Directional electromagnetic steel sheet

Abstract

In this grain-oriented electrical steel sheet, the insulating coating does not contain chromium compounds, the insulating coating has a coating tension of 4.9 MPa or more, and when the potassium intensity of a spectrum obtained by measuring the insulating coating by X-ray fluorescence analysis is defined as P(K) and the sodium intensity of the spectrum is defined as P(Na), the ratio of P(K) to P(Na), P(K) / P(Na), is greater than 13.0 and not greater than 100.

Description

[Technical Field]

[0001] The present invention relates to a grain-oriented electrical steel sheet coated with a chromate-free insulating coating, and in particular to a grain-oriented electrical steel sheet that exhibits little decrease in coating tension of the insulating coating even after long-term storage, despite not containing chromate. This application claims priority based on Japanese Patent Application No. 2024-070781, filed on April 24, 2024, the contents of which are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets are steel sheets that are primarily used as iron cores for transformers, etc. Such grain-oriented electrical steel sheets typically have two surface coating layers: a forsterite layer (also called a primary coating or forsterite coating) that is formed during high-temperature finish annealing, and a phosphate coating (also called a secondary coating or insulating coating) that is formed by applying a treatment solution containing phosphate as the main component and then baking it during heat flattening of the steel sheet.

[0003] Phosphate coatings are required to provide grain-oriented electrical steel sheets with electrical insulation and reduce eddy current loss, thereby improving core loss. Phosphate coatings are also required to have various other properties in addition to insulation, such as corrosion resistance, heat resistance, slipperiness, and adhesion. This is necessary to facilitate various manufacturing processes when grain-oriented electrical steel sheets are processed into iron cores for transformers and other devices. For example, if the heat resistance, slipperiness, and adhesion of a phosphate coating are poor, the phosphate coating may peel off during stress relief annealing in core manufacturing, preventing the phosphate coating from demonstrating its inherent insulating properties or hindering smooth lamination of steel sheets, resulting in poor workability.

[0004] Furthermore, an important characteristic of the insulating coating of grain-oriented electrical steel sheets is the ability to apply tension to the steel sheets. Applying tension to steel sheets facilitates domain wall motion, thereby improving the iron loss of grain-oriented electrical steel sheets. Applying tension can also reduce magnetostriction (one of the main causes of noise in transformers).

[0005] To improve the various properties of grain-oriented electrical steel sheets as described above, specific techniques such as those disclosed in the following Patent Documents 1 to 10 have been researched and developed.

[0006] For example, Patent Document 1 discloses that an insulating coating treatment solution containing a specific composition of aluminum phosphate, chromate, and colloidal silica as its main components is applied to a forsterite coating formed on the surface of a steel sheet after finish annealing, and then baked. The technology disclosed in Patent Document 1 allows an insulating coating with high tensile strength to be formed on the surface of the steel sheet, thereby reducing the iron loss and magnetostriction of the grain-oriented electrical steel sheet.

[0007] Patent Document 2 discloses a method in which a treatment liquid containing ultrafine colloidal silica particles with a particle size of 8 μm or less, primary phosphate, and chromate in specific proportions is applied to a steel sheet and then baked. The technology disclosed in Patent Document 2 makes it possible to maintain the high tensile strength of the insulating coating and further improve the smoothness of the insulating coating.

[0008] Furthermore, Patent Document 3 discloses a technology for forming a high-tensile insulating coating on the surface of a grain-oriented electrical steel sheet by applying a specific amount of insulating coating whose main components are phosphate, chromate, and colloidal silica with a glass transition point of 950°C to 1200°C.

[0009] The techniques disclosed in Patent Documents 1 to 3 above made it possible to form insulating coatings with significantly superior coating properties and improved coating tension. However, all of the techniques disclosed in Patent Documents 1 to 3 contain chromate, a chromium compound, in the insulating coating. In recent years, with increasing attention being paid to environmental issues, there has been a social demand to prohibit or restrict the use of compounds such as lead, chromium, and cadmium.

[0010] Therefore, research has been conducted into technologies that can form good insulating coatings without containing the above-mentioned chromium compounds.However, with insulating coatings that do not contain chromium compounds, there has been an issue of insufficient tension being applied to the steel sheet.

[0011] As a method for solving the above-mentioned problems, for example, Patent Document 4 discloses a method for treating an insulating coating on a grain-oriented electrical steel sheet, which involves baking at 300°C or higher a treatment solution containing 20 parts by weight of colloidal silica (SiO2 content), 10 to 120 parts by weight of aluminum phosphate, 2 to 10 parts by weight of boric acid, and 4 to 40 parts by weight in total of one or more sulfates selected from the group consisting of sulfates of Mg, Al, Fe, Co, Ni, and Zn.

[0012] Furthermore, Patent Document 5 discloses a technology relating to a coating agent for forming a film that contains a mixture of boric acid and alumina sol and an organic solvent that is compatible with water, and that has the effect of imparting tension to grain-oriented electrical steel sheets.

[0013] Patent Document 6 discloses a technology in which a surface treatment agent for grain-oriented electrical steel sheet contains primary phosphates of Al, Mg, and Ca and colloidal silica, and further contains one or more organic acid salts of Ca, Mn, Fe, Mg, Zn, Co, Ni, Cu, B, and Al. Patent Document 6 also lists formate, acetate, oxalate, tartrate, lactate, citrate, succinate, and salicylate as examples of organic acid salts.

[0014] Furthermore, Patent Document 7 discloses a technology in which, in an insulating coating treatment agent for grain-oriented electrical steel sheets containing phosphate and colloidal silica, the metal components in the phosphate are a combination of specific proportions of divalent metal elements, trivalent metal elements, and metal elements with a valence of tetravalent or higher.

[0015] Furthermore, Patent Document 8 discloses a grain-oriented electrical steel sheet comprising a steel sheet and an insulating coating containing a first metal phosphate which is a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, and Zn, a second phosphate which is a metal phosphate of one or more metals selected from Co, Mo, V, W, and Zr, and colloidal silica.

[0016] Furthermore, Patent Document 9 discloses an aqueous composition for coating grain-oriented electrical steel, which contains aluminum cations, manganese cations, dihydrogen phosphate, hydrogen phosphate and / or phosphate anions, colloidal silicon dioxide, and optionally iron cations.

[0017] Patent Document 10 also describes a method for forming a surface coating by applying a phosphate salt-based topcoat containing colloidal silica containing 0.01 to 1.0 mass% of Na as an impurity, and then applying a potassium compound in an amount of 10 to 60 mg / m in terms of potassium. 2 The method for producing a grain-oriented electrical steel sheet is disclosed, in which the coating is applied in the range of 100 to 150°C, dried, and then heat-treated at 500 to 850°C for 1 minute to 5 hours. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] Japanese Patent Publication No. 48-39338 [Patent Document 2] Japanese Patent Publication No. 61-41778 [Patent Document 3] Japanese Patent Application Publication No. 11-071683 [Patent Document 4] Japanese Patent Publication No. 54-143737 [Patent Document 5] Japanese Patent Application Publication No. 7-278828 [Patent Document 6] Japanese Patent Publication No. 2000-178760 [Patent Document 7] Japanese Patent Application Publication No. 2010-13692 [Patent Document 8] International Publication No. 2017 / 057513 [Patent Document 9] Japan Special Publication No. 2022-519691 [Patent Document 10] Japanese Patent Publication No. 2015-147988 Summary of the Invention [Problem to be solved by the invention]

[0019] These proposed technologies have improved various properties of insulating coatings, such as the ability to apply tension to steel sheets. However, previous research by the present inventors has revealed that, in the case of insulating coatings that do not contain chromium compounds, moisture absorption into the insulating coating gradually progresses with long-term storage, resulting in a gradual decrease in coating tension. After manufacturing, electrical steel sheets are often loaded onto ships in coil form and transported for long periods of time in high-temperature, high-humidity environments. Therefore, if moisture absorption progresses during long-term transportation, the coating tension may decrease, potentially preventing the expected iron loss value from being achieved. None of the above technologies has yet achieved the same level of coating tension after long-term storage as conventional coatings containing chromic acid, leaving room for improvement.

[0020] As described above, the insulating coating of grain-oriented electrical steel sheets must have electrical insulation properties and be capable of applying a large tension to the surface of the steel sheet. In addition, the insulating coating of grain-oriented electrical steel sheets must be resistant to changes in coating tension even when stored for long periods under high-temperature and high-humidity conditions.

