Grain-oriented electrical steel sheet and method for producing same

Abstract

The purpose of the present invention is to provide a grain-oriented electrical steel sheet in which a decrease in productivity is suppressed in magnetic domain control for forming a laser groove, and iron loss is improved. A grain-oriented electrical steel sheet according to the present invention has a plurality of grooves in the surface of a steel sheet, and has protrusions on the surface of the steel sheet on groove-side portions adjacent to the grooves. The crystal orientation of at least one crystal grain present inside the protrusions differs from the Gaussian orientation, which is the crystal orientation of crystal grains other than in the vicinity of the protrusions, of the steel sheet by at least 5 DEG, thereby improving the iron loss of the electromagnetic steel sheet and eliminating the need for a protrusion removal step.

Description

Technical Field

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

[0002] The grain-oriented electrical steel sheet is a steel sheet in which the crystal orientation is controlled by a combination of cold rolling and annealing so that the easy magnetization axis of the crystal grains is aligned with the rolling direction.

[0003] As a technology for reducing eddy current loss, which is one type of iron loss in grain-oriented electromagnetic steel sheets, it is known to form an insulating film on the surface of a base steel sheet with controlled crystal orientation. The insulating film not only has electrical insulation properties, but also has the functions of imparting tension and rust resistance to the base steel sheet.

[0004] In addition, as another method for reducing eddy current loss, a magnetic domain control method is known in which a strain region or groove is formed in a direction intersecting the rolling direction at a predetermined interval along the rolling direction to narrow the width of the 180° magnetic domain (refine the 180° magnetic domain). The magnetic domain control method is classified into a method of applying strain to a base steel sheet of a directional electromagnetic steel sheet and a method of forming grooves on the surface of a base steel sheet having a film that applies tension to the base steel sheet.

[0005] By using a grain-oriented electromagnetic steel sheet that has been subjected to magnetic domain control by grooves to manufacture the iron core (winding core) of the transformer, the grooves will not disappear even if strain relief annealing is performed, so the magnetic domain refinement effect can be maintained. Therefore, for the winding core, a magnetic domain control method based on groove formation is sometimes used as a method for reducing eddy current loss.

[0006] Figure 1 FIG. 1 is a diagram schematically showing an electromagnetic steel sheet having grooves formed therein. Figure 1 , a state is shown in which a plurality of grooves 2 are formed on the surface of a base steel plate 1 at intervals along the rolling direction of the base steel plate 1. Figure 1 In the figure, the symbol θ represents the angle between the direction (plate width direction) perpendicular to the rolling direction and the plate thickness direction of the base steel plate 1 and the length direction of the groove 2. The symbol W represents the width of the groove 2, the symbol D represents the depth of the groove 2, and the symbol P represents the interval between adjacent grooves 2 in the rolling direction.

[0007] Various methods of forming grooves in electromagnetic steel sheets have been proposed.

[0008] For example, Patent Document 1 discloses an electrolytic etching method for forming grooves on the surface of a grain-oriented electrical steel sheet by electrolytic etching.

[0009] Patent Document 2 discloses a gear pressing method in which a gear is mechanically pressed on the surface of a grain-oriented electromagnetic steel sheet to form grooves on the surface of the steel sheet.

[0010] However, the electrolytic etching method requires masking, etching, and mask removal, and has a problem of being more complicated than the mechanical method. The gear pressing method has a problem of wearing out the teeth in a short time due to the high hardness of the electromagnetic steel sheet. Furthermore, from the perspective of high-speed processing, it is difficult to achieve a production line speed of more than 100 mpm required in general steel manufacturing processes.

[0011] In addition, Patent Document 3 discloses a laser irradiation method, which melts and evaporates the laser irradiated portion of the steel plate surface of a grain-oriented electromagnetic steel plate by laser irradiation. The laser irradiation method does not cause the wear of the tooth profile or the complicated process, and can also perform high-speed processing. However, in the groove formation based on laser irradiation, due to the splash generated when the groove is formed, a molten protrusion is formed on the side of the groove. The molten protrusion deteriorates the magnetic properties, so a process for removing the molten protrusion is required, and the reduction in productivity is a problem.

[0012] Furthermore, Patent Document 5 proposes the following: since the molten protrusions formed by groove formation based on laser irradiation hinder the close contact between adjacent directional electromagnetic steel sheets in the laminated iron core, thereby increasing the noise, the size of the protrusions is suppressed and the metal structure of the protrusions is made consistent with the Goss orientation in order to maintain the iron loss.

[0013] Prior art literature

[0014] Patent Literature

[0015] Patent Document 1: Japanese Patent Publication No. 62-54873

[0016] Patent Document 2: Japanese Patent Publication No. 62-53579

[0017] Patent Document 3: Japanese Patent Application Publication No. 2003-129135

[0018] Patent Document 4: International Publication No. 2011 / 007771

[0019] Patent Document 5: International Publication No. 2017 / 171013 Summary of the invention

[0020] Problems to be solved by the invention

[0021] The present invention has been developed in view of the above-mentioned problems, and an object of the present invention is to provide a grain-oriented electrical steel sheet with the goal of suppressing a decrease in productivity and improving iron loss in magnetic domain control for forming laser grooves (grooves formed by laser irradiation).

