Grain-oriented electrical steel sheet

Abstract

The purpose of the present invention is to provide a grain-oriented electrical steel sheet which does not have a forsterite coating film (glass coating film), and which has excellent iron loss that has been subjected to heat-resistant magnetic domain control. This grain-oriented electrical steel sheet has no forsterite coating film on the surface of a base steel sheet, is provided with a tension coating film (insulating coating film), has a plurality of grooves in the surface, and has an SiO2 intermediate layer and an insulating coating film in this order on the surface of the steel sheet, and the coating film tension of the tension coating film is 10 MPa or more. Furthermore, an SiO2 internal oxide layer is provided directly below the surface of the base steel sheet, and the irregularities between the surface of the steel sheet and the internal oxide layer are 0.001 [mu] m-0. 100 [mu] m.

Description

Technical Field

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

[0002] Grain-oriented electrical steel sheets are mainly used for transformers. Transformers are continuously excited during a long period from installation to disposal, and energy losses are continuously generated. Therefore, the energy loss when magnetized by alternating current, that is, iron loss, becomes the main index determining the value of transformers.

[0003] To reduce the iron loss of grain-oriented electrical steel sheets, many methods have been proposed so far. For example, in the steel sheet structure, a method for increasing the aggregation in the {110}<001> orientation called Goss orientation, a method for increasing the content of solid solution elements such as Si that increase the resistivity in the steel sheet, a method for reducing the thickness of the steel sheet, and the like.

[0004] In addition, it is known that applying tension to the steel sheet is an effective method for reducing iron loss. Therefore, generally for the purpose of reducing iron loss, a film is formed on the surface of the grain-oriented electrical steel sheet. This film reduces the iron loss of the steel sheet as a single sheet by applying tension to the grain-oriented electrical steel sheet. When the grain-oriented electrical steel sheets are further laminated and used, this film reduces the iron loss of the iron core by ensuring electrical insulation between the steel sheets.

[0005] As the grain-oriented electrical steel sheet having a film formed thereon, there is the following grain-oriented electrical steel sheet, in which a Mg-containing oxide film, that is, a forsterite film, is formed on the surface of a mother steel sheet, and further an insulating film is formed on the surface of this forsterite film (hereinafter also referred to as a glass film). That is, in this case, the film on the mother steel sheet includes a forsterite film and an insulating film (hereinafter also referred to as a tension film). The forsterite film and the insulating film each perform two functions, an insulating function and a function of applying tension to the mother steel sheet.

[0006] The forsterite film is a Mg-containing oxide film, and is formed by the following method: in finish annealing for causing secondary recrystallization of the steel sheet, an annealing separating agent mainly composed of magnesium oxide (MgO) reacts with silicon oxide (SiO 2 ) formed on the mother steel sheet during decarburizing annealing in a heat treatment at 900 to 1200 °C for 30 hours or more.

[0007] The insulating film is formed by the following method: for example, a coating solution containing phosphoric acid or phosphate, colloidal silica, or chromic anhydride or chromate is applied to the mother steel sheet after finish annealing, and dried at 300 to 950 °C for 10 seconds or more.

[0008] In order for the insulating film to perform the insulating function and the function of applying tension to the mother steel sheet, high adhesion is required between these films and the mother steel sheet.

[0009] Conventionally, the adhesion between the insulating film and the steel plate has been ensured mainly by the anchoring effect generated by the unevenness at the interface between the mother steel plate and the forsterite film. However, in recent years, it has been found that the unevenness at this interface also becomes an obstacle to the movement of magnetic domain walls when the grain-oriented electrical steel sheet is magnetized, and thus also becomes a factor hindering the reduction of iron loss.

[0010] Therefore, in order to further reduce iron loss, a technique has been proposed in which, in the absence of an Mg-containing oxide film, i.e., a forsterite film, the adhesion of the insulating film is ensured in a state where the above interface is smoothed.

[0011] For example, Patent Document 1 proposes a technique in which the forsterite film is removed by pickling or the like, the surface of the mother steel plate is smoothed by chemical polishing or electric field polishing, and then a thin metal plating is applied to the surface. Patent Document 2 proposes a technique in which an annealing parting agent containing alumina (Al 2 O 3 ) is used during finish annealing to suppress the formation of the forsterite film itself and smooth the surface of the mother steel plate.

[0012] However, a grain-oriented electrical steel sheet without a forsterite film may sacrifice iron loss without performing non-heat-resistant magnetic domain control such as strain imparting by laser or electron beam irradiation. On the other hand, even when non-heat-resistant magnetic domain control such as strain imparting by laser or electron beam irradiation is performed, it cannot be used for materials for wound core transformers that require annealing in the transformer manufacturing process.

[0013] Therefore, Patent Document 3 proposes the application of heat-resistant magnetic domain control by pressing. However, in the absence of a forsterite film, it may affect the shape of the steel plate after magnetic domain control (after pressing).

[0014] In addition, for a grain-oriented electrical steel sheet without a forsterite film, even if a tension film is applied, the total film tension becomes small because there is no forsterite film. In the case of small film tension, even if heat-resistant magnetic domain control such as pressing is performed, the iron loss improvement effect becomes small. Therefore, a grain-oriented electrical steel sheet without a forsterite film is inferior in terms of iron loss compared to a grain-oriented electrical steel sheet with a forsterite film.

[0015] Prior Art Documents

[0016] Patent Documents

[0017] Patent Document 1: Japanese Patent Laid-Open No. 49-096920

[0018] Patent Document 2: International Publication No. 2002 / 088403

[0019] Patent Document 3: Japanese Patent Publication No. 62-053579

[0020] Patent Document 4: International Publication No. 2020 / 149321 Summary of the Invention

[0021] Problems to be Solved by the Invention

[0022] The present invention has been completed in view of the above problems, and an object thereof is to provide a grain-oriented electrical steel sheet that does not have a forsterite film and has undergone heat-resistant magnetic domain control, and to provide such a grain-oriented electrical steel sheet with excellent iron loss by improving the iron loss as a problem.

[0023] Means for Solving the Problems

[0024] The inventors of the present invention conducted in-depth research to solve the above problems. As a result, it was found that: by making efforts in the steel sheet manufacturing process, it is possible to manufacture a grain-oriented electrical steel sheet with excellent iron loss and steel sheet shape even without a forsterite film. The present invention has been completed based on the above knowledge, and its gist is as follows. [1]

[0026] A grain-oriented electrical steel sheet according to one aspect of the present invention has a plurality of grooves on its surface, and sequentially has a SiO 2 intermediate layer and an insulating film on the surface of the steel sheet serving as the base material. The film tension of the insulating film is 10 MPa or more, and it does not have a forsterite film. [2]

[0028] In the grain-oriented electrical steel sheet according to the above [1], the absolute value of the angle θ formed by the direction orthogonal to the rolling direction and the plate thickness direction of the groove and the length 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 50 μm, and the pitch P of the grooves in the rolling direction is 1 to 30 mm. [3]

[0030] In the grain-oriented electrical steel sheet according to the above [1] or [2], an SiO 2 internal oxidation layer is provided directly below the surface of the steel sheet serving as the base material. [4]

[0032] In the grain-oriented electrical steel sheet according to any one of the above [1] to [3], in the cross-section in the plate thickness direction of the steel sheet, the uneven height of the interface between the SiO 2 internal oxidation layer and the steel sheet serving as the base material is 0.001 μm to 0.100 μm in the plate thickness direction of the steel sheet. [5]

[0033] The oriented electromagnetic steel sheet according to any one of [1] to [4] above, wherein the grooves are formed by etching or laser.

[0034] Advantages of the Invention

[0035] According to the present invention, there is provided a method for manufacturing an oriented electromagnetic steel sheet that does not have a forsterite film and has excellent magnetic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram showing an electromagnetic steel sheet formed with grooves.

[0037] Figure 2 It is a sectional view in the thickness direction of the electromagnetic steel sheet of the present invention (a section perpendicular to the steel sheet surface), and is a schematic diagram for explaining the film structure of the electromagnetic steel sheet. DETAILED DESCRIPTION OF THE INVENTION

[0038] Hereinafter, the present invention will be described by taking an oriented electromagnetic steel sheet (hereinafter referred to as the present electromagnetic steel sheet) according to an embodiment of the present invention as an example.

