JPH09118921A - Manufacture of grain-oriented magnetic steel sheet having extremely low iron loss - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a grain-oriented magnetic steel sheet having extremely low iron loss since Si is contained, the degree of integration of the azimuth of (110) and [001] of a grain is higher and the grain diameter is is smaller. SOLUTION: In this manufacturing method of the grain-oriented magnetic steel sheet by which a strip, which is rolled to the thickness of the final products, consisting of, by weight, <=0.10% C, 2.5-7.0% Si, 0.02-0.15% Mn, 0.001-0.050% S, 0.010-0.040% acid-sol. Al, 0.0030-0.0200% N as an essential component and the balance Fe with inevitable impurities, is annealed for decarburization and the final finish annealing is executed, in heating process of the decarburization annealing, the strip is heated at a heating rate of >=80 deg.C/sec from a temp. range between the normal temp. and <=600 deg.C to the temp. range of at least 750 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to 2.5 to 7.0%.
And a high degree of integration of (110) [001] orientation of crystal grains and having a fine secondary recrystallized grain size, the present invention relates to a method for producing a grain-oriented electrical steel sheet having extremely low iron loss. It is a thing.

[0002]

2. Description of the Related Art Generally, the magnetic properties of a grain-oriented electrical steel sheet are evaluated based on both iron loss properties and excitation properties. Increasing the excitation characteristics is effective in reducing the size of equipment that increases the design magnetic flux density. On the other hand, reducing the iron loss characteristics is effective in that when it is used as an electric device, heat loss is reduced and power consumption can be saved. further,
Aligning the <100> axes of the crystal grains of the product in the rolling direction can improve the magnetization characteristics and lower the iron loss characteristics.
In recent years, many studies have been made particularly on this aspect, and various manufacturing techniques have been developed.

As a result, there are three typical manufacturing techniques for the typical industrially produced grain-oriented electrical steel sheet. The first technology is Japanese Examined Japanese Patent Publication 30-3651.
There is a manufacturing technique disclosed in Japanese Patent Application Laid-Open No. 2010-2004 that causes MnS to function as an inhibitor by a two-time cold rolling process. This manufacturing method has a relatively good iron loss due to a small particle size of the secondary recrystallization, but has a problem that a high magnetic flux density cannot be obtained.

On the other hand, in order to obtain a high magnetic flux density, there is an invention disclosed in Japanese Patent Publication No. 40-15644 as a second technique. This is a manufacturing technique in which AlN + MnS is made to function as an inhibitor and the rolling reduction in the final cold rolling step is under high pressure exceeding 80%. By this method, a grain-oriented electrical steel sheet having a high degree of integration of the (110) [001] orientation of secondary recrystallized grains and a high magnetic flux density of B ₈ of 1.870 (T) or more can be obtained.

A third technique is disclosed in Japanese Patent Publication No.
MnS or MnS disclosed in Japanese Patent No. 3469
A manufacturing technique has been developed in which e + Sb functions as an inhibitor by a double cold rolling process. However, in the manufacturing methods according to the second and third techniques, even if the grain-oriented electrical steel sheet having a high magnetic flux density is obtained, the secondary recrystallized grain size is 1 or less.
Only the big thing of 0mm order was obtained.

In general, iron loss is roughly divided into hysteresis loss and eddy current loss. Physical factors that affect the hysteresis loss include the purity of the material and internal strain in addition to the above-described crystal orientation. In addition, as physical factors that affect the eddy current loss, electrical resistance of the steel sheet (amount of components such as Si), sheet thickness,
The magnetic domain width (grain size) and the tension exerted on the steel sheet are included. In ordinary grain-oriented electrical steel, eddy current loss is 3 of total iron loss.
Since it occupies / 4 or more, lowering the eddy current loss than the hysteresis loss is more effective in reducing the total iron loss.

Therefore, in the manufacturing methods according to the second and third techniques, the secondary recrystallized grains are obtained even if the grain-oriented electrical steel sheet having a high magnetic flux density of B ₈ of 1.870 (T) or more is obtained. Since the diameter becomes large on the order of 10 mm, the magnetic domain width that affects the eddy current loss is large, and it is necessary to further improve the iron loss. In order to improve this, Japanese Patent Publication No. 57-22
Various methods for subdividing magnetic domains are disclosed, such as a method of subjecting a steel sheet disclosed in Japanese Patent Publication No. 52-52 to laser treatment, and a method of applying mechanical strain to the steel sheet disclosed in Japanese Patent Publication No. 58-2569. Has been done.

