KR102538120B1 - Grain oriented electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

Grain-oriented electrical steel sheet according to an embodiment of the present invention Si: 2.0 to 7.0% by weight, Sn: 0.01 to 0.10% by weight, Sb: 0.01 to 0.07% by weight, Al: 0.020 to 0.040% by weight, Mn: 0.01 to 0.20% by weight %, C: 0.005 wt% or less (excluding 0%), N: 0.005 wt% or less (excluding 0%), and S: 0.005 wt% or less (excluding 0%), the balance being Fe and Electrical steel substrate containing other unavoidable impurities; and an insulating coating layer positioned on the electrical steel sheet substrate, the insulation coating layer including pores having a particle size of 10 nm or more, and the electrical steel sheet substrate having an area (A) within 1500 μm in the RD direction from the center of the pores and the surface of the electrical steel sheet substrate. Sub-crystal grains exist in the region (B) of 50 to 100 μm in the inner direction of the electrical steel substrate, the crystal orientation of the sub-crystal grains forms an angle of 1 ° to 15 ° from {110} <001>, and the sub-crystal grains in the ND cross section The area fraction is 5% or less.

Description

Grain-oriented electrical steel sheet and its manufacturing method {GRAIN ORIENTED ELECTRICAL STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME}

It relates to a grain-oriented electrical steel sheet and a manufacturing method thereof. Specifically, the present invention relates to a method for manufacturing a grain-oriented electrical steel sheet in which the formation of subgrain boundaries is suppressed and magnetic properties are improved by controlling the tension applied to the steel sheet in the process of forming an insulating coating layer.

In general, a grain-oriented electrical steel sheet is one containing Si component in a steel sheet, and has an aggregate structure in which grain orientations are aligned in the {110} <001> direction, and thus has extremely excellent magnetic properties in the rolling direction. Obtaining such a {110}<001> texture is possible by a combination of various manufacturing processes, in particular, heating, hot rolling, hot-rolled sheet annealing, primary recrystallization annealing, and secondary recrystallization annealing including the components of the steel slab. A series of processes must be controlled very strictly. Specifically, the grain-oriented electrical steel sheet suppresses the growth of primary recrystallized grains and selectively grows crystal grains with {110}<001> orientation among the growth-suppressed grains to exhibit excellent magnetic properties by the secondary recrystallized structure obtained. Therefore, the growth inhibitor of primary recrystallized grains is more important. In addition, in the final annealing process, it is one of the main issues in the grain-oriented electrical steel sheet manufacturing technology to allow crystal grains having a stable {110} <001> orientation texture to grow preferentially among the growth-suppressed crystal grains. Examples of primary crystal grain growth inhibitors that can satisfy the above conditions and are currently widely used industrially include MnS, AlN, and MnSe. Specifically, MnS, AlN, and MnSe contained in the steel slab are reheated and dissolved at high temperature for a long time, followed by hot rolling, and in the subsequent cooling process, the components having an appropriate size and distribution are made into precipitates and used as the growth inhibitor. It can be. However, this has a problem in that the steel slab must be heated to a high temperature. In this regard, recently, efforts have been made to improve the magnetic properties of grain-oriented electrical steel sheets by heating a steel slab at a low temperature. To this end, a method of adding antimony (Sb) element to the grain-oriented electrical steel sheet has been proposed, but a problem in that noise quality of the transformer is inferior due to non-uniform and coarse crystal grain size after the final high-temperature annealing has been pointed out.

On the other hand, in order to minimize power loss of grain-oriented electrical steel sheet, it is common to form an insulating film (or tension coating layer) on the surface of the grain-oriented electrical steel sheet. It should have a uniform color without defects. In addition, due to the recent strengthening of international standards for noise in transformers and intensifying competition in related industries, research on magnetostriction (magnetostriction) is required in order to reduce the noise of the insulating film of grain-oriented electrical steel sheet. Specifically, when a magnetic field is applied to an electrical steel sheet used as a core of a transformer, contraction and expansion are repeated to induce vibration, and vibration and noise occur in the transformer due to vibration. In the case of a generally known grain-oriented electrical steel sheet, an insulating film is formed on the steel sheet and a Forsterite-based base film, and tensile stress is applied to the steel sheet using the difference in thermal expansion coefficient of the insulating film, thereby improving iron loss and magnetostriction. However, there is a limit to satisfying the noise level of high-grade grain-oriented electrical steel sheet, which is recently required. Meanwhile, a wet coating method is known as a method of reducing the 90° magnetic domain of a grain-oriented electrical steel sheet. Here, the 90° magnetic domain refers to a region having magnetization perpendicular to a direction in which a magnetic field is applied, and the smaller the amount of the 90° magnetic domain, the smaller the magnetostriction. However, in general wet coating methods, there are disadvantages in that the effect of reducing noise by applying tensile stress is insufficient, and that a thick film of coating thickness is required to be coated, resulting in deterioration of transformer occupancy rate and efficiency.

In addition, coating methods through vacuum deposition such as physical vapor deposition (PVD) and chemical vapor deposition (CVD) are known as a method of imparting high tensile properties to the surface of grain-oriented electrical steel sheet. However, this coating method is difficult to commercially produce, and the grain-oriented electrical steel sheet manufactured by this method has a problem in that the insulating properties are poor.

Provided is a method for manufacturing a grain-oriented electrical steel sheet. Specifically, a method of manufacturing a grain-oriented electrical steel sheet having improved magnetism and suppressing formation of sub-grain boundaries by controlling tension applied to the steel sheet during the formation of an insulating coating layer is provided.

