Grain-oriented electrical steel sheet

Abstract

By controlling the shape of a linear groove formed for magnetic domain subdivision and the Sa value of the surface roughness of the bottom surface and the side surface inside the groove within a certain range, the iron loss reduction effect of the obtained grain-oriented electromagnetic steel sheet can be further reduced without impairing the iron loss reduction effect of the obtained grain-oriented electromagnetic steel sheet. The grain-oriented electrical steel sheet is provided with a steel sheet which contains, in mass%, 2.50-4.50% of Si, 0.01-0.15% of Mn, and the balance of Fe and impurities, and which has a steel sheet surface formed at intervals of 2-10 mm in linear grooves extending in a direction at an angle of 0-30 DEG with respect to the direction perpendicular to the rolling direction, and a steel sheet surface formed at intervals of 2-10 mm in linear grooves extending in a direction at an angle of 0-30 DEG with respect to the direction perpendicular to the rolling direction. The depth D of the groove is 10 [mu] m to 40 [mu] m, the width W of the groove is 20 [mu] m to 200 [mu] m, the Sa bottom value of the surface roughness of the bottom surface inside the groove exceeds 5.0 [mu] m, and the Sa side value of the surface roughness of the side surface inside the groove is 1.0 [mu] m to 5.0 [mu] m.

Description

Technical Field

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

[0002] The grain-oriented electrical steel sheet generally contains about 2% to 5% by mass of Si as a steel sheet component, and is a steel sheet in which the orientation of the crystal grains of the steel sheet is highly concentrated in the {110}<001> orientation called the Goss orientation. The grain-oriented electrical steel sheet has excellent magnetic properties and is used, for example, as a core material for static inductors such as transformers.

[0003] In such a grain-oriented electrical steel sheet, various technical developments have been made to improve the magnetic properties. In particular, with the recent requirements for energy conservation, further reduction of iron loss is required for the grain-oriented electrical steel sheet. For the reduction of iron loss in the grain-oriented electrical steel sheet, it is effective to increase the degree of aggregation in the Goss orientation of the crystal grains of the steel sheet to increase the magnetic flux density and reduce the hysteresis loss.

[0004] For the grain-oriented electrical steel sheet used as a base material for a winding transformer, while further reduction of iron loss is required, further reduction of noise is also required. For the reduction of iron loss, magnetic domain refinement is performed in the electrical steel sheet. However, in a wound transformer, stress relief annealing is performed in the manufacturing process. Therefore, in the case of performing magnetic domain refinement, a heat-resistant magnetic domain refinement technique is required.

[0005] As a heat-resistant magnetic domain refinement method, there is a method of forming periodic grooves on the steel sheet. For example, in Patent Document 1, it is described that by imparting linear defects having a pitch of 5 mm or less, a width of 1 mm or less, a depth of 0.3 to 5.0 μm in terms of Ra value, and a Rmax value of 10 μm or less to the surface of the steel sheet before or after decarburizing annealing, a grain-oriented electrical steel sheet having extremely excellent iron loss and excellent cover film adhesion can be obtained.

[0006] In Patent Document 2, a grain-oriented electrical steel sheet is described, which has a steel sheet surface formed with grooves extending in a direction crossing the rolling direction and the groove depth direction being the plate thickness direction. The formed grooves are asymmetric with respect to the center of the groove width in the groove width direction. It is disclosed that by setting the average depth of the grooves having such a cross-sectional shape, the arithmetic mean height Ra of the roughness curve of the contour of the groove bottom region where the grooves are formed, and the average length RSm of the roughness curve elements of the contour of the groove bottom region within a specific range, an iron loss reduction effect can be obtained.

[0007] In Patent Documents 1 to 2, various proposals have been made regarding the magnetic domain refinement technique for obtaining the iron loss reduction effect during magnetic domain refinement, but no proposal has been made regarding noise reduction.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Japanese Unexamined Patent Application Publication No. 1-198429

[0011] Patent Document 2: WO 2016 / 171130 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] As a base material for a winding transformer, a grain-oriented electrical steel sheet is required to have lower iron loss and further lower noise. Heat-resistant magnetic domain refinement is generally carried out by forming linear grooves, but at present, sufficient noise reduction effect cannot be obtained.

[0014] It is considered that one of the causes of noise is the presence of crystal orientation deviation. When the magnetic domain structure changes during excitation (when the magnetic moment changes direction), the crystal lattice expands and contracts (magnetostriction). The magnetostriction is amplified and becomes vibration, which then becomes noise.

[0015] Therefore, an object of the present invention is to reduce the iron loss of the grain-oriented electrical steel sheet and achieve further lower noise.

[0016] Means for Solving the Problems

[0017] The inventors of the present invention have intensively studied to mitigate the change in the magnetic domain structure during excitation in order to reduce noise.

[0018] The change in the magnetic domain structure during excitation is greatly affected by the movement of stripe domains, which are the main magnetic domain structure of the grain-oriented electrical steel sheet. In the absence of factors that impede the movement of magnetic domain walls between stripe domains, the movement of magnetic domain walls (in other words, the movement of stripe domains) becomes smooth. As a result, the change in the magnetic domain structure becomes drastic (unstable), and thus the noise increases. Therefore, by impeding the movement of the magnetic domain walls, the noise can be reduced. On the other hand, if the movement of the magnetic domain walls is smooth, the iron loss can be reduced.

[0019] Here, as the main cause of hindering the movement of magnetic domain walls, a change in the cross-sectional area of the groove can be cited. (Since the groove extends in the longitudinal direction, its cross-sectional area may be different at a cross-section different from a certain cross-section. For example, in a groove extending from the front side to the inner side, the cross-sectional area may be different at the front-side cross-section and the inner-side cross-section. The cross-section here refers to a cross-section perpendicular to the longitudinal direction or the extending direction of the groove.) It can be considered that the less the cross-sectional area of the groove changes, that is, the more uniform the projected shape of the groove cross-section from the front side to the inner side of the groove, in other words, the smaller the surface roughness (also called surface roughness) inside the groove, the smoother the movement of the magnetic domain walls. On the contrary, it can be considered that the larger the surface roughness, the more the movement of the magnetic domain walls is hindered.

