JPH0673555A - Production of grain oriented electric steel sheet excellent in magnetic property and surface characteristic - Google Patents

Abstract

PURPOSE:To obtain a grain oriented electric steel sheet excellent in magnetic properties, having smooth surface, and improved in powdering resistance by forming a film consisting of a mixture of colloidal silica, primary phosphates of specific elements, CrO3, and dichromates of specific elements on the surface of a grain oriented electric steel sheet. CONSTITUTION:A silicon steel slab is hot-rolled, cold-rolled, and subjected to decarburizing annealing and to final finish annealing. The resulting steel sheet is cleaned by removing the unreacted separation agent at annealing from the surface. Subsequently, this steel sheet is coated with an insulating film having a composition expressed in terms of the ratio of dried and solidified solid matter consisting of, by weight, <=0.8% Na2O as a trace impurity, 30-60% of spheroidal colloidal silica with 5-50nm grain diameter and 0.3% SO4 concentration, 30-60% of one or more kinds among the primary phosphates of Al, Mg, Ca, Fe, Mn, Sr, etc., and 5-20% of CrO3 or one or more kinds among the dichromates of Mg, Ca, and Sr. By this method, the grain oriented electric steel sheet having superior magnetic properties such as improved core loss, having smooth surface, and excellent in powdering resistance can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and surface properties, and in particular, a top coat insulation coating formed after forming a forsterite coating on the grain-oriented electrical steel sheet surface. This is intended to improve the characteristics.

[0002]

2. Description of the Related Art Generally, a grain-oriented electrical steel sheet is coated on its surface in order to impart insulation, workability and rust prevention. Such a surface coating consists of a forsterite coating formed during final finish annealing and a phosphate-based topcoat coating applied thereon. Also, since these coatings are formed at high temperature and have a low coefficient of thermal expansion, tension is applied to the steel sheet due to the difference in the coefficient of thermal expansion between the steel sheet and the coating when the temperature drops to a low temperature, and iron loss is reduced. Since it is effective, it is desired to apply as much tension as possible to the steel sheet.

On the other hand, the steel sheet as the final product is cut into a certain length by a shear after passing through a length measuring roll called a measuring roll, but peeling powder of the film adheres to the surface of the steel sheet. If so, the peeling powder adheres to the measuring roll, and the diameter of the roll apparently changes, which may cause a deviation in the measurement length. In addition, such dusting also deteriorates the working environment. Such dusting is considered to be caused by unevenness of the surface, but this also has a harmful effect of lowering the space factor, and therefore it is preferable to coat a film having a smooth surface and not dusting. This is especially important in making a transformer.

In order to satisfy the above-mentioned various characteristics, various coating films have been conventionally proposed. For example, Japanese Patent Publication No. 56-52117 discloses a method of improving the stress characteristics of iron loss and magnetostriction by applying a coating solution containing colloidal silica and magnesium phosphate added at a molar ratio of 82/20. Further, JP-B-53-28375 discloses a method of improving iron loss and magnetostriction characteristics by applying a coating solution containing colloidal silica, aluminum phosphate, and chromic acid, together with the surface properties.
Each has been proposed.

It has been confirmed that the above-mentioned method has some effect on improving the iron loss, magnetostriction, insulating properties and surface properties of the coating of the grain-oriented electrical steel sheet. However, with the increase in energy demand and user's need for noise, further reduction of iron loss and improvement of magnetostriction characteristics are strongly demanded. In addition, manufacturers of transformers, etc., are increasing the automation and speed of processing machines when processing iron cores, and it is desirable to develop insulating coatings with better surface properties than the improved insulating coatings described above. The reality is that it is rare.

[0006]

It is needless to say that the present invention is excellent in iron loss improving effect by strengthening the tension of the insulating coating of the grain-oriented electrical steel sheet, and the coating surface is smoother than before and is free from dusting. It is an object of the present invention to propose an advantageous method for producing a grain-oriented electrical steel sheet having excellent coating properties.

