JPH04272183A - Method of forming insulating film on low temperature baked grain oriented electrical steel sheet excellent in iron-core workability - Google Patents

Abstract

PURPOSE:To form a grain-oriented electrical steel sheet excellent in iron-core workability by giving linear strain to a silicon steel sheet, then applying a coating agent of specified compsn. comprising CrO3, H3PO4 and MgO, etc., and baking at low temp. CONSTITUTION:An insulating film is formed by baking on a silicon steel sheet treated with finish annealing. Then the surface of the silicon steel sheet is treated to have linear strain by optical means or the like in order to improve the iron loss. Then a coating agent to form an insulating film is applied on the steel sheet and baked in a low temp. range below 500 deg.C. The coating material is prepared by compounding 10 pts.wt. of CrO3, 30-60 pts.wt. of H3PO4, 6-16 pts.wt. of at least one of MgO, CaO and Al2O3, and 0.5-5.0 pts.wt. of H3BO3 and/or Na2SiO3, and if required, by adding one or more compds of glycerin, adipic acid and succinic acid by 0.5-5.0 pts.wt., and further compounding a colloidal silica soln. of 80-500nm particle size by 1-10 pts.wt. in terms of SiO2.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an insulating coating on a grain-oriented electrical steel sheet by low temperature baking, which has excellent core workability and magnetic properties.

0002

[Prior art] Grain-oriented electrical steel sheets contain, for example, 2 to 4% Si.
After hot rolling and annealing the containing silicon steel slab, it is cold rolled once or twice or more with intermediate annealing to obtain the final thickness, and then decarburized and annealed to form an oxide film mainly composed of SiO2 on the surface of the steel sheet. After forming, an annealing separator mainly composed of MgO is applied, and final annealing is performed to develop secondary recrystallization with Goss orientation. Furthermore, impurities such as S and N are removed, and forsterite (Mg2 SiO4 ) A main glass film is formed, then a coating agent for forming an insulating film is applied, and a baking process is performed to produce a product.

[0003] Furthermore, for the purpose of further improving iron loss, fine linear strain is applied to the surface of grain-oriented electrical steel sheets at intervals to refine the magnetic domains after or before final annealing. (Japanese Unexamined Patent Publication No. 137016/1983,
(Japanese Unexamined Patent Publication No. 56-51522). As mentioned above, if linear strain occurs after the insulation film is formed, the film may be locally damaged, so a coating agent for forming the insulation film is applied again for rust prevention and insulation purposes, and iron loss due to linear strain is avoided. Baking treatment is carried out at a low temperature that does not reduce the improvement effect.

Incidentally, grain-oriented electrical steel sheets are mainly used as core materials for transformers and electrical equipment, but when manufacturing the core, the material is slit, sheared, or punched to a predetermined width and then continuously wound or laminated. It is used as a wound core or stacked core. In the case of a wound core, it goes through winding, compression molding, strain relief annealing, and a winding process called lacing, which is then put into a case and used as a transformer. In the case of stacked cores, the cores are assembled by hand and then wound to form a transformer.

In the manufacture of iron cores, for example, in the case of wound iron cores, the coating has good lubricity, allowing smooth winding and forming operations, and does not cause unevenness on the end face or lap portion of the steel plate after forming.
It is important that the shape is good. In the case of stacked iron cores, in addition to film properties such as insulation, the insulation film on the surface of the coil during the processing stage at the customer has a strength that prevents it from peeling or pulverizing when it comes into contact with or shears under the load of transport rolls, etc. required.

In particular, conventional coating agents for forming an insulating film on grain-oriented electrical steel sheets include colloidal silica-phosphate-chromate-based or phosphate-based coatings due to problems such as film tension, insulation, and corrosion resistance. Mainly used. In order to avoid the impact on the working environment due to powdering and film peeling during the transformer processing process of the chromium compounds and phosphorus compounds that are the components of this film, the insulation film is insulated to prevent powdering and peeling of the insulation film by improving the film properties. Development of coating agents for film formation and development of film formation methods are desired.

