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

Abstract

In this grain-oriented electromagnetic steel sheet, when measurement points of crystal orientation by x-ray diffraction are arranged at a 6-mm pitch in the rolling direction and the direction orthogonal to the rolling direction, respectively, the proportion of measurement points with an orientation difference of within 15° from [211]<011> to all measurement points is 5% or less. Oxygen intensity reduction regions are present periodically in an oxygen intensity profile of the surface of the primary coating film obtained by line analysis along the rolling direction by an electron beam microanalyzer, and the ratio Iomin / Iomax of the minimum oxygen intensity Iomin in an oxygen intensity reduction region and the maximum oxygen intensity Iomax of a region other than an oxygen intensity reduction region is 0.85-0.96 inclusive.

Description

[Technical Field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the grain-oriented electrical steel sheet. This application claims priority based on Japanese Patent Application No. 2023-065018, filed on April 12, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets are soft magnetic materials that are primarily used as iron core materials for transformers. Therefore, grain-oriented electrical steel sheets are required to have magnetic properties, such as high magnetization and low iron loss. Iron loss is the power loss consumed as thermal energy when an iron core is excited by an AC magnetic field, and from the perspective of energy conservation, iron loss should be as low as possible.

[0003] Iron loss is expressed as the sum of hysteresis loss, which depends on the crystal orientation and purity, and eddy current loss, which depends on the sheet thickness, resistivity, and size of the magnetic domain. Therefore, reducing hysteresis loss and eddy current loss are effective ways to reduce iron loss. One method for reducing hysteresis loss is to change the crystal orientation to the Goss orientation ({110}), which is good for magnetic properties. <001> One known method is to increase the magnetic flux density by accumulating the magnetic flux in the direction of the orientation (increasing the degree of orientation accumulation). Other known methods for reducing eddy current loss include increasing the silicon content, which increases electrical resistance, reducing the thickness of the steel sheet, and subdividing the magnetic domains.

[0004] In particular, cold rolling is often used to reduce the sheet thickness. However, there is a problem that good magnetic properties cannot be stably obtained with thin grain-oriented electrical steel sheets. For example, the following techniques have been disclosed as methods for improving the magnetic properties of thin grain-oriented electrical steel sheets.

[0005] Patent Document 1 discloses a method for manufacturing a grain-oriented electrical steel sheet that performs two cold rolling steps with intermediate annealing in between. Specifically, Patent Document 1 discloses that hot rolling is completed at 850°C or higher, followed by immediate cooling and coiling at 600°C or lower, and then, prior to the first cold rolling step, a carbide adjustment heat treatment is performed in which the sheet is soaked in a temperature range of 650 to 900°C for 2 to 10 seconds. This allows for stable and excellent magnetic flux density to be obtained in the longitudinal direction of the coil, even with a thin grain-oriented electrical steel sheet.

[0006] Patent Document 2 discloses a method for producing grain-oriented electrical steel sheet by cold rolling once or twice or more with intermediate annealing in between. Specifically, Patent Document 2 discloses that excellent magnetic flux density and iron loss can be obtained by setting the final cold rolling reduction to 89% or more and heat-treating the strip rolled to the final thickness at a heating rate of 50°C / s or more to a temperature of 700°C or higher immediately before decarburization annealing. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 6-145799 [Patent Document 2] Japanese Patent Application Publication No. 7-62438 Summary of the Invention [Problem to be solved by the invention]

[0008] However, conventional techniques can result in variations in magnetic flux density, and rapid heating in the decarburization annealing step can reduce the adhesion between the steel sheet and the insulating coating (hereinafter referred to as coating adhesion).

[0009] An object of the present disclosure is to provide a grain-oriented electrical steel sheet having excellent magnetic properties and coating adhesion, and a method for manufacturing the same. [Means for solving the problem]

[0010] The gist of the present disclosure is as follows. [1] A grain-oriented electrical steel sheet according to one embodiment of the present disclosure comprises a base steel sheet, a primary coating formed on the base steel sheet, and a secondary coating formed on the primary coating, The chemical composition of the base steel plate is, in mass%, Si: 2.50-4.00% Mn: 0.01 to 0.30%, N: 0.0001 to 0.0100%, C: 0.0005~0.010%, sol.Al: 0~0.010%, one or more selected from the group consisting of S and Se: 0 to 0.010% in total; Ti: 0.001 to 0.010%, Ni: 0 to 0.50% Cu: 0-0.50% Sb: 0 to 0.30% Sn: 0~0.30% Cr: 0~0.50%, P: 0~0.05%, Mo: 0 to 0.05%, Ta: 0 to 0.05%, Nb: 0 to 0.010% V: 0~0.50%, B: 0~0.010%, Bi: 0 to 0.0150%, and Te: 0 to 0.0150% Contains The balance is Fe and impurities. The magnetic flux density B8 is 1.902T or more, When crystal orientation measurement points by X-ray diffraction are arranged on the surface of the base steel sheet at 6 mm pitches in the rolling direction and in the direction perpendicular to the rolling direction, the {211} <011> The percentage of measurement points where the misorientation from the target is within 15° is 5% or less. an oxygen intensity profile on the surface of the primary coating obtained by line analysis along the rolling direction using an electron probe microanalyzer shows periodic regions of low oxygen intensity; The minimum value Io of the oxygen intensity in the oxygen intensity decreasing regionmin and the maximum value Io of the oxygen intensity in the region other than the oxygen intensity decreasing region. max Relative to Io min / Io max is between 0.85 and 0.96. [2] In the grain-oriented electrical steel sheet according to the above [1], the oxygen strength reduced regions may be present at intervals L of 5 to 30 mm. [3] In the grain-oriented electrical steel sheet according to the above [1] or [2], the chemical composition of the base steel sheet is, in mass%, Ni: 0.01 to 0.50% Cu: 0.01 to 0.50% Sb: 0.01 to 0.30%, Sn: 0.01 to 0.30% Cr: 0.01 to 0.50%, P: 0.01-0.05%, Mo: 0.01 to 0.05%, Ta: 0.01 to 0.05%, Nb: 0.001 to 0.010%, V: 0.01 to 0.50%, B: 0.001~0.010%, Bi: 0.0100% or less, and Te: 0.0100% or less The compound may contain one or more selected from the following: [4] In the grain-oriented electrical steel sheet according to any one of the above [1] to [3], the sheet thickness may be 0.15 to 0.23 mm. [5] In the grain-oriented electrical steel sheet according to any one of the above [1] to [4], the base steel sheet may have a thickness of 0.14 to 0.22 mm. [6] A method for producing a grain-oriented electrical steel sheet according to one embodiment of the present disclosure comprises, in mass %, Si: 2.50-4.00% Mn: 0.01 to 0.30%, N: 0.0030~0.0150%, C: 0.010~0.100%, sol.Al: 0.010~0.050%, One or more selected from the group consisting of S and Se: 0.010 to 0.050% in total, Ti: 0.001 to 0.010%, Ni: 0 to 0.50% Cu: 0-0.50% Sb: 0 to 0.30% Sn: 0~0.30% Cr: 0~0.50%, P: 0~0.05%, Mo: 0 to 0.05%, Ta: 0 to 0.05%, Nb: 0 to 0.010% V: 0~0.50%, B: 0~0.010%, Bi: 0 to 0.0200%, and Te: 0 to 0.0200% a hot rolling step of heating a slab containing the above-mentioned alloy and the balance being Fe and impurities, and hot rolling the heated slab to obtain a hot-rolled steel sheet; a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet; a cold rolling step of cold-rolling the hot-rolled steel sheet after the hot-rolled sheet annealing step to obtain a cold-rolled steel sheet; a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing to obtain a decarburization annealed steel sheet; a finish annealing step of applying an annealing separator to the decarburization-annealed steel sheet and then subjecting it to finish annealing to form a primary coating on the surface of the decarburization-annealed steel sheet, thereby obtaining a finish annealed sheet; and an insulating film forming step of forming an insulating film on the surface of the finish annealed sheet, The total reduction rate in the cold rolling step is 89% or more, The decarburization annealing step includes: a local heating process in which the surface of the cold-rolled steel sheet is partially heated by irradiating it with a laser beam in an air atmosphere at intervals of 5 to 30 mm in a direction at an angle of 30 to 150° to the rolling direction; a heating process in which the cold-rolled steel sheet after the local heating process is heated in a non-oxidizing atmosphere from a temperature range of 450°C or less to a temperature range of 750 to 950°C, which is the decarburization annealing temperature, at an average heating rate of 80°C / sec or more and 2000°C / sec or less; The cold-rolled steel sheet after the temperature rising process is heated to an oxygen potential P O and a soaking process in which decarburization annealing is performed. Including, In the local heating process, the laser beam irradiation conditions are as follows: the average intensity of the laser beam in W is denoted by P; The diameter of the focused spot in the rolling direction is Dl in mm, The focused diameter of the focused spot in the width direction perpendicular to the rolling direction is represented by Dc in mm, The irradiation time is expressed in seconds as t. The instantaneous input energy expressed as 4 / π×P / (Dl×Dc)×t is expressed in units of J / mm 2 When Up is set, the following formula (2) is satisfied. P O ≦ 0.6-0.04Up (1) 1 ≦ Up ≦ 5 (2) [7] In the method for producing a grain-oriented electrical steel sheet according to the above [6], the chemical composition of the slab is, in mass%, Ni: 0.01 to 0.50% Cu: 0.01 to 0.50% Sb: 0.01 to 0.30%, Sn: 0.01 to 0.30% Cr: 0.01 to 0.50%, P: 0.01-0.05%, Mo: 0.01 to 0.05%, Ta: 0.01 to 0.05%, Nb: 0.001 to 0.010%, V: 0.01 to 0.50%, B: 0.001~0.010%, Bi: 0.0100% or less, and Te: 0.0100% or less The compound may contain one or more selected from the following: [Effects of the Invention]

