Title of Invention: Grain-oriented electrical steel sheet and manufacturing method thereof
technical field
[One]
It relates to a grain-oriented electrical steel sheet and a method for manufacturing the same. More specifically, it relates to a grain-oriented electrical steel sheet having improved magnetic properties and improved adhesion to an insulating coating layer by appropriately forming an island by partially removing an oxide layer after forming a groove, and a method for manufacturing the same.
background
[2]
Since grain-oriented electrical steel sheet is used as an iron core material for electronic products such as transformers, in order to improve energy conversion efficiency by reducing power loss in equipment, a steel sheet with excellent iron loss and a high space factor during lamination and winding is required. .
[3]
Grain-oriented electrical steel sheet refers to a functional steel sheet having a texture (also called "Goss Texture") in which crystal grains secondary recrystallized through hot rolling, cold rolling and annealing processes are oriented in the {110}<001> direction in the rolling direction.
[4]
As a method of lowering the iron loss of a grain-oriented electrical steel sheet, a magnetic domain refining method is known. That is, the size of the large magnetic domain of the grain-oriented electrical steel sheet is miniaturized by scratching the magnetic domain or applying an energy impact. In this case, when the magnetic domain is magnetized and its direction is changed, the energy consumption can be reduced compared to when the size of the magnetic domain is large. As the magnetic domain refining method, there are permanent domain refining, which maintains the improvement effect even after heat treatment, and temporary domain refining, which is not.
[5]
The permanent magnetic domain refining method that shows the effect of improving iron loss even after stress relaxation heat treatment above the heat treatment temperature at which recovery occurs can be divided into etching method, roll method and laser method. Since the etching method forms a groove (groove) on the surface of the steel sheet through a selective electrochemical reaction in the solution, it is difficult to control the shape of the groove, and it is difficult to uniformly secure the iron loss characteristics of the final product in the width direction. In addition, it has a disadvantage that it is not environmentally friendly due to an acid solution used as a solvent.
[6]
The permanent magnetic domain refining method using a roll forms a groove with a certain width and depth on the plate surface by processing the protrusion on the roll and pressing the roll or plate, and then annealing to improve iron loss by partially causing recrystallization at the bottom of the groove. It is a magnetic domain refinement technique that represents. The roll method has disadvantages in that it is difficult to obtain stability against machining and stable iron loss according to thickness, and the process is complicated, and the iron loss and magnetic flux density characteristics deteriorate immediately after groove formation (before stress relief annealing).
[7]
The permanent magnetic domain refining method by laser uses a method of irradiating a high-power laser to the surface of an electrical steel sheet moving at high speed, and forming a groove accompanied by melting of the base portion by laser irradiation. However, it is difficult to refine the magnetic domain to a minimum size even in this permanent magnetic domain refining method.
[8]
In the case of temporary domain refining, the current technology is focused on not applying the laser once more after applying the laser in the coated state, so we do not try to irradiate the laser with an intensity above a certain level. This is because it is difficult to properly exert the tension effect due to damage to the coating if applied over a certain level.
[9]
In the case of permanent magnetic domain refinement, a groove is dug to widen the free charge area that can receive static magnetic energy, so a groove depth as deep as possible is required. Of course, side effects such as a decrease in magnetic flux density also occur due to the deep groove depth. Therefore, in order to reduce the deterioration of the magnetic flux density, an appropriate groove depth is maintained.