[0020] Here, in the evaluation of the surface shape (surface roughness) inside the groove as described in Patent Documents 1 to 3, Ra, which represents linear roughness, typically evaluates only one cross-section of the groove, so sometimes the change in the cross-sectional area of the groove (from the front side to the inner side) cannot be fully evaluated. Specifically, even if the linear roughness Ra is increased, sometimes the movement of the magnetic domain walls cannot be hindered, and thus the noise cannot be reduced. In contrast, the present inventors have obtained the following insight: by evaluating with surface roughness Sa instead of linear roughness Ra, the change in the cross-sectional area of the groove can be fully evaluated, and by increasing the surface roughness Sa, the movement of the magnetic domain walls can be hindered, and as a result, the noise can be reduced. That is, when evaluating the surface shape (surface roughness) inside the groove, by using surface roughness Sa instead of the conventional linear roughness Ra, the noise can be more effectively reduced.

[0021] However, in the case of excessively hindering the movement of magnetic domain walls, it will have an adverse effect on iron loss, so a moderate hindering factor is required. Thus, the present inventors have proposed the following concept: hinder the movement of magnetic domain walls required to reduce noise, and thicken the surface roughness of the bottom surface inside the groove. That is, the present inventors have proposed the following concept: even if the side surface inside the groove (sometimes also called the wall surface or side wall surface of the groove) is thickened, the noise can be similarly reduced, but the adverse effect on iron loss is relatively large, so only the bottom surface inside the groove is made rough, and the side surface inside the groove is smoothed to reduce iron loss.

[0022] In addition, the present inventors have also found that, in order to form grooves having a desired surface roughness Sa, it is useful to control the manufacturing conditions from the following viewpoints. That is, by performing pickling treatment using a special pickling solution before forming the grooves, the ratio of the heat transfer coefficient of the precipitate on the steel plate surface to the specific heat and heat transfer coefficient of the base metal is deviated. Moreover, it has been found that by utilizing the difference in heat transfer during groove formation by laser irradiation or the like, the unevenness of the bottom surface inside the groove can be promoted, thereby obtaining a noise reduction effect. In addition to this, it has also been found that by blowing air at a wind speed of 100 m / s or more using a blower when applying a heat source such as laser irradiation, the components (dust) melted or evaporated from the steel plate due to the heat source can be suppressed from flying and reattaching to the steel plate, laser, etc., and the smoothing of the side surface inside the groove can be promoted, thereby obtaining an iron loss reduction effect.

[0023] The present invention has been completed based on the above-mentioned insights. In the present invention, by controlling the shape of the linear grooves formed for magnetic domain refinement and the Sa value of the surface roughness of the bottom surface and the side surface inside the grooves within a certain range, the iron loss of the grain-oriented electrical steel sheet is reduced, and further low-noise performance is achieved.

[0024] The gist of the present invention relates to a grain-oriented electrical steel sheet including a steel plate which, by mass%, contains Si: 2.50 to 4.50%, Mn: 0.01 to 0.15%, the balance being Fe and impurities, and has a steel plate surface on which linear grooves extending in a direction at an angle of 0 to 30° with respect to the direction perpendicular to rolling are formed at intervals of 2 to 10 mm; the depth D of the grooves is 10 to 40 μm, the width W of the grooves is 20 to 200 μm, the Sa value of the surface roughness of the bottom surface inside the grooves exceeds 5.0 μm, and the Sa value of the surface roughness of the side surface inside the grooves is 1.0 to 5.0 μm.

[0025] In addition, the MnS on the bottom surface inside the grooves may not be replaced with one or more sulfides selected from Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni, or may not be coated with one or more selected from Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni.

[0026] Hereinafter, in the present specification, "one or more selected from Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni" will be abbreviated as "Cu etc.", and "one or more sulfides selected from Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni" will be abbreviated as "Cu etc. sulfides".

[0027] Advantages of the Invention

[0028] According to the present invention, in the groove formed by laser irradiation, by making the bottom surface inside the groove uneven (the surface roughness Sa is limited within a specified range), the movement of magnetic domain walls is hindered, and noise is reduced. By making the side surface inside the groove smooth (the surface roughness Sa is limited within a specified range), the movement of magnetic domain walls becomes smooth, and an iron loss reduction effect can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a cross-sectional view of the groove of the grain-oriented electrical steel sheet of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] Hereinafter, preferred embodiments of the present invention will be described in detail. In addition, unless otherwise specified, with respect to numerical values A and B, the notation "A to B" means "A or more and B or less". When only the unit is indicated for numerical value B in this notation, the same unit also applies to numerical value A.

[0031] [Composition of the steel sheet]

[0032] First, the composition of the steel sheet used in the grain-oriented electrical steel sheet of the invention will be described.

[0033] In addition, unless otherwise specified hereinafter, the notation "%" means "% by mass". The remainder of the steel sheet other than the elements described below is Fe and impurities.

[0034] The steel sheet used in the grain-oriented electrical steel sheet of the present invention contains components preferably used for controlling the texture in which crystal orientations are aggregated along the {110}<001> orientation (Goss orientation), and contains at least Si: 2.50 to 4.50%, Mn: 0.01 to 0.15%.

[0035] (Si: 2.50 to 4.50%)

[0036] The content of Si (silicon) is 2.50 to 4.50%. Si reduces eddy current loss, which is one of the causes of iron loss, by increasing the resistance of the steel sheet. When the content of Si is less than 2.50%, it is difficult to sufficiently suppress the eddy current loss of the final grain-oriented electrical steel sheet, so it is not preferred. When the content of Si exceeds 4.50%, the processability of the grain-oriented electrical steel sheet decreases, so it is not preferred. Therefore, the content of Si is 2.50 to 4.50%, preferably 2.70 to 4.00%.

