization grain size exceeds the desired size, thus also causing magnetic degradation after final annealing.

[0399] Furthermore, if the holding time is less than 10 seconds, decarburization cannot be sufficiently achieved. On the other hand, if it exceeds 600 seconds, productivity decreases, and the recrystallized grain size exceeds the desired size, resulting in magnetic degradation after final annealing.

[0400] Alternatively, the heating rate during the temperature rise process up to the annealing temperature can be controlled based on the oxidation degree (PH2O / PH2) mentioned above. For example, in the case of heating including induction heating, an average heating rate of 5 to 1000 °C / second is sufficient. Furthermore, in the case of heating including electrical heating, an average heating rate of 5 to 3000 °C / second is sufficient.

[0401] Furthermore, in the decarburization annealing process, annealing and nitriding treatment to nitrid the cold-rolled steel sheet can be further performed in an ammonia-containing atmosphere at any one or more stages before, during, or after the aforementioned holding process. When the slab heating temperature is low, it is preferable that the decarburization annealing process includes nitriding treatment. By further performing nitriding treatment in the decarburization annealing process, inhibitors such as AlN and (Al,Si)N are generated until secondary recrystallization in the final annealing process, thus enabling stable secondary recrystallization.

[0402] There are no particular limitations on the conditions for nitriding treatment, but it is preferable to perform nitriding treatment with an increase of 0.003% or more, more preferably 0.005% or more, and even more preferably 0.007% or more in nitrogen content. If the nitrogen (N) content is 0.030% or more, the effect will saturate, so nitriding treatment can also be performed with a nitrogen content of 0.030% or less.

[0403] There are no particular restrictions on the conditions for nitriding treatment; it can be carried out under known conditions.

[0404] For example, when performing nitriding after decarburization annealing at 750–900°C for 10–600 seconds with an oxidation state (PH2O / PH2) of 0.01–0.15, the cold-rolled steel sheet is not cooled to room temperature; instead, the nitriding process is carried out in an atmosphere containing ammonia during the cooling process. Preferably, the oxidation state (PH2O / PH2) is in the range of 0.0001–0.01 during the cooling process. When performing nitriding during decarburization annealing at 750–900°C for 10–600 seconds with an oxidation state (PH2O / PH2) of 0.01–0.15, ammonia gas can be introduced into the atmosphere with this oxidation state.

[0405] <Annexation Separator Coating Process>

[0406] In the annealing separator coating process, for decarburized annealed plates after the decarburization annealing process (including decarburized annealed plates that have undergone nitriding treatment), after magnetic domain control treatment is performed as needed, an annealing separator containing Al2O3 and MgO is coated and the coated annealing separator is dried.

[0407] When the annealing separating agent contains MgO but not Al2O3, a forsterite coating is formed on the steel plate through the final annealing process. On the other hand, when the annealing separating agent contains Al2O3 but not MgO, mullite (3Al2O3·2SiO2) is formed on the steel plate. This mullite becomes an obstacle to the movement of magnetic domain walls, and therefore, a cause of deterioration in the magnetic properties of the directional electromagnetic steel plate.

[0408] Therefore, in the manufacturing method of the directional electromagnetic steel sheet according to this embodiment, an annealing separating agent with Al2O3 and MgO as its main components is used. By using an annealing separating agent with Al2O3 and MgO as its main components, a steel sheet with a smooth surface without the formation of a forsterite coating can be obtained after final annealing. Furthermore, "Al2O3 and MgO as main components" means that the total content of Al2O3 and MgO in the annealing separating agent is 50% by mass or more.

[0409] The annealing separating agent makes the mass ratio of MgO to Al2O3, i.e., MgO / (MgO+Al2O3), 5-50%, and sets the hydration water content to below 1.5% by mass.

[0410] If the MgO / (MgO+Al2O3) ratio is less than 5%, a large amount of mullite is formed, thus deteriorating iron loss. On the other hand, if it exceeds 50%, forsterite is formed, thus deteriorating iron loss.

[0411] Furthermore, if the hydration content in the annealing separator exceeds 1.5% by mass, secondary recrystallization becomes unstable, or the steel surface is oxidized (forming SiO2) during final annealing, sometimes making surface smoothing difficult. There is no particular limit to the lower limit of hydration content, but for example, 0.1% by mass is acceptable.

