Grain-oriented electrical steel sheet and method for producing same

Abstract

This grain-oriented electrical steel sheet has a steel sheet in which a plurality of grooves extending in a direction intersecting the rolling direction and having a depth in the sheet thickness direction are formed on the surface, and in a cross-section parallel to the rolling direction of the steel sheet and parallel to the sheet thickness direction, at least one protrusion is present on the side surface or the bottom surface of the grooves. The maximum height of the protrusions is 2-50 [mu] m and the maximum width is 2-50 [mu] m, and the difference between the average crystal orientation of the protrusions and the Goss orientation is 10 degrees or more.

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2022-186168 filed in Japan on November 22, 2022, and the contents are incorporated herein by reference. Background Art

[0003] Grain-oriented electromagnetic steel sheets are soft magnetic materials and are mainly used as core materials for transformers. Therefore, grain-oriented electromagnetic steel sheets are required to have magnetic properties such as high magnetization characteristics and low iron loss. Iron loss is the power loss consumed as heat energy when the core is excited by an AC magnetic field. From the perspective of energy saving, iron loss is required to be as low as possible. The magnetic susceptibility, sheet thickness, film tension, impurity content, resistivity, crystal grain size, magnetic domain width, etc. have an impact on the level of iron loss. Even now that various technologies have been developed for grain-oriented electromagnetic steel sheets, research and development to reduce iron loss is continuing in order to improve energy conversion efficiency.

[0004] As one of the methods for reducing iron loss, a technique of laser irradiation has been proposed. This technique points out that by introducing strain into the surface through laser irradiation, the 180° magnetic domain width is subdivided, thereby reducing eddy current loss, which is a part of iron loss.

[0005] For example, Patent Document 1 discloses a method for manufacturing a directional electromagnetic steel sheet in which magnetic domains are controlled by laser irradiation, which method is characterized in that it comprises the following steps: a step of irradiating a surface of the directional electromagnetic steel sheet with a focused continuous wave laser while scanning it in a direction inclined from the rolling direction of the directional electromagnetic steel sheet; and a step of repeatedly scanning a portion of the continuous wave laser while staggering it at a predetermined interval, wherein the average power of the continuous wave laser is represented by P (W), the speed of the scanning is represented by Vc (mm / s), the predetermined interval is represented by PL (mm), and the input energy Ua is defined as Ua=P / (Vc×PL)(mJ / mm 2 ), 1.0mm≤PL≤3.0mm, and 0.8mJ / mm 2 ≤Ua≤2.0mJ / mm 2 .

[0006] Patent Document 1 shows that the iron loss in both the L direction and the C direction of a grain-oriented electrical steel sheet can be reduced easily while ensuring high productivity.

[0007] However, for example, in the case of manufacturing a wound core, since the grain-oriented electrical steel sheet is bent and formed, stress relief annealing becomes necessary. Therefore, in such a method, the strain introduced into the grain-oriented electrical steel sheet is released by stress relief annealing. Consequently, the effect of controlling magnetic domains by laser irradiation cannot be obtained.

[0008] Therefore, it has been proposed to form grooves on the steel sheet surface, thereby similarly to the introduction of strain, to subdivide the 180° magnetic domain width and reduce eddy current loss.

[0009] For example, in Patent Document 2, a method for improving the iron loss characteristics of a grain-oriented electrical steel sheet capable of applying stress relief annealing is disclosed, in which a laser beam is controlled and irradiated to form recesses having a width in the rolling direction of 0.5 mm or less and a depth of 10 μm or more.

[0010] In the case of forming grooves by laser irradiation, the melt generated by laser irradiation is blown away by an assist gas to form the grooves. However, in such a case, although the melt inside the grooves is substantially removed, protrusions may sometimes be formed due to the solidification of the melt around the grooves. When there are protrusions around the grooves, voids are generated when the steel sheets are laminated, making it difficult for magnetic flux to flow and increasing the iron loss.

[0011] The above-mentioned protrusions are removed to some extent by performing a brushing process or the like after laser irradiation. However, even when performing a brushing process or the like, it is carried out in a manner that does not reduce the plate thickness, so it is difficult to completely remove the protrusions. Patent Document 2 does not consider such protrusions.

[0012] Regarding the solidified portion of the melt, in Patent Document 3, a grain-oriented electrical steel sheet is disclosed, which is a grain-oriented electrical steel sheet having a steel sheet surface provided with grooves. In a region extending from the end portion in the groove width direction of the above-mentioned grooves toward the outside in the groove width direction, surface protrusions rising from the above-mentioned steel sheet surface extend along the groove length direction of the above-mentioned grooves. The average protrusion height of the above-mentioned surface protrusions exceeds 5 μm and is 10 μm or less. When observing the above-mentioned surface protrusions in a cross section including the groove length direction and the normal direction of the above-mentioned steel sheet surface, the total length in the groove length direction of the portion having a height of 50% or more of the height of the peak points appearing on the contour line of the above-mentioned surface protrusions with respect to the total length in the groove length direction of the above-mentioned surface protrusions is 30% or more of the length. Using a device capable of measuring the three-dimensional shape of the above-mentioned steel sheet surface, an image of the above-mentioned steel sheet surface including the above-mentioned grooves is obtained. The portion above the reference plane in the peripheral portion of the above-mentioned grooves is identified as the above-mentioned surface protrusions, and the above-mentioned cross section includes the peak portion of the height measured by the above-mentioned device.

[0013] However, regarding Patent Document 3, although it is possible to prevent an increase in hysteresis loss to some extent by controlling the protrusion height of surface protrusions, etc., it does not reduce eddy current loss, and there is a problem that a sufficient reduction effect of iron loss cannot be obtained.

[0014] In Patent Document 4, an electromagnetic steel sheet is disclosed, which has a groove formed in such a manner as to have a first side surface, a second side surface, and a bottom surface opposite to each other, and a solidified portion formed by solidification of molten by-products of the steel sheet during the formation of the groove on the first, second side surfaces, and the bottom surface. The solidified portion does not remain on the bottom surface but forms a solidified portion on the first and second side surfaces of the groove, or a solidified portion is formed on the bottom surface and the second side surface. When the solidified portion does not remain on the bottom surface but is formed on the first and second side surfaces of the groove, an open portion is formed on the bottom surface. When the solidified portion is formed on the bottom surface and the second side surface, the open portion is formed on the first side surface. The solidified portion formed on the first and second side surfaces becomes thinner as it approaches the bottom surface and is formed thicker as it approaches the surface portion of the steel sheet. The diameter (BW) of the groove in the rolling direction is 10 μm to 70 μm, and the length (BL) of the groove in the width direction of the steel sheet is 10 μm to 150 μm.

