Method for producing grain-oriented electrical steel sheet

Abstract

A method for producing a grain-oriented electrical steel sheet according to the present disclosure comprises a hot rolling step, a hot-rolled sheet annealing step, a cold rolling step, a decarburization annealing step, a finish annealing step, and an insulating coating film formation step. Before a temperature raising process in the decarburization annealing step, a cold-rolled steel sheet is irradiated with a laser beam in a direction intersecting the rolling direction, under conditions in which the wavelength λ (μm) of the laser beam, the irradiation energy density Up (J / mm2), and the laser beam irradiation interval d (mm) satisfy [0.3 ≤ λ ≤ 1.1], [0.63λ + 0.31 ≤ Up ≤ 4.25λ + 0.23], and [5 ≤ d ≤ 30]. In the temperature raising process, the temperature is raised from a temperature range of 450°C or lower to a temperature range of 750-950°C, and the average heating rate between 450°C and 750°C is 40-2000°C / second.

Description

Manufacturing method of grain-oriented electrical steel sheet

[0001] The present disclosure relates to a method for manufacturing a grain-oriented electrical steel sheet.

[0002] Grain-oriented electrical steel sheets are soft magnetic materials that are primarily used as iron core materials in 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 heat energy when an iron core is excited by an AC magnetic field. From the perspective of energy conservation, iron loss should be as low as possible.

[0003] One of the controlling factors of iron loss characteristics is magnetic flux density (for example, B8: magnetic flux density in a magnetic field of 800 A / m), and the higher the magnetic flux density value, the lower the iron loss tends to be. In grain-oriented electrical steel sheets, to increase the magnetic flux density, the crystal orientation is generally concentrated in the Goss orientation, which is good for magnetic properties, during the manufacturing process (increasing the degree of orientation concentration). Low iron loss is achieved by refining the magnetic domain structure of grain-oriented electrical steel sheets with high magnetic flux density.

[0004] To increase the degree of orientation concentration in the Goss orientation, a high-temperature, long-time finish annealing is usually performed. By performing the finish annealing, "Goss-oriented grains" in which the rolling direction of the steel sheet is the <100> direction and the surface direction of the steel sheet is the <110> direction grow to a size on the order of centimeters while encroaching on the surrounding crystal grains, and the crystal orientation becomes aligned (the degree of orientation concentration increases).

[0005] In order to increase the degree of orientation concentration in the Goss orientation, Patent Document 1 discloses a technique for efficiently enriching the Goss orientation in a steel sheet by irradiating the steel sheet with a laser beam or the like and rapidly heating the steel sheet in parts. The technique disclosed in Patent Document 1 makes it possible to obtain a grain-oriented electrical steel sheet having a high magnetic flux density.

[0006] International Publication No. 2023 / 191029

[0007] In recent years, there has been an increasing demand for smaller transformers, which has led to a corresponding demand for smaller iron cores. Smaller iron cores are sometimes designed with a high magnetic flux density, which may require grain-oriented electrical steel sheets to reduce iron loss in high magnetic field regions. However, Patent Document 1 does not fully consider iron loss in high magnetic field regions (hereinafter referred to as "high magnetic field iron loss").

[0008] The present disclosure has been made in view of the above-mentioned problems, and aims to provide a method for manufacturing a grain-oriented electrical steel sheet that has excellent magnetic properties and, in particular, low high-magnetic-field iron loss.

[0009] The present disclosure relates to the following method for manufacturing a grain-oriented electrical steel sheet.

[0010] (1) A method for manufacturing a steel sheet, comprising: a hot rolling process of heating a slab and hot rolling the heated slab to obtain a hot-rolled steel sheet; a hot-rolled sheet annealing process of annealing the hot-rolled steel sheet; a cold rolling process of cold-rolling the hot-rolled steel sheet after the hot-rolled sheet annealing process to obtain a cold-rolled steel sheet; a decarburization annealing process of decarburization annealing the cold-rolled steel sheet to obtain a decarburization annealed steel sheet; a finish annealing process of applying an annealing separator to the decarburization annealed steel sheet and then finish annealing it to obtain a finish annealed sheet; and an insulating coating forming process of forming an insulating coating on a surface of the finish annealed sheet, wherein before the temperature rising process of the decarburization annealing process, the cold-rolled steel sheet is irradiated in a direction intersecting with the rolling direction with a laser beam under conditions that satisfy the following formulas (i) to (iii): A method for producing a grain-oriented electrical steel sheet, wherein, during the temperature-raising process of the decarburization annealing step, the temperature is raised from a temperature range of 450°C or lower to a temperature range of 750 to 950°C, and the average heating rate from 450 to 750°C is 40 to 2000°C / sec. 0.3≦λ≦1.1 (i) 0.63λ+0.31≦Up≦4.25λ+0.23 (ii) 5≦d≦30 (iii) where λ in the above formulas (i) and (ii) is the wavelength (μm) of the laser beam, and Up in the above formula (ii) is the irradiation energy density (J / mm) expressed by 4 / π×P / (Dl×Vc), where P (W) is the average intensity of the laser beam, Dl (mm) is the average focused diameter of the focused spot in the rolling direction, and Vc (mm / sec) is the average scanning speed of the laser beam. ２ ) and d in the above formula (iii) is the irradiation interval (mm) of the laser beam.