Grain-oriented electrical steel sheet according to an embodiment of the present invention Si: 2.0 to 7.0% by weight, Sn: 0.01 to 0.10% by weight, Sb: 0.01 to 0.07% by weight, Al: 0.020 to 0.040% by weight, Mn: 0.01 to 0.20% by weight %, C: 0.005 wt% or less (excluding 0%), N: 0.005 wt% or less (excluding 0%), and S: 0.005 wt% or less (excluding 0%), the balance being Fe and Electrical steel substrate containing other unavoidable impurities; and an insulating coating layer positioned on the electrical steel sheet substrate, the insulation coating layer including pores having a particle size of 10 nm or more, and the electrical steel sheet substrate having an area (A) within 1500 μm in the RD direction from the center of the pores and the surface of the electrical steel sheet substrate. Sub-crystal grains exist in the region (B) of 50 to 100 μm in the inner direction of the electrical steel substrate, the crystal orientation of the sub-crystal grains forms an angle of 1 ° to 15 ° from {110} <001>, and the sub-crystal grains in the ND cross section The area fraction is 5% or less.

In the sub-crystal grain, the ratio (y/z) of the grain length (y) in the TD direction to the grain length (z) in the ND direction may be 1.5 or less.

Average particle diameter of the Goss grains in the ND cross-section, comprising Goss crystal grains having a crystal orientation of less than 1° from {110} <001> in a region (B) of 50 to 100 μm from the surface of the electrical steel sheet substrate toward the inside of the electrical steel sheet substrate The ratio ( _LS /L _G ) of the average particle diameter ( _LS ) of the sub-crystal grains to (L _G ) may be 0.20 or less.

1 to 300 pores having a particle size of 10 nm or more may be present per 1 mm in the RD direction.

A fine grain interface layer exists from the surface of the electrical steel sheet substrate toward the inside of the electrical steel sheet substrate, and the fine grain interface layer may have an average grain size of 0.1 to 5 μm.

The fine grain interface layer may have a residual stress in the RD direction of -10 to -1000 MPa.

The thickness of the fine grain interface layer may be 0.1 to 5 μm.

A base coating layer may be further included between the electrical steel substrate and the insulating coating layer.

The residual stress in the RD direction of the base coating layer may be -50 to -1500 MPa.

The thickness of the base coating layer may be 0.1 to 15 μm.

Residual stress in the RD direction of the insulating coating layer may be -10 to -1000 MPa.

The thickness of the insulating coating layer may be 0.1 to 15 μm.

The electrical steel substrate may have a residual stress in an RD direction of 1 to 50 MPa.

Production of grain-oriented electrical steel sheet according to an embodiment of the present invention Manufacturing a grain-oriented electrical steel sheet; coating an insulating coating layer-forming composition on a grain-oriented electrical steel sheet; and forming an insulating coating layer on the grain-oriented electrical steel sheet by heat-treating the grain-oriented electrical steel sheet, wherein a tension applied to the steel sheet in the step of forming the insulating coating layer is 0.2 to 0.7 kgf/mm ² .

For the entire length of the steel sheet, the maximum value (MA) and minimum value (MI) of tension may satisfy Equation 2 below.

[Equation 2]

[MI] ≥ 0.5 × [MA]

Forming the insulating coating layer may be heat-treated at a temperature of 550 to 1100 °C.

Grain-oriented electrical steel sheet according to an embodiment of the present invention can improve magnetism by suppressing sub-crystal grains that adversely affect magnetism.

In the grain-oriented electrical steel sheet according to an embodiment of the present invention, the residual stress of the base coating layer, the insulating coating layer, and the fine grain interface layer may increase, thereby improving magnetism.

1 is a schematic view of a steel sheet TD cross section according to an embodiment of the present invention.
2 is an electron backscattering diffraction (EBSD) photograph of the steel sheet prepared in Example 1.
3 is a view showing a film tension calculation method using a radius of curvature.
4 is a diagram showing a slope in the measurement of residual stress.

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 only used 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.

The terminology used herein is only for referring to specific embodiments 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. The meaning of "comprising" as used herein specifies particular characteristics, regions, integers, steps, operations, elements and/or components, and the presence or absence of other characteristics, regions, integers, steps, operations, elements and/or components. Additions are not excluded.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part or may be followed by another part therebetween. In contrast, when a part is said to be “directly on” another part, there is no intervening part between them.

Although not defined differently, all terms including technical terms 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 belongs. Terms defined in commonly used dictionaries are additionally interpreted as having meanings consistent with related technical literature and currently disclosed content, and are not interpreted in ideal or very formal meanings unless defined.

In addition, unless otherwise specified, % means weight%, and 1ppm is 0.0001 weight%.

In one embodiment of the present invention, the meaning of further including an additional element means replacing and including iron (Fe) as much as the additional amount of the additional element.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein.

1 schematically shows a TD cross section of a grain-oriented electrical steel sheet according to an embodiment of the present invention.

As shown in FIG. 1 , a grain-oriented electrical steel sheet 100 according to an embodiment of the present invention includes an electrical steel sheet substrate 10 and an insulating coating layer 30 positioned on the electrical steel sheet substrate 10 .

The insulating coating layer 30 is formed by applying a solvent-containing insulating coating layer-forming composition on a steel sheet and then heat-treating it. At this time, as the solvent volatilizes at a high temperature, some pores 31 are inevitably formed in the insulating coating layer 30 .

When the pores 31 are larger than 10 nm, the stress applied to the steel sheet is concentrated in the lower portion of the pores 31 to form sub-crystal grains 11. This has a disadvantageous effect on magnetism compared to Goss grains, which are the main grains of the grain-oriented electrical steel sheet, and is preferably suppressed as much as possible.

In one embodiment of the present invention, the formation of the sub grains 11 is suppressed as much as possible by analyzing the positional correlation between the pores 31 and the sub grains 11 and the cause of the formation of the sub grains 11 .

In FIG. 1, pores 31 and sub-crystal grains 11 are schematically represented.