[0037] (Mn: 0.01 to 0.15%)

[0038] The content of Mn (manganese) is 0.01 to 0.15%. Mn forms inhibitors that affect secondary recrystallization, such as MnS and MnSe. When the content of Mn is less than 0.01%, the absolute amounts of MnS and MnSe that cause secondary recrystallization are insufficient, so it is not preferred. When the content of Mn exceeds 0.15%, the solid solution of Mn during billet heating becomes difficult, so it is not preferred. In addition, when the content of Mn exceeds 0.15%, the precipitation sizes of MnS and MnSe as inhibitors tend to coarsen, damaging the optimal size distribution as inhibitors, so it is not preferred. Therefore, the content of Mn is 0.01 to 0.15%, preferably 0.03 to 0.13%.

[0039] Components other than Si and Mn can be components contained in ordinary grain-oriented electrical steel sheets.

[0040] For example, as components other than Si and Mn, by mass%, it may contain C: up to 0.085% or less, acid-soluble Al: up to 0.065% or less, N: up to 0.012% or less, Cr: up to 0.30% or less, Cu: up to 0.400% or less, P: up to 0.500% or less, Sn: up to 0.300% or less, Sb: up to 0.300% or less, Ni: up to 1.000% or less, S: up to 0.015% or less, Se: up to 0.015% or less, Bi: up to 0.020% or less. In addition, the contents of these components are the contents in the final product after purification annealing, etc., so the lower limit is not limited and can also be 0%.

[0041] The remainder of the steel sheet other than the above components is Fe and impurities. Here, impurity elements refer to components contained in raw materials or components mixed in during the manufacturing process, and are components that are not intentionally made to be contained in the steel sheet.

[0042] For magnetic domain refinement, grooves are formed on the steel sheet surface that extend in a direction crossing the rolling direction and whose depth direction is the sheet thickness direction. In addition, as long as the grooves are set to cross the rolling direction, it is not necessary for the extending direction of the grooves to be orthogonal to the rolling direction, but they are set in a direction at an angle of 0 to 30° with respect to the direction perpendicular to the rolling direction. In addition, when viewed from the sheet thickness direction (looking down at the grooves), the grooves do not necessarily have a straight shape and can also have an arcuate shape. The measurement of the following groove shape is carried out by removing at least the glass covering film and the insulating covering film inside the grooves from the final product using pickling, etc. In addition, the grooves can also include the inside of the grooves, where the inside of the grooves refers to the area that is recessed from the steel sheet surface and is delimited by the contour of the grooves. As described later, the grooves can also include the wall surface (also called the side surface) and the bottom surface inside the grooves.

[0043] The above-mentioned grooves are formed on the surface of the steel sheet at intervals of 2 to 10 mm. If the interval between the grooves is less than 2 mm, the effect of magnetic domain subdivision is saturated, and it is difficult to obtain the effect of reducing eddy current loss. On the other hand, since the hysteresis loss increases due to strain, the iron loss increases, which is not preferable. If the interval between the grooves exceeds 20 mm, the effect of magnetic domain subdivision decreases, and thus the effect of improving iron loss is insufficient, which is not preferable. The preferred interval of the grooves is 3 to 7 mm.

[0044] Figure 1 It is a cross-sectional view of the groove of the electromagnetic steel sheet of the present invention. In this cross-sectional view, the inside of the groove is in a shape close to a trapezoid, but the shape of the inside of the groove can also be an arc shape. In an embodiment of the electromagnetic steel sheet of the present invention, the depth D of the groove is in the range of 10 μm to 40 μm. When the depth D is less than 10 μm, the generation amount of magnetic poles from the side surfaces inside the groove decreases, and a sufficient iron loss reduction effect cannot be obtained. When the depth D exceeds 40 μm, the magnetic domains are subdivided, but the decrease in magnetic flux density caused by the formation of the groove increases, and a sufficient iron loss reduction effect cannot be obtained. The preferred depth is 15 μm to 30 μm.

[0045] (Measurement of the depth D of the groove)

[0046] The measurement method of the "depth D" of the present invention is as described below.

[0047] Select any part of the electromagnetic steel sheet, and Figure 1 Regarding the cross-sectional view of the groove shown, set the deeper one of the maximum depths of the cross-sections (A) and (B) of the groove at any two points 3 mm away from the front side and the back side in the extending direction of the groove as the depth d, and the shallower one as the depth d'. Measure using a laser microscope (a 3D laser microscope using a confocal optical system based on a pinhole). The depth D is the average value of these values.

[0048] The "width W of the groove" referred to in the present invention means the parts represented by w and w' in Figure 1 The width W of the groove is in the range of 20 μm to 200 μm. When the width W is less than 20 μm, the magnetic flux leaking from the side surface inside the groove enters the side surface of the opposite groove inside, and the generation amount of magnetic poles decreases, and a sufficient iron loss reduction effect cannot be obtained. When the width W exceeds 200 μm, the iron loss reduction effect is saturated, and the laser power required for forming the groove increases, resulting in an increase in manufacturing cost. The preferred width W is 30 to 100 mm.

[0049] (Measurement of the width W of the groove)

[0050] The measurement method of the "width W of the groove" of the present invention is as described below.

[0051] Select any part of the electromagnetic steel sheet, and Figure 1As shown in the cross-sectional view of the groove, for the cross-sections (A) and (B) of the groove at any two points 3 mm from the front side and the inner side in the extending direction of the groove, the width of the wider one of the widths where the groove depth becomes half of the maximum depth d or d' of each groove is set as w, and the narrower one is set as w'. Measurement is performed using a laser microscope (a 3D laser microscope adopting a confocal optical system based on a pinhole). The width W of the groove is the average value of these values.

[0052] The "Sa value of the surface roughness of the bottom surface inside the groove and the side surface inside the groove" as referred to in the present invention means Figure 1 the arithmetic mean height Sa value of the surface (three-dimensional surface) roughness of the bottom surface inside the groove and the side surface inside the groove between points (A) and (B) in []. In particular, sometimes the surface roughness of the bottom surface inside the groove is referred to as Sa 底 and the surface roughness of the side surface inside the groove is referred to as Sa 侧面 . The definition of the arithmetic mean height Sa of the surface (three-dimensional surface) roughness follows Japanese Industrial Standard JISB 0681-6:2014 (ISO25178-6:2010) "Geometrical Product Specifications (GPS) - Surface Texture: Areal - Part 6: Classification of Surface Texture Measuring Methods".

