Grain-oriented electrical steel sheet

Abstract

Provided is a grain-oriented electrical steel sheet with which sufficient magnetic flux density can be obtained and excellent iron loss characteristics can be obtained before and after a magnetic domain subdivision treatment. A grain-oriented electrical steel sheet according to an embodiment of the present invention comprises, in mass%, 2.5-4.5% of Si, 0.01-1.00% of Mn, 0.010% or less of N, 0.010% or less of C, 0.010% or less of sol.Al, 0.010% or less of one or more elements selected from S and Se in total, and 0.010% or less of Ti, with the remainder being Fe and impurities, and is characterized in that: the surface of the grain-oriented electrical steel sheet is provided with a grain-oriented layer formed on the surface of the grain-oriented electrical steel sheet; the magnetic flux density B8 is 1.910 T or more, and Ls / La > = 0.140 (1), where La is the total length of the grain boundaries of the crystal grains, and Ls is the total length of the grain boundaries having the orientation difference of 1-5 degrees among the grain boundaries, are satisfied, where La is the total length of the grain boundaries of the crystal grains, and Ls is the total length of the grain boundaries of the crystal grains, where Ls is the total length of the grain boundaries of the crystal grains having the orientation difference of 1-5 degrees, are measured by X-ray diffraction at measurement points disposed at a spacing of 2 mm in a first direction and a second direction which are orthogonal to each other.

Description

Technical Field

[0001] The present disclosure relates to a grain-oriented electromagnetic steel sheet. Background Art

[0002] Grain-oriented electrical steel sheets are used as soft magnetic materials in the cores of electrical equipment such as transformers. Grains oriented in the {110}<001> orientation (Goss-oriented grains) are known as Goss-oriented steel sheets. The size of these grains is on the order of millimeters. Grain-oriented electrical steel sheets are manufactured by preferentially growing Goss-oriented grains through a phenomenon known as secondary recrystallization.

[0003] Grain-oriented electrical steel sheets are required to have excellent magnetic properties (high magnetic flux density and low iron loss). In grain-oriented electrical steel sheets, the higher the degree of aggregation of Goss-oriented grains, the better the magnetic properties can be obtained.

[0004] The degree of aggregation of Goss-oriented grains due to secondary recrystallization can be evaluated based on the deviation angle from the ideal Goss-oriented orientation. Figure 1 Schematic diagram of the deviation angle from the ideal Gaussian orientation. Figure 1 The offset angles include angle α, the rotation angle of the grain-oriented electrical steel sheet around the axis normal to the rolling surface; angle β, the rotation angle around an axis perpendicular to the rolling direction and the axis normal to the rolling surface; and angle γ, the rotation angle around the rolling direction. Therefore, the relationship between angles α, β, and γ and the magnetic properties (magnetic flux density and iron loss) of grain-oriented electrical steel sheet has been studied.

[0005] In the grain-oriented electrical steel sheet proposed in Japanese Patent Application Laid-Open No. 2018-48377 (Patent Document 1), the area ratio of the region where the root mean square values of the α and β angles are 5.0° or less and the β angle is 0.50° or less is set to 20% or less. Patent Document 1 states that this can suppress degradation of iron loss.

[0006] In the grain-oriented electrical steel sheet proposed in Japanese Patent Application Laid-Open No. 2001-192785 (Patent Document 2), the average α angle is set to 6° or less, and the standard deviation σ(β) of the distribution of the β angle in the direction perpendicular to rolling (the width direction) is set to 2° or less. Patent Document 2 states that uniformizing the β angle within the steel sheet can suppress degradation of iron loss.

[0007] Furthermore, it is known that when the angles α and β are small, the influence of the angle γ on the magnetic properties is small.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2018-48377

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2001-192785 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] As described above, the grain-oriented electrical steel sheets proposed in Patent Documents 1 and 2 attempt to improve iron loss by adjusting the deviation angle from the ideal Gaussian orientation. However, in grain-oriented electrical steel sheets, methods for reducing iron loss through magnetic domain refinement are known. In grain-oriented electrical steel sheets, there are sometimes demands for improving not only the iron loss characteristics before but also after magnetic domain refinement. Patent Documents 1 and 2 do not investigate improving the iron loss characteristics after magnetic domain refinement.

[0014] An object of the present disclosure is to provide a grain-oriented electrical steel sheet that can obtain a sufficient magnetic flux density and exhibit excellent iron loss characteristics not only before but also after magnetic domain refining treatment.

[0015] Means for solving problems

[0016] The present disclosure relates to a grain-oriented electromagnetic steel sheet, wherein the grain-oriented electromagnetic steel sheet comprises a base steel sheet,

[0017] The chemical composition of the base steel plate is calculated by mass %.

[0018] Si: 2.5-4.5%,

[0019] Mn: 0.01~1.00%,

[0020] N: 0~0.010%,

[0021] C: 0~0.010%,

[0022] sol.Al: 0~0.010%,

[0023] One or more selected from S and Se: 0 to 0.010% in total,

[0024] Ti: more than 0% and less than 0.010%,

[0025] Ni: 0-1.00%,

[0026] Cr: 0-1.00%,

[0027] Cu: 0-1.00%,

[0028] P: 0~0.50%,

[0029] Mo: 0~0.10%,

[0030] Sn: 0-0.50%,

[0031] Sb: 0-0.50%,

[0032] Bi: 0 to 0.0500%, and

[0033] The rest is composed of Fe and impurities.

[0034] On the surface of the grain-oriented electromagnetic steel sheet, the crystal orientation is measured by X-ray diffraction at measurement points arranged at intervals of 2 mm in a first direction and a second direction perpendicular to the first direction, thereby determining the orientation difference of grain boundaries of the grains. The total length of the grain boundaries of the grains is defined as La, and the total length of the grain boundaries having an orientation difference of 1° to 5° is defined as Ls. When formula (1) is satisfied,

[0035] The magnetic flux density B8 is above 1.910T.

[0036] Ls / La≥0.140 (1).

[0037] Effects of the Invention

[0038] In the grain-oriented electrical steel sheet of the present disclosure, sufficient magnetic flux density can be obtained, and excellent iron loss characteristics can be obtained not only before the magnetic domain refining treatment but also after the magnetic domain refining treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic diagram of the deviation angle from the ideal Gaussian orientation.

[0040] Figure 2 This is a graph showing the magnetic flux density B8 (T) of grain-oriented electrical steel sheets manufactured by performing the cold rolling process of Patterns 1 to 4.

[0041] Figure 3 is the iron loss W before the magnetic domain refinement process in modes 1 to 4. 17 / 50 (W / kg) diagram.

[0042] Figure 4 is the iron loss W after the magnetic domain refinement process in modes 1 to 4 17 / 50 (W / kg) diagram.

[0043] Figure 5 It is a graph showing the angle α (°) and the angle β (°) of Modes 1 to 4.

[0044] Figure 6 This is a graph showing the average grain size of Patterns 1 to 4.

[0045] Figure 7 This is a diagram showing an example of analysis results of the misorientation angle in a grain-oriented electrical steel sheet.

[0046] Figure 8 is the ratio of small angle grain boundaries R in modes 1 to 4 SGB Picture.

[0047] Figure 9 This is a perspective view of a grain-oriented electrical steel sheet according to this embodiment.

[0048] Figure 10 It is a schematic diagram of a tandem rolling mill.

[0049] Figure 11 This is a schematic diagram of a multi-stage rolling mill used in the reversing rolling process. DETAILED DESCRIPTION

[0050] The present inventors have studied grain-oriented electrical steel sheets that can achieve sufficient magnetic flux density and excellent iron loss characteristics not only before but also after magnetic domain refining treatment.

[0051] The present inventors first manufactured grain-oriented electromagnetic steel sheets using different manufacturing methods, and then compared the magnetic flux density B8(T), the iron loss W before magnetic domain refinement, and the magnetic flux density B8(T) of each grain-oriented electromagnetic steel sheet. 17 / 50 (W / kg) and the iron loss W after magnetic domain refinement 17 / 50 Specifically, the following experiments were conducted.

[0052] A variety of steel slabs were prepared, whose chemical compositions, in mass %, included Si: 3.3%, Mn: 0.08%, N: 0.009%, C: 0.074%, sol.Al: 0.026%, S: 0.023% and Ti: 0.002%, with the remainder being Fe and impurities.

[0053] The steel slab was subjected to a hot rolling process. Specifically, the steel slab was heated in a heating furnace to 1340° C. The heated steel slab was hot rolled to produce a hot-rolled steel sheet with a thickness of 2.3 mm.

[0054] The hot-rolled steel sheet was subjected to a hot-rolled steel sheet annealing process at a hot-rolled steel sheet annealing temperature of 800 to 1200° C. for a holding time of 10 to 300 seconds. After the hot-rolled steel sheet annealing process, a cold-rolled steel sheet with a thickness of 0.22 mm was produced.

[0055] Cold rolling was carried out in the following four modes.

[0056] (Mode 1) Tandem rolling + reversing rolling with roll diameter difference

[0057] The hot-rolled steel sheet, after the hot-rolled sheet annealing process, was rolled using a tandem mill with work rolls having an average diameter of 450 mm to produce a 0.8 mm thick steel sheet. The steel sheet was then reversely rolled using a multi-stage mill with work rolls having an average diameter of 100 mm to produce a 0.22 mm thick cold-rolled steel sheet. The roll diameter difference between the upper and lower work rolls of the multi-stage mill was set to 2.0 mm. This means that a roll diameter difference was established between the upper and lower work rolls during reverse rolling.

[0058] (Mode 2) Tandem rolling + reversible rolling without roll diameter difference

[0059] The hot-rolled steel sheet, after the hot-rolled sheet annealing process, was rolled using a tandem mill with work rolls having an average diameter of 450 mm to produce a 0.8 mm thick steel sheet. The steel sheet was then reversely rolled using a multi-stage mill with work rolls having an average diameter of 100 mm to produce a 0.22 mm thick cold-rolled steel sheet. The diameter difference between the upper and lower work rolls of the multi-stage mill was set to 0.5 mm. In other words, there was essentially no diameter difference between the upper and lower work rolls during reverse rolling.

[0060] (Mode 3) Reversible rolling with only roll diameter difference

[0061] After the hot-rolled steel sheet annealing process, reverse rolling is performed on a multi-stage rolling mill with work rolls having an average diameter of 100 mm, resulting in a cold-rolled steel sheet with a thickness of 0.22 mm. In other words, unlike Modes 1 and 2, tandem rolling is not performed before reverse rolling in Mode 3. Furthermore, the roll diameter difference between the upper and lower work rolls of the multi-stage rolling mill is set to 2.0 mm; a roll diameter difference is provided between the upper and lower work rolls.

[0062] (Mode 4) Reversing rolling only without roll diameter difference

[0063] After the hot-rolled steel sheet annealing process, reverse rolling is performed on a multi-stage rolling mill with work rolls having an average diameter of 100 mm, resulting in a cold-rolled steel sheet with a thickness of 0.22 mm. In other words, in Mode 4, as in Mode 3, tandem rolling is not performed before reverse rolling. Furthermore, the roll diameter difference between the upper and lower work rolls of the multi-stage rolling mill is set to 0.5 mm, with virtually no roll diameter difference being applied between the upper and lower work rolls.

[0064] After the cold rolling process of Modes 1 to 4, the cold-rolled steel sheets were subjected to a decarburization annealing process. Specifically, after heating to 870°C in the temperature range of 400°C to 800°C at a rate of 600°C / s, the steel sheets were held at a decarburization annealing temperature of 830°C to 950°C for 80 to 150 seconds. The cold-rolled steel sheets were then cooled to room temperature to produce decarburization annealed steel sheets.

[0065] An annealing separator mainly composed of MgO is applied to the surface of the decarburized annealed steel sheet. Then, the decarburized annealed steel sheet coated with the annealing separator is subjected to final annealing to produce a final annealed steel sheet. The final annealing temperature in the final annealing is set to 1100°C to 1200°C, and the holding time at the final annealing temperature is set to 5 to 30 hours. A secondary coating forming process is performed on the steel sheet after the final annealing process. Specifically, a secondary coating forming agent mainly composed of colloidal silica and phosphate is applied to the surface of the final annealed steel sheet of each test number. Then, the final annealed steel sheet coated with the secondary coating forming agent is baked under the same conditions to form an insulating film on the primary coating. Through the above manufacturing process, a grain-oriented electrical steel sheet is produced.

[0066] The chemical composition of the produced grain-oriented electrical steel sheet includes Si: 3.3%, Mn: 0.08%, N: <0.002%, C: 0.002%, sol. Al: <0.001%, S: <0.001%, Ti: 0.002%, and the remainder is Fe and impurities. Numerical values marked with "<" indicate that the analyzer's calibration curve covers only the value following the "<". Specifically, "<0.001%" indicates that the analyzer's calibration curve covers only 0.001%.

[0067] The produced grain-oriented electrical steel sheets were subjected to magnetic flux density measurement tests shown in Examples described below, iron loss evaluation tests of the grain-oriented electrical steel sheets before magnetic domain refining treatment, and iron loss evaluation tests of the grain-oriented electrical steel sheets after magnetic domain refining treatment.

[0068] Figure 2 It is a graph of the magnetic flux density B8 (T) in Modes 1 to 4. Figure 3 is the iron loss W before the magnetic domain refinement process in modes 1 to 4. 17 / 50 (W / kg) diagram. Figure 4 is the iron loss W after the magnetic domain refinement process in modes 1 to 4 17 / 50 (W / kg) diagram.

