JPH11323436A - Production of silicon steel sheet excellent in magnetic property - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a silicon steel sheet in which both of low core loss and high magnetic flux density are satisfied, and the reduction of the cost by the simplification of the producing process is attained by attaining the optimizing of compositional components in a steel slab and executing hot finish rolling under optimum conditions. SOLUTION: A steel slab having a compsn. contg., by weight, <=0.005% C, >1 to 4% Si, <=1.5% Mn, <=0.35% P, <=0.010% S, <=2.0% Al, <=0.01% N and <=0.01% O is cast, or is furthermore reheated and is thereafter subjected to hot rough rolling to form a steel structure in which the volume fractional rate of recrystallized ferritic grains with <=100 μm grain size is <=20%, directly after that, finish rolling is executed under the conditions in which the rolling temp. is controlled to the temp. region from less than the Ar1 transformation point to >=500 deg.C as for the steel having a compsn. to cause eutectoid transformation and to the temp. region of <=1100 deg.C to >=500 deg.C as for the steel having a compsn. causing no eutectoid transformation, and the draft is controlled to at least 30%, subsequently, the steel is as it is or is furthermore subjected to annealing and is thereafter pickled, and subsequently, ordinary cold rolling and annealing are executed in succession.

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 magnetic steel sheet having a low iron loss and a high magnetic flux density and having excellent magnetic properties.

[0002]

2. Description of the Related Art In a conventional magnetic steel sheet, in order to reduce iron loss, it is necessary to increase the amount of addition of Si, Al, etc., which are known as components having the effect of increasing the specific resistance and reducing the eddy current loss. The method is widely used.

However, when these alloy components are added to reduce iron loss, the saturation magnetic flux density is reduced. Therefore, it is difficult to satisfy both low iron loss and high magnetic flux density by the above method.

As a method for improving iron loss without adding these alloy components, for example, several percents
After performing skin pass rolling of the above and punching work by a user, there is a method of performing strain relief annealing.

However, in the conventional method, when the finishing hot rolling temperature is 800 ° C. or higher, and the winding temperature is low, and recrystallization is not sufficiently advanced, 75% or more after hot-rolled sheet annealing is performed. In addition to performing cold rolling and further performing high-temperature short-time annealing, it is necessary to further perform skin-pass rolling of several percent, so that the manufacturing process becomes complicated and there is a disadvantage of increasing the manufacturing cost.

A method for improving the magnetic characteristics without complicating the manufacturing process is disclosed in Japanese Patent Publication No. Hei 7-23509. According to the above publication, the amount of Si is 1
% Or less, and by rolling coarse ferrite grains in the hot rolling stage from hot rough rolling to hot finishing rolling,
It states that both iron loss and magnetic flux density can be improved.

However, in this method, since the Si content is as small as 1% or less, the iron loss can be sufficiently reduced even when the above-described production conditions for rolling coarse ferrite grains in the hot rolling step are applied. Cannot be performed, and the production conditions are set to a Si content of 1
It has been clarified by the inventors of the present invention that a sufficient effect of improving the magnetic properties cannot be obtained even when applied to steels exceeding 0.1%. Therefore, the magnetic steel sheet manufactured by this method cannot satisfy the low iron loss required for the current global environment and energy environment.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to control the content of alloying elements, particularly Si elements, in a range of more than 1% to 4% and to perform hot finish rolling under appropriate conditions. Another object of the present invention is to provide a method of manufacturing an electromagnetic steel sheet that satisfies both low iron loss and high magnetic flux density and that can reduce costs by simplifying the manufacturing process.

[0009]

In order to achieve the above-mentioned object, the present invention relates to a method for producing a semiconductor device comprising:
Over 4%, Mn: 1.5% or less, P: 0.35% or less, S:
0.010% or less, Al: 2.0% or less, N: 0.01% or less, O:
After casting a steel slab with a composition containing 0.01% or less,
Or, after further reheating, hot rough rolling is performed to obtain a steel structure shown in the following (1), and then immediately finish rolling is performed under the conditions shown in the following (2), and then the steel structure is left as it is or after further annealing. An object of the present invention is to provide a method for producing an electrical steel sheet having excellent magnetic properties, characterized by sequentially performing ordinary cold rolling and annealing after washing.