[0022] Means for solving problems

[0023] The inventors of the present invention have repeatedly conducted in-depth research to solve the above-mentioned problems. In the process of repeatedly studying the laser irradiation conditions when forming laser grooves, it was found that the conditions under which the shape of the molten protrusion (protrusion) generated on the groove side adjacent to the groove on the surface of the steel plate caused by the spatter generated when the laser groove is formed will not have an adverse effect on the iron loss were found. Further research was conducted, and it was found that if there are grains in the protrusion whose crystal orientation differs from that of the base steel plate by more than 5°, the iron loss is improved. This is a completely new insight that is not found in Patent Documents 3 and 5 related to molten protrusions. The present invention is formed based on these new insights, and the main purpose of the present invention is as follows. [1]

[0025] A directional electromagnetic steel sheet according to one embodiment of the present invention is characterized in that it is a directional electromagnetic steel sheet having a plurality of grooves on its surface, wherein the surface of the steel sheet has a protrusion on the groove side adjacent to the groove, and the crystal orientation of at least one grain existing inside the protrusion differs by more than 5° from the crystal orientation of grains existing in a portion of the electromagnetic steel sheet other than the protrusion. [2]

[0027] According to one aspect of the present invention, the grain-oriented electrical steel sheet as described in the above [1] is characterized in that an average height of the protrusions is 2.5 μm to 10.0 μm. [3]

[0029] According to the directional electromagnetic steel sheet described in [1] or [2] above, the directional electromagnetic steel sheet of one embodiment of the present invention is characterized in that, in the directional electromagnetic steel sheet, the angle θ formed by the direction perpendicular to the rolling direction and the plate thickness direction and the length direction of the groove is less than 40°, the width W of the groove is 20μm to 300μm, the depth D of the groove is 10μm to 40μm, and the spacing P of the groove in the rolling direction is 1mm to 30mm. [4]

[0031] The method for producing a grain-oriented electrical steel sheet according to any one of [1] to [3] above is characterized in that:

[0032] The groove forming step includes irradiating the surface of the steel plate with laser light to form a groove. As the laser irradiation conditions, the laser spot diameter dL in the rolling direction and the laser spot diameter dC in the plate width direction satisfy equation (1).

[0033] 1.0≤dL / dC Formula (1)

[0034] Effects of the Invention

[0035] According to the present invention, even when laser grooves are formed on the surface of a steel sheet, a process of removing protrusions can be omitted, and a grain-oriented electrical steel sheet with excellent iron loss can be obtained without reducing productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a diagram schematically showing an electromagnetic steel sheet having grooves formed therein.

[0037] Figure 2 This is an optical microscope photograph of a cross section of a protrusion.

[0038] Figure 3 This is a SEM photograph obtained by SEM-EBSD in which a cross section of a protrusion is photographed obliquely.

[0039] Figure 4 yes Figure 3 ND-IPF (Inverse Pole Figure) map of the field of view. DETAILED DESCRIPTION

[0040] The inventors of the present invention have repeatedly conducted research to maximize the effect of magnetic domain refinement and improve productivity, and found that if the molten protrusions on the sides of the laser grooves (groove sides) on the surface of the steel sheet meet specific conditions, there will be no adverse effect on the magnetic properties. Hereinafter, the present invention will be described by taking a grain-oriented electromagnetic steel sheet (hereinafter referred to as the present electromagnetic steel sheet) according to one embodiment of the present invention as an example.

[0041] like Figure 1 As shown in , the electromagnetic steel sheet is an electromagnetic steel sheet having a plurality of grooves arranged approximately in parallel on the surface, and may or may not have a glass film on the surface of the steel sheet, and may or may not have a tension film (insulating film) on the outermost surface of the steel sheet. Figure 1 A conceptual diagram showing the present electromagnetic steel sheet having neither a glass film nor a tension film. The steel sheet surface refers to a surface including a glass film or a tension film when the steel sheet has these films unless otherwise specified.

[0042] <Protrusion>

[0043] The grooves on the steel plate surface are formed by the splashes (molten metal splashes) and molten metal flow generated when the laser grooves are formed by laser irradiation, thereby forming protrusions on the groove side on the steel plate surface. Figure 1As shown in the figure, the protrusion 3 is formed on the surface of the electromagnetic steel sheet 1 along the groove 2. Depending on the situation, other protrusions may be formed on the steel sheet surface between the protrusion 3 and the protrusion 3 of the adjacent groove (i.e., the steel sheet surface sandwiched by the protrusion 3 on the groove side), but the protrusion referred to in the electromagnetic steel sheet refers to the protrusion closest to the groove, i.e., the protrusion formed on the groove side.

[0044] Figure 2 to Figure 4 This is a diagram of the groove of the present electromagnetic steel sheet observed in a cross section perpendicular to the longitudinal direction of the groove. Figure 2 The dotted line represents an imaginary line on the steel plate surface (surface imaginary line), which is an imaginary line existing on the steel plate surface before the laser groove is formed. Figure 2 It is known that when a laser groove is formed, a protrusion is formed on the portion of the steel sheet surface adjacent to the laser groove (groove side). The protrusion is a portion located above the surface virtual line (upper portion in the steel sheet surface direction).

[0045] <Fine Grains in Protrusions>

[0046] In the present electromagnetic steel sheet, a protrusion is provided on the side of the steel sheet surface of the groove formed in the base steel sheet, and in a cross section perpendicular to the length direction of the groove, the protrusion is controlled so as to have at least one fine grain having a crystal orientation different from that of the base steel sheet (a portion other than the protrusion that is not affected by laser irradiation) by 5° or more. Specifically, Figure 2 and Figure 3 As shown in FIG. 1 , in a cross section perpendicular to the groove length direction, as long as any one of the crystal grains present in the protrusion is aligned with the Goss orientation {110} which is the crystal orientation of the base steel plate, <001> The difference between the orientation of the protrusion and the orientation of the base steel sheet may be 5° or more.

