JPH08222423A - Grain oriented silicon steel plate of low core loss and its manufacture - Google Patents

Abstract

PURPOSE: To obtain a grain oriented silicon steel plate having tension coating of good adhesion property by providing a composite metallic plating layer wherein oxide grain is dispersed between tension coating and a grain oriented silicon steel plate surface. CONSTITUTION: A silicon steel plate is electrolytically ground, a surface is magnetically smoothened and composite electroplating is applied to the obtained steel plate. The plating is carried out by performing cathode electrolysis for a steel plate in electrolytic bath wherein oxide colloidal grain is dispersed in plating bath containing matrix metallic ion. Thereafter, water-based treatment solution mainly composed of magnesium phosphate, colloidal silica and chromic acid anhydride is applied as tension coating and burnt, and a film is formed. In the process, oxide colloidal grain is one kind or two or more kinds selected from SiO2 , Al2 O3 , Cr2 O3 , Fe2 O3 , TiO2 , ZrO2 , Sb2 O5 , SnO2 and MgO.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low iron loss grain-oriented silicon steel sheet and a method for producing the same.

A grain-oriented silicon steel sheet is obtained by hot rolling a silicon steel material containing Si: 4 wt% or less (hereinafter simply referred to as%) and a small amount of a secondary recrystallization inhibitor such as MnS, MnSe or AlN. A cold rolled sheet of final product thickness is obtained by annealing and one or more cold rolling steps, and then primary recrystallization annealing that also serves as decarburization is performed to obtain a subscale containing SiO ₂ as a main component. After being formed, an annealing separating agent containing MgO as a main component is applied in the form of a water slurry, dried, and then wound into a coil and then subjected to final finishing annealing (110) [001].
Oriented secondary recrystallized grains are developed, and at the same time harmful impurities such as S and Se in the steel that has finished its role as a recrystallization inhibitor are removed, and the above SiO ₂ and MgO are reacted to
The product is usually manufactured through a series of manufacturing steps in which a forsterite (Mg ₂ SiO ₄ ) film having a thickness of ˜5 μm is formed, and sometimes an insulating coating is formed by baking on a phosphate-based treatment agent. .

The grain-oriented silicon steel sheet thus obtained is mainly used as an iron core of a transformer or other electric equipment, has a high magnetic flux density (represented by a B ₈ value) as a magnetic property, and has an iron loss ( ₍ Represented by W _17/50 ) is required to be low. In particular, from the viewpoint of energy saving, reduction of iron loss is becoming more important in order to prevent electric energy from being converted into heat energy and wasted as wasteful energy inside the iron core.

[0004]

2. Description of the Related Art By the way, it is known that if the forsterite coating film formed on the surface of a grain-oriented silicon steel sheet is finish-annealed and then the surface is finished to be smooth, a remarkable reduction in iron loss is recognized. For example, Japanese Patent Publication No.
Japanese Unexamined Patent Publication No. 9 (a method for producing ultra-low iron loss unidirectional silicon steel sheet) discloses a method in which after finish annealing, surface products are removed by pickling, and then chemical polishing or electrolytic polishing is performed to obtain a mirror-finished state. There is. Further, Japanese Patent Publication No. 4-72920 (method for producing low iron loss grain oriented silicon steel sheet) discloses a method of electrolytic treatment in an aqueous halide solution after removing surface products. Further, Japanese Patent Application Laid-Open No. 5-43943 (method for mirror-finishing grain-oriented silicon steel sheet) discloses a method in which the forsterite coating is removed and then thermal etching is performed in H ₂ at 1000 to 1200 ° C. The reason why the iron loss is reduced by such smoothing is that the hysteresis loss is reduced due to the reduction of pinning sites that hinder the domain wall movement in the magnetization process. It should be noted that the magnetically smooth surface that reduces the hysteresis loss is not generally represented by Ra (center line average roughness), which is so-called surface roughness alone. As shown in.

It is known that iron loss can be further reduced by applying tension to the surface smoothed as described above by coating. This is due to the action of reducing the magnetostatic energy when tension is applied in the magnetization direction,
This is because the magnetic domains are subdivided and the eddy current loss is reduced.

