JPH0665724B2 - Manufacturing method of electrical steel sheet with excellent magnetic properties - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing an electromagnetic steel sheet used as a core material for electric equipment, that is, rotating machines and small static machines.

[Conventional technology]

Applications of electromagnetic steel sheets can be broadly divided into two categories: rotating machines and stationary machines. These two applications require magnetic properties suitable for each. That is, isotropic magnetic properties in the plate plane are desired for materials for rotating machines, and materials having a (100) in-plane non-oriented texture are suitable for this purpose. On the other hand, it is desired that the static material has good magnetic properties in the L direction and the C direction, and a material having a (110) [001] texture or a (100) [001] texture is suitable for this. Is. However, although high-performance transformers and large transformers use grain oriented electrical steel sheets with (110) [001] texture, non-oriented electrical steel sheets are widely used for other small stationary devices and rotating machines. It's just that. The non-oriented electrical steel sheet is a material having magnetic properties that are relatively easy to use for such applications, but it is not always said that the optimal steel sheet is supplied for each application. That is, it is not usual to create a steel sheet texture for each application.

As a conventional technique for producing a steel sheet having such a special texture, some methods described below are known. For example, as disclosed in JP-A-57-89455, a method of adding an appropriate amount of B to silicon-containing steel to mix <001> in the longitudinal direction of casting, or JP-A-59-169.
As disclosed in Japanese Patent No. 26, for example, when sudden solidification is carried out, the structure of the metal cooling moving body is set to {100} <001>, and a crystal structure epitaxially grown so as to match this structure is obtained. However, since all of them are methods of as-casting or after-annealing after casting, it is difficult to control the surface roughness, plate thickness accuracy and the like to a quality that is sufficiently satisfactory.

In addition, as a method of forming (100) in-plane non-oriented texture,
A number of methods have been proposed, such as JP-B-38-22703, which uses a continuous cast material as a starting material, or JP-A-56-3625, which uses a rapidly solidified ribbon as a starting material.

The method disclosed in Japanese Examined Patent Publication No. Sho 38-22703 uses (10
(100) in-plane non-oriented steel sheet by continuous casting of which the surface is parallel to the surface of the sheet or hot-rolled material, which is substantially cold rolled by 60 to 80% and annealed. However, while it requires a high level of technology to manufacture a thin continuous cast piece of about 2.5 mm to 12.7 mm, it has not been put to practical use due to poor productivity.

In recent years, however, technological development for producing thin strips by the rapid solidification method has been widely carried out, and various methods for producing electrical steel sheets have been proposed by taking advantage of the characteristics of the solidification structure. A method for producing an electromagnetic steel sheet by rapidly solidifying a molten silicon steel using the same, followed by rolling and annealing, is disclosed in, for example, JP-A-56-87627.
JP-A-59-96219 and the like. However, as is clear from the fact that in the former, rolling is a pretreatment for tertiary recrystallization, and in the latter, rolling is not an essential condition, rolling is merely a means for obtaining the final thickness. It has only one meaning. Further, in all of these proposed techniques, a so-called tertiary recrystallization phenomenon in which a difference in surface energy is used as a driving force for crystal grain growth is utilized, and annealing in vacuum is an essential condition.

[Problems to be solved by the invention]

Using a rapidly solidified material, it is possible to anneal in a normal atmospheric pressure non-oxidizing, non-carburizing atmosphere, which makes industrial production easy and inexpensive, without relying on tertiary recrystallization which requires vacuum annealing, and rolling. By providing an extremely simple operation of controlling the rate, it is possible to provide a method of separately manufacturing magnetic steel sheets for stationary machines and rotating machines, which was difficult with the conventional method, and as a result, as a steel sheet product of the rapidly solidified steel strip. It is to solve defects such as surface roughness, plate thickness accuracy, and flatness at the same time.