As shown in FIG. 1 , sub-crystal grains 11 exist under the pores 31 . All of the sub-crystal grains 11 in the steel sheet substrate 10 exist in a specific region below the pores 31 . However, sub-crystal grains 11 do not exist under all pores 31, and there may be pores 31 in which sub-crystal grains 11 do not exist.

Hereinafter, each configuration according to an embodiment of the present invention will be described in detail.

The electrical steel sheet substrate 10 refers to a portion of the grain-oriented electrical steel sheet 100 excluding the base coating layer 20 and the insulating coating layer 30 .

In one embodiment of the present invention, it is expressed by the pores 31 in the insulating coating layer 30 and the sub-crystal grains 11 in the electrical steel substrate 10, regardless of the alloy components of the electrical steel substrate 10. Supplementally, the alloy components of the electrical steel base material 10 will be described.
The electrical steel substrate 10 includes Si: 2.0 to 7.0% by weight, Sb: 0.01 to 0.07% by weight, and the balance includes Fe and other unavoidable impurities.

Specifically, the electrical steel substrate 10 contains Si: 2.0 to 7.0 wt%, Sn: 0.01 to 0.10 wt%, Sb: 0.01 to 0.07 wt%, Al: 0.020 to 0.040 wt%, Mn: 0.01 to 0.20 wt%, C : 0.005 wt% or less (excluding 0%), N: 0.005 wt% or less (excluding 0%), and S: 0.005 wt% or less (excluding 0%), the balance being Fe and other unavoidable impurities can include

Si: 2.0 to 7.0% by weight

Silicon (Si) plays a role in reducing iron loss by increasing the specific resistance of the steel. If the content of Si is too small, the specific resistance of the steel becomes small, resulting in deterioration of iron loss characteristics, and there is a phase transformation section during secondary recrystallization annealing, resulting in secondary recrystallization. Instability problems may occur. If the content of Si is too large, brittleness may increase and cold rolling may be difficult. Therefore, the Si content can be adjusted within the above range. More specifically, Si may be included in an amount of 2.5 to 5.0% by weight.

Sn: 0.01 to 0.10% by weight

Tin (Sn) is a grain boundary segregation element that hinders the movement of grain boundaries. As a grain growth suppressant, tin (Sn) promotes the creation of Goss grains in the {110}<001> orientation so that secondary recrystallization develops well, so it is used to reinforce grain growth inhibition. is an important element.

If the Sn content is too small, the effect is reduced, and if the Sn content is too large, grain boundary segregation occurs severely, resulting in increased brittleness of the steel sheet and plate breakage during rolling. Therefore, the content of Sn can be adjusted within the above range. More specifically, Sn may be included in an amount of 0.02 to 0.08% by weight.

Sb: 0.01 to 0.07% by weight

Antimony (Sb) is an element that promotes the formation of Goss crystal grains in {110}<001> orientation. If the Sb content is too small, a sufficient effect as a Goss grain formation promoter cannot be expected, and if the Sb content is too small If there is a large amount, it is segregated on the surface, suppressing the formation of an oxide layer and causing surface defects. Therefore, the content of Sb can be controlled within the above range. More specifically, Sb may be included in an amount of 0.02 to 0.04% by weight.

Al: 0.020 to 0.040% by weight

Aluminum (Al) is an element that acts as an inhibitor by becoming a nitride in the form of AlN, (Al,Si)N, or (Al,Si,Mn)N. When the Al content is too small, a sufficient effect as an inhibitor cannot be expected. On the other hand, if the Al content is too large, the effect as an inhibitor is insufficient because Al-based nitrides precipitate and grow too coarsely. Therefore, the Al content can be adjusted within the above range. More specifically, Al may be included in an amount of 0.020 to 0.030% by weight.

Mn: 0.01 to 0.20% by weight

Manganese (Mn) has the effect of reducing iron loss by increasing specific resistance in the same way as Si, and reacts with nitrogen introduced by nitriding treatment together with Si to form precipitates of (Al,Si,Mn)N, which is the primary recrystallization. It is an important element in causing secondary recrystallization by inhibiting grain growth. However, when the content of Mn is too large, since austenite phase transformation is promoted during hot rolling, the size of primary recrystallized grains is reduced, thereby destabilizing secondary recrystallization. In addition, when the content of Mn is too small, as an austenite forming element, the austenite fraction is increased during hot-rolled reheating to increase the solid content of precipitates, so that the primary recrystallized grains through refining of precipitates and MnS formation during re-precipitation are not too excessive. can happen insufficiently. Therefore, the content of Mn can be controlled within the above range.

C: 0.005% by weight or less (excluding 0%)

Since carbon (C) is a component that does not greatly help improve the magnetic properties of the grain-oriented electrical steel sheet in the embodiment according to the present invention, it is preferable to remove carbon (C) as much as possible. However, when it is included at a certain level or more, it has an effect of helping to form a uniform microstructure by promoting the austenite transformation of the steel during the rolling process to refine the hot-rolled structure during hot rolling. The C content in the slab is preferably included at 0.04% by weight or more. However, if the C content is excessive, coarse carbides are formed and it is difficult to remove during decarburization, so it may be 0.07% by weight or less. Decarburization is performed in the primary recrystallization annealing process, and is included in an amount of 0.005% by weight or less in the grain-oriented electrical steel base material finally manufactured after decarburization.

N: 0.005% by weight or less (excluding 0%)

Nitrogen (N) is an element that refines crystal grains by reacting with Al and the like. When these elements are appropriately distributed, as described above, it may be helpful to secure an appropriate primary recrystallized grain size by properly refining the structure after cold rolling. However, if the content is excessive, primary recrystallized grains are excessively miniaturized, and as a result, due to the fine grains, the driving force that causes grain growth during secondary recrystallization increases, and thus grains may grow to undesirable orientations. In addition, if the N content is excessive, it is not preferable because it takes a lot of time to remove it in the final annealing process. Therefore, the upper limit of the nitrogen content can be set at 0.005% by weight. In the first recrystallization process, the amount of nitrogen may increase due to nitriding, and in this case, since it is removed again in the second recrystallization annealing process, the amount of nitrogen in the slab and the final grain-oriented electrical steel sheet substrate 10 may be the same.

