JPH10330893A - Nonoriented silicon steel sheet low in core loss after low temperature-short time magnetic annealing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a nonoriented silicon steel sheet in which fine MnS, AlN and oxides checking the growth of particles are made harmless, and low in core loss after low temp., short time magnetic annealing. SOLUTION: This steel sheet is the one having a compsn. contg., by weight, <=0.005% C, <=0.2% P, <=0.005% N, 0.1 to 1% Si, 0.2 to 0.5% Mn, <=0.02% S, <=0.02% T.O and sol.Al in the range satisfying the formula: sol.Al%/T.O %<=0.08, and the balance substantial Fe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-oriented electrical steel sheet having excellent magnetic properties after low-temperature short-time magnetic annealing.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are classified into full-process materials and semi-process materials according to their manufacturing methods. Among them, the full process material is to obtain predetermined magnetic properties by finish annealing on the steel maker side, while the semi-process material is to obtain the predetermined magnetic characteristics by performing strain relief annealing after punching at the customer. It is. In the case of the semi-process material, the crystal grains grow simultaneously with the removal of the processing strain during the strain relief annealing, so that the iron loss can be further reduced. For this reason, the strain relief annealing is also called “magnetic annealing”, and it is important to improve grain growth during magnetic annealing to reduce iron loss.

[0003] Since this magnetic annealing is usually performed at 750 ° C for 2 hours, low iron loss cannot be achieved if fine precipitates that inhibit grain growth are present in the steel. Among these precipitates, fine AlN, MnS, oxides and the like particularly hinder grain growth and significantly reduce iron loss.

[0004] As a technique for reducing fine AlN, Al as disclosed in JP-A-61-119652 has been proposed.
A method in which the amount is made 0.15% or more to coarsen AlN;
A method of fixing N as BN by adding B as described in JP-A-54-163720;
A method of suppressing the precipitation of AlN due to the addition of Zr as described in JP-A-4-4454 has been proposed.
However, in Al deoxidation, there is a concern that the formation of Al ₂ O ₃ may cause iron loss deterioration, and it is not possible to completely suppress the precipitation of AlN, and to sufficiently reduce iron loss after magnetic annealing. Have difficulty. Japanese Patent Application Laid-Open No. 8-3699 discloses a method of achieving high characteristics by adding a rare earth element by Al deoxidation, but the rare earth element is very expensive, resulting in a very high cost. That is inevitable.
Therefore, it can be seen that it is difficult to inexpensively manufacture a non-oriented electrical steel sheet having low iron loss after magnetic annealing with Al-added steel.

On the other hand, tr. As a technique for reducing fine MnS in Al steel, as disclosed in Japanese Patent Application Laid-Open No. 03-104844, Zr and Al are used as a deoxidizing agent, or the time from casting of the deoxidizing agent to casting is adjusted to precipitate MnS. A method for adjusting the number and size of oxides in steel as a core is disclosed.

As a technique for controlling the ductility of the oxide and reducing the fine oxide, as disclosed in JP-A-01-152239, the MnO ratio of the oxide is 15% or less and the SiO ₂ ratio is 7%.
5% or more.
(Mn) ² /Si≦0.45, Al ≦ 8
A method for controlling the concentration to ppm is disclosed, and a technique for preventing the formation of a low-melting oxide with high ductility has been proposed.

[0007]

However, in recent years,
From the viewpoints of productivity improvement and cost reduction, magnetic annealing performed by customers tends to be at a lower temperature and shorter time,
In order to obtain a non-oriented electrical steel sheet having excellent magnetic properties after magnetic annealing, it is necessary to further detoxify fine precipitates.

[0008] Further, from the viewpoint of improving the refining smelting technology such as de-P, de-S, and de-Mn and from the economical point of view, the blowing time in the converter is shortened, and the oxygen blowing amount is reduced to adjust the components. Technology has been introduced. As a result, the oxygen content in the steel is reduced,
The form of the oxide in the i-deoxidation system has changed greatly as compared with the conventional one.

