JP2012180545A - Method for manufacturing grain-oriented magnetic steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a grain-oriented magnetic steel sheet with which in the case of manufacturing a stacked transformer, especially, when the transformer is manufactured by using the grain-oriented magnetic steel sheet having magnetic flux density Bof ≥1.93T, even there is a part where the magnetic flux is shifted from a rolling direction and curved, such as a corner part, an iron loss deterioration can effectively be suppressed.SOLUTION: The surface of the steel sheet is irradiated with an electron beam prior to primary recrystallization annealing, and the surface of the steel sheet is made a flat surface having arithmetic average roughness RA of ≤0.15 μm.

Description

  The present invention relates to a method of manufacturing a grain-oriented electrical steel sheet excellent in iron loss characteristics used for a core material such as a transformer, and in particular, to obtain a grain-oriented electrical steel sheet capable of suppressing iron loss in a stacking transformer low. It is what.

Electrical steel sheets are roughly classified into two types: non-oriented electrical steel sheets and directional electrical steel sheets. Non-oriented electrical steel sheets are mainly used for iron core materials such as rotating machines, and directional electrical steel sheets are used mainly for iron cores for transformers and other electrical equipment. In order to reduce energy loss in any of these materials, low iron loss materials are required.
A grain-oriented electrical steel sheet containing Si and having a crystal orientation in the (110) [001] orientation or the (100) [001] orientation has excellent soft magnetic properties. Widely used as a material. At that time, as a characteristic required for electrical steel sheets, it is important that the iron loss expressed by W _17/50 (W / kg), which is a loss when magnetized to 1.7T at a frequency of 50 Hz, is generally low. It is.

By the accumulation of techniques to align the crystal orientation even years technology has in the magnetic flux density B ₈ or more products 1.93T is becoming to be stably manufactured, the 1.96T and 1.97T ultra-high magnetic flux density oriented electrical It is also possible to manufacture steel sheets.

  Here, when a transformer is manufactured using a directional electrical steel sheet having a high magnetic flux density as described above, a reduction in transformer iron loss corresponding to the reduction in material iron loss cannot be obtained, and the magnetic properties of the material are reduced. The improvement cost of the characteristic is not reflected in the improvement of the iron loss characteristic of the actual transformer. In other words, when evaluating this phenomenon, an index of the ratio of the iron loss value of the transformer to the iron loss value of the product, that is, the building factor (the value obtained by dividing the transformer iron loss by the product iron loss) is used. However, it is a problem that this building factor becomes large.

JP-A-6-65754 JP-A-6-65555 JP-A-6-299366

  A grain-oriented electrical steel sheet is a material that has been developed specifically for the magnetic properties in the rolling direction, and the properties in directions other than the rolling direction tend to become worse as the material sharpens. In other words, excellent magnetic properties in the rolling direction of the grain-oriented electrical steel sheet are fully exhibited in places where the magnetic flux flows straightly and linearly, such as the legs that are the main components of the transformer. For example, in a portion where the magnetic flux is bent out of the rolling direction, the excellent directivity is rather counterproductive and the iron loss increases locally.

Local iron loss increases as described above, remarkable particularly when the magnetic flux density B ₈ were prepared transformer with more grain-oriented electrical steel sheet 1.93 T.

The present invention has been developed in view of the situation described above, in the case of manufacturing the stacked transformer, in particular, when the magnetic flux density B ₈ were prepared transformer using the above-oriented electrical steel sheet 1.93T Furthermore, it is an object of the present invention to obtain a grain-oriented electrical steel sheet that can more effectively suppress the deterioration of iron loss even if there is a portion where the magnetic flux is bent from the rolling direction such as the corner portion.

