JP3162624B2 - Method for producing low iron loss unidirectional silicon steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has excellent adhesion and smoothness, and as a result, has a good appearance, reduces iron loss value by applying a greater tension to a steel sheet, and reduces the space factor. The present invention relates to a method for producing an improved unidirectional silicon steel sheet.

[0002]

2. Description of the Related Art A grain-oriented silicon steel sheet is (100) [00
1], and is widely used as a magnetic iron core material. In particular, a material having a small iron loss is required to reduce energy loss. As a means of reducing the iron loss of the unidirectional silicon steel sheet, the steel sheet surface after finish annealing is irradiated with a laser beam to give local strain,
Japanese Patent Application Laid-Open No. 58-26 discloses a method for subdividing magnetic domains.
No. 405. Further, a magnetic domain refining means which does not lose its effect even after performing stress relief annealing (stress relief annealing) after iron core processing is disclosed in, for example, JP-A-62-26161.
No. 75 discloses this.

On the other hand, an iron alloy containing iron and silicon has a large crystal magnetic anisotropy. Therefore, when an external tension is applied, magnetic domain segmentation occurs, and eddy current loss, which is a main element of iron loss, may be reduced. it can. Therefore, it is effective to apply a tension to the steel sheet to reduce iron loss of a unidirectional silicon steel sheet containing 5% or less of silicon, and it is effective to apply a tension up to about 1.5 kgf / mm ² to effectively reduce iron loss. It is known that loss can be reduced. This tension is usually provided by a coating formed on the surface.

Conventionally, a unidirectional silicon steel sheet has a primary coating mainly composed of forsterite produced by a reaction between an oxide on the steel sheet surface and an annealing separator in a finish annealing step, and Japanese Patent Application Laid-Open No. 48-39338. Patent Publication No. JP-A No. 10-133,009 discloses a two-layer coating film formed by baking a coating solution mainly composed of colloidal silica and phosphate, which is 1.0 kgf / mm for a plate thickness of 0.23 mm. ^{About 2} tensions are applied. Accordingly, in the case of these existing coatings, although there is room for improving iron loss by applying a larger tension, an increase in the applied tension by increasing the thickness of the coating is not preferable because it results in a decrease in the space factor.

Further, as another method for improving iron loss of a grain-oriented silicon steel sheet, mirror finishing is performed by removing irregularities on the surface of the steel sheet after finish annealing and an internal oxide layer near the surface, and performing metal finishing on the surface. The method of plating is Japanese Patent Publication No. 52-2.
Japanese Patent Publication No. 4499/1992, JP-B-56-4150, JP-A-61-201732, JP-B-63-54767, and JP-A-2-213483 disclose a method of forming a tension film on the surface. Is disclosed. Also in these cases, the greater the effect of applying a tension to the steel sheet by the coating, the greater the effect of improving iron loss. For these reasons, there has been a demand for a coating film having excellent adhesion and being thin and capable of applying a large tension to a steel sheet.

On the other hand, the present inventors have disclosed Japanese Patent Application Laid-Open No. 6-65.
754, JP-A-6-65755, etc., a method of forming an oxide film by applying a fine particle dispersion containing alumina sol and boric acid, drying and gelling, and baking, and the aluminum oxide obtained thereby. -We have proposed boron oxide based composite coatings and aluminum borate coatings. It has been found that this coating can apply a high tension to the steel sheet and consequently improve the magnetic properties of the steel sheet. Further, according to this manufacturing method, it has been found that good adhesion can be ensured even with the steel plate subjected to the above-mentioned mirror finishing, and a remarkable improvement in magnetic properties can be achieved.

[0007]

According to the present invention, there is provided a method for forming a coating film, comprising the steps of: providing a good space factor by securing better adhesion and surface smoothness; It is an object of the present invention to provide a method for forming a coating and a method for manufacturing a unidirectional silicon steel sheet, which improve the quality.

[0008]

The gist of the present invention is as follows. (1) In a method for producing a unidirectional silicon steel sheet in which a fine particle dispersion containing alumina sol and boric acid is applied to the surface of a steel sheet after finish annealing to form an oxide film through a drying / gelling and baking process, A low iron loss unidirectional silicon, wherein a mixture of an alumina sol group A having a flat plate shape and an alumina sol group B having an aspect ratio of 3 or more such as a rod shape, a needle shape, and a feather shape is used. Steel plate manufacturing method.