[0021] One aspect of the present invention has been made to solve the above-mentioned problems, and aims to provide a grain-oriented electrical steel sheet in which the insulating coating does not contain chromate, and which exhibits the same or better performance as conventional coatings in terms of tensioning the base steel sheet, and in which the coating tension decreases little even when stored for a long period of time in a high-temperature, high-humidity atmosphere. [Means for solving the problem]

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

[0023] (1) A grain-oriented electrical steel sheet according to one aspect of the present invention is A steel plate base material and an insulating coating are provided. the insulating coating does not contain a chromium compound, The coating tension of the insulating coating is 4.9 MPa or more, When the potassium intensity of a spectrum obtained by measuring the insulating coating by X-ray fluorescence analysis is defined as P(K) and the sodium intensity is defined as P(Na), the ratio of P(K) to P(Na), P(K) / P(Na), is greater than 13.0 and 100 or less. (2) In the grain-oriented electrical steel sheet described in (1) above, When the chromium intensity of the spectrum is defined as P(Cr) and the silicon intensity is defined as P(Si), the ratio of P(Cr) to P(Si), P(Cr) / P(Si), may be 0.01 or less. (3) In the grain-oriented electrical steel sheet described in (1) or (2) above, The base steel plate has a chemical composition, in mass%, C: 0.010% or less, Si: 2.00-4.00%, Mn: 0.05 to 1.00%, Al: 0.010~0.065%, N: 0.004% or less, S: 0.010% or less, Se: 0.010% or less, Cr: 0~0.30%, Cu: 0-0.40% P: 0~0.50%, Ni: 0 to 1.00% Sn: 0 to 0.30% Sb: 0 to 0.30% B: 0~0.0100%, Mo: 0 to 0.1%, Contains Bi: 0 to 0.01% The balance may consist of Fe and impurities. [Effects of the Invention]

[0024] According to the above aspect of the present invention, it is possible to reliably obtain grain-oriented electrical steel sheets in which the insulating coating does not contain chromate and the ability to apply tension to the base steel sheet is equal to or better than conventional methods, and in which the coating tension decreases little even when the steel sheet is stored for a long period of time in a high-temperature, high-humidity atmosphere. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a graph showing the relationship between the amount of potassium in an insulating coating treatment solution and the decrease in coating tension before and after maintaining constant temperature and humidity. [Figure 2] This is a reference diagram showing the bridging oxygen of phosphate, and also shows four types of Qn structures: Q0, Q1, Q2, and Q3. [Figure 3] FIG. 1 is a graph showing the relationship between the P(K) / P(Na) value of an insulating coating and the decrease in coating tension before and after being kept at constant temperature and humidity. DETAILED DESCRIPTION OF THE INVENTION

[0026] Preferred embodiments of the present invention will be described in detail below. However, the present invention is not limited to the configurations disclosed in the present embodiments, and various modifications are possible within the scope of the present invention. Furthermore, the numerical ranges shown in the present embodiments include the lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" do not include the numerical range. "%" regarding the content of each element means "mass %" unless otherwise specified.

[0027] The results of the preliminary experiments that led to the production of the grain-oriented electrical steel sheet according to this embodiment will be described below.

[0028] <Experiment> A finish-annealed grain-oriented electrical steel sheet with a thickness of 0.23 mm, manufactured by a known method, was sheared to a width of 60 mm and a length of 300 mm, and the annealing separator adhering to the surface was removed by rinsing with water to prepare a base steel sheet.

[0029] Next, 0 to 10 ml of a 30 mass % aqueous potassium hydroxide solution was added to 220 g of a stock solution containing 40 g of primary aluminum phosphate, 36 g of colloidal silica, and the remainder being water, to prepare 13 types of insulation coating treatment solutions, as shown in Table 1. Note that because sodium-stabilized colloidal silica was used, the amount of Na contained in the insulation coating treatment solution was 0.12 mass %.

[0030] [Table 1]

[0031] Then, the insulating coating treatment liquids were applied to the base steel sheets prepared above so that the coating adhesion amount after baking was 4.5 g / m per side. 2 The coating was applied to both sides using a roll coater so that the coating was as follows: Then, the coating was baked at a temperature of 850°C for 30 seconds.

[0032] The test specimens were prepared by applying an insulating coating solution to both sides of a base steel sheet and baking the solution. These steel sheets were then subjected to constant temperature and humidity conditions (temperature 50°C, humidity 90%, 1 week). By performing constant temperature and humidity conditions, it is possible to simulate long-term storage in a high-temperature, high-humidity environment. For example, the steel sheets can be placed in a constant temperature and humidity chamber (temperature 50°C, humidity 90%) for 1 week.

[0033] The coating tension was also measured before and after being kept at constant temperature and humidity. The coating tension refers to the tension applied to the steel sheet by the coating. The coating tension was measured using the following method. The steel sheet was sheared to a length of 300 mm and a width of 30 mm, and one side of the steel sheet was protected with tape. The steel sheet was then immersed in a 20% aqueous sodium hydroxide solution at 80°C to peel off the insulating coating from the side of the steel sheet that was not protected with tape. Using this steel sheet from which the insulating coating had been peeled off, the radius of curvature of the curve of the steel sheet caused by the peeling of the insulating coating was measured, and the coating tension was calculated using Stoney's formula: σ = Ed / {3 × (1 - v) × R}. where σ is the coating tension (unit: Pa), E is the Young's modulus of the steel sheet (unit: Pa), d is the thickness of the steel sheet (unit: m), ν is the Poisson's ratio of the steel sheet (unit: -), and R is the radius of curvature of the steel sheet (unit: 1 / m). Since the Young's modulus and Poisson's ratio of the steel sheet vary depending on the steel type, values ​​appropriate for the steel sheet used can be substituted as appropriate. In this experiment, a steel sheet with a thickness of 0.23 mm, a Young's modulus of 115 GPa, and a Poisson's ratio of 0.38 was used.

[0034] Based on the above evaluation results, the relationship between the amount of potassium in the insulating coating treatment solution and the decrease in coating tension before and after maintaining constant temperature and humidity is summarized in Figure 1.

[0035] As shown in Figure 1, increasing the amount of potassium in the insulating coating solution reduces the decrease in coating tension. In other words, increasing the amount of potassium in the insulating coating solution reduces the decrease in coating tension even after long-term storage in a high-temperature, high-humidity atmosphere.

[0036] Regarding the above experimental results, the details of the mechanism by which the decrease in coating tension before and after constant temperature and humidity maintenance decreases as the amount of potassium in the insulating coating treatment solution increases are not clear at present, but the inventors believe as follows.

[0037] The decrease in film tension caused by maintaining constant temperature and humidity is thought to be due to a hydrolysis reaction in which water molecules act on the POP bonds in the phosphate that forms the insulating film, breaking the POP bonds. Therefore, it is important to use POM (where M is a metal element) in which the P (phosphorus)-O (oxygen)-P (phosphorus) bonds are replaced with other bonds.

[0038] The structure of phosphates is a PO4 tetrahedron, where four oxygen atoms are coordinated around a phosphorus atom, and a three-dimensional structure is formed by sharing oxygen atoms with other PO4 tetrahedra at the vertices. The oxygen atoms connecting the tetrahedra are called bridging oxygens, and the number of bridging oxygens, n, is used as an index to calculate the Q n As shown in Figure 2, Q 0 , Q 1 , Q2 , Q 3 The four types of Q n They can be classified into structures.

[0039] As the number n of bridging oxygen atoms decreases, the polarity around the phosphorus atom decreases, weakening the interaction with highly polarizable water molecules, making the bond less likely to break.

[0040] Here, regarding the polarity around the phosphorus atom, the smaller the force with which M (M is a metal element) shown in POM attracts oxygen, the smaller the polarity around the phosphorus atom. The force with which M (metal element) attracts oxygen is expressed as field strength. Field strength is the value (Z / r) obtained by dividing the valence (Z) of the metal ion by the square of the ionic radius (r). 2 ) and Z / r 2 The value is very small at 0.4 (for example, Kobe Steel Pantec Technical Report, vol. 35, No. 1, 27).

[0041] As the amount of potassium in the insulating coating treatment solution increases, the POP bonds in the insulating coating are replaced by POM bonds, and the potassium acts as the M in POM, further reducing the polarity around the phosphorus atom. As a result, it is thought that the hydrolysis reaction of the insulating coating is suppressed even in a high-temperature, high-humidity atmosphere, thereby reducing the decrease in coating tension.

