Manufacturing method of grain-oriented electrical steel sheet

Abstract

To provide a method for manufacturing a grain oriented electrical steel sheet having a high magnetic flux density, capable of suppressing the formation of defective structure and ear cracking in an end portion in a sheet width direction.SOLUTION: A method for manufacturing a grain oriented electrical steel sheet includes: a hot-rolling step (S1) of setting an accumulative rolling reduction rate in a rough rolling step to less than 75%, setting a rolling reduction rate in the final rolling reduction in the rough rolling step to less than 50%, setting the temperature of a rough bar right after the final rolling reduction to 1,350°C or more, wherein intermediate time t1 from the completion of the final reduction against a back end of the slab in the rough rolling step to the completion of the first reduction against a back end of the rough bar in a finish rolling step is set to 150 seconds or less to satisfy the equation (1):-0.033 t1+44+2000[Bi]≤[Si] / [C]≤-0.033 t1+52+2000[Bi]; and a decarbonization annealing step (S4) of heating a steel sheet at the average temperature-rising rate of 800°C / sec or more until the temperature of the steel sheet reaches 550-800°C.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Grain-oriented electrical steel sheets contain approximately 0.5 to 7% Si by mass and have a crystal orientation of {110} <001> It is a steel sheet with grains assembled in a specific orientation (Goss orientation). Grain-oriented electrical steel is used as a soft magnetic material in the iron cores of transformers and other electrical equipment. The crystal orientation of grain-oriented electrical steel is controlled by a catastrophic grain growth phenomenon called secondary recrystallization.

[0003] The method for manufacturing grain-oriented electrical steel sheet is as follows: A slab is heated and hot-rolled to produce a hot-rolled steel sheet; The produced hot-rolled steel sheet is annealed; The hot-rolled steel sheet is pickled as necessary; The hot-rolled steel sheet is cold-rolled at a cold reduction rate of 80% or more to produce a cold-rolled steel sheet; The cold-rolled steel sheet is decarburization annealed to induce primary recrystallization; The cold-rolled steel sheet after decarburization annealing is finish annealed to induce secondary recrystallization. Grain-oriented electrical steel sheet is manufactured through the above steps.

[0004] Grain-oriented electrical steel sheets are required to have magnetic properties. Specifically, they are required to have excellent excitation properties and excellent iron loss. For example, the magnetic flux density B8 at a magnetic field strength of 800 A / m is used as an index of excitation properties. The iron loss W17 / 50 when magnetized to 1.7 T at 50 Hz is used as an index of iron loss.

[0005] One known method for increasing the magnetic flux density is to increase the concentration of Goss orientation. The degree of concentration of Goss orientation depends on the quality of secondary recrystallization during the final annealing process. To achieve excellent secondary recrystallization, it is important to develop precipitates (inhibitors) before the final annealing process, which induces secondary recrystallization. By uniformly dispersing fine inhibitors in the steel sheet, it is possible to suppress the growth of crystal orientations other than the Goss orientation that are inferior in magnetic properties during secondary recrystallization.

[0006] When MnS, MnSe, and AlN are used as inhibitors in the production of grain-oriented electrical steel sheets, slabs containing coarse MnS, MnSe, and AlN produced in the steelmaking process are heated to 1300°C or higher before hot rolling to completely dissolve MnS, MnSe, and AlN. Then, in the annealing process of the hot-rolled steel sheet produced by hot-rolling the heated slab, the precipitation of these inhibitors is controlled and finely dispersed, thereby controlling the growth of secondary recrystallization.

[0007] Methods for controlling the growth of secondary recrystallization have been proposed in JP 4-124218 A (Patent Document 1), JP 6-192736 A (Patent Document 2), JP 9-104924 A (Patent Document 3), and WO 2013 / 145784 (Patent Document 4).

[0008] Patent Document 1 aims to achieve both a refined structure of a hot-rolled steel sheet and fine, uniform precipitation of inhibitors. Patent Document 1 is characterized in that the final pass of rough rolling in the hot rolling process is performed under conditions where the temperature from the outermost layer of the steel sheet to a depth of 1 / 5 of the sheet thickness is in the range of 1200 to 1250°C and a rolling reduction of 50% or more. However, in the case of Patent Document 1, the rolling reduction of the final pass of rough rolling is 50% or more, so there is a possibility that coarse MnS and MnSe precipitate due to the strain introduced during rough rolling between the end of rough rolling and the start of finish rolling. In this case, secondary recrystallization in the finish annealing process tends to become unstable, resulting in the occurrence of defective secondary recrystallization regions at both ends of the grain-oriented electrical steel sheet in the sheet width direction, where Goss-oriented grains have not fully grown. The grains in the defective secondary recrystallization regions are much finer than those in the normal regions and are composed of grains that are not Goss-oriented. Hereinafter, such defective secondary recrystallization regions occurring at the ends in the sheet width direction of grain-oriented electrical steel sheets will be referred to as "defective structures."

[0009] Like Patent Document 1, Patent Document 2 also aims to achieve both finer microstructure refinement in hot-rolled steel sheets and finer, more uniform precipitation of inhibitors. Patent Document 2 features the following: the end temperature of the final pass of rough rolling in the hot rolling process is 1200°C or higher; the time from the end of rough rolling to the finish rolling exit side is 150 seconds or less; the finish rolling exit side temperature is 1000°C or lower; and the steel sheet is annealed before final cold rolling to reduce the carbon content in the surface layer. However, Patent Document 2 also aims to refine the microstructure of hot-rolled steel sheets by setting the exit side temperature of the final pass of rough rolling to less than 1300°C. Therefore, between the end of rough rolling and the start of finish rolling, coarse MnS and MnSe may precipitate due to the strain introduced in the rough rolling process. As a result, defective microstructures are likely to be generated in grain-oriented electrical steel sheets.

[0010] Like Patent Documents 1 and 2, Patent Document 3 also aims to achieve both finer structure in hot-rolled steel sheets and finer, uniform precipitation of inhibitors. Patent Document 3 is characterized in that the cumulative reduction rate in rough rolling is set to 75% or more, and rough rolling is completed within a time period appropriate for the slab heating temperature. However, Patent Document 3 sets the cumulative reduction rate in rough rolling to 75% or more in order to refine the structure in hot-rolled steel sheets. Therefore, between the end of rough rolling and the start of finish rolling, coarse MnS and MnSe may precipitate due to strain introduced in the rough rolling process. If coarse MnS and MnSe are generated, secondary recrystallization in the finish rolling process becomes unstable. Therefore, defective structures are likely to be generated in grain-oriented electrical steel sheets.

[0011] Like Patent Documents 1 to 3, Patent Document 4 also aims to achieve both finer microstructures in hot-rolled steel sheets and finer, uniform precipitation of inhibitors. Patent Document 4 is characterized in that the first pass of rough rolling is performed at a temperature corresponding to the Si, C, and Ni contents at a rate of 30% or more at which the α single phase appears, and then at least one pass in the finish rolling process is performed at a temperature at which the γ phase is maximized. However, in Patent Document 4, rolling is performed at a high reduction rate in the rough rolling process in order to refine the microstructure of the hot-rolled steel sheet. Therefore, between the end of rough rolling and the start of finish rolling, coarse MnS and MnSe may precipitate due to the strain introduced in the rough rolling process. If coarse MnS and MnSe are formed, secondary recrystallization in the finish rolling process becomes unstable. Therefore, grain-oriented electrical steel sheets are prone to develop defective microstructures. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Publication No. 4-124218 [Patent Document 2] Japanese Patent Application Publication No. 6-192736 [Patent Document 3] Japanese Patent Application Publication No. 9-104924 [Patent Document 4] International Publication No. 2013 / 145784 Summary of the Invention [Problem to be solved by the invention]

[0013] When defective structures occur at the edges of grain-oriented electrical steel sheets in the sheet width direction, the edges where the defective structures exist do not have sufficient magnetic properties. Therefore, it is necessary to cut off the edges of the grain-oriented electrical steel sheets that have the defective structures, which reduces the product yield. Therefore, it is preferable to suppress the formation of defective structures while maintaining sufficient magnetic properties (magnetic flux density and iron loss) of the grain-oriented electrical steel sheets.

[0014] Furthermore, in the hot rolling process, cracks may occur in the width direction of the hot-rolled steel sheet at its widthwise edges. Hereinafter, cracks extending in the width direction at the widthwise edges of the hot-rolled steel sheet are referred to as "edge cracks." When edge cracks occur, the edges must be cut off, which reduces product yield. Therefore, there is a need for a method for manufacturing grain-oriented electrical steel sheet that can suppress defective structures and edge cracks at the widthwise edges while maintaining sufficient magnetic properties (magnetic flux density and iron loss) required for grain-oriented electrical steel sheet.

[0015] An object of the present disclosure is to provide a method for manufacturing a grain-oriented electrical steel sheet that can obtain sufficient magnetic properties and can suppress defective structures and edge cracks at the ends in the sheet width direction. [Means for solving the problem]

[0016] The method for producing a grain-oriented electrical steel sheet according to the present disclosure includes: The chemical composition is, in mass%, C: 0.060~0.100%, Si: 3.00-4.00%, Mn: 0.01 to 0.30%, S and / or Se: 0.010 to 0.050% in total, sol.Al: 0.01~0.05%, N: 0.002 to 0.015%, Bi: 0 to 0.0100%, Sn: 0 to 0.50% Cr: 0~0.50%, Cu: 0 to 0.50%, and a hot rolling step of hot rolling a slab containing the remainder Fe and impurities to produce a steel plate; a cold rolling step in which the steel sheet after the hot rolling step is subjected to one or more cold rolling processes; A final pre-cold rolling annealing step in which annealing treatment is performed on the steel sheet before final cold rolling among one or more of the cold rolling steps; a decarburization annealing step of heating the steel sheet after the cold rolling step to a decarburization annealing temperature of 800 to 950°C and holding the steel sheet at the decarburization annealing temperature; an annealing separator application step of applying an annealing separator to the surface of the steel sheet after the decarburization annealing step; a final annealing step of performing final annealing on the steel sheet to which the annealing separator has been applied, The hot rolling step includes: a rough rolling step of performing rough rolling on the slab to produce a rough bar; a finish rolling step of performing finish rolling on the rough bar to produce the steel plate; In the rough rolling step, The slab is subjected to multiple reductions; The cumulative rolling reduction in the rough rolling step is less than 75%, The rolling reduction rate in the final rolling step is less than 50%, The temperature of the rough bar immediately after the final reduction in the rough rolling step is 1350°C or higher; When the time from the completion of the final rolling down of the rear end of the slab in the rough rolling process to the completion of the first rolling down of the rear end of the rough bar in the finish rolling process is defined as an intermediate time t1, the intermediate time t1 is set to 150 seconds or less and satisfies formula (1), In the decarburization annealing step, The steel plate is heated at an average temperature rising rate of 800°C / second or more until the temperature of the steel plate reaches from 550°C to 800°C. -0.033t1+44+2000[Bi]≦[Si] / [C]≦-0.033t1+52+2000[Bi] (1) In the formula (1), [Bi] is substituted with the Bi content (mass%) in the chemical composition of the slab, [Si] is substituted with the Si content (mass%) in the chemical composition of the slab, [C] is substituted with the C content (mass%) in the chemical composition of the slab, and t1 is substituted with the intermediate time t1 (seconds). If Bi is not contained, [Bi] is substituted with 0. [Effects of the Invention]

[0017] The manufacturing method of grain-oriented electrical steel sheet according to the present disclosure can obtain sufficient magnetic properties and can suppress defective structures and edge cracks at the ends in the sheet width direction. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing the relationship between the temperature (° C.) of a slab having the chemical composition of this embodiment and the volume fraction of austenite (%). [Figure 2] FIG. 2 is a schematic diagram for explaining the occurrence of edge cracks in the hot rolling process. [Figure 3] FIG. 3 is a flow diagram showing the manufacturing steps of the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment. [Figure 4] FIG. 4 is a schematic diagram showing a hot rolling equipment line for carrying out the hot rolling step in FIG. [Figure 5] FIG. 5 is a schematic diagram showing a hot rolling equipment line different from that shown in FIG. [Figure 6] FIG. 6 is a flow diagram showing the details of the hot rolling step in FIG. [Figure 7] FIG. 7 is a schematic diagram showing a cold rolling equipment line for carrying out the cold rolling step in FIG. [Figure 8] FIG. 8 is a schematic diagram showing a heat pattern in the decarburization annealing step in FIG. [Figure 9] FIG. 9 is a schematic diagram showing the shape of a sample used in the defective structure depth measurement test in the examples. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present inventors have investigated and examined the cause of coarsening of MnS and MnSe (hereinafter, MnS and MnSe are also referred to as Mn inhibitors). Specifically, they investigated the cause of the generation of coarse Mn inhibitors with a major axis length of 1 μm or more in a hot-rolled steel sheet when a grain-oriented electrical steel sheet is produced from a slab having a chemical composition, in mass%, of C: 0.060-0.100%, Si: 3.00-4.00%, Mn: 0.01-0.30%, S and / or Se: 0.010-0.050% in total, sol. Al: 0.01-0.05%, N: 0.002-0.015%, Bi: 0-0.0100%, Sn: 0-0.50%, Cr: 0-0.50%, Cu: 0-0.50%, and the balance being Fe and impurities. As a result, it was found that the precipitation and growth of Mn inhibitors are particularly affected by four conditions in the hot rolling process: the cumulative reduction rate TR in the rough rolling process (condition A), the reduction rate R1 in the final reduction in the rough rolling process (condition B), the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process (condition C), and the time (intermediate time) t1 from the completion of the final reduction in the rear end of the slab in the rough rolling process to the completion of the first reduction in the rear end of the rough bar in the finish rolling process (condition D).