[0011] (2) The method for producing a grain-oriented electrical steel sheet according to (1) above, wherein the cold-rolled steel sheet has a thickness of 0.30 mm or less.

[0012] (3) The chemical composition of the slab is, in mass %, Si: 3.00 to 3.80%, Mn: 0.01 to 0.30%, N: 0.0030 to 0.0150%, C: 0.010 to 0.100%, sol. 1. A method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the content of the elements is: Al: 0.010 to 0.050%, total of one or more elements selected from S and Se: 0.010 to 0.050%, Ti: 0 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 to 0.05%, Mo: 0 to 0.05%, Ta: 0 to 0.05%, Nb: 0 to 0.010%, V: 0 to 0.50%, B: 0 to 0.010%, Te: 0 to 0.0200%, Bi: 0 to 0.0200%, and the balance: Fe and impurities.

[0013] According to the present disclosure, it is possible to obtain a grain-oriented electrical steel sheet having excellent magnetic properties, particularly low iron loss in a high magnetic field.

[0014] As a result of investigations conducted by the present inventors to solve the above problems, the following findings were obtained.

[0015] The present inventors have produced grain-oriented electrical steel sheets by irradiating the steel sheet surface with a laser beam or the like before the temperature rise process in the decarburization annealing step, thereby performing partial rapid heating, and have confirmed that it is possible to efficiently improve the degree of orientation concentration in the Goss orientation. However, it has also been found that there are cases in which high magnetic field iron loss is inferior despite the improvement in the degree of orientation concentration in the Goss orientation.

[0016] The inventors investigated the cause and found that residual distortion was present in the areas that had been subjected to rapid partial heating by irradiation with a laser beam or the like. Distortion pins domain wall motion and increases hysteresis loss in particular. High magnetic field iron loss accounts for a high proportion of hysteresis loss. Therefore, it is believed that the residual distortion caused a slight deterioration in high magnetic field iron loss.

[0017] As a result of further investigations by the inventors, it became clear that by controlling the laser beam irradiation conditions, particularly the wavelength of the laser beam, it is possible to suppress residual distortion due to partial rapid heating and reduce high magnetic field iron loss.

[0018] The present disclosure has been made based on the above findings. Hereinafter, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present disclosure will be described.

[0019] 1. Manufacturing Method A manufacturing method of a grain-oriented electrical steel sheet according to this embodiment will be described. The manufacturing method of a grain-oriented electrical steel sheet according to this embodiment includes the following steps: (A) a hot rolling step of heating a slab and hot-rolling the heated slab to obtain a hot-rolled steel sheet, (B) a hot-rolled sheet annealing step of annealing the hot-rolled steel sheet, (C) 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, (D) a decarburization annealing step of decarburization annealing the cold-rolled steel sheet to obtain a decarburization-annealed steel sheet, (E) a finish annealing step of applying an annealing separator to the decarburization-annealed steel sheet and then finish annealing it to obtain a finish-annealed sheet, and (F) an insulating coating forming step of forming an insulating coating on the surface of the finish-annealed sheet.

[0020] In addition to the above steps, the method may further include (G) a magnetic domain refinement step of subjecting the obtained grain-oriented electrical steel sheet to magnetic domain refinement. Each step will be described below. Well-known steps or conditions can be applied to steps or conditions not described.

[0021] (A) Hot Rolling Process In the hot rolling process, a slab having the chemical composition described below is heated, and the heated slab is hot-rolled to produce a hot-rolled steel sheet. The heating temperature of the slab is not particularly limited, but can be, for example, 1280°C or higher. By setting the heating temperature to 1280°C or higher, inclusions formed in the slab can be dissolved, and inhibitors can be sufficiently formed in the hot rolling process or the hot-rolled sheet annealing process. Therefore, it is preferable to set the heating temperature of the slab to 1280°C or higher. There is no upper limit to the heating temperature of the slab, but if it is heated to a temperature above 1450°C, the slab will melt, making hot rolling difficult. Therefore, it is preferable that the heating temperature of the slab be 1450°C or lower.

[0022] 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 a range of 1.0 mm to 4.0 mm, for example.

[0023] [Chemical Composition of Slab] There are no particular limitations on the chemical composition of the slab, but the following may be used in mass %: Si: 3.00 to 3.80%, Mn: 0.01 to 0.30%, N: 0.0030 to 0.0150%, C: 0.010 to 0.100%, sol. It is preferable that the alloy contains 0.010 to 0.050% Al, 0.010 to 0.050% of a total of one or more elements selected from S and Se, 0 to 0.010% Ti, 0 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 to 0.05% Mo, 0 to 0.05% Ta, 0 to 0.05% Nb, 0 to 0.010% V, 0 to 0.50% B, 0 to 0.010% Te, and 0 to 0.0200% Bi. The balance other than the above elements preferably contains Fe and impurities, and more preferably Fe and impurities.

