Grain-oriented electrical steel sheets with excellent iron loss characteristics

Abstract

Further reducing the iron loss of the oriented electrical steel sheet obtained by controlling the shape of the grooves, the location of the deformation introduction part, and the stress caused thereby within a certain range for domain subdivision. A directional electrical steel sheet having a steel sheet surface having a groove formed therein that extends in a direction intersecting the rolling direction (RD direction) and in which the groove depth direction is the plate thickness direction (ND direction), wherein residual stress due to deformation exists in the vicinity of said groove, wherein the pitch in the RD direction of the groove is 2 to 10 mm, the depth of the groove is 10 μm or more and 40 μm or less, and the width of the groove is 10 μm or more and 200 μm or less, wherein a region having residual stress due to compressive deformation in the RD direction of 10 MPa or more exists within a range of 10 μm in the RD direction from the wall surface of the groove (the surface of the groove at a depth of 25 to 75% of the groove depth) and a region having residual stress due to tensile deformation in the RD direction of 10 MPa or more exists within a range of 10 μm in the ND direction from the bottom surface of the groove (the surface of the groove at a depth of 75% to 100% of the groove depth) and a region having residual stress due to tensile deformation in the RD direction of 10 MPa or more exists within a range of 10 μm in the ND direction. Electrical steel sheet.

Description

Technology Field

[0001] The present invention relates to a oriented electrical steel sheet, in particular to a oriented electrical steel sheet with excellent iron loss characteristics. Background Technology

[0002] Grain-oriented electrical steel is used as a magnetic core in many electrical devices. Grain-oriented electrical steel contains approximately 1.0% to 5.0% Si and the crystal orientation of the product is {110} <001> It is a steel sheet highly concentrated in orientation. Oriented electrical steel sheets have excellent magnetic properties and are used, for example, as core materials for stationary inductors such as transformers. Therefore, regarding magnetic properties, high magnetic flux density, represented by the B8 value, and low iron loss, represented by W17 / 50, are required.

[0003] Various technological developments have been made to improve magnetic properties in these grain-oriented electrical steel sheets. In particular, accompanied by the demand for energy conservation in recent years, there is a growing need for further reduction in iron loss in grain-oriented electrical steel sheets. To achieve lower iron loss in grain-oriented electrical steel sheets, it is effective to increase the density of Goss orientation in the sheet's grain orientation to improve magnetic flux density and thereby reduce hysteresis loss.

[0004] In particular, further reduction of iron loss is required for oriented electrical steel sheets used as base materials for wound transformers. While magnetic domain refinement is performed in electrical steel sheets to reduce iron loss, since stress relief annealing is conducted during the manufacturing process of wound transformers, heat-resistant magnetic domain refinement technology is required when performing such refinement.

[0005] As a method for subdividing heat-resistant self-reinforcing agents, there are methods such as forming periodic grooves in a steel plate or introducing deformation after finishing annealing, and appropriately combining these methods has also been considered. For example, Patent Document 1 discloses that since sufficient iron loss reduction effect is not obtained with deformation alone, and rather the deformation introduction part grows into fine crystals during stress relief annealing and causes deterioration of iron loss, only grooves are formed and the deformation introduction part is not present.

[0006] Reference 2 also discloses forming a groove of a specific shape without applying deformation, as the magnetic flux density may decrease as the deformation introduction part grows into a microcrystal.

[0007] Cited reference 3 experimentally confirmed that iron loss can be reduced by introducing minute pressure deformation to a grooved steel plate under certain conditions, and used a roll equipped with protrusions as a means of imparting deformation at a surface pressure of 70 kg / mm 2 It discloses use below. In addition, surface pressure 70 kg / mm 2 If it exceeds the limit, the amount of deformation is too large, and the hysteresis loss begins to deteriorate. Prior art literature

[0008] Japanese Patent Publication No. Sho 63-76819, Japanese Patent Publication No. Hei 6-158166, Japanese Patent Publication No. Hei 7-258739 The problem to be solved

[0009] For oriented electrical steel sheets used as base materials for wound transformers, further reduction in iron loss is required. In general, for heat-resistant magnetic domain segmentation, the 180° magnetic domain width is segmented by forming linear grooves or introducing deformation, and consequently, eddy current loss, which is part of iron loss, is reduced. However, there is a demand for further reduction in iron loss.

[0010] The present invention has been made in consideration of the above problem. It aims to further reduce the iron loss of the oriented electrical steel sheet obtained by controlling the shape of the groove, the position of the deformation introduction part, and the residual stress caused thereby within a certain range for magnetic domain subdivision. means of solving the problem

[0011] The inventors have discovered that further lower iron loss can be achieved by introducing both grooves and deformations into a steel plate, and by introducing both at nearly the same location on the steel plate within a specific range of groove shape and deformation amount (residual stress).

[0012] Although it is not desirable to be bound by a specific theory, the mechanism by which iron loss is reduced by the formation of both grooves and deformation is conceived as follows. First, the magnetic domain width is subdivided by the grooves, and accordingly, eddy current loss, which is a part of iron loss, is reduced. In addition, magnetic anisotropy at the grooves and the deformation introduction site changes due to deformation introduced near the grooves (at approximately the same location as the grooves). As a result, it is thought that the effect of magnetic domain subdivision by the grooves can be enhanced.

