JPH0967654A - Nonoriented silicon steel sheet excellent in core loss characteristics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a nonoriented silicon steel sheet excellent in core loss characteristics even by finish annealing at a low temp. in a short time and magnetic annealing at a low temp. in a short time. SOLUTION: This nonoriented silicon steel sheet has a compsn. consisting of, by weight, >1 to 3.5% Si, 0.1 to 1% Al, 0.1 to 0.8% Mn, <=0.05% Cu and <=0.01% S, and in which the size and the number of inclusions contained therein are regulated to: those having 0.1 to 0.5μm diameter are 500 to 5000 pieces/mm<2> and those having >0.5μm diameter are <=500 pieces/mm<2> . Furthermore, the content of C is regulated to <=0.005%, P to <=0.2% and N to <=0.005%.

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 having excellent iron loss characteristics.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are used in generators, electric motors,
Widely used in electrical equipment such as small transformers. Recently, in response to the trend of energy saving for these products, there is an increasing demand to keep the energy when electric equipment is used as low as possible, and it is even more important to supply steel sheets with less iron loss. It has been demanded.

It is generally known that the iron loss decreases as the crystal grain size of a steel sheet during use increases, and a steel sheet that can easily coarsen the crystal grain size in finish annealing or magnetic annealing is demanded. There is. In the case of medium- and high-grade non-oriented electrical steel sheets in which the amount of Si + Al is about 1 to 3%, which requires low iron loss, the finish annealing temperature is 1000
At present, the crystal grain is coarsened by increasing the temperature to ℃ or by decreasing the line speed during annealing to lengthen the annealing time, and the manufacturing cost is relatively high.

In response to the above demands, the amount of inclusions or precipitates that are likely to become pinning sites at grain boundaries is reduced, or the shape or composition of inclusions or precipitates in a steel sheet is controlled to function as a pinning site. Attempts have been made to lose the.

[0005] For example, in Japanese Patent Application Laid-Open No. 3-249115, by setting the amount of Mn in a specific range with respect to the amounts of Si and S, MnS in the solidification process is increased, and coarse MnS which does not easily function as a pinning site is obtained. It has been proposed to. Further, in Japanese Patent Laid-Open No. 62-199720, there is a method in which the slab heating temperature is set to a low temperature of 1150 ° C. or lower and the re-dissolved MnS is prevented so as to control the amount of re-precipitated MnS that is easily finely dispersed. Proposed. Furthermore, Japanese Patent Publication No. 56-33451 proposes that the slab is kept at a specific temperature to coarsen AlN and make it harmless to the growth of crystal grains.

On the other hand, in JP-A-1-152239, the composition of oxides in the steel sheet, specifically SiO ₂ and Mn.
It has been proposed to lower the ratio of MnO to O and Al ₂ O ₃ to raise the melting point of the oxide and prevent the dispersion of fine inclusions that tend to function as pinning sites. Further, in Japanese Examined Patent Publication No. 5-69910, 10 to 500 oxides / mm ² having a diameter of 0.5 to 5 μm are left, and MnS is agglomerated and precipitated using the oxides as nuclei to form fine Mn particles.
It has been proposed to reduce the precipitation of S.

[0007]

However, recently, not only energy saving of electric equipment but also energy saving is demanded not only in the manufacturing process of electromagnetic steel sheets and electric parts using the same, but the concrete One of the specific requests is to perform finish annealing at a lower temperature and shorter time than ever.

In such a case, according to the experiments by the present inventors, as described above, MnS coarsening or AlN coarsening, or the composition of the oxide-based inclusions, the formation of a relatively large oxide and the It has been proved that the grain growth cannot be sufficiently achieved by only adsorbing MnS according to the above, and the required iron loss characteristics cannot be obtained.

An object of the present invention is to provide a non-oriented electrical steel sheet which facilitates such crystal grain growth at low temperature and short time and has excellent iron loss characteristics even in finish annealing or magnetic annealing at low temperature and short time. I am trying.

[0010]

The first aspect of the present invention is, in weight% (hereinafter, the same), Si: more than 1% and 3.5% or less, Al: 0.
1 to 1%, Mn: 0.1 to 0.8%, Cu:
0.05% or less (including 0), S: 0.01% or less (0
500), which is a non-oriented electrical steel sheet having a diameter of 0.1 to 0.5 μm.
~ 5000 pieces / mm ² , 5 with diameter over 0.5 μm
It is a non-oriented electrical steel sheet having excellent iron loss characteristics, which is characterized in that it is not more than 00 pieces / mm ² .

