JPH09263909A - Nonoriented silicon steel sheet excellent in core loss characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a nonoriented silicon steel sheet excellent in core loss characteristics in with low core loss value below that obtd. by the existing method can be obtb. even if magnetic annealing is executed at a lower temp. for a shorter time. SOLUTION: This nonoriented silicon steel sheet excellent in core loss characteristics satisfies the following conditions: (1) being composed of a steel contg., by weight, <=0.01% C, <=1% Si, 0.1 to 0.8% Mn, <=0.01% S, <=0.004% Al and <=0.05 Cu and (2) in the case the number of secondary phase grains contained in the steel is obtd. as the number per unit area by microscopic obvervation, that of the secondary phase grains having 0.1 to 0.5μm diameter is regulated to 500 to 5,000pieces/mm<2> and that of the secondary phase grains having >0.5μm diameter to <=500pieces/mm<2> .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-oriented electrical steel sheet, and more particularly to a semi-processed non-oriented electrical steel sheet in which a component is magnetically annealed after working.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are used in generators, electric motors,
It is widely used in electrical equipment such as small transformers, but its low iron loss is indispensable for energy saving and has become an eternal theme.

On the other hand, when using a semi-processed non-oriented electrical steel sheet, not only the iron loss is reduced, but also the magnetic annealing performed after the parts are processed is made at a lower temperature for a shorter time to improve the productivity and reduce the cost. There is a desire from the user side.

FIG. 3 shows an example of the magnetic annealing temperature dependency of the iron loss value (W _15/50 ) of the existing semi-processed non-oriented electrical steel sheet. The data in the figure are values when the magnetic annealing time is set to the current 2 hours using the sample of the component system shown in the figure.

When the annealing temperature is 750 ° C. or higher, a low iron loss value can be stably obtained, but when the annealing temperature is lowered to less than 750 ° C., the iron loss value rapidly increases. Therefore, at present, magnetic annealing is performed at 750 ° C. for 2 hours, but there is a specific demand to reduce the temperature to 730 ° C. for 1 hour at a low temperature.

It is considered that the reason why the iron loss value rapidly increases when the annealing temperature in FIG. 3 is lowered is that the grain size becomes smaller as the annealing temperature lowers. In fact, 750
While the crystal grain size of the annealing at ℃ was about 45μm, 73
It was 25 μm or less at 0 ° C.

As a means for increasing the grain size to reduce iron loss, the number of second phase grains such as inclusions, precipitates and crystallized substances in the steel which are likely to become pinning sites for grain boundary migration during annealing. It has been proposed to reduce the number of lines and control its shape to lose the pinning function.

For example, the range of Mn content relative to Si and S content is
The enclosure is specified and MnS in the solidification process is coarsened to
Japanese Patent Laid-Open No. 3-249115, which loses the training function
In the method described in 1), the heating temperature of the slab is set to 1150 ° C or lower.
Temperature to suppress re-dissolution of MnS,
To prevent reprecipitation of fine MnS, which easily forms ligsite
62-199720 method, SiO in steel
_Two, MnO, Al_TwoO _ThreeOf the oxides of
It lowers the melting point of the oxide to increase the pinning site.
To prevent the formation of fine oxides that tend to be easily removed
39, the diameter of 0.5-5 μm in steel.
10-500 oxides / mm^TwoDisperse and use this as the core
A small amount of MnS tends to be aggregated and precipitated to form a pinning site.
Japanese Patent Publication No. 5-69910 which prevents reprecipitation of fine MnS
There is a method of description.

[0009]

However, the inventors of the present invention have described the method of controlling the second phase particles, which is advantageous for reducing iron loss, described in the above-mentioned patent publication, in the magnetic annealing of a semi-process non-oriented electrical steel sheet. As a result of studying whether it can be applied to a low temperature and a short time, it was not possible to obtain a low iron loss value as obtained by the current method under the condition of 730 ° C. × 1 hour.

The present invention has been made in order to solve such a problem, and has an iron loss characteristic which can obtain a low iron loss value equal to or less than that obtained by the current method even if the magnetic annealing is performed at a low temperature for a short time. An object is to provide an excellent non-oriented electrical steel sheet.

[0011]

The above problems can be solved by a non-oriented electrical steel sheet having excellent iron loss characteristics, which is characterized by satisfying the following conditions.