[0020] Based on the above findings, attempts were made to manufacture grain-oriented electrical steel sheets using slabs with the above-mentioned chemical compositions under various conditions A to D. As a result, it was found that by satisfying the following conditions, the occurrence of defective structures at the edges in the sheet width direction of the grain-oriented electrical steel sheets can be significantly suppressed. (Condition A) Cumulative reduction rate TR in the rough rolling process: Less than 75% (Condition B) Final reduction rate R1 in the rough rolling process: Less than 50% (Condition C) Temperature of the rough bar immediately after the final reduction in the rough rolling process T1: 1350°C or higher (Condition D) The time (intermediate time) t1 between the completion of the final reduction of the rear end of the slab in the rough rolling process and the completion of the first reduction of the rear end of the rough bar in the finish rolling process: 150 seconds or less

[0021] However, it was found that when grain-oriented electrical steel sheets are manufactured by carrying out a hot rolling process that satisfies the above-mentioned conditions A to D, although the occurrence of defective structures can be significantly suppressed, the magnetic flux density may deteriorate. Therefore, in order to investigate the cause of the deterioration of magnetic flux density, the microstructure of the grain-oriented electrical steel sheets was investigated. As a result, a linear defective region extending in the rolling direction (hereinafter referred to as the linear defective region) was found to have occurred in the center position in the sheet width direction of the grain-oriented electrical steel sheets. As a result of investigating the cause of the occurrence of this linear defective region, the following reasons were considered.

[0022] When the hot rolling process is carried out under the conditions that satisfy the above-mentioned conditions A to D, α-fiber orientation groups extending in the rolling direction may develop at the center position of the width of the hot rolled steel sheet. <110> This refers to a group of crystal grains whose axes are aligned in the rolling direction. The α-fiber orientations generated during the hot rolling process are stable orientations during rolling and remain in the steel sheet after the cold rolling process. These α-fiber orientations deteriorate the primary recrystallization structure and suppress the selective growth of the Goss orientation during secondary recrystallization in the finish annealing process. As a result, the α-fiber orientations remain in the grain-oriented electrical steel sheet as linear defective regions, reducing the degree of integration into the Goss orientation and degrading the magnetic properties (magnetic flux density).

[0023] Therefore, the present inventors further investigated a manufacturing method that can suppress the generation and development of α-fiber orientation groups even when the above-mentioned conditions A to D are implemented. As a result, in the decarburization annealing process after the cold rolling process, the average heating rate RR between 550°C and 800°C was 550-800 They found that if the decarburization annealing process is performed significantly faster than conventional processes, it is possible to promote recrystallization from the α-fiber orientation groups even if they are generated in the hot-rolled steel sheet, and as a result, it is possible to suppress the occurrence of linear defect regions and obtain high magnetic properties. Specifically, they found that excellent magnetic flux density can be obtained by satisfying the following condition F in the decarburization annealing process. (Condition F) Average heating rate RR in the decarburization annealing process 550-800 : 800℃ / sec or more

[0024] The reason for this is unclear, but the following is thought to be the reason. By increasing the temperature rise rate from 550 to 800°C during the decarburization annealing process, recrystallization from the α-fiber orientation group can be promoted in the primary recrystallization, and the Σ9 corresponding orientation ({411} <148> The Σ9 orientation grains increase the selective growth of Goss orientation grains. This increases the concentration of Goss orientation grains during secondary recrystallization, suppressing linear defect regions. As a result, it is believed that excellent magnetic properties can be obtained.

[0025] The present inventors further investigated the cause of edge cracks occurring in steel sheets during the hot rolling process, and as a result, obtained the following findings.

[0026] FIG. 1 is a diagram showing the relationship between the temperature (°C) of steel having the above-mentioned chemical composition and the volume fraction (%) of austenite. When a hot working process is performed on a slab having the above-mentioned chemical composition, the slab is first heated to 1300 to 1400°C. Referring to FIG. 1, the microstructure of the slab is essentially a single phase of ferrite. However, when rough rolling and finish rolling are performed in the hot rolling process, the temperature of the slab gradually decreases. The temperature of the slab at the start of finish rolling, particularly the temperature at the edges, can be about 1200°C. When the temperature of the slab decreases to 1200°C, the austenite content in the microstructure of the slab can increase to about 40% by volume. In other words, the finish rolling process involves rolling in a two-phase region (ferrite and austenite).

[0027] FIG. 2 is a schematic diagram illustrating the occurrence of edge cracks during the hot rolling process. Referring to FIG. 2, during the hot rolling process, the microstructure of a slab transforms from a single ferrite phase to a two-phase (ferrite + austenite). The solid solubility of S and Se in austenite is lower than that in ferrite. Therefore, when austenite is formed by transformation accompanied by a decrease in temperature, as shown in FIG. 2, S and Se in austenite 2 are expelled from the austenite grains to the interface between austenite 2 and ferrite 1. As a result, fine Mn inhibitors 3 (MnS and MnSe) are formed at the interface between austenite 2 and ferrite 1. The fine Mn inhibitors 3 formed at the interface between austenite 2 and ferrite 1 act as stress concentration sources and as initiation points for voids 4 at the interface between austenite 2 and ferrite 1. It is believed that the growth and coalescence of the generated voids 4 leads to edge cracks.

[0028] Based on the above findings, the inventors have considered that controlling the interfacial area between ferrite and austenite during finish rolling by the precipitation frequency of fine Mn inhibitors is effective in suppressing edge cracks. Specifically, in order to control the interfacial area between ferrite and austenite during finish rolling, the ratio of Si, an element that strongly stabilizes ferrite (a ferrite former), to C, an element that strongly stabilizes austenite (an austenite former) (=[Si] / [C]) is adjusted according to the rough rolling conditions, which correlate with the precipitation frequency of fine Mn inhibitors, particularly the intermediate time t1 between rough rolling and finish rolling, and thus edge cracks can be suppressed.

[0029] Furthermore, when the slab contains Bi, the Bi in the slab also increases the frequency of precipitation of fine Mn inhibitors. In other words, Bi is an element that promotes edge cracking. Therefore, we thought that edge cracking could be further suppressed by adjusting the [Si] / [C] ratio according to the Bi content along with the intermediate time t1.

[0030] Based on the above findings, the present inventors conducted research and investigation into the relationship between the Si content, C content, and Bi content of the slab and the occurrence of edge cracks, focusing on the intermediate time t1. As a result, they found that if the following condition E is satisfied in the hot rolling process, excellent magnetic properties can be obtained, and it is possible to suppress the occurrence of defective structures and edge cracks, provided that conditions A to D and F are also satisfied. (Condition E) Formula (1) is satisfied in the hot rolling process. -0.033t1+44+2000[Bi]≦[Si] / [C]≦-0.033t1+52+2000[Bi] (1) Here, in formula (1), [Bi] is the Bi content (mass%) in the chemical composition of the slab, [Si] is the Si content (mass%) in the chemical composition of the slab, [C] is the C content (mass%) in the chemical composition of the slab, and t1 is the intermediate time t1 (seconds). If Bi is not contained, [Bi] is substituted with 0.

[0031] As described above, the inventors have discovered that by using a slab having the above-mentioned chemical composition and carrying out a manufacturing process that satisfies conditions A to F, it is possible to manufacture a grain-oriented electrical steel sheet that has excellent magnetic properties and is capable of suppressing defective structures and edge cracks. (Condition A) Cumulative reduction rate in rough rolling process: Less than 75% (Condition B) Final reduction in the rough rolling process: Less than 50% (Condition C) Temperature of the rough bar immediately after the final reduction in the rough rolling process: 1350°C or higher (Condition D) The intermediate time t1 between the completion of the final rolling of the rear end of the slab in the rough rolling process and the completion of the first rolling of the rear end of the rough bar in the finish rolling process: 150 seconds or less (Condition E) Formula (1) is satisfied in the hot rolling process. -0.033t1+44+2000[Bi]≦[Si] / [C]≦-0.033t1+52+2000[Bi] (1) (Condition F) Average heating rate RR in the decarburization annealing process 550-800 : 800℃ / sec or more

[0032] The method for manufacturing a grain-oriented electrical steel sheet according to this embodiment, which was completed based on the above findings, is summarized as follows.

[0033] [1] The chemical composition is, in mass%, C: 0.060~0.100%, Si: 3.00-4.00%, Mn: 0.01 to 0.30%, S and / or Se: 0.010 to 0.050% in total, sol.Al: 0.01~0.05%, N: 0.002 to 0.015%, Bi: 0 to 0.0100%, Sn: 0 to 0.50% Cr: 0~0.50%, Cu: 0 to 0.50%, and a hot rolling step of hot rolling a slab containing the remainder Fe and impurities to produce a steel plate; a cold rolling step in which the steel sheet after the hot rolling step is subjected to one or more cold rolling processes; A final pre-cold rolling annealing step in which annealing treatment is performed on the steel sheet before final cold rolling among one or more of the cold rolling steps; a decarburization annealing step of heating the steel sheet after the cold rolling step to a decarburization annealing temperature of 800 to 950°C and holding the steel sheet at the decarburization annealing temperature; an annealing separator application step of applying an annealing separator to the surface of the steel sheet after the decarburization annealing step; a final annealing step of performing final annealing on the steel sheet to which the annealing separator has been applied, The hot rolling step includes: a rough rolling step of performing rough rolling on the slab to produce a rough bar; a finish rolling step of performing finish rolling on the rough bar to produce the steel plate; In the rough rolling step, The slab is subjected to multiple reductions; The cumulative rolling reduction in the rough rolling step is less than 75%, The rolling reduction rate in the final rolling step is less than 50%, The temperature of the rough bar immediately after the final reduction in the rough rolling step is 1350°C or higher; When the time from the completion of the final rolling down of the rear end of the slab in the rough rolling process to the completion of the first rolling down of the rear end of the rough bar in the finish rolling process is defined as an intermediate time t1, the intermediate time t1 is set to 150 seconds or less and satisfies formula (1), In the decarburization annealing step, Heating the steel plate at an average heating rate of 800°C / second or more until the temperature of the steel plate reaches from 550°C to 800°C. Manufacturing method for grain-oriented electrical steel sheets. -0.033t1+44+2000[Bi]≦[Si] / [C]≦-0.033t1+52+2000[Bi] (1) In the formula (1), [Bi] is substituted with the Bi content (mass%) in the chemical composition of the slab, [Si] is substituted with the Si content (mass%) in the chemical composition of the slab, [C] is substituted with the C content (mass%) in the chemical composition of the slab, and t1 is substituted with the intermediate time t1 (seconds). If Bi is not contained, [Bi] is substituted with 0.

[0034] [2] A method for producing the grain-oriented electrical steel sheet according to [1], The chemical composition of the slab is: Bi: 0.0001 to 0.0100%, containing Manufacturing method for grain-oriented electrical steel sheets.

[0035] [3] A method for producing a grain-oriented electrical steel sheet according to [1] or [2], The chemical composition of the slab is: Sn: 0.01 to 0.50% Cr: 0.01 to 0.50%, and Cu: 0.01 to 0.50% Contains one or more selected from the group consisting of Manufacturing method for grain-oriented electrical steel sheets.

[0036] The method for producing a grain-oriented electrical steel sheet according to this embodiment will be described in detail below. In this specification, % regarding the content of an element means % by mass unless otherwise specified.

[0037] [Manufacturing process flow] Fig. 3 is a flow diagram of a method for manufacturing a grain-oriented electrical steel sheet according to this embodiment. Referring to Fig. 3, this manufacturing method includes a hot rolling step (S1) in which a slab is hot-rolled to manufacture a steel sheet, a cold rolling step (S2) in which the steel sheet (hot-rolled steel sheet) after the hot rolling step is subjected to one or more cold rolling steps (S20), a pre-final cold rolling annealing step (S3) in which the steel sheet before the final cold rolling step (S20) among the one or more cold rolling steps (S20) is annealed, a decarburization annealing step (S4) in which decarburization annealing is performed on the steel sheet (cold-rolled steel sheet) after the cold rolling step (S2), an annealing separator application step (S5) in which an annealing separator is applied to the surface of the steel sheet after the decarburization annealing step (S4), and a final annealing step (S6) in which the steel sheet to which the annealing separator has been applied is subjected to final annealing. Each of steps S1 to S6 will be described below.

