Grain-oriented electrical steel sheet and its manufacturing method

Abstract

To provide a grain oriented electrical steel sheet capable of reducing a variation in groove shape in the grain oriented electrical steel sheet and reducing a variation in the core loss of each steel sheet.SOLUTION: A grain oriented electrical steel sheet includes a steel sheet including, by mass%, at least Si:2.5-4.5% and Mn:0.01-0.15% and the remainder consisting of Fe and impurities and having a steel sheet surface including a groove extended in a direction intersecting a rolling direction and having a groove depth direction being a plate thickness direction. The standard deviation of the half value width of the groove depth is 5 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] Grain-oriented electrical steel sheets generally contain 2% to 5% by mass of Si as a steel sheet component, and the grain orientation of the steel sheet is called the Goss orientation, {110} <001> Grain-oriented electrical steel has excellent magnetic properties and is used, for example, as the core material for static inductors in transformers and the like.

[0003] In order to improve the magnetic properties of such grain-oriented electrical steel sheets, various technological developments have been made. In particular, with the recent demand for energy saving, grain-oriented electrical steel sheets are required to have even lower iron loss. In order to reduce the iron loss of grain-oriented electrical steel sheets, it is effective to increase the concentration of the crystal grains in the Goss orientation of the steel sheet to improve the magnetic flux density and reduce the hysteresis loss.

[0004] Grain-oriented electrical steel sheets used as the base material for wound transformers are particularly required to reduce core loss variation. Magnetic domain refinement is performed on electrical steel sheets to reduce core loss, but because wound transformers are annealed to relieve distortion during manufacturing, a heat-resistant magnetic domain refinement technology is required.

[0005] One method for heat-resistant magnetic domain refinement is to form periodic grooves in a steel sheet. For example, Patent Document 1 describes a method for manufacturing a low-loss grain-oriented electrical steel sheet in which, after final cold rolling, an etching resist is applied to the steel sheet surface by printing, leaving continuous or discontinuous linear regions in a direction intersecting the rolling direction as non-applied regions, and then the steel sheet is baked and etched to form continuous or discontinuous linear grooves on the steel sheet surface.

[0006] Patent Document 2 describes a method in which a resist is applied to the surface of a grain-oriented electrical steel sheet, a laser is irradiated to remove the resist from the areas irradiated with the laser, and the grain-oriented electrical steel sheet from the areas where the resist has been removed is etched to form linear grooves. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 4-88121 [Patent Document 2] Re-tabled publication No. 2017-017908 Summary of the Invention [Problem to be solved by the invention]

[0008] The inventors of the present application considered that the cause of weakening the effect of groove formation in reducing iron loss and causing iron loss variation was the variation in the groove shape. In the method described in Patent Document 1, etching resist is applied except for the linear regions of the non-coated region. However, there may be variation in the width of the linear regions of the non-coated region. In the method described in Patent Document 2, the resist is removed from the portion irradiated with a laser, and the portion is etched to form a groove, but the width of the resulting groove varies. The inventors of the present application have discovered that the variation in the groove shape is caused by the width of the linear shape of the resist film before etching.

[0009] The present invention has been made in view of the above problems, and aims to reduce the variation in groove shape by uniformly forming the linear width of a resist film that needs to be etched to form a groove, thereby reducing the variation in iron loss of each steel sheet. [Means for solving the problem]

[0010] The gist of the present invention is as follows. By mass% 、 S i:2.5~4.5%, Mn: 0.01 to 0.15% 、 C: 0.085% or less, Acid-soluble Al: 0.065% or less, N: 0.012% or less, Cr: 0.3% or less, Cu: 0.4% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, S: 0.015% or less, Se: 0.015% or less, Bi:0.02% or less with the remainder being Fe and impurities, A grain-oriented electrical steel sheet comprising a steel sheet having a steel sheet surface on which grooves are formed extending in a direction intersecting the rolling direction and whose groove depth direction is the sheet thickness direction, The average depth of the groove is 10 μm to 50 μm, The average half width of the groove depth is 10 μm to 200 μm, The standard deviation of the half-value width of the groove depth is 5 μm or less. The present invention relates to a grain-oriented electrical steel sheet and a method for producing the same. Effect of the Invention

[0011] According to the present invention, it is possible to provide an electrical steel sheet having a small variation in groove width and, as a result, a small variation in iron loss of each steel sheet, and also to provide a manufacturing method for such an electrical steel sheet having a small variation in iron loss. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 shows a cross-sectional view of a groove in a grain-oriented electrical steel sheet of the present invention. [Diagram 2] FIG. 2 is a top view of a resist film having periodic gaps. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Preferred embodiments of the present invention will be described in detail below. Unless otherwise specified, the expression "A to B" for numerical values ​​A and B means "A or more and B or less." In such an expression, when a unit is added only to numerical value B, the unit is also applied to numerical value A.