[0013] The gist of the present invention is a oriented electrical steel sheet having a steel sheet surface having a groove formed therein that extends in a direction intersecting the rolling direction (RD direction) and the groove depth direction is the plate thickness direction (ND direction), and having residual stress due to deformation in the vicinity of said groove, wherein said groove and said residual stress due to deformation satisfy the following conditions.

[0014] a The pitch of the groove formed in the steel plate rolling direction (RD direction) is 2 to 10 mm.

[0015] b The depth of the groove formed is 10㎛ or more and 40㎛ or less, and the width of the groove is 10㎛ or more and 200㎛ or less.

[0016] c. Within a range of 10 μm in the steel plate rolling direction (RD direction) from the wall of the formed groove (the surface of the groove at a depth of 25 to 75% relative to the depth of the groove is the wall), there exists an area of ​​10% or more of residual stress due to compressive deformation in the steel plate rolling direction (RD direction) of 10 MPa or more.

[0017] d. Within a range of 10 μm in the plate thickness direction (ND direction) from the bottom surface of the formed groove (the surface of the groove at a depth of 75% to 100% of the groove depth is considered the bottom surface), there exists an area of ​​10% or more of residual stress due to tensile strain in the steel plate rolling direction (RD direction) of 10 MPa or more. Effects of the invention

[0018] According to the present invention, magnetic anisotropy in the groove and the deformation introduction part changes due to deformation introduced near the groove (at a location nearly identical to the groove), thereby enhancing the magnetic domain subdivision effect caused by the groove and reducing iron loss. Brief explanation of the drawing

[0019] FIG. 1 is a cross-sectional view (a cross-sectional view perpendicular to the extension direction of the groove) of a groove portion of a oriented electrical steel sheet according to one embodiment of the present invention. FIG. 2 is a schematic diagram of the shape of a laser irradiation part irradiated onto a steel plate to obtain a groove part and a deformation introduction part according to one embodiment of the present invention. Specific details for implementing the invention

[0020] Suitable embodiments of the present invention will be described in detail below. Furthermore, unless specifically stated otherwise, the notation "A to B" for numerical values ​​A and B shall mean "A or greater and B or less." In such notation, if a unit is attached only to numerical value B, said unit shall also apply to numerical value A.

[0021] [Composition of steel plates]

[0022] First, the oriented electrical steel sheet according to the present embodiment is not particularly limited, and an oriented electrical steel sheet made of known steel components may be used. An exemplary steel sheet that can be used for such an oriented electrical steel sheet according to the present invention will be described.

[0023] [Composition of steel plates]

[0024] The composition of typical steel sheets is described. Additionally, unless otherwise specified below, the notation "%" indicates "mass %".

[0025] The composition of the steel sheet used in the oriented electrical steel sheet according to the invention is such that the crystal orientation is {110} <001> It has a desirable composition for controlling the texture as an integrated orientation (Goss orientation), and may contain at least Si: 1.0 to 5.0%, Mn: 0.01 to 0.15%.

[0026] (Si: 1.0 to 5.0%)

[0027] The silicon (Si) content is 1.0 to 5.0%. Si reduces eddy current losses, which are one of the causes of iron loss, by increasing the electrical resistance of the steel sheet. If the Si content is less than 1.0%, it is undesirable because it becomes difficult to sufficiently suppress eddy current losses of the final oriented electrical steel sheet. If the Si content exceeds 5.0%, it is undesirable because the processability of the oriented electrical steel sheet is reduced. Therefore, the Si content is 1.0 to 5.0%, preferably 2.5 to 4.5%, and more preferably 2.7 to 4.0%.

[0028] (Mn: 0.01 to 0.15%)

[0029] The content of Mn (manganese) is 0.01 to 0.15%. Mn forms MnS and MnSe, which are inhibitors that influence secondary recrystallization. If the Mn content is less than 0.01%, it is undesirable because the absolute amount of MnS and MnSe that cause secondary recrystallization is insufficient. If the Mn content exceeds 0.15%, it is undesirable because it becomes difficult to dissolve Mn during slab heating. Furthermore, if the Mn content exceeds 0.15%, it is undesirable because the precipitation size of the inhibitors, MnS and MnSe, tends to coarsen, thereby damaging the optimal size distribution as an inhibitor. Therefore, the Mn content is 0.01 to 0.15%, and preferably 0.03 to 0.13%.

[0030] As for components other than Si and Mn, components contained in conventional oriented electrical steel sheets may be included.

