Grain-oriented electrical steel sheet and method for producing same

Abstract

The purpose of the present invention is to provide a grain-oriented electrical steel sheet in which iron loss is further improved in magnetic domain control for forming a laser groove in a steel sheet after decarburization annealing and before final annealing. A grain-oriented electrical steel sheet according to the present invention is provided with a steel sheet having a plurality of grooves in the surface of the steel sheet, and a glass coating film formed on the surface of the steel sheet, and is characterized in that the absolute value of an angle (theta) formed between a direction orthogonal to the rolling direction and the thickness direction of the steel sheet and the longitudinal direction of the grooves is 0-40 DEG, and the width (W) of the grooves is 20-300 [mu] m. The depth D of the grooves is 10-40 [mu] m, and the interval P between the grooves in the rolling direction is 1.0-30 mm; when the thickness of the glass coating film at the flat part (part other than the groove) of the steel sheet surface is set as t1 and the thickness of the glass coating film at the deepest part of the groove is set as t2, the relational expression of formula (1) is satisfied: t2 / t1lt; 1.00... formula (1).

Description

Technical Field

[0001] The present invention relates to a grain-oriented electrical steel sheet. Background Art

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

[0003] Control of crystal orientation is achieved by forming a primary recrystallized aggregate structure during annealing after cold rolling. High-temperature annealing then leads to preferential growth of an orientation that favors magnetic properties, known as secondary recrystallization. This crystal orientation control reduces hysteresis loss in grain-oriented electrical steel sheets.

[0004] As a technology for reducing eddy current loss, a type of iron loss in grain-oriented electrical steel sheets, known techniques involve forming an insulating film on the surface of a base steel sheet with controlled crystal orientation. This insulating film not only imparts electrical insulation to the base steel sheet but also plays a role in providing tension and rust resistance.

[0005] Another method for reducing abnormal eddy current losses is the known magnetic domain control method, which forms strained regions or grooves in a direction intersecting the rolling direction at predetermined intervals along the rolling direction, thereby narrowing the width of the 180° magnetic domain (180° domain refinement). Magnetic domain control methods are categorized into two methods: applying strain to the base steel sheet of a grain-oriented electrical steel sheet; and forming grooves on the surface of a base steel sheet containing a film that applies tension to the base steel sheet.

[0006] By using grain-oriented electromagnetic steel sheets with slot-based magnetic domain control to manufacture transformer cores (wound cores), the slots remain even after stress relief annealing, maintaining the magnetic domain refinement effect. Consequently, magnetic domain control using slots is sometimes used to reduce abnormal eddy current losses in wound cores.

[0007] Figure 1 This is a diagram schematically showing an electromagnetic steel sheet with grooves formed therein. Figure 1 : shows a state in which a plurality of grooves 2 are formed on the surface of a base steel plate 1 at intervals in the rolling direction of the base steel plate 1. Figure 1 In the figure, the symbol θ represents the angle formed by the direction perpendicular to the rolling direction and the thickness direction of the base steel plate 1 (plate width direction) and the longitudinal direction of the groove 2. The symbol W represents the groove width, the symbol D represents the groove depth, and the symbol P represents the interval between adjacent grooves 2 in the rolling direction.

[0008] Various methods of forming grooves in electromagnetic steel sheets have been proposed.

[0009] 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.

[0010] Patent Document 2 discloses a gear pressing method in which a gear is mechanically pressed against the surface of a grain-oriented electromagnetic steel sheet to form grooves on the surface of the steel sheet.

[0011] However, the gear press method suffers from rapid tooth wear due to the high hardness of the electromagnetic steel sheet. Furthermore, from a high-speed processing perspective, achieving the line speeds of 100 mpm or higher required by typical steelmaking processes is difficult. While electrolytic etching methods do not suffer from tooth wear, they require masking, etching, and mask removal, making the process more complex than mechanical methods.

[0012] Patent Document 3 discloses a laser irradiation method for melting and evaporating a laser irradiated portion of a grain-oriented electrical steel sheet surface by laser irradiation. The laser irradiation method does not cause problems such as tooth wear and process complexity, and can also perform high-speed processing.

[0013] Furthermore, some groove forming steps have been proposed in laser irradiation methods. For example, Patent Document 4 discloses a laser irradiation method in which a final product sheet coated with a tension insulating film is irradiated with a laser. However, this method requires a second application of the insulating tension film, resulting in poor productivity.

[0014] Meanwhile, Patent Document 5 discloses a method for forming grooves in a cold-rolled steel sheet. This method does not require re-application of an insulating tension film and offers excellent productivity. However, during the subsequent decarburization annealing, the primary recrystallization aggregate structure deteriorates, and secondary recrystallization during the subsequent high-temperature annealing no longer exhibits satisfactory results.