[0015] However, regarding Patent Document 4, the description of the shape of the solidified portion is only the difference in thickness between the bottom surface and the surface, and the increase in surface area caused by protrusions inside the groove and the accompanying reduction in eddy current loss are not assumed. Therefore, regarding Patent Document 4, there is a problem that a sufficient reduction effect of iron loss cannot be obtained.

[0016] Prior Art Documents

[0017] Patent Documents

[0018] Patent Document 1: Japanese Patent No. 4669565 Gazette

[0019] Patent Document 2: Japanese Patent Laid-Open No. 6-57335 Gazette

[0020] Patent Document 3: Japanese Patent No. 7010311 Gazette

[0021] Patent Document 4: Japanese Patent No. 6307441 Gazette Summary of the Invention

[0022] Problems to be Solved by the Invention

[0023] As described above, regarding the prior art, the effect is not sufficient for the higher requirements for reducing iron loss in recent years.

[0024] In view of the above, the inventors of the present invention provide, on the premise of a grain-oriented electromagnetic steel sheet in which grooves are formed by laser irradiation for magnetic domain refinement, a grain-oriented electromagnetic steel sheet having low iron loss and a method for manufacturing the same.

[0025] Means for Solving the Problem

[0026] In the method for manufacturing a grain-oriented electromagnetic steel sheet in which grooves are formed by laser irradiation for magnetic domain refinement, the inventors of the present invention studied reducing iron loss by reducing eddy current loss.

[0027] As a result, it was found that eddy current loss is reduced by forming protrusions with a specified shape inside the grooves. In addition, it was found that the effect of reducing iron loss is further improved by controlling the crystal orientation of the protrusions.

[0028] In addition, it was learned that the laser irradiation conditions and the injection conditions of the auxiliary gas have a great influence on the formation of the protrusions inside the grooves.

[0029] The present invention was made in view of the above recognition. The gist of the present invention is as follows.

[0030] [1] A grain-oriented electromagnetic steel sheet according to one aspect of the present invention has a steel sheet with a plurality of grooves formed on the surface extending in a direction crossing the rolling direction and having a depth in the plate thickness direction. In a cross-section parallel to the rolling direction of the steel sheet and parallel to the plate thickness direction, at least one protrusion exists on the side surface or bottom surface of the groove. The maximum height of the protrusion is 2 to 50 μm and the maximum width is 2 to 50 μm, and the orientation difference between the average crystal orientation of the protrusion and the Goss orientation is 10 degrees or more.

[0031] [2] In the grain-oriented electromagnetic steel sheet according to [1], it is also possible that: in the cross-section, when the distance from the entrance portion of the groove to the entrance portion of the opposite groove is defined as the width of the groove, and the region equal to the width of the groove in the direction opposite to the center of the groove in the rolling direction starting from the entrance portion of the groove of the steel sheet is defined as the groove edge portion, the maximum height of the protrusion in the groove edge portion is 5 μm or less and the maximum width is 5 μm or less.

[0032] [3] In the grain-oriented electromagnetic steel sheet according to [1] or [2], it is also possible that: a forsterite film is formed on the surface of the steel sheet.

[0033] [4] In the grain-oriented electromagnetic steel sheet according to [3], it is also possible that: an insulating film is formed on the surface of the forsterite film.

[0034] [5] In the grain-oriented electromagnetic steel sheet according to [1] or [2], it is also possible that: an insulating film is formed on the surface of the steel sheet.

[0035] [6] The manufacturing method of the grain-oriented electromagnetic steel sheet according to another aspect of the present invention is the manufacturing method of the grain-oriented electromagnetic steel sheet described in [1] or [2], and includes the following steps: Hot rolling step: heating a slab and hot rolling it to form a hot rolled sheet; Hot rolled sheet annealing step: annealing the hot rolled sheet after the above hot rolling step; Cold rolling step: pickling and cold rolling the hot rolled sheet after the above hot rolled sheet annealing step to form a steel sheet; Decarburizing annealing step: performing decarburizing annealing on the above steel sheet; Final annealing step: coating an annealing release agent on the above steel sheet after the above decarburizing annealing step and performing final annealing; and Groove forming step: between the above cold rolling step and the above final annealing step, forming grooves on the above surface of the above steel sheet by irradiating the surface of the above steel sheet with a laser, and forming protrusions on the side surface or bottom surface of the above grooves, wherein the above groove forming step includes: First stage: irradiating a laser with a laser output power of 200 to 3000 W, a condensing spot diameter in the rolling direction including 86% of the laser output power of 10 to 1000 μm, and a condensing spot diameter in the sheet width direction of 10 to 1000 μm at a scanning speed of 2 to 50 m / s, and blowing an auxiliary gas with a flow rate of 1 to 500 L / minute; and Second stage: irradiating a laser with a laser output power of 10 to 150 W, a condensing spot diameter in the rolling direction of 10 to 1000 μm, and a condensing spot diameter in the sheet width direction of 10 to 1000 μm at a scanning speed of 2 to 50 m / s for the same part as the part irradiated with the above laser in the above first stage.

[0036] [7] According to the manufacturing method of the grain-oriented electromagnetic steel sheet described in [6], it is also possible to further include a grinding step of grinding the above surface of the above steel sheet after the above groove forming step using a brush roll fixed with abrasive grains. In the above grinding step, the above brush roll rotates in a direction opposite to the conveying direction of the above steel sheet at a position where it abuts against the above steel sheet. The conveying speed of the above steel sheet is 5 to 100 mpm, the rotation speed of the above brush roll is 500 to 2000 rpm, the pressing amount of the above brush roll is 2 to 10 mm, the grain size of the above abrasive grains is #40 to #400, and the diameter of the above brush roll is 200 to 500 mm.

[0037] Advantages of the Invention

[0038] According to the above aspect of the present invention, it is possible to provide a grain-oriented electromagnetic steel sheet with low iron loss and a manufacturing method thereof. Description of the Drawings

[0039] Figure 1 It is a diagram showing an example of the formation state of the grooves of the grain-oriented electromagnetic steel sheet of the present embodiment.