[0007]

The gist of the present invention is as follows. 1. As a coating agent for applying tension coating to the surface of grain-oriented electrical steel sheet that has been final annealed,
Ingredient composition is dry solids ratio, colloidal silica: 30 ~
60wt% (simply shown as% below), Al, Mg, Ca, Fe, Mn and
One or more selected from Sr primary phosphates:
30-60%, and one or more selected from chromic anhydride and dichromates of Mg, Ca, Sr: 5-20% composition and trace impurities in colloidal silica A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and surface properties, which comprises using Na ₂ O having a concentration of 0.8% or less in a colloidal solution (first invention).

2. When applying tension coating to the surface of grain-oriented electrical steel sheet that has undergone final finish annealing, the composition of the composition is dry solids ratio, colloidal silica: 30-60%, Al, Mg, Ca, Fe, Mn And one or more selected from Sr primary phosphates: 30 to 60%,
And one or more selected from chromic anhydride and dichromate of Mg, Ca, Sr: a colloid of Na ₂ O, which is a trace impurity in colloidal silica and has a composition of 5 to 20% If the concentration in the liquid is 0.8% or less and the SO ₄ concentration is
A method for producing a grain-oriented electrical steel sheet excellent in magnetic characteristics and surface properties, characterized by using 0.3% or less (second invention).

In each of the above inventions, colloidal silica having a spherical shape and a particle size of 5 to 50 nm is particularly advantageously suited.

The experimental results that led to the invention will be described below. In the experiment, a sample was cut out from the final coil of grain-oriented silicon steel sheet having a plate thickness of 0.23 mm manufactured by a known method and subjected to stress relief annealing in N ₂ at 800 ° C. for 2 hours to remove the coil set. Was used as the starting material. The magnetic flux density of this material is 1.92 (T) at B ₈ , and the iron loss is W.
_It is 0.89 (W / kg) at _17/50 . On the surface of this steel sheet, magnesium phosphate: 50%, the concentration of Na ₂ O, which is an impurity in colloidal silica, in the Koirod solution varied (SO ₄ concentration was 0.5% and 0.3%, two types) Colloidal Silica: 40%, chromic anhydride: 10% A coating agent with a compounding ratio of 10% / mm ² (on both sides) was applied, and then N
_It was baked at 800 ℃ for 2 minutes in ₂ atmospheres. The colloidal silica used was spherical and had a particle size of 15 nm.

FIG. 1 and FIG. 2 show the results of examining the iron loss characteristics and the surface roughness before and after baking the coating, and show the amount of Na ₂ O in the colloidal silica (FIG. 1 shows the SO ₄ concentration).
0.5%, Fig. 2 shows the relationship between the SO ₄ concentration of 0.3%), the iron loss improvement amount (ΔW _17/50 ) after film formation, and the center line average roughness (Ra). As apparent from the figure, [Delta] W _17/50 is largely changed by the Na ₂ O content in the colloidal silica, not more than 0.8% concentration of Na ₂ O, [Delta] W _17/50 is 0.05 (W / It has been found that a large improvement margin over the previous kg) can be obtained.
Regarding the surface roughness, although a smooth surface was obtained even when the SO ₄ concentration was about 0.5%, it was found that a better smooth surface could be obtained if the SO ₄ concentration was 0.3% or less. did. Thus, Na ₂ O in colloidal silica
The fact that the iron loss improvement margin and the surface condition are improved by regulating the amount of SO ₄ , and further the amount of SO ₄ is a new finding discovered for the first time in the present invention.

Next, the suitable particle size and shape of the colloidal silica were examined. The same final finish annealed grain oriented silicon steel sheet as above was used for the experiment. Magnesium phosphate: 50%, Na ₂ O concentration 0.1%, SO ₄ concentration 0.05%
Colloidal silica with various particle sizes and shapes: 40%,
Chromic anhydride: A coating liquid having a compounding ratio of 10% was applied so that the coating amount was 10 g / m ² (on each side), and then baked at 800 ° C. for 2 minutes in an N ₂ atmosphere. The iron loss value of the thus-obtained electromagnetic steel sheet before and after baking was measured, and the difference was determined. At the same time, the surface roughness and dusting property were also investigated.

Table 1 shows the particle size of the colloidal silica used,
Shape and iron loss improvement before and after coating ΔW _17/50
Shows the relationship with. As is clear from the table, the particle size is 5
The iron loss is improved particularly stably when colloidal silica having a shape of 50 nm and a spherical shape is used.

