JPH02267278A - Production of grain oriented electrical steel sheet having uniform glass film and excellent magnetic characteristic - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is intended to form a uniform glass film with excellent insulation properties, adhesion, film tension, etc. in final annealing during the production of grain-oriented electrical steel sheets. , relates to a method for manufacturing a directional electromagnetic w4 tentative with excellent magnetic properties.

[Prior art]

Normally, a grain-oriented electrical steel sheet is made of a material containing 4% or less of Si and is hot-rolled, then annealed and cold-rolled once or twice or more with an intermediate annealing in between to obtain the final thickness. Next, decarburization annealing is performed by controlling PH2O/PI+2 in a humid atmosphere such as Nz+Hz or H2 to form an oxide film mainly composed of decarburization and Sing. After that, MgO was used as an annealing separator.
An annealing separator mainly composed of is applied in the form of a slurry using a coating roll, final annealing is performed, secondary recrystallization, purification reaction, and glass film formation are performed, followed by insulation film treatment and heat flattening as necessary. The final product is made by performing this process.

This grain-oriented electrical steel sheet has a <001> axis (110)<
001> Development is used in which crystals grow preferentially through high-temperature secondary recrystallization. In this secondary recrystallization process, (11,0) plane crystals with low surface energy grow preferentially, and AIN, Mn, which are finely dispersed as inhibitors in the steel, grow preferentially.
In order to invade other crystals whose growth is suppressed by S etc. (110) <001. >It is thought that crystals grow preferentially. Therefore, in order to produce an excellent grain-oriented electrical steel sheet, it is important to control the dispersion state of inhibitors such as AIN, MnS, etc. in the steel and their decomposition.

Changes in the inhibitor during final annealing are influenced by the oxide film formed on the surface of the steel sheet during decarburization annealing, the annealing separator, and the thermal cycle and atmospheric conditions during final annealing. Among these, MgO as an annealing separator has a particularly large influence. This has a great effect on changes in the oxide film during the temperature raising process in final annealing and the rate of formation of the glass film.
This is because this affects the stability of the reinhibitor.

MgO, which is an annealing separator, reacts with the SiO□ Wang Xiu acid film formed during decarburization annealing to form a forsterite film, which is usually called a glass film (2MgO + SiO□ → MgzS).
i04). As described above, the properties of MgO have a large influence on the formation of this glass film, as in the case of secondary recrystallization.

In this way, in determining the commercial value of grain-oriented electrical steel sheets,
Since MgO has a large influence on the most important magnetic properties and film properties, improving the quality of MgO has become an important issue for the manufacturing technology of electrical steel sheets.

Among the properties of MgO, factors that affect the glass film formation and the stability of the inhibitor include the activity (reactivity), purity, particle size, and adhesion of MgO. There are the degree of progress of the sum, the state of particle dispersion, and the amount of coating. Therefore, efforts are being made to optimize these conditions in order to obtain grain-oriented electrical steel sheets of good quality.

Usually, MgO is suspended in water, applied to a steel plate in the form of a slurry, and dried. At this time, depending on the manufacturing conditions of MgO, for example, in the case of high activity, MgO → Mg (OH) t
A hydration reaction occurs, making the atmospheric gas between the steel plates in the coil-1 high at a high dew point and non-uniform. This causes severe film defects such as bare spots, scale, gas marks, and discoloration due to overoxidation. However, for boat fishing, the method adopted to solve the problems with highly hydrated MgO is a high-temperature firing method. An example of this method is the method disclosed in Japanese Unexamined Patent Publication No. 55-73823. Such low-activity MgO obtained by raising the firing temperature has the drawback of reduced reactivity and adhesion.

In the method disclosed in JP-A-58-189374, MgO is forcibly hydrated, MgO with an ignition loss rate of 2.0 to 10% at 450°C or higher is coated on a steel plate, and then finish annealing is performed. This method forms an insulating film. In this method, it is difficult to obtain a uniform glass film due to the influence of moisture released from Mg (OH) 2 generated by the hydration reaction during the temperature rising process.

Furthermore, in JP-A-62-156226, the present inventors have proposed a method of activating the outermost layer of MgO particles. In this method, a hydration layer is formed only on the outermost layer of MgO particles fired at a high temperature.
Significant improvements in the glass film and magnetic properties have been obtained.

