Grain-oriented electrical steel sheet and magnetic domain refining method therefor

Abstract

A grain-oriented electrical steel sheet according to an embodiment of the present invention includes: a groove on a line formed on one surface of an electrical steel sheet in a direction crossing a rolling direction; and a thermal shock portion on a line formed on one surface of the electrical steel sheet in the direction crossing the rolling direction, wherein a distance between the groove and the thermal shock portion is 1 mm or less.

Claims

1. A grain-oriented electrical steel sheet, comprising: a groove on a line formed on one surface of an electrical steel sheet in a direction crossing a rolling direction; and a thermal shock portion on a line formed on one surface of the electrical steel sheet in the direction crossing the rolling direction, wherein a distance between the groove and the thermal shock portion is 1 mm or less, and wherein a plurality of the thermal shock portions are formed, and a distance between the thermal shock portions is 2 to 5 times the distance between the grooves.

2. The grain-oriented electrical steel sheet of claim 1, wherein a plurality of grooves are formed, and a distance between the grooves is 1.5 to 10 mm.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates a schematic view of a cross-section (TD surface) of a grain-oriented electrical steel sheet according to an embodiment of the present invention.

(2) FIG. 2 illustrates a schematic view of a rolled surface (ND surface) of a grain-oriented electrical steel sheet according to an embodiment of the present invention.

(3) FIG. 3 illustrates a schematic view of a cross-section (TD surface) of a grain-oriented electrical steel sheet according to another embodiment of the present invention.

(4) FIG. 4 illustrates a schematic view of a shape of a laser beam according to an embodiment of the present invention.

MODE FOR INVENTION

(5) It will be understood that, although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and/or sections, they are not limited thereto. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Therefore, a first part, component, area, layer, or section to be described below may be referred to as second part, component, area, layer, or section within the range of the present invention.

(6) The technical terms used herein are to simply mention a particular embodiment and are not meant to limit the present invention. An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. In the specification, it is to be understood that the terms such as “including”, “having”, etc., are intended to indicate the existence of specific features, regions, numbers, stages, operations, elements, components, and/or combinations thereof disclosed in the specification, and are not intended to preclude the possibility that one or more other features, regions, numbers, stages, operations, elements, components, and/or combinations thereof may exist or may be added.

(7) When referring to a part as being “on” or “above” another part, it may be positioned directly on or above another part, or another part may be interposed therebetween. In contrast, when referring to a part being “directly above” another part, no other part is interposed therebetween.

(8) Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meanings as those generally understood by those with ordinary knowledge in the field of art to which the present invention belongs. Terms defined in commonly used dictionaries are further interpreted as having meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as having idealized or very formal meanings unless defined otherwise.

(9) The present invention will be described more fully hereinafter, in which exemplary embodiments of the invention are shown. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

(10) FIG. 1 and FIG. 2 show a schematic view of a grain-oriented electrical steel sheet 10 in which magnetic domains are refined by an embodiment of the present invention.

(11) As shown in FIG. 1 and FIG. 2, the grain-oriented electrical steel sheet 10 according to the embodiment of the present invention includes: a groove 20 on a line formed on one surface 11 of the electrical steel sheet in a direction crossing a rolling direction (RD direction); and a thermal shock portion 30 on a line formed on one surface 11 of the electrical steel sheet in the direction crossing the rolling direction, and a distance g between the groove 20 and the thermal shock portion 30 is 1 mm or less.

(12) According to the embodiment of the present invention, the groove 20 and the thermal shock portion 30 are simultaneously formed, so that the magnetic domain may be refined to a minimum size, and as a result, iron loss may be ameliorated. When forming the groove 20 with a laser, energy is strong enough to generate iron powder, thus a temperature in the vicinity thereof increases very high. When the laser for forming the thermal shock portion 30 is irradiated in the vicinity, a peripheral portion of the groove 20 receives heat, and heat shrinkage occurs during cooling. Tensile stress acts on the steel sheet 10 due to the heat shrinkage. As a result, the tensile stress reduces a size of a magnetic domain. In addition, a free surface formed by the formation of the groove 20 generates a static magnetic energy surface charge to form a closed curve, two effects by different mechanisms are simultaneously formed, and the iron loss is further reduced due to synergy of the two effects.