[0031] For example, as components other than Si and Mn, in mass%, it may contain C: ~0.085% or less, acid-soluble Al: ~0.065% or less, N: ~0.012% or less, Cr: ~0.30% or less, Cu: ~0.40% or less, P: ~0.50% or less, Sn: ~0.30% or less, Sb: ~0.30% or less, Ni: ~1.000% or less, and S: ~0.0150% or less. In addition, B, Bi, Se, Pb, Sn, Ti, etc. may be added as other inhibitor constituent elements. The amount of addition may be appropriately adjusted, and the upper limit of the B content may be 0.080%, the upper limit of the Bi content may be 0.010%, the upper limit of the Se content may be 0.035%, the upper limit of the Pb content may be 0.10%, the upper limit of the Sn content may be 0.10%, and the upper limit of the Ti content may be 0.015%. Since these optional addition elements can be included according to known purposes, there is no need to provide a lower limit for the content of the optional addition elements, and for example, the lower limit may be 0%.

[0032] The remainder of the steel plate other than the above components is Fe and impurities. Here, "impurity elements" refers to components included in the raw materials or components introduced during the manufacturing process, and indicate components permitted within a range that does not substantially affect the present embodiment.

[0033] The chemical composition of the steel plate can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, the chemical composition is determined by measuring a square test specimen with sides of 35 mm taken from the steel plate under conditions based on a pre-made calibration curve using a Shimadzu Seisakusho ICPS-8100 (measuring device). In addition, C and S can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas melting-thermal conductivity method.

[0034] [home]

[0035] For the purpose of subdividing the grooves, a groove is formed on the surface of the steel plate, extending in a direction intersecting the rolling direction (RD direction) and having the groove depth direction as the plate thickness direction (ND direction). Additionally, the groove may be provided to intersect the rolling direction, and while the groove extension direction does not necessarily have to be orthogonal to the rolling direction, it may be provided in a direction forming an angle of 0 to 30° with the rolling perpendicular direction. Furthermore, when viewed from the plate thickness direction (when the groove is viewed as a plane), the groove does not necessarily have to have a straight shape and may have an arch shape. The following measurement of the groove shape is performed after removing at least the glass film and insulating film inside the groove from the final product by means of pickling, etc.

[0036] The above grooves are formed on the surface of the steel plate with a pitch (spacing width) of 2 to 20 mm in the steel plate rolling direction (RD direction). If the groove spacing is less than 2 mm, the magnetic domain segmentation effect becomes saturated, and almost no reduction effect on eddy current loss is obtained, which is undesirable. If it exceeds 20 mm, the magnetic domain segmentation effect decreases, resulting in insufficient improvement effect on iron loss, which is undesirable. The preferred groove spacing is 2 to 10 mm.

[0037] In addition, the pitch in the rolling direction can be measured, for example, by the following method. That is, consider any two adjacent grooves when viewed in a plane. Then, measure the rolling direction distance between the center points in the width direction of these grooves at several locations, and take the average value as the rolling direction pitch of the grooves.

[0038] FIG. 1 is a cross-sectional view (a cross-sectional view perpendicular to the extension direction of the groove) of a groove portion according to one embodiment of the present invention. In this drawing, the groove portion has a shape close to a trapezoid, but the groove shape may be arc-shaped. In one embodiment of the electrical steel sheet of the present invention, the depth D of the groove portion is in the range of 10 μm to 40 μm in the plate thickness direction (ND direction). If the depth D is less than 10 μm, the amount of magnetic poles generated from the groove wall is reduced, and magnetic domains are not subdivided, so a sufficient iron loss reduction effect is not obtained. If the depth D exceeds 40 μm, magnetic domains are subdivided, but the decrease in magnetic flux density due to groove formation is large, and a sufficient iron loss reduction effect is not obtained. The preferred depth is 15 μm to 30 μm.

[0039] (Measurement of groove depth D)

[0040] The method for measuring "depth D" according to the present invention is as follows.

[0041] An arbitrary groove was selected, and the maximum depth at a cross-section (a plane perpendicular to the extension direction of the groove) at an arbitrary point of the groove was measured using a laser microscope (a 3D laser microscope using a confocal optical system with a pinhole) as the groove depth D. The depth is measured in the normal direction of the steel plate surface (with the internal direction of the steel plate being positive), with the height of the steel plate surface adjacent to the edge of the groove set to 0.

[0042] The term "width W of the groove" as used in the present invention refers to the width of the groove at a depth (D / 2) where the groove depth D is half. The width W of the groove is in the range of 10 μm to 200 μm. If the width W is less than 10 μm, magnetic flux leaked from the groove wall enters the groove wall on the opposite side, but the amount of magnetic poles generated is reduced, and magnetic domains are not subdivided, so a sufficient iron loss reduction effect is not obtained. If the width W exceeds 200 μm, the iron loss reduction effect becomes saturated, and the laser power required to form the groove increases, only increasing manufacturing costs. A preferred width W is 30 to 100 mm.

[0043] (Measurement of groove width W)

[0044] The method for measuring “groove width W” according to the present invention is as follows.

[0045] An arbitrary groove was selected, and the groove depth D at each cross-section (a cross-section perpendicular to the extension direction of the groove) at an arbitrary point (A) of the groove and a point (B) located 3 mm away from it in the longitudinal direction of the groove was half at a depth (D / 2), the wider side of the groove was denoted as w and the narrower side as w', and the width was measured using a laser microscope (a 3D laser microscope using a confocal optical system with a pinhole). The groove width W is the average of these values.