[0412] Annealing separating agent is applied to the surface of steel plate through water slurry coating or electrostatic coating. In the annealing separating agent coating process, manganese nitride, iron nitride, chromium nitride, and other nitrides can be added to the annealing separating agent. These nitrides decompose before secondary recrystallization in the final annealing process, thereby nitriding the decarburized steel plate or decarburized nitrided plate.

[0413] <Final Annealing Process>

[0414] The decarburized annealed sheet coated with the aforementioned annealing separating agent is then subjected to final annealing to become a final annealed sheet. By performing final annealing on the decarburized annealed sheet coated with the annealing separating agent, secondary recrystallization occurs, and the crystal orientation aggregates in the {110}<001> orientation. In this embodiment, the steel sheet after the final annealing process is referred to as the final annealed sheet.

[0415] During final annealing, when the atmosphere (furnace atmosphere) contains hydrogen, the oxidation degree (PH2O / PH2) is 0.00010 to 0.2, and when formed by inert gases (nitrogen, argon, etc.) that do not contain hydrogen, the dew point is below 0°C.

[0416] By adjusting the dew point or oxidation level to the range described above according to the atmosphere, secondary recrystallization can be stably achieved, thereby increasing the degree of orientation aggregation.

[0417] In an atmosphere containing hydrogen, if the oxidation degree is below 0.00010, the dense surface silica film formed by decarburization annealing is reduced before the secondary recrystallization in the final annealing, making the secondary recrystallization unstable. On the other hand, if the oxidation degree exceeds 0.2, it promotes the decomposition of inhibitors such as AlN and (Al, Si)N, making the secondary recrystallization unstable. Furthermore, in an atmosphere of inert gas without hydrogen, if the dew point exceeds 0°C, it promotes the decomposition of inhibitors such as AlN and (Al, Si)N, making the secondary recrystallization unstable. There is no particular limitation on the lower limit of the dew point; for example, -30°C is acceptable.

[0418] <Annexation Separator Removal Process>

[0419] In the annealing separator removal process, excess annealing separators, such as unreacted annealing separators that did not react with the steel plate during final annealing, are removed from the surface of the final annealed steel plate (final annealed plate) by means of one or both of water washing or acid washing.

[0420] If the excess annealing separator on the steel plate surface is not removed sufficiently, the duty cycle deteriorates, and the performance of the core is reduced.

[0421] To remove excess annealing separator, in addition to water washing and acid pickling, a scrubber can also be used. By using a scrubber, excess annealing separator that deteriorates wettability during the insulating film formation process can be reliably removed.

[0422] Furthermore, when pickling is performed to remove excess annealing separator, an acidic solution with a volume fraction concentration of less than 20% can be used. For example, it is preferable to use a solution containing one or more of the following in total less than 20% by volume, more preferably less than 10% by volume: sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, chloric acid, aqueous solution of chromium oxide, chromium sulfate, permanganic acid, persulfate, and perphosphoric acid. There is no particular limitation on the lower limit of the volume fraction concentration; for example, 0.1% by volume is sufficient. By using such a solution, excess annealing separator on the surface of the steel plate can be removed efficiently. In addition, the volume fraction can be set as a ratio based on the volume at room temperature.

[0423] Furthermore, when performing pickling, it is preferable to keep the solution temperature between 20 and 80°C. By keeping the solution temperature within this range, excess annealing separating agent on the steel plate surface can be removed efficiently.

[0424] <Insulating film forming process>

[0425] In the insulating coating formation process, an insulating coating is formed after the surface of the final annealed plate, which has undergone magnetic domain control treatment following the annealing separator removal process, as required. In this embodiment, the steel plate after the insulating coating formation process is referred to as a directional electromagnetic steel plate.

[0426] The insulating coating reduces the iron loss of the steel sheet as a single sheet by applying tension to the directional electromagnetic steel sheet, and reduces the iron loss of the core by ensuring electrical insulation between the steel sheets when using directional electromagnetic steel sheets in a stacked manner.

[0427] The insulating coating is formed by the following process: coating the surface of the final annealed plate with a coating solution containing at least one of phosphate or colloidal silica as the main component and free of chromate, baking at 350 to 600°C, and then heat-treating at 800 to 1000°C.

[0428] Furthermore, the above-mentioned coating solution preferably does not contain chromate, but contains:

[0429] A metal phosphate salt selected from one or more metals of Al, Fe, Mg, Mn, Ni and Zn, with a solid content of 100% by mass, is called a metal phosphate salt.

[0430] Phosphate salts selected from one or more metals, namely Co, Mo, V, W and Zr, with a mass fraction of 3 to 20% based on solid content, are called metal diphosphates.