(13) In FIG. 1, the distance between the groove 20 and the thermal shock portion 30 is denoted by g. The distance g between the groove 20 and the thermal shock portion 30 may be 1 mm or less. When the distance g is increased, it may be a factor that hinders the reduction of iron loss by forming a bad magnetic domain rather than an effect of additional reduction of an intended iron loss. More specifically, the distance g between the groove 20 and the thermal shock portion 30 may be 1 μm to 0.5 mm. Even more specifically, the distance g between the groove 20 and the thermal shock portion 30 may be 0.1 mm to 0.45 mm.

(14) As shown in FIG. 1, when a plurality of grooves 20 and a plurality of thermal shock portions 30 are formed, a distance g is provided between an arbitrary groove 20 and a heat shock portion 30 closest to the groove 20. In addition, when a plurality of grooves 20 and a plurality of thermal shock portions 30 are formed, an average value between each distance g may satisfy the above-described range. Further, in the embodiment of the present invention, since a thickness exists in the groove 20 and the heat shock portion 30 in the rolling direction (RD direction), it means a distance g between a center line of the groove 20 and a center line of the heat shock portion 30.

(15) As shown in FIG. 1, the groove 20 means a portion of a surface of the steel sheet removed by laser irradiation. In FIG. 1, a shape of the groove 20 is illustrated as a wedge shape, but this is merely an example, and the groove may be formed in various shapes such as a square shape, a trapezoidal shape, a U-shape, a semi-circular shape, and a W-shape.

(16) A depth of the groove 20 may be 1 to 10% of the thickness of the steel sheet. When the depth of the groove 20 is too shallow, it is difficult to obtain a suitable iron loss ameliorating effect. When the depth of the groove is too deep, due to strong laser irradiation, texture characteristics of the steel sheet 10 are greatly changed, or a large amount of heel-up and spatter are formed, thus magnetic properties may be deteriorated. Therefore, it is preferable to control the depth of the groove 20 in the above-described range.

(17) As shown in FIG. 1, a plurality of grooves 20 are formed along the rolling direction (RD direction), and a distance d1 between the grooves 20 may be 1.5 to 10 mm. When the distance between the grooves 20 is too narrow or too wide, an appropriate effect of ameliorating iron loss may not be obtained. More specifically, the distance d1 between the grooves 20 may be 2 to 5 mm. In FIG. 1, the distance between grooves 20 is indicated by d1. More specifically, the distance d1 between the grooves 20 means a distance between center lines of the grooves 20.

(18) Unlike the groove 20, the thermal shock portion 30 is apparently indistinguishable from other surfaces of the steel sheet. The thermal shock portion 30 is a portion that is etched in a form of a groove when immersed in hydrochloric acid of a concentration of 5% or more for 10 minutes or more, and may be distinguished from other surface portions of the steel sheet.

(19) As shown in FIG. 1, a plurality of thermal shock portions 30 may be formed along the rolling direction (RD direction). In this case, a distance d2 between the thermal shock portions 30 may be 1 to 5 times (integer multiple) the distance d1 between the grooves 20. For example, when the distance d2 between the heat shock portions 30 is 1 times the distance d1 between the grooves 20, one heat shock portion 30 is formed for each groove 20. When the distance d2 between the heat shock portions 30 is 2 times the distance d1 between the grooves 20, two heat shock portions 30 are formed for each groove 20. FIG. 1 and FIG. 2 show a case in which the distance d2 between the heat shock portions 30 is 2 times the distance d1 between the grooves 20, and FIG. 3 shows a case in which the distance d2 between the heat shock portions 30 is 1 times the distance d1 between the grooves 20.

(20) FIG. 3 illustrates a schematic view of a grain-oriented electrical steel sheet 10 according to another embodiment of the present invention.

