JP3379058B2 - Manufacturing method of non-oriented electrical steel sheet with high magnetic flux density and low iron loss - Google Patents

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 non-oriented electrical steel sheet having excellent magnetic characteristics, which has a high magnetic flux density and a low iron loss, which is used as an iron core material for electric equipment.

[0002]

2. Description of the Related Art In recent years, in the field of electric machines, especially rotating machines and non-oriented electrical steel sheets used as iron core materials thereof, and small and medium-sized transformers, world-wide power and energy saving, and CFC regulation. In the movement of global environment conservation such as the above, the movement for higher efficiency is spreading rapidly. Therefore, there is an increasing demand for non-oriented electrical steel sheets to improve their properties, that is, to have high magnetic flux density and low iron loss.

By the way, in the non-oriented electrical steel sheet,
Conventionally, a method of increasing the content of Si, Al, or the like has been generally used as a means for reducing iron loss from the viewpoint of reducing eddy current loss due to increase in electrical resistance. However, this method, on the other hand, has a problem that the decrease in magnetic flux density cannot be avoided. In order to overcome such a problem, a method of improving both the magnetic flux density and the iron loss by coarsening the crystal grain size of the hot rolled sheet has been used.

Conventionally, in a non-oriented electrical steel sheet having a transformation, the hot rolling is terminated near the upper limit of the α range to secure the grain size before cold rolling, and as a result, the magnetic flux density and iron loss of the product are improved. Things have been done. From this point of view, Japanese Patent Laid-Open No. 56-38420 discloses that the hot rolling end temperature is 680 or lower between the Ar ₃ point and the Ar ₁ point.
A method for coarsening a hot rolled crystal structure by winding at a temperature of ℃ or more is disclosed. However, increasing the hot rolling finish temperature to the γ range should be avoided because the hot rolling structure becomes finer due to the progress of the transformation to the α phase after the hot rolling and the magnetic properties deteriorate as a result. It has been.

On the other hand, in an actual finishing hot rolling machine, since the rolling speed at the time of biting and the rolling speed in the steady rolling state are necessarily different, it is difficult to eliminate the temperature distribution in the coil longitudinal direction, In order to carry out hot rolling at the upper limit of the α range, there was the disadvantage that the rolling set temperature had to be lowered.

Further, since the Ar ₁ transformation point of a low-grade general non-oriented electrical steel sheet is around 860 ° C.,
There is a limit in increasing the hot rolling end temperature to grow the hot rolled crystal structure, and there is a limit in improving the magnetic properties by increasing the crystal structure before cold rolling.

As a technique for overcoming the limit of coarsening of the crystal structure before cold rolling by such controlled hot rolling, Japanese Patent Application Laid-Open No. 57-35 is known.
In Japanese Patent No. 628, the hot rolling end temperature is set to Ar ₃ point or higher to make the hot rolled crystal structure finer, and then the hot rolled sheet is annealed at a temperature of Ar ₃ point or lower to coarsen the crystal structure before cold rolling. A method for achieving the above is disclosed. Also, as a method of suppressing the increase in cost due to the addition of the hot-rolled sheet annealing step and coarsening the crystal structure before cold rolling, there is a self-annealing method in which the hot-rolled sheet is wound at high temperature and annealed by the heat retained by the coil. It is disclosed in JP-A-54-76422 and JP-A-58-136718.

However, the addition of the hot-rolled sheet annealing step is not preferable because it causes an increase in manufacturing cost, and it is practically not performed in the low grade non-oriented electrical steel sheet having a transformation. Further, in the self-annealing method, there has been a problem that the magnetic characteristics in the longitudinal direction of the coil fluctuate due to the non-uniform temperature inside the coil caused by winding the coil at high temperature.

On the other hand, in order to reduce iron loss, not only is the content of Si or Al, etc. increased, but also Japanese Patent Publication No. 6-8
As described in Japanese Patent No. 0169, there is disclosed a method of making a precipitate harmless by making high purity steel by reducing Mn and S. However, only the high-purification of steel cannot break the limit of coarsening of the crystal structure before cold rolling by the controlled hot rolling as described above, and there is a limit to the high magnetic flux density.

