JPH0225433B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention is designed to uniformly form a glass film with excellent insulation, adhesion, and appearance over the entire surface of the steel sheet during the production of grain-oriented electrical steel sheets, as well as to form a glass film with excellent magnetic properties. The present invention relates to an annealing separator for producing magnetic steel sheets. [Prior Art] Normally, a grain-oriented electrical steel sheet is obtained by hot rolling a material containing 4% or less Si, and then cold-rolling the material once with annealing or twice or more with an intermediate annealing in between to obtain the final thickness.
Next, after decarburization annealing in a humid atmosphere, magnesia MgO is applied as a slurry as an annealing separator using a coating roll, and after drying, final finish annealing is performed. In grain-oriented electrical steel sheets, the formation of the glass film at this time, that is, the uniformity and thickness of the film, the adhesion to the steel base steel, the insulation properties, etc., are excellent, and it is possible to form a glass film with excellent tension effects. , is important in determining product characteristics and commercial value. In a series of manufacturing processes for grain-oriented electrical steel sheets, MgO, which serves as an annealing separator, is SiO ₂ formed during decarburization annealing.
It reacts with the main oxide film to form a forsterite film (Mg ₂ SiO ₄ ), which is a glass film. However, inside the coil during final annealing,
This glass film formation reaction is greatly influenced by the properties of MgO. Normally, the factors that influence the glass film formation reaction include the purity, particle size, activity, and adhesion of MgO, and when used as an annealing separator, the degree of hydration when made into a slurry is ; Various additives have a great influence as well as the degree of aggregation of MgO particles and the amount of coating. Therefore, in order to obtain a high-quality glass film and excellent magnetic properties, the production conditions for MgO require efforts to optimize the production reaction conditions for the raw material Mg(OH) ₂ as well as the firing conditions for obtaining MgO. is being done. When applying MgO to a steel plate, it is suspended in water and applied as a slurry, so some
A hydration reaction from MgO to Mg(OH) ₂ occurs. As a result, moisture is brought into the coil, making the atmosphere between the plates high in dew point and non-uniform, causing film defects such as pinhole-like smudges, gas marks, scale, and discoloration due to peroxidation. As a countermeasure for this,
MgO property control by MgO manufacturing conditions,
Efforts are being made to reduce the amount of moisture carried between the plates by strengthening the cooling of the slurry during use. Alternatively, the conventional method uses MgO in which the hydration reactivity is suppressed by increasing the firing temperature of MgO.
There is a publication. MgO, whose hydration reaction is suppressed in this way, may cause spangles, gas marks, poor adhesion, decreased film tension, etc. due to decreased reactivity with the SiO ₂ layer of the oxide film. [Problems to be solved by the invention] In particular, the larger the coil, the greater the influence of the amount of water brought in due to the reactivity and hydration of MgO.
The development of an annealing separator that minimizes the amount of moisture carried between sheets and forms a uniform glass film is an important issue for companies in the same industry. Therefore, in order to eliminate the drawbacks of conventional annealing separators, the present inventors have conducted intensive research and have developed MgO that solves the various problems mentioned above by changing the physical properties of MgO, which is the main component. succeeded in. That is, the problem of overoxidation that occurs with conventional MgO is due to excessive moisture brought in due to the high activity of MgO, and the defective film formation that occurs during high temperature annealing is due to an extreme lack of moisture and reduced reactivity. As a solution to both of these problems, only the very outermost layer of low-activity MgO obtained by firing Mg compounds such as magnesium hydroxide and magnesium carbonate at relatively high temperatures is forced to undergo a certain amount of hydration treatment in gas. do,
It has been discovered that by activation, a grain-oriented electrical steel sheet with excellent reactivity, a uniform and excellent film, and excellent magnetic properties can be obtained. [Means for Solving the Problems] The present invention will be described in detail below. The present inventors have discovered that the decarburization annealing process is performed on the steel sheet surface.
We investigated the effects of processing conditions during the MgO production process on the magnetic properties and the glass film produced by the reaction between the SiO ₂ -based oxide layer and MgO used as an annealing separator. In this experiment, the starting material was a grain-oriented electrical steel sheet that had been cold-rolled to a final thickness of 0.295 mm and subjected to decarburization annealing in a humid atmosphere of N ₂ + H ₂ . It was obtained by firing magnesium hydroxide on this steel plate at 1100℃.
After pulverizing MgO to contain 85% or more of fine particles of 10 μm or less, the MgO is kept at a constant temperature and humidity (150℃, 20%).
The particles are passed through the air for 30 seconds to form a hydration layer, which converts the outermost surface layer of the particles into Mg(OH) ₂ to a concentration of 0.5% based on the MgO raw powder.
Activated. This MgO and as-fired MgO without activation treatment were added to the decarburized plate and 1 m ² of steel plate was added.
Apply at a rate of 16g per coat, dry at 1200℃ x 20hr
Final annealing was performed. After application and drying
When the hydration water content of MgO was confirmed, it was 0.2% without activation treatment, whereas it was 0.6% with activation treatment. When we investigated the formation state and film characteristics of the glass film formation at this time, we found that
As for the appearance of the film, without the activation treatment, the glass film was very thin and uneven with glass marks, whereas with the activation treatment, it was very thick, uniformly formed, and had an excellent gloss. A glass film was formed. When the surface of the glass film was observed using an electron mirror, as shown in Figure 1, forsterite grains were very sparse in MgO(B) without activation treatment, whereas forsterite grains were very sparse in MgO(B) without activation treatment, as shown in Figure 1.
