JP2007308770A - Low core loss grain-oriented electrical steel sheet and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low core loss grain-oriented electrical steel sheet requiring no application of insulation film restoration treatment even after the application of small strain for magnetic domain refinement and to provide a method of inexpensively manufacturing the steel sheet. <P>SOLUTION: In the method for manufacturing a grain-oriented electrical steel sheet by forming an insulation film on the surface of a finish annealed grain-oriented electrical steel sheet and then applying shot blasting treatment onto the surface of the insulation film to form a linear strain region at the surface of the steel sheet and carry out magnetic domain refinement, the shot blasting treatment is performed while regulating the average particle size of projection particles and projection air pressure to ≤100 μm and 0.025 to 0.15 MPa, respectively. This method provides the low core loss grain-oriented electrical steel sheet in which the linear strain region resulting from the shot blasting treatment is formed on the surface of the steel sheet and the insulation film formed in the strain region is free from damage due to the shot blasting treatment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a grain-oriented electrical steel sheet and a method for producing the grain-oriented electrical steel sheet, and more particularly to a grain-oriented electrical steel sheet excellent in iron loss characteristics subjected to magnetic domain refinement and a method for producing the same.

  Oriented electrical steel sheets are widely used as iron core materials for transformers and large generators because they have good excitation characteristics and iron loss characteristics. This grain-oriented electrical steel sheet developed so-called goth grains having a {110} plane on the rolling surface and a <001> axis that is the easy axis of magnetization in the rolling direction, utilizing the secondary recrystallization phenomenon in finish annealing. It has a stripe-like magnetic domain structure. And the development of the conventional grain-oriented electrical steel sheet increases the degree of integration of the {110} <001> orientation (Goss orientation) and reduces the deviation from the rolling direction as much as possible, so that the excitation characteristics, iron loss characteristics, etc. The main focus has been on improving this.

  However, if the degree of integration in the Goth direction is further increased, the Goth grains become coarse and the stripe-shaped magnetic domain width becomes wider. Therefore, there is a problem that eddy current loss increases and the iron loss characteristic deteriorates on the contrary.

  Various methods have been proposed for dealing with this problem. For example, Patent Document 1 discloses that fine recrystallized grains are added to a steel plate that has been finish-annealed or treated with an insulation coating by applying a processing strain (groove) in the form of a dotted line or a broken line with a gear roll or the like, and then annealing. A method for generating a magnetic domain and subdividing the magnetic domain is proposed in Patent Document 2, and a method for reducing the magnetic domain width by introducing a linear notch on the surface of the steel plate before the final finish annealing step is proposed. . These methods are excellent in that the magnetic domain refinement effect does not disappear even if strain relief annealing is performed, but there is a problem that the production efficiency is low and the production cost is high.

  Patent Documents 3 and 4 disclose a method in which a thermal strain region is formed by locally applying thermal energy to a steel plate surface using a laser beam, an electron beam, an ion beam, etc., and the magnetic domain width is reduced. Has been proposed. However, although this method is superior to the above-described method for forming the groove in terms of production efficiency and manufacturing cost, it requires a large amount of equipment for magnetic domain control, so that the equipment cost is high. There is.

  On the other hand, as a method of performing magnetic domain control with high productivity and low cost, a method of reducing the magnetic domain width by performing shot blasting on the surface of a grain-oriented electrical steel sheet to introduce micro strains has been proposed. For example, Patent Document 5 discloses a method of reducing the magnetic domain width by forming indentations having a diameter of 60 to 80 μm and a depth of 3 to 5 μm by steel shot.

  However, the method of performing the shot blasting process represented by Patent Document 5 is such that the shot blasting is usually performed in the manufacturing process of the grain-oriented electrical steel sheet, such as baking of a tension insulating film or flattening annealing for correcting the shape of the steel sheet. If applied before the heat treatment, the magnetic domain refinement effect is reduced. On the other hand, when the shot blasting is performed after the heat treatment, although the effect of subdividing the magnetic domain can be obtained, the tensile insulating coating is damaged, and another problem that the corrosion resistance of the steel sheet is deteriorated occurs.