[10]
On the other hand, grain-oriented electrical steel sheets manufactured by magnetic domain refining technology are manufactured into products such as transformer iron cores through forming and heat treatment processes. In addition, since the product is used in a relatively high temperature environment, it is necessary to secure adhesion with the insulating coating layer as well as the iron loss characteristics.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[11]
An embodiment of the present invention provides a grain-oriented electrical steel sheet and a method for manufacturing the same. Specifically, in one embodiment of the present invention, a grain-oriented electrical steel sheet having improved adhesion with an insulating coating layer with improved magnetic properties by removing a part of the oxide layer after forming the groove and appropriately forming an island, and a method for manufacturing the same aim to
means of solving the problem
[12]
A grain-oriented electrical steel sheet according to an embodiment of the present invention includes a groove located on the surface of the electrical steel sheet, a metal oxide layer located on the groove, and a metal oxide-based island located in a discontinuously distributed distribution located below the groove, and the bottom of the groove The average sphericity of the islands located in .
[13]
The density of the islands positioned under the groove may be 0.25 pieces/μm 2 or less.
[14]
With respect to the rolling vertical direction, there may be 2 to 10 intermittent grooves.
[15]
The longitudinal direction of the groove and the rolling direction of the steel sheet may form an angle of 75 to 88 °.
[16]
A method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises the steps of manufacturing a cold-rolled sheet; forming a groove by irradiating a laser on the cold-rolled sheet; and partially removing the oxide layer formed on the surface of the cold-rolled sheet so that the thickness of the oxide layer remains in the range of 1 to 5 nm.
[17]
At the stage of forming the groove. The scanning speed of the laser may be 10 m/s or more.
[18]
At the stage of forming the groove. Towards the groove, the gas can be injected at an angle of 70° or less with the rolling direction.
[19]
The pressure of the injected gas may be 0.02 kg/cm 2 or more.
[20]
The content of moisture in the injected gas may be 50 wt% or less.
[21]
After the step of forming the groove, an oxide layer having a thickness of 4 to 10 nm may be present on the surface of the cold rolled sheet.
Effects of the Invention
[22]
According to one embodiment of the present invention, by removing a part of the oxide layer after forming the groove, it is possible to improve the magnetic properties and improve the adhesion to the insulating coating layer.
Brief description of the drawing
[23]
1 is a schematic diagram of a rolled surface (ND surface) of a grain-oriented electrical steel sheet according to an embodiment of the present invention.
[24]
2 is a schematic diagram of a groove according to an embodiment of the present invention.
[25]
3 is a schematic diagram of a cross section of a groove according to an embodiment of the present invention.
Modes for carrying out the invention
[26]
Terms such as first, second and third are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.
[27]
The terminology used herein is for the purpose of referring to specific embodiments only, and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. As used herein, the meaning of "comprising" specifies a particular characteristic, region, integer, step, operation, element and/or component, and the presence or absence of another characteristic, region, integer, step, operation, element and/or component. It does not exclude additions.
[28]
When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part, or the other part may be involved in between. In contrast, when a part refers to being “directly above” another part, the other part is not interposed therebetween.
[29]
Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Commonly used terms defined in the dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and unless defined, they are not interpreted in an ideal or very formal meaning.
[30]
Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.
[31]
1 shows a schematic diagram of a grain-oriented electrical steel sheet 10 that has been refined into magnetic domains according to an embodiment of the present invention.
[32]
As shown in FIG. 1, the grain-oriented electrical steel sheet 10 according to an embodiment of the present invention has a linear groove 20 formed in a direction crossing the rolling direction (RD direction) on one or both sides of the electrical steel sheet; is formed has been
[33]
In an embodiment of the present invention, a groove is formed through a laser, and a portion of the oxide layer present in the groove formation process is removed, and then, a uniform metal oxide layer is formed in the secondary recrystallization annealing process, and ultimately, magnetic enhancement and Adhesiveness with the insulating coating layer can be improved. In this case, the metal oxide layer may be a forsterite (Frosterite FeMg 2 SiO 4 ) layer.
[34]
A method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises the steps of manufacturing a cold-rolled sheet; forming a groove by irradiating a laser on the cold-rolled sheet; and partially removing the oxide layer formed on the surface of the cold-rolled sheet so that the thickness of the oxide layer remains in the range of 1 to 5 nm.
[35]
Hereinafter, each step will be described in detail.
