JP2786576B2 - Manufacturing method of grain-oriented silicon steel sheet - 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 grain-oriented silicon steel sheet, and more particularly to improving the magnetic properties by devising a decarburizing annealing step.

[0002]

2. Description of the Related Art Oriented silicon steel sheets are used as soft magnetic materials.
It is mainly used as an iron core material of a transformer or a rotating machine, and is required to have high magnetic flux density and small iron loss and magnetostriction as magnetic characteristics.

[0003] Such a grain-oriented silicon steel sheet is subjected to hot rolling by heating a grain-oriented silicon steel slab containing an inhibitor required for secondary recrystallization, for example, MnS, MnSe, AlN, etc. Annealing is performed accordingly, and the final product thickness is obtained by cold rolling one time or two or more times with intermediate annealing, then decarburizing annealing, then applying an annealing separator such as MgO to the steel sheet, and finishing annealing Manufactured. The surface of the grain-oriented silicon steel sheet is usually formed with a forsterite (Mg ₂ SiO ₄ ) -based insulating coating except in special cases. This coating effectively improves iron loss and magnetostriction by applying tensile stress to the steel sheet by utilizing not only the electrical insulation of the surface but also its low thermal expansion property.

[0004] This coating is formed in finish annealing, and its formation behavior affects the behavior of inhibitors such as MnS, MnSe, and AlN in steel, and is a necessary process for obtaining excellent magnetism. It also affects the recrystallization itself. In addition, the formed coating absorbs an inhibitor component that is no longer necessary after the completion of the secondary recrystallization into the coating and purifies the steel, thereby helping the steel plate to sufficiently exert its magnetic properties. Therefore, controlling the film formation process to form a uniform film is one of the important points that affect the product quality of the grain-oriented silicon steel sheet.

[0005] That is, the formed film must be, of course, uniform and defect-free and have excellent adhesion that can withstand shearing, punching, bending and the like. In addition, it must have a high space factor when laminated as a smooth iron core.

[0006] In order to form a forsterite insulating coating on a grain-oriented silicon steel sheet, cold rolling is performed to a desired final thickness, followed by continuous annealing in a wet hydrogen atmosphere at a temperature of 700 to 900 ° C. In order to improve the magnetic characteristics by performing the secondary recrystallization completely at the same time as performing the primary recrystallization so that an appropriate secondary recrystallization occurs, the steel sheet after the rolling is subjected to 0.01 to 0.10
% Of carbon is reduced to about 0.003% or less.

Further, at the same time, by oxidation, SiO ₂
Is generated on the surface layer of the steel sheet.
Then, an annealing separator containing MgO as a main component is applied to the steel sheet, wound into a coil, and subjected to high-temperature finish annealing at a temperature of about 1000 ° C to 1200 ° C in a reducing or non-oxidizing atmosphere. The forsterite insulating film is formed by a solid phase reaction represented by the following formula. 2MgO + SiO ₂ → Mg ₂ SiO ₄

The forsterite insulating coating has a thickness of 1 μm.
This is a ceramic film in which the front and rear fine crystals are densely integrated. As described above, the oxide generated on the surface layer of the steel sheet is used as one raw material during decarburization annealing, and is formed on the steel sheet. The kind, quantity, distribution, etc.
In addition to affecting the nucleation and grain growth behavior of forsterite, it also affects the grain boundaries of the coating crystal grains and the strength of the grains themselves, and thus has a great effect on the coating quality after finish annealing.

Further, since the annealing separator mainly composed of MgO, which is the other raw material, is applied to a steel sheet as a slurry suspended in water, H ₂ O physically adsorbed even after being dried.
Other carrying, since a part is changed to Mg (OH) ₂ and hydrated, to around 800 ° C. during final annealing, a small amount while H ₂ O
Continue to release. Therefore steel sheet surface by the H ₂ O,
It undergoes so-called additional oxidation. This oxidation also affects the formation behavior of forsterite and leads to oxidation and decomposition of the inhibitor. Therefore, if this is too much, it becomes a factor of deteriorating the magnetic properties. The susceptibility to this additional oxidation is also greatly affected by the physical properties of the oxide layer on the steel sheet surface generated by the decarburizing annealing.

Further, in a grain-oriented silicon steel sheet using AlN as an inhibitor, the physical properties of this oxide layer affect the N-removing behavior during finish annealing or the N intrusion behavior from the annealing atmosphere, and the magnetic properties Also affect. As described above, controlling the state of the surface layer of the steel sheet during decarburization annealing is one of the important points in the production of a grain-oriented silicon steel sheet.

Regarding the decarburization annealing of grain-oriented silicon steel sheet,
For example, as disclosed in JP-A-59-185725, a method of controlling the dew point of the annealing atmosphere to 50 to 75 ° C., as disclosed in JP-A-54-160514, It is known that the degree of oxidation is set to 0.15 or more in the first half of decarburization and 0.75 or less in the second half and lower than that in the first half.

