Grain-oriented electrical steel sheet and laminated iron core

Abstract

Provided are a grain-oriented electromagnetic steel sheet and a laminated iron core which are capable of suppressing vibrations caused by electromagnetic force in a joint portion of the laminated iron core and which have both low iron loss and low noise characteristics of a transformer. The grain-oriented electrical steel sheet has, on at least one of the front and back surfaces thereof, a plurality of strain regions that extend linearly in a direction that passes through the rolling direction of the steel sheet in the transverse direction and that are arranged side by side at intervals in the rolling direction. The standard deviation [sigma] Br of the residual magnetic flux density Br of a hysteresis loop drawn when excitation is performed to 1.7 T using the rolling direction as the magnetization direction is 0.38 or less.

Description

Technical Field

[0001] The present invention relates to a grain-oriented electrical steel sheet, particularly a grain-oriented electrical steel sheet suitable as a material for a laminated iron core for a transformer and the like, and a laminated iron core using the same. Background Art

[0002] Grain-oriented electrical steel sheets are used, for example, as transformer core materials. These applications require suppressing energy loss and noise. The iron loss of the grain-oriented electrical steel sheet affects this energy loss, while the magnetostrictive properties of the grain-oriented electrical steel sheet also affect this noise.

[0003] In recent years, from the perspective of energy conservation and environmental regulations, there has been a strong demand to reduce transformer energy loss and operating noise. Therefore, it is extremely important to develop grain-oriented electrical steel sheets with excellent iron loss characteristics and magnetostrictive properties.

[0004] Among them, the iron loss of grain-oriented electromagnetic steel sheets is mainly composed of hysteresis loss and eddy current loss. As methods for improving hysteresis loss, methods such as highly orienting the (110)

[001] grain orientation, known as GOSS orientation, in the rolling direction of the steel sheet and reducing impurities in the steel sheet have been proposed. In addition, as methods for improving eddy current loss, methods such as increasing the resistance of the steel sheet by adding Si and applying film tension in the rolling direction of the steel sheet have been proposed. However, when pursuing further reduction of iron loss in grain-oriented electromagnetic steel sheets, these methods have manufacturing limitations.

[0005] Therefore, magnetic domain refinement technology has been developed as a method to further reduce iron loss in grain-oriented electrical steel sheets. This technology involves introducing magnetic flux inhomogeneity in the steel sheet after final annealing or after the insulating coating has been sintered, using physical methods such as forming grooves or inducing localized thermal strain. This reduces the width of the 180° magnetic domains (main magnetic domains) formed along the rolling direction, thereby reducing the iron loss, particularly eddy current loss, in the grain-oriented electrical steel sheet.

[0006] For example, Patent Document 1 proposes the following technology: by introducing linear grooves with a width of less than 300 μm and a depth of less than 100 μm into the surface of the steel plate, the iron loss of more than 0.80 W / kg is improved to less than 0.70 W / kg. In addition, Patent Document 2 proposes irradiating the steel plate surface with a plasma flame in the plate width direction after secondary recrystallization and locally introducing thermal strain. By introducing this thermal strain, in a steel plate with a magnetic flux density (B8) of 1.935 T when excited with a magnetizing force of 800 A / m, the iron loss (W 17 / 50 ) improved to 0.680W / kg.

[0007] It should be noted that the method of introducing linear grooves, as disclosed in Patent Document 1, does not lose its magnetic domain refinement effect even after stress relief annealing is performed on the core after forming, and is therefore referred to as heat-resistant magnetic domain refinement. On the other hand, the method of introducing thermal strain, as disclosed in Patent Document 2, does not achieve the effect of thermal strain introduction due to stress relief annealing, and is therefore referred to as non-heat-resistant magnetic domain refinement.