[36]
First, a cold-rolled sheet is manufactured. In an embodiment of the present invention, as a characteristic of the magnetic domain refining method after manufacturing the cold rolled sheet, the cold rolled sheet to be subjected to domain refining may be a cold rolled sheet used in the grain-oriented electrical steel sheet field without limitation. In particular, the effect of the present invention is expressed regardless of the 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. As an example, the cold rolled sheet is, by weight, C: 0.10% or less, Si: 1.0 to 6.5%, Mn: 0.005 to 3.0%, Nb+V+Ti: 0.015% or less, Cr+Sn: 1.0% or less, Al : 3.0% or less, P+S: 0.09% or less, the total of rare earth and other impurities: 0.3% or less, and the remainder may contain Fe.
[37]
The cold-rolled sheet manufacturing method used in the grain-oriented electrical steel sheet field may be used without limitation as to the cold-rolled sheet manufacturing method, and a detailed description thereof will be omitted.
[38]
Next, the cold-rolled sheet is irradiated with a laser to form a groove.
[39]
The groove can be formed by irradiating the surface of the cold-rolled sheet with a TEMoo (M 2 ≤1.25) laser beam with an average output of 500W to 10KW on the surface of the cold-rolled sheet. The laser oscillation method can be used without limitation. That is, continuous oscillation or pulsed mode can be used. In this way, the laser is irradiated so that the surface beam absorption rate is greater than or equal to the heat of fusion of the steel sheet, thereby forming the groove 20 shown in FIGS. 1 and 2 .
[40]
In this case, the scanning rate of the laser may be 10 m/s or more. If the scanning speed of the laser is too low, a problem in that the groove is not properly formed may occur. More specifically, the scanning speed of the laser may be 10 m/s to 30 m/s.
[41]
At the stage of forming the groove. Toward the groove, the gas can be injected at an angle of 70 degrees or less with respect to the rolling direction (RD direction). At this time, the angle is based on the rolling vertical plane (TD plane). By properly injecting the gas, it is possible to prevent the melt from solidifying in the groove. If the angle is too high, adequate melt removal may not be achieved.
[42]
At this time, the pressure of the gas may be 0.02 kg/cm 2 or more. If the gas pressure is too low, adequate melt removal may not be achieved. More specifically, the pressure of the gas may be 0.02 to 0.2 kg/cm 2 .
[43]
The content of moisture in the injected gas may be 50 wt% or less. If the moisture content is too high, a non-uniform and thick oxide layer may be formed on the surface of the steel sheet due to gas injection. This oxide layer may later form a non-uniform metal oxide layer in the secondary recrystallization annealing process, ultimately adversely affecting adhesion and magnetism. More specifically, the content of moisture in the injected gas may be 25 wt% or less.
[44]
As shown in Fig. 1, 2 to 10 grooves can be intermittently formed in the vertical direction of rolling. However, the present invention is not limited thereto, and it is also possible to continuously form the groove.
[45]
1 and 2 , the longitudinal direction (X direction) and the rolling direction (RD direction) of the groove 20 may form an angle of 75 to 88°. When forming the above-mentioned angle, it can contribute to improving the iron loss of the grain-oriented electrical steel sheet.
[46]
The width (W) of the groove may be 10 to 200㎛. If the width of the groove 20 is short or large, an appropriate magnetic domain refining effect may not be obtained.
[47]
In addition, the depth (H) of the groove may be 3 to 5% of the thickness of the steel sheet. If the depth (H) of the groove is too shallow, it is difficult to obtain an appropriate iron loss improvement effect. If the depth (H) of the groove is too deep, the structure properties of the steel sheet 10 may be greatly changed due to strong laser irradiation, or the magnetism may be deteriorated by forming a large amount of heel-up and spatter. Therefore, the depth of the groove 20 can be controlled within the above-described range.