(2) The alumina sol group A is mixed at a ratio of 10 to 95% by weight and the alumina sol group B is mixed at a ratio of 5 to 90% by weight in terms of solid content contained in the sol. A method for producing a low iron loss unidirectional silicon steel sheet according to the above.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a grain-oriented silicon steel sheet according to the present invention is directed to an alumina sol group A having an apparent particle shape of a flat plate and an elongated shape having a rod-like, needle-like, feather-like or other aspect ratio of 3 or more. This is a method in which a fine particle dispersion containing a shaped alumina sol group B and boric acid is applied to a silicon steel sheet that has undergone secondary recrystallization, dried, gelled, and then baked to form an oxide film on the surface. .

[0011] Alumina sol is a general term for a sol-like substance that becomes aluminum oxide after heat treatment.
A boehmite sol represented by the chemical formula of Al OOH is the most common, but a pseudo-boehmite sol having poor crystallinity,
Alternatively, an amorphous sol is used. Furthermore, an alumina sol having a crystal structure similar to aluminum oxide is also suitably used in the present invention.

FIG. 1 (a) shows a typical schematic diagram of a sol particle having an apparent particle shape of a flat plate, which is described as an alumina sol group A in the present invention. As can be seen from the figure, the flat plate shape described in the present invention is:
It has a clear polygonal outline, and its thickness is not always clear, but it is approximately １ ／ of the size in the plane direction.
About 1/10. That is, L is about 1/2 to 1/10 D. On the other hand, FIG. 1 shows a typical schematic view of a sol particle having an aspect ratio of 3 or more, such as a rod shape, a needle shape, or a feather shape, which is described as an alumina sol group B.
(B). As can be seen from the figure, although the particles are elongated, the aspect ratio in this specification is defined by the ratio of length in the long axis direction / length in the short axis direction. That is,
(1) L / D ≧ 3 or (2) (L1 + L2 + L3 +
...) / (D1 + D2 + D3 +...) ≧ 3.

Here, when the shape of the sol particles is complicatedly entangled like a feather, or when the particles are bent, the length in the major axis direction / minor axis when the particles are stretched straight. It is defined by the ratio of the length in the direction. For a particle that is recognized as a completely integrated particle and has a branched portion, the aspect ratio is defined for the particle that extends the longest in the major axis direction.

The difference in the shape of the alumina sol is usually caused by a different production method. The shape of particles described in the present invention is an apparent shape, that is, a shape of particles observed with a microscope or the like, and does not necessarily need to be primary particles. According to the studies by the inventors, this apparent particle shape most reflects the properties of the sol.

In general, in the case of tabular particles, the primary particles often coincide with the apparent particles, but in the case of rods, needles, feathers and other shapes having an aspect ratio,
There are various types of primary particles having such a shape, or very fine particles connected in a straight line to show the above-mentioned shape. In the present invention, any one of them has no problem. It can be used without.

The alumina sol groups A and B according to the present invention may be of a single nature, but may be of any type, but in each group, two or more types differing in particle shape, for example, particle size, particle size distribution, porosity, etc. Can be used in combination. These properties are not particularly limited,
In terms of the particle size, in the case of the sol group A, the largest portion in the plate-like planar direction, and in the case of the sol group B, the average particle diameter in the longitudinal direction is 10 to 1000 nm, more preferably 20 to 500 nm. Yes, by adjusting within this range, it is possible to obtain a glossy high-tensile film without cracks or cracks even after drying and gelling.

According to the studies by the inventors, plate-like particles are suitable for obtaining good adhesion, and a film having good adhesion can be obtained regardless of the influence of the underlayer, particularly with or without a primary film. Even with a steel sheet having a mirror-finished surface, good adhesion can be obtained under a relatively wide range of heat treatment conditions (temperature, time, atmosphere, etc.). Further, the sol composed of plate-like particles has a small change in viscosity even at a relatively high concentration, and is excellent in storage stability. On the other hand, a sol composed of elongated particles having an aspect ratio of 3 or more is excellent in film-forming ability, and a glossy and smooth film without any powderiness can be obtained.

Also, since the atmosphere is excellent in shielding properties, it is relatively hard to be affected by the atmosphere. Even when the mirror-finished steel sheet is baked in an oxidizing atmosphere, the oxidation of the interface can be considerably suppressed. it can. In the present invention, the advantage of mixing two types of sol groups is to balance the advantages of each of these sol groups, and to obtain a smooth, glossy and good-adhesion coating.