In MgO(A), dense fine powder was observed to be formed. Film adhesion after applying insulation coating and baking is 20
When tested by mmφ bending, most of the glass film fell off without activation treatment, whereas with activation treatment, no peeling occurred at all. When using MgO that has been activated in this way, even though it is a low hydrated MgO,
A significant improvement effect was observed in all film properties. Next, we will discuss the activation process of MgO. Methods for generating a hydration layer only on the outermost surface layer of particles for activation include pulverization, classification, particle size adjustment, etc. after calcination of raw materials such as magnesium hydroxide and magnesium carbonate to obtain MgO. It is carried out in a gas at a predetermined temperature and humidity during the process, during transportation during the manufacturing process, or just before it is actually applied to the coil. Naturally, it is important to strictly control temperature and humidity in order to stabilize the amount of hydrated layer produced. The appropriate amount of hydration layer to be treated is 0.3% to 2.0%. If it exceeds 2.0%, moisture inevitably increases between the coils, which tends to cause film defects due to overoxidation and deterioration of magnetism. On the other hand, if it is less than 0.3%, there will be an extreme water shortage, and during the finishing annealing process, the oxide film on the surface of the steel plate formed during decarburization will undergo a reduction reaction, resulting in a glass film due to the reaction with MgO. formation becomes insufficient. In this case as well, magnetism deteriorates due to destabilization of inhibitors such as AlN and MnS. The present inventors have diligently studied the relationship between the formation of a hydration layer only on the outermost surface layer of MgO grains, the film, and magnetism, and as a result, they have found this optimal processing condition. The requirements for MgO before activation treatment by forming a hydration layer are listed. The original purpose of activation by forming a hydration layer only on the outermost surface layer is to increase the reactivity of MgO particles with the oxidized layer of the steel sheet, and to stabilize the atmosphere between the sheets by moving it toward the dry side. For this, MgO
When suspended in water to form a slurry, it is necessary that the hydration reaction is difficult to proceed any further. For this purpose, the firing conditions for MgO are 900
It is preferable to calcinate at a temperature of ℃ or above to render the MgO itself essentially inert. Such high temperature firing
When MgO is used in the normal quick coating method, there is almost no progress of hydration reaction, and the stability is further increased. If the firing temperature exceeds 1200°C, a sintering phenomenon will occur, and even if it is pulverized, it will become coarse particles and the reactivity will decrease, which is undesirable, so the upper limit is set at 1200°C. There is no particular regulation regarding the particle size of MgO, but it is desirable that the main component is fine particles of 3 μ or less, as is generally used as an annealing separator for electrical steel sheets, and the BET specific surface area is 30 m ² /
g or less, preferably 8 to 25 m ² /g. this is,
This is because if it is too coarse, the glass film forming reaction with the base oxide film will be extremely reduced, and if it is too fine, it will be difficult to suppress the hydration reaction. When applying MgO, depending on the composition and thickness of the electrical steel sheet used, Ti compounds and B compounds may be added as necessary to stabilize film formation and inhibitors, and to provide an auxiliary effect for improving magnetism. , S compound is added. As the Ti compound, for example, TiO, _TiO2 , etc. are used, and the amount of Ti added is 0.5 to 15 parts by weight per 100 parts by weight of MgO, which has been subjected to a hydration layer formation treatment on the outermost surface layer of the particle. be. If the amount added is less than 0.5 parts by weight, the effect of promoting glass film formation is weak. For this reason, the sealing properties of the film against the annealing atmosphere during the final annealing temperature increase process become weaker, and the N
Inhibitor decomposition and alteration may occur due to absorption, de-S, etc. On the other hand, if the amount added is large, additional oxidation of the oxide film on the surface of the steel sheet occurs during the temperature rising process, easily resulting in overoxidation, and the oxide film becomes a bolus, resulting in an uneven glass film and poor magnetic properties. 15 parts by weight or less. SrS, SbS, Sb ₂ (SO ₄ ) ₃ , etc. are used as S compounds, but the amount added is
The amount is 0.03 to 1.0 parts by weight per 100 parts by weight of MgO.
If it is less than 0.03 parts by weight, problems similar to the reason for the lower limit of the Ti compound described above will occur. Moreover, if the amount added exceeds 1.0 parts by weight, overoxidation tends to occur, and the formed oxide film becomes a bolus, which is not preferable. B compounds include B ₂ O ₃ , H ₃ BO ₃ , NaBO ₂ ,
Na ₂ B ₄ O ₇ etc. are used. The amount of B added is 0.03 to 0.15 parts by weight per 100 parts by weight of MgO. If it is less than 0.03 parts by weight, problems similar to the reason for the lower limit of Ti compounds will occur, and if it exceeds 0.15 parts by weight, problems similar to the reasons for the upper limit of Ti compounds will occur and normal secondary recrystallized grains will not develop. This is because magnetic defects may occur due to no longer occurring. These Ti compounds, S compounds, and B compounds are 1
A species or two or more species are added. [Example] Next, an example will be described. Example 1 C: 0.065, Si: 3.30, Mn: 0.060, in weight%
A silicon steel slab consisting of Al: 0.029 and S: 0.025 was hot-rolled, annealed and cold-rolled by a known method to obtain a final plate thickness of 0.225.
mm, and decarburization annealing was performed at 850°C in a humid atmosphere of N ₂ + H ₂ . On this steel plate, a mixture of Mg(OH) ₂ and MgCO ₃ was fired at the temperature shown in Table 1, and a hydration layer was formed on the surface of the MgO in an amount shown in the table, and 100 parts by weight of the MgO was heated. Then, an annealing separator containing 3 parts by weight of TiO ₂ was applied in the form of a slurry, and after drying, final annealing was performed at 1200° C. for 20 hours. The results are shown in Table 2.