On the other hand, as a method for producing a grain-oriented electrical steel sheet having a finer secondary recrystallized grain size, which has a lower iron loss than before, as disclosed in, for example, JP-A 1-290716. In the publication, a cold rolled steel sheet is subjected to a super rapid annealing treatment at a heating rate of 100 ° C./sec or more to a temperature of 675 ° C. or higher, the strip is decarbonized, and a final high temperature annealing treatment is applied to carry out secondary growth. Done,
A method is thereby disclosed characterized in that said strips have secondary particles of reduced size and improved iron loss which persists without significant changes after stress relief annealing.

However, although this method surely produces small secondary recrystallized grains, in the rapid heat treatment, it is possible to obtain about 7 to about 675 ° C. or higher temperature from normal temperature low temperature range.
It is necessary to rapidly heat the temperature range of 00 ° C or higher. Therefore, in order to realize this, it is essential to make large facility modifications such as resistance electric heating and induction heating of decarburization annealing equipment, and there were many restrictions due to hardware aspects, such as insulation of conventional equipment, measures against leakage, It was necessary to take measures against interference waves due to higher frequencies.

[0010]

In the conventional method for producing a grain-oriented electrical steel sheet by the rapid heating method, the temperature range for rapid heating is wide, and there are many restrictions on equipment. The present invention
In order to solve such inconvenience, the present invention provides a manufacturing method in which the temperature range for rapid heating is reduced as much as possible.

[0011]

In the present invention, as a result of repeated studies to solve the above-mentioned problems, C: 0.10 by weight.
% Or less, Si: 2.5 to 7.0%, Mn:
0.02-0.15%, S: 0.001-0.
050%, acid-soluble Al: 0.010 to 0.040%,
N: 0.0030 to 0.0200% as a basic component,
In the method for producing a unidirectional electrical steel sheet in which the balance consists of Fe and unavoidable impurities, decarburization annealing is performed on the strip rolled to the final product thickness, and final finishing annealing is performed. A unidirectional electrical steel sheet having an extremely low iron loss can be obtained by heating the temperature range from ℃ or less to at least 750 ℃ at a heating rate of 80 ℃ / sec or more. I found it.

The present invention will be described in detail below. The grain-oriented electrical steel sheet can be manufactured by sufficiently causing secondary recrystallization during the final annealing in the manufacturing process to obtain a so-called Goss texture. In order to obtain this Goss texture, growth coarsening of primary recrystallized grains is suppressed, and only recrystallized grains of (110) <001> orientation are selectively grown in a certain temperature range.
That is, it is necessary to make a base material for secondary recrystallization. For that purpose, fine inclusions are uniformly dispersed in the material as an inhibitor (growth inhibitor) for the growth of primary recrystallized grains to enhance the grain growth suppression effect, and at the same time, the primary recrystallized texture before finish annealing is appropriately adjusted. It is important to.

Generally, when a cold-rolled sheet is heated to form a primary recrystallization texture, there are processes of recovery, nucleation, recrystallization and grain growth. Of these, especially in the nucleation and recrystallization process, there is a change in the texture after the primary recrystallization, depending on whether the nucleation occurs from inside the crystal grain or the nucleation from the grain boundary. The present inventors have found out. That is, like the present invention, in the temperature range of nucleation and recrystallization process which is a heating step rather than recovery, rapid heating causes nucleation in grain boundaries and grains, a difference in priority of recrystallization, (110) <0 compared with normal heating method with primary recrystallization texture
It was found that the 01> oriented grains increased. This allows
The nuclei of the subsequent secondary recrystallization are increased, and small secondary recrystallized grains are obtained.

On the other hand, the present inventors have found that the heating rate for recovery does not affect the change of primary recrystallization texture at all. FIG. 1 shows the change in hardness due to rapid heating. The recovery from the hardness change is completed up to about 600 ° C, and the nucleation and recrystallization processes are completed up to 750 ° C.