Several methods have conventionally been proposed as a method for performing tension coating treatment on a smoothed steel plate surface. For example, JP-B-52-24499 discloses a method of applying a coating agent and baking after performing thin metal plating. Further, Japanese Patent Publication No. 56-4150 (method for producing unidirectional silicon steel sheet with extremely low iron loss) discloses a method of forming a ceramic thin film by vapor deposition, sputtering or thermal spraying.
Japanese Unexamined Patent Publication (Heat Stability, Method of Manufacturing Ultra Low Iron Loss Unidirectional Silicon Steel Sheet) discloses a method of forming a nitride or carbide coating by ion plating or ion implantation. In addition, Japanese Patent Application Laid-Open No. 2-243770 (method for producing low iron loss unidirectional silicon steel sheet) discloses a method for forming a ceramic coating by a so-called sol-gel method.

These methods are certainly effective as a method for applying tension to a steel sheet having a smoothed surface, but have some problems. That is, the adhesion of the coating was not sufficient by the method of applying the thin metal plating as the base and applying the coating on it and baking the coating. In addition, the formation of a ceramic film by vapor deposition, sputtering spraying, ion plating, ion plantation, or the sol-gel method is expensive, and it is difficult to ensure uniformity when processing a large area in large quantities. There was a problem.

The tension coating currently applied to the grain-oriented silicon steel sheet having a forsterite coating is a mixed treatment liquid of phosphate, colloidal silica and chromic anhydride or a treatment mainly containing chromate. Many are formed by applying and baking a liquid. The vitreous coating formed by this method has a low coefficient of thermal expansion and therefore effectively applies tension to the steel sheet. For example, JP-B-53-28375 (method for forming an insulating coating on a grain-oriented silicon steel sheet) and Japanese Patent Publication No. 56-52117 (method of forming an insulating coating on a grain-oriented silicon steel sheet) discloses a method of forming the same.

These methods are excellent in cost, easy to perform uniform treatment, and industrially excellent. However, if this coating treatment is performed directly on the smoothed steel plate surface, the adhesion of the coating film is insufficient, and there is a problem that the coating film peels off during strain relief annealing, bending, shearing or punching.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems, and to propose a grain-oriented silicon steel sheet having a low iron loss and having a tension coating having excellent adhesion and a method for producing the same. And

[0011]

SUMMARY OF THE INVENTION The present invention provides a method for forming a phosphate / colloidal silica / chromic acid tension coating on a grain-oriented silicon steel sheet having a smoothed surface. As a result of various experiments and examinations, the base treatment that serves as a strong binder between the steel sheet and the tension coating has been achieved. That is, the gist of the present invention is as follows.

A grain-oriented silicon steel sheet having a low iron loss, which has a composite metal plating layer in which oxide particles are dispersed between the tension coating and the surface of the grain-oriented silicon steel sheet (No. 1).
invention).

[0013] The oxide particles in the first invention, SiO _2,
Al ₂ O ₃ , Cr ₂ O ₃ , Fe ₂ O ₃ , TiO ₂ , ZrO ₂ , Sb ₂ O ₅ , SnO ₂ and
It is one or more selected from MgO (second invention).

The tension coating in the first invention or the second invention is obtained by applying a treatment liquid containing a mixed treatment liquid containing a phosphate, colloidal silica and chromic acid as a main component to the surface of a plated steel sheet and then baking it ( Third invention).

A finish-annealed grain-oriented electrical steel sheet having no oxide film and having a magnetically smooth surface is subjected to composite metal plating in which oxide particles are dispersed, and then subjected to tension coating treatment. It is a characteristic method for producing a grain-oriented silicon steel sheet having a low iron loss (fourth invention).

Here, the magnetically smooth surface means a surface which can reduce pinning sites which hinder the domain wall movement in the magnetization process of the steel sheet.

[0017]

The function of the present invention will be described in detail below. The steel sheet used in the present invention is a grain-finished grain-oriented silicon steel sheet whose surface is magnetically smooth.
Such a steel plate can be manufactured as follows.

That is, Si: contains 4% or less, and MnS, M
After hot rolling a silicon steel slab containing inhibitors such as nSe and / or AlN, it is annealed if necessary and then rolled once or twice by intermediate rolling to the final product sheet thickness by cold rolling. . Next, decarburization and annealing for primary recrystallization are performed, and then an annealing separator is applied and dried,
Then, it is wound into a coil and then subjected to final finish annealing.
At this time, if MgO is used as the main component of the annealing separator,
By reacting with SiO ₂ generated during decarburization annealing, an oxide mainly composed of forsterite (Mg ₂ SiO ₄ ) is formed on the surface. In such cases, this product would be removed by pickling or mechanical polishing after finish annealing.