[0014]

[Table 1]

[0015]

According to the present invention, the reason why iron loss characteristics and surface properties are improved by reducing the concentration of trace impurities such as Na ₂ O in colloidal silica and further SO _{4 in} the colloidal liquid is not yet explained. Although not clearly clarified, it is considered as follows. That is, in colloidal silica, Na ₂ O is an additive necessary to uniformly disperse SiO ₂ as colloidal particles, but in phosphoric acid-silica glass used in this field, Na or Li,
An alkali metal oxide such as K cuts Si—O bonds and P—O bonds to reduce cross-linking oxygen and reduces the viscosity during glass melting. As a result, the glass film-forming property deteriorates, the coefficient of thermal expansion, which is a basic property of glass, increases, and the glass softening temperature also decreases. In addition, since the glass film-forming property is deteriorated, part of the coating is crystallized, and the thermal expansion coefficient is increased also from this point. Therefore, by using such colloidal silica containing as little Na ₂ O as possible, the glass transition point is increased and a coating having a low coefficient of thermal expansion is formed, so that the iron loss reduction effect is improved. Conceivable.

The colloidal silica is classified into two systems, an acidic type and an alkaline type, depending on the pH value. The acidic type colloidal silica having a high SO ₄ concentration has a large surface roughness. That is, it is known that the film-forming temperature of the glass film using magnesium phosphate-colloidal silica is about 600 ° C. When such a phosphoric acid-silica-based treatment liquid is applied to a steel sheet, the coating liquid undergoes a dehydration condensation reaction in the baking process to form a film, but in this process part of SO ₄ is gasified. To do. As a result, microscopic holes are formed on the surface of the coating film, or blisters occur, which deteriorates the surface smoothness and makes the surface easy to generate dust. In this respect, if the SO ₄ concentration is reduced, the above problems can be solved and good surface properties can be obtained.

Regarding the particle size, it is generally considered that the finer the particle size, the better the reactivity with the phosphate and the better the glass coating can be obtained. However, the reaction rate can be improved by appropriately increasing the particle size. It is considered that the tension can be further improved by delaying and forming the film at a higher temperature, that is, by increasing the reaction temperature. Therefore, it is expected that the tension will be improved by increasing the grain size and baking at a higher temperature.However, since baking of the coating is usually performed at the same time as flattening annealing, if the baking is performed at an excessively high temperature, the steel sheet will stretch and the magnetic properties will increase. Adversely affect. Therefore, the particle size has a suitable range, and only within this range, an excellent iron loss reducing effect can be obtained. Regarding the shape of the colloidal particles, spherical ones have better dispersibility in the coating liquid than filamentous ones and distorted ones, which makes it easier to control the reaction rate and keeps them within a certain temperature range. Since the reaction proceeds sufficiently, it is considered that an excellent iron loss reducing effect can be obtained.

By the way, as a technique for changing the type of colloidal silica, Japanese Patent Publication No. 62-53589 discloses a technique of 8 nm.
The following techniques have been disclosed for improving the tension-applying property and the slipperiness by blending the following ultrafine particles of colloidal silica. This means that by making the colloidal silica fine particles, the reactivity with the phosphate is improved, but in this respect, the spherical particles are preferably used in the present invention, and the particle size is increased to some extent. By positively controlling the reaction, the tension-adding property is improved. Further, JP-A-3-207868 and JP-A-3-3868.
Japanese Patent No. 9484 discloses a technique of improving slipperiness and tension imparting property by using a mixture of two kinds of fine particles and coarse particles as colloidal silica.
In this method, the stability of the colloid was deteriorated by mixing the colloidal silica as compared with the usual case, the agglomeration of the colloidal silica was caused, and the object was often not achieved. In this respect, according to the present invention, based on a novel finding, the Na ₂ O concentration and the SO ₄ concentration of the colloidal silica are reduced, and the particle size is regulated, so that excellent tension can be obtained without using the above technique. It is possible to obtain additivity and surface texture.

Next, the reasons for limitation of the present invention will be described. The electromagnetic steel sheet targeted by the present invention is obtained by performing hot rolling, cold rolling, decarburizing annealing, and final finishing annealing according to a conventional method. Fits.

