WO2024111630A1

WO2024111630A1 - Grain-oriented electrical steel sheet

Info

Publication number: WO2024111630A1
Application number: PCT/JP2023/042012
Authority: WO
Inventors: 尚茂木; 将嵩岩城; 直樹和田; 克高橋
Original assignee: 日本製鉄株式会社
Priority date: 2022-11-22
Filing date: 2023-11-22
Publication date: 2024-05-30

Abstract

The present invention further reduces iron loss of an obtained grain-oriented electrical steel sheet by controlling the shape of grooves to be within a predetermined range in order to subdivide a magnetic domain.　This grain-oriented electrical steel sheet comprises a steel sheet that has a steel sheet surface having formed therein grooves which extend in a direction intersecting the rolling direction and in which the groove depth direction is the sheet thickness direction. When the steel sheet surface is viewed in the thickness direction, the grain-oriented electrical steel sheet has groove groups each formed of a plurality of said grooves arranged in the sheet width direction, and the groove groups are arranged apart from each other in the rolling direction. In at least 75% of the groove groups, the average width of the grooves forming the groove groups is 42-62 μm. The grooves forming said groove groups are arranged so as to, in a projection plane in which the groove depth direction is parallel to the direction in which the grooves extend, overlap grooves adjacent thereto. In the projection plane, the size of overlap between a first groove and a second groove is 5-30 mm, and the size of undulation of edges of the grooves forming the groove groups is 0.5-5.0 μm.

Description

Grain-oriented electrical steel sheet

The present invention relates to grain-oriented electrical steel sheets, and in particular to grain-oriented electrical steel sheets that have excellent iron loss characteristics after stress relief annealing.

Grain-oriented electrical steel sheets are used as magnetic cores in many electrical devices. Grain-oriented electrical steel sheets are steel sheets that contain approximately 1.0% to 5.0% Si and have a highly concentrated crystal orientation in the {110}<001> direction. Grain-oriented electrical steel sheets have excellent magnetic properties and are used, for example, as core materials for static inductors such as transformers. For this reason, the magnetic properties required are a high magnetic flux density, as represented by the _B8 value, and a low iron loss, as represented by W17/50.

In order to improve the magnetic properties of such grain-oriented electrical steel sheets, various technological developments have been made. In particular, with the recent demand for energy conservation, there is a demand for further reduction in iron loss in grain-oriented electrical steel sheets. To reduce iron loss in grain-oriented electrical steel sheets, it is effective to increase the concentration of crystal grains in the Goss orientation in the steel sheet, improve magnetic flux density, and reduce hysteresis loss.

Grain-oriented electromagnetic steel sheets, which are used as the base material for wound transformers, are particularly required to have even lower iron loss. Magnetic domain refinement is performed on electromagnetic steel sheets to reduce iron loss, but wound transformers are annealed to remove distortion during the manufacturing process, so when performing magnetic domain refinement, heat-resistant magnetic domain refinement technology is required.

For example, as disclosed in Patent Document 1, it is widely known that a laser irradiation method can be used to relatively easily and stably form grooves on the surface of a steel sheet and control the magnetic domains.

Patent Document 2 discloses a grain-oriented electrical steel sheet with grooves that, when grooves are formed on the surface of the steel sheet, is highly productive and can improve iron loss.

International Publication No. 2016/1711124 International Publication No. 2016/1711129

Grain-oriented electrical steel sheets used as the base material for wound transformers are required to have even lower iron loss. Heat-resistant magnetic domain refinement is generally achieved by forming linear grooves or introducing distortion to refine the magnetic domain width by 180°, which reduces eddy current loss, which is part of the iron loss. However, there is a demand for even lower iron loss.

The present invention was made in consideration of the above problems. The purpose of the invention is to further reduce the iron loss of the resulting grain-oriented electrical steel sheet by controlling the shape of the grooves within a certain range in order to subdivide the magnetic domains.

The inventors discovered that the shape of the groove (particularly the groove width and the undulation of the groove edge, which is the boundary between the steel plate surface and the groove) and the overlap between adjacent grooves affect iron loss, and came up with the invention that can reduce iron loss by limiting these amounts.

The gist of the present invention is
The steel plate has a steel plate surface on which a groove is formed extending in a direction intersecting the rolling direction and having a groove depth direction in the plate thickness direction,
When the steel plate surface is viewed from the plate thickness direction, a groove group is formed by arranging a plurality of the grooves in the plate width direction,
A grain-oriented electrical steel sheet in which the groove groups are arranged at intervals in the rolling direction,
In at least 75% of the groove groups,
The grooves constituting the groove group have an average width of 42 to 62 μm;
the grooves constituting the groove group are arranged so as to overlap with adjacent grooves on a projection plane that is parallel to the groove extension direction and the groove depth direction,
In this grain-oriented electrical steel sheet, an end portion in the sheet width direction of the steel sheet is defined as a reference end portion, and adjacent grooves among the plurality of grooves in the groove group are defined as a first groove and a second groove in the order of proximity to the reference end portion,
Two groove ends in a direction in which the groove extends (longitudinal direction) of each groove constituting the groove group are designated as a first groove end and a second groove end in the order of proximity to the reference end portion,
an overlapping margin between the first groove end of the second groove and the second groove end of the first groove is 5 to 30 mm on the projection plane;
The grooves constituting the groove group have an edge waviness of 0.5 to 5.0 μm.

According to the present invention, it has been discovered that the shape of the groove (particularly the groove width and the undulation of the groove edge, which is the boundary between the steel plate surface and the groove) and the overlap between adjacent grooves affect iron loss, and by limiting these amounts, pinning during magnetic domain wall movement is eliminated, thereby reducing iron loss.