[0040] Figure 2It is a schematic diagram of observing the slots and the protrusions inside the slots of the directionality electromagnetic steel sheet of the present embodiment in a cross-section orthogonal to the extending direction of the slots.

[0041] Figure 3 It is a schematic diagram of observing the slots and the protrusions at the slot edge parts of the directionality electromagnetic steel sheet of the present embodiment in a cross-section orthogonal to the extending direction of the slots. Detailed implementation manners

[0042] Hereinafter, a directionality electromagnetic steel sheet (the directionality electromagnetic steel sheet of the present embodiment) and a manufacturing method thereof according to an embodiment of the present invention will be described.

[0043] <Directionality electromagnetic steel sheet>

[0044] As Figure 1 shown, the directionality electromagnetic steel sheet 1 of the present embodiment has a steel sheet 11 on the surface of which a plurality of slots 21 extending in a direction intersecting with the rolling direction RD and having a depth in the plate thickness direction are formed. The steel sheet 11 is, for example, a cold-rolled sheet via cold rolling.

[0045] On the surface of the steel sheet 11, a forsterite film or an insulating film may be formed.

[0046] In addition, an insulating film may also be formed on the surface of the forsterite film.

[0047] That is, the directionality electromagnetic steel sheet of the present embodiment not only includes the case of including a steel sheet (base steel sheet), but may also include the base steel sheet and the forsterite film formed on the surface of the base steel sheet, may include the base steel sheet and the insulating film formed on the surface of the base steel sheet, or may include the base steel sheet and the forsterite film formed on the surface of the base steel sheet and the insulating film formed on the surface of the forsterite film.

[0048] The forsterite film and the insulating film may be formed on one side, but may also be formed on both sides.

[0049] The following will be described separately.

[0050] [Steel sheet (base steel sheet)]

[0051] (Slots)

[0052] As Figure 1 shown, the steel sheet 11 has a plurality of slots 21 formed by laser irradiation on the surface, which extend in a direction intersecting with the rolling direction RD and have a depth in the plate thickness direction.

[0053] Magnetic domain control can be carried out by periodically forming linear grooves in a direction crossing the rolling direction RD. In the grain-oriented electrical steel sheet of the present embodiment, in order to obtain this effect, grooves 21 are formed on the surface of the steel sheet 11 (in the grain-oriented electrical steel sheet formed with a forsterite film and an insulating film, the so-called base material steel sheet excluding them).

[0054] Here, the direction crossing the rolling direction RD is a direction of 60 to 120° with respect to the rolling direction RD.

[0055] Regarding the shape of the grooves 21, there is no limitation as long as the effect of magnetic domain control can be obtained, but preferably the depth is 10 to 50 μm and the width is 10 to 200 μm. The interval in the rolling direction RD between adjacent grooves among a plurality of grooves is preferably 1 to 20 mm. The plurality of grooves 21 are preferably formed at substantially constant intervals (periodically) in the rolling direction RD. The interval of the grooves refers to the distance from the center in the width direction of one groove to the center in the width direction of the adjacent groove.

[0056] (Protrusions inside the grooves)

[0057] In the grain-oriented electrical steel sheet of the present embodiment, in a cross-section parallel to the rolling direction and parallel to the plate thickness direction, at least one protrusion exists inside the grooves (the side surface or the bottom surface of the grooves), and the maximum height of the protrusion is 2 to 50 μm and the maximum width is 2 to 50 μm.

[0058] By forming at least one or more protrusions on the bottom surface and the side surface of the grooves, and setting the width of the protrusions to 2 to 50 μm and the height of the protrusions to 2 to 50 μm, the surface area inside the grooves is increased. Due to the increase in the surface area inside the grooves, the leakage magnetic flux from inside the grooves during magnetization of the grain-oriented electrical steel sheet increases, and the magnetostatic energy increases. Since the magnetic domains are further subdivided to eliminate the increase in magnetostatic energy, the eddy current loss is reduced.

[0059] When there are no protrusions, or the height or width of the protrusions is less than 2 μm, the surface area inside the grooves is not sufficiently increased, and the eddy current loss is not reduced. On the other hand, when the width or height of the protrusions exceeds 50 μm, the protrusions become larger than the groove depth or width, so the protrusions protrude to the steel sheet surface. In this case, voids are generated when the steel sheets are laminated, so the iron loss increases. In the case where there are a plurality of protrusions, the evaluation is made based on the maximum height and the maximum width.

[0060] The maximum height and width of the protrusions are preferably 5 to 50 μm, more preferably 10 to 50 μm.

[0061] Regarding the crystal orientation of the protrusions inside the above-mentioned slots, the orientation difference between the average crystal orientation of the protrusions and the Goss orientation is 10 degrees or more. By setting the orientation difference between the average crystal orientation of the protrusions and the Goss orientation to 10 degrees or more, the magnetic domain subdivision effect is further improved.

[0062] The determination of whether there is at least one protrusion on the side or bottom surface of the slot, and the measurement of the height and width of the protrusion can be carried out by the following method.

[0063] The cross-sectional shape of the slot usually becomes a Gaussian function or a shape similar thereto. This is because the intensity distribution of the laser usually follows a Gaussian distribution. As Figure 2 shown, taking the imaginary line in the case where the cross-sectional shape of the slot 21 is assumed to be a Gaussian function as the reference curve RC, the width ( Figure 2 W in ) is 1 μm or more and the protrusion height (height in the direction perpendicular to the wiring at that position): H is 1 μm or more, and the region is defined as the protrusion 102. The height (protrusion height) H of the protrusion 102 is the height from the reference curve RC to the tip of the protrusion. The width W of the protrusion is the straight-line distance from one end to the other end at the position of the bottom surface of the protrusion. The measurement methods for the height and width of the protrusion are as follows.

[0064] First, a sample is collected from the oriented electromagnetic steel sheet to be measured in such a way that the cross-section in the plate thickness direction orthogonal to the length direction (extension direction) of the slot is exposed. By polishing this cross-section, Figure 2 after the cross-section including the slot and its peripheral part as shown appears, the presence, height, and width of the protrusion are measured by observing this cross-section with an optical microscope or a scanning electron microscope.