The second invention is C: 0.005% or less, P:
0.2% or less, N: 0.005% or less, Si: more than 1% and 3.5% or less, Al: 0.1-1%, Mn: 0.1-
A non-oriented electrical steel sheet containing 0.8%, Cu: 0.05% or less (including 0), S: 0.01% or less (including 0), which is included in the steel sheet. With a diameter of 0.
1 to 0.5 μm is 500 to 5000 pieces / mm ² ,
It is a non-oriented electrical steel sheet having excellent iron loss characteristics, characterized in that the number of those having a diameter exceeding 0.5 μm is 500 pieces / mm ² or less.

(1) Inclusions and Precipitates The basic idea of the reason for defining the size and the number of inclusions contained in the steel sheet in the present invention will be described along with the history of research.

The inclusions of the present invention are sulfides, oxides, carbides, nitrides, etc. in the steel sheet, or their binary, 3 and
It shows all of the original composite and is a general term including all of inclusions, precipitates, crystallized substances, etc. (hereinafter, in the specification,
Simply expressed as inclusions).

The inventors of the present invention first observed the inclusions and precipitates of the sample subjected to finish annealing at a low temperature. The chemical composition of the sample is C: 0.0030%, S
i: 1.12%, Mn: 0.13%, P: 0.051
%, S: 0.003%, Al: 0.13%, N: 0.0
It was 021%. Scanning electron microscope (hereinafter SE
(Hereinafter referred to as M) and a transmission electron microscope (hereinafter referred to as TEM), SEM observation was performed by directly observing a steel plate cross section, and TEM observation was performed by extraction replica observation.

As a result of SEM observation, Al ₂ O ₃ , AlN and MnS of about 0.2 to 0.5 μm were observed. Upon further TEM observation, extremely fine precipitates with a size of several tens nm were recognized, and it was confirmed that these were CuS. Until now, such fine precipitates were Al
It was thought to be N or MnS, but at low temperatures Cu
It was obtained as a new finding that S is preferentially precipitated. This is a very important and key finding for the present invention.

Therefore, a method for preventing the generation of such fine CuS was examined. In particular, in the present invention, a measure based on the premise that the existence of Cu and S is unavoidable to some extent was examined.

FIG. 3 shows the relationship between the cooling rate during casting of molten steel and the size and number of inclusions after finish annealing (850 ° C. for 1 minute). The chemical composition and cooling rate of the sample (plate thickness 0.5 mm) used are as shown in the figure. Although iron loss is also shown in the figure, Steel A with a high cooling rate is 4.
Steel B having a low cooling rate of 6 W / kg is 5.6 W / kg, and it can be seen that an increase in the cooling rate causes a decrease in iron loss.

When the inclusion distributions of these steels were compared, the size and number of inclusions having a diameter of more than 0.5 μm were almost the same. On the other hand, a difference was found in the number of inclusions of 0.1 to 0.5 μm, and the cooling rate during casting was fast and W15 /
Compared to Steel B, a larger amount of inclusions was recognized in Steel A having a low 50 of 4.6 W / kg. Furthermore, when observing the morphology of CuS, CuS was not observed so much in steel A having a high cooling rate during casting, whereas the cooling rate during casting was slow and W15 / 50 was as high as 5.6 W / kg. B has the number 1
A lot of very fine CuS having a size of about 0 nm was recognized.

Steel plate A with less iron loss and faster cooling rate
As a result of morphological observation of Cu and S,
And S are MnO as inclusions of 0.1 to 0.5 μm.
It was found to be -MnS-CuS. That is, the reason why the fine CuS decreased and the inclusions of 0.1 to 0.5 μm increased can be presumed to be that CuS aggregated and coarsened with MnO—MnS as the nucleus.

From the above, in order to reduce the adverse effects of CuS and ensure excellent iron loss characteristics, the diameter should be 0.1 to 0.1 mm.
It was found that 0.5 μm inclusions should be present in an appropriate amount to reduce fine CuS.

Next, an appropriate range of the number of inclusions having a diameter of 0.1 to 0.5 μm was examined.

