Grain-oriented electrical steel sheet and method for producing same

Abstract

This grain-oriented electrical steel sheet is provided with: a base steel sheet having a prescribed chemical composition; a glass cover film provided on the surface of the base steel sheet; and a tension-imparting insulating cover film provided on the surface of the glass cover film. The base steel sheet has an aggregate structure oriented in a Goss orientation. A base steel plate, when the average dispersion angle of the ideal Goss orientation offset from the rolling surface normal direction ND as the axis of rotation is defined as alpha (DEG), the average dispersion angle of the ideal Goss orientation offset from the rolling right-angle direction TD as the axis of rotation is defined as beta (DEG), and the average dispersion angle of the ideal Goss orientation offset from the rolling direction RD as the axis of rotation is defined as gamma (DEG), [alpha] (DEG) and [gamma] (DEG) are satisfied. [alpha], [beta], and [gamma] satisfy formula (1). 0.0 < = beta < 2.5 < alpha < 4.0 < = gamma < = 10.0 (1)

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2022-182571 filed on November 15, 2022, the content of which is incorporated herein by reference. Background Art

[0003] Generally, a grain-oriented electrical steel sheet is composed of three layers: a base steel sheet, a primary coating film (sometimes called a glass coating film) formed on the surface of the base steel sheet, and a secondary coating film that imparts insulation with surface tension formed on the surface of the primary coating film. The grain-oriented electrical steel sheet is a soft magnetic material and is mainly used as a core material for transformers. Therefore, high magnetization characteristics and magnetic properties such as low iron loss are required for the grain-oriented electrical steel sheet.

[0004] Iron loss refers to the power loss consumed as heat energy when the core is excited by an alternating magnetic field. From the viewpoint of energy conservation, it is required that the iron loss be as low as possible. The iron loss of the grain-oriented electrical steel sheet is affected by factors such as magnetic susceptibility, plate thickness, coating film tension, impurity content, resistivity, crystal grain size, and magnetic domain size. The iron loss of the grain-oriented electrical steel sheet is the sum of eddy current loss depending on resistivity, plate thickness, magnetic domain size, etc. and hysteresis loss depending on crystal orientation, surface smoothness, etc. Regarding the plate thickness, for example, thinning the base steel sheet (e.g., below 0.22 mm) is effective in reducing iron loss by reducing eddy current loss. However, there is a concern that due to thinning, the behavior of secondary recrystallization itself changes, and the aggregation degree of Goss orientation deteriorates.

[0005] The aggregation of Goss orientation is manifested through a phenomenon (secondary recrystallization) generated by strict control of the aggregate structure (texture) and precipitates (inhibitors). The texture is preferably in a state where there are many Goss orientations (nuclei of secondary recrystallization) and many orientations eaten by Goss orientation (corresponding orientations). On the other hand, the inhibitor is preferably in a state where the pinning force of the inhibitor gradually decreases during secondary recrystallization annealing (the inhibitor has high heat resistance). In other words, from the viewpoint of promoting the growth of Goss orientation during secondary recrystallization annealing, it is not preferable for the pinning force of the inhibitor to decrease rapidly.

[0006] Here, in order to obtain thin material, it is necessary to increase the reduction ratio (cold rolling ratio) in cold rolling. If rolling is performed under conditions of a high cold rolling ratio, the Goss orientation, which is the nucleus of secondary recrystallization, decreases, and thus secondary recrystallization becomes unstable.

[0007] In addition, in thin material, although the reason is not clear, the heat resistance of the inhibitor decreases, and the time for preferential growth of Goss orientation cannot be ensured, resulting in the instability of secondary recrystallization.

[0008] That is, in thin materials, from the viewpoints of texture and inhibitor, there is a problem of secondary recrystallization destabilization.

[0009] Based on such a situation, various studies have been conducted in the past to stabilize the secondary recrystallization of thin materials.

[0010] For example, in Patent Document 1 and Patent Document 2, techniques for avoiding texture deterioration by optimally controlling the cold rolling ratio through preliminary cold rolling are disclosed.

[0011] In addition, for example, in Patent Document 3, an inhibitor control technique via a primary covering film is disclosed. In Patent Document 3, by coating MgO containing 0.15 to 2.0% of Cl and / or SO3 as an annealing separating agent, the formation reaction of the glass covering film is significantly improved, and thus the primary covering film is controlled to a morphology preferable for magnetism.

[0012] Prior Art Documents

[0013] Patent Documents

[0014] Patent Document 1: Japanese Patent Application Laid-Open No. 59-126722

[0015] Patent Document 2: Japanese Patent No. 2562254

[0016] Patent Document 3: Japanese Patent No. 3021241 Summary of the Invention

[0017] Problems to be Solved by the Invention

[0018] In the case of the methods of Patent Documents 1 and 2, the number of processes in the cold rolling process increases, thus causing production problems.

[0019] In addition, according to the method of Patent Document 3, although inhibitor control can be performed, texture control is not considered. Therefore, for example, when this technology is applied to a thin electromagnetic steel sheet with a base material steel sheet thickness of less than 0.22 mm, there is a high possibility of not obtaining a high-quality secondary recrystallization orientation.

[0020] As described above, a method for stabilizing the secondary recrystallization of thin materials without reducing productivity and thus obtaining a grain-oriented electromagnetic steel sheet with good magnetic properties has not been disclosed.

[0021] In addition, in recent years, for grain-oriented electromagnetic steel sheets, in addition to magnetic properties such as high magnetization characteristics and low iron loss, a reduction in noise generated when the steel sheet is applied to transformers and the like is also required.

[0022] As described above, the subject of the present disclosure is to provide a grain-oriented electrical steel sheet having good magnetic properties and noise characteristics without reducing productivity, and a method for manufacturing the same.

[0023] Means for Solving the Problem

[0024] In order to achieve both good magnetic properties and good noise characteristics in thin materials due to the aggregation of Goss orientation by secondary recrystallization, the present inventors conducted research from the viewpoints of controlling both the aggregate structure (texture) and precipitates (inhibitors).

[0025] As a result, in some thin materials, the destabilization of secondary recrystallization is not caused, and magnetic properties far superior to those of conventional grain-oriented electrical steel sheets can be confirmed, and it can also be confirmed that good noise characteristics can be achieved. As a result of more detailed investigation, it was found that in the average variance angle of the secondary recrystallized structure deviated from the ideal Goss orientation, the average variance angle β (°) deviated from the ideal Goss orientation with the rolling transverse direction TD as the rotation axis, the average variance angle α (°) deviated from the ideal Goss orientation with the rolling plane normal direction ND as the rotation axis, and the average variance angle γ (°) deviated from the ideal Goss orientation with the rolling direction RD as the rotation axis respectively satisfy the sequence shown in the following formula (1). Thus, even in thin materials, secondary recrystallization is stabilized, and both good magnetic properties and good noise characteristics can be achieved.

[0026] Hitherto, as factors affecting magnetic properties, the average variance angle β (°) and the average variance angle α (°) have been known. However, in the prior art, it is limited to sufficiently reducing the average variance angles β and α, and further reduction of these average variance angles is desired. Furthermore, it is sometimes difficult to achieve a high level of balance between magnetic properties and noise characteristics only by reducing the average variance angles β and α. Therefore, the present inventors conducted intensive research and found that in order to achieve both magnetic properties and noise characteristics of thin materials, in addition to further reducing the average variance angle β, the balance of the average variance angles β, α, and γ also has a strong influence. In addition, a new means for further reducing the average variance angle β was also found.

[0027] Specifically, it was found that by appropriately controlling both the texture and the inhibitor, the average variance angle β can be significantly reduced, and the balance of the average variance angles β, α, and γ can be achieved. More specifically, it was found that by increasing the heating rate in a specified temperature range during the heating process of decarburizing annealing, a dense oxide film can be formed that can sufficiently ensure the Goss orientation and can stably exhibit the function of the inhibitor during secondary recrystallization annealing.

[0028] Hereinafter, the research results of the present inventors will be described in detail.

[0029] First, from the viewpoint of inhibitor control, the inventors investigated the cause of the deterioration of the effect of stabilizing secondary recrystallization caused by an inhibitor in thin materials. As a result, it was found that in thin materials, due to the relative increase in the surface area ratio of the steel itself, the decomposition rate of the inhibitor accelerates, resulting in the destabilization of secondary recrystallization. In addition, the inventors found that the trigger for inhibitor decomposition is the interaction between Mg2SiO4 as a primary coating film (glass coating film) and AlN as an inhibitor. Based on this novel insight, it was discovered that by reducing the formation rate of the primary coating film (i.e., increasing the formation temperature of the primary coating film), the deterioration of the stabilizing effect of secondary recrystallization caused by the inhibitor can be suppressed.

[0030] In addition, the inventors further conducted research and obtained the following insight. The high-temperatureization of the formation temperature of the primary coating film can be achieved by thickening and densifying the SiO2 film formed on the surface of the cold-rolled steel sheet during decarburizing annealing (especially during the heating process). The mechanism by which the formation temperature of the primary coating film during secondary recrystallization can be increased by thickening and densifying SiO2 is not clear, but it is considered that the reason is that the thickened and densified SiO2 reduces the mobility of Mg ions in SiO2.

[0031] Furthermore, from the viewpoint of texture, the inventors found that by accelerating the heating rate in a specified temperature range during decarburizing annealing, the Goss orientation increases. Furthermore, by adding P (phosphorus) to the steel, it is known that a texture preferable for secondary recrystallization can be obtained during cold rolling.

[0032] The present invention has been completed in view of the above insights. The gist of the present invention is as follows.