[0065] When observing more than 10 cross-sections, if there is 1 or more protrusions (regions with a width of 1 μm or more and a protrusion height of 1 μm or more from the reference curve) on the side or bottom surface of the slot, it is judged that there is at least one protrusion. When there are multiple protrusions, the maximum height and maximum width of each protrusion are taken as the measured values.

[0066] In addition, for the orientation difference between the average crystal orientation of the protrusion and the Goss orientation, it is measured by the following method.

[0067] First, a sample is collected from the oriented electromagnetic steel sheet to be measured in such a way that the cross-section orthogonal to the length direction (extension direction) of the slot is exposed. By polishing this cross-section, Figure 2After the cross-section including the groove and its peripheral portion as shown is revealed, the cross-section is observed. The crystal orientation is measured by the Electron BackScattering Diffraction Pattern (EBSD) method under the conditions described below. In the region measured by EBSD, a region with a width of 1 μm or more and a protrusion height of 1 μm or more from the reference curve is defined as a protrusion, and the average crystal orientation of the above protrusions is obtained. The orientation difference between the obtained average crystal orientation and the Goss orientation is obtained. In the case where there are multiple protrusions, the maximum value among the orientation differences between the average crystal orientation of each protrusion and the Goss orientation is taken as the orientation difference between the average crystal orientation of the protrusion and the Goss orientation.

[0068] The measurement conditions of EBSD are set as follows.

[0069] (a) Measuring device: FE-SEM "SU-70" (manufactured by Hitachi High-Tech Corporation)

[0070] EBSD device "DigiView" (manufactured by TSL SOLUTIONS)

[0071] (b) Magnification: 500 times

[0072] (c) Step interval: 0.25 μm

[0073] (d) Measurement area: 200 μm in the direction crossing the groove length direction × 70 μm in the plate thickness direction

[0074] (Groove edge portion (flat portion around the groove))

[0075] As Figure 3 In the cross-section parallel to the rolling direction RD and parallel to the plate thickness direction, when the distance from the inlet portion 31 of the groove (the position where the side surface of the groove that is concave with respect to the reference plane intersects the imaginary line obtained by extending the reference plane) to the inlet portion of the opposite groove is set as the width of the groove, and the region equal to the width of the groove 21 in the direction opposite to the center of the groove 21 in the rolling direction RD starting from the inlet portion 31 of the groove 21 of the steel plate 11 is defined as the groove edge portion 41 ( Figure 3 Although only the right side of the groove is described in, the left side is the same), it is preferable that the maximum height of the protrusion of the groove edge portion 41 is 5 μm or less and the maximum width is 5 μm or less.

[0076] If projections are formed not inside the slots but on the periphery of the slots (especially on the slot edge portions where the melt often adheres), voids are generated in the stacked portions when the directionality electromagnetic steel sheets are stacked, making it difficult for magnetic flux to flow and increasing iron loss. Especially when the maximum of the height or width of the projections exceeds 5 μm, the adverse effects are significant. It is preferable to reduce the projections on the slot edge portions, and it is more preferable to remove them.

[0077] The height and width of the projections on the slot edge portions can be obtained by the following method.

[0078] As Figure 3 shown in, the surface of the steel sheet in the region that is more than the width of the slot in the direction opposite to the center of the slot from the inlet portion 31 of the slot toward the rolling direction RD (i.e., the region farther from the slot than the slot edge portion) is set as the reference plane RS, and the region with a width of 1 μm or more and a protrusion height of 1 μm or more from the reference plane is defined as the projection 101. The height of the projection 101 is the height from the reference plane RS to the tip of the projection 101. The width of the projection 101 is the straight-line distance from one end to the other end of the projection 101.

[0079] First, samples are collected from the directionality electromagnetic steel sheet to be measured in such a way that a cross-section orthogonal to the length direction of the slot is exposed. At this time, in the cross-section, a region equal to the width of the slot in the direction opposite to the center of the slot from the slot edge is included. By grinding this cross-section, Figure 3 after the cross-section as shown in, which includes the slot 21 and its peripheral portion (slot edge portion 41), appears, the height and width of the projection 101 are measured by observing this cross-section with an optical microscope or a scanning electron microscope. Observe more than 10 cross-sections. In the case where there are multiple projections, the maximum values of the height and width of each projection are used as the measured values.

[0080] (Chemical composition)

[0081] The chemical composition of the steel sheet (base steel sheet) is not limited as long as it is equivalent to the base steel sheet of a known directionality electromagnetic steel sheet. For example, as the chemical composition, it may contain, by mass%, Si: 2.5 - 4.5%, Mn: 0.01 - 0.15%, C: 0 - 0.085%, acid-soluble Al: 0 - 0.065%, N: 0 - 0.012%, Cr: 0 - 0.30%, Cu: 0 - 0.40%, P: 0 - 0.50%, Sn: 0 - 0.30%, Sb: 0 - 0.30%, Ni: 0 - 1.000%, S: 0 - 0.015%, Se: 0 - 0.015%, Bi: 0 - 0.02%. In addition, it may also contain the above elements, and the remaining part is Fe and impurities.

[0082] When the grain-oriented electrical steel sheet is composed of a base steel sheet (in the case of not having a forsterite film or an insulating film), the chemical composition of the base steel sheet can be said to be the chemical composition of the grain-oriented electrical steel sheet.

[0083] The chemical composition of the steel sheet (base steel sheet) can be determined by general analytical methods for steel. For example, the chemical composition of the base steel sheet can be determined by using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, for example, by taking a test piece of 35 mm square (35 mm in the rolling direction and width direction respectively) from the central position of the base steel sheet and using an ICPS-8100 etc. (measurement device) manufactured by Shimadzu Corporation, and measuring under the conditions based on a pre-made standard curve, it can be determined. C and S that are difficult to measure by ICP-AES can be measured by using combustion-infrared absorption method, and N can be measured by using inert gas fusion-thermal conductivity method. In the case where the forsterite film and insulating film described later are formed, the chemical composition of the base steel sheet can be analyzed after removing the forsterite film and insulating film from the grain-oriented electrical steel sheet by a known method such as pickling.

[0084] (Thickness of the sheet)

[0085] The thickness of the base steel sheet of the grain-oriented electrical steel sheet of the present embodiment is not limited, but from the viewpoint of reducing eddy current loss when the thickness is thin, it is preferably 0.15 to 0.35 mm, for example.

