JPH07278671A - Manufacture of mirror surface oriented silicon steel sheet with low iron loss - Google Patents

Abstract

PURPOSE:To manufacture the mirror surface oriented silicon steel sheet with low iron loss by performing the decarburization annealing of the cold rolled silicon steel having the prescribed composition consisting of Si through the plating of Co, Ni, Cu, etc., and coating the Al2O3 separation agent for annealing as the separation agent for the annealing to perform the finish annealing. CONSTITUTION:The slab of the silicon steel having the composition consisting of, by weight, 0.8-4.8% Si is hot rolled and annealed as necessary. This hot rolled steel sheet is cold rolled in one or two or more cold rolling including the intermediate annealing. This cold-rolled steel sheet is decarburization annealed, and the separation agent for annealing is coated and laminated on this steel sheet to perform the finish annealing and provide the mirror surface. In the manufacturing method of the mirror surface oriented silicon steel sheet, one or more kinds of Co, Ni, and Cu difficult to be oxidated in the atmosphere of the decarburization annealing is plated preferably to the thickness of 0.1-2.0mum in the process before the decarburization annealing to prevent the formation of the oxide film during the decarburization annealing. Al2O3 is used as the separation agent for annealing to realize the secondary re-crystallization without forming the glass.

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 electrical steel sheet having extremely low iron loss.

[0002]

2. Description of the Related Art Unidirectional electrical steel sheets are used as magnetic iron cores in many electric devices. Unidirectional silicon steel sheet,
Si is contained in 0.8 to 4.8% and the crystal grain of the product is {11
It is a steel plate highly integrated in the 0} <001> direction. The magnetic properties are required to be high in magnetic flux density and low in iron loss. In particular, recently, there is an increasing demand for reduction of iron loss from the viewpoint of energy saving. In order to meet this demand, a technique for subdividing magnetic domains has been developed as a means for reducing iron loss in unidirectional silicon steel sheets.

In the case of a laminated iron core, a method of irradiating the steel sheet after finish annealing with a laser beam to apply a local minute strain to subdivide magnetic domains to reduce iron loss is disclosed in, for example, Japanese Patent Laid-Open No. 58-265405. It is disclosed in the official gazette. Further, in the case of a wound core, there is also a method in which the magnetic domain subdivision effect does not disappear even if stress relief annealing (Stress Release Annealing) is performed after processing the core.
No. 2-8617. By subdividing the magnetic domains by these technical means, iron loss has been greatly reduced. However, observing the movement of these magnetic domains has revealed that some magnetic domains do not move. Therefore, in order to further reduce the iron loss value of the grain-oriented electrical steel sheet, it is necessary to eliminate the pinning effect of the glass coating on the surface of the steel sheet and the inclusions immediately below the surface, which inhibits the movement of the magnetic domain together with the subdivision of the magnetic domain. It turned out to be important.

For that purpose, it is effective not to form a glass coating on the surface of the steel sheet which hinders the movement of magnetic domains. As a means for this, a method of not forming a glass coating by using coarse high-purity alumina as an annealing separator is disclosed in U.S. Pat. S. Patent 3785882. However, with this method, it is not possible to eliminate the inclusions directly under the surface, and the iron loss improvement rate is W _15/60 at most 2%.
Nothing more than.

As a method of controlling the inclusions immediately below the surface and achieving a mirror surface of the surface, there is a method of performing chemical polishing or mechanical polishing after finish annealing. However, although these methods are capable of processing a small amount of materials at the laboratory level, chemical concentration control, wastewater treatment, etc. are difficult to perform in chemical polishing, and mechanical polishing is difficult to perform on an industrial scale. However, it is difficult to smooth a surface having a large area with the same standard.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an industrial means for producing a material having a low iron loss by further smoothing the surface as compared with the conventional method,
It is intended to provide a method for suppressing the oxide film formed during decarburization annealing as much as possible to achieve a mirror finish on the surface during finish annealing. Especially, the secondary recrystallization process (finish annealing process) is completed without forming a forsterite (hereinafter referred to as glass) film on the surface, and then magnetic domain subdivision, tension coating, etc. are applied to the iron loss characteristics. It is intended to improve.