As a result of repeated detailed investigations as described above, 600 ° C. which is a nucleation and recrystallization process in the heating process of decarburization annealing.
To (750) to 750 ° C. at a heating rate of 80 ° C./sec or more to obtain (110) <001>.
It was found that the number of oriented grains increased, a fine secondary recrystallized grain size was obtained, and it became possible to obtain a grain-oriented electrical steel sheet having extremely low iron loss.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Next, in the present invention, the reason why the steel composition and manufacturing conditions are limited as described above will be explained in detail. The reasons for limiting the steel components are as follows. C
The upper limit of 0.10% is limited because the decarburization time becomes longer and the economical disadvantage becomes higher. The lower limit of Si is set to 2.5% in order to improve iron loss, but if it is too large, it is likely to break during cold rolling and processing becomes difficult, so the upper limit is set to 7.0%.

Further, in order to manufacture the grain-oriented electrical steel sheet, the following component elements are added as usual inhibitor components. When using MnS as an inhibitor,
Add Mn and S. Mn is limited to 0.02 to 0.15% in order to obtain an appropriate dispersed state of MnS. S is M
It is an element necessary for forming nS, (Mn.Fe) S, and is 0.001 to 0.05 in order to obtain an appropriate dispersed state.
%.

Further, since AlN is used as an inhibitor, acid-soluble Al and N are added. Acid soluble A
1, 0.01 to 0.
Limited to 04%. N is also limited to 0.003 to 0.02% in order to obtain a proper dispersed state of AlN. Other, C
At least one of u, Sn, Sb, Cr and Bi may be added in an amount of 1.0% or less for the purpose of strengthening the inhibitor.

Next, the above molten steel is subjected to a conventional ingot casting method or continuous casting method and hot rolling to obtain a strip having an intermediate thickness. At this time, the strip casting method can also be applied to the present invention. Furthermore, since a nitride is required as an inhibitor, it is desirable to perform intermediate annealing of the strip at 950 to 1200 ° C. for 30 seconds to 30 minutes for the precipitation of AlN or the like. Next, 1 to 2 including intermediate annealing
The final product thickness strip is obtained by rolling more than once. The final rolling reduction at this time is preferably 60% or more in order to obtain a product having a high degree of Goss accumulation. The lower limit of 60% is because the required Goss nucleus cannot be obtained below this.

Thus, the strip rolled to the final product thickness is subjected to decarburization annealing. In this heating process, above normal temperature,
From the temperature range of 600 ° C. or lower to the temperature range of at least 750 ° C., heat treatment is performed at a heating rate of 80 ° C./sec or more, and then decarburization annealing is performed in a wet hydrogen atmosphere. The upper limit of the temperature range of 600 ° C. at this time is only recovery in the process of forming the primary recrystallized texture below this,
Limited because nucleation and recrystallization do not start. Further, the lower limit of 750 ° C. in the temperature range is limited because nucleation and recrystallization in the formation process of the primary recrystallization texture are completed when the lower limit is exceeded. Further, in the temperature range of 750 ° C. or higher, the primary recrystallized grains are coarsened and the grains are grown.
The temperature was set to 0 ° C. or higher. Furthermore, the lower limit of heating rate of 80 ° C / sec is
Below this value, it is difficult to promote the nucleation of (110) <001> oriented grains and the progress of recrystallization. By performing the above heat treatment, the number of (110) <001> oriented grains after the primary recrystallization, which is the nucleus of the secondary recrystallization, increases, and fine secondary recrystallized grains are obtained.

In the present invention, the above-mentioned 600 ° C. to 75 ° C.
In the temperature range other than the temperature range of 0 ° C., the heating rate has no influence on the magnetic properties. Therefore, there is no problem even if the conventional heating method of about 20 ° C./sec is used in the low temperature region of 600 ° C. or lower and the high temperature region of 750 ° C. or higher.

The above-mentioned heat treatment is carried out, for example, at the end of the heating zone of the conventional decarburization annealing equipment, from the temperature range above room temperature to 600 ° C. to a minimum of 150 ° C.
A device for rapidly heating the temperature range of ° C may be provided. For example, the above temperature range may be heated by plasma heating, a high-output white arc lamp, or the like.

In the strips decarburized and annealed in the wet hydrogen atmosphere as described above, the carbon content must be reduced to 0.005% or less in order not to deteriorate the magnetic properties of the product. Furthermore, if the slab heating temperature in hot rolling is low,
Nitriding treatment may be added in an ammonia atmosphere.
Next, an annealing separator such as MgO is applied, and finish annealing is performed at 1100 ° C. or higher for secondary recrystallization and purification, thereby producing a unidirectional electrical steel sheet having extremely low iron loss characteristics. In order to further improve the iron loss of the obtained product, it is possible to subject the above-mentioned grain-oriented electrical steel sheet to a treatment for subdividing magnetic domains.