[0047] Fine grains can be obtained by laser irradiation of a steel plate after cold rolling, after decarburization annealing, after finished annealing, or after a tension film is further applied. In the case of irradiation after cold rolling, recrystallized grains are formed inside the protrusions during the decarburization annealing, and are not eroded by the Gaussian orientation of the base material during the secondary recrystallization, and an orientation that deviates by more than 5° from the Gaussian orientation of the base material remains. In the case of irradiation after decarburization annealing, recrystallized grains are formed inside the protrusions during the finished annealing, and are not eroded by the Gaussian orientation of the base material during the secondary recrystallization, and an orientation that deviates by more than 5° from the Gaussian orientation of the base material remains. In the case of irradiation of a steel plate after finished annealing or after a tension film is applied, recrystallized grains that deviate by more than 5° from the orientation of the base material steel plate that has become Gaussian oriented by secondary recrystallization are formed inside the protrusions during the subsequent coating baking and re-coating baking.

[0048] The reason why the fine grains in the protrusions reduce iron loss is considered as follows. The refinement of magnetic domains in oriented electromagnetic steel sheets increases the static magnetic energy by generating magnetic poles on the surface of the steel sheet. In order to eliminate this, the domain width is narrowed by newly generating 180° domain walls. If the domain width is narrowed, the moving distance of the domain wall when the steel sheet is magnetized becomes shorter, and the energy loss when the domain wall moves is reduced, that is, the iron loss is reduced. Therefore, the fine grains become the starting point for the generation of magnetic poles, promote the refinement of the 180° magnetic domain, and reduce the iron loss.

[0049] If the orientation difference between the fine grains of the protrusion and the grains of the parent steel plate is small, it will not become the starting point for the generation of magnetic poles, so the orientation difference between the fine grains of the protrusion and the grains of the parent steel plate is set to 5° or more. The crystal orientation difference is preferably 6° or more, 7° or more, 8° or more, 9° or more, 10° or more, 11° or more, 12° or more, 13° or more, 14° or more, 15° or more, 16° or more, 17° or more, 18° or more, 19° or more, or 20° or more. It should be noted that the orientation difference only needs to become the starting point for the generation of magnetic poles, so there is no upper limit to the crystal orientation difference between the fine grains and the parent steel plate.

[0050] Regarding the observation of fine grains inside the protrusion, the cross section cut perpendicular to the length direction of the groove can be electrolytically polished, and the inverse pole figure (IPF) map (crystal orientation map) can be obtained using SEM-EBSD (Electron BackScattered Diffraction Pattern) for measurement and determination. Figure 4 An example of an IPF map of SEM-EBSD for a protrusion is shown in FIG. Figure 3 It is shown in Figure 4 SEM-EBSD images of the same field of view. It should be noted that in the case of a glass film, the glass film itself exists in the base material and is difficult to distinguish using the IPF map based on EBSD, but by combining it with the SEM-EBSD image, it can be distinguished from a steel plate containing a glass film and a protrusion. As described above, the IPF map of EBSD can determine the fine grains in the protrusion, and further confirm the crystal orientation of the fine grains and the Gauss orientation of the base material.

[0051] If there are more than one fine grain in a protrusion in a cross section perpendicular to the length direction of the groove, a magnetic pole is generated to obtain a magnetic domain refinement effect. The upper limit of the number of fine grains in a protrusion is not particularly limited. For example, at least one arbitrary groove is selected, and the cross section when cut at a cross section perpendicular to the length direction of the groove is observed, and fine grains can be observed. That is, more than one fine grain can be observed for each protrusion. The upper limit is not particularly limited, but if there are too many, the protrusion height becomes higher, so each protrusion can also be set to less than 10.

[0052] If the size of the fine grains becomes larger, the magnetic properties may deteriorate, so the size of the fine grains is preferably 15.0 μm or less in terms of area equivalent circle diameter. Preferably, it is 14.0 μm or less, 13.0 μm or less, 12.0 μm or less, 11.0 μm or less, or 10.0 μm or less. The lower limit of the size of the fine grains is not particularly set, but from the perspective of the spatial resolution of EBSD, it can also be set to 1.0 μm or more.

[0053] The shape of the fine grains is not particularly limited, but if they are extremely long and flat in the rolling direction or the plate thickness direction, the iron loss reduction effect may be reduced. Therefore, the ratio of the length of the fine grains in the rolling direction to the length in the plate thickness direction, i.e., the shape ratio A, is preferably set to 0.2 to 5. Here, the shape ratio A of the fine grains is the maximum length L of the fine grains in the rolling direction. RD Maximum length L in the thickness direction ND Ratio L RD / L ND . The lower limit of the shape ratio A of the fine grains is preferably 0.25 or more, 0.3 or more, 0.4 or more or 0.5 or more. The shape ratio A is preferably 4 or less, 3.5 or less, 3 or less, 2.5 or less, 2 or less or 1.5 or less. From the perspective of the starting point for the generation of magnetic poles with reduced iron loss, it is believed that when the shape ratio is less than 1.0 (lower than 1.0), that is, when it is slender in the thickness direction of the plate, the flow of magnetic flux in the rolling direction is partially hindered and it is easy to become the starting point for the generation of magnetic poles, so it is preferred.

[0054] <Height of protrusion>

[0055] If there are fine grains, the magnetic domain refinement is promoted, so the height of the protrusion is not particularly limited. However, if the height of the protrusion is too low, the fine grains will become smaller and will not become the starting point for the generation of magnetic poles, and there will be no magnetic domain control effect. Therefore, it is appropriate to set the protrusion height to 2.5μm or more, preferably to 3.0μm or more, 4.0μm or more, or 5.0μm or more. On the other hand, if the height of the protrusion is too high, the fine grains will become larger and cause a decrease in magnetic flux density. Therefore, it is appropriate to set the protrusion height to 10.0μm or less, preferably to 9.0μm or less.