(21) As shown in FIG. 3, the grain-oriented electrical steel sheet 10 according to another embodiment of the present invention includes: a groove 20 on a line formed on one surface 11 of the electrical steel sheet in a direction crossing a rolling direction; and a thermal shock portion 30 on a line formed on the other surface 12 of the electrical steel sheet in the direction crossing the rolling direction, and a distance g between an imaginary line in which the groove 20 is symmetrically projected onto the other surface with respect to a center of thickness of the steel sheet and the thermal shock portion 30 is 1 mm or less.

(22) Another embodiment of the present invention is the same as in FIG. 1 except that the groove 20 is formed on one surface 11 and the thermal shock portion 30 is formed on the other surface 12. In addition, the distance g between the groove 20 and the thermal shock portion 30, that is, based on an imaginary line in which the groove 20 is symmetrically projected onto the other surface with respect to a center of thickness of the steel sheet, the distance g between the imaginary line and the thermal shock portion 30 is controlled. Since constituent elements of the another embodiment are the same as those described in the embodiment of the present invention, except that the thermal shock portion 30 is formed on the other surface 12, a duplicate description thereof will be omitted.

(23) In addition, in the embodiment of the present invention, the groove 20 may be formed on both surfaces, or the thermal shock part 30 may be formed on both surfaces, but the present invention is not limited thereto.

(24) A magnetic domain refining method of a grain-oriented electrical steel sheet according to an embodiment of the present invention includes preparing a grain-oriented electrical steel sheet 10; forming a groove 20 by irradiating a laser on one surface 11 of the grain-oriented electrical steel sheet in a direction crossing a rolling direction; and forming a thermal shock portion 30 by irradiating a laser on one surface 11 of the grain-oriented electrical steel sheet in the direction crossing the rolling direction.

(25) First, the grain-oriented electrical steel sheet 10 is prepared. The magnetic domain refining method according to the embodiment of the present invention has features in shapes of the groove 20 and the thermal shock portion 30, thus the grain-oriented electrical steel sheet for the magnetic domain refining may be used without limitation. Particularly, an effect of the present invention is realized regardless of an alloy composition of the grain-oriented electrical steel sheet. Therefore, a detailed description of the alloy composition of the grain-oriented electrical steel sheet will be omitted.

(26) In the embodiment of the present invention, as the grain-oriented electrical steel sheet, a grain-oriented electrical steel sheet rolled to a predetermined thickness through hot rolling and cold rolling from a slab, may be used.

(27) Next, one surface 11 of the grain-oriented electrical steel sheet is irradiated with a laser in a direction crossing the rolling direction (RD direction) to form the groove 20.

(28) In this case, energy density (Ed) of the laser may be 0.5 to 2 J/mm.sup.2. When the energy density is too small, the groove 20 having an appropriate depth is not formed, and thus it is difficult to obtain an effect of ameliorating iron loss. In contrast, when the energy density is too large, the groove 20 having a too large depth is formed, and thus it is difficult to obtain an effect of ameliorating iron loss.

(29) FIG. 4 shows a schematic diagram of a shape of a laser beam. In the forming of the groove, a beam length L of the laser in a rolling vertical direction (TD direction) of the steel sheet may be 300 to 5000 μm. When the beam length L in the rolling vertical direction (TD direction) is too short, a time for which the laser is irradiated is too short, so that an appropriate groove may not be formed, and it is difficult to obtain an effect of ameliorating iron loss. In contrast, when the beam length L in the rolling vertical direction (TD direction) is too long, a time for which the laser is irradiated is too long, so that the groove 20 having too large a depth is formed, and it is difficult to obtain an effect of ameliorating iron loss.

(30) A beam width W of the laser in the rolling direction (RD direction) of the steel sheet may be 10 to 200 μm. When the beam width W is too short or long, a width of the groove 20 may be short or long, and thus an appropriate magnetic domain refining effect may not be obtained.

