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

Abstract

An objective of the present invention is to provide a grain-oriented electromagnetic steel sheet that exhibits improved iron loss in magnetic domain control for forming laser grooves in a steel sheet that has been subjected to decarburization annealing but has not yet been subjected to final annealing.　The grain-oriented electromagnetic steel sheet according to the present invention, which comprises a steel sheet that has a plurality of grooves in the surface thereof, and a glass film that is formed on the surface of the steel sheet, is characterized in that: the absolute value of the angle θ formed by the longitudinal direction of the grooves and the direction perpendicular to the rolling direction and the sheet thickness direction the steel sheet is 0-40°, the width W of the grooves is 20-300 μm, the depth D of the grooves is 10-40 μm, and the spacing P between the grooves in the rolling direction is 1.0-30 mm; and relational expression (1) is satisfied, where t1 is the thickness of the portions of the glass film on the flat portions (portions other than the grooves) of the surface of the steel sheet, and t2 is the thickness of the portion of the glass film at the deepest portion of the grooves.　(1): t2 / t1<1.00

Description

[Technical Field]

[0001] This invention relates to grain-oriented electrical steel sheets. [Background technology]

[0002] Grain-oriented electrical steel sheets are steel sheets in which the crystal orientation is controlled by a combination of cold rolling and annealing treatments so that the easy magnetization axis of the crystal grains coincides with the rolling direction.

[0003] The crystal orientation is controlled by creating a primary recrystallized texture during the annealing process after cold rolling, and then inducing preferential growth of orientations favorable to magnetic properties, known as secondary recrystallization, through high-temperature annealing. This control of crystal orientation reduces hysteresis loss in grain-oriented electrical steel sheets.

[0004] As a technique to reduce eddy current loss, a type of iron loss in grain-oriented electrical steel sheets, grain-oriented electrical steel sheets are known in which an insulating film is formed on the surface of a base steel sheet with controlled crystal orientation. The insulating film not only provides electrical insulation but also plays a role in providing the base steel sheet with tensile strength and corrosion resistance.

[0005] Another method for reducing abnormal eddy current losses is known to be a magnetic domain control method that narrows the width of the 180° magnetic domain (subdivision of the 180° magnetic domain) by forming strain regions or grooves that are formed in a direction intersecting the rolling direction at predetermined intervals along the rolling direction. Magnetic domain control methods are classified into two types: one that applies strain to the base steel sheet of a grain-oriented electrical steel sheet, and another that forms grooves on the surface of the base steel sheet where a film that can be subjected to tension exists.

[0006] By using grain-oriented electrical steel sheets with magnetic domain control via grooves, the grooves do not disappear even after manufacturing the iron core (winding core) of a transformer and performing stress-relieving annealing treatment, thus maintaining the magnetic domain subdivision effect. For this reason, magnetic domain control by groove formation is sometimes adopted for winding cores as a method to reduce abnormal eddy current losses.

[0007] Figure 1 is a schematic diagram of an electrical steel sheet with grooves formed on it. In Figure 1, multiple grooves 2 are formed on the surface of the base steel sheet 1 at intervals in the rolling direction of the base steel sheet 1. In Figure 1, the symbol θ indicates the angle between the direction perpendicular to the rolling direction and thickness direction of the base steel sheet 1 (width direction) and the longitudinal direction of the groove 2. The symbol W indicates the width of the groove, the symbol D indicates the depth of the groove, and the symbol P indicates the spacing between adjacent grooves 2 in the rolling direction.

[0008] Various methods have been proposed for forming grooves in electrical steel sheets. For example, Patent Document 1 discloses an electrolytic etching method for forming grooves on the surface of a grain-oriented electrical steel sheet by electrolytic etching.

[0009] Patent Document 2 discloses a gear pressing method for forming grooves on the surface of a grain-oriented electrical steel sheet by mechanically pressing a gear onto the surface of the sheet.

[0010] However, the gear pressing method suffers from rapid wear of the gear teeth due to the high hardness of the electrical steel sheets. Furthermore, from the perspective of high-speed processing, it is difficult to achieve line speeds of 100 mpm or more, which are required in general steel manufacturing processes. While the electrolytic etching method does not have the problem of gear tooth wear, it requires masking, etching, and mask removal, making the process more complex compared to mechanical methods.

[0011] Patent Document 3 discloses a laser irradiation method in which the laser-irradiated portion of the steel sheet surface of a grain-oriented electrical steel sheet is melted and evaporated by laser irradiation. The laser irradiation method does not have problems such as tooth profile wear or complex processes, and high-speed processing is also possible.

[0012] Furthermore, several methods for forming grooves using laser irradiation have been proposed. For example, Patent Document 4 also describes a laser irradiation method, disclosing that a laser is irradiated onto a final product plate coated with a tension insulating film. However, in this case, it is necessary to reapply the insulating tension film, which presents a problem of poor productivity.