[0056] The height of the protrusion can be measured, for example, by a non-contact or contact roughness meter such as a 3D microscope or a three-dimensional roughness meter (hereinafter collectively referred to as a "roughness meter") as follows. First, the top of the protrusion on the surface of the steel plate is measured parallel to the groove for a length of 150 μm, and the maximum height of the protrusion is derived. Next, while maintaining the reference height, the roughness of the steel plate surface between the groove and the adjacent groove (preferably near the center between the grooves) is measured parallel to the groove for a length of 150 μm, and the average height of the steel plate surface between the grooves is measured. The difference between the maximum height of the protrusion obtained and the average height between the grooves is taken as the protrusion height.

[0057] Alternatively, the roughness meter is scanned on the steel plate surface in a manner that a straight line perpendicular to the groove crosses the protrusion, and the roughness distribution of the steel plate surface is measured to obtain the cross-sectional profile. At this time, the height of the highest point of the protrusion relative to the position between adjacent grooves can also be used as the protrusion height. Alternatively, a surface imaginary line can be drawn from the obtained cross-sectional profile, and the distance between the highest point of the protrusion and the surface imaginary line can be used as the protrusion height.

[0058] In this manner, the protrusion heights are randomly measured at 10 points on the steel plate, and the value obtained by taking the arithmetic average of the obtained protrusion heights is defined as the average height of the protrusions.

[0059] The average height of the protrusions can also be measured by other methods other than the roughness meter. For example, the average height of the protrusions can be measured on a cross section perpendicular to the longitudinal direction of the groove (e.g. Figure 2 The cross section is observed with an optical microscope, and the height of the protrusion from the imaginary line of the surface is measured, and the highest height is defined as the protrusion height. The protrusion height at each of the measuring points is arithmetically averaged and measured at 10 random points on the steel plate, and the average protrusion height is defined as the average protrusion height.

[0060] The average height of the protrusions may be measured by one of the above methods. When measured by a plurality of methods, the average height of the protrusions obtained by the respective methods may be averaged to obtain the average height of the protrusions.

[0061] This electromagnetic steel plate Figure 1 As shown in , a plurality of grooves are formed on the surface of the steel sheet in parallel so as to be adjacent to each other in the rolling direction of the steel sheet. The direction (angle θ), the width W, the depth D and the interval P of the grooves are the same as those of the ordinary oriented electromagnetic steel sheet and are determined in consideration of the iron loss.

[0062] <Angle θ between the length direction of the base steel plate and the length direction of the groove>

[0063] If the angle θ formed by the direction (plate width direction) orthogonal to the rolling direction and the plate thickness direction of the parent steel plate and the length direction of the groove is too large, there is no magnetic domain control effect, and it becomes impossible to obtain the iron loss improvement effect, so it is set to 40° or less. The angle θ is preferably smaller, and it is preferably set to less than 35°, less than 30°, less than 25°, less than 20°, less than 15°, less than 10°, less than 8°, less than 6° or less than 5°. The lower limit of the angle θ is 0°, that is, when the length direction of the groove is parallel to the plate width direction. In addition, the direction of the angle θ is not limited, and refers to the angle of the acute angle side of the angle formed by the length direction of the groove and the plate width direction. A plurality of grooves are arranged roughly in parallel on the surface of the parent steel plate, but the angle θ of each groove can be as long as it is in the above-mentioned range.

[0064] <Slot width W>

[0065] The groove width W refers to the width of the groove at the surface of the parent steel plate in the cross section of the groove in the plane perpendicular to the length direction of the groove (groove cross section). Even if the groove width W is too narrow, it does not become the starting point for the generation of magnetic poles, there is no magnetic domain control effect, and good iron loss cannot be obtained, so it is set to more than 20μm. On the other hand, if it is too wide, it does not become the starting point for the generation of magnetic poles, there is no magnetic domain control effect, only the magnetic flux density is significantly reduced, and good iron loss cannot be obtained, so it is set to less than 300μm. Therefore, it is appropriate to set the groove width W to 20μm to 300μm. The lower limit of the groove width W is preferably set to 25μm or 30μm. The upper limit of the groove width W is preferably set to 250μm, 200μm, 150μm, 100μm or 80μm.

[0066] <Groove Depth D>

[0067] When the groove depth D is too shallow, it does not become the starting point of the magnetic pole, there is no magnetic domain control effect, and good iron loss cannot be obtained, so it is preferably 10μm or more. On the other hand, when it exceeds 40μm and is too deep, the magnetic domain control effect reaches saturation, and only the magnetic flux density is significantly reduced, so good iron loss cannot be obtained. Therefore, it is appropriate to set the groove depth D to 10μm to 40μm. The lower limit of the groove depth D is preferably set to 11μm, 12μm, 13μm, 14μm or 15μm. The upper limit of the groove depth D is preferably set to 38μm, 36μm, 34μm, 32μm, 30μm, 28μm or 26μm.

[0068] <Slot spacing P>

[0069] The groove spacing P is the spacing between the center lines of the grooves in the longitudinal direction of the adjacent grooves arranged roughly parallel to each other on the steel plate surface, and refers to the distance in the rolling direction of the base steel plate. The center line of the groove refers to a line parallel to the longitudinal direction of the groove passing through the midpoint of the groove in the imaginary surface in the groove cross section.