[0014] One embodiment of the present invention is 、S i: 2.5-4.5%, Mn: 0.01-0.15% , C: 0.085% or less, acid-soluble Al: 0.065% or less, N: 0.012% or less, Cr: 0.3% or less, Cu: 0.4% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, S: 0.015% or less, Se: 0.015% or less, Bi: 0.02% or less. with the remainder being Fe and impurities, A grain-oriented electrical steel sheet comprising a steel sheet having a steel sheet surface on which grooves are formed extending in a direction intersecting the rolling direction and whose groove depth direction is the sheet thickness direction, The average depth of the groove is 10 μm to 50 μm, and the average half width of the groove depth is 10 μm to 200 μm, The standard deviation of the half-value width of the groove depth is 5 μm or less. The grain-oriented electrical steel sheet is characterized in that

[0015] [Steel plate composition] First, the chemical composition of the steel sheet used in the grain-oriented electrical steel sheet according to the present invention will be described. In the following, unless otherwise specified, the notation "%" represents "mass%." The balance of the steel sheet other than the elements described below is Fe and impurities.

[0016] The composition of the steel sheet used in the grain-oriented electrical steel sheet of the present invention is {110} <001> It has a favorable composition for controlling the Goss texture accumulated in the orientation. 、S Contains i: 2.50 to 4.50%, Mn: 0.01 to 0.15%.

[0017] (Si: 2.50~4.50%) The content of Si (silicon) is 2.50 to 4.50%. Si increases the electrical resistance of the steel sheet, thereby reducing eddy current loss, which is one of the causes of iron loss. If the content of Si is less than 2.50%, it is not preferable because it becomes difficult to sufficiently suppress the eddy current loss of the final grain-oriented electrical steel sheet. If the content of Si is more than 4.50%, it is not preferable because the workability of the grain-oriented electrical steel sheet decreases. Therefore, the content of Si is 2.50 to 4.50%, and preferably 2.70 to 4.00%.

[0018] (Mn: 0.01 to 0.15%) The content of Mn (manganese) is 0.01 to 0.15%. Mn forms MnS and MnSe, which are inhibitors that affect secondary recrystallization. If the content of Mn is less than 0.01%, the absolute amount of MnS and MnSe that cause secondary recrystallization is insufficient, which is not preferable. If the content of Mn is more than 0.15%, it is not preferable because it becomes difficult to dissolve Mn during slab heating. In addition, if the content of Mn is more than 0.15%, it is not preferable because the precipitate size of MnS and MnSe, which are inhibitors, tends to become coarse, and the optimal size distribution as an inhibitor is impaired. Therefore, the content of Mn is 0.01 to 0.15%, preferably 0.03 to 0.13%.

[0019] The components other than Si and Mn may be the components contained in ordinary grain-oriented electrical steel sheets. For example, the components other than Si and Mn are, by mass%, C :0 .085% or less, acid soluble Al :0 .065% or less, N :0 .012% or less, Cr :0 .3% or less, Cu :0 .4% or less, P :0 .5% or less, Sn :0 .3% or less, Sb :0 .3% or less, Ni :1 % or less, S :0 .015% or less, Se :0 .015% or less, Bi :0 It may contain up to .02%.

[0020] The balance of the steel sheet other than the above-mentioned components is Fe and impurities. Here, the impurity elements refer to components contained in raw materials or components mixed in during the manufacturing process, and are not intentionally contained in the steel sheet.

[0021] In order to refine the magnetic domains, grooves are formed on the surface of the steel sheet, which extend in a direction intersecting the rolling direction and have a depth direction in the sheet thickness direction. The grooves only need to be provided so as to intersect with the rolling direction, and the groove extension direction does not necessarily have to be perpendicular to the rolling direction. Furthermore, the grooves do not necessarily have to have a linear shape when viewed from the sheet thickness direction (when the grooves are viewed in plan), and may have an arched shape.

[0022] FIG. 1 is a cross-sectional view of a groove of an electromagnetic steel sheet of the present invention. d is the maximum depth of the groove, and the half width W' of the groove is the groove width at a height of the depth d / 2. The groove shown in FIG. 1 has a shape close to a trapezoid, but the groove shape may be an arch shape. In one embodiment of the electromagnetic steel sheet of the present invention, the average depth of the groove is 10 μm to 50 μm. If the average depth is less than 10 μm, the amount of magnetic poles generated from the groove wall surface is small, and a sufficient iron loss reduction effect cannot be obtained. If the average depth exceeds 50 μm, the magnetic domains are subdivided, but the decrease in magnetic flux density due to the formation of the groove is large, and a sufficient iron loss reduction effect cannot be obtained. The preferred average depth is 15 μm to 30 μm.