[0033] [1] One embodiment of the present invention relates to a grain-oriented electrical steel sheet, which includes:

[0034] A base steel sheet, the chemical composition of which contains, by mass%,

[0035] C: 0 to 0.010%,

[0036] Si: 3.00 to 4.00%,

[0037] Sol.Al: 0 to 0.010%,

[0038] Mn: 0.01 to 0.50%,

[0039] N: 0.010% or less,

[0040] S + Se: 0.0100% or less,

[0041] P: 0.005 to 0.100%,

[0042] Sn: 0 to 0.50%,

[0043] Cu: 0 to 0.50%,

[0044] Cr: 0 to 0.50%,

[0045] Sb: 0 to 0.20%,

[0046] Mo: 0 to 0.10%,

[0047] Ni: 0 to 0.20%,

[0048] Nb: 0 to 0.0200%,

[0049] B: 0 to 0.0200%,

[0050] Ti: 0 to 0.0200%, and

[0051] Bi: 0 to 0.0200%,

[0052] The balance consists of Fe and impurities;

[0053] A glass covering film provided on the surface of the base steel plate; and

[0054] A tension - imparting insulating covering film provided on the surface of the glass covering film;

[0055] The base steel plate has a texture oriented in the Goss orientation,

[0056] In the base steel plate,

[0057] When the average dispersion angle deviated from the ideal Goss orientation with the rolling - plane normal direction ND as the rotation axis is defined as α (°),

[0058] When the average dispersion angle deviated from the ideal Goss orientation with the rolling - right - angle direction TD as the rotation axis is defined as β (°),

[0059] When the average dispersion angle deviated from the ideal Goss orientation with the rolling direction RD as the rotation axis is defined as γ (°),

[0060] The α, the β, and the γ satisfy the following formula (1),

[0061] 0.0 ≤ |β| < 2.5 < |α| < 4.0 ≤ |γ| ≤ 10.0 (1).

[0062] [2] The direction - al electromagnetic steel plate according to [1] above, wherein the β may also satisfy the following formula (2),

[0063] 0.0 ≤ |β| ≤ 2.0 (2).

[0064] [3] The grain-oriented electrical steel sheet according to [1] or [2] above, wherein the thickness of the base steel sheet may be 0.16 mm or more and less than 0.20 mm.

[0065] [4] An embodiment of the present invention relates to a method for manufacturing a grain-oriented electrical steel sheet, which includes the following steps:

[0066] A heating step of heating a steel slab, the steel slab containing, by mass%,

[0067] C: 0.020 - 0.150%,

[0068] Si: 3.00 - 4.00%,

[0069] Sol.Al: 0.010 - 0.050%,

[0070] Mn: 0.01 - 0.50%,

[0071] N: 0.001 - 0.020%,

[0072] S + Se: 0.001 - 0.040%,

[0073] P: 0.005 - 0.100%,

[0074] Sn: 0 - 0.50%,

[0075] Cu: 0 - 0.50%,

[0076] Cr: 0 - 0.50%,

[0077] Sb: 0 - 0.20%,

[0078] Mo: 0 - 0.10%,

[0079] Ni: 0 - 0.20%,

[0080] Nb: 0 - 0.0200%,

[0081] B: 0 - 0.0200%,

[0082] Ti: 0 - 0.0200%, and

[0083] Bi: 0 - 0.0200%,

[0084] the balance including Fe and impurities;

[0085] A hot rolling step of hot rolling the steel slab after the heating step to obtain a hot rolled steel sheet;

[0086] A hot rolling sheet annealing process for annealing the hot rolling steel sheet to obtain a hot rolled and annealed steel sheet;

[0087] A cold rolling process for cold rolling the hot rolled and annealed steel sheet to obtain a cold rolled steel sheet;

[0088] A decarburizing annealing process for subjecting the cold rolled steel sheet to decarburizing annealing to obtain a decarburized and annealed steel sheet;

[0089] A final annealing process for coating an annealing release agent on the decarburized and annealed steel sheet and then performing final annealing to obtain a finally annealed steel sheet; and

[0090] An insulating cover film forming process for forming an insulating cover film on the surface of the finally annealed steel sheet;

[0091] The decarburizing annealing process includes a heating-up process and a soaking process.

[0092] In the heating-up process,

[0093] The average heating-up rate in the temperature range of 550 to 800 °C is set to 400 °C / second to 3000 °C / second.

[0094] The maximum heating temperature T1 (°C) is set to 850 °C to 950 °C.

[0095] The average heating-up rate in the temperature range of 800 to the maximum heating temperature T1 (°C) is set to 100 °C / second to 1500 °C / second.

[0096] The dew point of the atmosphere in the temperature range of 800 to the maximum heating temperature T1 (°C) is set to 0 °C or lower.

[0097] [5] The method for manufacturing a directionally electromagnetic steel sheet according to [4] above, wherein the annealing release agent may also contain MgO as a main component, and in the annealing release agent, 0.10 to 10.00% by weight of one or more selected from Ti, Sb, Sr, and Cl is contained relative to the weight of MgO.

[0098] Advantages of the Invention

[0099] According to the above-described aspect of the present disclosure, a directionally electromagnetic steel sheet having good magnetic properties and noise characteristics without reducing productivity and a method for manufacturing the same can be provided. Brief Description of the Drawings

[0100] Figure 1A It is a diagram schematically showing the structure of the directionally electromagnetic steel sheet of the present embodiment.

[0101] Figure 1BThis is a diagram schematically showing the structure of the grain-oriented electrical steel sheet of the present embodiment.

[0102] Figure 2 This is a schematic diagram illustrating the offset angles α, β, and γ.

[0103] Figure 3 This is a flowchart showing an example of the process of the manufacturing method of the grain-oriented electrical steel sheet of the present embodiment. Detailed Embodiment

[0104] Hereinafter, with reference to the drawings, preferred embodiments of the present disclosure will be described in detail. In this specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description thereof is omitted.

[0105] The grain-oriented electrical steel sheet of one embodiment of the present disclosure (the grain-oriented electrical steel sheet of the present embodiment) includes: a base steel sheet having a chemical composition described later; a glass covering film formed on the base steel sheet; and a tension-imparting insulating covering film formed on the glass covering film. Further, the base steel sheet has an aggregate structure oriented in the Goss orientation. Further, in the base steel sheet, when the average dispersion angle deviated from the ideal Goss orientation with the rolling plane normal direction ND as the rotation axis is defined as α (°), the average dispersion angle deviated from the ideal Goss orientation with the rolling width direction TD as the rotation axis is defined as β (°), and the average dispersion angle deviated from the ideal Goss orientation with the rolling direction RD as the rotation axis is defined as γ (°), the α, the β, and the γ satisfy the following formula (1).

[0106] 0.0 ≤ |β| < 2.5|α| < 4.0 ≤ |γ| ≤ 10.0 (1)

[0107] Hereinafter, the grain-oriented electrical steel sheet of the present embodiment will be described.

[0108] [Grain-Oriented Electrical Steel Sheet]

[0109] Figure 1A And Figure 1B This is a diagram schematically showing the structure of the grain-oriented electrical steel sheet of the present embodiment.

[0110] As Figure 1A shown, the grain-oriented electrical steel sheet 10 of the present embodiment has a base steel sheet 11, a primary covering film (glass covering film) 13 formed on the surface of the base steel sheet 11, and a secondary covering film (tension-imparting insulating covering film) 15 as an example of the insulating covering film formed on the surface of the glass covering film 13. The glass covering film 13 and the tension-imparting insulating covering film 15 only need to be formed on at least one surface of the base steel sheet 11, but usually asFigure 1B As schematically shown, it is formed on both sides of the base material steel plate 11.

[0111] Next, the directionally electromagnetic steel sheet 10 of the present embodiment will be described centering on its characteristic structure. In the following description, detailed descriptions of well-known structures and some structures that can be implemented by those skilled in the art may sometimes be omitted.

[0112] (Base material steel plate 11)

[0113] The base material steel plate 11 is manufactured from a steel slab containing the chemical components described in detail below, and thus can exhibit excellent noise characteristics and magnetic characteristics. Regarding the chemical components of the base material steel plate 11, they will be described in detail again below.

[0114] (Glass covering film 13)

[0115] The glass covering film 13 is an inorganic covering film disposed on the surface of the base material steel plate 11 and mainly composed of magnesium silicate. The glass covering film 13 is formed by reacting an annealing release agent containing magnesium oxide (MgO) coated on the surface of the base material steel plate with the components on the surface of the base material steel plate 11 during final annealing. That is, the glass covering film 13 has a composition derived from the annealing release agent and the components of the base material steel plate (more specifically, a composition mainly composed of Mg2SiO4).

[0116] (Tension - imparting insulating covering film 15)

[0117] The tension - imparting insulating covering film 15 is disposed on the surface of the glass covering film 13. By imparting electrical insulation to the directionally electromagnetic steel sheet 10 using the tension - imparting insulating covering film 15, eddy current losses can be reduced, thereby improving the iron loss of the directionally electromagnetic steel sheet 10. In addition, the tension - imparting insulating covering film 15 realizes various properties such as corrosion resistance, heat resistance, and slidability in addition to the electrical insulation as described above.

[0118] Furthermore, the tension - imparting insulating covering film 15 has a function of imparting tension to the directionally electromagnetic steel sheet 10. By imparting tension to the directionally electromagnetic steel sheet 10 using the tension - imparting insulating covering film 15, the movement of magnetic domain walls in the directionally electromagnetic steel sheet 10 becomes easier, and thus the iron loss of the directionally electromagnetic steel sheet 10 can be improved.

[0119] Magnetic domain refinement treatment can also be performed on the surface of the tension - imparting insulating covering film 15 using a continuous - wave laser beam or an electron beam. In this case, linear thermal strains at a prescribed angle φ with respect to the direction orthogonal to the rolling direction, i.e., the sheet width direction, are periodically formed at prescribed intervals along the rolling direction. Thereby, in the directionally electromagnetic steel sheet of the present embodiment, magnetic characteristics can be further improved.

[0120] The tension-imparting insulating cover film 15 is formed, for example, by applying a coating liquid mainly composed of a metal phosphate and silica to the surface of the glass cover film 13 and baking it.

[0121] (Plate thickness)

[0122] The plate thickness of the base material steel plate of the directionality electromagnetic steel sheet 10 in the present embodiment ( Figure 1A and Figure 1B the plate thickness t therein) is not particularly limited, and can be set to, for example, 0.16 mm to 0.30 mm. Further, in the present embodiment, the smaller the plate thickness of the cold-rolled plate (base material steel plate 11) after cold rolling, the more the reduction effect of iron loss can be obtained sufficiently. Therefore, the plate thickness t of the base material steel plate of the directionality electromagnetic steel sheet 10 is preferably 0.24 mm or less, more preferably 0.23 mm or less. Further, for example, when the cold-rolled plate is a thin material (i.e., thin stock) with a plate thickness less than 0.22 mm, the above effect becomes remarkable and the iron loss becomes more excellent. Therefore, from the viewpoint of magnetic properties, the plate thickness t of the base material steel plate of the directionality electromagnetic steel sheet 10 is further preferably less than 0.20 mm, for example. The lower limit of the plate thickness t can also be 0.16 mm or more, and can also be 0.17 mm or more.