As a technique for improving the above problems, Patent Document 6 discloses a grain-oriented electrical steel sheet in which iron loss is improved by applying a small strain to the steel sheet without damaging the tension insulating coating to reduce the magnetic domain width. ing. However, in the technique of Patent Document 6, laser irradiation is employed as a strain imparting method for reducing the magnetic domain width, and there is a problem that the equipment cost is high, and minute strain is imparted from the tension insulating coating. Due to the generation of compressive stress, the actual machine characteristics after assembly to a transformer or the like are likely to deteriorate, and in order to avoid this, it is necessary to heat treat the steel sheet after applying microstrain in a temperature range not exceeding 500 ° C. There is a problem that it is said.
JP 61-117218 A Japanese Examined Patent Publication No. 03-069968 Japanese Patent Publication No.57-002252 JP 59-229419 A Japanese Patent Publication No. 60-056404 Japanese Patent Publication No. 06-017511

  Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a low iron loss direction-oriented electrical steel sheet that does not need to be subjected to an insulating coating repair treatment even after application of micro strain for magnetic domain subdivision, The object is to propose a method for producing a steel sheet at low cost.

  In order to achieve the above-mentioned problems, the inventors have repeatedly studied a magnetic domain subdivision method using a shot blasting process in which equipment costs and running costs are low. As a result, when the shot blasting process (particle material, particle diameter, and projection pressure) is optimized in performing shot blasting on the grain-oriented electrical steel sheet on which the insulating film is formed, the insulating film on the steel sheet surface is damaged. It has been found that a directional electrical steel sheet with low iron loss can be produced without applying an insulating coating repairing process for ensuring corrosion resistance even after shot blasting. Completed the invention.

  That is, the present invention relates to a grain-oriented electrical steel sheet in which an insulating film is formed after finish annealing, and a linear strain region is formed by shot blasting on the surface of the steel plate, and is formed in the strain region. The insulating coating film is a low iron loss grain-oriented electrical steel sheet characterized in that it is not damaged by shot blasting.

  In addition, the present invention forms an insulating coating on the surface of the grain-oriented electrical steel sheet after finish annealing, and performs shot blasting on the insulating coating to form a linear strain region on the surface of the steel sheet to form a magnetic domain subdivision. In the method for producing a grain-oriented electrical steel sheet, the shot-blasting process is carried out with an average particle size of the projected particles of 100 μm or less and a projection air pressure of 0.025 to 0.15 MPa. Suggest a method.

  The projected particles in the present invention are alumina particles.

  According to the present invention, by applying a shot blast treatment of fine particles under specific conditions from above the insulating coating, a linear micro-strain region is applied only to the extreme surface layer of the steel sheet, so that the insulating coating is damaged. Domain subdivision can be realized without causing Therefore, according to the present invention, a grain-oriented electrical steel sheet having low iron loss characteristics and excellent corrosion resistance can be obtained. In addition, according to the present invention, as the magnetic domain subdivision method, an inexpensive shot blasting process with low equipment cost and running cost is used, and the obtained steel sheet does not need to be subjected to a repair process of the insulating film, so that it has excellent iron loss characteristics. The oriented electrical steel sheet can be provided at low cost.

  The grain-oriented electrical steel sheet according to the present invention is obtained by subjecting fine particles to shot blasting from an insulating coating formed on the surface of the steel sheet to form a linear microstrain region only on the pole surface layer of the steel sheet. Therefore, the iron loss is reduced by 3% or more as compared with that before the shot blasting process.

  The grain-oriented electrical steel sheet may be any conventional grain-oriented electrical steel sheet. The insulating coating formed on the surface of the electrical steel sheet may be a conventionally known insulating coating, but is preferably a glassy tension insulating coating made of aluminum phosphate or magnesium phosphate. Note that the shot blasting may be performed on one or both surfaces of the steel plate.

  As the shot blasting method, any conventionally known method can be used as long as it is a method of projecting particles using high-pressure air. In addition, the method of forming a linear micro-distortion region by shot blasting is not particularly limited, but a method of scanning a nozzle with a narrowed projection region on the steel plate, and placing a mask provided with a linear slit on the steel plate Thus, a method of ejecting particles from the mask can be suitably used.

  The fine particles used for the shot blast treatment are preferably those having a hardness that is relatively close to that of the glassy insulating coating, and for example, particles such as alumina, silica, alumina silica compound, and glass particles are suitable. This is because in conventional steel balls and SUS balls, indentations are formed on the surface of the insulating coating when the iron loss is projected at 3% or more compared to before shot blasting. This is because damage is caused and the corrosion resistance of the coating is significantly reduced.

  The average particle size of the fine particles must be 100 μm or less. This is because if it exceeds 100 μm, it is difficult to achieve both reduction in iron loss and ensuring corrosion resistance of the coating. Preferably, it is the range of 30-50 micrometers.

  Moreover, the air pressure (projection pressure) of the high-pressure air used for projecting the fine particles needs to be in the range of 0.025 to 0.15 MPa. If it is less than 0.025 MPa, the magnetic domain fragmentation effect is small. Conversely, if it exceeds 0.15 MPa, an indentation is formed on the surface of the insulating coating, resulting in deterioration of corrosion resistance, but the projection pressure is 0.025 to 0.15 MPa. This is because if it is within the range, an iron loss reduction effect of 3% or more can be obtained without causing damage to the insulating coating.