[0431] Colloidal silica, calculated as 35-125 parts by weight of solids; and

[0432] Polymerization aids in the range of 0.3 to 6.0 g / L.

[0433] It does not contain chromates.

[0434] Furthermore, the average primary particle size of the colloidal silica described above is preferably 7 to 30 nm.

[0435] Furthermore, the aforementioned polymerization aid is preferably selected from one or more of the group consisting of nitrous acid, sodium nitrite, potassium nitrite, nitric acid, sodium nitrate, potassium nitrate, chlorite, sodium chlorite, phosphonic acid, sodium phosphonate, triphosphate, sodium triphosphate, polyphosphate, and sodium polyphosphate.

[0436] Furthermore, the above-mentioned coating solution preferably contains one or more of the following: boric acid, sodium borate, titanium dioxide, molybdenum oxide, pigment, and barium titanate.

[0437] If the baking temperature of the insulating film is below 350°C, liquid dripping will occur during the board-through process, resulting in poor appearance and insufficient adhesion. Furthermore, if the baking temperature exceeds 600°C, the heating rate is too rapid, causing only the outermost surface of the insulating film to cure, while the internal curing is delayed, leading to poor film formation and insufficient adhesion. Additionally, if the heat treatment temperature after baking is below 800°C, poor film formation (insufficient curing) results in insufficient film tension. Moreover, temperatures exceeding 1000°C cause phosphate decomposition, also resulting in poor film formation and insufficient adhesion.

[0438] During the heat treatment of the insulating coating, the atmosphere was set to a mixture of 5-100% by volume hydrogen and 95-0% by volume nitrogen, and the oxidation degree of the atmosphere (PH2O / PH2) was set to 0.001-0.15. In addition, the holding time at 800-1000°C during the heat treatment was set to 10-120 seconds.

[0439] After heat treatment under the above conditions, the steel plate is cooled. During cooling after heat treatment, the atmosphere is set to a mixture of hydrogen (5-100% by volume) and nitrogen (95-0% by volume), and the oxidation degree of the atmosphere (PH2O / PH2) is set to 0.001-0.1. Furthermore, during cooling after heat treatment, the average cooling rate within the temperature range of 800-500°C is set to 5-45°C / second.

[0440] In addition, the oxidation degree of the atmosphere during cooling after heat treatment of the insulating coating is changed to a value lower than that of the atmosphere during heat treatment of the insulating coating. However, if the total content of V+W+Zr+Co+Mo in the phosphate-based coating is 0.1 atomic% or more and 10 atomic% or less, it is not necessary to change the oxidation degree of the atmosphere during cooling after heat treatment of the insulating coating to a value lower than that of the atmosphere during heat treatment of the insulating coating.

[0441] The change of the atmosphere and oxidation degree during the heat treatment of the insulating coating, the atmosphere, oxidation degree and cooling rate during cooling after heat treatment, and the oxidation degree of the atmosphere during heat treatment and cooling of the insulating coating falls under condition (III) above. Condition (III) must be met in order to form the first crystalline phosphate and the second crystalline phosphate in the phosphate-based coating.

[0442] <Magnetic domain control process>

[0443] In the manufacturing method of the directional electromagnetic steel sheet according to this embodiment, a magnetic domain control process for performing magnetic domain control processing may be included in any one of the following: between the cold rolling process and the decarburization annealing process (first), between the decarburization annealing process and the annealing separating agent coating process (second), between the annealing separating agent removal process and the insulating film forming process (third), or after the insulating film forming process (fourth).

[0444] By performing magnetic domain control processing, the iron loss of directional electromagnetic steel sheets can be further reduced. When magnetic domain control processing is performed between the cold rolling process and the decarburization annealing process, between the decarburization annealing process and the annealing separating agent coating process, and between the annealing separating agent removal process and the insulating film formation process, linear or dotted grooves extending in a direction intersecting the rolling direction are formed at specified intervals along the rolling direction, thereby narrowing the width of the 180° magnetic domains (subdividing the 180° magnetic domains).

[0445] Furthermore, when performing magnetic domain control processing after the insulating coating formation process, linear or dot-shaped stress-strain portions and grooves extending in a direction intersecting the rolling direction are formed at specified intervals along the rolling direction, thereby narrowing the width of the 180° magnetic domains (subdividing the 180° magnetic domains).