[Means for solving problems]

In order to solve the above-mentioned problems, the inventors of the present invention perform rolling on a rapidly solidified steel strip to ensure various properties that the product should have and to control the texture of the product at this time. As a result of many experiments to examine the conditions, we finally found a method that facilitates industrial production. In the normal rolling recrystallization process, the larger the so-called initial grain size before rolling, that is, the lower the grain boundary density in the steel sheet, the less the development of the (111) plane, which is disadvantageous to magnetism, in the texture after recrystallization. It is already well known that it is easy to obtain good magnetism, but in the present invention, this idea is applied to a rapidly solidified steel strip for the first time.

That is, in the present invention, molten steel containing Si: 2.0 to 7.0 wt% and the balance substantially consisting of Fe is rapidly solidified on the surfaces of two moving cooling bodies to form a continuous steel strip, and then rolled. In the manufacturing method of electrical steel sheet with excellent magnetic properties that is subjected to post-annealing, the average grain size of the rapidly solidified continuous steel strip is set to 0.05 mm or more, and then the continuous steel strip is rolled at a rolling rate of 50% or more. By controlling the rolling rate at that time, the texture of the product is controlled to use the (100) [001] type for stationary machines and the (100) [025] type for rotating machines. It is a method of manufacturing an electrical steel sheet that makes it possible to create a suitable texture for each.

The present invention will be described in detail below.

The steel composition contains Si: 2.0 to 7.0 wt% and the balance is substantially Fe. Si is 2% to avoid α-γ transformation
Is set as the lower limit, and even if the content exceeds 7%, improvement in magnetic properties cannot be expected so much, so this is set as the upper limit. Incidentally, in the present invention, as an additional element other than Si, in order to improve magnetic properties, mechanical strength, rust resistance, etc.,
It is also possible to contain Al, Ni, Mn, P, Cr, Cu, Mo, W, Co, B and the like.

As a result of studying rolling recrystallization in the above steel using a hot-rolled sheet by a normal process treatment, as the so-called initial grain size before rolling becomes larger, the texture after recrystallization becomes (10
0) confirms that the direction component parallel to the plate surface increases,
Based on this finding, we tried to increase the average grain size of the rapidly solidified continuous steel strip.If the average grain size of the rapidly solidified continuous steel strip was 0.05 mm or more, this was rolled and recrystallized. It was newly found that the orientation component of (100) parallel to the plate surface increases in the obtained texture. Therefore, in the present invention, the lower limit of the average grain size of the rapidly solidified continuous steel strip is set to 0.05 mm. Next, a specific method for obtaining a rapidly solidified steel strip having an average crystal grain size of 0.05 mm or more will be described.

When the molten steel is rapidly solidified on two moving and renewing cooling body surfaces such as a twin roll casting machine to form a continuous steel strip,
When the initial set value of the gap formed by the two cooling bodies is Go, set the casting speed so that the plate thickness t of the obtained continuous steel strip is 1.05 times or more than Go and And that it is possible to increase the average grain size of the continuous steel strip by the two points of controlling the cooling of the continuous steel strip after the contact with the cooling body used for rapid solidification disappears. I found it.

When rapidly solidifying to form a continuous steel strip, while maintaining other casting conditions constant, the casting speed, that is, in the case of twin roll casting, as the roll peripheral speed is decreased, The plate thickness gradually increases. This means that with the development of the solidification shell of the steel strip that is being formed during rapid solidification, the gap formed by the two cooling bodies that are moving and renewing is wider than the initially set gap. ing. Conversely, it is considered that the steel strip which is solidifying as the casting speed is slowed is in a state of being subjected to a larger stress through the two cooling body surfaces. The magnitude of the stress received by the steel strip at this time can be estimated by the ratio of the steel strip plate thickness t to the initially set gap Go. As a result of various experiments, it was newly found that it is necessary to satisfy the condition of t / Go1.05 together with the control of the cooling conditions described below in order to make the average grain size of the steel strip 0.05 mm or more. . Next, the cooling conditions for the continuous steel strip obtained by rapid solidification will be described.

The average grain size obtained by investigating the average grain size obtained by changing the various conditions for cooling the continuous steel strip after the contact between the continuous steel strip and the cooling body used for rapid solidification is lost, It has been found that a continuous steel strip having an average grain size of 0.05 mm or more can be obtained by setting the G value defined in the above to 2.02 × 10 ⁴ or more.

