JPH06228645A - Production of silicon steel sheet for compact stationary device - Google Patents

Abstract

PURPOSE:To provide the method for producing a silicon steel sheet for a compact stationary device excellent in magnetic properties in the rolling direction. CONSTITUTION:Steel stock contg. <=0.005% C, <=0.005% N, <=1.0% Mn, <=0.006% S and >=0.1% sol.Al and satisfying (Si+sol.Al): 2.0 to 4.0% is subjected to hot rolling at a finishing temp. of 700 to 850 deg.C and is thereafter coiled at <=600 deg.C. Next, before or after descaling, it is annealed at >=800 deg.C and is furthermore subjected to a single cold rolling at <=80% draft. After that, its temp. is raised at >=100 deg.C/sec heating rate, and it is annealed at 800 to 1100 deg.C. In this way, the non-oriented silicon steel sheet having low core loss and high magnetic flux density and suitable as the iron core material for a compact stationary device can be produced without executing a complicated stage such as two times cold rolling.

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 an electromagnetic steel sheet having excellent magnetic properties in the rolling direction, which is used as an iron core material for a small static device.

[0002]

2. Description of the Related Art Magnetic steel sheets are strongly required to have improved magnetic characteristics such as low iron loss and high magnetic flux density in order to reduce power loss and downsize equipment. Among them, magnetic steel sheets for stationary devices such as transformers and ballasts have a limited magnetization direction, and therefore it is rather advantageous in terms of device performance that the magnetic properties have anisotropy (direction). That is, a grain-oriented electrical steel sheet having excellent magnetic properties in only one direction is desirable.

However, the disadvantages of grain-oriented electrical steel sheets are:
High cost due to its manufacturing method including complicated steps such as high temperature annealing for a long time can be mentioned. Therefore, for a small static device that does not require as low iron loss as a large static device, a less expensive non-oriented electrical steel sheet is used, but for applications where the magnetization direction is limited, such as a static device, It goes without saying that it is preferable to use an electromagnetic steel sheet having directionality in one direction as much as possible and having as low iron loss as possible. From such a viewpoint, development of non-oriented electrical steel sheets having excellent magnetic properties in the rolling direction has been promoted.

For example, Japanese Patent Publication No. 56-43294 discloses S
i: 0.1 to 1.0%, and the total Al was adjusted to 0.007% or less. A hot-rolled steel sheet was cold-rolled twice with intermediate annealing so that the second rolling reduction was 2 to 15%, and A method for producing a non-oriented electrical steel sheet having a high magnetic permeability, which has a surface roughness of 15 μ-in, rms or less, has a magnetic permeability μ _15/50 in the rolling direction of 4500 or more is _disclosed .

In Japanese Patent Laid-Open No. 61-119618, C: 0.020%
The steel slab containing Si: 1.0% or less, Mn: 0.1 to 1.0%, and Al: 0.40% or less is hot-rolled and then cold-rolled twice with intermediate annealing without hot-rolled sheet annealing. A method for producing a magnetic steel sheet for iron core material of a small static device, in which the second rolling reduction is 3 to 7%, is shown.

In Japanese Patent Laid-Open No. 2-305920, C: 0.015%
Below, Si: 0.1-1.5%, Mn: 0.1-1.5%, P: 0.15
% Or less, S: 0.008% or less, sol.Al: 0.01 to 1.0%, total N: 0.0050% or less and total O (oxygen): 0.02
% Or less, (sol.Al/Si): 0.02 or more, Al ₂ O ₃ / (
SiO ₂ + MnO + Al ₂ O ₃ ) × 100: After hot rolling a steel slab satisfying 40% or more, two cold rolling steps with intermediate annealing are performed.
The second rolling reduction is 3-10%, and the surface roughness of the steel sheet is
A method for producing a semi-process non-oriented electrical steel sheet with excellent magnetic properties and weldability of 15 μ-in, rms or less is shown.

However, in each of the methods disclosed in these publications, cold rolling is carried out twice with intermediate annealing, so that the manufacturing process is complicated and economically disadvantageous. . Furthermore, since the Si content is as low as 1.5% or less, only non-oriented electrical steel sheets suitable for applications that require low iron loss can be obtained.