[0038] [Hot rolling process (S1)] In the hot rolling step (S1), the prepared slab is hot rolled to produce a steel sheet. The chemical composition of the slab contains the following elements:

[0039] [Essential elements in the chemical composition of the slab] C: 0.060 to 0.100% Carbon (C) is effective for controlling the structure until the completion of the decarburization annealing step during the manufacturing process. If the C content is less than 0.060%, the above effect cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the C content exceeds 0.100%, and the contents of other elements are within the ranges of this embodiment, even if the decarburization annealing step described below is performed, decarburization will be insufficient, causing magnetic aging, and in this case, sufficient iron loss characteristics will not be obtained. Therefore, the C content is 0.060 to 0.100%. The lower limit of the C content is preferably 0.065%, and more preferably 0.070%. The upper limit of the C content is preferably 0.090%, and more preferably 0.080%.

[0040] Si: 3.00 to 4.00% Silicon (Si) increases the resistivity of grain-oriented electrical steel sheets and reduces eddy current loss, which is one of the iron losses. If the Si content is less than 3.00%, the above effects cannot be sufficiently obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the Si content exceeds 4.00%, the cold workability of the steel will decrease even if the contents of other elements are within the ranges of this embodiment. Therefore, the Si content is 3.00 to 4.00%. The lower limit of the Si content is preferably 3.10%, more preferably 3.20%, and even more preferably 3.30%. The upper limit of the Si content is preferably 3.90%, more preferably 3.80%, and even more preferably 3.70%.

[0041] Mn: 0.01 to 0.30% Manganese (Mn) increases the resistivity of grain-oriented electrical steel sheets and reduces iron loss. Mn also improves hot workability and suppresses cracking during hot rolling. Mn further combines with S and / or Se to form fine MnS and / or fine MnSe during the hot rolling process. The fine MnS and fine MnSe act as precipitation nuclei for fine AlN, which acts as an inhibitor. Therefore, if the amount of fine MnS and fine MnSe precipitated during the hot rolling process is large, a sufficient amount of fine AlN can be obtained in the subsequent annealing process before final cold rolling. If the Mn content is less than 0.01%, the above effects cannot be sufficiently obtained. On the other hand, if the Mn content exceeds 0.30%, the magnetic flux density of the grain-oriented electrical steel sheet decreases even if the contents of other elements are within the ranges of this embodiment. Therefore, the Mn content is 0.01 to 0.30%. The lower limit of the Mn content is preferably 0.02%, and more preferably 0.03%. The upper limit of the Mn content is preferably 0.20%, and more preferably 0.15%.

[0042] S and / or Se: 0.010 to 0.050% in total During the hot rolling process, sulfur (S) and selenium (Se) combine with Mn to form the above-mentioned fine MnS and / or fine MnSe. As described above, the fine MnS and fine MnSe serve as precipitation nuclei for fine AlN, which are utilized as inhibitors. Therefore, if the amount of fine MnS and fine MnSe precipitated in the hot rolling process is large, a sufficient amount of fine AlN can be obtained. If the total content of S and / or Se is less than 0.010%, the above-mentioned effects cannot be sufficiently obtained, even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the total content of S and / or Se exceeds 0.050%, even if the contents of other elements are within the ranges of this embodiment, MnS and / or MnSe may remain in the steel sheet after the final annealing process, resulting in a deterioration in magnetic properties. Therefore, the total content of S and / or Se is 0.010 to 0.050%. The lower limit of the total content of S and / or Se is preferably 0.012%, and more preferably 0.014%. The upper limit of the total content of S and / or Se is preferably 0.040%, and more preferably 0.030%.

[0043] sol.Al: 0.01-0.05% Aluminum (Al) bonds with N to form AlN during the manufacturing process of grain-oriented electrical steel sheet, and functions as an inhibitor. If the sol. Al content is less than 0.01%, a sufficient amount of AlN to function as an inhibitor cannot be obtained even if the contents of other elements are within the ranges of this embodiment. On the other hand, if the sol. Al content exceeds 0.05%, even if the contents of other elements are within the ranges of this embodiment, the inhibitor function becomes excessive, and good secondary recrystallization does not occur. Therefore, the sol. Al content is 0.01 to 0.05%. The lower limit of the sol. Al content is preferably 0.02%, and the upper limit of the sol. Al content is preferably 0.04%. In this specification, the sol. Al content means the content of acid-soluble Al.

[0044] N: 0.002 to 0.015% Nitrogen (N) combines with Al to form AlN during the manufacturing process of grain-oriented electrical steel sheets, acting as an inhibitor. To limit the N content to less than 0.002%, excessive refining is required in the steelmaking process, which increases manufacturing costs. Therefore, the lower limit of the N content is 0.002%. On the other hand, if the N content in the steel material exceeds 0.015%, even if the contents of other elements are within the ranges of this embodiment, a large number of blisters (voids) are likely to be generated in the steel sheet during cold rolling. Therefore, the N content is 0.002 to 0.015%. The lower limit of the N content is preferably 0.004%, more preferably 0.006%, and the upper limit of the N content is preferably 0.012%, more preferably 0.010%.

[0045] The balance of the chemical composition of the slab according to this embodiment is composed of Fe and impurities. Here, the term "impurities" refers to substances that are mixed in from raw materials such as ore and scrap, or from the manufacturing environment, during industrial production of slabs, which are the raw material for grain-oriented electrical steel sheets, and are acceptable within a range that does not adversely affect the grain-oriented electrical steel sheets manufactured by the manufacturing method according to this embodiment.

[0046] [Optional elements in the chemical composition of the slab] The chemical composition of the slab described above may contain one or more elements selected from the group consisting of Bi, Sn, Cr and Cu in place of a portion of Fe.

[0047] Bi: 0 to 0.0100% Bismuth (Bi) is an optional element and may not be contained, that is, the Bi content may be 0%. When contained, Bi stabilizes MnS and MnSe and enhances their inhibitor function. Even if even a small amount of Bi is contained, the above effect can be obtained to some extent. However, if the Bi content exceeds 0.0100%, the adhesion of the primary coating formed on the steel sheet decreases even if the contents of other elements are within the ranges of this embodiment. If the Bi content exceeds 0.0100%, edge cracks are more likely to occur. Therefore, the Bi content is 0 to 0.0100%. In order to more effectively obtain the above effects, the lower limit of the Bi content is preferably 0.0001%, more preferably 0.0003%, even more preferably 0.0005%, even more preferably 0.0007%, and even more preferably 0.0010%. The upper limit of the Bi content is preferably 0.0070%, more preferably 0.0050%, and even more preferably 0.0040%.

[0048] Sn: 0 to 0.50% Tin (Sn) is an optional element and may not be contained, that is, the Sn content may be 0%. When contained, Sn increases the density of the oxide layer formed during the decarburization annealing process. As a result, the properties of the primary coating formed using this oxide layer during the final annealing process are also improved. Furthermore, Sn stabilizes the formation of the oxide layer and the primary coating, thereby improving the magnetic properties of the grain-oriented electrical steel sheet and suppressing variations in the magnetic properties. Furthermore, Sn is a grain boundary segregation element and stabilizes secondary recrystallization. Even if even a small amount of Sn is contained, the above effects can be obtained to some extent. However, if the Sn content exceeds 0.50%, the surface of the steel sheet becomes difficult to oxidize, and the formation of the primary coating may become insufficient. Therefore, the Sn content is 0 to 0.50%. In order to more effectively obtain the above effects, the lower limit of the Sn content is preferably 0.01%, and more preferably 0.02%. The upper limit of the Sn content is preferably 0.30%, and more preferably 0.20%.

[0049] Cr: 0 to 0.50% Chromium (Cr) is an optional element and may not be contained, that is, the Cr content may be 0%. When contained, Cr improves the properties of the oxide layer formed during the decarburization annealing process and also improves the properties of the primary coating formed using this oxide layer during the finish annealing process. Furthermore, Cr stabilizes the formation of the oxide layer and primary coating, thereby improving the magnetic properties of the grain-oriented electrical steel sheet and suppressing variations in the magnetic properties. Even if even a small amount of Cr is contained, the above effects can be obtained to some extent. However, if the Cr content exceeds 0.50%, the formation of the primary coating may become unstable even if the contents of other elements are within the ranges of this embodiment. Therefore, the Cr content is 0 to 0.50%. In order to more effectively obtain the above effects, the lower limit of the Cr content is preferably 0.01%, and more preferably 0.02%. The upper limit of the Cr content is preferably 0.20%, and more preferably 0.15%.

[0050] Cu: 0 to 0.50% Copper (Cu) is an optional element and may not be contained, that is, the Cu content may be 0%. When contained, Cu promotes the precipitation of fine MnS, which becomes the nuclei for the formation of AlN, in the hot rolling process.Even if only a small amount of Cu is contained, the above effect can be obtained to some extent. However, if the Cu content exceeds 0.50%, CuS precipitates may form and remain after final annealing even if the contents of other elements are within the ranges of this embodiment. If CuS precipitates remain in the steel, the magnetic properties of the grain-oriented electrical steel sheet may deteriorate. Therefore, the Cu content is 0 to 0.50%. In order to more effectively obtain the above effects, the lower limit of the Cu content is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%. The upper limit of the Cu content is preferably 0.40%, and more preferably 0.30%.

[0051] [Method of manufacturing slabs having the above chemical composition] An example of a method for producing a slab having the above chemical composition is as follows: Molten steel having the above chemical composition is produced (melted), and a slab is produced using the molten steel by continuous casting.

[0052] [Hot rolling process using the above slab] The prepared slab having the above chemical composition is hot-rolled using a hot rolling mill to produce a steel sheet (hot-rolled steel sheet). In this embodiment, the hot-rolling step is an important step. Details will be described below.

[0053] Fig. 4 is a schematic diagram showing a hot rolling facility line including a row of hot rolling mills that perform a hot rolling process. Referring to Fig. 4, the hot rolling facility line 1 is equipped, in this order from upstream to downstream, with a roughing mill RM and a finishing mill FM. The roughing mill RM and the finishing mill FM are arranged on a pass line PL. Here, the pass line PL means a virtual line through which slabs (and steel sheets being hot rolled) pass.

[0054] The roughing mill RM is provided with one roughing stand RMS arranged on the pass line PL, or with multiple roughing stands RMS lined up in a row on the pass line PL. In FIG. 4, the roughing mill RM is provided with one roughing stand RMS. However, as shown in FIG. 5, the roughing mill RM is provided with multiple roughing stands RMS1 to RMS m(m is a natural number of 2 or more). Each roughing stand RMS includes a plurality of work rolls arranged one above the other. When the roughing mill RM has one roughing stand RMS, the roughing stand RMS is a reversing type rolling mill. When the roughing mill RM has a plurality of roughing stands RMS, the roughing stands RMS may be of the reversing type or of the tandem type.

[0055] The finishing mill FM is made up of multiple finishing rolling stands FMS1 to FMS2 arranged in a row on the pass line PL. n (n is a natural number of 2 or more) Multiple finishing rolling stands FMS1 to FMS n Of these, finishing rolling stand FMS1 is located at the most upstream of hot rolling equipment line 1, and finishing rolling stand FMS n is arranged at the most downstream of the hot rolling equipment line 1. Each finishing rolling stand FMS includes a plurality of work rolls arranged above and below. n The finishing mill FM including the above is a tandem type.

[0056] Fig. 6 is a flow diagram showing details of the hot rolling step (S1) shown in Fig. 3. Referring to Fig. 6, the hot rolling step (S1) includes a heating step (S11), a rough rolling step (S12) using a roughing mill RM, and a finish rolling step (S13) using a finish rolling mill FM. Each step will be described below.

[0057] [Heating process (S11)] In the heating step (S11), the slab is heated. For example, the slab is charged into a known heating furnace or a known soaking furnace and heated. The preferred heating temperature of the slab is 1300 to 1400°C. The preferred lower limit of the heating temperature is 1320°C.

[0058] [Rough rolling process (S12)] In the rough rolling step (S12), rough rolling is performed on the heated slab to produce a rough bar. Here, rough rolling means hot rolling the slab using a rough rolling mill RM. A rough bar means a steel plate after rough rolling is completed but before finish rolling begins. In the rough rolling step, a rough bar is produced by applying multiple reductions to the slab using the rough rolling mill RM. Here, when a reduction is applied to the slab as it passes through one rough rolling stand RMS, this means that one reduction has been applied. In the case of reverse rolling, one reduction is applied to the slab as it passes through the rough rolling stand RMS from upstream to downstream. Also, one reduction is applied to the slab as it passes through the same rough rolling stand RMS from downstream to upstream. Note that there are cases where no reduction is applied to the slab as it passes through the rough rolling stand RMS.