[0069] Reference Figure 2Regarding the magnetic flux density B8, the magnetic flux density B8 of Mode 1 and Mode 2 (tandem rolling + reversing rolling in the cold rolling process) is better than that of Mode 3 and Mode 4 (only reversing rolling in the cold rolling process). On the other hand, the magnetic flux density B8 of Mode 1 and Mode 2 is equivalent.

[0070] On the other hand, regarding iron loss, there is a clear difference between Mode 1 and Mode 2. Specifically, refer to Figure 3 , about the iron loss W before magnetic domain subdivision 17 / 50 , iron loss W of mode 1 and mode 2 (tandem rolling + reversible rolling in the cold rolling process) 17 / 50 Compared with the iron loss W of mode 3 and mode 4 (only reversible rolling is performed in the cold rolling process), 17 / 50 Furthermore, if we compare Mode 1 and Mode 2, the iron loss W of Mode 1 with the roll diameter difference is 17 / 50 Significantly lower iron loss W than in mode 2 where no roll diameter difference is set 17 / 50 .

[0071] The iron loss after the magnetic domain refinement treatment also shows the same tendency as the iron loss before the magnetic domain refinement treatment. Figure 4 , iron loss W of mode 1 and mode 2 (tandem rolling + reversible rolling in the cold rolling process) 17 / 50 Compared with the iron loss W of mode 3 and mode 4 (only reversible rolling is performed in the cold rolling process), 17 / 50 Furthermore, if we compare Mode 1 and Mode 2, the iron loss W of Mode 1 with the roll diameter difference is 17 / 50 Significantly lower iron loss W than in mode 2 where no roll diameter difference is set 17 / 50 .

[0072] Based on the above results, in the cold rolling process, tandem rolling and reversible rolling are implemented, and in the mode 1 in which the roll diameter difference is set in the reversible rolling, an excellent magnetic flux density B8 can be obtained, and the iron loss W 17 / 50 Therefore, by analyzing the structure of grain-oriented electrical steel sheets produced using Pattern 1, we attempted to identify a configuration of grain-oriented electrical steel sheets that could achieve sufficient magnetic flux density and exhibit excellent iron loss characteristics both before and after magnetic domain refining treatment.

[0073] First, the present inventors considered that the deviation angles α and β from the ideal Gossian orientation affect iron loss, as described in Patent Documents 1 and 2. Therefore, they determined the α and β angles for grain-oriented electrical steel sheets produced in Patterns 1 to 4 using the following method.

[0074] For grain-oriented electrical steel sheets with patterns 1 to 4, a rectangular area measuring 60 mm in the width direction and 250 mm in the rolling direction was used as the observation area. Within the observation area, X-ray diffraction using the Laue method was performed at 3906 measurement points distributed at 2 mm intervals in the rolling and width directions. The spot diameter during measurement was set to 1 mm.

[0075] For each pattern of grain-oriented electrical steel sheet, X-ray diffraction was performed on 10 observation areas. The α and β angles were determined at each measurement point within the observation area. The arithmetic mean of the α angles at the measurement points was used as the α angle (°) for that pattern. Similarly, the arithmetic mean of the β angles at the measurement points was used as the β angle (°) for that pattern.

[0076] Figure 5 This is a graph showing the angles α (°) and β (°) for modes 1 to 4. Figure 5 The α and β angles for Modes 1 and 2 are slightly lower than those for Modes 3 and 4, which correlates with the results of magnetic flux density B8. However, the α and β angles for Mode 1 are approximately the same as those for Mode 2. Therefore, the improvement in the iron loss characteristics of the grain-oriented electromagnetic steel sheet in Mode 1 is not related to the α and β angles.

[0077] Therefore, the present inventors further investigated the correlation between the structure of grain-oriented electrical steel sheets other than the α angle and the β angle and the iron loss.

[0078] The present inventors investigated the relationship between grain size and iron loss in grain-oriented electrical steel sheets of Modes 1 to 4. Specifically, using the crystal orientation data obtained by X-ray diffraction, a region consisting of grain boundaries with an orientation misorientation angle of 1° or greater and consisting of at least one measurement point was defined as a single grain. The equivalent circular diameter of a specific grain was calculated. Here, the equivalent circular diameter refers to the diameter of a circle with the same area as the grain. The arithmetic mean of the obtained equivalent circular diameters of the grains was defined as the average grain size (mm) for that mode.

[0079] Figure 6 This is a graph of the average grain size of Modes 1 to 4. Figure 6 The average grain sizes of modes 1 to 4 are roughly the same and are not related to the iron loss.

[0080] As described above, no correlation was observed between the angle α, the angle β, the average grain size, and the iron loss. Therefore, as a new perspective on the structure of grain-oriented electrical steel sheets, the present inventors focused on the misorientation angle of adjacent grains in the grains constituting the grain-oriented electrical steel sheets.

[0081] Specifically, the misorientation angle of crystal grains in the steel sheet is determined by the method described below. Figure 7This is a diagram showing an example of the analysis results of the misorientation angle at the grain boundary of a grain-oriented electrical steel sheet. Figure 7 The enclosed area surrounded by the grain boundary is the grain. The thick lines in the grain boundary are grain boundaries with an orientation misorientation angle of 1° to 5°. In the following description, grain boundaries with an orientation misorientation angle of 1° to 5° are referred to as "small-angle grain boundaries." The areas outside the thick lines in the grain boundary are grain boundaries with an orientation misorientation angle exceeding 5°.

[0082] The total length of the grain boundaries of the grains in the observation area is defined as La (mm). Furthermore, the total length of the grain boundaries with extremely small orientation angles (small angle grain boundaries) with an orientation angle of 1 to 5 degrees among the grain boundaries of the grains in the observation area is defined as Ls (mm). The small angle grain boundary ratio R is defined as follows SGB .

[0083] R SGB =Ls / La

[0084] Figure 8 is the ratio of small angle grain boundaries R in modes 1 to 4 SGB Refer to the diagram. Figure 8 , the ratio of small angle grain boundaries R in mode 1 SGB It is significantly larger than other modes 2 to 4. Figure 8 The results are related to the results of iron loss.

[0085] Based on the above research results, the present inventors believe that the greater the proportion of micro-angle grain boundaries in the grain boundaries, the lower the iron loss. The reason for this is not clear, but the present inventors believe it as follows.

[0086] The crystal orientation of grain-oriented electrical steel sheets is concentrated in a Gossian orientation. Therefore, the misorientation angle at the grain boundaries of each grain is generally less than 15°. In a steel sheet composed of grain boundaries with such small misorientation angles, if the proportion of small-angle grain boundaries with even smaller misorientation angles of 1 to 5° increases, the misorientation angles of adjacent grains are mostly small. Consequently, local variations in the magnetic flux density distribution within the steel sheet are suppressed, resulting in a uniform magnetic flux density distribution. This uniform magnetic flux density distribution is believed to contribute to excellent iron loss characteristics both before and after magnetic domain refinement.

[0087] In addition, it is also possible to obtain excellent iron loss characteristics before and after the magnetic domain refining treatment based on a mechanism different from this presumed mechanism. SGB The fact that excellent iron loss characteristics can be obtained is also demonstrated in the examples described later.

[0088] Based on the above findings, the present inventors have completed a grain-oriented electrical steel sheet according to the present embodiment having the following configuration.

[0089] A first configuration relates to a grain-oriented electromagnetic steel sheet comprising a base steel sheet.

[0090] The chemical composition of the base steel plate is calculated by mass %.

[0091] Si: 2.5-4.5%,

[0092] Mn: 0.01~1.00%,

[0093] N: 0~0.010%,

[0094] C: 0~0.010%,

[0095] sol.Al: 0~0.010%,

[0096] One or more selected from S and Se: 0 to 0.010% in total,

[0097] Ti: more than 0% and less than 0.010%,

[0098] Ni: 0-1.00%,

[0099] Cr: 0-1.00%,

[0100] Cu: 0-1.00%,

[0101] P: 0~0.50%,

[0102] Mo: 0~0.10%,

[0103] Sn: 0-0.50%,

[0104] Sb: 0-0.50%,

[0105] Bi: 0 to 0.0500%, and

[0106] The rest is composed of Fe and impurities.

[0107] On the surface of the grain-oriented electromagnetic steel sheet, the crystal orientation is measured by X-ray diffraction at measurement points arranged at intervals of 2 mm in a first direction and a second direction perpendicular to the first direction, thereby determining the orientation difference of grain boundaries of the grains. The total length of the grain boundaries of the grains is defined as La, and the total length of the grain boundaries having an orientation difference of 1° to 5° is defined as Ls. When formula (1) is satisfied,

[0108] The magnetic flux density B8 is above 1.910T.

[0109] Ls / La≥0.140 (1).

[0110] The grain-oriented electromagnetic steel sheet of the second structure is based on the grain-oriented electromagnetic steel sheet of the first structure.

[0111] The chemical composition of the base steel plate is calculated by mass %, and contains

[0112] Ni: 0.01~1.00%,

[0113] Cr: 0.01~1.00%,

[0114] Cu: 0.01-1.00%,

[0115] P: 0.01~0.50%,

[0116] Mo: 0.01~0.10%,

[0117] Sn: 0.01~0.50%,

[0118] Sb: 0.01 to 0.50%, and

[0119] Bi: one or more kinds of Bi in the range of 0.0001 to 0.0500%.

[0120] The grain-oriented electromagnetic steel sheet of the third configuration is further

[0121] A plurality of linear thermal strains or grooves extending linearly and arranged in a direction perpendicular to the extending direction are formed on the surface of the grain-oriented electrical steel sheet.

[0122] The grain-oriented electrical steel sheet of this embodiment will be described below. "%" of an element means mass % unless otherwise specified.

[0123] [About the composition of grain-oriented electrical steel sheets]

[0124] Figure 9 This is a perspective view of a grain-oriented electromagnetic steel sheet according to this embodiment. Direction L in the figure indicates the rolling direction of the grain-oriented electromagnetic steel sheet. Direction W indicates the direction perpendicular to the rolling direction of the grain-oriented electromagnetic steel sheet (the sheet width direction). Direction T indicates the direction normal to the rolled surface of the grain-oriented electromagnetic steel sheet (the sheet thickness direction).

[0125] Reference Figure 9 The grain-oriented electrical steel sheet 1 of this embodiment includes a base steel sheet 10, a lower coating 11, and a secondary coating 12. The lower coating 11 is formed on the base steel sheet 10. Figure 9In the embodiment of the present invention, the lower coating 11 is formed on the surface of the base steel plate 10 in direct contact with the surface. The lower coating 11 is either a primary coating composed mainly of forsterite or an intermediate layer composed mainly of oxides such as silica and alumina. When reducing iron loss is important, the lower coating 11 is set as the primary coating. When punching workability is important, the lower coating 11 is set as the intermediate layer. The lower coating 11 is a well-known coating.

[0126] The secondary cover film 12 is formed on the lower cover film 11. Figure 9 As shown, the lower coating 11 and the secondary coating 12 are formed on a pair of surfaces (ie, the front and back surfaces) of the base steel plate 10. The secondary coating 12 is a well-known insulating coating.

[0127] As is known, a grain-oriented electrical steel sheet includes a base steel sheet, a lower coating, and a secondary coating.

[0128] [Characteristics of Grain-Oriented Electrical Steel Sheet 1]

[0129] The grain-oriented electrical steel sheet 1 of the present embodiment satisfies characteristics 1 to 3.

[0130] (Feature 1)

[0131] The chemical composition of the base material steel plate 10 includes, in mass%, Si: 2.5-4.5%, Mn: 0.01-1.00%, N: 0-0.010%, C: 0-0.010%, sol.Al: 0-0.010%, one or more selected from S and Se: 0-0.010% in total, Ti: more than 0% and 0.010% or less, Ni: 0-1.00%, Cr: 0-1.00%, Cu: 0-1.00%, P: 0-0.50%, Mo: 0-0.10%, Sn: 0-0.50%, Sb: 0-0.50% and Bi: 0-0.0500%, with the remainder being Fe and impurities.

[0132] (Feature 2)

[0133] On the surface of the base steel plate 10, the crystal orientation is measured by X-ray diffraction at measurement points arranged at intervals of 2 mm in a first direction and a second direction perpendicular to the first direction, thereby determining the orientation difference of the grain boundaries of the crystal grains. When the total length of the grain boundaries of the crystal grains is defined as La, and the total length of the grain boundaries with an orientation difference of 1 to 5° is defined as Ls, formula (1) is satisfied.

[0134] Ls / La≥0.140 (1)

[0135] (Feature 3)

[0136] The magnetic flux density B8 is greater than or equal to 1.910T.

[0137] Features 1 to 3 are described below.

[0138] [(Feature 1) About chemical composition]

[0139] The chemical composition of the base steel sheet 10 of the grain-oriented electrical steel sheet 1 includes the following elements.

[0140] Si: 2.5-4.5%

[0141] Silicon (Si) increases the electrical resistance (resistivity) of the steel sheet and reduces the iron loss of the grain-oriented electrical steel sheet 1. If the Si content is less than 2.5%, the above effect cannot be fully achieved. On the other hand, if the Si content exceeds 4.5%, the steel sheet becomes brittle.

[0142] Therefore, the Si content is 2.5 to 4.5%.

[0143] The lower limit of the Si content is preferably 2.8%, more preferably 3.0%, and even more preferably 3.2%.

[0144] The upper limit of the Si content is preferably 4.2%, more preferably 4.0%, more preferably 3.7%, more preferably 3.6%, and even more preferably 3.5%.