[0042] The grain-oriented electrical steel sheet according to this embodiment will be described in detail below.

[0043] The grain-oriented electrical steel sheet according to this embodiment includes a base steel sheet and an insulating coating, The insulating coating does not contain a chromium compound, The coating tension of the insulating coating is 4.9 MPa or more, When the potassium intensity of a spectrum obtained by measuring the insulating coating by X-ray fluorescence analysis is defined as P(K) and the sodium intensity is defined as P(Na), the ratio of P(K) to P(Na), P(K) / P(Na), is greater than 13.0 and 100 or less.

[0044] <Base steel sheet for grain-oriented electrical steel sheet> First, the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment will be described. The base steel sheet of the grain-oriented electrical steel sheet is not particularly limited, but the chemical composition may contain, in mass%, C: 0.010% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.010 to 0.065%, N: 0.004% or less, S: 0.010% or less, with the balance being Fe and impurities. Hereinafter, % relating to the chemical composition refers to mass% relative to the total mass of the base steel sheet.

[0045] C: 0.010% or less Carbon (C) is an element effective in controlling the primary recrystallization structure, but it adversely affects magnetic properties, so it is removed by decarburization annealing before final annealing. If the C concentration in the final product exceeds 0.010%, C precipitates during aging, deteriorating hysteresis loss. Therefore, the C concentration is set to 0.010% or less. The C concentration is preferably 0.007% or less, and more preferably 0.005% or less. The lower limit of the C concentration includes 0%, but the C concentration may exceed 0%. However, reducing the C concentration to less than 0.0001% significantly increases manufacturing costs, so 0.0001% is the practical lower limit for practical steel sheets. In grain-oriented electrical steel sheets, the C concentration is usually reduced to approximately 0.001% or less by decarburization annealing.

[0046] Si: 2.00 to 4.00% Silicon (Si) is an element that increases the electrical resistance of steel sheets and improves iron loss characteristics. If the Si concentration is less than 2.00%, γ transformation of the steel structure occurs during finish annealing, damaging the crystal orientation of the steel sheet. Therefore, the Si concentration is set to 2.00% or more. The Si concentration is preferably 2.50% or more, and more preferably 3.00% or more. On the other hand, if the Si concentration exceeds 4.00%, the workability of the grain-oriented electrical steel sheet decreases and cracks occur during rolling, so the Si concentration is set to 4.00% or less. The Si concentration is preferably 3.50% or less.

[0047] Mn: 0.05 to 1.00% Manganese (Mn) is an element that prevents cracking during hot rolling and combines with S and / or Se to form MnS and MnSe, which function as inhibitors. If the Mn concentration is less than 0.05%, the effect of adding Mn is not fully realized, so the Mn concentration is set to 0.05% or more. The Mn concentration is preferably 0.07% or more, and more preferably 0.09% or more. On the other hand, if the Mn concentration exceeds 1.00%, the precipitation and dispersion of MnS and MnSe becomes non-uniform, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the Mn concentration is set to 1.00% or less. The Mn concentration is preferably 0.80% or less, and more preferably 0.60% or less.

[0048] Al: 0.010 to 0.065% Al (aluminum) is an element that combines with N to form (Al, Si)N or AlN, which functions as an inhibitor. If the Al concentration is less than 0.010%, the effect of adding Al is not fully realized, and secondary recrystallization does not proceed sufficiently. Therefore, the Al concentration is set to 0.010% or more. The Al concentration is preferably 0.015% or more, and more preferably 0.020% or more. On the other hand, if the Al concentration exceeds 0.065%, the precipitation and dispersion of the inhibitor becomes non-uniform, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the Al concentration is set to 0.065% or less. The Al concentration is preferably 0.050% or less, and more preferably 0.040% or less.

[0049] N: 0.004% or less N (nitrogen) is an element that combines with aluminum to form AlN and other elements that function as inhibitors. However, if the N concentration in the final product exceeds 0.004%, the N in the steel sheet precipitates as AlN, degrading hysteresis loss, so the N concentration must be 0.004% or less. The lower limit of the N concentration includes 0%, but reducing the N concentration to less than 0.0001% significantly increases manufacturing costs, so 0.0001% is the practical lower limit for practical steel sheets. In grain-oriented electrical steel sheets, the N concentration is usually reduced to around 0.001% or less by finish annealing.

[0050] S: 0.010% or less S (sulfur) is an element that combines with Mn to form MnS, which functions as an inhibitor. However, if the S concentration in the final product exceeds 0.010%, the S in the steel sheet precipitates as MnS, degrading hysteresis loss, so the S concentration must be 0.010% or less. The lower limit of the S concentration includes 0%, but reducing the S concentration to less than 0.0001% significantly increases manufacturing costs, so 0.0001% is the practical lower limit for practical steel sheets. In grain-oriented electrical steel sheets, the S concentration is usually reduced to approximately 0.005% or less by finish annealing.

[0051] In the present embodiment, the base steel sheet may contain impurities. Note that the term "impurities" refers to substances that are mixed in from raw materials such as ore or scrap, or from the manufacturing environment, when steel is industrially manufactured.

[0052] Furthermore, in this embodiment, the base steel sheet may contain optional elements in addition to the above-described elements and impurities. For example, instead of a portion of the remaining Fe, at least one of Se, Cr, Cu, P, Ni, Sn, Sb, B, Mo, and Bi may be contained as an optional element. These optional elements may be contained according to the purpose. Therefore, there is no need to set a lower limit for these optional elements, and the lower limit may be 0%. Furthermore, even if these optional elements are contained as impurities, the effects obtained by the grain-oriented electrical steel sheet according to this embodiment are not impaired.

[0053] For example, in this embodiment, the base steel sheet may contain one or more of the following optional elements (optionally added elements): Se: 0.010% or less, Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or less, Ni: 1.00% or less, Sn: 0.30% or less, Sb: 0.30% or less, B: 0.0100% or less, Mo: 0.1% or less, and Bi: 0.01% or less, without impairing its magnetic properties and for the purpose of enhancing other properties.

[0054] Se: 0 to 0.010% Se (selenium) is an element that combines with Mn to form MnSe, which functions as an inhibitor. However, if the Se concentration in the final product exceeds 0.010%, the Se in the steel sheet precipitates as MnSe, deteriorating hysteresis loss. Therefore, the Se concentration must be 0.010% or less. The lower limit of the Se concentration may be 0%, or even 0.0001%. In grain-oriented electrical steel sheets, the Se concentration is usually reduced to approximately 0.005% or less by finish annealing.

[0055] Cr: 0 to 0.30% Cr (chromium) is an element that improves the oxide layer during decarburization annealing and is effective in forming a glass film. Therefore, Cr may be added to the base steel sheet in a range of 0.30% or less. If the Cr concentration exceeds 0.30%, decarburization is significantly impaired, so the upper limit of the Cr concentration is preferably 0.30%.

[0056] Cu: 0 to 0.40% Copper (Cu) is an element that is effective in increasing the resistivity of the base steel sheet and reducing iron loss. If the Cu concentration exceeds 0.40%, the iron loss reduction effect saturates and it becomes a cause of surface defects called "copper scuffs" during hot rolling. Therefore, the upper limit of the Cu concentration is preferably 0.40%.

[0057] P: 0 to 0.50% P (phosphorus) is an element that is effective in increasing the resistivity of the base steel sheet and reducing iron loss. If the P concentration exceeds 0.50%, problems arise in the rollability, so the upper limit of the P concentration is preferably 0.50%.

[0058] Ni: 0 to 1.00% Ni (nickel) is an element that is effective in increasing the resistivity of the base steel sheet and reducing iron loss. Ni is also an element that is effective in controlling the steel structure of the hot-rolled sheet and improving the magnetic properties. However, if the Ni concentration exceeds 1.00%, secondary recrystallization becomes unstable, so the upper limit of the Ni concentration is preferably 1.00%.

[0059] Sn: 0 to 0.30% Sb: 0 to 0.30% Sn (tin) and Sb (antimony) are well-known grain boundary segregation elements. In this embodiment, since the base steel sheet contains Al, depending on the conditions of the final annealing, Al may be oxidized by moisture released from the annealing separator, resulting in fluctuations in inhibitor strength at the coil position. As a result, magnetic properties may vary at the coil position. One solution to this problem is to add these grain boundary segregation elements to prevent Al oxidation. For this purpose, Sn and Sb may be added to the base steel sheet at a concentration of 0.30% or less. On the other hand, if the concentration of these elements exceeds 0.30%, Si is less likely to be oxidized during decarburization annealing, resulting in insufficient glass film formation and significantly impairing decarburization annealing performance. For this reason, the upper limit of the concentration of these elements is preferably 0.30%.