[0053] In the grain-oriented electrical steel sheet of the present invention, the Sa of the bottom surface inside the groove 底 exceeds 5.0 μm, preferably 6.0 μm or more. The upper limit is 10.0 μm or less, preferably 8.0 μm or less. This is because when Sa 底 is 5.0 μm or less, the noise reduction effect cannot be obtained. When Sa 底 exceeds 10.0 μm, the increase effect of iron loss (hysteresis loss) increases, and a grain-oriented electrical steel sheet with low noise and low iron loss cannot be obtained. In addition, in the grain-oriented electrical steel sheet of the present invention, precipitates such as MnS on the bottom surface inside the groove may not be replaced with sulfides such as Cu or coated with Cu or the like. Here, "the precipitates such as MnS on the bottom surface inside the groove are not replaced with sulfides such as Cu or coated with Cu or the like" means that the replacement rate of the precipitates such as MnS replaced with sulfides such as Cu is 0%, and the coverage rate of MnS covered with Cu or the like is 0%.

[0054] In the grain-oriented electrical steel sheet of the present invention, the Sa of the side surface inside the groove 侧面 is 1.0 to 5.0 μm, preferably 1.5 to 4.0 μm, and more preferably 2.0 to 3.0 μm. When Sa 侧面 is less than 1.0 μm, there is no problem with the magnetic properties, but it is difficult to achieve in manufacturing technology. When Sa 侧面 exceeds 5.0 μm, the movement of magnetic domain walls becomes unsmooth, the hysteresis loss increases, and a sufficient iron loss reduction effect cannot be obtained.

[0055] In the directionally oriented electromagnetic steel sheet of the present invention, by making the Sa of the bottom surface inside the groove 底 exceed 5.0 μm and making the surface roughness Sa of the side surface inside the groove 侧面 fall within the range of 1.0 to 5.0 μm, the reason for achieving both low iron loss and low noise is considered to be that by controlling the surface roughness Sa of the side surface inside the groove 侧面 , an iron loss reduction effect is obtained, and by controlling the surface roughness Sa of the bottom surface inside the groove 底 , a noise reduction effect is obtained.

[0056] In addition, in one embodiment of the present invention, precipitates such as MnS on the bottom surface inside the groove may not be replaced with sulfides such as Cu or coated with Cu or the like. If MnS or the like is replaced or coated with Cu or the like, the heat transfer coefficient of the steel sheet surface layer can be made constant. In the case of forming a groove by a heat source such as laser irradiation, since heat is easily transferred uniformly, here, the surface roughness Sa inside the groove is limited to a specified range. In a portion where the heat transfer coefficient is not constant, since heat is difficult to transfer uniformly, here, the surface roughness Sa inside the groove tends to increase. Thus, it is possible to easily achieve a larger surface roughness of the bottom surface inside the groove than that of the side surface inside the groove.

[0057] (Method for measuring the surface roughness Sa of the bottom surface inside the groove and the side surface inside the groove)

[0058] Measure Sa using a laser microscope (a 3D laser microscope using a confocal optical system based on a pinhole). Select any one groove of the electromagnetic steel sheet, and connect the points d and d' of the maximum depth of the cross-sections (A) and (B) of the groove at arbitrary two points 3 mm from the front side and the back side in the extending direction of the groove shown in the cross-sectional view of the Figure 1 groove into a straight line. Take the range with a unilateral width of 0.5 μm (a total width of 1.0 μm) in the right-angle direction (and in the right-angle direction from the thickness of the electromagnetic steel sheet) from this straight line as the bottom surface inside the groove, and regard the unevenness of the bottom surface inside the groove as the surface roughness Sa of the bottom surface inside the groove of the present invention 底 . In addition, among the points (d / 2, d' / 2) at a depth that is half of the maximum depth d and d' of the cross-sections (A) and (B) of the two grooves, connect the points on the same side with respect to the maximum depth into a straight line. Take the range with a unilateral width of 0.5 μm (a total width of 1.0 μm) in the right-angle direction (and in the thickness direction of the electromagnetic steel sheet) from this straight line as the side surface inside the groove, and derive the Sa 左 and Sa 右 of the unevenness of the side surface inside the groove, and set the average value of their values as the Sa 侧面 of the side surface inside the groove.

[0059] For reference, the linear surface roughness Ra is described. The "Ra value of the linear surface roughness of the bottom surface and the side surface inside the groove" means Figure 1 the arithmetic mean height Ra value of the roughness curve of the bottom surface and the side surface inside the groove between two points (A) and (B) in

[0060] (Method for measuring the surface roughness Ra of the bottom surface and the side surface inside the groove)

[0061] Using a laser microscope (a 3D laser microscope adopting a confocal optical system based on a pinhole), each Ra is measured. Select any one groove of the electromagnetic steel sheet, and Figure 1 the unevenness of the bottom surface inside the groove of the straight line formed by the points d and d' at the maximum depths of the cross-sections (A) and (B) of the groove connecting any two points 3 mm apart in the front and back sides in the extending direction of the groove shown in the cross-sectional view of the 底 groove is set as the surface roughness Ra of the bottom surface inside the groove of the present invention 左 and Ra 右 of the unevenness of the side surface inside the groove of the straight line formed by connecting the points on the same side on the left and right sandwiching the maximum depth among the points (d / 2, d' / 2) at a depth of 1 / 2 of the maximum depths d and d' of the cross-sections (A) and (B) of the two grooves respectively, and the average value of these values is set as the Ra of the side surface inside the groove 侧面 .

[0062] [Manufacturing method of the anisotropic electromagnetic steel sheet]

[0063] The manufacturing process of the anisotropic electromagnetic steel sheet of the present invention is described by dividing it into the process of obtaining a cold-rolled steel sheet until then and the subsequent magnetic domain control process.

[0064] [Process from the slab to obtaining the cold-rolled steel sheet]

[0065] A slab containing Si: 2.50% to 4.50%, Mn: 0.01% to 0.15% by mass and the balance being Fe and impurities is hot-rolled to obtain a hot-rolled steel sheet.