However, it cannot be said that satisfactory results have been obtained yet because problems such as poor film properties and magnetic properties tend to occur depending on the heat cycle during decarburization annealing and final finish annealing and the degree of oxidation of the atmospheric gas.

[Problems to be Solved by the Invention] The present invention solves the problem of increasing moisture carried between steel plates due to hydrated moisture of MgO in the production of grain-oriented electrical steel sheets, and
In order to solve the problem of film defects and magnetic deterioration due to poor glass forming ability caused by poor reactivity of MgO, we conducted extensive laboratory and field experiments on the physical properties and processing methods of MgO used as an annealing separator. A study was conducted.

As a result, the present inventors significantly improved the reactivity of MgO by subjecting the final product of calcined MgO to surface treatment in the gas phase and chemically adsorbing the OH layer. We have discovered a method that can solve the problems of MgO. As a result, we succeeded in producing grain-oriented electrical steel sheets that form a uniform glass film and have excellent magnetic properties.

In other words, the problems of film defects and magnetic defects caused by overoxidation caused by conventional MgO and poor glass film formation reactions are caused by excessive water brought in when the activity is high, poor reactivity when the activity is low, or MgO particles. This is due to a decrease in reactivity due to aggregation before and after slurry preparation. These lead to glass film formation and adverse effects on the inhibitor.

In particular, unless the problems of low hydration, improved reactivity, and cohesiveness of MgO are solved, the problems cannot be fundamentally solved, and solving the cohesiveness of MgO is an important problem. Even if low hydration and high reactivity are strictly controlled by the calcination temperature, particle shape, particle size, impurities, etc., the MgO particles themselves and the agglomeration of MgO particles during the slurry preparation stage during coating may be affected. This is because, if it is not resolved, it will be meaningless because the reactivity will be greatly reduced.

That is, Mg with uncontrolled (large) cohesiveness
In the case of O, poor hydration further promotes poor glass film formation, and even in the case of fine particle MgO, the particle size increases by several times to several tens of times due to agglomeration during the practical stage (during application).
Significantly reduces reactivity.

Because of these problems, it is desired to develop an annealing separator that has low hydration, high reactivity, and no agglomeration.

[Means to solve the problem]

As a solution to the above-mentioned problems with magnesium oxide (MgO) used as an annealing separation agent, magnesium hydroxide, basic magnesium carbonate, magnesium carbonate, magnesila 12 sulfate, magnesium oxalate, magnesium chloride, and magnesium nitrate are used as raw materials. When producing MgO as a chemical, contact treatment is carried out in a vapor phase containing water vapor at a temperature of 100°C or higher immediately before slurry preparation between calcination, pulverization, and classification, and an OH chemiabsorption phase is added to the crystal surface atomic layer. By adjusting and applying MgO at a concentration of 0.8 to 2.5% (calculated as 0), it has low hydration, yet has good dispersibility in the slurry, and has an extremely excellent reaction with the base film. I found out. As a result, we succeeded in manufacturing a grain-oriented electrical steel sheet with a uniform glass coating and good magnetic properties over the entire surface of the steel sheet, something that could not be achieved using conventional techniques.

The present invention will be explained in detail below.

In this experiment, C in weight %; 0.07B, S
t; 3.35, Mn; 0.067, S; 0
．． 023. A 1; 0.031. N; 0.0
An electromagnetic steel slab consisting of 078 balance Fe was hot rolled, hot rolled plate annealed, and cold rolled to a final plate thickness of 0.225 mm using a known method. This steel plate was decarburized and annealed in a humid atmosphere of Nz +1 (2), and the conditions for the annealing separator MgO were as follows:
An annealing separator containing 5% TiO□ was applied to the Mgo that had formed a chemically adsorbed phase, and after drying, it was wound into a coil and heated to 1200
Final finish annealing was performed at °C for 20 hours.

The aggregation state of the MgO slurry at this time, the glass film after final annealing, and the magnetic properties are shown in the table above.

As a result of this experiment, as in Nα1 (Comparative Example 1), when chemical adsorption treatment was not performed, the slurry agglomerated significantly and, perhaps due to poor reactivity, both the glass film and the magnetic properties were significantly worse. Ta. Also, as in Nα4 (Comparative Example 2) by the present inventors, Mg (OH)! In the case of the one subjected to the formation treatment, some aggregation was observed in the slurry, and the glass film and magnetism were both good, but the results were slightly inferior to those of the present invention.