As a coating agent, its composition is a dry solid content ratio, colloidal silica: 30 to 60%, Al,
One or more selected from the primary phosphates of Mg, Ca, Fe, Mn and Sr: 30-60%, chromic anhydride and Mg, C
One or more selected from a and Sr dichromates: 5 to 20% is used. The tension effect cannot be expected when the content of colloidal silica is less than 30% or the content of monobasic magnesium phosphate is more than 60%. Further, if the content of colloidal silica exceeds 60% or the content of primary magnesium phosphate is less than 30%, a uniform coating cannot be formed and the adhesion becomes poor. The primary phosphate here is A
Since the effect of tension is small except for l, Mg, Ca, Fe, Mn and Sr, the present invention is limited to the above 6 types. Chromic anhydride and dichromate of Mg, Ca, Sr are added to improve the moisture absorption resistance and heat resistance, but if it is less than 5%, it has no effect. Since the property deteriorates,
The range is limited to 5 to 20%. In addition to these, silica powder and alumina powder can be used. All of these are useful components for improving the sticking resistance, and the addition amount is preferably about 0.1 to 4%.

Next, colloidal silica having a Na ₂ O concentration of 0.8% or less is used. This is because when the Na ₂ O concentration exceeds 0.8%, the iron loss reduction effect and the smooth surface cannot be sufficiently satisfactory as shown in FIG. 1 above. Furthermore, to obtain even better surface smoothness, S
It is advantageous to set the O ₄ concentration to 0.3% or less.

As the colloidal silica, spherical ones having a particle diameter of 5 to 50 nm are particularly suitable, and by using silica particles having such a shape and size, the magnetic properties and surface properties are further improved. be able to. The coating amount is preferably about 4 to 15 g / m ^{2 on} both sides. This is because if it is less than 4 g / m ² , the insulation problem remains, while if it is more than 15 g / m ² , the space factor decreases. Further, the baking treatment is preferably carried out at a temperature range of about 700 to 950 ° C. for about 5 to 120 seconds.

[0023]

【Example】

Example 1 With respect to grain-oriented silicon steel sheet having a plate thickness of 0.23 mm and having been subjected to final finish annealing, after removing unreacted separating agent adhering to the surface thereof, strain relief annealing and phosphoric acid pickling treatment were performed, and thereafter, the composition of components was changed. The dry solids ratio was 50% for colloidal silica, 40% for magnesium phosphate and 10% for chromic anhydride. At this time, as the colloidal silica, as shown in Table 2, those having various shapes, particle sizes, and Na ₂ O and SO ₄ concentrations were used. Table 2 also shows the results of examining various characteristics of the coated silicon steel sheet thus obtained.

[0024]

[Table 2]

[0025]

[Table 3] * 2 Evaluation by surface observation by SEM. A: Almost no irregularities on the surface O: Slight irregularities on the surface B: Severe irregularities on the surface * 3 Improvement in iron loss before and after coating.
The magnetic flux density B ₈ of the final finish annealed plate is 1.92 T. * 4 10 pieces of 50 x 50 mm test piece are 2 kg in dry nitrogen atmosphere.
500g after annealing at 800 ℃ for 2h under compressive load of / mm ²
The weight was dropped and all test pieces were peeled off. ◎… 20 cm ○… 40 cm △… 60 cm ×… 80 cm * 5 Compressive stress value (kg / mm ² ) at which λ _pp is 4 × 10 ⁻⁴ . * 6 Non-peel minimum bending diameter (mm). * 7 According to JIS 2550 method. * 8 Temperature: 50 ° C, dew point: 50 ° C
Observe the surface. ○: Almost no rust occurred △: Some rust occurred ×…
Severe rust

As is clear from Table 2, the Na ₂ O concentration was 0.80.
%, The magnetic properties were particularly good, and when the SO ₄ concentration was 0.30 or less, the surface properties were also particularly good.