[0086] [Forsterite film]

[0087] In the grain-oriented electrical steel sheet of the present embodiment, a forsterite film can also be formed on the surface of the base steel sheet.

[0088] The forsterite film is an inorganic film mainly composed of magnesium silicate. The forsterite film is formed by the reaction of an annealing release agent containing magnesium oxide (MgO) coated on the surface of the base steel sheet with the surface components of the base steel sheet during final annealing, and has a composition derived from the annealing release agent and the components of the base steel sheet (more specifically, a composition mainly composed of Mg2SiO4).

[0089] On the other hand, in the case of using an annealing release agent mainly composed of Al2O3 during final annealing, a forsterite film may not be formed sometimes.

[0090] [Insulating film]

[0091] In the grain-oriented electrical steel sheet of the present embodiment, an insulating film may also be formed on the surface of the base steel sheet or on the surface of the forsterite film.

[0092] The insulating film reduces the eddy current loss by imparting electrical insulation to the grain-oriented electrical steel sheet, thereby reducing the iron loss of the grain-oriented electrical steel sheet. The insulating film has a function of imparting tension to the grain-oriented electrical steel sheet. By imparting tension to the grain-oriented electrical steel sheet, the movement of magnetic domain walls in the grain-oriented electrical steel sheet becomes easier, and the iron loss of the grain-oriented electrical steel sheet can be reduced.

[0093] In addition, depending on the insulating film, various properties such as corrosion resistance, heat resistance, and slidability can be obtained in addition to the electrical insulation as described above.

[0094] In the grain-oriented electrical steel sheet of the present embodiment, the insulating film can be, for example, a known film formed by coating a coating solution mainly composed of phosphate and colloidal silica on the surface of the forsterite film and baking it.

[0095] <Manufacturing method>

[0096] The grain-oriented electrical steel sheet of the present embodiment is not dependent on the manufacturing method, and as long as it has the above characteristics, its effects can be obtained. However, as long as it is a manufacturing method including the following processes, it can be stably manufactured, and thus it is preferred.

[0097] (I) A hot rolling process of heating and hot rolling a slab to form a hot rolled sheet;

[0098] (II) A hot rolled sheet annealing process of annealing the hot rolled sheet after the above hot rolling process;

[0099] (III) A cold rolling process of pickling the hot rolled sheet after the above hot rolled sheet annealing process and cold rolling it to form a steel sheet (cold rolled sheet);

[0100] (IV) A decarburizing annealing process of decarburizing annealing the above steel sheet;

[0101] (V) A final annealing process of coating an annealing release agent on the above steel sheet after the above decarburizing annealing process and performing final annealing;

[0102] (VI) A groove forming process of forming grooves on the surface of the above steel sheet by laser irradiating the surface of the above steel sheet between the above cold rolling process and the above final annealing process.

[0103] In addition, the grain-oriented electrical steel sheet of the present embodiment may further have one or more of the following processes.

[0104] (VII) A nitriding treatment process of increasing the nitrogen content of the above steel sheet after the above decarburizing annealing process;

[0105] (VIII) A grinding process of grinding the surface of the steel sheet after the above-mentioned groove forming process;

[0106] (IX) An insulating film forming process of forming an insulating film on the surface of the steel sheet after the above-mentioned final annealing process (or on the surface of the forsterite film formed on the surface of the steel sheet).

[0107] [Hot rolling process]

[0108] In the hot rolling process, a slab having a specified chemical composition (a chemical composition corresponding to the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet of the present embodiment) is heated and hot rolled to produce a hot rolled sheet.

[0109] Its conditions are not limited. For example, the heating temperature is 1050 to 1400 °C.

[0110] The chemical composition of the slab to be hot rolled can be determined by considering the change in chemical composition in each process according to the chemical composition desired for the grain-oriented electrical steel sheet.

[0111] For example, in the case of obtaining the chemical composition of the base steel sheet of the preferred grain-oriented electrical steel sheet of the present embodiment, it is preferable to use a slab having the following chemical composition.

[0112] That is, as the chemical composition of the slab, it may contain, by mass%, Si: 2.5 to 4.5%, Mn: 0.01 to 0.15%, C: 0.02 to 0.10%, acid-soluble Al: 0 to 0.065%, N: 0.002 to 0.030%, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0 to 0.50%, Sn: 0 to 0.30%, Sb: 0 to 0.30%, Ni: 0 to 1.000%, S: 0.001 to 0.050%, Se: 0 to 0.050%, Bi: 0 to 0.02%. In addition, it may contain the above elements, and the balance is Fe and impurities.

[0113] The method for obtaining the slab is not limited. For example, as long as molten steel having a specified chemical composition is melted and used to manufacture it. The slab can be manufactured by continuous casting, or an ingot can be manufactured using molten steel and the ingot can be bloomed to manufacture the slab. In addition, the slab can also be manufactured by other methods.

[0114] The thickness of the slab is not particularly limited. For example, it is 150 to 350 mm. The thickness of the slab is preferably 220 to 280 mm. It is also possible to use a so-called thin slab having a thickness of 10 to 70 mm.

[0115] [Hot rolled sheet annealing process]

[0116] In the annealing process of the hot-rolled sheet, the above-mentioned hot-rolled sheet after the hot-rolling process is annealed. By performing such annealing treatment, recrystallization occurs in the steel sheet structure, and good magnetic properties can be achieved.

[0117] In the annealing process of the hot-rolled sheet of the present embodiment, it is only necessary to anneal the hot-rolled sheet manufactured through the hot-rolling process according to a known method. Regarding the means of heating the hot-rolled sheet during annealing, there is no particular limitation, and a known heating method can be adopted. In addition, there is no particular limitation on the annealing conditions either. However, for example, for the hot-rolled sheet, annealing can be performed in a temperature range of 900 to 1200 °C for 10 seconds to 5 minutes.

[0118] [Cold rolling process]

[0119] In the cold rolling process, the hot-rolled sheet after the hot-rolled sheet annealing process is pickled and then cold-rolled to form a steel sheet (cold-rolled sheet). The cold rolling can be single-pass (a series of cold rolling without intermediate annealing), or the cold rolling can be interrupted and at least 1 or 2 or more intermediate annealings can be performed before the final pass of the cold rolling process, and multi-pass cold rolling with intermediate annealing can be performed.