As a means of improving the properties of the film by improving the coating agent for forming an insulating film, for example, Japanese Patent Application Laid-Open No. 61-4773 discloses that Al, Al,
Primary phosphate such as Mg, ultrafine colloidal silica with a particle size of 8 nm or less, chromic acid, or one or both of chromates.
A mixed solution containing more than 10% of the above ingredients is applied to the steel plate after finish annealing,
A technique has been disclosed for improving the slipperiness of an insulating film through baking treatment.

[0008] These improvements in the insulation coating improve the iron loss, magnetostriction, and insulation properties of grain-oriented electrical steel sheets, as well as the lubricity of the coating.As a result, the workability during core processing and the phenomenon of powdering and peeling of the coating are improved. An improvement effect has been obtained. However, in low-core-loss grain-oriented electrical steel sheets, in which linear strain is applied to the product using a laser, etc. to reduce core loss, and the insulation film is baked again at a low temperature, the effect of improving core loss due to linear strain can be maintained. Therefore, the baking process must be performed at a low temperature of 500°C or less, and therefore, the film formation is not fully completed with the conventional coating agent for forming an insulating film, so the strength (hardness) of the insulating film is not enough.

[0009] As a result, flaws are likely to occur in the insulating film in subsequent processing steps, causing problems such as contamination of the working environment due to powdering and peeling phenomena, and deterioration of characteristics due to surface flaws. For this reason, in the case of grain-oriented electrical steel sheets with ultra-low core loss, which is the subject of the present invention, one way to fully exhibit the characteristics in the manufactured transformer is to improve the core processability by improving the insulation coating characteristics. It is important to further improve this.

0010

[Problems to be Solved by the Invention] The present invention relates to a steel sheet in which linear strain is applied to a grain-oriented electrical steel sheet using a laser or the like to reduce core loss, and the present invention is directed to a steel sheet in which linear strain is applied to the grain-oriented electrical steel sheet using a laser or the like to reduce iron loss. When forming an insulating film on a steel plate,
The purpose of the present invention is to provide a method for forming an insulating film that has good slip properties, excellent iron core workability, and is free from powdering, peeling, etc.

[0011]

[Means for Solving the Problems] The gist of the present invention is as follows. (1) A silicon steel slab is hot-rolled, either as it is or after hot-rolled plate annealing, cold-rolled once or twice or more with intermediate annealing to give the final plate thickness, and then decarburized. Annealed,
After applying an annealing separation agent and winding it up to form a strip coil, it is subjected to final annealing, and then a coating agent for forming an insulating film is applied, and the surface of the baked grain-oriented electrical steel sheet is subjected to optical, mechanical, chemical, etc. In the method of applying linear strain by a target or thermal means, applying a coating agent for forming an insulating film again, and forming an insulating film by baking at a low temperature range of 500 ° C. or less, the final step is performed. CrO3:10 as a coating agent for forming an insulating film
H3 PO4: 30 to 60 parts by weight, M
6 to 16 parts by weight of one or more of gO, CaO and Al2O3, H3BO3 and Na2S
A method for forming an insulating film on a low-temperature baking grain-oriented electrical steel sheet having excellent core workability, the method comprising using a mixture of 0.5 to 5.0 parts by weight of one or both of iO3.

(2) A silicon steel slab is hot-rolled, either as it is or after being subjected to hot-rolled plate annealing, and then cold-rolled once or twice or more with intermediate annealing in between to obtain the final plate thickness; Next, the surface of the grain-oriented electrical steel sheet was subjected to decarburization annealing, coated with an annealing separator, wound to form a strip coil, subjected to final annealing, coated with a coating agent for forming an insulating film, and coated with an optical fiber. In a method of applying linear strain by physical, mechanical, chemical or thermal means, applying a coating agent for forming an insulating film again, and baking at a low temperature of 500°C or less to form an insulating film, As a coating agent for forming the final insulation film, Cr
O3: 10 parts by weight, H3 PO4: 30-6
0 parts by weight, 6 to 16 parts by weight of one or more of MgO, CaO and Al2 O3, and 0.5 to 5 parts of one or both of H3 BO3 and Na2 SiO3.
0 parts by weight, and further contains 0.5 to 5.0 parts by weight of one or more of glycerin, adipic acid, and succinic acid.A low-temperature baking direction with excellent iron core workability. A method for forming an insulation film on a magnetic steel sheet.