[0060] B: 0 to 0.0100% Boron (B) is an element that combines with N in the base steel sheet and precipitates together with MnS to form BN, which functions as an inhibitor. The lower limit of the B concentration is not particularly limited and may be 0% as described above. However, to fully exert the effect of adding B, the lower limit of the B concentration is preferably 0.0005%. The B concentration is preferably 0.0010% or more, more preferably 0.0015% or more. On the other hand, if the B concentration exceeds 0.0100%, the precipitated BN becomes non-uniformly dispersed, the desired secondary recrystallized structure cannot be obtained, and the magnetic flux density decreases. Therefore, the B concentration is preferably 0.0100% or less. The B concentration is preferably 0.0080% or less, more preferably 0.0060% or less, and more preferably 0.0040% or less.

[0061] Mo: 0 to 0.1% Mo (molybdenum) is an element that is effective in improving surface properties during hot rolling. However, if the Mo concentration exceeds 0.1%, the effect of adding Mo becomes saturated, so the upper limit of the Mo concentration is preferably 0.1%.

[0062] Bi: 0 to 0.01% Bi (bismuth) has the effect of stabilizing precipitates such as sulfides and strengthening its inhibitory function. However, if the Bi concentration exceeds 0.01%, Bi has a negative effect on glass film formation, so the upper limit of the Bi concentration is preferably 0.01%.

[0063] The above-mentioned chemical composition may be measured by a general analytical method for steel. For example, the chemical composition may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Al may be measured as total aluminum in accordance with JIS G1257-10-1:2013. C and S may be measured using the combustion-infrared absorption method, N may be measured using the inert gas fusion-thermal conductivity method, and, if necessary, O may be measured using the inert gas fusion-non-dispersive infrared absorption method.

[0064] The above chemical composition is that of the base steel sheet. If the grain-oriented electrical steel sheet to be measured has an insulating coating on its surface, remove the insulating coating by the following method before measuring the chemical composition.

[0065] For example, the insulating coating can be removed by immersing the grain-oriented electrical steel sheet having the coating in a high-temperature alkaline solution. Specifically, the insulating coating can be removed from the grain-oriented electrical steel sheet by immersing the sheet in a sodium hydroxide solution containing 30-50% by mass of NaOH and 50-70% by mass of HO at 80-90°C for 5-10 minutes, followed by rinsing with water and drying. The time for immersion in the sodium hydroxide solution can be adjusted depending on the thickness of the insulating coating.

[0066] <Insulating coating of grain-oriented electrical steel sheet> Next, the insulating coating of the grain-oriented electrical steel sheet according to this embodiment will be described. The insulating coating of grain-oriented electrical steel sheets does not contain chromium compounds, The coating tension of the insulating coating is 4.9 MPa or more, When the potassium intensity of the spectrum obtained by measuring the insulating coating by X-ray fluorescence analysis is defined as P(K) and the sodium intensity as P(Na), the ratio of P(K) to P(Na), P(K) / P(Na), is required to be greater than 13.0 and not greater than 100. Note that wavelength dispersive X-ray fluorescence analysis may be used, with the measurement atmosphere being a vacuum, and the measurement conditions being an X-ray source of Rh, an X-ray tube voltage of 40 kV, a tube current of 75 mA, and a LiF analyzing crystal.

[0067] P(K) / P(Na) ratio: over 13.0 and less than 100 The inventors conducted a detailed study of insulating coatings and found that the decrease in coating tension before and after constant temperature and humidity maintenance decreases as the ratio of potassium intensity to sodium intensity in the fluorescent X-ray spectrum of the insulating coating, i.e., the value of P(K) / P(Na), increases, as shown in Figure 3. In particular, they found that when the value of P(K) / P(Na) is in the range of more than 13.0 and not more than 100, the decrease in coating tension before and after constant temperature and humidity maintenance can be suppressed to an acceptable level.

[0068] If the P(K) / P(Na) value is 13.0 or less, potassium does not sufficiently suppress the hydrolysis reaction of the phosphate in the insulating coating. On the other hand, if the P(K) / P(Na) value exceeds 100, potassium excessively cuts the network structure of the phosphate in the insulating coating, causing the coating tension to become excessively low immediately after baking the insulating coating (before maintaining it at constant temperature and humidity).

[0069] The value of P(K) / P(Na) is preferably 30 or more, and more preferably 35 or more. The value of P(K) / P(Na) is preferably 70 or less, and more preferably 45 or less.

[0070] The above-mentioned P(K) / P(Na) value can be determined by subjecting the surface of the insulating coating to X-ray fluorescence analysis in accordance with JIS K0119:2008, measuring the potassium intensity (fluorescent X-ray intensity at K Kα of 0.3742 nm, cps) and the sodium intensity (fluorescent X-ray intensity at Na Kα of 1.191 nm, cps) in the X-ray fluorescence spectrum, and then dividing the potassium intensity by the sodium intensity. Since the intensity ratio is being calculated, the same X-ray irradiation conditions can be used when measuring the potassium intensity and the sodium intensity. For example, the X-ray fluorescence analysis can be performed using a wavelength-dispersive optical system with an Rh X-ray source, a tube voltage of 40 kV, a tube current of 75 mA, and a LiF analyzing crystal. Other well-known conditions can be applied. Furthermore, the measurement conditions are not limited to those described above. Any X-ray irradiation conditions that provide sufficient energy to generate fluorescent X-rays of potassium and sodium and provide sufficient fluorescent X-ray intensity can be used. The above-mentioned P(K) / P(Na) can also be determined by X-ray fluorescence analysis using an energy-dispersive optical system. When making the measurement, it is preferable to carry out the X-ray fluorescence analysis of the insulating coating in at least 10 or more different regions that are sufficiently separated from one another, and to obtain an average value from the results of these multiple measurements.

[0071] Moreover, the insulating coating of the grain-oriented electrical steel sheet according to this embodiment is When the chromium intensity and silicon intensity of the spectrum obtained by subjecting the insulating coating to fluorescent X-ray analysis under the above conditions are defined as P(Cr) and P(Si), respectively, the ratio of P(Cr) to P(Si), P(Cr) / P(Si), may be 0.01 or less.

[0072] The insulating coating of the grain-oriented electrical steel sheet according to this embodiment does not contain chromium compounds. Therefore, the ratio of the chromium intensity to the silicon intensity in the fluorescent X-ray spectrum of the insulating coating, i.e., the value of P(Cr) / P(Si), may be 0.01 or less. The lower limit of the value of P(Cr) / P(Si) is not particularly limited and may be 0. However, the value of P(Cr) / P(Si) may not be 0 due to Cr contained in the base steel sheet, etc. Therefore, the lower limit of the value of P(Cr) / P(Si) may be greater than 0.

[0073] Moreover, the insulating coating of the grain-oriented electrical steel sheet according to this embodiment is When the phosphorus intensity of the spectrum obtained by subjecting the insulating coating to fluorescent X-ray analysis under the above conditions is defined as P(P) and the silicon intensity is defined as P(Si), the ratio of P(P) to P(Si), P(P) / P(Si), may be 0.8 or more and 1.0 or less.

[0074] The insulating coating of the grain-oriented electrical steel sheet according to this embodiment is formed by baking an insulating coating treatment solution containing mainly colloidal silica and phosphate. The phosphate functions as a binder for the colloidal silica, forming the coating. It is preferable that the phosphate and colloidal silica are present in an appropriate ratio when the coating is formed. Therefore, the value of P(P) / P(Si) may be 0.8 or more and 1.0 or less.

[0075] When the value of P(P) / P(Si) is 0.8 or more, a coating is preferably formed, and when the value of P(P) / P(Si) is 1.0 or less, sufficient coating tension is preferably obtained.

[0076] The above-mentioned P(Cr) / P(Si) and P(P) / P(Si) values ​​can be obtained by subjecting the surface of the insulating coating to X-ray fluorescence analysis in accordance with JIS K0119:2008, measuring the chromium intensity (Cr Kα X-ray intensity at 0.2291 nm, cps), phosphorus intensity (P Kα X-ray intensity at 0.6155 nm, cps), and silicon intensity (Si Kα X-ray intensity at 0.7126 nm, cps) in the X-ray fluorescence spectrum, and then calculating the respective ratios. The measurement conditions for the X-ray fluorescence analysis can be the same as those described above.