[0070] When the slot spacing P is too narrow, the magnetic domain control effect is saturated, and only the magnetic flux density is significantly reduced, so it is not possible to obtain good iron loss, so it is preferably set to 1 mm or more. On the other hand, when it is too wide and exceeds 30 mm, the magnetic domain control effect cannot be fully obtained, and good iron loss cannot be obtained. Therefore, it is appropriate that the slot spacing P is 1 mm to 30 mm. The slot spacing P may not be equally spaced, but it is appropriate that the slot spacing P with adjacent slots is within the above range. The lower limit of the slot spacing P is preferably 1.2 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.8 mm or 2.0 mm. The upper limit of the slot spacing P is preferably 25.0 mm, 20.0 mm, 15.0 mm, 10.0 mm, 7.0 mm or 5.0 mm.

[0071] <Manufacturing method>

[0072] First, a cold-rolled steel sheet for the present electromagnetic steel sheet is manufactured by a known method. The steel sheet composition and the manufacturing method of the cold-rolled steel sheet are not particularly limited, and a known method, such as the steel sheet composition and the steel sheet manufacturing method described in Patent Documents 4 or 5, can be used.

[0073] After decarburization and nitridation of the cold-rolled steel sheet by a known method, an annealing separator is applied, and the steel sheet is heated, maintained, and then cooled. In order to enhance the magnetic domain control effect, a tension film (insulating film) may be formed on the steel sheet.

[0074] The decarburization conditions may be known conditions. For example, after heating to 850°C, the temperature is maintained for 60 seconds and then cooled. The decarburization atmosphere is preferably a hydrogen-inert gas atmosphere. H2O / P H2 Good characteristics can be obtained by setting the ratio within the range of 0.15 to 0.80, and particularly within the range of 0.30 to 0.60.

[0075] The nitridation can also be performed by a known method. The nitridation amount can be set to, for example, a range of 50 to 400 ppm, and good properties can be obtained particularly in a range of 180 to 250 ppm.

[0076] The composition of the annealing separator can also be a known composition. In the case where a glass film is formed on the surface of the steel plate, for example, it can be set to 100 parts by mass of MgO and 5 parts by mass of TiO2. As an additive, for example, FeCl2 can be added in a manner of 200 ppm in terms of chlorine. In addition, in the case where a glass film is not formed on the surface of the steel plate, for example, an annealing separator mainly composed of aluminum oxide (Al2O3) is used.

[0077] The glass film is formed by the following steps: the steel sheet coated with the annealing separator is coiled into a coil, kept at 1150-1250° C. for 10-30 hours, and then cooled. The composition of the annealing separator can adopt a known composition, for example, it can be set to 100 parts by mass of MgO and 5 parts by mass of TiO2, and as an additive, for example, FeCl2 can be added in a manner of 200 ppm calculated as chlorine.

[0078] Thereafter, an insulating film coating is applied and baked. The type of the insulating film is not particularly limited, and all conventionally known insulating films are suitable for the grain-oriented electrical steel sheet.

[0079] As an example of an insulating film, there can be cited a film formed by applying an aqueous coating solution containing phosphate and colloidal silica. In this case, as the phosphate, for example, phosphates such as Ca, Al, and Sr can be cited. Among them, aluminum phosphate is more preferred. Preferably, the insulating film coating liquid is applied to the surface of the steel plate by a wet coating method such as a roll coater, and baked at a temperature of 800 to 900° C. for 10 to 60 seconds in an air atmosphere, thereby forming a tension insulating film. Furthermore, re-coating and baking can also be performed.

[0080] Laser irradiation is performed on a steel plate after cold rolling, after decarburization annealing, after decarburization nitriding annealing or after finishing annealing, or on a steel plate to which a tension film is further applied. It is preferable to make it easy for the protrusions formed by laser irradiation to remain on the steel plate after the final process. For example, in the case of laser irradiation on a cold-rolled steel plate, it is preferable to perform laser irradiation after removing the cold rolling oil. This is because: by removing excess oil, it becomes easy to transfer the energy of the laser to the steel plate, and if there is an oil film between the surface of the steel plate and the splash, the splash becomes easy to peel off. In the case of laser irradiation on a steel plate after decarburization annealing, it is preferable to perform laser irradiation before applying the annealing separator. In the case of irradiation after cold rolling, recrystallized grains are formed inside the protrusions during decarburization annealing, and are not cannibalized by the Gauss orientation of the base material during secondary recrystallization, and an orientation that deviates from the Gauss orientation of the base material by more than 5° remains; in the case of irradiation after decarburization annealing, recrystallized grains are formed inside the protrusions during final annealing, and are not cannibalized by the Gauss orientation of the base material during secondary recrystallization, and an orientation that deviates from the Gauss orientation of the base material by more than 5° remains. In the case of laser irradiation of the steel sheet after final annealing, laser irradiation can also be performed before applying the insulating film.

[0081] When the steel sheet after finish annealing or given a tension film is irradiated, recrystallized grains deviating by 5° or more from the orientation of the base steel sheet that has become Goss-oriented by secondary recrystallization are formed inside the protrusions during the subsequent coating baking and re-coating baking.

[0082] <Groove Forming Process: Laser Irradiation Conditions>

[0083] Next, by irradiating the steel sheet after cold rolling, decarburization annealing, decarburization nitriding annealing or finish annealing, or the steel sheet further provided with a tension film, a plurality of grooves are formed on the surface of the steel sheet in a direction intersecting the rolling direction in such a manner that the groove width W, groove depth D, and a specified interval (groove interval P) are within a specified range (groove forming process). The type of laser light source, laser output power, laser scanning speed, and steel sheet moving speed during laser irradiation conditions are not particularly limited, but it is sufficient as long as not only the groove width W, groove depth D, and the specified interval (groove interval P) of the grooves are appropriately selected, but also the conditions that the protrusions and the fine grains therein are within a specified range are appropriately selected. Since the conditions vary depending on the device, atmosphere, or the presence or absence of a film, for example, it is sufficient to derive appropriate conditions by experimentally performing laser irradiation in advance.