[0145] Mn: 0.01~1.00%

[0146] Manganese (Mn) increases the resistivity of the steel sheet and reduces iron loss. Mn further improves the hot workability of the steel sheet and suppresses cracking during hot rolling. If the Mn content is less than 0.01%, these effects are not fully achieved. On the other hand, if the Mn content exceeds 1.00%, the magnetic flux density of the grain-oriented electrical steel sheet 1 decreases, and the iron loss also deteriorates.

[0147] Therefore, the Mn content is 0.01 to 1.00%.

[0148] The lower limit of the Mn content is preferably 0.02%, more preferably 0.03%, and even more preferably 0.05%.

[0149] The upper limit of the Mn content is preferably 0.70%, more preferably 0.50%, further preferably 0.30%, further preferably 0.10%.

[0150] N: 0~0.010%

[0151] Nitrogen (N) forms nitrides and deteriorates the iron loss of the grain-oriented electrical steel sheet 1. If the N content exceeds 0.010%, the iron loss of the grain-oriented electrical steel sheet 1 deteriorates significantly.

[0152] Therefore, the N content is 0.010% or less. Alternatively, the N content may be 0%. In other words, the N content is 0 to 0.010%.

[0153] The lower limit of the N content is preferably more than 0%, more preferably 0.001%, and even more preferably 0.002%.

[0154] The upper limit of the N content is preferably 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0155] C: 0~0.010%

[0156] Carbon (C) is an essential element in steel slabs to improve magnetic flux density. However, C is removed from the steel sheet during the manufacturing process of the grain-oriented electrical steel sheet 1. If more than 0.010% of C remains in the finished grain-oriented electrical steel sheet 1, magnetic aging occurs, degrading the iron loss of the grain-oriented electrical steel sheet 1.

[0157] Therefore, the C content is 0.010% or less. Alternatively, the C content may be 0%. In other words, the C content is 0 to 0.010%.

[0158] The lower limit of the C content is preferably more than 0%, more preferably 0.001%, and even more preferably 0.002%.

[0159] The upper limit of the C content is preferably 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0160] sol.Al: 0~0.010%

[0161] Acid-soluble aluminum (sol.Al) bonds with nitrogen during the manufacturing process of grain-oriented electrical steel sheet 1 to form AlN, acting as an inhibitor. However, if the sol.Al content exceeds 0.010%, Al-based inclusions remain in the steel sheet. In this case, the iron loss of grain-oriented electrical steel sheet 1 deteriorates.

[0162] Therefore, the sol.Al content is 0.010% or less. Alternatively, the sol.Al content may be 0%. In other words, the sol.Al content is 0 to 0.010%.

[0163] The lower limit of the sol.Al content is preferably more than 0%, more preferably 0.001%, and even more preferably 0.002%.

[0164] The upper limit of the sol.Al content is preferably 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0165] In addition, in this specification, sol.Al means acid-soluble Al.

[0166] One or more selected from S and Se: 0 to 0.010% in total

[0167] Sulfur (S) and selenium (Se) combine with Mn during the manufacturing process to form fine MnS or MnSe, which serve as inhibitors. Therefore, S and Se are essential elements in steel slabs. However, S and Se are removed from the steel sheet during the manufacturing process of the grain-oriented electrical steel sheet 1. If the combined content of one or more selected from S and Se in the grain-oriented electrical steel sheet 1 exceeds 0.010%, MnS or MnSe remains in the steel sheet. In this case, the iron loss of the grain-oriented electrical steel sheet 1 deteriorates.

[0168] Therefore, the total content of one or more selected from S and Se is 0.010% or less. Alternatively, the total content of one or more selected from S and Se may be 0%. In other words, the total content of one or more selected from S and Se is 0 to 0.010%.

[0169] The lower limit of the total content of one or more selected from S and Se is preferably more than 0%, more preferably 0.001%, and even more preferably 0.002%.

[0170] The upper limit of the total content of one or more selected from S and Se is preferably 0.008%, more preferably 0.006%, and even more preferably 0.004%.

[0171] Ti: more than 0% and less than 0.010%

[0172] Titanium (Ti) forms nitrides or carbides to deteriorate the iron loss of the grain-oriented electrical steel sheet 1. If the Ti content exceeds 0.010%, the iron loss of the grain-oriented electrical steel sheet 1 is significantly deteriorated.

[0173] Therefore, the Ti content exceeds 0% and is 0.010% or less.

[0174] The lower limit of the Ti content is preferably 0.001%, more preferably 0.002%.

[0175] The upper limit of the Ti content is preferably 0.009%, more preferably 0.008%, and even more preferably 0.007%.

[0176] The remainder of the chemical composition of the base steel sheet 10 of the grain-oriented electrical steel sheet 1 is composed of Fe and impurities. Impurities are substances that enter from raw materials such as ore and scrap, or from the manufacturing environment, during industrial production of the base steel sheet 10 constituting the grain-oriented electrical steel sheet 1. These substances are permissible within a range that does not adversely affect the grain-oriented electrical steel sheet 1 of this embodiment.

[0177] About Optional Elements

[0178] The chemical composition of the base steel sheet 10 of the grain-oriented electrical steel sheet 1 may further contain one or more selected from the first group and the second group in place of a portion of Fe.

[0179] [Group 1]

[0180] Selected from Ni: 0-1.00%,

[0181] Cr: 0-1.00%,

[0182] Cu: 0-1.00%,

[0183] P: 0-0.50%, and

[0184] Mo: one or more kinds of Mo in the range of 0 to 0.10%

[0185] [Group 2]

[0186] Selected from Sn: 0-0.50%,

[0187] Sb: 0-0.50%, and

[0188] Bi: one or more of 0 to 0.0500%

[0189] The following describes Group 1 and Group 2.

[0190] [Group 1: Ni, Cr, Cu, P and Mo]

[0191] Ni, Cr, Cu, P, and Mo are all optional elements. These elements change the microstructure formation behavior during the manufacturing process and improve the magnetic properties of the grain-oriented electrical steel sheet 1 .

[0192] Ni: 0-1.00%

[0193] Nickel (Ni) is an optional element and may not be contained. In other words, the Ni content may be 0%.

[0194] When Ni is present, that is, when the Ni content exceeds 0%, Ni changes the microstructure formation behavior until the final annealing step, promoting secondary recrystallization in a Goss orientation. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 are improved. Even a small amount of Ni can achieve these effects to some extent.

[0195] However, when the Ni content exceeds 1.00%, secondary recrystallization may become unstable.

[0196] Therefore, the Ni content is 0 to 1.00%, and when contained, it is 1.00% or less.

[0197] The lower limit of the Ni content is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0198] The upper limit of the Ni content is preferably 0.90%, more preferably 0.80%, and even more preferably 0.70%.

[0199] Cr: 0~1.00%

[0200] Chromium (Cr) is an optional element and may not be contained. In other words, the Cr content may be 0%.

[0201] When Cr is present, that is, when the Cr content exceeds 0%, Cr changes the microstructure formation behavior until the final annealing step, promoting secondary recrystallization in the Goss orientation. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 are improved. Even a small amount of Cr can achieve this effect to some extent.

[0202] However, if the Cr content exceeds 1.00%, Cr oxides are generated in the steel sheet, thereby deteriorating the iron loss of the grain-oriented electrical steel sheet 1 .

[0203] Therefore, the Cr content is 0 to 1.00%, and when contained, it is 1.00% or less.

[0204] The lower limit of the Cr content is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0205] The upper limit of the Cr content is preferably 0.90%, more preferably 0.80%, and even more preferably 0.70%.

[0206] Cu: 0-1.00%

[0207] Copper (Cu) is an optional element and may not be contained. In other words, the Cu content may be 0%.

[0208] When Cu is present, that is, when the Cu content exceeds 0%, Cu changes the microstructure formation behavior until the final annealing step, promoting secondary recrystallization in the Goss orientation. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 are improved. Even a small amount of Cu can achieve these effects to some extent.

[0209] However, if the Cu content exceeds 1.00%, the hot workability of the steel sheet decreases.

[0210] Therefore, the Cu content is 0 to 1.00%, and when contained, it is 1.00% or less.

[0211] The lower limit of the Cu content is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0212] The upper limit of the Cu content is preferably 0.40%, more preferably 0.30%, further preferably 0.20%, and further preferably 0.10%.

[0213] P: 0~0.50%

[0214] Phosphorus (P) is an optional element and may not be contained. In other words, the P content may be 0%.

[0215] When P is present, that is, when the P content exceeds 0%, P changes the microstructure formation behavior until the final annealing step, promoting secondary recrystallization in a Goss orientation. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 are improved. Even a small amount of P can achieve these effects to some extent.

[0216] However, if the P content exceeds 0.50%, the workability of the steel sheet decreases.

[0217] Therefore, the P content is 0 to 0.50%, and when contained, it is 0.50% or less.

[0218] The lower limit of the P content is preferably 0.01%, more preferably 0.02%, and even more preferably 0.05%.

[0219] The upper limit of the P content is preferably 0.40%, more preferably 0.30%, and even more preferably 0.20%.

[0220] Mo: 0~0.10%

[0221] Molybdenum (Mo) is an optional element and may not be contained. In other words, the Mo content may be 0%.

[0222] When Mo is present, that is, when the Mo content exceeds 0%, Mo changes the microstructure formation behavior until the final annealing step, promoting secondary recrystallization in a Goss orientation. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 are improved. Even a small amount of Mo can achieve these effects to some extent.

[0223] However, if the Mo content exceeds 0.10%, the workability of the steel sheet decreases.

[0224] Therefore, the Mo content is 0 to 0.10%, and when contained, it is 0.10% or less.

[0225] The lower limit of the Mo content is preferably 0.01%, more preferably 0.02%, and even more preferably 0.03%.

[0226] The upper limit of the Mo content is preferably 0.09%, more preferably 0.08%, and even more preferably 0.07%.

[0227] [Group 2: Sn, Sb, and Bi]

[0228] Sn, Sb, and Bi are all optional elements and act as inhibitors to stabilize secondary recrystallization.

[0229] Sn: 0~0.50%

[0230] Tin (Sn) is an optional element and may not be contained. In other words, the Sn content may be 0%.

[0231] When Sn is contained, it acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the grain-oriented electrical steel sheet 1. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 are improved. The above-mentioned effects can be achieved to some extent even with a small amount of Sn.

[0232] However, if the Sn content exceeds 0.50%, the magnetic properties of the grain-oriented electrical steel sheet 1 are deteriorated.

[0233] Therefore, the Sn content is 0 to 0.50%, and when contained, it is 0.50% or less.

[0234] The lower limit of the Sn content is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0235] The upper limit of the Sn content is preferably 0.45%, more preferably 0.40%, and even more preferably 0.35%.

[0236] Sb: 0~0.50%

[0237] Antimony (Sb) is an optional element and may not be contained. In other words, the Sb content may be 0%.

[0238] When contained, Sb acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the grain-oriented electrical steel sheet 1. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 are improved. The above-mentioned effects can be achieved to some extent even with a small amount of Sb.

[0239] However, if the Sb content exceeds 0.50%, the magnetic properties of the grain-oriented electrical steel sheet 1 are deteriorated.

[0240] Therefore, the Sb content is 0 to 0.50%, and when contained, it is 0.50% or less.

[0241] The lower limit of the Sb content is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0242] The upper limit of the Sb content is preferably 0.45%, more preferably 0.40%, and even more preferably 0.35%.

[0243] Bi: 0~0.0500%

[0244] Bismuth (Bi) is an optional element and may not be contained. In other words, the Bi content may be 0%.

[0245] When Bi is present, it acts as an inhibitor, stabilizing secondary recrystallization during the manufacturing process of the grain-oriented electrical steel sheet 1. As a result, the magnetic properties of the grain-oriented electrical steel sheet 1 are improved. Even a small amount of Bi can achieve these effects to some extent. However, if the Bi content exceeds 0.0500%, the magnetic properties of the grain-oriented electrical steel sheet 1 are actually reduced.

[0246] Therefore, the Bi content is 0 to 0.0500%, and when contained, it is 0.0500% or less.

[0247] The lower limit of the Bi content is preferably 0.0001%, more preferably 0.0005%, further preferably 0.0010%, further preferably 0.0050%.

[0248] The upper limit of the Bi content is preferably 0.0400%, more preferably 0.0300%, further preferably 0.0200%, and further preferably 0.0100%.

[0249] [Method for measuring the chemical composition of grain-oriented electrical steel sheet 1]

[0250] The chemical composition of the grain-oriented electrical steel sheet 1 according to the present embodiment can be measured by a well-known component analysis method.

[0251] First, when the lower film 11 and the secondary film 12 are formed on the grain-oriented electrical steel sheet 1, the lower film 11 and the secondary film 12 are removed from the base steel sheet 10 by the following method. Specifically, the grain-oriented electrical steel sheet 1 having the secondary film 12 is removed by immersing it in a high-temperature alkaline solution. The composition, temperature, and immersion time of the alkaline solution can be adjusted as appropriate. For example, the grain-oriented electrical steel sheet 1 having the secondary film 12 is immersed in an aqueous sodium hydroxide solution consisting of 30-50 mass% NaOH and 50-70 mass% H₂O at 80°C to 90°C for 5-10 minutes, followed by water washing and drying. This process removes the secondary film 12 from the grain-oriented electrical steel sheet 1.

[0252] Then, the grain-oriented electromagnetic steel sheet 1 from which the secondary coating 12 has been removed and the lower coating 11 remains is immersed in high-temperature hydrochloric acid to remove it. The concentration, temperature, and immersion time of the hydrochloric acid can be appropriately adjusted. For example, the grain-oriented electromagnetic steel sheet 1 from which the secondary coating 12 has been removed and the lower coating 11 remains is immersed in 30-40 mass % hydrochloric acid at 80-90°C for 1-5 minutes. The immersed grain-oriented electromagnetic steel sheet 1 is washed with water and dried. Through the above steps, the grain-oriented electromagnetic steel sheet 1 (base steel sheet 10) from which the secondary coating 12 and the lower coating 11 have been removed is obtained.