[0011] According to the present disclosure, it is possible to provide a grain-oriented electrical steel sheet having excellent magnetic properties and coating adhesion, and a method for manufacturing the same. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is a diagram showing an example of a cold-rolled steel sheet on which a linear heating portion is formed. [Figure 2] 10A and 10B are diagrams for explaining the focused diameter and scanning speed of a laser beam. [Figure 3] FIG. 1 is a schematic diagram of the oxygen intensity profile measured by line analysis of the primary coating surface using an EPMA. DETAILED DESCRIPTION OF THE INVENTION

[0013] <1. Investigation by the Inventors> An embodiment of the present invention will be described below. First, the investigations conducted by the present inventors will be described. The present inventors investigated the causes of deterioration and variation in magnetic flux density in grain-oriented electrical steel sheets. As a result, they found that the deterioration of magnetic properties is caused by the {211} <011> This was due to secondary recrystallized grains with a crystal orientation that was inferior in magnetic properties. It was also found that the magnetic properties varied in the longitudinal direction of the coil, with the deterioration of the magnetic properties being particularly noticeable at the ends of the coil in the longitudinal direction.

[0014] {211} <011> The reason why oriented grains undergo secondary recrystallization at the ends in the longitudinal direction of the coil is not clear, but is presumed to be as follows. The longitudinal ends of the coil may be heated more than desired during hot rolling, and decarburization easily progresses in the steel sheet surface layer at such overheated portions during hot rolling. When decarburization progresses in the steel sheet surface layer, the austenite ratio during hot rolling decreases, and as a result, the {211} ferrite, which is the rolling stable orientation, is formed in the steel sheet surface layer. <011> This makes it easier for the direction to develop. <011> The orientation is inherited and further developed after cold rolling, resulting in {211} <011> Secondary recrystallized grains with a {211} orientation (hereinafter referred to as {211} <011> In particular, in the case of grain-oriented electrical steel sheets manufactured at a high cold rolling rate, the {211} grains developed during hot rolling are thought to be the cause of the formation of many recrystallized grains. <011> It is assumed that the orientation is more easily inherited during cold rolling.

[0015] As mentioned above, this <011> Secondary recrystallized grains are a factor that deteriorates magnetic properties. <011> We have conducted extensive research into ways to suppress the formation of secondary recrystallized grains. First, <011> We investigated the factors that facilitate secondary recrystallization of oriented grains and found that the Goss orientation ({110} <001> In particular, when grain-oriented electrical steel sheets are manufactured at high cold rolling reduction rates, the decrease in Goss orientation is more pronounced, resulting in a decrease in the {211} <011> It is thought that this facilitates secondary recrystallization of oriented grains.

[0016] Therefore, we investigated a method to enrich the Goss orientation. A technique for enriching the Goss orientation has been known in the past, where the temperature is increased rapidly during the decarburization annealing process. However, in grain-oriented electrical steel sheets, the {211} orientation, which is inferior in magnetic properties, is often <011> Secondary recrystallization of oriented grains may occur, resulting in failure to obtain good magnetic properties or variations in magnetic properties.

[0017] In light of this background, the present inventors have worked to further improve the rapid heating process technology during the temperature rise process of the decarburization annealing process. As a result, it has been found that precise control of the irradiation conditions of the localized rapid heating process using a laser beam and control of the oxygen potential during the decarburization annealing process in accordance with the laser beam irradiation conditions can be combined to achieve the {211} <011> It was found that this is effective in suppressing secondary recrystallization of oriented grains.

[0018] Conventional heating methods, such as radiation heating, resistance heating, and induction heating, increase the heating rate during the annealing process to enrich Goss-oriented grains, which serve as nuclei for secondary recrystallization. However, these conventional heating methods tend to increase the {111} orientation, which promotes the growth of Goss-oriented grains in the center of the steel plate thickness direction. <112> However, there is a tendency for the number of Goss-oriented grains in the vicinity to decrease, and there is a limit to how much the magnetic properties can be improved by increasing the heating rate during the annealing process. In particular, in thin grain-oriented electrical steel sheets, the reduction of Goss-oriented grains, which act as the nuclei for secondary recrystallization grains, is an issue, but when conventional heating methods are applied, the entire thickness of the sheet is heated, and for the reasons mentioned above, sufficient effects cannot be obtained.

[0019] On the other hand, localized rapid heating treatment using a laser beam rapidly heats only the surface layer of the steel sheet (especially the 1 / 5 thickness), so Goss-oriented grains, which act as nuclei for secondary recrystallization, are enriched in the surface layer of the steel sheet, while the {111} <112> This can suppress the decrease of neighboring oriented grains, thereby promoting the secondary recrystallization of Goss-oriented grains, which are advantageous for magnetic properties.

[0020] However, when the inventors investigated the relationship between the laser beam irradiation conditions and the properties of the electrical steel sheet, they found that coating adhesion may deteriorate. Specific investigation revealed that the annealing conditions (particularly the soaking conditions) in the decarburization annealing process affect coating adhesion, and that controlling both the laser beam irradiation conditions and the annealing conditions within appropriate ranges is effective in improving coating adhesion.

[0021] The decrease in coating adhesion was due to a decrease in the primary coating, forsterite (Mg2SiO4), in the laser beam irradiated area. The reason for the decrease in the primary coating in the laser beam irradiated area is not clear, but it is thought that the internal SiO2 oxide layer is less likely to form in the laser beam irradiated area during the decarburization annealing process, and the amount of primary coating formed in the subsequent finish annealing process is reduced locally. Therefore, the inventors have thoroughly investigated the annealing conditions in the decarburization annealing process in order to promote the formation of an internal SiO2 oxide layer in the laser beam irradiated area, and have found that suppressing the oxygen potential during the soaking process in the decarburization annealing process in accordance with the laser beam irradiation conditions is effective in promoting the formation of an internal SiO2 oxide layer. This is thought to be because, although the oxygen adhesion amount of the entire steel sheet is reduced by suppressing the oxygen potential during the soaking process, the formation of an internal SiO2 oxide layer, rather than an iron-based oxide layer, is promoted in the laser beam irradiated area.

[0022] Hereinafter, a grain-oriented electrical steel sheet and a method for producing the same according to an embodiment of the present invention, which have been made based on the above findings, will be described in detail.

[0023] <2. Method of manufacturing grain-oriented electrical steel sheets> First, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present disclosure (a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment) will be described. The method for manufacturing a grain-oriented electrical steel sheet according to this embodiment includes the following steps. (I) a hot rolling step of heating a slab having a predetermined chemical composition and hot rolling the heated slab to form a hot-rolled steel sheet; (II) a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet; (III) a cold rolling step of cold rolling the hot-rolled steel sheet after the hot-rolled sheet annealing step to obtain a cold-rolled steel sheet; (IV) a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing to obtain a decarburization annealed steel sheet; (V) A final annealing step of subjecting the decarburized annealed steel sheet to final annealing. Each step will be described below. For steps or conditions not described, known steps and conditions can be applied.

[0024] (Hot rolling process) In the hot rolling step, a slab having a chemical composition described below is heated to 1280°C or higher, and the heated slab is hot rolled to form a hot-rolled steel sheet. If the heating temperature is lower than 1280°C, the inclusions formed in the slab cannot be dissolved, and the inhibitors are not sufficiently formed in the hot rolling process and the hot-rolled sheet annealing process described below. Therefore, the slab heating temperature is set to 1280°C or higher. There is no upper limit to the slab heating temperature, but if the slab is heated at a temperature higher than 1450°C, the slab will melt, making hot rolling difficult. Therefore, the slab heating temperature is preferably 1450°C or lower. The hot rolling conditions are not particularly limited and may be appropriately set based on the desired properties. The thickness of the hot rolled steel sheet obtained by hot rolling is preferably within the range of 1.0 mm to 4.0 mm, for example.

[0025] [Chemical composition of slab] In order to obtain desirable magnetic properties for grain-oriented electrical steel sheets, the chemical composition of the slabs subjected to hot rolling must be within the following range. In the following description, unless otherwise specified, "%" refers to "mass %." In addition, the numerical ranges described below, separated by "to" include the lower and upper limits. Numerical values ​​indicated as "less than" and "greater than" do not include the numerical range.

[0026] C: 0.010 to 0.100% Carbon (C) is an element that improves magnetic flux density. However, if the C content of the slab exceeds 0.100%, productivity in the decarburization annealing process decreases. Furthermore, if the C content of the slab is high and decarburization is insufficient, the steel undergoes phase transformation during secondary recrystallization annealing (i.e., finish annealing), and secondary recrystallization does not proceed sufficiently. This prevents good magnetic flux density and low iron loss, and magnetic properties deteriorate due to magnetic aging. Therefore, the C content of the slab is set to 0.100% or less. The lower the C content, the better for productivity and reduced iron loss. From the viewpoints of productivity and reduced iron loss, the C content is preferably 0.090% or less, and more preferably 0.080% or less. On the other hand, if the C content of the slab is less than 0.010%, the effect of improving the magnetic flux density cannot be obtained. Therefore, the C content of the slab is set to 0.010% or more. The C content is preferably 0.040% or more, and more preferably 0.060% or more.