[0123] (Chemical composition)

[0124] Next, the chemical compositions of the base material steel plate 11 of the directionality electromagnetic steel sheet 10 in the present embodiment and the steel slab used when manufacturing the directionality electromagnetic steel sheet 10 will be described in detail. Hereinafter, unless otherwise specified, the notation of "%" means "mass%".

[0125] When a steel slab (for example, a slab) having the following chemical composition becomes a directionality electromagnetic steel sheet through the manufacturing process described in detail below, for the components of the base material steel plate 11 other than carbon (C), acid-soluble aluminum (sol.Al), nitrogen (N), sulfur (S), and bismuth (Bi), the same content as that in the steel slab state is maintained. That is, the contents of the components of the base material steel plate 11 other than carbon (C), acid-soluble aluminum (sol.Al), nitrogen (N), and sulfur (S) are substantially the same in the steel slab state and the product plate state. On the other hand, for carbon (C), acid-soluble aluminum (sol.Al), nitrogen (N), sulfur (S), and bismuth (Bi) of the base material steel plate 11, their contents change compared with the composition in the steel slab state through the manufacturing process described in detail below. Further, regarding silicon (Si), manganese (Mn), chromium (Cr), boron (B), and titanium (Ti) of the base material steel plate 11, since they are absorbed into the glass cover film during the manufacturing process, their contents sometimes slightly decrease compared with the composition in the steel slab state.

[0126] C: 0.020 to 0.150%

[0127] C (carbon) is an element that has the effect of increasing the magnetic flux density. When the C content in the steel slab is less than 0.020%, the improvement effect of the magnetic flux density cannot be obtained. Therefore, the C content in the steel slab is set to 0.020% or more. The C content is preferably 0.040% or more, and more preferably 0.050% or more.

[0128] On the other hand, when the C content in the steel slab exceeds 0.150%, a phase change occurs in the steel during secondary recrystallization annealing (i.e., final annealing), and secondary recrystallization is not fully carried out, and good magnetic flux density and iron loss characteristics cannot be obtained. Therefore, the C content in the steel slab is set to 0.150% or less. The lower the C content, the more preferable it is for reducing iron loss. From the viewpoint of reducing iron loss, the C content is preferably 0.120% or less, and more preferably 0.100% or less.

[0129] The C content in the steel slab as described above becomes the C content in the oriented electrical steel sheet 10 of the present embodiment through the processes described in detail below, and the C content in the base steel sheet 11 becomes 0.010% (100 ppm) or less. The C content in the base steel sheet 11 may also be 0%. However, it is difficult to set the C content to 0% in practical steel sheets, so the C content may also be set to more than 0%.

[0130] Si: 3.00 - 4.00%

[0131] Si (silicon) is an element that is extremely effective in increasing the electrical resistance (resistivity) of steel and reducing eddy current loss, which is part of the iron loss. When the Si content in the steel slab is less than 3.00%, a phase change occurs in the steel during secondary recrystallization annealing, and secondary recrystallization is not fully carried out, and good magnetic flux density and iron loss characteristics cannot be obtained. Therefore, the Si content in the steel slab is set to 3.00% or more. The Si content in the steel slab is preferably 3.10% or more, and more preferably 3.20% or more.

[0132] On the other hand, when the Si content in the steel slab exceeds 4.00%, the steel sheet becomes brittle, and the sheet passing property during the manufacturing process deteriorates significantly. Therefore, the Si content in the steel slab is set to 4.00% or less. The Si content in the steel slab is preferably 3.80% or less, and more preferably 3.50% or less.

[0133] The Si content in the steel slab as described above sometimes decreases to become the grain-oriented electrical steel sheet 10 of the present embodiment through the processes described in detail below. For example, since Si is consumed as a glass coating film, the Si content in the base steel sheet 11 sometimes slightly decreases. However, as long as the decrease amount does not hinder the effects of the present embodiment, by setting the Si content of the steel slab within the above range, the effects of the present embodiment can be enjoyed. In addition, considering the above decrease amount of the Si content, the Si content of the base steel sheet 11 can also be set to 2.80 to 3.80%.

[0134] sol.Al: 0.010 to 0.050%

[0135] sol.Al (acid-soluble aluminum) is a constituent element of the main inhibitor among the compounds called inhibitors that influence secondary recrystallization in the grain-oriented electrical steel sheet. In the base steel sheet of the present embodiment, it is an essential element from the viewpoint of the appearance of secondary recrystallization. When the sol.Al content of the steel slab is less than 0.010%, AlN that functions as an inhibitor cannot be sufficiently generated, and secondary recrystallization becomes insufficient, so that the iron loss characteristics are not improved. Therefore, the sol.Al content in the steel slab is set to 0.010% or more. The sol.Al content is preferably 0.020% or more.

[0136] On the other hand, when the sol.Al content exceeds 0.050%, the embrittlement of the steel sheet becomes significant. Therefore, the sol.Al content of the steel slab is set to 0.050% or less. The sol.Al content is preferably 0.040% or less, and more preferably 0.030% or less.

[0137] The sol.Al content in the steel slab as described above becomes the grain-oriented electrical steel sheet 10 of the present embodiment through the processes described in detail below, whereby the sol.Al content in the base steel sheet 11 becomes 0.010% (100 ppm) or less. The lower limit value of the sol.Al content in the base steel sheet 11 is not particularly limited, and thus can also be 0%.

[0138] Mn: 0.01 to 0.50%

[0139] Mn (manganese) is an important element for forming MnS, which is one of the main inhibitors. When the Mn content of the steel slab is less than 0.01%, the absolute amount of MnS required for secondary recrystallization is insufficient. Therefore, the Mn content of the steel slab is set to 0.01% or more. The Mn content is preferably 0.03% or more, and more preferably 0.06% or more.

[0140] On the other hand, when the Mn content of the steel slab exceeds 0.50%, a phase change occurs in the steel during secondary recrystallization annealing, and the secondary recrystallization is not fully carried out, so that good magnetic flux density and iron loss characteristics cannot be obtained. Therefore, the Mn content of the steel slab is set to 0.50% or less. The Mn content is preferably 0.20% or less, more preferably 0.10% or less.

[0141] The Mn content in the steel slab as described above sometimes decreases to become the grain-oriented electrical steel sheet 10 of the present embodiment through the processes described in detail below. For example, since Mn is absorbed into the glass coating film, the Mn content in the base metal steel sheet 11 sometimes slightly decreases. However, the amount of decrease is within the range that does not hinder the effects of the present embodiment. By setting the Mn content of the steel slab within the above range, the effects of the present embodiment can be enjoyed. In addition, considering the above-mentioned decrease amount of the Mn content, the Mn content of the base metal steel sheet 11 can also be set to 0 to 0.40%.

[0142] N: 0.001 - 0.020%

[0143] N (nitrogen) is an element that reacts with the above-mentioned acid-soluble Al to form AlN that functions as an inhibitor. In order to bond with Al to form AlN that functions as an inhibitor, the N content of the steel slab is set to 0.001% or more. The N content is preferably 0.004% or more, more preferably 0.006% or more.

[0144] On the other hand, when the N content of the steel slab exceeds 0.020%, blisters (pores) are generated in the steel sheet during cold rolling, and the strength increases, deteriorating the plate passing property during manufacturing. Therefore, the N content of the steel slab is set to 0.020% or less. The N content is preferably 0.015% or less, more preferably 0.010% or less.

[0145] The N content in the steel slab as described above becomes the grain-oriented electrical steel sheet 10 of the present embodiment through the processes described in detail below, whereby the N content in the base metal steel sheet 11 becomes 0.010% (100 ppm) or less. The lower limit value of the N content in the base metal steel sheet 11 is not particularly limited, and thus may be 0%.

[0146] S + Se: 0.0010 - 0.0400%

[0147] S (sulfur) and Se (selenium) are important elements that form MnS or MnSe as inhibitors by reacting with the above-mentioned Mn. When the total of the S content and the Se content in the steel slab is less than 0.0010%, a sufficient inhibitor effect cannot be obtained. Therefore, the total of the S content and the Se content in the steel slab is set to 0.0010% or more. The total of the S content and the Se content is preferably 0.0100% or more, more preferably 0.0150% or more.

[0148] On the other hand, when the total of the S content and the Se content in the steel slab exceeds 0.0400%, it causes hot brittleness and hot rolling becomes significantly difficult. Therefore, the total of the S content and the Se content in the steel slab is set to 0.0400% or less. The total of the S content and the Se content is preferably 0.0300% or less.

[0149] In addition, the S content in the steel slab as described above sometimes decreases through the processes described in detail below to become the grain-oriented electrical steel sheet 10 of the present embodiment. In this case, the S content in the base material steel sheet 11 sometimes becomes 0.0100% (100 ppm) or less. The lower limit of the total of the S content and the Se content in the base material steel sheet 11 is not particularly limited and may be 0.0005%. The lower limit of the total of the S content and the Se content in the base material steel sheet 11 may include 0%. In addition, careful attention needs to be paid to the identification of S or Se below 0.0005%. When the S content or the Se content is below the detection limit of the analysis device, the total of the S content and the Se content is sometimes regarded as 0%. In practical steel sheets, the lower limit value of the total of the substantial S content and the Se content is 0.0005%.

[0150] P: 0.005 to 0.100%

[0151] P (phosphorus) helps to obtain a texture that is preferable for secondary recrystallization and is an element having an effect of improving magnetic properties. Therefore, the P content of the steel slab is set to 0.005% or more. It is preferably set to 0.010% or more.

[0152] On the other hand, P is an element that reduces the workability during rolling. When the P content exceeds 0.100%, the rolling workability decreases and there may be a risk of fracture of the steel sheet during manufacturing. Therefore, the P content is set to 0.100% or less. The P content is preferably set to 0.070% or less, and more preferably 0.030% or less.