As an advantage of forming a smooth and glossy film, not only a good appearance can be obtained, but also one of the important characteristics of a grain-oriented silicon steel sheet is a space factor (a predetermined number of sheets are stacked. In this case, the ratio of the magnetic material (iron-silicon alloy) to the entire length can be increased. Further, as a general tendency, by improving the smoothness of the coating film surface, the slipperiness of the steel sheet can be increased, and the workability at the time of manufacturing the transformer can be improved.

The mixing ratio of the sol groups A and B may be appropriately determined by comprehensively considering the properties of the base steel sheet to be applied, the properties of the target coating, and the like. In any case, in any case of the steel sheet in which the primary coating is present, and the steel sheet in which the primary coating has been removed and subjected to mirror finishing, the alumina sol group A is 10 to 95% by weight,
By mixing the alumina sol group B at a ratio of 5 to 90% by weight, a film having good properties can be obtained. As a more desirable mixing ratio, the alumina sol group A is 20 to 90% by weight,
Alumina sol group B is 10 to 80% by weight.

When the mixing ratio of the alumina sol group A exceeds the above range and is less than 10%, a film having extremely excellent smoothness is obtained, but the adhesion is poor, and conversely, when the mixing ratio is more than 95%. Is a film having poor smoothness, and as a result, problems such as a decrease in space factor occur.

The inventors of the present invention have so far proposed a crystalline aluminum borate-amorphous (vitreous) film, an alkali metal, an alkaline earth, in addition to a boric acid-aluminum oxide composite oxide film and a crystalline aluminum borate film. High tensile strength coatings containing trace additives such as metals and transition metal elements have been proposed. In the sol mixing process of the present invention, any of these can be used without any particular problem.

Next, an example of a specific film forming method of the present invention will be described. As the boric acid used for preparing the fine particle dispersion liquid containing boric acid and alumina sol, orthoboric acid is most preferable in terms of workability, cost, etc., but metaboric acid, boron oxide, etc., boron oxide after the baking process is completed Any compound can be used without any particular problem.
As described above, boehmite sol, pseudo-boehmite sol, aluminum oxide sol, and the like are preferably used as the alumina sol.

The fine particle dispersion may contain components, additives and the like other than boric acid and alumina sol. These are not particularly limited in their constituent components, and any components can be suitably used, but commonly used components include alkali metal compounds, alkaline earth metal compounds, transition metal compounds, and rare earth element compounds. And the like.

The amount of solids contained in the fine particle dispersion is
The content is 5 to 50%, preferably 5 to 30% from the viewpoint of workability of coating, stability of the liquid, and the like. The mixing ratio of boric acid and alumina sol, as the inventors have pointed out,
The molar ratio of B ₂ O ₃ / Al ₂ O _{3 in} terms of oxide is 0.1 to
5 is preferred, more preferably 0.1-2, and still more preferably 0.2-1.

The fine particle dispersion is applied to a surface of a unidirectional silicon steel sheet which has been finish-annealed by a conventionally known method by a coater such as a roll coater, a dipping method, spray spraying onto a steel sheet at room temperature or heated, or electrophoresis. Apply to. The thickness to be applied may be appropriately determined in consideration of the characteristics required for the steel sheet, but is usually about 0.1 to 2% of the thickness of the sheet after baking, preferably 0.1 to 2%.
1 to 1.5%.

The steel sheet which has been subjected to the finish annealing herein means (1) a steel sheet having a forsterite primary coating formed on its surface by finish annealing by a conventionally known method.
(2) a steel sheet obtained by immersing the primary coating and the accompanying interfacial oxide layer by immersion in an acid; (3) a steel sheet obtained by smoothing and annealing the steel sheet obtained in the above (2) in hydrogen; Polishing, electropolishing and other polished steel plates, (4) Alumina powder or the like which is inactive against film formation, or a conventionally known annealing separator containing a small amount of an additive such as chloride is applied. It refers to a steel sheet or the like that has been subjected to finish annealing under conditions that do not generate a primary coating.

After the coated steel sheet is dried and the fine particle dispersion is gelled, the temperature is 500 to 1350 ° C., preferably 500 to 1350 ° C.
By baking in a temperature range of 1250 ° C., more preferably 700 to 1100 ° C., an oxide film mainly composed of boron oxide and aluminum oxide or an aluminum borate film is formed on the surface. The baking atmosphere is preferably a reducing atmosphere such as an inert gas atmosphere such as nitrogen, or a mixed atmosphere of nitrogen and hydrogen. An atmosphere containing air or oxygen is not preferable because it may oxidize the steel sheet surface.