[0066] Next, the hot-rolled steel sheet is pickled to obtain a pickled sheet; or the hot-rolled steel sheet is annealed to obtain a hot-rolled annealed sheet, and then the hot-rolled annealed sheet is pickled to obtain a pickled sheet. The pickling solution used here contains one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni (also referred to as "Cu etc."), and the total concentration of each element is 0.0001 to 0.1000 mass% or less with respect to the pickling solution, and the pH is -1 to 5. The liquid temperature of the pickling solution is 15°C to 100°C, and the time for which the steel sheet is immersed in the pickling solution is 5 seconds to 200 seconds. A pickled sheet is obtained through this pickling process, and then the pickled sheet is cold-rolled to obtain a cold-rolled steel sheet.

[0067] [Composition of the slab]

[0068] The composition of the slab used in the production of the inventive grain-oriented electrical steel sheet contains at least Si: 2.50 to 4.50% and Mn: 0.01 to 0.15%.

[0069] The content of Si (silicon) is 2.50 to 4.50%. By increasing the resistance of the steel sheet, Si reduces the eddy current loss, which is one of the causes of iron loss. When the content of Si is less than 2.50%, it is difficult to sufficiently suppress the eddy current loss of the final grain-oriented electrical steel sheet, so it is not preferred. When the content of Si exceeds 4.50%, the workability of the grain-oriented electrical steel sheet deteriorates, so it is not preferred. Therefore, the content of Si is 2.50% to 4.50%, preferably 2.70 to 4.00%.

[0070] The content of Mn (manganese) is 0.01 to 0.15%. Mn forms inhibitors that affect secondary recrystallization, such as MnS and MnSe. When the content of Mn is less than 0.01%, the absolute amounts of MnS and MnSe that cause secondary recrystallization are insufficient, so it is not preferred. When the content of Mn exceeds 0.15%, it becomes difficult for Mn to dissolve during billet heating, so it is not preferred. In addition, when the content of Mn exceeds 0.15%, the precipitation sizes of MnS and MnSe as inhibitors tend to become coarser, damaging the optimal size distribution as inhibitors, so it is not preferred. Therefore, the content of Mn is 0.01 to 0.15%, preferably 0.03 to 0.13%.

[0071] The components other than Si and Mn can be the following components.

[0072] For example, as components other than Si and Mn, it may contain C: 0.020 to 0.100% by mass, a total of one or two of S and Se: 0.001 to 0.050%, acid-soluble Al: 0.010 to 0.050%, N: 0.002 to 0.015%, Cr: up to 0.30% or less, Cu: up to 0.400% or less, P: up to 0.500% or less, Sn: up to 0.300% or less, Sb: up to 0.300% or less, Ni: up to 1.000% or less, Bi: up to 0.020% or less.

[0073] The content of C (carbon) is 0.020 to 0.100%. C has various functions. However, when the content of C is less than 0.020%, the crystal grain size increases too much during the heating of the slab, resulting in an increase in the iron loss value of the final grain-oriented electrical steel sheet, so it is not preferred. When the content of C exceeds 0.100%, during decarburization after cold rolling, the decarburization time becomes very long and the manufacturing cost increases, so it is not preferred. In addition, when the content of C exceeds 0.100%, decarburization is likely to be incomplete, and magnetic aging may occur in the final grain-oriented electrical steel sheet, so it is not preferred. Therefore, the content of C is 0.020 to 0.100%, preferably 0.050 to 0.090%.

[0074] The total content of S (sulfur) and Se (selenium) is 0.001 to 0.050%. S and Se together with the above-mentioned Mn form an inhibitor. Both S and Se can be included in the slab, but at least any one of them can be included in the slab. When the total content of S and Se deviates from the above range, a sufficient inhibitor effect cannot be obtained, so it is not preferred. Therefore, the total content of S and Se is 0.001 to 0.050%, preferably 0.001 to 0.040%.

[0075] The content of acid-soluble Al (acid-soluble aluminum) is 0.010 to 0.050%. Acid-soluble Al constitutes an inhibitor required for manufacturing a grain-oriented electrical steel sheet with a high magnetic flux density. When the content of acid-soluble Al is less than 0.010%, the amount of acid-soluble Al is insufficient and the inhibitor strength is insufficient, so it is not preferred. When the content of acid-soluble Al exceeds 0.050%, the AlN precipitated as an inhibitor coarsens and the inhibitor strength decreases, so it is not preferred. Therefore, the content of acid-soluble Al is 0.010 to 0.050%, preferably 0.010 to 0.040%.

[0076] The content of N (nitrogen) is 0.002 to 0.015%. N and the above-mentioned acid-soluble Al together form AlN as an inhibitor. When the content of N deviates from the above range, a sufficient inhibitor effect cannot be obtained, so it is not preferred. Therefore, the content of N is 0.002 to 0.015%, preferably 0.002 to 0.012%.

[0077] In addition, in the slab used in the production of the directionally oriented electrical steel sheet of the present embodiment, in addition to the above elements, in order to improve the magnetic properties, part of the remaining Fe can be replaced with one or more selected from Cu: 0.400% or less, P: 0.500% or less, Sn: 0.300% or less, Sb: 0.300% or less, Ni: 1.000% or less, S: 0.025% or less, Se: 0.025% or less, Bi: 0.020% or less by mass%. In the slab of one embodiment, the content of Cr can be 0.02% or more, the content of Bi can be 0.0005% or more, the content of Sb can be 0.005% or more, the content of Se can be 0.001% or more, and the content of Mo can be 0.005% or more by mass%.

[0078] The molten steel with the above-described composition is cast to form a slab. In addition, the casting method of the slab is not particularly limited. In addition, in research and development, even if an ingot is formed in a vacuum melting furnace or the like, the same effect as when forming a slab can be confirmed for the above composition.

[0079] [Process of making hot-rolled steel sheet]

[0080] The cast slab is heated at a specified temperature, and the heated slab is hot-rolled to be processed into a hot-rolled steel sheet. The thickness of the processed hot-rolled steel sheet can be, for example, 1.8 mm to 3.5 mm. When the thickness of the hot-rolled steel sheet is less than 1.8 mm, the temperature of the steel sheet after hot rolling is lowered, and the precipitation amount of AlN in the steel sheet increases, whereby secondary recrystallization becomes unstable, and the magnetic properties are reduced in the directionally oriented electrical steel sheet with a final thickness of 0.23 mm or less, so it is not preferred. When the thickness of the hot-rolled steel sheet exceeds 3.5 mm, the rolling load in the cold rolling process increases, so it is not preferred.