Under these circumstances, none of the above proposals is satisfactory as a technique for meeting the demand for a low-temperature, short-time magnetic annealing temperature. That is, Japanese Patent Laid-Open No. 03-10
In the method disclosed in Japanese Patent No. 4844, when Zr or Al is used as a deoxidizing agent in order to adjust the number and size of oxides, deterioration of grain growth due to precipitation of nitrides is expected, and casting is performed from the input of the deoxidizing agent. The time is extremely short, resulting in extremely high cost. In addition, it does not mention the ductility of the oxide, and if the oxide spreads during rolling, the grain growth is deteriorated, and it is possible to stably reduce the iron loss particularly after low-temperature magnetic annealing. become unable.

In the method disclosed in Japanese Patent Application Laid-Open No. H01-152239, although the ductility of the oxide is certainly reduced, the melting point of the oxide may be lowered due to the incorporation of a small amount of Al, and the reduction of the ductility cannot be said to be sufficient. In addition, since the reduction of fine MnS is not performed, the grain growth by low-temperature magnetic annealing becomes unstable.

In the method disclosed in Japanese Patent Application Laid-Open No. 07-070719, the ductility of the oxide is certainly reduced, but the amount of Si is reduced to 0.1.
When the content is less than 5%, the Si deoxidizing power is reduced, the oxide has a low melting point even with a small amount of Al, and the ductility is increased. Also,
Since the amount of added Mn is reduced to ensure non-ductility of the oxide, precipitation of fine MnS cannot be prevented. Therefore, when the temperature of the magnetic annealing is lowered, the grain growth becomes insufficient and the iron loss is not sufficiently reduced.

As described above, none of these methods responds to the demand for shortening the magnetic annealing time at low temperatures.
The advent of a new technology for further reducing fine precipitates in steel was envied.

In view of the above-mentioned conventional problems, an object of the present invention is to detoxify MnS, AlN, and oxides, which hinder grain growth, so that iron loss after low-temperature and short-time magnetic annealing is characterized. The object is to provide a non-oriented electrical steel sheet having a low density.

[0014]

In order to solve the above problems and achieve the object, the present invention uses the following means. (1) The steel sheet of the present invention has a weight percentage of C ≦ 0.005%.
, P ≦ 0.2%, N ≦ 0.005%, and Si: 0.
1 to 1%, Mn: 0.2 to 0.5%, and S ≦ 0.02
% And T. O ≦ 0.02% and sol. In a range satisfying the following equation (1). A non-oriented electrical steel sheet having low iron loss after low-temperature short-time magnetic annealing, characterized by containing Al and the balance being substantially Fe. sol. Al% / T. O% ≦ 0.08 (1)

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied a technique for reducing iron loss after low-temperature and short-time magnetic annealing in a Si deoxidized magnetic steel sheet in order to realize the above-mentioned object. An experiment was performed.

In order to investigate the effect of oxygen content on iron loss after low-temperature short-time magnetic annealing, C = 0.0025%, Si =
0.15%, Mn = 0.3%, P = 0.1%, S = 0.
005%, sol. Al = 0.0005%, N = 0.0
03%, T.P. Lab was melted and cast from O = 0.003 to 0.02% steel to produce an ingot. These ingots were hot-rolled and pickled, and then the hot-rolled sheet was 0.5 m thick.
m, subjected to finish annealing at 750 ° C. × 1 minute, and further magnetically annealed. The magnetic annealing was carried out at two levels of normal conditions of 750 ° C. × 2 hours and 725 ° C. × 1 hour.

FIG. 1 shows the iron loss W15 / 50 of these samples after magnetic annealing. Here, the magnetic properties were measured using a 25 cm Epstein test piece. Magnetic annealing condition is 750
When the temperature is 2 hours, the iron loss W15 / 50 is hardly affected by the amount of oxygen. On the other hand, the magnetic annealing condition is 725 ° C.
× 1 hour, T. O content (total oxygen content) is 0.
Although the iron loss W15 / 50 at 006% or more increases only about 0.1 W / kg compared to the properties after magnetic annealing at 750 ° C. × 2 hours, the T.V. When the O content is less than 0.006%, the iron loss increases sharply, and the iron loss W15 / 50 becomes 4.7 W / k.
g or more.