[0013] On the other hand, Patent Document 5 discloses a method for forming grooves in cold-rolled steel sheets. This method does not require recoating of the insulating tension coating and is highly productive. However, it has the problem that the primary recrystallized texture deteriorates during subsequent decarburization annealing, and secondary recrystallization does not occur well during subsequent high-temperature annealing. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Special Publication No. 62-54873 [Patent Document 2] Special Publication No. 62-53579 [Patent Document 3] Japanese Patent Publication No. 2003-129135 [Patent Document 4] Japanese Patent Publication No. 2012-087332 [Patent Document 5] International Publication No. 2019 / 156127 [Patent Document 6] International Publication No. 2011 / 007771 [Overview of the project] [Problems that the invention aims to solve]

[0015] This invention was developed in view of the above-mentioned problems, and aims to further improve iron loss in magnetic domain control for forming laser grooves (grooves formed by laser irradiation) in steel sheets, and to provide such a grain-oriented electrical steel sheet. [Means for solving the problem]

[0016] The inventors diligently conducted research to solve the above problems. They found conditions under which laser grooves are formed on grain-oriented electrical steel sheets after decarburization annealing and before finish annealing, without degrading the primary recrystallized texture of the laser groove formation area. The present invention is based on this finding, and its gist is as follows.

[0017] [1] The grain-oriented electrical steel sheet according to one aspect of the present invention has a plurality of grooves on the surface of the steel sheet and is provided with a glass film on the surface. The absolute value of the angle θ formed by the direction orthogonal to the rolling direction and the sheet thickness direction of the steel sheet and the longitudinal direction of the groove is 0 to 40°, the width W of the groove is 20 to 300 μm, the depth D of the groove is 10 to 40 μm, and the pitch P of the grooves in the rolling direction is 1.0 to 30 mm. When the thickness of the glass film on the flat part (the part other than the groove) of the steel sheet is t1 and the thickness of the glass film at the deepest part of the groove is t2, the grain-oriented electrical steel sheet is characterized by satisfying the relational expression of formula (1). t2 / t1 < 1.00 ··· Formula (1) [2] The grain-oriented electrical steel sheet according to one aspect of the present invention is the grain-oriented electrical steel sheet described in [1] above. When the thickness of the embedded part of the glass film on the flat part of the base metal steel sheet is s1 and the thickness of the embedded part of the glass film at the deepest part of the groove is s2, the grain-oriented electrical steel sheet described in [1] is characterized by satisfying the relational expression of formula (2). s2 / s1 < 1.00 ··· Formula (2) [3] The method for manufacturing a grain-oriented electrical steel sheet according to one aspect of the present invention is a method for manufacturing the grain-oriented electrical steel sheet described in [1] or [2] above, including a groove forming step of forming grooves on the surface of the steel sheet after decarburizing annealing and before finish annealing with a laser. In the groove forming step, the grain-oriented electrical steel sheet manufacturing method is characterized in that the condensing spot diameter dL of the laser beam in the rolling direction of the steel sheet and the condensing spot diameter dC of the laser beam in the sheet width direction satisfy formula (3). 0.10 ≤ dL / dC < 1.00 ··· Formula (3) [Advantages of the Invention]

[0018] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet with good iron loss controlled by magnetic domains by laser grooves. [Brief Description of the Drawings]

[0019] [Figure 1] It is a diagram showing an outline of an electrical steel sheet in which grooves are formed. [Figure 2]This is a schematic diagram of a steel plate cross-section in a section perpendicular to the longitudinal direction of the groove near the groove. [Modes for carrying out the invention]

[0020] The present invention will be described below using a grain-oriented electrical steel sheet (hereinafter referred to as "this electrical steel sheet") according to one embodiment of the present invention as an example.

[0021] As shown in Figures 1 and 2, this electrical steel sheet comprises a base steel sheet 1 having a plurality of grooves 2 on its surface, and a glass coating 8 formed on the surface of the base steel sheet 1. In this electrical steel sheet, a tension coating (insulating coating) (not shown) may be formed on the surface of the glass coating 8. As shown in Figure 1, on the surface of the base steel sheet 1, the plurality of grooves 2 are formed adjacent to each other in the rolling direction of the base steel sheet 1. The direction (angle θ) of the grooves, the width W, the depth D, and the spacing P of the grooves are determined considering iron loss, as in ordinary grain-oriented electrical steel sheets.

[0022] <Angle θ between the longitudinal direction of the base steel plate and the longitudinal direction of the groove> The angle θ between the direction perpendicular to the rolling direction and thickness direction of the base steel sheet (sheet width direction) and the longitudinal direction of the groove should be between 0 and 40° (0° to 40°) because if it is too large, there will be no magnetic domain control effect and the iron loss improvement effect will not be obtained. A smaller angle θ is preferable, and it should be 35° or less, 30° or less, 25° or less, 20° or less, 15° or less, 10° or less, 8° or less, 6° or less, or 5° or less. The lower limit of angle θ is 0°, that is, when the longitudinal direction of the groove is parallel to the sheet width direction. Note that the direction of angle θ is irrelevant and refers to the acute angle of the angle formed between the longitudinal direction of the groove and the sheet width direction. Multiple grooves are arranged roughly parallel to each other on the surface of the base steel sheet, but the angle θ of each groove should be within the range described above.