[0023] The average depth was measured by measuring the grooves of the cold-rolled sheet after groove formation at 20 points at 1 mm intervals using a laser microscope, and the average value of the maximum depth at each point was taken as the average depth.

[0024] The "half width" used in the present invention refers to the width of the groove at a depth where the groove depth is half (hereinafter also referred to as "groove depth half width"). Specifically, it is part W' in FIG. 1. The average value of the half width is 10 μm to 200 μm, and preferably 30 μm to 100 μm. In the electrical steel sheet of the present invention, the standard deviation of the half width is 5 μm or less. As can be seen from the results of the examples shown below, when the standard deviation of the half width is 5 μm or less, the iron loss value at a magnetic flux density of 1.7 T is about 0.74 W / kg on average, and the standard deviation is 0.03 W / kg or less, and a sufficient iron loss reduction effect is obtained. The lower limit of the standard deviation of the groove depth half-width is 0.1 μm. If it is less than 0.1 μm, there is no problem with the iron loss value and its variation, but it is difficult to realize from a manufacturing technology standpoint.

[0025] (Measurement of standard deviation of half-width of groove depth) The groove shape of the cold-rolled sheet after groove formation was measured at 1 mm intervals using a laser microscope, and the groove depth half width was averaged over 20 points to obtain the standard deviation.

[0026] (Measurement of standard deviation of iron loss) The iron loss W17 / 50 of each electrical steel sheet was measured under the conditions specified in JIS C 2556 when subjected to AC excitation with a frequency of 50 Hz and a magnetic flux density amplitude of 1.7 T. The values ​​were then averaged over 10 steel sheets to obtain the standard deviation.

[0027] [Method of manufacturing grain-oriented electrical steel sheets] The inventors have found that the variation in the iron loss values ​​of the obtained electrical steel sheets is related to the variation in the half-depth width of the grooves formed on the surface of the steel sheet for magnetic domain refinement, and is further caused by the variation in the linear width of the resist film that needs to be etched to form the grooves. Therefore, as a result of extensive research into the manufacturing method of grain-oriented electrical steel sheets, the inventors have discovered the following.

[0028] Specifically, the inventors discovered that by devising the pickling treatment conditions when pickling the hot-rolled steel sheet obtained by hot rolling a slab, the linear width of the resist film that is later formed on the surface of the electrical steel sheet can be made uniform, thereby reducing the iron loss of the steel sheet and improving its magnetic properties.

[0029] One embodiment of the present invention is a method for producing a grain-oriented electrical steel sheet comprising the following steps: Hereinafter, the manufacturing process of the grain-oriented electrical steel sheet of the present invention will be described separately for a process for obtaining a cold-rolled steel sheet and a subsequent magnetic domain control process.

[0030] [Process from slab to cold-rolled steel sheet] By mass% 、S i: 2.5%~4.5%, Mn: 0.01%~0.15% , C: 0.02-0.10%, acid-soluble Al: 0.01-0.05%, N: 0.002-0.015%, Cr: 0.3% or less, Cu: 0.4% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, S and Se: 0.001-0.050% in total, Bi: 0.02% or less and the balance being Fe and impurities, the slab is subjected to hot rolling to obtain a hot rolled steel sheet, A process of obtaining a pickled sheet by subjecting the hot-rolled steel sheet to pickling, or obtaining a hot-rolled annealed sheet by subjecting the hot-rolled steel sheet to hot-rolled sheet annealing, and then obtaining a pickled sheet by subjecting the hot-rolled annealed sheet to pickling, in which the pickling solution contains one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni, the total concentration of each element is 0.0001 to 0.1000%, the pH is -1 to 5, the solution temperature is 15°C to 100°C, and the steel sheet is immersed in the pickling solution for a time of 5 seconds to 200 seconds, and The pickled steel sheet was subjected to cold rolling to obtain a cold rolled steel sheet.

[0031] [Slab composition] The composition of the slab used in the manufacture of the grain-oriented electrical steel sheet according to the invention is 、S Contains i: 2.50 to 4.50%, Mn: 0.01 to 0.15%.

[0032] The Si (silicon) content is 2.5 to 4.5%. Si increases the electrical resistance of the steel sheet, thereby reducing eddy current loss, which is one of the causes of iron loss. If the Si content is less than 2.5%, it is not preferable because it becomes difficult to sufficiently suppress the eddy current loss of the final grain-oriented electrical steel sheet. If the Si content exceeds 4.5%, it is not preferable because the workability of the grain-oriented electrical steel sheet decreases. Therefore, the Si content is 2.5% to 4.5%, and preferably 2.7 to 4.0%.