[0012]

However, the above-mentioned atmosphere control does not always produce a forsterite film having a sufficient quality, and may cause a poor adhesion portion in the strip width direction or the longitudinal direction. A case in which the appearance, the thickness of the film, the forsterite particle size, and the like become uneven is likely to occur. Further, the coating may be locally peeled off in a dotted or streak-like manner, or may become a porous coating.

SUMMARY OF THE INVENTION The present invention has been made to advantageously solve the above problems, and is intended to obtain a grain-oriented silicon steel sheet having a defect-free uniform and excellent adhesion over the entire width and the entire length of a coil. It is an object of the present invention to propose a production method with high productivity.

[0014]

SUMMARY OF THE INVENTION According to the present invention, a directional silicon steel material is hot-rolled, and then subjected to one or two cold-rolling steps with intermediate annealing, followed by decarburizing annealing and then annealing separation. In a method for producing a grain-oriented silicon steel sheet, which consists of a series of steps of applying a finishing agent and then performing final finish annealing, decarburizing annealing reduces the ratio of steam partial pressure to hydrogen partial pressure to less than 0.7 during the soaking process. A method for producing a grain-oriented silicon steel sheet, characterized in that the ratio of the partial pressure of water vapor to the partial pressure of hydrogen in the temperature raising step is set lower than in the soaking step.

[0015]

The present inventors have conducted a detailed investigation on the cause of the quality variation of the forsterite film on the strip,
It was found that the amount and quality of the subscale generated on the surface of the steel sheet during decarburization annealing had a large effect.
This means that the subscale formation reaction does not always occur uniformly in the width direction or the longitudinal direction of the strip. Further, it has been newly found that the cause is related to a change in the oxidizing property of the atmosphere particularly during the temperature rising process of the decarburizing annealing. Therefore, the oxidizing atmosphere in decarburization annealing, that is, the ratio of the partial pressure of water vapor to the partial pressure of hydrogen (hereinafter referred to as P (H ₂ O) / P (H ₂ ))
An experiment was conducted to investigate the effect on the forsterite coating. Hereinafter, the results of the experiment will be described.

Including MnSe and Sb as inhibitors
A 3.3 wt% silicon steel sheet (sheet thickness 0.23 mm) was annealed at 840 ° C. for 2 minutes in a humid hydrogen atmosphere. At this time, the oxidizing properties of the atmosphere during the temperature raising process and the soaking process were separately controlled in the range of P (H ₂ O) / P (H ₂ ): 0.2 to 0.8 by adjusting the dew point and the H ₂ gas concentration. . Next, an annealing separator containing MgO as a main component was applied to the steel sheet, and a secondary recrystallization annealing at 850 ° C. × 50 hours and a subsequent purification annealing at 1200 ° C. × 5 hours in an H ₂ atmosphere were performed. Thereafter, the uniformity of the forsterite film was evaluated. These results are shown in FIG. The heating process is generally in accordance with the production of grain-oriented silicon steel sheets.
The experiment was performed at a heating rate of 25 ° C./s.

As shown in FIG. 1, P (H ₂ O) /
When P (H ₂ ) is less than 0.7 and P (H ₂ O) / P (H ₂ ) in the heating process is lower than that in the soaking process, a beautiful glossy gray uniform coating is obtained. Was done. On the other hand, P (H ₂ O)
Assuming that / P (H ₂ ) is 0.7 or more, P (H ₂ O) / P
Even when (H ₂ ) was lower than that in the soaking process, a film with excellent characteristics was not obtained.

Here, according to the equilibrium diagram of the oxide formed on the surface of the silicon steel sheet shown in FIG. 2, P (H ₂ O) / P (H
₂ ): 0.7 is clearly the FeO generation region, and it is considered that the subscale formed under such conditions has poor protection and additional oxidation during the final annealing becomes severe, resulting in deterioration of the forsterite film. . Although it is not clear why the quality of the forsterite film is improved by lowering the atmosphere oxidizing property during the temperature raising process, the subscale generated during the temperature raising process is not protected by the subscale generated during the soaking process. It is thought to increase.

Further, it has been found from the following experiment that the reduction of the atmospheric oxidizability during the temperature raising process also has the effect of promoting decarburization and oxidation. That is, C: 0.045
When decarburizing annealing is performed on a 0.23 mm thick silicon steel sheet containing wt% (hereinafter simply referred to as%) in a wet hydrogen atmosphere at 840 ° C. for 2 minutes, the P (H ₂ O) / P (H ₂ )
Is constant at 0.55, and P (H ₂ O) / P
(H ₂ ) was adjusted to the range of 0.2 to 0.7, and the C content and the oxygen basis weight of the surface of the obtained steel sheet were measured. Table 1 shows the results.

[0020]

[Table 1]

From Table 1, it can be seen that the atmosphere P (H ₂ O) / P
By lowering (H ₂ ), it is possible to realize a process in which the C content is lower and the oxygen basis weight is higher. Therefore,
It is possible to increase the speed in the operation line, which greatly contributes to the improvement of productivity. This is presumably because the surface reaction in the soaking process is promoted by decreasing P (H ₂ O) / P (H ₂ ) in the heating process.