However, an additive such as an alkali metal such as Na or K or a chloride such as chloride which inhibits the formation of a forsterite film is added to the annealing separator, or the main component of the separator is Al ₂ O ₃ . By using such an oxide that hardly reacts with SiO ₂ , it is possible to significantly reduce the generation of oxides on the surface of the steel sheet after finish annealing. In such a case, the surface can be directly smoothed without performing pickling or mechanical polishing for removing oxides.

This smoothing is a smoothing in a magnetic sense, and does not mean merely a mirror finish or a reduction in surface roughness. That is, the surface of which the number of pinning sites that hinder the domain wall movement during the magnetization process of the steel sheet is reduced is magnetically smooth even if the surface roughness is large. This can be easily determined by measuring the iron loss (hysteresis loss) of the steel sheet.

To obtain such a surface, electrolytic polishing using a bath of phosphoric acid type, sulfuric acid type, phosphoric acid / sulfuric acid type or perchloric acid type, or HF-H ₂ is conventionally known.
Chemical polishing with O ₂ or H ₃ PO ₄ —H ₂ O ₂ can be applied. Further, anodic electrolysis in a halide aqueous solution is also a method that meets this purpose. It is also possible to combine these with mechanical polishing with less distortion using fine-grained abrasives. On the other hand, such a surface can be obtained by thermal etching in a reducing atmosphere at 1000 ° C. or higher.

Next, the thus-obtained grain-oriented silicon steel sheet having a magnetically smooth surface is subjected to composite metal plating in which oxide fine particles are dispersed. This plating layer has strong adhesion to steel sheets, which is characteristic of electroplating, and since it contains oxide fine particles, it also has a strong affinity for the tension coating formed on the plating layer. And the adhesion of the tension coating becomes very strong. Due to this effect, even if the steel sheet is subjected to bending, shearing, punching, strain relief annealing, etc., the tension imparting effect of the coating and the surface coating effect do not deteriorate.

The composite metal plating is formed by electroplating a steel sheet in a plating bath in which fine oxide particles (colloidal particles) are dispersed. The matrix metal for this plating is Ni, Co, Fe, Zn, Cu, Cr and Sn.
Etc. can be used alone or as composite or alloy plating. As oxides, SiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ ,
Fe ₂ O ₃ , TiO ₂ , ZrO ₂ , Sb ₂ O ₅ , SnO ₂ and MgO 1
One kind or two or more kinds can be used, and fine particles in the form of a composite of these oxides can also be used. Even if the form of particles in the plating bath or in the deposited plating layer is in the form of hydroxide, it decomposes during baking after application of the tension coating treatment solution and becomes an oxide. Fits the invention.

The particle size of the oxide is about 50 m
A size of not more than μm is preferable because a uniform electrodeposition layer can be obtained and the effect of improving the adhesion of the tension coating is excellent. In addition, as the content of the oxide,
0.5 to 50% is suitable. If it is too small, the adhesion of the tension coating will be insufficient, and if it is too large, the adhesion of the plating layer to the steel sheet will deteriorate, which is not preferable. The thickness of the plated layer is preferably in the range of 0.1 to 5 μm. If it is too thin, the adhesion of the tension coating will be insufficient, and if it is too thick, the space factor of the silicon steel sheet will decrease, which is not preferable. The plating conditions vary depending on the type of bath, so it cannot be said in any way, but the current density is suitable for forming the target plating layer in the range of approximately 1 to 100 A / dm ² .

A tension coating is formed on the composite metal plating layer containing the oxide particles. As for the type of tension coating, phosphate, which is conventionally used for grain-oriented silicon steel sheets with forsterite coating,
Colloidal silica / chromic acid type coating is preferable from the viewpoints of its effect, cost, uniform processability, and the like.

This tension coating effectively imparts tension to the steel sheet due to the coefficient of thermal expansion lower than that of the steel sheet, and as a result, reduces iron loss (eddy current loss). As the treatment liquid, an aqueous liquid prepared by mixing a phosphate such as aluminum phosphate, magnesium phosphate or calcium phosphate with colloidal silica, and chromic anhydride or a chromate as a main component is used. These are applied to the surface of the steel sheet and then baked in a temperature range of 500 to 900 ° C to form a glassy film. The thickness of the coating is 0.3 from the viewpoint of tension application effect, space factor, coating adhesion, etc.
The range of about 5 μm is preferable. Besides, as the tension coating, Al ₂ O ₃ -B ₂ O _{3 and the} like proposed in JP-A-6-65754, JP-A-6-65755, JP-A-6-299366 and the like are also used. It is also possible to apply an oxide coating.