[0024] The reasons for limiting the content of each element are as follows: In the following description, "%" in the content means "% by mass."

[0025] Si: 3.00 to 3.80% Si (silicon) is an extremely effective element for increasing the electrical resistance (resistivity) of steel and reducing eddy current loss, which constitutes part of iron loss. By setting the Si content of the slab to 3.00% or more, eddy current loss can be sufficiently reduced. Furthermore, by suppressing the phase transformation of the steel during finish annealing and sufficiently promoting secondary recrystallization, it exhibits the effect of improving magnetic flux density and iron loss. Therefore, the Si content of the slab is preferably 3.00% or more, more preferably 3.10% or more, and even more preferably 3.20% or more. On the other hand, by setting the Si content to 3.80% or less, embrittlement of the steel sheet can be suppressed and sheet threadability during the manufacturing process can be improved. Therefore, the Si content of the slab is preferably 3.80% or less, more preferably 3.70% or less, and even more preferably 3.60% or less.

[0026] Mn: 0.01 to 0.30% Mn (manganese) is an element that forms MnS, one of the main inhibitors. In order to ensure the absolute amount of MnS necessary to cause secondary recrystallization, the Mn content of the slab is preferably 0.01% or more, more preferably 0.03% or more, and even more preferably 0.06% or more. On the other hand, in order to suppress the phase transformation of the steel during finish annealing, sufficiently promote secondary recrystallization, and reliably obtain good magnetic flux density and low iron loss, the Mn content of the slab is preferably 0.30% or less, more preferably 0.28% or less, and even more preferably 0.26% or less.

[0027] N: 0.0030 to 0.0150% N (nitrogen) is an element that reacts with Al to form AlN, which functions as an inhibitor. In order to sufficiently form AlN, which functions as an inhibitor, the N content is preferably 0.0030% or more, more preferably 0.0040% or more, and even more preferably 0.0050% or more. On the other hand, in order to suppress the formation of blisters (voids) in the steel sheet during cold rolling, suppress an increase in the strength of the steel sheet, and ensure sheet passability during production, the N content of the slab is preferably 0.0150% or less, more preferably 0.0120% or less, and even more preferably 0.0100% or less.

[0028] C: 0.010 to 0.100% C (carbon) is an element that exhibits an effect of improving magnetic flux density. Therefore, the C content of the slab is preferably 0.010% or more, more preferably 0.015% or more, and even more preferably 0.020% or more. On the other hand, by setting the C content of the slab to 0.100% or less, it is possible to suppress a decrease in productivity in the decarburization annealing process. Furthermore, by setting the C content of the slab to 0.100% or less, sufficient decarburization is achieved, and secondary recrystallization progresses sufficiently during finish annealing, resulting in good magnetic flux density and low iron loss. Therefore, the C content of the slab is preferably 0.100% or less, more preferably 0.070% or less, and even more preferably 0.050% or less.

[0029] Sol. Al: 0.010 to 0.050% Al (aluminum) is an element that reacts with N to form AlN, which functions as an inhibitor. In order to generate sufficient AlN, which functions as an inhibitor, and to obtain sufficient secondary recrystallization, the sol. Al content of the slab is preferably 0.010% or more, and more preferably 0.020% or more. On the other hand, by setting the sol. Al content of the slab to 0.050% or less, AlN, which functions as an inhibitor, can be stably generated, and secondary recrystallization is more likely to be promoted. Therefore, the sol. Al content is preferably 0.050% or less, more preferably 0.040% or less, and even more preferably 0.030% or less. Note that sol. Al refers to acid-soluble aluminum.

[0030] Total of one or more selected from S and Se: 0.010 to 0.050% S (sulfur) and Se (selenium) are elements that react with Mn to form MnS and MnSe, respectively, which are inhibitors. In order to sufficiently form MnS and / or MnSe, which function as inhibitors, the total content of one or more selected from S and Se in the slab is preferably 0.010% or more, more preferably 0.020% or more. On the other hand, by setting the total content of one or more selected from S and Se in the slab to 0.050% or less, it is possible to improve hot workability. Therefore, the total content of S and Se in the slab is preferably 0.050% or less, more preferably 0.040% or less, and even more preferably 0.030% or less.

[0031] Ti: 0 to 0.010% Ti (titanium) is an element that can be contained in the slab as an impurity, but by reducing its content, it is possible to reduce iron loss (hysteresis loss). Therefore, the Ti content of the slab is preferably 0.010% or less, more preferably 0.005% or less, and even more preferably 0.003% or less. The lower the Ti content, the better, so the lower limit is 0%.

[0032] Ni: 0 to 0.50% Ni (nickel) is an element effective in increasing the electrical resistance of steel and reducing iron loss. Ni is also an element effective in controlling the metal structure of hot-rolled steel sheets during the hot rolling process and improving the magnetic properties of grain-oriented electrical steel sheets. Therefore, Ni may be added as needed. On the other hand, by setting the Ni content of the slab to 0.50% or less, secondary recrystallization is more stabilized. Therefore, the Ni content is preferably 0.50% or less, more preferably 0.40% or less, and even more preferably 0.30% or less. To reliably achieve the above effects, the Ni content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.