[0027] Si: 2.50 to 4.00% Silicon (Si) is an extremely effective element for increasing the electrical resistance (resistivity) of steel and reducing eddy current loss, which constitutes part of iron loss. If the Si content of the slab is less than 2.50%, the resistivity is low and eddy current loss cannot be sufficiently reduced. Furthermore, the steel undergoes phase transformation during secondary recrystallization annealing, which prevents sufficient secondary recrystallization, making it difficult to achieve good magnetic flux density and low iron loss. Therefore, the Si content of the slab is set to 2.50% or more. The Si content of the slab is preferably 2.70% or more, and more preferably 2.80% or more. On the other hand, if the Si content exceeds 4.00%, the steel sheet becomes embrittled and the sheet passing property during the manufacturing process deteriorates significantly. Therefore, the Si content of the slab is set to 4.00% or less. The Si content of the slab is preferably 3.90% or less, and more preferably 3.80% or less.

[0028] Mn: 0.01 to 0.30% Mn (manganese) is an important element that forms MnS, one of the main inhibitors. If the Mn content of the slab is less than 0.01%, the absolute amount of MnS required to cause secondary recrystallization is insufficient. Therefore, the Mn content of the slab is set to 0.01% or more. The Mn content is preferably 0.03% or more, and more preferably 0.06% or more. On the other hand, if the Mn content of the slab exceeds 0.30%, the steel undergoes phase transformation during secondary recrystallization annealing, and secondary recrystallization does not proceed sufficiently, making it impossible to obtain good magnetic flux density and low iron loss. Therefore, the Mn content of the slab is set to 0.30% or less, preferably 0.28% or less, and more preferably 0.26% or less.

[0029] One or more selected from the group consisting of S and Se: 0.010 to 0.050% S (sulfur) and Se (selenium) are elements that react with Mn to form inhibitors MnS and MnSe. Since it is sufficient to form MnS or MnSe as inhibitors, one of S and Se may be contained in the slab, or both may be contained in the slab. If the total content of one or two of S and Se is less than 0.010%, sufficient inhibitors are not formed. Therefore, the total content of one or two of S and Se is set to 0.010% or more. The total content of one or two of S and Se is preferably 0.020% or more. On the other hand, if the total content of one or two of S and Se exceeds 0.050%, hot embrittlement occurs, making hot rolling extremely difficult. Therefore, the total content of one or two of S and Se is set to 0.050% or less. The total content of one or two of S and Se is preferably 0.040% or less, more preferably 0.030% or less.

[0030] sol.Al: 0.010~0.050% Sol.Al (acid-soluble aluminum) is a constituent element of a major inhibitor among compounds called inhibitors that affect secondary recrystallization in grain-oriented electrical steel sheets, and is an essential element in the base steel sheet according to this embodiment from the viewpoint of secondary recrystallization occurrence. If the sol.Al content of the slab is less than 0.010%, AlN, which functions as an inhibitor, is not sufficiently generated, resulting in insufficient secondary recrystallization. Therefore, the sol.Al content is set to 0.010% or more. The sol.Al content is preferably 0.020% or more. On the other hand, if the sol.Al content exceeds 0.050%, AlN, which functions as an inhibitor, is not sufficiently generated, resulting in insufficient secondary recrystallization. Therefore, the sol.Al content is set to 0.050% or less. The sol.Al content is preferably 0.040% or less, and more preferably 0.030% or less.

[0031] N: 0.0030~0.0150% N (nitrogen) is an element that reacts with the acid-soluble Al to form AlN, which functions as an inhibitor. To form a sufficient amount of AlN that functions as an inhibitor, the N content is set to 0.0030% or more. The N content is preferably 0.0050% or more. On the other hand, if the N content exceeds 0.0150%, blisters (voids) are formed in the steel sheet during cold rolling, and the strength of the steel sheet increases, resulting in poor sheet passing properties during production. Therefore, the N content of the slab is set to 0.0150% or less. The N content is preferably 0.0130% or less, and more preferably 0.0100% or less.

[0032] Ni: 0 to 0.50% Ni (nickel) is an element effective in increasing electrical resistance and reducing iron loss. Ni is also an element effective in controlling the metal structure of a hot-rolled steel sheet and improving its magnetic properties. Therefore, Ni may be contained. To obtain the above effects, the Ni content is preferably 0.01% or more. The Ni content is more preferably 0.02% or more. On the other hand, if the Ni content exceeds 0.50%, secondary recrystallization may become unstable. Therefore, the Ni content is set to 0.50% or less, and preferably 0.30% or less.

[0033] Cu: 0 to 0.50% Copper (Cu) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallization structure and also contributes to improving the adhesion of the glass coating. Therefore, it may be added. To obtain the above effects, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Cu content exceeds 0.50%, the steel sheet becomes embrittled during hot rolling. Therefore, the Cu content of the slab is set to 0.50% or less. The Cu content is preferably 0.30% or less, and more preferably 0.10% or less.

[0034] Sb: 0 to 0.30% Sb (antimony) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Sb is contained, the content is preferably 0.01% or more in order to effectively exhibit the effect of improving magnetic properties. The Sb content is more preferably 0.02% or more. On the other hand, if the Sb content exceeds 0.30%, the adhesion of the glass coating deteriorates. Therefore, the Sb content is set to 0.30% or less, and preferably 0.20% or less.

[0035] Sn: 0 to 0.30% Sn (tin) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Sn is contained, the Sn content is preferably 0.01% or more to effectively exhibit the effect of improving magnetic properties. In consideration of achieving both magnetic properties and coating adhesion, the Sn content is preferably 0.02% or more, and more preferably 0.03% or more. On the other hand, if the Sn content exceeds 0.30%, the glass coating deteriorates significantly and sufficient tension for magnetic domain refinement is not obtained, resulting in poor core loss characteristics. Therefore, the Sn content is set to 0.30% or less. The Sn content is preferably 0.20% or less, and more preferably 0.15% or less.

[0036] Cr: 0 to 0.50% Like Sn and Cu described below, Cr (chromium) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure, thereby improving magnetic properties, and also contributes to improving the adhesion of the glass coating. Therefore, Cr may be added. To achieve the above effects, the Cr content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Cr content exceeds 0.50%, Cr oxides are formed, resulting in a deterioration in magnetic properties. Therefore, the Cr content is set to 0.50% or less. The Cr content is preferably 0.30% or less, and more preferably 0.10% or less.

[0037] P: 0 to 0.05% P (phosphorus) is an element that reduces workability in rolling. By setting the P content to 0.05% or less, it is possible to prevent excessive reduction in rolling workability and prevent breakage during manufacturing. From this perspective, the P content is set to 0.05% or less. The P content is preferably 0.04% or less. The lower limit of the P content is not limited and may include 0%, but P is also an element that has the effect of improving the texture and magnetic properties. To obtain this effect, the P content may be 0.005% or more, or 0.01% or more.

[0038] Mo: 0 to 0.05% Mo (molybdenum) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Mo is contained, the Mo content is preferably 0.01% or more in order to effectively exhibit the effect of improving magnetic properties. The Mo content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Mo content exceeds 0.05%, the cold rolling property deteriorates and there is a possibility of fracture. Therefore, the Mo content is set to 0.05% or less, and preferably 0.04% or less.

[0039] Ta: 0 to 0.05% Ta (tantalum) is a useful element that functions as an inhibitor by bonding with N and C. To obtain this effect, the Ta content may be more than 0.0000%, or may be 0.0005% or more. On the other hand, if the Ta content exceeds 0.05%, the magnetic properties may be deteriorated. Therefore, the Ta content should be 0.05% or less. The Ta content is preferably 0.04% or less.

[0040] Nb: 0 to 0.010% Nb (niobium) has the effect of stabilizing secondary recrystallization. To obtain the above effect, the Nb content may be more than 0.0000% or may be 0.0005% or more. On the other hand, if the Nb content exceeds 0.010%, the secondary recrystallization may become unstable. Therefore, the Nb content should be 0.010% or less. The Nb content is preferably 0.0050% or less.

[0041] V: 0 to 0.50% V (vanadium) is an effective element that functions as an inhibitor by bonding with N and C. Therefore, V may be contained. To obtain the above effects, the V content is preferably 0.01% or more, and more preferably 0.02% or more. On the other hand, if the V content exceeds 0.50%, the magnetic properties may deteriorate. Therefore, the V content is set to 0.50% or less. The V content is preferably 0.30% or less, and more preferably 0.20% or less.

[0042] B: 0 to 0.0200% B (boron) has the effect of stabilizing secondary recrystallization. To obtain the above effect, the B content may be more than 0.0000%, or may be 0.0005% or more. On the other hand, if the B content exceeds 0.0200%, secondary recrystallization may become unstable. Therefore, the B content should be 0.0200% or less. The B content is preferably 0.0100% or less, and more preferably 0.0050% or less.

[0043] Bi: 0 to 0.0200% Bi (bismuth) has the effect of improving magnetic properties. Therefore, Bi may be contained. To obtain the above effect, the Bi content may be more than 0.0000%, or may be 0.0005% or more. On the other hand, if the Bi content exceeds 0.0200%, the sheet threadability during cold rolling may deteriorate. Furthermore, if the purification during finish annealing is insufficient and excessive Bi remains, it may have an adverse effect on the magnetic properties. Therefore, the Bi content should be 0.0200% or less. The Bi content is preferably 0.0150% or less, and more preferably 0.0100% or less.

