JPH0733546B2 - High magnetic flux density bi-directional electrical steel sheet manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has an easy axis <001> orientation in the longitudinal direction of a steel sheet and a direction perpendicular to the longitudinal direction, and a {100} plane appears on the rolling surface. Yes (Mirror index {100} <001>
(Indicated by the following), a so-called bi-directional electrical steel sheet composed of crystal grains.

Bi-directional electrical steel sheet has an easy axis of magnetization (<001> axis) in the rolling direction and in the direction perpendicular to the rolling direction, and has excellent magnetic properties in the two directions, so magnetic properties are excellent only in the rolling direction. It is advantageous to use it as a magnetic core material for equipment that needs to flow magnetic flux in two directions as compared with existing unidirectional electrical steel sheet, for example, a large rotating machine. Also, in the field of small static devices, non-oriented electrical steel sheets that do not highly integrate the easy axis of magnetization are generally used, but by using bi-directional electrical steel sheets, downsizing and higher efficiency can be achieved. There is a nature.

[Prior Art] As described above, since the grain-oriented electrical steel sheet has excellent properties, it has been widely used as an industrial product until now, despite the long-awaited commercialization thereof. Not in.

There are mainly the following two methods as a conventional manufacturing technique for a grain-oriented electrical steel sheet.

One of them is high temperature annealing in an atmosphere containing a polar gas such as hydrogen sulfide as disclosed in JP-B-37-7110, and {100} <001> using surface energy.
This is a method of secondarily recrystallizing oriented grains. However,
This method requires strict control of the surface energy of the steel sheet and is not suitable as a mass production process.

The other is, as disclosed in Japanese Patent Publication No. 35-2657, a so-called "crossover" in which cold rolling is performed in one direction and then cold rolling is performed in a direction intersecting with the cold rolling. Cold rolling method ". However, the magnetic flux density (B ₈ ) of the product obtained by this method is 1.85 Tesla or less, and it does not have the excellent magnetic characteristics commensurate with the high cost due to the complexity of the manufacturing process, so it is one-way Can't compete with electrical magnetic steel sheet.

The magnetic flux density (B ₈ ) of unidirectional electrical steel sheet is as follows.
Since the technology disclosed in Japanese Patent Publication No. 4 and Japanese Patent Publication No. 51-13469 was invented, it has made rapid progress, and the magnetic flux density (B ₈ ) is currently increasing.
Products with a high magnetic flux density of 1.92T are also commercially available.

Regarding bi-directional electrical steel sheets, improved technology was proposed in Japanese Patent Publication No. 35-17208 and Japanese Patent Publication No. 38-8213 in order to improve magnetic properties. Products with magnetic flux density have not been manufactured stably.

[Problems to be Solved by the Invention]

The present invention solves the problem in the manufacturing technology that a product having a high magnetic flux density cannot be stably obtained in a grain-oriented electrical steel sheet.

[Means for Solving the Problems]

In order to solve the above problems, the present invention provides Si; 0.8% by weight.
~ 6.7%, acid-soluble Al; 0.008-0.048%, N≤0.010%,
A hot rolled sheet consisting of the balance Fe and unavoidable impurities
Cold rolling at 40 to 80%, further cold rolling at a reduction rate of 30 to 70% in a direction intersecting with the cold rolling, then after primary recrystallization annealing, an annealing separator is applied, and secondary recrystallization is performed. In the manufacturing method of bi-directional electrical steel sheet that is subjected to finish annealing for the purpose of refining and refining, the bi-directional electromagnetic sheet is characterized by removing the hot-rolled sheet surface layer from both sides in the thickness direction by 1/10 A method for manufacturing a steel sheet is provided.

[Work]

The present inventors have obtained the following new findings from a survey of products of the grain-oriented electrical steel sheet produced by the cross cold rolling method.

The characteristic crystal orientation of the grain-oriented electrical steel sheet is {100} <001
> Orientation, but in the secondary recrystallized grains, the orientation grains and {110} <uuw> orientation are mixed, and the latter orientation grains cause the magnetic flux density to decrease. . Therefore,
In order to achieve a high magnetic flux density, secondary recrystallization of {110} <uuw> oriented grains may be suppressed.

As a result of detailed studies on these oriented grains, the present inventors have found that the primary recrystallized plate before secondary recrystallization has different textures in the thickness direction, and {110} <uuw> oriented grains are different from the surface layer. ,
It has been found that {100} <001> oriented grains develop from the central layer.