[0008] While non-heat-resistant magnetic domain refinement materials are known to significantly reduce eddy current losses by introducing localized thermal strain into steel sheets, this strain also degrades magnetic properties, such as increased hysteresis losses and magnetostriction. Magnetostriction is particularly known to be a source of noise in transformers, and it is also known that greater magnetostriction increases noise. Thus, with non-heat-resistant magnetic domain refinement materials, transformer iron loss and noise are in a trade-off relationship, leading to the development of methods that achieve both low iron loss and low noise.

[0009] In addition to magnetostriction, electromagnetic vibration of the iron core is also known as a cause of transformer noise. The grain-oriented electromagnetic steel sheet with non-heat-resistant magnetic domain refinement is mainly used as a laminated iron core (laminated iron core) for transformers. The schematic diagram of the structure of the laminated iron core is shown in FIG. Figure 1 The laminated core is a core having a structure in which grain-oriented electromagnetic steel sheets cut into obliquely cut members 1 such as the column portion 11 and the yoke portion 12 are stacked in the sheet thickness direction. Figure 1 The left side is a top view of a laminated core with the steel plates facing upward, and examples of the X-X cross-sectional view and the YY cross-sectional view of the laminated core are shown in FIG. Figure 1 On the right. Figure 1 As shown, in a laminated core, there are joints 2 between the chamfered members 1. Due to the magnetic flux circulating within the steel sheets, magnetic flux is periodically transferred at these joints 2. During this magnetic flux transfer at these joints 2, the ends of the steel sheets become magnetized. Consequently, electromagnetic vibrations are generated by the magnetic attraction between the ends and the magnetic repulsion between the layers. Suppressing this electromagnetic vibration has been proposed as a method for improving transformer noise.

[0010] As a method for suppressing noise caused by such electromagnetic vibration, Patent Document 3 proposes making the core cross-sectional area of ​​the yoke larger than that of the column. Furthermore, Patent Document 4 proposes a method for suppressing vibration by providing a viscoelastic resin layer between stacked steel plates.

[0011] Prior art literature

[0012] Patent Literature

[0013] Patent Document 1: Japanese Patent Publication No. 6-22179

[0014] Patent Document 2: Japanese Patent Application Laid-Open No. 7-192891

[0015] Patent Document 3: Japanese Patent Application Laid-Open No. 11-307368

[0016] Patent Document 4: Japanese Patent Application Laid-Open No. 2009-224531 Summary of the Invention

[0017] While the aforementioned measures for suppressing vibrations caused by electromagnetic forces between steel plates are somewhat effective, they present the following problems. For example, the method described in Patent Document 3, which ensures that the cross-sectional area of ​​the yoke is larger than that of the column, tends to increase the size of the transformer itself, leading to increased manufacturing costs.

[0018] Furthermore, the method proposed in Patent Document 4, which involves providing a viscoelastic resin layer between stacked steel plates, reduces the effective cross-sectional area of ​​the steel plates within the pillars. Consequently, each steel plate is excited to a higher magnetic field than a core of the same size, increasing losses (iron loss). To avoid this, the core must be larger.

[0019] The present invention has been made in view of the above-mentioned circumstances, and its object is to provide a grain-oriented electromagnetic steel sheet and a laminated iron core that have the characteristics of low iron loss and low noise in a transformer by a mechanism different from that of conventional technologies, specifically, by suppressing vibrations caused by electromagnetic forces in the joints of the laminated iron core.

[0020] The inventors have conducted intensive research to solve the above-mentioned problems.

[0021] The vibrations of the steel plates in the core joint 2 include vibrations caused by the magnetic forces acting on both end faces of the joint 2 and vibrations caused by the magnetic forces acting in the vertical direction of the stacked layers of the joint 2. A detailed investigation of these vibrations revealed that the phase of the vertical vibrations differs, particularly depending on the position between layers. In particular, when the external magnetic field H applied to the column 11 reaches 0 (zero), the phase shift varies significantly, resulting in increased transformer noise.