In this way, the products (No., 2, Nα3) formed for chemical adsorption in the gas phase at high temperatures according to the present invention have extremely good dispersion in the slurry, and are superior in both glass film and magnetic properties to the comparative examples. Considerable improvement was seen.

Next, the reason why a uniform glass film is formed and the magnetic properties are improved by applying MgO with an OH chemisorption phase formed in the gas phase as in the present invention will be explained.

First of all, in the present invention, the chemical adsorption group formation process is performed at 100%
It is characterized in that the treatment is carried out in a gas phase containing water vapor with a temperature of 100 °C or higher.
9. The chemically adsorbed phase having a temperature of 9°C or higher is formed by the following reaction formula.

When gaseous H□0 is brought into contact with MgO particles in this way,
The HtO molecules, which have a diameter of approximately 300 nm, pass almost all the way through the MgO crystal grain intervals and are chemically adsorbed on almost all the crystal grain surfaces, producing OH groups on the 3 surfaces.

Due to the action of this hydrophilic OH group, the previously hydrophobic MgO crystal surface is converted to hydrophilic.

As a result, when added to water after this chemical adsorption treatment, it disperses without agglomerating.

On the other hand, when brought into contact with M2O at a temperature below ioo'c, liquid 11□0 exists, which causes agglomeration of the crystal particles where the force < hgo and hydrates the MgO crystal particles only near the surface of the aggregate. to produce Mg(OH)t. Since H2O does not enter the inside of the aggregate, it remains aggregated, and moreover, the MgO crystal particles inside the aggregate remain hydrophobic.

Due to the formation of this MgO1 (phase), the high surface energy of MgO is extremely reduced, and the compatibility with water is improved as shown in reaction (2) in the above formula, so that no agglomeration of MgO particles occurs.

Due to this effect, when applying it as a slurry to a steel plate?
'1gO particles are applied in an extremely well-dispersed state. In addition, 1. This increases the adhesion of MgO to the steel plate surface. As a result, the forsterite forming reaction with the SiO□ phase on the surface of the steel sheet is enhanced. In fact, when observing the dispersion state of particles in the slurry of MgO applied in the present invention and MgO not subjected to chemical adsorption group formation treatment, it was found that the MgO of the present invention
While M does not aggregate and is uniformly dispersed, M
g In the case where the OI+ phase generation treatment was not performed, agglomeration of several to several tens of particles occurred almost all over the surface, and substantial coarsening of the particles occurred.

In MgO subjected to Mg0H phase generation treatment in this way, MgO
The good dispersibility of the particles and the good reactivity of the particle surface enhance the glass film formation reaction, and the formation of the glass film during final annealing is accelerated.This effect stabilizes the inhibitor in the steel. Improves magnetic properties.

Next, the reasons for limitations in the present invention will be described.

First, the chemisorption efficiency of MgO applied to the present invention is important to cause only chemisorption by gaseous 11□0, and the MgO chemisorption efficiency by liquid 820 molecules is
0! ( ) is important for preventing the z-forming reaction. Considering chemisorption efficiency, preferably 150 to 600°
C has a water content of 10mg//! It is best to do this under the above conditions.

This is because chemisorption reactions become difficult to occur when the temperature exceeds 500°C. The reason for setting the Mg0H phase production amount to 0.8 to 2.5% in terms of 11□O is because if it is less than 0.8%, Mg0
This is because the reduction in surface energy due to the generation of g0H is not sufficient, and at the time of glass film formation, OHM acts as an ○ source to assist the glass film forming reaction. 0,8
If it is less than %, this reaction aiding effect is weak. On the other hand, if it exceeds 2.5%, this effect is too strong, resulting in a state of overoxidation, causing unevenness in the glass film and inhibiting the inhibitor components MnS, A1. N
It is undesirable because it accelerates the decomposition reactions such as, and causes magnetic deterioration. Within the range of 0.8 to 2.5%, a stable and uniform glass film can be formed and the magnetic properties can be improved.

The second requirement is the C of MgO after OH chemical adsorption shadow formation.
The AA value of 80'' to 250'' is determined from the viewpoints of suppression of hydration reaction during slurry preparation and reactivity of MgO particles. If it is less than 80'', there is a problem of progress of oxidation and aggregation due to progress of hydration reaction, which is not preferable.

At 250" or more, M
g It is excluded because the effect of OH group formation cannot be fully utilized. The most preferred range is 90'' to 150''.