【table】

[Table] No activation treatment was applied to form the outermost hydration layer.
All of the products using MgO hardly formed a glass film and had poor magnetic properties, whereas the products using activated MgO
The glass film was uniform and excellent, and the magnetic properties were also good. Example 2 C: 0.045, Si: 3.15, Mn: 0.072 in weight%
A silicon steel slab consisting of S: 0.023 was hot-rolled by a known method and then rolled two times with annealing to give a final plate thickness of 0.30 mm. Next, after decarburization annealing in the same manner as in Example 1, fine particles of MgO obtained by firing Mg(OH) ₂ at 1100°C were added to form a hydration layer on the surface to give a concentration of 0.4% and 1.3% based on the raw powder. Activated MgO was applied in the form of a slurry and final annealing was performed at 1200°C for 20 hours. The results are shown in Table 3.

[Table] When using MgO that has been activated to form a surface hydration layer in the same manner as in Example 1, glass film,
Very good results were obtained in terms of magnetism. Example 3 C: 0.070, Si: 3.20, Mn: 0.068 in weight%
A silicon steel slab consisting of Al: 0.027 and S: 0.028 was hot-rolled, annealed, and cold-rolled by a known method to obtain a final plate thickness of 0.295.
mm. Then, after decarburization annealing in the same manner as in Example 1, fine powder obtained by firing Mg(OH) ₂ at 1080 ° C.
Form a hydration layer on the surface of MgO to a concentration of 1.0% and activate it, and add 0.1 part by weight of B ₂ O ₃ as B and 0.05 part of H ₃ BO ₃ as B to 100 parts by weight of MgO.
Part by weight and an annealing separator containing 0.05 part by weight of Sb ₂ (SO ₄ ) ₃ as S are made into a slurry, applied and dried.
Final annealing was performed at 1200°C for 20 hours. The results are shown in Table 4.

〔Effect of the invention〕

As is clear from these Examples, according to the present invention, a glass film with excellent adhesion, film tension, and appearance is formed, and grain-oriented electrical steel sheets with excellent iron loss and magnetic flux density can be obtained.

[Brief explanation of drawings]

Figure 1 is a metallographic photograph of the surface of the glass coating after final finish annealing observed with an electron microscope (magnification x 5000). is a photograph showing the glass coating of a finished board coated with as-fired MgO without activation treatment.

Claims (1)

[Claims] 1. Using one or more Mg compounds of magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, magnesium sulfate, magnesium chloride, and magnesium nitrate as raw materials, at 900 to 1200°C
The film characteristics and magnetic properties are characterized in that the outermost layer of the particles of low-activity magnesia fired in An excellent annealing separator for grain-oriented electrical steel sheets. 2 Using one or more of the following Mg compounds as raw materials: magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, magnesium sulfate, magnesium chloride, and magnesium nitrate, at 900 to 1200℃.
The outermost layer of the particles of the low-activity magnesia fired with is subjected to a hydration layer forming treatment in a gas in the range of 0.3 to 2.0% based on the weight of the magnesia after firing. _{B2O3 , H3BO3 ,}
NaBO ₂ , Na ₂ B ₄ O ₇ B compound is 0.03~
0.15 parts by weight, SrS, SbS, Sb ₂ (SO ₄ ) ₃ S compounds as S, 0.03 to 1.0 parts by weight, TiO, TiO ₂ Ti compounds as Ti, 0.5 to 15 parts by weight of one or more added. An annealing separator for grain-oriented electrical steel sheets with excellent film properties and magnetic properties.