JP2650817B2 - Method for producing unidirectional silicon steel sheet with excellent coating and magnetic properties - Google Patents

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 unidirectional silicon steel sheet having a high magnetic flux density and having a (110) <001> orientation as a main orientation, which is suitable for use in an iron core of a transformer or the like. is there.

[0002]

2. Description of the Related Art A method for producing a grain-oriented silicon steel sheet in which AlN is used as a main inhibitor and the final cold rolling is performed at a rolling reduction of 80% or more is disclosed in Japanese Patent Publication No. 40-15644. Is disclosed. The feature of the grain-oriented silicon steel sheet with AlN as the main inhibitor is that high magnetic flux density can be obtained. On the other hand, the large secondary recrystallized grain size increases the eddy current loss, resulting in low iron loss. Loss was not obtained, secondary recrystallization was not stabilized, and the magnetic flux density had a large variation.

[0003] Among these drawbacks, reduction of eddy current loss is described by a method of irradiating a steel sheet with a laser beam disclosed in Japanese Patent Publication No. 57-2252 and a method disclosed in Japanese Patent Publication No. 61-39395. Improvements have been made by techniques for artificially subdividing magnetic domains, such as a method of forming regions having different expansion coefficients. On the other hand, secondary recrystallization is a stochastic phenomenon that fluctuates even when manufactured under the same conditions, so it is difficult to control for stabilization. Especially in the case of a thin plate having a thickness of 0.23 mm or less, AlN or the like is used. Inhibitors tend to decompose during finish annealing, and their inhibitory power tends to be unstable, thus making secondary recrystallization more and more unstable. As a technique for stabilizing the secondary recrystallization, Japanese Patent Publication No. 57-9419 and Japanese Patent Application Laid-Open No. 58-217630 disclose a method of adding Sn and / or Cu. Japanese Patent Laid-Open Publication No. H11-181131 discloses methods of adding Sb and Cu, respectively.

[0004]

However, in a component system containing AlN as a main inhibitor and further containing Sb, both sol. Al and Sb are concentrated on the surface during decarburization annealing.
Since the oxidation of the surface is suppressed, the formation of a forsterite film on the surface in the subsequent final finish annealing process tends to be non-uniform, which tends to result in a film having weak adhesion.

[0005] When the film is inferior as described above, not only does the insulation resistance of the surface deteriorate, but also the film peels off during the shearing process and the production of the winding transformer, which greatly impairs the characteristics of the actual machine. Also, since the tensile stress of the coating decreases,
Iron loss (eddy current loss) characteristics are degraded, and magnetostriction is increased, thereby increasing transformer noise. Furthermore, when the film formation is not performed normally, the behavior of the inhibitor on the surface layer is adversely affected, and the probability that the secondary recrystallization is not performed normally increases.

The present invention advantageously solves the above-mentioned problem which has been particularly concerned in the production of a component-oriented unidirectional silicon steel sheet containing Al-Sb, and has excellent coating characteristics and excellent magnetic characteristics. The purpose is to propose a manufacturing method that can obtain a product.

[0007]

The present invention relates to a method for producing a grain-oriented silicon steel sheet containing AlN and Sb as essential components of an inhibitor. After various studies to stabilize, MgO with specific properties was
It has been found that the object can be achieved by using as a main component of the annealing separator. The present invention is based on the above findings.

[0008] That is, the present invention provides a method for producing Si: 2.5 to 4.0 wt.
%, Acid-soluble Al: 0.01 to 0.05 wt% and Sb: 0.01 to 0.20 wt%
% Of silicon steel slabs containing hot-rolled steel, hot-rolled sheet annealing and cold rolling once or twice with intermediate annealing to obtain the final sheet thickness, then decarburization and primary recrystallization Subject to annealing,
Next, after applying an annealing separator containing MgO as a main component, in a method for manufacturing a grain-oriented silicon steel sheet comprising a series of manufacturing steps of performing finish annealing, MgO of the annealing separator component has a citric acid activity of 100-400 seconds at a final reaction rate of 40%,
1000-4000 seconds at a final reaction rate of 80%, and a hydrated water content of 2.5% or less at 20 ° C. for 60 minutes.
Further, the present invention provides a method for producing a unidirectional silicon steel sheet having excellent coating properties and magnetic properties, characterized in that the average particle diameter is 2.5 μm or less and the non-passage of 325 mesh is 5% or less.