[0022] In order to conduct a more detailed investigation, SST samples were cut out from each layer of steel plates constituting the above-mentioned core, and the hysteresis loop (BH curve, refer to Figure 2 ), resulting in variations in the magnetic flux density Br(T) remaining in the steel sheets when the external magnetic field H is zero. Specifically, the researchers discovered that when these steel sheets are stacked, each stacked sheet has a different magnetic flux density when the external magnetic field is 0 A / m. This results in sparse magnetic attraction and repulsion between the layers at the core joint. This results in irregular vibrations, which increase the aforementioned noise.

[0023] The present invention has been completed based on the above findings.

[0024] That is, the gist of the present invention is as follows.

[0025] [1] A grain-oriented electrical steel sheet having, on at least one of its front and back surfaces, a plurality of strain regions extending linearly in a direction transversely passing through the rolling direction of the steel sheet and arranged side by side at intervals in the rolling direction, wherein the standard deviation σBr of the residual magnetic flux density Br (the value of the sample magnetic flux density B(T) when the intensity of the external magnetic field H=0) of a hysteresis loop drawn when the magnetization direction is set as the rolling direction and the steel sheet is excited to 1.7 T is 0.38 or less.

[0026] [2] The grain-oriented electrical steel sheet according to [1] above, wherein the standard deviation σBr is 0.36 or less.

[0027] [3] A laminated iron core formed by laminating a plurality of grain-oriented electromagnetic steel sheets according to [1] or [2].

[0028] According to the present invention, even in a non-heat-resistant magnetic domain refining material with linear (thermal) strain regions, variations in residual magnetic flux density can be suppressed. By using the grain-oriented electrical steel sheet of the present invention in a laminated core, a transformer with low iron loss and low noise can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a schematic diagram showing the structure of a laminated core.

[0030] Figure 2 This is a diagram showing a typical example of a hysteresis loop.

[0031] Figure 3 It is a graph showing the effect of σBr on transformer loss.

[0032] Figure 4 This is a graph showing the effect of σBr on transformer noise.

[0033] Figure 5 This diagram shows the concept of board running speed. DETAILED DESCRIPTION

[0034] Hereinafter, the experimental results obtained by completing the present invention will be described.

[0035] (Experiment 1)

[0036] The surface of a grain-oriented electrical steel strip having a forsterite coating and an insulating coating (tension coating) was irradiated with an electron beam to perform a magnetic domain refinement treatment. The electron beam output was varied between 800 and 1200 W, with a beam irradiation interval of 5 mm in the sheet feed direction and a beam scanning speed of 80 m / s. Beveled sections were cut from various locations of the resulting samples. For each beveled section, the iron loss was measured using the single-plate magnetic measurement method specified in JIS C2556, and the hysteresis loop was measured to calculate the residual magnetic flux density Br (T). From all the beveled sections for which Br was calculated, subgroups of beveled sections were selected such that the average Br value matched the average value of the parent distribution and the standard deviation σBr varied. Three-phase laminated core model transformers (core weight 50 kg) were fabricated for each subgroup. For each manufactured three-phase laminated iron-core model transformer, the core loss characteristics (transformer loss) were measured at a frequency of 50 Hz and a magnetic flux density of 1.7 T in the core leg portion. The no-load loss was measured using a power meter based on the core loss characteristics at 1.7 T and 50 Hz. Simultaneously, each model transformer was excited in a soundproof room at a maximum magnetic flux density of Bm = 1.7 T and a frequency of 50 Hz, and the noise level (dBA) (transformer noise) was measured using a noise meter.

[0037] [Table 1]

[0038]

[0039] As for the influence of σBr on transformer loss, the results of the measurement of transformer loss and transformer noise are summarized as follows: Figure 3 .like Figure 3 As shown, the transformer's iron loss remains largely unchanged, regardless of σBr. This is believed to be because the chamfered components were selected to maintain the same average value of Br, resulting in the same average effect of magnetic domain refinement. In other words, it was found that the iron loss reduction effect of non-heat-resistant magnetic domain refinement applied to the steel sheet is unaffected by the standard deviation σBr of the residual magnetic flux density, provided the average value of the residual magnetic flux density Br remains constant.

