JP2000160249A - Method for producing hot-rolled electromagnetic steel sheet excellent in magnetic properties in L and C directions - Google Patents

Abstract

[PROBLEMS] To provide a method for manufacturing a hot-rolled electromagnetic steel sheet having excellent magnetic properties in the L and C directions even if a cold rolling step and a finish annealing step are omitted. is there. SOLUTION: A steel slab containing Si: 4.0 wt% or less is hot rough-rolled to have a predetermined steel structure, immediately hot-rolled under predetermined conditions, and then recrystallized. And

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is used for an AC magnetic core, and does not perform cold rolling and finish annealing.
It is called "L direction". ) And a method of manufacturing a hot-rolled electromagnetic steel sheet having particularly excellent magnetic properties in two directions (hereinafter, referred to as “C direction”) perpendicular thereto.

[0002]

2. Description of the Related Art Iron core materials for transformers and motors are required to have high magnetic flux density and low iron loss in order to increase the efficiency and miniaturization of these devices. As a magnetic alloy to be provided for this type of iron core material, an Fe-Si alloy is known, and is widely used as a non-oriented electrical steel sheet.In order to improve the magnetic properties of this steel sheet, the texture is improved. Various attempts have been made.

[0003] Among them, {011} <100> orientation,
That is, by enriching crystal grains in the Goss orientation, iron loss is reduced, and in particular, magnetic flux density is increased.
No. 54-110121. Usually, the Goss orientation improves the magnetic properties in the L direction, and consequently the average magnetic properties including the C direction.

[0004] However, since the magnetic properties in the C direction are only improved to some extent, there is naturally a limit in improving the average magnetic properties.

On the other hand, it is known that the {100} <001> orientation, that is, the cubic orientation on the surface, simultaneously improves the magnetic properties in both the L and C directions.

[0006] However, in order to obtain a structure which is accumulated only in the cubic orientation on the surface, a method of performing high-temperature intermediate annealing as described in JP-B-46-23814 is disclosed.
The method of cold rolling a quenched ribbon at a predetermined rolling reduction as described in 6438, the γ → α transformation method involving decarburization as described in JP-A-1-108345, etc. However, all of them require complicated or long-time steps and increase the cost, so that it is presumed that they will not establish industrial practicality.

Further, as means for improving the magnetic characteristics, it is useful to promote crystal grains having an orientation that improves the magnetic characteristics and to suppress crystal grains having an orientation that deteriorates the magnetic characteristics. As crystal grains having an orientation that deteriorates magnetic properties, there are crystal grains having a <111> // ND (direction perpendicular to the steel sheet surface) orientation, and it is desirable to suppress the generation of crystal grains having such an orientation. Except for the case where special and expensive means are used, it has been difficult to reduce the crystal grains in the <111> // ND orientation in the conventional methods for producing non-oriented electrical steel sheets.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide particularly excellent magnetic properties in the L-direction and C-direction even when recrystallized after hot rolling without performing cold rolling and finish annealing. To provide a method for manufacturing a hot-rolled electromagnetic steel sheet.

[0009]

As a result of extensive research on means for practically improving the magnetic properties of non-oriented electrical steel sheets, the present inventors have found that assembling is performed by hot finishing rolling after hot rough rolling. He found that he could control the organization, and filed Japanese Patent Application No. 10-2138.
No. 83 proposed. The essence is that the coarse ferrite grain size is reduced by the hot rolling speed /
The ratio of the hot rolling reduction ratio is large, that is, hot finish rolling is performed at a high hot rolling speed, whereby {015} <100> oriented grains are generated in the recrystallization process after hot rolling, and this is carried out by cold rolling and cold rolling. {100} <00 which is the most favorable for the magnetic properties during annealing
1> It utilizes the fact that it develops as an orientation grain.