[0044] Te: 0 to 0.0200% Te (tellurium) has the effect of stabilizing secondary recrystallization. To obtain the above effect, the Te content may be more than 0.0000% or may be 0.0005% or more. If the Te content exceeds 0.0200%, fracture may occur during hot rolling or cold rolling. Therefore, the Te content should be 0.0200% or less. The Te content is preferably 0.0150% or less, and more preferably 0.0100% or less.

[0045] Remainder: Fe and impurities The chemical composition of the slab used in the method for producing a grain-oriented electrical steel sheet according to this embodiment may contain the above-mentioned elements, with the balance being Fe and impurities. Here, the impurities refer to elements that are mixed in from raw materials such as ore or scrap, or from the production environment, during industrial production of the base steel sheet, and that are permissible to be contained in amounts that do not adversely affect the function of the grain-oriented electrical steel sheet according to this embodiment.

[0046] (Hot-rolled sheet annealing process) The hot-rolled steel sheet annealing process is a process of annealing the hot-rolled steel sheet manufactured through the hot rolling process. By performing such annealing treatment, recrystallization occurs in the steel sheet structure, making it possible to achieve good magnetic properties. In the hot-rolled steel sheet annealing step of this embodiment, the hot-rolled steel sheet manufactured through the hot rolling step may be annealed according to a known method. The means for heating the hot-rolled steel sheet during annealing is not particularly limited, and known heating methods can be adopted. The annealing conditions are also not particularly limited, but for example, the hot-rolled steel sheet may be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes.

[0047] (Cold rolling process) In the cold rolling process, the hot-rolled steel sheet after the hot-rolled sheet annealing process is subjected to cold rolling including multiple passes to obtain a cold-rolled steel sheet. The cold rolling may be a single cold rolling, or may be multiple cold rolling passes with intermediate annealing interposed therebetween, with the cold rolling interrupted before the final pass of the cold rolling process and at least one or two intermediate annealings being performed. When intermediate annealing is performed, it is preferable to hold the steel sheet at a temperature of 1000 to 1200° C. for 5 to 180 seconds. The annealing atmosphere is not particularly limited. In consideration of production costs, it is preferable to perform intermediate annealing three times or less.

[0048] The total reduction in the cold rolling step is 89% or more. If the total reduction is less than 89%, a suitable primary recrystallization texture cannot be obtained. Specifically, if the total reduction is less than 89%, the sharpness of the Goss orientation that serves as the nucleus for secondary recrystallization cannot be sufficiently obtained, and good magnetic properties may not be obtained. The total reduction in the cold rolling step is preferably 90% or more, more preferably 91% or more, and even more preferably 92% or more. Before the cold rolling step, the surface of the hot-rolled steel sheet may be subjected to pickling under known conditions.

[0049] (Decarburization annealing process) In the decarburization annealing step, the cold-rolled steel sheet is subjected to decarburization annealing to produce a decarburization annealed steel sheet. In decarburization annealing, the cold-rolled steel sheet is subjected to primary recrystallization and C, which has an adverse effect on magnetic properties, is removed from the steel sheet. In the method for producing a grain-oriented electrical steel sheet according to this embodiment, however, the steel sheet is locally heated before being heated to the annealing temperature. That is, the decarburization annealing step in this embodiment is (IV-1) a local heating process in which the surface of the cold-rolled steel sheet is partially heated by irradiating the surface with a laser beam in an air atmosphere at intervals of 5 to 30 mm in a direction at an angle of 30 to 150° to the rolling direction; (IV-2) A heating process in which the cold-rolled steel sheet after the local heating process is heated in a non-oxidizing atmosphere from a temperature range of 450 ° C or less to a temperature range of 750 to 950 ° C, which is the decarburization annealing temperature, at an average heating rate of 80 ° C / s or more; (IV-3) After the temperature rising process, the cold-rolled steel sheet is heated to an oxygen potential P O and a soaking process in which decarburization annealing is performed. Includes:

[0050] [Local heating process] In the local heating process, the surface of the cold-rolled steel sheet is partially heated in an air atmosphere by irradiating it with a laser beam at intervals of 5 to 30 mm in a direction forming an angle of 30 to 150° with respect to the rolling direction. More specifically, in the local heating process, the surface of the cold-rolled steel sheet is heated in an atmospheric environment so that the heated areas formed by the laser beam are in the form of multiple lines extending in a direction at an angle of 30 to 150° to the rolling direction (a direction at an angle of ±60° to the direction perpendicular to the rolling direction) and spaced at intervals of 5 to 30 mm in the rolling direction. The cold-rolled steel sheet after local heating has linear heated areas as shown in Figure 1.

[0051] In the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment, the steel sheet is locally heated to enrich the Goss-oriented grains in the heated area. The Goss-oriented grain-enriched region may be arranged in a line extending in a direction intersecting the rolling direction as described above, or may be repeatedly arranged at predetermined intervals in the rolling direction.

[0052] The extending direction of the linear heating portion is at an angle of less than 30° or more than 150° with respect to the rolling direction. When the orientation is nearly parallel to the rolling direction (30° or more or 150° or less), the misalignment angle of the secondary recrystallized Goss-oriented grains increases, which may result in a decrease in magnetic flux density, although the cause is unknown.

[0053] If the interval between the linearly heated sections exceeds 30 mm, the Goss-oriented grains that serve as nuclei for secondary recrystallization may not be obtained sufficiently, resulting in a decrease in magnetic flux density.On the other hand, if the interval between the linearly heated sections is less than 5 mm, the number of Goss-oriented grains will be excessive, and the number of grains with the corresponding orientation that promotes the growth of the Goss-oriented grains will decrease, resulting in a decrease in the degree of accumulation of the Goss-oriented grains.

[0054] The intervals between the linear heating parts may be approximately equal, but the intervals between adjacent linear heating parts may be controlled to be different as long as they are within the above-mentioned range of intervals between the linear heating parts. For example, in the finish annealing process in which annealing is performed in a coiled state, the intervals between the heating parts may be narrowed in the inner peripheral part with a small curvature to enrich Goss-oriented grains that serve as nuclei for secondary recrystallization and reduce the diameter of the secondary recrystallized grains.

[0055] The width of the linear heated portion is preferably 0.2 to 1.0 mm. If it is less than 0.2 mm, the heated portion is small, and the effect of enriching Goss-oriented grains is reduced. On the other hand, if it exceeds 1.0 mm, the effect of enriching Goss-oriented grains is maintained, but the number of corresponding-oriented grains decreases, resulting in a large deviation angle from the Goss orientation after secondary recrystallization.

[0056] The length of the linear heating portion is not limited, but it is preferable that the heating portion be formed over the entire width of the steel sheet, or over the entire width excluding the edge portions.

[0057] Furthermore, local heating (forming a linear heated portion) is performed by irradiating a laser beam, which allows localized heating and has little effect on the surrounding area.

[0058] When heating is performed by laser beam irradiation, the average intensity of the laser beam is P (W), the focal diameter of the focused spot in the rolling direction is Dl (mm), the focal diameter of the focused spot in the width direction is Dc (mm), and the irradiation time is t (seconds). The instantaneous input energy, expressed as 4 / π × P / (Dl × Dc) × t, is Up (J / mm 2 ), the laser beam is irradiated under the condition that the following formula (2) is satisfied.

[0059] The focused diameter Dc is the diameter of the focused spot in the rolling direction shown in Figure 2. The focused diameter Dc is the diameter of the focused spot in the width direction (direction perpendicular to the rolling direction) shown in Figure 2. The laser beam is irradiated onto the steel sheet being passed for a predetermined time t. When irradiating the entire width direction of the steel sheet, multiple irradiation spots may be arranged in series in the width direction.

[0060] 0.5 ≦ Up ≦ 5 (2) By satisfying the condition of formula (2), the length of the secondary recrystallized grains in the rolling direction can be reduced, and the difference in the degree of orientation accumulation to the Goss orientation can be reduced. If formula (2) is not satisfied, sufficient effects cannot be obtained.

[0061] In this embodiment, the purpose of irradiating the laser beam is not to control magnetic domains but to control the structure as described above. In other words, during the temperature increase process in the decarburization annealing step of this embodiment, only the surface layer of the steel sheet is locally heated, and grooves are not formed on the surface of the steel sheet as in general magnetic domain control.

[0062] [Temperature rise process] In the heating process, the cold-rolled steel sheet after the local heating process is heated in a non-oxidizing atmosphere from a temperature range of 450°C or less to a temperature range of 750 to 950°C, which is the decarburization annealing temperature, at an average heating rate of 80°C / sec or more.

[0063] The above-mentioned temperature increase promotes the nucleation of GOSS-oriented grains. If the average heating rate within the above-mentioned temperature range is less than 80°C / s, nucleation will be insufficient, resulting in a large grain size of secondary recrystallized grains. Furthermore, if localized heating is performed to reduce the grain size of secondary recrystallized grains in the rolling direction, sufficient secondary recrystallized grains will be required to completely cover the entire steel sheet with GOSS orientation, which is favorable for magnetic properties. Therefore, the average heating rate is preferably 160°C / s or more, and more preferably 240°C / s or more. There is no upper limit to the heating rate, which may be determined based on the equipment capacity. For example, it is 2000°C / s or less.