The inventors have an essential development issue of maintaining the sharpness of the magnetic characteristics specialized in the rolling direction while at the same time satisfying the magnetic characteristics other than the rolling direction required by the actual transformer, that is, the degree of integration in the Goss direction. to a high B ₈ high magnetic flux density oriented electrical steel sheet above 1.93 T, the result of intensive studies how to facilitate rotation of the magnetization, the base steel surface, i.e., the primary recrystallization annealing prior to the base iron surface We found that it can be solved by improving the geometric shape.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. Silicon-containing steel hot-rolled sheet is subjected to hot-rolled sheet annealing as necessary, then subjected to cold or warm rolling once or two times including intermediate annealing to the final sheet thickness, and then primary recrystallization after annealing, it consists in performing the secondary recrystallization annealing are coated with the annealing separator, in the manufacturing method of a grain-oriented electrical steel sheet having a high magnetic flux density of more than 1.93T at B _8,
Prior to the primary recrystallization annealing, the surface of the steel sheet is irradiated with an electron beam to make the surface of the steel sheet a smooth surface with an arithmetic average roughness Ra of 0.15 μm or less. A method for producing a grain-oriented electrical steel sheet.

2. 2. The irradiation distance of the electron beam to the surface of the steel sheet is 0 to 15% shorter or longer than the irradiation distance at which the electron beam has a maximum irradiation energy density on the surface of the steel sheet. Method of grain-oriented electrical steel sheet with excellent transformer iron loss.

According to the present invention, when the degree of integration is high B ₈ even with high magnetic flux density oriented electrical steel sheet described above 1.93 T, since it is easy to rotate the magnetization, the transformer, used especially loading transformer Thus, a grain-oriented electrical steel sheet that exhibits excellent low iron loss characteristics can be obtained.

Hereinafter, the present invention will be specifically described.
Usually, the ground iron surface of the grain-oriented electrical steel sheet is in contact with the forsterite film, and both maintain adhesion by an anchor effect. However, the size of the anchor is extremely small, and it is considered that the anchor is not directly involved in the domain wall motion that regulates the magnetization rotation. Therefore, it is considered that the smoothness of the surface of the iron core averaged excluding the anchor is important for the rotation of the magnetic domain.

  Conventionally, surface roughness (Ra) in the rolling direction has been paid attention to the smoothness of the surface of the iron core. In the present invention, however, the surface roughness in the direction perpendicular to the rolling is a particular problem. This is because the surface roughness in the direction perpendicular to the rolling is not involved in the sharpening of the crystal orientation in the rolling direction and the accompanying decrease in the iron loss value, but when considering the magnetization rotation as described above, rolling This is because it is considered that the surface roughness in the perpendicular direction affects the ease of magnetization rotation.

Therefore, the inventors examined the smoothing of the steel sheet surface in the direction perpendicular to the rolling. As a result, it has been found that by applying the above smoothing to the surface of the steel sheet before the primary recrystallization annealing, it is possible to obtain an excellent iron loss characteristic of the transformer as compared with the conventional case.
Furthermore, compared with smoothing treatment by buffing or electrolytic polishing, the relationship between the focal length and the steel plate position is variously changed with an electron beam, and the steel plate surface is irradiated to clean and smooth the surface over the entire steel plate. As a result, it was found that a further reduction effect of transformer iron loss can be obtained.

Here, the main reason for the effect of reducing transformer iron loss is not clearly clarified, but the inventors consider as follows.
Electron beam irradiation is performed in a vacuum, but because of the vacuum, surface oxidation does not occur during the irradiation process. That is, in the surface cleaning treatment by the electron beam in vacuum, not only the smoothing treatment of the steel sheet surface is performed, but a surface containing almost no oxide can be obtained. It is presumed that it has a good influence on the form of oxide mainly composed of SiO ₂ . On the other hand, in the smoothing process by buffing or electrolytic polishing, even if an equivalent smooth surface is obtained, oxides or the like may be slightly involved, and this oxide has an adverse effect. It is thought that. Further, when surface treatment is performed by laser irradiation or the like, there is a problem that the surface is oxidized by the irradiation heat.

In the present invention, it was found that the average roughness of the surface of the steel sheet should be 0.15 μm or less in terms of arithmetic average roughness Ra by the electron beam irradiation.
In addition, as a specific electron beam irradiation condition for achieving the above-mentioned surface roughness, basically, it is sufficient that only the very surface of the steel sheet is heated and melted. It doesn't matter. Further, although the reason why the oxide is removed is not clear, a smooth steel plate surface without oxide can be obtained when electron beam irradiation is performed under appropriate conditions.
In addition, since the electron beam irradiation is performed two-dimensionally by irradiating an electron beam in a planar manner, the average roughness in the rolling direction and in the direction perpendicular to the rolling is basically the same.