(B) Weight%, C: 0.01% or less, S
i: 1% or less, Mn: 0.1 to 0.8%, S: 0.01
% Or less, Al: 0.004% or less, Cu: 0.05% or less, and (b) the number of second phase particles contained in the steel as the number per unit area by microscopic observation. When determined, the number of second phase particles having a diameter of 0.1 to 0.5 μm is 500 to 5000 particles / mm ² , and the number of second phase particles having a diameter of more than 0.5 μm is 500 particles / mm ² or less.

First, for the purpose of investigating the existing state of the second phase particles in the steel existing before the magnetic annealing of the existing semi-processed non-oriented electrical steel sheet, the sample shown in FIG. 3 was observed by an electron microscope. . As a result, M with a diameter of 0.1 to 0.5 μm
nS-MnO, SiO ₂ over 0.5 μm, Si
O ₂ -MnS and many CuS with a diameter of about 10 nm
Was observed.

Therefore, in order to examine how the state of existence of such second phase particles influences the iron loss value after magnetic annealing, the steel of the component system shown in FIG. The sample was prepared by changing the cooling rate of the second phase particles to change the existing state of the second phase particles, and observed by an electron microscope before magnetic annealing or at 730 ° C.
The iron loss value was measured after magnetic annealing for × 1 hour.

FIG. 4 shows the relationship between the cooling rate during solidification by casting and the state of existence of the second phase particles. Note that the iron loss value (W
_15/50 ) is also shown.

Here, the number of the second phase particles is counted by size by observation with an electron microscope, and the unit visual field area (1 m
m ² ) is the number expressed per number (hereinafter, the number of second phase particles is according to this definition).

Whether the cooling rate at the time of solidification by casting is the current 2 ° C / sec
When accelerated to 10 ° C / sec from the
The number of two-phase particles has increased, and even in magnetic annealing at 730 ° C for 1 hour
The iron loss value (W_15/50= 4.
5w / kg) lower value (W _15/50= 3.9w / kg)
You can see that

When the morphological analysis of the second phase particles of the sample with the faster cooling rate during casting and solidification was performed, fine CuS was drastically reduced, and most of Cu and S had a diameter of 0.1 to 0. 5
Cu in the MnS-MnO particles that are the second phase particles of μm
It was found to exist as S. From this,
By increasing the cooling rate during solidification of casting, MnS-M
It is presumed that the number of nO particles increased, the coagulation and coarsening of CuS centered on the nO particles were promoted, the grain growth property was improved, and the iron loss was reduced.

As described above, if the adverse effect of fine CuS is reduced by increasing the number of the second phase particles having a diameter of 0.1 to 0.5 μm, the value is less than the value obtained by the current method even in the magnetic annealing at low temperature for a short time. Since it was found that a low iron loss value was obtained, the suitable range of the number was investigated.

Using steels 1 to 4 of the composition system shown in Table 1, the cooling rate at the time of solidification by casting was changed to change the number of second phase particles having a diameter of 0.1 to 0.5 μm, and 730 ° C. for 1 hour. The iron loss value (W _15/50 ) after magnetic annealing was investigated.

FIG. 1 shows the relationship between the number of second phase particles having a diameter of 0.1 to 0.5 μm and the iron loss value (W _15/50 ) of each steel. The black mark in the figure indicates the iron loss value obtained by the current method, that is, when the current 750 ° C x 2 hours magnetic annealing is performed using each steel having the existing state of the second phase particles. (W _15/50 ) It shows the sample below.

By adjusting the number of the second phase particles having a diameter of 0.1 to 0.5 μm to 500 to 5000 particles / mm ² ,
It can be seen that even at 730 ° C. for 1 hour, a lower iron loss value can be obtained than in the current case. In addition, 800 to 3500 pieces / mm ²
By doing so, a low iron loss value can be stably obtained without depending on the number of particles.

The reason why the iron loss value becomes high when the number of the second phase particles having a diameter of 0.1 to 0.5 μm is less than 500 particles / mm ² is, as described above, the existence state of the second phase particles. Then, it is considered that a large number of fine CuS exist and inhibit grain growth. Further, the reason why the iron loss value becomes high when the number exceeds 5000 / mm ² is presumed that even particles of this size have an effect of hindering grain growth when the number is too large.

The number of the second phase particles having a diameter of more than 0.5 μm in these samples was 500 particles / mm ² or less, but particles of this size may have some influence on iron loss. Using Steels 1 to 4 shown in Table 1, the number of particles was changed by changing the degassing time (refluxing time after deoxidation) of the molten steel, and the same investigation as above was performed. At this time, the diameter is 0.
The number of 1-0.5 μm second phase particles is within the scope of the invention.