(1) The volume fraction of recrystallized ferrite grains having a grain size of 100 μm or less is 20% or less. (2) The rolling temperature is set to a temperature range of 500 ° C. or lower below the Ar ₁ transformation point for steel having a composition that causes eutectoid transformation, and 1100 ° C. or lower to 500 ° C. for steel having a composition that does not cause eutectoid transformation.
Temperature range above and rolling reduction at least 30%.

When it is necessary to effectively promote the diameter growth of ferrite grains and increase the size of ferrite recrystallized grains before finish rolling to further improve the magnetic properties, the C content in the steel slab is required. The P content is preferably 0.002% or less, and when it is necessary to further improve the magnetic properties, the P content in the steel slab is preferably 0.02% or more and 0.20% or less. Reduce the C content in the slab to 0.
It is more preferable that the content of P is 002% or less and the P content is 0.02% or more and 0.20% or less.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, the reason for limiting the composition of the steel slab to the above range in the present invention will be described.

C: 0.005 wt% or less C content is preferably small from the viewpoint of improving iron loss.
0.005wt% to prevent magnetic deterioration due to aging
It is preferable to set the following. In addition, when using the process of the present invention, if the C content is more than 0.005 wt%, the recrystallized ferrite grains before the finish rolling become finer, and the volume fraction of the recrystallized ferrite grains having a grain size of 100 μm or less is reduced. 20% rate
Since the magnetic properties deteriorate beyond
The upper limit of the C content was set to 0.005 wt%. In particular, the C content
At 0.002 wt% or less, the growth of ferrite grains is dramatically improved, the ferrite recrystallized grain size immediately before finish rolling becomes coarse, and the magnetic properties of the product sheet are greatly improved. More preferably, it is not more than wt%.

Si: More than 1 wt% and not more than 4 wt% Si is added for the purpose of improving iron loss. If the Si content is 1 wt% or less, the effect of improving the iron loss by adding Si is small.
Since the effect of improving iron loss by the manufacturing process of the present invention cannot be sufficiently obtained, the lower limit of the Si content is set to 1 wt%. Also,
When the Si content exceeds 4 wt%, the magnetic flux density is considerably reduced by the addition of Si. Therefore, even if the magnetic flux density is increased by the manufacturing method of the present invention, the superior difference with respect to the magnetic flux density when manufactured by the conventional method is remarkable. Therefore, the upper limit of the Si content was set to 4%.

[0015] Mn: 1.5 wt% or less Mn is an effect on the magnetic improvement exceeds 1.5 wt% Ar ₁
Since the transformation point is lowered, the ferrite-austenite transformation is likely to occur at the time of annealing, and magnetic deterioration is recognized, the upper limit of the Mn content is set to 1.5 wt%.

P: 0.35% by weight or less P has an effect of improving iron loss, but if it exceeds 0.35% by weight, workability is deteriorated, and hot rolling cracking and punching property may be deteriorated. The upper limit of the P content was 0.35 wt%. Incidentally, by adding P, the volume fraction of fine ferrite recrystallized grains existing in the steel structure immediately before the finish rolling is reduced, and the magnetic properties are dramatically improved, but this effect is effectively exhibited. What can be done is that the P content is 0.02
Since the case of not less than 0.2 wt% and not more than 0.2 wt%, the P content is 0.1 wt%.
It is more preferable that the content be 02 wt% or more and 0.2 wt% or less.

S: not more than 0.010 wt% S is a component which is liable to bond to Mn and the like and is a cause of generating nonmetallic inclusions such as MnS which are harmful to the improvement of magnetism.
The upper limit of the S content was set to 0.010 wt%.

Al: 2.0 wt% or less Al may be added for the purpose of improving iron loss as in the case of Si.
If the addition amount is too large, the magnetic flux density decreases and the effect of the present invention is diminished. Therefore, the upper limit of the content is set to 2.0 wt%.

N and O: 0.01% by weight or less for both N and O When the content of both N and O increases, the recrystallized ferrite grains before finish rolling become finer and the volume of the recrystallized ferrite grains having a grain size of 100 μm or less. Since the magnetic properties deteriorate when the fraction exceeds 20%, the upper limit of their content is
0.01 wt%.

Further, the present inventors have proposed that a steel having a composition that causes eutectoid transformation of austenite-ferrite should be made of Ar.
_A detailed examination of the relationship between the grain size before rolling performed in the temperature range below the transformation point and the texture of the recrystallized texture after rolling and the texture of the product sheet revealed that the volume fraction of fine recrystallized grains was a certain value. By controlling the finish rolling temperature and the rolling reduction within a predetermined range, it is possible to manufacture a product sheet having a texture with a {100} <001> orientation which is considered to be preferable for magnetic properties and is strongly developed. Was found.