[0253] The chemical composition of the resulting grain-oriented electrical steel sheet 1 (base steel sheet 10) is measured using a well-known component analysis method in accordance with JIS G0321:2017. Specifically, chips are collected from the grain-oriented electrical steel sheet 1. The collected chips are dissolved in acid to obtain a solution. The solution is subjected to ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) to perform elemental analysis of the chemical composition. The C and S contents are determined using the well-known high-frequency combustion method (combustion-infrared absorption method). The N content is determined using the well-known inert gas fusion-thermal conductivity method. For example, the chemical composition of the grain-oriented electrical steel sheet 1 can be analyzed using a component analyzer manufactured by Shimadzu Corporation (trade name: ICPS-8000).

[0254] In addition, the content of each element is rounded off based on the significant figures specified in this embodiment, and is set to a value up to the minimum digit of the content of each element specified in this embodiment. For example, the Si content in this embodiment is specified by a value to the first decimal place. Therefore, the Si content is set to the value obtained by rounding off the second decimal place of the measured value to the first decimal place.

[0255] Similarly, the content of elements other than Si in the grain-oriented electrical steel sheet 1 of the present embodiment is determined by rounding off the measured value to the minimum number of digits specified in the present embodiment.

[0256] Furthermore, rounding means discarding the digit if it is less than 5 and rounding up the digit if it is greater than 5.

[0257] [Regarding the lower covering film 11]

[0258] As described above, the lower coating 11 can be either a primary coating or an intermediate layer. The primary coating is a well-known coating mainly composed of forsterite (Mg2SiO4). More specifically, in the primary coating, the content of forsterite is 60% or more in mass%. The primary coating is formed by reacting an annealing separator containing magnesium oxide with an oxide film such as SiO2 on the surface of the base steel plate 10 or elements contained in the base steel plate 10 during final annealing. Therefore, the lower coating 11 has a composition derived from the chemical composition of the annealing separator and the base steel plate 10. For example, the lower coating 11 contains spinel (MgAl2O4). When the reduction of iron loss is emphasized, the lower coating 11 is set as a primary coating. On the other hand, the intermediate layer is a coating mainly composed of silicon dioxide and aluminum oxide. When the punching workability is emphasized, the lower coating 11 is set as an intermediate layer.

[0259] [About the secondary covering film 12]

[0260] The secondary coating 12 is formed on the lower coating 11. When a plurality of grain-oriented electromagnetic steel sheets 1 are stacked and used, the secondary coating 12 ensures insulation between the stacked grain-oriented electromagnetic steel sheets 1. In other words, the secondary coating 12 is an insulating coating. The secondary coating 12 has a well-known structure. Specifically, the secondary coating 12 contains at least one inorganic substance such as a metal chromate, a phosphate compound, colloidal silica, a Zr compound, and a Ti compound. Preferably, the secondary coating 12 is a coating mainly composed of a phosphate compound. In other words, the secondary coating 12 contains a phosphate compound. When the secondary coating is mainly composed of a phosphate compound, the content of the phosphate compound is 50% or more by mass.

[0261] The secondary coating 12 may contain, for example, one or more selected from colloidal silica and polytetrafluoroethylene together with a phosphoric acid compound. Examples of the phosphoric acid compound include sodium phosphate, aluminum phosphate, and magnesium phosphate.

[0262] [(Feature 2) Regarding formula (1)]

[0263] In the grain-oriented electromagnetic steel sheet 1 of the present embodiment, the crystal orientation of measurement points arranged at intervals of 2 mm along a first direction and a second direction perpendicular to the first direction on the surface (rolled surface) of the grain-oriented electromagnetic steel sheet 1 is further measured by X-ray diffraction, thereby determining the orientation difference of the grain boundaries of the grains. When the total length of the grain boundaries of the grains is defined as La and the total length of the grain boundaries having an orientation difference of 1° to 5° is defined as Ls, formula (1) is satisfied.

[0264] Ls / La≥0.140 (1)

[0265] Here, the first direction and the second direction are not particularly limited as long as they are mutually orthogonal directions. The first direction is, for example, the rolling direction of the grain-oriented electromagnetic steel sheet 1. When the first direction is the rolling direction of the grain-oriented electromagnetic steel sheet 1, the second direction is the sheet width direction of the grain-oriented electromagnetic steel sheet 1.

[0266] The fine-angle grain boundary ratio R is defined as follows: SGB .

[0267] R SGB =Ls / La

[0268] Ratio of small angle grain boundaries R SGB The ratio of the total length Ls of small-angle grain boundaries with an orientation misorientation angle of 1 to 5° to the total length La of grain boundaries on the surface (rolled surface) of the grain-oriented electromagnetic steel sheet 1 is denoted as small-angle grain boundary ratio R. SGB It shows the ratio of the fine-angle grain boundaries to the entire grain boundaries on the surface of the grain-oriented electrical steel sheet 1 .

[0269] Here, the misorientation angle is defined as follows. Focusing on the grain boundaries between adjacent grains on the surface (rolled surface) of the grain-oriented electromagnetic steel sheet 1, the relative angular difference between the crystal orientation of one grain and the crystal orientation of another grain at the grain boundary between adjacent grains is defined as the misorientation angle (°).

[0270] In the case of small angle grain boundary ratio R SGB When the ratio is large, the proportion of small-angle grain boundaries relative to the total grain boundaries increases. Consequently, among adjacent grains, the proportion of grains with large misorientation angles decreases, while the proportion of grains with small misorientation angles increases. Consequently, local variations in magnetic flux density are suppressed in the grain-oriented electrical steel sheet 1. In other words, the magnetic flux density distribution becomes uniform.

[0271] In the case of small angle grain boundary ratio R SGBWhen the ratio is greater than 0.140, the ratio of the micro-angle grain boundary to the entire grain boundary is large enough. In this case, the magnetic flux density distribution is sufficiently uniform. In the case where there is a region with locally high magnetic flux density, hysteresis loss occurs in this region. Such hysteresis loss cannot be eliminated even if magnetic domain segmentation is implemented. If the magnetic flux density distribution is sufficiently uniform, the generation of hysteresis loss can be fully suppressed. Therefore, not only can excellent iron loss characteristics be obtained before the magnetic domain segmentation treatment, but also excellent iron loss characteristics can be obtained after the magnetic domain segmentation treatment.

[0272] Ratio of small angle grain boundaries R SGB The preferred lower limit of is 0.145, more preferably 0.148, further preferably 0.150.

[0273] Ratio of small angle grain boundaries R SGB Therefore, the small angle grain boundary ratio R SGB The upper limit of the ratio of small angle grain boundaries R is preferably 1.000. SGB A more preferred upper limit is 0.800, more preferably 0.600, more preferably 0.400, and even more preferably 0.300.

[0274] [Ratio of small angle grain boundary R SGB Determination method of

[0275] Ratio of small angle grain boundaries R SGB It can be measured by the following method.

[0276] X-ray diffraction based on the Laue method is performed on the rolled surface of the grain-oriented electromagnetic steel sheet 1. Specifically, one or more rectangular observation areas AR of the grain-oriented electromagnetic steel sheet 1 with a length of 250 mm in the first direction and 60 mm in the second direction are selected from an arbitrary position on the rolled surface of the grain-oriented electromagnetic steel sheet 1. n (n is a natural number). n , measurement points (3906 measurement points) were arranged at intervals of 2 mm along the rolling direction and the width direction, and X-ray diffraction based on the Laue method was performed to obtain the crystal orientation of each measurement point. At this time, the spot diameter was set to 1 mm. Based on the crystal orientation obtained at each measurement point, the boundary with an orientation difference angle of 1 to 180° was regarded as the grain boundary. The area surrounded by the grain boundary was regarded as the grain. In addition, the ray source in the X-ray diffraction based on the Laue method was a W target, the tube voltage was 40 kV, and the tube current was 40 mA.

[0277] Whenever each observation area AR n When the measurement is completed, it is determined whether the total number of the determined grains is more than 100. When the total number of the grains is more than 100, the entire observation area AR in which the measurement is completed isn The total length of the grain boundaries of all the identified crystal grains is defined as La. Furthermore, the total length of the grain boundaries of all the identified crystal grains having a misorientation angle of 1 to 5° is defined as Ls.

[0278] For example, when the number of crystal grains identified after the measurement of the crystal orientation in the first observation area AR1 is completed is 100 or more, La and Ls are determined using all the crystal grains identified in the observation area AR1.

[0279] On the other hand, after the measurement in the observation area AR1 is completed, if the number of crystal grains identified is less than 100, measurement is performed in the second observation area AR2. Then, after the measurement in the observation area AR2 is completed, if the total number of crystal grains identified in the observation areas AR1 and AR2 is 100 or more, La and Ls are determined using all the crystal grains identified in the observation areas AR1 and AR2.

[0280] In short, continue to observe the area AR1 ~ AR n The measurement is continued until the total number of the determined grains is 100 or more. Then, when the total number of the grains is 100 or more, all the observation areas AR1 to AR2 are used. n For all identified grains, La and Ls were determined.

[0281] Using the obtained La and Ls, the fine-angle grain boundary ratio R is calculated by the following formula: SGB .

[0282] Ratio of small angle grain boundaries R SGB =Ls / La

[0283] Based on the crystal orientation at each measurement point, La and Ls can be determined by using OIMAnalysis (trade name, manufactured by TSL Solutions Co., Ltd.) as analysis software.

[0284] In addition, at the measurement points corresponding to grains or grain boundaries with a grain size of less than 1 mm, it is difficult to identify the crystal orientation, and sometimes the identification is poor. Therefore, at such measurement points (hereinafter referred to as poor measurement points), the crystal orientation data of adjacent measurement points are substituted. Specifically, among the two measurement points (+X and -X) adjacent to the poor measurement point in the first direction, and the two measurement points (+Y and -Y) adjacent to the measurement point in the second direction, the crystal orientation data are substituted in the priority order of +X, -X, +Y, and -Y. First, as the crystal orientation data of the poor measurement point, the crystal orientation data of the measurement point +X is substituted. If the crystal orientation data of the measurement point +X is also poor, the crystal orientation data of the measurement point -X is substituted. As described above, the data that can be substituted is determined according to the priority order. In addition, such a method of substituting crystal orientation data is set as the "Clean up" function in the above-mentioned OIMAnalysis. The X direction is, for example, the rolling direction, and the Y direction is, for example, the width direction.

[0285] [(Feature 3) Regarding magnetic flux density B8]

[0286] In the grain-oriented electrical steel sheet 1 of this embodiment, the magnetic flux density B8 is greater than or equal to 1.910 T. In other words, the grain-oriented electrical steel sheet 1 of this embodiment can achieve excellent magnetic flux density. The lower limit of the magnetic flux density B8 is preferably 1.911 T, and more preferably 1.912 T.

[0287] [Measurement method of magnetic flux density B8]

[0288] The magnetic flux density B8 of the grain-oriented electrical steel sheet 1 was measured using the following method. A test piece was collected from the grain-oriented electrical steel sheet 1, encompassing the center of the sheet width. The test piece dimensions were set to 100 mm x 500 mm x sheet thickness. A single-sheet magnetic properties test (SST test) was conducted in accordance with JIS C2556:2015. In the SST test, an 800 A / m magnetic field was applied to the test piece, and the magnetic flux density B8 (T) was determined.

[0289] [Effects of the Grain-Oriented Electrical Steel Sheet 1 of the Present Embodiment]

[0290] The grain-oriented electrical steel sheet 1 of this embodiment satisfies Characteristics 1 to 3. Therefore, sufficient magnetic flux density can be obtained. Furthermore, excellent iron loss characteristics can be obtained not only before magnetic domain refinement but also after magnetic domain refinement.

[0291] [Other aspects of the grain-oriented electrical steel sheet 1 of this embodiment]

[0292] The grain-oriented electrical steel sheet 1 of this embodiment may further include a plurality of linear thermal strains extending linearly and arranged in a direction perpendicular to the extending direction, or a plurality of grooves extending linearly and arranged in a direction perpendicular to the extending direction.

[0293] Linear thermal strain or grooves are formed on the surface (rolled surface) of the grain-oriented electrical steel sheet 1 through a well-known magnetic domain refinement process. The linear thermal strain or grooves refine the magnetic domains of the grain-oriented electrical steel sheet 1. In the grain-oriented electrical steel sheet 1 of this embodiment, even after the magnetic domain refinement process, the iron loss characteristics are significantly improved.

[0294] [Method for Manufacturing Grain-Oriented Electrical Steel Sheet 1 of the Present Embodiment]

[0295] An example of a method for manufacturing the grain-oriented electromagnetic steel sheet according to the present embodiment will be described below. The method for manufacturing the grain-oriented electromagnetic steel sheet 1 described below is an example for manufacturing the grain-oriented electromagnetic steel sheet 1 according to the present embodiment. Therefore, the grain-oriented electromagnetic steel sheet 1 having characteristics 1 to 3 described above can also be manufactured using other manufacturing methods besides the manufacturing method described below. However, the manufacturing method described below is a preferred example of a method for manufacturing the grain-oriented electromagnetic steel sheet 1 according to the present embodiment.

[0296] [Manufacturing process flow]

[0297] An example of a method for manufacturing the grain-oriented electrical steel sheet 1 according to the present embodiment includes the following steps 1 to 6.