(3) A silicon steel slab is hot-rolled, either as it is or after hot-rolled plate annealing, cold-rolled once or twice or more with intermediate annealing in between to obtain the final plate thickness; Next, the surface of the grain-oriented electrical steel sheet was subjected to decarburization annealing, coated with an annealing separator, wound to form a strip coil, subjected to final annealing, coated with a coating agent for forming an insulating film, and coated with an optical fiber. In a method of applying linear strain by physical, mechanical, chemical or thermal means, applying a coating agent for forming an insulating film again, and baking at a low temperature of 500°C or less to form an insulating film, As a coating agent for forming the final insulation film, Cr
O3: 10 parts by weight, H3 PO4: 30-6
0 parts by weight, 6 to 16 parts by weight of one or more of MgO, CaO and Al2 O3, and 0.5 to 5 parts of one or both of H3 BO3 and Na2 SiO3.
0 parts by weight, and 0.5 to 5.0 parts by weight of one or more of glycerin, adipic acid, and succinic acid, and 1 to 10 parts by weight of colloidal silica solution with a particle size of 80 to 500 nm as SiO2. A method for forming an insulation film on a grain-oriented electrical steel sheet by low temperature baking and having excellent iron core workability, characterized by using a blended material.

The present invention will be explained in detail below. The present inventors have solved the above-mentioned conventional problems in the process of applying linear strain to the surface of a steel plate at intervals using a laser or the like, applying a coating agent for forming an insulating film before and after applying the linear strain, and baking at a low temperature. We conducted an investigation to resolve the issue. As a result, in such low-temperature baking films, film formation does not proceed sufficiently with conventional phosphate-colloidal silica-chromium compound-based coatings or phosphate-based coating agents, and film strength and lubricity are affected. It turned out that I couldn't get it. As a result of considering this countermeasure, we found that chromic acid-Al
Based on an oxide-phosphoric acid composition such as Ca, Mg, etc., with the addition of a reducing agent such as glycerin and coarse particle colloid, the lubricity is extremely good and the hardness is significantly increased despite low temperature baking. It has been found. It has been found that this coating agent significantly improves the lubricity, corrosion resistance, adhesion, etc. of the insulating film, and allows the formation of an insulating film that does not cause problems in the working environment due to powdering, film peeling, etc. during the processing process.

[0015] A detailed explanation will be given below based on experimental data. A sample was cut from a coil after final annealing of a high magnetic flux density grain-oriented electrical steel sheet with a plate thickness of 0.23 mm manufactured by a known method, and strain relief annealing was performed at 850° C. for 4 hours to remove the coil set and strain. Then 8 with 2% H2SO4
After light pickling at 0°C for 20 seconds, 100 ml of 20% colloidal silica with a particle size of 10 nm, 50% monophosphoric acid Al55
A coating agent having a composition of 7 g of chromic acid anhydride was applied so that the weight after baking was 4.5 g/m 2 , and a baking treatment was performed at 800° C. for 20 seconds in a N 2 atmosphere. Next, laser treatment was applied to the surface of the product sheet to impart linear strain at intervals of 5 mm in the direction perpendicular to the rolling direction, thereby improving iron loss characteristics.

A coating agent for forming an insulating film having the composition shown in Table 1 was applied to this steel plate at a weight of 2.5 g/m2 after baking.
It was coated so as to have the following properties, and then subjected to low-temperature baking treatment at 350° C. for 20 seconds in the air. A sample was cut out from the obtained product board, and the insulation film lubricity (A
method, B method). In addition, using a separately cut sample, the baking state of the film after strain relief annealing was measured using the method shown in FIGS. 3 and 4. Furthermore, we investigated the corrosion resistance of the coating and its effect on magnetic properties. The results are shown in Table 2. As a result, coating agents for forming insulating films that do not use fine-particle colloidal silica as a main component, as in the present invention, have excellent film properties and remarkable improvements in lubricity, etc., especially when coarse-particle colloidal silica is used in combination A significant improvement in the lubrication properties was obtained.

Next, a method for forming an insulating film according to the present invention will be described. The coating agent for forming an insulating film in the present invention includes 10 parts by weight of chromic acid, 30 to 60 parts by weight of phosphoric acid, 6 to 16 parts by weight of one or more oxides of Al, Ca, and Mg, as necessary. Glycerin, succinic acid, depending on
S
It has a composition of 1 to 10 parts by weight as iO2.