[0039] <Tension of Insulating Film>

[0040] The present electromagnetic steel sheet is a base material steel sheet having a plurality of grooves on the surface, and does not have a forsterite film (glass film) on the surface of the base material steel sheet. However, an insulating film having a tension of 10 MPa or more can be obtained, and good iron loss characteristics can be obtained. The tension of the insulating film is preferably 11 MPa or more, 12 MPa or more, 13 MPa or more, 14 MPa or more, or 15 MPa or more.

[0041] Regarding the measurement of the tension of the insulating film, for example, the present electromagnetic steel sheet can be cut into 30×300 mm, and after removing the insulating film on one side, one end (any short side) of the steel sheet is fixed to measure the warpage of the steel sheet, and it is obtained from the following formula (1).

[0042] σ = 1.39×t×χ / T Formula (1)

[0043] σ: Tension of insulating film (MPa)

[0044] t: Plate thickness after removing the film on one side (mm)

[0045] T: Plate thickness before removing the film on one side (mm)

[0046] χ: Warpage (mm)

[0047] The composition of the insulating film is not particularly limited, but it is preferable to form a film by coating an aqueous coating solution (insulating film forming solution) mainly composed of phosphate and colloidal silica. As the phosphate, for example, phosphates such as Ca, Al, Sr, etc. are preferable, and among them, aluminum phosphate is more preferable. The type of colloidal silica is not particularly limited, and its particle size (average particle diameter) can also be appropriately selected. However, if the particle size exceeds 200 nm, it may settle in the treatment solution. Therefore, the particle size (average particle diameter based on the number) of colloidal silica is preferably 200 nm or less, and more preferably set to 190 nm or less, 180 nm or less, or 170 nm or less.

[0048] The film thickness of the insulating film is not particularly limited. However, if the film thickness is too thin, it is difficult to generate tension. Therefore, the film thickness is preferably set to 3 μm or more, more preferably set to 4 μm or more, 5 μm or more, or 6 μm or more. On the other hand, if the film thickness is too thick, the proportion of the non-magnetic layer in the steel plate becomes large, resulting in deterioration of iron loss accompanied by a decrease in magnetic flux density. Therefore, the film thickness is preferably set to 30 μm or less, more preferably set to 25 μm or less, or 20 μm or less.

[0049] <SiO 2 Intermediate layer>

[0050] It is difficult to form a high-tension insulating film on an electromagnetic steel plate that does not have a glass film on the steel plate surface to bear the anchoring effect of the insulating film. The inventors of the present invention found that by appropriately controlling the baking atmosphere of the insulating film, a high-tension insulating film can be formed. Although the mechanism is not yet clear, it is believed that during the baking annealing of the insulating film, an SiO 2 intermediate layer (SiO 2 intermediate layer) is formed, which plays an anchoring role. Therefore, the insulating film is closely adhered and high tension can be achieved.

[0051] As Figure 2 shown, the cross-section of the electromagnetic steel plate 1 of the present invention is composed of the steel plate 10 serving as the base material, the SiO 2 internal oxide layer 11 directly below the surface of the base material steel plate, the SiO 2 intermediate layer 12 on the surface of the base material steel plate, and the insulating film 13 thereon in this order. It is believed that since the lattice constants of the base material steel plate and SiO 2 are close, the lattice matching is good, and there is an internally oxidized SiO 2 (SiO 2 internal oxide layer 11) generated by finish annealing on the surface 10 of the base material steel plate, and an SiO 2 intermediate layer 12 is formed thereon, so it becomes stable in crystal structure. In addition, the insulating film 13 is based on SiO 2As a main component, it is formed on the intermediate layer 12 of SiO 2 and thus becomes stable in crystal structure. Therefore, it is considered that: by the presence of SiO 2 intermediate layer 12, a bonding state 1 stronger than that of direct contact between the steel plate and the insulating film 13 is produced. As a result, high tension of the insulating film can be obtained. The SiO 2 intermediate layer 12 can be confirmed by observing the cross-section in the plate thickness direction of the electromagnetic steel plate formed with the insulating film 13.

[0052] <SiO 2 Internal oxide layer>

[0053] If an SiO 2 internal oxide layer 11 is formed on the surface of the electromagnetic steel plate 10 without a glass film, and an SiO 2 intermediate layer 12 and a high-tension insulating film 13 are formed thereon, the adhesion between the insulating film and the steel plate can be made firmer. Although the mechanism of the strengthened adhesion has not been clarified, it is considered that: since the SiO 2 internal oxide layer 11 is formed along with minute irregularities on the steel plate surface, the anchoring effect of the SiO 2 intermediate layer is further strengthened.

[0054] The SiO 2 internal oxide layer and the irregular structure of the steel plate surface can be confirmed by TEM observation of the cross-section in the plate thickness direction (a cross-section perpendicular to the steel plate surface) of the electromagnetic steel plate formed with the insulating film. By confirming the surface position of the steel plate 10 as the base material through EDS analysis and the contrast of the bright field image, the SiO 2 internal oxide layer directly below the surface of the steel plate as the base material can be confirmed. In the TEM image of the cross-section in the thickness direction of the steel plate, the interface between the base material steel plate and the SiO 2 internal oxide layer (since it appears as a curved line in the cross-sectional view, this curve is called the interface curve) is determined. The SiO 2 internal oxide layer and the irregular structure of the steel plate surface can be evaluated by the irregularities of this interface. If it is described in Figure 2 , in an arbitrarily selected observation surface with a width of 1 μm, by measuring the distance (referred to as the irregularity height 14) between the line 16 formed by connecting the front end on the steel plate surface side of the interface curve 15 between the base material steel plate 10 and the SiO 2 internal oxide layer 11 and the line 17 formed by connecting the front end on the steel plate center side of the interface curve 15, the SiO 2The concavo-convex structure of the internal oxide layer and the steel plate surface. When the line 16 formed at the front end on the steel plate surface side of the connection interface curve 15 and the line 17 formed by connecting the front ends on the steel plate center side are not parallel, it is advisable to take the arithmetic mean of the distances at both ends of the lines (both ends of the observation surface with a width of 1 μm) as the distance between the two lines (concavo-convex height 14).

[0055] SiO 2 The concavo-convex structure (concavo-convex height) of the internal oxide layer and the steel plate surface is preferably 0.001 μm to 0.100 μm. In SiO 2 When the concavo-convex structure (concavo-convex height) of the internal oxide layer and the steel plate surface is too shallow, the effect of strengthening the adhesion of the insulating film formed by the internal oxide layer cannot be obtained. Therefore, preferably, the concavo-convex structure (concavo-convex height) is preferably 0.001 μm or more, more preferably 0.003 μm or more, 0.005 μm or more, 0.010 μm or more, or 0.020 μm or more. In SiO 2 When the concavo-convex structure (concavo-convex height) of the internal oxide layer and the steel plate surface is too deep, the iron loss deteriorates. Therefore, it is preferably 0.100 μm or less, more preferably 0.095 μm or less, 0.090 μm or less, 0.085 μm or less, or 0.080 μm or less.

[0056] <<Grooves on the steel plate surface>>

[0057] As Figure 1 shown, on the surface of the base steel plate, a plurality of grooves are formed in such a way that they are adjacent in the rolling direction of the base steel plate. The direction (angle θ) of the grooves, the width W, the depth D, and the interval P of the grooves are determined in consideration of the iron loss in the same way as that of a normal grain-oriented electrical steel sheet.

[0058] <The angle θ formed by the length direction of the base steel plate and the length direction of the groove>

[0059] If the angle θ formed by the direction orthogonal to the rolling direction and the plate thickness direction (plate width direction) of the base steel plate and the length direction of the groove is too large, there is no magnetic domain control effect and the iron loss improvement effect cannot be obtained. Therefore, it is set to 40° or less. The angle θ is preferably smaller, and it is advisable to set it to 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 the angle θ is 0°, that is, when the length direction of the groove is parallel to the plate width direction. It should be noted that the direction of the angle θ is not limited, and it refers to the acute angle side of the angle formed by the length direction of the groove and the plate width direction. A plurality of grooves are arranged substantially parallel to each other on the surface of the base steel plate, but as long as the angle θ of each groove is within the above range, it is acceptable.