By the way, generally, as one of the methods for improving the magnetic properties of a non-oriented electrical steel sheet, it is known to increase the heating rate before annealing after cold rolling. For example, in Japanese Unexamined Patent Publication No. 2-54720, the heating rate after cold rolling before annealing is 200 ° C./min or more, annealing is performed at an Ac ₃ transformation point or more, and cooling is performed at a rate of 10 ° C./sec or more. , A method of manufacturing a non-oriented electrical steel sheet having excellent magnetic properties in the circumferential direction is shown.

However, this method improves the average magnetic properties in each direction in the plate surface, but cannot obtain a non-oriented electrical steel sheet having particularly excellent magnetic properties in the rolling direction.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a magnetic steel sheet for a small stationary machine, which is capable of solving the above-mentioned problems and is excellent in magnetic characteristics in the rolling direction.

[0011]

The gist of the present invention resides in the following manufacturing method.

% By weight, C: 0.005% or less, N: 0.005% or less, Mn: 1.0% or less, S: 0.006% or less and sol.Al: 0.
After hot rolling a steel material containing 1% or more and satisfying (Si + sol.Al): 2.0 to 4.0% with the balance being Fe and unavoidable impurities at a finishing temperature of 700 ° C to 850 ° C. , Coiling at a temperature of 600 ° C or less, then annealing at a temperature of 800 ° C or more before or after descaling, and
After cold rolling once at a rolling reduction of 80% or less, 100 ℃
A method of manufacturing a magnetic steel sheet for a small static device having excellent magnetic properties, which comprises heating at a heating rate of not less than 1 / sec and annealing at a temperature of 800 ° C or more and 1100 ° C or less.

The inventors of the present invention have studied the manufacturing method of the above-mentioned magnetic steel sheet by the single cold rolling method having a simple process, and have obtained the following new findings.

By suppressing the reduction ratio of cold rolling to a low level and performing the temperature rise before finish annealing after cold rolling at a heating rate of 100 ° C./sec or more, excellent magnetic properties in the rolling direction can be obtained in a simple process. It is possible to obtain a non-oriented electrical steel sheet. This 100 ℃
Although a heating rate of at least 1 second / second is not possible with ordinary continuous annealing, the direct current heating method developed by the present applicant, that is, by contacting two or more pairs of pinch rolls that also serve as electrodes with the steel sheet, Method of heating by energizing (for example, Japanese Patent Application No. 3-
This can be easily achieved by using together (see No. 14291).

[0015]

The knowledge on which the present invention is based will be described with reference to FIG.

In FIG. 1, C: 0.002 is used as the base component.
%, Si: 2.7%, Mn: 0.24%, P: 0.01%, S: 0.0012
% And sol.Al:0.22%, the cold rolling reduction ratio is in the range of 67 to 83%, the heating rate for finish annealing is in the range of 10 to 180 ° C./sec, in the case where each varied, a graph showing changes in iron loss (W _15/50) and flux density (B _50). Here, for these steel materials, the finishing temperature for hot rolling was 780 ° C, the coiling temperature was 500 ° C, and
Hot rolled to 3.0 mm. After descaling these hot-rolled sheets by pickling, they are annealed at 850 ℃ for 30 seconds, and the surface thickness is reduced to 1.5 ~ by changing the reduction ratio of cold rolling.
The thickness was changed in the range of 3.0 mm, and then the final thickness was 0.5 mm by cold rolling. The cold rolling reduction ratios at this time are 67, 75 and 83% shown in the figure. After heating by direct current heating method to 950 ° C at a heating rate of 10 to 180 ° C / sec, continuous annealing was performed at 950 ° C for 30 seconds, and strip samples in the rolling direction were taken from the obtained steel sheet. The magnetic properties were investigated by the method specified in 2550.

Incidentally, in the non-oriented electrical steel sheet, the above-mentioned magnetic properties are usually obtained by collecting strip-shaped samples not only in the rolling direction but also in the direction perpendicular to the rolling direction, as defined in JIS C 2550. In the case of static machines, only the magnetic properties in the rolling direction are important.

As shown in the figure, the cold rolling reduction rate is 80%.
If it exceeds, the iron loss increases and the magnetic flux density decreases. This tendency of decreasing the magnetic flux density becomes particularly remarkable when the heating rate is lower than 100 ° C / sec.