[0077] In the grain-oriented electrical steel sheet according to this embodiment, the coating tension of the insulating coating may be 4.5 MPa or more, but is preferably 4.9 MPa or more. Specifically, the coating tension is preferably 4.9 MPa or more, regardless of whether the coating tension is before or after constant temperature and humidity maintenance. If the coating tension does not satisfy this value, the iron loss improvement effect may be insufficient, and good magnetic properties may not be obtained. The coating tension of the insulating coating is preferably 5.0 MPa or more, more preferably 6.0 MPa or more, even more preferably 6.5 MPa or more, and even more preferably 7.0 MPa or more. On the other hand, although there is no upper limit to the coating tension, the iron loss improvement effect saturates, so the coating tension should be 10 MPa or less.

[0078] Furthermore, in the grain-oriented electrical steel sheet according to this embodiment, it is more preferable that the coating tension before being kept at constant temperature and humidity is 4.9 MPa or more. Since the coating tension is likely to decrease due to being kept at constant temperature and humidity, it is preferable that the coating tension before being kept at constant temperature and humidity is a high value. The coating tension before being kept at constant temperature and humidity is preferably 5.0 MPa or more, more preferably 6.0 MPa or more, even more preferably 6.5 MPa or more, even more preferably 7.0 MPa or more, and even more preferably 7.5 MPa or more.

[0079] Furthermore, in the grain-oriented electrical steel sheet according to this embodiment, it is more preferable that the coating tension after being kept at a constant temperature and humidity is 4.9 MPa or more. Since the coating tension is likely to decrease due to being kept at a constant temperature and humidity, it is preferable that the coating tension after being kept at a constant temperature and humidity is a high value. The coating tension after being kept at a constant temperature and humidity is preferably 5.0 MPa or more, more preferably 6.0 MPa or more, even more preferably 6.5 MPa or more, and even more preferably 7.0 MPa or more.

[0080] The coating tension of the insulating coating can be measured in the same manner as above. Specifically, a steel sheet is sheared to a length of 300 mm and a width of 30 mm, and one side of the steel sheet is protected with tape. The steel sheet is then immersed in a 20% aqueous solution of sodium hydroxide at 80°C to remove the insulating coating from the side of the steel sheet that is not protected with tape. Using this steel sheet from which the insulating coating on one side has been removed, the radius of curvature of the steel sheet caused by the removal of the insulating coating can be measured, and the coating tension can be calculated using Stoney's formula: σ = Ed / {3 × (1 - v) × R}. where σ is the coating tension (unit: Pa), E is the Young's modulus of the steel sheet (unit: Pa), d is the thickness of the steel sheet (unit: m), ν is the Poisson's ratio of the steel sheet (unit: -), and R is the radius of curvature of the steel sheet (unit: 1 / m). Note that the Young's modulus and Poisson's ratio of steel sheets are values ​​that vary depending on the steel type, so values ​​appropriate for the steel sheet used can be substituted as appropriate.

[0081] In this embodiment, the chemical composition of the insulating coating is not particularly limited, but may, for example, satisfy the following as main contained elements: P: 5 to 30 atomic %, Si: 5 to 30 atomic %, O: 30 to 80 atomic %, Al: 0.1 to 10 atomic %, Cr: less than 1 atomic %, Fe: less than 25 atomic %, Mg: 0 to 10 atomic %, Mn: 0 to 10 atomic %, Ni: 0 to 10 atomic %, Zn: 0 to 10 atomic %, V: 0 to 10 atomic %, W: 0 to 10 atomic %, Zr: 0 to 10 atomic %, Co: 0 to 10 atomic %, and Mo: 0 to 10 atomic %.

[0082] The insulating coating of the grain-oriented electrical steel sheet according to this embodiment does not contain chromium compounds. For example, in this embodiment, when the Cr concentration in the insulating coating is less than 1 atomic %, the insulating coating is determined to contain no chromium compounds. The Cr concentration is preferably 0.8 atomic % or less, and more preferably 0.5 atomic % or less.

[0083] The chemical composition of the insulating coating can be determined by, for example, analyzing the composition of a cut surface using SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) or TEM-EDS (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy). During measurement, the composition analysis can be performed by irradiating the insulating coating on the cut surface with an electron beam. The composition analysis can also be performed under well-known conditions.

[0084] In addition, in the grain-oriented electrical steel sheet according to this embodiment, the coating weight of the insulating coating is not particularly limited, but is preferably 2.0 to 7.0 g / m per side. 2 The coating weight of the insulating coating is 2.0 g / m 2 In the above cases, high tension can be preferably imparted to the grain-oriented electrical steel sheet, and the grain-oriented electrical steel sheet can also be provided with favorable insulation properties and corrosion resistance. 2 In the following cases, the decrease in the space factor of the grain-oriented electrical steel sheet can be suppressed and the transformer characteristics can be favorably improved. The coating weight of the insulating coating is more preferably 3.0 g / m 2 More preferably, 4.0 g / m 2 The coating weight of the insulating coating is more preferably 6.0 g / m 2 or less, more preferably 5.0 g / m 2 The following is the result.

[0085] The coating weight of the insulating coating can be determined from the change in mass before and after removing the insulating coating. The insulating coating can be removed by the method described above.

[0086] Furthermore, the insulating coating of the grain-oriented electrical steel sheet according to this embodiment means an insulating coating that minimizes insufficient baking or cracking due to poor baking conditions. If the insulating coating suffers from insufficient baking or excessive cracking due to poor baking conditions, the insulating coating may not satisfy the electrical insulation, tensioning, corrosion resistance, heat resistance, slip properties, adhesion, and other properties required of the insulating coating.

[0087] <Method of manufacturing grain-oriented electrical steel sheets> Next, a method for manufacturing the grain-oriented electrical steel sheet according to this embodiment will be described. Note that the method for manufacturing the grain-oriented electrical steel sheet according to this embodiment is not limited to the method described below. The manufacturing method described below is one example for manufacturing the grain-oriented electrical steel sheet according to this embodiment.

[0088] Molten steel having a predetermined chemical composition is cast by a conventional method to produce a silicon steel slab. The chemical composition of the silicon steel slab is not limited to a specific composition as long as it can provide the magnetic and mechanical properties required for grain-oriented electrical steel sheets. An example of the chemical composition of a silicon steel slab is as follows: For example, the silicon steel slab contains, in mass %, C: 0.085% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.010 to 0.065%, N: 0.004 to 0.012%, and S: 0.010% or less.

[0089] C: 0.085% or less Carbon (C) is an element effective in controlling the primary recrystallization structure, but it has a negative effect on magnetic properties, so it is removed by decarburization annealing before final annealing. If the C concentration exceeds 0.085%, the decarburization annealing time becomes longer and productivity decreases, so the C concentration is set to 0.085% or less. The C concentration is preferably 0.070% or less, and more preferably 0.050% or less. There is no particular restriction on the lower limit of the C concentration, and it may be 0% or more. When considering productivity in industrial production and the magnetic properties of the product, 0.0001% is the practical lower limit of the C concentration. In grain-oriented electrical steel sheets, the C concentration is usually reduced to approximately 0.001% or less by decarburization annealing.

[0090] Si: 2.00 to 4.00% Silicon (Si) is an element that increases the electrical resistance of steel sheets and improves their iron loss characteristics. If the Si concentration is less than 2.00%, γ transformation occurs during finish annealing, damaging the crystal orientation of the steel sheet. Therefore, the Si concentration is set to 2.00% or more. The Si concentration is preferably 2.50% or more, and more preferably 3.00% or more. On the other hand, if the Si concentration exceeds 4.00%, workability decreases and cracks occur during rolling, so the Si concentration is set to 4.00% or less. The Si concentration is preferably 3.50% or less.

[0091] Mn: 0.05 to 1.00% Manganese (Mn) is an element that prevents cracking during hot rolling and also combines with S and / or Se to form MnS and MnSe, which function as inhibitors. If the Mn concentration is less than 0.05%, the effect of the addition is not fully realized, so the Mn concentration is set to 0.05% or more. The Mn concentration is preferably 0.07% or more, and more preferably 0.09% or more. On the other hand, if the Mn concentration exceeds 1.00%, the precipitation and dispersion of MnS and MnSe becomes non-uniform, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the Mn concentration is set to 1.00% or less. The Mn concentration is preferably 0.80% or less, and more preferably 0.06% or less.