[0060] <Groove width W>

[0061] The slot width W refers to the width of the slot at the surface of the base metal steel plate in the cross-section of the slot (slot cross-section) in a plane perpendicular to the length direction of the slot. If the slot width W is too narrow, it will not be the starting point for the generation of magnetic poles, there will be no magnetic domain control effect, and good iron loss cannot be obtained. Therefore, it is preferably set to 20 μm or more. On the other hand, if it is too wide, it will not be the starting point for the generation of magnetic poles, there will be no magnetic domain control effect, and only the magnetic flux density will be significantly reduced, and good iron loss cannot be obtained. Therefore, it is preferably set to 300 μm or less. The lower limit of the slot width W is preferably set to 25 μm, 30 μm, or 35 μm. The upper limit of the slot width W is preferably set to 250 μm, 200 μm, 150 μm, 100 μm, or 80 μm.

[0062] <Slot depth D>

[0063] When the slot depth D is too shallow, it will not be the starting point of the magnetic pole, there will be no magnetic domain control effect, and good iron loss cannot be obtained. Therefore, it is preferably set to 10 μm or more. On the other hand, when it is too deep, the magnetic domain control effect reaches saturation, and only the magnetic flux density is significantly reduced. Therefore, good iron loss cannot be obtained. Therefore, it is preferably set to 40 μm or less. The lower limit of the slot depth D is preferably set to 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm. The upper limit of the slot depth D is preferably set to 38 μm, 36 μm, 34 μm, 32 μm, 30 μm, 28 μm, or 26 μm.

[0064] <Slot pitch P>

[0065] The slot pitch P is the distance between the center lines in the length direction of the slot and the adjacent slot arranged substantially parallel to the surface of the base metal steel plate, and refers to the distance in the rolling direction of the base metal steel plate. The center line of the slot refers to a line parallel to the length direction of the slot passing through the midpoint of the slot in the surface of the base metal steel plate in the slot cross-section. When the slot pitch P is too narrow, the magnetic domain control effect reaches saturation, and only the magnetic flux density is significantly reduced. Therefore, good iron loss cannot be obtained. Therefore, it is preferably set to 1 mm or more. On the other hand, when it is too wide, the magnetic domain control effect cannot be obtained sufficiently, and good iron loss cannot be obtained. Therefore, it is preferably 30 mm or less. The pitch P of the slots may not be equally spaced, but the slot pitch P from the adjacent slot is preferably within the above range. The lower limit of the slot pitch 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 slot pitch P is preferably 25.0 mm, 20.0 mm, 15.0 mm, 10.0 mm, 7.0 mm, or 5.0 mm.

[0066] <<Manufacturing method>>

[0067] An example of the manufacturing method of this electromagnetic steel sheet will be described. First, a cold-rolled steel sheet for this electromagnetic steel sheet is manufactured by a known method. The steel sheet composition and the manufacturing method of the cold-rolled steel sheet are not particularly limited, and known methods can be adopted, such as the steel sheet composition and the steel sheet manufacturing method described in Patent Document 4. The following shows an example of specific processes, but the present invention is not limited to this example of processes.

[0068] (i) A hot rolling process of hot rolling a steel billet having a prescribed chemical composition to obtain a hot-rolled steel sheet;

[0069] As needed, there may also be a hot-rolled sheet annealing process of annealing the above hot-rolled steel sheet, and a hot-rolled sheet pickling process of pickling the above hot-rolled steel sheet and hot-rolled annealed steel sheet.

[0070] (ii) A cold rolling process of subjecting the above hot-rolled steel sheet to one cold rolling or two or more cold rollings with intermediate annealing to obtain a cold-rolled steel sheet

[0071] (iii) A decarburizing annealing process of subjecting the above cold-rolled steel sheet to decarburizing annealing and, as needed, nitriding treatment to obtain a decarburized annealed sheet.

[0072] (iv) An annealing separation agent coating process of coating an annealing separation agent on the above decarburized annealed sheet and drying it.

[0073] (v) A finish annealing process of subjecting the above decarburized annealed sheet coated with an annealing separation agent to finish annealing to obtain a finish annealed steel sheet

[0074] (vi) An annealing separation agent removing process of removing the remaining annealing separation agent from the surface of the above finish annealed steel sheet by a method including one or both of water washing and pickling.

[0075] (vii) An insulating film forming process of forming an insulating film on the surface of the above finish annealed steel sheet (viii) A magnetic domain control process of performing magnetic domain control treatment

[0076] It should be noted that the magnetic domain control process is to form grooves on the steel sheet surface, and can be performed on the steel sheet after cold rolling, decarburizing annealing, decarburizing nitriding annealing or finish annealing, or the steel sheet further provided with a tension film.

[0077] <Steel sheet composition>

[0078] As described above, the composition of the steel sheet is not particularly limited. As described above, for example, the steel sheet composition described in Patent Document 4 can also be used. Further, for example, in the case of a hot-rolled steel sheet, those having the following composition can also be used: containing C: 0.030 to 0.100%, Si: 0.80 to 7.00%, Mn: 0.01 to 1.00%, S + Se: 0.060% or less, acid-soluble Al: 0.010 to 0.065%, N: 0.004 to 0.012% by mass, and the balance being composed of Fe and impurities. The reasons for limiting the chemical composition of the steel slab in this case will be described. Hereinafter, unless otherwise specified, "%" for the chemical composition means "% by mass".

[0079] [C: 0.030 to 0.100%]

[0080] C (carbon) is an element effective for controlling the primary recrystallized structure, but has an adverse effect on magnetic properties, and thus is an element removed by decarburization annealing before finish annealing. If the C content of the steel slab is high, the decarburization annealing time becomes long and the productivity decreases, and thus the C content is preferably set to 0.100% or less. It is preferably 0.085% or less, more preferably 0.070% or less.

[0081] The C content is preferably low and is not particularly limited, but in consideration of productivity in industrial production and magnetic properties of the product, the substantial lower limit of the C content is preferably set to 0.030%.

[0082] [Si: 0.80 to 7.00%]

[0083] Silicon (Si) increases the electrical resistance of the steel sheet and reduces iron loss. If the Si content is low, γ (austenite) phase transformation occurs during finish annealing, and the crystal orientation of the grain-oriented electrical steel sheet is impaired, and thus the Si content is preferably set to 0.80% or more. The Si content is preferably 1.00% or more, 1.50% or more, 2.00% or more, and more preferably 2.50% or more.

[0084] On the other hand, if the Si content is high, the cold workability decreases and cracking is likely to occur during cold rolling, and thus the Si content is preferably 7.00% or less. The Si content is preferably 6.50% or less, 5.00% or less, 4.50% or less, and further preferably 4.00% or less.

[0085] [Mn: 0.01 to 1.00%]

[0086] Manganese (Mn) also increases the electrical resistance of the steel sheet and reduces iron loss. In addition, Mn combines with S or Se to form MnS or MnSe, which functions as an inhibitor. Whether the Mn content is too low or too high, secondary recrystallization is unstable. Therefore, the Mn content is preferably set to 0.01% to 1.00%. The preferred lower limit of the Mn content is 0.03%, 0.05%, 0.08%, and more preferably 0.09%. The preferred upper limit of the Mn content is preferably 0.80%, 0.50%, 0.30%, or 0.20%.

[0087] [Total of any one or both of S and Se: 0.060% or less]

[0088] S (sulfur) and Se (selenium) combine with Mn to form MnS and / or MnSe, which function as inhibitors.

[0089] If the total content of S and Se (S + Se) increases, the precipitation dispersion of MnS and MnSe becomes uneven after hot rolling. In this case, the desired secondary recrystallized structure cannot be obtained, the magnetic flux density decreases, or MnS remains after purification, and the hysteresis loss deteriorates. Therefore, the total content of S and Se is preferably set to 0.060% or less. The lower limit is not particularly limited and may not be included (0%), but in order to reliably obtain the effect, it is preferably 0.003% or more, 0.005% or more, 0.010% or more, or 0.015% or more.

[0090] [Acid-soluble Al (Sol.Al): 0.010 - 0.065%]

[0091] Acid-soluble aluminum (Al) (Sol.Al) combines with N to form AlN, (Al, Si)N, which functions as an inhibitor. If the acid-soluble Al is less, the effect will not be fully exhibited and secondary recrystallization will not proceed sufficiently. Therefore, the acid-soluble Al content is preferably set to 0.010% or more. The acid-soluble Al content is preferably 0.015% or more, and more preferably 0.020% or more. On the other hand, if the acid-soluble Al content is high, the precipitation dispersion of AlN and (Al, Si)N becomes uneven, and the required secondary recrystallized structure cannot be obtained, and the magnetic flux density decreases. Therefore, the acid-soluble Al (Sol.Al) is preferably set to 0.065% or less. The acid-soluble Al is preferably 0.055% or less, and more preferably 0.050% or less.