[0040] On the other hand, the results of the measurement of the transformer noise are summarized as follows: Figure 4 .like Figure 4As shown in the figure, the transformer noise shows a dependence on σBr. The inventors believe that this is because the deviation of the residual magnetic flux of the steel plate increases when the excitation magnetic field is 0A / m, resulting in irregular vibration with phase deviation, which results in increased noise. In particular, when σBr exceeds 0.38, the noise increases significantly. Therefore, if σBr is 0.38 or less, the transformer noise can be improved while maintaining the low iron loss effect brought about by the refinement of the magnetic domain. Figure 4 As shown, σBr is more preferably 0.30 or less, further preferably 0.26 or less, and further preferably 0.21 or less.

[0041] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in the present embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0042] [Grain-oriented electrical steel sheet]

[0043] In the present invention, the composition of the slab for grain-oriented electrical steel sheets may be any composition that causes secondary recrystallization. In addition, when using inhibitors, for example, when using AlN-based inhibitors, appropriate amounts of Al and N may be contained, and when using MnS·MnSe-based inhibitors, appropriate amounts of Mn and Se and / or S may be contained. Of course, two inhibitors may also be used in combination. In this case, the preferred contents of Al, N, S, and Se are:

[0044] Al: 0.010-0.065 mass%,

[0045] N: 0.0050-0.0120 mass%,

[0046] S: 0.005 to 0.030 mass% and

[0047] Se: 0.005 to 0.030 mass %.

[0048] Furthermore, the present invention can also be applied to grain-oriented electrical steel sheets without using inhibitors, in which the contents of Al, N, S, and Se are limited. In this case, the contents of Al, N, S, and Se are preferably limited to

[0049] Al: less than 0.010 mass%,

[0050] N: less than 0.0050 mass%,

[0051] S: less than 0.0050 mass% and

[0052] Se: less than 0.0050 mass%.

[0053] Representative basic components and optional added components used in the steel billet (slab) for the grain-oriented electrical steel sheet of the present invention will be described in detail.

[0054] C: 0.08 mass % or less

[0055] C is added to improve the hot-rolled sheet structure. However, if the C content exceeds 0.08 mass%, decarburization to 50 mass ppm or less, which does not cause magnetic aging, becomes difficult during the manufacturing process. Therefore, the C content is preferably 0.08 mass% or less. Furthermore, secondary recrystallization can be performed even in steel billets that do not contain C, so there is no particular lower limit on the C content.

[0056] Si: 2.0-8.0 mass%

[0057] Si is an element that is effective in increasing the electrical resistance of steel and improving iron loss. However, if the content is less than 2.0 mass%, the improvement effect is not fully realized. On the other hand, if it exceeds 8.0 mass%, the workability and sheet-forming properties are significantly deteriorated, and the magnetic flux density is also reduced. Therefore, the Si content is preferably within the range of 2.0 to 8.0 mass%.

[0058] Mn: 0.005-1.0 mass%

[0059] Mn is an element necessary for improving hot workability, but its effect is not fully achieved if the content is less than 0.005 mass%. On the other hand, if it exceeds 1.0 mass%, the magnetic flux density deteriorates. Therefore, the Mn content is preferably within the range of 0.005-1.0 mass%.

[0060] In addition to the above-mentioned essential components, the following optional additive components known to be effective for improving magnetic properties may be appropriately contained.

[0061] One or more selected from the group consisting of Ni: 0.03-1.50 mass%, Sn: 0.01-1.50 mass%, Sb: 0.005-1.50 mass%, Cu: 0.03-3.0 mass%, P: 0.03-0.50 mass%, Mo: 0.005-0.10 mass% and Cr: 0.03-1.50 mass%.