[0009]

As to MgO used as an annealing separator for unidirectional silicon steel sheets, various physical properties have been proposed so far. For example, in Japanese Patent Publication No. 49-29409,
It has been shown that heavy low-activity MgO with a bulk weight of 0.18-0.30 g / cc is applied as a slurry with a hydration of 1-4%. Japanese Patent Publication No. 52-31296 discloses MgO having an SO ₃ content of 0.2% or less, a Cl content of 0.04% or less, a bulk weight of 0.18 to 0.30 g / cc, and a particle size distribution in a specific range. Japanese Patent Publication No. 54-14566 discloses that MgO having an impurity in a specific range, a hydration amount of 20% at 30 ° C. for 8 minutes or less, and a 325 mesh non-passing portion of 1% to 20% passing through 100 mesh. It is shown. Furthermore, Japanese Patent Publication No. 57-45472 discloses MgO 2 having a citric acid activity in a specific range, which is indicated by the reaction time with citric acid.

By the way, the forsterite film formed by the final finish annealing is an oxide (SiO ₂ , Fe ₂ SiO _4, etc.) generated in the surface layer of the steel sheet during the decarburization / first recrystallization annealing.
Is generated by a solid phase reaction with MgO applied as an annealing separating agent, so that not only physical properties of MgO but also
It is strongly affected by the properties of the oxide layer on the surface of the steel sheet. That is, if the amount of the oxide is insufficient, only a non-uniform and poorly adhered film is generated. If the amount of iron oxide in the oxide is too large, a very poor quality coating in which the base iron is exposed in a pinhole shape is formed.

Here, in the production of a unidirectional silicon steel containing AlN as a main inhibitor and containing Sb, MgO which has been proposed so far as described above is used.
Was too active to form a good coating stably. The reason for this is that, as described above, silicon steel of a component system containing AlN 2 as a main inhibitor and containing Sb is not easily oxidized in decarburization / primary recrystallization annealing. Therefore, if the decarburizing annealing temperature and the dew point of the atmosphere are increased to increase the oxidation amount, the iron oxide in the oxidized layer increases, so that the forsterite film formed in the final finish annealing must be inferior. Did not.

[0012] From these facts, the present inventors have conducted various studies on suitable physical properties of MgO to be used as an annealing separator for a component-oriented unidirectional silicon steel sheet containing Al-Sb. Is even less active than
MgO has been found to be suitable.

At first glance, it seems like a contradictory phenomenon that MgO having lower activity is more suitable for forming a film for a material which is hardly oxidized in decarburization / first recrystallization annealing. However, the reason is considered as follows.
When a silicon steel sheet wound in a coil shape with an annealing separator applied is finish annealed, MgO is used up to around 800 ° C during the temperature rise process.
Is gradually released, so that the coil layers are kept in a wet state. At this time, the surface of the steel sheet is subjected to so-called additional oxidation by H ₂ O, and the amount of the oxidation depends on the properties of the oxide layer generated by the decarburization / primary recrystallization annealing. In a component-oriented unidirectional silicon steel containing Al-Sb, since the amount of oxidation generated in the surface layer is small, a large amount of iron oxide is generated during this additional oxidation. Among the iron oxides generated here, FeO forms a solid solution with MgO and x
Produces FeO.yMgO and has an adverse effect on forsterite film formation at high temperatures. In addition, Fe ₂ SiO ₄ also dissolves with MgO to form forsterite (Mg ₂ SiO ₄ ) and releases FeO, thereby causing the same adverse effect. In addition, decarburization 1
The additional oxidation itself is also non-uniform due to the uneven concentration of Al and Sb in the surface layer from the time of the next recrystallization annealing, and the non-uniform H ₂ O partial pressure between the coil layers. , Which also had an adverse effect on the uniformity of the coating.

As described above, the cause of the adverse effect on the forsterite film is the additional oxidation derived from the hydrated water of MgO and its unevenness. Thus, according to the present invention, it is possible to suppress this additional oxidation by using lower activity MgO 2, so that even unidirectional silicon steel containing Al—Sb can be coated uniformly and well. It is considered that the following can be formed.