FIG. 2 is a schematic diagram showing grooves formed on a steel sheet surface of a grain-oriented electrical steel sheet according to an embodiment of the present invention. 2 is a diagram showing a cross-sectional shape of a groove (longitudinal direction) taken along line AA in FIG. 1. 2 is a diagram showing a cross-sectional shape of a groove (short side direction) taken along line BB shown in FIG. 1. FIG. 1 is an explanatory diagram regarding the definition of a groove. FIG. 1 is an explanatory diagram regarding the definition of a groove. FIG. 1 is an explanatory diagram regarding the definition of a groove. FIG. 1 is an explanatory diagram regarding the definition of a groove. FIG. 4 is a diagram showing groove longitudinal projection lines of adjacent grooves of the grain-oriented electrical steel sheet according to the present embodiment. FIG. 13 is a diagram showing the relationship between the average width of a groove and the waviness of the edge of the groove. 11 is a diagram showing the relationship between the overlapping margin between adjacent grooves and the waviness of the groove edges. FIG.

The preferred embodiment of the present invention will be described in detail below. Unless otherwise specified, the notation "A-B" for numerical values A and B means "greater than or equal to A and less than or equal to B." In such notations, when a unit is added only to numerical value B, the unit is also applied to numerical value A.

[Steel plate composition]
First, the grain-oriented electrical steel sheet according to the present embodiment is not particularly limited, and grain-oriented electrical steel sheets made of known steel components can be used. Such steel sheets that can be used for the grain-oriented electrical steel sheet according to the present invention will be described by way of example.

[Steel plate composition]
The chemical composition of a typical steel sheet will be described below. Note that, hereinafter, unless otherwise specified, the notation "%" represents "mass %".

The steel sheet used in the grain-oriented electrical steel sheet of the present invention has a composition that is favorable for controlling the crystal orientation to a Goss texture that is concentrated in the {110}<001> orientation, and can contain at least Si: 1.0-5.0% and Mn: 0.01-0.15%.

(Si: 1.0 to 5.0%)
The content of Si (silicon) is 1.0 to 5.0%. Si increases the electrical resistance of the steel sheet, thereby reducing eddy current loss, which is one of the causes of iron loss. If the content of Si is less than 1.0%, it is not preferable because it becomes difficult to sufficiently suppress the eddy current loss of the final grain-oriented electrical steel sheet. If the content of Si is more than 5.0%, it is not preferable because the workability of the grain-oriented electrical steel sheet decreases. Therefore, the content of Si is 1.0 to 5.0, preferably 2.50 to 4.50%, and more preferably 2.70 to 4.00%.

(Mn: 0.01 to 0.15%)
The content of Mn (manganese) is 0.01 to 0.15%. Mn forms MnS and MnSe, which are inhibitors that affect secondary recrystallization. If the content of Mn is less than 0.01%, the absolute amount of MnS and MnSe that cause secondary recrystallization is insufficient, which is not preferable. If the content of Mn is more than 0.15%, it is not preferable because it becomes difficult to dissolve Mn during slab heating. In addition, if the content of Mn is more than 0.15%, the precipitation size of MnS and MnSe, which are inhibitors, tends to become coarse, which is not preferable because the optimal size distribution as an inhibitor is impaired. Therefore, the content of Mn is 0.01 to 0.15%, preferably 0.03 to 0.13%.

The components other than Si and Mn may be the components contained in ordinary grain-oriented electrical steel sheets.
For example, as components other than Si and Mn, the following may be contained in mass %: 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 added elements may be contained according to known purposes, there is no need to set a lower limit for the content of the optional added elements, and the lower limit may be, for example, 0%.

The remainder of the steel plate other than the above components is Fe and impurities. Here, impurity elements refer to components contained in the raw materials or components mixed in during the manufacturing process, and are permissible to the extent that they do not substantially affect this embodiment.

The chemical composition of steel plate can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Specifically, the chemical composition is determined by measuring a 35 mm square test piece taken from the steel plate using a Shimadzu ICPS-8100 or other measuring device under conditions based on a pre-created calibration curve. C and S can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas fusion-thermal conductivity method.

[groove]
Hereinafter, grooves according to embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the configurations disclosed in the present embodiments, and various modifications are possible without departing from the spirit of the present invention.

FIG. 1 is a plan view of a grain-oriented electromagnetic steel sheet 1 according to this embodiment. FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1. In the figure, the rolling direction of the grain-oriented electromagnetic steel sheet 1 is defined as X, the sheet width direction of the grain-oriented electromagnetic steel sheet 1 (direction perpendicular to the rolling direction in the same plane) as Y, and the sheet thickness direction of the grain-oriented electromagnetic steel sheet 1 (direction perpendicular to the XY plane) as Z. The grain-oriented electromagnetic steel sheet 1 according to this embodiment has grooves 3 for magnetic domain refinement on the steel sheet surface 2a. FIG. 1 is a schematic diagram showing the grooves 3 when the grain-oriented electromagnetic steel sheet according to this embodiment is viewed from the sheet thickness direction Z (hereinafter sometimes referred to as "planar view").

As shown in FIG. 1, when the groove 3 is viewed from the plate thickness direction Z (when the groove 3 is viewed in a plan view), the extension direction of the groove 3 (arrow L shown in FIG. 1) is called the groove longitudinal direction L. When the groove 3 is viewed in a plan view, the direction perpendicular to the groove longitudinal direction L of the groove 3 (arrow Q shown in FIG. 1) is called the groove width direction Q. Although the steel plate surface 2a and the groove 3 of an actual grain-oriented electromagnetic steel plate are not uniformly formed, at least a part of them is shown in FIG. 1 to FIG. 3 and FIG. 5 to FIG. 8 in order to explain the features of the invention. In addition, the groove 3 may have a bow-like shape when viewed from the plate thickness direction Z (when the groove 3 is viewed in a plan view). However, in this embodiment, for convenience of explanation, a groove 3 having a linear shape is illustrated.