[0298] (Process 1) Hot rolling process

[0299] (Process 2) Hot-rolled plate annealing process

[0300] (Process 3) Cold rolling process

[0301] (Process 4) Decarburization annealing process

[0302] (Process 5) Final annealing process

[0303] (Step 6) Secondary Covering Film Formation Step

[0304] The hot-rolled sheet annealing step (step 2) is an optional step. Therefore, the hot-rolled sheet annealing step may or may not be performed.

[0305] The cold rolling process (process 3) further includes the following two processes.

[0306] (Process 31) Tandem rolling process

[0307] (Process 32) Reversible rolling process

[0308] In the manufacturing method of the present embodiment, the following manufacturing conditions are satisfied in the cold rolling step (step 3) and the decarburization annealing step (step 4).

[0309] (Conditions of the Tandem Rolling Process (Process 31))

[0310] Condition 1: Tandem rolling is performed before reversing rolling.

[0311] Condition 2: The average diameter D1 of the work rolls is set to 200 mm or more.

[0312] Condition 3: The cumulative reduction ratio CR1 is set to 30% or more.

[0313] (Conditions of the Reversible Rolling Step (Step 32))

[0314] Condition 4: The intermediate steel plate that has not been subjected to heat treatment after the tandem rolling process is the rolling target.

[0315] Condition 5: Reversible rolling is performed using a multi-stage rolling mill.

[0316] Condition 6: The average diameter D2 of the work rolls is set to 100 mm or less.

[0317] Condition 7: The cumulative reduction ratio CR2 is set to 20% or more.

[0318] Condition 8: Rolling is performed in one or more passes so that the difference in roll diameter between the upper work roll and the lower work roll of the reversing rolling mill becomes 2.0 mm or more.

[0319] (Conditions of Decarburization Annealing Step (Step 4))

[0320] Condition 9: The average heating rate HR in the temperature range of 400° C. to 800° C. is set to 400° C. / second or more.

[0321] Next, steps 1 to 6 will be described.

[0322] [(Process 1) Hot rolling process]

[0323] In the hot rolling process, a steel slab is hot-rolled to produce a hot-rolled steel sheet. Here, the chemical composition of the prepared steel slab is adjusted so that the chemical composition of the grain-oriented electrical steel sheet 1 satisfies Feature 1.

[0324] The chemical composition of the steel slab is, for example, in mass %, composed of Si: 2.5-4.5%, Mn: 0.01-0.30%, N: 0.003-0.015%, C: 0.010-0.100%, sol.Al: 0.010-0.050%, one or more selected from S and Se: 0.010-0.050% in total, Ti: more than 0% and less than 0.010%, Ni: 0-0.50%, Cr: 0-0.50%, Cu: 0-0.50%, P: 0-0.05%, Mo: 0-0.05%, Sn: 0-0.30%, Sb: 0-0.30%, and Bi: 0-0.0200%, and the remainder: Fe and impurities.

[0325] In this manufacturing method, AlN is used as an inhibitor. Therefore, the Al content in the chemical composition of the steel slab is within the above range. When the method for manufacturing grain-oriented electrical steel sheet using the inhibitor-free method is applied, the Al content in the steel slab is 0.010% or less.

[0326] The steel slab is produced by a well-known steelmaking process, a continuous casting process or an ingot casting and bloom rolling process. The steel slab can also be made into a thickness of 100 mm or less by direct casting.

[0327] The hot rolling process using the prepared steel slab includes the following steps.

[0328] (Step 11) Heating Step

[0329] (Process 12) Rough rolling process

[0330] (Process 13) Finishing Rolling Process

[0331] Each of steps 11 to 13 will be described below.

[0332] [(Step 11) Heating Step]

[0333] In the heating step, the steel slab is heated. For example, the steel slab is placed in a well-known heating furnace or a well-known soaking furnace and heated. The preferred heating temperature of the steel slab is 1100 to 1450°C.

[0334] [(Process 12) Rough rolling process]

[0335] In the rough rolling process, a heated steel slab is subjected to rough rolling to produce a rough section. Here, rough rolling refers to hot rolling of the steel slab using a well-known rough rolling mill. A rough section refers to the steel plate after the rough rolling process is completed and before the finish rolling process begins. In the rough rolling process, the rough rolling mill applies multiple passes of reduction to the steel slab to produce a rough section.

[0336] [(Process 13) Finishing Rolling Process]

[0337] In the finishing rolling process, the rough sections produced in the roughing rolling process are subjected to well-known finishing rolling to produce hot-rolled steel sheets. Here, finishing rolling refers to hot rolling the rough sections using a well-known finishing mill. In the finishing rolling process, a continuous rolling mill consisting of multiple tandem finishing stands arranged in a row on a rolling line is used to apply multiple passes of reduction to the rough sections to produce hot-rolled steel sheets.

[0338] [(Process 2) Hot-rolled sheet annealing process]

[0339] The hot-rolled steel sheet annealing step is an optional step. In other words, it is not necessary to perform the hot-rolled steel sheet annealing step. If performed, the hot-rolled steel sheet produced during the hot rolling step is annealed. This annealing step recrystallizes the steel sheet structure, improving its magnetic properties.

[0340] In the hot-rolled sheet annealing step, a well-known hot-rolled sheet annealing method may be performed. The method for heating the hot-rolled steel sheet during the hot-rolled sheet annealing is not particularly limited; a well-known heating method may be employed. The hot-rolled sheet annealing temperature is, for example, 800 to 1200°C. The holding time at the hot-rolled sheet annealing temperature is, for example, 10 to 300 seconds. Furthermore, when the hot-rolled sheet annealing step is performed, the hot-rolled steel sheet may be pickled after the hot-rolled sheet annealing step and before the cold rolling step.

[0341] [(Process 3) Cold Rolling Process]

[0342] In the cold rolling process, the produced hot-rolled steel sheet is cold-rolled to produce a cold-rolled steel sheet. As described above, the cold rolling process includes the following two steps.

[0343] (Process 31) Tandem rolling process

[0344] (Process 32) Reversible rolling process

[0345] In the cold rolling process, the tandem rolling process is first carried out, followed by the reverse rolling process. The tandem rolling process and the reverse rolling process will be described below.

[0346] [(Process 31) Tandem rolling process]

[0347] In the tandem rolling process, cold rolling is performed using a tandem rolling mill.

[0348] Figure 10 This is a schematic diagram of a tandem rolling mill. Figure 10 The tandem rolling mill CM is arranged between the uncoiler (unwinding device) 21 and the tension winding roller (winding device) 22 from upstream to downstream.

[0349] The uncoiler 21 unwinds the coiled hot-rolled steel sheet ST0. The tension winding roll 22 winds up the intermediate steel sheet ST1 manufactured by the tandem rolling mill CM.

[0350] The tandem rolling mill CM continuously rolls the uncoiled hot-rolled steel sheet ST through a plurality of passes to produce an intermediate steel sheet ST1.

[0351] The tandem rolling mill CM includes a plurality of rolling stands CMS1 to CMS2 arranged in a row from upstream to downstream. j (j is a natural number greater than or equal to 2.) Each rolling stand CMS includes a pair of horizontally extending work rolls WR1. The pair of work rolls WR1 contacts the hot-rolled steel sheet to be cold-rolled, cold-rolling the hot-rolled steel sheet. The rolling stand CMS may also include a plurality of backup rolls BR1. The backup rolls BR1 support the work rolls WR1, suppressing deflection of the work rolls WR1 during rolling.

[0352] In continuous rolling using a tandem rolling mill CM, reducing the hot-rolled steel sheet using each rolling stand CMS as it passes through the rolling stand CMS is referred to as performing "one pass." Continuous rolling refers to performing reduction in multiple passes using the tandem rolling mill CM. Furthermore, the hot-rolled steel sheet may not be reduced using all of the rolling stands CMS in the tandem rolling mill CM. For example, if the tandem rolling mill CM has six rolling stands CMS1 to CMS6, and the hot-rolled steel sheet passes through rolling stand CMS6 without undergoing reduction, five continuous rolling passes are performed.

[0353] [(Process 32) Reversible rolling process]

[0354] Figure 11 This is a schematic diagram of a multi-stage rolling mill used in the reversing rolling process. Figure 11 In the reversible rolling process, a multi-stage rolling mill SM is used to perform reversible rolling of multiple passes on the intermediate steel sheet ST1 after the tandem rolling process, thereby manufacturing a cold-rolled steel sheet.

[0355] The multi-stage rolling mill SM is, for example, a Sendzimir-type cluster mill. The multi-stage rolling mill SM includes a pair of work rolls WR2 and a plurality of backup rolls BR2. In the multi-stage rolling mill SM, the pair of work rolls WR2 are supported by the plurality of backup rolls BR2, minimizing deflection of the work rolls WR2. This allows for a high reduction ratio. The pair of work rolls WR2 includes an upper work roll WR2U and a lower work roll WR2L. The lower work roll WR2L is positioned below the upper work roll WR2U.

[0356] Here, when the intermediate steel plate ST1 is subjected to reduction while passing through the multi-stage rolling mill SM, it is said that "one pass" of reduction is performed. In the case of reversible rolling, reduction is performed when the intermediate steel plate ST1 moves from upstream to downstream, and also when the intermediate steel plate ST1 moves from downstream to upstream. More specifically, when the intermediate steel plate ST1 passes through the multi-stage rolling mill SM from upstream to downstream, one pass of reduction is applied to the intermediate steel plate ST1. Furthermore, when the intermediate steel plate ST1 passes through the same multi-stage rolling mill SM from downstream to upstream, one pass of reduction is also applied to the intermediate steel plate ST1. In other words, when reduction is performed reciprocally, two passes of reduction are performed on the intermediate steel plate ST1. Furthermore, sometimes, no reduction is applied to the intermediate steel plate ST1 while passing through the multi-stage rolling mill SM.

[0357] In the cold rolling process, the above-described tandem rolling process and reverse rolling process are performed to produce a cold-rolled steel sheet.

[0358] [Manufacturing conditions in the cold rolling process]

[0359] In the cold rolling process, the following conditions 1 to 8 are satisfied.

[0360] (Conditions of tandem rolling process)

[0361] Condition 1: Tandem rolling is performed before reversing rolling.

[0362] Condition 2: The average diameter D1 of the work rolls is set to 200 mm or more.

[0363] Condition 3: The cumulative reduction ratio CR1 is set to 30% or more.

[0364] (Conditions of the reversible rolling process)

[0365] Condition 4: The intermediate steel plate that has not been subjected to heat treatment after the tandem rolling process is the rolling target.

[0366] Condition 5: Use a multi-stage rolling mill and perform reversible rolling with multiple passes.

[0367] Condition 6: The average diameter D2 of the work rolls is set to 100 mm or less.

[0368] Condition 7: The cumulative reduction ratio CR2 is set to 20% or more.

[0369] Condition 8: Rolling is performed in one or more passes so that the difference in roll diameter between the upper work roll and the lower work roll of the reversing rolling mill becomes 2 mm or more.

[0370] Conditions 1 to 8 are explained below.

[0371] [Conditions of the tandem rolling process]

[0372] [Regarding Condition 1]

[0373] In the tandem rolling process, prior to the reversing rolling process, the tandem mill CM is used to perform continuous rolling in multiple passes to produce the intermediate steel plate ST1. As described above, tandem rolling allows for the use of work rolls with larger diameters than reversing rolling. Therefore, tandem rolling can minimize the shear strain imparted to the steel plate compared to reversing rolling. As a result, the size of Goss-oriented grains can be minimized in the final annealing process described later.

[0374] [Regarding Condition 2]

[0375] In tandem rolling, the average diameter D1 of the multiple work rolls used in each pass is set to 200 mm or greater. In the multi-stage rolling mill (Sendzimir mill) used in the reversing rolling process described later, the average diameter D2 of the work rolls is kept below 100 mm to prevent deflection of the work rolls, and the work rolls are supported by multiple backup rolls. In a multi-stage rolling mill, the combination of a pair of work rolls and the multiple backup rolls supporting them exerts high pressure. However, due to the small diameter of the work rolls, rolling using a Sendzimir mill imparts significant shear strain to the rolled steel sheet.

[0376] When the applied shear strain is large, the α-fiber orientation group develops in the surface layer of the cold-rolled steel sheet. If the α-fiber orientation group develops, the number of Gauss-oriented grains that serve as nuclei for secondary recrystallization decreases due to grain growth just before the onset of secondary recrystallization. Consequently, the secondary recrystallized grains coarsen. Consequently, the magnetic properties (magnetic flux density and iron loss) of the grain-oriented electrical steel sheet 1 deteriorate.

[0377] In this embodiment, the average diameter D1 of the working rolls in the tandem rolling process is set to 200 mm or more. In this case, the amount of shear strain imparted to the surface layer of the steel sheet during cold rolling can be reduced. Therefore, during cold rolling, the γ fiber orientation group is more stabilized than the α fiber orientation group. As a result, in the surface layer of the cold-rolled steel sheet, the α fiber orientation group is suppressed, and the γ fiber orientation group remains. The γ fiber orientation group generates {111}<112> recrystallized grains when undergoing primary recrystallization. In the final annealing process, the {111}<112> recrystallized grains and the Goss orientation grains are in a Σ9 corresponding orientation relationship, which has the effect of promoting the secondary recrystallization of the Goss orientation grains in the surface layer. Therefore, the degree of aggregation in the Goss orientation after secondary recrystallization can be increased. As a result, the magnetic properties of the grain-oriented electromagnetic steel sheet can be improved.

[0378] The average diameter D1 is set as the arithmetic mean of the diameters (mm) of a plurality of pairs of work rolls used in each pass.