The secondary recrystallization temperature of a unidirectional silicon steel containing AlN as a main inhibitor is around 900 to 1000 ° C. due to the strong inhibitory power of the inhibitor. Secondary recrystallization temperature of steel 800 ~
Higher than 900 ° C. For this reason, surface oxidation during finish annealing affects the decomposition and coarsening of the inhibitor, and strongly affects the secondary recrystallization behavior. Therefore, if the amount of additional oxidation is large, not only the surface coating but also the magnetic properties often deteriorate significantly. Therefore, in the production of a component-oriented unidirectional silicon steel containing Al-Sb, the use of low-activity MgO is important from the viewpoint of stabilization of magnetic properties.

Based on the above findings, various experiments were conducted, and it was found that the suitable activity of MgO can be indicated by the citric acid activity and the amount of water of hydration. First, the evaluation method of citric acid activity will be described. 1) 0.4 takes define the aqueous acid solution 100 cm ³ citric beaker,
Keep at 30 ° C. The magnetic rotor is put in the beaker. 2) Put the weighed MgO into the beaker. The amount of MgO charged depends on the desired final conversion, with a final conversion of 40.
% Is 2.00 g, and 80% is 1.00 g. (
100 cm ³ of a 0.4N aqueous citric acid solution reacts with 0.8 g of MgO. 3) Turn on the stirrer exactly 10 seconds after MgO is put into the beaker, and rotate the magnetic rotor.
During this time, the liquid temperature is kept at 30 ° C. ± 1 ° C. 4) The reaction was terminated when the pH of the slurry reached 8.0.
Measure the time from when O was injected, and let the number of seconds be citric acid activity.

In the citric acid activity evaluated in this way, MgO conventionally used as an annealing separator for unidirectional silicon steel is, for example, MgO disclosed in the above-mentioned JP-B-57-45472. The citric acid activity is about 40 to 80 seconds when the final reaction rate is 40% even though the activity is low.
The activity was higher than that of MgO. In addition, Tokuhei 4
No. -25349 discloses that CaO and B are added to MgO as annealing separators.
It is stated that citric acid activity of 60 to 250 seconds is effective for excellent glass coating and magnetic properties of a grain-oriented electrical steel sheet, but MgO of the present invention is
The feature is that not only the citric acid activity at a final reaction rate of 40% but also the citric acid activity at 80% is considered. In other words, the activity distribution changes depending on the preparation conditions of MgO. Even if the activity at the final citric acid reaction rate of 40% is the same, the one with a narrow activity distribution is the value of citric acid activity at 80%. Is small as described in Japanese Patent Publication No. 57-45472, cited above, wherein the Mg used in the present invention is used.
O: Citric acid activity at a final conversion of 80% is 1000-
It has a wide activity distribution of 4000 seconds.

As described above, the citric acid activity is less than 100 seconds at a final reaction rate of 40%, and 10% at a final reaction rate of 80%.
In the case of an activity distribution of less than 00 seconds, only a film which is too active and is non-uniform and has many defects is generated. The final reaction rate is 40%
If the activity distribution exceeds 400 seconds under the conditions of above and 4000 seconds under the condition of the final reaction rate of 80%, the reactivity of MgO is too low and only a thin, coarse, poorly adhered film is formed. .
A more suitable activity distribution is 150% at a final conversion of 40%.
It is 1500 to 3500 seconds under the conditions of ~ 350 seconds and a final reaction rate of 80%.

In the production of MgO with citric acid activity according to the present invention, in the firing of raw materials (eg, magnesium hydroxide, magnesium carbonate, basic magnesium carbonate, etc.), different activities fired at a high temperature of 950 ° C. or more are used. By the method of mixing things and batch furnace firing,
By adjusting the temperature distribution in the firing furnace, MgO 2 having the desired activity distribution can be obtained.

Further, with respect to the activity of MgO, the temperature was 20 ° C., 60 ° C.
The amount of water of hydration under the condition of one minute must be 2.5% or less. If the hydrated water content exceeds 2.5%, additional oxidation during the final finish annealing increases, and both the coating and the magnetic properties become poor.