[0062] Nickel is an element effective in improving the magnetic properties by improving the hot-rolled sheet structure. However, if the content is less than 0.03 mass%, the contribution to magnetic properties is small. On the other hand, if it exceeds 1.50 mass%, secondary recrystallization becomes unstable and the magnetic properties deteriorate. Therefore, the Ni content is preferably within the range of 0.03 to 1.50 mass%.

[0063] Sn, Sb, Cu, P, Mo, and Cr are also elements that improve magnetic properties. However, if the content is less than the lower limit, the effect is insufficient. If the content exceeds the upper limit, the growth of secondary recrystallized grains is inhibited, thereby deteriorating the magnetic properties. Therefore, the content of each is preferably within the above range.

[0064] In addition, components other than the above components are composed of Fe and inevitable impurities.

[0065] In the production of the grain-oriented electrical steel sheet of the present invention, a steel billet (slab) comprising the aforementioned composition is hot-rolled and then annealed. Subsequently, it is cold-rolled once or twice to form a steel strip of the final thickness. The steel strip is then decarburized and annealed, coated with an annealing separator primarily composed of MgO, and wound into a coil. A final annealing is then performed to form secondary recrystallization and a forsterite coating. After the final annealing, the steel strip is flattened and then subjected to a magnesium phosphate tension coating to produce the final steel strip.

[0066] The production of grain-oriented electrical steel sheet according to the present invention includes a magnetic domain refining step in which thermal strain is introduced into the surface of the finished steel strip, i.e., the grain-oriented electrical steel sheet (steel strip) after the tension coating has been formed, by energy beam irradiation. Even if thermal strain is introduced by energy beam irradiation before the tension coating is formed, the thermal strain is mitigated or released by the heat treatment (sintering) performed during the tension coating formation, and the desired magnetic domain refining effect cannot be achieved.

[0067] The standard deviation σBr of the residual magnetic flux density Br is less than 0.38

[0068] For the grain-oriented electrical steel sheet of the present invention, it is important to suppress the deviation (deviation) of the residual magnetic flux density Br in the steel sheet. Specifically, it is important that the standard deviation σBr of the residual magnetic flux density Br in the steel sheet (the value of the sample magnetic flux density B(T) when the intensity of the external magnetic field H=0) is 0.38 or less. That is, as mentioned above, if σBr is 0.38 or less, the noise of the transformer can be improved while maintaining the low iron loss effect brought about by the refinement of the magnetic domain. σBr is preferably 0.36 or less, more preferably 0.34 or less, and further preferably 0.32 or less. The smaller σBr is, the more significantly the noise of the transformer can be reduced. The lower limit of σBr is not particularly limited and is theoretically zero.

[0069] The variation in residual magnetic flux density Br, a key factor in the present invention, includes variations caused by factors such as grain orientation, internal strain, the amount of fine grains and precipitates present in the steel plate, as well as variations caused by magnetic domain refinement processing, such as the uniformity of thermal strain in the plate direction and across the plate width. While the former has a minor impact and is difficult to suppress, suppressing variations in plate temperature during the rolling and annealing processes is effective.

[0070] On the other hand, the latter is presumed to be due to slight variations in the heat input pattern of the energy beam irradiation due to changes in the line speed during operation. Specifically, the greater the amount of thermal strain introduced into the steel sheet, the easier it is to reverse the magnetization, thus reducing the residual magnetic flux density (Br). In magnetic domain refinement, when the processing frequency (line speed / processing interval) is kept constant and the same process is performed, if the line speed is changed, the spacing of the thermally strained regions in the sheet feed direction changes, and the amount of strain per unit area varies depending on the position in the longitudinal direction. As a result, the residual magnetic flux density (Br) varies in grain-oriented electrical steel sheets that have undergone magnetic domain refinement. It is speculated that in such cases, variations in Br can be suppressed by controlling the amount of heat input to maintain a constant amount of strain per unit area by varying the line speed.