[0033] Cu: 0 to 0.50% Cu (copper) 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, Cu may be added as needed. On the other hand, by setting the Cu content of the slab to 0.50% or less, it is possible to improve hot workability. Therefore, the Cu content is preferably 0.50% or less, more preferably 0.30% or less, and even more preferably 0.10% or less. To ensure the above effects, the Cu content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.

[0034] Sb: 0 to 0.30% Sb (antimony) is an element that has the effect of improving magnetic properties. Therefore, Sb may be contained as necessary. On the other hand, by setting the Sb content of the slab to 0.30% or less, the adhesion of the glass coating is further improved. Therefore, the Sb content is preferably 0.30% or less, more preferably 0.20% or less, and even more preferably 0.10% or less. To ensure the above effect, the Sb content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.

[0035] Sn: 0 to 0.30% Sn (tin) is an element that has the effect of improving magnetic properties. Therefore, Sn may be contained as necessary. On the other hand, by setting the Sn content of the slab to 0.30% or less, deterioration of the glass coating can be suppressed and iron loss properties can be further improved. Therefore, the Sn content is preferably 0.30% or less, more preferably 0.20% or less, and even more preferably 0.10% or less. To ensure the above effects, the Sn content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.

[0036] Cr: 0 to 0.50% Cr (chromium) 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, Cr may be added as needed. On the other hand, by setting the Cr content of the slab to 0.50% or less, the formation of Cr oxides is suppressed and magnetic properties are further improved. Therefore, the Cr content is preferably 0.50% or less, more preferably 0.30% or less, and even more preferably 0.10% or less. To ensure 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.

[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, better rolling workability can be obtained. From this perspective, the P content is preferably set to 0.05% or less, more preferably 0.04% or less, and even more preferably 0.03% 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 texture and magnetic properties. To achieve this effect, the P content may be set to 0.005% or more, or may be set to 0.01% or more.

[0038] Mo: 0 to 0.05% Mo (molybdenum) is an element that has the effect of improving magnetic properties. Therefore, Mo may be contained as necessary. On the other hand, by setting the Mo content of the slab to 0.05% or less, better cold rolling properties can be obtained. Therefore, the Mo content is preferably 0.05% or less, more preferably 0.04% or less, and even more preferably 0.03% or less. To ensure the above effects, the Mo content is preferably 0.005% or more, more preferably 0.01% or more, and even more preferably 0.02% or more.

[0039] Ta: 0 to 0.05% Ta (tantalum) is an element that has the effect of stabilizing secondary recrystallization. Therefore, Ta may be contained as necessary. On the other hand, by setting the Ta content of the slab to 0.05% or less, secondary recrystallization is further stabilized. Therefore, the Ta content is preferably 0.05% or less, more preferably 0.04% or less, and even more preferably 0.03% or less. To reliably obtain the above effect, the Ta content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.001% or more.

[0040] Nb: 0 to 0.010% Nb (niobium) is an element that has the effect of stabilizing secondary recrystallization. Therefore, Nb may be contained as necessary. On the other hand, secondary recrystallization is stabilized by setting the Nb content of the slab to 0.010% or less. Therefore, the Nb content is preferably 0.010% or less, more preferably 0.0050% or less, and even more preferably 0.0030% or less. To reliably obtain the above effect, the Nb content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.

[0041] V: 0 to 0.50% V (vanadium) is an effective element that bonds with N or C and functions as an inhibitor. Therefore, V may be contained as needed. On the other hand, by setting the V content of the slab to 0.50% or less, the magnetic properties are further improved. Therefore, the V content is preferably 0.50% or less, more preferably 0.40% or less, and even more preferably 0.30% or less. To ensure the above effects, the V content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably 0.03% or more.

[0042] B: 0 to 0.010% B (boron) is an element that has the effect of stabilizing secondary recrystallization. Therefore, B may be contained as necessary. On the other hand, secondary recrystallization is stabilized by setting the B content of the slab to 0.010% or less. Therefore, the B content is preferably 0.010% or less, more preferably 0.0050% or less, and even more preferably 0.0030% or less. To reliably obtain the above effect, the B content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.

[0043] Te: 0 to 0.0200% Te (tellurium) is an element that has the effect of stabilizing secondary recrystallization. Therefore, Te may be contained as necessary. On the other hand, by setting the Te content of the slab to 0.0200% or less, better rolling workability can be obtained. Therefore, the Te content is preferably 0.0200% or less, more preferably 0.0150% or less, and even more preferably 0.0100% or less. To reliably obtain the above effect, the Te content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.