[0033] The content of Mn (manganese) is 0.01 to 0.15%. Mn forms MnS and MnSe, which are inhibitors that affect secondary recrystallization. If the content of Mn is less than 0.01%, the absolute amount of MnS and MnSe that cause secondary recrystallization is insufficient, which is not preferable. If the content of Mn is more than 0.15%, it is not preferable because it becomes difficult to dissolve Mn during slab heating. In addition, if the content of Mn is more than 0.15%, it is not preferable because the precipitate size of MnS and MnSe, which are inhibitors, tends to become coarse, and the optimal size distribution as an inhibitor is impaired. Therefore, the content of Mn is 0.01 to 0.15%, preferably 0.03 to 0.13%.

[0034] The components other than Si and Mn may be the components contained in ordinary grain-oriented electrical steel sheets. For example, components other than Si and Mn are, by mass%, C: 0.02~0.10% , acid-soluble Al: 0.01~0.05% , N: 0.002~0.015% , Cr :0 .3% or less, Cu :0 .4% or less, P :0 .5% or less, Sn :0 .3% or less, Sb :0 .3% or less, Ni :1 %below, S and Se: 0.001 to 0.050% in total , Bi :0 It may contain up to .02%.

[0035] The C (carbon) content is 0.02 to 0.10%. C has various roles, but if the C content is less than 0.02%, the grain size becomes excessively large when the slab is heated, which increases the iron loss value of the final grain-oriented electrical steel sheet, which is not preferable. If the C content exceeds 0.10%, the decarburization time becomes long during decarburization after cold rolling, which increases the manufacturing cost, which is not preferable. Also, if the C content exceeds 0.10%, decarburization is likely to be incomplete, which is not preferable because it may cause magnetic aging in the final grain-oriented electrical steel sheet. Therefore, the C content is 0.02 to 0.10%, and preferably 0.05 to 0.09%.

[0036] The total content of S (sulfur) and Se (selenium) is 0.001 to 0.050%. S and Se form an inhibitor together with the above-mentioned Mn. Both S and Se may be contained in the slab, but at least one of them should be contained in the slab. If the total content of S and Se is outside the above range, it is not preferable because a sufficient inhibitor effect cannot be obtained. Therefore, the total content of S and Se is 0.001 to 0.050%, preferably 0.001 to 0.040%.

[0037] The content of acid-soluble Al (acid-soluble aluminum) is 0.01 to 0.05%. Acid-soluble Al constitutes an inhibitor necessary for producing a grain-oriented electrical steel sheet with high magnetic flux density. If the content of acid-soluble Al is less than 0.01%, the amount of acid-soluble Al is insufficient, and the inhibitor strength is insufficient, which is not preferable. If the content of acid-soluble Al is more than 0.05%, the AlN precipitated as an inhibitor becomes coarse, which is not preferable, and therefore the inhibitor strength is reduced. Therefore, the content of acid-soluble Al is 0.01 to 0.05%, and preferably 0.01 to 0.04%.

[0038] The N (nitrogen) content is 0.002 to 0.015%. N forms AlN, which is an inhibitor, together with the above-mentioned acid-soluble Al. If the N content is outside the above range, it is not preferable because a sufficient inhibitor effect cannot be obtained. Therefore, the N content is 0.002 to 0.015%, and preferably 0.002 to 0.012%.

[0039] Furthermore, the slab used in the manufacture of the grain-oriented electrical steel sheet according to this embodiment may contain, in addition to the above-mentioned elements, one or more of Cu, P, Sn, Ni, Cr, Sb, and Bi as elements that stabilize secondary recrystallization. When the slab contains the above-mentioned elements, the magnetic flux density of the grain-oriented electrical steel sheet to be manufactured can be further improved.

[0040] A slab is formed by casting molten steel adjusted to the above-described composition. The method for casting the slab is not particularly limited. In research and development, even if a steel ingot is formed in a vacuum melting furnace or the like, the same effect as when a slab is formed can be confirmed for the above-described components. Next, the slab is heated and hot-rolled to be processed into a hot-rolled steel sheet.

[0041] [Process to make hot-rolled steel sheet] Next, the heated slab is hot-rolled to be processed into a hot-rolled steel sheet. The thickness of the hot-rolled steel sheet after processing may be, for example, 1.8 mm to 3.5 mm. If the thickness of the hot-rolled steel sheet is less than 1.8 mm, the temperature of the steel sheet after hot rolling becomes low, and the amount of AlN precipitated in the steel sheet increases, making secondary recrystallization unstable, which is undesirable because the magnetic properties of the grain-oriented electrical steel sheet having a final thickness of 0.23 mm or less deteriorate. If the thickness of the hot-rolled steel sheet is more than 3.5 mm, the rolling load in the cold rolling process becomes large, which is undesirable.

[0042] [Pickling process] Subsequently, the processed hot-rolled steel sheet is pickled or hot-rolled sheet annealed to obtain a hot-rolled annealed sheet, which is then pickled.

