JPH0967653A - Nonoriented silicon steel sheet excellent in core loss characteristics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a semiprocess silicon steel sheet product and to produce a nonoriented silicon steel sheet excellent in core loss characteristics after the semiprocess product is subjected to magnetic annealing. SOLUTION: This nonoriented silicon steel sheet has a composition consisting of by weight, <=1% 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> . Preferably, the content of C is regulated to <=0.005%, P to <=0.2% and N to <=0.005% as well.

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.

Non-oriented electrical steel sheets are subjected to finish annealing or the like when the steel sheets are shipped from a steel mill, and are manufactured so as to have final magnetic properties and after the final annealing. The steel sheet is subjected to punching and shearing processes in the consumer side, and then magnetic annealing is performed to remove the processing strain and coarsen the crystal grains to divide into semi-processed products in which predetermined magnetic properties are taken into consideration.

The present invention belongs to the latter and provides a non-oriented electrical steel sheet having excellent iron loss characteristics after magnetic annealing of a semi-processed product.

[0004]

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 difficult to supply steel sheets with less iron loss. It has been demanded.

It is generally known that 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 magnetic annealing is demanded. In response to such demands, attempts were made to reduce the amount of inclusions or precipitates that tend to become pinning sites at grain boundaries, and to control the shape and composition of inclusions or precipitates in the steel sheet to lose the function as pinning sites. Has been done.

[0006] For example, in Japanese Patent Laid-Open No. 3-249115, MnS in the solidification process is increased by setting the amount of Mn in a specific range with respect to the amounts of Si and S, and coarse MnS that does not easily function as a pinning site. It is suggested to do so. 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 likely to be 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 the oxide 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 obtain fine Mn
It has been proposed to reduce the precipitation of S.

[0008]

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 demands is to carry out magnetic annealing at a lower temperature and shorter time than ever before. For example, conventional 7
What was carried out under the conditions of 50 ° C. and 2 hours was changed to 730
It is carried out under the condition of 1 ° C. for 1 hour.

In such a case, according to the experiments conducted by the present inventors, as described above, MnS is coarsened or AlN is coarsened, or the composition of oxide-based inclusions is defined, and formation of a relatively large oxide and its formation. 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 magnetic annealing at low temperature and short time.

[0011]

The first aspect of the present invention is, by weight (hereinafter the same), Si: 1% or less, Al: 0.1 to 1%,
A non-oriented electrical steel sheet containing Mn: 0.1 to 0.8%, Cu: 0.05% or less (including 0), S: 0.01% or less (including 0), Inclusions contained in the steel sheet with a diameter of 0.1 to 0.5 μm are 500 to 5000 pieces / mm ² , and inclusions with a diameter exceeding 0.5 μm are 500 pieces / mm.
It is a non-oriented electrical steel sheet excellent in iron loss characteristics characterized by being ² or less.

The second invention is C: 0.005% or less, P:
0.2% or less, N: 0.005% or less, Si: 1% or less, Al: 0.1 to 1%, Mn: 0.1 to 0.8%, Cu: 0.05% or less (Including 0), S: 0.0
A non-oriented electrical steel sheet containing 1% or less (including 0), which is an inclusion contained in the steel sheet and has a diameter of 0.1 to 0.5 μm.
500 to 5000 pieces / mm ² , diameter 0.5 μm
It is a non-oriented electrical steel sheet having excellent iron loss characteristics, characterized by exceeding 500 pieces / mm ² .

(1) Inclusions and Precipitates The basic 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).

FIG. 3 shows the relationship between magnetic annealing conditions and iron loss. The components of the steel sheet are as shown in the figure.
After making the plate thickness 0.5 mm by cold rolling, 730 to 760
Magnetic annealing is performed at 2 ° C. for 2 hours, and iron loss (W15 / 50) is measured by a 25 cm Epstein test (JISC2550).

From FIG. 3, when the magnetic annealing temperature is 750 ° C. or higher, the iron loss is as low as about 5.0 W / kg, but only 20 ° C.
When magnetic annealing is carried out at a low temperature of 730 ° C., it can be rapidly increased to 6.6 W / kg. The crystal grain size in this case was as large as about 40 μm in the magnetic annealing at 750 ° C. or higher, and was 20 μm or less at 730 ° C., which was less than half of the former. From this, it can be seen that when the magnetic annealing temperature is lowered, grain growth is rapidly suppressed in the conventional steel sheet, and as a result, iron loss is increased.

Then, for the purpose of investigating such a factor inhibiting the grain growth property at a low temperature, the inclusions in the steel sheet before magnetic annealing were observed. Here, the size and number of inclusions were measured and observed by using a scanning electron microscope (SEM) up to a diameter of 0.1 μm, and by using a transmission electron microscope (TEM) for diameters smaller than 0.1 μm. The SEM observation was performed by directly observing the cross section of the steel sheet, and the TEM observation was performed using an extraction replica.

As a result of SEM observation, Al ₂ O ₃ and AlN of about 0.2 to 0.5 μm and MnS of about 0.1 to 1 μm were obtained.
Was observed. Further TEM observation revealed that
Al ₂ O ₃ and MnS of less than 1 μm were not observed, but many CuS of several tens of nm were observed.