FIG. 1 shows the relationship between the number of inclusions having a diameter of 0.1 to 0.5 μm and iron loss. The sample used here is
Using the steel sheet components 1 and 5 shown in Table 1, the cooling rate during casting was changed, and the diameter after finish annealing was 0.1 to 0.5 μ.
The number of inclusions of m is adjusted.

[0023]

[Table 1]

The balance not shown in Table 1 is Fe and inevitable impurities. The plate thickness of the steel plate is 0.5 mm, the number of inclusions exceeding 0.5 μm contained in the steel plate is 112 to 131, and the value of the iron loss W15 / 50 is 850 ° C. for 1 minute after finish annealing. It is a thing.

As is apparent from FIG. 1, it is clear that the number of inclusions having a diameter of 0.1 to 0.5 μm has a great influence on the iron loss, and that there is an appropriate region, It is understood that the value of should be in the range of 500 to 5000 pieces / mm ² , preferably 1000 to 3000 pieces / mm ² . When the number of inclusions having a diameter of 0.1 to 0.5 μm is less than 500 / mm ^{2, a} large number of very fine CuS having a size of about 10 mm are precipitated, which hinders grain growth during finish annealing, I think that it has deteriorated. On the other hand, the number of inclusions having a diameter of 0.1 to 0.5 μm is 500 to 500.
In the case of 0 pieces / mm ² , very fine Cu of about 10 mm
S is not found, MnS-M of about 0.1 to 0.5 μm
Many nO-CuS were recognized. Conventionally, 0.1-0.5
It was thought that the presence of a large number of inclusions of about μm hinders the growth of crystal grains. It was found that CuS is reduced and a non-oriented electrical steel sheet having iron loss characteristics superior to those of conventional steel sheets can be obtained. Also, the number of inclusions having a diameter of 0.1 to 0.5 μm is 5
If it exceeds 000 pieces / mm ² , the iron loss tends to be high, but it is considered that this is because the number of inclusions increases, and many of them function as pinning sites. Here, the composition of the inclusions of 0.1 to 0.5 μm is not particularly specified. Any inclusions may be used as long as they can agglomerate and coarsen CuS.

Next, an appropriate range of the number of inclusions having a diameter exceeding 0.5 μm will be described. FIG. 2 shows the relationship between the number of inclusions having a diameter exceeding 0.5 μm and iron loss. This figure shows
It was obtained by using the steel sheets 1 and 5 shown in Table 1 and changing the degassing time of the molten steel before casting to adjust the number of inclusions exceeding 0.5 μm after finish annealing. Also,
The number of inclusions of 0.1 to 0.5 μm is adjusted within the range of the invention by changing the cooling rate during casting. The balance not shown in Table 1 is Fe and inevitable impurities. The plate thickness of the steel plate is 0.5 mm, and the value of iron loss W15 / 50 is that after the finish annealing is performed under the conditions shown in the figure.

From FIG. 2, it is recognized that W15 / 50 tends to be low when the number of inclusions having a diameter of more than 0.5 μm is 500 pieces / mm ² or less, and is stable when the number is 300 pieces / mm ² or less. It can be seen that low iron loss can be obtained. When it exceeds 500 pieces / mm ² , W15 / 50 becomes high. It is estimated that this is because the movement of the domain wall is hindered, the hysteresis loss increases, and the iron loss increases due to the increase.

From the above, the number of inclusions having a diameter of more than 0.5 μm should be 500 / mm ² or less, preferably 30.
It is defined as 0 pieces / mm ² or less.

(2) Component Cu is a harmful component which forms CuS. 0.05%
If it exceeds the range, even if the size and number of inclusions are within the range of the present invention, it is not possible to prevent the generation of fine CuS, so the content is made 0.05% or less.

S forms sulfides which are harmful components such as MnS and CuS. In addition, it causes red hot brittleness, so the content is made 0.01% or less.

Si is an effective component for increasing the specific resistance of the steel sheet and reducing iron loss, and is set to more than 1%. Meanwhile, 3.
If it exceeds 5%, the magnetic flux density decreases with the decrease of the saturation magnetic flux density, so the upper limit is made 3.5%.