[0059] As described above, in the rough rolling process, a slab is subjected to multiple reductions to produce a rough bar. At this time, the cumulative reduction rate TR in the rough rolling process, the reduction rate R1 in the final reduction, and the temperature T1 of the rough bar immediately after the final reduction are as follows: (Condition A) Cumulative reduction rate TR in the rough rolling process: Less than 75% (Condition B) Final reduction rate R1 in the rough rolling process: Less than 50% (Condition C) Temperature of the rough bar immediately after the final reduction in the rough rolling process T1: 1350°C or higher

[0060] [(Condition A) Cumulative reduction rate TR in the rough rolling process] In this embodiment, the cumulative reduction rate TR in the rough rolling step is less than 75%. If the cumulative reduction rate TR in the rough rolling step is 75% or more, excessive strain accumulates in the rough bar. The excessive strain induces the precipitation of MnS and / or MnSe. If the cumulative reduction rate TR is 75% or more, excessive strain is introduced into the rough bar. Therefore, after the completion of the rough rolling step, MnS and / or MnSe precipitate, grow, and coarsen during the period from when the rear end of the rough bar is subjected to the first reduction in the finish rolling step, that is, from when the rear end of the slab passes through the rough rolling stand RMS, which performs the final reduction, until the rear end of the rough bar passes through the first finish rolling stand FMS1.

[0061] If the cumulative reduction rate TR in the rough rolling step is less than 75%, it is possible to prevent excessive strain from accumulating in the rough bar. Therefore, provided that conditions B and C and the condition D described below are satisfied, it is possible to prevent the formation of coarse MnS and / or MnSe in the rough bar after the rough rolling step. A preferred upper limit of the cumulative reduction rate TR in the rough rolling step is 74%, more preferably 73%, even more preferably 72%, and even more preferably 71%. The lower limit of the cumulative reduction rate TR in the rough rolling step is not particularly limited, but is, for example, 55%, and more preferably 60%.

[0062] [(Condition B) Regarding the reduction ratio R1 in the final rolling of the rough rolling process] In this embodiment, the reduction ratio R1 in the final reduction in the rough rolling step is less than 50%. Here, the reduction ratio R1 in the final reduction is defined as follows. Final reduction ratio R1 = (1 - rough bar thickness / slab thickness before final reduction) x 100

[0063] For example, when a rough bar is produced by performing m reductions (m is a natural number of 2 or more) in a rough rolling process, the thickness of the slab after the (m-1)th reduction is completed corresponds to the "thickness of the slab before the final reduction."

[0064] If the reduction rate R1 in the final reduction is 50% or more, excessive strain also accumulates in the rough bar. As described above, excessive strain induces the precipitation of MnS and / or MnSe. Therefore, if the reduction rate R1 in the final reduction is 50% or more, MnS and / or MnSe precipitate, grow, and coarsen after the completion of the rough rolling process until the rear end of the rough bar undergoes the first reduction in the finish rolling process, that is, after the rear end of the slab passes through the rough rolling stand RMS, which performs the final reduction, until the rear end of the rough bar passes through the first finish rolling stand FMS1.

[0065] If the reduction ratio R1 in the final reduction in the rough rolling step is less than 50%, it is possible to prevent excessive strain from accumulating in the rough bar. Therefore, provided that conditions A, C, and D are satisfied, it is possible to prevent the formation of coarse MnS and / or MnSe in the rough bar after the rough rolling step. A preferred upper limit of the reduction ratio R1 in the final reduction in the rough rolling step is 49%, more preferably 48%, even more preferably 47%, even more preferably 46%, and even more preferably 45%. The lower limit of the reduction ratio R1 in the final reduction in the rough rolling step is not particularly limited, but is, for example, 20%, even more preferably 25%.

[0066] [(Condition C) Temperature T1 of the rough bar immediately after the final reduction in the rough rolling process] In this embodiment, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process is 1350°C or higher. Here, "the temperature of the rough bar immediately after the final reduction in the rough rolling process" means the temperature of the rough bar immediately after the completion of rough rolling. More specifically, it means the average temperature at the center of the width and thickness of the rough bar in the longitudinal direction from the front to rear end of the rough bar immediately after the rear end of the slab (corresponding to the rear end of the rough bar) passes through the rough rolling stand RMS where the final reduction is being performed. Hereinafter, the temperature at the center of the width and thickness of the rough bar will be simply referred to as the "center of thickness temperature." The center of thickness temperature of the rough bar may be measured by inserting a thermocouple at the center of the width and thickness of the rough bar. The center of thickness temperature of the rough bar may also be determined by heat transfer calculation from the surface temperature of the steel sheet measured by a thermometer installed on the outlet side of the rough rolling stand RMS where the final reduction is performed in the rough rolling process. The thermometer may be, for example, a radiation thermometer.

[0067] If the temperature T1 of the rough bar immediately after the final reduction in the rough rolling step is less than 1350°C, the temperature of the rough bar will drop to the temperature range promoting the formation of MnS and MnSe after the completion of the rough rolling step and before the rear end of the rough bar is subjected to the first reduction in the finish rolling step. In this case, MnS and MnSe will precipitate and grow, causing coarsening over the entire length of the rough bar before the first reduction in the finish rolling step is applied.

[0068] If the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process is 1350°C or higher, the temperature of the rough bar can be prevented from dropping to the temperature range promoting the formation of MnS and MnSe after the completion of the rough rolling process and before the rear end of the rough bar receives the first reduction in the finish rolling process. Therefore, assuming that conditions A, B, and D are satisfied, precipitation of MnS and MnSe can be prevented over the entire length of the rough bar before the first reduction in the finish rolling process is applied. The preferred lower limit of the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process is 1355°C, more preferably 1360°C, and even more preferably 1370°C. The preferred upper limit of the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process is 1400°C.

[0069] [Finishing rolling process (S13)] In the finish rolling step (S13), the rough bar produced in the rough rolling step (S12) is subjected to finish rolling to produce a steel plate (hot-rolled steel plate). Here, finish rolling means hot rolling the rough bar using a finishing mill FM. In the finish rolling step, a plurality of tandem finishing rolling stands FMS1 to FMS2 are arranged in a row on a pass line PL. n A hot-rolled steel sheet is produced by applying a rolling reduction to a rough bar using a rolling mill. In the finish rolling process, the rough bar passes through each finish rolling stand FMS from upstream to downstream of the finish rolling stand FMS, and as the rough bar passes through each finish rolling stand FMS, it is subjected to a rolling reduction from the work rolls of each finish rolling stand FMS. Among the multiple finish rolling stands FMS, there may be a finish rolling stand FMS that does not apply a rolling reduction.

[0070] As described above, in the finish rolling (S13), multiple reductions are performed on the rough bar to produce a steel plate (hot-rolled steel plate). Here, the time t1 from the completion of the final reduction of the rear end of the slab in the rough rolling step (S12) to the completion of the first reduction of the rear end of the rough bar in the finish rolling step (S13) is defined as the "intermediate time" t1, i.e., the time t1 from the time the rear end (bottom) of the slab passes through the rough rolling stand RMS where the final reduction is being performed to the time the rear end (bottom) of the rough bar passes through the first finishing rolling stand FMS1. Here, the intermediate time t1 is set to satisfy the following conditions D and E. (Condition D) Intermediate time t1: 150 seconds or less (Condition E) -0.033t1 + 44 + 2000 [Bi] ≤ [Si] / [C] ≤ -0.033t1 + 52 + 2000 [Bi] (1) Here, in formula (1), [Bi] is the Bi content (mass%) in the chemical composition of the slab, [Si] is the Si content (mass%) in the chemical composition of the slab, [C] is the C content (mass%) in the chemical composition of the slab, and t1 is the intermediate time t1 (seconds). If Bi is not contained, [Bi] is substituted with 0.

[0071] [(Condition D) Intermediate time t1] If the intermediate time t1 exceeds 150 seconds, the temperature of the rough bar will drop to the temperature range that promotes the formation of Mn inhibitors during the intermediate time t1, even if the rough rolling process satisfies conditions A to C. As a result, Mn inhibitors (MnS, MnSe) will precipitate in the rough bar during the intermediate time t1, growing and coarsening.

[0072] If the intermediate time t1 is 150 seconds or less, finish rolling can be started over the entire length of the rough bar before the temperature of the rough bar drops to the temperature range that promotes Mn inhibitor formation, provided that the rough rolling process satisfies conditions A to C. In this case, the formation of Mn inhibitors during the intermediate time t1 can be suppressed. As a result, coarse Mn inhibitors with a major axis length of 1 μm or more can be suppressed in the steel sheet (hot-rolled steel sheet) after finish rolling, and fine Mn inhibitors with a major axis length of less than 1 μm can be dispersed in the steel sheet (hot-rolled steel sheet). The upper limit of the intermediate time t1 is preferably 145 seconds, more preferably 140 seconds, even more preferably 135 seconds, even more preferably 130 seconds, and even more preferably 125 seconds. The shorter the intermediate time t1, the better. There is no particular limitation on the lower limit of the intermediate time t1. The lower limit of the intermediate time t1 may be 0 seconds, 1 second, or 3 seconds.

[0073] [(Condition E) Regarding Equation (1)] The intermediate time t1 further satisfies equation (1). -0.033t1+44+2000[Bi]≦[Si] / [C]≦-0.033t1+52+2000[Bi] (1) Here, in formula (1), [Bi] is the Bi content (mass%) in the chemical composition of the slab, [Si] is the Si content (mass%) in the chemical composition of the slab, [C] is the C content (mass%) in the chemical composition of the slab, and t1 is the intermediate time t1 (seconds). If Bi is not contained, [Bi] is substituted with 0.

[0074] As described above, in a slab having the chemical composition of this embodiment, if a large number of fine Mn inhibitors precipitate at the interface between ferrite and austenite, cracks are likely to occur at the interface, resulting in edge cracks. Therefore, to suppress the occurrence of edge cracks, it is effective to control the phase interface between ferrite and austenite in accordance with the frequency of precipitation of fine Mn inhibitors. Specifically, it is effective to suppress the transformation from ferrite to austenite as much as possible during hot rolling. Among the elements in the chemical composition of the slab, Si is a strong ferrite former, and C is a strong austenite former. Therefore, increasing the [Si] / [C] ratio can easily suppress the interface area between ferrite and austenite during hot rolling. On the other hand, although increasing the Si content of Bi can stabilize secondary recrystallization and improve magnetic properties, it also has the characteristic of promoting the formation of fine Mn inhibitors during hot rolling. In other words, the Bi content is correlated with the frequency of precipitation of fine Mn inhibitors. Furthermore, the intermediate time t1 between rough rolling and finish rolling also correlates with the frequency of precipitation of fine Mn inhibitors. Therefore, by adjusting the [Si] / [C] ratio according to the Bi content and the intermediate time t1, the occurrence of edge cracks can be sufficiently suppressed. Specifically, in the manufacturing method of this embodiment, the formula (1) is satisfied in the hot rolling process. -0.033t1+44+2000[Bi]≦[Si] / [C]≦-0.033t1+52+2000[Bi] (1)

[0075] The formula is F1 = -0.033t1 + 44 + 2000 [Bi]. If [Si] / [C] is less than F1, the phase boundary between ferrite and austenite where fine Mn inhibitors are precipitated increases during the finish rolling process, making voids more likely to occur. As a result, edge cracks are more likely to occur.

[0076] The definition is F2 = -0.033t1 + 52 + 2000 [Bi]. If the [Si] / [C] ratio exceeds F2, the occurrence of edge cracks can be suppressed, but secondary recrystallization does not stabilize. In this case, the magnetic properties deteriorate.

[0077] If [Si] / [C] is greater than or equal to F1 and less than or equal to F2, i.e., if [Si] / [C] satisfies formula (1), excellent magnetic properties can be obtained and defective structures and cracked edges can be suppressed, provided that other conditions A to D and F are met. A preferred lower limit for [Si] / [C] is -0.033t1+45+2000[Bi], and more preferably -0.033t1+46+2000[Bi]. A preferred upper limit for [Si] / [C] is -0.033t1+51+2000[Bi], and more preferably -0.033t1+50+2000[Bi].

[0078] Note that F1, [Si] / [C], and F2 are all values ​​rounded to three decimal places. In other words, F1, [Si] / [C], and F2 are values ​​rounded to three decimal places.

[0079] A hot-rolled steel sheet is manufactured by the above-described hot rolling step (S1). In the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment, fine inhibitors (MnS, MnSe) are built into the hot-rolled steel sheet by performing hot rolling that satisfies all of conditions A to E in the hot-rolling step.

[0080] [Cold rolling process (S2)] In the cold rolling step (S2), the produced hot-rolled steel sheet is subjected to one or more cold rolling passes. Fig. 7 is a schematic diagram showing a cold rolling equipment line in which the cold rolling step is performed. Referring to Fig. 7, the cold rolling equipment line 2 is equipped, from upstream to downstream, with a pay-off reel (unwinding device) 21, a cold rolling mill CM, and a tension reel (winding device) 22. The pay-off reel 21 unwinds the wound steel sheet (hot-rolled steel sheet or cold-rolled steel sheet) ST. The tension reel 22 winds up the cold-rolled steel sheet ST. The cold rolling mill CM performs cold rolling on the unwinded steel sheet (hot-rolled steel sheet or cold-rolled steel sheet). In Fig. 7, the cold rolling mill CM is equipped with a plurality of cold rolling stands CMS1 to CMS2 arranged in a row from upstream to downstream. j(j is a natural number of 2 or more). Each cold rolling stand CMS has a pair of work rolls extending horizontally. In FIG. 7, the cold rolling mill CM has a plurality of cold rolling stands CMS1 to CMS j However, the cold rolling mill CM may also be a reversing rolling mill with one cold rolling stand CMS.