[0015] Prior art literature

[0016] Patent Literature

[0017] Patent Document 1: Japanese Patent Publication No. 62-54873

[0018] Patent Document 2: Japanese Patent Publication No. 62-53579

[0019] Patent Document 3: Japanese Patent Application Laid-Open No. 2003-129135

[0020] Patent Document 4: Japanese Patent Application Laid-Open No. 2012-087332

[0021] Patent Document 5: International Publication No. 2019 / 156127

[0022] Patent Document 6: International Publication No. 2011 / 007771 Summary of the Invention

[0023] Problems to be solved by the invention

[0024] The present invention has been developed in view of the above-mentioned problems, and aims to further improve the iron loss in the magnetic domain control of laser grooves (grooves formed by laser irradiation) formed in steel sheets, with the object of providing such a grain-oriented electrical steel sheet.

[0025] Means used to solve problems

[0026] The inventors have conducted extensive research to address the aforementioned challenges. They have discovered conditions that prevent degradation of the primary recrystallized aggregate structure in the laser-grooved portion of a grain-oriented electrical steel sheet formed with laser grooves after decarburization annealing and before final annealing. The present invention is based on this knowledge and has the following main aspects.

[0027] [1] A grain-oriented electromagnetic steel sheet according to one embodiment of the present invention is characterized in that a plurality of grooves are provided on the surface of the steel sheet, and a glass film is provided on the surface. The absolute value of the angle θ formed by the direction perpendicular to the rolling direction and the 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 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 (the portion other than the groove) of the steel sheet is t1 and the thickness of the glass film at the deepest portion of the groove is t2, the relationship of formula (1) is satisfied.

[0028] t2 / t1<1.00…Formula (1).

[0029] [2] A grain-oriented electromagnetic steel sheet according to one embodiment of the present invention is characterized in that, in the grain-oriented electromagnetic steel sheet described in [1], when the thickness of the embedded portion of the glass film on the flat portion of the base steel sheet is s1 and the thickness of the embedded portion of the glass film at the deepest portion of the groove is s2, the relationship of formula (2) is satisfied.

[0030] s2 / s1<1.00…Formula (2).

[0031] [3] A method for manufacturing a grain-oriented electromagnetic steel sheet according to one embodiment of the present invention is the method for manufacturing a grain-oriented electromagnetic steel sheet according to [1] or [2], characterized in that it includes a groove forming step of forming grooves on the surface of the steel sheet after decarburization annealing and before final annealing using a laser, wherein in the groove forming step, a focal spot diameter dL of the laser in the rolling direction of the steel sheet and a focal spot diameter dC of the laser in the sheet width direction satisfy equation (3),

[0032] 0.10≤dL / dC<1.00…Formula (3).

[0033] Effects of the Invention

[0034] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet having excellent iron loss and magnetic domain control by laser grooves. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a diagram schematically showing an electromagnetic steel sheet having grooves formed therein.

[0036] Figure 2 This is a schematic diagram of the cross section of the steel plate in the cross section perpendicular to the longitudinal direction of the groove near the groove. DETAILED DESCRIPTION

[0037] Hereinafter, the present invention will be described by taking a grain-oriented electromagnetic steel sheet according to one embodiment of the present invention (hereinafter simply referred to as the present electromagnetic steel sheet) as an example.

[0038] like Figure 1 、 Figure 2 As shown in FIG. 1 , the electromagnetic steel sheet comprises: a base steel sheet 1 having a plurality of grooves 2 on its surface; and a glass film 8 formed on the surface of the base steel sheet 1. In the electromagnetic steel sheet, a tension film (insulating film) (not shown) may also be formed on the surface of the glass film 8. Figure 1 As shown, a plurality of grooves 2 are formed on the surface of a base steel plate 1 so as to be adjacent to each other in the rolling direction of the base steel plate 1. The groove direction (angle θ), groove width W, depth D, and spacing P are determined in consideration of iron loss, similar to those of conventional grain-oriented electromagnetic steel sheets.

[0039] <Angle θ between the long side of the base steel plate and the long side of the groove>

[0040] If the angle θ formed by the direction perpendicular to the rolling direction and thickness direction of the base steel plate (plate width direction) and the long side direction of the groove is too large, there will be no magnetic domain control effect, and the iron loss improvement effect can no longer be obtained, so it is preferably 0 to 40° (0° or more and 40° or less). The angle θ is preferably smaller, preferably set to less than 35°, less than 30°, less than 25°, less than 20°, less than 15°, less than 10°, less than 8°, less than 6° or less than 5°. The lower limit of the angle θ is 0°, that is, when the long side direction of the groove is parallel to the plate width direction. In addition, the direction of the angle θ is not limited, and refers to the angle on the acute angle side of the angle formed by the long side direction of the groove and the plate width direction. A plurality of grooves are arranged roughly in parallel on the surface of the base steel plate, but the angle θ of each groove can be as long as it is within the above range.

[0041] <Slot width W>

[0042] The groove width W refers to the width of the groove in the surface of the parent steel plate in the cross section of the groove perpendicular to the long side direction of the groove (groove cross section). Even if the groove width W is too narrow, it does not become the starting point for the generation of magnetic poles, there is no magnetic domain control effect, and good iron loss cannot be obtained, so it is preferably 20 μm or more. On the other hand, if the groove width W is too wide, it does not become the starting point for the generation of magnetic poles, there is no magnetic domain control effect, only the magnetic flux density decreases significantly, and good iron loss cannot be obtained, so it is preferably 300 μm or less. Therefore, 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 set to 25 μm, 30 μm or 35 μm. The upper limit of the groove width W is preferably set to 250 μm, 200 μm, 150 μm, 100 μm or 80 μm.