[0120] The cold rolling conditions can be according to known methods. For example, the final reduction ratio can be set within a range of 80% or more and 95% or less.

[0121] The final reduction ratio refers to the cumulative reduction ratio of cold rolling. In the case of performing intermediate annealing, it is the cumulative reduction ratio of cold rolling after the final intermediate annealing.

[0122] In the case of performing intermediate annealing, for example, it is held at a temperature of 1000 to 1200 °C for 5 to 180 seconds. The annealing atmosphere is not particularly limited. Considering the manufacturing cost, the number of intermediate annealings is preferably within 3 times.

[0123] In addition, pickling can also be performed under known conditions.

[0124] [Decarburizing annealing process]

[0125] In the decarburizing annealing process, the steel sheet (cold-rolled sheet) is subjected to decarburizing annealing. In this decarburizing annealing, carbon that has an adverse effect on magnetic properties is removed from the steel sheet (decarburization), and at the same time, the steel sheet undergoes primary recrystallization.

[0126] The decarburizing annealing conditions are not limited, but for example, they can be set to the conditions of heating at 700 to 900 °C for 1 to 3 minutes.

[0127] [Nitriding treatment process]

[0128] After the decarburizing annealing process and before the final annealing process, a nitriding process for increasing the nitrogen content of the grain-oriented electrical steel sheet may also be performed. The nitriding process may be carried out by a known method, for example, by annealing in an atmosphere containing a gas having nitriding ability such as ammonia to allow nitrogen to penetrate into the steel. Thereby, an inhibitor for secondary recrystallization can be formed by nitriding.

[0129] [Groove forming process]

[0130] In the groove forming process, grooves are formed on the surface of the steel sheet (cold-rolled sheet) by irradiating the surface of the steel sheet with a laser. In addition, at this time, protrusions are simultaneously formed in the grooves (side surfaces or bottom surfaces). In addition, the crystal orientation of the protrusions is also controlled.

[0131] The groove forming process is carried out between the cold rolling process and the final annealing process, that is, between the cold rolling process and the decarburizing annealing process, or between the decarburizing annealing process and the final annealing process, or between the nitriding process and the final annealing process, etc., as required.

[0132] In the groove forming process, in order to form protrusions simultaneously with the formation of grooves, laser irradiation is carried out in two stages: the first stage and the second stage.

[0133] At this time, in the first stage, it is necessary to control the laser irradiation conditions and the injection conditions of the auxiliary gas for removing the melt generated by laser irradiation from the surface using the auxiliary gas. In the second stage, it is necessary to control the laser irradiation conditions.

[0134] Specifically, in the first stage, during laser irradiation, a laser with a laser output power of 200 - 3000 W, a condensing spot diameter in the rolling direction (i.e., the diameter including 86% of the laser output power) of 10 - 1000 μm, and a condensing spot diameter in the sheet width direction (i.e., the diameter including 86% of the laser output power) of 10 - 1000 μm is irradiated at a scanning speed of 2 - 50 m / s. At the same time, an auxiliary gas with a blowing flow rate of 1 - 500 L / min is blown. By performing laser irradiation and blowing of the auxiliary gas under the above conditions, grooves are formed on the surface of the steel sheet, and protrusions of a specified size are formed in the grooves (side surfaces or bottom surfaces).

[0135] In the second stage, for the same part as the part irradiated with the laser in the first stage above, a laser with a laser output power of 10 - 150 W, a condensing spot diameter in the rolling direction of 10 - 1000 μm, and a condensing spot diameter in the sheet width direction of 10 - 1000 μm is irradiated at a scanning speed of 2 - 50 m / s.

[0136] By irradiating the laser immediately after the first stage under the above conditions, the orientation difference between the average crystal orientation of the protrusions and the Goss orientation can be set to 10 degrees or more.

[0137] In the first stage, when the laser output power is less than 200 W, since the generation of the molten material is insufficient, only protrusions smaller than the preferred shape are formed inside the groove, or no protrusions are formed. On the other hand, when it exceeds 3000 W, since the laser output power is too strong, an excessive amount of molten material is generated, and protrusions larger than the preferred shape are formed inside the groove.

[0138] In addition, when the diameter of the focused laser spot in the rolling direction and the width direction of the laser is less than 10 μm, grooves of the preferred shape are not formed, and the protrusions formed inside the groove become smaller than the preferred shape, so the iron loss reduction effect cannot be obtained. On the other hand, when it exceeds 1000 μm, grooves of the preferred shape are not formed, and the protrusions formed inside the groove become larger than the preferred shape, so the iron loss reduction effect cannot be obtained.

[0139] In addition, when the scanning speed is less than 2 m / s, an excessive amount of molten material is generated, and protrusions larger than the preferred shape are formed inside the groove. On the other hand, when it exceeds 50 m / s, since the generation of the molten material is insufficient, only protrusions smaller than the preferred shape are formed inside the groove, or no protrusions are formed.

[0140] When the flow rate of the assist gas is less than 1 L / minute, the removal of the molten material is insufficient, and protrusions larger than the preferred shape are formed inside the groove. On the other hand, if it exceeds 500 L / minute, the molten material is removed excessively, so only protrusions smaller than the preferred shape are formed inside the groove, or no protrusions are formed.

[0141] Preferably, the laser output power is 500 - 3000 W, the diameter of the focused laser spot in the rolling direction of the laser (i.e., the diameter including 86% of the laser output power) is 10 - 500 μm, the diameter of the focused laser spot in the plate width direction of the laser (i.e., the diameter including 86% of the laser output power) is 10 - 500 μm, the laser scanning speed is 5 - 50 m / s, and the flow rate of the assist gas is 1 - 200 L / minute.

[0142] In the second stage, when the laser output power is less than 10 W, since the protrusions are not heated sufficiently, no effect is obtained. On the other hand, when it exceeds 150 W, the protrusions melt.

[0143] When the diameter of the focused laser spot in the rolling direction and the width direction of the laser is less than 10 μm, since the laser output power per unit area is too high, the protrusions melt. On the other hand, when it exceeds 1000 μm, parts other than the protrusions are also heated, so it is not preferred.