The steel sheet thus obtained is irradiated with a laser or a plasma flame to subdivide the magnetic domains for the purpose of further reducing the iron loss, whereby the adhesion of the tension coating is enhanced. So there is no problem.
Further, at any stage of the production process of the grain-oriented silicon steel sheet of the present invention, to form grooves at a constant interval by etching or tooth profile rolls for magnetic domain subdivision, as a means for further reducing iron loss, It is valid.

[0028]

【Example】

Example 1 C: 0.040%, Si: 3.40%, Mn: 0.07%, Mo: 0.012
%, S: 0.004%, Se: 0.021% and Sb: 0.025%, hot-rolled silicon steel sheet was homogenized at 900 ° C for 3 minutes and then an intermediate anneal at 950 ° C was performed. By rolling, a cold rolled sheet having a final sheet thickness of 0.23 mm was obtained. Then, perform decarburization and primary recrystallization annealing at 820 ° C for 2 minutes in a wet hydrogen atmosphere,
Then, MgO containing 1% each of SrSO ₄ and TiO ₂ as an annealing separator was applied in a water slurry state and dried. After that, a secondary recrystallization process was performed in N ₂ at 860 ° C. for 50 hours,
Followed by a purification process in H ₂ at 1180 ° C. for 10 hours,
Final finish annealing was performed. This steel plate in N ₂ + H ₂ in 820
After performing a flattening annealing (removal of coil winding) for 1 minute at 80 ° C., the forsterite film on the surface was removed by pickling in H ₂ SO ₄ at 10% and 80 ° C. Next, electrolytic polishing was performed in a H ₃ PO ₄ —CrO ₃ bath at 70 ° C. and 100 A / dm ² to magnetically smooth the surface. The steel sheet thus obtained was subjected to the composite electroplating shown in Table 1.

[0029]

[Table 1]

This plating was carried out by cathodic electrolysis of the steel sheet in an electrolytic bath in which colloidal oxide particles were dispersed in a plating bath containing matrix metal ions. As shown in the table, for comparison, plating containing no oxide was also performed. After that, an aqueous treatment liquid containing magnesium phosphate, colloidal silica and chromic anhydride as main components was applied as a tension coating,
Baking was performed at 0 ° C. to form a film having a thickness of about 2.0 μm.

Magnetic flux density of the steel sheet thus obtained
(B ₈ ) and iron loss (W _17/50 ) were measured, and the film adhesion was evaluated. The adhesion of the coating film was evaluated by measuring the minimum diameter (mm) where the coating film was not peeled off by winding a sample around a round bar having various diameters. These results are collectively shown in Table 1.

As is clear from Table 1, sample No. 17 of the comparative example, which was not plated, has poor core loss and poor coating adhesion. Further, the sample Nos. 12 to 16 of the comparative example plated with no oxide also have improved iron loss and coating adhesion as compared with sample No. 17, but they are not at a sufficient level. On the other hand, the sample Nos. 1 to 11 of the conforming examples conforming to the present invention exhibit excellent iron loss and coating adhesion.

Example 2 C: 0.062%, Si: 3.12%, Mn: 0.076%, Se: 0.022
%, S: 0.003%, Al: 0.025%, N: 0.0085% and
Sb: Grain-oriented silicon steel hot-rolled sheet containing 0.028%, 1050
After heating at ℃ for 2 minutes, it was rapidly cooled by mist injection and then cold-rolled to obtain a cold-rolled sheet having a sheet thickness of 0.23 mm. Then, after decarburization and primary recrystallization annealing at 830 ° C for 3 minutes in a wet hydrogen atmosphere, Al ₂ O ₃ powder as an annealing separator: 60%, Ca
A water slurry mixed at a ratio of SiO ₃ powder: 30% and MgO powder: 10% was applied and dried. After that, finish annealing was performed in H ₂ at 1200 ° C. for 10 minutes. 820 this steel sheet in N ₂ + H ₂
After subjecting to flattening annealing at ℃ for 1 minute, HC at 5%, 40 ℃
The surface oxide was removed by lightly pickling in 1 l. Then HF-
Chemical polishing was performed in a H ₂ O ₂ bath to magnetically smooth the surface. The steel sheet thus obtained was subjected to the composite electroplating shown in Table 2.