S: 0.005% by weight or less (excluding 0%)

If the sulfur (S) content exceeds 0.005% by weight, it is re-dissolved and finely precipitated when the hot-rolled slab is heated, thereby reducing the size of the primary recrystallization grains and lowering the secondary recrystallization start temperature to deteriorate magnetism. In addition, since it takes a lot of time to remove S in solid solution in the secondary cracking section of the final annealing process, productivity of the grain-oriented electrical steel sheet is reduced. On the other hand, when the S content is as low as 0.005% or less, the initial grain size before cold rolling has the effect of coarsening, so the number of grains having {110} <001> orientation nucleated in the deformation band in the primary recrystallization process increases. Therefore, in order to improve the magnetism of the final product by reducing the size of secondary recrystallized grains, the S content is preferably 0.005% by weight or less.

The balance includes Fe and unavoidable impurities. The unavoidable impurity is an element that is unavoidably added in the process of manufacturing steel and grain-oriented electrical steel sheet, and since it is widely known, the description of unavoidable impurities will be omitted. In one embodiment of the present invention, the addition of elements other than the above-described alloy components is not excluded, and may be variously included within a range that does not impair the technical spirit of the present invention. When additional elements are included, they are included in place of Fe, which is the remainder.

As shown in FIG. 1 , sub crystal grains 11 exist in the electrical steel base material 10 .

The sub-grains 11 are distinguished from the rest of the Goss grains except for the sub-grains in that the crystal orientation forms an angle of 1° to 15° from {110} <001>. Specifically, the crystal orientation of the Goss grains is less than 1° from {110} <001>. The crystal orientation is represented by the Miller index.

In one embodiment of the present invention, the sub-crystal grains 11 are located below the pores 31. Specifically, sub-crystal grains 11 exist in an area (A) within 1500 μm in the RD direction from the pore center and in an area (B) within a range of 50 to 100 μm from the surface of the electrical steel sheet substrate toward the inside of the electrical steel sheet substrate. In FIG. 1, the positions defined by regions A and B are indicated by dotted rectangles. Specifically, all regions of the sub-crystal grains 11 may be included in positions defined as region A and region B. In one embodiment of the present invention, the sub-crystal grains 11 exist only in the aforementioned region, and the sub-crystal grains 11 do not exist in the other regions.

In an embodiment of the present invention, magnetic properties can be improved by suppressing these sub-crystal grains 11. Specifically, the area fraction of sub-crystal grains in the cross-section of the ND may be 5% or less. If the area fraction of the sub-crystal grains 11 is too large, this causes deterioration of magnetism. More specifically, the area fraction of the sub-crystal grains in the cross section of the ND may be 0.1 to 5%. More specifically, it may be 1 to 3%. The ND cross section means a plane perpendicular to the ND direction.

The grain size of the sub-crystal grain 11 is 1 to 500 nm, and it is possible to distinguish it from the rest of the Goss grains even with the grain size. Specifically, the average particle diameter of the Goss crystal grains excluding sub-crystal grains may be 5 to 100 mm. At this time, it is the grain size in the crystal grain ND cross section. More specifically, the sub-crystal grains 11 may have a particle diameter of 10 to 250 nm, and an average particle diameter of the Goss grains excluding the sub-crystal grains may be 10 to 50 mm.

A ratio ( _LS /L _G ) of the average grain diameter ( _LS ) of the sub-crystal grains to the average grain diameter (L _G ) of the goss grains on the ND surface may be 0.20 or less. More specifically, it may be 0.10 or less.

In one embodiment of the present invention, the particle diameter means the diameter of an imaginary circle having the same area as the corresponding area.

In one embodiment of the present invention, the electrical steel substrate 10 may have a residual stress in the RD direction of 1 to 50 MPa. The reason why residual stress exists in this range is due to the base coating layer 20 and the insulating coating layer 30 present on the electrical steel substrate 10 . Due to the presence of the residual stress in the above-mentioned range, the film tension is imparted to the base iron and the magnetism is improved. Specifically, the electrical steel substrate 10 may have a residual stress in the RD direction of 16.0 to 30.0 MPa. The residual stress of the electrical steel substrate 10 can be obtained as a value that makes the sum of the residual stresses of the fine grain interface layer 12, the base coating layer 20, and the insulating coating layer 30 zero.

t _i : thickness of each layer

σ _i : Residual stress in each layer

i: base coating layer/fine grain interface layer/base steel sheet

As shown in FIG. 1 , the fine grain interface layer 12 may exist from the surface of the electrical steel sheet substrate 10 toward the inside of the electrical steel sheet substrate. The fine grain interface layer 12 may have an average grain size of 0.1 to 5 µm. The fine grain interface layer 12 is formed due to the influence of surface energy non-uniformity.

The thickness of the fine grain interface layer 12 may be 0.1 to 5 μm. If the fine grain crystal layer 12 is too thick, it is advantageous to reduce its thickness by deteriorating the magnetism. More specifically, the thickness of the fine grain interface layer 12 may be 0.5 to 3 μm.

The fine grain interface layer 12 may have a residual stress in the RD direction of -10 to -1000 MPa. In this case, a negative sign means a stress applied to the electrical steel substrate 10 by the fine grain interface layer 12 . More specifically, the fine grain interface layer 12 may have a residual stress in the RD direction of -100 to -500 MPa. More specifically, the fine grain interface layer 12 may have a residual stress in the RD direction of -400 to -500 MPa.

As shown in FIG. 1 , the grain oriented electrical steel sheet 100 according to an embodiment of the present invention may further include a base coating layer 20 positioned between the electrical steel substrate 10 and the insulating coating layer 30 .