As a method for improving the magnetic properties of a non-oriented electrical steel sheet by improving the primary recrystallization texture, Sn addition as disclosed in JP-A-55-158252 and JP-A-6-58252 is disclosed.
There is disclosed a method for producing a non-oriented electrical steel sheet having excellent magnetic properties by improving the texture by adding Sn, Cu as in JP-A 2-180014 or by adding Sb as in JP-A-59-100217. However, the addition cost of Sn, Cu, Sb, etc., which is a texture control element, is not low at all, and there has been a limit to the provision of a low-cost method for producing a non-oriented electrical steel sheet.

In addition, although measures in the manufacturing process such as devising a finish annealing cycle as described in JP-A-57-35626 have been taken, even if the iron loss is reduced in any case, There was not much effect on the magnetic flux density.

As described above, the prior art has not been able to manufacture a non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss, and has not been able to meet the above-mentioned demand for a non-oriented electrical steel sheet.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems in the prior art and to provide a non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss.

[0014]

The gist of the present invention is as follows. That is, (1) in steel, in weight%, 0.10% ≦ Si ≦ 2.50%, C ≦ 0.0025
%, N ≦ 0.0020%, S ≦ 0.0020
%, Ti ≦ 0.0030%, Nb ≦ 0.0030
%, V ≦ 0.0050%, As ≦ 0.0030
%, With the balance being Fe and inevitable impurities α
Using a slab with a γ-transformed component, hot rolling it into a hot-rolled sheet, subjecting it to one cold rolling step followed by finish annealing.
In the method for producing a non- oriented electrical steel sheet, the hot rolling finish temperature is set to a temperature range of Ar ₃ points or higher, and the non-oriented electrical steel sheet is produced in the following manner. %, 0.10% ≦ Si ≦ 2.50%, at least one of Mn and Al and 0.10% ≦ Al
≦ 1.00%, 0.10% ≦ Mn ≦ 2.00%, and the total amount of Si and Al is Si + 2Al ≦ 2.50%
And C ≦ 0.0025%, N ≦ 0.0020
%, S ≦ 0.0020%, Ti ≦ 0.0030
%, Nb ≦ 0.0030%, V ≦ 0.0050
%, As ≦ 0.0030%, and the balance α consisting of Fe and unavoidable impurities
using slab component having a γ transformation, the hot rolling hot rolled sheet, in the manufacturing method of the non-oriented electrical steel sheet subjected to subjected then finish annealing the single cold rolling step, the hot rolling finishing temperature Ar ₃ (3) Furthermore, in each of the above inventions, the winding temperature is 68
0 ℃ or more, or skin after finishing annealing
A pass rolling process is performed .

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below. As a result of intensive studies of the problems in the prior art in order to simultaneously achieve low iron loss and high magnetic flux density, the inventors have found that in a non-oriented electrical steel sheet having a transformation, Si is 0.1%.
~ 2.5%, Al 0.1% to 1.0%, Mn 0.1
% To 2.0% of the steel with αγ transformation, C,
S and N contents are reduced, and Ti, V, Nb,
If a high-purity steel is obtained by simultaneously reducing the As content, the hot-rolled crystal structure is coarsened and the magnetic flux density is high and the iron loss is low even if the finish hot-rolling end temperature is set to a temperature range of Ar ₃ or higher. The inventors have found that it is possible to manufacture a non-oriented electrical steel sheet and have completed the invention.

The magnetic properties of the non-oriented electrical steel sheet can be improved by coarsening the crystal structure before cold rolling. Therefore, conventionally, in finish hot rolling, the hot rolling end temperature is raised to coarsen the hot rolled structure, increase the magnetic flux density of the product, and reduce the iron loss. However, when the hot rolling finish temperature is raised to reach the α + γ2 phase region or γ region, the transformation from the γ phase to the α phase progresses after the hot rolling is completed, and the hot rolled structure becomes fine-grained, resulting in poor magnetic properties. Because of this, it has been said to be something that should be avoided. Therefore, αγ
It has been said that it is indispensable to carry out hot rolling in the upper limit of the α range in the non-oriented electrical steel sheet having a transformation, but in the low-grade non-oriented electrical steel sheet having a low Si content, the Ar ₁ transformation point Is 900 ° C. or less, there is a limit to the coarsening of the hot rolled crystal structure due to an increase in the hot rolling end temperature, and as a result, there is a limit to the improvement of magnetic properties.