[0024]

Next, an embodiment of the present invention will be described. (Example 1) A strip containing the composition shown in Table 1 and finally cold rolled to a thickness of 0.27 mm was heat-treated to 840 ° C. In this heating process, the temperature range shown in Table 2 was set to 8
Rapidly heats at 5 ° C / sec and 20 at other temperature ranges
It was heated at a heating rate of ° C / sec. However, only the condition I was heated in the entire temperature range at a heating rate of 20 ° C./sec. The strip was subsequently decarburized annealed in wet hydrogen at a uniform temperature of 840 ° C. for 180 seconds. Then, after applying MgO powder,
High temperature annealing was performed at 00 ° C. for 10 hours in a hydrogen gas atmosphere.

Table 2 shows the magnetic properties of the obtained products. The magnetic properties of the product are as follows:
At least 750 from room temperature above 600 ℃
By rapidly heating a temperature range of ℃ or more, a grain-oriented electrical steel sheet having an extremely low iron loss almost equal to that of the conventional rapid heat treatment has been obtained.

[0026]

[Table 1]

[0027]

[Table 2]

(Example 2) A molten steel containing the chemical composition shown in Table 3 was cast, heated to a slab, and hot-rolled to 2.3 mm.
Was obtained. This was annealed at 1100 ° C. for 5 minutes, further pickled, and then cold rolled to a thickness of 0.23 mm. The rolled steel sheet is heated to 580 ° C by normal gas heating, and the temperature from 580 ° C to 780 ° C is 250 ° C /
It was heated by plasma heating at a heating rate of 2 seconds. As a comparative example, the rolled steel sheet was heated from room temperature of 25 ° C. to 745 ° C. at a heating rate of 220 ° C./sec by an electric induction heating device.

After being heated, the strip was subsequently decarburized and annealed in wet hydrogen at a uniform temperature of 840 ° C. for 180 seconds. Next, after applying MgO powder, high-temperature annealing was performed at 1200 ° C. for 10 hours in a hydrogen gas atmosphere.

The characteristics of the product thus obtained are as follows: B ₈ = 1.93T when the product subjected to the rapid heat treatment in the temperature range of 580 ° C. to 780 ° C. in the heating process of decarburization annealing,
_{W 17/50 = 0.81 (W} / kg), that of the heat treatment of Comparative Example _{B 8 = 1.94T, W 17/} 50 = 0.80 (W / kg)
Met. In the heating process of decarburization annealing, the temperature exceeds room temperature, 60
By rapidly heating the temperature range from 0 ° C. or lower to at least 750 ° C. or higher, a grain-oriented electrical steel sheet having an extremely low iron loss almost equal to that of the conventional heat treatment was obtained.

[0031]

[Table 3]

[0032]

According to the present invention, by rapidly heat-treating only a specific temperature range in the heating process of decarburization annealing, a high magnetic flux density and a fine secondary recrystallized grain size are obtained. Since it is possible to manufacture a grain-oriented electrical steel sheet having extremely low iron loss characteristics, the industrial contribution is extremely large.

[Brief description of the drawings]

FIG. 1 shows a change in hardness of a cold rolled sheet depending on heating temperature.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location H01F 1/16 H01F 1/16 B (72) Inventor Ryutaro Chikuma Fujimachi, Hirohata-ku, Himeji City, Hyogo Prefecture No. 1 Shin Nippon Steel Co., Ltd. Hirohata Works (72) Inventor Tadao Kiriyama No. 1 Fuji-machi, Hirohata-ku, Himeji City, Hyogo Prefecture Shin Nippon Steel Co., Ltd. Hirohata Works

Claims (1)

[Claims] 1. By weight, C: 0.10% or less, Si: 2.5 to 7.0%, Mn: 0.02 to 0.15%, S: 0.001 to 0.050%, acid Soluble Al: 0.010 to 0.040%, N: 0.0030 to 0.0200% as a basic component, and the balance consisting of Fe and inevitable impurities. In the manufacturing method of the unidirectional electrical steel sheet for final finish annealing, in the heating process of decarburizing annealing, a temperature range from room temperature over 600 ° C. to at least 750 ° C.
A method for producing a grain-oriented electrical steel sheet having extremely low iron loss, which comprises heating at a heating rate of 80 ° C./second or more.