[48]
After the step of forming the groove, the surface of the steel sheet may be partially oxidized by the heat generated by the laser, oxygen and moisture in the air, and oxygen and moisture in the jet gas, so that an oxide layer may exist. Specifically, the thickness of the oxide layer may be 4 to 10 nm. In addition, the oxide layer may be non-uniformly formed over the entire surface of the steel sheet, and the thickness of the above-described oxide layer means an average thickness over the entire surface of the steel sheet.
[49]
If the oxide layer is formed too thick, there may be a problem in that the oxide layer remains thick even when the oxide layer is removed in the step of removing the oxide layer to be described later.
[50]
A re-solidification layer may be formed on the bottom and side of the groove due to the heat effect of the laser. The re-solidification layer may have a thickness of 6.5 μm or less. When the re-solidification layer is formed too thickly, adhesion and iron loss may be inferior due to an increase in the heat-affected zone. The re-solidification layer includes recrystallization having an average particle diameter of 1 to 10 μm, and is distinguished from the entire structure of the electrical steel sheet being manufactured.
[51]
Next, the oxide layer formed on the surface of the cold-rolled sheet is partially removed to leave the thickness of the oxide layer in the range of 1 to 5 nm.
[52]
If the oxide layer is not removed, the non-uniform oxide layer remains thick, and the metal oxide layer formed in the secondary recrystallization annealing process is non-uniform and thick, which causes deterioration of the adhesion between the magnetic and metal oxide layer and the matrix.
[53]
Techniques for removing the heal-up or spatter formed in the process of forming the groove through brush or pickling are known, but the removal of the heal-up or spatter and the removal of the oxide layer when the melt is solidified are not at all in terms of removing the oxide layer in addition to the heal-up or spatter. different
[54]
As a method of removing the oxide layer, it can be removed through friction between the abrasive roll (paper) and the oxide layer using abrasive paper or an abrasive roll.
[55]
The thickness of the oxide layer remains between 1 nm and 5 nm. When the thickness of the oxide layer is left too thick, the metal oxide layer is formed non-uniformly and thickly, which causes deterioration of magnetism and adhesion. If the thickness of the oxide layer is left too thin, an appropriate metal oxide layer is not formed, which causes deterioration of magnetism and adhesion. More specifically, 2 to 5 nm of the oxide layer may remain.
[56]
After the step of leaving the oxide layer, the step of primary recrystallization annealing of the cold-rolled sheet may be further included.
[57]
Since the step of primary recrystallization annealing is widely known in the field of grain-oriented electrical steel sheet, a detailed description thereof will be omitted. The primary recrystallization annealing process may include decarburization, or decarburization and nitridation, and may be annealed in a wet atmosphere for decarburization or decarburization and nitridation. The cracking temperature in the primary recrystallization annealing step may be 800 to 950 ℃.
[58]
After the primary recrystallization annealing, the step of applying an annealing separator and performing secondary recrystallization annealing may be further included. Since the annealing separator is widely known, a detailed description thereof will be omitted. As an example, an annealing separator containing MgO as a main component may be used.
[59]
The purpose of the secondary recrystallization annealing is broadly, the formation of {110}<001> texture by secondary recrystallization and the formation of a glassy film by the reaction of the oxide layer and MgO formed during the primary recrystallization annealing. Impurities that impart insulation and impair magnetic properties is to remove In the secondary recrystallization annealing method, in the temperature rising section before secondary recrystallization occurs, a mixed gas of nitrogen and hydrogen is maintained to protect nitride, which is a grain growth inhibitor, so that secondary recrystallization can be well developed, and after secondary recrystallization is completed In the cracking stage, impurities are removed by maintaining it in a 100% hydrogen atmosphere for a long time.
[60]
The secondary recrystallization annealing may be performed at a cracking temperature of 900 to 1210 °C.