[0043] <Groove Depth D>

[0044] If the groove depth D is too shallow, it does not become the starting point of the magnetic pole and there is no magnetic domain control effect, and good iron loss cannot be obtained, so it is preferably greater than 10μm. On the other hand, if it is too deep, the magnetic domain control effect reaches saturation, and only the magnetic flux density decreases significantly, so good iron loss cannot be obtained, so it is preferably less than 40μm. Therefore, it is preferred to set the groove depth D to 10 to 40μm (more than 10μm and less than 40μm). The lower limit of the groove depth D is preferably set to 11μm, 12μm, 13μm, 14μm or 15μm. The upper limit of the groove depth D is preferably set to 38μm, 36μm, 34μm, 32μm, 30μm, 28μm or 26μm.

[0045] <Slot spacing P>

[0046] The slot spacing P refers to the spacing between the center lines of the adjacent slots arranged roughly parallel to each other on the surface of the base steel plate in the longitudinal direction, and is the distance in the rolling direction of the base steel plate. The center line of the slot is a line that passes through the midpoint of the slot on the surface of the base steel plate in the slot cross section and is parallel to the longitudinal direction of the slot. If the slot spacing P is too narrow, the magnetic domain control effect is saturated, only the magnetic flux density is significantly reduced, and good iron loss cannot be obtained, so it is preferably 1 mm or more. On the other hand, if it is too wide, the magnetic domain control effect cannot be fully obtained and good iron loss cannot be obtained, so it is preferably 30 mm or less. Therefore, the slot spacing P is preferably 1 to 30 mm (1 mm or more and 30 mm or less). In addition, the slot spacing P may not be an equal spacing, but the slot spacing P of the adjacent slots is preferably within the above range. The lower limit of the slot 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 interval P is preferably 25 mm, 20 mm, 15 mm, 10 mm, 7 mm, or 5 mm.

[0047] <Glass Film Thickness>

[0048] use Figure 2 The glass film on the flat part of the base steel plate in this electromagnetic steel plate (referring to the part where no groove is formed on the surface of the steel plate, that is, the part outside the groove, which is more than 1 / 2 of the groove width away from the groove edge. Hereinafter, it is simply referred to as the "flat part") and the laser groove concave part (hereinafter, it is simply referred to as the "groove") is described.

[0049] Figure 2 It is a cross-sectional view of the groove concave portion in a cross section perpendicular to the groove long side direction, and is a view of the area including the groove. The following, unless otherwise specifically denied, is based on the cross-sectional view in a cross section perpendicular to the groove long side direction ( Figure 2 ) for explanation.

[0050] The present electromagnetic steel sheet is a grain-oriented electromagnetic steel sheet characterized in that, when the thickness of the glass film on the flat portion of the base steel sheet is t1 and the thickness of the glass film at the deepest portion of the groove in the concave portion of the groove is t2, the relationship of formula (1) is satisfied.

[0051] t2 / t1<1.00…Formula (1)

[0052] The thickness t1 and t2 of the coating film at each part will be described. Figure 2 The embedded structure is shown. The embedded structure refers to a structure in which the end of the glass membrane extends into the base steel plate like the root of a plant. The part of the glass membrane embedded in the steel plate like the root of a plant is called the embedded part of the glass membrane. Therefore, in the cross section of the steel plate, there is a case where the end of the embedded structure appears to be separated from the glass membrane. For example, Figure 2 In the figure, the glass membrane embedded portion 9 can be seen as an isolated island at the location separated from the glass membrane 8 on the flat portion or the groove concave surface. However, this is to observe the cross section of the end portion of the glass membrane embedded portion 9, which forms the embedded structure. Hereinafter, the term "end of the glass membrane" refers to the portion of the glass membrane embedded portion 9 that is farthest from the glass membrane surface, including not only the glass membrane 8 but also the embedded structure portion that appears to be separated from the glass membrane, in the cross section of the steel plate perpendicular to the longitudinal direction of the groove.

[0053] Below, through Figure 2 The following describes a method for measuring the thicknesses t1 and t2 of the glass film at each portion.

[0054] like Figure 2 As shown, a straight line indicating the glass film surface in the flat portion 4 is designated as L1U, and a line passing through the deepest end in the thickness direction of the embedded structure of the glass film in the flat portion and parallel to L1U is designated as L1L.

[0055] Let L2U be the line parallel to L1U, passing through the glass film surface at the deepest part of the groove (the deepest point in the groove profile in the plate thickness direction). Furthermore, let L2L be the line parallel to L2U, passing through the end of the glass film embedded structure near the deepest part of the groove at the deepest end in the plate thickness direction.

[0056] The glass film thickness t1 at the flat portion is defined as the distance from L1U to L1L, and the glass film thickness t2 at the deepest portion of the groove is defined as the distance from L2U to L2L.