[0046] [strain]

[0047] According to the present embodiment, a groove is formed on the surface of a steel plate for magnetic domain subdivision. To enhance the effect of this magnetic domain subdivision, a deformation is introduced near the groove (at a location nearly identical to the groove). Due to the residual stress of the deformation introduced near the groove (at a location nearly identical to the groove), the magnetic anisotropy at the groove and the deformation introduction site changes. As a result, the effect of magnetic domain subdivision by the groove can be enhanced.

[0048] In a cross-section perpendicular to the extension direction of the groove, within a range of 10 μm in the rolling direction (RD direction) from the wall of the groove (the surface of the groove at a depth of 25 to 75% relative to the depth D of the groove) there exists a region of 10% or more of residual stress due to compressive deformation in the rolling direction (RD direction) of 10 MPa or more. According to the method of forming the groove described in the following section, compressive deformation can be introduced near the wall when forming the groove, and residual stress due to such compressive deformation exists. In a range greater than 10 μm in the rolling direction from the wall, the influence of residual stress due to deformation on the groove is small, so the magnetic domain subdivision effect by the groove cannot be sufficiently enhanced. If the residual stress due to deformation is less than 10 MPa, the residual stress due to deformation is small, so the magnetic domain subdivision effect by the groove cannot be sufficiently enhanced. The upper limit of residual stress is not specifically limited, and the practical upper limit is the yield strength of the material; however, since being too large conversely worsens magnetic properties including iron loss, it may generally be 30 MPa or less. Furthermore, given the concern that excessive residual stress may affect magnetic properties, the upper limit of residual stress may be limited, and it may generally be 20 MPa or less. Also, if the area of ​​a region where residual stress of 10 MPa or more exists is less than 10 area%, the magnetic domain segmentation effect is not sufficiently obtained. The upper limit of the area% of the said region is not specifically limited, and it may be 100 area%. However, the magnetic domain segmentation effect shows signs of saturation. Additionally, if the residual stress is large and the said area% is large, the low iron loss effect due to the magnetic domain segmentation effect and the effect of worsening iron loss due to stress as described above may offset each other, thereby worsening magnetic properties including iron loss. The upper limit of the area% of the said region may be adjusted, and it may generally be 50 area% or less. In addition, depending on the desired characteristics, the upper limit of the area % of the area may be adjusted, or it may be 30% or less, or 20% or less.

[0049] In a cross-section perpendicular to the extension direction of the groove, within a range of 10 μm in the plate thickness direction (ND direction) from the bottom surface of the groove (the surface of the groove at a depth of 75 to 100% with respect to the depth D of the groove) there exists a region of 10% or more of residual stress due to tensile deformation in the rolling direction (RD direction) of 10 MPa or more. According to the method of forming the groove described in the following section, tensile deformation can be introduced near the bottom surface when forming the groove, and stress due to the compressive deformation exists. In a range greater than 10 μm in the plate thickness direction from the bottom surface, the influence of residual stress due to deformation on the groove is small, so the magnetic domain subdivision effect by the groove cannot be sufficiently enhanced. If the residual stress due to deformation is less than 10 MPa, the residual stress due to deformation is small, so the magnetic domain subdivision effect by the groove cannot be sufficiently enhanced. The upper limit of residual stress is not specifically limited, and the practical upper limit is the yield strength of the material; however, since being too large conversely worsens magnetic properties including iron loss, it may generally be 30 MPa or less. Furthermore, given the concern that excessive residual stress may affect magnetic properties, the upper limit of residual stress may be limited, and it may generally be 20 MPa or less. Also, if the area of ​​a region with residual stress of 10 MPa or more is less than 10 area%, the magnetic domain segmentation effect is not sufficiently obtained. The upper limit of the area% of the said region is not specifically limited, and it may be 100 area%. However, the magnetic domain segmentation effect shows signs of saturation. Additionally, if the residual stress is large and the said area% is large, the low iron loss effect due to the magnetic domain segmentation effect and the effect of worsening iron loss due to stress as described above may offset each other, thereby worsening magnetic properties including iron loss. The upper limit of the area% of the said region may be adjusted, and it may generally be 50 area% or less. In addition, depending on the desired characteristics, the upper limit of the area % of the area may be adjusted, or it may be 30% or less, or 20% or less.

[0050] (Measurement of residual stress due to deformation)

[0051] Residual stress due to deformation is measured by EBSD. At this time, it is preferable to perform the measurement without removing the glass film and the insulating film.

[0052] Map measurement is performed using electron beam backscatter diffraction (EBSD) with the measurement area defined as the total thickness in the plate thickness direction of a cross-section in the plate thickness direction perpendicular to the scanning direction of the energy beam (in the case of oriented electrical steel sheets, the energy beam is generally irradiated while scanning in the plate width direction, and in that case, a cross-section in the plate thickness direction perpendicular to the plate width direction) and a width twice the irradiation width of the energy beam centered at the irradiation position of the energy beam (rolling direction). During map measurement, an electron beam is irradiated in steps of 2 μm or less onto a sample in which the observation surface (steel plate surface) is tilted 70 degrees with respect to the direction of electron beam irradiation (the tilt angle is defined as 0 degrees when the incident direction of the electron beam and the cross-section of the steel plate are perpendicular), and an EBSD image is obtained. The obtained image is saved as 956×956 pixels, and deformation calculation is performed using BLG Vantage’s CrossCourt4 to calculate the deformation intensity.