The base coating layer 20 forms a coating layer by reacting the oxide layer formed in the primary recrystallization process with components in the annealing separator. The base coating layer 20 improves adhesion between the insulating coating layer 30 and the electrical steel sheet substrate 10 and, together with the insulating coating layer 30, imparts insulation to the grain-oriented electrical steel sheet 100.

The base coating layer 20 component is not particularly limited, but when MgO is included in the annealing separator component, forsterite (Mg ₂ SiO ₄ ) may be included. The base coating layer 20 may be omitted if necessary. That is, the electrical steel substrate 10 and the insulating coating layer 30 may directly contact each other.

The thickness of the base coating layer 20 may be 0.1 to 15 μm. If the thickness of the base coating layer 20 is too thin, it cannot sufficiently perform the role of insulating and improving adhesion with the insulating coating layer 30 described above. If the base coating layer 20 is too thick, the area occupancy rate may decrease, and adhesion to the insulating coating layer 30 may deteriorate. More specifically, the thickness of the base coating layer 20 may be 0.5 to 3 μm.

The residual stress in the RD direction of the base coating layer 20 may be -50 to -1500 MPa. More specifically, it may be -500 to -1000 MPa. More specifically, it may be -760 to -1000 MPa.

As shown in FIG. 1 , the insulating coating layer 30 is positioned on the electrical steel substrate 10 . When the base coating layer 20 is positioned on the electrical steel substrate 10, the insulating coating layer 30 is positioned on the base coating layer 20. The insulating coating layer 30 imparts insulation to the grain-oriented electrical steel sheet 100 and also serves to improve iron loss by imparting tension to the electrical steel substrate 10.

The insulating coating layer 30 may use a material capable of imparting insulating properties to the surface of the electrical steel sheet 100 . Specifically, phosphate (H ₃ PO ₄ ) may be included.

The insulating coating layer 30 is formed by applying a solvent-containing insulating coating layer-forming composition on a steel sheet and then heat-treating it. At this time, as the solvent volatilizes at a high temperature, some pores 31 are inevitably formed in the insulating coating layer 30 . The pore 31 means a state in which nothing exists in the corresponding part, that is, an empty space.

1 to 300 pores having a particle size of 10 nm or more may be present per 1 mm in the RD direction. More specifically, 1 to 30 may be present per 1 mm. At this time, the particle diameter of the pores can be measured based on the ND surface or the TD surface. The number of pores can be measured based on the TD surface.

There are 1 to 30 sub-crystal grains per pore having a particle size of 10 nm or more. As described above, the sub-crystal grain 11 may not exist in the regions A and B below the pore 31, and it is also possible that two or more sub-crystal grains 11 exist. However, the sub-crystal grains 11 may not exist other than the regions A and B below the pores 31 .

The thickness of the insulating coating layer 30 may be 0.1 to 15 μm. If the thickness of the insulating coating layer 30 is too thin, the aforementioned insulating role cannot be sufficiently performed. If the insulating coating layer 30 is too thick, the space factor may be lowered, and adhesion to the steel sheet substrate 10 may be deteriorated. More specifically, the thickness of the insulating coating layer 30 may be 1.0 to 5.0 μm.

Residual stress in the RD direction of the insulating coating layer 30 may be -10 to -1000 MPa. More specifically, it may be -70 to -500 MPa.

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of manufacturing a grain-oriented electrical steel sheet; coating an insulating coating layer-forming composition on a grain-oriented electrical steel sheet; and heat-treating the grain-oriented electrical steel sheet to form an insulating coating layer-forming composition on the grain-oriented electrical steel sheet.

Hereinafter, each step is described in detail.

First, a grain-oriented electrical steel sheet is manufactured. At this time, the grain-oriented electrical steel sheet may use a grain-oriented electrical steel sheet in which the base coating layer 20 is formed or not, and only the electrical steel substrate 10 exists.

The grain-oriented electrical steel sheet on which the base coating layer 20 is not formed may be manufactured in a variety of ways, for example, adjusting the annealing separator component, or forming the base coating layer 20 and then removing it by a physical or chemical method. method can be used.

In one embodiment of the present invention, there is a technical feature in adjusting the tension applied to the steel sheet in the step of forming the insulating coating layer, and various conventionally known methods may be used as a method for manufacturing a grain-oriented electrical steel sheet.

Hereinafter, an example of a method for manufacturing a grain-oriented electrical steel sheet before forming an insulating coating layer will be described.

A method of producing a grain-oriented electrical steel sheet includes preparing a hot-rolled sheet by hot-rolling a slab; Cold-rolling a hot-rolled sheet to produce a cold-rolled sheet; Primary recrystallization annealing of the cold-rolled sheet; and performing secondary recrystallization annealing on the cold-rolled sheet on which the primary recrystallization annealing is completed.

The slab contains Si: 2.0 to 7.0 wt%, Sn: 0.01 to 0.10 wt%, Sb: 0.01 to 0.07 wt%, Al: 0.020 to 0.040 wt%, Mn: 0.01 to 0.20 wt%, C: 0.04 to 0.07 wt%, N: 10 to 50 ppm by weight, S: 0.001 to 0.005% by weight, the rest Fe and other unavoidable impurities may be included.

First, a hot-rolled sheet is manufactured by hot-rolling a slab.

Hereinafter, since the slab alloy components are the same as those of the electrical steel base material 10 except for the content of C, overlapping descriptions will be omitted.

A step of heating the slab to 1230° C. or less may be further included before the step of manufacturing the hot-rolled sheet. Through this step, the precipitate may be partially dissolved. In addition, since the coarse growth of the columnar structure of the slab is prevented, it is possible to prevent cracks from occurring in the width direction of the plate in the subsequent hot rolling process, thereby improving the actual yield. If the slab heating temperature is too high, the heating furnace may be repaired by melting the surface of the slab and the life of the heating furnace may be shortened. More specifically, the slab may be heated to 1130 to 1200 ° C. It is also possible to hot-roll a continuously cast slab as it is without heating the slab.