[0044] Bi: 0 to 0.0200% Bi (bismuth) is an element that effectively stabilizes precipitates such as sulfides and enhances their inhibitory function. Therefore, Bi may be added as needed. On the other hand, by setting the Bi content of the slab to 0.0200% or less, better insulation coating adhesion and magnetic properties can be obtained. Therefore, the Bi content is preferably 0.0200% or less, more preferably 0.0150% or less, and even more preferably 0.0100% or less. To ensure the above effects, the Bi content is preferably 0.0005% or more, more preferably 0.0010% or more, and even more preferably 0.0020% or more.

[0045] In the chemical composition of the slab of this embodiment, the balance preferably contains Fe and impurities, and more preferably Fe and impurities. Here, "impurities" refer to components that are mixed in due to various factors in raw materials such as ores and scraps and manufacturing processes during industrial steel production, and are acceptable within a range that does not adversely affect the effects of the present disclosure.

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

[0047] (C) Cold Rolling Step In the cold rolling step, the hot-rolled steel sheet after the hot-rolled sheet annealing step is subjected to cold rolling to obtain a cold-rolled steel sheet. Cold rolling may be a single cold rolling, or multiple cold rolling passes may be performed, with the cold rolling interrupted before the final pass of the cold rolling step and at least one or two intermediate anneals performed between the cold rolling passes. Furthermore, each cold rolling pass may be performed in one pass or multiple passes. When intermediate annealing is performed, it is preferable to hold the steel at a temperature of 1000 to 1200°C for 5 to 180 seconds. The annealing atmosphere is not particularly limited. Considering production costs, the number of intermediate anneals is preferably three or less. Furthermore, before the cold rolling step, the surface of the hot-rolled steel sheet may be pickled under known conditions. The thickness of the cold-rolled steel sheet is not particularly limited and may be adjusted appropriately depending on the application, but it is preferably 0.14 to 0.30 mm, for example. From the viewpoint of reducing iron loss, the plate thickness is more preferably 0.20 mm or less.

[0048] (D) Decarburization Annealing Step In the decarburization annealing step, the cold-rolled steel sheet is subjected to decarburization annealing to produce a decarburization annealed steel sheet. In the decarburization annealing step, the cold-rolled steel sheet is subjected to primary recrystallization, and C (carbon), which adversely affects magnetic properties, is removed from the cold-rolled steel sheet. The decarburization annealing step according to this embodiment includes a laser beam irradiation step, a temperature-raising step, and a soaking step. In the method for producing a grain-oriented electrical steel sheet according to this embodiment, partial rapid heating is performed by laser beam irradiation before the temperature-raising step.

[0049] To obtain the above-mentioned effect, more specifically, before the temperature rising process, the cold-rolled steel sheet is irradiated with a laser beam in a direction intersecting the rolling direction under the conditions that satisfy the following formulas (i) to (iii). Note that the "rolling direction" here means the rolling direction of the hot rolling and cold rolling described above. 0.3≦λ≦1.1 (i) 0.63λ+0.31≦Up≦4.25λ+0.23 (ii) 5≦d≦30 (iii) In the above formulas (i) and (ii), λ is the wavelength (μm) of the laser beam, and Up in the above formula (ii) is the irradiation energy density (J / mm) expressed by 4 / π×P / (Dl×Vc), where P (W) is the average intensity of the laser beam, Dl (mm) is the average focused diameter of the focused spot in the rolling direction, and Vc (mm / sec) is the average scanning speed of the laser beam. ２ ) and d in the above formula (iii) is the irradiation interval (mm) of the laser beam.

[0050] By performing partial rapid heating by laser beam irradiation and instantaneously heating the surface layer of the steel sheet (for example, from the surface to about 1 / 5 of the thickness) to a temperature range where recrystallization occurs, it is possible to efficiently improve the degree of orientation concentration in the Goss orientation. In this case, the wavelength λ of the laser beam needs to satisfy the above formula (i). If λ is less than 0.3 μm, recrystallization and grain growth in the surface layer of the steel sheet do not proceed sufficiently, and the effects of rapid heating cannot be obtained. On the other hand, if λ exceeds 1.1 μm, the amount of residual strain due to partial rapid heating becomes excessive. λ is preferably 0.5 μm or less.

[0051] Furthermore, the irradiation energy density Up must be adjusted in relation to λ, and the above formula (ii) must be satisfied: Up is 0.63λ + 0.31 J / mm ２ If Up is less than 4.25λ+0.23 J / mm, recrystallization and grain growth in the surface layer of the steel sheet do not proceed sufficiently, and the effect of rapid heating cannot be obtained. ２ If the temperature exceeds this value, the residual strain due to the partial rapid heating becomes excessive.

[0052] Similarly, if d exceeds 30 mm, the irradiation interval is too wide, resulting in insufficient recrystallized and grain-grown regions in the steel sheet surface, and the effects of rapid heating cannot be obtained. On the other hand, if d is less than 5 mm, the residual strain due to partial rapid heating becomes excessive. The direction of laser beam irradiation may be any direction intersecting the rolling direction, but is preferably a direction forming an angle of 30 to 150° with respect to the rolling direction. When laser beam irradiation is performed in multiple rows, all irradiation intervals must satisfy the above formula (iii).