[0081] In this specification, "one cold rolling run" means that a cold rolled steel sheet having a desired final thickness is obtained by rolling multiple times, including one or more round trips, using a reverse cold rolling mill CM, or by rolling multiple cold rolling stands CMS1 to CMS2 arranged in a row using a tandem cold rolling mill CM. j From the first rolling stand CMS1 to the last rolling stand CMS j This means that the steel sheet is passed through a line up to the desired thickness to be rolled into a cold-rolled steel sheet of the desired final thickness. Note that when cold rolling is performed, the sheet is passed through a separate line for intermediate annealing and / or pickling, and then cold rolling is performed again to roll into a cold-rolled steel sheet of the desired final thickness, this corresponds to "performing two cold rolling passes." When rolling is performed multiple times without intermediate annealing in between, this corresponds to "performing one cold rolling pass."

[0082] As described above, in the cold rolling step of this embodiment, cold rolling may be performed once or multiple times. When cold rolling is performed only once, the hot-rolled steel sheet rewound by the payoff reel 21 is passed once through the cold rolling mill CM to apply a rolling reduction, thereby producing a cold-rolled steel sheet. On the other hand, when cold rolling is performed multiple times, the steel sheet (hot-rolled steel sheet or cold-rolled steel sheet) rewound by the payoff reel 21 is passed once through the cold rolling mill CM to apply a rolling reduction, and is taken up by the tension reel 22, and then the taken-up steel sheet is rewound again by the payoff reel 21, passed once through the cold rolling mill CM to apply a rolling reduction, and is taken up again by the tension reel.

[0083] When cold rolling is performed multiple times in the cold rolling process, intermediate annealing is performed after each cold rolling, and then the next cold rolling is performed. Known conditions are sufficient for the intermediate annealing treatment performed between cold rolling and the next cold rolling. The annealing temperature in the intermediate annealing treatment is, for example, 900 to 1200°C, and the holding time at the annealing temperature is 30 to 180 seconds. After the intermediate annealing treatment reduces the strain introduced into the steel sheet in the previous cold rolling (softens the steel sheet), the next cold rolling is performed.

[0084] In the cold rolling step, as described above, only one cold rolling may be performed.

[0085] The cumulative reduction in one or more cold rolling passes is not particularly limited. A preferred cumulative reduction in the cold rolling step (S2) is 80 to 95%. Here, the cumulative reduction (%) in the cold rolling step (S2) is defined as follows: Cold rolling rate (%) = (100 - thickness of steel plate after the last cold rolling / thickness of steel plate before the first cold rolling) x 100

[0086] In addition, when only one cold rolling is performed in the cold rolling step, the above cold reduction ratio is the cold reduction ratio in only one cold rolling. The steel sheet produced by the cold rolling step is wound into a coil.

[0087] [Annealing process before final cold rolling (S3)] In the annealing step (S3) before final cold rolling, an annealing treatment is performed on the steel sheet before final cold rolling (S20) of one or more cold rollings (S20) in the cold rolling step (S2). In the annealing step (S3) before final cold rolling, two-stage heat treatment (first heat treatment, second heat treatment) is performed. First, the first heat treatment is performed. In the first heat treatment, the steel sheet is heated to the first heat treatment temperature. The first heat treatment temperature is 1000 to 1200°C. After the steel sheet is heated to the first heat treatment temperature, the second heat treatment is performed. In the second heat treatment, the steel sheet is cooled from the first heat treatment temperature to the second heat treatment temperature and held at the second heat treatment temperature. The second heat treatment temperature is 850 to 950°C. The holding time at the second heat treatment temperature is 30 to 180 seconds. By carrying out the above-described final pre-cold annealing treatment, AlN can be finely dispersed across the width of the steel sheet.

[0088] [Decarburization annealing process (S4)] In the decarburization annealing step (S4), the steel sheet (cold-rolled steel sheet) after the cold rolling step (S2) is subjected to decarburization annealing to induce primary recrystallization.

[0089] FIG. 8 is a schematic diagram showing a heat pattern in the decarburization annealing step (S4). Referring to FIG. 8, the decarburization annealing step (S4) includes a temperature-raising step (S41), a decarburization step (S42), and a cooling step (S43). In the temperature-raising step (S41), the steel sheet is heated to a decarburization annealing temperature Ta. In the decarburization step (S42), the steel sheet is maintained at the decarburization annealing temperature Ta to perform decarburization annealing and induce primary recrystallization. In the cooling step (S43), the steel sheet after the decarburization step (S42) is cooled by a known method. In this embodiment, in the temperature-raising step (S41), the temperature rise rate in the temperature range from 550 to 800°C, which corresponds to the recrystallization temperature range of the steel sheet, is significantly increased. This promotes recrystallization of α-fiber orientation groups developed at the widthwise center of the steel sheet in the hot rolling step (S1), thereby suppressing the survival of α-fiber orientation groups. As a result, it is possible to suppress the occurrence of linear defect regions extending in the rolling direction at the widthwise center of the grain-oriented electrical steel sheet, which are caused by the remaining α-fiber orientation group. As a result, it is possible to suppress the deterioration of the magnetic properties of the grain-oriented electrical steel sheet caused by the linear defect regions. Each step will be described in detail below.

[0090] [Temperature increasing step (S41)] In the temperature-raising step, first, the steel sheet after the cold-rolling step (S2) is loaded into a heat treatment furnace. In the heat treatment furnace for decarburization annealing in this embodiment, the cold-rolled steel sheet is heated to the decarburization annealing temperature Ta by, for example, high-frequency induction heating. The temperature-raising step satisfies the following condition F. (Condition F) Average heating rate RR 550-800 : 800℃ / sec or more

[0091] [(Condition F) Average heating rate RR 550-800 About In the heating process, the average heating rate from 550°C to 800°C is defined as the average heating rate RR. 550-800 (°C / sec). The average heating rate RR 550-800 If the rolling rate is less than 800°C / s, the strain energy that drives recrystallization is released before recrystallization begins. In this case, recrystallization from the α-fiber orientations extending in the rolling direction at the center of the steel sheet width is not promoted, and the α-fiber orientations remain. As a result, linear defects extending in the rolling direction are formed in the grain-oriented electrical steel sheet. In this case, the magnetic properties of the grain-oriented electrical steel sheet are degraded.

[0092] Average heating rate RR 550-800 If the heating rate is 800°C / sec or higher, the release of strain energy is suppressed until recrystallization begins. This promotes recrystallization from the α-fiber orientation group and suppresses the persistence of the α-fiber orientation group. As a result, the formation of linear defective regions can be suppressed in the grain-oriented electrical steel sheet, resulting in excellent magnetic properties.

[0093] The average heating rate RR 550-800 However, the upper limit of the average temperature rise rate RR 550-800 If the average heating rate RR is faster than 2400°C / s, the above effect will saturate. 550-800 The upper limit is 2400°C / sec.

[0094] Average heating rate RR550-800 The preferred lower limit of the average heating rate RR is 850°C / sec, more preferably 860°C / sec, even more preferably 880°C / sec, and even more preferably 900°C / sec. 550-800 The upper limit of the heating rate is preferably 2300° C. / sec, more preferably 2200° C. / sec, and even more preferably 2100° C. / sec.

[0095] Average heating rate RR 550-800 is measured by the following method. Multiple thermometers are installed in the heat treatment furnace to measure the surface temperature of the steel plate. The multiple thermometers are arranged from the upstream to the downstream of the heat treatment furnace. The average heating rate RR is calculated based on the temperature of the steel plate measured by the thermometers and the time it takes for the steel plate temperature to rise from 550°C to 800°C. 550-800 Average heating rate RR 550-800 may be obtained by attaching a thermocouple to the sample steel plate and actually measuring the change in temperature over time.

[0096] [Decarburization process (S42)] In the decarburization step (S42) of the decarburization annealing step (S4), the steel sheet after the temperature increasing step (S41) is held at the decarburization annealing temperature Ta to perform decarburization annealing. This causes primary recrystallization to occur in the steel sheet. The atmosphere during the decarburization step may 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, causing primary recrystallization to occur. The manufacturing conditions for the decarburization step (S42) are as follows:

[0097] Decarburization annealing temperature Ta: 800 to 950°C As described above, the decarburization annealing temperature Ta corresponds to the furnace temperature of the heat treatment furnace in which the decarburization annealing is performed, and corresponds to the temperature of the steel sheet during the decarburization annealing. If the decarburization annealing temperature Ta is less than 800°C, the crystal grains of the steel sheet after the onset of primary recrystallization are too small. In this case, secondary recrystallization does not occur sufficiently in the final annealing step (S6). On the other hand, if the decarburization annealing temperature Ta exceeds 950°C, the crystal grains of the steel sheet after the onset of primary recrystallization are too large. In this case, secondary recrystallization also does not occur sufficiently in the final annealing step (S6). If the decarburization annealing temperature Ta is 800 to 950°C, the crystal grains of the steel sheet after the onset of primary recrystallization will be of an appropriate size, and secondary recrystallization will occur sufficiently in the final annealing step (S6).

[0098] In the decarburization step (S42), the holding time at the decarburization annealing temperature Ta is not particularly limited, and is, for example, 15 to 150 seconds.

[0099] [Cooling process (S43)] In the cooling step (S43), the steel sheet after the decarburization step (S42) is cooled to room temperature by a well-known method. The cooling method may be natural cooling or water cooling. Preferably, the steel sheet after the decarburization step is natural cooling. Through the above steps, the steel sheet is subjected to decarburization annealing treatment in the decarburization annealing step (S4).

[0100] By carrying out the above-described decarburization annealing step (S4), it is possible to promote recrystallization from the α-fiber orientation groups generated in the steel sheet during the hot rolling step, and to suppress the persistence of the α-fiber orientation groups. As a result, it is possible to grow Goss-oriented grains in the finish annealing step (S6), and it is possible to suppress the formation of linear defect regions extending in the rolling direction in the grain-oriented electrical steel sheet, which are caused by the α-fiber orientation groups.

[0101] [Annealing separator application process (S5)] The steel sheet after the decarburization annealing step (S6) is subjected to an annealing separator application step (S5). In the annealing separator application step (S5), an annealing separator is applied to the surface of the steel sheet. Specifically, an aqueous slurry containing the annealing separator is applied to the surface of the steel sheet. The aqueous slurry is prepared by adding water to the annealing separator and stirring. The annealing separator contains magnesium oxide (MgO). Preferably, MgO is the main component of the annealing separator. Here, "main component" means that the MgO content in the annealing separator is 60.0% by mass or more. The annealing separator may contain well-known additives in addition to MgO.

[0102] In the annealing separator application step (S5), an aqueous slurry of annealing separator is applied to the surface of the steel sheet. The steel sheet with the annealing separator applied to its surface is wound into a coil. After the steel sheet is coiled, a finish annealing step (S6) is carried out.

[0103] After the annealing separator in the form of an aqueous slurry is applied to the surface of the steel sheet and the steel sheet is formed into a coil, a baking treatment may be carried out before the final annealing step (S6) is carried out. In the baking treatment, the coiled steel sheet is placed in a furnace maintained at 400 to 1000°C and held there (baking treatment). This allows the annealing separator applied to the surface of the steel sheet to dry. The holding time is, for example, 10 to 90 seconds.

[0104] The coiled steel sheet coated with the annealing separator may be subjected to the finish annealing step (S6) without being subjected to the baking treatment.

[0105] [Finishing annealing process (S6)] The steel sheet after the annealing separator application step (S5) is subjected to a finish annealing step (S6) to induce secondary recrystallization. The finish annealing step (S6) is performed using a heat treatment furnace. The manufacturing conditions for the finish annealing step (S6) are, for example, as follows. The atmosphere in the furnace during the finish annealing is a well-known atmosphere.

[0106] Finishing annealing temperature: 1150~1250℃ Holding time at final annealing temperature: 5 to 30 hours If the final annealing temperature is less than 1150°C, sufficient secondary recrystallization does not occur, and the precipitates used in the secondary recrystallization are not sufficiently removed for purification. As a result, the magnetic properties of the manufactured grain-oriented electrical steel sheet are poor. On the other hand, if the final annealing temperature exceeds 1250°C, the effects of secondary recrystallization and purification are low, and problems such as deformation of the steel sheet occur. If the final annealing temperature is 1150 to 1250°C, sufficient secondary recrystallization occurs and the magnetic properties are improved, provided that the above-mentioned holding time is appropriate. Furthermore, a primary coating containing forsterite is formed soundly on the steel sheet surface.

[0107] In the manufacturing method of this embodiment, fine Mn inhibitors (MnS and MnSe) with a major axis length of less than 1 μm are finely dispersed in the steel sheet in the hot rolling step (S1). Therefore, these fine Mn inhibitors and fine AlN inhibitors generated in the final pre-cold rolling annealing step (S3) stabilize secondary recrystallization in the finish annealing step (S5). As a result, it is possible to suppress the occurrence of secondary recrystallization defects at both ends of the grain-oriented electrical steel sheet in the sheet width direction.