[0092] [N: 0.004 - 0.012%]

[0093] N (nitrogen) combines with Al to form AlN and (Al, Si)N, which function as inhibitors. If the N content is low, the formation of AlN and (Al, Si)N becomes insufficient. Therefore, it is advisable to set N at 0.004% or more. Preferably, it is 0.005% or more, 0.006% or more, or 0.007% or more. On the other hand, if the N content is high, there is a possibility of forming blisters (voids) in the steel sheet. Therefore, the N content is set at 0.012% or less.

[0094] [Cr: 0% to 0.30%]

[0095] Cr (chromium) may not be particularly contained, but like Si, it is an element effective in increasing resistance and reducing iron loss. Therefore, it may also be contained. To reliably obtain the effect, the Cr content is preferably 0.02% or more, and more preferably 0.05% or more.

[0096] On the other hand, if the Cr content is high, the reduction of magnetic flux density becomes a problem. Therefore, the upper limit of the Cr content is preferably 0.30%, and preferably 0.20% or 0.12%.

[0097] [Cu: 0% to 0.40%]

[0098] Cu (copper) may also not be particularly contained, but it is an element effective in increasing resistance and reducing iron loss. Therefore, it may also be contained. To reliably obtain the effect, the Cu content is preferably 0.05% or more, and more preferably 0.10% or more.

[0099] On the other hand, if the Cu content is high, there is a possibility that the effect of reducing iron loss saturates, and it becomes the cause of surface defects called "copper scaly fold" during hot rolling. Therefore, the upper limit of the Cu content is preferably 0.40%, and preferably 0.30% or 0.20%.

[0100] [P: 0% to 0.50%]

[0101] P (phosphorus) may also not be particularly contained, but it is an element effective in increasing resistance and reducing iron loss. Therefore, it may also be contained. To reliably obtain the effect, the P content is preferably 0.005% or more, and more preferably 0.010% or more.

[0102] On the other hand, if the P content is high, there is a possibility of problems with rollability. Therefore, the upper limit of the P content is preferably 0.50%, and preferably 0.20% or 0.15%.

[0103] [Sn: 0% to 0.30%]

[0104] [Sb: 0% to 0.30%]

[0105] Sn (tin) and Sb (antimony) may not be specifically contained, but they are elements that stabilize secondary recrystallization and promote the development of the Goss orientation ({110}<001> orientation). Therefore, they may also be contained. When it is necessary to reliably obtain the effect, the Sn content is preferably 0.02% or more, more preferably 0.05% or more, and the Sb content is preferably 0.01% or more, more preferably 0.03% or more.

[0106] On the other hand, if the amounts of Sn and Sb are large, it may have an adverse effect on the magnetic properties. Therefore, it is appropriate to set the upper limits of the Sn content and the Sb content to 0.30% respectively. The upper limits of the Sn content and the Sb content are further preferably 0.15% or 0.10% respectively.

[0107] [Ni: 0% to 1.00%]

[0108] Ni (nickel) may not be specifically contained, but it is an element effective in increasing the resistance and reducing the iron loss. In addition, Ni is an element effective in controlling the microstructure of the hot-rolled steel sheet and improving the magnetic properties. Therefore, it may also be contained. When it is necessary to reliably obtain the effect, the Ni content is preferably 0.01% or more, more preferably 0.02% or more.

[0109] On the other hand, if the Ni content is large, the secondary recrystallization may become unstable. Therefore, it is appropriate to set the Ni content to 1.00% or less, preferably 0.20% or less or 0.10% or less.

[0110] [B: 0% to 0.008%]

[0111] B (boron) may not be specifically contained, but it combines with N to form BN and exhibits an inhibitor effect. Therefore, it may also be contained. When it is necessary to reliably obtain the effect, the B content is preferably 0.0005% or more, more preferably 0.001% or more.

[0112] On the other hand, if the B content is large, it may have an adverse effect on the magnetic properties. Therefore, the upper limit of the B content is preferably 0.008%, more preferably 0.005% or 0.003%.

[0113] [V: 0% to 0.15%]

[0114] [Nb: 0% to 0.20%]

[0115] [Ti: 0% to 0.015%]

[0116] V (vanadium), Nb (niobium), and Ti (titanium) may not be specifically contained, but they are elements that function as inhibitors in combination with N and C. Therefore, they may also be contained. When it is necessary to reliably obtain these effects, the V content is preferably 0.002% or more, more preferably 0.010% or more. The Nb content is preferably 0.005% or more, more preferably 0.020% or more. The Ti content is preferably 0.002% or more, more preferably 0.004% or more.

[0117] On the other hand, if a large amount of V, Nb, and Ti is contained, there is a possibility that the magnetic properties of the final product (electromagnetic steel sheet) will deteriorate. Therefore, the upper limit of the V content is preferably 0.150%, more preferably 0.100% or 0.050%. The upper limit of the Ti content is preferably 0.0150%, more preferably 0.010% or 0.008%. The upper limit of the Nb content is preferably 0.200%, more preferably 0.100% or 0.080%.

[0118] [Mo: 0% to 0.10%]

[0119] Mo (molybdenum) may not be specifically contained, but it is an element effective in increasing the resistance and reducing iron loss. Therefore, it may also be contained. When it is necessary to reliably obtain the effect, the Mo content is preferably 0.005% or more, more preferably 0.01% or more.

[0120] On the other hand, if the Mo content is high, there is a possibility that problems will occur in the rollability of the steel sheet. Therefore, the upper limit of the Mo content is preferably 0.10%, more preferably 0.08% or 0.05%.

[0121] [Bi: 0% to 0.010%]

[0122] Bi (bismuth) may not be specifically contained, but it is an element effective in stabilizing precipitates such as sulfides and strengthening the function as an inhibitor. Therefore, it may also be contained. When it is necessary to reliably obtain the effect, the Bi content is preferably 0.001% or more, more preferably 0.002% or more.

[0123] On the other hand, if the Bi content is high, there is a possibility of adverse effects on the magnetic properties. Therefore, the upper limit of the Bi content is preferably 0.010%, more preferably 0.008% or 0.006%.

[0124] The remainder other than the above elements is Fe and impurities. Here, "impurities" refer to components mixed in due to various factors such as raw materials such as ores and scraps and manufacturing processes during the industrial production of steel, and components that are allowed within the range that does not adversely affect the present invention.

[0125] <Manufacturing method>

[0126] Next, an example of an embodiment of the method for manufacturing an electromagnetic steel sheet of the present invention will be described. The method for manufacturing an electromagnetic steel sheet of the present invention is not limited to the embodiment described herein.

[0127] <Hot rolling process>

[0128] There is no limitation on the method for manufacturing the steel billet (slab) supplied to the hot rolling process. For example, molten steel having a predetermined chemical composition is melted, and the slab can be manufactured using this molten steel. The slab can also be manufactured by continuous casting, or an ingot can be manufactured using molten steel and the ingot can be bloomed to manufacture the slab. In addition, the slab can be manufactured by other methods.

[0129] The thickness of the slab is not particularly limited, but for example, it is 150 to 350 mm. The thickness of the slab is preferably 220 to 280 mm. As the slab, a so-called thin slab having a thickness of 10 to 70 mm can also be used.

[0130] Next, the conditions for hot rolling the above steel billet will be described.

[0131] There is no particular limitation on the hot rolling conditions. For example, the conditions are as follows.

[0132] Before hot rolling, the slab is heated. The slab is charged into a well-known heating furnace or a well-known soaking furnace for heating. As one method, the slab is heated to 1100°C to 1280°C. By setting the heating temperature of the slab to 1280°C or lower, various problems (such as the need for a dedicated heating furnace and a large amount of molten scale) generated when heating at a temperature higher than 1280°C can be avoided, for example. When the heating temperature is too low, hot rolling may become difficult and the productivity may decrease. Therefore, the heating temperature can be set in consideration of productivity within the range of 1280°C or lower. The preferred lower limit of the heating temperature of the slab is 1100°C. The preferred upper limit of the heating temperature of the slab is 1250°C.