In the step of manufacturing the hot-rolled sheet, a hot-rolled sheet having a thickness of 1.8 to 2.3 mm may be manufactured by hot rolling.

After manufacturing the hot-rolled sheet, a step of annealing the hot-rolled sheet may be further included. The step of annealing the hot-rolled sheet may be performed by heating to a temperature of 950 to 1,100 ° C, cracking at a temperature of 850 to 1,000 ° C and then cooling.

Next, the hot-rolled sheet is cold-rolled to manufacture a cold-rolled sheet.

Cold rolling may be performed through one round of strong cold rolling or through a plurality of passes. Gives a pass aging effect through warm rolling at a temperature of 200 to 300 ° C. one or more times during rolling, and can be manufactured with a final thickness of 0.14 to 0.25 mm. The cold-rolled cold-rolled sheet is subjected to decarburization, recrystallization of the deformed structure, and nitriding treatment through nitriding gas in the primary recrystallization annealing process.

Next, the cold-rolled sheet is subjected to primary recrystallization annealing.

Decarburization or nitriding may be performed in the primary recrystallization annealing process.

The primary recrystallization annealing step may be performed at a temperature of 800 to 900 °C. If the temperature is too low, primary recrystallization may not be performed or nitriding may not be performed smoothly. If the temperature is too high, primary recrystallization grows too large, which may cause deterioration of magnetism.

For decarburization, oxidation capacity (PH ₂ O/PH ₂ ) may be performed in an atmosphere of 0.5 to 0.7. By decarburization, the steel sheet may contain less than 0.005% by weight of carbon, more specifically, less than 0.003% by weight of carbon.

Next, an annealing separator is applied to the cold-rolled sheet on which the primary recrystallization annealing is completed, followed by secondary recrystallization annealing. Various separators may be used as the annealing separator. For example, an annealing separator containing MgO as a main component may be applied. At this time, after secondary recrystallization annealing, a base coating layer 20 including forsterite is formed.

The purpose of secondary recrystallization annealing is to form {110}<001> texture by secondary recrystallization and to remove impurities that harm magnetic properties. As a method of secondary recrystallization annealing, 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 develops well, and after completion of secondary recrystallization, 100 It can be maintained for a long time in a % hydrogen atmosphere to remove impurities.

After the secondary recrystallization annealing step, a flattening annealing process may be included.

Returning to the description of the manufacturing process of the grain-oriented electrical steel sheet according to an embodiment of the present invention, the insulating coating layer forming composition is applied on the grain-oriented electrical steel sheet. In one embodiment of the present invention, the composition for forming the insulating coating layer may be used in various ways, and is not particularly limited. For example, a composition for forming an insulating coating layer containing phosphate may be used.

Next, an insulating coating layer is formed on the grain-oriented electrical steel sheet by heat-treating the grain-oriented electrical steel sheet.

At this time, as the solvent volatilizes at a high temperature during the heat treatment process, some pores 31 are inevitably formed in the insulating coating layer 30 . At this time, the stress applied to the steel sheet is concentrated in the lower part of the pores 31 to form the sub-crystal grains 11. In one embodiment of the present invention, the formation of the sub-crystal grains 11 is suppressed as much as possible by adjusting the tension applied to the steel sheet in the process of forming the insulating coating layer.

Specifically, the tension applied to the steel sheet in the step of forming the insulating coating layer is 0.20 to 0.70 kgf/mm ² .

At this time, if the tension applied to the steel sheet is too small, scratches may occur on the surface, resulting in poor corrosion resistance. If the tension applied to the steel sheet is too great, a large amount of sub-crystal grains 11 may be formed, which may adversely affect magnetism. More specifically, it may be 0.20 to 0.50 kgf/mm ² . More specifically, it may be 0.3 to 0.47kgf/mm ² . At this time, the tension is the average tension in the longitudinal direction of the steel sheet measured at the exit side of the heat treatment process.

In the step of forming the insulating coating layer, tension applied in the longitudinal direction (RD direction) of the steel sheet may be different. In one embodiment of the present invention, the residual stress applied to each layer is appropriately controlled by minimizing the difference between the maximum value (MA) and the minimum value (MI) of tension with respect to the entire length of the steel sheet, and the formation of sub-crystal grains 11 can suppress

Specifically, for the entire length of the steel sheet, the maximum value (MA) and minimum value (MI) of tension satisfy Equation 2 below.

[Equation 2]

[MI] ≥ 0.5 × [MA]

When Equation 2 is not satisfied and there is a large variation in tension along the longitudinal direction (RD direction) of the steel sheet, the local non-uniformity increases, so that the residual stress cannot be properly controlled, and a large amount of sub-crystal grains 11 are formed.

In the conventional case, there is a problem in that the variation of the line speed (Line Speed) is large in the flattening annealing process, so there is a large variation in tension along the longitudinal direction (RD direction) of the steel sheet, resulting in a local increase in non-uniformity. In detail, laser welding is performed by minimizing the line speed to join the preceding coil tail part and the following coil top part at the entrance of the flattening annealing. When welding is completed, there is a large tension deviation because the line speed is increased to improve the productivity of the final product. More specifically, as the line speed changes, the speed change width of the bridle roll and hearth roll increases, resulting in tension along the length direction (RD direction) of the steel sheet at high temperatures that inevitably accompany flattening annealing. There is a large deviation, and there is a problem that the residual stress cannot be properly controlled due to an increase in local non-uniformity, so the minimum value (MI) of the tension is inevitably less than 0.5 × [MA].