CrO3 is important because it densifies the film and provides hardness, and because it reacts with free phosphoric acid and phosphates to suppress moisture absorption of phosphoric acid and phosphates. If there is too much chromic acid, the free chromic acid may cause stickiness or impair the density of the film. On the other hand, if the amount is too low, free phosphoric acid will remain after baking the film and will absorb moisture, causing stickiness and rust.

Oxides of Al, Ca, and Mg react with phosphoric acid and chromic acid to form stable compounds. This densifies the film, improves insulation and film tension, and forms a film with good adhesion. When the amount is less than 6 parts by weight per 10 parts by weight of CrO3, free Cr increases and the area where stickiness occurs expands. Furthermore, film properties such as insulation and corrosion resistance deteriorate. On the other hand, if the amount is more than 16 parts by weight, undissolved oxide content will occur, impairing the appearance and adhesion, which is not preferable.

[0020] Phosphoric acid reacts with other components to form a phosphoric acid compound, which has a strong effect of forming a dense glass film.
It has a large influence on lubricity, film tension, etc. Chromic acid 1
If it is less than 30 parts by weight compared to 0 parts by weight, the effect of improving lubricity will be weak, and insoluble portions of oxides such as Al will occur, impairing the film properties. On the other hand, when more than 60 parts by weight is added, problems such as stickiness due to hygroscopicity occur due to the increase in free phosphoric acid content.

[0021] In the low-temperature baking film as in the present invention, the blending ratios of chromic acid, oxides such as Al, Ca, Mg, etc., and phosphoric acid are precisely controlled as described above. H3
BO3 and/or Na2 SiO3 are added at a ratio of 0.5 to 5.0 parts by weight per 10 parts by weight of chromic acid. These additions are effective in vitrifying and densifying the film, and are also effective in lowering the baking film forming temperature at the same time. The amount added is 0.5 per 10 parts by weight of chromic acid.
If the addition amount is less than 5.0 parts by weight, such vitrification effect will be weak, and if the addition amount exceeds 5.0 parts by weight, the hardness of the film may decrease or Na2
SiO3 is not preferred because it causes a sticky phenomenon.

Glycerin, adipic acid, and succinic acid, which are added as necessary, are effective in lowering the baking temperature of the film. In the process of applying linear strain using a laser or the like to control magnetic domains and improve iron loss as in the present invention, the baking temperature should be as low as 500°C or less in order to maintain the linear strain. is important. Reducing agents such as glycerin are CrO3
It is added in an amount of 0.5 to 5.0 parts by weight per 10 parts by weight. If the amount is less than 0.5 parts by weight, this effect will be small. On the other hand, if the amount is more than 5.0 parts by weight, it is not preferable because the stability of the solution decreases, and in this case, the increase in organic components causes compressive stress during baking, resulting in the problem of magnetic deterioration.

Coarse particles of colloidal silica are added with a particle diameter of 80 to 500 nm, and the amount added is 1 to 10 parts by weight as SiO2 per 10 parts by weight of chromic acid. Coarse particle colloidal silica forms fine spherical protrusions on the coating due to the spherical shape of its particles. This shape effect and particles improve the lubricity and hardness of the coating, improving core workability. The particle size of the coarse colloidal silica particles is 80 to 500 nm. When the particle size is smaller than 80 nm, the effect of improving lubricity is small. If the particle size exceeds 500 nm, in a coating with a relatively small coating amount as in the present invention, the space factor may deteriorate or there may be problems with the stability of the coating solution. Most preferred is a particle size of 100-300 nm.

The reason why the amount of coarse particle colloidal silica added is 1 to 10 parts by weight in terms of SiO2 per 10 parts by weight of chromic acid is that if it is less than 1 part by weight, the effect of improving lubricity etc. will be small; If the amount is too large, the space factor will decrease as in the case where the particle size is large, which is not preferable. A coating agent for forming an insulating film having these compositions is made into an aqueous solution, applied to a steel plate using a coating roll or the like, and subjected to a baking treatment. The drying conditions at this time are baking treatment at a steel plate temperature of 500°C or less. The atmospheric condition in this case may be either an atmospheric gas such as N2 or the atmosphere.