The (015) [100] oriented grains undergo cold rolling and recrystallization annealing to form (001) [10]
0] has already been described in the known literature (Taoka et al .:
Although disclosed in Iron and Steel, 54 (1968) 162.), a production method capable of industrially producing (015) [100] has not been known at all. For this reason, we have (015)
[100] The present inventors have newly found a technique for expressing and controlling grains.

Also, the presence of (015) [100] grains suppresses the degree of integration of <111> // ND orientation, which degrades the magnetic properties of the steel sheet that has been cold rolled and annealed, and also suppresses the L direction. {011} <100 to improve magnetic properties
> It has been newly found that the average magnetic properties in the L direction and the C direction are improved as a result of the increase in the orientation grains.

When the above technique is applied to an actual process, it is important to increase the ratio of the hot rolling speed / rolling reduction in each rolling stand, that is, to increase the hot rolling speed, among the above manufacturing conditions. However, applying a large hot rolling speed to the manufacturing process of the electrical steel sheet has been accompanied by difficulties in terms of rolling mill performance and shape control. Since the finish rolling mill currently applied industrially is of the tandem type, the ratio of the hot rolling speed / reduction ratio generally becomes larger in the latter stage, and usually this ratio becomes the smallest. Indicates rolling at the first stage (first) stand.

The inventors of the present invention have further conducted studies on the effect of the rolling reduction at the first stand of the hot finishing rolling mill, and as a result, have found that the present invention has a greater effect than the prior invention (Japanese Patent Application No. 10-213883). The present inventors have found a method for producing an electromagnetic steel sheet which is easier to apply industrially and has magnetic properties equivalent to those of the prior invention.

That is, if the reduction ratio in the first stand is small to some extent, even if the ratio of hot rolling speed / reduction ratio is small, the adverse effect is very small.
The inventor has found that since the ratio of the hot rolling speed / reduction ratio naturally increases, the expected effect of the large hot rolling speed / reduction ratio is exhibited.

Further, the present inventors have studied the texture and magnetic properties after hot rolling and recrystallization. As a result, the hot-rolled steel sheet which has been subjected to the hot finish rolling and recrystallization described above exhibits a texture favorable for magnetic properties centered on {015} <100> -oriented grains and has excellent magnetic properties. discovered. This means that {015} <
100> orientation grain is most suitable for magnetic properties {100} <0
It is presumed that the vicinity orientation of 01> worked effectively.

From the above, a hot rolled electromagnetic steel sheet having particularly excellent magnetic properties in the L and C directions even if recrystallization is performed after hot rolling without performing cold rolling and finish annealing. The present inventors have found a production method that can be easily industrially produced in the current electromagnetic steel sheet production process, and have completed the present invention.

According to the present invention, specifically, after a steel slab containing Si: 4.0 wt% or less is hot rough-rolled to have a steel structure shown in the following 1 (1), immediately after the following 1 (2) And (3)
And then recrystallizing after hot finish rolling under the conditions shown in (1) to (3), which is a method for producing a hot-rolled electromagnetic steel sheet having excellent magnetic properties in the L and C directions.

Note 1 (1) The volume fraction of equiaxed ferrite grains having an average grain size of 300 μm or more and a grain size of 100 μm or less is
20% or less. (2) The steel sheet temperature at the time of entering the finish rolling mill is set to a temperature range of not more than Ar ₁ transformation point and not more than 900 ° C and not less than 500 ° C for a steel having an austenitic phase, and a component composition which does not generate an austenitic phase. 900 for steel having
Temperature range below 500 ° C. (3) The rolling reduction at the first stand of the finishing mill should be 15% or more and 30% or less.

The steel slab more preferably further contains Mn: 2.0 wt% or less, P: 0.3 wt% or less, and Al: 2.0 wt% or less.

The term "equiaxed ferrite grains" used herein means ferrite grains having a ratio of the major axis to the minor axis of 2 or less.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the reasons for limiting the steel composition components of the present invention will be described. Si: 4.0 wt% or less Si has the effect of increasing the specific resistance and reducing the eddy current loss, and is an essential additive element in the present invention. However, if the Si content exceeds 4.0%, the magnetic flux density is greatly reduced and the workability is also reduced. Therefore, the Si content is 4.0wt
% Or less.