The inventors of the present invention have conducted extensive studies to overcome the limit of the control hot rolling of conventional non-oriented electrical steel sheets having such transformation, and as a result, in the non-oriented electrical steel sheet having transformations, Si 0.1% to 2.5%, Al 0.10% to
In a steel containing 1.0% and 0.10% to 2.0% of Mn and having an αγ transformation, the contents of C, S and N are reduced,
Further, if the Ti, V, Nb, As contents are simultaneously reduced to obtain a high-purity steel, even if the hot rolling end temperature is increased to the γ range, the crystal structure of the α phase after transformation does not become fine grain. We have found a completely new finding that the hot-rolled crystal structure becomes coarser as the hot-rolling end temperature rises. By using the hot-rolled sheet obtained by such a method as the starting material, the magnetic flux density in the product after finish annealing is extremely high, and the non-oriented electrical steel sheet with good iron loss (low iron loss value) is inexpensive. Succeeded in manufacturing.

First, the components will be described. Si is added to increase the specific resistance of the steel sheet, reduce the eddy current loss, and improve the iron loss value. If the Si content is less than 0.10%, a sufficient specific resistance cannot be obtained, so it is necessary to add 0.10% or more. On the other hand, the Si content is 2.50%
.Alpha..gamma.

Al, like Si, also has the effect of increasing the specific resistance of the steel sheet and reducing eddy current loss. For this purpose, it is necessary to add 0.10% or more. On the other hand, Al
If the content exceeds 1.00%, the magnetic flux density decreases and the cost also increases, so the content is made 1.00% or less. further,
If (Si + 2Al) exceeds 2.50%, αγ transformation does not occur, so (Si + 2Al) ≦ 2.50% must be satisfied. Also, the Al content in the steel is 0.10%
Even if it is less than the above, the effect of the present invention is not impaired at all.

Mn, like Al and Si, has the effect of increasing the specific resistance of the steel sheet and reducing eddy current loss. Therefore, the Mn content needs to be 0.10% or more.
On the other hand, if the Mn content exceeds 2.0%, the deformation resistance during hot rolling increases and hot rolling becomes difficult, and the crystal structure after hot rolling tends to become finer, which deteriorates the magnetic properties of the product. The Mn content needs to be 2.0% or less.

The control of the C content is an essential point of the component definition of the present invention, and it is necessary to control it to 0.0025% or less. If the C content exceeds 0.0025%, the crystal structure becomes finer due to the α + γ region after hot rolling or the transformation from the γ region to the α phase, so the content must be 0.0025% or less.

S and N are partially re-dissolved during heating of the slab in the hot rolling process, and sulfides such as MnS and A during hot rolling.
Form a nitride such as 1N. The presence of these elements provides nuclei of the α phase during the transformation from the γ phase to the α phase after hot rolling, and prevents the grain growth of the α phase crystal structure after transformation, so that their content is both 0.0020% or less. And need to.

Further, the Ti content, V content, and Nb content are 0.0030%, 0.0030%, and 0.00, respectively.
If it exceeds 50%, precipitation of nitrides such as TiN, VN, NbN becomes remarkable, coarsening of the hot rolled crystal structure is hindered, and crystal grain growth in the finish annealing step is hindered to deteriorate magnetic properties. Therefore, the Ti content, V content, and Nb content must be 0.0030% or less, 0.0030% or less, and 0.0050% or less, respectively.

Further, the As content must be suppressed as a factor that influences the formation of precipitates that inhibit crystal grain growth. As, by itself, does not form precipitates such as the above-mentioned sulfides and nitrides in the steel within the composition range of the present invention. However, when a certain amount of As or more is contained in the steel, the sulfide size becomes fine, so that the coarsening of the hot rolled crystal structure is significantly hindered. From this perspective, A
The s content must be 0.0030% or less.

In order to improve the mechanical characteristics of the product, the magnetic characteristics, the rust resistance, or other purposes, P,
Even if one or more of B, Ni, Cr, Sb, Sn, and Cu are contained in the steel, the effect of the present invention is not impaired.
For example, P is added within the range of up to 0.1% in order to improve the punchability of the product. P ≦ 0.2
%, There is no problem from the viewpoint of magnetic properties of the product. B
Is added in order to form BN during hot rolling to prevent fine precipitation of AlN and render N harmless. B content is N
It is necessary to balance the amount of B and N, and the content thereof preferably satisfies the ratio of both B% / N% of 0.5 to 1.5.