[0025] The baking temperature is 500°C or less. 500
When the temperature is higher than ℃, the iron loss improvement effect due to linear strain caused by laser etc. is reduced due to the release of strain. Preferably 250-45
It is 0°C. The optimal points of these drying and baking conditions vary depending on the composition of the coating agent. Examples will be described below.

[0026]

[Example] Example 1 C: 0.0082%, Si: 3.35%, Mn in weight%
;0.067%,S;0.024%,Al;0.032
%, the balance being iron and unavoidable impurities, is hot rolled, annealed, and cold rolled by known methods to obtain a final plate thickness of 0.23.
mm. Next, after decarburizing annealing in a N2 + H2 humid atmosphere, an annealing separator was applied, and annealing was performed at 1200°C x 20H.
Finish annealing was performed to form a glass film. Next, excess MgO was removed by water washing, and after light pickling, the particle size was reduced to 10 nm.
A known coating agent for forming an insulating film consisting of 100 ml of 20% colloidal silica, 55 ml of 50% monophosphoric acid, and 4 g of chromic acid anhydride was applied so that the weight after baking was 4.0 g/m2, 810℃×2
A baking process was performed in N2 for 0 seconds. Thereafter, linear strain was applied to the steel plate at intervals of 5 mm in the direction orthogonal to the rolling direction by laser irradiation to perform iron loss improvement treatment. Next, a coating agent for forming an insulating film having the composition shown in Table 3 was applied so that the film weight after baking was 2.0 g/m 2 , and baking treatment was performed at 450° C. for 60 seconds in the air. Samples were cut from this steel plate and the film properties were investigated. The results are shown in Table 4.

[0027] The film formed by the coating agent for forming an insulating film of the present invention has properties such as lubricity and corrosion resistance, which are all equivalent or better than the conventional particulate colloidal silica-chromic acid-phosphate film. was gotten. Example 2 Using a laser-treated steel plate obtained in the same manner as in Example 1 as a starting material, a coating agent for forming an insulating film was added to this steel plate with coarse particle colloidal silica having the composition shown in Table 5 as in Example 1. It was applied in the same manner and baked at 350° C. for 30 seconds in the air.

[0028] Samples were cut out from the steel plate after the baking treatment, and the film properties were investigated. The results are shown in Table 6. Similar to Example 1, the coating agent for forming an insulating film of the present invention gave good results in terms of lubricity, corrosion resistance, etc. despite being baked at a low temperature.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

[0033]

[Table 5]

[0034]

[Table 6]

[0035]

Effects of the Invention According to the present invention, the lubricity of the steel sheet is extremely good despite the low-temperature baking treatment, and the problem of contamination of the working environment due to powdering, peeling, etc. of the coating components during transformer processing at customers is avoided. It is possible to provide a method for forming an insulating film that is not previously available. Also,
The insulating film has good corrosion resistance, can form an insulating film that does not deteriorate the magnetic improvement effect caused by applying linear strain using a laser, etc., and can form a dense insulating film that does not absorb moisture at low temperatures.

As a result, as shown in FIG. 3, the lubricity and corrosion resistance at low temperature baking are significantly improved compared to conventional coating agents for forming insulating films.

[Brief explanation of the drawing]

[Figure 1] Figure 1 is an explanatory diagram of method A, with sandwich plates 1-1, 1-2
Place the sample 2 between them, apply a load N using a weight 3, measure the force A that pulls out the sample 2 with a spring scale, and calculate the sliding friction coefficient μ.
Determine from (FF)=A/N.

[Figure 2] Figure 2 is an explanatory diagram of method B, in which a steel ball with a constant load is placed on the insulation coating, the steel ball is moved back and forth, and the resistance value that the steel ball receives from the insulation coating is measured using a strain gauge. Measure continuously.

[Figure 3] Figure 3 is an explanatory diagram of the method of laminating steel plates, with a length of 3 x 4
Steel plates sheared to cm are laminated alternately as shown in the figure.

[Fig. 4] Fig. 4 is an explanatory diagram of a method for evaluating the seizure state of steel plates. After laminating steel plates as shown in Fig. 3, a pressure of 60 kg/
Tighten the bolts at cm2, then 850℃×4Hr
After annealing in N2 and DP 10°C, the peeling load was measured using a spring scale as shown in the figure to evaluate the seizure state.