In order to obtain a more uniform coating, the MgO particles need to have an average particle size of 2.5 μm or less. Since the forsterite film forming reaction is a solid-phase reaction between MgO and oxides (SiO ₂ , Fe ₂ SiO ₄ ) on the steel sheet surface,
It is strongly influenced by the particle size of MgO. 2.5 μm average particle size
If m is exceeded, the solid phase reaction becomes non-uniform and a good film cannot be obtained. For the same reason, regarding the particle size distribution of MgO, it is necessary that the non-passage of 325 mesh is 5% or less in order to obtain the expected product quality. If the non-passage exceeds 5%, The coating becomes uneven.

As the annealing separator of the present invention, it is possible to add components normally added to the separator, for example, TiO ₂ , titanate, boric acid or borate, Sr compound, Mn compound and the like.

Next, the reasons for limiting the component composition range of the silicon steel material to which the production method of the present invention is applied are as follows. Si: 2.5 to 4.0 wt% If the amount of Si is less than 2.5 wt%, good iron loss cannot be obtained.
On the other hand, if the content exceeds 4.0 wt%, the cold rolling property is remarkably deteriorated, so the content is set in the range of 2.5 to 4.0 wt%. Acid-soluble Al: 0.01 to 0.05 wt% Acid-soluble Al is necessary to form AlN 2 as an inhibitor, and its content is in the range of 0.01 to 0.05 wt%. If the content of acid-soluble Al is less than 0.01 wt%, the action as an inhibitor is reduced, leading to a decrease in the magnetic flux density of the product, while if it exceeds 0.05 wt%, secondary recrystallization becomes unstable. Become. Sb: 0.01 to 0.20 wt% Sb is necessary for improving the primary recrystallization texture, improving the growth of (110) <001> oriented crystal grains, and stably improving the magnetic properties. If the Sb content is less than 0.01 wt%, the effect is poor, while if it exceeds 0.20 wt%, the decarburizing property and the forsterite film forming property are impaired, so the content is set in the range of 0.01 to 0.20 wt%.

In addition to the above, as a steel component, C is 0.02 to 0.12.
It contains about wt% and N as an inhibitor component in the usual range (about 0.004 to 0.01 wt%), and may further contain Mn, S, Se, etc., if necessary. The content thereof is about 0.03 to 0.15 wt% of Mn, and about 0.01 to 0.05 wt% of S and / or Se in total. Further, in order to make the secondary recrystallization more advantageous in terms of magnetic properties, Cu, Sn, and the like can be contained at about 0.02 to 0.20 wt% and about 0.02 to 0.20 wt%, respectively.

Next, in the manufacturing process, the silicon steel material adjusted to the above-mentioned composition is heated to a high temperature of usually 1400 ° C. or more, and then a hot rolled base plate having a thickness of about 2 to 3 mm is formed by a known method. And Next, hot-rolled sheet annealing is performed in a temperature range of 900 to 1200 ° C., and after pickling, one cold rolling or
Cold rolling with a final thickness of about 0.15 to 0.35 mm is performed by cold rolling two or more times with annealing at a temperature in the range of 900 to 1200 ° C. The rate is preferably in the range of 80-95%. After degreased, the final cold-rolled sheet is decarburized and annealed in a wet hydrogen atmosphere at a temperature in the range of 800 to 900 ° C. to reduce the C content to 0.003 wt% or less. Then, after applying an annealing separator mainly composed of MgO, dry H ₂ atmosphere
Finish annealing is performed at a high temperature of 1100 to 1250 ° C. Finally, an insulating coating is applied to form a unidirectional silicon steel sheet product.