In the present invention, as for the composition of the components in the steel slab, only the Si content was regarded as an essential additive component. However, as other components, Mn: 2.0 wt% or less, P: 0.3 wt% or less, Al: 0.3 wt% or less, : 2.0 wt% or less is more preferable.

Mn: 2.0 wt% or less, Al: 2.0 wt% or less, Mn
Both Al and Al have the effect of increasing the specific resistance and reducing the eddy current loss, and are effective as auxiliary elements of Si. However, the content of Al and Mn is 2.0
If the content exceeds wt%, the magnetic flux density and the workability are greatly reduced. Therefore, the contents of Al and Mn are both limited to the range of 2.0 wt% or less.

P: 0.3 wt% or less P has the effect of increasing the specific resistance and reducing the eddy current loss, and is effective as an auxiliary element of Si. However, when the P content exceeds 0.3 wt%, the processability is reduced. Therefore, P
The content is limited to the range of 0.3 wt% or less.

In the present invention, Si: 4 wt% or less is an essential item of the invention, and other components are not particularly limited. Therefore, all steel types satisfying the above-mentioned Si content can be used.

Next, the manufacturing conditions of the present invention will be described. (I) Before Hot Finish Rolling In the present invention, the average grain size of equiaxed ferrite grains is 300 μm or more and 100 μm before hot finish rolling.
It is essential that the volume fraction of the following equiaxed ferrite grains be 20% or less.

That is, when the average grain diameter of equiaxed ferrite before hot finish rolling is 300 μm or more, the (015) [100] orientation grains after hot rolling or annealing increase. As a result, {011} <100 after cold rolling and finish annealing are performed.
This is because, since this leads to an increase in the orientation grains and a suppression of the degree of integration of the <111> // ND orientation, the texture after finish annealing is improved and the magnetic properties are improved.

However, the average ferrite grain size is 300 μm.
Even if it is larger than m, if a large number of fine grains having a grain size of 100 μm or less coexist, the growth of (015) [100] oriented grains from the coarse grains is suppressed, thereby deteriorating the magnetic characteristics.
It is important to suppress the volume fraction of fine grains at the same time.
Therefore, the volume fraction of crystal grains of 100 μm or less is set to 20% or less.

According to the present invention, the volume fraction of equiaxed ferrite grains having an average grain size of 300 μm or more and a grain size of 100 μm or less before hot finish rolling is 20 μm or more.
% Is specified as an essential invention-specific matter, but as an example of a specific means for achieving these, the slab heating temperature is set in a range of 1100 to 1500 ° C., or the heating before hot finish rolling is performed. Alternatively, a method of keeping the temperature in a temperature range of 1000 to 1150 ° C can be considered.

In other words, when the slab heating is performed at a temperature of 1100 ° C. or higher, the crystal grains during heating are coarsened, and the crystal grains before hot finish rolling are also likely to be coarsened. This is because it is effective to improve the magnetic characteristics, and if it exceeds 1500 ° C., there is a possibility that a problem such as a decrease in yield due to an increase in scale may be caused.

Further, in the present invention, in order to obtain coarse grains before hot finishing rolling, after the hot rough rolling, before setting the steel sheet temperature at the time of entering the hot finishing rolling mill to the appropriate temperature, It is more preferable to make the crystal grains coarse by heating or keeping the temperature within the range of 1000 ° C. or more and 1150 ° C. or less. The steel that becomes the austenitic phase during heating and heat retention undergoes ferrite transformation during subsequent cooling.However, since the initial austenite grain size is large, it is also effective in increasing the ferrite grain size when entering the finish rolling mill. is there.

In addition, the grain boundary of the unrecrystallized grains has undergone local recrystallization after hot rough rolling, and has a (015) [100] orientation grain from the grain boundary after hot finish rolling. Does not contribute to generation. Therefore, the volume fraction of equiaxed ferrite grains recrystallized after hot rough rolling,
Although not particularly limited, it is more preferable that the content be 80% or more.