Conventionally, it has been reported that the orientation of recrystallized grains generated when rolling coarse grains is mainly in the {110} orientation. The effects of the grain volume fraction, the finish rolling temperature, and the rolling reduction on the recrystallization texture were examined in detail, and when the finish rolling of coarse grains was performed under a specific range of conditions, the main recrystallization texture was reduced. The orientation was found to be the {015} <100> orientation, which was then subjected to cold rolling and annealing to make the texture of the final product a {100} <001> orientation that is particularly advantageous for magnetic properties. It was found that the texture became the main orientation.

That is, the grain size distribution of the recrystallized ferrite grains present in the steel immediately before the finish rolling at or below the Ar ₁ transformation point has a great effect on the subsequent texture formation, and
It has been found that the magnetism of the final product is significantly improved by subjecting a structure having a volume fraction of recrystallized ferrite grains of 100 μm or less to a volume fraction of 20% or less to hot finish rolling at an appropriate rolling temperature and rolling reduction. It is.

[0023] Further, the above-mentioned production method also sets the volume fraction of fine recrystallized grains of the ferritic single phase steel having a composition that does not cause eutectoid transformation in the same range as the steel having a composition that causes eutectoid transformation. Also, it has been found that when the finish rolling temperature and the rolling reduction are within the predetermined ranges, the magnetism of the final product can be significantly improved as in the case of the steel having the composition causing the above-mentioned eutectoid transformation.

From the above findings, the production method of the present invention
A steel slab in which the content of each component is adjusted to the above range,
After casting, or after further reheating, perform hot rough rolling,
After the finish rolling, as it is, or after pickling after further annealing, it is to sequentially perform normal cold rolling and annealing, particularly, the component composition in the steel slab is limited to the above range. The main feature of the present invention is that after the steel slab has a predetermined steel structure immediately before finish rolling, finish rolling is performed under predetermined rolling conditions.

Here, “predetermined steel structure” means that the volume fraction of ferrite grains having a grain size of 100 μm or less present in the steel is 20% or less, and this volume fraction is Specifically, it is determined by measuring each crystal grain size using an optical microscope.

The “predetermined rolling conditions” specifically means that for steel having a composition that causes austenite-ferrite eutectoid transformation, the rolling temperature during finish rolling is defined as Ar
₍₁₎ A temperature range of 500 ° C. or lower below the transformation point, and 1100 ° C. or lower for steel having a composition that does not cause the eutectoid transformation.
It means that the temperature range is 0 ° C. or higher, and the rolling reduction in finish rolling is at least 30% in any steel.

Therefore, the steel structure immediately before the finish rolling, which is a feature of the present invention, and the reasons for limiting the rolling conditions during the finish rolling will be described below.

(I) Steel structure immediately before finish rolling: 100 μm
The volume fraction of ferrite grains with the following grain size is 20% or less The steel structure just before finish rolling is adjusted so that the volume fraction of ferrite grains with a grain size of 100 μm or less is 20% or less. The reason is that if recrystallized ferrite grains of 100 μm or less are present in the steel in a volume fraction of more than 20%, the magnetic properties of the magnetic steel sheet as a product are deteriorated.

The grain size existing in the steel immediately before the finish rolling is 100
As a means for reducing the volume fraction of the recrystallized ferrite grains of not more than 20 μm to 20% or less, for example, after hot rough rolling, the steel sheet may be held at an appropriate temperature and subjected to a recrystallization treatment. After cooling, it may be heated again at an appropriate temperature for recrystallization.

(II) Predetermined rolling conditions (a) Rolling temperature in finish rolling: For a steel having a composition that causes eutectoid transformation, a temperature range of 500 ° C. or lower below the Ar ₁ transformation point and a composition that does not cause eutectoid transformation. For steel having
Temperature range below 1100 ℃ and above 500 ℃

With respect to steel having a composition that causes eutectoid transformation, if the finish rolling temperature is higher than the Ar ₁ transformation point, fine ferrite grains increase to deteriorate the magnetic properties of the product. Since the ferrite grains are refined by the subsequent eutectoid transformation and the magnetic properties of the product are deteriorated by rolling the fine ferrite grains during the finish rolling, the upper limit of the finish rolling temperature is set to the Ar ₁ transformation point or lower.