[Figure 5] Figure 5 shows the baking temperature of the insulation coating and the corrosion resistance of the coating (
It is a figure showing hygroscopicity). The inventive material marked with ☆ is the insulating film component No. of Example 2. 4 is the material coated and baked, ★ is the material No. 4 of Example 2. A material coated and baked with a coating agent according to Japanese Patent Publication No. 53-28375 as a comparative example of No. 6 was exposed to air for 50 minutes.
The results of investigating the surface condition after being left at 98% humidity at 48° C. are shown.

FIG. 6 is a diagram showing the composition of an insulating film and the lubricity of the film after baking (lubricity according to the method shown in FIG. 4). All films having the composition of the present invention exhibit good lubricity.

Claims (3)

[Claims] [Claim 1] A silicon steel slab is hot-rolled, either as it is or after hot-rolled sheet annealing, either once or twice with intermediate annealing in between.
The plate is cold rolled several times to achieve the final thickness, then decarburized and annealed, coated with an annealing separator, wound to form a strip coil, finished annealed, and then coated with a coating agent for forming an insulating film. Then, a linear strain is applied to the surface of the baked grain-oriented electrical steel sheet by optical, mechanical, chemical, or thermal means, and a coating agent for forming an insulating film is applied again, and then the surface is heated at a low temperature of 500°C or less. In the method of forming an insulating film by baking in a
: 10 parts by weight, H3 PO4 : 30 to 60 parts by weight, 6 to 16 parts by weight of one or more of MgO, CaO and Al2 O3, H3 BO3 and Na
2. A method for forming an insulating film on a grain-oriented electrical steel sheet by low-temperature baking and having excellent core workability, the method comprising using one or both of 0.5 to 5.0 parts by weight of SiO3. [Claim 2] A silicon steel slab is hot-rolled, either as it is or after hot-rolled plate annealing, either once or twice with intermediate annealing.
The plate is cold-rolled several times to obtain the final thickness, then decarburized and annealed, coated with an annealing separator, wound to form a strip coil, finished annealed, and then coated with a coating agent for forming an insulating film. Then, a linear strain is applied to the surface of the baked grain-oriented electrical steel sheet by optical, mechanical, chemical, or thermal means, and a coating agent for forming an insulating film is applied again, and then the surface is heated at a low temperature of 500°C or less. In the method of forming an insulating film by baking in a
: 10 parts by weight, H3 PO4 : 30 to 60 parts by weight, 6 to 16 parts by weight of one or more of MgO, CaO and Al2 O3, H3 BO3 and Na
2. Use a mixture containing 0.5 to 5.0 parts by weight of one or both of SiO3 and 0.5 to 5.0 parts by weight of one or more of glycerin, adipic acid, and succinic acid. A method for forming an insulation film on a low-temperature baking grain-oriented electrical steel sheet with excellent core workability. [Claim 3] A silicon steel slab is hot-rolled, either as it is or after hot-rolled sheet annealing, either once or twice with intermediate annealing.
The plate is cold-rolled several times to obtain the final thickness, then decarburized and annealed, coated with an annealing separator, wound to form a strip coil, finished annealed, and then coated with a coating agent for forming an insulating film. Then, a linear strain is applied to the surface of the baked grain-oriented electrical steel sheet by optical, mechanical, chemical, or thermal means, and a coating agent for forming an insulating film is applied again, and then the surface is heated at a low temperature of 500°C or less. In the method of forming an insulating film by baking in a
: 10 parts by weight, H3 PO4 : 30 to 60 parts by weight, 6 to 16 parts by weight of one or more of MgO, CaO and Al2 O3, H3 BO3 and Na
0.5 to 5.0 parts by weight of one or both of 2 SiO3, and 0.5 to 5.0 parts by weight of one or more of glycerin, adipic acid, and succinic acid, and particle size: 80 to 5.0 parts by weight. A method for forming an insulation film on a low-temperature baking grain-oriented electrical steel sheet having excellent core workability, the method comprising using a 500 nm colloidal silica solution containing 1 to 10 parts by weight of SiO2.