[0144] If the production efficiency is considered, the scanning speed is preferably the same as that in the first stage. However, as long as it is in the range of 2 to 50 m / s, the heating of the protrusions is sufficient, so it can also be appropriately changed within the above range.

[0145] The following reasons can be conceived for the control of the crystal orientation of the protrusions by laser irradiation.

[0146] By laser irradiation, recrystallization and grain growth occur near the protrusions. Or, due to the application of thermal strain, recrystallization and grain growth occur with this strain as the driving force in the front stage (before the start of secondary recrystallization) of the decarburization annealing or final annealing in the subsequent process, and become coarser compared to the matrix grains before secondary recrystallization (grains engulfed by secondary recrystallized grains). These coarse grains are difficult to be engulfed by secondary recrystallized grains, and in addition, since they have a random orientation, the orientation difference from the Goss orientation is large. Therefore, the orientation difference between the average crystal orientation of the protrusions and the Goss orientation can be set to 10 degrees or more.

[0147] [Grinding process]

[0148] In the grinding process, the surface of the steel sheet (cold-rolled sheet) after the groove forming process is ground using a brush roll fixed with abrasive grains. Thereby, the height of the protrusions on the flat part at the groove edge (around the groove) can be reduced, or the protrusions can be removed.

[0149] When grinding, the brush roll is controlled to rotate in a direction opposite to the conveying direction of the steel sheet at the position where it contacts the steel sheet. The conveying speed (linear speed) of the steel sheet is set to 5 to 100 mpm (meter per minutes), and grinding is performed under the conditions that the rotational speed of the brush roll is 500 to 2000 rpm, the pressing amount of the brush roll is 2 to 10 mm, the grain size of the abrasive grains is #40 to #400, and the diameter of the brush roll is 200 to 500 mm.

[0150] When it is outside the above range, sufficient effects cannot be obtained.

[0151] The grinding conditions preferably set the conveying speed of the steel sheet to 5 to 100 mpm, the rotational speed of the brush roll to 1000 to 2000 rpm, the pressing amount of the brush roll to 4 to 10 mm, the grain size of the abrasive grains to #40 to #100, and the diameter of the brush roll to 200 to 500 mm. In this case, the effect of removing the protrusions at the groove edge is improved.

[0152] [Final annealing process]

[0153] In the final annealing process, an annealing release agent is coated on the steel sheet after the decarburization annealing process, and final annealing is performed.

[0154] Since final annealing is carried out after coiling the steel sheet into a coil shape, during final annealing, the annealing parting agent is applied in a manner that the steel sheet is not baked. Generally, an annealing parting agent mainly containing MgO or Al2O3 is used. After applying such an annealing parting agent, final annealing is carried out. For example, if an annealing parting agent with MgO as the main component is used, a layer of forsterite (Mg2SiO4) film is formed. In the case of using an annealing parting agent with Al2O3 as the main component, sometimes no forsterite film is formed.

[0155] In addition, in the final annealing process, by heating to the annealing temperature, secondary recrystallization of the primary recrystallized grains obtained in the decarburizing annealing process is carried out to obtain crystallized grains that are all in the Goss orientation, and by maintaining for a specified time at the annealing temperature, impurities (such as N, S, etc.) that have an adverse effect on magnetic properties are removed (purified).

[0156] The conditions for final annealing are not limited, but for example, it is heated to 1100 - 1300 °C and maintained for 20 - 24 hours.

[0157] [Insulating film forming process]

[0158] In the insulating film forming process, an insulating film is formed on the steel sheet after the final annealing process (the surface of the forsterite film in the case where a forsterite film is formed on the surface of the steel sheet through final annealing).

[0159] For example, the insulating film can be formed by applying a coating solution containing phosphoric acid or phosphate, colloidal silica, and anhydrous chromic acid or chromate on the steel sheet after final annealing (including the case with a forsterite film), and baking and drying at 300 - 950 °C for 10 seconds or more.

[0160] Through these processes, a grain-oriented electrical steel sheet having a base steel sheet and, if necessary, a forsterite film and / or an insulating film can be obtained.

[0161] Examples

[0162] A slab having a chemical composition containing, by mass fraction, Si: 3.3%, C: 0.060%, acid-soluble Al: 0.028%, N: 0.008%, Mn: 0.12%, Cr: 0.05%, Cu: 0.04%, P: 0.01%, Sn: 0.02%, Ni: 0.005%, S: 0.007%, and the balance containing Fe and impurities was subjected to a hot rolling process to produce a hot-rolled sheet with a thickness of 2.6 mm.

[0163] The hot-rolled sheet was subjected to hot-rolled sheet annealing under the conditions of heating to 1000 °C and maintaining for 1 minute.

[0164] The hot-rolled sheet after annealing is pickled and then cold-rolled to produce a steel sheet (cold-rolled sheet) with a thickness of 0.23 mm.

[0165] The steel sheet is irradiated with a laser under the conditions shown in Table 1A and Table 1B to form grooves on the surface extending in a direction perpendicular to the rolling direction. In addition, a plurality of these grooves are formed at intervals of 5 mm in the rolling direction in parallel with each other.

[0166] The surface of the steel sheet with the grooves formed thereon is ground under the conditions shown in Table 2 using a brush roll that rotates in a direction opposite to the conveying direction of the steel sheet.

[0167] After grinding, decarburization annealing is carried out under the conditions of heating to 800 °C and holding for 2 minutes.

[0168] An annealing parting agent mainly composed of magnesium oxide (MgO) is coated on the steel sheet after decarburization annealing, and final annealing is carried out under the conditions of heating to 1200 °C and holding for 20 hours. As a result, a grain-oriented electrical steel sheet with a forsterite film formed on the surface of the steel sheet (base steel sheet) is obtained.

[0169] An insulating film is formed by coating a coating solution containing colloidal silica and phosphate on the obtained grain-oriented electrical steel sheet and carrying out heat treatment under the conditions of heating to 850 °C and holding for 1 minute.

[0170] The chemical composition of the base steel sheet of the obtained grain-oriented electrical steel sheet is determined. The result is a chemical composition containing, by mass fraction, Si: 3.3%, C: 0.001% or less, acid-soluble Al: 0.004% or less, N: 0.001% or less, Mn: 0.12%, Cr: 0.05%, Cu: 0.04%, P: 0.01%, Sn: 0.02%, Ni: 0.005%, S: 0.001% or less, and the balance containing Fe and impurities.