[0023] <Groove width W> The groove width W refers to the width of the groove on the surface of the base steel plate in the groove cross-section (groove cross-section) in a plane perpendicular to the longitudinal direction of the groove. If the groove width W is too narrow, it will not serve as a starting point for magnetic pole generation, there will be no magnetic domain control effect, and good iron loss will not be obtained, so it is preferable to have a groove width of 20 μm or more. On the other hand, if the groove width W is too wide, it will not serve as a starting point for magnetic pole generation, there will be no magnetic domain control effect, only the magnetic flux density will decrease significantly, and good iron loss will not be obtained, so it is preferable to have a groove width of 300 μm or less. For this reason, the groove width W is preferably 20 to 300 μm (20 μm or more and 300 μm or less). The lower limit of the groove width W is preferably 25 μm, 30 μm, or 35 μm. The upper limit of the groove width W is preferably 250 μm, 200 μm, 150 μm, 100 μm, or 80 μm.

[0024] <Groove depth D> If the groove depth D is too shallow, it will not serve as a starting point for the magnetic poles, resulting in no magnetic domain control effect and poor iron loss. Therefore, it is preferable that the groove depth be 10 μm or greater. On the other hand, if it is too deep, the magnetic domain control effect will reach saturation, and only the magnetic flux density will decrease significantly, resulting in poor iron loss. Therefore, it is preferable that the groove depth be 40 μm or less. For this reason, the groove depth D should be between 10 and 40 μm (10 μm or more and 40 μm or less). The lower limit of the groove depth D is preferably 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm. The upper limit of the groove depth D is preferably 38 μm, 36 μm, 34 μm, 32 μm, 30 μm, 28 μm, or 26 μm.

[0025] <Groove spacing P> The groove spacing P is the distance between the longitudinal centerlines of adjacent grooves that are generally arranged parallel to each other on the surface of the base steel sheet, and refers to the distance in the rolling direction of the base steel sheet. The groove centerline is a line parallel to the longitudinal direction of the groove that passes through the midpoint of the groove on the surface of the base steel sheet in the groove cross-section. If the groove spacing P is too narrow, the magnetic domain control effect will saturate, and only the magnetic flux density will decrease significantly, resulting in poor iron loss, so it is preferable that it be 1 mm or more. On the other hand, if it is too wide, the magnetic domain control effect will not be sufficiently obtained, resulting in poor iron loss, so it is preferable that it be 30 mm or less. Therefore, a groove spacing P of 1 to 30 mm (1 mm or more and 30 mm or less) is preferable. Note that the groove spacing P does not have to be equal, but the groove spacing P between adjacent grooves should be within the above range. The lower limit of the groove spacing P is preferably 1.2 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.8 mm, or 2.0 mm. The upper limit of the groove spacing P is preferably 25 mm, 20 mm, 15 mm, 10 mm, 7 mm, or 5 mm.

[0026] <Thickness of glass coating> Figure 2 illustrates the glass coating on the flat portion of the base steel sheet (the portion on the steel sheet surface where no grooves are formed, i.e., the portion other than the groove, which is at least half the groove width away from the groove edge; hereinafter sometimes simply referred to as the "flat portion") and the laser groove recess (hereinafter sometimes simply referred to as the "groove") of this electrical steel sheet. Figure 2 is a cross-sectional view of the groove recess in a section perpendicular to the longitudinal direction of the groove, showing the area including the groove. Unless otherwise specified, the following explanation will be based on this cross-sectional view perpendicular to the longitudinal direction of the groove (Figure 2). This electrical steel sheet is characterized by satisfying the relationship given by equation (1) when the thickness of the glass coating on the flat portion of the base steel sheet is t1 and the thickness of the glass coating at the deepest part of the groove is t2. t2 / t1<1.00... Equation (1)

[0027] The coating thickness t1 and t2 of each part will be explained. The glass coating in this electrical steel sheet has an embedded structure as shown in Figure 2. An embedded structure is a structure in which the ends of the glass coating extend into the base steel sheet, like the roots of a plant. The part in which the glass coating is embedded in the steel sheet like the roots of a plant is called the embedded part of the glass coating. Therefore, in the cross-section of the steel sheet, the ends of the embedded structure may appear separated from the glass coating. For example, in Figure 2, the embedded part 9 of the glass coating can be seen like an isolated island, separated from the glass coating 8 on the flat parts and groove recesses. This is because the cross-section of the end of the embedded part of the glass coating embedded part 9 is being observed. Hereinafter, the end of the glass coating refers to the part furthest from the glass coating surface in the cross-section of the steel sheet perpendicular to the longitudinal direction of the groove, including not only the glass coating 8 but also the embedded part 9 of the embedded structure that appears to be separate from these glass coatings.

[0028] The measurement methods for the glass coating thicknesses t1 and t2 of each part are explained below in Figure 2. As shown in Figure 2, L1U is defined as the straight line representing the glass film surface in the flat section 4, and L1L is defined as the line parallel to L1U that passes through the deepest end in the thickness direction of the glass film embedding structure in the flat section. Let L2U be a line parallel to L1U that passes through the glass coating surface at the deepest point of the groove (the point where the groove contour is deepest in the thickness direction). Also, let L2L be a line parallel to L2U that passes through the deepest end of the glass coating embedded structure near the deepest point of the groove in the thickness direction. The glass coating thickness t1 in the flat section is defined as the distance from L1U to L1L, and the glass coating thickness t2 in the deepest part of the groove is defined as the distance from L2U to L2L.

