JPH06188114A - Non-oriented magnetic steel plate for low core loss - Google Patents

Abstract

PURPOSE:To provide a non-oriented magnetic steel plate for low core loss by specifying the average interval between a recessed section and a projecting section of the surface of the steel plate. CONSTITUTION:A steel containing 0.004% C, 3.18% Si, 0.22% Mn, 0.019% P, 0.0015% S, 0.61% Al, 0.0018% N, 0.0015% O, and with the balance of Fe and unavoidable impurity is hot-rolled into sheet steel and is annealed. After descaling, the sheet steel is cold-rolled. The cold-rolled sheet steel may be ground chemically with a (90% H2O2 + 10$ HF) solution, or electrolytically with a (phosphoric acid + saturated chromic acid) solution, or mechanically with emery paper. At that time, the average interval Sm between a recessed section and a projecting section on the external surface of the sheet steel should meet the expression. By this method, a non-oriented magnetic steel plate for lower core loss than the conventional one can be obtained with the same material.

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 in a high frequency region, not to mention commercial frequencies.

[0002]

2. Description of the Related Art Non-oriented electrical steel sheets are specified for each grade in JIS 2552 according to the iron loss level. Low-Si low-grade products, which have relatively large iron loss, are often used for small appliances such as home appliances because of their low cost. On the other hand, the high Si type with low iron loss is used for large equipment such as generators, which has a large effect of reducing iron loss. By the way, in recent years, in electrical equipment, whether small or large, there is an increasing demand for energy saving, and it is desired to improve the characteristics of the non-oriented electrical steel sheet, particularly the iron loss characteristics.

Conventionally, as a technique for reducing the iron loss of a non-oriented electrical steel sheet, (1) increasing the Si or Al content, (2)
Reduce or detoxify impurities (C, S, O, etc.) in steel,
(3) Optimize the grain size after finish annealing, (4) adjust cold rolling reduction, (5) suppress surface oxidation, (6) reduce surface roughness of product sheet, etc. The method has been adopted.
Due to such efforts to reduce the iron loss, the properties of the non-oriented electrical steel sheet have been improved year by year, but recently, further improvement of the iron loss properties is desired.

However, in the above method (1), although it is relatively easy to reduce the iron loss, there is a drawback that the magnetic flux density is lowered on the other hand, so that the result is merely a grade change. The method of (2) above is
Although it is a very important method, from the viewpoint of process production in the present situation, it has reached the highest level that can be reached technically, and there is not much room for improving iron loss by this method without progress in steelmaking technology. Can be said. Further above (3),
As for (4) and (5), due to the efforts so far, (3),
Optimization has been achieved for (4), and the dew point of the annealing atmosphere in (5) has reached a sufficient level. Therefore, low iron loss due to improvement of these manufacturing processes cannot be expected. On the other hand, with regard to the method of (6) above, measures have been taken so far using Ra as an index, and when rolling with a bright roll on the current rolling mill, Ra is approximately 0.2 to
It is in the range of 0.4 μm.

The influence of surface roughness on the magnetic properties has been well studied in the past, for example, Japanese Patent Publication No. 58-1.
According to JP-A-0445 and JP-B-58-10446, excellent core loss can be obtained if the center line average roughness Ra <0.4 μm. The reason for this is that, as is often seen with, for example, semi-processed dull material (Ra ≈ 1 μm), when rolling with a high surface roughness, the vicinity of the surface undergoes more complicated deformation than the inside. As a result, it is considered that surface fine grains are not generated. Therefore, as Ra is decreased, the surface fine grains are decreased and the iron loss characteristics are improved.

By the way, Japanese Patent Publication No. 58-10445 and Japanese Patent Publication No. 58-10446 mentioned above indicate that further reduction of Ra below 0.4 μm results in further lower iron loss.
According to the knowledge of the inventors, the iron loss stably decreases until Ra is about 0.4 μm, but the iron loss does not always decrease in the range of 0.4 μm or less, and the iron loss is almost leveled off. found. As described above, in terms of the surface roughness, the present situation is that it is not the deciding factor for further lowering the iron loss.