[0057] like Figure 2 As shown, the thickness t1 of the glass film on the flat portion of the base steel plate is the distance from the surface of the glass film to the end of the glass film embedding structure, that is, the maximum embedding depth of the glass film in the flat portion.

[0058] like Figure 2 As shown, in the recessed portion of the groove, the glass film thickness t2 at the deepest portion of the groove is the distance from the surface of the glass film at the deepest portion of the groove to the end of the embedded structure of the glass film, that is, the maximum embedding depth of the glass film at the deepest portion of the groove.

[0059] The thickness of the glass film can be measured, for example, by observing with an optical microscope or SEM after grinding the cross section of the steel plate. The observation range used to measure the embedding depth of the glass film can be set to a range that includes a distance equal to the width of the groove while clamping the groove. That is, the observation range is preferably such that, in a cross section perpendicular to the long side of the groove, the length in the rolling direction is set to an amount that ensures the width of the groove on both sides while clamping the groove (i.e., a length that is more than 3 times the width of the groove with the groove as the center), and the length in the plate thickness direction is set to about 2 times the depth of the groove. The thickness of the glass film in the flat portion is set to about 2 times the depth of the groove on each side of the groove (on each side of the groove). Figure 2 The thickness of the glass film on the flat portion is measured at a distance from the groove edge of more than 1 / 2 of the groove width W and within the groove width W (with the groove sandwiched on the left or right side). The average value (arithmetic mean) is taken as the thickness of the glass film on the flat portion.

[0060] Next, the iron loss improvement effect achieved by reducing the glass film thickness t2 at the deepest portion of the groove relative to the glass film thickness t1 at the flat portion of the base steel plate will be described.

[0061] Magnetic domain refinement in grain-oriented electrical steel sheets is achieved by generating high magnetostatic energy due to magnetic poles on the steel sheet surface. To counteract this, 180° domain walls are formed, narrowing the domain width. This narrowing of the domain width shortens the distance the domain walls travel when the steel sheet is magnetized, reducing energy loss during domain wall movement and eddy current loss.

[0062] In addition, by applying a glass film with a different expansion coefficient from the steel sheet at high temperature and thermally bonding it, after cooling, tensile tension is applied in the rolling direction due to the difference in expansion coefficients between the steel sheet and the glass film, thereby refining the magnetic domains and improving eddy current loss.

[0063] Furthermore, because the glass film is composed of a non-magnetic oxide and has a different magnetic permeability from the steel sheet, magnetic poles are generated at the interface, resulting in finer magnetic domains. Therefore, the glass film serves as the starting point for magnetic pole generation, and it is thought that this reduction in magnetic domains reduces eddy current losses.

[0064] Although tension is difficult to apply to the groove portion in the rolling direction, if a groove is formed at right angles to the rolling direction, magnetic poles are generated on the concave surface of the groove, which promotes magnetic domain refinement through the superposition effect with the magnetic poles brought by the glass film.

[0065] On the other hand, because the glass film is a non-magnetic oxide, thicker glass films reduce magnetic flux density, resulting in poorer hysteresis loss. Iron loss in electromagnetic steel sheets is the sum of hysteresis loss and eddy current loss, so it is desirable to minimize iron loss by controlling the glass film.

[0066] Therefore, the inventors of this application increased the thickness of the glass film in the flat portion of the base steel sheet, which occupies the majority of the surface area when viewed from above, to ensure magnetic pole generation starting points and promote magnetic domain refinement. Meanwhile, in the steel sheet grooves, the grooves themselves function as magnetic pole generation starting points, eliminating the need for magnetic pole generation starting points provided by the glass film. Specifically, they discovered that by reducing the thickness of the glass film at the deepest portion of the steel sheet grooves to suppress a decrease in magnetic flux density, magnetic pole generation starting points can be effectively ensured throughout the steel sheet, thereby improving iron loss.

[0067] That is, it was found that it is preferable to control so that the glass film thickness t1 of the flat part of the base steel plate and the glass film thickness t2 of the deepest part of the groove satisfy t2 / t1<1.00 of formula (1). As a result, the glass film composed of non-magnetic oxide in the groove forming portion is controlled to be less than the glass film of the flat part of the base steel plate, resulting in the suppression of the decrease in magnetic flux density, the hysteresis loss does not deteriorate, and the overall iron loss is improved. t2 / t1 is preferably less than 0.95, less than 0.90, less than 0.85, less than 0.80, less than 0.75, less than 0.70, less than 0.65, less than 0.60, less than 0.55 or less than 0.50. The lower limit of t2 / t1 is not particularly limited and can also be 0. In reality, t2 / t1 can also be greater than 0.05.

[0068] <Thickness of the Embedded Portion of the Glass Film>

[0069] Furthermore, in this electromagnetic steel sheet, when the thickness (depth) of the embedded portion of the glass film in the flat portion of the base steel sheet is s1 and the thickness (depth) of the embedded portion of the glass film in the deepest portion of the groove is s2, it is preferable to satisfy the relationship of formula (2).