[0084] [Laser light source]

[0085] As the laser light source, for example, a high-output laser generally used for industrial use, such as a fiber laser, a YAG laser, a semiconductor laser, or a CO2 laser, can be used. As long as the groove can be formed stably, it can be a pulsed laser or a continuous wave laser.

[0086] [Laser output power]

[0087] If the laser output power is too small, the laser scanning speed is significantly reduced in order to form the desired groove, and the industrial productivity is reduced, so it is preferably set to 200W or more. It is preferably 1000W or more, and more preferably 1500W or more. In addition, if the laser output power is too large, the power supply capacity becomes large and the equipment cost becomes huge, so it becomes unrealistic in industry, so it is preferably set to 3000W or less. It is preferably 2800W or less, and more preferably 2500W or less.

[0088] [Laser scanning speed]

[0089] When the laser scanning speed is too slow, the steel plate passing speed needs to be slowed down so that the productivity is reduced, so it is set to 5 m / s or more. It is preferably 20 m / s or more, and more preferably 40 m / s or more. In addition, when the laser scanning speed is too fast, high output becomes necessary accordingly, and the equipment cost increases, so it is preferably set to 100 m / s or less. It is preferably 80 m / s or less, and more preferably 60 m / s or less.

[0090] [Laser spot shape]

[0091] The shape of the laser spot is set to be circular or slightly expanded in the rolling direction on the surface of the base steel plate, so that a protrusion can be effectively formed on the surface of the steel plate. As the laser irradiation conditions, for example, the laser spot diameter dL in the rolling direction is set to 5 to 100 μm, the laser spot diameter dC in the plate width direction is set to 5 to 100 μm, the laser output power is set to 200 to 3000 W, and the laser scanning speed V is set to 5 to 100 m / s. It is preferable to satisfy formula (1).

[0092] dL / dC≧1.0 Formula (1)

[0093] When dL / dC is greater than 1.0, the laser spot diameter becomes an oblong shape in the rolling direction, forming a molten protrusion. When dL / dC is less than 1.0, although a protrusion is also formed, a part of the molten splash is accumulated inside the groove, and the protrusion height becomes low. The lower limit of dL / dC is preferably set to 1.1, 1.2, 1.3, 1.5, 1.7 or 2.0. The upper limit of dL / dC is not particularly limited, but when dL / dC is too large, the groove width widens and cannot enjoy the magnetic domain control effect brought by the groove, so it is preferably set to 30.0, 25.0, 20.0, 18.0, 15.0 or 10.0.

[0094] As long as dL and dC satisfy the prescribed relationship, the focusing spot diameter is not particularly limited, but the focusing spot diameter is preferably selected in such a way that the groove width becomes less than 300 μm and in relation to other characteristics of the electromagnetic steel sheet. For example, the upper limit of dC is set to 300 μm, preferably 280 μm, 250 μm, 200 μm, 150 μm or 100 μm.

[0095] [Assist gas]

[0096] While irradiating the laser, the auxiliary gas is blown onto the portion of the steel plate irradiated with the laser. 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 stably reaches the steel plate, thereby stably forming the groove. The flow rate of the auxiliary gas is preferably set to 10 to 1000 liters per minute, for example.

[0097] In addition, the assist gas is preferably air or an inert gas.

[0098] [Omission of protrusion removal step]

[0099] The present electromagnetic steel sheet can improve iron loss by having fine grains in the protrusions, so the protrusion removal step is omitted. That is, there is no protrusion removal step after laser groove formation, which has been a problem in the past, so productivity is not reduced accordingly.

[0100] Example

[0101] Next, an embodiment of the present invention will be described, but the conditions in the embodiment are an example of conditions used to confirm the feasibility and effect of the present invention, and the present invention is not limited to this one example of conditions. The present invention can adopt various conditions as long as it does not deviate from the gist of the present invention and achieves the purpose of the present invention.

[0102] <Example 1>

[0103] A slab containing Si: 3.3 mass %, Mn: 0.10 mass %, S: 0.006 mass %, C: 0.060 mass %, acid-soluble Al: 0.027 mass %, N: 0.008 mass % and the remainder being Fe and impurities was used as a raw material, hot rolled by a known method, annealed the hot-rolled sheet, and cold rolled with a final sheet thickness of 0.22 mm to obtain steel sheets A1 to A12 and a1 to a12.

[0104] Next, for A1 to A3 and a1 to a3, the surface of the steel plate was irradiated with laser light to form a plurality of grooves extending in a direction intersecting the rolling direction at intervals of 3 mm in the rolling direction. The groove forming direction was set to be a direction inclined 10° to the L direction (rolling direction) relative to the C direction (plate width direction) of the steel plate, and the output power of the laser was controlled at 1500 to 2000 W so that the groove depth became 25 μm. The groove width was in the range of 40 to 220 μm.

[0105] The laser spot diameter dL in the rolling direction is adjusted to 25 to 120 μm, and the laser spot diameter dC in the plate width direction is adjusted to 25 to 140 μm. The laser scanning speed is set to 45 m / s. During laser irradiation, in order to effectively remove the metal of the steel plate melted and evaporated by the laser, an auxiliary gas of air is blown at 100 liters / minute.

[0106] Steel sheets A1 to A3, a1 to a3 with grooves formed by laser irradiation after cold rolling (cold rolled sheets) and steel sheets A4 to A12 and a4 to a12 without grooves were decarburized and then nitrided. The decarburization conditions were set as follows: heating to 850°C, holding for 60 seconds and cooling. The decarburization atmosphere was a hydrogen-nitrogen atmosphere in which the partial pressure ratio of water vapor to hydrogen, PH2O / PH2, was set to 0.33. In addition, the nitriding amount was set to 200 ppm.