[0379] The lower limit of the average diameter D1 is preferably 250 mm, more preferably 300 mm, further preferably 325 mm, further preferably 350 mm.

[0380] The upper limit of the average diameter D1 is preferably 1000 mm, more preferably 900 mm, more preferably 800 mm, more preferably 700 mm, and even more preferably 650 mm.

[0381] [Regarding Condition 3]

[0382] The cumulative reduction ratio CR1 in the tandem rolling process is set to 30% or more. Here, the cumulative reduction ratio CR1 (%) is defined by the following formula (A).

[0383] CR1 = (thickness of the hot-rolled steel sheet before the tandem rolling process - thickness of the intermediate steel sheet after the tandem rolling process) / thickness of the hot-rolled steel sheet before the tandem rolling process × 100 (A)

[0384] If the cumulative reduction ratio CR1 is less than 30%, the reduction in the tandem rolling process is insufficient. In this case, the reduction in the reversing rolling process increases. Consequently, the shear strain imparted to the cold-rolled steel sheet increases excessively. Consequently, the concentration of the Goss orientation after secondary recrystallization decreases. Consequently, the magnetic properties of the grain-oriented electrical steel sheet deteriorate. Therefore, the cumulative reduction ratio CR1 is set to 30% or higher.

[0385] The lower limit of the cumulative reduction ratio CR1 is preferably 35%, more preferably 40%, and even more preferably 45%.

[0386] The upper limit of the cumulative reduction ratio CR1 is preferably 90%, more preferably 85%, further preferably 80%, and further preferably 75%.

[0387] [Conditions of the reversible rolling process]

[0388] [Regarding Condition 4]

[0389] The reversible rolling process involves rolling the intermediate steel plate that has not been heat-treated after the tandem rolling process. In other words, the reversible rolling process involves rolling the intermediate steel plate, which is already in the tandem rolling process. Here, "heat treatment" refers to heating the steel plate to a temperature of 500°C or higher and / or maintaining the temperature for a specified period of time. An example of heat treatment is annealing.

[0390] When the intermediate steel sheet produced through the tandem rolling process is subjected to heat treatments such as annealing, recovery and recrystallization occur within the intermediate steel sheet. Therefore, the total strain introduced by cold rolling is reduced. As a result, the magnetic properties of the grain-oriented electromagnetic steel sheet deteriorate. This is because, as described above, when the intermediate steel sheet is heat treated, the strain is reduced, resulting in a degradation of the primary recrystallization texture in the center layer of the steel sheet. Specifically, the center layer of the steel sheet inherits the α-fiber orientation group formed during the hot rolling process. After the reversing rolling process, the α-fiber orientation group in the center layer of the steel sheet is significantly more developed than in the surface layer of the steel sheet.

[0391] When the intermediate steel plate is subjected to heat treatment such as annealing, even if reversible rolling is performed, the recrystallization of the α-fiber orientation group in the center layer of the steel plate cannot be promoted. If the recrystallization of the α-fiber orientation group in the center layer of the steel plate is not sufficiently promoted, the {411}<148> recrystallized orientation in the center layer of the steel plate decreases. <148> The recrystallization orientation is in a Σ9 correspondence relationship with the Goss orientation, which promotes secondary recrystallization of the Goss orientation. Therefore, the rolling object in the reversing rolling process is the intermediate steel plate that has not been heat-treated after the tandem rolling process.

[0392] [Regarding Condition 5]

[0393] In the reversing rolling process, a multi-stage rolling mill SM is used to perform multiple passes of reversing rolling on the intermediate steel sheet ST1, which has not been heat-treated after the tandem rolling process, to produce a cold-rolled steel sheet. Reversing rolling using a multi-stage rolling mill allows for a higher reduction than tandem rolling, thus enabling the cold-rolled steel sheet to be thinned.

[0394] [Regarding Condition 6]

[0395] In reverse rolling using a multi-stage rolling mill, the average diameter D2 of the multiple work rolls used in each pass is set to 100 mm or less. If the average diameter D2 exceeds 100 mm, sufficient reduction cannot be applied to the intermediate steel plate undergoing reverse rolling. In this case, sufficient shear strain cannot be applied to the intermediate steel plate.

[0396] If the average diameter D2 is 100 mm or less, sufficient shear strain can be imparted to the intermediate steel plate undergoing reversible rolling in each pass. As a result, sufficient shear bands, which serve as the origin of primary recrystallization of Goss-oriented grains, can be formed. Therefore, a sufficient amount of Goss-oriented grains are generated during the decarburization annealing step.

[0397] When reverse rolling is performed using a single multi-stage rolling mill SM, the average diameter D2 is set to the arithmetic mean of the diameters (mm) of each pair of work rolls used in each pass. When reverse rolling is performed using multiple multi-stage rolling mills SM, the average diameter D2 is set to the arithmetic mean of the diameters (mm) of multiple pairs of work rolls used in each pass.

[0398] The upper limit of the average diameter D2 is preferably 95 mm, more preferably 90 mm, and even more preferably 85 mm.

[0399] The lower limit of the average diameter D2 is not particularly limited, but is preferably 50 mm, more preferably 55 mm, and even more preferably 60 mm.

[0400] [Regarding Condition 7]

[0401] The cumulative reduction ratio CR2 in the reverse rolling process is set to 20% or more. Here, the cumulative reduction ratio CR2 (%) is defined by the following formula (B).

[0402] CR2 = (thickness of the intermediate steel plate before the reversible rolling process, i.e., thickness of the cold-rolled steel plate - thickness of the cold-rolled steel plate after the reversible rolling process) / thickness of the intermediate steel plate before the reversible rolling process × 100 (B)

[0403] If the cumulative reduction ratio CR2 is less than 20%, the reduction in the reverse rolling process is insufficient. In this case, insufficient shear bands, which serve as the origin of primary recrystallization in the Goss orientation, are formed. During the subsequent decarburization annealing process, sufficient nuclei for the Goss-oriented grains generated during primary recrystallization are not generated. Consequently, the concentration of Goss-oriented grains after secondary recrystallization decreases. Consequently, the magnetic properties of the grain-oriented electrical steel sheet are degraded. Therefore, the cumulative reduction ratio CR2 is set to 20% or higher.

[0404] The lower limit of the cumulative reduction ratio CR2 is preferably 30%, more preferably 35%, and even more preferably 40%.

[0405] The upper limit of the cumulative reduction ratio CR2 is preferably 90%, more preferably 80%, further preferably 75%, and further preferably 70%.

[0406] [Regarding Condition 8]

[0407] In the reversing rolling process, the roll diameter difference between the upper and lower work rolls of the multi-stage rolling mill is set to 2.0 mm or greater in at least one pass. In other words, the maximum roll diameter difference between the upper and lower work rolls in each pass is 2.0 mm or greater.

[0408] If the roller diameter difference is 2.0 mm or more, shear strain is introduced into the center layer of the steel plate during reversible rolling. As a result, shear strain is introduced into the α-fiber orientation group developed in the center layer of the steel plate. The α-fiber orientation group has low strain and is therefore known to be an orientation group that is difficult to recrystallize in the past. However, in this embodiment, as described above, sufficient shear strain is introduced into the α-fiber orientation group. Therefore, the recrystallization of the α-fiber orientation group is promoted. As a result, in the center layer of the steel plate, {411} <148> The recrystallization orientation increases. As a result, after the secondary recrystallization, the secondary recrystallization of the Goss-oriented grains is promoted. Furthermore, the orientation difference angle between adjacent grains can be reduced, and a sufficient small-angle grain boundary ratio R can be obtained. SGB .

[0409] The upper limit of the roll diameter difference is not particularly limited. For example, the upper limit of the roll diameter difference is 10.0 mm. The upper limit of the roll diameter difference is preferably 9.0 mm, and more preferably 8.0 mm.

[0410] In the cold rolling process, tandem rolling and reverse rolling are performed to satisfy the aforementioned conditions 1 to 8, thereby producing a cold-rolled steel sheet with controlled shear strain in the steel sheet surface. By using this cold-rolled steel sheet in subsequent steps, the grain-oriented electrical steel sheet 1 produced can satisfy characteristic 2.

[0411] [(Step 4) Decarburization Annealing Step]

[0412] In the decarburization annealing step, the cold-rolled steel sheet after the cold rolling step is subjected to decarburization annealing to exhibit primary recrystallization.

[0413] The decarburization annealing process includes the following steps.

[0414] (Step 41) Heating Step

[0415] (Process 42) Decarburization process

[0416] (Process 43) Cooling process

[0417] In the heating step (step 41), the steel sheet is heated to an optional temperature (reaching temperature) of 800-950°C. In the decarburization step (step 42), the steel sheet is held at a decarburization annealing temperature of 800-950°C to perform decarburization annealing, thereby causing primary recrystallization. In the cooling step (step 43), the steel sheet after the decarburization step is cooled using a well-known method. The reaching temperature and the decarburization annealing temperature may be the same temperature, or the reaching temperature may be higher than the decarburization annealing temperature.

[0418] In this embodiment, during the heating step, the average heating rate (HR) in the temperature range of 400°C to 800°C, corresponding to the recrystallization temperature range of the steel sheet, is significantly accelerated. This promotes recrystallization in the Goss orientation. This increases the concentration of grains in the Goss orientation after secondary recrystallization. Consequently, the magnetic properties of the grain-oriented electrical steel sheet can be improved.

[0419] The details of each process are described below.

[0420] [(Step 41) Heating Step]

[0421] In the heating step, the cold-rolled steel sheet, after the cold rolling step, is first loaded into a heat treatment furnace. In the decarburization annealing heat treatment furnace of this embodiment, the cold-rolled steel sheet is heated to a temperature of 800-950°C, for example, by high-frequency induction heating or electric heating. The heating step satisfies the following condition 9.

[0422] Condition 9: The average heating rate HR in the temperature range of 400° C. to 800° C. is set to 400° C. / second or more.

[0423] [Regarding Condition 9]

[0424] In the temperature rising step, the average temperature rising rate in the temperature range of 400° C. to 800° C. of the cold-rolled steel sheet is defined as an average temperature rising rate HR (° C. / second).

[0425] As mentioned above, strain accumulates in cold-rolled steel sheets. If the average heating rate HR is lower than 400°C / s, the strain energy, which serves as the driving force for recrystallization, is released before recrystallization begins. In this case, a sufficient amount of Goss-oriented grains cannot be generated in the cold-rolled steel sheet after primary recrystallization (i.e., after decarburization annealing).

[0426] When the average heating rate HR is 400°C / s or higher, primary recrystallization occurs while strain energy is sufficiently accumulated in the cold-rolled steel sheet. Consequently, a sufficient amount of Goss-oriented grains can be generated in the cold-rolled steel sheet after primary recrystallization. Consequently, during the subsequent final annealing step, most of the Goss-oriented grains remain when secondary recrystallization occurs. This increases the degree of Goss-oriented concentration after secondary recrystallization. Consequently, the magnetic properties of the grain-oriented electrical steel sheet can be improved while also suppressing variations in the magnetic properties.

[0427] The upper limit of the average heating rate HR is not particularly limited. However, even if the average heating rate HR is faster than 3000°C / second, the above-mentioned effect is saturated. Therefore, the upper limit of the average heating rate HR is 3000°C / second.

[0428] The preferred lower limit of the average heating rate HR is 450°C / second, more preferably 500°C / second, more preferably 550°C / second, more preferably 600°C / second, more preferably 700°C / second, more preferably 800°C / second, more preferably 900°C / second, more preferably 1000°C / second, and more preferably 1100°C / second.

[0429] The average heating rate (HR) is measured using the following method. Multiple thermometers are installed within the heat treatment furnace to measure the surface temperature of the steel sheet. The thermometers are arranged from upstream to downstream of the heat treatment furnace. The average heating rate (HR) (°C / second) is calculated based on the steel sheet temperature measured by the thermometers and the time it takes for the steel sheet temperature to rise from 400°C to 800°C.

[0430] [(Step 42) Decarburization Step]

[0431] In the decarburization process, the cold-rolled steel sheet after the heating process is held at a decarburization annealing temperature to perform decarburization annealing. As a result, the cold-rolled steel sheet exhibits primary recrystallization. The atmosphere in the decarburization process can be a well-known atmosphere, for example, a wet nitrogen-hydrogen mixed atmosphere containing hydrogen and nitrogen. By performing decarburization annealing, carbon in the steel sheet is removed from the steel sheet, thereby exhibiting primary recrystallization. The decarburization annealing temperature and the holding time at the decarburization annealing temperature are not particularly limited. The decarburization annealing temperature is, for example, 800 to 950°C. The holding time at the decarburization annealing temperature is, for example, 15 to 150 seconds.

[0432] [(Step 43) Cooling Step]

[0433] In the cooling step, the cold-rolled steel sheet after the decarburization step is cooled to room temperature using a well-known method to produce a decarburization-annealed steel sheet. The cooling method can be either standing or water cooling. Standing cooling is preferred. Through the above steps, a decarburization-annealed steel sheet is produced in the decarburization annealing step.

[0434] [(Step 5) Final Annealing Step]

[0435] In the final annealing step, an annealing separator is applied to the decarburized annealed steel sheet, and the decarburized annealed steel sheet coated with the annealing separator is subjected to final annealing to produce a final annealed steel sheet.

[0436] The final annealing process includes the following steps.

[0437] (Step 51) Annealing Separator Coating Step

[0438] (Process 52) Annealing process

[0439] Each process is described below.