[0108] In the manufacturing method of this embodiment, in the hot rolling step (S1), conditions A to E are implemented to prioritize the refinement of Mn inhibitors. Therefore, there is a possibility that α-fiber orientation groups extending in the rolling direction are generated at the center of the sheet width of the hot-rolled steel sheet after the hot rolling step (S2). However, in the decarburization annealing step (S4), the average heating rate RR in the temperature range between 550°C and 800°C is 550-800 By setting the temperature at 800°C / s or higher (Condition F), the release of strain energy in the steel sheet before recrystallization begins is suppressed, and recrystallization from the α-fiber orientation group is promoted. This makes it possible to suppress the residual linear defect regions caused by the α-fiber orientation group in the grain-oriented electrical steel sheet, resulting in excellent magnetic properties.

[0109] The final annealing step (S6) removes some of the elements in the chemical composition of the steel sheet. In particular, S, Al, N, and other elements that function as inhibitors are largely removed. Furthermore, a primary coating containing forsterite is formed on the surface of the grain-oriented electrical steel sheet after the final annealing step (S6).

[0110] [Secondary film formation process] In the method for producing a grain-oriented electrical steel sheet according to this embodiment, a well-known secondary coating step may be performed after the final annealing step (S6), if necessary. In the secondary coating step, a well-known insulating coating agent mainly composed of colloidal silica and phosphate is applied to the surface (on the primary coating) of the grain-oriented electrical steel sheet after cooling in the final annealing step (S6), and then baked. This forms a secondary coating, which is a well-known tension-applying insulating coating, on the primary coating.

[0111] [Magnetic domain refining process] The grain-oriented electrical steel sheet according to this embodiment may further be subjected to a magnetic domain refinement treatment step, if necessary, after the finish annealing step (S6) or the secondary coating step. In the magnetic domain refinement treatment step, the surface of the grain-oriented electrical steel sheet is irradiated with a laser beam that has a magnetic domain refinement effect, or grooves are formed in the surface. In this case, a grain-oriented electrical steel sheet with even better magnetic properties can be produced.

[0112] As described above, in the method for producing a grain-oriented electrical steel sheet according to this embodiment, in the hot rolling step (S1), a hot-rolled steel sheet is produced under conditions that satisfy conditions A to E, and in the decarburization annealing step (S4), decarburization annealing is performed under conditions that satisfy condition F. This allows the produced grain-oriented electrical steel sheet to have sufficient magnetic properties and suppresses defective structures and edge cracks at the ends in the sheet width direction.

[0113] In the manufacturing method of the grain-oriented electrical steel sheet of this embodiment, if any of conditions A to D is not satisfied, not only will a defective structure occur, but in some cases, magnetic properties (magnetic flux density and / or iron loss) may also decrease. Furthermore, in condition E, if the [Si] / [C] is too low, not only will edge cracks occur, but iron loss may also decrease.

[0114] Hereinafter, aspects of the present invention will be described in detail with reference to examples. These examples are examples for confirming the effects of the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment, and are not intended to limit the present invention. [Example]

[0115] In Example 1, grain-oriented electrical steel sheets were manufactured by varying the chemical composition of a slab consisting only of essential elements. The manufactured grain-oriented electrical steel sheets were examined for the presence or absence of edge cracks, the presence or absence of defective structures, and the magnetic properties (magnetic flux density B8 and iron loss W17 / 50). Specifically, slabs with the chemical compositions shown in Table 1 were prepared.

[0116] [Table 1]

[0117] The symbol "-" next to the element content in Table 1 means that the corresponding element content is 0% when rounded to the nearest significant figure (the lowest digit) as specified in the above embodiment. For example, the Bi content specified in this embodiment is specified as a numerical value up to four decimal places. Therefore, in test number 1 in Table 1, the measured Bi content was 0% when rounded to the fifth decimal place. Furthermore, the Sn content specified in this embodiment is specified as a numerical value up to two decimal places. Therefore, in test number 1 in Table 1, the measured Sn content was 0% when rounded to the third decimal place. Rounding off means that if the digit (fraction) below the specified minimum digit is less than 5, it is rounded down, and if it is 5 or more, it is rounded up.

[0118] The slab was heated to 1370°C in a heating furnace. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate). In all test numbers, the cumulative reduction TR in the rough rolling process was 73%, and the reduction R1 in the final reduction in the rough rolling process was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a plate thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in all cases.

[0119] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0120] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was 800°C / sec.

[0121] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was subjected to finish annealing. The finish annealing temperature was 1200°C, and the holding time at the finish annealing temperature was 20 hours. The steel sheet after finish annealing was allowed to cool.

[0122] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0123] [Evaluation test] [Magnetic property evaluation test] As a magnetic property evaluation test, the magnetic flux density B8 and iron loss W17 / 50 were measured. Specifically, the magnetic flux density B of each grain-oriented electrical steel sheet was evaluated in accordance with JIS C2556 (2015). Samples were taken from each grain-oriented electrical steel sheet. A magnetic field of 800 A / m was applied to the taken sample, and the magnetic flux density B8 (T) was measured. Furthermore, the iron loss W17 / 50 was measured using the sample when magnetized to 1.7 T at 50 Hz. The obtained magnetic flux density B8 and iron loss W17 / 50 are shown in Table 1. In this example, a magnetic flux density B8 of 1.900 T or higher was considered to have a high magnetic flux density, and an iron loss W17 / 50 of 0.770 W / kg or lower was considered to have an excellent iron loss. When the magnetic flux density B8 was less than 1.900 T, the iron loss W17 / 50 was not measured.

[0124] [Cracked ear confirmation test] Using steel plates after the hot rolling process in the manufacturing process for each test number, the presence or absence of edge cracks was confirmed at both ends in the plate width direction. If edge cracks were present, the length of the edge cracks in the plate width direction was measured. If even one edge crack exceeding 20 mm in length in the plate width direction was confirmed, it was determined that edge cracks had occurred ("X" in Table 1). On the other hand, if no edge cracks exceeding 20 mm in length in the plate width direction were confirmed, it was determined that edge cracks had not occurred ("○" in Table 1).

[0125] [Defective structure depth measurement test] FIG. 9 shows the shape of the samples used in the defect structure depth measurement test. Referring to FIG. 9, the sheet width of the grain-oriented electrical steel sheet of each test number was defined as W. A sample measuring 100 mm in the rolling direction RD and W mm in the sheet width direction TD was taken from each grain-oriented electrical steel sheet of each test number. The primary coating and secondary coating were removed from the taken sample using the following method. The grain-oriented electrical steel sheet was immersed in an aqueous sodium hydroxide solution containing 40 mass% NaOH and 60 mass% HO at 80 to 90°C for 7 minutes. After immersion, the grain-oriented electrical steel sheet was rinsed with water. After rinsing, it was dried with a hot air blower for just under 1 minute. This process produced a grain-oriented electrical steel sheet from which the secondary coating had been removed (i.e., a base steel sheet with a primary coating). Furthermore, the grain-oriented electrical steel sheet from which the secondary coating had been removed was immersed in hydrochloric acid at 80 to 90°C for 5 to 30 seconds to remove the primary coating from the base steel sheet. The base steel sheet from which the primary coating had been removed was rinsed with water and then dried with a hot air blower for just under one minute. By using the above method, samples were prepared from which the primary and secondary coatings had been removed and in which the rolled surface (surface) had been etched.

[0126] As shown in Figure 9, when defective structure IA is generated at both ends of the sheet width direction TD in the etched sample, the grain size of the defective structure IA is much smaller than the grain size of the normal structure NA. Therefore, the defective structure IA can be easily identified by visual inspection. Therefore, the etched sample was visually inspected to determine whether or not defective structure IA was present at both ends. When defective structure IA was generated at the left end of the sheet width direction TD in Figure 9, the maximum length of the defective structure IA in the sheet width direction TD was defined as the defective structure depth WL (mm). Furthermore, when defective structure IA was generated at the right end of the sheet width direction TD in Figure 9, the maximum length of the defective structure IA in the sheet width direction TD was defined as the defective structure depth WR (mm). The larger of the defective structure depths WL and WR was defined as the defective structure depth WO (mm) of the grain-oriented electrical steel sheet of that test number. When the defective structure depth WO was 5 mm or more, it was determined that defective structure had occurred (marked "X" in Table 1). On the other hand, when the defective structure depth WO was less than 5 mm, it was determined that no defective structure was observed ("◯" in Table 1).

[0127] In addition, for steel sheets with test numbers in which edge cracks occurred in the above-mentioned edge crack confirmation test, trimming was performed on the steel sheet edge before the annealing process before final cold rolling, and the edge was cut off. Therefore, the depth of the defective structure from the edge of the sheet width was not measured (indicated by "-" in the "Defective structure 5 mm or more" column in Table 1). Furthermore, for test numbers in which [Si] / [C] exceeded the upper limit of equation (1) (i.e., exceeded F2), secondary recrystallization was poor across the entire sheet width. Therefore, the depth of the defective structure from the edge of the sheet width was not measured (indicated by "-" in the "Defective structure 5 mm or more" column in Table 1). The test results are shown in Table 1.

[0128] [Test Results] The test results are shown in Table 1. Referring to Table 1, in test numbers 2, 5, 6, 9, 11, 12, 15, 16, 19, and 20, the chemical composition of the slab was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred, and no defective structure was observed. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0129] On the other hand, in test numbers 1, 3, 4, 8, 14 and 18, the [Si] / [C] value was less than the lower limit (=F1) of formula (1), and as a result, edge cracking was confirmed.

[0130] In test numbers 7, 10, 13, 17, and 21, the [Si] / [C] value exceeded the upper limit (=F2) of formula (1), resulting in a magnetic flux density B8 of less than 1.900 T and poor magnetic properties. [Example]

[0131] In Example 2, grain-oriented electrical steel sheets were manufactured by changing the chemical composition of the slab. The manufactured grain-oriented electrical steel sheets were measured for the presence or absence of edge cracks, the presence or absence of defective structures, and the magnetic properties (magnetic flux density B8 and iron loss W17 / 50). Specifically, slabs with the chemical compositions shown in Table 2 were prepared.

[0132] [Table 2]

[0133] As in Table 1, "-" in Table 2 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0134] The slab was heated to 1370°C in a heating furnace. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate). In all test numbers, the cumulative reduction TR in the rough rolling process was 73%, and the reduction R1 in the final reduction in the rough rolling process was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a plate thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in all cases.

[0135] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0136] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was 800°C / sec.

[0137] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was subjected to finish annealing. The finish annealing temperature was 1200°C, and the holding time at the finish annealing temperature was 20 hours. The steel sheet after finish annealing was allowed to cool.

[0138] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0139] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was carried out to measure the magnetic flux density B8 and iron loss W17 / 50 in the same manner as in Example 1. Furthermore, an edge crack confirmation test and a defective structure depth measurement test were carried out in the same manner as in Example 1. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained.

[0140] [Test Results] The test results are shown in Table 2. Referring to Table 2, in test numbers 1 to 7, the chemical composition of the slab was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred and no defective structure was generated. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties. [Example]

[0141] In Example 3, the chemical composition of the slab was changed, and the average heating rate RR 550-800 Grain-oriented electrical steel sheets were manufactured by changing the temperature. The produced grain-oriented electrical steel sheets were examined for the presence or absence of edge cracks and defective structures, and their magnetic properties (magnetic flux density B8 and iron loss W17 / 50) were measured. Specifically, slabs with the chemical compositions shown in Table 3 were prepared.

[0142] [Table 3]

[0143] As in Table 1, "-" in Table 3 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0144] The slab was heated to 1370°C in a heating furnace. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate). In all test numbers, the cumulative reduction TR in the rough rolling process was 73%, and the reduction R1 in the final reduction in the rough rolling process was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a plate thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in all cases.

[0145] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0146] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The results were as shown in Table 4.

[0147] [Table 4]

[0148] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was subjected to finish annealing. The finish annealing temperature was 1200°C, and the holding time at the finish annealing temperature was 20 hours. The steel sheet after finish annealing was allowed to cool.

[0149] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0150] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was conducted in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17 / 50 were measured. Furthermore, in the same manner as in Example 1, a cracked edge confirmation test and a defective structure depth measurement test were conducted. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained. If the magnetic flux density B8 was less than 1.900 T, the iron loss W17 / 50 was not measured.

[0151] [Test Results] The test results are shown in Table 4. Referring to Table 4, in test numbers 3, 4, 7, 8, and 11 to 27, the chemical composition of the slabs was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no defective structure was observed, and no edge cracks occurred. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0152] On the other hand, in Test Nos. 1, 2, 5, 6, 9 and 10, the average heating rate RR 550-800 The recrystallization time was too slow. As a result, the magnetic flux density B8 was less than 1.900 T, and the magnetic properties were poor. In test numbers 1, 2, 5, 6, 9, and 10, the magnetic flux density B8 was a very poor value, and secondary recrystallization was poor across the entire width of the sheet. For this reason, the depth of the defective structure from the widthwise end of the sheet was not measured ("-" is entered in the "Defective structure 5 mm or more" column in Table 4). [Example]

[0153] In Example 4, the cumulative reduction rate TR (Condition A) in the rough rolling step of the hot rolling step was changed, and the occurrence of edge cracks, the occurrence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17 / 50) were measured. Specifically, slabs having the chemical compositions shown in Table 5 were prepared.