[0070] s2 / s1<1.00…Formula (2)

[0071] As mentioned above, the glass membrane has an embedded structure, where the end of the glass membrane extends into the base steel plate, similar to a plant root. The embedded portion of the glass membrane refers to the portion of the glass membrane embedded in the steel plate, similar to a plant root. The thickness of the embedded portion refers to the depth of the embedded portion in the thickness direction of the steel plate.

[0072] The thickness s1 of the embedded portion of the glass film in the flat portion of the steel plate is the distance between the deepest portion of the glass film in the flat portion of the base steel plate continuously observed from the surface and the deepest portion of the glass film including the end of the embedded portion of the glass film that appears as an isolated island.

[0073] The thickness s2 of the embedded portion of the glass film at the deepest part of the groove is the distance between the deepest part of the glass film in the deepest part of the groove of the base steel plate where the glass film is continuously observed from the surface and the deepest part of the glass film including the end of the embedded portion of the glass film.

[0074] use Figure 2 The following describes the measurement method of the thickness s1 and s2 of the embedded portion of the glass film at each part. Figure 2 As shown, let L1M be the line parallel to L1U, passing through the deepest portion of the glass membrane 8 at the end 9 of the glass membrane embedded structure in the flat portion 4 of the steel plate, as viewed continuously from the surface. Furthermore, let L2M be the line parallel to L2U, passing through the deepest portion of the glass membrane embedded structure near the deepest portion of the groove, as viewed continuously from the surface. The thickness s1 of the glass membrane embedded portion in the flat portion is defined as the distance from L1U to L1M, while the thickness s2 of the glass membrane embedded portion in the deepest portion of the groove is defined as the distance from L2U to L2M.

[0075] For example, similar to the thickness of the glass membrane, the thickness of the embedded portion of the glass membrane can be measured by polishing the steel plate cross section and observing it with an optical microscope or SEM. The observation range for measuring the thickness of the embedded portion of the glass membrane is the same as that for the glass membrane thickness. Furthermore, the thickness of the embedded portion in the flat portion is calculated in the same manner as the thickness of the glass membrane: the average of the measured values ​​at the flat portions on both sides of the groove is used.

[0076] The iron loss improvement effect achieved by the glass film embedded portion having a thinner thickness s2 at the deepest part of the groove than the glass film embedded portion having a thinner thickness s1 at the flat part of the base steel plate is speculated as follows. Specifically, it is speculated that the embedded structure of the glass film is more likely to serve as a starting point for magnetic pole generation than a continuous glass film on the surface side of the base steel plate, and the magnetic domain refinement effect is accordingly greater. On the other hand, in the concave portion of the laser groove, the groove itself serves as the starting point for magnetic pole generation. Even if a glass film embedded portion is formed on the side deeper than the groove, the magnetic pole generation effect is small. Furthermore, the magnetic flux density decreases, and the hysteresis loss worsens. If the embedded portion is inserted deeper, a complex structure is formed, which may accordingly cause a deterioration in magnetic properties.

[0077] Therefore, it was found that it is preferable to control the thickness s1 of the embedded part of the glass film in the flat part of the base steel plate and the thickness s2 of the embedded part of the glass film in the deepest part of the groove to satisfy s2 / s1<1.00. As a result, the embedded part of the glass film in the deepest part of the groove can be thinned to suppress the complexity of the embedded structure, so the decrease in magnetic flux density can be further suppressed and the overall iron loss can be improved. The value of s2 / s1 is preferably less than 0.95, less than 0.90, less than 0.85, less than 0.80, less than 0.75, less than 0.70, less than 0.65, less than 0.60, less than 0.55 or less than 0.50. The lower limit of s2 / s1 is not particularly limited and can also be 0. In reality, s2 / s1 can also be greater than 0.05.

[0078] <Manufacturing method>

[0079] First, a cold-rolled steel sheet for the present electromagnetic steel sheet is manufactured by a known method. The steel sheet composition and the method for manufacturing the cold-rolled steel sheet are not particularly limited, and known methods such as the steel sheet composition and method for manufacturing the steel sheet described in Patent Document 6 can be used.

[0080] <Decarburization annealing>

[0081] Next, decarburization annealing can be performed by a known method, and nitriding annealing can be performed as needed at this time.

[0082] Decarburization conditions can be known conditions. For example, it is preferred to heat the steel plate to 850°C, hold for 60 seconds and then cool. The decarburization atmosphere is preferably a hydrogen-inert gas atmosphere. H2O / P H2 In the range of 0.15 to 0.65. H2O / P H2 Good properties can be obtained when the ratio is around 0.33. Nitriding can also be performed using a known method. The amount of nitriding can be set to, for example, 50 to 400 ppm, and good properties can be obtained particularly when the ratio is around 200 ppm.

[0083] <Groove Forming Process: Groove Formation by Laser>

[0084] A steel sheet that has undergone decarburization annealing or nitriding annealing after decarburization annealing is irradiated with laser light to form a plurality of grooves at predetermined intervals in a direction intersecting the rolling direction (groove forming step). The laser irradiation conditions, including the type of laser light source, laser output power, laser scanning speed, and steel sheet travel speed during laser irradiation, are not particularly limited; the conditions may be appropriately selected so that the groove width W, groove depth D, and predetermined groove spacing (groove spacing P) are within predetermined ranges.