On the other hand, for steel having a composition that does not cause eutectoid transformation, it is not particularly necessary to set the upper limit of the finish rolling temperature from the viewpoint of magnetic properties.
Even if the temperature is higher than 1100 ° C., only the production cost is increased, so the upper limit of the finish rolling temperature is set to 1100 ° C.

If the lower limit of the finish rolling temperature is less than 500 ° C. for any steel, the rolling load increases and the cost increases.
500 ° C.

(B) Reduction rate in finish rolling: at least
If the rolling reduction in the 30% finish rolling is less than 30%, coarse ferrite grains are not broken by rolling and grow by strain induction, so the texture before rolling is dragged, and the effect of improving magnetic properties according to the present invention is exhibited. Therefore, the lower limit of the rolling reduction in finish rolling was set to 30%.

According to the method of the present invention, even if the raw material is immediately sent to the cold rolling step after hot rolling, the iron loss characteristics are remarkably improved as compared with a case where a material of the same component is manufactured by a conventional process. However, when hot-rolled sheet annealing is performed on this, the improvement in iron loss characteristics appears more remarkably, and the magnetic flux density also increases.

The hot-rolled sheet rolled under the above manufacturing conditions is cold-rolled,
The magnetic steel sheet manufactured by annealing is compared with the conventional magnetic steel sheet manufactured by the method described in Japanese Patent Publication No. Hei 7-23509.
It has low iron loss and high magnetic flux density, and has excellent magnetic properties. In addition, it is possible to provide an electromagnetic steel sheet having low iron loss which is close to that obtained by performing skin pass rolling of several percent and performing strain relief annealing with a semi-process material.

The above is merely an example of the embodiment of the present invention, and various changes can be made within the scope of the claims. For example, in the present invention, in addition to the above configuration, it is possible to further perform skin pass rolling of 2 to 10% and use it as a semi-process material to perform strain relief annealing, thereby further improving magnetic flux density and iron loss. The effect can be expected.

[0038]

EXAMPLES Table 1 shows the chemical composition (%) in steel and the grain size immediately before hot finish rolling for the inventive examples and comparative examples.
Volume fraction (%) of recrystallized ferrite grains of 100 μm or less,
The production conditions of the rolling temperature (° C.) and the rolling reduction (%) in hot finish rolling, and the _Ar1 transformation point (° C.) are shown. For these materials, continuous cast slabs are reheated in the range of 1250 ° C to 1000 ° C, and then hot-rolled to a thickness of 2.5 mm by continuous hot rolling of rough rolling and finish rolling, followed by cold rolling. To a final thickness of 0.5 mm. The recrystallization treatment after the cold rolling was performed by continuous annealing at 800 to 900 ° C for 1 minute. The material annealed by hot rolling was subjected to continuous annealing at 700 to 1000 ° C for 10 minutes. About each test steel plate manufactured in this way,
L, measured C both iron loss W _15/50 and the magnetic flux density B _50, were evaluated the magnetic properties. Table 1 shows the evaluation results.

[0039]

[Table 1]

From the results in Table 1, all of the steel Nos.
The amount of Si is 1.17%, of which No. 1 which is an example of the present invention.
It can be seen that the steels of Nos. 4 and 6 to 8 have superior magnetic properties as compared with the steels of Nos. 5 and 9 to 11 which are comparative examples having the same Si content. In addition, N which is a comparative example
The steel of No. 5 has a rolling reduction in finish rolling lower than the proper range of the present invention, and No. 9 and No. 10 have a volume fraction of recrystallized ferrite grains having a grain size of 100 μm or less immediately before finish rolling. No. 11 has a finish rolling temperature of over 20%
It is the case where it is higher than the A _r1 transformation point.

The comparative examples No. 12 and No. 13 are as follows:
This is the case where the amount of Si is less than the proper range of the present invention.
No. 12 is a case where the manufacturing conditions of the present invention are applied to this steel slab, and No. 13 is a case where the conventional manufacturing conditions are applied.
Even if the production conditions of the present invention are applied to steel whose Si content is outside the appropriate range of the present invention (1 wt% or less), there is almost no difference in the effect of improving the magnetic properties as compared with the case where the conventional production conditions are applied. Therefore, it can be confirmed that the production conditions of the present invention show a remarkable effect of improving the magnetic properties only when applied to steel having a Si content of more than 1%.