[0092] Al: 0.010 to 0.065% Al (aluminum) is an element that combines with N to form (Al, Si)N or AlN, which functions as an inhibitor. If the Al concentration is less than 0.010%, the additive effect is not fully realized and secondary recrystallization does not proceed sufficiently, so the Al concentration is set to 0.010% or more. The Al concentration is preferably 0.015% or more, more preferably 0.020% or more. On the other hand, if the Al concentration exceeds 0.065%, the precipitation dispersion of (Al, Si)N and the like becomes non-uniform, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases, so the Al concentration is set to 0.065% or less. The Al concentration is preferably 0.050% or less, more preferably 0.040% or less.

[0093] N: 0.004 to 0.012% N (nitrogen) is an element that combines with Al to form AlN and other compounds that function as inhibitors, but it is also an element that forms blisters (voids) in steel sheets during cold rolling. If the N concentration is less than 0.004%, the formation of AlN will be insufficient, so the N concentration is set to 0.004% or more. The N concentration is preferably 0.006% or more, more preferably 0.007% or more. On the other hand, if the N concentration exceeds 0.012%, there is a concern that blisters (voids) will form in the steel sheets during cold rolling, so the N concentration is set to 0.012% or less. The N concentration is preferably 0.010% or less, more preferably 0.009% or less.

[0094] S: 0.010% or less S (sulfur) is an element that combines with Mn to form MnS, which functions as an inhibitor. If the S concentration exceeds 0.010%, the precipitation and dispersion of MnS becomes non-uniform after purification, the desired secondary recrystallization structure cannot be obtained, the magnetic flux density decreases, and hysteresis loss deteriorates. Alternatively, MnS remains after purification, deteriorating hysteresis loss. Although there is no particular lower limit, the S concentration may be 0%, and is preferably 0.003% or more. The S concentration is more preferably 0.007% or more.

[0095] In this embodiment, the silicon steel slab may contain impurities. The term "impurities" refers to substances that are mixed in from raw materials such as ore or scrap, or from the manufacturing environment, during industrial steel production.

[0096] In this embodiment, the silicon steel slab may contain selective elements in addition to the above-described elements and impurities. For example, instead of a portion of the remaining Fe, at least one of Se, Cr, Cu, P, Ni, Sn, Sb, B, Mo, or Bi may be contained as a selective element. These selective elements may be contained according to their intended purpose. Therefore, there is no need to set a lower limit for these selective elements, and the lower limit may be 0%. Furthermore, even if these selective elements are contained as impurities, the above-described effects are not impaired.

[0097] For example, in this embodiment, the silicon steel slab may contain one or more of Se: 0.010% or less, Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or less, Ni: 1.00% or less, Sn: 0.30% or less, Sb: 0.30% or less, B: 0.0100% or less, Mo: 0.1% or less, and Bi: 0.01% or less, within a range that does not impair the magnetic properties of the grain-oriented electrical steel sheet and can enhance other properties.

[0098] In the hot rolling process, a slab having the above chemical composition is hot-rolled to obtain a hot-rolled sheet. The hot-rolling conditions are not particularly limited, and ordinary conditions can be used. The hot-rolled sheet obtained by the hot-rolling process is wound into a coil.

[0099] Before the slab is subjected to hot rolling, it may be heated to a temperature exceeding 1300°C in order to sufficiently dissolve the inhibitor components MnS and AlN. From the viewpoint of productivity and manufacturing costs, the slab may also be heated to about 1250°C on the premise that the inhibitors will be strengthened by a nitriding treatment in a subsequent process.

[0100] In the hot-rolled sheet annealing process, the coiled hot-rolled sheet is recoiled into a strip-shaped hot-rolled sheet, and then the strip-shaped hot-rolled sheet is subjected to hot-rolled sheet annealing to obtain an annealed hot-rolled sheet. The hot-rolled sheet annealing conditions are not particularly limited, and conventional conditions can be used.

[0101] In the cold rolling process, the annealed hot-rolled sheet is subjected to cold rolling once or twice or more times to obtain a cold-rolled sheet having a final thickness. In this cold rolling process, the annealed hot-rolled sheet may be subjected to cold rolling twice or more times with intermediate annealing in between to obtain a cold-rolled sheet. Annealing performed before the finish (final) cold rolling homogenizes the crystal structure. The cold rolling conditions are not particularly limited, and ordinary conditions can be used.

[0102] In the decarburization annealing process, a decarburization annealed sheet is obtained by subjecting the cold-rolled sheet to decarburization annealing. In this decarburization annealing process, the cold-rolled sheet is heat-treated in wet hydrogen to reduce the carbon content in the cold-rolled sheet to an amount that will not cause deterioration due to magnetic aging in the product steel sheet, and primary recrystallization occurs in the cold-rolled sheet, preparing it for the subsequent secondary recrystallization. The decarburization annealing conditions are not particularly limited, and conventional conditions can be used. An SiO2 oxide film is formed on the surface of the decarburization annealed sheet obtained by this decarburization annealing process. When a cold-rolled sheet is produced from a slab heated to approximately 1250°C, the decarburization annealed sheet is annealed in an ammonia atmosphere after decarburization annealing to produce AlN, which functions as an inhibitor, in the decarburization annealed sheet.

[0103] In the method for producing a grain-oriented electrical steel sheet according to this embodiment, the steel sheet on which the insulating coating is formed may be a grain-oriented electrical steel sheet having a normal forsterite coating, or may be a grain-oriented electrical steel sheet without a forsterite coating.

[0104] In the case of grain-oriented electrical steel sheets with a normal forsterite coating, an annealing separator containing MgO as the main component is applied in the annealing separator application process, which is the process following the decarburization annealing process, to prevent seizure during the finish annealing process. The amount of annealing separator applied is 6.0 to 14.0 g / m per side of the decarburization annealed sheet. 2 is.

[0105] In the case of grain-oriented electrical steel sheets that do not have a forsterite coating, an annealing separator whose main component is alumina (Al2O3) is applied during the annealing separator application process. The decarburized annealed sheet to which the annealing separator has been applied is then wound into a coil after the annealing separator has dried.

[0106] In the final annealing process, the coil-shaped decarburized annealed sheet coated with an annealing separator is subjected to final annealing to obtain the base steel sheet for the final product (grain-oriented electrical steel sheet). In this final annealing process, secondary recrystallization occurs in the decarburized annealed sheet by performing final annealing at a temperature of 1100°C or higher. Note that, in order to reduce hysteresis loss in the final product, the finish-annealed sheet after completion of secondary recrystallization may be subjected to purification annealing so that the precipitates used as inhibitors are rendered harmless.

[0107] An insulating coating is formed on the surface of the steel sheet after secondary recrystallization. The method for forming this insulating coating includes a mixing step of an insulating coating treatment liquid, a coating step of applying the insulating coating treatment liquid to the surface of the steel sheet, and a baking step of baking the insulating coating treatment liquid. The insulating coating is formed through these steps.

[0108] In the mixing step, metal phosphate salt, colloidal silica, etc. are mixed, as will be described in detail later in the section "Manufacturing Method of Insulation Coating Solution for Grain-Oriented Electrical Steel Sheets." At this time, sodium and potassium are included in the insulation coating solution. For example, sodium may be derived from sodium or sodium borate contained in colloidal silica, and potassium may be derived from potassium hydroxide, potassium chloride, or dipotassium hydrogen phosphate.

[0109] In the method for producing grain-oriented electrical steel sheet according to this embodiment, it is necessary to control the stirring time of the insulating coating treatment solution prepared as described above in the mixing step. Specifically, the stirring time of the insulating coating treatment solution in the mixing step is set to 60 minutes or more.

[0110] The stirring time for the insulation coating treatment solution described above is longer than the stirring time conventionally considered. Conventional insulation coating treatment solutions that do not contain both sodium and potassium have a stirring time of approximately 30 minutes. For example, a short stirring time is preferable industrially, and therefore, in conventional techniques, the stirring time is set to approximately 30 minutes. In contrast, in this embodiment, the stirring time for the insulation coating treatment solution in the mixing step is set to 60 minutes or more. The present inventors have found that when the insulation coating treatment solution contains potassium and sodium, the grain-oriented electrical steel sheet according to this embodiment can be obtained by stirring the insulation coating treatment solution for 60 minutes or more. Note that there is no particular upper limit to this stirring time; for example, it may be set to 150 minutes.

[0111] Additionally, in the manufacturing method of grain-oriented electrical steel sheet according to this embodiment, it is necessary to control the holding time of the insulating coating treatment solution after stirring in the mixing step. Specifically, the holding time of the insulating coating treatment solution after stirring is set to within 300 minutes before application to the steel sheet.