[0029] The thickness t1 of the glass coating on the flat portion of the base steel sheet is the distance from the surface of the glass coating to the end of the glass coating embedding structure, as shown in Figure 2, i.e., the maximum glass coating embedding depth in the flat portion. In the recess of the groove, the glass film thickness t2 at the deepest part of the groove is the distance from the surface of the glass film at the deepest part of the groove to the end of the glass film embedding structure, as shown in Figure 2, i.e., the maximum glass film embedding depth at the deepest part of the groove. The thickness of the glass coating can be measured, for example, by observing the cross-section of the steel plate with an optical microscope or SEM after polishing. The observation range for measuring the glass coating penetration depth should be a range that includes a distance approximately equal to the groove width, straddling the groove. That is, the observation range should be a cross-section perpendicular to the longitudinal direction of the groove, with a length in the rolling direction equal to the groove width on both sides of the groove (i.e., a length of at least three times the groove width with the groove as the center), and a length in the thickness direction approximately twice the groove depth. The glass coating thickness in the flat section is measured on each side of the groove (left or right side of the groove in Figure 2), within a range from the groove edge at a distance of at least half the groove width W up to the groove width W, and the average value (arithmetic mean) of these measurements is taken as the glass coating thickness in the flat section.

[0030] Next, we will explain the effect of improving iron loss due to the glass coating thickness t2 being thinner at the deepest part of the groove compared to the glass coating thickness t1 at the flat part of the base steel plate.

[0031] In grain-oriented electrical steel sheets, magnetic domain refinement occurs when the magnetostatic energy increases due to the magnetic poles generated on the steel sheet surface. To counteract this, new 180° domain walls are generated, narrowing the magnetic domain width. A narrower magnetic domain width reduces the distance the domain walls travel when the steel sheet is magnetized, reducing energy loss during domain wall movement and thus reducing eddy current losses.

[0032] Furthermore, by applying a glass coating with a different coefficient of thermal expansion from the steel plate at high temperatures and baking it, after cooling, the difference in the coefficients of thermal expansion between the steel plate and the glass coating applies tensile tension in the rolling direction, which subdivides the magnetic domains and improves eddy current loss.

[0033] Furthermore, since the glass film is made of a non-magnetic oxide and has a different magnetic permeability than the steel plate, magnetic poles are generated at the interface and magnetic domains are subdivided. Therefore, it is thought that the glass film acts as a starting point for magnetic pole generation and reduces eddy current losses by promoting magnetic domain subdivision. Although tension is less likely to be applied in the rolling direction in the grooved sections, forming grooves perpendicular to the rolling direction generates magnetic poles on the recessed surfaces of the grooves. This, combined with the magnetic pole generation by the glass coating, promotes the subdivision of magnetic domains.

[0034] On the other hand, since glass coatings are nonmagnetic oxides, if the glass coating is thick, the magnetic flux density decreases, and as a result, hysteresis loss worsens. Iron loss in electrical steel sheets is the sum of hysteresis loss and eddy current loss, and it is desirable to control the glass coating so that iron loss is minimized.

[0035] Therefore, the inventors found that by increasing the thickness of the glass coating on the flat portion, which occupies most of the surface area when viewed from above on the base steel sheet, they can secure a starting point for magnetic pole generation and promote the subdivision of magnetic domains. On the other hand, in the grooves of the steel sheet, the grooves themselves function as a starting point for magnetic pole generation, so a starting point for magnetic pole generation by the glass coating is unnecessary. In other words, in the grooves of the steel sheet, they found that by thinning the glass coating at the deepest part of the groove to suppress the decrease in magnetic flux density, they can efficiently secure a starting point for magnetic pole generation throughout the entire steel sheet, thereby improving iron loss.

[0036] In other words, it was found that it is desirable to control the glass film thickness t1 of the flat portion of the base steel sheet and the glass film thickness t2 of the deepest part of the groove so that t2 / t1 < 1.00 in equation (1). As a result, the glass film made of nonmagnetic oxide in the groove-forming portion is controlled to be less than the glass film in the flat portion of the base steel sheet, which suppresses the decrease in magnetic flux density, prevents deterioration of hysteresis loss, and improves total iron loss. t2 / t1 is preferably 0.95 or less, 0.90 or less, 0.85 or less, 0.80 or less, 0.75 or less, 0.70 or less, 0.65 or less, 0.60 or less, 0.55 or less, or 0.50 or less. The lower limit of t2 / t1 is not particularly limited and may be 0. In practice, t2 / t1 may be 0.05 or more.

[0037] <Thickness of the glass coating inlay area> Furthermore, in this electrical steel sheet, it is preferable that the relationship shown in equation (2) is satisfied when s1 is the thickness (depth) of the glass coating embedded in the flat portion of the base steel sheet and s2 is the thickness (depth) of the glass coating embedded in the deepest part of the groove. s2 / s1<1.00... Equation (2)

[0038] As mentioned above, the glass coating exhibits an embedded structure, meaning that the ends of the glass coating extend into the base steel sheet, much like the roots of a plant. The embedded portion of the glass coating refers to the part of the glass coating that is embedded in the steel sheet like the roots of a plant, and the thickness of the embedded portion refers to the depth in the thickness direction of the steel sheet to which the embedded portion is embedded. The thickness s1 of the embedded portion of the glass coating on the flat portion of the steel plate is the distance between the deepest part of the glass coating on the flat portion of the base steel plate where it is observed to be continuous from the surface, and the deepest part of the glass coating including the end of the embedded portion of the glass coating which appears as an isolated island. The thickness s2 of the embedded portion of the glass coating at the deepest part of the groove is the distance between the deepest part of the glass coating in the deepest part of the groove of the base steel plate where it is observed to be continuous from the surface, and the deepest part of the glass coating including the end of the embedded portion of the glass coating.