[0085] [Laser light source]

[0086] As the laser light source, a high-power laser commonly used in industry, such as fiber laser, YAG laser, semiconductor laser, or CO2 laser, can be used. Either a pulsed laser or a continuous wave laser can be used as long as the groove can be formed stably.

[0087] [Laser output power]

[0088] If the laser output power is too low, the laser scanning speed required to form the desired grooves will decrease significantly, reducing industrial productivity. Therefore, it is preferably set to 200 W or higher. It is preferably 1000 W or higher, and more preferably 1500 W or higher. Furthermore, if the laser output power is too high, the power supply capacity increases, which increases equipment costs, making it impractical in industry. Therefore, it is preferably set to 3000 W or lower. It is preferably 2800 W or lower, and more preferably 2500 W or lower.

[0089] [Laser scanning speed]

[0090] If the laser scanning speed is too slow, productivity will decrease. Therefore, it should be set to 5 m / s or higher. It is preferably 20 m / s or higher, and more preferably 40 m / s or higher. Furthermore, if the laser scanning speed is too fast, high output power is required, increasing equipment costs. Therefore, it should be set to 100 m / s or lower. It is preferably 80 m / s or lower, and more preferably 60 m / s or lower.

[0091] [Laser spot shape]

[0092] As the laser irradiation conditions, for example, it is preferred to set the focusing spot diameter dL of the laser in the rolling direction to 5 to 100 μm, set the focusing spot diameter dC of the laser in the plate width direction to 5 to 100 μm, set the laser output power to 200 to 3000 W, and set the laser scanning speed to 5 m / s to 100 m / s, satisfying formula (3).

[0093] 0.10≤dL / dC<1.00…Formula (3)

[0094] When dL / dC is greater than 1, the laser spot diameter becomes an elongated ellipse in the rolling direction, making it difficult to control the laser groove shape. The spot diameter ratio dL / dC is preferably less than 1.00, and its upper limit is preferably 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less.

[0095] When dL / dC is less than 0.10, the laser spot diameter becomes an elongated ellipse in the plate width direction, making it difficult to control the laser groove shape. Therefore, the spot diameter ratio dL / dC is preferably greater than 0.1, and its lower limit is preferably 0.15 or 0.20.

[0096] The contribution of laser irradiation conditions to the control of the thickness of the glass film in the groove concave portion can be considered as follows.

[0097] First, in the area not irradiated by the laser (flat portion), the internal oxide layer SiO2 generated inside the base steel plate by decarburization annealing reacts with the annealing separation material MgO coated on the surface of the steel plate before the final annealing under high-temperature annealing of 1200°C in the final annealing process to generate an oxide composed of Mg2SiO4, namely a glass film.

[0098] Meanwhile, in the laser grooves, the internal oxide layer formed during the decarburization annealing prior to laser irradiation is removed by the laser, leaving the base metal exposed on the inner surface of the grooves. A molten zone remains along the sides of the grooves, but this molten zone grows orientated during solidification, forming columnar crystals. As the columnar crystals develop, their grain boundaries become diffusion paths for oxygen, forming an internal oxide layer. During the subsequent final annealing, the base metal partially oxidizes due to the moisture in the MgO slurry used as the annealing separator. However, 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 on the flat areas, forming a glass film.

[0099] Therefore, by setting the spot diameter ratio dL / dC to less than 1.00, the laser spot shape becomes an elongated ellipse in the direction perpendicular to the rolling direction (the sheet width direction). This reduces the heat input to the steel sheet, allowing thin columnar crystals to form along the groove sides, restricting the diffusion path and preventing the development of an internal oxide layer. As a result, a thin glass film is formed in the deepest part of the groove.

[0100] Furthermore, in order to control t2 / t1 < 0.90, the upper limit of the spot diameter ratio dL / dC may be set to 0.90, and is preferably set to 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less.

[0101] [Assist gas]

[0102] While laser irradiation is in progress, an assist gas is sprayed onto the area of ​​the steel sheet irradiated by the laser. The assist gas removes components melted or evaporated from the steel sheet by the laser irradiation. The spraying of the assist gas ensures that the laser light reaches the steel sheet stably, thereby ensuring stable groove formation. The assist gas flow rate is preferably set to, for example, 10 to 1000 liters per minute. The assist gas is preferably air or an inert gas.

[0103] Annealing separator coating

[0104] Then, an annealing separator is applied to the surface of the steel sheet. Regarding the final annealing described later, it is sometimes performed while the steel sheet is coiled in a coiled state. When the final annealing is performed in such a state, the coil may become sticky and difficult to unwind. Therefore, in this embodiment, an annealing separator is applied so that the coil can be unwound after the final annealing. Here, the main component of the annealing separator is MgO. During the final annealing, the MgO in the annealing separator undergoes a solid-phase reaction with the SiO2 in the internal oxide layer to form a glass film. The composition of the annealing separator can adopt a known composition, for example, it can be set to 100 parts by mass of MgO and 5 parts by mass of TiO2. As an additive, for example, FeCl2 can be added so that the chlorine content is 200 ppm.