The reason why the particle size is set to be 3p or less in terms of average particle size is that in the present invention, the first requirement is to improve the reactivity due to the Mg0)1 phase.If the particle size is 3p or more, the contact area between the particles and the steel plate increases as the particle size increases. This is because the amount will decrease and the effect will not be fully utilized.

By applying IgO (adjusted in this way), conventional Mg
The problems of film defects and magnetic deterioration that were observed when using O were eliminated.

This is because conventional film formation using MgO uses hydration water generated by the hydration reaction between MgO and water as an essential element at the stage of preparing slurry, but in the present invention, MgO The OH phase generated in the outermost layer of crystal atoms very efficiently promotes the reaction of MgO with the SiO□ phase on the surface of the steel sheet.

Therefore, for the present invention to be applicable, the CAA value is 80.
Because it is used in an extremely low activity state of ``~250'',
In the slurry, as long as the water temperature is kept low, the hydration reaction will not proceed.
By effectively utilizing the phases, it is possible to produce coils with uniform coatings and improved magnetism. When using this annealing separator, a Ti compound, B compound, S compound, etc. may be added for the purpose of forming a film or stabilizing the inhibitor depending on the composition, thickness, etc. of the applied electrical steel sheet.

Next, a description will be given based on an example.

[Example] C in weight%: 0.076, Si; 3.15,
Mn; 0.060. S; 0.024. A1.
0.028. A grain-oriented electrical steel sheet material consisting of N, 0.0078 balance unavoidable impurities, and Fe was hot rolled, annealed, and cold rolled by a known method to give a final thickness of 0.295 mm.

After this, decarburization annealing is performed in a humid atmosphere of N, +Hz, and a second
An annealing separator prepared by adding 7% TiO
It was wound up as a coil and subjected to final finish annealing at 1200°C x 20 hours. Thereafter, the insulation film was baked and heat flattened to produce a final product.

Table 3 shows the state of dispersion of MgO in the slurry, the state of glass film formation, and the magnetic properties in this test.

Remains below (Note) g Table 2 Loss: Calculated using the formula below. Weight of separator annealed after coating and drying (A) After baking at 1000°C. (B) Table 3 Glass film adhesion; After insulation film baking treatment. Adhesion by 20mmφ bending ◎; No peeling at all, 0%) Δ: Slightly peeling (25%) ○: Slightly peeling (5%) ×: Large area of peeled part (50%) The MgO of the present invention was observed under an electron microscope. As a result of observing the dispersion state of MgO, it was found that the MgO was dispersed very uniformly and no agglomerated particles were observed. In addition, the glass film was formed uniformly over the entire length of the coil, good magnetic properties were obtained, and good reactivity was observed.

In contrast, a comparative example (6
) and Comparative Example (1), which was subjected to less generation processing, had poor slurry dispersion and both glass film properties and magnetic properties were considerably inferior to those of the present invention.

〔Effect of the invention〕

In the present invention, the reactivity of MgO can be significantly improved by subjecting the final product of fired MgO to a surface treatment in the gas phase, thereby making it possible to significantly improve film defects, thereby achieving excellent magnetic properties. It has become possible to produce grain-oriented electrical steel sheets, and its industrial effects are enormous.

hand Continued Supplementary Positive book (spontaneous) February 1990 ? Day

Claims (1)

[Claims] 1. After forming a scale layer mainly composed of SiO_2 by decarburizing annealing a cold-rolled grain-oriented silicon steel material having a final plate thickness, an annealing separator mainly composed of MgO is applied. , in a method for producing a grain-oriented electrical steel sheet, which comprises performing finish annealing, the MgO is one or two of magnesium hydroxide, basic magnesium carbonate, magnesium carbonate, magnesium sulfate, magnesium oxalate, magnesium chloride, and magnesium nitrate. After obtaining the above-mentioned Mg compound by firing, the MgO is treated in a steam-containing gas phase at 100°C or higher to form an OH chemisorption layer of 0.8 to 2. 5%, and then applying the annealing separator containing MgO to a decarburized annealed steel plate,
A method for producing a grain-oriented electrical steel sheet with a uniform glass film and excellent magnetic properties, characterized by final annealing. 2. MgO after formation of OH chemisorption layer has a CAA value of 80″
~250″ and an average secondary particle diameter of 3 μm or less
Method described.