This is considered to be due to the following reason. That is, if the reduction ratio of the cold rolling is too high, as shown in Japanese Examined Patent Publication No. 64-55338, it approaches the magnetic properties averaged in the in-plane direction. It is understood that it has deteriorated. Further, when the heating rate becomes slower, the magnetic flux density tends to decrease, which is considered to be due to the development of texture which is disadvantageous to the magnetic properties. The reason for this is not clear, but as the heating rate increases, the magnetic properties favored during recrystallization (1
00) It is thought that this is because the texture easily develops.

Next, the reason why the composition of the steel material which is the object of the method of the present invention is limited as described above will be explained.

C: The C content is preferably as small as possible from the viewpoint of reducing iron loss. If the C content exceeds 0.005%, iron loss increases due to magnetic aging, so 0.005% was made the upper limit.
0.003% or less is desirable. There is no particular restriction on the lower limit.

The N: N content is also preferably low from the viewpoint of reducing iron loss. If the N content exceeds 0.005%, nitrides such as AlN are generated, and by suppressing grain growth during annealing,
Since the magnetic properties deteriorate, 0.005% was made the upper limit.
0.003% or less is desirable. There is no restriction on the lower limit as with C.

Mn: Mn is an element that increases the specific resistance like Si or the like and effectively contributes to the reduction of iron loss due to the reduction of eddy current loss, and it is desirable to positively contain it. However, if the content exceeds 1.0%, the magnetic flux density decreases, so the Mn content was made 1.0% or less.

S: Mn and MnS are formed, and the S content is 0.006.
%, MnS acts to prevent the growth of crystal grains during annealing and to prevent the reduction of iron loss, and causes hot brittleness. It is also harmful in promoting recrystallization and grain growth of the hot rolled sheet. Therefore, the S content is set to 0.006% or less. 0.003% or less is desirable. Note that the lower limit is not necessary in terms of magnetic characteristics.

Sol.Al: If the sol.Al content is less than 0.1%,
In addition to insufficient deoxidation in molten steel, AlN precipitates finely and inhibits the growth of crystal grains after recrystallization, which adversely affects the magnetic properties. Therefore, the sol.Al content is set to 0.1% or more.

Si + sol.Al: Si and sol.Al are elements that both increase the specific resistance and effectively contribute to the reduction of iron loss due to the reduction of eddy current loss. Especially, Si is used in applications where low iron loss is required.
+ Sol.Al must be contained at 2.0% or more. on the other hand,
If the content of Si + sol.Al exceeds 4.0%, the steel plate becomes brittle and problems such as plate cracking occur during cold rolling, so the content was made 4.0% or less.

P may be contained in order to adjust the hardness of the steel sheet, but if the P content exceeds 0.1%, the steel sheet becomes brittle and fracture easily occurs in cold rolling. Therefore, it should be 0.1% or less. desirable.

Next, the reason why the manufacturing process and manufacturing conditions are limited as described above will be explained.

The steel material having the above composition is melted in a converter or the like according to a conventional method, and is continuously cast or ingot-slab-rolled into a slab. Then, this slab is hot rolled,
After that, winding is performed, annealing is performed before or after descaling, and one cold rolling is performed to perform annealing. Each step after hot rolling will be described in detail below.

Hot rolling, winding In this step, the rolling finishing temperature is 700 ° C. or higher and 850 ° C. or lower,
The condition is that the coiling temperature is 600 ℃ or less.

As described above, the method of the present invention has an important point in improving the magnetic properties by promoting recrystallization and grain growth in the step of annealing the hot rolled sheet.

In order to sufficiently promote recrystallization and grain growth during annealing of the hot rolled sheet, sufficient strain is accumulated at the end of hot rolling, and the strain energy is not released until after winding. Must remain. Hot rolling
From this point of view, the rolling finishing temperature is preferably 850 ° C. or lower, and the winding is preferably performed at a low temperature at which strain energy is not released as much as possible.

In this case, the rolling finishing temperature is limited to the upper limit of 850 ° C. or less from the meaning of recrystallization and grain growth during annealing of the hot rolled sheet, but in reality it is the rolling finishing temperature. If the temperature falls below 700 ° C, the rolling load will become too large and it will be difficult to operate with ordinary rolling mills. From the above, the rolling finishing temperature was set to 700 ° C to 850 ° C.