[0043] The pickling solution contains one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni, the total concentration of each element is 0.0001 to 0.1000%, and the pH is -1 to 5. The temperature of the pickling solution is 15°C to 100°C, and the steel sheet is immersed in the pickling solution for 5 to 200 seconds.

[0044] If the total concentration of one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni in the pickling solution is less than 0.0001%, the formation of sulfides with these elements is insufficient, which is not preferable. If the total concentration of one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni in the pickling solution is more than 0.1000%, the effect of improving magnetic properties is saturated, and the cost of the pickling solution increases, which is not preferable. Therefore, the total concentration of one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni in the pickling solution is 0.0001 to 0.1000%.

[0045] If the pH of the pickling solution is less than -1, it is undesirable because the acidity becomes too strong and the handling of the pickling solution becomes difficult. If the pH of the pickling solution is more than 5, the generation of sulfides with those elements by the pickling treatment becomes insufficient, which is undesirable. Therefore, the pH of the pickling solution is -1 or more and 5 or less.

[0046] If the temperature of the pickling solution is less than 15°C, the generation of sulfides with these elements by the pickling treatment will be insufficient, which is not preferable. If the temperature of the pickling solution is more than 100°C, the handling of the pickling solution will be difficult, which is not preferable. Therefore, the temperature of the pickling solution is 15°C or more and 100°C or less.

[0047] If the time for which the steel sheet is immersed in the pickling solution in the pickling treatment is less than 5 seconds, the generation of sulfides with these elements by the pickling treatment becomes insufficient, which is not preferable. If the time for which the steel sheet is immersed in the pickling solution in the pickling treatment exceeds 200 seconds, the equipment becomes long and large, which is not preferable. Therefore, the time for which the steel sheet is immersed in the pickling solution in the pickling treatment is 5 seconds or more and 200 seconds or less.

[0048] [Process to make cold-rolled steel sheet] After the hot-rolled steel sheet is pickled, it is processed into cold-rolled steel sheet by rolling it in one cold rolling process or multiple cold rolling processes with intermediate annealing. In addition, the steel sheet may be heat-treated at about 300°C or less between passes of cold rolling, between rolling roll stands, or during rolling. In such a case, the magnetic properties of the final grain-oriented electrical steel sheet can be improved. The hot-rolled steel sheet may be rolled by three or more cold rolling passes, but since multiple cold rolling passes increase the manufacturing cost, it is preferable that the hot-rolled steel sheet is rolled by one or two cold rolling passes. When cold rolling is performed by reverse rolling such as a Sendzimir mill, the number of passes in each cold rolling pass is not particularly limited, but is preferably 9 passes or less from the viewpoint of manufacturing cost.

[0049] The steps from the slab to obtaining a cold-rolled steel sheet have been explained above, but the method for producing a grain-oriented electrical steel sheet of the present invention is characterized in that the hot-rolled steel sheet is pickled using the above pickling treatment conditions.

[0050] [Process for forming a resist film on the steel sheet surface] The step of forming a resist film having linear non-coated portions on the surface of a cold-rolled steel sheet is carried out according to the following embodiment 1 or embodiment 2. In both processes, a resist film is formed on the steel sheet surface, with periodic linear non-coated resist film portions. The resist film functions to prevent etching of the steel sheet other than the groove formation portions in the etching process described below. For this reason, any material can be used for the resist film as long as it can prevent etching of the steel sheet. In this case, from the viewpoint of enhancing the iron loss reduction effect, the linear non-resist coating portion is preferably at an angle of 30° or less with respect to the width direction of the steel sheet. In addition, by setting the removal interval of the resist coating to 1.5 to 10 mm, the magnetic properties of the grain-oriented electrical steel sheet can be further improved.

[0051] (Aspect 1 of forming a resist film) A resist film having periodic gaps is formed on the cold-rolled steel sheet by, for example, gravure printing, and then electrolysis and pickling etching are performed to form periodic grooves. In this process, for example, a gravure printing method using a gravure roll is used to apply a resist film. A gravure offset printing apparatus consisting of a gravure roll with a textured surface and a gravure offset roll is used to form a resist film having periodic linear non-coated portions on the surface of the steel sheet.

[0052] (Aspect 2 of forming a resist film) A solution for forming a resist film is applied to the cold-rolled steel sheet, and then the steel sheet is irradiated with a laser, arc lamp, plasma, electron beam, etc. (to remove the resist) to form a resist film with periodic gaps. In this process, a resist film is applied to the entire surface of the steel sheet by any method, and then the resist film is irradiated with a laser, an arc lamp, plasma, an electron beam, or the like, so that the resist film in the irradiated areas is locally heated, vaporized, and removed, forming periodic linear areas where the resist film is not applied.