(31) In addition, 2 to 6 grooves 20 and thermal shock portions 30 may be intermittently formed with respect to the rolling vertical direction (TD direction) of the steel sheet, and may form an angle of 82° to 98° with respect to the rolling direction (RD direction), and the laser beam may be irradiated along such a shape.

(32) A type of the laser beam is not particularly limited, and a single fiber laser may be used.

(33) Next, one surface 11 of the grain-oriented electrical steel sheet is irradiated with a laser in a direction crossing the rolling direction (RD direction) to form the thermal shock portion 30.

(34) In this case, energy density (Ed) of the laser may be 0.05 to 0.2 J/mm.sup.2. When the energy density is too small, an appropriate thermal shock portion 30 is not formed, and thus it is difficult to obtain an effect of ameliorating iron loss. In contrast, when the energy density is too large, a surface of the steel sheet is damaged, and thus it is difficult to obtain an effect of ameliorating iron loss.

(35) In the forming of the thermal shock portion, the beam length L of the laser in the rolling vertical direction (TD direction) of the steel sheet may be 1500 to 10,000 μm, and the beam width W of the laser in the rolling direction (RD direction) of the steel sheet may be 100 to 1000 μm.

(36) The forming of the groove 20 and the forming of the thermal shock portion 30 described above may be performed without limitation before and after the time. Specifically, after the forming of the groove 20, the thermal shock portion 30 may be formed. In addition, after the forming of the thermal shock portion 30, the groove 20 may be formed.

(37) The magnetic domain refining method of the grain-oriented electrical steel sheet according to the embodiment of the present invention may further include forming an insulating coating layer. The forming of the insulating coating layer may be included after the preparing of the grain-oriented electrical steel sheet, after the forming of the groove, or after the forming of the thermal shock portion. More specifically, it may be included after the forming of the groove. When the insulating coating layer is formed after the forming of the groove, there is an advantage in that the insulating coating may be performed only once.

(38) A method of forming the insulating coating layer may be used without particular limitation, and for example, the insulating coating layer may be formed by applying an insulating coating solution containing a phosphate. It is preferable to use a coating solution containing colloidal silica and a metal phosphate as the insulating coating solution. In this case, the metal phosphate may be Al phosphate, Mg phosphate, or a combination thereof, and a content of Al, Mg, or a combination may be 15 wt % or more with respect to a weight of the insulating coating solution.

(39) A magnetic domain refining method of a grain-oriented electrical steel sheet according to another embodiment of the present invention includes: preparing a grain-oriented electrical steel sheet 10; forming a groove 20 by irradiating a laser on one surface 11 of the grain-oriented electrical steel sheet in a direction crossing a rolling direction; and forming a thermal shock portion 30 by irradiating a laser on the other surface 12 of the grain-oriented electrical steel sheet in the direction crossing the rolling direction, and a distance between an imaginary line in which the groove 20 is symmetrically projected onto the other surface with respect to a center of thickness of the steel sheet and the thermal shock portion 30 is 1 mm or less.

(40) The magnetic domain refining method of the grain-oriented electrical steel sheet according to another embodiment of the present invention is the same as the above-described method except that the irradiation of the laser for the formation of the thermal shock portion 30 is performed on the other surface 12 of the steel sheet, so a duplicate description thereof will be omitted.

(41) Hereinafter, the present invention will be described in more detail through examples. However, the examples are only for illustrating the present invention, and the present invention is not limited thereto.

Experimental Example 1: Interval Between Groove and Thermal Shock Line

(42) A grain-oriented electrical steel sheet having a cold rolled thickness of 0.20 mm was prepared. A groove was formed by irradiating a laser beam of a fiber continuous laser on one surface of the electrical steel sheet with a copper mirror. A width W of the laser beam was 50 μm, and a length L of the laser beam was 5000 μm. Energy density of the laser was 1.5 J/mm.sup.2, and a depth of the groove was 10 μm.

(43) The grooves were formed at distances d1 between the grooves shown in Table 1 below, and an insulating film was formed.