[0105] To reduce the thickness of the glass film in the grooves, it is preferable to adjust the moisture content of the annealing separator after drying as needed when applying it to the steel sheet surface. If the moisture content of the annealing separator is too low, the glass film will not form sufficiently, resulting in poor appearance. Therefore, it is preferably set to 0.5% or higher. On the other hand, if the moisture content of the annealing separator is too high, the glass film thickness may increase, which may deteriorate magnetic properties. Therefore, it is preferably set to 6.0% or lower. In other words, the moisture content of the annealing separator is preferably set to 0.5% or higher and 6.0% or lower.

[0106] The moisture content of the annealing separator can be calculated, for example, by recovering the annealing separator from the surface of the steel sheet before final annealing, measuring its weight, and then measuring its weight again after heating to 1000°C. The weight difference between the two weights can also be used when heating to 1000°C.

[0107] <Final Annealing>

[0108] The final annealing step, also known as the secondary recrystallization annealing step, promotes secondary recrystallization of the steel sheet structure while also forming a glass film. The final annealing step involves coiling the steel sheet, coated with an annealing separator, at a temperature of 1150-1250°C for 10-30 hours, followed by cooling.

[0109] The dew point temperature of the atmosphere gas supplied to the finish annealing furnace is preferably not more than 0° C. If the dew point temperature is higher than 0° C., the glass film thickness becomes too large, and the magnetic properties may deteriorate, which is not preferable.

[0110] <Tension film formation>

[0111] Although tension can be applied to the steel sheet using only a glass film, a tension film (insulating film) is usually formed on the glass film to enhance the magnetic domain control effect. The tension film may contain, for example, aluminum phosphate as its main component and may have a thickness of 1 μm.

[0112] Example

[0113] Next, examples of the present invention will be described. The conditions in the examples are one embodiment of the present invention, and the present invention is not limited to this one embodiment.

[0114] <Example 1>

[0115] A slab containing 3.3 mass% Si, 0.10 mass% Mn, 0.006 mass% S, 0.060 mass% C, 0.027 mass% acid-soluble Al, 0.008 mass% N, and the remainder being Fe and impurities was used as a raw material. After hot rolling by a known method, the hot-rolled plate was annealed and cold rolled to obtain steel plates A1 to A11 and a1 to a10 with a final plate thickness of 0.22 mm.

[0116] The cold rolled steel sheet is decarburized and annealed, and then nitrided. The decarburization annealing conditions are as follows: the steel sheet is heated to 850°C, kept for 60 seconds, and then cooled. The decarburization atmosphere is a hydrogen-nitrogen atmosphere. H2O / P H2 The nitrogen content was adjusted within the range of 0.15 to 0.65. The nitriding amount was set to 200 ppm.

[0117] Next, the surface of the steel sheet is irradiated with laser light, forming a plurality of grooves extending in a direction intersecting the rolling direction at intervals of 1 to 40 mm along the rolling direction. The grooves are formed in an angle of 0 to 45° with respect to the C direction (the width of the steel sheet) in the L direction (the rolling direction). The groove depth is 5 to 45 μm, and the groove width is 15 to 400 μm.

[0118] The laser irradiation conditions are as follows: the laser output power is 2000W, the focusing spot diameter of the laser in the rolling direction is 5 to 100μm, the focusing spot diameter of the laser in the plate width direction is 5 to 100μm, and the laser scanning speed is adjusted within the range of 5 to 100m / s.

[0119] During laser irradiation, air was blown at 100 liters / minute as an assist gas in order to effectively remove the metal of the steel plate melted and evaporated by the laser.

[0120] Then, the annealing separator composed mainly of MgO was applied at a coating amount of 4 g / m2 per side. 2 The annealing separator was composed of 100 parts by mass of MgO and 5 parts by mass of TiO2, with FeCl2 added so that the chlorine content was 200 ppm. The water content of the annealing separator was 2.5%.

[0121] Next, the steel sheet coated with the annealing separator was coiled into a coil, held at 1200°C for 20 hours, and then cooled to form a glass film on the surface. The dew point of the atmosphere supplied to the final annealing furnace was -20°C. Furthermore, a tension film composed primarily 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.

[0122] Measure the iron loss W after applying the tension insulation film 17 / 50 The results are shown in Table 1: (Energy loss measured under excitation conditions of 1.7 T and 50 Hz) and magnetic flux density B8 (magnetic flux density at a magnetizing force of 800 A / m).

[0123] In inventive examples A1 to A11 and comparative examples a1 to a10, for inventive examples A1 to A11 satisfying formula (3), the iron loss is better than 0.075 W / kg, in which the absolute value of the angle θ with the long side direction of the groove is in the range of 0 to 40°, the width W of the groove is in the range of 20 to 300 μm, the depth D of the groove is in the range of 10 to 40 μm, and the spacing P of the groove in the rolling direction is in the range of 1.0 to 30 mm.