[0053] There is no particular limitation on the average intensity P of the laser beam, but from the viewpoint of reliably preventing recrystallization due to rapid heating not only in the surface layer of the steel sheet but also throughout the entire thickness of the steel sheet by laser beam irradiation, the average intensity P is preferably set to 300 W or less, more preferably to 200 W or less, and even more preferably to 100 W or less.

[0054] The laser beam is preferably applied along a line extending from one end to the other end in the width direction of the cold-rolled steel sheet. The line may be discontinuous between one end and the other end in the width direction of the cold-rolled steel sheet. The line may be in any direction as long as it intersects with the rolling direction, and is preferably angled at 30 to 150°, more preferably 60 to 120°, and even more preferably 80 to 100°, relative to the rolling direction.

[0055] The atmosphere in which partial rapid heating is performed by laser beam irradiation is not particularly limited, and may be an air atmosphere or a controlled atmosphere. From the viewpoint of suppressing deterioration of the coating adhesion, the oxygen potential (PH) in the atmosphere in which the laser beam irradiation is performed is important. ２ O / PH２ ) is preferably 0.20 or less.

[0056] After the partial rapid heating, a temperature-raising process is carried out. In the temperature-raising process, the cold-rolled steel sheet 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. This temperature rise promotes the nucleation of Goss-oriented grains. The average heating rate between 450°C and 750°C is 40°C / sec or more. The average heating rate is preferably 400°C / sec or more. The average heating rate is 2000°C / sec or less. If the average heating rate exceeds 2000°C / sec, although the nucleation of Goss-oriented grains can be promoted, the corresponding orientation that promotes nucleus growth decreases, the preferential growth of Goss orientation decreases, and the magnetic properties deteriorate.

[0057] In addition, if the atmosphere during temperature rise is not a non-oxidizing atmosphere, the surface layer of the steel sheet will have a tight SiO ２ In this embodiment, the non-oxidizing atmosphere is a nitrogen atmosphere or a nitrogen / hydrogen mixed atmosphere, and the dew point is an atmosphere of -50°C or more and 0°C or less. The dew point is the SiO ２ From the viewpoint of suppressing the generation of carbon dioxide and promoting decarburization, the dew point is preferably −5° C. or lower, more preferably −10° C. or lower. From the viewpoint of promoting internal oxidation to facilitate process control, the dew point may be −40° C. or higher.

[0058] The temperature rise process is followed by a soaking process. The conditions for the soaking process are not particularly limited. For example, the oxygen potential (PH) in the annealing atmosphere (furnace atmosphere) ２ O / PH ２ ) is set to 0.15 to 1.0, and the temperature is held in the temperature range of 750 to 950°C for 10 to 600 seconds.

[0059] (E) Finish Annealing Step In the finish annealing step, a predetermined annealing separator is applied to one or both sides of the decarburization-annealed steel sheet obtained in the decarburization-annealing step, and then the steel sheet is subjected to finish annealing to obtain a finish annealed sheet. Finish annealing is generally performed for a long period of time while the steel sheet is wound into a coil. Therefore, prior to the finish annealing, an annealing separator is applied to the decarburization-annealed steel sheet and dried in order to prevent the steel sheets from seizing together when wound into a coil.

[0060] The annealing separator to be applied is an annealing separator containing MgO as the main component (for example, containing 80% or more by mass fraction). By using an annealing separator containing MgO as the 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) is not formed. This is because the primary coating contains Mg ２ SiO ４ or MgAl ２ O ４ This is because it is a compound, and if MgO is not the main component, there will be a shortage of Mg, which is necessary for the formation reaction.

[0061] 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 for 10 to 60 hours.

[0062] (F) Insulating Coating Forming Step In the insulating coating forming step, excess annealing separator is removed from the surface of the finish-annealed sheet obtained in the finish-annealing step by water washing, pickling, or the like, and then a secondary coating, which is an insulating coating, is formed.

[0063] This insulating coating applies tension to the grain-oriented electrical steel sheet, thereby reducing the iron loss of each steel sheet. In addition, the presence of the insulating coating ensures electrical insulation between the steel sheets when the grain-oriented electrical steel sheets are stacked, thereby reducing the iron loss of the iron core.

[0064] In the insulating coating formation process, a coating solution containing aluminum phosphate and colloidal silica as its main components is applied to the surface of the finish-annealed sheet. The finish-annealed sheet to which the coating solution has been applied is then subjected to a baking treatment. The baking temperature is, for example, 350 to 600°C. The finish-annealed sheet after the baking treatment is then subjected to a heat treatment. The heat treatment temperature is, for example, 800 to 1000°C. Through the above processes, an insulating coating is formed on the surface of the finish-annealed sheet.

[0065] (G) Magnetic Domain Refinement Treatment Step The grain-oriented electrical steel sheet obtained by the above steps may be further subjected to a magnetic domain refinement treatment. By performing the magnetic domain refinement treatment, the eddy current loss of the grain-oriented electrical steel sheet is further reduced, and as a result, the iron loss is further reduced. As the magnetic domain refinement treatment, a well-known method may be used, for example, by forming grooves on the steel sheet surface by a mechanical method, or by irradiating the steel sheet surface with a laser beam or an electron beam to introduce local strain.