[0007]

Therefore, the inventors of the present invention have conducted extensive studies on the relationship between the surface roughness and the magnetic properties in order to further reduce the iron loss of the non-oriented electrical steel sheet.
It was found that it is necessary to control the average interval Sm of the surface irregularities in order to further reduce the iron loss in the region where Ra is small (the region where surface fine particles are not generated). The present invention is based on the above findings.

[0008]

Means for Solving the Problems That is, the present invention is based on Si
+ Al: a non-oriented electrical steel sheet having a composition containing 4 wt% (hereinafter simply referred to as%) or less, wherein the average spacing Sm of the irregularities on the surface of the steel sheet is

[Equation 2] Is a non-oriented electrical steel sheet with excellent iron loss.

The experimental results that led to the invention will be described below. C: 0.004%, Si: 3.18%, Mn:
0.22%, P: 0.019%, S: 0.0015%, Al: 0.61%,
A steel slab containing N: 0.0018% and O: 0.0015% and having a composition of balance Fe and unavoidable impurities was formed into a hot-rolled sheet with a thickness of 2 mm by a normal hot-rolling process. After annealing under the conditions, descaling and cold rolling
A cold rolled sheet with a thickness of 0.5 mm was used. This cold rolled sheet as it is, or chemical polishing with (90% H ₂ O ₂ + 10% HF) solution or electrolytic polishing with (phosphoric acid + saturated chromic acid) solution or # 320 to # 15
00 After mechanical polishing with emery paper, 1000 ℃, 30
Annealed under the condition of s. The results of examining the iron loss value of the thus obtained annealed plate are shown in FIGS. 1 and 2 in relation to Ra or Sm, respectively.

Here, the average spacing Sm of the surface irregularities means that when the spacing between the peaks between the measurement lengths is Sm _i ,
The following formula

[Equation 3] Is the value indicated by, and the number of peaks is the upper peak count between the two peak count levels and the two points where the curve crosses parallel to the average line of the cross-section curve and is separated by ± 0.05 μm. When there is a point at which the level and the curve intersect one or more times, this is the number obtained as one peak during the measurement length (see FIG. 3).

As is clear from FIGS. 1 and 2, there is no particular correlation between Ra and iron loss, which are generally used for surface roughness evaluation, in the region of 0.5 μm or less. On the other hand, a strong correlation was observed with Sm, and it was found that iron loss was remarkably reduced by setting Sm to 100 μm or more.

The reason why the iron loss improved as Ra was lowered from several μm to about 0.4 to 0.5 μm is thought to be that the surface fine grains decreased. Grain is not reduced, and iron loss is not directly related to Ra. Then, as shown in FIG. 2, it has a strong correlation with Sm. This means that another factor related to Sm influences iron loss. Although this factor is still unknown, the meaning of Sm is the average interval between mountains, so the iron loss decreases when Sm is large because the interval between mountains increases, that is, the small unevenness decreases. It is estimated that this is because the resistance of domain wall movement on the surface is reduced.

In the past, efforts have been made to reduce the surface roughness Ra in order to reduce iron loss, and the Ra of a normal product is generally controlled within the range of 0.2 to 0.5 μm except for the dull material. However, further reduction of Ra does not lead to a significant reduction in iron loss, and therefore the actual situation is that no further improvement in surface roughness has been made to reduce iron loss. The Sm obtained by the conventional surface roughness adjustment is about 20 to 50 μm.
It was about. On the other hand, the inventors newly arrived at the idea of a surface roughness parameter Sm different from Ra, and by controlling the surface roughness by this Sm, it is possible to further improve the iron loss characteristics. Found and completed this invention.

[0014]

In the present invention, the reason why the component composition of the raw material is limited to the above range is as follows. Si + Al: 4% or less Si and Al are both effective elements for improving iron loss, but if the total amount exceeds 4%, cold rolling becomes difficult, so the total amount is limited to 4% or less. did. The lower limit is not particularly limited because the present invention is essentially unrelated to the components, and the reason why Si + Al is specified with an upper limit is to limit the use to electrical steel sheets.

In the present invention, the Sm is limited to 100 μm or more, as is apparent from FIG.
This is because a reduction in iron loss is clearly recognized by setting the thickness to 100 μm or more, compared to the usual case of 20 to 50 μm.