[0039] The measurement method for the embedded glass coating thicknesses s1 and s2 in each section is explained in Figure 2. As shown in Figure 2, L1M is defined as a line parallel to L1U that passes through the deepest part of the portion where the glass coating 8 is continuously observed from the surface, among the ends 9 of the embedded glass coating structure in the flat section 4 of the steel plate. Also, L2M is defined as a line parallel to L2U that passes through the deepest part of the portion where the glass coating is continuously observed from the surface, among the ends of the embedded glass coating structure near the deepest part of the groove. The embedded glass coating thickness s1 in the flat section is L1 L At the distance from L1M, the thickness s2 of the embedded portion of the glass coating at the deepest part of the groove is L2 L These are defined by the distance from L2M. The thickness of the embedded portion of the glass coating can be measured, for example, by polishing the cross-section of the steel plate and observing it with an optical microscope or SEM, similar to the thickness of the glass coating itself. The observation range for measuring the thickness of the embedded portion of the glass coating is the same as that for the thickness of the glass coating. Furthermore, the method for determining the thickness of the embedded portion in the flat area is the same as for the thickness of the glass coating; it is calculated by averaging the measurements taken from the flat areas on both sides of the groove.

[0040] The effect of improving iron loss due to the thinner thickness s2 of the glass coating embedded in the deepest part of the groove compared to the thickness s1 of the glass coating embedded in the flat part of the base steel sheet is estimated to be as follows: That is, the embedded structure of the glass coating is more likely to become a magnetic pole generation initiation point than a continuous glass coating present on the surface side of the base steel sheet, and the magnetic domain subdivision effect is estimated to be greater as a result. On the other hand, in the recessed part of the laser groove, the groove itself is the initiation point of magnetic pole generation, and even if the embedded part of the glass coating is formed on the deeper side than the groove, not only is the magnetic pole generation effect small, but the magnetic flux density decreases and the hysteresis loss worsens. Furthermore, if the embedded part penetrates deeply, a complex structure of the embedded part is formed, which may become a factor in the deterioration of magnetic properties.

[0041] Therefore, it was found that it is desirable to control the thickness s1 of the glass coating embedded in the flat part of the base steel plate and the thickness s2 of the glass coating embedded in the deepest part of the groove so that s2 / s1 < 1.00. This makes it possible to thin the glass coating embedded in the deepest part of the groove and suppress the complexity of the embedded structure, thereby further suppressing the decrease in magnetic flux density and improving the total iron loss. The value of s2 / s1 is preferably 0.95 or less, 0.90 or less, 0.85 or less, 0.80 or less, 0.75 or less, 0.70 or less, 0.65 or less, 0.60 or less, 0.55 or less, or 0.50 or less. The lower limit of s2 / s1 is not particularly limited and may be 0. In reality, s2 / s1 may be 0.05 or more.

[0042] <Manufacturing method> First, cold-rolled steel sheets for electrical steel sheets are manufactured using known methods. The steel sheet components and the method of manufacturing the cold-rolled steel sheets are not particularly limited, and known methods, such as those described in Patent Document 6, can be used.

[0043] <Decarburization annealing> Next, decarburization annealing can be performed using known methods, and nitriding annealing may be performed as needed. Decarburization conditions can be those of known origin. For example, the steel plate is heated to 850°C, held for 60 seconds, and then cooled, and the decarburization atmosphere is a hydrogen-inert gas atmosphere with P H2O / P H2 It is best to set it in the range of 0.15 to 0.65. Especially P H2O / P H2 Good properties can be obtained at around 0.33. Known methods can also be used for nitriding. The amount of nitriding can be in the range of, for example, 50 to 400 ppm, but particularly good properties can be obtained at around 200 ppm.

[0044] <Groove formation process: Groove formation using a laser> In the process of forming grooves at predetermined intervals in a direction intersecting the rolling direction, a laser is irradiated onto a steel sheet that has undergone decarburization annealing or decarburization annealing followed by nitriding annealing (groove formation process). The type of laser light source, laser output, laser scanning speed, and steel sheet movement speed during laser irradiation are not particularly limited, but conditions should be appropriately selected so that the groove width W, groove depth D, and predetermined groove interval (groove spacing P) are within the specified range.

[0045] [Laser light source] As the laser light source, high-power lasers commonly used in industry, such as fiber lasers, YAG lasers, semiconductor lasers, or CO2 lasers, can be used. Both pulsed lasers and continuous-wave lasers are acceptable, as long as they can stably form grooves.