[0107] Steel sheets A4 to A6 and a4 to a6 in which grooves were formed by laser irradiation after decarburization and nitriding treatment (decarburized and nitrided sheets) were irradiated with laser light under the same conditions as above to form grooves of the same shape.

[0108] Then, for the steel sheets A1 to A12 and a1 to a12, the coating amount was 4 g / m per side. 2 The annealing separator mainly composed of MgO was applied in the following manner. The composition of the annealing separator was 100 parts by mass of MgO, 5 parts by mass of TiO2, and FeCl2 was added in a manner to give 200 ppm in terms of chlorine.

[0109] Next, the steel sheet was coiled into a coil shape, maintained at a maximum temperature of 1200° C. for 20 hours, and then cooled to form a glass film on the surface.

[0110] Steel plates (glass plates) A7 to A9 and a7 to a9 in which grooves were formed by laser irradiation after forming a glass film on the surface, were irradiated with laser light under the same conditions as above to form grooves of the same shape.

[0111] Then, a tension film containing aluminum phosphate as a main component was further formed on the steel sheets A1 to A12 and a1 to a12 so as to have a thickness of 1 μm. The tension at this time was 12 MPa in the rolling direction including the glass film.

[0112] The steel sheets A10 to A12 and a10 to a12 in which grooves were formed by laser irradiation after tension coating (tension coating sheets) were irradiated with laser light under the same conditions as above to form grooves.

[0113] Thereafter, a tension film containing aluminum phosphate as a main component was formed again on A10 to A12 and a10 to a12 so as to have a thickness of 1 μm.

[0114] For A1 to A12 and a1 to a12, measure the iron loss W 17 / 50 (Energy loss measured under the excitation conditions of 1.7 T and 50 Hz.) Table 1 shows the results.

[0115] In the invention examples A1 to A12 and the comparative examples a1 to a12, the conditions of the slot angle, slot depth, and slot spacing that affect the iron loss are all the same, and the magnetic flux density is at the same level. In contrast, the iron loss in the invention examples 1 to 12 is less than 0.750 W / kg, which is good, while in contrast, the iron loss in the comparative examples a1 to a12 is more than 0.750 W / kg, which is inferior. In the invention examples A1 to A12, it can be seen from the cross-sectional EBSD observation that there are fine grains in the protrusion, and their crystal orientation deviates from the Gauss orientation of the parent material by more than 5°. It should be noted that when there are two or more fine grains in the protrusion, the deviation angle of the side with an angle difference from the Gauss orientation of the parent material is recorded.

[0116] It should be noted that the shape of the protrusion and the properties of the microscopic grains in the protrusion were determined by arbitrarily selecting three grooves in the steel plate, measuring one cross section arbitrarily selected in each groove by the method described above, and arithmetically averaging the measured values.

[0117] <Example 2>

[0118] A slab containing Si: 3.3 mass %, Mn: 0.10 mass %, S: 0.006 mass %, C: 0.060 mass %, acid-soluble Al: 0.027 mass %, N: 0.008 mass % and the remainder being Fe and impurities was used as a raw material, hot rolled by a known method, annealed the hot-rolled sheet, and cold rolled with a final sheet thickness of 0.22 mm to obtain steel sheets B1 to B12.

[0119] Next, for steel sheets B1 to B3, lasers were irradiated on the surfaces of the steel sheets to form multiple grooves extending in a direction intersecting the rolling direction at intervals of 5 mm along the rolling direction. The groove forming direction was set to be a direction inclined 5° to the L direction relative to the C direction of the steel sheet, and the output power of the laser was controlled in the range of 1800 to 2300 W so that the groove depth became 30 μm. The groove width was set to 35 to 50 μm.

[0120] The laser spot diameter in the rolling direction is controlled to be 90-100 μm, and the laser spot diameter in the plate width direction is controlled to be in the range of 5-10 μm. The laser scanning speed is set to 60 m / s. During laser irradiation, in order to effectively remove the metal of the steel plate melted and evaporated by the laser, an auxiliary gas of air is blown at 100 liters / minute.

[0121] Steel sheets B1 to B3 with grooves formed by laser irradiation after cold rolling and cold rolled steel sheets B4 to B12 without grooves were decarburized and then nitrided. The decarburization conditions were set as follows: heating to 850°C, holding for 60 seconds and cooling. The decarburization atmosphere was a hydrogen-nitrogen atmosphere with PH2O / PH2 set to 0.33. In addition, the nitriding amount was set to 200 ppm.

[0122] Decarbonized and nitrided steel sheets B4 to B6 were irradiated with laser light under the same conditions as above to form grooves of the same shape.

[0123] Then, for B1 to B12, the coating amount was 4 g / m per side. 2 The annealing separator mainly composed of MgO was applied in the following manner. The composition of the annealing separator was 100 parts by mass of MgO, 5 parts by mass of TiO2, and FeCl2 was added in a manner to give 200 ppm in terms of chlorine.

[0124] Next, the steel sheet was coiled into a coil shape, maintained at a maximum temperature of 1200° C. for 20 hours, and then cooled to form a glass film on the surface, thereby obtaining a glass plate.

[0125] Glass plates B7 to B9 were irradiated with laser light under the same conditions as above to form grooves of the same shape.

[0126] Then, a tension film mainly composed of aluminum phosphate was formed on B1 to B12 to have a thickness of 1 μm to obtain a tension film sheet. The tension at this time was 12 MPa in the rolling direction including the glass film.