The grain-oriented electrical steel sheet 1 comprises a steel sheet (base steel) 2 whose crystal orientation has been controlled by a combination of cold rolling and annealing so that the magnetization easy axis of the crystal grains coincides with the rolling direction X, and has grooves 3 on the surface of the steel sheet 2 (steel sheet surface 2a).

As shown in FIG. 1, the grooves 3 extend in a direction intersecting the rolling direction X and are formed so that their depth direction is the plate thickness direction Z. When the steel plate surface 2a is viewed from the plate thickness direction Z, the grain-oriented electrical steel sheet 1 has a groove group 30 composed of a plurality of grooves 3 arranged in the plate width direction Y, and the groove groups are arranged at intervals in the rolling direction. The extension direction of the grooves 3 is not particularly limited, but when the plate width direction Y is set to 0°, the angle between the extension direction of the plate width grooves 3 and the plate width direction Y may be in the range of 0° to ±60°. The grooves 3 constituting the groove group 30 are approximately parallel to each other, and may have an angle difference of several degrees from approximately parallel, and for example, an angle difference within ±5° or ±3° is allowed.

In 75% or more of all groove groups,
The grooves constituting the groove group have specific average groove widths, overlaps between adjacent grooves, and waviness of the groove edges, which makes it possible to effectively improve iron loss. Note that the groove shape is measured after removing at least the glass coating and insulating coating inside the grooves from the final product by pickling or the like.
In the following description, terms are defined.

(Average Groove Depth D)
The depth of the groove 3 refers to the length in the plate thickness direction Z from the height of the steel plate surface 2a to the surface (bottom 4) of the groove 3, as shown in the example of FIG. 2. The average groove depth D may be measured as follows. When the groove 3 is viewed from the plate thickness direction Z (when the groove 3 is viewed in plan), the observation range is set to a part of the groove 3. It is desirable to set the observation range to a region excluding the end portion in the groove longitudinal direction L of the groove 3 (i.e., a region where the shape of the groove bottom is stable). For example, the observation range may be an observation region that is approximately the center of the groove longitudinal direction L and has a length in the groove longitudinal direction L of about 30 μm to 300 μm. Next, a height distribution (groove depth distribution) within the observation range is obtained using a laser microscope, and the maximum groove depth within this observation range is obtained. The same measurement is performed in at least three regions, more preferably 10 regions, by changing the observation range. Then, the average value of the maximum groove depth in each observation region is calculated, and this is defined as the average groove depth D. In order to obtain the desired effect of refining the magnetic domains, the average groove depth D of the grooves 3 in this embodiment is preferably, for example, 5 μm or more and 100 μm or less, and more preferably more than 10 μm and 40 μm or less.
In order to measure the distance between the steel plate surface 2a and the surface of the groove 3, it is necessary to measure the position (height) of the steel plate surface 2a in the plate thickness direction Z in advance. For example, the position (height) in the plate thickness direction Z may be measured using a laser microscope for each of a plurality of points on the steel plate surface 2a within each observation range, and the average value of the measurement results may be used as the height of the steel plate surface 2a. In addition, in this embodiment, the groove short cross section is used when measuring the groove average width W as described later, so the steel plate surface 2a may be measured from this groove short cross section. In addition, when observing a steel plate sample with a laser microscope, it is preferable that the two plate surfaces (the observation surface and the back surface) of the steel plate sample are approximately parallel.

(Average groove width W)
The width of the groove 3 refers to the length of the groove opening in the groove short-side direction Q when the groove 3 is viewed in a cross section perpendicular to the groove long-side direction L (groove width direction cross section or groove short-side cross section) as shown in the example of Fig. 3. The average groove width W may be measured as follows. As with the average groove depth D, when the groove 3 is viewed from the plate thickness direction Z (when the groove 3 is viewed in plan), the observation range is set to a part of the groove 3. It is desirable to set the observation range to a region excluding the end portions of the groove 3 in the groove long-side direction L (i.e., a region where the shape of the groove bottom is stable).
For example, the observation range may be an observation region that is approximately at the center of the groove longitudinal direction L and has a length in the groove longitudinal direction L of about 30 μm to 300 μm. Next, a laser microscope is used to obtain a groove short-side cross section perpendicular to the groove longitudinal direction L at any one location within the observation range (for example, the position of the maximum groove depth in the observation region). The length of the groove opening is obtained from the contour curves of the steel sheet surface 2a and the groove 3 that appear in this groove short-side cross section.

Specifically, a low-pass filter (cutoff value λs) is applied to the measured cross-sectional curve MCL that forms the contour of the steel plate surface 2a and groove 3 that appear in the short cross-section of the groove to obtain a cross-sectional curve, and then a band-pass filter (cutoff values λf, λc) is applied to the cross-sectional curve to remove long and short wavelength components from the cross-sectional curve, resulting in a waviness curve WWC that forms the contour of the groove 3 in the short cross-section of the groove, as shown in Figure 3. A waviness curve is a type of contour curve that is suitable for simplifying the contour shape itself with a smooth line.

As shown in FIG. 3 , on the waviness curve WWC of the groove 3 at the short cross section of the groove, the length _Wn of the line segment connecting two points (third point 33 and fourth point 34) separated by the groove 3 on the steel sheet surface 2a is found (groove opening).
Similar measurements are performed in at least three regions, more preferably ten regions, by changing the observation range. Then, the average value of the groove opening in each observation region is calculated, and this is defined as the average groove width W. In this embodiment, the average groove width W of the grooves 3 is, for example, 42 μm or more and 62 μm or less in order to preferably obtain the effect of magnetic domain refinement.
In order to measure the two points (third point 33 and fourth point 34) separated by the groove 3 on the steel sheet surface 2a, it is necessary to measure the position (height) of the steel sheet surface 2a in the sheet thickness direction Z in advance. For example, the position (height) in the sheet thickness direction Z may be measured for each of a plurality of points on the steel sheet surface 2a on the waviness curve in each groove short cross section, and the average value of the measurement results may be used as the height of the steel sheet surface 2a.