[0133] In addition, as another method, the slab can also be heated to a high temperature of 1320°C or higher. By heating to a high temperature of 1320°C or higher, AlN and Mn(S, Se) are dissolved, and by finely precipitating them in subsequent processes, secondary recrystallization can be stably exhibited. The upper limit temperature in this case is 1350°C at which the slab melts.

[0134] The slab heating process itself can also be omitted, and hot rolling can be started after casting until the temperature of the slab drops to a specified temperature.

[0135] Next, hot rolling is performed on the heated slab. The hot rolling mill includes, for example, a rough rolling mill and a finish rolling mill disposed downstream of the rough rolling mill. The rough rolling mill includes a series of rough rolling stands arranged in a row. Each rough rolling stand includes a plurality of rolls arranged vertically. Similarly, the finish rolling mill includes a series of finish rolling stands arranged in a row. Each finish rolling stand includes a plurality of rolls arranged vertically. After the heated steel material is rolled by the rough rolling mill, it is further rolled by the finish rolling mill to produce a hot rolled steel sheet. The finish rolling temperature in the hot rolling process (the temperature of the steel sheet on the outlet side of the finish rolling stand where the steel sheet is finally reduced in the finish rolling mill) is, for example, 700 to 1150 °C. Through the above hot rolling process, a hot rolled steel sheet is produced.

[0136] <Hot rolled sheet annealing process>

[0137] In the hot rolled sheet annealing process, if necessary, the hot rolled steel sheet obtained through the hot rolling process is annealed (hot rolled sheet annealing) to obtain a hot rolled annealed sheet.

[0138] Hot rolled sheet annealing is carried out for the following purposes, etc., to make the non-uniform structure generated during hot rolling as uniform as possible, control the precipitation (fine precipitation) of AlN as an inhibitor, and control the second phase / solid solution carbon. The annealing conditions can be selected from known conditions according to the purpose. For example, in the case of making the non-uniform structure generated during hot rolling uniform, it is advisable to hold the hot rolled steel sheet at an annealing temperature (the furnace temperature in the hot rolled sheet annealing furnace) of 750 to 1200 °C for 30 to 600 seconds.

[0139] Hot rolled sheet annealing is not necessarily required, and the implementation or not of the hot rolled sheet annealing process can be determined according to the characteristics and manufacturing cost required for the finally manufactured grain-oriented electrical steel sheet.

[0140] <Hot rolled sheet pickling process>

[0141] In the hot rolled sheet pickling process, for the hot rolled steel sheet after the hot rolling process or the hot rolled annealed sheet after the hot rolled sheet annealing process, pickling is carried out as needed to remove the scale formed on the surface. There are no particular restrictions on the pickling conditions, and it can be carried out under known conditions.

[0142] <Cold rolling process>

[0143] In the cold rolling process, for the hot rolled steel sheet or hot rolled annealed sheet after the hot rolling process, the hot rolled sheet annealing process, or the hot rolled sheet pickling process, one cold rolling or two or more cold rollings with intermediate annealing are carried out to produce a cold rolled steel sheet.

[0144] The preferred cold rolling rate in the final cold rolling is 80% or more, more preferably 90% or more. The preferred upper limit of the cold rolling rate is 95%.

[0145] Here, the cold rolling rate (%) is defined as follows.

[0146] Cold rolling rate (%) = (1 - thickness of the cold-rolled steel sheet / thickness of the steel sheet before cold rolling) × 100

[0147] <Decarburizing annealing process>

[0148] In the decarburizing annealing process, for the cold-rolled steel sheet manufactured through the cold rolling process, decarburizing annealing is carried out to cause primary recrystallization.

[0149] In decarburizing annealing, the oxidation degree (PH2O / PH2 2 O / PH 2 : the partial pressure ratio of water vapor to hydrogen) in the annealing atmosphere (furnace atmosphere) is set to 0.01 - 0.15, and it is held at an annealing temperature of 750 - 900 °C for 10 - 600 seconds.

[0150] If the oxidation degree (PH2O / PH2 2 O / PH 2 ) is too small, not only does the decarburization rate slow down, resulting in reduced productivity, but also poor decarburization occurs, and the magnetic properties deteriorate after finish annealing. On the other hand, if the oxidation degree is too large, it becomes easy to form Fe-based oxides, and it becomes difficult to smooth the interface after finish annealing. Therefore, it is appropriate to set the oxidation degree to 0.01 - 0.15.

[0151] If the annealing temperature is too low, not only does the decarburization rate slow down, resulting in reduced productivity, but also poor decarburization occurs, and the magnetic properties deteriorate after finish annealing. On the other hand, if the annealing temperature is too high, the primary recrystallization grain size exceeds the desired size, so the magnetic properties deteriorate after finish annealing. Therefore, it is appropriate to set the annealing temperature to 750 °C - 900 °C.

[0152] If the holding time is too short, decarburization cannot be carried out sufficiently. On the other hand, if the holding time is too long, productivity decreases, and the primary recrystallization grain size exceeds the desired size, so the magnetic properties deteriorate after finish annealing. Therefore, it is appropriate to set the holding time to 10 seconds - 600 seconds (10 minutes).

[0153] <Nitriding treatment>

[0154] In the decarburizing annealing process, nitriding treatment can also be carried out as needed. By further performing nitriding treatment in the decarburizing annealing process, inhibitors such as AlN, (Al, Si)N, etc. are generated before secondary recrystallization in the finish annealing process, so that secondary recrystallization can be stably exhibited.

[0155] There are no particular limitations on the conditions for nitriding treatment. However, preferably, nitriding treatment is carried out in such a manner that the nitrogen content in the vicinity of the steel plate surface (surface layer) increases by 0.003 mass% or more, preferably by 0.005 mass% or more, and more preferably by 0.007 mass% or more. If the nitrogen (N) content exceeds 0.030 mass%, the effect also saturates. Therefore, nitriding treatment may also be carried out in such a manner that the nitrogen content becomes 0.030 mass% or less.

[0156] There are no particular limitations on the conditions for nitriding treatment, and it may be carried out under known conditions. For example, when the oxidation degree (PH 2 O / PH 2 ) is 0.01 to 0.15, and after holding at 750 to 900 °C for 10 to 600 seconds, nitriding treatment is carried out without cooling the cold-rolled steel sheet to room temperature, but by holding in an atmosphere containing ammonia during the temperature drop process. Preferably, during the temperature drop process, the oxidation degree (PH 2 O / PH 2 ) is set in the range of 0.0001 to 0.01. When the oxidation degree (PH 2 O / PH 2 ) is 0.01 to 0.15 and nitriding treatment is carried out while holding at 750 to 900 °C for 10 to 600 seconds, it is only necessary to introduce ammonia into the atmosphere gas of this oxidation degree.

[0157] <Annealing release agent coating process>

[0158] In the annealing release agent coating process, an annealing release agent containing Al 2 O 3 and MgO is coated on the decarburized annealed sheet, and the coated annealing release agent is dried.

[0159] When the annealing release agent contains MgO and does not contain Al 2 O 3 , in the final annealing process, a forsterite film is formed on the steel plate. On the other hand, when the annealing release agent contains Al 2 O 3 and does not contain MgO, mullite (3Al 2 O 3 ·2SiO 2 ) is formed on the steel plate. This mullite becomes an obstacle to the movement of magnetic domain walls and thus causes deterioration of the magnetic properties of the oriented electrical steel sheet.

[0160] Therefore, as the annealing release agent, by containing Al 2 O 3 and MgO, the mass ratio of MgO, that is, MgO / (MgO + Al 2 O 3) It is set to 5 to 50%, so that after finish annealing, no forsterite film is formed on the steel plate surface. In addition, a small amount of mullite is generated, but it is removed in the annealing separator removal process in a powdery state and does not remain on the steel plate surface. Therefore, a steel plate with a smooth surface can be obtained.

[0161] If the MgO ratio MgO / (MgO + Al 2 O 3 ) is too small, a large amount of mullite is formed and a part of it remains on the steel plate surface. Therefore, the iron loss deteriorates, so it is set to 5% or more. It is preferably that the MgO ratio MgO / (MgO + Al 2 O 3 ) is 7% or more, 9% or more, or 10% or more. On the other hand, if the MgO ratio MgO / (MgO + Al 2 O 3 ) is too large, forsterite is formed, so the iron loss deteriorates, so it is set to 50% or less. It is preferably that the MgO ratio MgO / (MgO + Al 2 O 3 ) is 48% or less, 46% or less, 44% or less, 42% or less, or 40% or less.