[0446] When forming stress-strain regions, laser beam irradiation or electron beam irradiation can be used. Furthermore, when forming grooves, mechanical groove forming methods based on gears or the like, chemical groove forming methods using electrolytic etching, and thermal groove forming methods based on laser irradiation can be used. If the formation of stress-strain regions or grooves causes damage to the insulating film, resulting in deterioration of insulation properties, the insulating film can be re-formed to repair the damage.

[0447] Example 1

[0448] Next, the effects of one aspect of the present invention will be described in more detail through embodiments. However, the conditions in the embodiments are merely examples used to confirm the feasibility and effects of the present invention, and the present invention is not limited to these single examples. Various conditions can be used in the present invention as long as they do not depart from its spirit and achieve its objectives.

[0449] A steel slab with its chemical composition adjusted to the composition shown in Table 1 was heated to 1150°C for hot rolling to produce a hot-rolled steel sheet with a thickness of 2.6 mm. After hot-rolled annealing as needed, the hot-rolled steel sheet underwent a single cold rolling or multiple cold rolling processes with intermediate annealing to produce a cold-rolled steel sheet with a final thickness of 0.22 mm. The cold-rolled steel sheet was then subjected to decarburization annealing, and nitriding treatment was performed midway through cooling in an atmosphere containing ammonia. Furthermore, known conditions were used from slab heating to nitriding treatment.

[0450] The decarburized annealed plates described above were coated with an annealing separating agent with an Al2O3 to MgO ratio (MgO / (Al2O3+MgO)) and hydration levels as shown in Tables 2-5, and then dried. Furthermore, the combined Al2O3 and MgO content in the annealing separating agent was 50% by mass or more. The decarburized annealed plates coated with the annealing separating agent were then subjected to a final annealing at 1200°C for 20 hours.

[0451] Subsequently, the coating solution for forming the insulating film with adjusted composition was applied and baked, and then further heat-treated under the conditions shown in Tables 2-5. After heat treatment, the film was cooled under the conditions shown in Tables 2-5 to form the insulating film.

[0452] Furthermore, magnetic domain control was performed after the insulating coating formation process. In magnetic domain control, stress-strain regions or grooves were formed using a laser.

[0453] For the obtained oriented electrical steel sheets No. 1 to 73, the chemical composition of the silicon steel sheet, the average coating composition and average film thickness of the intermediate layer, the average coating composition and average film thickness of the insulating coating, and the state of the crystalline phosphide in the insulating coating were measured based on the above method. These results are shown in Tables 1 to 17. In addition, in the tables, "Region 1" represents "Inner Region 1", and "Region 2" represents "Inner Region 2".

[0454] In addition, for the obtained oriented electrical steel sheets No. 1 to 73, the iron loss and coating adhesion were evaluated.

[0455] <Iron loss>

[0456] For the specimens selected from the produced oriented electrical steel sheets, based on JIS C 2550-1:2000, the iron loss W17 / 50 (W / kg) at an excitation magnetic flux density of 1.7 T and a frequency of 50 Hz was measured by the Epstein test. A case where the iron loss W17 / 50 is less than 0.68 W / kg was judged as qualified.

[0457] <Coating adhesion>

[0458] The coating adhesion of the insulating coating was evaluated by winding (bending 180°) the test piece selected from the produced oriented electrical steel sheets around a cylinder with a diameter of 20 mm or 15 mm and the residual area ratio of the coating when bending back. The evaluation of the coating adhesion of the insulating coating was judged by visually observing the presence or absence of peeling of the insulating coating. A case where there is no peeling from the steel sheet and the residual area ratio of the coating is 90% or more was regarded as "very good", 86% or more and less than 90% as "good", 80% or more and less than 86% as "poor", and less than 80% as "bad". A case where the residual area ratio of the coating is 86% or more (the above "very good" or "good") under any one of the test conditions of a diameter of 20 mm or 15 mm was judged as qualified.

[0459] The results are shown in Tables 18 to 21.

[0460] As can be seen from Tables 1 to 21, the product characteristics of the inventive examples among No. 1 to 73 satisfy the scope of the present invention, and the coating adhesion is excellent. In addition, the iron loss characteristics are also excellent.

[0461] In contrast, at least one of the product characteristics of the comparative examples among No. 1 to 73 deviates from the scope of the present invention, and the iron loss and / or coating adhesion is poor.