[0124] <Example 2>

[0125] A slab containing 3.3 mass% Si, 0.10 mass% Mn, 0.006 mass% S, 0.060 mass% C, 0.027 mass% acid-soluble Al, 0.008 mass% N, and the remainder being Fe and impurities was used as a raw material. After hot rolling by a known method, the hot-rolled plate was annealed and cold rolled to obtain steel plates B1 to B4 and b1 to b4 with a final plate thickness of 0.22 mm.

[0126] The cold rolled steel sheet is decarburized and annealed, and then nitrided. The decarburization annealing conditions are as follows: the steel sheet is heated to 850°C, kept for 60 seconds, and then cooled. The decarburization atmosphere is a hydrogen-nitrogen atmosphere. H2O / P H2The nitrogen content was adjusted within the range of 0.10 to 0.80. The nitriding amount was set to 200 ppm.

[0127] Next, the surface of the steel sheet was irradiated with laser light, forming multiple grooves extending in a direction intersecting the rolling direction at 5 mm intervals along the rolling direction. The grooves were formed in a direction inclined 10° in the L direction (rolling direction) relative to the C direction (steel sheet width), with a groove depth of 20 μm and a groove width of 50 μm.

[0128] The laser irradiation conditions are as follows: the laser output power is 2000W, the focusing spot diameter of the laser in the rolling direction is 5 to 100μm, the focusing spot diameter of the laser in the plate width direction is 5 to 100μm, and the laser scanning speed is adjusted within the range of 5 to 100m / s.

[0129] During laser irradiation, air was blown at 100 liters / minute as an assist gas in order to effectively remove the metal of the steel plate melted and evaporated by the laser.

[0130] Then, the annealing separator composed mainly of MgO was applied at a coating amount of 4 g / m2 per side. 2 The annealing separator was composed of 100 parts by mass of MgO and 5 parts by mass of TiO2, with FeCl2 added to achieve a chlorine concentration of 200 ppm. The water content of the annealing separator was 1.5%.

[0131] Next, the steel sheet coated with the annealing separator was coiled into a coil, held at 1200°C for 20 hours, and then cooled to form a glass film on the surface. The dew point of the atmosphere supplied to the final annealing furnace was -10°C. Furthermore, a tension film composed primarily of aluminum phosphate was formed to a thickness of 1 μm to produce a grain-oriented electrical steel sheet. The tension at this time, including the glass film, was 12 MPa in the rolling direction.

[0132] Measure the iron loss W after applying the tension insulation film 17 / 50 The results are shown in Table 2: (Energy loss measured under excitation conditions of 1.7 T and 50 Hz) and magnetic flux density B8 (magnetic flux density at a magnetizing force of 800 A / m).

[0133] Inventive Examples B1 to B4 and Comparative Examples b1 to b4, the conditions affecting the iron loss, such as the groove angle, groove depth, groove spacing, and groove width, are all the same. However, in the comparative examples, the focused spot diameter does not satisfy equation (3), resulting in poor iron loss.

[0134] <Example 3>

[0135] 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 portion of the groove in the recessed portion of the groove, for the sample produced in Example 2. Good iron loss was achieved when the relationship t2 / t1 < 1.00 and s2 / s1 < 1.00 were satisfied.

[0136]

[0137]

[0138] Industrial Applicability

[0139] The present invention can be used for industrial equipment using a grain-oriented electromagnetic steel sheet, such as a winding core for a transformer.

[0140] Label Description

[0141] 1 base steel plate; 2 groove; 3 base steel plate; 4 flat portion; 8 glass film; 9 glass film embedded portion; θ is the angle formed by the direction perpendicular to the rolling direction of the base steel plate (plate width direction) and the long side direction of the groove; W is the width of the groove; D is the depth of the groove; P is the spacing of the groove; t1 is the thickness of the glass film on the flat portion of the base steel plate; t2 is the thickness of the glass film at the deepest part of the groove.

Claims

1. A grain-oriented electromagnetic steel sheet, There are multiple grooves on the surface of the steel plate. A glass film is provided on the surface, The grain-oriented electromagnetic steel sheet is characterized in that The absolute value of the angle θ formed by the direction perpendicular to the rolling direction and the thickness direction of the steel plate and the long side 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 interval P of the grooves in the rolling direction is 1.0 to 30 mm. When the thickness of the glass film in the flat portion of the surface other than the groove is t1 and the thickness of the glass film in the deepest portion of the groove is t2, the relationship (1) is satisfied. t2 / t1<1.00…Formula (1).

2. The grain-oriented electrical steel sheet according to claim 1, wherein In the grain-oriented electromagnetic steel sheet, when the thickness of the glass film embedded in the flat portion is s1 and the thickness of the glass film embedded in the deepest portion of the groove is s2, the relationship of formula (2) is satisfied. s2 / s1<1.00…Formula (2).

3. A method for manufacturing a grain-oriented electrical steel sheet, comprising: The method for manufacturing the grain-oriented electrical steel sheet is characterized in that: The process includes forming grooves on the surface of the steel sheet after decarburization annealing and before final annealing using a laser. In the groove forming step, the focused spot diameter dL of the laser light in the rolling direction of the steel plate and the focused spot diameter dC of the laser light in the plate width direction satisfy equation (3), 0.10≤dL / dC<1.00…Formula (3).

Images