The oriented silicon steel sheet is made of Mn-Sb due to the difference of the inhibitor used for the secondary recrystallization.
System, AlN-MnS system, AlN-MnSe system, Mn-S system, etc., but the present invention can be applied to any steel type.

[0023]

EXAMPLES Example 1 C: 0.062%, Si: 3.31%, Mn: 0.078%, Se: 0.024
%, Sol. Al; 0.023%, N: 0.008%, Sb: 0.027%, after hot rolling to a 2.8mm thickness, then performing uniform annealing at 1100 ° C. The thickness of the sheet was reduced to 0.30 mm in each cold rolling. Then 130 seconds at 840 ° C., H ₂
Was decarburization annealed in -N ₂ -H ₂ O atmosphere. At this time, H ₂
By changing the concentration and the dew point, the P (H ₂ O) of the atmosphere during the heating process (heating rate: 10 ° C./s) and the soaking process
/ P (H ₂ ) was adjusted to the value shown in Table 2. Next, Ti is added to MgO.
O ₂ : Apply an annealing separator containing 3%, and in an H ₂ atmosphere,
It was subjected to secondary recrystallization and purification annealing at 00 ° C. for 10 hours. Thereafter, a coating containing magnesium phosphate and colloidal silica as main components was applied.

The iron loss W _17/50 value at 1.7 T, 50 Hz of the product thus obtained, the magnetic flux density B at a magnetic field of 800 A / m
_Eight values, bending adhesion of the coating and appearance of the coating were investigated. The bending adhesion of the coating was indicated by a minimum diameter at which the coating was not peeled off by winding a test piece around a round bar having various diameters (5 mm intervals). Further, the C content and the oxygen basis weight of the steel sheet after the decarburizing annealing were also analyzed. Table 2 shows these results.
It is described together.

[0025]

[Table 2]

As is clear from Table 2, P (H
₂ O) / P (H ₂ ) is equal to or higher than the soaking process.
8-10 and the soaking process _{P (H 2 O) / P} (H 2) is 0.70 FeO
No. 11, which was the formation region, was inferior in film uniformity, adhesion and magnetic properties. In contrast, Nos. 1 to 7 obtained according to the present invention clearly improved both the film properties and the magnetic properties. Further, in Nos. 1 to 7, since the C content after decarburizing annealing was low and the oxygen basis weight was high as compared with the comparative example, it can be seen that decarburization and oxidation were promoted.

Example 2 C: 0.041%, Si: 3.32%, Mn: 0.07%, Se: 0.023%
Directional silicon steel material containing 0.024% and Sb;
After hot rolling to a thickness of 2.0 mm, the sheet was subjected to uniform annealing at 900 ° C., and was further cold rolled twice with intermediate annealing at 980 ° C. for 2 minutes to obtain a sheet thickness of 0.23 mm. Then, decarburizing annealing was performed at 820 ° C. for 120 seconds in an H ₂ —N ₂ —H ₂ O atmosphere. At this time, by changing the H ₂ concentration and the dew point, the P of the atmosphere in the heating process (heating rate: 20 ° C./s) and the soaking process
(H ₂ O) / P (H ₂ ) was adjusted to the value shown in Table 3. Then Mg
An annealing separator containing 1% of TiO ₂ and 2% of SrSO ₄ : 2 was applied to O 2, and a secondary recrystallization was performed at 1180 ° C. for 7 hours in an H ₂ atmosphere.
It was subjected to purification annealing. Thereafter, the same processing as in Example 1 is performed,
The same investigation as in Example 1 was conducted on the obtained product.
The results are also shown in Table 3.

[0028]

[Table 3]

As is apparent from Table 3, P (H
The _{2 O) / P (H 2} ) lower than that of the soaking process, and and was of the soaking process P (H ₂ O) / P a (H ₂₎ is 0.6 or less Nanba1～6,
As compared with the comparative examples, all were superior in the film properties and the magnetic properties, and the decarburization and oxidation rates were promoted.

[0030]

According to the present invention, it is possible to stably produce a grain-oriented silicon steel sheet having excellent coating properties and good magnetic properties. In addition, the decarburization and oxidation rates are increased, which can contribute to an improvement in productivity.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between P (H ₂ O) / P (H ₂ ) and the appearance of a forsterite coating after finish annealing.

FIG. 2 is an equilibrium diagram of oxides produced in 3% silicon steel in wet hydrogen.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Takehiro Suzuki 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref. Kawasaki Steel Corporation Mizushima Works (58) Fields surveyed (Int.Cl. ⁶ , DB Name) C21D 9/46 501 C21D 8/12 C21D 3/04

Claims (1)

(57) [Claims] (1) After hot rolling a directional silicon steel material,
A method for producing a grain-oriented silicon steel sheet comprising a series of steps of performing cold rolling once or twice with an intermediate annealing therebetween, followed by decarburizing annealing, applying an annealing separator, and then performing final finishing annealing. In the decarburization annealing, the ratio of the steam partial pressure to the hydrogen partial pressure in the soaking process is set to less than 0.7, and the ratio of the steam partial pressure to the hydrogen partial pressure in the heating process is set to be lower than that in the soaking process. A method for producing a grain-oriented silicon steel sheet.