[0053] [Electrolysis and pickling etching process] After the resist film is formed, linear grooves are formed on the surface of the steel sheet by etching. Any method can be used for etching the steel sheet, but electrolytic etching or acid-washing etching is preferred. For example, NaCl, KCl, etc. can be used for electrolytic etching. For acid-washing etching, FeCl3, HCl, etc. can be used.

[0054] [Primary recrystallization annealing process] After forming linear grooves on the steel sheet surface, the cold-rolled steel sheet is heated and then decarburized annealed. These processes are also called primary recrystallization annealing, and are preferably performed continuously. By rapidly raising the temperature in the primary recrystallization annealing, it is possible to increase the number of Goss-oriented grains before secondary recrystallization in the cold-rolled steel sheet, and it is expected that grains with an orientation closer to the ideal Goss orientation will be secondary recrystallized in the secondary recrystallization process.

[0055] Such a rapid temperature rise can be achieved, for example, by using a current heating method or an induction heating method.

[0056] Here, the heating process may be performed by a plurality of devices. For example, holding or slow cooling at a temperature lower than 550°C at which recovery of the steel sheet occurs, i.e., a decrease in dislocation density in the steel sheet, may be performed because this can improve the temperature uniformity of the steel sheet before heating. Furthermore, the heating process including heating from 550°C to 700°C may also be performed by one or more devices.

[0057] The point at which heating starts is the point at which the temperature of the steel plate transitions from a decreasing state to an increasing state on the low-temperature side of 550°C or less (i.e., the point at which the temperature change is at a minimum value), while the point at which heating ends is the point at which the temperature of the steel plate transitions from an increasing state to a decreasing state on the high-temperature side of 700°C or more (i.e., the point at which the temperature change is at a maximum value).

[0058] However, depending on the arrangement of the multiple heating devices, there is a possibility that the temperature of the steel sheet may continue to rise at a temperature higher than the temperature of the heating process including 700° C. In such a case, for example, the end point of the rapid heating may be a point at or above 700° C. where the rate of change of the heating rate is a negative value and is minimal.

[0059] Here, the method of determining the temperature rise start point and the rapid temperature rise end point is not particularly limited, but for example, it is possible to determine by measuring the steel sheet temperature using a radiation thermometer or the like. The method of measuring the steel sheet temperature is not particularly limited. Furthermore, even if the temperature rise end temperature of the primary recrystallization is lower or higher than the subsequent decarburization annealing temperature, the effect of the present invention is not impaired. When the temperature rise end temperature of the primary recrystallization is lower than the decarburization annealing temperature, the steel sheet may be heated in the decarburization annealing process. When the temperature rise end temperature of the primary recrystallization is higher than the decarburization annealing temperature, the steel sheet may be cooled by performing a heat radiation treatment or a gas cooling treatment. Furthermore, after cooling to a temperature lower than the decarburization annealing temperature, the steel sheet may be reheated in the decarburization annealing process.

[0060] However, when it is difficult to measure the steel sheet temperature and difficult to estimate the exact positions of the temperature rise start point and the rapid temperature rise end point, these positions may be estimated by analogy with the heat patterns of the temperature rise process and the cooling process. Furthermore, the entry and exit temperatures of the steel sheet into the temperature rise device during the temperature rise process may be set as the temperature rise start point and the rapid temperature rise end point.

[0061] In the step of primary recrystallization annealing, the cold-rolled steel sheet may be subjected to reduction annealing following decarburization annealing in order to improve magnetic properties and coating properties.

[0062] [Finish annealing process] Thereafter, the cold-rolled steel sheet after the primary recrystallization annealing is subjected to a finish annealing. In this case, an annealing separator mainly composed of MgO may be applied before the finish annealing for the purpose of preventing seizure between steel sheets, forming a primary coating, controlling secondary recrystallization behavior, etc. The annealing separator is generally applied to the steel sheet surface in the form of a water slurry and dried, but an electrostatic application method or the like may also be used.

[0063] Then, the coiled steel sheet is subjected to a finish annealing for the purpose of forming a primary coating and secondary recrystallization. The finish annealing may be performed by heat treating the coiled steel sheet using, for example, a batch-type heating furnace. Furthermore, in order to further reduce the iron loss value of the final grain-oriented electrical steel sheet, the coiled steel sheet may be subjected to a purification treatment in which the temperature is raised to about 1200°C and then held at that temperature. Finish annealing is generally performed by raising the temperature from about room temperature, and the temperature raising rate of finish annealing is various, but is not particularly limited in the present invention, and general finish annealing conditions can be used. For example, the rate may be 5°C / h to 100°C / h from the viewpoint of productivity and general equipment constraints. In addition, other known heat patterns may be used. The heat pattern in the cooling process is also not particularly limited.

[0064] The atmosphere gas composition in the final annealing is not particularly limited. In the secondary recrystallization process, a mixed gas of nitrogen and hydrogen may be used. A dry atmosphere or a wet atmosphere may be used. In the purification annealing, dry hydrogen gas may be used.