(II) Hot finishing rolling (i) Temperature of steel sheet at the time of entering hot finishing rolling mill: For steel having a component composition that causes phase transformation, it is below the Ar ₁ transformation point and below 900 ° C and above 500 ° C. For steels with a component composition that does not cause phase transformation, the temperature range should be 900 ° C or lower and 500 ° C or higher for effective effect of coarse grains before hot finish rolling. It is important to suppress the miniaturization due to recrystallization in rolling, and for that purpose, it is effective to perform rolling at a low temperature. Therefore, the upper limit of the finish hot rolling temperature is set to be below the Ar ₁ transformation point and below 900 ° C for steels having a component composition that generates austenite phase (phase transformation), For steel having a composition, it is necessary to keep the temperature below 900 ° C.

That is, for steel having a component composition that causes phase transformation, the rolling in the two-phase region or austenite region loses the effect of coarse grains due to the subsequent transformation. This is because the region must be lower in temperature than the ferrite phase region, that is, the Ar ₁ transformation point.

Further, in the manufacturing method of the present invention, coarse grains before hot finish rolling, which is an essential feature of the invention, are
In order to maintain the finish rolling at all stands, it is essential to suppress the refining during refining during the finish rolling. For that purpose, it is effective to perform rolling at a low temperature of 900 ° C or less. The upper limit is 900 ° C.

Further, the lower limit of the hot finish rolling temperature is set in any of the steels when rolling in a low temperature range of less than 500 ° C., because the accumulated strain increases and the recrystallization texture deteriorates. 500 ° C.

(Ii) The rolling reduction at the first stand of the hot finishing mill is 15% or more and 30% or less. The rolling reduction at the first stand of the hot finishing rolling mill is the same as that of a normal tandem rolling mill. In the case, it is about 30-50%, but 30
%, The ratio of hot rolling speed / reduction ratio becomes small under normal rolling conditions, and the texture and magnetic properties deteriorate. Therefore, the rolling reduction at the first stand was set to 30% or less. The rolling reduction at the first stand is
It is more preferable to set the content to 25% or less, at which the adverse effect of deterioration of the texture and magnetic properties hardly appears.

On the other hand, if the rolling reduction in the first stand is less than 15%, the rolling reduction in the second and subsequent stands will have to be increased. Ratio tends to be small, and as a result, the magnetic properties tend to deteriorate. Therefore, the rolling reduction at the first stand is set to 15% or more.

(III) After Hot Finish Rolling In the present invention, recrystallization after hot finish rolling is an essential feature of the invention. That is, in the present invention, (015) [10
0] The orientation grains are utilized. Therefore, the structure of the hot rolled steel sheet as a product needs to be a recrystallized structure. As means to recrystallize after hot finish rolling,
Self-annealing after hot finish rolling or annealing by reheating may be used. The volume fraction of the recrystallized grains is preferably set to 70% or more.

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.

[0041]

EXAMPLES Steel shown in Table 1 was melted in a converter and continuously cast.
The slab was 200 mm thick. These slabs were reheated to 1200 ° C and subjected to hot rough rolling on a 40 mm thick sheet bar.
Subsequently, hot finish rolling was performed. Table 2 shows the conditions of the hot finish rolling and the grain size immediately before the rolling. The thickness of the sheet after hot finish rolling was 0.8 mm. Then, after hot finish rolling, a recrystallization treatment was performed at 850 to 1000 ° C. to produce hot-rolled electromagnetic steel sheets (steel Nos. 1 to 19). For comparison, for each steel type a to f shown in Table 1, a sheet thickness of 2.3 m
m, hot-finish rolling, recrystallization treatment, cold rolling to a thickness of 0.80 mm, and finish annealing at 850 to 1000 ° C by the conventional method.
4) Manufactured.