[0081] [Pickling process]

[0082] Next, the hot-rolled steel sheet is pickled, or after hot-rolling annealing is performed and a hot-rolled annealed sheet is obtained, the hot-rolled annealed sheet is pickled.

[0083] 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 mass% relative to the pickling solution, and the pH is -1 to 5. The liquid temperature of the pickling solution is 15°C to 100°C, and the time for immersing the steel sheet in the pickling solution is 5 seconds to 200 seconds.

[0084] When 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 mass% relative to the pickling solution, the effect of inhibitor control in the plate thickness direction (replacement with CuS or coating with MnS, etc.) becomes insufficient, which is not preferred. When the total concentration of one or more of Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni in the pickling solution exceeds 0.1000 mass% relative to the pickling solution, the effect of improving magnetic properties saturates, and the cost of the pickling solution increases, so it is not preferred. 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 mass% relative to the pickling solution.

[0085] When the pH of the pickling solution is less than -1, the acidity becomes too strong, and the treatment of the pickling solution becomes difficult, so it is not preferred. When the pH of the pickling solution exceeds 5, the effect of inhibitor control in the plate thickness direction due to pickling treatment is not sufficient, so it is not preferred. Therefore, the pH of the pickling solution is -1 to 5.

[0086] When the liquid temperature of the pickling solution is less than 15°C, the effect of inhibitor control in the plate thickness direction due to pickling treatment is not sufficient, so it is not preferred. When the liquid temperature of the pickling solution exceeds 100°C, the treatment of the pickling solution becomes difficult, so it is not preferred. Therefore, the liquid temperature of the pickling solution is 15°C to 100°C.

[0087] When the time for immersing the steel sheet in the pickling solution during pickling treatment is less than 5 seconds, the effect of inhibitor control in the plate thickness direction due to pickling treatment is not sufficient, so it is not preferred. When the time for immersing the steel sheet in the pickling solution during pickling treatment exceeds 200 seconds, the equipment becomes large-sized, so it is not preferred. Therefore, the time for immersing the steel sheet in the pickling solution during pickling treatment is 5 seconds to 200 seconds.

[0088] When pickling the steel sheet under the above conditions, precipitates such as MnS in the steel are replaced by CuS etc. on the surface layer of the steel sheet, or coated with Cu etc., whereby the heat transfer coefficient of the surface layer of the steel sheet containing the precipitates becomes constant. Here, "replacement" means that the Mn part of the originally formed MnS etc. is replaced by Cu etc. from the pickling solution, and MnS etc. are replaced by CuS etc. In addition, "coating" means that Cu etc. from the pickling solution newly precipitate around the originally formed MnS etc. Such a phenomenon in the present invention is not affected by the precipitation method of Cu etc., and thus either the replacement of MnS etc. by CuS etc. or the coating of Cu etc. can occur during the pickling treatment. Thereby, the heat propagation effect such as laser irradiation can be made constant on the surface layer of the steel sheet. Under the above conditions, by performing pickling, only the heat transfer coefficient of the surface layer is made uniform, and thus Sa of the side surface inside the groove closer to the surface layer is reduced. In contrast, the Mn part of the precipitates such as MnS near the bottom surface inside the groove far from the surface layer is not replaced by the metal (Cu etc.) in the pickling solution, nor is it coated. Therefore, the heat transfer coefficient is not made uniform, and Sa of the bottom surface inside the groove does not decrease compared with the side surface inside the groove. In that case, during pickling, if MnS etc. are not sufficiently replaced by CuS etc. or not coated with Cu etc., the deviation of the heat transfer coefficient is large, and Sa of the bottom surface inside the groove increases. On the other hand, even if the pickling time, pickling solution concentration, etc. are set to a certain level or more, the effect of making the heat transfer coefficient constant saturates, and the effect of making the heat transfer coefficient constant in the depth direction cannot be obtained, the Sa of the side surface inside the groove will not be further reduced, and Sa of the bottom surface inside the groove will not change either.

[0089] [Process for manufacturing cold-rolled steel sheet]

[0090] After pickling the hot-rolled steel sheet or hot-rolled annealed sheet, it is rolled by one-time cold rolling or multiple cold rollings with intermediate annealing in between, thereby processing it into a cold-rolled steel sheet.

[0091] In addition, between cold rolling passes, between rolling mill stands, or during rolling, the steel sheet can be heat-treated at about 300°C or lower. In such a case, the magnetic properties of the final grain-oriented electrical steel sheet can be improved. In addition, the hot-rolled steel sheet can also be rolled by cold rolling three or more times, but multiple cold rollings increase the manufacturing cost, so it is preferably rolled by one or two cold rollings of the hot-rolled steel sheet. When performing cold rolling using a reversible rolling mill such as Sendzimir mill, the number of passes in each cold rolling is not particularly limited, but from the viewpoint of manufacturing cost, it is preferably 9 or less.

[0092] Above, the process from the slab to obtaining the cold-rolled steel sheet has been described.

[0093] Next, decarburizing annealing is carried out. For cold-rolled steel sheets, heat treatment (i.e., decarburizing annealing treatment) is performed under specified temperature conditions (for example, heating at 700 to 900 °C for 1 to 3 minutes). If the decarburizing annealing treatment is carried out, in the cold-rolled steel sheet, carbon is reduced to below a specified amount, and a primary recrystallized structure is formed. In addition, in decarburizing annealing, an oxide layer containing silicon dioxide (SiO2) as a main component is formed on the surface of the cold-rolled steel sheet.

[0094] Next, an annealing release agent is coated. In this process, an annealing release agent containing magnesium oxide (MgO) as a main component is coated on the surface of the cold-rolled steel sheet (the surface of the oxide layer).