[0065] [Planarization annealing process] Next, after the finish annealing, an insulating coating mainly composed of, for example, aluminum phosphate or colloidal silica is applied to the surface of the steel sheet in order to provide the steel sheet with insulation and tension. Then, flattening annealing is performed in order to bake the insulating coating and flatten the shape of the steel sheet by the finish annealing. Note that the components of the insulating coating are not particularly limited as long as the steel sheet is provided with insulation and tension. Note that in this embodiment, it goes without saying that the grain-oriented electrical steel sheet may be subjected to a magnetic domain control treatment depending on the purpose of the customer.

[0066] The standard deviation of the half width of the groove depth of the final groove shape formed in the grain-oriented electrical steel sheet was measured using the above-mentioned measurement method. As shown in the Examples, in the embodiment 1 in which linear grooves are formed, the standard deviation of the half width of the groove depth in the invention example was 5 μm or less, and a uniform groove shape was formed. Although the details of the mechanism by which the groove shape formed in mode 1, in which linear grooves are formed, becomes uniform is unknown, it is presumed as follows: MnS precipitated on the steel sheet surface is replaced or coated with sulfides of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni by the pickling treatment, so that the friction between the resist film forming solution and the steel sheet becomes constant over the entire surface, and no difference occurs in dripping.

[0067] Similarly, as shown in the following Examples, in the second aspect of forming linear grooves, in the invention examples, the standard deviation of the half-width of the groove depth was 5 μm or less, and a uniform groove shape was formed. Although the details of the mechanism by which the groove shape formed in Mode 2, in which linear grooves are formed, becomes uniform, are unknown, it is presumed as follows: MnS precipitated on the steel sheet surface is replaced or coated with sulfides of Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni by the pickling treatment, so that the heat transfer coefficient on the steel sheet surface becomes constant and the roughness of the steel sheet surface becomes constant, which allows the resist coating to be peeled off uniformly by a laser or the like.

[0068] The above steps allowed the final grain-oriented electrical steel sheet to be manufactured. The manufacturing method according to the present embodiment allowed the manufacture of grain-oriented electrical steel sheets with reduced iron loss variation and excellent magnetic properties.

[0069] The grain-oriented electrical steel sheet according to the present embodiment has been described above. The grain-oriented electrical steel sheet according to the present embodiment can be manufactured by the above-mentioned method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment. However, the method is not limited to this method. EXAMPLES

[0070] The method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention and the grain-oriented electrical steel sheet will be described in more detail below with reference to examples. Note that the examples shown below are merely examples of the grain-oriented electrical steel sheet according to this embodiment, and the grain-oriented electrical steel sheet according to this embodiment is not limited to the examples shown below.

[0071] Pickling was performed using a pickling solution containing Cu, Hg, Ag, Pb, Cd, Co, Zn and Ni. The temperature of the pickling solution was set at 25°C. For safety reasons, pickling was not performed with a pH of -1 or less.

[0072] The components, concentrations, pH values, and immersion times of the pickling solutions used in Examples I and II are shown in Table 1. [Table 1]

[0073] Example I The effect of the present invention will be specifically described. A grain-oriented electrical steel sheet was produced by a process using gravure offset printing using a silicon steel slab that had been subjected to the above-mentioned hot-rolled sheet annealing. The composition ratio of the silicon steel slab was, in mass%, 3.3% Si, 0.1% Mn, 0.007% S, 0.03% acid-soluble Al, 0.008% N, 0.06% Sn, with the balance being Fe and unavoidable impurities. After the hot-rolled annealed sheet was pickled using the pickling solution described above, a coating having periodic linear resist film non-coated areas of about 40 μm in width was formed on the sample steel sheet that had been subjected to the cold rolling process described above using gravure offset printing.Then, electrolytic etching was performed to form grooves of about 50 μm in width and about 20 μm in depth at 5 mm intervals in a direction at 10 degrees from the perpendicular direction to the rolling direction (a direction at 80 degrees to the rolling direction), as shown in Figure 2. Thereafter, the above-mentioned steps from the primary recrystallization onwards were carried out. Regarding the groove shape formed, the groove shape of the cold-rolled sheet after groove formation was measured at 1 mm intervals using a laser microscope using the measurement method described above. The average value of 20 groove depth half-width values ​​was calculated, and the standard deviation of the half-width was obtained.

[0074] The variation in iron loss in the obtained grain-oriented electrical steel sheets was evaluated by the standard deviation value of the iron loss at 1.7 T and 50 Hz. The standard deviation value of the iron loss was obtained by measuring the iron loss W17 / 50 of each electrical steel sheet under the conditions specified in JIS C 2556, and averaging the values ​​for 10 sheets to obtain the standard deviation value. A standard deviation value of the iron loss of 0.03 W / kg or less was deemed to be acceptable. The results are shown in Table 2. The comparative examples are the results obtained with grain-oriented electrical steel sheets using the pickling conditions of the comparative examples shown in Table 1.