When Al is added in a small amount, fine A
It forms 1N, inhibits the growth of crystal grains, and increases iron loss. Therefore, 0.1% or more is added. In this case, AlN coarsens, does not hinder the growth of crystal grains, and increases the specific resistance, thereby reducing iron loss. on the other hand,
If it exceeds 1%, the magnetic flux density is lowered. Therefore, 0.1
To 1%.

Mn is a component effective for increasing the specific resistance of the steel sheet and reducing iron loss, and is set to 0.1% or more in order to prevent red hot embrittlement during hot rolling. Also, 0.
If it exceeds 8%, the magnetic flux density decreases, so 0.1 to 0.
8%.

Further, in order to obtain a non-oriented electrical steel sheet having more excellent iron loss characteristics, C is a harmful component which increases iron loss and causes the magnetic aging due to the precipitation of C, so 0.00
5% or less.

P is a component necessary for improving the punchability of the steel sheet, but if it is added in an amount exceeding 0.2%, the steel sheet becomes brittle, so P is made 0.2% or less.

N is an A that inhibits the growth of crystal grains during annealing.
Since 1N increases and iron loss increases, the content is made 0.005% or less.

In the present invention, Sb, Sn, B, Zr
It may be added at all to improve the magnetic properties.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION The method for manufacturing a steel sheet according to the present invention is only required to be able to adjust the number of inclusions having a diameter of more than 0.5 μm and a diameter of 0.1 to 0.5 μm within a predetermined range.

Diameter of 0.5 μm, which is mainly a primary deoxidation product
The control of extra inclusions is performed by, for example, increasing the reflux time of the molten steel degassing process or adjusting the reoxidation from the slag by adjusting the slag composition.

The diameter of the secondary deoxidation product is 0.1 to 0.1
The inclusions of 0.5 μm are controlled by adjusting the solidification cooling rate of the molten steel such as casting speed, heating during casting, auxiliary heating, heat retention, casting thickness, and cooling conditions.

For example, in order to adjust the size and number of inclusions of more than 0.5 μm in the steel plate, degassing treatment is performed before the molten steel casting for 6 minutes or more, or the flow of molten steel during casting is adjusted. , By adjusting the electromagnetic stirring during casting.

In order to adjust the size and number of inclusions of 0.1 to 0.5 μm in the steel sheet, the cooling rate during solidification of molten steel casting is set to about 10 ° C./sec to 20 ° C./sec. In order to secure this cooling rate, the thickness of the slab should be reduced,
Strengthen the cooling spray.

Further, it is preferable to use a raw material containing a small amount of Cu and an auxiliary raw material for refining. It is preferable that S is also desulfurized by desulfurization of hot metal, ladle refining, or the like, or is refined by using a raw material having a small amount of S and auxiliary raw materials.

The molten steel thus obtained in the vacuum melting furnace, converter or electric furnace is subjected to degassing treatment, etc., and then ingot casting, continuous casting or casting with a strip caster, and direct rolling in a hot piece state or steel Hot working is performed after reheating one side.
Hot working, slab rolling, rough rolling, finish hot rolling, finish hot rolling is essential, but slab rolling, rough rolling is a steel ingot after casting,
Select by the thickness of steel slabs, cast plates, etc., and suppression of ridging.

Next, after pickling, hot-rolled sheet annealing may be performed, but it is not essential. Then, 60 to 95% by one cold rolling or two or more cold rollings with intermediate annealing.
The reduction ratio is taken to obtain a predetermined plate thickness.

The finish annealing is carried out in the temperature range of 700 to 1000 ° C. If necessary, magnetic annealing is performed after punching or shearing to manufacture a non-oriented electrical steel sheet with more excellent iron loss characteristics.

[0047]

[Examples] Table 2 shows degassing time before molten steel casting, cooling rate during solidification of molten steel casting, finish annealing conditions, magnetic annealing conditions, size and number of inclusions, 25 cm Epstein test (JISC2550) Average iron loss W15 / 50 and magnetic flux density B50 measured in the longitudinal and width directions
The results of and are displayed.

Table 1 shows the components of the steel sheet.

[0049]

[Table 2]

A steel plate having a plate thickness of 2 mm was obtained by hot rolling, pickled, and steel plate components Nos. 4 to 7 and 11 to 12 were 8
The hot-rolled sheet was annealed at 50 ° C. for 3 hours.