[0046] [Laser output] If the laser output is too low, the laser scanning speed will decrease significantly in order to form the desired groove, reducing industrial productivity. Therefore, it is preferable to set it to 200W or higher. Preferably, it is 1000W or higher, and more preferably, 1500W or higher. On the other hand, if the laser output is too high, the power supply capacity will increase, resulting in enormous equipment costs, which is not industrially practical. Therefore, it is preferable to set it to 3000W or lower. Preferably, it is 2800W or lower, and more preferably, 2500W or lower.

[0047] [Laser scanning speed] The laser scanning speed should be 5 m / s or higher, preferably 20 m / s or higher, and more preferably 40 m / s or higher, because if it is too slow, productivity will decrease. On the other hand, if the laser scanning speed is too fast, high power output will be required, increasing equipment costs, so it should be 100 m / s or lower, preferably 80 m / s or lower, and more preferably 60 m / s or lower.

[0048] [Laser beam focusing spot shape] For example, the irradiation conditions for the laser beam should be such that the focused spot diameter dL in the rolling direction of the laser beam is 5 to 100 μm, the focused spot diameter dC in the plate width direction of the laser beam is 5 to 100 μm, the laser output is 200 to 3000 W, and the laser scanning speed is 5 m / s to 100 m / s, satisfying equation (3). 0.10≦dL / dC<1.00 ··· Formula (3)

[0049] When dL / dC is 1 or greater, the laser spot diameter becomes elongated elliptical in the rolling direction, making it difficult to control the laser groove shape. The spot diameter ratio dL / dC should preferably be less than 1.00, and its upper limit should preferably be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less.

[0050] If dL / dC is less than 0.10, the laser spot diameter becomes an extremely elongated ellipse in the plate width direction, making it difficult to control the laser groove shape. Therefore, it is preferable for the spot diameter ratio dL / dC to be greater than 0.1, and its lower limit should preferably be 0.15 or higher, or 0.20 or higher.

[0051] The mechanism by which laser irradiation conditions contribute to controlling the thickness of the glass coating in groove recesses is thought to be as follows. First, in areas without laser irradiation (flat areas), the internal oxide layer SiO2 formed inside the base steel sheet during decarburization annealing and the annealing separator MgO applied to the surface of the steel sheet before finish annealing react at the high temperature annealing of 1200°C during the finish annealing process to form a glass film, which is an oxide made of Mg2SiO4.

[0052] On the other hand, in the laser-grooved sections, the internal oxide layer formed by decarburization annealing before laser irradiation is removed by the laser, leaving the base metal exposed on the inner surface of the grooves. At this time, molten areas remain along the sides of the grooves, and these molten areas undergo oriented growth during solidification, generating columnar crystals. When columnar crystals develop, the grain boundaries of the columnar crystals become diffusion paths for oxygen, forming an internal oxide layer. In the subsequent finish annealing, the base metal is oxidized by the moisture in the annealing separator MgO slurry. At this time, oxygen diffuses along the grain boundaries of the columnar crystals, causing oxidation and forming an internal oxide layer (SiO2) on the sides of the grooves. The newly formed SiO2 along the grooves reacts with MgO in the same way as in the flat areas, forming a glass film.

[0053] Therefore, by making the spot diameter ratio dL / dC less than 1.00, if the laser spot shape is made into an elongated ellipse perpendicular to the rolling direction (plate width direction), the heat input to the steel plate is reduced, columnar crystals are formed thinly along the groove sides, the diffusion path is limited, and the internal oxide layer does not develop. As a result, a thin glass film is formed at the deepest part of the groove.

[0054] Furthermore, in order to control t2 / t1 < 0.90, it is good to set the upper limit of the spot diameter ratio dL / dC to 0.90, and preferably to 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less.

[0055] [Assist gas] Simultaneously with the irradiation of the laser beam, an assist gas is blown onto the area of ​​the steel plate being irradiated by the laser beam. The assist gas plays a role in removing components that have melted or evaporated from the steel plate due to the laser irradiation. Because the laser beam reaches the steel plate stably due to the blowing of the assist gas, grooves are formed stably. The flow rate of the assist gas is preferably, for example, 10 to 1000 liters per minute. Furthermore, the assist gas is preferably air or an inert gas.

[0056] <Application of annealing separating agent> Subsequently, an annealing release agent is applied to the surface of the steel plate. The finish annealing, described later, may be performed with the steel plate wound into a coil. If finish annealing is performed in this state, the coil may seize up, making it difficult to unwind. Therefore, in this embodiment, an annealing release agent is applied so that the coil can be unwound after finish annealing. Here, the main component of the annealing release agent is MgO, and the MgO in the annealing release agent reacts with SiO2 in the internal oxide layer during finish annealing to form a glass film. The composition of the annealing release agent can be one of known compositions, for example, MgO: 100 parts by mass, TiO2: 5 parts by mass, and as an additive, for example, FeCl2 can be added with chlorine to a concentration of 200 ppm.