The steels of Nos. 14 and 15 each have a Si content of 1.65%.
The steel of No. 15 which is a comparative example has a volume fraction of recrystallized ferrite grains having a grain size of 100 μm or less immediately before finish rolling exceeds the appropriate range of the present invention. Therefore, it can be confirmed that the steel of No. 14 has better magnetic properties than the steel of No. 15.

Nos. 16 to 20 are all ferritic single-phase steels, and Nos. 16 and 17 each have a Si content of 1.85%, which is within the proper range of the present invention. Steel No. 17 has a lower rolling reduction in finish rolling than the proper range of the present invention, and thus it can be confirmed that steel No. 16 has better magnetic properties than steel No. 17.

The steels of Nos. 18 to 20, which are examples of the present invention, have high Si contents of 2.10%, 3.20% and 3.40%, respectively, so that the effect of improving iron loss is particularly remarkable, and the magnetic flux density is also low. ,
It can be confirmed that the steel has the same level as the steels of Comparative Examples No. 12 and No. 13 in which the Si content is as small as 0.82%.

The steels of No. 21 to No. 24 are all examples of the present invention. When No. 21 has the C content within an appropriate range (0.005%), No. 22 has the C content within a suitable range (0.005%). 0.002%)
No. 23 is the case where the P content is within the preferred range (0.130%), and No. 24 is the case where both the C content (0.002%) and the P content (0.120%) are within the preferred range.

When comparing the steels of No. 21 and No. 22, the amount of C was
It can be seen that the magnetic properties of No. 22 steel reduced to 0.002% are more excellent. Further, when comparing the steels of No. 21 and No. 23, it can be confirmed that the magnetic properties of the steel of No. 23 with the P content within the preferred range are more excellent. No.
When comparing the steel of No. 22 or No. 23 with the steel of No. 24, the steel of No. 24 in which both the C amount and the P amount are within the preferable ranges has dramatically improved magnetic properties. Can be confirmed.

[0047]

According to the manufacturing method of the present invention, it is possible to manufacture a magnetic steel sheet having a low iron loss without lowering the magnetic flux density, and it is possible to manufacture an excellent magnetic steel sheet which can be obtained only by a conventional semi-process. Magnetic properties can be obtained easily,
This is industrially advantageous because the cost can be reduced.

Claims (4)

[Claims] 1. C .: 0.005% or less by weight, Si: more than 1% and 4% or less, Mn: 1.5% or less, P: 0.35% or less, S: 0.
010% or less, Al: 2.0% or less, N: 0.01% or less, O: 0.
After casting, or after further reheating, a steel slab having a composition containing not more than 01% is subjected to hot rough rolling to obtain the following (1)
Immediately after finish rolling under the conditions shown in the following (2) after the steel structure shown in (1), pickling is performed as it is or after further annealing, then normal cold rolling and annealing are sequentially performed. A method for producing an electromagnetic steel sheet having excellent magnetic properties. (1) The volume fraction of recrystallized ferrite grains having a grain size of 100 μm or less is 20% or less. (2) The rolling temperature is set to a temperature range of 500 ° C. or lower below the Ar ₁ transformation point for steel having a composition that causes eutectoid transformation, and 1100 ° C. or lower to 500 ° C. for steel having a composition that does not cause eutectoid transformation.
Temperature range above and rolling reduction at least 30%. 2. The steel slab according to claim 1, wherein:
C: 0.002% or less, Si: more than 1% and 4% or less, Mn: 1.5
%, P: 0.35% or less, S: 0.010% or less, Al: 2.0
% Or less, N: 0.01% or less, and O: 0.01% or less. 3. The steel slab according to claim 1, wherein
C: 0.005% or less, Si: more than 1% and 4% or less, Mn: 1.5
%, P: 0.02% to 0.20%, S: 0.010% or less, Al: 2.0% or less, N: 0.01% or less, O: 0.01% or less Manufacturing method of electrical steel sheet. 4. The steel slab according to claim 1, wherein:
C: 0.002% or less, Si: more than 1% and 4% or less, Mn: 1.5
%, P: 0.02% to 0.20%, S: 0.010% or less, Al: 2.0% or less, N: 0.01% or less, O: 0.01% or less Manufacturing method of electrical steel sheet.