[0034]

[Table 2]

Plating was performed in the same manner as in Example 1.
For comparison, plating containing no oxide was also performed. Then, an aqueous treatment liquid containing aluminum phosphate, colloidal silica and chromic anhydride as main components was applied as a tension coating, and baked at 800 ° C. to form a film having a thickness of about 1.2 μm. With respect to the grain-oriented silicon steel sheet thus obtained, magnetic properties and coating adhesion were evaluated in the same manner as in Example 1. These results are collectively shown in Table 2.

As is clear from Table 2, sample No. 10 of the comparative example, which was not plated, has poor iron loss and coating adhesion. In addition, the samples Nos. 7 to 9 of the comparative examples plated with no oxide are also improved as compared with the sample No. 10, but the iron loss and coating adhesion are still insufficient. On the other hand, sample N of the conforming example that conforms to the present invention
o.1 to 6 have very good iron loss and coating adhesion.

Example 3 The same cold-rolled sheet having the final sheet thickness of 0.23 mm as in Example 1 was decarburized and subjected to primary recrystallization annealing under the same conditions as in Example 1, and then Al ₂ O ₃ : 55.
%, CaSiO ₃ : 25%, MgO: 20%, and the annealing separator was applied as a water slurry and dried. Next, final finishing annealing and flattening annealing were performed under the same conditions as in Example 1, and then light pickling was performed in 5% 40 ° C. HCl to remove surface oxides. Then NaCl containing polyethylene glycol
Anodic electrolysis with a current density of 70 A / dm ² was performed in an aqueous solution to magnetically smooth the surface. Then, the composite electroplating shown in Table 3 was performed.

[0038]

[Table 3]

Plating was carried out in the same manner as in Example 1, and for comparison, plating containing no oxide was also carried out. After that, an aqueous treatment liquid containing calcium phosphate, colloidal silica and magnesium chromate as main components was applied as a tension coating and baked at 800 ° C. to form a film having a thickness of about 1.7 μm. After this, 800 more in N ₂
Strain relief annealing was performed at 3 ° C. for 3 hours. With respect to the grain-oriented silicon steel sheet thus obtained, magnetic properties and coating adhesion were evaluated in the same manner as in Example 1. These results are collectively shown in Table 3.

As is clear from Table 3, the sample No. 9 of the comparative example, which was not plated, is poor in both iron loss and coating adhesion. Similarly, sample Nos. 7 and 8 of the comparative examples plated with no oxide are not good. On the other hand, the sample Nos. 1 to 6 of the conforming examples conforming to the present invention still show excellent iron loss and coating adhesion even after the strain relief annealing.

[0041]

INDUSTRIAL APPLICABILITY The present invention is a grain-oriented silicon steel sheet having a composite metal plating layer in which oxide particles are dispersed as a binder, between a tension coating and a smoothed grain-oriented silicon steel sheet surface. According to the present invention, it is possible to obtain a grain-oriented silicon steel sheet having an extremely low iron loss, which is excellent in film adhesion of the tension coating, and is advantageous as an iron core of electric equipment such as a transformer from the viewpoint of energy saving. Can be used for

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location // C21D 9/46 501 H01F 1/16 B

Claims (4)

[Claims] 1. A grain-oriented silicon steel sheet having a low iron loss, which comprises a composite metal plating layer in which oxide particles are dispersed between the tension coating and the surface of the grain-oriented silicon steel sheet. 2. The oxide fine particles are SiO ₂ , Al ₂ O ₃ , Cr ₂ O ₃ ,
The grain-oriented silicon steel sheet with low iron loss according to claim 1, which is one or more selected from Fe ₂ O ₃ , TiO ₂ , ZrO ₂ , Sb ₂ O ₅ , SnO ₂ and MgO. 3. The tension coating according to claim 1, wherein the surface of the plated steel sheet is coated with a treatment liquid containing a mixed treatment liquid containing phosphate, colloidal silica and chromic acid as a main component and then baked. Grain-oriented silicon steel sheet with low iron loss. 4. A finish-annealed grain-oriented electrical steel sheet having no oxide film and having a magnetically smooth surface is subjected to composite metal plating in which oxide particles are dispersed, and then subjected to tension coating treatment. A method for producing a grain-oriented silicon steel sheet having a low iron loss.