The dew point of the atmospheric gas is not particularly limited. If the baking temperature is lower than 500 ° C., a dense film may not be formed, and the baking temperature is low, so that sufficient tension is not developed, which is not preferable. On the other hand, 135
If it exceeds 0 ° C., it is not economical, although there is no particular inconvenience.

[0030]

【Example】

Example 1 Commercially available boric acid reagent, hexagonal plate-like boehmite sol A having a primary particle diameter of 60 nm and almost no aggregation
A fibrous boehmite sol B having a size of × 100 nm was mixed at a ratio shown in Table 1 to prepare a fine particle dispersion. This was applied to a 0.2-mm-thick unidirectional silicon steel sheet containing 3.2% of Si and subjected to finish annealing so that the coating weight after baking was about 4 g / m ² per side, followed by drying and drying. After gelation, 850 in an N ₂ atmosphere containing 3 vol% of H _2.
C. for 1 minute to form an oxide film containing aluminum borate. Table 1 shows the properties of the obtained unidirectional silicon steel sheet and the surface coating.

The adhesion of the coating film was evaluated by a winding test around a 20 mmφ cylinder at an angle of 180 °, and the peeling state was evaluated. Film tension, B ₈ , W
_17/50 is the average value of 10 test materials. In Table 1, coating properties outside the scope of the present invention are also described as comparative examples. From the evaluation results of adhesion (peeling state) and appearance, it can be seen that all of the films produced by the production method of the present invention are extremely good. In addition, it can be seen that the unidirectional silicon steel sheet having the coating of the present invention achieves remarkable improvement in magnetic properties.

[0032]

[Table 1]

Example 2 The boric acid reagent, hexagonal plate-like boehmite sol A and fibrous boehmite sol B used in Example 1 were mixed at the ratio shown in Table 2 to prepare a fine particle dispersion. This was added with 3.3% of Si, decarburized, coated with alumina as an annealing separator, and then subjected to finish annealing, whereby the surface without a primary coating was smooth and had a thickness of 0.2%.
Coating after baking is applied to a unidirectional silicon steel sheet having a thickness of about 4 g / m ² per side, dried and gelled, and then dried in an N ₂ atmosphere containing 10 vol% of H _2.
C. for 1 minute to form an oxide film containing aluminum borate. Table 2 shows the properties of the obtained unidirectional silicon steel sheet and the surface coating.

Table 2 also shows film properties outside the scope of the present invention as comparative examples. From the evaluation results of adhesion (peeling state) and appearance, it can be seen that all of the films produced by the production method of the present invention are extremely good. Also,
It can be seen that the unidirectional silicon steel sheet having the coating of the present invention achieves remarkable improvement in magnetic properties.

[0035]

[Table 2]

[0036]

According to the present invention, an alumina sol composed of flat particles and an alumina sol composed of rod-like, needle-like or feather-like particles having an aspect ratio of 3 or more are mixed in a predetermined ratio, and the starting materials are mixed. By forming an oxide film containing aluminum borate on the surface, a film having a good appearance and excellent adhesion, which imparts a greater tension to the steel sheet than before, is provided. Provided is a method for manufacturing a grain-oriented silicon steel sheet. Except for changing the starting material, the production method can be exactly the same as the conventional one, and the industrial effect is enormous from the viewpoint of industrial mass productivity and versatility.

[Brief description of the drawings]

1A is a schematic diagram of an alumina sol group A, and FIG. 1B is a schematic diagram of an alumina sol group B.

Continuation of the front page (56) References JP-A-3-207868 (JP, A) JP-A-7-228977 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 22 / 00-22/86 C22C 38/00 303 C23C 26/00 H01F 1/16 H01F 41/02

Claims (2)

(57) [Claims] 1. A method for producing a unidirectional silicon steel sheet, comprising applying a fine particle dispersion containing alumina sol and boric acid to a surface of a steel sheet after finish annealing to form an oxide film through a drying / gelling and baking step. Alumina sol group A whose apparent particle shape is a flat plate shape, and rod-like, needle-like,
A method for producing a low iron loss unidirectional silicon steel sheet, comprising mixing and using an alumina sol group B having an aspect ratio of 3 or more such as feathers. 2. An alumina sol group A of 10 to 95% by weight and an alumina sol group B of 5
The method for producing a low iron loss unidirectional silicon steel sheet according to claim 1, wherein the mixing is carried out at a ratio of -90% by weight.