(44) Then, a thermal shock line was formed by irradiating a laser beam of a fiber continuous laser on one surface or the other surface of the electrical steel sheet with a copper mirror. A width W of the laser beam was 500 μm, and a length L of the laser beam was 10,000 μm. Energy density of the laser was 0.1 J/mm.sup.2.

(45) The thermal shock lines were formed at distances d2 between the thermal shock lines shown in Table 1 below, and average distances g between the grooves and the thermal shock lines are shown in Table 1.

(46) Table 1 below shows amelioration rates of iron loss. The iron loss amelioration rate was calculated as (W.sub.1−W.sub.2)/W.sub.1 by measuring iron loss W.sub.1 of the electrical steel sheet before the groove was formed by irradiating the laser and iron loss W.sub.2 of the electrical steel sheet after the groove was formed by irradiating the laser. The iron loss was measured by the iron loss value (W17/50) at a frequency of 50 Hz when a magnetic flux density was 1.7 Tesla.

(47) TABLE-US-00001 TABLE 1 Distance Distance Distance between thermal Thermal shock between groove and Iron loss between grooves shock lines line formation thermal shock line amelioration (d1, mm) (d2, mm) surface (g, mm) rate (%) Example 1 4 4 One surface 0.55 12 Example 2 3 3 One surface 0.63 10 Example 3 2.5 2.5 One surface 0.86 9 Example 4 2 4 One surface 0.39 15 Example 5 2.5 5 One surface 0.23 16 Example 6 2 4 Other surface 0.43 15 Example 7 2.5 5 Other surface 0.16 16 Comparative 4 None None None 8 Example 1 Comparative 4 4 One surface 1.03 4 Example 2

(48) As shown in Table 1, it can be confirmed that Comparative Example 1, in which the thermal shock line was not formed, and Comparative Example 2, in which the thermal shock line was formed at more than 1 mm apart from the groove, had poor iron loss amelioration rate compared to the examples.

(49) Even among the examples, it can be confirmed that the smaller the average distance g between the groove and the thermal shock line was, the better the iron loss amelioration rate was, and it can be confirmed that even if a thermal shock line was formed per two grooves or a thermal shock line was formed on an opposite side of the groove, there was no significant effect on the iron loss amelioration rate.

Experimental Example 2: Groove Depth

(50) A grain-oriented electrical steel sheet having a cold rolled thickness of 0.20 mm was prepared. A groove was formed by irradiating a laser of a fiber continuous laser on one surface of the electrical steel sheet with a copper mirror. A width W of the laser beam was 50 μm, and a length L of the laser beam was 5000 μm. Energy density of the laser and a depth of the groove were respectively changed to values shown in Table 2 below.

(51) The grooves were formed at distances d1 between the grooves shown in Table 2 below, and an insulating film was formed.

(52) The thermal shock line was formed on one surface of the steel sheet at the distance d2 between the thermal shock lines, wherein the distance d2 is the same as the distance d1 between the grooves, and the average distance (g) between the grooves and the thermal shock lines was adjusted in 0.7 to 0.8 mm.

(53) TABLE-US-00002 TABLE 2 Distance Iron loss between grooves Groove depth amelioration rate (d1, mm) (μm) (%) Example 3 2.5 10 9 Example 8 2.7 11 9 Example 9 3 13 10 Example 10 4 14 12 Example 11 5 15 14

(54) As shown in Table 2, it can be confirmed that even if the distance between the grooves increased, the iron loss amelioration rate increased as the depth of the groove increased.

(55) The present invention may be embodied in many different forms, and should not be construed as being limited to the disclosed embodiments. In addition, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the technical spirit and essential features of the present invention. Therefore, it is to be understood that the above-described exemplary embodiments are for illustrative purposes only, and the scope of the present invention is not limited thereto.

(56) TABLE-US-00003 <Description of symbols> 10: grain-oriented electrical steel sheet 11: one surface of steel sheet, 12: other surface of steel sheet 20: groove 30: thermal shock portion