[0153] The balance: Fe and impurities

[0154] The chemical compositions of the steel slab and the base material steel sheet 11 of the present embodiment contain the above elements (basic elements), and the balance is substantially Fe and impurities. However, for the purpose of improving magnetic properties and the like, one or more (optional elements) selected from Sn, Cu, Cr, Sb, Mo, Ni, Nb, B, Ti, and Bi may be further contained within the ranges shown below. Sn, Cu, Cr, Sb, Mo, Ni, Nb, B, Ti, and Bi are optional elements in the steel slab and the base material steel sheet 11 of the present embodiment, and thus the lower limit of their content is 0%.

[0155] Sn: 0 to 0.50%

[0156] Sn (tin) is an element with the effect of improving magnetic properties. Therefore, it can also be contained. When Sn is contained, in order to exhibit the effect of improving magnetic properties well, it is preferable to set the Sn content to 0.01% or more. Considering both magnetic properties and the adhesion of the cover film, the Sn content is more preferably 0.03% or more.

[0157] On the other hand, if the Sn content exceeds 0.50%, the adhesion of the glass cover film deteriorates significantly. Therefore, when it is contained, the Sn content is set to 0.50% or less. The Sn content is preferably 0.40% or less, and more preferably 0.30% or less.

[0158] Cu: 0 to 0.50%

[0159] Cu (copper) is an element that contributes to an increase in the Goss orientation occupancy in the structure that aids secondary recrystallization and also contributes to an improvement in the adhesion of the glass cover film. When the above effects are obtained, it is preferable to set the Cu content to 0.01% or more. The Cu content is more preferably 0.05% or more.

[0160] On the other hand, when the Cu content exceeds 0.50%, the hot-rolled medium steel plate becomes brittle. Therefore, when it is contained, the Cu content of the steel billet is set to 0.50% or less. The Cu content is preferably 0.40% or less, and more preferably 0.30% or less.

[0161] Cr: 0 to 0.50%

[0162] Cr (chromium), like Sn and Cu, is an element that contributes to an increase in the Goss orientation occupancy in the secondary recrystallized structure, thereby improving magnetic properties, and also contributes to an improvement in the adhesion of the glass cover film. In order to obtain the above effects, it is preferable to set the Cr content to 0.01% or more. The Cr content is more preferably 0.03% or more.

[0163] On the other hand, when the Cr content exceeds 0.50%, Cr oxides are formed and the magnetic properties are reduced. Therefore, when it is contained, the Cr content is set to 0.50% or less. The Cr content is preferably 0.40% or less, and more preferably 0.30% or less.

[0164] Sb: 0 to 0.20%

[0165] Sb (antimony) is an element with the effect of improving magnetic properties. Therefore, it can also be contained. When Sb is contained, in order to exhibit the effect of improving magnetic properties well, it is preferable to set its content to 0.01% or more.

[0166] On the other hand, if the Sb content exceeds 0.20%, the glass coating film deteriorates significantly. Therefore, when it is contained, the upper limit of the Sb content is set to 0.20%. The Sb content is preferably 0.15% or less, more preferably 0.10% or less.

[0167] Mo: 0 to 0.10%

[0168] Mo (molybdenum) is an element with an effect of improving magnetic properties. Therefore, it can also be contained. When Mo is contained, in order to exhibit the magnetic property improvement effect well, the Mo content is preferably set to 0.01% or more.

[0169] On the other hand, if the Mo content exceeds 0.10%, the cold rolling property deteriorates and fracture may occur. Therefore, when it is contained, the Mo content is set to 0.10% or less. The Mo content is preferably 0.05% or less, more preferably 0.03% or less.

[0170] Ni: 0 to 0.20%

[0171] Ni (nickel) is an effective element for affecting the crystal orientation rotation during cold rolling and obtaining a texture preferable for secondary recrystallization. In addition, it is also an element effective for increasing the resistivity and reducing iron loss. Therefore, it can also be contained. When Ni is contained, in order to obtain these effects, the Ni content is preferably set to 0.01% or more.

[0172] On the other hand, when the Ni content exceeds 0.20%, secondary recrystallization sometimes becomes unstable. Therefore, when it is contained, the Ni content is set to 0.20% or less. The Ni content is preferably 0.15% or less, more preferably 0.10% or less.

[0173] Nb: 0 to 0.0200%

[0174] Nb (niobium) is an element effective for stabilizing secondary recrystallization by strengthening the action of the inhibitor. Therefore, it can also be contained. When Nb is contained, in order to stably obtain secondary recrystallization, the Nb content is preferably set to 0.0005% or more. The Nb content is more preferably 0.0010% or more.

[0175] On the other hand, when the Nb content exceeds 0.0200%, secondary recrystallization sometimes becomes unstable. Therefore, when it is contained, the Nb content is set to 0.0200% or less. The Nb content is preferably 0.0100% or less, more preferably 0.0050% or less.

[0176] B: 0 to 0.0200%

[0177] B (boron) is an element effective for stably obtaining secondary recrystallization by strengthening the action of the inhibitor. Therefore, it may also be contained. When containing B, in order to stably obtain secondary recrystallization, the B content is preferably set to 0.0005% or more. The B content is more preferably 0.0010% or more.

[0178] On the other hand, when the content of B exceeds 0.0200%, secondary recrystallization sometimes becomes unstable. Therefore, when contained, the B content is set to 0.0200% or less. The B content is preferably 0.0100% or less, and more preferably 0.0050% or less.

[0179] Ti: 0 to 0.0200%

[0180] Ti (titanium) is an element that increases the degree of aggregation of Goss orientation and improves magnetism. The reason is not clear, but it may form TiN by bonding with N and function as an inhibitor. When containing Ti, the Ti content is set to 0.0005% or more, preferably set to 0.0010% or more.

[0181] On the other hand, when the content of Ti exceeds 0.0200%, excessive precipitation of TiN occurs and the iron loss deteriorates. Therefore, the Ti content is set to 0.0200% or less. It is preferably 0.0100% or less. More preferably, it is set to 0.0050% or less.

[0182] Bi: 0 to 0.0200%

[0183] Bi (bismuth) is an element that increases the degree of aggregation of Goss orientation and improves magnetism. When containing Bi, the Bi content is set to 0.0010% or more, preferably set to 0.0020% or more.

[0184] On the other hand, when Bi exceeds 0.0200%, the adhesion of the coating film deteriorates. Therefore, the Bi content is set to 0.0200% or less. It is preferably set to 0.0100% or less.

[0185] In addition, the Bi content in the steel slab as described above becomes the Bi content in the mother material steel plate 11 of 0.0100% (100 ppm) or less in the directionally electromagnetic steel plate 10 of the present embodiment through the processes described in detail below. The lower limit value of the Bi content in the mother material steel plate 11 is not particularly limited, and thus may be set to 0%. It may also be set to more than 0%.

[0186] Here, the respective contents of Cr, B, and Ti in the steel slab as described above sometimes decrease to become the grain-oriented electrical steel sheet 10 of the present embodiment through the processes described in detail below. For example, by absorbing Cr in the glass coating film or forming inclusions such as BN and TiN, the respective contents of these elements in the base metal steel sheet 11 sometimes slightly decrease. However, the amount of decrease is within a range that does not affect the effects of the present embodiment.

[0187] In addition, in order to obtain the total amount of the chemical components in the base metal steel sheet 11 from the grain-oriented electrical steel sheet 10, it is sufficient to perform measurement using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, first, the grain-oriented electrical steel sheet 10 is subjected to a cleaning treatment with an alkaline solution to remove the tension-imparting insulating coating film 15, and then the glass coating film 13 is removed by pickling. Then, measurement is performed using ICP-AES. At this time, C and S can be measured by combustion-infrared absorption method, N can be measured by inert gas fusion-thermal conductivity method, and O can be measured by inert gas fusion-non-dispersive infrared absorption method.

[0188] As a method for removing the tension-imparting insulating coating film, a method of immersing the grain-oriented electrical steel sheet having the coating film in a high-temperature alkaline solution can be applied. Specifically, the grain-oriented electrical steel sheet having the coating film is immersed in an aqueous sodium hydroxide solution (NaOH: 30 to 50 mass% + H2O: 50 to 70 mass%) at 80°C to 90°C for 5 minutes to 10 minutes, and then washed with water and dried. Thereby, the tension-imparting insulating coating film can be removed from the grain-oriented electrical steel sheet. The immersion time in the aqueous sodium hydroxide solution can be appropriately changed according to the thickness of the tension-imparting insulating coating film.

[0189] In addition, as a method for removing the glass coating film, the grain-oriented electrical steel sheet in a state where the tension-imparting insulating coating film has been removed is immersed in hydrochloric acid (concentration: 30% to 40%) at 80 to 90°C for 1 minute to 5 minutes, and then washed with water and dried. Thereby, the glass coating film can be removed from the grain-oriented electrical steel sheet.

[0190] In this way, it is preferably separately used and removed such that an alkaline solution is used for removing the tension-imparting insulating coating film and hydrochloric acid or the like is used for removing the glass coating film. By removing the tension-imparting insulating coating film and the glass coating film, the base metal steel sheet can be made to appear, and the chemical composition of the base metal steel sheet can be measured.

[0191] In addition, for the steel components of the slab (steel slab), it is sufficient to collect a sample from the molten steel before casting and perform a composition analysis, or to remove the surface oxide film or the like from the slab after casting and perform a composition analysis.

[0192] For the steel billet of the present embodiment and the base metal steel sheet 11, the remainder of the chemical components other than the above elements (basic elements, optional elements) is substantially Fe and impurities. Here, the "impurities" are present in the steel billet and the base metal steel sheet 11 regardless of the intention of addition. That is, it refers to the elements mixed in from ores, scraps, or manufacturing environments as raw materials during the industrial production of the base metal steel sheet, and are elements allowed to be contained in amounts that do not adversely affect the function of the grain-oriented electrical steel sheet of the present embodiment.

[0193] (Aggregate structure)

[0194] The base metal steel sheet 11 of the present embodiment has a secondary recrystallization aggregate structure aggregated along the {110}<001> orientation (Goss orientation). In addition, in the base metal steel sheet 11, when the average dispersion angle deviated from the ideal Goss orientation with the rolling plane normal direction ND as the rotation axis is defined as α (°), the average dispersion angle deviated from the ideal Goss orientation with the rolling right angle direction TD as the rotation axis is defined as β (°), and the average dispersion angle deviated from the ideal Goss orientation with the rolling direction RD as the rotation axis is defined as γ (°), the α, the β, and the γ satisfy the following formula (1). The β preferably satisfies the following formula (2).