(Groove overlap)
The grooves 3 constituting the groove group 30 are arranged so that adjacent grooves overlap when viewed on a projection plane (cross section indicated by dashed line 11a in Figure 1) that is parallel to the groove extension direction (or groove longitudinal direction L) and the groove depth direction (or plate thickness direction Z).
With this configuration, when multiple grooves 3 are formed in the plate width direction Y, the grain-oriented electrical steel sheet 1 can ensure that the grooves 3 are formed in the plate width direction Y, thereby improving iron loss.

When one end of the steel plate in the plate width direction Y is defined as the reference end 21a, the grooves 3 constituting the groove group 30 are formed in the order of proximity to the reference end 21a, that is, the first groove 31, the second groove 32, and the n-th groove 3n. As shown in Fig. 1, the first groove 31, the second groove 32, and the n-th groove 3n are arranged such that the ends of adjacent grooves 3 overlap each other on a projection plane that is parallel to the groove extension direction (or groove longitudinal direction L) and the groove depth direction (or plate thickness direction Z).
As shown in FIG. 1 , the groove groups 30 are arranged so as to be spaced apart from each other in the rolling direction X.

The grooves 3 can be arranged so that the ends of adjacent grooves 3 overlap on a projection plane that is parallel to the groove extension direction (or groove longitudinal direction L) and the groove depth direction (or plate thickness direction Z), thereby effectively improving iron loss.

When a plane parallel to the groove longitudinal direction L and the plate thickness direction Z is used as a projection plane and the contour of the groove longitudinal direction L of the groove 3 is projected onto this projection plane, the contour of the groove longitudinal direction L projected onto the projection plane is defined as the groove longitudinal projection line LWP. The groove longitudinal projection line LWP may be measured as follows. When the groove 3 is viewed in plan from the plate thickness direction Z (see FIG. 6), an area including the entire groove 3 or an area including the end of the groove 3 (i.e., an area including from the start of the groove longitudinal direction L of the groove 3 to the area where the shape of the groove bottom is stable) is set as the observation range. Within this observation range, multiple virtual lines are virtually set along the groove longitudinal direction L. The virtual lines L1 to Ln can be set at any height in the plate thickness direction Z. Then, of the above virtual lines L1 to Ln, a virtual line that is along the groove longitudinal direction L and satisfies the condition that the average depth of the groove is maximized is selected as the groove reference line BL. For example, as shown in FIG. 6, when the groove depth D2 is the maximum among the groove depths D1 to Dn obtained for each of the virtual lines L1 to Ln, the virtual line L2 is defined as the groove reference line BL. The curve obtained when the groove depth distribution along the selected virtual line is projected onto the projection plane as the overall contour (waviness curve) of the groove 3 in the groove longitudinal direction L is defined as the groove longitudinal projection line LWP. Note that it is preferable to set the observation range as an area including the entire two adjacent grooves, or an area including the overlapping ends of the two adjacent grooves (i.e., an area including an area where the shape of the groove bottom of one groove is stable, an area where the groove ends of the two adjacent grooves overlap, and an area where the shape of the groove bottom of the other groove is stable). The two groove ends in the groove longitudinal direction L of each groove constituting the groove group 30 are defined as the first groove end and the second groove end in the order of proximity to the reference end 21a. 8 shows a schematic diagram of the first groove end 31a and the second groove end 31b of the first groove longitudinal projection line LWP1 of the first groove 31, and the first groove end 32a and the second groove end 32b of the second groove longitudinal projection line LWP2 of the second groove 32. Note that, in order to explain the positional relationship between adjacent grooves in the groove longitudinal direction L, FIG. 8 shows only two

grooves

31, 32 adjacent to each other in the groove longitudinal direction L among the multiple grooves 3 of the grain-oriented electrical steel sheet 1 according to this embodiment.

As shown in FIG. 1, in the grain-oriented electromagnetic steel sheet 1 according to this embodiment, the second groove end 31b of the first groove 31 and the first groove end 32a of the second groove 32 adjacent in the groove longitudinal direction L are arranged so as to overlap in the groove longitudinal direction L. FIG. 1 illustrates an example of an arrangement in which the ends of the first groove 31 and the second groove 32 adjacent in the groove longitudinal direction L do not overlap when viewed from the plate thickness direction Z. However, the ends of the first groove 31 and the second groove 32 may overlap when viewed from the plate thickness direction Z. For example, if the ends of the first groove 31 and the second groove 32 completely overlap when viewed from the plate thickness direction Z, they can be considered to be a single groove.

　Adjacent grooves overlap in the groove longitudinal direction L so that the position in the groove longitudinal direction L of the first groove end 32a of the second groove 32 on the second groove longitudinal projection line LWP2 is located closer to the reference end 21a than the position in the groove longitudinal direction L of the second groove end 31b of the first groove 31 on the first groove longitudinal projection line LWP1. As shown in FIG. 8, the area R where the first groove 31 and the second groove 32 overlap in the groove longitudinal direction L is between the second groove end 31b of the first groove 31 and the first groove end 32a of the second groove 32.