[0112] The above-described holding time of the insulating coating treatment solution after stirring is shorter than the holding time conventionally considered. Conventional insulating coating treatment solutions that do not contain both sodium and potassium were considered to be sufficient for a holding time of within one week after stirring. For example, because it is industrially preferable to prepare the insulating coating treatment solution in advance, conventional techniques have sometimes held the insulating coating treatment solution for approximately one week after stirring. In contrast, in this embodiment, the holding time from the end of stirring the insulating coating treatment solution until application to the steel sheet is set to within 300 minutes. The present inventors have found that when the insulating coating treatment solution contains potassium and sodium, the grain-oriented electrical steel sheet according to this embodiment can be obtained by holding the insulating coating treatment solution after stirring for within 300 minutes. Note that the lower limit of this holding time is not particularly limited and may be, for example, 0 minutes.

[0113] In the coating process, the insulating coating solution prepared in the mixing process is applied to the steel sheet within 300 minutes after mixing. After finish annealing or purification annealing, the steel sheet is rinsed with water to remove excess annealing separator, then pickled in a sulfuric acid bath or similar, and then rinsed with water. This cleans and activates the surface of the steel sheet, and then the insulating coating solution is applied to the steel sheet in the coating process.

[0114] There are no limitations on the method for applying the insulating coating solution to the steel sheet, but it is usually applied using a roll coater. The grain-oriented electrical steel sheet to which the insulating coating solution has been applied is subjected to a baking process under the conditions described below, thereby forming an insulating coating on the surface.

[0115] In the baking process, the grain-oriented electrical steel sheet coated with the insulating coating treatment liquid is heated to a baking soaking temperature, held at the baking soaking temperature, and then cooled.

[0116] The baking soaking temperature (°C) refers to the sheet temperature (maximum sheet temperature) reached during the baking process, and must be 800°C or higher and 1000°C or lower. If the baking soaking temperature is lower than 800°C, the coating formation reaction of the insulating coating will not proceed sufficiently, resulting in a poor coating appearance and insufficient tension being imparted to the steel sheet. On the other hand, if the baking soaking temperature is higher than 1000°C, cracks may occur in the insulating coating, reducing the coating tension and insulating properties, and scratches may also occur on the steel sheet. The baking soaking temperature is more preferably 850°C or higher and 950°C or lower.

[0117] The soaking time (seconds) indicates the time required to hold the coating at the baking temperature. A soaking time of 10 seconds or more is required. If the soaking time is less than 10 seconds, the insulating coating may not be baked properly, which may reduce the coating tension. A soaking time of 20 seconds or more is desirable. On the other hand, the soaking time should be 60 seconds or less. If the soaking time exceeds 60 seconds, excessive crystallization of the insulating coating may occur, causing cracks and reducing the coating tension. A soaking time of 45 seconds or less is more preferable, as this provides sufficient coating properties.

[0118] As mentioned above, there are no particular limitations on the type of base steel sheet to be treated with the insulating coating. The grain-oriented electrical steel sheet according to this embodiment is primarily characterized by the configuration of the insulating coating, and the effects of the insulating coating of the grain-oriented electrical steel sheet according to this embodiment, namely, the ability to apply large tension to the surface of the steel sheet, good adhesion and corrosion resistance, and excellent long-term stability despite not containing chromate, can be achieved regardless of the type of base steel sheet.

[0119] Preferably, the above-mentioned insulating coating treatment is applied to grain-oriented electrical steel sheets manufactured using the technology disclosed in, for example, Japanese Patent Laid-Open Publication No. 7-268567. In this case, the effect of further reducing iron loss can be obtained. Specifically, by applying the above-mentioned insulating coating treatment to grain-oriented electrical steel sheets containing, by mass, at least 0.005% or less of C and 2.5 to 7.0% of Si, and optionally containing other alloying elements (e.g., 0 to 1.0% of Mn, 0 to 0.03% of Al, 0.01% or less of N, 0.01% or less of P, and 0.01% or less of S) within ranges that do not impair the properties, with the balance being Fe and impurities, an average grain size of 1 to 10 mm, and an average angle between the (110)

[0001] crystal orientation and the rolling direction of 8° or less, the effect of further reducing iron loss can be obtained.

[0120] <Insulating coating treatment solution for grain-oriented electrical steel sheets> Next, the insulating coating treatment liquid (hereinafter simply referred to as "insulating coating treatment liquid") used for the grain-oriented electrical steel sheet according to this embodiment will be described.

[0121] The insulating coating treatment solution contains colloidal silica and a metal phosphate salt of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, but does not contain chromate. The colloidal silica used in the insulating coating treatment solution typically contains 0.010 to 1.0 mass% sodium to enhance dispersion stability. Therefore, the amount of sodium in the insulating coating can be controlled by appropriately selecting the colloidal silica. Alternatively, the amount of sodium in the insulating coating can be controlled by adding a sodium compound to the insulating coating treatment solution.

[0122] The metal phosphate is preferably one or more phosphates selected from Al, Mg, Ni, V, and W. This is because when these phosphates are selected, a flat and uniform appearance can be obtained under a wide range of baking conditions.

[0123] Furthermore, potassium must be added to improve the hydrolysis resistance of the insulating coating. The amount of potassium contained in the insulating coating treatment solution is preferably 0.10 mol / kg or more, more preferably 0.13 mol / kg or more. On the other hand, the upper limit is not particularly limited, but is, for example, 0.30 mol / kg or less, preferably 0.20 mol / kg or less. If the potassium amount is less than 0.10 mol / kg, the coating tension may decrease if the insulating coating is stored for a long period of time under a high-temperature and high-humidity atmosphere. On the other hand, if the potassium amount exceeds 0.30 mol / kg, the potassium may excessively cut the phosphate network structure of the insulating coating, resulting in an excessively low coating tension immediately after baking the insulating coating (before maintaining the insulating coating at a constant temperature and humidity).

[0124] In this embodiment, the amount of potassium in the insulation coating treatment solution can be analyzed as follows: The amount of potassium contained in the insulation coating treatment solution is measured by atomic absorption spectrometry and converted into the amount of substance. The amount of potassium can then be calculated by dividing the amount by the weight of the insulation coating treatment solution.

[0125] <Method of manufacturing an insulating coating treatment solution for grain-oriented electrical steel sheets> Next, a method for producing the insulating coating solution used for the grain-oriented electrical steel sheet according to this embodiment (hereinafter simply referred to as "the method for producing the insulating coating solution") and the reasons for the limitations thereon will be described.

[0126] The method for producing the insulating coating solution includes a mixing step of metal phosphate, colloidal silica, sodium, and potassium. The sodium may be derived from the sodium contained in the colloidal silica. The method for adding potassium is not particularly limited as long as a predetermined amount can be added to the insulating coating solution. An example is as follows:

[0127] The phosphate is based on a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, and potassium can also be contained in the insulation coating treatment solution in the form of potassium hydroxide, potassium chloride, or dipotassium hydrogen phosphate.

[0128] The size of the colloidal silica (silica particles) used in this embodiment is not particularly limited, but the average particle size (average primary particle size) is preferably 4 to 35 nm. If the average particle size of the colloidal silica is less than 4 nm, the colloidal silica tends to aggregate, which may reduce the stability of the insulating coating treatment solution, or the insulating coating may become porous with large gaps, resulting in a decrease in coating tension of the insulating coating. On the other hand, if the average particle size of the colloidal silica exceeds 35 nm, the reactivity of the colloidal silica may decrease, which may result in insufficient mixing of the phosphate binder with the colloidal silica, or cracks may occur in the insulating coating, resulting in a decrease in coating tension.

[0129] Furthermore, since the smaller the particle size of the colloidal silica, the denser the coating film formed and the higher the coating tension, the upper limit of the average particle size of the colloidal silica is more preferably 31 nm, 22 nm, 18 nm, or 12 nm. Furthermore, it is even more preferable that the surface of the colloidal silica is chemically treated with aluminum. The average particle size (average primary particle size) of the colloidal silica can be determined, for example, by conversion from the specific surface area measured by the BET adsorption method (in accordance with JIS Z 8830:2013).

[0130] In the method for producing an insulating coating solution, the ratio of metal phosphate to colloidal silica is not particularly limited. As long as the insulating coating solution contains sodium and potassium, and the potassium content is between 0.10 mol / kg and 0.30 mol / kg, the insulating coating of grain-oriented electrical steel sheet produced using this insulating coating solution will exhibit excellent properties. Preferred values ​​are listed below.