[0162] In addition, if the hydrated moisture of the annealing separator is too much, there is a possibility that secondary recrystallization becomes unstable, or the steel plate surface is oxidized (forming SiO 2 ) during finish annealing, and it becomes difficult to smooth the steel plate surface. Therefore, the hydrated moisture of the annealing separator is set to 1.5 mass% or less.

[0163] The annealing separator is coated on the steel plate surface by aqueous slurry coating or electrostatic coating, etc. In the annealing separator coating process, nitrides such as manganese nitride, iron nitride, and chromium nitride that decompose before secondary recrystallization in the finish annealing process to nitride the decarburized annealed plate can be further added to the annealing separator.

[0164] <Finish Annealing Process>

[0165] The decarburized annealed plate coated with the annealing separator is subjected to finish annealing to produce a finish annealed steel plate. By performing finish annealing on the decarburized annealed plate coated with the annealing separator, secondary recrystallization proceeds, and the crystal orientation aggregates in the Goss orientation ({110}<001> orientation).

[0166] During finish annealing, when the furnace atmosphere contains hydrogen, the oxidation degree (PH 2 O / PH 2 ) is set to 0.0001 to 0.2000, and when it contains an inert gas without hydrogen (nitrogen, argon, etc.), the dew point is set to 0°C or lower. Thus, secondary recrystallization can be stably exhibited and the orientation aggregation degree can be improved.

[0167] When the furnace atmosphere contains hydrogen, if the degree of oxidation is too small, the dense silica film (SiO 2 film) formed during decarburizing annealing is reduced before secondary recrystallization in finish annealing, and the secondary recrystallization becomes unstable. Therefore, the degree of oxidation is set to 0.0001 or more. Preferably, the degree of oxidation is set to 0.0005 or more, 0.0010 or more, 0.0020 or more, or 0.0050 or more. Furthermore, in order to form an internal oxide layer of SiO 2 on the steel plate surface, and further to form the uneven structure (uneven height) of the internal oxide layer and the steel plate in a manner to achieve a specified size, the degree of oxidation (PH 2 O / PH 2 ) in the temperature range of 800°C to 900°C during the heating process of finish annealing is preferably set to 0.0050 or more, more preferably set to 0.0060 or more, 0.0070 or more, 0.0080 or more, 0.0090 or more, or 0.0100 or more.

[0168] On the other hand, if the degree of oxidation is too large, the decomposition of inhibitors such as AlN and (Al, Si)N is promoted, and the secondary recrystallization becomes unstable. Therefore, the degree of oxidation is set to 0.2000 or less. Preferably, the degree of oxidation is set to 0.1900 or less, 0.1800 or less, 0.1700 or less, 0.1600 or less, or 0.1500 or less.

[0169] In addition, when the furnace atmosphere does not contain hydrogen, that is, when the furnace atmosphere is an inert gas, if the dew point is too high, the decomposition of inhibitors such as AlN and (Al, Si)N is promoted, and the secondary recrystallization becomes unstable. Therefore, the dew point is set to 0°C or less. Preferably, the dew point is set to -5°C or less, or -10°C or less. Furthermore, in order to form an internal oxide layer of SiO 2 on the steel plate surface, and further to form the unevenness of the internal oxide layer and the steel plate surface in a manner to achieve a specified size, the dew point is set to -20°C or more, preferably set to -18°C or more, -16°C or more, or -15°C or more.

[0170] <Annealing release agent removal process>

[0171] In the annealing release agent removal process, the annealing release agent is removed from the surface of the steel plate (finish annealed steel plate) after finish annealing by a method including one or both of water washing and pickling.

[0172] When the removal of the remaining annealing release agent on the steel plate surface is insufficient, the duty factor deteriorates, and the performance of the iron core decreases.

[0173] In order to remove the remaining annealing release agent, in addition to water washing and pickling, a scrubber can be further used for removal. By using the scrubber, it is possible to reliably remove the remaining annealing release agent that deteriorates the wettability in the insulating film coating process.

[0174] In addition, when pickling is performed to remove the remaining annealing release agent, it is preferable to use a solution containing one or more of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, chloric acid, aqueous chromium oxide solution, chromium sulfate, permanganic acid, peroxymonosulfuric acid, and peroxymonophosphoric acid in a total amount of 20% by weight or less, preferably 10% by weight or less. By using such a solution, the remaining annealing release agent on the surface of the steel sheet can be effectively removed.

[0175] In addition, when pickling is performed, it is preferable to set the liquid temperature of the solution to 20 to 80°C. By setting the liquid temperature within the above range, the remaining annealing release agent on the surface of the steel sheet can be effectively removed.

[0176] <Insulating film forming process>

[0177] In the insulating film forming process, an insulating film is formed on the surface of the finished annealed steel sheet after the annealing release agent removal process. This insulating film reduces the iron loss of the steel sheet as a single plate by applying tension to the grain-oriented electrical steel sheet, and when the grain-oriented electrical steel sheets are laminated and used, it reduces the iron loss of the core by ensuring electrical insulation between the steel sheets.

[0178] The type of the insulating film is not limited. For example, it is formed by coating a coating liquid of an insulating film having at least one of phosphate or colloidal silica as the main component, baking at 350 to 600°C, and then performing heat treatment at a temperature of 800 to 1000°C.

[0179] The colloidal silica is not particularly limited to a colloidal silica having a specific property. The particle size is also not particularly limited to a specific particle size, but it is preferably 200 nm (number average particle size) or less, for example, 5 to 30 nm is appropriate. If the particle size exceeds 200 nm, sedimentation may occur in the coating liquid. In addition, the coating liquid may further contain chromic anhydride or chromate. As the phosphate, phosphates such as Ca, Al, and Sr are preferred, and among them, aluminum phosphate is more preferred.

[0180] If the baking temperature of the insulating film is too low, the insulating film causes liquid sagging in the through-panel, which becomes the cause of poor appearance, and an insulating film with sufficient adhesion cannot be obtained. Therefore, it is set to 350 °C or higher. It is preferably set to 370 °C or higher, or 400 °C or higher. On the other hand, if the baking temperature of the insulating film is too high, the heating rate becomes excessively fast. Therefore, only the outermost surface of the insulating film is hardened, and the hardening of the interior is delayed, which becomes the cause of poor film formation and the adhesion of the film becomes insufficient. Therefore, it is set to 600 °C or lower. It is preferably set to 580 °C or lower, 560 °C or lower, or 540 °C or lower. It is preferable to set the heating rate up to the baking temperature to 100 °C / s or lower, preferably set to 70 °C / s or lower, 50 °C / s or lower, or 30 °C / s or lower. By slowing down the heating rate during baking, the film components can be fully hardened.

[0181] For example, it is appropriate to maintain it in the temperature range of 350 °C to 600 °C for 2.5 seconds to 100 seconds. When the degree of oxidation in the atmosphere at this time contains hydrogen in the furnace atmosphere, in order to form the SiO 2 intermediate layer, it only needs to be 0.01 or more, but in order to form the SiO 2 intermediate layer thick enough, for example, the degree of oxidation during baking is preferably set to 1.00 or more, preferably set to 1.50 or more, 1.60 or more, 1.70 or more, 1.80 or more, 1.90 or more, or 2.00 or more. On the other hand, if the degree of oxidation is too large, the SiO 2 intermediate layer and internal oxidation in the steel plate proceed excessively. Therefore, for example, the degree of oxidation is preferably set to 4.00 or less, preferably set to 3.50 or less, or 3.00 or less. When the furnace atmosphere does not contain hydrogen, the dew point temperature of the atmosphere can be set to 0 °C to 50 °C.

[0182] In addition, if the heat treatment temperature after baking is too low, it will lead to poor film formation (insufficient hardening), and the adhesion of the film becomes insufficient. Therefore, the heat treatment temperature after baking is set to 800 °C or higher. It is preferably set to 820 °C or higher, or 850 °C or higher. On the other hand, if the heat treatment temperature after baking is too high, it will cause the decomposition of phosphate, leading to poor film formation and the adhesion of the film becoming insufficient. Therefore, it is set to 1000 °C or lower. It is preferably set to 970 °C or lower, or 950 °C or lower. The heat treatment temperature after baking is preferably maintained in the specified temperature range for 10 to 300 seconds.