In the overlapping region R, the distance in the longitudinal direction L between the second groove end 31b of the first groove 31 and the first groove end 32a of the second groove 32 is called the "overlap". The grain-oriented electromagnetic steel sheet 1 according to this embodiment has an "overlap" of 5 to 30 mm. In the grain-oriented electromagnetic steel sheet 1, a plurality of grooves are formed in the groove longitudinal direction L, and

adjacent grooves

31, 32 overlap each other, and the "overlap" is 5 to 30 mm, so that iron loss can be kept low. If the overlap is less than 5 mm, the effect of magnetic domain refinement decreases as the groove end is approached, and the magnetic domains are difficult to refine. Therefore, the magnetic domains in the overlap area are not refined, and the effect of reducing iron loss cannot be expected. On the other hand, if the overlap is more than 30 mm, the number of places where the groove spacing is narrow increases relatively. If the groove spacing is narrow, the magnetic domains are refined, but the magnetic domain walls are fixed in the groove area, and the magnetic domain walls are difficult to move in response to changes in the external magnetic field. This increases the hysteresis loss that constitutes the iron loss, negating the effect of magnetic domain refinement. As a result, iron loss increases and no improvement in magnetic properties can be expected. In other words, by arranging multiple grooves 3 in the groove longitudinal direction L and arranging both ends of adjacent grooves so that they overlap moderately in the groove longitudinal direction L, it is possible to improve iron loss in the same way as when a single groove of uniform depth is formed in the groove longitudinal direction L.

The distance in the rolling direction X between the first groove 31 and the second groove 32 adjacent in the plate width direction Y (distance F1 shown in FIG. 1) may be set to be smaller than the distance in the rolling direction X between adjacent groove groups 30 in the rolling direction X (distance F2 shown in FIG. 1). When the average depth of the groove group of the

multiple grooves

31, 32, ..., 3n provided in the plate width direction Y is DA, the first groove 31 and the second groove 32 may be arranged so that the distance between the first groove end 32a of the second groove 32 and the reference end 21a of the steel plate 2 is shorter than the distance between the second groove end 31b of the first groove 31 and the reference end 21a of the steel plate 2. This allows multiple grooves 3 to be arranged in the plate width direction Y, and both ends of the

adjacent grooves

31 and 32 to overlap in the plate width direction Y, improving iron loss in the same way as when one groove of uniform depth is formed in the plate width direction Y.

(Waviness of the groove edge)
The edge of the groove 3, i.e., the ridge line (boundary line) between the groove 3 and the steel sheet 2, is not necessarily linear as shown in Fig. 6, but may be curved and wavy. Therefore, it is necessary to clarify the wavy edge of the groove when the groove 3 is viewed from the plate thickness direction Z (when the groove 3 is viewed in plan). Below, a method for identifying the wavy edge of the groove when the groove 3 is viewed in plan will be described.

When the groove 3 is viewed from the plate thickness direction Z (when the groove 3 is viewed in a plane), the edge of the groove 3 in the groove extension direction is measured using a laser microscope or the like, and a measured edge curve MEL forming the edge of the groove 3 as shown in FIG. 7 is obtained. Here, the boundary between the groove 3 and the steel plate 2 is the point where the position (height) of the steel plate surface 2 starts to drop toward the bottom of the groove. The connection of these boundaries is the ridge line (boundary line) between the groove 3 and the steel plate 2, and defines the edge of the groove. In order to measure the edge of the groove 3, i.e., the ridge line (boundary line) between the groove 3 and the steel plate 2, it is necessary to measure the position (height) of the steel plate surface 2 in the Z direction in advance. For example, for each of multiple points on the steel plate surface 2 within the observation range 50, the position (height) in the Z direction may be measured using a laser surface roughness measuring device, and the average value of these measurement results may be used as the height of the steel plate surface 2. If the groove 3 is longer in the groove extension direction than the observation field of the laser microscope or the like, the groove 3 may be divided into several observation ranges 50 from one end 31a to the other end 31b and observed. For example, the observation range 50 may be an observation area whose length in the groove extension direction is about 300 μm.

After applying a low-pass filter (cutoff value λs) to the measured edge curve MEL obtained as described above to obtain an edge curve, a bandpass filter (cutoff values λf, λc) is applied to the edge curve to remove long and short wavelength components from the measured edge curve, and a waviness curve EWC that forms the edge contour in the groove extension direction of the groove 3 is obtained as shown in FIG. 7. The waviness curve is a contour curve that is suitable for simplifying the contour shape itself with a smooth line. On the other hand, among the virtual lines L1 to Ln, a virtual line that is aligned in the groove longitudinal direction L and satisfies the condition that the difference with the measured edge curve MEL of the groove is minimized is selected as the edge reference line EBL. For example, as shown in FIG. 6, for each of the virtual lines L1 to Ln, the virtual line Ln that has the smallest displacement difference with the measured edge curve MEL by the least squares method is defined as the edge reference line EBL. As shown in FIG. 7, by using the difference between the edge reference line EBL and the waviness curve EWC, the waviness of the groove edge can be evaluated with high accuracy.

(Rag)
In this embodiment, the waviness of the groove edge is 0.5 to 5.0 μm. If the waviness of the groove edge is less than 0.5 μm, the effect as a starting point for the generation of domain walls is small, and magnetic domains may not be sufficiently refined. If the waviness of the groove edge is more than 5.0 μm, pinning occurs that inhibits domain wall movement during the magnetization process of the magnetic steel sheet, making it difficult to reduce iron loss.

The waviness of the groove edge can be defined by the following formula (1).

[Method of manufacturing grain-oriented electrical steel sheet]
The manufacturing process of the grain-oriented electrical steel sheet of the present invention will be described below by way of example. Note that this is merely one example of the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment, and may be arbitrarily modified as long as the effects of the present embodiment are not impaired.