[0053] As a method for deriving the area %,

[0054] (Area of ​​region with compressive strain of 10 MPa or more) / (groove depth (25 to 75% depth) × 10 µm) × 100

[0055] (Area of ​​region with tensile strain of 10 MPa or more) / (groove width (width at depth of 75% or less) × 10 µm) × 100

[0056] The formula was used. Figure 1 schematically illustrates a range within 10㎛ from the wall or bottom surface of the groove.

[0057] Regarding the calculation of the area %, the surface for which map measurement is performed is defined as the surface including the midpoint between the point where the groove formation with the laser was started and the point where it was finished.

[0058] [Method for manufacturing grain-oriented electrical steel sheets]

[0059] The manufacturing process of the oriented electrical steel sheet of the present invention is described below by way of example. Furthermore, this is merely an example of the method for manufacturing the oriented electrical steel sheet according to the present embodiment, and may be modified at will within the scope that does not impair the effects of the present embodiment.

[0060] (Casting Process S1)

[0061] In the casting process S1, a slab is prepared. An example of a method for manufacturing a slab is as follows. First, molten steel is prepared (melted). Subsequently, a slab is manufactured using the molten steel. The method of manufacturing the slab is not particularly limited, but for example, the slab may be manufactured by a continuous casting method. An ingot may be manufactured using the molten steel, and the ingot may be broken down and rolled to manufacture the slab. The thickness of the slab is not particularly limited. For example, the thickness of the slab may be 150 mm to 350 mm. The thickness of the slab is preferably 220 mm to 280 mm. As the slab, a so-called thin slab with a thickness of 10 mm to 70 mm may be used. When a thin slab is used, rough rolling before finish rolling can be omitted in the hot rolling process S2.

[0062] The composition of the slab must be such that secondary recrystallization occurs. The basic components and arbitrary elements of the slab are described in detail as follows. Additionally, the % notation used for the components refers to mass %.

[0063] Si is an important element for increasing electrical resistance and lowering iron loss. If the content exceeds 5.0%, the material becomes prone to cracking during cold rolling, making rolling impossible. On the other hand, lowering the Si content causes α→γ transformation during finish annealing, which damages the crystal orientation; therefore, a lower limit of 1.0% can be used to avoid affecting the crystal orientation during finish annealing. Accordingly, the Si content may be between 1.0% and 5.0%.

[0064] Mn and S precipitate as MnS and act as inhibitors. If the Mn content is less than 0.01% and the S content is less than 0.005%, there is a possibility that a predetermined amount of effective MnS inhibitor cannot be secured. In addition, if the Mn content is greater than 0.15% and the S content is greater than 0.015%, the solution treatment during slab heating becomes insufficient, and there is a possibility that secondary recrystallization will not be carried out stably. Therefore, the Mn content may be 0.01 to 0.15% and the S content may be 0.005 to 0.015%.

[0065] Although carbon is an element effective for controlling the primary recrystallization structure in the manufacturing process, an excessive content in the final product may have an adverse effect on magnetic properties. Therefore, the carbon content may be 0.085% or less. The preferred upper limit for the carbon content is 0.080%. Carbon is purified in the decarburization annealing process S5 and the finishing annealing process S8 described later, and after the finishing annealing process S8, it may be 0.005% or less. When the slab contains carbon, considering productivity in industrial production, the lower limit for the carbon content may be greater than 0% or 0.001%.

[0066] Acid-soluble Al is an element that functions as an inhibitor when combined with N to form AlN or (Al, Si)N. The content of acid-soluble Al may be 0.012% to 0.065%, which increases magnetic flux density.

[0067] Since 0.012% or more of N is added during steelmaking, voids in the steel sheet known as blisters occur, so the upper limit of the N content may be 0.012%. Since N can be introduced by nitriding during the manufacturing process, the lower limit is not specifically limited and may be 0%. However, since the detection limit of N is 0.0001%, the actual lower limit is 0.0001%.

[0068] In the slab, other inhibitor constituent elements such as B, Bi, Se, Pb, Sn, and Ti may be added. The amount of addition may be appropriately adjusted, and the upper limit of the B content may be 0.080%, the upper limit of the Bi content may be 0.010%, the upper limit of the Se content may be 0.035%, the upper limit of the Pb content may be 0.10%, the upper limit of the Sn content may be 0.10%, and the upper limit of the Ti content may be 0.015%. Since these optional added elements can be included in the slab according to known purposes, there is no need to provide a lower limit for the content of the optional added elements, and for example, the lower limit may be 0%.

[0069] The remainder of the chemical composition of the slab consists of Fe and impurities. In addition, the term “impurities” as used herein refers to components that are incorporated into the slab due to raw materials such as ore and scrap, or various factors of the manufacturing process when the slab is manufactured industrially, and are permitted within a range that does not substantially affect the oriented electrical steel sheet according to the present embodiment.