This fact is obtained by the following experiment.

C; 0.055%, Si; 3.3%, acid soluble Al; 0.028%, N; 0.007
%, The balance Fe and unavoidable impurities, and annealed a 1.8 mm thick hot-rolled sheet at 1125 ° C. for 2 minutes.
Cold rolling at a rolling reduction of
Cross cold rolling was performed at a rolling reduction of 55% to obtain a final plate thickness of 0.35 mm.
The cold-rolled sheet was subjected to primary recrystallization annealing in wet hydrogen at 810 ° C for 210 seconds which also serves as decarburization. When the texture of this primary recrystallized sheet was investigated, {111} was observed on the surface as shown in Fig. 1.
<Uvw> direction is the main direction and {211} <124 at the center
>, {211} <231> orientation is the main orientation, and it has been found that they are different in the plate thickness direction. The secondary recrystallization orientation is, for example, KTAust, JWRutter; Trans.Met.Soc.AI.
ME215 (1959) P119 / 127, Ushigami et al. Japan Institute of Metals 96th
As described in P373 of the Annual Meeting, it is strongly influenced by the primary recrystallization texture. As a result of investigating the cause of this primary recrystallization texture having different textures in the sheet thickness direction, it was found that it is greatly influenced by the texture gradient in the sheet thickness direction in the hot rolled sheet as shown in FIG. I understood. Therefore, the surface portion and the central portion were cut out from the hot-rolled sheet, respectively, and after primary recrystallization under the same conditions as above, an annealing separator containing MgO as a main component was applied and finish annealing was performed.

FIG. 3 shows the orientation distribution of the secondary recrystallized grains of each sample thus obtained. From Fig. 3, the {110} <uuw> oriented grains are shown in the sample cut from the surface of the hot rolled sheet,
It can be seen that the 0} <001> oriented grains are developed in the sample cut out from the central portion.

Therefore, the {110} <uuw> oriented grains that cause a decrease in the magnetic flux density can be suppressed by removing the surface portion of the hot rolled sheet.

Fig. 4 shows the relationship between the amount removed by a grinder from the surface of the hot-rolled sheet and the magnetic flux density (B ₈ value) of the product. From this result, it can be seen that a grain-oriented electrical steel sheet having a high magnetic flux density can be manufactured by removing 1/10 or more, preferably 1/5 or more of the total thickness from the surface layer.

The magnetic properties saturate when the amount removed from the steel sheet surface layer is about 1/3 of the total thickness.

Next, an embodiment of the present invention will be described.

The components of the steel sheet in the present invention are Si: 0.8 to 6.7%, acid-soluble Al: 0.008 to 0.048%, N ≦ 0.010%, balance Fe and unavoidable impurities.

If Si exceeds 4.8%, cracking tends to occur during cold rolling. The upper limit is 6.7% that can be rolled by warm rolling. On the other hand, when the amount of Si is small, α → γ transformation occurs during finish annealing and destroys the crystal orientation. Therefore, the lower limit is 0.8%, which does not substantially affect the crystal orientation.

Oxidizing Al forms a nitride as AlN, (Al, Si) N, etc., and forms an inhibitor. The limiting range is 0.008 to 0.048%, preferably 0.018 to 0.036%, which increases the magnetic flux density of the product.

If N is contained in excess of 0.010%, vacancies in the steel sheet called blisters occur, so the upper limit is 0.010%.

In addition, an inhibitor constituent element such as Mn, S, Se, B, Bi, Nb, Sn, or Ti can be added.

The raw material composed of the above components is made into a hot-rolled sheet through a usual process. It is a feature of the present invention to remove at least 1/10 or more of the total thickness from both surfaces of the hot rolled sheet. The method of this removal is not particularly limited. Either method such as mechanical grinding with a grinder or chemical polishing with hydrochloric acid may be used.

Further, the step of removing this surface layer is not limited to the hot rolled sheet,
The effect is exhibited in any of the steps of annealing after hot rolling, cold rolling and after primary recrystallization annealing, but it is considered that the hot rolling step is preferable from the cost of removing the surface layer.

The hot rolled sheet is cold rolled immediately or after an annealing step. The above annealing is performed in the temperature range of 750 to 1200 ° C for 30 seconds to 3 seconds.
It is desirable to run for 0 minutes. This annealing is effective in increasing the magnetic flux density of the product, and it is advisable to decide whether or not to adopt it in consideration of the desired level of magnetic flux density and the cost.