There are many ways to reduce the difference between the maximum value (MA) and the minimum value (MI) of tension, but in one embodiment of the present invention, for example, bridle roll control and hearth roll speed can be used to control In detail, the bridle roll control is a method of controlling feedback tension by following the value of a tension meter. More specifically, it is a method of controlling the speed of the bridle roll to reduce the difference between the maximum value and the minimum value of tension. Also, in detail, the hearth roll control is a method of controlling feedforward tension following a bridle roll speed. More specifically, in order to reduce the difference between the maximum value and the minimum value of tension, it can be adjusted by controlling the tension to decrease as the speed of the hearth roll increases. In one embodiment of the present invention, even if the line speed is varied in the flattening annealing process, it is possible to reduce the difference between the maximum value (MA) and the minimum value (MI) while adjusting the tension within a specific range.

In the step of forming the insulating coating layer, the heat treatment temperature may be 550 to 1100 °C. At the above-described temperature, fewer pores 31 are generated, and residual stress of the insulating coating layer 30 can be appropriately applied.

Preferred examples and comparative examples of the present invention are described below. However, the following example is only a preferred embodiment of the present invention, but the present invention is not limited to the following example.

Si: 3.4 wt%, Sn: 0.05 wt%, Sb: 0.02 wt%, Al: 0.02 wt%, Mn: 0.10 wt%, C: 0.05 wt%, N: 0.002 wt%, and S: 0.001 wt% , The rest of the components were vacuum melted for steel containing Fe and other unavoidable impurities, and then heated at 1150 ° C. for 210 minutes, followed by hot rolling to prepare a hot-rolled sheet with a thickness of 2.0 mm. After pickling, it was cold-rolled to a thickness of 0.220 mm.

The cold-rolled sheet is maintained in a humid atmosphere of 50v% hydrogen and 50v% nitrogen and an ammonia mixed gas atmosphere at a temperature of about 800 to 900 ° C. Decarburization and nitriding annealing so that the carbon content is less than 30ppm and the total nitrogen content is increased to 130ppm or more heat treated.

The steel sheet was coated with MgO as an annealing separator and finally annealed into a coil shape. Final annealing was carried out in a mixed atmosphere of 25 v% nitrogen and 75 v% hydrogen up to 1200 ° C, and after reaching 1200 ° C, maintained in a 100% hydrogen atmosphere for more than 10 hours and then furnace cooled.

An insulation coating layer forming composition containing phosphate and silica was applied to the steel sheet, and heat treatment was performed at a temperature of about 820° C. for 2 hours to form an insulation coating layer.

When forming the insulating coating layer, the average tension at the exit side was adjusted as shown in Table 1 below.

The pores, sub-grains, and other crystal grain characteristics of the grain-oriented electrical steel sheet produced are summarized in Table 1, and the characteristics and iron loss of the interface layer, base coating layer, and insulating coating layer are summarized in Table 2.

It was confirmed that the positions of the sub-crystal grains existed only in a specific region below the pores.

As for the number of pores, only pores having a particle diameter of 10 nm or more were measured.

The sub-grain fraction was measured for volume per unit area by electron backscatter diffraction (EBSD).

Iron loss and magnetic flux density were measured immediately after forming the insulating coating layer and after heat treatment at 820 ° C for 2 hours assuming stress relief annealing. Iron loss (W17/50) and magnetic flux density (B8) were measured. Iron loss was measured under the condition of 1.7 Tesla, 50 Hz using the single sheet measurement method. In addition, the magnetic flux density induced in a magnetic field of 800 A/m was measured.

The residual stress of the insulating coating layer was measured using a 3D curvature measuring instrument (ATOS core 45). Only the insulating coating layer on one side was removed, and the amount of bending of the steel sheet was measured.

Insulation was measured on the top of the coating using a Franklin measuring instrument according to the ASTM A717 international standard.

Corrosion resistance indicates the area of rust generated on the surface under the condition of 35 ° C, 5% NaCL, 8 hours according to JIS Z2371 international standard. The diagram below is a film tension calculation method using the radius of curvature (reference M. Bielawski et all., Surf. & Coat. Techno., 200 (2006) 2987). The film tension can be calculated from the measured image using the 3D scanner software. R values can be measured for specimens before (R2) and after (R1) removal of the phosphate coating layer.

Residual stress of the base coating layer and the fine grain interface layer was measured using synchrotron XRD equipment. The X-ray residual stress measurement method uses the distance between lattice planes of crystal grains as a strain gauge. When the sample is under stress, the distance between the lattice planes changes according to the direction of the stress and the relative angle of the crystal plane. It can be said that the distance between lattice planes parallel to the tensile direction, that is, ψ = 0°, is smaller than when the stress is zero due to the Poisson effect, and the distance between lattice planes with an inclined ψ angle to the tensile direction is larger than when the stress is zero. The X-ray residual stress measures the peak shift according to the tilting angle Ψ. Therefore, X-ray residual stress calculation follows the sin2Ψ method and can be expressed as the following formula.

exit tension Whether or not Expression 2 is satisfied Sub grain area fraction (%) (kgf/mm ² ) Example 1 0.20 O 0.01 Example 2 0.34 O 0.01 Example 3 0.42 O 0.06 Example 4 0.44 O 0.22 Example 5 0.46 O 0.03 Example 6 0.48 O 0.17 Example 7 0.58 O 0.50 Example 8 0.60 O 1.12 Example 9 0.70 O 1.21 Comparative Example 1 0.55 X 8.82 Comparative Example 2 0.10 O 9.10 Comparative Example 3 0.77 O 9.05 Comparative Example 4 0.86 O 11.52 Comparative Example 5 0.95 O 22.30 Comparative Example 6 0.70 X 33.50