[0057] To reduce the thickness of the glass film in the grooves, the moisture content after drying should be adjusted as needed when applying the annealing release agent to the steel plate surface. If the moisture content of the annealing release agent is too low, the glass film formation will be insufficient, resulting in a poor appearance, so it should be 0.5% or higher. On the other hand, if the moisture content of the annealing release agent is too high, the glass film thickness may become excessive, potentially degrading the magnetic properties, so it should be 6.0% or lower. In other words, the moisture content of the annealing release agent should be between 0.5% and 6.0%. The moisture content of the annealing release agent can be calculated, for example, by collecting the annealing release agent from the surface of the steel plate before finish annealing, measuring its weight, and then measuring its weight again after raising the temperature to 1000°C, using the difference in weight before and after heating. A crucible may be used when raising the temperature to 1000°C.

[0058] <Finishing annealing> The finish annealing process, also known as the secondary recrystallization annealing process, is a process that promotes secondary recrystallization of the steel sheet structure while simultaneously generating a glass film. The finish annealing process is performed by applying an annealing release agent to the steel sheet, winding it into a coil, holding it at a temperature of 1150-1250°C for 10-30 hours, and then cooling it. The dew point temperature of the atmospheric gas supplied to the finish annealing furnace should be 0°C or lower. If the dew point temperature is above 0°C, the glass coating thickness may become excessive, which can degrade the magnetic properties and is therefore undesirable.

[0059] <Formation of tension film> Although tension can be applied to a steel plate with a glass coating alone, a tension coating (insulating coating) is usually formed on top of the glass coating to enhance the magnetic domain control effect. The tension coating can be, for example, mainly composed of aluminum phosphate, and its thickness can be 1 μm. [Examples]

[0060] Next, embodiments of the present invention will be described. The conditions in the embodiments are one embodiment of the present invention, and the present invention is not limited to this embodiment.

[0061] <Example 1> Using a slab as the raw material, which contained Si:3.3 mass%, Mn:0.10 mass%, S:0.006 mass%, C:0.060 mass%, acid-soluble Al:0.027 mass%, and N:0.008 mass%, with the remainder being Fe and impurities, steel sheets A1-A11 and a1-a10 were obtained by hot rolling using a known method, followed by hot-rolled sheet annealing, and then cold-rolling to obtain steel sheets A1-A11 and a1-a10 with a final sheet thickness of 0.22 mm.

[0062] Cold-rolled steel sheets were decarburized and then subjected to nitriding. The decarburization annealing conditions involved heating the steel sheets to 850°C, holding for 60 seconds, and then cooling. The decarburization atmosphere was a hydrogen-nitrogen atmosphere, with P H2O / P H2 The coefficient was adjusted within the range of 0.15 to 0.65. The nitriding amount was set to 200 ppm.

[0063] Next, a laser was irradiated onto the surface of the steel plate to form multiple grooves extending in a direction intersecting the rolling direction, at intervals of 1 to 40 mm along the rolling direction. The groove formation direction was inclined at 0 to 45° in the L direction (rolling direction) with respect to the C direction (steel plate width direction) of the steel plate, with groove depths of 5 to 45 μm and groove widths of 15 to 400 μm.

[0064] The laser irradiation conditions were adjusted as follows: laser output of 2000W, focused spot diameter of 5-100μm in the rolling direction of the laser beam, focused spot diameter of 5-100μm in the plate width direction of the laser beam, and laser scanning speed in the range of 5-100m / s.

[0065] During laser irradiation, air was blown in at a rate of 100 liters / minute as an assist gas to efficiently remove the metal from the steel plate that had melted and evaporated due to the laser.

[0066] Subsequently, an annealing separation agent mainly composed of MgO was applied at a rate of 4 g / m² per side. 2 The coating was applied in this manner. The composition of the annealing separation agent was 100 parts by mass of MgO and 5 parts by mass of TiO2, to which FeCl2 was added with chlorine to a concentration of 200 ppm. The water content of the annealing separation agent was 2.5%.

[0067] Next, the steel sheet coated with the annealing release agent was wound into a coil, held at 1200°C for 20 hours, and then cooled to form a glass film on the surface. The dew point temperature of the atmospheric gas supplied to the finish annealing furnace was -20°C. Furthermore, a tension film mainly composed of aluminum phosphate was formed to a thickness of 1 μm to obtain a grain-oriented electrical steel sheet. The tension at this time, including the glass film, was 12 MPa in the rolling direction.

[0068] Iron loss W after application of tension-resistant insulating film 17 / 50 Energy loss (measured under excitation conditions of 1.7T, 50Hz) and magnetic flux density B8 (magnetic flux density at a magnetization force of 800 A / m) were measured. The results are shown in Table 1.

[0069] In Invention Examples A1 to A11 and Comparative Examples a1 to a10, the absolute value of the angle θ between the groove and the longitudinal direction is 0 to 40°, the groove width W is 20 to 300 μm, the groove depth D is 10 to 40 μm, and the groove spacing P in the rolling direction is in the range of 1.0 to 30 mm, and simultaneously satisfies equation (3), in Invention Examples A1 to A11, the iron loss is 0 .750 This is better than W / kg.

[0070] <Example 2> Slab containing 3.3 mass% Si, 0.10 mass% Mn, 0.006 mass% S, 0.060 mass% C, 0.027 mass% acid-soluble Al, and 0.008 mass% N, with the balance being Fe and impurities, was hot-rolled by a known method and then annealed. Steel plates B1 - B4 and b1 - b4 with a final plate thickness of 0.22 mm were obtained by cold rolling.