(Casting process S1)
In the casting step S1, a slab is prepared. An example of a method for producing a slab is as follows. First, molten steel is produced (melted). Then, a slab is produced using the molten steel. The method for producing the slab is not particularly limited, and for example, the slab may be produced by a continuous casting method. An ingot may be produced using the molten steel, and the ingot may be bloomed to produce a slab. The thickness of the slab is not particularly limited. The thickness of the slab may be, for example, 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 having 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 step S2.

The composition of the slab may be any composition that allows secondary recrystallization to occur. The basic components and optional elements of the slab are specifically described below. Note that the percentages used for the components refer to mass percent.

Si is an important element for increasing electrical resistance and reducing iron loss. If the content exceeds 5.0%, the material will be prone to cracking during cold rolling, making rolling impossible. On the other hand, lowering the amount of Si will cause α→γ transformation during final annealing, impairing the crystal orientation, so the lower limit may be set at 1.0%, which does not affect the crystal orientation during final annealing. Therefore, the Si content may be 1.0-5.0%.

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%, it may not be possible to secure the required amount of effective MnS inhibitors. Furthermore, if the Mn content is more than 0.15% and the S content is more than 0.150%, solutionization during slab heating may be insufficient, and secondary recrystallization may not occur stably. Therefore, the Mn content may be 0.01-0.15%, and the S content may be 0.005-0.150%.

Although C is an effective element for controlling the primary recrystallization structure in the manufacturing process, excessive C content in the final product may adversely affect the magnetic properties. Therefore, the C content may be 0.085% or less. The preferred upper limit of the C content is 0.080%. C is purified in the decarburization annealing step S5 and the finish annealing step S8 described below, and becomes 0.005% or less after the finish annealing step S8. When the slab contains C, the lower limit of the C content may be more than 0%, or may be 0.001%, taking into account the productivity in industrial production.

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

If 0.012% or more of N is added during steelmaking, voids in the steel plate called blisters will form, so the upper limit of the N content may be 0.012%. Since N can be added by nitriding during the manufacturing process, there is no particular lower limit and it may be 0%. However, since the detection limit for N is 0.0001%, the effective lower limit is 0.0001%.

Other inhibitor constituent elements such as B, Bi, Se, Pb, Sn, and Ti can also be added to the slab. The amounts added can be adjusted as appropriate, and the upper limit for the B content can be 0.080%, the upper limit for the Bi content can be 0.010%, the upper limit for the Se content can be 0.035%, the upper limit for the Pb content can be 0.10%, the upper limit for the Sn content can be 0.10%, and the upper limit for the Ti content can be 0.015%. These optional added elements can be added to the slab according to known purposes, so there is no need to set a lower limit for the content of the optional added elements, and the lower limit can be 0%, for example.

The remainder of the chemical composition of the slab consists of Fe and impurities. Note that "impurities" here refer to components that are mixed into the slab due to various factors in the manufacturing process and raw materials such as ores and scraps when the slab is industrially manufactured, and are acceptable to the extent that they do not substantially affect the grain-oriented electrical steel sheet according to this embodiment.

　In consideration of the strengthening of the inhibitor function by compound formation and the effect on magnetic properties, the slab may contain (add) a known optional element in place of a portion of Fe. Examples of optional elements to be contained in the slab in place of a portion of Fe include Cu, P, Sb, Sn, Cr, and Ni. Any one 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 may be contained in the slab according to a known purpose, there is no need to set a lower limit for the content of the optional added element, and the lower limit may be 0%.

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 35 mm square test piece taken from the slab using a Shimadzu ICPS-8100 or other measuring device under conditions based on a previously prepared calibration curve. C and S can be measured using the combustion-infrared absorption method, and N can be measured using the inert gas fusion-thermal conductivity method.

(Hot rolling process S2)
The hot rolling step S2 is a step of hot rolling a slab heated to a predetermined heating temperature (for example, 1100°C to 1400°C) to obtain a hot-rolled steel sheet. The heating temperature during hot rolling may be, for example, 1100°C or higher from the viewpoint of ensuring the temperature during hot rolling, and may be 1280°C or lower from the viewpoint of not completely dissolving AlN, which is an inhibitor component. Note that, when AlN and MnS are used as main inhibitors, the heating temperature during hot rolling may be 1300°C or higher at which these inhibitor components are completely dissolved.

(Hot-rolled steel sheet annealing process S3)
The hot-rolled steel sheet annealing step S3 is a step in which the hot-rolled steel sheet obtained in the hot rolling step S2 is annealed immediately or for a short time to obtain an annealed steel sheet. The annealing may be performed in a temperature range of 750°C to 1200°C for 30 seconds to 30 minutes. This annealing is effective for improving the magnetic properties of the product.

(Cold rolling process S4)
The cold rolling step S4 is a step of obtaining a cold-rolled steel sheet by performing a single cold rolling process or performing multiple cold rolling processes (two or more times) via annealing (intermediate annealing) (for example, a total cold rolling rate of 80% to 95%) on the annealed steel sheet obtained in the hot-rolled steel sheet annealing step S3. The thickness of the cold-rolled steel sheet may be, for example, 0.10 mm to 0.50 mm.

(Decarburization annealing step S5)
The decarburization annealing step S5 is a step of performing decarburization annealing on the cold-rolled steel sheet obtained in the cold rolling step S4 to obtain a decarburization annealed steel sheet in which primary recrystallization has occurred (a cold-rolled steel sheet that has been subjected to the decarburization annealing step). The decarburization annealing may be performed at 700°C to 900°C for 1 minute to 3 minutes, for example.

By subjecting cold-rolled steel sheet to decarburization annealing, the C components contained in the cold-rolled steel sheet are removed. Decarburization annealing is preferably performed in a humid atmosphere in order to remove the C components contained in the cold-rolled steel sheet.