[0131] For example, the insulating coating treatment solution may be prepared by mixing 100 parts by mass of metal phosphate (solids content), 30 to 130 parts by mass of colloidal silica (sodium stabilized) (solids content), and potassium hydroxide or dipotassium hydrogen phosphate as potassium. The insulating coating treatment solution thus prepared may contain 0.10 mol / kg or more and 0.30 mol / kg or less of potassium.

[0132] The insulating coating treatment solution preferably contains colloidal silica in an amount of 25 to 55% by mass, calculated as solids, based on the total mass of the insulating coating treatment solution. A colloidal silica content of less than 25% by mass is undesirable because the insulating coating may not have sufficient coating tension. A colloidal silica content of more than 55% by mass is undesirable because it may reduce the adhesion of the insulating coating or cause the insulating coating to contain too much sodium, resulting in a significant decrease in coating tension. The insulating coating treatment solution preferably contains colloidal silica in an amount of 27% by mass or more, more preferably 30% by mass or more, 32% by mass or more, or 35% by mass or more, calculated as solids, based on the total mass of the insulating coating treatment solution. The insulating coating treatment solution preferably contains colloidal silica in an amount of 45% by mass or less, and even more preferably 40% by mass or less.

[0133] In the mixing step, various oxides such as titanium oxide and molybdenum oxide, boric acid, sodium borate, pigments, and inorganic compounds such as barium titanate may be further mixed into the insulating coating treatment solution.

[0134] As described above, the stirring time of the insulating coating treatment solution in the mixing step is set to 60 minutes or more, and the holding time from the end of stirring of the insulating coating treatment solution until application to the steel sheet is set to 300 minutes or less. [Example]

[0135] Next, the effects of one embodiment of the present invention will be explained in more detail using examples, but the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0136] A slab (slab satisfying the chemical composition of the silicon steel slab described above) whose chemical composition was adjusted so that the final product base steel sheet had the chemical composition shown in Table 2 was heated to 1150°C and hot-rolled to obtain a hot-rolled steel sheet with a thickness of 2.6 mm. This hot-rolled steel sheet was subjected to hot-rolled sheet annealing as necessary, followed by one cold rolling or multiple cold rolling with intermediate annealing in between to obtain a cold-rolled steel sheet with a final thickness of 0.23 mm. This cold-rolled steel sheet was subjected to decarburization annealing and then nitriding annealing in which the sheet was held in an ammonia-containing atmosphere during cooling. Well-known conditions were applied in the processes from slab heating to nitriding annealing.

[0137] The decarburization-annealed steel sheets after the above-mentioned decarburization annealing and nitriding annealing were coated with an annealing separator mainly composed of MgO and dried. The decarburization-annealed steel sheets coated with the annealing separator were then subjected to finish annealing at 1200°C for 20 hours.

[0138] After that, the excess annealing separator was removed by water rinsing using a scrubber. The insulation coating solution was mixed under the conditions shown in Tables 3, 5, and 6. The insulation coating solution was then applied and baked under the conditions shown in Table 4 to form an insulation coating on the base steel sheet. The sodium content in the insulation coating solution was adjusted by adjusting the sodium content in the colloidal silica to enhance dispersion stability. The potassium content was adjusted by adding alkali metal salts such as a 30% potassium hydroxide aqueous solution, a 5% potassium chloride aqueous solution, or a 5% potassium dihydrogen phosphate aqueous solution. Insulation coating solution B5 contained 0.5 mass% titanium oxide, and insulation coating solution B13 contained 0.5 mass% boric acid. In Table 3, the contents of the metal phosphate salt, colloidal silica, sodium content, alkali metal salt, titanium oxide, and boric acid are expressed in mass% solids. In Tables 5 and 6, the "mixing step" refers to the mixing step of the insulation coating solution.

[0139] For the obtained grain-oriented electrical steel sheets Nos. D1 to D33, d1 to d15, and E1 to E6, the chemical composition of the base steel sheet, the chemical composition of the insulating coating, the coating weight of the insulating coating, the fluorescent X-ray intensity ratio of the insulating coating, etc. were measured based on the above-mentioned methods.

[0140] Furthermore, the coating tension of the obtained grain-oriented electrical steel sheets Nos. D1 to D33, d1 to d15, and E1 to E6 was evaluated based on the above-mentioned method.

[0141] The coating tension was measured before and after the following constant temperature and humidity holding, and the decrease in coating tension was calculated. For the constant temperature and humidity holding, the grain-oriented electrical steel sheet with the insulating coating was placed in a constant temperature and humidity chamber (temperature 50°C, humidity 90%) for one week. A test piece was judged to have passed if the coating tension was 4.9 MPa or higher both before and after the constant temperature and humidity holding, and if the decrease in coating tension after the constant temperature and humidity holding was 50% or less compared to the coating tension before the constant temperature and humidity holding.

[0142] For the obtained grain-oriented electrical steel sheets, the fluorescent X-ray intensity ratio of the insulating coating, the coating tension of the insulating coating, and the decrease in strength before and after being kept at constant temperature and humidity are evaluated and the results are shown in Tables 5 and 6.

[0143] Although not shown in the table, the chemical composition of the insulating coating of Examples D1 to D33 and E1 to E6 of the present invention satisfied the following main elements: P: 5 to 30 atomic %, Si: 5 to 30 atomic %, O: 30 to 80 atomic %, Al: 0.1 to 10 atomic %, Cr: less than 1 atomic %, Fe: less than 25 atomic %, Mg: 0 to 10 atomic %, Mn: 0 to 10 atomic %, Ni: 0 to 10 atomic %, Zn: 0 to 10 atomic %, V: 0 to 10 atomic %, W: 0 to 10 atomic %, Zr: 0 to 10 atomic %, Co: 0 to 10 atomic %, and Mo: 0 to 10 atomic %. The coating weight of the insulating coating was 2.0 to 7.0 g / m per side. 2 was met.

[0144] As can be seen from Tables 2 to 6, the product characteristics of the present invention examples D1 to D33 and E1 to E6 satisfied the range of the present invention, and were excellent in terms of the decrease in coating tension before and after maintaining constant temperature and humidity, and in terms of the decrease in coating tension after maintaining constant temperature and humidity. In contrast, the comparative examples d1 to d15 did not satisfy the product characteristics within the scope of the present invention, and were inferior in at least one of the following: the film tension before and after being kept at constant temperature and humidity, and the decrease in film tension after being kept at constant temperature and humidity. Note that the comparative example d1 contains chromate (chromium compound), and is therefore outside the scope of the present invention.

[0145] [Table 2]

[0146] [Table 3]

[0147] [Table 4]

[0148] [Table 5]

[0149] [Table 6] [Industrial Applicability]

[0150] According to the above aspect of the present invention, it is possible to reliably obtain a grain-oriented electrical steel sheet in which the insulating coating does not contain chromate, and the ability to apply tension to the base steel sheet is equal to or better than conventional methods, and in which the coating tension decreases little even when the steel sheet is stored for a long period of time in a high-temperature, high-humidity atmosphere, thereby providing high industrial applicability.

Claims

1. A steel plate base material and an insulating coating are provided. the insulating coating does not contain a chromium compound, The coating tension of the insulating coating is 4.9 MPa or more, When the potassium intensity of a spectrum obtained by measuring the insulating coating by X-ray fluorescence analysis is defined as P(K) and the sodium intensity is defined as P(Na), the ratio of P(K) to P(Na), P(K) / P(Na), is greater than 13.0 and not greater than 100. A directional electrical steel sheet characterized by:

2. When the chromium intensity of the spectrum is defined as P(Cr) and the silicon intensity is defined as P(Si), the ratio of P(Cr) to P(Si), P(Cr) / P(Si), is 0.01 or less. The grain-oriented electrical steel sheet according to claim 1 .

3. The base steel plate has a chemical composition, in mass%, of C: 0.010% or less, Si: 2.00-4.00%, Mn: 0.05-1.00%, Al: 0.010-0.065%, N: 0.004% or less, S: 0.010% or less, Se: 0.010% or less, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0-0.50%, Ni: 0 to 1.00%, Sn: 0 to 0.30%, Sb: 0 to 0.30%, B: 0 to 0.0100%, Mo: 0-0.1%, Contains Bi: 0 to 0.01%; The balance is Fe and impurities. The grain-oriented electrical steel sheet according to claim 1 .