[0183] When forming the film, by setting the degree of oxidation of the atmosphere (PH 2 O / PH 2)It is set to 0.01 to 1.50, so that the insulating film can be formed without decomposing phosphate more than necessary, so it is preferred. If the degree of oxidation is too low, the SiO 2 intermediate layer becomes thinner, so the degree of oxidation is preferably set to 0.01 or more, more preferably set to 0.05 or more, 0.10 or more, 0.15 or more, or 0.20 or more. On the other hand, if the degree of oxidation is too high, not only the SiO 2 intermediate layer becomes excessively thick, but also the internal oxidation of the steel plate proceeds excessively, so it is preferably set to 1.50 or less, more preferably set to 1.40 or less, 1.20 or less, or 1.00 or less. In addition, the degree of oxidation in the heat treatment after baking is preferably lower than that during baking.

[0184] The coating liquid for forming the insulating film can be coated on the surface of the steel plate by a wet coating method such as a roll coater.

[0185] As described above, it is preferred to coat in such a way that the thickness of the insulating film becomes 3 to 30 μm.

[0186] The SiO 2 intermediate layer formed between the base steel plate and the insulating film is formed during the baking of the insulating film and the heat treatment after baking.

[0187] Alternatively, before coating the coating liquid for the insulating film, a SiO 2 intermediate layer can be formed on the surface of the base steel plate by heat treatment. In this case, the formation of the SiO 2 intermediate layer and the formation of the insulating film become different processes.

[0188] In the case where the SiO 2 intermediate layer is not formed, the adhesion between the insulating film and the base steel plate cannot be ensured, and the insulating film may peel off, which is not preferred.

[0189] After the insulating film is formed by high-temperature heat treatment and cooled to room temperature, due to the difference in the coefficient of thermal expansion between the insulating film and the base steel plate, it has the function of applying tension to the steel plate. Therefore, stress may be generated between the base steel plate and the insulating film, and the film adhesion deteriorates.

[0190] On the other hand, in a heat-resistant magnetic domain control-oriented electromagnetic steel plate in which grooves are provided on the base steel plate, increasing the tension on the base steel plate can more enjoy the magnetic domain control effect, which is preferred. However, if the tension is increased, there is a problem that the possibility of the film peeling off easily increases. The inventors of the present invention found that by irradiating the base steel plate with a laser to provide grooves, even if the tension of the insulating film is increased, by providing SiO 2The intermediate layer can also achieve the effect of suppressing the reduction of film adhesion. Regarding this mechanism, although it is not necessarily clear, it is presumed that in the formed grooved surface, the film adhesion is improved by the unevenness of the grooves. On the other hand, it is presumed that in the opposite surface of the groove formation, the slight undulations of the steel plate shape generated during laser irradiation contribute to the improvement of adhesion.

[0191] <Magnetic domain control process>

[0192] This grain-oriented electrical steel sheet has a magnetic domain control process for performing magnetic domain control treatment at any of the following time points: between the cold rolling process and the decarburizing annealing process, between the decarburizing annealing process (or decarburizing nitriding treatment process) and the annealing separator coating process, between the annealing separator removing process and the insulating film forming process, or after the insulating film forming process.

[0193] The magnetic domain control treatment can further reduce the iron loss of the grain-oriented electrical steel sheet by forming grooves on the steel plate surface.

[0194] <Method for forming grooves>

[0195] The method for forming grooves is not particularly limited. In mechanical methods such as pressing and rolling, the shape of the steel plate may be deformed, so methods such as etching and laser are preferably used. The method for forming grooves by laser irradiation will be described below.

[0196] <Laser irradiation conditions>

[0197] By irradiating a cold-rolled steel plate with laser, a plurality of grooves are formed on the steel plate surface in a direction intersecting the rolling direction such that the groove width W, the groove depth D, and the specified interval (groove interval P) are within a specified range. The type of laser light source, the laser output power, the laser scanning speed, and the steel plate moving speed during laser irradiation in the laser irradiation conditions are not particularly limited, but conditions can be appropriately selected as long as the groove width W, the groove depth D, and the specified interval (groove interval P) of the grooves are within a specified range.

[0198] [Laser light source]

[0199] As the laser light source, for example, a high-output power laser generally used in industry such as a fiber laser, a YAG laser, a semiconductor laser, or a CO2 laser can be used. As long as the grooves can be stably formed, it can be a pulsed laser or a continuous wave laser.

[0200] [Laser output power]

[0201] If the laser output power is lower than 200 W, in order to form the desired groove, the laser scanning speed is significantly reduced, and the industrial productivity is reduced. Therefore, it is preferably set to be above 200 W. It is more preferably above 1000 W, and still more preferably above 1500 W. In addition, when the laser output power exceeds 3000 W, the power supply capacity becomes large and the equipment cost becomes huge. Therefore, it is not practical industrially, and thus it is preferably set to be below 3000 W. It is more preferably below 2800 W, and still more preferably below 2500 W.

[0202] [Laser scanning speed]

[0203] When the laser scanning speed is lower than 5 m / s, it is necessary to slow down the passing speed of the steel plate, resulting in a reduction in productivity. Therefore, it is set to be 5 m / s or more. It is more preferably 20 m / s or more, and still more preferably 40 m / s or more. In addition, when the laser scanning speed is as fast as exceeding 100 m / s, a high output power becomes required and the equipment cost increases. Therefore, it is set to be 100 m / s or less. It is more preferably 80 m / s or less, and still more preferably 60 m / s or less.

[0204] [Laser focusing spot shape]

[0205] The shape of the laser focusing spot is not particularly limited. It is preferably circular or elliptical on the surface of the base material steel plate. In order not to expand excessively, for example, the ratio (dL / dC) of the diameter dL of the focusing spot of the laser in the rolling direction to the diameter dC of the focusing spot of the laser in the plate width direction satisfies 0.01 to 100, which is preferable.

[0206] <Auxiliary gas>

[0207] Simultaneously with the irradiation of the laser, an auxiliary gas can also be blown onto the part of the steel plate irradiated with the laser. The auxiliary gas serves to remove the components melted or evaporated from the steel plate due to the laser irradiation. By blowing the auxiliary gas, the laser can reach the steel plate stably, and thus the groove is formed stably. The flow rate of the auxiliary gas is preferably set to be 10 to 1000 liters per minute, for example. In addition, the auxiliary gas is preferably air or an inert gas.

[0208] Examples

[0209] <Example 1>

[0210] Slabs containing Si: 3.3% by mass, Mn: 0.10% by mass, S: 0.006% by mass, C: 0.060% by mass, acid-soluble Al: 0.027% by mass, N: 0.008% by mass, and the balance being Fe and impurities were used as raw materials. After hot rolling by a known method, hot rolled plate annealing was carried out, and in cold rolling, the final plate thickness was 0.22 mm to obtain steel plates A1 to A12 and a1 to a12.

[0211] Next, decarburize the cold-rolled steel sheet among A1 to A12 and a5 to a12, and further perform nitriding treatment. The decarburization conditions are set as follows: after heating to 850 °C, hold for 60 seconds and then cool. The decarburization atmosphere is in a hydrogen-nitrogen atmosphere where PH 2 O / PH 2 is set to 0.1. The nitriding amount is set to 200 ppm. In addition, decarburize the cold-rolled steel sheet among a1 to a4, and further perform nitriding treatment. The decarburization conditions are set as follows: after heating to 850 °C, hold for 60 seconds and then cool. The decarburization atmosphere is in a hydrogen-nitrogen atmosphere where PH 2 O / PH 2 is set to 0.3. In addition, the nitriding amount is set to 200 ppm.

[0212] After that, among A1 to A12 and a5 to a12, coat MgO / (MgO + Al 2 ) at 40% with an alumina (Al 2 O 3 ) as the main component as an annealing release agent so that the coating amount becomes 4 g / m 2 O 3 ) on one side. Among a1 to a4, use magnesium oxide (MgO) as the annealing release agent and coat it in such a way that the coating amount becomes 4 g / m 2 ) on one side.