FIG. 2 shows the relationship between the number of second phase particles of each steel having a diameter of more than 0.5 μm and the _iron loss value (W _15/50 ). Like in FIG. 1, the black-filled marks in the figure indicate samples having _iron loss values (W _15/50 ) or less obtained by the current method.

It can be seen that when the number of second phase particles having a diameter of more than 0.5 μm is 500 particles / mm ² or less, a lower iron loss value can be obtained even at 730 ° C. for 1 hour than in the current case. If the number is 400 particles / mm ² or less, a low iron loss value can be stably obtained without depending on the number of particles.

The reason why the iron loss value becomes high when the number of second phase particles having a diameter of more than 0.5 μm exceeds 500 particles / mm ² is as follows.
It is considered that when the number of particles of this size increases, the domain wall movement is hindered and the hysteresis loss increases.

As described above, the core of the present invention is to control the existence form of the second phase particles, but in order to bring out the effect effectively and to satisfy other properties required as a magnetic steel sheet. Needs to limit the components as follows.

C: If it exceeds 0.01%, the iron loss value increases and the magnetic flux density decreases, so the content is made 0.01% or less.

Si: If it exceeds 1%, the number of SiO ₂ increases and the effect of the present invention cannot be obtained, so the content is made 1% or less.

If Mn: less than 0.1%, red hot embrittlement may occur during hot rolling, and if it exceeds 0.8%,
Since it causes a decrease in magnetic flux density, it is set to 0.1 to 0.8%.

S: If it exceeds 0.01%, CuS, Mn
Since the number of sulfides such as S increases, the effect of the present invention cannot be obtained, and red hot brittleness may occur.
It is set to 01% or less.

Al: If it exceeds 0.004%, fine A
Since 1N increases and the effect of the present invention cannot be obtained, 0.00
4% or less.

Cu: If it exceeds 0.05%, the formation of fine CuS that inhibits grain growth cannot be sufficiently controlled,
The effect of the present invention cannot be obtained, so the content is made 0.05% or less.

In addition to the contents of the above component elements, weight%
C: 0.005% or less, P: 0.2% or less, N:
It is preferably 0.005% or less for the following reason.

C: 0.005% or less is preferable because magnetic aging can be prevented.

P: A component that improves the punchability of the steel sheet, but if added in a large amount, the steel sheet becomes brittle, so it is preferably made 0.2% or less.

N: Depending on the content of Al, fine AlN increases and hinders grain growth, leading to an increase in iron loss value, so it is preferably 0.005% or less.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION In order to reduce the Cu content to 0.05% by weight or less, refining may be performed using a raw material or an auxiliary raw material having a low Cu content.

In order to reduce the S content to 0.01% by weight or less, either S removal by hot metal or S removal by ladle refining may be used, and a raw material or an auxiliary raw material having a low S content may be used. You may refine it.

Sb, Sn, B, Z for improving magnetic characteristics
Addition of r does not impair the effects of the present invention.

The number of the second phase particles having a diameter of more than 0.5 μm can be adjusted by adjusting the flow of molten steel and electromagnetic stirring during casting in addition to the degassing time.

Such molten steel can be manufactured by a converter or an electric furnace. The cooling rate at the time of solidification by casting can be increased by enhancing the ability of cooling spray or by reducing the thickness of the slab.

The casting may be either ingot casting or continuous casting. After casting, it undergoes slabbing in the case of ingot casting, as it is in the case of continuous casting, and is hot-rolled after reheating or without reheating. It is manufactured in the same process as the magnetic electrical steel sheet.

The effect of the present invention can be obtained even if heat treatment of a hot-rolled sheet is performed or cold rolling and annealing are repeated.

As the second phase particles which are a constituent feature of the present invention, MnS--MnO (-Cu) having a diameter of 0.1 to 0.5 .mu.m.
S), SiO ₂ over 0.5 μm, SiO ₂ -M
Although nS is exemplified, the effect of the present invention is not limited to these types of particles, and other sulfides, oxides, carbides,
A similar effect can be obtained with nitride or the like.

[0047]

EXAMPLES Table 1 shows the steels of the 17 kinds of components used in this example. Steels 1 to 11 are steels of the present invention, and steels 12 to 17 are comparative steels based on steel 2. S for Steel 12
i amount, Mn amount in Steel 13, S amount in Steel 15, Steel 1
6, the amount of Al is larger than that of the present invention, and the amount of Cu of steel 17 is larger than that of the present invention, and the amount of Mn of steel 14 is smaller than that of the present invention. The balance of any of the steels is Fe and inevitable impurities.

After smelting these steels, as shown in Tables 2 and 3, the degassing time and the cooling rate after casting and solidification were changed to prepare slabs in which the state of existence of the second phase particles was variously changed.