Example 2 With respect to grain-oriented silicon steel sheet having a plate thickness of 0.23 mm and having been subjected to final finish annealing, after removing unreacted separating agent adhering to the surface thereof, strain relief annealing followed by phosphoric acid pickling treatment was carried out, Various colloidal silicas and primary phosphates as shown in Table 4 were used, and the composition of the components was a dry solids ratio.
50%, primary phosphate: 40%, and chromic anhydride: 10
% Coating was applied. Table 4 also shows the results of examining various characteristics of the coated silicon steel sheet thus obtained.

[0028]

[Table 4]

As is clear from the table, any of the primary phosphates specified in the present invention has excellent magnetic properties and surface properties.

Example 3 With respect to grain-finished grain-finished grain oriented silicon steel sheets having various thicknesses, the unreacted separating agent adhering to the surface thereof was removed, strain-relief annealing was performed, and then phosphoric acid pickling was performed. The colloidal silica as shown was coated to a dry solids ratio of 50%, the same monobasic magnesium phosphate: 40% and chromic anhydride: 10%. Table 5 also shows the results of examining various properties of the coated silicon steel sheet thus obtained.

[0031]

[Table 5]

As is clear from the table, particularly when the plate thickness is thin, the tension effect is particularly large and particularly good magnetic characteristics are obtained.

Example 4 With respect to a grain-finished 0.23 mm thick grain-finished grain-oriented silicon steel sheet, the unreacted separating agent adhering to the surface thereof was removed, strain-relief annealing was carried out, and then phosphoric acid pickling was carried out. As silica, chromic anhydride or dichromate, various compounds as shown in Table 6 are used, and the component composition is a dry solid content ratio, colloidal silica: 50%, primary magnesium phosphate: 40%. Chromic anhydride or dichromic acid compound: 10% coating was applied. Table 6 also shows the results of examining various properties of the coated silicon steel sheet thus obtained.

[0034]

[Table 6]

As is clear from the table, excellent magnetic properties and surface properties are obtained regardless of which dichromate or chromic anhydride specified in the present invention is used.

[0036]

As described above, according to the present invention, it is possible to stably obtain a grain-oriented electrical steel sheet having excellent magnetic properties, smooth surface properties, and good dusting resistance.

[Brief description of drawings]

Fig. 1 Na ₂ O concentration in colloidal silica (SO ₄ concentration is
FIG. 5 is a graph showing the relationship between (0.5%), the amount of improvement in iron loss before and after coating, and the average roughness of the surface.

Fig. 2 Na ₂ O concentration in colloidal silica (SO ₄ concentration is
(0.3%) and the improvement margin of iron loss before and after coating and the average roughness of the surface.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Michio Komatsubara 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Technical Research Division, Kawasaki Steel Corporation (72) Inventor Katsuo Iwamoto 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Iron & Steel Co., Ltd. Technical Research Headquarters (72) Inventor Mr. Hiroshi Nishiike 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Iron & Steel Co., Ltd. Technical Research Headquarters

Claims (3)

[Claims] 1. When applying a tension coating to the surface of a grain-oriented electrical steel sheet that has undergone final finish annealing, as a coating agent, the composition of components is a dry solid content ratio, colloidal silica: 30-60 wt%, Al, Mg, One or more selected from primary phosphates of Ca, Fe, Mn and Sr: 30-60wt
%, And one or more selected from chromic anhydride and dichromates of Mg, Ca, Sr: 5 to 20 wt% in composition, and Na which is a trace impurity in colloidal silica.
_A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and surface properties, characterized in that the concentration of ₂ O in a colloidal solution is 0.8 wt% or less. 2. When applying a tension coating to the surface of the grain-oriented electrical steel sheet that has been subjected to final finish annealing, as a coating agent, the component composition is a dry solid content ratio, colloidal silica: 30-60 wt%, Al, Mg, One or more selected from primary phosphates of Ca, Fe, Mn and Sr: 30-60wt
%, And one or more selected from chromic anhydride and dichromates of Mg, Ca, Sr: 5 to 20 wt% in composition, and Na which is a trace impurity in colloidal silica.
_A method for producing a grain-oriented electrical steel sheet having excellent magnetic properties and surface properties, characterized in that the concentration of ₂ O in a colloidal solution is 0.8 wt% or less and the SO ₄ concentration is 0.3 wt% or less. 3. The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the colloidal silica has a spherical shape and a particle size of 5 to 50 nm.