Then, cold rolling is performed to a plate thickness of 0.5 mm,
The finish annealing shown in Table 2 was performed. As shown in Table 2, in the steel sheet of the present invention, under the same hot-rolled sheet annealing condition, finish annealing condition, and magnetic annealing condition, a steel sheet with a small iron loss while maintaining the magnetic flux density is obtained.

Incidentally, the results of SEM observation and TEM observation of the steel sheet of the comparative example in which the number of inclusions having a diameter of 0.1 to 0.5 μm is less than 500 pieces / mm ² show that there are many very fine CuS particles of about 10 nm. Was observed. It is presumed that this inhibits the growth of crystal grains during annealing and increases iron loss.

The SEM of the steel sheet of the comparative example in which the number of inclusions having a diameter of 0.1 to 0.5 μm exceeds 5000 pieces / mm ²
As a result of observation and TEM observation, very fine CuS of about 10 nm was not recognized. This allows fine C
Although there is no adverse effect of uS, it is presumed that the large number of inclusions of 0.1 to 0.5 μm hinders the growth of crystal grains during annealing and causes a large iron loss.

The steel plate No. 1 (steel plate component No. 1) which is the steel plate of the invention of claim 2 is the steel plate No. 24 of the steel plate of the present invention.
The composition, finish annealing conditions, and the number of inclusions are almost the same as those of (Steel plate composition No. 8), but the iron loss is better because the C content is small.

Steel plate No. 1 (steel plate component No. 1) which is the steel plate of the invention of claim 2 is steel plate No. 25 of the steel plate of the present invention.
Compared with (Steel plate composition number 9), the composition, finish annealing conditions, and the number of inclusions are almost the same, but the iron content is smaller and it is excellent because the N content is small.

The steel plate No. 1 (steel plate component No. 1) which is the steel plate of the invention of claim 2 is the steel plate No. 26 of the steel plate of the present invention.
(Steel plate composition number 10), composition, finish annealing conditions,
Although the number of inclusions is almost the same, since the amount of P is small, the iron loss is small and it is excellent. The steel plate number 27 (steel plate component number 11) of the comparative steel plate has a large amount of Si in the steel plate, and the steel plate number 28 (steel plate component number 12) is A in the steel plate.
Since the amount of 1 is large, the iron loss is excellent, but the magnetic flux density is largely reduced.

Steel plate number 31 of the comparative steel plate (steel plate component number 1
5) has a large amount of Mn in the steel sheet and is excellent in iron loss, but steel sheet number 1 (steel sheet component number 1) which is a steel sheet of the present invention having substantially the same composition, finish annealing conditions, and the number of inclusions. The decrease in magnetic flux density is larger than that of.

[0058]

INDUSTRIAL APPLICABILITY The present invention regulates the amount of Cu and the amount of S in a steel sheet and the size and number of inclusions in the steel sheet, thereby maintaining the magnetic flux density and achieving excellent non-directionality of iron loss characteristics. A magnetic steel sheet was obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the number of inclusions having a diameter of 0.1 to 0.5 μm and iron loss.

FIG. 2 is a diagram showing a relationship between the number of inclusions having a diameter exceeding 0.5 μm and iron loss.

FIG. 3 is a diagram showing the relationship between the cooling rate during molten steel casting, the size and number of inclusions, and iron loss.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kunikazu Tomita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (2)

[Claims] 1. By weight%, Si: more than 1% and 3.5% or less, A
A non-oriented electrical steel sheet containing l: 0.1-1%, Mn: 0.1-0.8%, Cu: 0.05% or less, S: 0.01% or less, 500 to 5000 inclusions contained in the steel sheet and having a diameter of 0.1 to 0.5 μm
mm ² and diameter over 0.5 μm 500 pieces / mm ²
A non-oriented electrical steel sheet excellent in iron loss characteristics characterized by being as follows. 2. C: 0.005% or less by weight%, P:
0.2% or less, N: 0.005% or less, Si: more than 1% and 3.5% or less, Al: 0.1-1%, Mn: 0.1-
Contains 0.8%, Cu: 0.05% or less, S: 0.0
A non-oriented electrical steel sheet having a content of 1% or less, the inclusions included in the steel sheet having a diameter of 0.1 to 0.5 μm is 500.
~ 5000 pieces / mm ² , 5 with diameter over 0.5 μm
A non-oriented electrical steel sheet having excellent iron loss characteristics, which is less than 00 pieces / mm ² .