Table 2 shows the respective manufacturing conditions, and also shows the texture after hot rolling and recrystallization (expressed by the ratio of the degree of integration of (015) [100] to the random structure) and the magnetic properties. .

[0043]

[Table 1]

[0044]

[Table 2]

The results of the improvement of the magnetic characteristics according to the present invention will be described below with reference to Table 2. Here, the present invention also includes a specific resistance increasing component for improving iron loss.
Therefore, the magnetic characteristics shown in Table 2 were comprehensively evaluated from both the results of the iron loss and the magnetic flux density.

The steels Nos. 1,5 and 6,1 produced according to the invention
1,15 and 16, and steel No. 20, 21, 22, which are cold rolled annealed materials manufactured by the conventional method using the same steel slab as those used for each and performing cold rolling and finish annealing.
Compared with 23, the former has better magnetic properties than the latter, and therefore, according to the present invention, the steps of cold rolling and annealing are unnecessary, and the hot rolling is easy for industrial application. It is clear that an inexpensive electromagnetic steel sheet having excellent magnetic properties can be obtained.

Incidentally, except that the Si content was outside the proper range of the present invention, steel No. 19 manufactured according to the present invention had a remarkable difference in magnetic properties as compared with steel No. 24 manufactured according to the conventional method. I was not able to admit.

In addition, steel Nos. 2 to 4, 7 to 10, 12 to 14, 17 in which at least one of the invention-specifying matters of the present invention is out of the appropriate range.
1818 were inferior in magnetic properties to steel Nos. 1,5 and 6,11,15 and 16, respectively.

Further, steel Nos. 5 and 15 manufactured under the condition that the rolling reduction in the first stand during the hot finish rolling is within the preferred range of the present invention are within the proper range of the present invention, but are preferably It can be seen that the magnetic properties are much better than those of steels Nos. 6 and 16 manufactured under conditions outside the range.

In Table 2, (015) after hot rolling and recrystallization
The ratio of the degree of accumulation of (100) to the random organization is 3.
It can be seen that good magnetic properties are obtained when the value is 0 times or more. Therefore, in the present invention, (01) after hot rolling and recrystallization
5) The ratio of the degree of accumulation of [100] to the random organization is more preferably 3.0 times or more.

[0051]

According to the manufacturing method of the present invention, even if the cold rolling step and the annealing step are omitted, the electrical steel sheet having excellent magnetic properties in the L and C directions as compared with the conventional method passing through these steps. Can be manufactured, and can be manufactured industrially and at low cost without depending on special or complicated manufacturing conditions and steps.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shigeaki Takagi 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel Corporation (72) Inventor Takako Yamashita 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki 4K033 AA03 CA08 FA02 FA05 5E041 AA02 AA11 AA19 CA02 CA04 HB07 NN01 NN06 NN17 NN18

Claims (2)

[Claims] 1. A steel slab containing Si: 4.0 wt% or less is subjected to hot rough rolling to obtain a steel structure shown in the following 1 (1).
Production of a hot-rolled electromagnetic steel sheet having excellent magnetic properties in the L-direction and C-direction characterized by immediately performing hot finish rolling under the following conditions (2) and (3) and then recrystallizing. Method. Note 1 (1) The volume fraction of equiaxed ferrite grains having an average grain diameter of 300 μm or more and a grain diameter of 100 μm or less is 1 μm.
20% or less. (2) The steel sheet temperature at the time of entering the finish rolling mill is set to a temperature range of not more than Ar ₁ transformation point and not more than 900 ° C and not less than 500 ° C for a steel having an austenitic phase, and a component composition which does not generate an austenitic phase. 900 for steel having
Temperature range below 500 ° C. (3) The rolling reduction at the first stand of the finishing mill should be 15% or more and 30% or less. 2. The steel slab further contains Mn: 2.0 wt% or less,
The method for producing a hot-rolled steel sheet for electromagnetic steel according to claim 1, wherein P: 0.3 wt% or less and Al: 2.0 wt% or less.