[0462]

[0463]

[0464]

[0465]

[0466]

[0467]

[0468]

[0469]

[0470]

[0471]

[0472]

[0473]

[0474]

[0475]

[0476]

[0477]

[0478]

[0479] Table 18

[0480]

[0481] Table 19

[0482]

[0483] Table 20

[0484]

[0485] Table 21

[0486]

[0487] Industrial applicability

[0488] According to the above-described solution of the present invention, it is possible to provide a directional electromagnetic steel sheet with excellent adhesion of the insulating coating even without the presence of a magnesium olivine coating. Therefore, it has high industrial applicability.

[0489] Explanation of reference numerals in the attached figures

[0490] 1. Base material: steel plate (silicon steel plate)

[0491] 2. Intermediate layer (oxide film)

[0492] 3. Insulating coating (phosphate-based coating)

[0493] 31 Internal Area

[0494] 31a First internal region

[0495] 31b Second Internal Region

[0496] 32 Surface Area

Claims

1. A directional electromagnetic steel sheet, comprising: a base steel sheet as a silicon steel sheet; an intermediate layer disposed in contact with the silicon steel sheet; and an insulating coating disposed in contact with the intermediate layer. The directional electromagnetic steel plate is characterized in that... The intermediate layer is an oxide film that satisfies the following composition: Si content: ≥20 atomic% and ≤70 atomic%; O content: 30 atomic% or more and 80 atomic% or less; Mg content: less than 20 atomic percent; P content: less than 5 atomic percent; Fe content: less than 20 atomic percent; Furthermore, the average thickness of the oxide film is greater than 2 nm and less than 500 nm. The insulating coating is a phosphoric acid-based coating that satisfies the following composition: P content: 5 atomic% or more and 30 atomic% or less; Si content: 5 atomic% or more and 30 atomic% or less; O content: 30 atomic% or more and 80 atomic% or less; Fe content: ≥1 atomic% and ≤25 atomic%; Cr content: less than 1.0 atomic percent; Al content: 0 atomic% or more and 10 atomic% or less; Mg content: ≥0 atomic% and ≤10 atomic%; Mn content: ≥0 atomic% and ≤10 atomic%; Ni content: 0 atomic% or more and 10 atomic% or less; Zn content: 0 atomic% or more and 10 atomic% or less; The total content of Al + Mg + Mn + Ni + Zn is ≥0.1 atomic% and ≤10 atomic%. V content: 0 atomic% or more and 10 atomic% or less; W content: 0 atomic% or more and 10 atomic% or less; Zr content: 0 atomic% or more and 10 atomic% or less; Co content: 0 atomic% or more and 10 atomic% or less; Mo content: 0 atomic% or more and 10 atomic% or less; The total content of V + W + Zr + Co + Mo is ≥0.1 atomic% and ≤10 atomic%. Furthermore, the average thickness of the phosphate-based coating is greater than 0.1 μm and less than 10 μm. The phosphoric acid coating contains a first crystalline phosphate with a crystal structure corresponding to Fe2P2O7 and a second crystalline phosphate with a crystal structure corresponding to Fe7(P2O7)4. The second crystalline phosphate contains at least one element selected from the group consisting of V, W, Zr, Co, and Mo. When the phosphoric acid coating is divided into an internal region in contact with the oxide film and a surface region not in contact with the oxide film on a cutting surface parallel to the thickness direction along the thickness direction 2, the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the internal region is greater than the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the surface region. When the internal region is divided into a first internal region in contact with the oxide film and a second internal region not in contact with the oxide film along the thickness direction 2 on the cut surface, and the percentage of the area ratio of the second crystalline phosphate contained in the first internal region divided by the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the first internal region is used as the first area ratio, and the percentage of the area ratio of the second crystalline phosphate contained in the second internal region divided by the total area ratio of the first crystalline phosphate and the second crystalline phosphate contained in the second internal region is used as the second area ratio, the second area ratio is greater than the first area ratio.

2. The directional electromagnetic steel plate according to claim 1, characterized in that, The total area percentage of the first crystalline phosphate and the second crystalline phosphate contained in the surface region is 0% or more and 30% or less, and the total area percentage of the first crystalline phosphate and the second crystalline phosphate contained in the interior region is 3% or more and 50% or less.

3. The directional electromagnetic steel plate according to claim 1, characterized in that, The first area ratio is 0% or more and 70% or less, and the second area ratio is 50% or more and 100% or less.

4. The directional electromagnetic steel plate according to any one of claims 1 to 3, characterized in that, The equivalent circle diameter of the second crystalline phosphate has an average value of 5 nm or more and 300 nm or less.

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