Regarding the coiling temperature, when the temperature exceeds 600 ° C., the strain energy in the steel sheet is released and this energy is not accumulated, and recrystallization also begins to occur. The crystal grain growth becomes poor. Therefore, the upper limit of the coiling temperature was set to 600 ° C. The lower limit need not be set from the viewpoint of suppressing the release of strain energy.

Descaling Descaling is often carried out by pickling, but various mechanical descaling methods such as shot blasting and roll bender combination may be used. Descaling is performed before or after annealing the hot rolled sheet.

Annealing of Hot Rolled Sheet This step is for recrystallization and grain growth of the hot rolled sheet which has been hot rolled and wound.

As the annealing method, either box annealing or continuous annealing can be adopted. In order to stably complete the recrystallization and the growth of crystal grains, the temperature must be 800 ° C or higher for box annealing and 850 ° C or higher for continuous annealing. Annealing temperature
It is based on this that the temperature above 800 ℃ is set. The upper limit is not particularly limited, but is naturally determined from the viewpoint of the balance between the effect of performance improvement and the equipment cost. That is, originally, it is advantageous that the annealing temperature is higher from the viewpoint of its effect, but very expensive equipment is required to set the temperature above the upper limit, and in this case, performance sufficient to meet the equipment cost is required. No improvement can be expected.

Cold rolling The reduction ratio of cold rolling is one of the important conditions of the present invention.
It should be below 80%. By performing cold rolling at such a reduction rate, the magnetic properties in the rolling direction of the product are improved. The lower limit is determined solely by operational constraints and is not limited. For example, in the case of the most common product with a plate thickness of 0.5 mm, the hot-rolled plate thickness is 1 mm if 50% reduction is to be achieved.
Therefore, it is practically impossible to carry out cold rolling at a rolling reduction of 50% or less.

Annealing after cold rolling Annealing after cold rolling is one of the important conditions of the present invention.
This annealing is intended to generate recrystallized grains advantageous for magnetic properties and to sufficiently grow the recrystallized grains in the process of recrystallizing the work structure after the cold rolling. Since the heating rate before annealing is increased in the method of the present invention, it is preferable to combine the heating by the direct current method and the continuous annealing method.

The heating rate for finish annealing after cold rolling is
At less than 100 ° C / sec, iron loss increases and magnetic flux density decreases (see Fig. 1 above). Therefore, by direct current heating, etc.
It is necessary to set the heating rate to 100 ° C / sec or more.

The annealing temperature is 800 ° C. or higher and 1100 ° C. or lower. It does not recrystallize at low temperatures below 800 ° C, or grain growth does not occur sufficiently even if recrystallized. On the other hand, 1100
If the temperature exceeds ℃, the crystal grains will grow too much and the magnetic properties, especially the iron loss, will deteriorate.

In the case of producing an electromagnetic steel sheet, a step of applying an insulating coating after the above annealing is usually performed.
Also in the method of the present invention, it is possible to add this coating step as the final step of manufacturing. In addition, non-oriented electrical steel sheets are given full-process products that are shipped with given magnetic properties, and after shipping, they are subjected to strain relief annealing (750 ° C x 2 hours) after punching and other processing, and then predetermined There are semi-processed products that retain the magnetic properties of.
In the former case as well, the user side is naturally subjected to strain relief annealing. Therefore, in this case, it is required that the prescribed magnetic characteristics are exhibited not only at the time of shipment but also after the user side is strain relief annealed. The method of the present invention can be applied to any of the above products.

[0043]

[Examples] Steel of each chemical composition shown in Table 1 (1) was melted in a converter and formed into a slab by continuous casting, followed by hot rolling, hot-rolled sheet continuous annealing, cold rolling and Finishing continuous annealing was performed. The manufacturing process and its conditions are shown in Table 1 (2). However,
When the heating rate before finishing continuous annealing was more than 100 ° C./sec, the direct current heating was also used under the following conditions. The line speed was 50 m / min, the final plate thickness was 0.5 mm, and the plate width was 1000 mm.

The direct electric heating was performed by arranging two pairs of pinch rolls having a roll diameter of 500 mm in front and back with a distance of 5 m from the traveling direction of the plate, and supplying power consumption of 1300 kW between the front and rear pinch rolls. .