[0195] 0.0 ≤ |β| < 2.5 < |α| < 4.0 ≤ |γ| ≤ 10.0 (1)

[0196] 0.0 ≤ |β| ≤ 2.0 (2)

[0197] In the present embodiment, two types of {110}<001> orientations, namely, the "{110}<001> orientation of the actual crystal" and the "{110}<001> orientation of the ideal", are distinguished. The reason is that in the present embodiment, it is necessary to distinguish the {110}<001> orientation when representing the crystal orientation of the practical steel sheet from the {110}<001> orientation as the crystal orientation in academia.

[0198] Generally speaking, in the measurement of the crystal orientation of the practical steel sheet after recrystallization, the crystal orientation is specified without strictly distinguishing the angular difference of about ±2.5°. For the conventional grain-oriented electrical steel sheet, an angular range of about ±3.0° centered on the geometrically strict {110}<001> orientation is defined as the "{110}<001> orientation". However, in the present embodiment, it is also necessary to clearly distinguish the angular difference of 3.0° or less.

[0199] Therefore, in the present embodiment, when referring to the orientation of the grain-oriented electrical steel sheet in a practical sense, it is abbreviated as "{110}<001> orientation (Goss orientation)" as in the past. On the other hand, when referring to the {110}<001> orientation as a geometrically strict crystal orientation, in order to avoid confusion with the {110}<001> orientation used in previous known documents, etc., it is denoted as "ideal {110}<001> orientation (ideal Goss orientation)".

[0200] In the present embodiment, the deviation of the actual crystal orientation of the grain-oriented electrical steel sheet from the ideal Goss orientation is defined using the following three angles α, β, γ (unit: °).

[0201] Average spread angle (deviation angle) α: The deviation angle rotated around the normal direction (ND) of the rolling plane.

[0202] Average spread angle (deviation angle) β: The deviation angle rotated around the transverse direction (TD) perpendicular to rolling.

[0203] Average spread angle (deviation angle) γ: The deviation angle rotated around the rolling direction (RD).

[0204] Schematic diagrams of the above deviation angle α, deviation angle β, and deviation angle γ are as Figure 2 shown.

[0205] As Figure 2 shown, the deviation angle α refers to the angle formed between the <001> direction of the crystal projected onto the rolling plane when observed from the normal direction ND of the rolling plane and the rolling direction RD. The deviation angle β refers to the angle formed between the <001> direction of the crystal projected onto the L cross-section (the cross-section with the transverse direction TD as the normal) when observed from the transverse direction TD (sheet width direction) perpendicular to rolling and the rolling direction RD. The deviation angle γ refers to the angle formed between the <110> direction of the crystal projected onto the C cross-section (the cross-section with the rolling direction RD as the normal) when observed from the rolling direction RD and the normal direction ND of the rolling plane.

[0206] It is known that the deviation angles α and β among the deviation angles α, β, and γ affect the magnetic properties. Among them, the deviation angle β affects the magnetostriction. Magnetostriction refers to the phenomenon in which a magnetic material undergoes a shape change when a magnetic field is applied. In the grain-oriented electrical steel sheet used in transformers, etc., magnetostriction becomes the cause of noise, and thus a smaller magnetostriction is required. Generally speaking, in order to reduce the magnetostriction, the crystal orientation is controlled in such a way that the deviation angle β is reduced (specifically, in such a way that the maximum value and the average value of the absolute value |β| of the deviation angle β are reduced). However, in the past grain-oriented electrical steel sheets, there is a limit to the reduction of the deviation angle β, and further reduction is desired.

[0207] Therefore, the present inventors conducted research and found that by stably ensuring the effect of stabilizing secondary recrystallization caused by the inhibitor and increasing the heating rate of the heating process in the decarburizing annealing conditions, the deviation angle β can be significantly reduced compared to the prior art, and the Goss orientation can be sufficiently ensured.

[0208] In the secondary recrystallized aggregate structure of the base metal steel sheet of the present embodiment, the above formula (1) is satisfied, and preferably the above formula (2) is satisfied.

[0209] In the case where the deviation angle γ in the formula (1) exceeds 10.0°, the magnetic properties may deteriorate. In addition, compared with the deviation angle γ, the deviation angles α and β have a greater impact on the magnetic properties. Therefore, the deviation angles α and β are made smaller than the deviation angle γ. However, the deviation angle γ affects the noise characteristics, so it is not preferable to increase it too much. Therefore, in the formula (1), the deviation angle γ is set to 10.0° or less. In addition, if it is desired to control the deviation angle γ to be less than 4.0°, the deviation angle β may exceed 2.5°. If the deviation angle β exceeds 2.5°, the noise characteristics may deteriorate. Therefore, the lower limit of the deviation angle γ is set to 4.0° or more. Furthermore, by controlling the deviation angles α and β to be less than 4.0°, the magnetic flux density with respect to the rolling direction is improved, and good magnetic properties can be obtained. From the viewpoint of improving the magnetic properties, the deviation angles α and β are preferably less than 3.5°, more preferably less than 3.0°. However, if it is desired to control the deviation angle α to be 2.5° or less, the deviation angle β will be 2.5° or more. The reason for this is not clear, but it can be speculated that this is because there is a trade-off relationship between the primary recrystallized aggregate structure that can reduce the deviation angle α and the primary recrystallized aggregate structure that can reduce the deviation angle β. If the deviation angle β is 2.5° or more, the noise characteristics may deteriorate. Therefore, the lower limit of the deviation angle α is set to exceed 2.5°, and the upper limit of the deviation angle β is set to be less than 2.5°. As described above, from the viewpoint of taking into account both the magnetic properties and the noise characteristics, it is effective for the deviation angles α, β, and γ to satisfy the following relationship in the present embodiment.

[0210] 0.0 ≤ |β| < 2.5 < |α| < 4.0 ≤ |γ| ≤ 10.0 (1)

[0211] In addition, in the above formula (2), if the deviation angle β exceeds 2.0°, the noise characteristics may deteriorate. Therefore, the deviation angle β is preferably set to 2.0° or less, more preferably set to 1.8° or less. The smaller the deviation angle β is, the more preferable it is, so its lower limit value is not limited. The deviation angle β can be 0° as well.

[0212] The crystal orientation of the grain-oriented electrical steel sheet can be obtained experimentally using, for example, a Laue diffraction apparatus (RIGAKU RASCO-L II V). For example, X-rays are irradiated onto a grain-oriented electrical steel sheet with a width of 60 mm and a length of 300 mm at intervals of 5 mm in the length direction and 5 mm in the width direction to obtain Laue diffraction spots. Then, the obtained Laue diffraction spots are fitted using analysis software on a PC, and thus the Euler angles φ1, Φ, and φ2 can be obtained. For example, the Euler angles of the Goss orientation are given by φ1 = 0°, Φ = 45°, φ2 = 0° or φ1 = 90°, Φ = 90°, φ2 = 45° in the Bunge notation. Therefore, by comparing the orientation angles obtained from the experiment with the angles of the Goss orientation, the deviation angles α, β, and γ can be obtained.

[0213] [Manufacturing Method of Grain-Oriented Electrical Steel Sheet]

[0214] Next, with reference to Figure 3 a grain-oriented electrical steel sheet and a manufacturing method thereof according to an embodiment of the present invention (the manufacturing method of the grain-oriented electrical steel sheet of the present embodiment) will be described. Figure 3 It is a flowchart showing an example of the process of the manufacturing method of the grain-oriented electrical steel sheet of the present embodiment.

[0215] The manufacturing method of the grain-oriented electrical steel sheet of the present embodiment includes:

[0216] (I) a heating step of heating a steel slab having a predetermined chemical composition,

[0217] (II) a hot rolling step of hot rolling the steel slab after the heating step to obtain a hot rolled steel sheet (step S101),

[0218] (III) a hot rolled sheet annealing step of annealing the hot rolled steel sheet to obtain a hot rolled annealed steel sheet (step S103),

[0219] (IV) a cold rolling step of cold rolling the hot rolled annealed steel sheet to obtain a cold rolled steel sheet (step S105),

[0220] (V) a decarburizing annealing step of subjecting the cold rolled steel sheet to decarburizing annealing to obtain a decarburized annealed steel sheet (step S107),

[0221] (VI) a final annealing step of performing final annealing after coating an annealing separating agent on the decarburized annealed steel sheet to obtain a final annealed steel sheet (step S109), and

[0222] (VII) an insulating coating film forming step of forming an insulating coating film on the surface of the final annealed steel sheet (step S111).

[0223] Hereinafter, the preferred conditions for each process will be described. For the conditions not described, well-known conditions can be applied.

[0224] (Heating process)

[0225] In the heating process, before hot rolling, a steel billet such as a slab having the above chemical composition is heated. The heating temperature of the steel billet is not particularly limited, and is preferably set in the range of 1100 to 1450 °C. The heating temperature is more preferably 1300 to 1400 °C.

[0226] (Hot rolling process: S101)

[0227] In the hot rolling process (step S101), the steel billet after the heating process is hot rolled to obtain a hot rolled steel sheet. Regarding the hot rolling conditions, there is no particular limitation, and they can be appropriately set based on the required properties. For example, the thickness of the hot rolled steel sheet after hot rolling is preferably in the range of 2.0 mm to 3.0 mm.

[0228] (Hot rolled sheet annealing process: S103)

[0229] The hot rolled sheet annealing process is a process of annealing the hot rolled steel sheet manufactured through the hot rolling process to produce a hot rolled annealed steel sheet. By performing such an annealing treatment, the steel sheet structure undergoes recrystallization, and good magnetic properties can be achieved.

[0230] In the hot rolled sheet annealing process of the present embodiment, the hot rolled steel sheet manufactured through the hot rolling process may be annealed according to a well-known method. Regarding the method of heating the hot rolled steel sheet during annealing, there is no particular limitation, and a well-known heating method can be adopted. In addition, there is no particular limitation on the annealing conditions either. 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.

[0231] (Cold rolling process: S105)

[0232] In the cold rolling process (step S105), the hot rolled annealed steel sheet is subjected to cold rolling including at least one pass or more to obtain a cold rolled steel sheet. Cold rolling may not include one or more intermediate annealings between each rolling pass. It is also possible to interrupt the cold rolling and perform at least one or more intermediate annealings before the final pass of the cold rolling process, thereby performing multiple cold rollings sandwiching the intermediate annealing.