(Nitriding process S6)
The nitriding process S6 is a process that is carried out as necessary to adjust the strength of the inhibitor in the secondary recrystallization. The nitriding process is a process that increases the nitrogen content of the cold-rolled steel sheet by about 40 ppm to 200 ppm from the start of the decarburization annealing process to the start of the secondary recrystallization in the finish annealing process. Examples of the nitriding process include a process of annealing the decarburization annealed steel sheet in an atmosphere containing a nitriding gas such as ammonia, and a process of applying an annealing separator containing a powder having a nitriding ability such as MnN to the decarburization annealed steel sheet in the annealing separator application process S7 described later.

(Annealing separator application step S7)
The annealing separator application step S7 is a step of applying an annealing separator to the decarburized annealed steel sheet. As the annealing separator, for example, an annealing separator mainly composed of alumina (Al ₂ O ₃ ) can be used. The decarburized annealed steel sheet after the annealing separator application is wound into a coil and finish-annealed in the next finish-annealing step S8.
When forming a glass coating containing Mg ₂ SiO ₄ , an annealing separator containing magnesia (MgO) as a main component is used.

(Finish annealing step S8)
The final annealing step S8 is a step in which the decarburized annealed steel sheet coated with the annealing separator is subjected to final annealing to cause secondary recrystallization. This final annealing step S8 involving secondary recrystallization causes the {100}<001> oriented grains to grow preferentially by promoting secondary recrystallization in a state in which the growth of primary recrystallized grains is suppressed by an inhibitor, and thus dramatically improves the magnetic flux density.
In addition, when magnesia (MgO) is applied in the above-mentioned annealing separator application step S7, a glass coating containing Mg ₂ SiO ₄ is formed in this finish annealing step S8. In this embodiment, such a glass coating is also included in the base steel sheet (finish annealed steel sheet described later). Therefore, for example, when a glass coating is formed on a finish annealed steel sheet, the "surface of the finish annealed steel sheet" means the surface of the glass coating. It is expected that the properties of the grain-oriented electrical steel sheet finally obtained will be further improved by forming a glass coating.

(Groove forming step S9)
The groove forming step S9 is a step of forming grooves in the steel sheet for the purpose of magnetic domain control (magnetic domain refinement). The grooves can be formed by a known method such as a laser, an electron beam, plasma, a mechanical method, or etching.

In the above explanation, the groove forming process S9 is performed after the finish annealing process S8. However, the groove forming process S9 may also be performed on a steel sheet that has been subjected to the cold rolling process S4 (i.e., a cold-rolled steel sheet). In this case as well, it is possible to maintain the cross-sectional shape of the linear grooves G that is ideal for magnetic domain refinement. Therefore, the timing for performing the groove forming process S9 may be before or after the finish annealing process S8. However, if the tension coating application process S10 described below is performed, the groove forming process S9 must be performed before that process S10.

When using a laser to form the grooves, the electromagnetic steel sheet according to this embodiment can be obtained by using the following example laser irradiation conditions.

In the laser irradiation process, a laser may be irradiated onto the surface of the steel plate (one side only) to form multiple grooves on the surface of the steel plate extending in a direction intersecting the rolling direction at a desired pitch interval in the range of 2 to 20 mm along the rolling direction.

In the laser irradiation process, the laser irradiation device may rotate a polygon mirror to irradiate the laser light onto the surface of the steel plate, and may also scan the laser light in a direction that forms an angle of 0 to 30 degrees with the direction perpendicular to the rolling direction.

At the same time as the laser light is irradiated, a water jet may be sprayed onto the area of the steel plate irradiated with the laser light. In the water jet, water pressurized by a high-pressure water pump is discharged from a nozzle and an ultra-high-speed water stream is collided with the target part, thereby cleaning, peeling, cutting, etc. of the target part. The pressure can be up to 50 to 350 MPa, the nozzle can be about 0.1 mm to 1 mm in size, and an abrasive (sandblasting garnet, etc.) can be added to the solvent (water). The material and grain size (#) of the abrasive can be appropriately selected. The grain size (#) may be in the range of 10 to 1000. The water jet plays a role in removing the components melted or evaporated from the steel plate by the laser irradiation. By spraying the water jet, it is possible to prevent the above-mentioned melted or evaporated components from remaining in the groove, and the undulation of the edge of the groove can be stably formed within the desired range.

At the same time as the laser light is irradiated, an assist gas such as air or an inert gas may be sprayed onto the area of the steel plate where the laser light is irradiated. Examples of inert gas 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. By spraying the assist gas, the laser light can reach the steel plate without being obstructed by the melted or evaporated components, so that grooves are formed stably.

As the laser light source, for example, a high-power laser generally used for industrial purposes, such as a fiber laser, a YAG laser, a semiconductor laser, or a _CO2 laser, can be used. In addition, a pulsed laser or a continuous wave laser may be used as the laser light source as long as it can stably form a groove. As the laser light, a single mode laser with high light-collecting ability is generally used for forming a groove, but a multimode laser with an appropriately distributed power peak may also be used.

As an example of the laser light irradiation conditions, the laser output is set to 200W to 3000W, and the laser beam shape is changed when forming the grooves.

The diameter of the focused spot of the laser light (i.e. the diameter containing 86% of the laser output, hereinafter sometimes abbreviated as 86% diameter) may be set to 10 μm to 1000 μm, the laser scanning speed to 1 m/s to 100 m/s, and the laser scanning pitch (spacing PL) to 2 mm to 10 mm. These laser irradiation conditions are adjusted as appropriate to obtain the desired groove.

(Tension coating step S10)
The tension coating step S10 is a step of applying a coating solution to the groove-formed surface of the finish-annealed steel sheet and baking it to form an insulating coating (tensile coating) on the groove-formed surface. By forming the insulating coating (tensile coating), it is expected that the properties of the finally obtained grain-oriented electrical steel sheet will be further improved.