[0007]

[Means for Solving the Problems] The present inventors suppress the oxide film on a decarburized plate by plating a metal that does not oxidize in the degree of oxidation in a decarburization annealing atmosphere in a step before decarburization annealing. succeeded in. The details will be described below. The present inventors, when realizing a low iron loss material by the mirror secondary recrystallization method, which is a means for simultaneously performing secondary recrystallization and surface mirroring during finish annealing, an oxide film formed during decarburization annealing. It was confirmed that has a great influence on the magnetic properties of the finish annealed sheet. When the oxide film was reduced by pickling the decarburized annealed plate, the surface of the finish annealed plate had better specularity (surface smoothness) as the amount of oxygen immediately after decarburization annealing was smaller.
Further, as for the relationship between the surface oxide layer and the iron loss value of the product plate, it can be seen that the thinner the oxide layer, the lower the iron loss tends to be, as shown in FIG. From the above, it is understood that the oxide film formed during decarburization annealing should be suppressed as much as possible in order to reduce the iron loss of the product sheet.

Decarburization annealing is usually carried out in the temperature range of 800 to 850 ° C., and the degree of oxidation is PH ₂ O / PH ₂ = 0.01 to 1.0.
Within the range (hatched area in FIG. 2). This area is
As shown in Fig. ₂ , since it is above the curve for forming SiO ₂ and crosses the curve for forming Fe ₂ SiO ₄ , the surface of the steel sheet after decarburization annealing is SiO ₂ or SiO ₂ and Fe ₂ SiO 4. ₄ are formed. In order to suppress the amount of these oxides as much as possible, the present inventors have selected a metal that does not oxidize in the atmosphere during decarburization annealing, that is, a metal shown in the oxidation reaction equilibrium curve above the sloped region in FIG. , I thought about plating on the surface of the steel sheet.

In the present invention, Co,
Ni and Cu are listed. These metals (1) do not oxidize in a decarburization annealing atmosphere, (2) can be plated, and (3) have a melting point of a decarburization annealing temperature (800).
˜850 ° C.). The reason that the melting point of (3) is higher than the decarburization annealing temperature is that if the plating metal becomes a liquid during annealing, there will be many non-uniform plating thicknesses on the steel sheet, and This is because the amount of oxidation will change.

Experiments were conducted to confirm the effect of actually plating the surface of the steel sheet with metal. The purpose is to suppress oxygen content while performing decarburization during decarburization annealing. By weight, Si: 3.3%, Mn: 0.14%, C: 0.05%,
S: 0.007%, acid-soluble Al: 0.028%, N:
A 0.008% silicon steel slab was heated at 1150 ° C. and then hot-rolled to a plate thickness of 1.6 mm. This hot rolled sheet is 1100 ° C
After annealing for 2 minutes, it was cold rolled to a final plate thickness of 0.15 mm. The cold-rolled sheet is plated with the metals listed above, and 8
Decarburization annealing at 30 ° C. degree of oxidation PH ₂ O / PH ₂ = 0.32
I went there. The result is shown in FIG. If the plating thickness is thin, decarburization is sufficient, but the amount of oxidation increases, and conversely, if the plating thickness is increased, the amount of oxidation will be suppressed to a low level as expected, but decarburization will be insufficient. Therefore, the plating thickness has an appropriate value, which is a feature of the present invention, and is 0.1 to 2.0 μm in the final cold-rolled sheet.