[0075] [Table 2]

[0076] Example II The silicon steel slab that had been subjected to the above-mentioned hot-rolled sheet annealing was used to manufacture grain-oriented electrical steel sheets by the above-mentioned process. The composition ratio of the silicon steel slab was, in mass%, 3.3% Si, 0.1% Mn, 0.007% S, 0.03% acid-soluble Al, 0.008% N, 0.06% Sn, with the balance being Fe and unavoidable impurities. The hot-rolled annealed sheet was pickled using the pickling solution described above, and then the sample steel sheet that had been subjected to the cold rolling process described above was coated with a resist film using gravure offset printing over the entire surface of the steel sheet. A laser was then applied to partially remove a portion of the resist film with a width of approximately 40 μm. Thereafter, electrolytic etching was performed to form grooves with a width of approximately 50 μm and a depth of approximately 20 μm at intervals of 5 mm in a direction at an angle of 10 degrees from the direction perpendicular to the rolling direction (a direction at an angle of 80° to the rolling direction). Thereafter, the above-mentioned steps from the primary recrystallization onwards were carried out. For the formed groove shape, the standard deviation of the half-value width was measured using the above-mentioned measurement method.

[0077] The iron loss values ​​of 10 grain-oriented electrical steel sheets obtained were measured at 1.7 T and 50 Hz, the average value was calculated, and the variation in iron loss of each electrical steel sheet was evaluated by the standard deviation of iron loss. A standard deviation of iron loss of 0.03 W / kg or less was deemed to be acceptable. The results are shown in Table 2. The comparative examples are results obtained with grain-oriented electrical steel sheets that were pickled under the comparative pickling conditions shown in Table 1.

[0078] [Table 3]

Claims

1. In mass percent, Si: 2.5-4.5%, Mn: 0.01 to 0.15%, C: 0.085% or less, Acid-soluble Al: 0.065% or less, N: 0.012% or less, Cr: 0.3% or less, Cu: 0.4% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, S: 0.015% or less, Se: 0.015% or less, Bi: 0.02% or less, the balance being Fe and impurities; A grain-oriented electrical steel sheet having a steel sheet having a steel sheet surface on which grooves are formed extending in a direction intersecting the rolling direction and whose groove depth direction is the sheet thickness direction, The average depth of the groove is 10 μm to 50 μm, The average half width of the groove depth is 10 μm to 200 μm, The grain-oriented electrical steel sheet is characterized in that the standard deviation of the half-value width of the groove depth is 5 μm or less.

2. A grain-oriented electrical steel sheet as described in claim 1, in which the standard deviation of iron loss at a frequency of 50 Hz and a magnetic flux density of 1.7 T is 0.03 W / kg or less.

3. In mass percent, Si: 2.5% to 4.5%, Mn: 0.01% to 0.15%, C: 0.02-0.10%, Acid-soluble Al: 0.01 to 0.05%, N: 0.002-0.015%, Cr: 0.3% or less, Cu: 0.4% or less, P: 0.5% or less, Sn: 0.3% or less, Sb: 0.3% or less, Ni: 1% or less, S and Se: 0.001 to 0.050% in total, A step of hot rolling a slab containing Bi: 0.02% or less and the balance being Fe and impurities to obtain a hot rolled steel sheet; A process of obtaining a pickled sheet by subjecting the hot-rolled steel sheet to pickling, or obtaining a hot-rolled annealed sheet by subjecting the hot-rolled steel sheet to hot-rolled sheet annealing, and then obtaining a pickled sheet by subjecting the hot-rolled annealed sheet to pickling, in which the pickling solution contains one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni, the total concentration of each element is 0.0001 to 0.1000%, the pH is -1 to 5, the solution temperature is 15°C to 100°C, and the steel sheet is immersed in the pickling solution for a time of 5 seconds to 200 seconds, and A step of obtaining a cold-rolled steel sheet by cold rolling the pickled sheet; forming a resist film having periodic gaps on the cold-rolled steel sheet by printing; A step of forming periodic grooves by subjecting the cold-rolled steel sheet on which the resist film has been formed to electrolysis and pickling etching. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, further comprising the steps of:

4. Instead of the step of forming a resist film having periodic gaps by printing, the method includes a step of applying a solution for forming a resist film to the cold-rolled steel sheet, and then removing the resist linearly by irradiating the cold-rolled steel sheet with a laser, an arc lamp, plasma or an electron beam, A step of forming periodic grooves by subjecting the cold-rolled steel sheet on which the linear resist film has been formed to electrolysis and pickling etching. The method for producing a grain-oriented electrical steel sheet according to claim 3, further comprising the steps of:

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