[0213] Next, wind the steel sheet into a coil shape, keep it at a maximum temperature of 1200 °C for 20 hours in a nitrogen atmosphere containing 5% hydrogen, and then cool to obtain a finished annealed sheet. Set the oxidation degree PH 2 O / PH 2 in the temperature range of 800 °C to 900 °C during the heating process of the finished annealing to 0.010. After that, remove the excess annealing release agent on the surface of the steel sheet.

[0214] Next, coat an aqueous coating solution (insulating film forming liquid) with phosphate and colloidal silica as the main components on the steel sheet, and then heat the steel sheet coated with this insulating film forming liquid to 500 °C at a heating rate of 20 °C / s in an atmosphere where the in-furnace oxidation degree (PH 2 O / PH 2 ) is adjusted to 2.00 to bake and harden the insulating film. After that, bake the steel sheet at 850 °C and then perform annealing (soaking) to form an insulating film. In this example, aluminum phosphate is used, and the particle size (average particle diameter based on the number) of colloidal silica is set to 100 nm. Set the in-furnace oxidation degree (PH 2 O / PH 2)Adjusted to 1.00. The film thickness of the insulating film is measured after film formation. The specifications of the insulating film are shown in Table 1.

[0215] As the magnetic domain control process, groove formation is carried out by etching or laser at any of the following time points: between the cold rolling process and the decarburizing annealing process, between the decarburizing annealing process and the annealing release agent coating process, between the annealing release agent removal process and the insulating film formation process, or after the insulating film formation process. The specifications of the grooves are shown in Table 1.

[0216] Regarding A1 to A12 and a1 to a12, the iron loss W17 / 50 (energy loss measured under the excitation conditions of 1.7 T and 50 Hz) is measured. The results are shown in Table 1.

[0217] Table 1

[0218]

[0219] In Invention Examples A1 to A12 and Comparative Examples a1 to a8, the conditions of the groove angle, groove depth, groove interval, and groove width that affect the iron loss are all the same, and the magnetic flux density is at the same level. In contrast, the iron loss of Invention Examples A1 to A12 is less than 0.600 W / kg, which is good. The film tension at this time is all 10 MPa or more.

[0220] Comparative Examples a1 to a4 are grain-oriented electrical steel sheets with a glass film, the film tension is 10 MPa or more, the groove shape is the same as that of Invention Examples A1 to A12, but the iron loss is higher than that of the invention examples, which is inferior.

[0221] <Example 2>

[0222] A slab containing Si: 3.3 mass%, Mn: 0.10 mass%, S: 0.006 mass%, C: 0.060 mass%, acid-soluble Al: 0.027 mass%, N: 0.008 mass% and the balance being Fe and impurities is used as the raw material. After hot rolling by a known method, hot rolled plate annealing is carried out, and in cold rolling, the final plate thickness is 0.22 mm to obtain steel sheets B1 to B12.

[0223] Next, the cold rolled steel sheet is decarburized and further nitrided. The decarburizing conditions are set as follows: after heating to 850 °C, it is held for 60 seconds and then cooled. The decarburizing atmosphere is in a hydrogen-nitrogen atmosphere with PH 2 O / PH 2 set to 0.1. In addition, the nitriding amount is set to 200 ppm.

[0224] After that, MgO / (MgO + Al 2 is coated in such a way that the coating amount is 4 g / m 2 on one side.3 ) is an annealing release agent with 40% alumina (Al 2 O 3 ) as the main body.

[0225] Next, the steel sheet is wound into a coil shape, and after being held at a maximum temperature of 1200 °C for 20 hours and then cooled under the same conditions as in Example 1, a finished annealed sheet is obtained.

[0226] Furthermore, an insulating film is formed in the same manner as in Example 1. The specifications of the insulating film are shown in Table 2.

[0227] Regarding the directionally electromagnetic steel sheet of the present embodiment, groove formation is performed by etching or laser at any of the following time points: between the cold rolling process and the decarburizing annealing process, and between the decarburizing annealing process and the annealing release agent coating process. The specifications of the grooves are shown in Table 2.

[0228] Regarding B1 to B12, the iron loss W17 / 50 (energy loss measured under the excitation conditions of 1.7 T and 50 Hz) is measured. The results are shown in Table 2.

[0229] Table 2

[0230]

[0231] The iron loss of Invention Examples B1 to B12 is less than 0.550 W / kg, which is even better. At this time, the film tension is all 10 MPa or more, the absolute value of the angle θ formed with the length 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 50 μm, and the interval P of the grooves in the rolling direction is 1 to 30 mm.

[0232] <Example 3>

[0233] A slab containing Si: 3.3 mass%, Mn: 0.10 mass%, S: 0.006 mass%, C: 0.060 mass%, acid-soluble Al: 0.027 mass%, N: 0.008 mass% and the balance being Fe and impurities is used as a raw material. After hot rolling by a known method, hot rolled sheet annealing is performed, and in cold rolling, the final sheet thickness is 0.22 mm to obtain steel sheets C1 to C16.

[0234] Next, the cold rolled steel sheet is decarburized and further nitrided. The decarburizing conditions are set as follows: after heating to 850 °C, it is held for 60 seconds and then cooled. The decarburizing atmosphere is in a hydrogen-nitrogen atmosphere where PH 2 O / PH 2 is set to 0.1. The nitriding amount is set to 200 ppm.

[0235] After that, according to the coating amount, it becomes 4 g / m on one side2 The MgO / (MgO + Al 2 O 3 ) is 40% of the annealing release agent with alumina (Al 2 O 3 ) as the main body.

[0236] Next, the steel sheet is coiled into a coil shape, and under the same conditions as in Examples 1 and 2, it is held at a maximum temperature of 1200 °C for 20 hours and then cooled to obtain a finished annealed sheet.

[0237] Furthermore, an insulating film is formed in the same manner as in Examples 1 and 2. The specifications of the insulating film are shown in Table 3.

[0238] Regarding the grain-oriented electromagnetic steel sheet of the present embodiment, groove formation is carried out by etching or laser at any of the following time points: between the cold rolling process and the decarburizing annealing process, between the decarburizing annealing process and the annealing release agent coating process, between the annealing release agent removal process and the insulating film formation process, or after the insulating film formation process. The specifications of the grooves are shown in Table 3.

[0239] Regarding C1 to C16, the iron loss W17 / 50 (energy loss measured under the excitation conditions of 1.7 T and 50 Hz) is measured. The results are shown in Table 3.

[0240] Table 3

[0241]

[0242] The iron losses of Invention Examples C1 to C16 are lower than 0.600 W / kg, which is good.

[0243] Industrial Applicability

[0244] The present invention can be used in industrial machines that utilize grain-oriented electromagnetic steel sheets, such as coil cores for transformers.

[0245] Symbol Explanation

[0246] 1 Steel sheet

[0247] 2 Groove

[0248] θ Groove angle

[0249] W Groove width

[0250] D Groove depth

[0251] d Groove pitch

[0252] 10 Base metal steel sheet

[0253] 11 Internal oxide layer

[0254] 12 SiO2 Intermediate layer

[0255] 13 Insulating film

[0256] 14 Concavo-convex height

[0257] 15 Interface curve

[0258] 16 Line formed by connecting the front end portions on the steel plate surface side of the interface curve

[0259] 17 Line formed by connecting the front end portions on the steel plate center side of the interface curve

Claims

1. A directionality electromagnetic steel sheet, characterized in that, it has a plurality of grooves on the surface of the steel sheet, On the surface of a steel plate serving as a base material, there are successively SiO 2 an intermediate layer and an insulating film, it does not have a forsterite film, the film tension of the insulating film is 10 MPa or more.

2. The directionality electromagnetic steel sheet according to claim 1, characterized in that, the angle θ formed by the direction orthogonal to the rolling direction and the plate thickness direction of the steel sheet and the length direction of the groove is 40° or less, the width W of the groove is 20 to 300 μm, the depth D of the groove is 10 to 50 μm, the pitch P of the grooves in the rolling direction is 1.0 to 30.0 mm.

3. The directionality electromagnetic steel sheet according to claim 1 or claim 2, characterized in that, There is an internal oxide layer directly below the surface of the steel plate that becomes the base material and contains SiO 2 inside it.

4. The directionally electromagnetic steel sheet according to any one of claims 1 to 3, in a cross-section in the sheet thickness direction of the steel sheet, the uneven height of the interface between the internal oxide layer and the steel sheet serving as the base material is 0.001 μm to 0.100 μm in the sheet thickness direction of the steel sheet. 2 ​

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