When the structures of these samples were observed with an optical microscope, the magnetic annealing conditions were 725 ° C. × 1 hour and T.V. When the O content was less than 0.006%, it was found that the ferrite grains were fine. In order to investigate the cause of the decrease in grain growth, SEM observation of the steel sheet after magnetic annealing was performed. As a result, T.I. When the O content was less than 0.006%, precipitates of 0.1 μm or less spread in the rolling direction were observed on the grain boundaries. When these precipitates were analyzed by an energy dispersive X-ray analyzer (EDX), each element of Mn-Si-Al-O was detected. From this, the magnetic annealing conditions are 7
T. at 25 ° C for 1 hour. It is considered that the decrease in grain growth at O <0.006% is due to the spread of the ternary oxide of Si—Mn—Al due to a decrease in the melting point.

As described above, even with a very small amount of Al of 5 ppm, which was not a problem in ordinary magnetic annealing, T.P. O
When the amount is reduced, the ductility of the oxide is increased, and when the magnetic annealing conditions are low temperature and short time as in this experiment, the improvement of the magnetic properties cannot be achieved.

That is, when the amount of oxygen in the steel is reduced in accordance with the recent reduction in the amount of oxygen blown into the converter, even a small amount of Al, which was conventionally considered to have little effect on the grain growth, is used. To obtain a non-oriented electrical steel sheet that inhibits grain growth and has low iron loss especially after low-temperature short-time magnetic annealing, T.I. It has been found that adjustment of the amount of O is an important factor.

Based on the above findings, the present inventors have found that (s
ol. Al) / (TO) and the amount of Mn within a certain range to suppress precipitation of fine MnS, AlN and oxides, and to reduce iron loss after low-temperature short-time magnetic annealing. The present inventors have found a conductive electrical steel sheet and completed the present invention. That is, the present invention specifies the steel composition in the following range to detoxify MnS, AlN, and oxides, which hinder grain growth, thereby reducing iron loss after low-temperature short-time magnetic annealing. A low non-oriented electrical steel sheet can be provided.

The reasons for adding the components of the present invention and the reasons for limiting the components will be described below. (1) Component composition range sol. Al: sol. Al% / T. O% ≦ 0.08 sol. Al content is sol. Al% / T. 0.08 at O%
If it exceeds, iron loss cannot be reduced. So so
l. Al content is sol. Al% / T. O% ≦ 0.08.

This has been made clear by the following experiments by the present inventors. C = 0.0025%, Si = 0.1
5%, Mn = 0.35%, P = 0.1%, S = 0.00
5%, sol. Al = 0.0001 to 0.002%, N
= 0.003%; Lab was melted and cast from O = 0.003 to 0.02% steel to produce an ingot. After hot rolling of these ingots, pickling was performed, and subsequently, the sheet thickness was 0.5 mm.
Cold-rolled to 750 ° C for 1 minute,
Further, magnetic annealing was performed at 725 ° C. × 1 hour.

FIG. 2 shows the iron loss W15 / 50 of these samples after magnetic annealing. Here, the magnetic properties were measured using a 25 cm Epstein test piece. From FIG. 2, the iron loss W15 / 50 after the magnetic annealing is O and sol. Al is greatly affected by the amount of sol. Al% / T. O% ≦ 0.0
In the case of No. 8, it can be seen that W15 / 50 <4.7 W / kg.

From the above results, T.I. O and sol. Al content was sol. Al% / T. By adjusting O% ≦ 0.08, it was possible to prevent the formation of ductile oxide, and it was found that a non-oriented electrical steel sheet having excellent magnetic properties could be obtained after low-temperature short-time magnetic annealing. is there. Mn: 0.2 to 0.5% When the amount of Mn is less than 0.2% or more than 0.5%, low iron loss cannot be achieved after low-temperature short-time magnetic annealing. for that reason,
The Mn content is 0.2 to 0.5%.