Next, the process conditions of the present invention will be described. In the prior art, the main focus is to coarsen the grain size of the hot-rolled sheet, that is, the grain size before cold rolling as much as possible. It is considered to be harmful because it is refined, and the finishing hot rolling temperature is set to Ar ₁
If the temperature is raised above the point, the hot-rolled crystal structure becomes rather fine-grained, so the use of the method of increasing the finish hot-rolling end temperature to the γ region as in the present invention was not omitted. However, as a result of intensive investigations by the inventors, C, N, S and other T
By controlling the content of impurities such as i, V, Nb and As, the hot-rolled crystal structure is coarsened even when finishing rolling is completed with Ar ₃ or more in the hot rolling process, and as a result, the magnetic properties of the product are improved. The inventors have found that they can be significantly improved, and completed the present invention.

The following experiment was conducted to examine the difference in hot rolled crystallographic structure formation depending on the hot rolling conditions depending on the purity of the steel. Steel with the components shown in Table 1 was melted and finish hot rolling was performed. Finish hot rolling finish temperature is 800 ℃ to 1000
The temperature was set in the range of ℃ and finished to a thickness of 2.5 mm. This was pickled, cold rolled to a thickness of 0.5 mm, degreased, then annealed at 720 ° C. for 30 seconds, and an Epstein sample was cut out to measure the magnetic properties. Changes in the crystal grain size of the hot-rolled sheet with respect to the hot-rolling finishing temperature, product iron loss, and product magnetic flux density are shown in FIGS. 1, 2 and 3, respectively.

[0028]

[Table 1]

In the high purity steel of component 1, the hot rolling finish temperature is A
Although the hot-rolled crystal structure becomes coarse at r ₃ or higher, the hot-rolled crystal structure of the comparative material of component 2 becomes finer when the hot-rolling finishing temperature is ₁ or higher at Ar. As a result, in the high-purity steel of component 1, the iron loss decreases as the hot rolling end temperature increases,
Although the magnetic flux density is improved, in the comparative example of component 2, the magnetic properties are deteriorated, such as an increase in iron loss and a decrease in magnetic flux density. Thus, starting with C, N, S, Ti, V, N
High-purity steel with reduced impurities such as b and As is finished at the hot rolling end temperature of Ar ₃ or higher to reduce iron loss in products, increase magnetic flux density, and non-oriented electrical steel sheet with excellent magnetic properties. It is possible to manufacture

The steel slab consisting of the above components is melted in a converter and manufactured by continuous casting or ingot-slab rolling. The steel slab is heated by a known method. This slab is hot-rolled to a predetermined thickness. At this time, the finish hot-rolling temperature is set to an Ar ₃ point or higher. Winding temperature is 680
If it is at least ℃, it is possible to further promote the coarsening of the hot rolled crystal structure in the present invention.

When the hot rolling end temperature is lower than the Ar ₃ point, the growth of the hot rolled crystal structure becomes insufficient and a non-oriented electrical steel sheet having excellent magnetic properties cannot be obtained. For this reason, it is preferable that the hot rolling end temperature is at or above the Ar ₃ point. The upper limit of the hot rolling end temperature is not particularly set, but the upper limit of the slab heating temperature during hot rolling and the hot rolling schedule inevitably determine the upper limit. Further, if the coiling temperature is 680 ° C. or lower, the growth of the hot-rolled crystal structure becomes insufficient, and a non-oriented electrical steel sheet having excellent magnetic properties cannot be obtained. Therefore, the winding temperature is 680 ° C or higher, preferably 70 ° C.
It is preferably 0 ° C. or higher.

The hot rolled sheet thus obtained is made into a product by one cold rolling and continuous annealing. Further, a skin pass rolling process may be added to obtain a product. If the skin pass rolling ratio is less than 2%, the effect cannot be obtained, and if it is 20% or more, the magnetic properties deteriorate, so the skin pass rolling ratio is set to 2% to 20%.

[0033]

EXAMPLES Next, examples of the present invention will be described. [Example 1] A slab for non-oriented electrical steel having the components and transformation points shown in Table 2 was heated by a usual method and hot rolled to a thickness of 2.5 mm. At this time, the hot rolling finish temperature is 9
The temperature was set to 50 ° C. and all were set to the Ar ₃ transformation point or higher. The winding temperature for hot rolling was 700 ° C. After that, it was pickled and cold-rolled to 0.50 mm. This was annealed at 730 ° C. for 30 seconds in a continuous annealing furnace. Then, it cut | disconnected to the Epstein sample and measured the magnetic characteristic. In Table 2, the components of the present invention and the comparative example and the magnetic measurement results are shown together. If the purity of the steel is controlled in this way, it is possible to obtain a non-oriented electrical steel sheet having a high magnetic flux density value and a low iron loss value and excellent magnetic properties by controlling the winding temperature to be Ar ₃ or higher. It is possible.