[0064] If the atmosphere during temperature rise is not a non-oxidizing atmosphere, a tight SiO2 film will be formed on the surface layer of the steel sheet, resulting in poor decarburization and poor coating after finish annealing. In this embodiment, the non-oxidizing atmosphere is a nitrogen atmosphere or a nitrogen / hydrogen mixed atmosphere, and is an atmosphere with a dew point of -50°C or higher and 0°C or lower. From the viewpoint of suppressing SiO2 generation in the surface layer of the steel sheet and promoting good decarburization, the dew point is preferably -5°C or lower, or -10°C or lower. From the viewpoint of promoting good internal oxidation for ease of process control, the dew point may be, for example, -40°C or higher.

[0065] Annealing after the temperature is raised to 750 to 950°C during the temperature rise process is not limited, but for example, the oxidation degree (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) may be set to 0.15 to 1.0, and the material may be held in that temperature range for 10 to 600 seconds.

[0066] [Soaking process] In the soaking process, the cold-rolled steel sheet after the temperature rising process is heated to an oxygen potential P that satisfies the following formula (1): O Decarburization annealing is performed.

[0067] P O ≦ 0.6-0.04Up (1)

[0068] As described above, it is thought that an SiO2 internal oxide layer is less likely to form in the laser beam irradiated area during the soaking process than in the non-irradiated area, and therefore the amount of primary coating formed in the laser beam irradiated area decreases in the subsequent finish annealing process, resulting in a decrease in coating adhesion. Therefore, in the soaking process of this embodiment, the oxygen potential P O By keeping the oxygen potential P low, the formation of an SiO2 internal oxide layer during the soaking process is promoted. Specifically, the oxygen potential P satisfies the formula (1). O Annealing is carried out at .

[0069] By undergoing the above-described decarburization annealing process, Goss-oriented grains, which act as nuclei for secondary recrystallization, are enriched only in the surface layer of the steel sheet through localized rapid heating by the laser beam. This promotes secondary recrystallization of Goss-oriented grains, which are advantageous for magnetic properties, and also promotes the formation of an internal SiO2 oxide layer throughout the entire steel sheet, including the laser beam-irradiated area, making it possible to achieve both excellent magnetic properties and coating adhesion.

[0070] (finish annealing process) In the final annealing step, a predetermined annealing separator is applied to one or both sides of the decarburized annealed steel sheet obtained in the decarburization annealing step, followed by final annealing. Final annealing is generally performed for a long period of time while the steel sheet is wound into a coil. Therefore, prior to the final annealing, an annealing separator is applied to the decarburized annealed steel sheet and then dried in order to prevent seizure between the inside and outside of the coil winding.

[0071] The annealing separator to be applied is one that contains MgO as its main component (for example, at a weight fraction of 80% or more). By using an annealing separator that contains MgO as its main component, a glass coating can be formed on the surface of the base steel sheet. If MgO is not the main component, the primary coating (glass coating) will not be formed. This is because the primary coating is an Mg2SiO4 or MgAl2O4 compound, and if MgO is not the main component, there will be a shortage of Mg, which is necessary for the formation reaction.

[0072] The finish annealing may be carried out, for example, in an atmospheric gas containing hydrogen and nitrogen, by raising the temperature to 1150 to 1250°C and annealing at that temperature range for 10 to 60 hours.

[0073] <3. Grain-oriented electrical steel sheet> Next, the grain-oriented electrical steel sheet obtained by the above manufacturing method will be described.

[0074] (3-1. Chemical composition of base steel plate) First, the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet will be described. In the following description, unless otherwise specified, the notation "%" represents "mass %" with respect to the total mass of the base steel sheet.

[0075] C: 0.0005 to 0.010% Since C (carbon) is an element that adversely affects the magnetic properties of grain-oriented electrical steel sheets, it is preferable to keep the C content as low as possible. In this embodiment, the C content is 0.010% or less. It is industrially difficult to reduce the C content to exactly 0%. Therefore, approximately 0.0005% is the practical lower limit of the C content.

[0076] Si: 2.50 to 4.00% Silicon (Si) is an extremely effective element for increasing the electrical resistance (resistivity) of steel and reducing eddy current loss, which is a component of iron loss. If the Si content is less than 2.50%, the resistivity is low and eddy current loss cannot be sufficiently reduced. Furthermore, the steel undergoes phase transformation during secondary recrystallization annealing, which prevents sufficient secondary recrystallization, making it impossible to achieve good magnetic flux density and low iron loss. Therefore, the Si content is set to 2.50% or more, preferably 2.70% or more, and more preferably 2.80% or more. On the other hand, if the Si content exceeds 4.00%, the steel sheet becomes embrittled and the sheet passing property during the manufacturing process deteriorates significantly. Therefore, the Si content is set to 4.00% or less. The Si content is preferably 3.90% or less, and more preferably 3.80% or less.

[0077] Mn: 0.01 to 0.30% Mn (manganese) is an important element that forms MnS, one of the main inhibitors. If the Mn content is less than 0.01%, the absolute amount of MnS required to cause secondary recrystallization is insufficient. Therefore, the Mn content is set to 0.01% or more. The Mn content is preferably 0.03% or more, and more preferably 0.06% or more. On the other hand, if the Mn content exceeds 0.30%, the steel undergoes a phase transformation during secondary recrystallization annealing, and secondary recrystallization does not proceed sufficiently, making it difficult to obtain good magnetic flux density and low iron loss. Therefore, the Mn content is set to 0.30% or less. The Mn content is preferably 0.28% or less, and more preferably 0.26% or less.

[0078] One or more selected from the group consisting of S and Se: 0 to 0.010% S and Se are raw materials for the inhibitors MnS and MnSe, but they also have a negative effect on the magnetic properties of grain-oriented electrical steel sheets, so their content in the base steel sheet is preferably as low as possible. In this embodiment, the total content of S and Se is 0.010% or less. The total content of S and Se may be 0%. The total content of S and Se may be 0.0005% or more.

[0079] sol.Al:0~0.010% As mentioned above, sol.Al is a raw material for AlN, which is an inhibitor. However, since it is also an element that adversely affects the magnetic properties of grain-oriented electrical steel sheets, it is preferable that its content in the base steel sheet be as low as possible. In this embodiment, the sol.Al content is 0.010% or less. The sol.Al content may be 0%. The sol.Al content may be 0.0005% or more.

[0080] N: 0.0001 to 0.0100% As mentioned above, N is a raw material for AlN, which is an inhibitor. However, since N also has a negative effect on the magnetic properties of grain-oriented electrical steel sheets, it is preferable that its content in the base steel sheet be as low as possible. In this embodiment, the N content is set to 0.0100% or less. Since it is industrially difficult to reduce the N content to exactly 0%, approximately 0.0001% is the practical lower limit of the N content.

[0081] Ni: 0 to 0.50% Ni (nickel) is an element effective in increasing electrical resistance and reducing iron loss. Ni is also an element effective in controlling the metal structure of a hot-rolled steel sheet and improving its magnetic properties. Therefore, Ni may be contained. To obtain the above effects, the Ni content is preferably 0.01% or more. The Ni content is more preferably 0.02% or more. On the other hand, if the Ni content exceeds 0.50%, secondary recrystallization may become unstable. Therefore, the Ni content is set to 0.50% or less, and preferably 0.30% or less.

[0082] Cu: 0 to 0.50% Copper (Cu) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallization structure and also contributes to improving the adhesion of the glass coating. Therefore, it may be added. To obtain the above effects, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Cu content exceeds 0.50%, the steel sheet becomes embrittled during hot rolling. Therefore, the Cu content of the slab is set to 0.50% or less. The Cu content is preferably 0.30% or less, and more preferably 0.10% or less.

[0083] Sb: 0 to 0.30% Sb (antimony) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Sb is contained, the content is preferably 0.01% or more in order to effectively exhibit the effect of improving magnetic properties. The Sb content is more preferably 0.02% or more. On the other hand, if the Sb content exceeds 0.30%, the adhesion of the glass coating deteriorates. Therefore, the Sb content is set to 0.30% or less, and preferably 0.20% or less.

[0084] Sn: 0 to 0.30% Sn (tin) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Sn is contained, the Sn content is preferably 0.01% or more to effectively exhibit the effect of improving magnetic properties. In consideration of achieving both magnetic properties and coating adhesion, the Sn content is preferably 0.02% or more, and more preferably 0.03% or more. On the other hand, if the Sn content exceeds 0.30%, the glass coating deteriorates significantly and sufficient tension for magnetic domain refinement is not obtained, resulting in poor core loss characteristics. Therefore, the Sn content is set to 0.30% or less. The Sn content is preferably 0.20% or less, and more preferably 0.15% or less.

[0085] Cr: 0 to 0.50% Like Sn and Cu described below, Cr (chromium) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure, thereby improving magnetic properties, and also contributes to improving the adhesion of the glass coating. Therefore, Cr may be added. To achieve the above effects, the Cr content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Cr content exceeds 0.50%, Cr oxides are formed, resulting in a deterioration in magnetic properties. Therefore, the Cr content is set to 0.50% or less. The Cr content is preferably 0.30% or less, and more preferably 0.10% or less.