This has been made clear by the following experiments by the present inventors. C = 0.0025%, Si = 0.1
5%, Mn = 0.1-1%, P = 0.1%, S = 0.0
05%, sol. Al = 0.0001%, N = 0.00
3%, T.P. O = 0.01% steel was melted in a laboratory and cast to produce an ingot. These ingots are hot-rolled, pickled, and then cold-rolled to a thickness of 0.5 mm,
Finish annealing was performed at 1 ° C. × 1 minute, and magnetic annealing was further performed at 725 ° C. × 1 hour.

FIG. 3 shows the iron loss W15 / 50 of these samples after magnetic annealing. Here, the magnetic properties were measured using a 25 cm Epstein test piece. FIG. 3 shows that the iron loss W15 / 50 becomes 4.7 W / kg or more when the Mn content is less than 0.2%, and the characteristics are not stable and vary when the Mn content exceeds 0.5%. . When the structures of these samples were observed with an optical microscope, iron loss W15 /
It was found that the sample with 50 of 4.7 W / kg or more had fine grains.

The above reason is considered as follows. Mn
With an increase in the amount, the amount of MnS redissolved during hot rolling is reduced, and the amount of MnS finely precipitated during hot rolling is reduced, so that grain growth is improved. This tendency is remarkable up to an Mn content of about 0.5%. This can easily be inferred from the solubility product of MnS at 1200 ° C. (FIG. 4). Also, from the viewpoint of increasing the electric resistance, the addition of Mn is advantageous for reducing iron loss. However, the amount of Mn increases in the low-Si electrical steel sheet of the Si deoxidized system, and the ratio of MnO to the total oxides, that is, MnO / (SiO ₂ + MnO + Al ₂ O ₃ ).
If it exceeds about 50%, the ductility of the oxide increases, so excessive addition of Mn causes deterioration of the grain growth. That is, when the amount of Mn exceeds 0.5%, the oxide M
It is considered that since the nO ratio was changed to cause ductility and the grain growth during the low-temperature short-time magnetic annealing was deteriorated, the characteristics were varied. As described above, since excessive addition of Mn leads to an increase in cost, the upper limit of the amount of Mn is 0.5%.

On the other hand, when the added amount of Mn decreases, the amount of MnS re-dissolved during hot rolling increases, and the amount of MnS finely precipitated during hot rolling increases, and the grain growth property decreases. This is illustrated in FIG.
Can be inferred from Therefore, if the amount of added Mn is reduced in order to ensure non-ductility of the oxide, the grain growth during magnetic annealing at a low temperature for a short time is deteriorated. From the above, the lower limit of the amount of Mn is 0.2
%. The present invention has been made based on such findings of the present inventors, and the reasons for limiting other component compositions will be described below.

C ≦ 0.005% C is 0.005% or less because it causes magnetic aging and deteriorates magnetic properties. Si: 0.1 to 1% Since Si is an element whose iron loss decreases with an increase in the amount of addition, it is necessary to add 0.1% or more in order to reduce iron loss after magnetic annealing. However, if it exceeds 1%, the magnetic flux density decreases, so the upper limit is 1%.

P ≦ 0.2% P is an element necessary for improving the punching property of the steel sheet, but if added over 0.2%, the steel sheet becomes brittle, so that the content is 0.2% or less. S ≦ 0.02% S bonds with Mn and precipitates finely as MnS, and hinders grain growth. Therefore, it is desirable that S be as small as possible. However, excessive reduction causes a significant increase in cost and is not the object of the present invention. Therefore, the upper limit is 0.02%.

N ≦ 0.005% When N is large, the precipitation amount of nitride increases,
Since the grain growth during magnetic annealing decreases and the iron loss increases, 0.
005% or less.