[0070] In the slab, any known element may be included (added) in place of some Fe, taking into account the enhancement of inhibitor function through compound formation or the influence on magnetic properties. Examples of any element included in the slab in place of some Fe include Cu, P, Sb, Sn, Cr, Ni, etc. Any one or two or more of these may be added to the slab. The upper limit of the Cu content may be 0.3%, the upper limit of the P content may be 0.5%, the upper limit of the Sb content may be 0.3%, the upper limit of the Sn content may be 0.3%, the upper limit of the Cr content may be 0.30%, and the upper limit of the Ni content may be 1.0%. Since these optional added elements can be included in the slab according to known purposes, there is no need to provide a lower limit for the content of the optional added elements, and the lower limit may be 0%.

[0071] The chemical composition of the slab can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, the chemical composition is determined by measuring a square test specimen with sides of 35 mm taken from the slab under conditions based on a calibration curve prepared in advance using a measuring device such as the ICPS-8100 manufactured by Shimadzu Seisakusho. Additionally, C and S can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas melting-thermal conductivity method.

[0072] (Hot rolling process S2)

[0073] The hot rolling process S2 is a process for obtaining a hot-rolled steel sheet by performing hot rolling on a slab heated to a predetermined heating temperature (e.g., 1100°C to 1400°C). The heating temperature during hot rolling may be 1100°C or higher from the perspective of securing the temperature during hot rolling, and may be 1280°C or lower from the perspective of not completely dissolving AlN, which is an inhibitor component. In addition, when AlN and MnS are used as the main inhibitors, the heating temperature during hot rolling may be 1300°C or higher, at which these inhibitor components are completely dissolving.

[0074] (Hot-rolled steel sheet annealing process S3)

[0075] The hot-rolled steel sheet annealing process S3 is a process of obtaining an annealed steel sheet by immediately or in a short time annealing the hot-rolled steel sheet obtained from the hot-rolling process S2. The annealing may be performed for 30 seconds to 30 minutes in a temperature range of 750°C to 1200°C. This annealing is effective for increasing the magnetic properties of the product.

[0076] (Cold rolling process S4)

[0077] The cold rolling process S4 is a process for obtaining a cold-rolled steel sheet by performing a cold rolling process (e.g., 80% to 95% of the total cold rolling rate) on the annealed steel sheet obtained in the hot-rolled steel sheet annealing process S3, or by performing multiple cold rolling (two or more times) with annealing (intermediate annealing) interposed therein. The thickness of the cold-rolled steel sheet may be, for example, 0.10 mm to 0.50 mm.

[0078] (Decarburization annealing process S5)

[0079] The decarburization annealing process S5 is a process of performing decarburization annealing on a cold-rolled steel sheet obtained from the cold rolling process S4, and obtaining a decarburization annealed steel sheet (a cold-rolled steel sheet that has undergone the decarburization annealing process) in which primary recrystallization has occurred. The decarburization annealing can be performed, for example, at 700°C to 900°C for 1 minute to 3 minutes.

[0080] By performing decarburization annealing on cold-rolled steel sheets, the carbon components contained in the cold-rolled steel sheets are removed. It is preferable to perform decarburization annealing in a humid atmosphere to remove the carbon components contained in the cold-rolled steel sheets.

[0081] (Nitriding process S6)

[0082] Nitriding process S6 is a process performed as needed to adjust the strength of the inhibitor in secondary recrystallization. Nitriding is a process that increases the nitrogen content of the cold-rolled steel sheet by about 40 ppm to 200 ppm between the start of the decarburization annealing process and the start of secondary recrystallization in the finishing annealing process. Examples of nitriding processes include annealing the decarburization annealed steel sheet in an atmosphere containing a gas capable of nitriding, such as ammonia, and applying an annealing separator containing a powder capable of nitriding, such as MnN, to the decarburization annealed steel sheet in the annealing separator application process S7 described later.

[0083] (Annealing separator application process S7)

[0084] The annealing separator application process S7 is a process of applying an annealing separator to a decarburized annealed steel sheet. As the annealing separator, for example, an annealing separator with alumina (Al2O3) as the main component may be used. After applying the annealing separator, the decarburized annealed steel sheet is wound into a coil shape and then subjected to final annealing in the subsequent final annealing process S8.

[0085] In addition, when forming a glass film containing Mg2SiO4, an annealing separator with magnesia (MgO) as the main component is used.

[0086] (Final annealing process S8)

[0087] The finishing annealing process S8 is a process of performing finishing annealing on a decarburized annealed steel plate coated with an annealing separator to induce secondary recrystallization. This finishing annealing process S8 involving secondary recrystallization proceeds with secondary recrystallization while the growth of primary recrystallized grains is suppressed by an inhibitor, thereby {110} <001> Prioritize the growth of orientation particles to dramatically improve magnetic flux density.