[0071] The cold-rolled steel plate was decarburized and annealed, and then nitrided. The decarburization annealing conditions were as follows: the steel plate was heated to 850 °C and then held for 60 seconds and cooled. The decarburization atmosphere was a hydrogen-nitrogen atmosphere, and P H2O / P H2 was adjusted within the range of 0.10 - 0.80. Also, the nitriding amount was set to 200 ppm.

[0072] Subsequently, the surface of the steel plate was irradiated with a laser, and a plurality of grooves extending in a direction intersecting the rolling direction were formed at intervals of 5 mm along the rolling direction. The groove formation direction was inclined 10° in the L direction (rolling direction) with respect to the C direction (steel plate width direction) of the steel plate, the groove depth was 20 μm, and the groove width was 50 μm.

[0073] The irradiation conditions of the laser light were adjusted within the range where the laser output was 2000 W, the spot diameter of the laser light in the rolling direction was 5 - 100 μm, the spot diameter of the laser light in the plate width direction was 5 - 100 μm, and the laser scanning speed was 5 - 100 m / s.

[0074] During laser irradiation, air was blown at 100 liters / minute as an assist gas to efficiently remove the metal of the steel plate melted and evaporated by the laser.

[0075] Thereafter, an annealing release agent mainly composed of MgO was applied so that the coating amount was 4 g / m on one side. 2 The composition of the annealing release agent was MgO: 100 parts by mass, TiO2: 5 parts by mass, and FeCl2 was added so that the chlorine content was 200 ppm. The water content of the annealing release agent was 1.5%.

[0076] Next, the steel sheet coated with the annealing release agent was wound into a coil, held at 1200°C for 20 hours, and then cooled to form a glass film on the surface. The dew point temperature of the atmospheric gas supplied to the finish annealing furnace was -10°C. Furthermore, a tension film mainly composed of aluminum phosphate was formed to a thickness of 1 μm to obtain a grain-oriented electrical steel sheet. The tension at this time, including the glass film, was 12 MPa in the rolling direction.

[0077] Iron loss W after application of tension-resistant insulating film 17 / 50 Energy loss (measured under excitation conditions of 1.7T, 50Hz) and magnetic flux density B8 (magnetic flux density at a magnetization force of 800A / m) were measured. The results are shown in Table 2.

[0078] In Invention Examples B1-B4 and Comparative Examples b1-b4, the conditions for groove angle, groove depth, groove spacing, and groove width that affect iron loss were all the same. However, in the Comparative Examples, the focusing spot diameter did not satisfy equation (3), resulting in inferior iron loss.

[0079] <Example 3> Table 2 shows the results of measuring the thickness s1 of the glass coating embedded in the flat portion of the base steel plate and the thickness s2 of the glass coating embedded in the deepest part of the groove in the recess of the groove, in the sample prepared in Example 2. The iron loss was good when t2 / t1 < 1.00 and the relationship s2 / s1 < 1.00 was satisfied.

[0080] [Table 1]

[0081] [Table 2] [Industrial applicability]

[0082] The present invention can be used in industrial equipment that utilizes grain-oriented electrical steel sheets, such as winding cores for transformers. [Explanation of Symbols]

[0083] 1 Base steel plate 2 grooves 3 Base steel plate 4 Flat area 8 Glass coating 9. Glass coating insertion part θ is the angle between the direction perpendicular to the rolling direction of the base steel sheet (the width direction of the sheet) and the longitudinal direction of the groove. W groove width D. Depth of groove P groove spacing t1 Glass coating thickness of the flat portion of the base steel plate t2 Glass coating thickness at the deepest part of the groove

Claims

1. The surface of the steel plate has multiple grooves, A grain-oriented electrical steel sheet having a glass coating on the aforementioned surface, The absolute value of the angle θ between the direction perpendicular to the rolling direction and thickness direction of the steel plate and the longitudinal direction of the groove is 0 to 40°, the width W of the groove is 20 to 300 μm, the depth D of the groove is 10 to 40 μm, and the spacing P of the grooves in the rolling direction is 1.0 to 30 mm. When the thickness of the glass film on the flat portion of the surface other than the groove is t1, and the thickness of the glass film on the deepest part of the groove is t2, the relationship in equation (1) is satisfied, A grain-oriented electrical steel sheet characterized by having an iron loss W 17 / 50 of 0.750 W / kg or less. 0.05≦t2 / t1<1.00... Formula (1)

2. The grain-oriented electrical steel sheet according to claim 1, characterized in that when the thickness of the glass coating embedded in the flat portion is s1 and the thickness of the glass coating embedded in the deepest part of the groove is s2, the relational expression of formula (2) is satisfied. 0.05≦s2 / s1<1.00... Formula (2)

3. A method for manufacturing a grain-oriented electrical steel sheet as described in claim 1, The process includes forming grooves on the surface of a steel sheet after decarburization annealing and before finish annealing using a laser, In the groove forming step, the laser focusing spot diameter dL in the rolling direction of the steel sheet and the laser focusing spot diameter dC in the sheet width direction satisfy equation (3). A method for manufacturing grain-oriented electrical steel sheets, characterized by the following features. 0.10≦dL / dC<1.00... Formula (3)

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