[0127] The tension membrane plates B10 to B12 were irradiated with laser light under the same conditions as above to form grooves of the same shape.

[0128] Thereafter, a tension film containing aluminum phosphate as a main component was formed again on B10 to B12 so as to have a thickness of 1 μm.

[0129] For B1 to B12, the iron loss W was measured. 17 / 50 (Energy loss measured under the excitation conditions of 1.7 T and 50 Hz.) Table 2 shows the results.

[0130] Inventive Examples B1 to B12, the iron loss was lower than 0.730 W / kg, which was even better, and the groove height of the protrusions observed under a 3D microscope was 4 μm to 10 μm in all cases.

[0131] <Example 3>

[0132] A slab containing Si: 3.3 mass %, Mn: 0.10 mass %, S: 0.006 mass %, C: 0.060 mass %, acid-soluble Al: 0.027 mass %, N: 0.008 mass % and the remainder being Fe and impurities was used as a raw material, hot rolled using a known method, then annealed, and cold rolled to obtain steel plates C1 to C8 with a final plate thickness of 0.22 mm.

[0133] Next, the surface of the steel sheet is irradiated with laser light to form a plurality of grooves extending in a direction intersecting the rolling direction at intervals of 1 to 25 mm along the rolling direction. The groove forming direction is set to be a direction inclined 0 to 40 degrees to the L direction relative to the C direction of the steel sheet, the groove depth is set to 11 to 35 μm, and the groove width is set to 20 to 290 μm.

[0134] The laser irradiation conditions were controlled within the range of laser output power of 1500-2500W, laser spot diameter in the rolling direction of the laser of 100-300μm, and laser spot diameter in the plate width direction of 10-250μm. The laser scanning speed was set to 60m / s. During laser irradiation, in order to effectively remove the metal of the steel plate melted and evaporated by the laser, an auxiliary gas of air was blown at 100 liters / minute.

[0135] The grooved cold-rolled steel sheet was decarburized and then nitrided. The decarburization conditions were set as follows: heating to 850°C, holding for 60 seconds, and cooling. The decarburization atmosphere was a hydrogen-nitrogen atmosphere with PH2O / PH2 set to 0.33. In addition, the nitriding amount was set to 200 ppm.

[0136] After that, the coating amount is 4g / m2 per side. 2 The annealing separator mainly composed of MgO was applied in the following manner. The composition of the annealing separator was 100 parts by mass of MgO, 5 parts by mass of TiO2, and FeCl2 was added in a manner to give 200 ppm in terms of chlorine.

[0137] Next, the steel sheet was coiled into a coil shape, maintained at a maximum temperature of 1200° C. for 20 hours, and then cooled to form a glass film on the surface, thereby obtaining a glass plate.

[0138] Furthermore, a tension film mainly composed of aluminum phosphate was formed to a thickness of 1 μm to obtain a tension film plate. The tension at this time was 12 MPa in the rolling direction including the glass film.

[0139] For C1 to C8, measure the iron loss W 17 / 50 (Energy loss measured under the excitation conditions of 1.7 T and 50 Hz.) Table 3 shows the results.

[0140] In inventive examples C1 to C8, the iron loss is lower than 0.750 W / kg, which is good. The absolute value of the angle θ formed with the length direction of the groove is 0 to 40°, the width W of the groove is 20 to 300 μm, the depth D of the groove is 10 to 40 μm, and the spacing P of the grooves in the rolling direction is 1 to 30 mm.

[0141] <Example 4>

[0142] The results of measuring the frequency of existence of fine crystal grains and the aspect ratio of fine crystal grains in some of the samples prepared in Examples 1 to 3 are shown in Table 4. It was confirmed that the frequency of existence of fine crystal grains per protrusion was 0.05 to 10 and that the magnetic properties became good when the aspect ratio of fine crystal grains in the protrusion was in the range of 0.2 to 5.

[0143] Table 1

[0144]

[0145] Table 2

[0146]

[0147] Table 3

[0148]

[0149] Industrial Applicability

[0150] The present invention can be used for industrial equipment using a grain-oriented electromagnetic steel sheet, such as a winding core for a transformer.

[0151] Explanation of symbols

[0152] 1 Steel plate (base steel plate)

[0153] 2 slots

[0154] 3. Protrusion

[0155] 4 Surface imaginary line

[0156] 5 Fine grains

[0157] θ Slot angle

[0158] W Slot width

[0159] D groove depth

[0160] d Slot spacing

Claims

1. A directional electromagnetic steel sheet, characterized in that: It is a directional electromagnetic steel plate having a plurality of grooves on its surface, wherein the surface of the steel plate has a protrusion on the groove side adjacent to the groove, and the crystal orientation of at least one grain existing inside the protrusion differs by more than 5° from the crystal orientation of the grains existing in the portion of the steel plate other than the protrusion.

2. The grain-oriented electrical steel sheet according to claim 1, characterized in that: The average height of the protrusions is 2.5 μm to 10.0 μm.

3. The grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that: In the directional electromagnetic steel sheet, the angle θ formed by the direction perpendicular to the rolling direction and the plate thickness direction and the length direction of the groove is less than 40°, the width W of the groove is 20μm to 300μm, the depth D of the groove is 10μm to 40μm, and the spacing P of the groove in the rolling direction is 1mm to 30mm.

4. The method for producing a grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that: The groove forming step includes irradiating the surface of the steel plate with laser light to form a groove. As the laser irradiation conditions, the laser spot diameter dL in the rolling direction and the laser spot diameter dC in the plate width direction satisfy the formula (1). 1.0≤dL / dC formula (1).

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