[0088] In addition, if magnesia (MgO) is applied in the aforementioned annealing separator application process S7, a glass film containing Mg2SiO4 is formed by this finishing annealing process S8. Furthermore, in this embodiment, such a glass film is also included in the base steel sheet (the finishing annealed steel sheet described later). Therefore, for example, when a glass film is formed on the finishing annealed steel sheet, the "surface of the finishing annealed steel sheet" refers to the surface of the glass film. By forming a glass film, it is expected that the properties of the finally obtained oriented electrical steel sheet will be further enhanced.

[0089] (Home forming process S9)

[0090] The groove forming process S9 is a process of forming a groove in a steel plate for the purpose of magnetic domain control (magnetic domain subdivision). The groove can be formed by known methods such as laser, electron beam, plasma, mechanical method, etching, etc. In the groove forming process, a deformation introduction portion may be formed near the groove.

[0091] In the flow of the above description, the groove forming process S9 is performed after the finishing annealing process S8. However, the groove forming process S9 may also be performed on a steel sheet that has undergone the cold rolling process S4 (i.e., a cold-rolled steel sheet). Even in this case, the cross-sectional shape of the linear groove G, which is ideal for magnetic domain refinement, can be maintained. Therefore, the timing for performing the groove forming process S9 may be before or after the finishing annealing process S8. However, if the insulating film application process S10 described later is to be performed, it is necessary to perform the groove forming process 9 before said process S10.

[0092] When a laser is used to form a groove, an electrical steel sheet according to the present embodiment, i.e., an electrical steel sheet having a predetermined groove and residual stress due to deformation in the vicinity thereof, can be obtained by the following examples of laser irradiation conditions.

[0093] In the laser irradiation process, a laser is irradiated onto the surface of the steel plate (only one side) to form a plurality of grooves on the surface of the steel plate that extend in a direction intersecting the rolling direction, at a desired pitch interval of 2 to 20 mm along the rolling direction.

[0094] In the laser irradiation process, the laser irradiation device may irradiate the laser light toward the surface of the steel plate by rotating the polygon mirror, and may also scan the laser light in a direction that forms an angle of 0 to 30° with the direction perpendicular to the rolling.

[0095] Simultaneously with the irradiation of laser light, an assist gas, such as air or an inert gas, may be sprayed onto the portion of the steel plate irradiated by the laser light. Examples of inert gases include nitrogen or argon. The assist gas serves to remove components that have melted or evaporated from the steel plate due to the laser irradiation. Because the laser light reaches the steel plate without being obstructed by the aforementioned melted or evaporated components due to the spraying of the assist gas, the groove and the deformation introduction area in its vicinity are stably formed.

[0096] As a laser light source, high-power lasers commonly used for industrial purposes, such as fiber lasers, YAG lasers, semiconductor lasers, or CO2 lasers, may be used. Additionally, pulsed lasers or continuous wave lasers may be used as laser light sources, provided that the groove and the deformation introduction area near it can be stably formed. As for the laser light, a single-mode laser with high focusing power is generally used for forming the groove, but in this embodiment, it is preferable to use a multi-mode laser with appropriately distributed power peaks so that the desired deformation introduction area near the groove is also obtained.

[0097] As an example of laser light irradiation conditions, for instance, the laser output is set to 200W to 3000W, and the laser beam shape is changed to a teardrop shape when forming the groove. FIG. 2 schematically illustrates an example of the shape of the beam irradiation section. As shown in FIG. 2, the front portion in the beam's propagation direction (scan direction) is made semi-circular to increase light concentration, thereby facilitating the formation of a groove with a desired width and depth. The rear portion in the beam's propagation direction (scan direction) is made semi-elliptical, with the long diameter being at least five times longer than the short diameter, thereby facilitating the formation of a deformation introduction section with a desired residual stress near the formed groove. Furthermore, the front and rear of the beam are defined based on the point where the beam diameter is maximum in the rolling direction of the steel plate (RD direction) as the reference (boundary), with the beam's propagation direction side being the front and the opposite direction being the rear. In other words, the ratio of the longer diameter of the semi-ellipse in the rear part to the diameter of the semicircle in the front part may be five times or more.

[0098] The focused spot diameter at the part where the beam diameter is maximum in the steel plate rolling direction may be set to 10㎛ to 200㎛, the focused spot diameter in the plate width direction (or beam travel direction) may be set to 30㎛ to 1000㎛, and the laser scanning speed may be set to 5m / s to 50m / s. These laser irradiation conditions are appropriately adjusted so that a desired groove and a deformation introduction part (residual stress) in the vicinity thereof are obtained.

[0099] (Insulation film application process S10)

[0100] The insulating film application process S10 is a process of forming an insulating film on the groove-forming surface of a finishing annealed steel sheet by applying a coating solution and baking it. By forming an insulating film, it is expected that the properties of the finally obtained oriented electrical steel sheet will be further enhanced. Furthermore, by selecting a film type having tensile strength-imparting capability as the insulating film, it is expected that the properties will be further improved.

[0101] Here, the coating solution preferably comprises, for example, a compound of phosphoric acid, phosphate, chromate anhydride, chromate, alumina, or silica. Baking may be performed, for example, at 350°C to 1150°C for 5 seconds to 300 seconds.