Thereafter, in the case of this experiment, in order to strengthen the inhibitor, the nitrogen content of the decarburized plate was increased to 0.02% by ammonia nitriding. If more nitrogen is added to the slab than in this experiment, nitriding is not necessary. And, even if the water slurry is applied, it does not hydrate, and Si
Alumina, which has low reactivity with O ₂ , was applied to a steel sheet as an annealing separator and dried. Finish annealing is N up to 1200 ℃
₂ : Performed at 100% (heating rate 15 ° C / h), 1200
From ° C. H _2: was purification annealing switching 20 hours 100%. As a result, the plating thickness on the final cold-rolled sheet was 0.1.
With a thickness of up to 2.0 μm, a mirror finish on the surface could be achieved after finish annealing. From the above results, it is understood that the surface of the cold-rolled sheet can be mirror-finished after finish annealing by applying metal plating to the cold-rolled sheet.

Embodiments will be described below. As a basic manufacturing method, a manufacturing method using AlN and MnS as inhibitors by Taguchi and Sakakura et al.
644), or a production method using (Al, Si) N as a main inhibitor by Komatsu et al.
No. 5285) may be applied.

Si is an important element for increasing electric resistance and reducing iron loss. If the content exceeds 4.8%, the material is likely to crack during cold rolling, making rolling impossible. On the other hand, if the amount of Si is reduced, α → γ transformation occurs during finish annealing, and the crystal orientation is impaired. Therefore, the lower limit is 0.8%, which does not substantially affect the crystal orientation.

Acid-soluble Al is an essential element for binding N and functioning as AlN or (Al, Si) N as an inhibitor. Higher magnetic flux density 0.012
˜0.050% is the limited range. N is 0.0 during steelmaking
If it is added in an amount of 1% or more, vacancies in the steel sheet called blister are generated, so the upper limit is 0.01%. As other inhibitor constituent elements, B, Bi, Se, Pb, Sn, T
i, etc. can also be added.

The molten steel having the above components is formed into a hot-rolled sheet by a usual process, or the molten steel is continuously cast into a ribbon. This hot-rolled sheet or continuous casting strip is cold-rolled immediately or after a short time annealing. This annealing is effective to enhance the magnetic properties of the product, and is performed in the temperature range of 750 to 1200 ° C. for 30 seconds to 30 minutes. It is advisable to decide whether to accept or reject the product considering the characteristic level and cost of the desired product.

Cold rolling is basically carried out in Japanese Examined Patent Publication No. 40-15.
As disclosed in Japanese Patent No. 644, the final cold rolling reduction rate is 8
It may be 0% or more.

It is preferable that the cold-rolled sheet is plated with any one of Co, Ni, and Cu, or two or more kinds, so that the final cold-rolled sheet has a plating thickness of 0.1 to 2.0 μm. Is the point. Decarburization annealing is performed in the temperature range of 800 to 850 ° C. for several tens of seconds for primary recrystallization, and at the same time, the degree of oxidation is adjusted to a range of PH ₂ O / PH ₂ = 0.01 to 1.0. , It reduces by oxidizing carbon in steel to CO.

A manufacturing method using (Al, Si) N as a main inhibitor for this decarburized annealed sheet (see, for example, Japanese Examined Patent Publication No. 62-
No. 45285), a nitriding treatment is performed. The method of this nitriding treatment is not particularly limited, and there is a method of performing it in an atmosphere gas having a nitriding ability such as ammonia.
Quantitatively, 0.005% or more, preferably, the total nitrogen content may be nitrided by Al equivalent or more in the steel. When laminating these decarburized annealed plates, alumina is dry-coated as an annealing separator by a water slurry or an electrostatic coating method.

This laminated plate is finish annealed to carry out secondary recrystallization and purification of nitride. Secondary recrystallization is described in JP-A-2-2.
As disclosed in Japanese Patent No. 58929, it is effective to increase the magnetic flux density by carrying out in a predetermined temperature range by means such as holding at a constant temperature. After the completion of the secondary recrystallization, annealing is performed with 100% hydrogen at a temperature of 1100 ° C. or higher in order to purify the nitride and smooth the surface. Since the surface has already been smoothed after the finish annealing, tension coating treatment may be performed, and magnetic domain subdivision treatment such as laser irradiation may be performed as necessary.