In addition, the above-mentioned electron beam irradiation can effectively reduce the irradiation distance by 0-15% shorter or longer than the irradiation distance at which the electron beam has the maximum irradiation energy density on the surface of the steel sheet. Is preferable because it can be smoothed. More preferably, it is 0 to 5% shorter or longer.
As the irradiation condition for realizing the above-mentioned appropriate condition, the irradiation distance at which the electron beam becomes the maximum irradiation energy density may be performed at a so-called just focus, but by making the irradiation distance ± 15% shorter or longer than the just focus. The surface can be smoothed efficiently. In other words, a wide range can be uniformly processed at a time by using the beam profile as a trapezoidal shape.
However, when the lens is removed from the just focus, the incident energy such as the beam current is increased. However, this increases the amount of incident energy per unit time, so that the steel plate temperature rises and problems such as deformation of the steel plate occur. . For this reason, the deviation from the just focus is preferably within ± 15%, and more preferably within ± 5%.

Next, the desirable component composition of the electrical steel sheet according to the present invention will be described. In addition, unless otherwise indicated, "%" display regarding a steel plate component shall mean the mass%.
Si: 1.5-7.0%
As a component of the steel sheet used in the present invention, it is desirable to contain Si in a range of 1.5 to 7.0%.
Si is an effective component for increasing the electrical resistance of the product and reducing iron loss. However, if it exceeds 7.0%, the hardness of the steel sheet becomes high, making it difficult to manufacture and process. On the other hand, if it is less than 1.5%, a structural transformation occurs during final finish annealing, and a stable secondary recrystallized structure cannot be obtained. Therefore, Si is desirably in the range of 1.5 to 7.0%.

  In the case of an electromagnetic steel sheet using an inhibitor, the crystal orientation of the steel sheet can be further improved by containing 0.006% or more of Al as an inhibitor element in the initial steel. On the other hand, the upper limit is 0.06%, and if it exceeds this, the crystal orientation deteriorates again.

  N is set to about 100 ppm or less from the viewpoint of occurrence of blistering defects. On the other hand, the lower limit is not particularly specified, but it is economically difficult to industrially set it to 20 ppm or less, so it is desirable to set it to about 20 ppm.

  Moreover, in this invention, the process of performing a nitrogen increase process after primary recrystallization annealing can also be employ | adopted. When the nitriding treatment is not performed, the initial steel has a value of [% Se] + [% S] ([% X] means the content of element X), and about 0.01 to 0.06% of Se. In addition, in order to precipitate Se and S as the Mn compound, it is effective to contain about 0.02 to 0.2% of Mn.

  Furthermore, the present invention includes B, Bi, Sb, Mo, Te, Sn, P, Ge, As, Nb, as an inhibitor component suitable for the production of a known grain-oriented electrical steel sheet in addition to the above elements in steel. Cr, Ti, Cu, Pb, Zn, and In are known, and these elements can be added alone or in combination.

  In the case of a magnetic steel sheet that does not use an inhibitor, it is effective to reduce sol.Al to 100 ppm or less, N to 50 ppm or less, and preferably 30 ppm or less, in order to develop secondary recrystallization well. It is advantageous to reduce S and Se, which are conventional inhibitor elements, to 50 ppm or less, preferably 30 ppm or less.

The basic components excluding Si of the slab for grain-oriented electrical steel sheets suitable for the present invention will be specifically described as follows.
C: 0.08% or less C is finally required to be 30 ppm or less in the reached value after decarburization treatment in order to prevent magnetic aging deterioration. In addition, in order to obtain a good secondary recrystallization orientation, there are suitable addition amounts for each process from the viewpoint of microstructure control before and after rolling or before and after primary recrystallization annealing, but the decarburization load throughout the entire manufacturing process. In consideration of the above, it is desirable to suppress to about 0.08% at the time of melting.

Mn: 0.005 to 1.0%
Mn is an element necessary for improving the hot workability, but if the content is less than 0.005%, the effect of addition is poor, while if it exceeds 1.0%, the magnetic flux density of the product plate decreases. Therefore, the Mn content is preferably in the range of 0.005 to 1.0%.

In addition to the above basic components, the present invention can appropriately contain elements added to conventionally known grain-oriented electrical steel sheets, such as magnetic property improving components.
The balance other than the above components is inevitable impurities and Fe mixed in the manufacturing process.

Next, conditions for the method for manufacturing the electrical steel sheet of the present invention will be described.
The steel slab adjusted to a predetermined component is subjected to normal slab heating and then hot rolled into a hot rolled coil. The heating temperature of this slab is set to a high temperature of 1300 ° C or higher. Any of the cases where the temperature is 1250 ° C. or lower is acceptable. In recent years, a method of performing direct hot rolling after continuous casting without performing slab heating has been developed, but hot rolling may be performed by this method.

  The hot-rolled steel sheet is subjected to hot-rolled sheet annealing as necessary, and is made into a final cold-rolled sheet by a plurality of rollings sandwiching one cold rolling or intermediate annealing. About these rolling, what was called warm rolling aiming at dynamic aging, and what performed aging between passes aiming at static aging may be used.

  The final cold-rolled sheet is then subjected to primary recrystallization annealing that also serves as decarburization treatment and secondary recrystallization annealing that also serves as forsterite film formation, but prior to primary recrystallization annealing, irradiation with electron beams in a vacuum chamber There is a feature of the present invention in that the surface cleaning process is performed. That is, by irradiating with an electron beam under the above-described conditions, the steel sheet surface is made a smooth surface with an arithmetic average roughness Ra of 0.15 μm or less.

The surface must be smoothed without forming fine oxides on the surface, and the arithmetic average roughness Ra of the smoothed steel plate surface must be 0.15 μm or less. This is because when the size is larger than 0.15 μm, the increase amount of the transformer iron loss with respect to the material iron loss when the transformer is assembled increases, and the so-called building factor increases.
The arithmetic average roughness Ra in the present invention is based on JIS B 0601 (1994).

Although it is not possible to quantify the fine oxide remaining on the surface after electron beam irradiation, the inventors believe that if the average roughness Ra of the steel sheet surface is 0.15 μm or less, the effect of the oxide will be almost eliminated. Have estimated.
Here, the surface of the steel sheet can be smoothed even by laser irradiation, etc. performed in the atmosphere. However, if surface oxidation is unavoidable and surface oxidation occurs, it is mainly composed of SiO ₂ during the subsequent primary recrystallization annealing. Therefore, it is presumed that the iron loss reduction effect is not as high as that of the present invention.

  As described above, the steel sheet after the final cold rolling is subjected to primary recrystallization annealing also serving as decarburization treatment, and then subjected to secondary recrystallization treatment by final finish annealing, and is accumulated in the (110) [001] orientation. . When the final finish annealing is performed, an annealing separator is usually applied after the primary recrystallization annealing, thereby forming an oxide film. By adjusting the composition of the annealing separator, an oxide on the steel sheet surface is formed. The formation of a film can also be suppressed.

  In particular, in the process of producing a grain-oriented electrical steel sheet with ultra-low iron loss by intentionally forming a forsterite film on the surface and finishing it in a mirror state, no additional surface smoothing treatment is performed after secondary recrystallization annealing. In this case, since the degree of smoothing of the surface reflects the degree of the surface of the final cold-rolled sheet, the mirror surface state can be achieved very easily by applying the present invention.

Since the grain-oriented electrical steel sheet is used by being laminated when producing a transformer, an insulating layer for interlayer insulation is required. In that case, as the additionally applied insulating coating, an inorganic coating used for the grain-oriented electrical steel sheet is preferable.
In particular, a coating having a tension-imparting effect is extremely effective in reducing iron loss in combination with a grain-oriented electrical steel sheet whose surface has been smoothed to reduce iron loss. As a type of coating having a tension-imparting effect, a coating containing silica that lowers the coefficient of thermal expansion is effective, and phosphate-colloidal silica-chromic acid conventionally used for grain-oriented electrical steel sheets having a forsterite film A coating of a system or the like is preferable from the viewpoint of its effect and cost, uniform processability and the like.
The thickness of the coating is preferably in the range of about 0.3 μm or more and 10 μm or less from the viewpoint of tension application effect, space factor, film adhesion, and the like.

  In addition to this, an oxide-based film such as boric acid-alumina proposed in Patent Document 1, Patent Document 2, and Patent Document 3 can also be applied as a tension coating.

  In addition, in this invention, conventionally well-known manufacturing methods of a grain-oriented electrical steel sheet can be applied except the process and manufacturing conditions mentioned above.

Contains Si: 3.2%, Mn: 0.06%, Se: 0.001%, C: 0.05%, Al: 0.02%, N: 80ppm, Sn: 0.10%, and Cu: 0.10%, the balance from Fe and inevitable impurities The resulting slab was heated to 1400 ° C. and then hot rolled to obtain a hot rolled sheet having a thickness of 2.0 mm, and finished to a thickness of 0.23 mm by cold rolling including warm rolling. The final rolled material thus obtained was sheared into a steel plate having a length of 600 mm and a width: 100 mm and subjected to electron beam irradiation treatment in a vacuum chamber in order to change the properties of the steel plate surface. Surface treatment was performed on both sides of 100mm x 100mm square while scanning the electron beam two-dimensionally in a processing tank vacuum degree of 2.0Pa, electron acceleration voltage of 60kV and beam current in the range of 1-5mA. .
While the irradiation distance that is the maximum irradiation energy density of electron beam irradiation is 540 mm, No. 6 has an irradiation distance of 550 mm and test no. No. 7 was irradiated under the condition that the irradiation distance was 540 mm.
For comparison, a material not subjected to electron beam irradiation treatment or a material from which surface oxides were removed by hydrochloric acid pickling treatment was prepared. For each material, the arithmetic average roughness Ra in the rolling direction and the direction perpendicular to the rolling direction was measured.

Thereafter, primary recrystallization annealing also used for decarburization was performed, and an annealing separator added with 4 parts by weight of TiO _{2 with} respect to 100 parts by weight of MgO was applied with 10 g / m ² of water slurry and dried. The temperature is increased to 50 ° C in an N ₂ atmosphere at an average of 50 ° C / h, the temperature is increased from 800 ° C to 900 ° C at an average of 5 ° C / h in a mixed atmosphere of nitrogen at 25 vol%; The temperature was raised at an average temperature of 20 ° C./h in a hydrogen atmosphere. Next, secondary recrystallization annealing was performed in hydrogen at 1150 ° C. for 10 hours, and then allowed to cool to obtain a grain-oriented electrical steel sheet having a forsterite film. Furthermore, an insulating coating made of Mg phosphate and colloidal silica was applied. In addition, linear domain irradiation was performed at intervals of 5 mm in the direction perpendicular to the rolling direction with a single mode fiber laser to perform magnetic domain refinement treatment.
The magnetic flux density (B ₈ ) and iron loss (W _17/50 ) in the rolling direction of the product thus obtained were measured.
In addition, shearing the material, creating a three-phase model transformer with _70mm laminated 500mm square with V notch and step lap stack (5 layers), and evaluating the iron loss (W _17/50 ) of the transformer, The results are listed in Table 1, respectively.

As shown in the table, test no. 6 and 7 are materials whose arithmetic average roughness Ra of the steel sheet surface is 0.15 μm or less by electron beam irradiation. These steel sheets _exhibited good transformer characteristics with a transformer iron loss W _{17/50 of 0.8} W / kg or less and a building factor of less than 1.2. On the other hand, when the surface roughness of the steel sheet exceeds 0.15 μm, the transformer iron loss value increases and the building factor increases.

Claims (2)

Silicon-containing steel hot-rolled sheet is subjected to hot-rolled sheet annealing as necessary, then subjected to cold or warm rolling once or two times including intermediate annealing to the final sheet thickness, and then primary recrystallization after annealing, it consists in performing the secondary recrystallization annealing are coated with the annealing separator, in the manufacturing method of a grain-oriented electrical steel sheet having a high magnetic flux density of more than 1.93T at B _8,
Prior to the primary recrystallization annealing, the surface of the steel sheet is irradiated with an electron beam to make the surface of the steel sheet a smooth surface with an arithmetic average roughness Ra of 0.15 μm or less. A method for producing a grain-oriented electrical steel sheet.   The irradiation distance of the electron beam to the surface of the steel sheet is 0 to 15% shorter or longer than the irradiation distance at which the electron beam reaches the maximum irradiation energy density on the surface of the steel sheet. The manufacturing method of the grain-oriented electrical steel sheet excellent in the transformer iron loss of description.