[0102] Examples

[0103] Hereinafter, a oriented electrical steel sheet according to one embodiment of the present invention will be described in more detail with reference to examples. Furthermore, the examples described below are merely illustrative examples of the oriented electrical steel sheet according to the present embodiment, and the oriented electrical steel sheet according to the present embodiment is not limited to the examples described below.

[0104] Hot rolling was performed on a slab prepared to have a chemical composition in which, by mass fraction, the oriented electrical steel sheet contains Si: 3.0%, C: 0.080%, acid-soluble Al: 0.028%, N: 0.010%, Mn: 0.12%, Cr: 0.05%, Cu: 0.04%, P: 0.01%, Sn: 0.02%, Sb: 0.01%, Ni: 0.005%, S: 0.007%, Se: 0.001%, and the remainder consists of Fe and impurities, to obtain a hot-rolled steel sheet with a thickness of 2.3 mm.

[0105] Next, an annealing treatment was performed on the above hot-rolled steel sheet under temperature conditions of heating at 1000°C for 1 minute.

[0106] After annealing treatment, cold rolling was performed to obtain a cold-rolled steel sheet with a thickness of 0.23 mm. Subsequently, a decarburization annealing treatment was performed on this cold-rolled steel sheet under a temperature condition of heating at 800°C for 2 minutes, and then an annealing separator containing magnesia (MgO) as a main component was applied to the surface of the cold-rolled steel sheet.

[0107] Next, a finishing annealing treatment was performed on a cold-rolled steel sheet coated with an annealing separator under the temperature condition of heating at 1200°C for 20 hours. As a result, a steel sheet was obtained having the chemical composition described above and having a glass film formed on its surface, with the crystal orientation controlled so that the magnetization ease axis of the crystal grains coincides with the rolling direction.

[0108] Next, a laser was irradiated onto the surface of the steel plate to impart either a groove or a deformation to the surface of the steel plate.

[0109] A fiber laser manufactured by IPG was used as the laser light irradiation device. The laser light irradiation conditions were adjusted so that the laser output was 1800W, the laser scanning speed was 50m / s, and the laser scanning pitch (spacing PL) was 3mm. The focused spot diameter at the part where the beam diameter in the steel plate rolling direction of the laser light is maximum was 40㎛, and the focused spot diameter in the plate width direction of the laser light was adjusted so that the beam aspect ratio (longer diameter of the rear semi-ellipse / diameter of the front semi-circle) shown in Table 1 was achieved. Linear grooves with a width w of approximately 50㎛ and a depth D of approximately 20㎛ were formed at 3mm intervals in a direction perpendicular to the rolling direction. However, for No. 5, the laser output was adjusted to 300W. Additionally, for Nos. 6 to 9, the depth of the grooves was varied by changing the laser scanning speed.

[0110] For the vicinity of the formed groove, residual stress due to the introduced deformation was measured using the measurement method described above. The measurement results, along with the iron loss W17 / 50, are shown in Table 1. Additionally, regarding residual stress, measurements were taken without removing the glass film, and regarding the shape of the groove (depth of the groove), measurements were taken after removing the glass film.

[0111] [Self-Assessment]

[0112] A sample with a width of 60 mm × a length of 300 mm was taken, including the center position of the plate width of the oriented electrical steel sheet of each test number. The length of the sample was parallel to the rolling direction.

[0113] Using this sample, the magnetic flux density (T) was determined by a single-plate magnetic characteristic test (SST test) in accordance with JIS C 2256 (2011). Specifically, the magnetic flux density (T) was determined by applying a magnetic field of 800 A / m to the sample.

[0114] In addition, using the above sample, the iron loss W when the frequency is 50 Hz and the maximum magnetic flux density is 1.7 T in accordance with JIS C 2256 (2011). 17 / 50 (W / kg) was measured.

[0115]

[0116] From this result, it can be seen that in the electrical steel sheet according to the embodiment of the present invention, where residual stress due to deformation exists in the groove and its vicinity, the iron loss is further reduced compared to the comparative example.

Claims

Claim 1 A oriented electrical steel sheet having a steel sheet surface having a groove formed therein that extends in a direction intersecting the rolling direction and in which the groove depth direction is the plate thickness direction, wherein residual stress due to deformation exists in the vicinity of said groove, the pitch of said groove in the steel sheet rolling direction is 2 to 10 mm, the depth of said groove is 10 μm or more and 40 μm or less, the width of said groove is 10 μm or more and 200 μm or less, and within a range of 10 μm in the rolling direction from the wall surface of said groove (wherein the surface of said groove at a depth of 25 to 75% of the depth of said groove is defined as the wall surface), there exists an area % or more of a region in which residual stress due to compressive deformation in said rolling direction of 10 MPa or more exists, and within a range of 10 μm in the plate thickness direction from the bottom surface of said groove (wherein the surface of said groove at a depth of 75% to 100% of the depth of said groove is defined as the bottom surface), there exists a tensile stress in said rolling direction of 10 MPa or more A oriented electrical steel sheet characterized by having an area of ​​10% or more of residual stress due to deformation.

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