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

Below, the grain-oriented electromagnetic steel sheet according to one embodiment of the present invention will be described in more detail, with reference to examples. Note that the examples shown below are merely examples of the grain-oriented electromagnetic steel sheet according to this embodiment, and the grain-oriented electromagnetic steel sheet according to this embodiment is not limited to the examples shown below.

The grain-oriented electrical steel sheet contained, by mass fraction, 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%, with the remainder being Fe and impurities. The slab was then hot-rolled to obtain a hot-rolled steel sheet having a thickness of 2.3 mm.

Next, the above hot-rolled steel sheets were subjected to an annealing treatment under temperature conditions of heating at 1000° C. for 1 minute.
After the annealing treatment, cold rolling was performed to obtain a cold-rolled steel sheet having a thickness of 0.23 mm. Subsequently, the cold-rolled steel sheet was subjected to a decarburization annealing treatment 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.

Then, the cold-rolled steel sheet coated with the annealing separator was subjected to a final annealing process under the temperature conditions of heating at 1200°C for 20 hours. As a result, a steel sheet was obtained with the above-mentioned chemical composition, a glass film formed on the surface, and a crystal orientation controlled so that the magnetization easy axis of the crystal grains coincided with the rolling direction.

Then, a water jet was applied to the surface of the steel plate under the conditions shown in Table 1, while a laser was irradiated to create grooves on the surface of the steel plate. For the water jet, Sandblast Garnet (high hardness garnet Type-2 (800-300 μm) manufactured by Nitchu Co., Ltd.) was used as the abrasive.

The laser light irradiation device used was a fiber laser manufactured by IPG. The laser light irradiation conditions were adjusted to a laser output of 300 W, a laser scanning speed of 50 m/s, and a laser scanning pitch (spacing PL) of 3 mm. The focused spot diameter of the laser light was adjusted to 50 μm. Linear grooves with a depth D of approximately 20 μm were formed at intervals of 3 mm in the direction perpendicular to the rolling direction. Grain-oriented electrical steel sheets were manufactured so that 75% of all groove groups had groove widths, overlaps between adjacent grooves, and undulations at the edges of the grooves adjusted to satisfy the conditions shown in Table 1. The groove formation process was performed either after finish annealing or after the cold rolling process.

A wound core with a capacity of 25 kVA was manufactured from the obtained magnetic steel sheet, and after stress relief annealing (holding at a soaking temperature of 750°C for 4 hours), the core loss W17/50 was measured. The results are shown in Table 1.

[Magnetic property evaluation]
For the wound core, measurements are performed using the excitation current method described in JIS C 2550-1:2011 under conditions of a frequency of 50 Hz and a magnetic flux density of 1.7 T to measure the iron loss value (sometimes referred to as iron core iron loss or core iron loss) WA of the wound core.

These results show that the magnetic properties of the prototype wound core made from electromagnetic steel sheets within the scope of this invention are good, and that it is possible to suppress an increase in core iron loss. In more detail, when a Tranco-type core was made using a material with a material iron loss of 0.74 W/kg, the actual measured core iron loss deteriorated. When a criterion was set for the core iron loss not to exceed 0.80 W/kg, conditions No. 2 and No. 5 met this.

In No. 10, as an example of groove formation using laser light without applying a water jet, grooves were formed with a laser output of 3100 W, a focused spot diameter of 8 μm, a laser scanning speed of 1 m/s, and a laser scanning pitch (spacing PL) of 2 mm. In this case, the waviness of the groove edge was 15 μm, and the iron loss was large at 0.89 W/kg.

Separately, an investigation was carried out in which the overlap between adjacent grooves was fixed at 25 mm, and the groove width and undulation of the groove edges were varied. The results are shown in Figure 9. Figure 9 confirms that the magnetic properties are good when the groove width and undulation of the groove edges are within the range of the present invention. Even in this case, when the core iron loss was measured using a material with a core density of 0.74 W/kg, good magnetic properties were obtained, not exceeding 0.80 W/kg.

Separately, we investigated the case where the groove width was fixed at 50 μm and the overlap between adjacent grooves and the waviness of the groove edges were changed. The results are shown in Figure 10. In Figure 10, it was confirmed that the magnetic properties were good when the overlap between adjacent grooves and the waviness of the groove edges were within the range of the present invention. Even in this case, when the core iron loss was measured using a material with a material strength of 0.74 W/kg, good magnetic properties were obtained that did not exceed 0.80 W/kg.

Claims

The steel plate has a steel plate surface on which a groove is formed extending in a direction intersecting the rolling direction and having a groove depth direction in the plate thickness direction,
A grain-oriented electrical steel sheet having a groove group formed by arranging a plurality of the grooves in the sheet width direction when the steel sheet surface is viewed from the sheet thickness direction, and the groove groups are arranged at intervals in the rolling direction,
In at least 75% of the groove groups,
The grooves constituting the groove group have an average width of 42 to 62 μm;
the grooves constituting the groove group are arranged so as to overlap with adjacent grooves on a projection plane that is parallel to the groove extension direction and the groove depth direction,
In this grain-oriented electrical steel sheet, an end portion in the sheet width direction of the steel sheet is defined as a reference end portion, and adjacent grooves among the plurality of grooves in the groove group are defined as a first groove and a second groove in the order of proximity to the reference end portion,
two groove ends in an extending direction of each groove constituting the groove group are designated as a first groove end and a second groove end in the order of being closer to the reference end portion;
an overlapping margin between the first groove end of the second groove and the second groove end of the first groove is 5 to 30 mm on the projection plane;
The groove group includes an edge waviness of the grooves of 0.5 to 5.0 μm.