[0071] On the other hand, when the spacing between thermally strained regions in the plate feed direction is kept constant, the aforementioned processing frequency changes, and the balance between the energy beam's scan and standby times changes. Here, during the beam standby period, the energy beam is irradiated onto a beam receiving device called a beam dump. Furthermore, if the scan and standby time balance changes, the appropriate focusing conditions may change due to beam scattering caused by smoke and gas generated by the beam receiving device. In this case, improving σBr by presetting appropriate focusing conditions for each production line speed and then changing the focusing conditions according to the operating line speed is effective. As an example of a method for setting appropriate focus, a method can be considered in which the beam is continuously irradiated in a pattern simulating actual operating conditions until a stable state is reached, and then the focus is adjusted within this stable state. Furthermore, even without taking the aforementioned measures, deviations can be improved by performing magnetic measurements during the production of beveled components and eliminating beveled components that deviate significantly from the average value. From the perspective of both time and yield, each measure can be implemented in a well-balanced manner.

[0072] ·Method for measuring the standard deviation σBr of residual magnetic flux density Br

[0073] The method for measuring the standard deviation σBr of the residual magnetic flux density Br in the present invention is as follows. SST test pieces (samples) with a width of 100 mm and a length of 280 mm are taken from multiple positions in the longitudinal direction of the grain-oriented electromagnetic steel sheet (steel strip) after magnetic domain refinement treatment. The hysteresis loop is measured by the single-plate magnetic measurement method in accordance with JIS C2556, and the residual magnetic flux density Br (T) of each sample is calculated. The standard deviation σBr of Br of all samples calculated in this way is used as an evaluation standard for the deviation of the residual magnetic flux density Br. The more the number (N) of samples taken and provided for measurement in the longitudinal direction of the grain-oriented electromagnetic steel sheet (steel strip), the better. However, this may increase the time required to cut out the sample and reduce the yield. Therefore, the number N is preferably 9 to 90, and more preferably 15 to 75.

[0074] <Non-heat-resistant magnetic domain refinement>

[0075] Next, the non-heat-resistant magnetic domain refining method used in the magnetic domain refining step of the present invention will be described.

[0076] In order to perform non-heat-resistant magnetic domain refinement, it is effective to use a laser beam having a wavelength of 400 nm to 1200 nm with a high absorption rate for metal or an electron beam with high transmittance.

[0077] The conditions inherent to electron beam irradiation when implementing the present invention will be described in further detail below.

[0078] Accelerating voltage: 60kV~300kV

[0079] The acceleration voltage is preferably higher to increase the electron's straightness and reduce the thermal effects on the outside of the beam irradiation area. For this reason, the acceleration voltage is 60 kV or higher. It is more preferably 90 kV or higher, and even more preferably 120 kV or higher.

[0080] On the other hand, if the accelerating voltage is too high, it becomes difficult to shield the X-rays generated by electron beam irradiation. Therefore, from a practical point of view, it is preferably 300 kV or less. More preferably, it is 200 kV or less.

[0081] Beam current: 0.5~40mA

[0082] From the perspective of beam diameter, a low beam current is preferred. This is because increasing the current tends to expand the beam diameter due to Coulomb repulsion. Therefore, in the present invention, the beam diameter is preferably kept below 40 mA. On the other hand, if the beam current is too low, insufficient energy is generated to generate strain. Therefore, a beam current of 0.5 mA or above is preferred.

[0083] Vacuum degree within the beam irradiation area

[0084] If the electron beam is scattered by gas molecules, the beam diameter and halo diameter will increase, and the energy will decrease. Therefore, the vacuum degree in the beam irradiation area is preferably high, and the pressure is preferably below 3 Pa. There is no particular lower limit, but if it is too low, the cost of the vacuum system such as the vacuum pump will increase. Therefore, it is preferably 10 -5 Pressure above Pa.

[0085] The conditions inherent to laser irradiation when implementing the present invention will be described in further detail below.