[0026]

【Example】

Example 1 C: 0.060 wt%, Si: 3.12 wt%, Mn: 0.075 wt%, Se:
0.023 wt%, acid soluble Al: 0.024 wt%, N: 0.0084 wt
%, Sb: 0.032 wt%, the remainder being a silicon steel slab substantially composed of Fe, heated at 1420 ° C. for 20 minutes, and then hot-rolled into a 2.3 mm-thick hot-rolled sheet. This hot rolled sheet is
After heating at 50 ℃ for 2 minutes, quench by mist spray,
Then, it was subjected to cold rolling to finish to 0.30 mm. After this cold rolling, 840% in an atmosphere of H ₂ 45% -N ₂ 55% and a dew point of 63 ° C.
Decarburization and primary recrystallization annealing were performed at 4 ° C. for 4 minutes. A large number of test pieces were cut out from this plate, and an annealing separator was applied in a slurry state and dried. MgO having various properties shown in Table 1 was used as an annealing separator at this time.
Further, 2% of TiO ₂ was added as an additive. The physical properties of MgO were changed by changing the calcination conditions and pulverization conditions during the production of MgO. Steel sheet coated with annealing separator
The sample was subjected to finish annealing at 1200 ° C. for 20 hours in an H ₂ atmosphere.

[0027]

[Table 1]

Table 1 also shows the coating appearance, coating adhesion and magnetic properties of the product thus obtained. Here, the average particle diameter is measured by a light transmission method, and the adhesion of the coating film is represented by a minimum bending diameter at which the coating film does not peel off. As is clear from Table 1, in the applicable example, a product having good appearance and adhesion and excellent magnetic properties is obtained.

Example 2 C: 0.062 wt%, Si: 3.09 wt%, Mn: 0.076 wt%, Se:
0.021 wt%, S: 0.004 wt%, acid-soluble Al: 0.025 wt
%, N: 0.0080 wt%, Sb: 0.030 wt%, Mo: 0.02 wt%,
Cu: 0.01wt%, Sn: 0.10wt%, with the balance substantially
A silicon steel slab having a Fe composition was heated at 1420 ° C. for 20 minutes, and then hot-rolled into a hot-rolled sheet having a thickness of 2.0 mm. This hot-rolled sheet was heated at 1050 ° C. for 2 minutes, rapidly cooled by mist injection, and then cold-rolled to a finish of 0.23 mm. After this cold rolling, decarburization and primary recrystallization annealing were performed at 830 ° C. for 3 minutes in an atmosphere of H ₂ 55% -N ₂ 45% and a dew point of 65 ° C. A large number of test pieces were cut out from this plate, and an annealing separator was applied in a slurry state and dried. As the annealing separator at this time, MgO having various properties shown in Table 2 was used, and SrSO ₄ : 1% and MnO ₂ : 1.5% as additives.
Was added to each. The steel sheet coated with the annealing separator was subjected to finish annealing at 1200 ° C. for 10 hours in an H ₂ atmosphere.

[0030]

[Table 2]

The appearance, adhesion and magnetic properties of the film of the product thus obtained are also shown in Table 2. The measurement of the average particle diameter and the coating adhesion is the same as in Example 1. As is clear from Table 2, in the applicable example, a product having good appearance and adhesion and excellent magnetic properties is obtained.

[0032]

According to the method for producing a grain-oriented silicon steel sheet of the present invention, as the MgO as a component of the annealing separator, the citric acid activity is 100 to 400 seconds at a final reaction rate of 40%, and the final reaction rate is 40%. It is 1000-4000 seconds under the condition of 80%, and the hydrated water content is 2.5% or less under the condition of 20 ° C. for 60 minutes, and the average particle diameter is 2.5 μm or less and 325 mesh is not passed. Is 5% or less by using Al and
In the production of an Sb-containing steel sheet, a product having a uniform and excellent adhesion film and excellent magnetic properties can be stably obtained.

Claims (1)

(57) [Claims] 1. Si: 2.5-4.0 wt%, acid-soluble Al: 0.01
A hot rolled silicon steel slab containing 0.050.05 wt% and Sb: 0.01-0.20 wt%, and then subjected to hot rolled sheet annealing and cold rolling twice, once or once with intermediate annealing And then subjecting it to decarburization / primary recrystallization annealing, then applying an annealing separator containing MgO as a main component, and then performing finish annealing. The MgO of the annealing separator component has a citric acid activity of 100-400 seconds at a final reaction rate of 40% and a final reaction rate of 80%.
1000 to 4000 seconds, and the hydrated water content is 2.5% or less at 20 ° C. for 60 minutes, and the average particle size is 2.5% or less.
A method for producing a grain-oriented silicon steel sheet having excellent coating properties and magnetic properties, characterized in that the thickness is not more than μm and the non-passage of 325 mesh is not more than 5%.