[0440] [(Step 51) Annealing Separator Coating Step]

[0441] The annealing separator coating step coats the decarburized annealed steel sheet with an annealing separator. Specifically, an aqueous slurry containing the annealing separator is coated on the decarburized annealed steel sheet. The aqueous slurry is prepared by adding water to the annealing separator and stirring.

[0442] Annealing separators may be primarily composed of magnesium oxide (MgO) or silicon dioxide and aluminum oxide. "Main component" means that the primary component accounts for 60.0% or more of the annealing separator by mass. Annealing separators may contain well-known additives in addition to MgO or silicon dioxide and aluminum oxide.

[0443] When emphasis is placed on reducing iron loss, the annealing separator contains MgO as the main component. When emphasis is placed on blanking workability, the annealing separator contains silica and alumina as the main components.

[0444] In the annealing separator coating step, an aqueous slurry of annealing separator is applied to the surface of the decarburized annealed steel sheet. The steel sheet coated with the annealing separator is then coiled into a coil. After the coil is formed, the annealing step is performed.

[0445] [(Step 52) Annealing Step]

[0446] After the annealing separator application step, the steel sheet is subjected to an annealing step to induce secondary recrystallization. The final annealing step is performed by loading the coiled steel sheet into a heat treatment furnace. The manufacturing conditions during the annealing step are, for example, as described below. The furnace atmosphere during the annealing step is a well-known atmosphere.

[0447] Final annealing temperature: 800~1200℃

[0448] Holding time at final annealing temperature: 5 to 60 hours

[0449] If the final annealing temperature is lower than 800°C, secondary recrystallization will not occur sufficiently, and purification to remove precipitates required for secondary recrystallization will also be insufficient. Consequently, the magnetic properties of the resulting grain-oriented electrical steel sheet will deteriorate. On the other hand, even if the final annealing temperature exceeds 1200°C, the effects on secondary recrystallization and purification are low, and problems such as deformation of the steel sheet may occur. If the final annealing temperature is between 800 and 1200°C, sufficient secondary recrystallization will occur, provided the aforementioned holding time is appropriate, leading to improved magnetic properties. Furthermore, an undercoat film will form on the steel sheet surface.

[0450] Through the above-mentioned manufacturing steps, a finish annealed steel sheet is manufactured in the finish annealing step.

[0451] Furthermore, the final annealing process removes elements from the steel sheet's chemical composition to a certain extent. In particular, S, Se, Al, and N, which act as inhibitors, are significantly removed. Furthermore, an underlying film (primary film or intermediate layer) forms on the surface of the grain-oriented electrical steel sheet after the final annealing process.

[0452] [(Step 6) Secondary Covering Film Formation Step]

[0453] In the secondary film forming step, a secondary film (insulating film) forming agent is applied to the finish annealed steel sheet. The finish annealed steel sheet coated with the secondary film forming agent is then heat treated. This forms a secondary film (insulating film) on the finish annealed steel sheet.

[0454] Specifically, a well-known secondary film-forming agent containing at least one inorganic substance selected from the group consisting of metal chromates, metal phosphates, colloidal silica, Zr compounds, and Ti compounds is applied to the surface of the finish-annealed steel sheet (on the lower film). The finish-annealed steel sheet coated with the secondary film-forming agent is then baked. This forms a well-known secondary film on the lower film.

[0455] [Other optional steps]

[0456] [Nitriding treatment process]

[0457] The method for manufacturing the grain-oriented electrical steel sheet 1 according to this embodiment may, if necessary, further perform a nitriding step after the decarburization annealing step (step 4) and before the final annealing step (step 5). The nitriding step can be performed under well-known conditions. The nitriding temperature is, for example, 700 to 850°C. The atmosphere within the nitriding furnace (nitriding atmosphere) contains, for example, a gas having nitriding properties, such as hydrogen, nitrogen, and ammonia.

[0458] If the nitriding temperature is 700°C or higher, or 850°C or lower, nitrogen easily penetrates the steel sheet during nitriding. Performing the nitriding treatment within this temperature range ensures a favorable nitrogen content within the steel sheet. Therefore, fine AlN is preferably formed in the steel sheet before secondary recrystallization. Consequently, secondary recrystallization is favorably exhibited during final annealing. The time the steel sheet is held at the nitriding temperature is not particularly limited, but is, for example, 10 to 60 seconds.

[0459] [Magnetic domain refinement process]

[0460] The grain-oriented electrical steel sheet of this embodiment may, if necessary, undergo a magnetic domain refinement treatment step after the final annealing step (step 5) or the secondary coating formation step (step 6). In this magnetic domain refinement treatment step, the surface (rolled surface) of the grain-oriented electrical steel sheet is irradiated with a laser beam that has a magnetic domain refinement effect, thereby creating linear thermal strain or physically forming grooves on the surface of the steel sheet. This allows the production of grain-oriented electrical steel sheet with even better magnetic properties.

[0461] Through the above-described manufacturing steps, the grain-oriented electrical steel sheet 1 according to the present embodiment is manufactured.

[0462] The following examples specifically describe the grain-oriented electrical steel sheet of the present embodiment. These examples are provided to confirm the effects of the method for producing the grain-oriented electrical steel sheet of the present embodiment, and do not limit the grain-oriented electrical steel sheet disclosed herein.

[0463] Example 1

[0464] In Example 1, conditions 1 to 9 in the above-mentioned manufacturing process were changed to manufacture a grain-oriented electrical steel sheet.

[0465] Specifically, a steel slab was prepared. The chemical composition of the steel slab, in mass%, was as follows: Si: 3.3%, Mn: 0.08%, N: 0.008%, C: 0.075%, sol. Al: 0.025%, a total of 0.022% of one or more selected from S and Se, Ti: 0.001%, Ni: 0.03%, Cr: 0.04%, Cu: 0.05%, P: 0.01%, Mo: 0.00%, Sn: 0.10%, Sb: 0.00%, Bi: 0.0000%, and the balance: Fe and impurities.

[0466] The prepared steel slabs were subjected to a hot rolling process. Specifically, the steel slabs of each test number were heated in a heating furnace to 1340° C. The heated steel slabs were hot rolled to produce hot-rolled steel sheets with a thickness of 2.3 mm.

[0467] After the hot rolling process, the hot-rolled steel sheet was subjected to a hot-rolled sheet annealing process at a temperature of 800-1200°C for a holding time of 10-300 seconds. Following the hot-rolled sheet annealing process, a cold rolling process was performed to produce a cold-rolled steel sheet with a thickness of 0.22 mm. Specifically, the first cold rolling process shown in Table 1 was followed by a second cold rolling process. Conditions 1 to 8 are shown in Table 1.

[0468] Table 1

[0469]

[0470] Specifically, "Tandem" in the "Condition 1, Rolling Method" column of the "First Cold Rolling Process" column in Table 1 means that a tandem rolling process is performed as the first cold rolling process. "Reversible" means that a reversible rolling process is performed as the first cold rolling process.

[0471] The average diameter D1 (mm) of the work rolls used in each pass is recorded in the "Condition 2, Average Diameter D1 (mm)" column of the "First Cold Rolling Process" column in Table 1. The cumulative reduction ratio CR1 (%) in the first cold rolling process is recorded in the "Condition 3, Reduction Ratio CR1 (%)" column of the "First Cold Rolling Process" column in Table 1.

[0472] In Table 1, the "Condition 4, Heat Treatment" column under the "Second Cold Rolling Process" column indicates whether the cold-rolled steel sheet being rolled was heat-treated. "No" indicates that the cold-rolled steel sheet in the unannealed as-rolled state was subjected to the second cold rolling process. "Yes" indicates that the cold-rolled steel sheet was annealed. During annealing, the cold-rolled steel sheet was held at 1100°C for 80 seconds.

[0473] In Table 1, "Reversible" in the "Condition 5, Rolling Method" column of the "Second Cold Rolling Step" column indicates that a reverse rolling step was performed as the second cold rolling step. "Tandem" indicates that a tandem rolling step was performed as the second cold rolling step. "-" indicates that the second cold rolling step was not performed.

[0474] The average diameter D2 (mm) of the work rolls used in each pass is recorded in the "Condition 6, Average Diameter D2 (mm)" column of the "Second Cold Rolling Process" column in Table 1. The cumulative reduction ratio CR2 (%) in the second cold rolling process is recorded in the "Condition 7, Reduction Ratio CR2 (%)" column of the "Second Cold Rolling Process" column in Table 1.

[0475] In the "Condition 8, Roller Diameter Difference (mm)" column in Table 1, "Yes" means that the roll diameter difference between the upper work roll and the lower work roll was 2.0 mm or greater in at least one pass. "No" means that the roll diameter difference was less than 2.0 mm in any pass.

[0476] After the cold rolling process, the cold-rolled steel sheet was subjected to a decarburization annealing process. Specifically, after heating to a final temperature of 870°C, the sheet was held at a decarburization annealing temperature of 830°C for 80 seconds. The cold-rolled steel sheet was then allowed to cool to room temperature, producing a decarburization annealed steel sheet. The average heating rate (HR) from 400°C to 800°C during the heating process is reported in the "Condition 9, Heating Rate (HR) (°C / sec)" column of the "Decarburization Annealing Process" section in Table 1.

[0477] An annealing separator containing MgO as a main component is applied to the surface of the decarburized annealed steel sheet. The decarburized annealed steel sheet coated with the annealing separator is then coiled into a coil.

[0478] The coil is subjected to final annealing to produce a final annealed steel sheet. The final annealing temperature is set to 1100 to 1200° C., and the holding time at the final annealing temperature is set to 5 to 30 hours.

[0479] The steel sheets after the final annealing step were subjected to a secondary film-forming step. Specifically, a secondary film-forming agent composed primarily of colloidal silica and phosphate was applied to the surface of the final annealed steel sheets of each test number. The final annealed steel sheets coated with the secondary film-forming agent were then baked under the same conditions to form a secondary film on top of the primary film. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were produced.

[0480] Furthermore, the chemical composition of the grain-oriented electrical steel sheet for each test number was measured according to the aforementioned "Method for Measuring the Chemical Composition of Grain-Oriented Electrical Steel Sheet 1." The chemical composition of the grain-oriented electrical steel sheet for each test number contained 3.3% Si, 0.08% Mn, less than 0.002% N, 0.002% C, less than 0.001% sol. Al, less than 0.001% S, and 0.002% Ti, with the remainder consisting of Fe and impurities.

[0481] [Evaluation test]

[0482] The following evaluation tests were performed on the produced grain-oriented electrical steel sheets.

[0483] (Test 1) Micro-angle grain boundary ratio R SGB Determination test

[0484] (Test 2) Magnetic flux density measurement test

[0485] (Test 3) Iron Loss Evaluation Test of Grain-Oriented Electrical Steel Sheet Before Magnetic Domain Refinement Treatment

[0486] (Test 4) Iron Loss Evaluation Test of Grain-Oriented Electrical Steel Sheet After Magnetic Domain Refinement Processing Tests 1 to 4 will be described below.

[0487] [(Test 1) Micro-angle grain boundary ratio R SGB Determination test of

[0488] For each test number of the grain-oriented electrical steel sheet, the [micro-angle grain boundary ratio R SGB The obtained La, Ls, and small angle grain boundary ratio R SGBAs shown in the “Ls (mm)” column, “La (mm)” column and “R SGB ” column.

[0489] Table 2

[0490]

[0491] [(Test 2) Magnetic flux density measurement test]

[0492] Test specimens were collected from the center of the width of each grain-oriented electrical steel sheet produced for each test number. The test specimen dimensions were set to 100 mm x 500 mm x sheet thickness. A single-sheet magnetic properties test (SST test) was conducted in accordance with JIS C2556:2015, applying a magnetic field of 800 A / m to the test specimens to determine the magnetic flux density B8 (T). The resulting magnetic flux density B8 is shown in "Magnetic Flux Density B8 (T)" in Table 2.

[0493] [(Test 3) Iron Loss Evaluation Test of Grain-Oriented Electrical Steel Sheet Before Magnetic Domain Refinement Treatment]

[0494] A test piece was collected from the center of the grain-oriented electrical steel sheet with each test number. The test piece dimensions were set to 100 mm x 500 mm x sheet thickness. The iron loss W was calculated using the test piece in accordance with JIS C2556:2015 at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T. 17 / 50 (W / kg). The iron loss W 17 / 50 As shown in Table 2, the iron loss W before magnetic domain refinement 17 / 50 (W / kg)”. If the iron loss W 17 / 50 If the threshold value W0 = -3.571 x B8 + 7.693 or less, it is determined that excellent iron loss can be obtained in the grain-oriented electrical steel sheet before the magnetic domain refining treatment.

[0495] [(Test 4) Iron Loss Evaluation Test of Grain-Oriented Electrical Steel Sheet After Magnetic Domain Refinement Treatment]

[0496] Laser irradiation was used to refine the magnetic domains of the grain-oriented electrical steel sheets for each test number, thereby introducing linear thermal strain into the grain-oriented electrical steel sheets. During the laser irradiation, the irradiation interval was set to 4 mm. Furthermore, the energy density Ua was set to 1.25 mJ / mm. 2 .

[0497] A test piece was collected from the center of the width of a grain-oriented electrical steel sheet after magnetic domain refinement. The test piece dimensions were set to 100 mm x 500 mm x sheet thickness. Using the test piece, the iron loss W was determined at a frequency of 50 Hz and a maximum magnetic flux density of 1.7 T in accordance with JIS C2556:2015.17 / 50 (W / kg). The iron loss W 17 / 50 As shown in Table 2, the iron loss W after magnetic domain refinement 17 / 50 (W / kg)”. If the iron loss W 17 / 50 If the threshold value W1 = -3.500 x B8 + 7.450 or less, it is determined that excellent iron loss can be obtained in the grain-oriented electrical steel sheet after the magnetic domain refining treatment.