T. O ≦ 0.02% When the oxide is non-ductile, the effect of the oxide on the grain growth is small, but when the amount is large, the grain growth is suppressed.
T. The upper limit of O is 0.02%. It should be noted that Sb and Sn may be added for improving the magnetic properties.

The manufacturing method is not particularly limited in the present invention. That is, the smelting method of the steel, the rolling method of the electromagnetic steel sheet, and the heat treatment method may be any conditions that are usually adopted. For example, molten steel whose composition is adjusted in a converter is cast and hot-rolled. Hot rolled sheet annealing may be performed, but is not essential. Next, a method of performing cold rolling after pickling, or performing cold rolling two or more times including intermediate annealing to obtain a predetermined thickness, and then performing finish annealing may be employed. The following are examples of the present invention,
The effect of the present invention will be proved.

[0035]

EXAMPLES Steel having the components shown in Table 1 (Examples of the present invention: No. 1 to No. 1)
9, Comparative Example: No. 10 to 20), the mixture was blown in a converter and then degassed, adjusted to predetermined components, and cast. Next, this ingot was heated at a slab heating temperature of 120.
Heating was performed at 0 ° C. for 1 hour, and hot rolling was performed to a thickness of 2 mm. In this case, the finishing temperature was 800 ° C. and the winding temperature was 675 ° C. Next, the hot-rolled sheet was pickled, cold-rolled to a thickness of 0.5 mm, subjected to finish annealing at 750 ° C. × 1 minute, and then to magnetic annealing at 725 ° C. × 1 hour.

The magnetic properties were measured using a 25 cm Epstein test piece. Magnetic properties of each steel sheet (iron loss W15 / 5
0, magnetic flux density B50) are also shown in Table 1. From the table,
Invention Example No. 1 to 9 have an iron loss W15 / 50 of 4.7 W.
/ Kg or less and the magnetic flux density is 1.74 T or more, and both iron loss and magnetic flux density are good. On the other hand, in Comparative Example No. 10, 12 to 20 have a magnetic flux density of 1.74 T or more, but C, Mn, S, N, T.P. O content and (sol.A
l) / (TO) value is out of the range specified in the present invention, so that the iron loss W15 / 50 is inferior to 4.8 W / kg or more. Also, in Comparative Example No. 11 is iron loss W15 /
50 is 4.7 W / kg or less, but the magnetic flux density B50 is inferior to 1.71 T or less due to the large amount of Si. From the above, it can be seen that when the steel sheet component is controlled within the range of the present invention (Examples Nos. 1 to 9), a non-oriented electrical steel sheet with low iron loss after low-temperature short-time magnetic annealing is obtained.

[0037]

[Table 1]

[0038]

As described above, according to the present invention, by specifying the steel composition, it is possible to provide a non-oriented electrical steel sheet having low iron loss after low-temperature short-time magnetic annealing.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between an oxygen amount (TO) and iron loss (W15 / 50) after magnetic annealing according to an embodiment of the present invention.

FIG. 2 shows oxygen (TO) and s according to an embodiment of the present invention.
ol. The figure which shows the relationship between the amount of Al and the iron loss (W15 / 50) after magnetic annealing.

FIG. 3 is a diagram showing a relationship between the amount of Mn and iron loss (W15 / 50) after magnetic annealing according to the embodiment of the present invention.

FIG. 4 is a diagram showing a solubility curve of MnS according to the embodiment of the present invention.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shunji Iizuka 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd.

Claims (1)

[Claims] 1. The method according to claim 1, wherein C ≦ 0.005% and P ≦
0.2%, N ≦ 0.005%, and Si: 0.1 to 1%
And Mn: 0.2-0.5%, S ≦ 0.02%,
T. O ≦ 0.02% and sol. In a range satisfying the following equation (1). A non-oriented electrical steel sheet having low iron loss after low-temperature short-time magnetic annealing, characterized by containing Al and the balance being substantially Fe. sol. Al% / T. O% ≦ 0.08 (1)