[0034]

[Table 2]

Example 2 A slab for non-oriented electrical steel having the components and transformation points shown in Table 3 was heated by a usual method and hot rolled to a thickness of 2.5 mm. At this time, the hot rolling end temperature is 950 ° C., which is Ar ₃ or higher, and 850, which is Ar ₁ or lower.
The temperature was set to 2 ° C. and the coiling temperature was set to 700 ° C. by cooling control. After that, pickling and cold rolling 0.50mm
And 0.55 mm. A sheet having a thickness of 0.50 mm was annealed at 730 ° C. for 30 seconds in a continuous annealing furnace. afterwards,
Annealing was performed at 750 ° C. for 2 hours, which is equivalent to that of a consumer. In addition, a sheet with a thickness of 0.55 mm is kept at 700 ° C for 20 minutes in a continuous annealing furnace.
It is annealed for 2 seconds, and is subjected to a skin pass rolling with a reduction rate of 9% to give a 0.2.
Finished to a thickness of 50 mm, and annealed at 750 ° C for 2 hours, which is equivalent to that of consumers. Epstein test pieces were cut out from these samples and the magnetic properties were measured. Tables 4 and 5 also show the hot rolling finish temperature, winding temperature and magnetic measurement results of the present invention and comparative examples described in the examples.

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

[Table 5]

As described above, by setting the hot rolling end temperature to the Ar ₃ point or higher, it can be seen that a material having a high magnetic flux density and a low iron loss value can be obtained by both the single pass method and the skin pass rolling method.

[0040]

As described above, according to the present invention, it is possible to manufacture a non-oriented electrical steel sheet having high magnetic flux density, low iron loss, and excellent magnetic properties.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a hot rolling finish temperature and a hot rolled sheet crystal grain size.

FIG. 2 is a diagram showing a relationship between hot rolling end temperature and product iron loss.

FIG. 3 is a diagram showing a relationship between a hot rolling finish temperature and a product magnetic flux density.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-3-193822 (JP, A) JP-A-6-336609 (JP, A) JP-A-6-57332 (JP, A) JP-A-6- 108149 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C21D 8/12 H01F 1/16 C22C 38/00 303

Claims (4)

(57) [Claims] 1. By weight% in steel, 0.10% ≦ Si ≦ 2.50%, C ≦ 0.0025%, N ≦ 0.0020%, S ≦ 0.0020%, Ti ≦ 0.0030 %, Nb ≦ 0.0030%, V ≦ 0.0050%, As ≦ 0.0030%, and the balance α consisting of Fe and inevitable impurities.
Using a slab with a γ-transformed component, hot rolling it into a hot-rolled sheet, subjecting it to one cold rolling step followed by finish annealing.
In the method for producing a non- oriented electrical steel sheet, the hot rolling finish temperature is set to a temperature range of Ar ₃ points or higher. 2. In steel, in weight%, 0.10% ≦ Si ≦ 2.50%, at least one of Mn and Al, and 0.10% ≦ Al ≦ 1.00%, 0.10% ≦ Mn ≦ 2.00%, and the total amount of Si and Al is Si + 2Al ≦ 2.50%, C ≦ 0.0025%, N ≦ 0.0020%, S ≦ 0.0020%, Ti ≦ 0.0030%, Nb ≦ 0.0030%, V ≦ 0.0050%, As ≦ 0.0030%, and the balance α consisting of Fe and unavoidable impurities
Using a slab with a γ-transformed component, hot rolling it into a hot-rolled sheet, subjecting it to one cold rolling step followed by finish annealing.
In the method for producing a non- oriented electrical steel sheet, the hot rolling finish temperature is set to a temperature range of Ar ₃ points or higher. 3. A skin pass rolling step after finish annealing.
The method according to claim 1 or 2, characterized in that
Method for manufacturing tropic electrical steel sheet. 4. The process for producing a non-oriented electrical steel sheet according to any one of claims 1 to 3 hot-rolled sheet winding temperature, characterized in that a 680 ° C. or higher.