The cold rolling process is basically the same as that disclosed in JP-B-35-2657 or JP-B-38-8213. In the present invention, cold rolling is performed in one direction at a reduction rate of 40 to 80%, and then cold rolling is performed at a reduction rate of 30 to 70% in a direction intersecting the direction. In particular, when cold rolling in a direction intersecting with the first cold rolling, according to the method disclosed in Japanese Patent Publication No. 62-45007, cold rolling can be carried out in the form of strip, which is economically effective. is there.

The material after cold rolling usually serves to remove C contained in steel, and if necessary, is subjected to primary recrystallization annealing in a wet atmosphere in a temperature range of 750 to 1000 ° C. for 30 seconds to 10 minutes.

The material thus obtained is coated with an annealing separating agent containing MgO as a main component, dried, and then subjected to finish annealing. Finish annealing is usually 900-120 for the purpose of secondary recrystallization and purification.
Annealed at a temperature of 0 ° C.

In particular, as shown in Japanese Patent Application No. 63-293645, secondary recrystallization and purification are separated, secondary recrystallization is performed in a temperature range of 950 to 1100 ° C, and then the temperature is raised to 1100 ° C or higher for purification. Is desirable to increase the magnetic flux density.

〔Example〕

Example 1. By weight%, C; 0.048%, Si; 3.40%, Mn; 0.14%, acid soluble Al; 0.023%, N; 0.0072%, the balance of 1.8 mm thick hot-rolled Fe and inevitable impurities Two types of samples, a sample (A) and a sample (B) without grinding, were prepared by grinding the steel plate from both sides by 1/4 of the total thickness with a grinder.
These samples were cross-rolled by subjecting them to 55% cold rolling in the same direction as hot rolling and then 55% in a direction intersecting the cold rolling direction. These cold-rolled sheets were subjected to primary recrystallization annealing at 810 ° C for 120 seconds, which also serves as decarburization. Then, after applying MgO as an annealing separator, the temperature was raised to 1025 ° C at a temperature rising rate of 15 ° C / hr in an atmosphere of N ₂ 25% + H ₂ 75%, and the temperature was maintained at 1025 ° C for 20 hours for the second time. The recrystallization was completed. Then at 1200 ℃ 20
Purification annealing was performed in an atmosphere of H ₂ 100% for a time. The magnetic properties of these products were as shown in Table 1.

Example 2 A hot rolled steel sheet similar to that of Example 1 was used as two types of samples, a sample (A) ground from both sides of the steel sheet by 1/4 of the total thickness by a grinder and a sample (B) without grinding. . These samples were annealed at 1070 ° C. for 2 minutes and then processed in the same steps as in Example 1.

The magnetic properties of these products were as shown in Table 2.

[Advantages of the Invention] As described above, the present invention is capable of industrially stably producing a bidirectional electrical steel sheet having a high magnetic flux density equal to or higher than that of the currently highest level unidirectional electrical steel sheet. Is enormous.

[Brief description of drawings]

FIG. 1 is a (200) pole figure showing the texture of the (a) surface layer and (b) center layer of the primary recrystallized sheet, and FIG. 2 shows the texture of the hot rolled sheet in the sheet thickness direction. FIG. 3 is a (200) pole figure showing the orientation distribution of the secondary recrystallization of the sample cut out from the respective parts of (a) the surface layer and (b) the central layer, and FIG. FIG. 3 is a diagram showing the relationship between the amount of reduction in thickness from the surface of the hot rolled sheet and the magnetic flux density of the product.

Claims (2)

[Claims] 1. Si: 0.8-6.7%, acid-soluble Al;
008 ~ 0.048%, N ≤ 0.010%, the hot rolled sheet consisting of balance Fe and unavoidable impurities is cold rolled at a reduction rate of 40 to 80%,
Further, cold rolling is performed at a reduction rate of 30 to 70% in a direction intersecting with the cold rolling, then after primary recrystallization annealing, an annealing separator is applied, and secondary annealing and finishing annealing for the purpose of purification are performed. A method for producing a bi-directional electrical steel sheet having a high magnetic flux density, which comprises removing the surface layer portion of the hot-rolled sheet from both sides in the thickness direction by 1/10 or more of the total thickness in the production method of the bi-directional electrical steel sheet. 2. Before cold rolling, the temperature is in the range of 750 to 1200 ° C.
The method according to claim 1, wherein annealing is performed for seconds to 30 minutes.