  As described above, the mechanism by which iron loss can be reduced despite the absence of damage to the surface of the insulating film by shot blasting is not necessarily clear, but it is relatively close to the vitreous insulating film as fine particles to be projected. By using a hard material, it is considered that local strain can be introduced only on the surface of the iron core without causing damage to the insulating coating.

  As in the conventional magnetic domain refinement process, it is most effective to apply the fine strain region generated on the steel plate surface linearly in the direction perpendicular to the rolling direction of the steel plate, that is, along the plate width direction. However, it is not necessarily perpendicular to the rolling direction, and the effect of the present invention can be sufficiently obtained as long as it is within a range of 15 degrees from the direction perpendicular to the rolling direction.

  The line width of the linear minute strain region is preferably in the range of 100 to 1000 μm. This is because if it is less than 100 μm, a sufficient iron loss reduction effect cannot be obtained, and even if it exceeds 1000 μm, there is no change in the iron loss reduction effect.

  Further, the interval for forming the linear strain region needs to be appropriately adjusted so as to obtain an iron loss reduction effect according to the material, particle diameter, projection speed, etc. of the fine particles projected by the shot blasting process. Is projected at a projection pressure of 0.025 MPa to 0.15 MPa, the spacing is preferably 2.5 to 15 mm, and more preferably 3 to 8 mm.

After finishing annealing to produce secondary recrystallized grains, from a highly oriented grain-oriented electrical steel sheet having a sheet thickness of 0.23 mm, coated and baked with a tensile insulating film, the width is 100 mm × length is 400 mm. The iron loss W _17/50 before performing the shot blast treatment was measured using a single plate magnetometer. On the other hand, a SUS plate having a plate thickness of 1 mm, a width of 150 mm and a length of 500 mm is prepared, and this SUS plate is subjected to electrical discharge machining with a slit of 120 mm in length and 0.25 mm in width at a pitch of 5 mm, and shot blasting. A mask was prepared.
This mask is overlaid on the above-mentioned test piece of electromagnetic steel sheet, and alumina fine particles having an average particle size of 50 μm are projected from above by slitting them with high pressure air, and the surface of the insulating coating after projection is projected with an optical microscope. Observed and observed the occurrence of indentation and damage to the coating.
Moreover, the iron loss W _17/50 is measured using a single-plate magnetometer, and the iron loss reduction rate by shot blasting is _expressed by the following formula:
Iron loss improvement rate (%) = 100 × (shot blasting before the iron loss _{W 17/50} - iron loss _W after the shot blast _17/50) / (shot blasting before the iron loss _{W 17/50)}
I asked for it.
Next, after performing a constant temperature and high humidity test for 50 hours in an atmosphere having a temperature of 50 ° C. and a humidity of 100% using the electromagnetic steel sheet after shot blasting, occurrence of red rust generated on the surface of the insulating coating Was visually observed to evaluate the corrosion resistance.
As a comparative example, the same evaluation was performed on an example using alumina particles exceeding 100 μm and an example using 50 μm steel balls as shot blast fine particles.

  The results are summarized in Table 1. FIG. 1 shows the relationship between the shot blast projection pressure and the iron loss reduction rate. From these results, if iron particles with an average particle size of 50 μm are shot blasted at a projection pressure of 0.025 MPa to 0.15 MPa, the iron and insulating coatings have no indentation or damage, and there is no deterioration in corrosion resistance. It can be seen that a grain-oriented electrical steel sheet can be obtained.

It is a graph which shows the influence which the projection pressure in a shot blast process has on the iron loss reduction rate.

Claims (3)

In the grain-oriented electrical steel sheet in which an insulating film is formed after finish annealing, a linear strain region is formed by shot blasting on the surface of the steel plate, and the insulating film formed in the strain region is A low iron loss grain-oriented electrical steel sheet characterized by no damage caused by shot blasting. A grain-oriented electrical steel sheet that forms an insulating coating on the surface of a grain-oriented electrical steel sheet after finish annealing, performs shot blasting on the insulating coating, forms a linear strain region on the steel sheet surface, and subdivides the magnetic domain. A method for producing a low iron loss grain-oriented electrical steel sheet, characterized in that shot blasting is performed with an average particle size of projected particles of 100 μm or less and a projected air pressure of 0.025 to 0.15 MPa. The method for producing a low iron loss directional electrical steel sheet according to claim 2, wherein the projected particles are alumina particles.

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