[0233] In the case of performing intermediate annealing, it is preferably held at a temperature of 1000 to 1200 °C for 5 to 180 seconds. The annealing atmosphere is not particularly limited. Considering the manufacturing cost, the number of intermediate annealings is preferably within 3 times.

[0234] In addition, before performing rolling reduction in the cold rolling process, pickling of the surface of the hot rolled steel sheet can also be carried out under known conditions.

[0235] The cold rolling conditions are not limited. For example, the final rolling reduction rate can be set within the range of 80% to 95%. When the final rolling reduction rate is less than 80%, the possibility of not obtaining a Goss nucleus with a high degree of aggregation of the {110}<001> orientation in the rolling direction increases, which is not preferable.

[0236] On the other hand, when the final rolling reduction rate exceeds 95%, in the subsequent final annealing process, the possibility of unstable secondary recrystallization increases, so it is not preferable. By setting the final rolling reduction rate within the above range, a Goss nucleus with a high degree of aggregation of the {110}<001> orientation in the rolling direction can be obtained, and the destabilization of secondary recrystallization can be suppressed.

[0237] The final rolling reduction rate refers to the cumulative rolling reduction rate in cold rolling. In the case of performing intermediate annealing, it refers to the cumulative rolling reduction rate in cold rolling after the final intermediate annealing.

[0238] Here, the thickness of the cold rolled steel sheet after cold rolling is usually different from the thickness of the finally manufactured grain-oriented electrical steel sheet (the product thickness including the thickness of the tension-imparting insulating coating film). The product thickness of the grain-oriented electrical steel sheet is as mentioned before.

[0239] (Decarburizing annealing process: S107)

[0240] The decarburizing annealing process (step S107) is a process of performing decarburizing annealing on the cold rolled steel sheet to obtain a decarburized annealed steel sheet. In the present embodiment, it is an important process for appropriately controlling both the texture and the inhibitor to reduce the average misorientation angle β.

[0241] In the decarburizing annealing process, the cold rolled steel sheet is recrystallized once, and C (carbon) that has an adverse effect on the magnetic properties is removed from the steel sheet. In addition, in the decarburizing annealing process, stable secondary recrystallization in the subsequent final annealing process is promoted, so the Goss nucleus increases, and the SiO2 thick film formed by annealing becomes thicker and denser. In the manufacturing method of the grain-oriented electrical steel sheet of the present embodiment, annealing treatment is performed under specified heat treatment conditions in this decarburizing annealing process, whereby the secondary recrystallization structure can be finely controlled in the next final annealing process.

[0242] The decarburizing annealing process of the present embodiment includes two processes: a heating process (step S131) and a soaking process (step S133) in order to obtain a desired secondary recrystallization structure.

[0243] The heating process (step S131) is a process of heating the cold-rolled steel sheet obtained in the cold rolling process from room temperature to a temperature (maximum heating temperature) T1 (°C) within the range of 850°C to 950°C at a specified heating rate. In addition, the soaking process (step S131) is a process of annealing by cooling the cold-rolled steel sheet heated at a specified heating rate to a specified temperature and holding it for a specified time in a specified temperature range.

[0244] <Heating process>

[0245] The heating process of the present embodiment is an important process for finely controlling the aggregate structure of secondary recrystallized grains.

[0246] For thin materials, since the plate thickness is reduced, the reduction ratio (cold rolling ratio) in cold rolling increases. However, if the cold rolling ratio increases, the Goss orientation decreases and the secondary recrystallization becomes unstable. In contrast, in the heating process of the decarburizing annealing process of the present embodiment, the average heating rate in the temperature range of 550 to 800°C is set to 400°C / second or more, thereby increasing the Goss orientation. In addition, the temperature range of 550 to 800°C affects the behavior of recrystallization, that is, transformation. In the heating process, recrystallization ends at the maximum temperature reached via the recovery of the structure. The recovery and recrystallization have the greatest influence on the final annealing process (secondary recrystallization annealing process) as a subsequent process. In the present embodiment, by setting the average heating rate in the temperature range of 550 to 800°C to 400°C / second or more, nuclei with a geometrically strict Goss orientation of {110}<001> can be increased. On the other hand, when the average heating rate in this temperature range is less than 400°C / second, nuclei with a geometrically strict Goss orientation of {110}<001> cannot be sufficiently increased.

[0247] The upper limit of the average heating rate in the temperature range of 550°C to 800°C does not need to be limited from the perspective of characteristics, but from the perspective of the load on the equipment and devices used, it is not desirable to make the average heating rate rise excessively. Therefore, the average heating rate in the temperature range of 550 to 800°C is set to 3000°C / second or less.

[0248] As described above, the temperature range for controlling the average heating rate is set to 550 to 800°C because this temperature range is an important temperature range for the enrichment and recovery of the Goss orientation. This temperature range is a range discovered by the present inventors through investigating the influence of the residence time at each temperature on the existence frequency and recovery of the Goss orientation.

[0249] That is, the inventors investigated the effects of the residence time at each temperature on the presence frequency and recovery of the Goss orientation, and found that due to the residence in the temperature range of 550 to 800 °C, the Goss orientation frequency in the primary recrystallized aggregate structure decreased. In other words, by increasing the heating rate in the temperature range of 550 to 800 °C, the presence frequency of the Goss orientation can be increased. If the presence frequency of the Goss orientation can be increased, then in the final annealing process, the coarsening probability of the Goss orientation can be increased, leading to an improvement in magnetic properties.

[0250] Furthermore, it was found that in the heating process of the present embodiment, by setting the average heating rate in the temperature range of 800 to 850 °C to 100 °C / second or more, the SiO2 thick film formed on the steel sheet surface can be thickened and densified.

[0251] Hereinafter, the relationship between the formation morphology of SiO2 and the stabilization of secondary recrystallization will be described.

[0252] In thin materials, the proportion of the surface area is large, so the decomposition rate of the inhibitor is fast and the secondary recrystallization is destabilized. The trigger for the decomposition of the inhibitor is the interaction between Mg2SiO4 and AlN as the primary coating film. To inhibit the decomposition of the inhibitor, it is effective to reduce the formation rate of the primary coating film, that is, to increase the formation temperature of the primary coating film. In addition, the formation rate of the primary coating film is affected by the amount of SiO2 present in the decarburized annealed steel sheet.

[0253] In addition, the inventors conducted more detailed research and obtained the following insights. The high-temperatureization of the formation temperature of the primary coating film can be achieved by thickening and densifying the SiO2 formed in the heating process of the decarburizing annealing process. The mechanism by which the formation temperature of the primary coating film can be high-temperatureized through the thickening and densification of SiO2 is not clear, but it is considered that the reason is that the thickened and densified SiO2 reduces the mobility of Mg ions in SiO2.

[0254] The morphology of SiO2 formed in the heating process is roughly divided into an "outer oxide film" formed on the surface of the steel sheet and an "inner oxide film" formed in the surface layer of the steel sheet. The "inner oxide film" is further divided into "spherical oxides" and "flake oxide films". The inventors of the present invention have particularly focused on the "outer oxide film" among them, and found that by forming a thick and dense outer oxide film in the heating process, the formation rate of the primary covering film (i.e., the generation temperature of the primary covering film) can be reduced in the subsequent final annealing process, and the stabilization of the inhibitor (the reduction of the decomposition rate) can be achieved. The mechanism by which the decomposition of the inhibitor is suppressed and stabilization can be achieved is not clear, but it is considered that the intrusion of Mg into the steel sheet is suppressed by the thick and dense outer oxide film of SiO2, and the generation of the primary covering film (glass covering film) may be delayed. It is considered that the reason is that the generation of Mg2SiO4 itself is delayed, and thus the reaction between Mg2SiO4 and AlN (i.e., the decomposition reaction of AlN) is also delayed. The high-temperature of the decomposition reaction of AlN is related to ensuring the grain growth rate of Goss orientation, and thus it is a preferred direction as magnetic properties.

[0255] In addition, in the heating process of the present embodiment, the cold-rolled steel sheet is heated to a temperature T1 (°C) in the range of 850 °C to 950 °C (the maximum heating temperature). The maximum heating temperature T1 is an effective factor for suppressing internal oxidation in the subsequent soaking process. In order to enable the cold-rolled steel sheet to undergo sufficient external oxidation in the heating process and cover the surface of the steel sheet with the outer oxide film, the maximum heating temperature T1 is set to 850 °C or higher. Thereby, the suppression of internal oxidation (the suppression of the generation of spherical oxides and flake oxide films) in the soaking process can be achieved. The maximum heating temperature T1 is preferably 870 °C or higher, more preferably 900 °C or higher. On the other hand, excessively increasing the maximum heating temperature T1 will cause an excessive burden on the equipment, so the maximum heating temperature T1 is set to 950 °C or lower.

[0256] In the heating process, by setting the average heating rate in the temperature range of 800 to the maximum heating temperature T1 (°C) to 100 °C / second or more, as described above, an external oxide film of SiO2 formed on the steel sheet surface can be formed thick and dense. On the other hand, when the average heating rate in the temperature range of 800 to the maximum heating temperature T1 (°C) is less than 100 °C / second, in addition to the insufficient thickness of the external oxide film of SiO2, the formation of oxide films other than SiO2 (such as Fe2SiO4, etc.) may also occur. Oxide films other than SiO2 may promote the decomposition of the inhibitor during the final annealing process. The reason is not clear yet, but it can be cited that the affinity of oxide films such as Fe2SiO4 with AlN may be higher than that of SiO2. Therefore, the average heating rate in the temperature range of 800 to the maximum heating temperature T1 (°C) is set to 100 °C / second or more, preferably 200 °C / second or more, and more preferably 400 °C / second or more. In order to further suppress the formation of oxide films other than SiO2 (especially Fe2SiO4) and further promote the formation of the external oxide film of SiO2, in the heating process, the control range of the average heating rate is preferably set to 550 to the maximum heating temperature T1 (°C). That is, preferably, the average heating rate in the temperature range of 550 to the maximum heating temperature T1 (°C) is set to 100 °C / second or more. From the viewpoint of suppressing the formation of Fe2SiO4, the preferred temperature range to be controlled is 600 to the maximum heating temperature T1 (°C), and more preferably 650 to the maximum heating temperature T1 (°C).