[0095] Next, the cold-rolled steel sheet coated with the annealing release agent for final annealing is subjected to heat treatment (i.e., final annealing treatment) under specified temperature conditions (for example, heating at 1100 to 1300 °C for 20 to 24 hours). If the final annealing treatment is carried out, secondary recrystallization occurs in the cold-rolled steel sheet, and the cold-rolled steel sheet is purified. As a result, a cold-rolled steel sheet having the chemical composition of the above-described steel sheet and having its crystal orientation controlled such that the easy magnetization axis of the crystal grains is aligned with the rolling direction X can be obtained.

[0096] In addition, if the final annealing treatment as described above is carried out, the oxide layer containing silicon dioxide as a main component reacts with the annealing release agent containing magnesium oxide as a main component, thereby forming a glass film containing a composite oxide such as forsterite (Mg2SiO4) on the surface of the steel sheet. In the final annealing process, the final annealing treatment is carried out in a state where the steel sheet is wound into a coil shape. By forming a glass film on the surface of the steel sheet during the final annealing treatment, welding on the steel sheet wound into a coil shape can be prevented.

[0097] [Process of forming linear grooves on the steel sheet surface]

[0098] In the subsequent laser irradiation process, the surface (only one side) of the steel sheet formed with the glass film is irradiated with a laser, thereby forming a plurality of grooves extending in a direction crossing the rolling direction at intervals of 2 to 10 mm along the rolling direction on the surface of the steel sheet.

[0099] In the laser irradiation process, the laser irradiation device irradiates the surface of the steel sheet with a laser by rotating a polygon mirror, and scans the laser in a direction at an angle of 0° to 30° with respect to the direction perpendicular to the rolling direction.

[0100] While irradiating the laser, an auxiliary gas such as air or an inert gas is blown onto the part of the steel plate irradiated with the laser. The inert gas refers to, for example, nitrogen or argon. The auxiliary gas serves to remove the components melted or evaporated from the steel plate due to the laser irradiation. By blowing the auxiliary gas, the laser can reach the steel plate without being blocked by the melted or evaporated components, and thus a groove can be formed substantially stably.

[0101] However, since the auxiliary gas is blown restrictively onto the laser irradiation spot, although it has the effect of blowing up the components (dust) melted or evaporated from the steel plate generated inside the groove into the auxiliary gas and not staying inside the groove, it is difficult to prevent reattachment to the steel plate, laser, etc. outside the groove. This sometimes causes fluctuations in the surface roughness Sa of the bottom and side surfaces of the groove, and sometimes the desired surface roughness Sa cannot be obtained. In order to prevent such reattachment and to make the dust removed to the outside of the groove further away from the steel plate, a blowing gas can be used. From this viewpoint, it is preferable to blow the blowing gas in the TD direction (width direction of the plate) of the steel plate and in a direction as parallel as possible to the steel plate surface (typically, the steel plate surface is set to 0 degrees and within ± several degrees or within ± 10 degrees). In addition, a blower is used to blow air onto the laser irradiation surface during laser irradiation at a wind speed of 100 m / s to 200 m / s. When it is below 100 m / s, the effect of suppressing reattachment is not sufficient, and when it exceeds 200 m / s, the steel plate vibrates due to the wind. Thus, a groove with the desired surface roughness Sa is formed.

[0102] As the laser light source, for example, a high-output laser commonly used in industry such as a fiber laser, a YAG laser, a semiconductor laser, or a CO2 laser can be used. In addition, as long as a groove can be formed stably, a pulsed laser or a continuous-wave laser can also be used as the laser light source. As the laser, a single-mode laser with high focusing performance and suitable for groove formation is preferably used.

[0103] As the irradiation conditions of the laser, for example, it is preferable to set the laser output to 200 W to 3000 W, set the focused spot diameter in the rolling direction of the laser (i.e., the diameter including 86% of the laser output, hereinafter abbreviated as 86% diameter) to 10 μm to 200 μm, set the focused spot diameter in the width direction of the laser (86% diameter) to 10 μm to 1000 μm, set the laser scanning speed to 5 m / s to 50 m / s, and set the laser scanning pitch (interval PL) to 2 mm to 10 mm. These laser irradiation conditions are appropriately adjusted to obtain a groove depth D of 10 μm to 40 μm.

[0104] In the final insulating film forming step, an insulating coating liquid containing, for example, colloidal silica and phosphate is applied onto the surface of the steel sheet with grooves formed by the above-described laser irradiation from the glass film. Then, by performing heat treatment under specified temperature conditions (for example, 840 to 920 °C), a grain-oriented electromagnetic steel sheet of the present invention having grooves and provided with a glass film and an insulating film is finally obtained.

[0105] Regarding the shape of the grooves formed on the obtained grain-oriented electromagnetic steel sheet, using the above-described measuring method, the depth D of the grooves, the width W of the grooves, and the surface roughness Sa of the bottom surface inside the grooves and the side surfaces inside the grooves are measured.

[0106] Examples

[0107] Examples are shown below to more specifically describe the grain-oriented electromagnetic steel sheet of the present invention. In addition, the examples shown below are merely examples of the grain-oriented electromagnetic steel sheet of the present embodiment, and the grain-oriented electromagnetic steel sheet of the present embodiment is not limited to the examples shown below.

[0108] The chemical components of the grain-oriented electromagnetic steel sheet contain, by mass fraction, Si: 3.00%, C: 0.080%, acid-soluble Al: 0.050%, N: 0.010%, Mn: 0.12%, Cr: 0.05%, Cu: 0.040%, P: 0.010%, Sn: 0.020%, Sb: 0.010%, Ni: 0.005%, S: 0.007%, Se: 0.001%, and the balance is composed of Fe and impurities. A slab having the above chemical components is hot-rolled to obtain a hot-rolled steel sheet with a thickness of 2.3 mm.

[0109] Next, the above hot-rolled steel sheet is subjected to annealing treatment under temperature conditions of heating at 1000 °C for 1 minute to obtain a hot-rolled annealed sheet.

[0110] The surface of the hot-rolled annealed sheet is subjected to pickling treatment under the pickling solution and pickling conditions shown below.

[0111] Pickling is performed within the following ranges for the components, concentration, pH value, temperature, and immersion time of the pickling solution.

[0112] (Components and concentration of the pickling solution) One or more of Cu, Hg, Ag, Pb, Cd, Co, Zn, and Ni having a total concentration of each element of 0.0001 to 0.1000 mass% with respect to the pickling solution.