[0171] Samples are collected from the obtained grain-oriented electrical steel sheet according to the above-mentioned procedure, and the presence or absence of protrusions in the grooves and at the groove edges, the maximum height and maximum width of the protrusions, and the orientation difference between the average crystal orientation of the protrusions in the grooves and the Goss orientation are measured.

[0172] The results are shown in Table 3.

[0173] The obtained grain-oriented electrical steel sheet is cut into a width of 30 mm and a length of 320 mm to collect test pieces. The length of the test pieces is set parallel to the rolling direction. For the collected test pieces, according to JIS C2550-1(2011), Epstein tests are carried out to measure the iron loss W17 / 50 at a frequency of 50 Hz with a maximum magnetic flux density set at 1.7 T.

[0174] If W17 / 50 is 0.750 W / kg or less, it is judged that low iron loss is obtained.

[0175] The results are shown in Table 3.

[0176] [Table 1A]

[0177]

[0178] [Table 1B]

[0179]

[0180] Table 2

[0181]

[0182] Table 3]

[0183]

[0184] As shown in Tables 1A to 3, when the laser irradiation conditions or the auxiliary gas injection conditions are outside the ranges specified in the present invention, protrusions having a preferable shape are not formed in the grooves. Alternatively, the average crystal orientation of the protrusions is outside the scope of the present invention. In these grain-oriented electrical steel sheets, the iron loss is high (Comparative Examples 1 to 20).

[0185] On the other hand, when the laser irradiation conditions and the auxiliary gas injection conditions are within the ranges specified in the present invention, protrusions specified in the present invention are formed in the grooves. In addition, the orientation difference between the average crystal orientation of the protrusions and the Goss orientation is 10 degrees or more. The iron loss of these grain-oriented electrical steel sheets is low (Inventive Examples 1 to 21).

[0186] In addition, among them, when the grinding conditions using a brush roll are carried out under specified conditions, the protrusions at the groove edge portions become smaller and the iron loss becomes further lower (Inventive Examples 1 to 15).

[0187] Industrial Applicability

[0188] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet having low iron loss and a method for manufacturing the same. Therefore, the industrial applicability is high.

[0189] Description of Reference Numerals

[0190] 1 Grain-oriented electrical steel sheet

[0191] 11 Steel sheet (base steel sheet)

[0192] 21 Groove

[0193] 31 Entrance portion of groove

[0194] 41 Groove edge portion

[0195] 102 Protrusion (inside the groove)

[0196] H Protrusion height (height of the protrusion)

[0197] W Width of the protrusion

[0198] RD Rolling direction

[0199] TD Plate width direction

[0200] RC Reference curve

[0201] 101 Protrusion (groove edge part)

[0202] RS Reference plane

Claims

1. A directional electromagnetic steel sheet, characterized in that, It has a steel plate with a plurality of grooves formed on the surface, extending in a direction crossing the rolling direction and having a depth in the plate thickness direction. In a cross-section parallel to the rolling direction of the steel plate and parallel to the plate thickness direction, at least one protrusion exists on the side surface or bottom surface of the groove. The maximum height of the protrusion is 2 to 50 μm and the maximum width is 2 to 50 μm. The orientation difference between the average crystal orientation of the protrusion and the Goss orientation is 10 degrees or more.

2. The directional electromagnetic steel sheet according to claim 1, characterized in that, In the cross-section, when the distance from the entrance portion of the groove to the entrance portion of the opposite groove is defined as the width of the groove, and the region equal to the width of the groove in the direction opposite to the center of the groove toward the rolling direction starting from the entrance portion of the groove of the steel plate is defined as the groove edge portion, the maximum height of the protrusion in the groove edge portion is 5 μm or less and the maximum width is 5 μm or less.

3. The directionally electromagnetic steel sheet according to claim 1 or 2, wherein A forsterite film is formed on the surface of the steel plate.

4. The directionality electromagnetic steel sheet according to claim 3, wherein An insulating film is formed on the surface of the forsterite film.

5. The directional electromagnetic steel sheet according to claim 1 or 2, characterized in that, An insulating film is formed on the surface of the steel plate.

6. A method for manufacturing a directional electromagnetic steel sheet, characterized in that, It is a method for manufacturing a directional electromagnetic steel plate according to claim 1 or 2, comprising the following steps: Hot rolling step: heating and hot rolling a slab to produce a hot rolled sheet. Hot rolled sheet annealing step: annealing the hot rolled sheet after the hot rolling step. Cold rolling step: pickling and cold rolling the hot rolled sheet after the hot rolled sheet annealing step to produce a steel plate. Decarburizing annealing step: performing decarburizing annealing on the steel plate. Final annealing step: coating an annealing release agent on the steel plate after the decarburizing annealing step and performing final annealing; and Groove forming step: between the cold rolling step and the final annealing step, forming grooves on the surface of the steel plate by laser irradiation on the surface of the steel plate, and forming protrusions on the side surface or bottom surface of the grooves. Among them, the groove forming step includes: The first stage: irradiating a laser with a scanning speed of 2 to 50 m / s, a laser output power of 200 to 3000 W, a diameter of the condensing spot including 86% of the laser output power in the rolling direction of 10 to 1000 μm, and a diameter of the condensing spot in the plate width direction of 10 to 1000 μm, and blowing an auxiliary gas with a flow rate of 1 to 500 L / minute. The second stage: for the same part as the part irradiated with the laser in the first stage, irradiating a laser with a scanning speed of 2 to 50 m / s, a laser output power of 10 to 150 W, a diameter of the condensing spot in the rolling direction of 10 to 1000 μm, and a diameter of the condensing spot in the plate width direction of 10 to 1000 μm.

7. The manufacturing method of the directional electromagnetic steel sheet according to claim 6, characterized in that, It further includes a grinding step of grinding the surface of the steel plate after the groove forming step using a brush roll fixed with abrasive grains. In the grinding step, the brush roll rotates in a direction opposite to the conveying direction of the steel plate at the position where it abuts against the steel plate. The conveying speed of the steel plate is 5 to 100 mpm. The rotational speed of the brush roll is 500 to 2000 rpm. The pressing amount of the brush roll is 2 to 10 mm. The particle size of the abrasive grains is #40 to #400. The diameter of the brush roll is 200 to 500 mm.

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