[0086] P: 0 to 0.05% P (phosphorus) is an element that reduces workability in rolling. By setting the P content to 0.05% or less, it is possible to prevent excessive reduction in rolling workability and prevent breakage during manufacturing. From this perspective, the P content is set to 0.05% or less. The P content is preferably 0.04% or less. The lower limit of the P content is not limited and may include 0%, but P is also an element that has the effect of improving the texture and magnetic properties. To obtain this effect, the P content may be 0.005% or more, or 0.01% or more.

[0087] Mo: 0 to 0.05% Mo (molybdenum) is an element that has the effect of improving magnetic properties. Therefore, it may be contained. When Mo is contained, the Mo content is preferably 0.01% or more in order to effectively exhibit the effect of improving magnetic properties. The Mo content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Mo content exceeds 0.05%, the cold rolling property deteriorates and there is a possibility of fracture. Therefore, the Mo content is set to 0.05% or less, and preferably 0.04% or less.

[0088] Ta: 0 to 0.05% Ta (tantalum) has the effect of stabilizing secondary recrystallization. To obtain the above effect, the Ta content may be more than 0.0000% or may be 0.0005% or more. On the other hand, if the Ta content exceeds 0.05%, secondary recrystallization may become unstable. Therefore, the Ta content should be 0.05% or less. The Ta content is preferably 0.04% or less.

[0089] Nb: 0 to 0.010% Nb (niobium) has the effect of stabilizing secondary recrystallization. To obtain the above effect, the Nb content may be more than 0.0000% or may be 0.0005% or more. On the other hand, if the Nb content exceeds 0.010%, the secondary recrystallization may become unstable. Therefore, the Nb content should be 0.010% or less. The Nb content is preferably 0.0050% or less.

[0090] V: 0 to 0.50% V (vanadium) is an effective element that functions as an inhibitor by bonding with N and C. Therefore, V may be contained. To obtain the above effects, the V content is preferably 0.01% or more, and more preferably 0.02% or more. On the other hand, if the V content exceeds 0.50%, the magnetic properties may deteriorate. Therefore, the V content is set to 0.50% or less. The V content is preferably 0.30% or less, and more preferably 0.20% or less.

[0091] B: 0 to 0.0200% B (boron) has the effect of stabilizing secondary recrystallization. To obtain the above effect, the B content may be more than 0.0000%, or may be 0.0005% or more. On the other hand, if the B content exceeds 0.0200%, secondary recrystallization may become unstable. Therefore, the B content should be 0.0200% or less. The B content is preferably 0.0100% or less, and more preferably 0.0050% or less.

[0092] Bi: 0 to 0.0200% Bi (bismuth) has the effect of improving magnetic properties. Therefore, Bi may be contained. To obtain the above effect, the Bi content may be more than 0.0000%, or may be 0.0005% or more. On the other hand, if the Bi content exceeds 0.0200%, the sheet threadability during cold rolling may deteriorate. Furthermore, if the purification during finish annealing is insufficient and excessive Bi remains, it may have an adverse effect on the magnetic properties. Therefore, the Bi content should be 0.0200% or less. The Bi content is preferably 0.0150% or less, and more preferably 0.0100% or less.

[0093] Te: 0 to 0.0200% Te (tellurium) has the effect of stabilizing secondary recrystallization. To obtain the above effect, the Te content may be more than 0.0000% or may be 0.0005% or more. If the Te content exceeds 0.0200%, fracture may occur during hot rolling or cold rolling. Therefore, the Te content should be 0.0200% or less. The Te content is preferably 0.0150% or less, and more preferably 0.0100% or less.

[0094] Remainder: Fe and impurities The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment may contain the above-mentioned elements, with the balance being Fe and impurities. Here, the impurities refer to elements that are mixed in from raw materials such as ore or scrap, or from the manufacturing environment, during industrial production of the base steel sheet, and that are permissible to be contained in amounts that do not adversely affect the function of the grain-oriented electrical steel sheet according to this embodiment.

[0095] The chemical compositions of the slab and base steel plate described above can be measured by common analytical methods. For example, the steel compositions can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). C and S can be measured using the combustion-infrared absorption method, N can be measured using the inert gas fusion-thermal conductivity method, and O can be measured using the inert gas fusion-non-dispersive infrared absorption method.

[0096] (3-2. Configuration and Properties of Grain-Oriented Electrical Steel Sheet) Next, the configuration and properties of the grain-oriented electrical steel sheet according to the present embodiment will be described.

[0097] <Crystal Orientation> As described above, in the decarburization annealing process of the grain-oriented electrical steel sheet according to the present embodiment, precise control of the irradiation conditions of local rapid heat treatment by a laser beam and control of the oxygen potential in the decarburization annealing process according to the laser beam irradiation conditions are executed together. As a result, in the obtained grain-oriented electrical steel sheet, the secondary recrystallization of {211}<011> orientation grains is sufficiently suppressed, the secondary recrystallization of Goss orientation grains superior in magnetic properties is promoted, and the variation in magnetic properties can be reduced.

[0098] Specifically, when arranging measurement points of crystal orientation by X-ray diffraction method at a pitch of 6 mm in the rolling direction and the direction orthogonal to the rolling direction on the surface of the base steel sheet, the ratio of the measurement points with an azimuth difference of 15° or less from {211}<011> to all the measurement points is 5% or less. Thereby, the magnetic properties of the grain-oriented electrical steel sheet can be further enhanced.

[0099] The method for measuring the crystal orientation is as follows. A sample of 60 mm × 300 mm × sheet thickness is taken from the grain-oriented electrical steel sheet, and crystal orientation measurement by the Laue method is carried out. In the Laue measurement, azimuth data of 171 measurement points are acquired at a pitch of 6 mm in the rolling direction and the direction orthogonal to the rolling direction at the center of the plate. The number of crystal orientation data with a deviation angle of 15° or less from {211}<011> is analyzed from the azimuth data of all the measurement points, and the ratio R occupied in all the measurement points (171 points) is calculated.

[0100] <EPMA Analysis> Also, as described above, since the film adhesion in the laser beam irradiation part is considered to be correlated with the formation amount of forsterite which is the primary film, in the grain-oriented electrical steel sheet of the present embodiment, the formation amount is defined by the analysis data of an electron probe microanalyzer (EPMA). Specifically, in the grain-oriented electrical steel sheet of this embodiment, in the oxygen intensity profile of the surface of the primary coating obtained by line analysis along the rolling direction using EPMA, there are periodically present regions of reduced oxygen intensity, and the minimum value Io of the oxygen intensity in the regions of reduced oxygen intensity is min and the maximum oxygen intensity Io in the region other than the oxygen intensity decreasing region. max Relative to Io min / Io max is between 0.85 and 0.96.

[0101] Fig. 3 is a schematic diagram of the oxygen intensity profile measured by line analysis of the primary coating surface using EPMA. As shown in Fig. 3, in the oxygen intensity profile in the rolling direction of the primary coating surface measured using EPMA, an oxygen intensity-decreasing region appears in the laser beam irradiated area. This means that the amount of forsterite, which is the primary coating, formed is reduced by the laser beam irradiated area. In this embodiment, since the irradiation interval L of the laser beam irradiation is 5 to 30 mm, the oxygen intensity-decreasing region also appears at intervals L of 5 to 30 mm.

[0102] In the grain-oriented electrical steel sheet of this embodiment, the amount of decrease in the oxygen intensity in the oxygen intensity decreased region is suppressed. Specifically, the minimum value Io of the O intensity in the oxygen intensity decreased region is min and the oxygen intensity Io of other parts max Relative to Io min / Io max Io must be 0.85 or greater. min / Io max If Io is less than 0.85, the coating adhesion at the laser beam irradiated area will be poor. min / Io max is 0.85 or more, preferably 0.87 or more. min / Io max The upper limit of the oxygen intensity ratio is not particularly limited, and may be 1 in theory, but when local heating is actually performed by laser beam irradiation, the upper limit is about 0.96. In order to obtain such an oxygen intensity ratio, for example, in the soaking step of the above-mentioned decarburization annealing step, the oxygen potential P O should be set to 0.6-0.04Up or less.

[0103] The specific method of EPMA analysis is as follows. First, a 50 mm square test piece is taken from a grain-oriented electrical steel sheet having a secondary coating. Next, the secondary coating is removed using an alkaline solution. For example, the grain-oriented electrical steel sheet having the secondary coating is immersed in a sodium hydroxide aqueous solution of 30 to 50 mass % NaOH and 50 to 70 mass % HO at 80 to 90°C for 5 to 10 minutes, and then rinsed with water and dried, thereby removing the secondary coating from the grain-oriented electrical steel sheet. Next, the surface of the primary coating after removing the secondary coating is subjected to line analysis using an EPMA (JEOL, JXA-8230) to obtain an oxygen intensity profile. The EPMA analysis conditions are an acceleration voltage of 15.0 kV, a probe current of 100 nA, and a beam shape of 10 μm x 300 μm strip shape. Measurements are made continuously in the rolling direction at 10 μm intervals over a distance of 3 mm 15 times (total of 45 mm), and line analysis is performed in the rolling direction. The obtained O intensity measurement data in the rolling direction is calculated as a moving average of 10 sections, and the maximum intensity Io max and minimum intensity Io min From the ratio Io min / Io max was calculated.

[0104] In order to observe the oxygen intensity-decreased region, the distance of the line analysis should be set longer than the laser irradiation width. For example, if the laser irradiation width is 30 mm, the distance of the line analysis should be 30 mm or more.