[61]
In the secondary recrystallization annealing process, the MgO component in the annealing separator may react with the oxide layer formed on the surface of the steel sheet to form a metal oxide layer on the surface of the steel sheet and the groove. 3 schematically shows the metal oxide layer 30 . In an embodiment of the present invention, since the groove is formed before the secondary recrystallization annealing, the metal oxide layer 30 may be formed on the surface of the groove as well as the steel sheet.
[62]
In one embodiment of the present invention, since the oxide layer is partially removed from the surface of the steel sheet after the groove is formed, the thickness of the oxide layer is thin, and MgO in the annealing separator penetrates or passes through the oxide layer to the metal oxide layer 30 and the island 40 on the lower side. ) can be formed. This island 40 may include forsterite.
[63]
3 schematically shows the island 40 . As shown in FIG. 3 , the island 40 may be formed under the metal oxide layer 30 by being separated from the metal oxide layer 30 . Since the island 40 is made of an alloy component similar to the metal oxide layer 30 , it is distinguished from the electrical steel sheet matrix structure.
[64]
By appropriately forming the island 40 discontinuously, it can contribute to improving the adhesion between the metal oxide layer 30 and the steel sheet. Specifically, the density of the islands including the metal oxide under the groove may be 0.25 pieces/μm 2 or less. In this case, the reference means the density of the island with respect to a depth area within 5 μm below the groove 20 in the cross section (TD surface) including the steel sheet rolling direction (RD direction) and the thickness direction (ND direction).
[65]
The island 40 positioned below the groove 20 may have an average sphericity (short axis/long axis) of 0.5 to 0.9. At this time, the reference is a cross section (TD surface) including the steel sheet rolling direction (RD direction) and the thickness direction (ND direction). The island 40 positioned below the surface on which the groove 20 is not formed is excluded from the above-described average particle diameter calculation. By controlling the average sphericity of the island 40 , it is possible to improve magnetic properties and improve adhesion with the insulating coating layer. More specifically, the island 40 positioned below the groove 20 may have an average sphericity (short axis/long axis) of 0.6 to 0.8.
[66]
After the secondary recrystallization annealing, the method may further include forming an insulating coating layer on the metal oxide layer.
[67]
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. As the insulating coating solution, it is preferable to use a coating solution containing colloidal silica and metal phosphate. In this case, the metal phosphate may be Al phosphate, Mg phosphate, or a combination thereof, and the content of Al, Mg, or a combination thereof relative to the weight of the insulating coating solution may be 15% by weight or more.
[68]
The grain-oriented electrical steel sheet according to an embodiment of the present invention has a groove 20 located on the surface of the electrical steel sheet 10, a metal oxide layer 30 located on the groove 20, and an island 40 located under the groove. ) is included.
[69]
The average sphericity (short axis/long axis) of the island 40 positioned below the groove may be 0.5 to 0.9. By controlling the average sphericity of the island 40 , it is possible to improve magnetic properties and improve adhesion with the insulating coating layer. More specifically, the island 40 positioned below the groove 20 may have an average sphericity of 0.6 to 0.8. When the average sphericity was less than 0.5, the diameter of the cylinder was 20 mm or more during the adhesion test due to cracks or bursts of forsterite after insulation coating due to poor adhesion between forsterite and the base.
[70]
The density of the islands 40 in the lower portion of the groove 20 may be 0.25 pieces/μm 2 or less. In this case, the reference means the density of the island with respect to a depth area within 5 μm below the groove 20 in the cross section (TD surface) including the steel sheet rolling direction (RD direction) and the thickness direction (ND direction). More specifically, the density of the islands 40 in the lower portion of the groove 20 may be 0.1 number/㎛ 2 or less.
[71]
Hereinafter, the present invention will be described in more detail through examples. However, these examples are only for illustrating the present invention, and the present invention is not limited thereto.