These slabs were hot-rolled under the conditions of finishing temperature of 810 ° C. and winding temperature of 670 ° C. to prepare hot-rolled sheets having a plate thickness of 2.3 mm.

After pickling these hot rolled sheets, the sheet thickness is 0.5 mm.
Cold rolled to 690 to 730 ° C and annealed to sample N
o. 1-32 semi-process electromagnetic steel sheets were produced.

These samples were subjected to magnetic annealing at 730 ° C. for 1 hour or 750 ° C. for 1 to 2 hours, and iron loss W _15/50
And the magnetic flux density B ₅₀ was determined. Here, the iron loss W _15/50 and the magnetic flux density B ₅₀ are measured by the 25 cm Epstein test (JISC25
50) is a value obtained by measuring in the longitudinal direction and the width direction of the steel sheet and averaging them.

Further, the existence state of the second phase particles in the steel before magnetic annealing of each sample was observed with an electron microscope of SEM or TEM, and the number of the second phase particles per unit area was obtained for each size.

For comparison, Table 1 also shows the iron loss W _15/50 and the magnetic flux density B ₅₀ when magnetically annealing the samples produced by the current method for each steel at the current 750 ° C. for 2 hours. .

The results are shown in Tables 2 and 3. In the sample in which the state of existence of the components and the second phase particles is within the range of the present invention, 730
By magnetic annealing at ℃ × 1 hour, the iron loss value below the value obtained by the current method can be obtained. For some samples, 75
Magnetic annealing was also performed at 0 ° C for 1 to 2 hours.
Even lower iron loss values can be obtained than in the case of magnetic annealing at 30 ° C. for 1 hour.

On the other hand, if the amount of Si, S, Al, Cu is larger than the range of the present invention or the state of the second phase particles is outside the range of the present invention, the magnetic annealing at 730 ° C. for 1 hour can be obtained by the current method. The iron loss value below the value cannot be obtained.

When the amount of Mn is more than the range of the present invention, there is no problem in the iron loss value, but the magnetic flux density is remarkably reduced.

Further, if the amount of Si is larger than the range of the present invention, the magnetic flux density is remarkably lowered, but it is a value of the magnetic flux density which is not a problem when applied to a high-grade high-grade electrical steel sheet of high Si.

In Sample 14, in which the amount of Mn was less than the range of the present invention, cracking was observed during hot rolling.

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

[Table 3]

[0062]

Since the present invention is configured as described above, a non-oriented electrical steel sheet which can obtain a low iron loss value equal to or less than that obtained by the current method even if the magnetic annealing is performed at a low temperature for a short time. And the manufacturing method for the same can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the number of second phase particles having a diameter of 0.1 to 0.5 μm and the _iron loss value (W _15/50 ).

FIG. 2 is a diagram showing the relationship between the number of second phase particles having a diameter of more than 0.5 μm and the _iron loss value (W _15/50 ).

FIG. 3 is a diagram showing an example of the magnetic annealing temperature dependency of the iron loss value (W _15/50 ) of a current semi-process non-oriented electrical steel sheet.

FIG. 4 is a diagram showing a relationship between a cooling rate during solidification by casting and a state of existence of second phase particles.

Claims (2)

[Claims] 1. A non-oriented electrical steel sheet having excellent iron loss characteristics, which satisfies the following conditions. (A) In% by weight, C: 0.01% or less, Si: 1% or less, Mn: 0.1 to 0.8%, S: 0.01% or less, A
l: 0.004% or less, Cu: 0.05% or less, and (b) When the number of second phase particles contained in the steel is determined as the number per unit area by microscopic observation. , The second phase particles having a diameter of 0.1 to 0.5 μm are 500 to 5
The number of second-phase particles exceeding 000 particles / mm ² and a diameter of 0.5 μm is 500 particles / mm ² or less. 2. A non-oriented electrical steel sheet having excellent iron loss characteristics, which satisfies the following conditions. (A) In% by weight, C: 0.005% or less, Si: 1% or less, Mn: 0.1 to 0.8%, P: 0.2% or less, S:
0.01% or less, Al: 0.004% or less, N: 0.0
A steel containing 0.05% or less and Cu: 0.05% or less,
Moreover, when the number of the second phase particles contained in the steel (b) is determined as the number per unit area by microscopic observation, the second phase particles having a diameter of 0.1 to 0.5 μm are 500 to 5000 particles / mm ^2. , 500 second phase particles with a diameter of more than 0.5 μm
The number of pieces / mm ² or less.