Therefore, to set the average grain size of the rapidly solidified continuous steel strip to 0.05 mm or more, the initial set value Go (mm) of the two cooling body surface gaps (narrowest portions) that are moved and updated is the thickness of the rapidly solidified continuous steel strip. When the length is t (mm), t / Go is limited to 1.05 or more, and the G value defined in claim 1 is limited to 2.02 × 10 ⁴ or more.

Ts is based on the solidification temperature known from the equilibrium diagram.

However, the change according to the Si content is according to the following formula.

Ts = (solid phase temperature of Fe-C phase diagram) -20.5 [% Si] -6.5 [% Mn] -2 [% Cr] -11.5 [% Ni] -5.5 [% Al] -500 [% P]- 700 [% S] If there was a scale on the surface of the steel strip thus obtained, it was removed and then cold-rolled or warm-rolled. In addition, in order to improve the cold rolling property of high Si steel of 3.5% or more, the technology of adding Al, Mn, Ni, etc. is Kenji Narita et al. "Recent Progress of Silicon Steel Sheets" , No. 1, 1979, P.8), but it is of course possible to apply this to the present invention. The cold-rolled sheet thus obtained was annealed at 700-1300 ° C for 15 seconds to 30 minutes in a non-oxidizing, non-carburizing atmosphere at atmospheric pressure. At this time, when the cold rolling reduction ratio was changed in the range of 10 to 85%, the magnetic properties after annealing showed interesting behavior. That is, as the rolling ratio is increased from 10% to 70%, the magnetic flux density in the L direction and the C direction both increase. However, when the rolling ratio is further increased to 85%, the magnetic flux density is also increased in the L direction and the C direction. It was newly found that both will decrease. This situation is shown in FIG.

As a result of investigating the texture, it was found that the change in the magnetic flux density due to the rolling ratio was due to the following change in texture. That is, when the rolling ratio is less than 50%, the degree of integration of the (100) plane is relatively weak and the directionality within the plate surface is close to random, but when the rolling ratio is 50 to 75%, ,
The degree of integration of the (100) plane is increasing, and moreover, the (100) [001] vicinity orientation is mainly used. If the rolling rate is further increased to 80%, (100) [013] near orientation, and to 85% (10
0) [025] It was confirmed that the azimuths in the vicinity were the main components. The (100) [025] texture is such that the [100] axes are evenly distributed at intervals of about 45 ° in the plate surface.

The magnetic properties of the thus obtained product with a plate thickness of 0.5 mm are compared with those of non-oriented electrical steel sheets currently on the market.
As shown in the figure.

As is apparent from FIG. 1, the present invention is
It is an object of the present invention to provide a method for extremely easily manufacturing a magnetic steel sheet having markedly improved magnetic flux density and iron loss.

Examples of the present invention will be shown below.

[Example 1] Molten steel (Ts = 3.0%) containing Si: 3.0% and the balance being substantially Fe composition
(1475 ℃) is rapidly solidified by the twin roll method to form a continuous steel strip, the initial Go of the roll gap is set to 0.50 mm, and the plate thickness of the continuous steel strip obtained by changing the roll peripheral speed and its average crystal The particle size was measured. The results are shown in Table 1. still,
The cooling time in the table means the time required to cool the steel strip to 800 ° C after leaving the roll.

The continuous steel strip No. 11 thus obtained is pickled and the rolling rate is 23 to 85%.
Cold rolled.

The obtained cold-rolled sheet was annealed at 1100 ° C for 30 minutes with H ₂ 20% and Ar80.
% Atmospheric pressure atmosphere. The magnetic flux densities in the L direction and the C direction of the thus obtained annealed sheets with different rolling ratios are shown in Table 2 and Table 2.
Shown in the figure.

By rolling 50% to 75%, it was possible to obtain a product having a higher magnetic flux density in both the L and C directions than in the case of rolling less than 50%.

If the rolling ratio increases above 75%, the texture of the annealed sheet changes from (100) [001] type to (100) [013] type and further to (100) [025] type, so the L direction , The characteristic difference in the C direction becomes smaller. The torque curve is shown in Fig. 3. The peak value is maximum when the rolling ratio is 70%, and decreases to when the rolling ratio is 80%.