[0257] On the other hand, the upper limit of the average heating rate in the temperature range of 800 to the maximum heating temperature T1 (°C) does not need to be limited from the viewpoint of characteristics, but in order to obtain an average heating rate exceeding 1500 °C / second, special equipment is required, so the average heating rate is set to 1500 °C / second or less.

[0258] In addition, in the heating process of the present embodiment, the dew point of the atmosphere during heating in the temperature range from 800 °C to the maximum heating temperature T1 (°C) is set to 0 °C or less. The dew point in the heating process also affects the formation of oxide films other than SiO2. In order to promote the formation of SiO2 and suppress the formation of oxide films other than SiO2, it is effective to reduce the oxidation degree of the atmosphere in the heating process. Therefore, the dew point of the atmosphere in the temperature range of 800 to the maximum heating temperature T1 (°C) is set to 0 °C or less, preferably -5 °C or less, and more preferably -10 °C or less. In addition, setting the dew point of the atmosphere in the temperature range above room temperature and below 800 °C to 0 °C or less in the heating process does not damage the effect of the present invention.

[0259] <Homogenizing process>

[0260] After the heating process, a soaking process is carried out.

[0261] When carbon remains in the steel sheet, the iron loss characteristics deteriorate over time (known as magnetic aging). Therefore, in order to reduce the carbon content, the atmosphere during decarburization annealing is usually set to a relatively high oxygen potential. However, during the annealing process, when the oxygen potential of the atmosphere is high, the amount of SiO2 generated increases and the formation rate of the primary coating film increases.

[0262] Therefore, the soaking process needs to be carried out in an annealing atmosphere with a lower oxygen potential. Thereby, the formation rate of the primary coating film is reduced.

[0263] Specifically, the soaking process is preferably carried out in an atmosphere with a temperature of 780 to 860 °C and an oxygen potential (PH2O / PH2) of 0.20 to 0.60, and the cold-rolled steel sheet is held for 100 seconds to 300 seconds. In addition, in this embodiment, during the heating process, heating is carried out beyond the holding temperature of the soaking process. Therefore, when transferring to the soaking process, cooling is performed by air cooling, natural cooling, etc. until the specified soaking holding temperature is reached, but this cooling does not impair the effects shown in this embodiment.

[0264] If the holding temperature during the soaking process is lower than 780 °C, decarburization defects occur due to the restriction of the diffusion control step. If decarburization defects occur, carbon remains in the steel sheet, which becomes a cause of iron loss deterioration. Or, due to the occurrence of phase transformation, secondary recrystallization itself does not occur.

[0265] On the other hand, if the holding temperature exceeds 860 °C, decarburization defects still occur due to the restriction of the interface velocity control step. This is because a covering oxide film harmful to decarburization is formed.

[0266] In addition, if the oxygen potential during the soaking process is lower than 0.20, decarburization defects occur. Decarburization is a chemical reaction between carbon in the steel sheet and oxygen in the annealing atmosphere. A low oxygen potential is synonymous with a low oxygen partial pressure, meaning a situation where the decarburization reaction is difficult to occur.

[0267] On the other hand, if the oxygen potential during the soaking process exceeds 0.60, decarburization defects still occur. This is because a covering oxide film that hinders decarburization is formed.

[0268] In addition, without controlling the oxygen potential, as a mixed gas of nitrogen and hydrogen or nitrogen, the dew point temperature of the atmosphere can also be set to 30 °C to 80 °C.

[0269] (Nitriding treatment process)

[0270] In the manufacturing method of the grain-oriented electrical steel sheet of this embodiment, nitriding treatment can also be carried out between the decarburization annealing process and the final annealing process described later.

[0271] In the nitriding process, for example, the cold-rolled steel sheet after the decarburizing annealing process is maintained at about 700 to 850 °C in a nitriding atmosphere (an atmosphere containing gases having nitriding ability such as hydrogen, nitrogen, and ammonia). Here, it is preferable to perform nitriding treatment on the steel sheet such that the N content of the cold-rolled steel sheet is 40 to 1000 ppm based on mass. When the N content of the cold-rolled steel sheet after nitriding treatment is less than 40 ppm, AlN in the cold-rolled steel sheet cannot be sufficiently precipitated, and thus AlN may not function as an inhibitor. Therefore, when AlN is used as an inhibitor, the N content of the cold-rolled steel sheet is preferably set to 40 ppm or more.

[0272] On the other hand, when the N content of the cold-rolled steel sheet exceeds 1000 ppm, AlN excessively exists in the steel sheet even after secondary recrystallization ends in the final annealing. Such AlN causes deterioration of iron loss. Therefore, the N content of the steel sheet is preferably set to 1000 ppm or less.

[0273] (Final annealing process (secondary recrystallization annealing process): S109)

[0274] In the final annealing process (step S109), an annealing parting agent is applied to the decarburized annealing steel sheet (after the decarburizing annealing process or after the nitriding process), and then final annealing is performed to obtain a final annealed steel sheet.

[0275] The final annealing conditions are not limited. For example, as long as it is carried out under the conditions of heating to 1150 to 1250 °C and annealing (holding) for 10 to 60 hours in an atmosphere gas containing hydrogen and nitrogen.

[0276] Generally speaking, the final annealing is carried out for a long time in a state where the steel sheet is wound into a coil shape. Therefore, before the final annealing, an annealing parting agent is applied to the cold-rolled steel sheet and dried for the purpose of preventing welding of the inside and outside of the coil winding. As the applied annealing parting agent, an annealing parting agent mainly composed of MgO is used. By using an annealing parting agent mainly composed of MgO, a glass covering film can be formed on the surface of the base steel sheet. When it is not mainly composed of MgO, a primary covering film (glass covering film) will not be formed. The reason for this is that the primary covering film is a Mg2SiO4 or MgAl2O4 compound, and thus lacks Mg necessary for the formation reaction.

[0277] In the manufacturing method of the grain-oriented electrical steel sheet of the present embodiment, the annealing parting agent applied to the decarburized annealing steel sheet preferably contains one or more selected from Ti, Sb, Sr, and Cl in a total amount of 0.10 to 10.00% based on the weight of MgO.

[0278] By containing one or more selected from Ti, Sb, Sr, and Cl in an annealing parting agent mainly composed of MgO, the reactivity between the primary covering film and AlN can be suppressed, thereby improving magnetic properties. The mechanism is not yet clear, but it is considered that these elements segregate at the interface between the primary covering film and the base steel sheet, thereby suppressing the reaction between the primary covering film and AlN. The total content of Ti, Sb, Sr, and Cl is preferably 0.10 to 10.00% by weight. When the total content of Ti, Sb, Sr, and Cl is less than 0.10% by weight relative to MgO, the improvement effect of magnetic properties may sometimes not be obtained sufficiently. On the other hand, when the total content of Ti, Sb, Sr, and Cl exceeds 10.00%, a sufficient amount of the primary covering film cannot be formed, and the covering film tension effective for improving magnetic properties cannot be ensured, so that the iron loss may be disadvantageous.

[0279] In addition, the existence forms (i.e., addition means) of Ti, Sb, Sr, and Cl in the annealing parting agent can exist either in the form of compounds or in the form of simple substances. For example, when the annealing parting agent contains Ti, it can be contained in the form of Ti simple substance or in the form of Ti oxide (such as TiO2).

[0280] (Insulating covering film forming step: S111)

[0281] In the insulating covering film forming step (step S111), an insulating covering film (tension-imparting insulating covering film) is formed on the surface (one side or both sides) of the finally annealed steel sheet. Regarding the forming conditions of the insulating covering film, there are no particular limitations. A known insulating covering film treatment liquid is used, and the treatment liquid is coated and dried by a known method. By forming an insulating covering film on the steel sheet surface, the magnetic properties of the grain-oriented electrical steel sheet can be further improved.

[0282] The surface of the steel sheet on which the insulating covering film is formed may be a surface that has been subjected to any pretreatment such as degreasing treatment using an alkali or the like, pickling treatment using hydrochloric acid, sulfuric acid, phosphoric acid, etc. before coating the treatment liquid, or a surface that has not been subjected to these pretreatments and remains in the state after final annealing unchanged.

[0283] The insulating coating film formed on the surface of the steel sheet is not particularly limited as long as it is an insulating coating film used as the insulating coating film of the grain-oriented electrical steel sheet, and a known insulating coating film can be used. As such an insulating coating film, for example, a coating film mainly composed of phosphate and colloidal silica can be cited. In addition, a composite insulating coating film mainly composed of inorganic substances and further containing organic substances can be cited. Here, the composite insulating coating film refers to an insulating coating film in which, for example, at least one of inorganic substances such as metal chromate, metal phosphate, colloidal silica, Zr compound, and Ti compound is used as the main component and fine organic resin particles are dispersed. In particular, from the viewpoint of reducing the environmental load during manufacturing, which has been increasing in recent years, an insulating coating film using a metal phosphate, a coupling agent of Zr or Ti, or their carbonate or ammonium salt as a starting material may be used.

[0284] (Magnetic domain refinement process)

[0285] In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, a magnetic domain refinement process may be provided after the insulating coating film forming process.

[0286] In the magnetic domain refinement process, by irradiating energy rays such as laser beams and electron beams on the surface of the insulating coating film at a predetermined interval in the rolling direction, a plurality of linear strains (thermal strains generated by rapid heating based on energy ray irradiation and subsequent rapid cooling) are introduced. The interval for forming a plurality of linear strains (that is, the interval between adjacent strains) is preferably set to 3.0 to 9.0 mm in the rolling direction. As the energy rays, laser beams and electron beams can be cited. The laser beam can be a continuous wave laser or a pulsed laser. Examples of the type of laser beam can include fiber laser, YAG laser, or CO2 laser. The electron beam can be a continuous beam or an intermittent beam.

[0287] Examples

[0288] As shown in Table 1, slabs with different chemical compositions for each steel number (No.a to l) were prepared. Then, grain-oriented electrical steel sheets (test numbers 1 to 19) were manufactured using each slab.

[0289] Specifically, the slab was heated to a temperature of 1100 to 1380 °C and then hot-rolled to produce a hot-rolled steel sheet with a thickness of 2.3 mm.