[0105] <Thickness> The thickness of the grain-oriented electrical steel sheet according to this embodiment is preferably 0.15 to 0.35 mm from the viewpoint of reducing iron loss, and more preferably 0.18 mm or less. Furthermore, the thickness of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment is preferably 0.14 to 0.22 mm from the viewpoint of reducing iron loss, and more preferably 0.17 mm or less. [Example]

[0106] Next, examples of the present invention will be described, 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.

[0107] A slab was prepared whose chemical composition contained the components shown in Tables 1A to 1D, with the balance being Fe and impurities. The slab was heated to 1340°C in a heating furnace. The heated slab was subjected to a hot rolling process to produce hot-rolled steel sheets having thicknesses shown in Tables 3A to 3D. Next, the hot-rolled steel sheets were subjected to a hot-rolled annealing process at a hot-rolled annealing temperature of 900 to 1200°C for a holding time of 10 to 300 seconds. After the hot-rolled annealing process, the cold-rolled steel sheets were subjected to a cold-rolling process to produce cold-rolled steel sheets having thicknesses shown in Tables 3A to 3B.

[0108] Next, the obtained cold-rolled steel sheet was locally heated with a laser beam in an air atmosphere so that the heated parts extended so that the angle between them and the rolling direction was the inclination angle (deg.) shown in Tables 3A to 3D and formed multiple straight lines aligned in the rolling direction at the pitch (spacing L) (mm) shown in Tables 3A to 3B. The irradiation conditions were as shown in Tables 3A to 3B.

[0109] Next, regardless of whether or not heating was performed with a laser beam, the sample was heated in a nitrogen / hydrogen mixed gas (non-oxidizing atmosphere) with a dew point of -20°C from a temperature range below 400°C to a temperature range of 750-900°C at an average heating rate as shown in Tables 3C-3D.

[0110] After the temperature rise, the oxygen potential P in the annealing atmosphere O As shown in Tables 3C to 3D, decarburization annealing was performed by soaking at 850°C for 120 seconds to obtain decarburization annealed steel sheets.

[0111] An annealing separator (water slurry) containing MgO as the main component was applied to the surface of the decarburized annealed steel sheet. The decarburized annealed steel sheet coated with the annealing separator was then wound into a coil. The coil was subjected to finish annealing to produce a finish annealed steel sheet. The finish annealing temperature was set to 1100°C to 1200°C, and the holding time at the finish annealing temperature was set to 5 to 30 hours.

[0112] The steel sheet after the finish annealing step was subjected to a secondary coating formation step (insulating coating formation step). Specifically, a secondary coating agent (insulating coating agent) mainly composed of colloidal silica and phosphate was applied to the surface (on the glass coating) of each finish-annealed steel sheet, and then the finish-annealed steel sheet to which the secondary coating agent had been applied was baked to form a secondary coating, which is a tension insulating coating, on the primary coating. Grain-oriented electrical steel sheets with each test number were manufactured using the above manufacturing process.

[0113] The chemical composition of the base steel sheet was measured by the following elemental analysis method. First, the primary coating and secondary coating were removed from the base steel sheet by the following method. Specifically, the grain-oriented electrical steel sheet on which the secondary coating was formed was immersed in a sodium hydroxide aqueous solution of 30-50 mass% NaOH + 50-70 mass% HO at 80-90°C for 5-10 minutes, and after immersion, was washed with water and dried. Through this process, the secondary coating was removed from the grain-oriented electrical steel sheet.

[0114] Furthermore, the grain-oriented electrical steel sheet from which the secondary coating had been removed and from which the primary coating remained was immersed in high-temperature hydrochloric acid to remove the coating. Specifically, the grain-oriented electrical steel sheet from which the primary coating remained was immersed in 30-40 mass% hydrochloric acid at 80-90°C for 1-5 minutes, and after immersion, was washed with water and dried. Through these steps, a base steel sheet from which the secondary coating and primary coating had been removed was obtained.

[0115] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet of each test number was measured by the following method. First, the primary coating and secondary coating were removed from the grain-oriented electrical steel sheet by the method described above to extract the base steel sheet. The base steel sheet was used to analyze its chemical composition based on the following measurement methods.

[0116] The chemical composition of the obtained steel sheet was measured according to a method in accordance with JIS G0321:2017. Specifically, chips were first collected from the obtained base steel sheet, and the collected chips were dissolved in acid to obtain a solution. Next, the solution was subjected to ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) to perform elemental analysis of the chemical composition. The C content and S content were determined by the well-known high-frequency combustion method (combustion-infrared absorption method). The N content was determined using the well-known inert gas fusion-thermal conductivity method. Specifically, the measurements were performed using a Shimadzu component analyzer (product name: ICPS-8000).

[0117] As a result of the analysis, the chemical composition of the base steel sheet contained the elements shown in Tables 2A to 2D, with the balance being Fe and impurities. Note that "0.00", "0.000", and "0.0000" in Tables 1A to 1D and Tables 2A to 2D indicate that the content of the corresponding element was below the detection limit.

[0118] <Evaluation> The obtained grain-oriented electrical steel sheets were subjected to the following measurements and evaluations.

[0119] [Magnetic property measurement] Test specimens were taken from the grain-oriented electrical steel sheet coils of each test number. The test specimens were taken from two locations: the outer periphery, approximately 10 m from the outer periphery of the coil after final annealing, and the center, 50% of the total length of the coil. The test specimens measured 60 mm x 300 mm x sheet thickness. The test specimens included the center of the grain-oriented electrical steel sheet width. In accordance with JIS C2556:2015, a single sheet magnetic property test (SST test) was conducted, applying a magnetic field of 800 A / m to the test specimens to determine the magnetic flux density B8 (T). The obtained magnetic flux density B8 is shown in the "Magnetic Flux Density B8 (T)" column in Table 1-3. A magnetic flux density B8 of 1.902 T or higher was evaluated as having excellent magnetic properties and was deemed to have passed the test.

[0120] [Crystal orientation measurement] After measuring the magnetic properties, the crystal orientation was measured by the Laue method on the 60mm x 300mm x thickness sample. The Laue measurement was carried out at the center of the plate, and orientation data was obtained from 171 measurement points at a 6mm pitch. From the orientation data of all measurement points, {211} <011> The number of crystal orientation data with a deviation angle of 15° or less from the target was analyzed, and the percentage R of these data points to the total number of measurement points (171 points) was calculated. In the magnetic property measurement described above, when the magnetic flux density B8 was less than 1.700 T, it was determined to be secondary recrystallization failure, and crystal orientation measurement was not performed.

[0121] [Coating adhesion evaluation] Test specimens were taken from the grain-oriented electrical steel sheets of each test number. The test specimens were taken from two locations: the outer periphery, approximately 10 m from the outer periphery of the coil after finish annealing, and the center, 50% of the total length of the coil. The test specimens were 15 mm long in the direction perpendicular to the rolling direction and 60 mm long in the rolling direction. The specimens were wound around round bars of various diameters, and the coating adhesion was evaluated based on the smallest diameter at which the coating did not peel off visually (hereinafter referred to as the bending peeling diameter). The smaller the bending peeling diameter, the better the coating adhesion. A bending peeling diameter of 40 mm or more was deemed a failure due to increased concerns about coating peeling during core manufacturing.

[0122] [EPMA analysis (primary coating evaluation)] A 50 mm square test piece was taken from each grain-oriented electrical steel sheet. The secondary coating was removed using the method described above. The surface of the primary coating after the secondary coating was removed was subjected to line analysis using an EPMA (JEOL, JXA-8230) to obtain an oxygen intensity profile. The EPMA analysis conditions were an acceleration voltage of 15.0 kV, a probe current of 100 nA, and a beam shape of 10 μm x 300 μm strip. Line analysis was performed in the rolling direction, with measurements of 3 mm distances at 10 μm intervals, 15 times in succession. The obtained oxygen intensity measurement data in the rolling direction was calculated as a moving average of 10 sections, and the maximum intensity Io max and minimum intensity Io min From the ratio Io min / Io max was calculated.

[0123] <Evaluation results> The thickness and chemical composition of the grain-oriented electrical steel sheets were as shown in Tables 2A to 2D. The magnetic property measurement results, crystal orientation measurement results, and coating adhesion evaluation results for the grain-oriented electrical steel sheets are shown in Tables 3E to 3F. When the magnetic flux density B8 was less than 1.700 T, crystal orientation measurement and coating adhesion evaluation were not performed, so the fields are left blank.

[0124] All conditions were appropriate for test numbers 1 to 30. Therefore, the magnetic flux density B8 at the center and outer periphery of the coil was 1.902 T or more, and the {211} <011> The proportion of magnetically inferior grains was less than 5%. min / Io max Since the value was 0.85 to 0.96, the bending peeling diameter was 30 mm or less, indicating good coating adhesion.

[0125] Test numbers 31, 32, 51, and 52 had inappropriate rolling reductions. Test numbers 31 and 51, which had rolling reductions of less than 89%, had {211} <011> Although the ratio was low, the magnetic flux density B8 was low. This is thought to be because the rolling reduction was low, so although there was a lot of Goss orientation, the deviation angle was large. On the other hand, in test numbers 32 and 52, where the rolling reduction was 94% or more, the {211} <011> The ratio was high and the magnetic flux density B8 was low. This is because the rolling reduction was high. <011> It is thought that this developed during cold rolling, making secondary recrystallization more likely to occur.