[0086] Laser output: 50W~5000W

[0087] If the laser output is low, the scanning speed needs to be reduced to provide sufficient energy to impart thermal strain. However, if the speed is too low, manufacturing efficiency will deteriorate. On the other hand, if the output is high, thermal strain will be more easily imparted, but this will also increase damage to the laser delivery system and the frequency of maintenance, thereby reducing manufacturing efficiency. Based on this perspective, the laser output is preferably between 50W and 5000W.

[0088] In addition, the irradiation conditions common to electron beam irradiation and laser beam irradiation will be described below.

[0089] Beam diameter or spot diameter: 300μm or less

[0090] A smaller beam diameter for electron beam irradiation or a smaller spot diameter for laser beam irradiation is preferred because it allows for more localized strain introduction. Therefore, in the present invention, the beam diameter or spot diameter of the energy beam is preferably 300 μm or less, more preferably 280 μm or less, and even more preferably 260 μm or less. In the present invention, the beam diameter or spot diameter refers to the full width at half maximum of the beam pattern of the electron beam or laser beam, obtained using a slit method with a 30 μm width.

[0091] Deflection speed: 5~400m / s

[0092] The slower the beam deflection speed, the greater the amount of heat incident on the steel sheet per unit length, so a slower speed is preferred. However, if the speed is too low, the processing area per unit time is reduced, thereby reducing manufacturing efficiency. Therefore, a speed of 5 m / s or higher is preferred. Furthermore, if the speed is too high, the power supply capacity required to provide the input heat required to melt the steel sheet increases, resulting in larger equipment. Therefore, a speed of 400 m / s or lower is preferred.

[0093] Angle between thermal strain formation direction and rolling direction: within ±30°

[0094] The more the direction of thermal strain generation is tilted relative to the plate width, the fewer magnetic poles are generated at the interface between the return magnetic domain and the main magnetic domain, thus deteriorating the magnetic domain refinement effect. Therefore, the angle between the direction of thermal strain generation and the plate width is preferably within ±30°.

[0095] [Laminated core]

[0096] The laminated iron core of the present invention is formed by laminating a plurality of grain-oriented electromagnetic steel sheets of the present invention, each having a standard deviation σBr of the residual magnetic flux density Br(T) in the steel sheets when the external magnetic field H is zero, of 0.38 or less. Therefore, the laminated iron core of the present invention can suppress vibrations caused by electromagnetic forces at the joints between the laminated steel sheets, achieving both low iron loss and low noise in the transformer.

[0097] The laminated core of the present invention is not particularly limited, but preferably has a structure in which a plurality of cut sheets of grain-oriented electromagnetic steel sheets are combined so that the magnetization direction inside the core coincides with the rolling direction of the grain-oriented electromagnetic steel sheets to form a magnetic circuit. Examples of such a laminated core include: Figure 1 In a laminated core having such a structure, there are portions (joints) where the cut plates meet and overlap, and electromagnetic vibrations generated at these locations can be effectively suppressed.

[0098] As an example of the method for manufacturing the laminated core of the present invention, the following is described: Figure 1 The method for manufacturing a three-phase laminated core composed of three columns 11 and two yokes 12 is shown. The steel strip of the oriented electromagnetic steel sheet of the present invention is cut into the desired column and yoke plate width to produce a sub-steel strip. The sub-steel strip is sheared in a manner to achieve the target steel plate length to produce a steel plate (bevel cut component). At this time, the shearing direction can be 90 degrees relative to the rolling direction (rolling right angle direction), or it can be inclined to a certain degree. In addition, it can also be as shown in FIG. Figure 1 The beveled components thus produced are combined in such a way that the rolling direction of the steel plates is consistent with the magnetization direction inside the core to form a layer. In addition, the joint at this time may be a structure in which all the steel plates are in the same plane (butt joint), or a structure in which the steel plates overlap each other in at least one or more joints (lap joint). Next, a laminated core is produced by stacking this layer in the direction of the plate thickness. At this time, the width of the cut plate can be changed according to the thickness direction of the laminated core, or different oriented electromagnetic steel plates can be applied according to the position inside the structure of the laminated core. In addition, the stacking method of the joint may be selected from Figure 1 Any of the straight-joint stacking, step-joint stacking, and overlapped stacking shown may be used, or they may be combined as desired.