[0290] Next, hot-rolled sheet annealing was performed on the obtained hot-rolled steel sheet. Specifically, the hot-rolled steel sheet was annealed under the conditions of an annealing temperature of 1100 °C and a holding time of 20 seconds.

[0291] Next, the surface scale of the hot-rolled steel sheet (hot-rolled annealed steel sheet) after hot rolling and annealing is removed by pickling or the like, and then cold rolling including a plurality of passes without intermediate annealing is performed to produce a cold-rolled steel sheet having a thickness of 0.16 to 0.23 mm.

[0292] For the obtained cold-rolled steel sheet, decarburizing annealing is performed under the conditions shown in Table 3. The holding time in the soaking process is set to 120 seconds during the soaking process.

[0293] For Test Nos. 1, 2, 9, 10, 14, and 15, nitriding treatment is further performed to increase the nitrogen content to 200 ppm.

[0294] Next, a final annealing process is performed on the decarburized annealed steel sheet. Specifically, on the surface of the cold-rolled steel sheet, an annealing release agent mainly composed of MgO and containing the elements described in Table 3 is coated on the steel sheet surface using an aqueous slurry coating. In addition, the contained components of the annealing release agent described in Table 3 represent the weight fractions of elemental substances.

[0295] Next, the decarburized annealed steel sheet coated with the annealing release agent is held at 1200 °C for 20 hours to produce a steel sheet (final annealed steel sheet) having a primary coating film (glass coating film) on the base metal steel sheet.

[0296] Next, an insulating coating film is formed on this steel sheet. Specifically, a liquid for forming an insulating coating film mainly composed of colloidal silica and phosphate is coated on the surface of the steel sheet (more specifically, on the surface of the glass coating film as the primary coating film) and heat treatment (baking) is performed. Thereby, a grain-oriented electrical steel sheet having a base metal steel sheet, a glass coating film formed on the base metal steel sheet, and an insulating coating film formed on the glass coating film is obtained. The chemical composition of the base metal steel sheet of the obtained grain-oriented electrical steel sheet is shown in Table 2. In addition, the notation "-" in the chemical composition of Table 2 means that the content of the corresponding element is 0% in the significant figures (up to the least significant digit) specified in the embodiment.

[0297]

[0298]

[0299]

[0300] Table 4

[0301]

[0302] For the obtained grain-oriented electrical steel sheet, the magnetic properties (iron loss and magnetic flux density) were evaluated according to the following procedure. The results are shown in Table 4.

[0303] [Iron loss]

[0304] The obtained steel plate samples were cut out in dimensions of 60 mm in the direction parallel to the plate width and 300 mm in the direction parallel to the rolling direction. These samples were held at 800 ± 50 °C for 2 hours to perform stress relief annealing. Then, magnetic domain refinement was carried out by laser irradiation.

[0305] The samples after laser irradiation were subjected to magnetic evaluation using a single sheet tester (SST) apparatus, and the iron loss (W 17 / 50 ) was measured. In addition, a magnetic field of 800 A / m was applied to the samples, and the magnetic flux density B8 (T) was also measured.

[0306] The iron loss (W 17 / 50 ) was evaluated according to the following criteria. If the evaluation is A - C, it is judged that the iron loss characteristic is excellent (low iron loss). If the evaluation is D, it is judged that the iron loss characteristic is poor.

[0307] Less than 0.70: A evaluation

[0308] 0.70 or more and less than 0.75: B evaluation

[0309] 0.75 or more and less than 0.80: C evaluation

[0310] 0.80 or more: D evaluation

[0311] In addition, regarding the magnetic flux density (B8), 1.88 T or more was set as qualified, and less than 1.88 T was set as unqualified.

[0312] [Noise characteristics]

[0313] For the samples with a width of 60 mm × length of 300 mm on which the above magnetic domain control was performed, magnetostriction was measured using a magnetostriction measuring apparatus by the alternating current magnetostriction measurement method. The magnetostriction measuring apparatus is defined as a device equipped with a laser Doppler vibrometer, an exciting coil, an exciting power supply, a magnetic flux detection coil, an amplifier, and an oscilloscope.

[0314] Specifically, an alternating magnetic field was applied to the samples such that the maximum magnetic flux density in the rolling direction was 1.7 T. The change in the length of the samples caused by the expansion and contraction of the magnetic domains was measured using a laser Doppler vibrometer to obtain a magnetostriction signal. Fourier analysis was performed on the obtained magnetostriction signal to obtain the amplitude Cn of each frequency component fn (n is a natural number of 1 or more) of the magnetostriction signal. Using the A correction coefficient αn of each frequency component fn, the magnetostriction velocity level LVA (dB) shown in the following formula was obtained.

[0315]

[0316] Here, ρc is the characteristic acoustic impedance, and it is specified that ρc = 400. Pe0 is the minimum audible sound pressure, and Pe0 = 2×10 -5 (Pa). The A correction coefficient αn uses the values described in Table 2 of JIS C 1509-1 (2005).

[0317] Based on the obtained magnetostrictive velocity level (LVA), the noise characteristics were evaluated according to the following criteria.

[0318] If the magnetostrictive velocity level is 60.0 dBA or less, it is judged as "excellent noise characteristics" (C evaluation). If it is 57.5 dBA or less, it is judged as even better (B evaluation), and if it is 55.0 dBA or less, it is judged as particularly excellent (A evaluation). When the magnetostrictive velocity level exceeds 60.0 dBA, it is determined as "insufficient noise characteristics" (D evaluation).

[0319] Samples with a magnetic flux density (B8) of 1.88 T or more and iron loss and noise characteristics of C evaluation or more were set as qualified.

[0320] As can be seen from Tables 1 to 4, in the steel sheets where the offset angles α, β, and γ satisfy the above formula (1), good magnetic characteristics and noise characteristics can be achieved simultaneously.

[0321] Symbol description:

[0322] 10 Directional electromagnetic steel sheet, 11 Base material steel sheet, 13 Primary covering film (glass covering film), 15 Secondary covering film (tension - imparting insulating covering film)

[0323] Industrial applicability

[0324] According to the above - mentioned method of the present disclosure, it is possible to provide a directional electromagnetic steel sheet and its manufacturing method that have good magnetic characteristics and noise characteristics without reducing productivity, and thus the industrial applicability is high.

Claims

1. A directional electromagnetic steel sheet, characterized in that, Comprising: A base metal steel plate, the chemical composition of which contains, by mass%, C：0～0.010％、 Si: 3.00 - 4.00%, Sol.Al: 0 - 0.010%, Mn: 0.01 - 0.50%, N: 0.010% or less, S + Se: 0.0100% or less, P：0.005～0.100％、 Sn: 0 - 0.50%, Cu: 0 - 0.50%, Cr：0～0.50％、 Sb: 0 - 0.20%, Mo: 0 - 0.10%, Ni: 0 - 0.20%, Nb: 0 - 0.0200%, B：0～0.0200％、 Ti: 0 - 0.0200%, Bi: 0 - 0.0200%, The balance including Fe and impurities; A glass covering film provided on the surface of the base metal steel plate; And A tension - imparting insulating covering film provided on the surface of the glass covering film; The base metal steel plate has a texture oriented in the Goss orientation, In the base metal steel plate, When the average dispersion angle deviated from the ideal Goss orientation with the rolling - plane normal direction ND as the rotation axis is defined as α (°), The average dispersion angle deviated from the ideal Goss orientation with the rolling - right - angle direction TD as the rotation axis is defined as β (°), The average dispersion angle deviated from the ideal Goss orientation with the rolling direction RD as the rotation axis is defined as γ (°), The α, the β, and the γ satisfy the following formula (1), 0.0 ≤ |β| < 2.5 < |α| < 4.0 ≤ |γ| ≤ 10.0 (1).

2. The directionality electromagnetic steel sheet according to claim 1, characterized in that, The β satisfies the following formula (2), 0.0≤|β|≤2.0 (2)。 3. The directional electromagnetic steel sheet according to claim 1 or 2, characterized in that, The thickness of the base metal steel plate is 0.16 mm or more and less than 0.20 mm.

4. A method for manufacturing a directional electromagnetic steel sheet, characterized in that, Including the following steps: A heating step of heating a steel slab, the steel slab containing, by mass%, C：0.020～0.150％、 Si: 3.00 - 4.00%, Sol.Al: 0.010 - 0.050%, Mn: 0.01 - 0.50%, N：0.001～0.020％、 S + Se: 0.0010 - 0.0400%, P：0.005～0.100％、 Sn: 0 - 0.50%, Cu: 0 - 0.50%, Cr：0～0.50％、 Sb: 0 - 0.20%, Mo: 0 - 0.10%, Ni: 0 - 0.20%, Nb: 0 - 0.0200%, B：0～0.0200％、 Ti: 0 - 0.0200%, Bi: 0 - 0.0200%, The balance including Fe and impurities; A hot - rolling step of hot - rolling the steel slab after the heating step to obtain a hot - rolled steel plate; A hot - rolled plate annealing step of annealing the hot - rolled steel plate to obtain a hot - rolled annealed steel plate; A cold - rolling step of cold - rolling the hot - rolled annealed steel plate to obtain a cold - rolled steel plate; A decarburizing annealing step of subjecting the cold - rolled steel plate to decarburizing annealing to obtain a decarburized annealed steel plate; A final annealing step of coating an annealing separating agent on the decarburized annealed steel plate and then performing final annealing to obtain a final annealed steel plate; And An insulating covering film forming step of forming an insulating covering film on the surface of the final annealed steel plate; The decarburizing annealing step includes a heating - up step and a soaking step, In the heating - up step, The average heating - up speed in the temperature range of 550 - 800 °C is set to 400 °C / second - 3000 °C / second, The maximum heating temperature T1 (°C) is set to 850 °C - 950 °C, Set the average heating rate in the temperature range from 800 to the maximum heating temperature T1 (°C) to 100 °C / second to 1500 °C / second. Set the dew point of the atmosphere in the temperature range from 800 to the maximum heating temperature T1 (°C) to 0 °C or lower.

5. The method for manufacturing a directional electromagnetic steel sheet according to claim 4, wherein the annealing separating agent contains MgO as a main component, in the annealing separating agent, 0.10 to 10.00% by weight of MgO contains one or more selected from Ti, Sb, Sr, and Cl.

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