[0154] [Table 5]

[0155] As in Table 1, "-" in Table 5 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0156] The slab was heated in a heating furnace to 1370° C. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate).

[0157] For each test number, the cumulative reduction ratio TR in the rough rolling process was as shown in Table 6. For all test numbers, the reduction ratio R1 in the final reduction in the rough rolling process was 46%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds for all test numbers.

[0158] [Table 6]

[0159] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0160] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was set to 1000°C / sec.

[0161] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was then subjected to finish annealing. The finish annealing temperature was 1150°C, and the holding time at the finish annealing temperature was 10 hours. The steel sheet after finish annealing was allowed to cool.

[0162] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0163] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was carried out to measure the magnetic flux density B8 and iron loss W17 / 50 in the same manner as in Example 1. Furthermore, an edge crack confirmation test and a defective structure depth measurement test were carried out in the same manner as in Example 1. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained.

[0164] [Test Results] The test results are shown in Table 6. Referring to Table 6, in test numbers 1 to 9, the chemical composition of the slab was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred and no defective structure was generated. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0165] On the other hand, in Test Nos. 10 to 15, the cumulative reduction rate TR in rough rolling was too high, resulting in a defective structure depth of 5 mm or more, and excessive defective structures occurring at both ends in the sheet width direction TD. [Example]

[0166] In Example 5, the rolling reduction R (condition B) in the final rolling in the rough rolling step in the hot rolling process was changed, and the occurrence of edge cracks, the occurrence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17 / 50) were measured. Specifically, slabs having the chemical compositions shown in Table 7 were prepared.

[0167] [Table 7]

[0168] As in Table 1, "-" in Table 7 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0169] The slab was heated in a heating furnace to 1370° C. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate).

[0170] For all test numbers, the cumulative reduction rate TR in the rough rolling process was 73%. For each test number, the reduction rate R1 in the final reduction in the rough rolling process was as shown in Table 8. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds for all test numbers.

[0171] [Table 8]

[0172] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0173] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was set to 1000°C / sec.

[0174] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was then subjected to finish annealing. The finish annealing temperature was 1150°C, and the holding time at the finish annealing temperature was 10 hours. The steel sheet after finish annealing was allowed to cool.

[0175] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0176] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was carried out to measure the magnetic flux density B8 and iron loss W17 / 50 in the same manner as in Example 1. Furthermore, an edge crack confirmation test and a defective structure depth measurement test were carried out in the same manner as in Example 1. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained.

[0177] [Test Results] The test results are shown in Table 8. Referring to Table 8, in test numbers 1 to 6, the chemical composition of the slab was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred and no defective structure was generated. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0178] On the other hand, in Test Nos. 7 to 12, the reduction rate in the final reduction in the rough rolling step was too high, resulting in a defective structure depth of 5 mm or more, and excessive defective structures occurring at both ends in the sheet width direction TD. [Example]

[0179] In Example 6, the temperature of the rough bar immediately after the final reduction in the rough rolling step in the hot rolling process (Condition C) was changed, and the occurrence of defective structures, edge cracks, and magnetic properties (magnetic flux density B8 and iron loss W17 / 50) were measured. Specifically, slabs having the chemical compositions shown in Table 9 were prepared.

[0180] [Table 9]

[0181] As in Table 1, "-" in Table 9 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0182] The slab was heated in a heating furnace to 1370° C. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate).

[0183] For each test number, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was as shown in Table 10. For all test numbers, the cumulative reduction TR in the rough rolling process was 73%, and the reduction R1 in the final reduction in the rough rolling process was 48%. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a thickness of 2.3 mm. The intermediate time t1 was 120 seconds for all test numbers.

[0184] [Table 10]

[0185] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0186] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was set to 1000°C / sec.

[0187] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was then subjected to finish annealing. The finish annealing temperature was 1150°C, and the holding time at the finish annealing temperature was 10 hours. The steel sheet after finish annealing was allowed to cool.

[0188] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0189] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was carried out to measure the magnetic flux density B8 and iron loss W17 / 50 in the same manner as in Example 1. Furthermore, an edge crack confirmation test and a defective structure depth measurement test were carried out in the same manner as in Example 1. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained.

[0190] [Test Results] The test results are shown in Table 10. Referring to Table 10, in test numbers 7 to 12, the chemical composition of the slab was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred and no defective structure was generated. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0191] On the other hand, in Test Nos. 1 to 6, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling step was too low, resulting in a defective structure depth of 5 mm or more, and excessive defective structures occurring at both ends in the plate width direction TD. [Example]

[0192] In Example 7, the time (intermediate time) t1 (condition D) from the completion of the final reduction of the rear end of the slab in the rough rolling process to the completion of the first reduction of the rear end of the rough bar in the finish rolling process in the hot rolling process was varied, and the occurrence of edge cracks, the occurrence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17 / 50) were measured. Specifically, slabs having the chemical compositions shown in Table 11 were prepared.

[0193] [Table 11]

[0194] As in Table 1, "-" in Table 11 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0195] The slab was heated in a heating furnace to 1370° C. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate).

[0196] For each test number, the time (intermediate time) t1 from the completion of the final reduction of the rear end of the slab in the rough rolling process to the completion of the first reduction of the rear end of the rough bar in the finish rolling process was as shown in Table 11. For each test number, the cumulative reduction rate TR in the rough rolling process was 73%, and the reduction rate R1 in the final reduction in the rough rolling process was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a thickness of 2.3 mm.

[0197] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0198] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was set to 1000°C / sec.

[0199] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was then subjected to finish annealing. The finish annealing temperature was 1150°C, and the holding time at the finish annealing temperature was 10 hours. The steel sheet after finish annealing was allowed to cool.

[0200] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0201] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was carried out to measure the magnetic flux density B8 and iron loss W17 / 50 in the same manner as in Example 1. Furthermore, an edge crack confirmation test and a defective structure depth measurement test were carried out in the same manner as in Example 1. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained.

[0202] [Test Results] The test results are shown in Table 11. In test numbers 2 to 6, the chemical composition of the slabs was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, in all test numbers, no defective structure was observed, and no edge cracks occurred. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0203] On the other hand, in test number 1, the [Si] / [C] value was less than the lower limit (=F1) of formula (1), resulting in edge cracks of more than 20 mm.

[0204] In Test Nos. 7, 8, and 10, the intermediate time t1 between the completion of the final reduction of the rear end of the slab in the rough rolling process in the hot rolling process and the completion of the first reduction of the rear end of the rough bar in the finish rolling process was too long. As a result, the defective structure depth WO was 5 mm or more, and excessive defective structures were generated at both ends in the plate width direction TD.

[0205] In test numbers 9, 11, and 12, the [Si] / [C] value exceeded the upper limit (=F2) of formula (1), resulting in a magnetic flux density B8 of less than 1.900 T and poor magnetic properties. [Example]

[0206] In Example 8, grain-oriented electrical steel sheets were produced by varying the chemical composition of a slab consisting of essential elements and Bi. The produced grain-oriented electrical steel sheets were examined for the presence or absence of edge cracks, the presence or absence of defective structures, and their magnetic properties (magnetic flux density B8 and iron loss W17 / 50). Specifically, slabs with the chemical compositions shown in Table 12 were prepared.

[0207] [Table 12]

[0208] As in Table 1, "-" in Table 12 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0209] The slab was heated to 1370°C in a heating furnace. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate). In all test numbers, the cumulative reduction TR in the rough rolling process was 73%, and the reduction R1 in the final reduction in the rough rolling process was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a plate thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in all cases.

[0210] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0211] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was 800°C / sec.

[0212] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was subjected to finish annealing. The finish annealing temperature was 1200°C, and the holding time at the finish annealing temperature was 20 hours. The steel sheet after finish annealing was allowed to cool.

[0213] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0214] [Evaluation test] [Magnetic property evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was conducted in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17 / 50 were measured. Furthermore, in the same manner as in Example 1, a cracked edge confirmation test and a defective structure depth measurement test were conducted. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained. If the magnetic flux density B8 was less than 1.900 T, the iron loss W17 / 50 was not measured.

[0215] [Test Results] The test results are shown in Table 12. Referring to Table 12, in test numbers 3, 5, 6, 8 to 14, 16, 17, 19, and 20, the chemical composition of the slab was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred, and no defective structure occurred. Furthermore, the magnetic flux density B8 was high at 1.906 T or more, and the iron loss W17 / 50 was 0.727 W / kg or less, indicating excellent magnetic properties.

[0216] On the other hand, in test numbers 1, 2, 4 and 7, the [Si] / [C] value was less than the lower limit (=F1) of formula (1), and as a result, edge cracking was confirmed.

[0217] In test numbers 15, 18, and 21, the [Si] / [C] value exceeded the upper limit (=F2) of formula (1), resulting in a magnetic flux density B8 of less than 1.900 T and poor magnetic properties. [Example]

[0218] In Example 9, grain-oriented electrical steel sheets were manufactured by varying the chemical composition of a slab consisting of essential elements and Bi. The manufactured grain-oriented electrical steel sheets were examined for the presence or absence of edge cracks, the presence or absence of defective structures, and the magnetic properties (magnetic flux density B8 and iron loss W17 / 50). Specifically, slabs with the chemical compositions shown in Table 13 were prepared.

[0219] [Table 13]

[0220] As in Table 1, "-" in Table 13 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0221] The slab was heated to 1370°C in a heating furnace. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate). In all test numbers, the cumulative reduction TR in the rough rolling process was 73%, and the reduction R1 in the final reduction in the rough rolling process was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a plate thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in all cases.

[0222] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0223] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was 800°C / sec.

[0224] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was subjected to finish annealing. The finish annealing temperature was 1200°C, and the holding time at the finish annealing temperature was 20 hours. The steel sheet after finish annealing was allowed to cool.

[0225] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0226] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was conducted in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17 / 50 were measured. Furthermore, in the same manner as in Example 1, a cracked edge confirmation test and a defective structure depth measurement test were conducted. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained. If the magnetic flux density B8 was less than 1.900 T, the iron loss W17 / 50 was not measured.

[0227] [Test Results] The test results are shown in Table 13. Referring to Table 13, in test numbers 1 to 3, 7 to 9, 13 to 15, and 20 to 22, the chemical composition of the slab was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred, and no defective structures were generated. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0228] On the other hand, in test numbers 4 to 6, 10 to 12, 16 to 18, 23 and 24, the [Si] / [C] value was less than the lower limit (=F1) of formula (1), and as a result, edge cracking was confirmed.

[0229] In test number 19, the [Si] / [C] value exceeded the upper limit (=F2) of formula (1). As a result, the magnetic flux density B8 was less than 1.900 T, and the magnetic properties were poor. In test number 19, the magnetic flux density B8 was a very poor value, and secondary recrystallization was poor across the entire width of the sheet. For this reason, the depth of the defective structure from the end of the sheet width was not measured ("-" is entered in the "Defective structure 5 mm or more" column in Table 13). [Example]

[0230] In Example 10, the chemical composition of the slab containing the essential elements and Bi was changed, and the average heating rate RR 550-800Grain-oriented electrical steel sheets were manufactured by varying the temperature. The manufactured grain-oriented electrical steel sheets were examined for the presence or absence of edge cracks and defective structures, and their magnetic properties (magnetic flux density B8 and iron loss W17 / 50) were measured. Specifically, slabs with the chemical compositions shown in Table 14 were prepared.

[0231] [Table 14]

[0232] As in Table 1, "-" in Table 14 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0233] The slab was heated to 1370°C in a heating furnace. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate). In all test numbers, the cumulative reduction TR in the rough rolling process was 73%, and the reduction R1 in the final reduction in the rough rolling process was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a plate thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds in all cases.

[0234] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0235] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The results are shown in Table 15.

[0236] [Table 15]

[0237] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was subjected to finish annealing. The finish annealing temperature was 1200°C, and the holding time at the finish annealing temperature was 20 hours. The steel sheet after finish annealing was allowed to cool.

[0238] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0239] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was conducted in the same manner as in Example 1, and the magnetic flux density B8 and iron loss W17 / 50 were measured. Furthermore, in the same manner as in Example 1, a cracked edge confirmation test and a defective structure depth measurement test were conducted. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained. If the magnetic flux density B8 was less than 1.900 T, the iron loss W17 / 50 was not measured.