[0066] 2. Magnetic Properties The grain-oriented electrical steel sheet manufactured by the method according to this embodiment has excellent magnetic properties, and in particular, low high-field iron loss. Specifically, the magnetic flux density B8 in the rolling direction is preferably 1.930 T or more. Furthermore, in the grain-oriented electrical steel sheet according to this embodiment, the iron loss W after magnetic domain refinement treatment is １７／５０ Iron loss W １９／５０ From this viewpoint, it is possible to reduce the ratio of W １９／５０ / W １７／５０ It is preferable that the iron loss W １７／５０ is preferably 0.65 W / kg or less, and the iron loss W １９／５０ is preferably 1.10 W / kg or less.

[0067] Magnetic flux density B8, iron loss W １７／５０ and iron loss W １９／５０The magnetic flux density and core loss are measured by the following method. First, a test piece measuring 100 mm x 500 mm x thickness is prepared from the center of the sheet width of the grain-oriented electrical steel sheet. Then, using a small single sheet tester corresponding to the test piece, the magnetic flux density and core loss are measured. The measurement principle follows the Single Sheet Tester (SST) method defined in JIS C 2556:2015.

[0068] In addition, test pieces measuring 100 mm x 500 mm x thickness were prepared from several types of grain-oriented electrical steel sheets in advance, and the magnetic flux density and iron loss were measured by SST using the small single sheet tester described above. Furthermore, Epstein test pieces measuring 30 mm x 320 mm x thickness were obtained from the same types of grain-oriented electrical steel sheets by electrical discharge machining, and the magnetic flux density and iron loss were also measured by the Epstein method specified in JIS C 2550-1:2011. A conversion formula was then derived from the relationship between the values ​​measured by SST and those measured by the Epstein method. Using the resulting conversion formula, the values ​​measured by SST were corrected to be equivalent to the magnetic property values ​​measured by the Epstein method.

[0069] When measuring the magnetic flux density and iron loss, the excitation direction is parallel to the rolling direction. Note that the magnetic flux density B8 means the magnetic flux density in a magnetic field of 800 A / m, and the iron loss W １７／５０ means the iron loss that occurs under the condition that the maximum magnetic flux density is 1.7 T and the frequency is 50 Hz, and the iron loss W １９／５０ means the iron loss that occurs under the conditions of a maximum magnetic flux density of 1.9 T and a frequency of 50 Hz.

[0070] The present embodiment will be described in more detail below with reference to examples, but is not limited to these examples.

[0071] A slab having the chemical composition shown in Table 1 was heated to 1340°C in a heating furnace. The heated slab was subjected to a hot rolling process to produce a hot-rolled steel sheet having a thickness of 2.3 mm. Next, the hot-rolled steel sheet was subjected to a hot-rolled sheet annealing process. Specifically, the hot-rolled steel sheet was heated to a temperature of 1100°C to recrystallize, and then annealed at 900°C for 30 seconds to produce a hot-rolled sheet annealed steel sheet. After the hot-rolled sheet annealing, a cold-rolling process was carried out to produce a cold-rolled steel sheet having a thickness shown in Table 2.

[0072]

[0073] After cold rolling, a decarburization annealing process was carried out. Before the temperature-raising process, laser beam irradiation was carried out in an air atmosphere under the conditions shown in Table 2. The laser beam irradiation interval was 10 mm in the rolling direction, and irradiation was carried out in a direction perpendicular to the rolling direction. After the laser beam irradiation, the temperature was raised from a temperature range of 450°C or less to 850°C at an average heating rate shown in Table 2. Thereafter, the oxygen potential (PH) in the annealing atmosphere was measured. ２ O / PH ２ ) was set to 0.40, and decarburization annealing was performed by soaking at 850°C for 150 seconds to obtain decarburization annealed steel sheets.

[0074]

[0075] An annealing separator (water slurry) containing MgO as a main component was applied to the surface of a 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 1150°C, and the holding time at the finish annealing temperature was 30 hours.

[0076] After the finish annealing process, the annealing separator was removed from the steel sheets, and then an insulating coating formation process was carried out. Specifically, a coating solution mainly containing 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 coating solution had been applied was baked, thereby forming a secondary coating, which was an insulating coating, on the primary coating. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0077] Next, characteristic evaluation test pieces measuring 100 mm in width and 500 mm in length were taken from the center of the longitudinal direction and the center of the width direction of the coil of the grain-oriented electrical steel sheet of each test number above. The magnetic flux density B8 of the taken characteristic evaluation test pieces was measured using the method described above. In this example, when the magnetic flux density B8 was 1.930 T or more, the magnetic properties were evaluated as excellent and the test piece was deemed to have passed. Thereafter, the characteristic evaluation test pieces were subjected to a magnetic domain refining process by irradiating them with a laser beam. Specifically, the irradiation pitch was set to 4 mm intervals, and the energy density Ua was set to 1.25 mJ / mm ２ The iron loss W of the characteristic evaluation test piece after the magnetic domain refining treatment was measured by the above-mentioned method. １７／５０ and iron loss W １９／５０ In this example, the iron loss W after the magnetic domain refining treatment was measured. １７／５０ Iron loss W １９／５０ Ratio of W １９／５０ / W １７／５０ If the value of the magnetic flux density and the iron loss were less than 1.80, it was determined that low high-field iron loss was obtained. The measured values ​​of the magnetic flux density and the iron loss were corrected by the above-mentioned method so that they were equivalent to the magnetic property values ​​measured by the Epstein method.