[0498] [Evaluation results]

[0499] With reference to Table 1 and Table 2, the grain-oriented electrical steel sheets of Test Nos. 1 to 31 satisfy Characteristics 1 to 3. Therefore, the magnetic flux density B8 is 1.910 T or more, and the iron loss W before the magnetic domain refining treatment is 17 / 50 All of them are below the threshold value W0, and excellent iron loss can be obtained before the magnetic domain refinement treatment. 17 / 50 All of them are below the threshold value W1, and excellent iron loss characteristics can be obtained not only before the magnetic domain refining treatment but also after the magnetic domain refining treatment.

[0500] On the other hand, in test numbers 32 to 46, condition 8 was not satisfied in the manufacturing process. That is, the roll diameter difference between the upper work roll and the lower work roll of the multi-stage rolling mill for reversible rolling was less than 2.0 mm. Therefore, the small angle grain boundary ratio R SGB As a result, the iron loss W before the magnetic domain refinement process is 17 / 50 If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0501] In test number 47, condition 2 was not satisfied in the manufacturing process. Therefore, a sufficient magnetic flux density could not be obtained. SGB Therefore, the iron loss W before magnetic domain refinement is 17 / 50 If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0502] In test number 48, condition 3 was not satisfied in the manufacturing process. Therefore, a sufficient magnetic flux density could not be obtained. SGB Therefore, the iron loss W before the magnetic domain refinement treatment is 17 / 50If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0503] In test number 49, condition 6 was not satisfied in the manufacturing process. Therefore, a sufficient magnetic flux density could not be obtained. SGB Therefore, the iron loss W before the magnetic domain refinement treatment is 17 / 50 If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0504] In test number 50, condition 7 was not satisfied in the manufacturing process. Therefore, a sufficient magnetic flux density could not be obtained. SGB Therefore, the iron loss W before the magnetic domain refinement treatment is 17 / 50 If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0505] In test number 51, condition 4 was not satisfied in the manufacturing process. Therefore, a sufficient magnetic flux density could not be obtained. SGB Therefore, the iron loss W before the magnetic domain refinement treatment is 17 / 50 If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0506] In test number 52, only the reversible rolling process was performed in the cold rolling process. Therefore, sufficient magnetic flux density could not be obtained. SGB Therefore, the iron loss W before the magnetic domain refinement treatment is 17 / 50 If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0507] In test numbers 53 to 56, condition 9 was not satisfied in the manufacturing process. Therefore, a sufficient magnetic flux density could not be obtained. SGB Therefore, the iron loss W before the magnetic domain refinement treatment is 17 / 50 If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0508] Example 2

[0509] In Example 2, grain-oriented electrical steel sheets having the chemical compositions shown in Table 3 (Table 3A and Table 3B) were manufactured.

[0510] Table 3A

[0511]

[0512] Table 3B

[0513]

[0514] The numerical values marked with “<” in Table 3 indicate that the measurement results were lower than the detection limit.

[0515] Specifically, a plurality of steel slabs having different chemical compositions are prepared. The chemical composition of the steel slab is, in mass%, 3.1-3.6% Si, 0.05-0.10% Mn, 0.005-0.010% N, 0.050-0.100% C, 0.015-0.030% sol.Al, 0.015-0.030% of one or more selected from S and Se, 0.015-0.030% in total, 0.001-0.005% Ti, 0.01-0.10% Ni, 0.01-0.10% Cr, 0.01-0.08% Cu, 0.01-0.10% P, 0.01-0.02% Mo, 0.00-0.05% Sn, 0.01-0.25% Sb, 0.00-0.05% Bi, and the remainder Fe and impurities.

[0516] The prepared steel slabs were subjected to a hot rolling process. Specifically, the steel slabs of each test number were heated in a heating furnace to 1340° C. The heated steel slabs were hot rolled to produce hot-rolled steel sheets with a thickness of 2.3 mm.

[0517] After the hot rolling process, the hot-rolled steel sheet was subjected to a hot-rolled sheet annealing process at a temperature of 800-1200°C for a holding time of 10-300 seconds. Following the hot-rolled sheet annealing process, a cold rolling process was performed to produce a cold-rolled steel sheet with a thickness of 0.22 mm. Specifically, the first cold rolling process was followed by a second cold rolling process. Conditions 1 to 8 are shown in Table 4.

[0518] Table 4

[0519]

[0520] After the cold rolling process, the cold-rolled steel sheet was subjected to a decarburization annealing process. Specifically, after heating to an ultimate temperature of 870°C, the sheet was held at a decarburization annealing temperature of 830°C for 80 seconds. The cold-rolled steel sheet was then cooled to room temperature to produce a decarburization annealed steel sheet. The average heating rate (HR) from 400°C to 800°C during the heating process is reported in the "Condition 9, Heating Rate (HR) (°C / sec)" column of the "Decarburization Annealing Process" section in Table 4.

[0521] An annealing separator containing MgO as a main component is applied to the surface of the decarburized annealed steel sheet. The decarburized annealed steel sheet coated with the annealing separator is then coiled into a coil.

[0522] The coil is subjected to final annealing to produce a final annealed steel sheet. The final annealing temperature is set to 1100° C. to 1200° C., and the holding time at the final annealing temperature is set to 5 to 30 hours.

[0523] The steel sheets after the final annealing step were subjected to a secondary film-forming step. Specifically, a secondary film-forming agent composed primarily of colloidal silica and phosphate was applied to the surface of the final annealed steel sheets of each test number. The final annealed steel sheets coated with the secondary film-forming agent were then baked under the same conditions to form a secondary film on top of the underlying film. Through the above manufacturing process, grain-oriented electrical steel sheets of each test number were produced.

[0524] The chemical composition of the grain-oriented electrical steel sheet of each test number was measured according to the above-mentioned [Method for measuring the chemical composition of grain-oriented electrical steel sheet 1]. The chemical composition of the grain-oriented electrical steel sheet of each test number is shown in Table 3 (Table 3A and Table 3B).

[0525] [Evaluation test]

[0526] In the same manner as in Example 1, the small angle grain boundary ratio R SGBThe results are shown in Table 5.

[0527] Table 5

[0528]

[0529] Referring to Tables 3 to 5, the grain-oriented electrical steel sheets of Test Nos. 1 and 2 satisfy Characteristics 1 to 3. Therefore, the magnetic flux density B8 is 1.910 T or more, and the iron loss W before the magnetic domain refining treatment is 17 / 50 All of them are below the threshold value W0, and excellent iron loss can be obtained before the magnetic domain refinement treatment. 17 / 50 All of them are below the threshold value W1, and excellent iron loss characteristics can be obtained not only before the magnetic domain refining treatment but also after the magnetic domain refining treatment.

[0530] On the other hand, in test numbers 3 and 4, condition 8 was not satisfied in the manufacturing process. Therefore, the small angle grain boundary ratio R SGB As a result, the iron loss W before the magnetic domain refinement treatment is 17 / 50 If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0531] In test numbers 5 to 12, none of conditions 1 to 7 and condition 9 were satisfied. Therefore, a sufficient magnetic flux density could not be obtained. SGB Therefore, the iron loss W before magnetic domain refinement is 17 / 50 If the threshold W0 is exceeded, sufficient iron loss cannot be obtained before the magnetic domain refinement process. 17 / 50 If the threshold value W1 is exceeded, sufficient iron loss characteristics cannot be obtained not only before the magnetic domain refining process but also after the magnetic domain refining process.

[0532] Example 3

[0533] In Example 3, grain-oriented electrical steel sheets having the chemical compositions shown in Table 6 (Table 6A and Table 6B) were manufactured.

[0534] Table 6A

[0535]

[0536] Table 6B

[0537]

[0538] Steel slabs of each test number were prepared and subjected to a hot rolling process. Specifically, the steel slabs of each test number were heated in a heating furnace to 1340° C. The heated steel slabs were hot rolled to produce hot-rolled steel sheets with a thickness of 2.3 mm.

[0539] The hot-rolled steel sheet after the hot rolling step is subjected to a hot-rolled sheet annealing step at a hot-rolled sheet annealing temperature of 800 to 1200° C. for a holding time of 10 to 300 seconds.

[0540] After the hot-rolled sheet annealing process, a cold rolling process is performed to produce a cold-rolled steel sheet with a thickness of 0.22 mm. Specifically, the hot-rolled steel sheet is first subjected to a tandem rolling process to produce an intermediate steel sheet. The average diameter D1 of the working rolls in the tandem rolling process is 450 mm, and the cumulative reduction ratio CR1 is 65%. The intermediate steel sheet is not subjected to heat treatment, but is subjected to a reversible rolling process. The average diameter of the working rolls in the reversible rolling process is 75 mm, and the cumulative reduction ratio CR2 is 73%. Furthermore, the difference in roll diameter between the upper and lower working rolls of the reversible rolling mill is at least 2.0 mm. Through the above processes, a cold-rolled steel sheet with a thickness of 0.22 mm is produced.

[0541] After the cold rolling process, the cold-rolled steel sheet undergoes a decarburization annealing process. Specifically, after heating to a final temperature of 870°C, the sheet is held at a decarburization annealing temperature of 830°C for 80 seconds. The cold-rolled steel sheet is then cooled to room temperature to produce a decarburization annealed steel sheet. During the heating process, the average heating rate (HR) from 400°C to 800°C is 800°C / second.

[0542] An annealing separator containing MgO as a main component is applied to the surface of the decarburized annealed steel sheet. The decarburized annealed steel sheet coated with the annealing separator is then coiled into a coil.

[0543] The coil is subjected to final annealing to produce a final annealed steel sheet. The final annealing temperature in the final annealing is set to 1100° C. to 1200° C., and the holding time at the final annealing temperature is set to 5 to 30 hours.

[0544] The steel sheets after the final annealing process were subjected to a secondary film forming process. Specifically, a secondary film forming agent consisting mainly of colloidal silica and phosphate was applied to the surface of the final annealed steel sheets of each test number. Then, the final annealed steel sheets coated with the secondary film forming agent were baked under the same conditions to form a secondary film on the primary film. Through the above manufacturing process, grain-oriented electromagnetic steel sheets of each test number were manufactured. In addition, the chemical composition of the grain-oriented electromagnetic steel sheets of each test number was measured based on the above-mentioned [Method for Determining the Chemical Composition of Grain-Oriented Electromagnetic Steel Sheet 1]. As a result, the chemical composition of the grain-oriented electromagnetic steel sheets of each test number is shown in Table 6 (Table 6A and Table 6B).

[0545] [Evaluation test]

[0546] In the same manner as in Example 1, the small angle grain boundary ratio R SGB The results are shown in Table 7.

[0547] Table 7

[0548]

[0549] [Test results]

[0550] With reference to Tables 6 and 7, all of the grain-oriented electrical steel sheets in Test Nos. 1 to 35 satisfy Characteristics 1 to 3. Therefore, the magnetic flux density B8 is 1.910 T or more, and the iron loss W before the magnetic domain refining treatment is 17 / 50 All of them are below the threshold value W0, and excellent iron loss can be obtained before the magnetic domain refinement treatment. 17 / 50 All of them are below the threshold value W1, and excellent iron loss can be obtained not only before the magnetic domain refining treatment but also after the magnetic domain refining treatment.

[0551] The embodiments of the present disclosure have been described above. However, the above embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above embodiments and can be implemented by appropriately modifying the above embodiments without departing from the scope of the present disclosure.

[0552] Explanation of symbols:

[0553] 10 base steel plate

[0554] 11 Lower covering film

[0555] 12 Secondary covering film

Claims

1. A grain-oriented electromagnetic steel sheet, wherein: The grain-oriented electromagnetic steel sheet comprises a base steel sheet, The chemical composition of the base steel plate is calculated by mass %. Si: 2.5-4.5%, Mn: 0.01~1.00%, N：0～0.010％、 C：0～0.010％、 sol.Al: 0~0.010%, One or more selected from S and Se: 0 to 0.010% in total, Ti: more than 0% and less than 0.010%, Ni: 0-1.00%, Cr：0～1.00％、 Cu: 0-1.00%, P：0～0.50％、 Mo: 0~0.10%, Sn: 0-0.50%, Sb: 0-0.50%, Bi: 0 to 0.0500%, and The rest is composed of Fe and impurities. On the surface of the grain-oriented electromagnetic steel sheet, the crystal orientation is measured by X-ray diffraction at measurement points arranged at intervals of 2 mm in a first direction and a second direction perpendicular to the first direction, thereby determining the orientation difference of grain boundaries of the grains. The total length of the grain boundaries of the grains is defined as La, and the total length of the grain boundaries having an orientation difference of 1 to 5° is defined as Ls. When formula (1) is satisfied, The magnetic flux density B8 is above 1.910T. Ls / La≥0.140 (1).

2. The grain-oriented electromagnetic steel sheet according to claim 1, wherein The chemical composition is expressed in mass %, and contains Ni: 0.01~1.00%, Cr：0.01～1.00％、 Cu: 0.01-1.00%, P：0.01～0.50％、 Mo: 0.01~0.10%, Sn: 0.01~0.50%, Sb: 0.01 to 0.50%, and Bi: one or more kinds of Bi in the range of 0.0001 to 0.0500%.

3. The grain-oriented electromagnetic steel sheet according to claim 1 or 2, wherein Furthermore, a plurality of linear thermal strains or grooves extending linearly and arranged in a direction perpendicular to the extending direction are formed on the surface of the grain-oriented electrical steel sheet.

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