Next, the manufacturing process of the non-oriented electrical steel sheet according to the present invention will be specifically described. A molten steel having a predetermined component composition is melted by a converter-degassing device or the like, and then continuously cast or ingot-slab-rolled to form a slab, which is then heated and then hot-rolled to form a hot-rolled sheet. The hot rolled sheet may be annealed as necessary. Then, after descaling, cold rolling is performed once or twice or more with intermediate annealing sandwiched between them, and then subjected to finish annealing. In the case of a semi-processed material, light reduction is subsequently applied to obtain a product.

Here, the Sm of the product plate surface is 20 to 50% of the current value.
As a means for increasing the thickness to more than μm, a method in which the rolling before finish annealing is a low speed rolling (for example, 100 m / min or less) using a small diameter roll (for example, 100 mmφ or less) is particularly advantageous. Other methods include chemical polishing or electrolytic polishing of cold-rolled sheet or finish-annealed sheet before finish annealing, method of mechanically polishing the cold-rolled sheet before finish annealing with an elastic grindstone or a non-woven fabric roll, finish annealing. Examples include a method of performing the previous rolling or the light rolling of the semi-processed material without using oil using a super bright roll (for example, Sm ≧ 100 μm on the roll surface). In short, it is important to control the Sm of the surface of the product steel sheet to 100 μm or more.

[0018]

EXAMPLES Example 1 C: 0.003%, Si: 1.81%, Mn: 0.19%, P: 0.021
%, S: 0.0022%, Al: 0.34%, N: 0.0017% and O:
A steel slab containing 0.0017% with the balance being essentially Fe is formed into a hot-rolled sheet with a thickness of 2 mm by ordinary hot rolling.
After hot-rolled sheet annealing for 30 s, after descaling, cold-rolled to 0.35 mm thick cold-rolled sheet, then (90% H ₂ O ₂ +
(30% H ₂ + 70% N ₂ ) dry atmosphere, 900 ° C, 20s
Was annealed. Also, after annealing the cold rolled sheet as it is,
A product subjected to the same chemical polishing as above was also prepared. Table 1 shows the results of examining Sm, Ra and iron loss of each of the obtained steel sheets.

[0019]

[Table 1]

As is apparent from Table 1, reduction of iron loss is not sufficient by simply reducing Ra, and sufficient reduction of iron loss is achieved only by setting Sm to 100 μm or more.

Example 2 C: 0.003%, Si: 0.12%, Mn: 0.26%, P: 0.075
%, S: 0.0038%, Al: 0.001%, N: 0.0022%, and O: 0.0135%, the balance being a steel slab having a substantially Fe composition, hot rolled to a thickness of 2.5 mm by ordinary hot rolling. After being formed into a plate, it was descaled, and then cold rolled into a 0.40 mm-thick cold rolled plate, which was then annealed at 750 ° C. for 15 s. After that, normal cold rolling conditions (roll diameter 500mmφ,
A 0.20 mm thick roll at a speed of 600 mpm) and a 0.20 mm thick roll rolled at a low speed of 30 mpm using a small diameter roll of 65 mmφ were annealed at 800 ° C. for 10 s. Table 2 shows the results of examining Sm, Ra and iron loss of each of the obtained steel sheets.

[0022]

[Table 2]

As is clear from the table, Sm is 100 μm
According to the above, a remarkable iron loss improving effect is recognized not only in the commercial frequency but also in the high frequency. The reason for this seems to be that the state of the surface where more magnetic flux flows in the high-frequency region has a large effect on iron loss.

[0024]

As described above, according to the present invention, Sm is adopted instead of Ra, which has been used as an index of surface roughness, and the Sm is controlled to 100 μm or more. A non-oriented electrical steel sheet with excellent iron loss can be obtained. Further, according to the present invention, since the surface of the steel sheet is improved, further reduction of iron loss can be achieved in the high frequency region where the flow of magnetic flux concentrates on the surface.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between Sm and iron loss.

FIG. 2 is a graph showing the relationship between Ra and iron loss.

FIG. 3 is a diagram illustrating the concept of Sm.

Claims (1)

[Claims] 1. A non-oriented electrical steel sheet having a composition containing Si + Al: 4 wt% or less, wherein the average spacing Sm of the irregularities on the surface of the outer steel sheet is expressed by the following formula: A non-oriented electrical steel sheet with excellent iron loss, which satisfies: