JP2001303215A - Low core loss grain oriented silicon steel sheet and its producing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a grain oriented silicon steel sheet in which the surface of ferrite in a silicon steel sheet subjected to mirror finishing or not formed with a forsterite film can be formed with a film with tight adhesion and a grain oriented silicon steel sheet extremely low in core loss obtained by further forming a tension application type insulating film thereon and to provide a method for producing the same grain oriented silicon steel sheets extremely low in core loss. SOLUTION: In the grain oriented silicon steel sheet, the surface of ferrite is provided with fine, stripy grooves with a depth of 0.05 to 2 μm directly applied thereon at the intervals of 0.05 to 2 μm. The fine, stripy grooves suitably elongate to the direction orthogonal to the rolling direction or to the direction within ±45 deg. from the above orthogonal direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic steel sheet and a method of manufacturing the same, and more particularly to a grain-oriented magnetic steel sheet having extremely low iron loss and a method of manufacturing the same.

[0002]

2. Description of the Related Art Grain-oriented electrical steel sheets used for iron cores of transformers are required to have low iron loss, and various iron loss reduction techniques are used. In particular, the most typical is the high integration of crystal grains in the rolling direction of the <001> axis, the formation of a tension coating using low thermal expansion, the reduction of sheet thickness, and the refinement of magnetic domains by the introduction of thermal strain and surface grooves. It has achieved great results in reducing iron loss.

On the other hand, the surface of the base steel of the magnetic steel sheet is mirror-finished by, for example, chemical polishing or the like, so that the unevenness of the base steel surface which hinders the movement of the domain wall due to the magnetization is reduced, and thereby, the component of iron loss Of these, it is known that the hysteresis loss can be reduced, and efforts have been made to put it to practical use. However, this means has not yet reached an industrially completed stage.

[0004] The main reason for this is that when the above-mentioned mirror finishing is performed, the forsterite coating formed as an insulating coating on the surface of the grain-oriented electrical steel sheet is removed. This is because the coating cannot be formed with good adhesion, and even if the hysteresis loss is reduced, eddy current loss increases and strain sensitivity deteriorates. In other words, the forsterite coating formed as an insulating coating just below the surface of the grain-oriented electrical steel sheet has a shape in which it bites into the ground iron surface in a complicated manner, and a tension-imparting coating, such as a special coating, is formed by the anchor effect due to the bite. Although it has a function of preventing peeling of a silica-phosphate type coating as shown in Japanese Patent Laid-Open No. 52-25296, the forsterite coating having the anchor effect is removed by the smoothing. This makes it impossible to form a tension imparting insulating film on the magnetic steel sheet with good adhesion.

[0005] In order to solve this problem, for example, Japanese Patent Publication No. 2671076 discloses an electromagnetic steel sheet having a smooth surface.
A method for improving the adhesion of a tension-imparting insulating film by forming fine and sharp pits on the surface densely by immersion in a sulfuric acid solution of 5% is disclosed. However, although the product obtained by this method shows good adhesion when the steel sheet after the application of the tension-imparting insulating coating is flat, it can be coiled by winding the steel or processed into a winding transformer to obtain the tension-enhancing coating. However, there is a problem that it is easy to peel off. It is conceivable to improve the adhesion by increasing the number of pits by increasing the concentration of sulfuric acid to be immersed or lengthening the immersion time.However, in this case, the unevenness of the surface of the base iron becomes large and the hysteresis loss is reduced. Can not be adopted because it deteriorates.

[0006]

There have been many other methods of applying a tension-imparting coating directly or indirectly to the surface of a base steel of an electrical steel sheet which has been mirror-finished or does not form a forsterite coating. However, to date, these proposals have not yet been industrially completed.

The present invention is directed to a grain-oriented electrical steel sheet capable of forming a coating with good adhesion on the surface of a ground iron of such an electromagnetic steel sheet which is mirror-finished or does not form a forsterite coating, and a tension-imparting coating thereon. It is an object of the present invention to propose a grain-oriented electrical steel sheet having an extremely low iron loss and a method of manufacturing a grain-oriented electrical steel sheet having an extremely low iron loss.

[0008]

Means for Solving the Problems It is extremely advantageous to form fine streaks on the surface of the steel sheet of the magnetic steel sheet in order to secure the adhesion of the coating and to reduce the iron loss. The present inventor has completed the present invention by repeatedly studying the conditions that the fine streak-like grooves must have and the method of forming the same.

The grain-oriented electrical steel sheet of the present invention has fine streak grooves having a depth of 0.05 μm or more and 2 μm or less directly provided on the surface of the ground iron of the grain-oriented electrical steel sheet at intervals of 0.05 μm or more and 2 μm or less.

As a result, an insulating coating can be formed directly on the surface of the grain-oriented electrical steel sheet with good adhesion.
Further, the fine streak grooves extend in a direction perpendicular to the rolling direction of the steel sheet or in a direction within ± 45 ° from the orthogonal direction, so that high magnetic permeability and low permeability, which are important properties for an electromagnetic steel sheet, are obtained. It is good to secure iron loss.

In the present invention, it is preferable that the insulating coating formed on the surface of the ground iron be a tension-imparting coating, whereby the iron loss can be further reduced.

Further, it is preferable that the surface area of the base steel of the grain-oriented electrical steel sheet of the present invention is adjusted so that the area ratio occupied by forsterite crystals is 20% or less and the surface roughness Ra is 0.4 μm or less. . Thereby, the effect of the present invention can be reliably obtained. In the present invention, the grain-oriented electrical steel sheet is a one-way electrical steel sheet or a two-way electrical steel sheet.

Further, as a method for manufacturing a grain-oriented electrical steel sheet having an extremely low iron loss according to the invention described above, a grain-oriented electrical steel sheet having an exposed surface of a ground iron is manufactured, and Fine streak grooves with a depth of 0.05 μm or more and 2 μm or less
It is preferable to perform the coating at intervals of 5 μm or more and 2 μm or less. A tension-imparting insulating coating can be formed on the surface of the ground iron having the fine streak grooves obtained in this manner.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described specifically. The grain-oriented electrical steel sheet of the present invention has fine streak grooves having a depth of 0.05 μm or more and 2 μm or less directly provided on the surface of the ground iron of the grain-oriented electrical steel sheet at intervals of 0.05 μm or more and 2 μm or less.

FIG. 1 shows that when the material of a grain-oriented electrical steel sheet is finally annealed, magnesia containing 5% of iron chloride is used as an annealing separator and magnesia is used, and the surface has substantially no forsterite coating. Schematic diagram of a magnetic steel sheet obtained, and fine stripe grooves 3 formed by electron beam lithography on the surface 1 of a unidirectional magnetic steel sheet having a smooth and exposed ground iron surface obtained by further chemical polishing. It is. Figure 2, on the other hand,
Surface 1 of grain-oriented electrical steel sheet obtained by the same process as above
FIG. 5 is a schematic diagram when fine pits 2 are formed by electron beam lithography. In the figure, (a) is a plan view, and (b) is a cross-sectional view.

When the fine grooves 3 are formed as shown in FIG. 1, the surface area of the magnetic steel sheet 1 increases. As a result, the area of the interface between the insulating film formed by applying and baking thereon and the base iron increases, and the adhesion between them increases. By bringing the tension-imparting insulating coating into close contact with the ground iron in this way, it is possible to impart tension to the steel sheet, and it is possible to greatly reduce iron loss. Although the surface area increases when the pits 2 are formed as shown in FIG. 2, as described later, when the pits 2 are formed, the electromagnetic characteristics of the steel sheet are reduced. Employs fine streak grooves 3.

The specifications, that is, the depth, width, and length of the fine streak-like grooves may be determined mainly based on the adhesive strength between the steel sheet and the insulating film, together with the arrangement intervals. Generally, its depth is
The thickness is preferably 0.05 μm or more and 2 μm or less. If it is less than 0.05 μm, the adhesion becomes insufficient, and if it is too large, hysteresis loss increases. On the other hand, the interval is preferably 0.05 μm or more and 2 μm or less. Adhesion is inferior if it is larger or smaller than the above range. In addition, the said space shall measure by the space between center lines. The width and length may be determined mainly based on the adhesive strength between the steel sheet and the insulating film. Generally, it is sufficient that the length is about 5 times the center line interval. The shape of the groove is not particularly limited, for example, U-shaped, V-shaped,
You can freely select a W shape or the like. Further, a V-shaped groove may be formed in a continuous shape in the lateral direction without providing a flat portion.

The direction of the fine streaks is important. When a grain-oriented electrical steel sheet whose easy axis of magnetization is oriented in the rolling direction is magnetized by alternating current in the rolling direction, the domain wall 4 moves repeatedly in a direction perpendicular to the rolling direction of the steel sheet. Therefore, when the fine grooves 3 are formed in a direction perpendicular to the rolling direction as shown in FIG. 1, the domain wall 4 can be moved while always maintaining the same cross-sectional shape, and the domain walls are pinned by the fine grooves 3. Therefore, even if the fine groove 3 is provided, it is unlikely that the magnetic permeability decreases and the iron loss increases. However, when the direction of the fine grooves 3 deviates from the direction orthogonal to the rolling direction, iron loss gradually increases. Its tolerance is approximately ± 45 ° from the rolling direction. Therefore, in the present invention, the fine streak grooves are formed in a direction orthogonal to the rolling direction of the steel sheet or ± 45 degrees from the orthogonal direction.
Preferably, it extends in a direction of less than °.

On the other hand, when the pits are distributed on the surface of the ground iron as shown in FIG. 2, the domain wall 4 must pass through the pit 2 repeatedly. Therefore, the movement of the domain wall 4 is hindered by the pits 2, so-called pinning is likely to occur, and a decrease in magnetic permeability and an increase in iron loss are likely to occur. Therefore, as described above, in the present invention, the interfacial area between the ground iron surface and the insulating coating is increased by the fine streak grooves 3. It should be noted that if the pit 2 is arranged with a very small interval and acts substantially like a groove, it is obvious that the pit 2 is equivalent to the fine streak groove 3.

The fine streak-like grooves need not necessarily be formed in a straight line. In addition, it is not necessarily a continuous state, but may be formed intermittently. Some curvature or misalignment is allowed as long as it does not hinder domain wall movement. However, if the fine streaks are in the direction perpendicular to the rolling direction of the steel sheet,
For example, peeling of the insulating coating hardly occurs at the time of bending to bend in the rolling direction, such as when winding a steel sheet into a coil. This tendency is more remarkable as the angle between the micro-streak groove and the rolling direction of the steel sheet is larger. Therefore, it is preferable to set the direction of the micro-streak grooves in a direction perpendicular to the rolling direction in order to improve the adhesion of the coating at the time of bending the steel sheet as described above.

The micro-streak groove according to the present invention is different from a groove formed for the purpose of so-called magnetic domain subdivision. That is, the grooves formed on the surface of the grain-oriented electrical steel sheet for magnetic domain refinement are usually at least 5 μm in depth and at least 2 μm in interval,
Obviously, it is larger than the micro-streak groove according to the present invention. Also, the purpose is different. Therefore, it is possible to use the fine streak groove and the groove formed for the purpose of magnetic domain subdivision together,
In that case, both effects can be obtained together.

As described above, an insulating coating is formed on the grain-oriented electrical steel sheet having the fine streaks formed on the surface of the ground iron according to a conventional method. Although there is no particular limitation on the type of insulating coating and the method of forming the insulating coating, phosphate-based coatings and chromate-based coatings conventionally used as insulating coatings on grain-oriented electrical steel sheets have corrosion resistance, smoothness, and chemical stability. It can be advantageously used in terms of properties, stability of the coating solution, and ease of the coating operation.

In particular, for the purpose of imparting tension to a steel sheet and thereby reducing magnetostriction in an alternating magnetic field to reduce iron loss,
It is desirable to form a so-called tension-providing insulating film. Such coating liquids for forming a film include:
Coating liquids mainly composed of phosphate and colloidal silica, and coating liquids of colloidal silica, magnesium phosphate or aluminum phosphate with chromium trioxide, chromate, dichromate, etc. can be used and applied.・ After drying, baking in a non-oxidizing atmosphere at 800 to 900 ° C. makes it possible to obtain a tension-imparting insulating film. The thickness of the tension-imparting insulating film is suitably 1 to 5 μm from the viewpoint of reduction of iron loss due to tension and space factor. As the tension-imparting insulating film, an inorganic film having a smaller thermal expansion coefficient than that of ground iron, such as an aluminum borate-based film or a SiO ₂ —B ₂ O ₃ —ZnO glass film, can be used.

According to the present invention, as described above, fine streaks are directly formed on the surface of the ground iron of the grain-oriented electrical steel sheet. Therefore, it is basically desirable that the present invention be applied to a grain-oriented electrical steel sheet in which the base iron is almost completely exposed. However, it is not always necessary that the ground iron be completely exposed, that is, a state in which the forsterite coating does not exist on the steel sheet surface at all, and a state in which the forsterite coating is divided and does not form a coating. Including. For example,
If the area ratio of forsterite crystals on the surface of the base iron confirmed by observation with a reflection electron microscope is 20% or less, a sufficient effect can be obtained by applying the present invention. Incidentally, according to the present invention, in order to obtain the effect of reducing the hysteresis loss during iron loss, the oxygen basis weight of the steel sheet is 0.2g / m
² or less is preferable, and the surface roughness of
0.4 μm or less is preferable.

The composition and manufacturing conditions of the steel sheet to which the present invention is applied are not particularly limited. For example, the steel content is 2.
5-6%, plate thickness can be in the range of 0.1-0.8 mm.
In order to reduce iron loss, it is desirable to increase the degree of orientation of the grain-oriented electrical steel sheet in the rolling direction as much as possible. However, the effect of the present invention can be obtained without necessarily doing so. As already described, it can be combined with the magnetic domain refining process. Furthermore, the crystal is (100) [001]
It is also possible to use a bidirectional electrical steel sheet oriented in the same direction.

Although the low iron loss grain-oriented electrical steel sheet according to the present invention has been described above, its manufacturing method is preferably as follows. First, a grain-oriented electrical steel sheet having an exposed surface of a base iron is manufactured. The method for producing the grain-oriented electrical steel sheet may be any known method, and is not particularly limited. There are no restrictions on the type of inhibitor, rolling, or heat treatment. Further, in the final finish annealing, whether or not to apply a so-called forsterite coating may be freely determined. However, it is economically advantageous not to form a forsterite film because it is easy to obtain a grain-oriented electrical steel sheet exposing the surface of the ground iron.

A known method may be used to bring the grain-oriented electrical steel sheet into a state where the surface of the ground iron is exposed. Specifically, there is a method of performing a final finish annealing so as not to form a forsterite film, or a method of removing a once formed forsterite film. The former means is to apply an annealing separator mainly composed of alumina before the final annealing, or to add a chloride, calcia, etc. to the annealing separator mainly composed of magnesia and apply the final separation annealing. And a method of adjusting the conditions of decarburizing annealing before the final finish annealing to adjust the composition and morphology of the silicon oxide near the steel sheet surface so as to suppress the formation of a forsterite film. On the other hand, as the latter means, there is a method of removing the forsterite film by a method such as mechanical polishing, pickling, electrolytic etching, and chemical polishing after the final finish annealing. It is preferable that the surface roughness is reduced when the forsterite coating is removed or the surface of the ground iron is polished by a means such as chemical polishing, because the hysteresis loss is further reduced.

In the grain-oriented electrical steel sheet with the surface of the ground iron exposed as described above, the fine streak-like grooves are formed according to the present invention.
The means for this is not particularly questionable, and a depth of 0.05
Any material that can form fine streak-like grooves of not less than 2 μm and not more than 0.05 μm and not more than 2 μm can be used regardless of mechanical means, chemical means or physical means. As the mechanical means, for example, electron beam lithography can be used, and as the chemical means, electrolytic etching, pickling, or the like can be used. In addition, physical means such as fine electric discharge machining can also be used. The above means can be used together.

The thus obtained grain-oriented electrical steel sheet having finely grooved grooves on the surface of the base iron is coated with an insulating film in accordance with a conventional method, but the means for this is not limited. This has already been described.

[0030]

EXAMPLES (Example 1) A final cold-rolled sheet for a grain-oriented electrical steel sheet having a thickness of 0.23 mm and containing 3.4% Si and AlN as an inhibitor component was prepared. After forming grooves for magnetic domain subdivision in a direction perpendicular to the rolling direction by electrolytic etching in the final cold-rolled sheet, primary recrystallization annealing combined with decarburizing annealing is performed, and then 5% iron chloride is contained. An annealing separator containing magnesia as a main component was applied and subjected to a final finish annealing at 1200 ° C. for 24 hours. The obtained steel sheet had a (110) [001] structure highly accumulated in the rolling direction, but no forsterite film was formed on the steel sheet surface.

A rectangular sample of 10 mm × 50 mm was cut out from the obtained steel sheet, subjected to strain relief annealing, and further chemically polished and smoothed until Ra became 0.1 μm to obtain a sample for evaluation. The sample was subjected to surface processing by electron beam lithography to form fine streaks and pits. The surface state after processing, that is, the shapes and dimensions of the grooves and pits formed on the surface were measured by observation with a scanning electron microscope capable of measuring a three-dimensional shape.

The thus obtained steel plate having the fine streak grooves formed thereon is further coated with a coating solution of magnesium phosphate containing 50% by mass of colloidal silica to a final thickness of 1.5 μm. And apply it with a roll coater
The product was baked at 800 ° C. to form a tension-imparting insulating film, and used as a product sample.

The iron loss of the obtained product sample was measured, and the adhesion of the coating was evaluated. Iron loss was evaluated by iron loss when magnetized 1.7 T, at 50Hz using a small veneer magnetic measuring device (W _17/50). On the other hand, the adhesion of the coating is a flat state in the state manufactured as described above, and a state in which the product sample is stretched flat after being wound around a 50 mm round bar,
In other words, in the state after the bending, the cellotape (registered trademark)
Was evaluated by measuring the area ratio of the film to be peeled off by a cellophane tape test.

Table 1 shows the evaluation results. According to the present invention, when a fine streak-like groove was formed, the iron loss value was low, and the adhesion of the coating was good, but in the case of a sample in which only pit-shaped concave portions were formed, the iron loss value was low. Although good, the peeling area ratio was 30% or more in the state where the adhesion of the film was after bending. In the case of the sample which had been smoothed by chemical polishing, the iron loss value was high and the adhesion to the coating film was poor even in a flat state.

[0035]

[Table 1]

(Example 2) A sample whose surface was smoothed in the same manner as in Example 1 was prepared, and fine streak-like grooves having different depths and intervals were formed on the sample surface by electron beam lithography. Colloidal silica was added to the obtained sample by mass ratio.
A magnesium phosphate-based treatment solution containing 60% was applied by a roll coater and baked at 800 ° C. to form a 1.5 μm-thick tension imparting insulating film.

The iron loss and coating adhesion of the obtained sample were determined as follows:
Evaluation was performed in the same manner as in Example 1. Table 2 shows the evaluation results. When the depth and interval of the fine streak grooves are within the range of the present invention, the iron loss value is low and the adhesion of the coating is good, but if the groove depth is too shallow, the groove depth is appropriate. If the spacing is too narrow or too wide, the adhesion of the coating is insufficient. On the other hand, if the groove depth is too deep, the adhesion of the coating is sufficient, but the iron loss deteriorates.

[0038]

[Table 2]

Example 3 A sample whose surface was smoothed in the same manner as in Example 1 was prepared and immersed in a treatment solution containing 3% by mass of hydrochloric acid at 95 ° C. for 60 seconds. By this immersion treatment, streak-shaped fine grooves having a depth of 0.5 μm and an interval of 0.6 μm were formed on the sample surface.

Then, a magnesium phosphate-based treatment solution containing colloidal silica at a mass ratio of 60% by weight of the obtained steel sheet sample was applied by a roll coater and baked at 800 ° C. to a thickness of 1.5%.
A μm tension-type insulating film was formed.

The obtained sample was evaluated for iron loss and film adhesion in the same manner as in Example 1. As a result, the iron loss W _{17/50 of the} sample was 0.64 W / kg, and the adhesion of the coating was flat,
No peeling with cellophane tape was observed after bending.
Both were good.