[0099] In addition, in the present invention, in addition to the above-mentioned steps and manufacturing conditions, known methods for manufacturing grain-oriented electrical steel sheets and laminated iron cores may be appropriately used.

[0100] Example 1

[0101] Next, the present invention will be specifically described based on the embodiments. The following examples represent a preferred example of the present invention and are not subject to any limitation of the present embodiment. Changes can also be added to implement within the scope of the present invention, and such schemes are also included in the technical scope of the present invention.

[0102] A single surface of a 300 mm wide product steel strip, after final annealing and insulation coating, produced from a steel slab having the chemical composition shown in Table 1 or Table 2 through a conventional grain-oriented electrical steel sheet production process, was subjected to a magnetic domain refinement treatment by irradiating it with a laser beam or electron beam. A conceptual diagram of the plate feed speed of the production line for this magnetic domain refinement treatment is shown in FIG. Figure 5 .like Figure 5 As shown, the production line speed LS is repeatedly accelerated at regular intervals, from 10m / min to 140m / min. Figure 5 The "..." in the figure indicates repeated acceleration and dwelling. The energy beam irradiation conditions used were the nine conditions listed in Table 3, with one steel strip produced for each condition. When the processing frequency was varied, the beam irradiation interval in the steel sheet feed direction was adjusted to 6 mm. When the processing frequency was constant, the frequency was set to 194.4 Hz, resulting in a 6 mm processing interval at a line speed of 70 m / min. The beam scanning speed was 120 m / s.

[0103] [Table 2]

[0104]

[0105]

[0106] From each of the nine steel strips manufactured under the above nine conditions, 45 test pieces (samples) with a width of 100 mm and a long side of 280 mm were cut out for each steel strip. The hysteresis loop of each test piece was measured by the single-plate magnetic measurement method described in JIS C2556, and the residual magnetic flux density Br (T) and its standard deviation σBr were calculated. Then, beveled components were cut out from each steel strip to make a three-phase laminated core model transformer (core weight 50 kg). For each transformer (transformer) manufactured, the iron loss characteristics were measured when the magnetic flux density of the core leg part was 1.7 T at a frequency of 50 Hz. For the iron loss characteristics at 1.7 T and 50 Hz, the no-load loss was measured using a power meter. At the same time, in a soundproof room, the model transformer was excited under the conditions of maximum magnetic flux density Bm = 1.7 T and frequency 50 Hz, and the noise level (dBA) was measured using a noise meter. Their results are shown in Table 4.

[0107] It can be confirmed from Table 4 that E2, E4, L2, and L4, which satisfy the configuration of the present invention, are transformers that satisfy both low iron loss and low noise. Figure 4 Similarly, it can be seen that the smaller σBr is, the more significant the improvement in transformer noise is.

[0108] [Table 4]

[0109]

[0110] Explanation of symbols

[0111] 1 Mitered components

[0112] 11 Column

[0113] 12 yoke

[0114] 2 Joint

Claims

1. A grain-oriented electrical steel sheet having, on at least one of its front and back surfaces, a plurality of strain regions extending linearly in a direction transverse to a rolling direction and arranged side by side at intervals in the rolling direction; The standard deviation σBr of the residual magnetic flux density Br of the hysteresis loop drawn when the magnetization is excited to 1.7 T with the rolling direction as the magnetization direction is 0.38 or less.

2. The grain-oriented electrical steel sheet according to claim 1, wherein The standard deviation σBr is 0.36 or less.

3. A laminated iron core formed by laminating a plurality of grain-oriented electrical steel sheets according to claim 1 or 2.

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