[0240] [Test Results] The test results are shown in Table 15. Referring to Table 15, in test numbers 3, 4, 7, 8, and 11 to 25, the chemical composition of the slabs was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred, and no defective structures were generated. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0241] On the other hand, in Test Nos. 1, 2, 5, 6, 9 and 10, the average heating rate RR 550-800 The recrystallization time was too long. As a result, the magnetic flux density B8 was less than 1.900 T, and the magnetic properties were poor. In test numbers 1, 2, 5, 6, 9, and 10, the magnetic flux density B8 was a very poor value, and secondary recrystallization was poor across the entire width of the sheet. Therefore, the depth of the defective structure from the widthwise end of the sheet was not measured ("-" is entered in the "Defective structure 5 mm or more" column in Table 15). [Example]

[0242] In Example 11, the cumulative reduction ratio TR (Condition A) in the rough rolling step in the hot rolling step was changed, and the occurrence of edge cracks, the occurrence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17 / 50) were measured. Specifically, slabs having the chemical compositions shown in Table 16 were prepared.

[0243] [Table 16]

[0244] As in Table 1, "-" in Table 16 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0245] The slab was heated in a heating furnace to 1370° C. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate).

[0246] For each test number, the cumulative reduction ratio TR in the rough rolling process was as shown in Table 17. For all test numbers, the reduction ratio R1 in the final reduction in the rough rolling process was 46%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds for all test numbers.

[0247] [Table 17]

[0248] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0249] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the temperature-raising process of the decarburization annealing process was set to 120 seconds. 550-800The heating rate was set to 1000°C / sec.

[0250] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was then subjected to finish annealing. The finish annealing temperature was 1150°C, and the holding time at the finish annealing temperature was 10 hours. The steel sheet after finish annealing was allowed to cool.

[0251] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0252] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was carried out to measure the magnetic flux density B8 and iron loss W17 / 50 in the same manner as in Example 1. Furthermore, an edge crack confirmation test and a defective structure depth measurement test were carried out in the same manner as in Example 1. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained.

[0253] [Test Results] The test results are shown in Table 17. Referring to Table 17, in test numbers 1 to 15, the chemical composition of the slab was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred and no defective structures were generated. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0254] On the other hand, in Test Nos. 16 to 25, the cumulative reduction rate TR in rough rolling was too high, resulting in a defective structure depth WO of 5 mm or more, and excessive defective structures occurring at both ends in the sheet width direction TD. [Example]

[0255] In Example 12, the rolling reduction R (condition B) in the final rolling in the rough rolling step in the hot rolling process was changed, and the occurrence of edge cracks, the occurrence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17 / 50) were measured. Specifically, slabs having the chemical compositions shown in Table 18 were prepared.

[0256] [Table 18]

[0257] As in Table 1, "-" in Table 18 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0258] The slab was heated in a heating furnace to 1370° C. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate).

[0259] For all test numbers, the cumulative reduction rate TR in the rough rolling process was 73%. For each test number, the reduction rate R1 in the final reduction in the rough rolling process was as shown in Table 19. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a thickness of 2.3 mm. At this time, the intermediate time t1 was 120 seconds for all test numbers.

[0260] [Table 19]

[0261] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0262] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was set to 1000°C / sec.

[0263] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was then subjected to finish annealing. The finish annealing temperature was 1150°C, and the holding time at the finish annealing temperature was 10 hours. The steel sheet after finish annealing was allowed to cool.

[0264] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0265] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was carried out to measure the magnetic flux density B8 and iron loss W17 / 50 in the same manner as in Example 1. Furthermore, an edge crack confirmation test and a defective structure depth measurement test were carried out in the same manner as in Example 1. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained.

[0266] [Test Results] The test results are shown in Table 19. Referring to Table 19, in test numbers 1 to 6, the chemical composition of the slab was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred and no defective structures were generated. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0267] On the other hand, in Test Nos. 7 to 12, the reduction rate in the final reduction in the rough rolling step was too high, resulting in a defective structure depth of 5 mm or more, and excessive defective structures occurring at both ends in the sheet width direction TD. [Example]

[0268] In Example 13, the temperature of the rough bar immediately after the final reduction in the rough rolling step in the hot rolling process (Condition C) was changed, and the occurrence of edge cracks, the occurrence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17 / 50) were measured. Specifically, slabs having the chemical compositions shown in Table 20 were prepared.

[0269] [Table 20]

[0270] As in Table 1, "-" in Table 20 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0271] The slab was heated in a heating furnace to 1370° C. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate).

[0272] For each test number, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was as shown in Table 21. For all test numbers, the cumulative reduction TR in the rough rolling process was 73%, and the reduction R1 in the final reduction in the rough rolling process was 48%. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a thickness of 2.3 mm. The intermediate time t1 was 120 seconds for all test numbers.

[0273] [Table 21]

[0274] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0275] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was set to 1000°C / sec.

[0276] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was then subjected to finish annealing. The finish annealing temperature was 1150°C, and the holding time at the finish annealing temperature was 10 hours. The steel sheet after finish annealing was allowed to cool.

[0277] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0278] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was carried out to measure the magnetic flux density B8 and iron loss W17 / 50 in the same manner as in Example 1. Furthermore, an edge crack confirmation test and a defective structure depth measurement test were carried out in the same manner as in Example 1. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained.

[0279] [Test Results] The test results are shown in Table 21. Referring to Table 21, in test numbers 7 to 12, the chemical composition of the slabs was appropriate, and conditions A to F in the manufacturing process were appropriate. Therefore, in all test numbers, no edge cracks occurred and no defective structures were generated. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0280] On the other hand, in Test Nos. 1 to 6, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling step was too low, resulting in a defective structure depth of 5 mm or more, and excessive defective structures occurring at both ends in the plate width direction TD. [Example]

[0281] In Example 14, the time (intermediate time) t1 (condition D) from the completion of the final reduction of the rear end of the slab in the rough rolling process to the completion of the first reduction of the rear end of the rough bar in the finish rolling process was varied to measure the occurrence of edge cracks, the occurrence of defective structures, and magnetic properties (magnetic flux density B8 and iron loss W17 / 50). Specifically, slabs having the chemical compositions shown in Table 22 were prepared.

[0282] [Table 22]

[0283] As in Table 1, "-" in Table 22 means that the content of the corresponding element is 0% when rounded to the nearest significant figure (the number to the least significant digit) as specified in the above embodiment.

[0284] The slab was heated in a heating furnace to 1370° C. The heated slab was subjected to a hot rolling process to produce a steel plate (hot-rolled steel plate).

[0285] For each test number, the intermediate time t1 from the completion of the final reduction of the rear end of the slab in the rough rolling process to the completion of the first reduction of the rear end of the rough bar in the finish rolling process was as shown in Table 22. For each test number, the cumulative reduction rate TR in the rough rolling process was 73%, and the reduction rate R1 in the final reduction in the rough rolling process was 48%. Furthermore, the temperature T1 of the rough bar immediately after the final reduction in the rough rolling process was 1350°C. After the rough rolling process, a finish rolling process was carried out to produce a steel plate with a thickness of 2.3 mm.

[0286] The steel sheet manufactured by the hot rolling process was subjected to an annealing process before final cold rolling. In the annealing process before final cold rolling, a first heat treatment and a second heat treatment were performed. In the first heat treatment, the steel sheet was heated to 1120°C to recrystallize. After the first heat treatment, a second heat treatment was performed. Specifically, in the second heat treatment, the steel sheet was annealed at an annealing temperature of 900°C for a holding time of 30 seconds at the annealing temperature.

[0287] The steel sheet after the annealing process before final cold rolling was subjected to one cold rolling (final cold rolling) to produce a cold-rolled steel sheet with a thickness of 0.22 mm. The cold-rolled steel sheet after the cold rolling process was subjected to a decarburization annealing process. In the decarburization annealing process, the decarburization annealing temperature Ta was set to 800°C, and the holding time at the decarburization annealing temperature was set to 120 seconds. Furthermore, the average heating rate RR from 550°C to 800°C in the heating process of the decarburization annealing process was set to 0.22 mm. 550-800 The heating rate was set to 1000°C / sec.

[0288] A sintering separator (aqueous slurry) mainly composed of MgO was applied to the surface of the steel sheet after decarburization annealing, and then the steel sheet was wound into a coil. The coiled steel sheet was then subjected to finish annealing. The finish annealing temperature was 1150°C, and the holding time at the finish annealing temperature was 10 hours. The steel sheet after finish annealing was allowed to cool.

[0289] A secondary coating formation process was carried out on the steel sheets after the final annealing process. In the secondary coating formation process, an insulating coating agent mainly composed of colloidal silica and phosphate was applied to the surface (on the primary coating) of the grain-oriented electrical steel sheets after the final annealing process, and then baking was carried out. The baking temperature was 900°C, and the holding time at the baking temperature was 30 seconds. In this way, a secondary coating, which is a tension-applying insulating coating, was formed on the primary coating. After the secondary coating was formed, a magnetic domain refinement process was carried out. Specifically, the steel sheet surface was irradiated with a laser beam under the same conditions for each test number to carry out the magnetic domain refinement process. Grain-oriented electrical steel sheets of each test number were manufactured using the above manufacturing process.

[0290] [Evaluation test] For the grain-oriented electrical steel sheets of each test number, a magnetic property evaluation test was carried out to measure the magnetic flux density B8 and iron loss W17 / 50 in the same manner as in Example 1. Furthermore, an edge crack confirmation test and a defective structure depth measurement test were carried out in the same manner as in Example 1. In this example, if the magnetic flux density B8 was 1.900 T or more, it was determined that a high magnetic flux density had been obtained, and if the iron loss W17 / 50 was 0.770 W / kg or less, it was determined that an excellent iron loss had been obtained.

[0291] [Test Results] The test results are shown in Table 22. In test numbers 2 to 10, the chemical composition of the slabs was appropriate, and conditions A to F during the manufacturing process were appropriate. Therefore, no edge cracks or defective structures occurred in any of the test numbers. Furthermore, the magnetic flux density B8 was high at 1.900 T or more, and the iron loss W17 / 50 was 0.770 W / kg or less, indicating excellent magnetic properties.

[0292] On the other hand, in Test Nos. 11 to 18, the intermediate time t1 between the completion of the final reduction of the rear end of the slab in the rough rolling process in the hot rolling process and the completion of the first reduction of the rear end of the rough bar in the finish rolling process was too long. As a result, the defective structure depth was 5 mm or more, and excessive defective structures were generated at both ends in the plate width direction TD.

[0293] In addition, in test number 1, although the intermediate time t1 was 150 seconds or less, the [Si] / [C] value was less than the lower limit (=F1) of formula (1). As a result, edge cracking was confirmed.

[0294] The embodiments of the present invention have been described above. However, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and the above-described embodiments can be appropriately modified and carried out without departing from the spirit of the present invention.

Claims

1. The chemical composition, in mass%, is C: 0.060-0.100%, Si: 3.00-4.00%, Mn: 0.01 to 0.30%, S and / or Se: 0.010 to 0.050% in total, sol. Al: 0.01 to 0.05%, N: 0.002-0.015%, Bi: 0.0011-0.0100%, Sn: 0 to 0.50%, Cr: 0-0.50%, Cu: 0 to 0.50%, and a hot rolling step of hot rolling a slab containing the remainder Fe and impurities to produce a steel plate; a cold rolling step in which the steel sheet after the hot rolling step is subjected to one or more cold rolling processes; a final pre-cold rolling annealing step in which annealing treatment is performed on the steel sheet before final cold rolling among one or more of the cold rolling steps; a decarburization annealing step of heating the steel sheet after the cold rolling step to a decarburization annealing temperature of 800 to 950°C and holding the steel sheet at the decarburization annealing temperature; an annealing separator application step of applying an annealing separator to the surface of the steel sheet after the decarburization annealing step; a final annealing step of performing final annealing on the steel sheet to which the annealing separator has been applied, The hot rolling step includes: a rough rolling step of performing rough rolling on the slab to produce a rough bar; a finish rolling step of performing finish rolling on the rough bar to produce the steel plate; In the rough rolling step, The slab is subjected to multiple reductions; The cumulative reduction rate in the rough rolling step is less than 75%, The rolling reduction rate in the final rolling step is less than 50%; The temperature of the rough bar immediately after the final reduction in the rough rolling step is 1350°C or higher; When the time from the completion of the final rolling down of the rear end of the slab in the rough rolling process to the completion of the first rolling down of the rear end of the rough bar in the finish rolling process is defined as an intermediate time t1, the intermediate time t1 is set to 150 seconds or less and satisfies formula (1), In the decarburization annealing step, The temperature of the steel plate is increased by an average of 800°C / second or more from 550°C to 800°C. heating the steel plate at a rate Manufacturing method for grain-oriented electrical steel sheets. -0.033t1+44+2000[Bi]≦[Si] / [C]≦-0.033t1+52+2000[Bi] (1) Here, in formula (1), [Bi] is substituted with the Bi content (mass%) in the chemical composition of the slab, [Si] is substituted with the Si content (mass%) in the chemical composition of the slab, [C] is substituted with the C content (mass%) in the chemical composition of the slab, and t1 is substituted with the intermediate time t1 (seconds).

2. A method for producing the grain-oriented electrical steel sheet according to claim 1, The chemical composition of the slab is: Sn: 0.01-0.50%, Cr: 0.01 to 0.50%, and Cu: 0.01 to 0.50%, Contains one or more selected from the group consisting of Manufacturing method for grain-oriented electrical steel sheets.

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