Example 4 A sample whose surface was smoothed in the same manner as in Example 1 was prepared, and fine streaks having a depth of 0.6 μm and an interval of 0.8 μm were formed by electron beam lithography in the rolling direction of the steel sheet.
It was formed to have an angle of 0 to 90 °. Then the mass ratio is 6
A magnesium phosphate-based treatment solution containing 0% colloidal silica is applied with a roll coater and baked at 800 ° C.
A 1.5-μm-thick tension-imparting insulating film was formed.

The obtained samples were evaluated for iron loss and film adhesion in the same manner as in Example 1. In addition, in the case of this example, the evaluation of the adhesion was also performed for a case where the diameter of the round bar was 30 mm. Table 3 shows the evaluation results. When the angle formed by the fine streak grooves with the rolling direction is 45 ° or more, it can be confirmed that the iron loss value is low and the adhesion of the coating film is good.

[0044]

[Table 3]

[0045]

According to the present invention, an insulating coating, particularly a tension-imparting insulating coating, can be formed on a grain-oriented electrical steel sheet having a smooth surface without deterioration of iron loss, with good adhesion. Thereby, the coating adhesion of the grain-oriented electrical steel sheet accompanied by bending is improved, the iron loss value can be reduced, and the energy loss in the wound iron core transformer can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram when fine stripe grooves are formed on the surface of a grain-oriented electrical steel sheet having a smooth and exposed ground iron surface. (a) is a plan view, and (b) is a cross-sectional view.

FIG. 2 is a schematic diagram when pits are formed on the surface of a grain-oriented electrical steel sheet having a smooth and exposed ground iron surface. (a) is a plan view, and (b) is a cross-sectional view.

[Explanation of symbols]

 1: magnetic steel sheet 2: pit 3: fine streak groove 4: domain wall

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Mineo Muraki 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. CA23 CA41 DA02 DA11 EA01 EA03 EA06 EB11 4K033 AA02 BA01 PA09 PA12 4K057 WA04 WA07 WA20 WB02 WC03 WE08 WG01 WG02 WG03 WK06 WK10 WN10 5E041 AA02 BC01 CA02 HB14 NN06

Claims (7)

[Claims] 1. A fine streak groove having a depth of 0.05 μm or more and 2 μm or less directly applied to the surface of a base steel of a grain-oriented electrical steel sheet having a thickness of 0.05 μm
A grain-oriented electrical steel sheet having extremely low iron loss, characterized by having an interval of not less than 2 μm. 2. The iron loss according to claim 1, wherein the fine streaks extend in a direction perpendicular to the rolling direction of the steel sheet or in a direction within ± 45 ° from the perpendicular direction. Extremely low grain electrical steel. 3. The grain-oriented electrical steel sheet according to claim 1, wherein a tension-imparting insulating coating is applied to the surface of the ground iron. 4. The base steel surface of the grain-oriented electrical steel sheet has an area ratio of forsterite crystal of 20% or less and a surface roughness R
The low-loss-oriented electrical steel sheet according to any one of claims 1 to 3, wherein a is adjusted to 0.4 µm or less. 5. The grain-oriented electrical steel sheet is a one-way electrical steel sheet or a two-way electrical steel sheet.
4. A grain-oriented electrical steel sheet according to any one of 4 above, wherein the iron loss is extremely low. 6. A grain-oriented electrical steel sheet having an exposed surface of a base iron is manufactured, and a depth of 0.05 μm or more is formed on the surface of the grain-oriented electrical steel sheet.
A method for producing a grain-oriented electrical steel sheet having extremely low iron loss, characterized in that fine streak grooves of 2 μm or less are formed at intervals of 0.05 μm or more and 2 μm or less. 7. A grain-oriented electrical steel sheet having an exposed surface of a base iron is manufactured, and a depth of 0.05 μm or more is formed on the surface of the grain-oriented electrical steel sheet.
A method for producing a grain-oriented electrical steel sheet having an extremely low iron loss, characterized by forming fine streak grooves of 2 μm or less at intervals of 0.05 μm or more and 2 μm or less, and further forming a tension imparting film.