[0078] The results of the measurement of the magnetic properties are also shown in Table 2.

[0079] In test numbers 1 to 33, all of the manufacturing conditions were appropriate. Therefore, the magnetic flux density was 1.930 T or more, and W １９／５０ / W １７／５０ The magnetic properties were good, with a value of less than 1.80, and the high magnetic field iron loss was particularly low. Among these, for example, as can be seen by comparing Test No. 1 with Test No. 7, and Test No. 2 with Test No. 9, which were the same conditions except for λ, the high magnetic field iron loss was significantly reduced when λ was 0.5 μm or less.

[0080] In contrast, in test numbers 34 to 44, the manufacturing conditions were outside the specified range, and therefore the high magnetic field core loss could not be reduced sufficiently.

[0081] Specifically, in test number 34, the wavelength of the laser beam was outside the specified range, and although the magnetic flux density B8 was 1.930 T or more, the high magnetic field core loss was inferior.

[0082] In test numbers 35 to 38, the value of Up was large in relation to the wavelength of the laser beam. As a result, although the magnetic flux density B8 was 1.930 T or more, the high magnetic field core loss was inferior.

[0083] In test numbers 39 to 42, the value of Up was small in relation to the wavelength of the laser beam. As a result, the magnetic flux density B8 was less than 1.930 T, and the high magnetic field core loss was also inferior.

[0084] In test number 43, the average heating rate during the temperature rise process in the decarburization annealing step was excessively high. As a result, the magnetic flux density B8 was less than 1.930 T, and the high magnetic field core loss was also poor.

[0085] No laser beam irradiation was performed in the decarburization annealing step for test number 44. As a result, the magnetic flux density B8 was less than 1.930 T, and the high magnetic field core loss was also inferior.

[0086] As described above, the manufacturing method of the present disclosure is widely applicable to the manufacture of grain-oriented electrical steel sheets having excellent high magnetic field core loss.

Claims

1. A method for manufacturing a steel sheet, comprising: a hot rolling process of heating a slab and hot rolling the heated slab to obtain a hot-rolled steel sheet; a hot-rolled sheet annealing process of annealing the hot-rolled steel sheet; a cold rolling process of cold-rolling the hot-rolled steel sheet after the hot-rolled sheet annealing process to obtain a cold-rolled steel sheet; a decarburization annealing process of decarburization annealing the cold-rolled steel sheet to obtain a decarburization annealed steel sheet; a finish annealing process of applying an annealing separator to the decarburization annealed steel sheet and then finish annealing it to obtain a finish annealed sheet; and an insulating coating formation process of forming an insulating coating on the surface of the finish annealed sheet, wherein, before the temperature rising process in the decarburization annealing process, the cold-rolled steel sheet is irradiated in a direction intersecting the rolling direction with a laser beam under conditions that satisfy the following formulas (i) to (iii): A method for producing a grain-oriented electrical steel sheet, wherein, during the temperature-raising process of the decarburization annealing step, the temperature is raised from a temperature range of 450°C or lower to a temperature range of 750 to 950°C, and the average heating rate from 450 to 750°C is 40 to 2000°C / sec. 0.3≦λ≦1.1 (i) 0.63λ+0.31≦Up≦4.25λ+0.23 (ii) 5≦d≦30 (iii) where λ in the above formulas (i) and (ii) is the wavelength (μm) of the laser beam, and Up in the above formula (ii) is the irradiation energy density (J / mm) expressed by 4 / π×P / (Dl×Vc), where P (W) is the average intensity of the laser beam, Dl (mm) is the average focused diameter of the focused spot in the rolling direction, and Vc (mm / sec) is the average scanning speed of the laser beam. ２ ) and d in the above formula (iii) is the irradiation interval (mm) of the laser beam.

2. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the cold-rolled steel sheet has a thickness of 0.30 mm or less.

3. The chemical composition of the slab is, in mass %, Si: 3.00 to 3.80%, Mn: 0.01 to 0.30%, N: 0.0030 to 0.0150%, C: 0.010 to 0.100%, sol.

3. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the total content of one or more elements selected from S and Se is 0.010 to 0.050%, Ti: 0 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 to 0.05%, Mo: 0 to 0.05%, Ta: 0 to 0.05%, Nb: 0 to 0.010%, V: 0 to 0.50%, B: 0 to 0.010%, Te: 0 to 0.0200%, Bi: 0 to 0.0200%, and the balance: Fe and impurities.

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