[0126] Test Nos. 33, 34, 53, and 54 were not heated by a laser beam. Test Nos. 33 and 53 had a low heating rate in the subsequent decarburization annealing process, and the magnetic flux density B8 was significantly low. Test Nos. 34 and 54 had a high heating rate in the subsequent decarburization annealing process, but the {211} <011> The ratio was high, so the magnetic flux density B8 was inferior. Since no laser beam heating was performed, sufficient Goss orientation was not obtained, and the {211} <011> It is thought that secondary recrystallization occurred.

[0127] Test numbers 35, 36, 55, and 56 were heated by a laser beam, but Up was inappropriate. In test numbers 35 and 55, where Up was 0 or less, heating by the laser beam was insufficient, and the {211} <011> In test numbers 36 and 56, where Up was 6 or more, the heating by the laser beam was excessive, and the {211} <011> This is thought to be because excessive heating caused the precipitates in the laser beam irradiated area to coarsen, resulting in a loss of orientation selectivity during secondary recrystallization of Goss-oriented grains from the laser beam irradiated area.

[0128] Tests 37, 38, 57, and 58 were heated with a laser beam, but the irradiation interval was inappropriate. As a result, the magnetic flux density B8 was low. <011> The proportion of crystal orientations with a deviation angle of 15° or less from the normal was also 5% or more. This is thought to be because the effect of the laser beam on enrichment of Goss-oriented grains became insufficient.

[0129] Test numbers 39, 40, 59, and 60 were heated with a laser beam, but the tilt of the irradiated area was inappropriate. <011> Although the magnetic flux density B8 was low. Although the reason is unclear, when the tilt of the irradiated area is inappropriate, secondary recrystallization frequently occurs even in Goss-oriented grains with large deviations, resulting in {211} <011> Although secondary recrystallization is suppressed, it is thought that the orientation selectivity of Goss-oriented grains is lost.

[0130] In test numbers 41, 42, 61, and 62, the heating rate during the ACL heating process was inappropriate. When the heating rate was less than 80°C / s, the effect of enriching Goss-oriented grains was insufficient even when the laser beam was applied, and the {211} <011> When the heating rate was over 2000°C / s, the magnetic flux density B8 was low due to the decrease in the corresponding orientation grains, which reduced the selective growth of Goss orientation grains.

[0131] In test numbers 43 to 50 and 63 to 70, the oxygen potential Po during the ACL soaking process was inappropriate, so the magnetic properties were good, but the coating adhesion deteriorated. min / Io max The value of Io was 0.97 or more. This is thought to be due to insufficient oxidation in the decarburization annealing process, which resulted in insufficient primary coating formation during finish annealing, resulting in poor coating adhesion. When Po exceeds 0.6-0.04Up, Io min / Io max was less than 0.85, and the coating adhesion in the vicinity of the laser beam irradiated area was poor.

[0132] [Table 1A]

[0133] [Table 1B]

[0134] [Table 1C]

[0135] [Table 1D]

[0136] [Table 2A]

[0137] [Table 2B]

[0138] [Table 2C]

[0139] [Table 2D]

[0140] [Table 3A]

[0141] [Table 3B]

[0142] [Table 3C]

[0143] [Table 3D]

[0144] [Table 3E]

[0145] [Table 3F] [Industrial Applicability]

[0146] According to the above-described aspects of the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties and coating adhesion can be obtained. Therefore, the grain-oriented electrical steel sheet obtained can be suitably used as an iron core material for transformers, and therefore has high industrial applicability.

Claims

1. A steel sheet is provided with a base steel sheet, a primary coating formed on the base steel sheet, and a secondary coating formed on the primary coating, The chemical composition of the base steel plate is, in mass%, Si: 2.50-4.00%, Mn: 0.01 to 0.30%, N: 0.0001 to 0.0100%, C: 0.0005-0.010%, sol. Al: 0 to 0.010%, One or more selected from the group consisting of S and Se: 0 to 0.010% in total; Ti: 0.001 to 0.010%, Ni: 0 to 0.50%, Cu: 0 to 0.50%, Sb: 0 to 0.30%, Sn: 0 to 0.30%, Cr: 0 to 0.50%, P: 0-0.05%, Mo: 0 to 0.05%, Ta: 0 to 0.05%, Nb: 0 to 0.010%, V: 0-0.50%, B: 0 to 0.010%, Bi: 0 to 0.0200%, and Te: 0~0.0200% Contains The balance is Fe and impurities. The magnetic flux density B8 is 1.902 T or more, When measurement points for crystal orientation by X-ray diffraction method are arranged on the surface of the base steel sheet at a pitch of 6 mm in each of the rolling direction and the direction orthogonal to the rolling direction, the proportion of measurement points having an orientation difference from {211}<011> of 15° or less to all measurement points is 5% or less, an oxygen intensity profile of the surface of the primary coating obtained by line analysis along the rolling direction using an electron probe microanalyzer shows periodic regions of low oxygen intensity; The minimum value Io of the oxygen intensity in the oxygen intensity decreasing region ｍｉｎ and the maximum value Io of the oxygen intensity in the region other than the oxygen intensity decreasing region. ｍａｘ Relative to Io ｍｉｎ / Io ｍａｘ A grain-oriented electrical steel sheet characterized in that the tensile strength is 0.85 or more and 0.96 or less.

2. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the oxygen intensity reduced regions are present at intervals L of 5 to 30 mm.

3. The chemical composition of the base steel plate is, in mass%, Ni: 0.01-0.50%, Cu: 0.01 to 0.50%, Sb: 0.01 to 0.30%, Sn: 0.01-0.30%, Cr: 0.01-0.50%, P: 0.01-0.05%, Mo: 0.01-0.05%, Ta: 0.01-0.05%, Nb: 0.001 to 0.010%, V: 0.01-0.50%, B: 0.001 to 0.010%, Bi: 0.0100% or less, and Te: 0.0100% or less The grain-oriented electrical steel sheet according to claim 1 or 2, comprising one or more selected from the following:

4. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the sheet thickness is 0.15 to 0.23 mm.

5. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein the base steel sheet has a thickness of 0.14 to 0.22 mm.

6. In mass%, Si: 2.50-4.00%, Mn: 0.01 to 0.30%, N: 0.0030-0.0150%, C: 0.010-0.100%, sol. Al: 0.010 to 0.050%, One or more selected from the group consisting of S and Se: 0.010 to 0.050% in total; Ti: 0.001 to 0.010%, Ni: 0 to 0.50%, Cu: 0 to 0.50%, Sb: 0 to 0.30%, Sn: 0 to 0.30%, Cr: 0 to 0.50%, P: 0-0.05%, Mo: 0 to 0.05%, Ta: 0 to 0.05%, Nb: 0 to 0.010%, V: 0-0.50%, B: 0 to 0.010%, Bi: 0 to 0.0200%, and Te: 0~0.0200% a hot rolling step of heating a slab containing the above-mentioned alloy and the balance being Fe and impurities, and hot rolling the heated slab to obtain a hot-rolled steel sheet; a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet; a cold rolling step of cold-rolling the hot-rolled steel sheet after the hot-rolled sheet annealing step to obtain a cold-rolled steel sheet; a decarburization annealing step of subjecting the cold-rolled steel sheet to decarburization annealing to obtain a decarburization annealed steel sheet; a finish annealing step of applying an annealing separator to the decarburization-annealed steel sheet and then subjecting it to finish annealing to form a primary coating on the surface of the decarburization-annealed steel sheet, thereby obtaining a finish annealed sheet; and an insulating film forming step of forming an insulating film on the surface of the finish annealed sheet, The total reduction rate in the cold rolling step is 89% or more and 93% or less, The decarburization annealing step includes: a local heating process in which the surface of the cold-rolled steel sheet is partially heated by irradiating it with a laser beam in an air atmosphere at intervals of 5 to 30 mm in a direction forming an angle of 30 to 150° with respect to the rolling direction; a temperature-raising process in which the cold-rolled steel sheet after the local heating process is heated in a non-oxidizing atmosphere from a temperature range of 450°C or less to a temperature range of 750 to 950°C, which is a decarburization annealing temperature, at an average heating rate of 80°C / sec or more and 2000°C / sec or less; The cold-rolled steel sheet after the temperature rising process is heated to an oxygen potential P Ｏ and a soaking process in which decarburization annealing is performed. Including, In the local heating process, the laser beam irradiation conditions are as follows: The average intensity of the laser beam is denoted by P in units of W; The diameter of the focused spot in the rolling direction is Dl in mm, The focused diameter of the focused spot in the width direction perpendicular to the rolling direction is denoted by Dc in mm, The irradiation time is represented by t in units of seconds. The instantaneous input energy expressed as 4 / π×P / (Dl×Dc)×t is expressed in units of J / mm ２ and Up satisfies the following formula (2): 0.3≦P Ｏ ≦ 0.6-0.04 Up (1) 1 ≦ Up ≦ 5 (2)

7. The chemical composition of the slab, in mass %, is Ni: 0.01 to 0.50%, Cu: 0.01 to 0.50%, Sb: 0.01-0.30%, Sn: 0.01-0.30%, Cr: 0.01-0.50%, P: 0.01-0.05%, Mo: 0.01-0.05%, Ta: 0.01-0.05%, Nb: 0.001 to 0.010%, V: 0.01-0.50%, B: 0.001 to 0.010%, Bi: 0.0100% or less, and Te: 0.0100% or less The method for producing a grain-oriented electrical steel sheet according to claim 6, further comprising the step of:

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