fine grain interfacial layer
Average grain size 2.5㎛ base coating layer Insulation coating layer steel sheet material thickness
(μm) RD direction residual stress
(MPa) thickness
(μm) RD direction residual stress
(MPa) thickness
(μm) RD direction residual stress
(MPa) thickness
(μm) RD direction residual stress
(MPa) Example 1 1.4 -480 1.1 -914 1.9 -325 220 20.6 Example 2 1.4 -477 1.1 -895 1.9 -312 220 2.01 Example 3 1.4 -441 1.1 -868 1.9 -267 220 18.6 Example 4 1.4 -414 1.1 -867 1.9 -272 220 18.4 Example 5 1.4 -481 1.1 -858 1.9 -169 220 17.4 Example 6 1.4 -467 1.1 -870 1.9 -149 220 16.9 Example 7 1.4 -454 1.1 -853 1.9 -94 220 15.7 Example 8 1.4 -427 1.1 -833 1.9 -82 220 14.0 Example 9 1.4 -415 1.1 -780 1.9 -77 220 14.2 Comparative Example 1 1.4 -247 1.1 -523 1.9 -37 220 8.8 Comparative Example 2 1.4 -345 1.1 -752 1.9 -55 220 9.7 Comparative Example 3 1.4 -315 1.1 -524 1.9 -45 220 9.9 Comparative Example 4 1.4 -245 1.1 -447 1.9 -26 220 7.9 Comparative Example 5 1.4 -194 1.1 -398 1.9 -7 220 6.4 Comparative Example 6 1.4 -190 1.1 -225 1.9 -6 220 4.7

Iron loss (W17/50, W/kg) Magnetic flux density (B8, T) Insulation (mA) corrosion resistance Example 1 0.735 1.935 35 - Example 2 0.739 1.935 55 - Example 3 0.752 1.934 30 - Example 4 0.753 1.935 35 - Example 5 0.76 1.933 42 - Example 6 0.761 1.932 32 - Example 7 0.772 1.928 55 - Example 8 0.77 1.93 55 - Example 9 0.782 1.927 42 0.7 Comparative Example 1 0.847 1.921 95 5.5 Comparative Example 2 0.844 1.922 360 8.2 Comparative Example 3 0.843 1.923 277 7.7 Comparative Example 4 0.912 1.915 345 9 Comparative Example 5 0.998 1.88 678 15 Comparative Example 6 1.052 1.876 850 42.3

As shown in Tables 1 to 3, when the tension is properly controlled during the formation of the insulating coating layer, the sub-crystal grain is suppressed, the residual stress of the fine grain interface layer, the base coating layer and the insulating coating layer increases, and the magnetic, insulating and corrosion resistance You can see that this improves. On the other hand, when the tension is not properly controlled during the formation of the insulating coating layer, a large amount of sub-crystal grains are formed, and it can be confirmed that the magnetic properties, insulating properties, or corrosion resistance are poor.

The present invention is not limited to the above embodiments, but can be manufactured in a variety of different forms, and those skilled in the art to which the present invention pertains may take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting.

100: grain-oriented electrical steel sheet, 10: electrical steel substrate,
11: sub crystal grain, 12: fine grain interface layer,
20: base coating layer, 30: insulating coating layer,
31: pore

Claims (12)

Si: 2.0 to 7.0 wt%, Sn: 0.01 to 0.10 wt%, Sb: 0.01 to 0.07 wt%, Al: 0.020 to 0.040 wt%, Mn: 0.01 to 0.20 wt%, C: 0.005 wt% or less (0% excluding), N: 0.005% by weight or less (excluding 0%), and S: 0.005% by weight or less (excluding 0%), the balance of which includes Fe and other unavoidable impurities;
Including an insulating coating layer located on the electrical steel substrate,
The insulating coating layer includes pores having a particle size of 10 nm or more,
The electrical steel sheet substrate has sub-crystal grains in an area (A) within 1500 μm in the RD direction from the center of the pores and in an area (B) within 50 to 100 μm from the surface of the electrical steel sheet substrate toward the inside of the electrical steel sheet substrate,
The sub-crystal grains form an angle of 1 ° to 15 ° from {110} <001>,
A grain-oriented electrical steel sheet in which the area fraction of the sub-crystal grains in the ND cross section is 5% or less. According to claim 1,
The grain-oriented electrical steel sheet in which the ratio (y/z) of the grain length (y) in the TD direction to the grain length (z) in the ND direction is 1.5 or less. According to claim 1,
A Goss crystal grain having a crystal orientation of less than 1° from {110} <001> is included in a region (B) of 50 to 100 μm from the surface of the electrical steel sheet substrate toward the inside of the electrical steel sheet substrate,
Grain-oriented electrical steel sheet wherein the ratio ( _LS /L _G ) of the average grain diameter ( _LS ) of the sub-crystal grains to the average grain diameter (L _G ) of the Goss grains in the ND cross section is 0.20 or less. According to claim 1,
A fine grain interface layer exists from the surface of the electrical steel sheet toward the inside of the electrical steel substrate,
The grain-oriented electrical steel sheet has an average grain size of 0.1 to 5 μm. According to claim 4,
The fine grain interface layer is a grain-oriented electrical steel sheet having a residual stress in the RD direction of -10 to -1000 MPa. According to claim 4,
The grain-oriented electrical steel sheet has a thickness of 0.1 to 5 μm of the fine grain interface layer. According to claim 1,
Grain-oriented electrical steel sheet further comprising a base coating layer between the electrical steel substrate and the insulating coating layer. According to claim 7,
Grain-oriented electrical steel sheet having a residual stress in the RD direction of the base coating layer of -50 to -1500 MPa. According to claim 7,
The thickness of the base coating layer is 0.1 to 15㎛ grain-oriented electrical steel sheet. According to claim 1,
Grain-oriented electrical steel sheet having a residual stress in the RD direction of the insulating coating layer of -10 to -1000 MPa. According to claim 1,
The thickness of the insulating coating layer is 0.1 to 15㎛ grain-oriented electrical steel sheet. According to claim 1,
The electrical steel sheet substrate is a grain-oriented electrical steel sheet having a residual stress in the RD direction of 1 to 50 MPa.

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