The (200) pole figure after annealing at the rolling ratios of 70% and 80% is shown in FIGS. 4 and 5.

[Example 2] Molten steel (Ts = 2.0) containing Si: 2.0% and the balance being substantially Fe composition
(1496 ℃) was rapidly solidified by the twin roll method to form a continuous steel strip with a roll gap initial setting Go of 0.7 mm and a roll peripheral speed of 12 m / min, and a continuous steel strip with a plate thickness of 1.7 mm. .
At this time, the continuous steel strip was cooled by air, and the cooling time was 10 seconds.
The G value was 2.196 × 10 ⁴ . The average grain size of the continuous steel strip thus obtained was 0.25 mm.

Then, after pickling, cold rolling with a rolling rate of 59,71,75% was performed.
Cold rolled sheets of 0.70 mm, 0.50 mm, 0,35 mm were obtained. Then, annealing was performed at 1100 ° C for 30 minutes in an atmosphere of H ₂ 20% and Ar 80% at atmospheric pressure. The magnetic properties obtained are shown in Table 3.

[Example 3] Molten steel (Ts = 6.5%) containing Si: 6.5% and the balance being substantially Fe composition
(1404 ℃) is rapidly solidified by the twin roll method to form a continuous steel strip, the initial setting Go of the roll gap is set to 0.30 mm, and the continuous steel strip obtained by changing the roll peripheral speed and the initial setting Go of the roll gap are set. 0.45 mm, roll peripheral speed 50 m / min, plate thickness approx.
Table 4 shows the average grain sizes of the respective 7 mm continuous steel strips. In the case of No. 34, the average grain size obtained did not reach 0.05 mm because both t / Go and G value were small.

After pickling the No. 57 continuous steel strip, it was warm-rolled at a rolling rate of 50% to 0.35 mm, and then annealed at 1100 ° C for 30 minutes for H ₂
It was applied in an atmosphere of 20% and 80% Ar. The magnetic properties thus obtained are shown in Table 5.

[Effect of the invention] The average grain size of the rapidly solidified steel strip is increased and the rolling ratio is increased.
By rolling at 50% or more and annealing, it became possible to manufacture magnetic steel sheets with excellent magnetic properties as well as excellent surface quality and plate thickness accuracy. In addition, by controlling the rolling rate, it has become possible to easily make electromagnetic steel sheets that are close to bidirectional and electromagnetic steel sheets that are close to in-plane non-oriented from the same material.

[Brief description of drawings]

FIG. 1 shows the magnetic properties obtained by the method of the present invention in comparison with those of non-oriented electrical steel sheets currently on the market, and FIG. 2 shows the change in magnetic flux density depending on the rolling ratio of cold rolling. Fig. 3 is a diagram showing the state, Fig. 3 is a diagram showing the change of the torque curve depending on the rolling rate of cold rolling, and Fig. 4 is obtained when the rolling rate is 70% (100) [0
The (200) pole figure showing the texture of the [01] type, and Fig. 5 were obtained when the rolling rate was 85% (100) [0
25] is a (200) pole figure showing the texture of type [25].

Claims (1)

[Claims] 1. A molten steel comprising Si: 2.0 to 7.0% by weight and the balance being substantially Fe is rapidly solidified on the surfaces of two moving and renewing cooling bodies to form a continuous strip. By controlling the speed so that the thickness of the continuous strip becomes 1.05 times or more of the initial setting value of the two cooling body surface gaps (the narrowest part), the continuous strip is made into the two cooling body surfaces. The cooling of the continuous strip from the time when the continuous strip was separated from was made so that the G value defined by the following formula was 2.02 × 10 ⁴ or more, and the average grain size of the continuous strip was 0.05 mm or more. A method for producing an electromagnetic steel sheet having excellent magnetic properties, which comprises rolling within a range of 50% or more and controlling a rolling ratio at this time to control a crystal orientation after annealing. Here, T: time required for the temperature to cool to 800 ° C. from the time when the continuous strip is separated from the two cooling body surfaces [h
r] Ts: Solidification temperature of molten steel (in the present invention) [° C]