The inventors have continued their research to prevent the precipitation of fine CuS or coarsen the aggregate of CuS to accelerate the growth of crystal grains during magnetic annealing and reduce iron loss, and to improve the inclusions. In order to change the morphology, a test was conducted in which the cooling rate during casting of molten steel was changed.

FIG. 4 shows the relationship between the cooling rate during casting of molten steel and the size and number of inclusions after magnetic annealing (730 ° C. for 1 hour). 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 W having a cooling rate of 0 W / kg and a low cooling rate was 6.1 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 /
In Steel A having a low 50 of 4.0 W / kg, a large amount of inclusions was recognized as compared with Steel B. Further, observing the morphology of CuS, CuS was not observed so much in the steel A having a high cooling rate during casting, whereas the cooling rate during casting was slow and W15 / 50 was as high as 6.1 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 of 0.1 to 0.1
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 2 and 6 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.

[0026]

[Table 1]

The balance not shown in Table 1 is Fe and unavoidable 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 110 to 240, and the value of the core loss W15 / 50 is 730 ° C. for 1 hour after magnetic 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 magnetic 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 2 and 7 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 steel plate has a thickness of 0.5 mm and the core loss W15 / 50 is 73
After magnetic annealing at 0 ° C. for 1 hour.

From FIG. 2, it is recognized that W15 / 50 tends to be lowered 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.

Therefore, 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 the iron loss, but if it exceeds 1%, the magnetic flux density decreases, so the upper limit is made 1%.

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 in 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 that 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 inhibits the growth of crystal grains during annealing A
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.

(3) Manufacturing method 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 casting and solidification in the casting of molten steel is set to 1
The rate is 0 ° C / sec to 30 ° C / sec. In order to secure this cooling rate, the thickness of the slab is reduced, or cooling spray is strengthened.

In order to adjust the size and number of inclusions exceeding 0.5 μm in the steel sheet, degassing treatment before casting of molten steel is performed for 10 minutes or more, or the flow of molten steel during casting is adjusted, It is carried out by adjusting the electromagnetic stirring during casting.

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 obtained in such a converter or electric furnace is subjected to ingot casting or continuous casting and hot working. For hot working, finish rolling is indispensable among slab rolling, rough rolling and finish hot rolling, but slab rolling and rough rolling are the thickness dimensions of steel ingot, steel slab, cast plate, etc. after casting. , Ridging suppression, etc.

Annealing of the hot rolled sheet after hot rolling may be performed, but is not essential. Next, finish annealing is performed after one cold rolling or two or more cold rollings with intermediate annealing to obtain a predetermined plate thickness.

Further, magnetic annealing is carried out after punching and shearing to produce a non-oriented electrical steel sheet having excellent iron loss characteristics after magnetic annealing.

[0047]

[Examples] Table 1 shows the composition of the steel sheet, and the balance not shown is Fe.
And unavoidable impurities.

Table 2 shows the degassing treatment time before casting of molten steel, the cooling rate during casting and solidification of casting of molten steel, finish annealing conditions, magnetic annealing conditions, size and number of inclusions, and iron loss W15 / 5.
0 and magnetic flux density B50 of 25 cm Epstein test (JI
SC2550), the result of the average value measured in the longitudinal direction and the width direction of the steel sheet is displayed.

[0049]

[Table 2]

A steel plate having a plate thickness of 2 mm was obtained by hot rolling, pickled, and then cold rolled to a plate thickness of 0.5 mm, and finish annealing and magnetic annealing shown in Table 2 were performed.

As shown in Table 2, the steel sheet of the present invention is a steel sheet having a high magnetic flux density and a small iron loss even when the magnetic annealing is performed at a low temperature for a short time.

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 hindered the growth of crystal grains during magnetic annealing and increased 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 hindered the growth of crystal grains during magnetic annealing and increased iron loss.

[0054]

EFFECTS OF THE INVENTION The present invention regulates the size and number of inclusions in a steel sheet so that crystal grains can grow even at a short time at a low temperature of magnetic annealing, and the iron loss characteristics are excellent in non-oriented. A magnetic electrical steel sheet was obtained.

[Brief description of drawings]

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

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 a relationship between magnetic annealing conditions and iron loss.

FIG. 4 is a diagram showing the relationship between the cooling rate during the casting of molten steel and the size and number of inclusions.

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

Claims (2)

[Claims] 1. By weight%, Si: 1% or less, Al: 0.1
˜1%, Mn: 0.1-0.8%, Cu:
A non-oriented electrical steel sheet having 0.05% or less and S: 0.01% or less, in which inclusions included in the steel sheet have a diameter of 0.1.
A non-oriented electrical steel sheet having excellent iron loss characteristics, characterized in that the number of particles of 0.5 to 0.5 μm is 500 to 5000 pieces / mm ² , and the diameter of particles exceeding 0.5 μm is 500 pieces / mm ² or less. 2. C: 0.005% or less by weight%, P:
0.2% or less, N: 0.005% or less, Si: 1% or less, Al: 0.1 to 1%, Mn: 0.1 to 0.8%, Cu: 0.05% or less , S: 0.01% or less in the non-oriented electrical steel sheet, the inclusions included in the steel sheet having a diameter of 0.1 to 0.5 μm are 500 to 5000 pieces / mm ² , and a diameter of 0.5 μm. Over 500 pieces / mm
A non-oriented electrical steel sheet with excellent iron loss characteristics characterized by being ² or less.