The magnetic flux density B ₅₀ and the iron loss W _15/50 were measured from each of the obtained steel plates by the methods specified in JIS C 2550. The strip samples at this time were also limited to the rolling direction for the same reason as in the case of FIG. The results are shown in the right column of Table 1 (2).

[0046]

[Table 1 (1)]

[0047]

[Table 1 (2)]

No. 1 to No. 3 show the effects of the (Si + sol.Al) content. In No. 2 in which this content exceeds the range specified in the present invention, fracture occurred during cold rolling. On the other hand, in No. 3 in which this content is lower than the range specified in the present invention, the iron loss is deteriorated.

No. 4 and No. 5 show the influence of the sol.Al content. sol.Al content is lower than the range specified in the present invention
In No. 5, AlN is finely precipitated, and the grain growth property during finish annealing after hot-rolled sheet annealing and cold rolling is deteriorated, so that iron loss is particularly deteriorated.

No. 6 and No. 7 show the influence of the C content. In No. 7 in which the C content exceeds the upper limit defined in the present invention, the precipitated carbide deteriorates the grain growth property during finish annealing after hot-rolled sheet annealing and cold rolling, so that iron loss is particularly deteriorated.

No. 8 and No. 9 show the influence of N content. In No. 9 in which the N content exceeds the range specified in the present invention, the precipitated nitride deteriorates the grain growth property during finish annealing after hot-rolled sheet annealing and cold rolling, and thus iron loss is particularly deteriorated. .

No. 10 and No. 11 are S contents, No. 12 and N
o.13 shows the effect of Mn content.
In No. 11 in which the S content exceeds the range specified in the present invention, the precipitated sulfide MnS deteriorates the grain growth property during finish annealing after hot-rolled sheet annealing and cold rolling, and thus iron loss is particularly deteriorated. is doing. Mn content exceeds the range specified in the present invention
In No. 13, the magnetic flux density is low.

Nos. 14 to 20 are the effects of the manufacturing conditions on the component systems within the range defined by the present invention. Of these, in No. 15 to No. 20 in which any one of the manufacturing conditions is out of the range defined by the present invention, both magnetic flux density and iron loss are worse than No. 14 satisfying the conditions of the present invention. No.15
However, since the finishing temperature of hot rolling was too high, strain energy was not accumulated in the hot rolled sheet, and recrystallization and grain growth were not sufficiently performed during annealing of the hot rolled sheet, so that improvement in magnetic properties was not observed. In No. 16, the coiling temperature for hot rolling was too high, so no improvement in magnetic properties was observed for the same reason as No. 15. In No. 17, since the annealing temperature of the hot rolled sheet is too low,
Grain growth does not occur sufficiently and magnetic properties are not improved. In No. 18, the reduction ratio of cold rolling was too high, and the magnetic properties approached in the in-plane non-direction averaged magnetic properties, so the magnetic properties in the rolling direction deteriorated. In No. 19, since the heating rate before finish annealing was slow, the magnetic flux density deteriorated. Also
In No. 20, since the temperature of continuous annealing is too low, sufficient grain growth does not occur and magnetic properties are not improved.

[0054]

According to the method of the present invention, it is possible to produce a non-oriented electrical steel sheet having a low iron loss, a high magnetic flux density, and excellent magnetic properties, which is suitable as a material for an iron core of a small static device. You can Moreover, there is no need to go through complicated processes such as double cold rolling as in the prior art.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a reduction rate in cold rolling, a heating rate before finish annealing, a magnetic flux density, and an iron loss W.

Claims (1)

[Claims] 1. By weight%, C: 0.005% or less, N: 0.005% or less, Mn: 1.0% or less, S: 0.006% or less and sol.Al: 0.
After hot rolling a steel material containing 1% or more and satisfying (Si + sol.Al): 2.0 to 4.0% with the balance being Fe and unavoidable impurities at a finishing temperature of 700 ° C to 850 ° C. , Coiling at a temperature of 600 ° C or less, then annealing at a temperature of 800 ° C or more before or after descaling, and
After cold rolling once at a rolling reduction of 80% or less, 100 ℃
A method of manufacturing a magnetic steel sheet for a small static device having excellent magnetic properties, which comprises heating at a heating rate of not less than 1 / sec and annealing at a temperature of 800 ° C to 1100 ° C.