[72]
Example
[73]
A cold-rolled sheet having a thickness of 0.27 mm was prepared. The cold-rolled sheet was irradiated with a 1.0 kW Gaussian mode continuous wave laser at a scanning speed of 10 m/s to form a groove at an angle of 85° to the RD direction. When forming the groove, dry air from which moisture was removed at a pressure of 0.02 kg /cm 2 was sprayed at an angle of 70° to the rolling direction. Thereafter, the entire surface of the steel sheet was polished using a polishing cloth to adjust the oxide layer thickness to 5 nm or less as shown in Table 1 below. When the thickness of the oxide layer exceeds 5 nm, the adhesion is inferior. After that, the primary recrystallization annealing was performed, and after the secondary recrystallization was performed after MgO application, an insulating coating layer was formed.
[74]
For adhesion, the minimum diameter that the insulating coating layer does not peel or crack is indicated by bending the plate into a rod-shaped cylinder with various diameters. As the adhesion is excellent, the diameter of the rod shape gradually decreases.
[75]
[Table 1]
[76]
As shown in Table 1, it can be confirmed that the Example in which the oxide layer is appropriately removed after the groove is formed has superior adhesion and excellent iron loss compared to the Comparative Example.
[77]
In Examples 1 to 10 , core loss and adhesion were confirmed when the average sphericity of the islands 40 under the groove was 0.5 to 0.90, respectively, and the density was 0.25 pieces/㎛ 2 or less.
[78]
On the other hand, in the comparative example, it was confirmed that the average sphericity of the islands 40 was less than 0.5, and it was also confirmed that the density of the islands 40 was greater than 0.25 pieces/μm 2 .
[79]
The present invention is not limited to the embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can use other specific forms without changing the technical spirit or essential features of the present invention. It will be appreciated that this may be practiced. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.
[80]
[Explanation of code]
[81]
10: grain-oriented electrical steel sheet,
[82]
20: Groove,
[83]
30: metal oxide layer;
[84]
40: Ireland
Claims
[Claim 1]
a groove positioned on the surface of the electrical steel sheet, a metal oxide layer positioned on the groove, and discontinuously distributed and distributed metal oxide-based islands positioned under the groove, wherein the average sphericity of the islands positioned under the groove is A grain-oriented electrical steel sheet of 0.5 to 0.9.
[Claim 2]
The grain-oriented electrical steel sheet according to claim 1, wherein a density of the metal oxide-based islands positioned under the grooves is 0.25 pieces/㎛ 2 or less.
[Claim 3]
The grain-oriented electrical steel sheet according to claim 1, wherein 2 to 10 grooves are intermittently present with respect to the vertical direction of rolling.
[Claim 4]
The grain-oriented electrical steel sheet according to claim 1, wherein the longitudinal direction of the groove and the rolling direction of the steel sheet form an angle of 75 to 88°.
[Claim 5]
manufacturing a cold-rolled sheet; forming a groove by irradiating a laser on the cold-rolled sheet; and partially removing the oxide layer formed on the surface of the cold-rolled sheet so that the thickness of the oxide layer remains in the range of 1 to 5 nm; A method of manufacturing a grain-oriented electrical steel sheet comprising a.
[Claim 6]
The method according to claim 5, wherein in the step of forming the groove. A method of manufacturing a grain-oriented electrical steel sheet in which the scanning speed of the laser is 10 m/s or more.
[Claim 7]
The method according to claim 5, wherein in the step of forming the groove. A method of manufacturing a grain-oriented electrical steel sheet in which gas is sprayed toward the groove at an angle of 70° or less to the rolling direction.
[Claim 8]
The method of claim 7, wherein the pressure of the injected gas is 0.02 kg/cm 2 or more.
[Claim 9]
The method of claim 7, wherein the moisture content in the sprayed gas is 50 wt% or less.
[Claim 10]
The method of claim 5, wherein after the step of forming the groove, an oxide layer having a thickness of 4 to 10 nm is present on the surface of the cold-rolled sheet.