[0113] (pH value) -1 to 5

[0114] (Temperature) 15 °C to 100 °C

[0115] (Immersion time): 5 seconds to 200 seconds

[0116] After pickling treatment, cold rolling is carried out to obtain a cold-rolled steel sheet with a thickness of 0.23 mm. Then, for this cold-rolled steel sheet, decarburization annealing treatment is carried out under the temperature condition of heating at 800 °C for 2 minutes, and then an annealing separating agent containing magnesium oxide (MgO) as the main component is coated on the surface of the cold-rolled steel sheet.

[0117] Next, for the cold-rolled steel sheet coated with the annealing separating agent, final annealing treatment is carried out under the temperature condition of heating at 1200 °C for 20 hours. As a result, a steel sheet is obtained which has the above chemical composition, the crystal orientation of which is controlled so that the easy magnetization axis of the crystal grains is in the same direction as the rolling direction, and a glass film is formed on the surface.

[0118] Next, a laser is irradiated on the surface of the steel sheet with the glass film, and a plurality of grooves extending in a direction crossing the rolling direction are formed at a predetermined interval along the rolling direction on the surface of the steel sheet.

[0119] Regarding the laser irradiation conditions, in order to obtain the desired groove depth D, the laser output power is adjusted in the range of 200 W to 3000 W, the focused spot diameter (86% diameter) of the laser in the rolling direction is adjusted in the range of 10 μm to 500 μm, the focused spot diameter (86% diameter) of the laser in the sheet width direction is adjusted in the range of 10 μm to 1000 μm, the laser scanning speed is adjusted in the range of 5 m / s to 50 m / s, and the laser scanning pitch (interval PL) is adjusted in the range of 2 mm to 10 mm.

[0120] In the example of the present invention, when irradiating the steel sheet with a laser, a blower is used to blow air on the laser irradiation surface of the steel sheet in the TD direction (sheet width direction) and as parallel to the steel sheet surface as possible at a wind speed of 100 m / s or more, which suppresses the flying of the components melted or evaporated from the steel sheet due to laser irradiation and the reattachment to the steel sheet, laser, etc.

[0121] As described above, for the steel sheet with grooves formed thereon, an insulating coating liquid containing colloidal silica and phosphate is coated on the glass film, and then heat treatment is carried out under the temperature condition of heating at 850 °C for 1 minute, so as to finally obtain a directionality electromagnetic steel sheet with grooves formed thereon, having a glass film and an insulating film.

[0122] In the comparative example, when irradiating the steel sheet with a laser, a blower is not used to blow air on the laser irradiation part and its periphery of the laser irradiation surface of the steel sheet, or pickling is carried out under pickling conditions outside the above range.

[0123] Regarding the shape of the formed groove, using the above measurement method, the depth D of the groove, the width W of the groove, the surface roughness Sa of the bottom surface inside the groove, and the side surface inside the groove were measured. The measurement results, together with the linear roughness Ra and the iron loss W17 / 50, are shown in Table 1. In addition, setting the good iron loss W17 / 50 to 0.75 (W / kg) or less, those meeting this criterion are marked with ○ (Good: Good). In particular, those with a low iron loss, 0.73 (W / kg) or less, are marked with ◎ (Excellent: Excellent). The iron loss was measured in accordance with JISC 2556:2015.

[0124] For the noise measurement, samples with a width of 100 mm × a length of 500 mm were collected from the electromagnetic steel sheets in each direction. The length direction of the sample corresponds to the rolling direction RD, and the width direction corresponds to the sheet width direction TD.

[0125] For the sample, using a magnetostriction measurement device, the magnetostriction was measured by the alternating current magnetostriction measurement method. The magnetostriction measurement device is defined as a device equipped with a laser Doppler vibrometer, an exciting coil, an exciting power supply, a magnetic flux detection coil, an amplifier, and an oscilloscope.

[0126] Specifically, an alternating magnetic field was applied to the sample in such a way that the maximum magnetic flux density in the rolling direction was 1.7 T and the frequency was 50 Hz. The length change of the sample caused by the expansion and contraction of the magnetic domains was measured using a laser Doppler vibrometer to obtain a magnetostriction signal. Fourier analysis was performed on the obtained magnetostriction signal to obtain the amplitude Cn of each frequency component fn (n is a natural number of 1 or more) of the magnetostriction signal. Using the A correction coefficient αn of each frequency component fn, the noise characteristic (dB) shown in the following formula was obtained.

[0127]

[0128] Here, ρc is the characteristic acoustic impedance, and ρc = 400 is defined. Pe0 is the minimum audible sound pressure, and Pe0 = 2×10 -5 (Pa) is used. The A correction coefficient αn uses the values recorded in Table 2 of JIS C 1509-1 (2017). Σ is 10 points every 100 Hz in the frequency components from 100 to 1000 Hz.

[0129] The measurement results, together with the iron loss W17 / 50 and the noise (dB), are shown in Table 1. In addition, regarding the noise characteristic, a noise characteristic of 50 dBA or less is set as good, and those meeting this criterion are marked with ○ (Good: Good).

[0130] Table 1

[0131]

[0132] From the results, it can be seen that by performing the pickling treatment of the example (invention example), the Sa value of the surface roughness of the bottom surface inside the tank and the side surface inside the tank can be controlled within a certain range. Compared with the comparative example, it is possible to reduce the noise without impairing the good iron loss.

Claims

1. A directional electromagnetic steel sheet, which includes a steel sheet. The steel sheet contains, by mass%, Si: 2.50 to 4.50%, Mn: 0.01 to 0.15%, with the balance being Fe and impurities, and has a steel sheet surface on which linear grooves extending in a direction at an angle of 0 to 30° with respect to the direction perpendicular to rolling are formed at intervals of 2 to 10 mm; The depth D of the groove is 10 μm to 40 μm, The width W of the groove is 20 to 200 μm, The Sa of the surface roughness of the bottom surface inside the groove 底 value exceeds 5.0 μm, The Sa of the surface roughness of the side surface inside the groove 侧面 is 1.0 to 5.0 μm.

Images