[0020]

【Example】

Example 1 By weight, Si: 3.3%, Mn: 0.1%, C: 0.0
5%, S: 0.007%, acid-soluble Al: 0.03%,
A 1.8 mm thick silicon steel hot rolled sheet having N: 0.008% and Sn: 0.05% was cold rolled to 1.4 mm. Then 1100 ° C
After annealing for 2 minutes, it was cold rolled to a final plate thickness of 0.14 mm. The cold-rolled sheet was plated with Ni while changing the plating thickness.
Then, the plated cold-rolled sheet was decarburized and annealed in a mixed gas of nitrogen and hydrogen at an oxidation degree of 0.18 and 830 ° C. for 70 seconds. Then, by annealing in an ammonia atmosphere, the amount of nitrogen was increased to about 0.025% to strengthen the inhibitor.

Then, after applying a water slurry of alumina to these steel sheets, finish annealing was performed. The finish annealing is performed at a temperature rising rate of 10 ° C./h in an atmosphere gas of N ₂ : 100% up to 1200 ° C., and H ₂ : 10 at 1200 ° C.
It switched to 0% and annealed for 20 hours. These samples were subjected to tension coating treatment, and then irradiated with laser to subdivide the magnetic domains. The magnetic properties of the obtained product are shown in Table 1.

[0022]

[Table 1]

Example 2 By weight, Si: 3.3%, Mn: 0.07%, C: 0.
07%, S: 0.025%, acid-soluble Al: 0.026
%, N: 0.008%, Sn: 0.1%, plate thickness 2.0 mm
The hot-rolled silicon steel sheet was annealed at 1200 ° C. for 2 minutes and then cold-rolled to a final sheet thickness of 0.23 mm. Co plating was performed on the cold rolled sheet by changing the plating thickness. Then, the plated cold-rolled sheet was subjected to an oxidation degree of 0.3 in a mixed gas of nitrogen and hydrogen.
Decarburization annealing was performed at 2,850 ° C. for 90 seconds. Then, these steel sheets were subjected to finish annealing after applying a water slurry of alumina. The finish annealing is up to 1200 ° C. in an atmosphere gas of N ₂ : 15% + H ₂ : 85% at 15 ° C. /
The heating was performed at a heating rate of h, and the temperature was changed to H ₂ : 100% at 1200 ° C. and annealing was performed for 20 hours. These samples were subjected to tension coating treatment, and then irradiated with laser to subdivide the magnetic domains. The magnetic properties of the obtained product are shown in Table 2.

[0024]

[Table 2]

[0025]

According to the present invention, the oxide film formed during decarburization annealing can be suppressed as much as possible, and the surface can be mirror-finished during finish annealing to realize a low iron loss material.

[Brief description of drawings]

FIG. 1 is a diagram _showing the relationship between the oxidation amount of a decarburized plate and iron loss (W _13/50 ).

FIG. 2 is a diagram showing the equilibrium of oxidation reaction by H ₂ O.

FIG. 3 is a chart of elemental analysis results when decarburizing and annealing a cold-rolled sheet plated with metal.

Claims (2)

[Claims] 1. A silicon steel slab containing Si: 0.8 to 4.8% by weight is hot-rolled and, if necessary, annealed,
One cold rolling or two or more cold rollings sandwiching an intermediate annealing is performed, and then decarburization annealing is performed, and then an inter-plate annealing separator for laminating the steel sheets is applied, and the surface is finished after finishing annealing. In a method for producing a mirror-oriented grain-oriented electrical steel sheet characterized by having a mirror surface, Co, Ni,
A method for producing a low iron loss mirror-oriented grain-oriented electrical steel sheet, which comprises plating one or more types of Cu and using alumina as an annealing separator. 2. The thickness of the plated metal during decarburization annealing is set to 0.
The method for producing a low iron loss specular grain-oriented electrical steel sheet according to claim 1, wherein the thickness is 1 to 2.0 μm.