JP2024030809A - Soft magnetic steel plate - Google Patents

Abstract

The present invention provides a soft magnetic steel plate that can achieve insulation without forming a thick insulation coating. [Solution] Contains 1.6%≦Al≦3.8% in mass %, the remainder consists of Fe and unavoidable impurities, the surface has Al as the main component, the thickness is 0.15 μm or more, 0. A soft magnetic steel plate 1 has an oxide film 2 of .50 μm or less. The soft magnetic steel plate 2 may further contain at least one of 0%<Co≦25% and 0%<Ni≦2.5% in mass %. [Selection diagram] Figure 1

Description

The present invention relates to a soft magnetic steel plate, and more particularly to a soft magnetic steel plate having an oxide film on its surface.

Soft magnetic steel plates are sometimes used to construct the iron cores of motors and generators. BACKGROUND ART In recent years, the spread of hybrid vehicles and electric vehicles has accelerated, and demand for soft magnetic steel sheets that constitute the iron cores of motors installed in these vehicles has also increased. For example, such soft magnetic steel sheets are disclosed in Patent Documents 1 and 2 below. In this type of soft magnetic steel sheet, the composition of the soft magnetic alloy is set so as to obtain desired magnetic properties and mechanical properties. When forming a thick member such as an iron core of a motor, soft magnetic steel plates are used in a plurality of laminated layers.

JP2017-57456A JP2022-22832A

As described above, when a soft magnetic steel plate is used as an iron core of a motor, a plurality of soft magnetic steel plates are laminated to form a shape having a predetermined thickness. In this case, from the viewpoint of reducing eddy current loss, an insulating coating is often provided on the surface of the soft magnetic steel plate in order to achieve insulation between the soft magnetic steel plates of each layer. Formation of an insulating film has conventionally been generally carried out by chemical treatment such as phosphate treatment, or by applying a substance that forms an insulating film to the surface. However, insulating coatings formed by these methods tend to become thick. As a result, in the soft magnetic steel sheet, the volume fraction of the alloy portion that does not constitute the insulating coating decreases, making it difficult for the soft magnetic steel sheet to fully exhibit its original properties as a result of the effects of its composition, including magnetic properties. .

The problem to be solved by the present invention is to provide a soft magnetic steel plate that can achieve insulation without forming a thick insulation coating.

In order to solve the above problems, a soft magnetic steel plate according to the present invention has the following configuration.
[1] The soft magnetic steel sheet according to the present invention contains 1.6%≦Al≦3.8% in mass %, the remainder consists of Fe and inevitable impurities, and has Al as the main component on the surface, It has an oxide film with a thickness of 0.15 μm or more and 0.50 μm or less.

[2] In the aspect of [1] above, the soft magnetic steel sheet may further contain at least one of 0%<Co≦25% and 0%<Ni≦2.5% in mass %.

[3] In the aspect of [1] or [2] above, it is preferable that the volume fraction of the unoxidized alloy is 99.5% or more.

[4] In the aspect of any one of [1] to [3] above, the soft magnetic steel sheet has the oxide film on both the front and back surfaces, and the insulation resistance between the oxide films on both the front and back surfaces is 3× It is preferable that it is 10 ⁸ Ω·cm ² or more.

Since the soft magnetic steel sheet according to the present invention having the configuration [1] above contains the predetermined amount of Al, a thin and highly insulating oxide film is likely to be formed on the surface. In fact, the soft magnetic steel sheet according to the present invention has an oxide film with a thickness of 0.15 μm or more and 0.50 μm or less. When the thickness of the oxide film is 0.15 μm or more, the film has sufficiently high insulation properties. On the other hand, by suppressing the thickness of the oxide film to 0.50 μm or less, the volume fraction of unoxidized alloy increases in the soft magnetic steel sheet, making efficient use of the characteristics of the soft magnetic alloy. be able to.

In the aspect [2] above, the characteristics of the soft magnetic steel sheet can be improved because the soft magnetic steel sheet contains a predetermined amount of at least one of Co and Ni. Specifically, by containing Co, the saturation magnetic flux density of the soft magnetic steel sheet increases, and by containing Ni, the electrical resistance of the soft magnetic steel sheet improves. Co and Ni do not substantially contribute to the formation of an oxide film, and even if Co and Ni are added, a thin and highly insulating oxide film can be obtained by containing a predetermined amount of Al. is retained.

In the aspect [3] above, the volume fraction of the unoxidized alloy is 99.5% or more. Therefore, in the soft magnetic steel sheet, the excellent magnetic properties exhibited by the soft magnetic alloy can be efficiently utilized.

In the aspect [4] above, the insulation resistance between the oxide films on both the front and back surfaces of the soft magnetic steel plate is 3×10 ⁸ Ω·cm ² or more. Therefore, when soft magnetic steel plates are used in a laminated manner, insulation between the layers is sufficiently maintained, and the magnetic properties of the soft magnetic steel plates can be utilized while suppressing eddy current loss.

1 is a cross-sectional view schematically showing a soft magnetic steel plate according to an embodiment of the present invention.

Below, a soft magnetic steel plate according to an embodiment of the present invention will be described in detail. The soft magnetic steel plate according to this embodiment has the following composition and has an oxide film of a predetermined thickness on the surface. In this specification, the content of each element is expressed in mass %. Further, the alloy composition refers to the component composition excluding oxygen contained in the oxide film on the surface, and corresponds to the alloy composition of the unoxidized region inside covered with the oxide film. In this specification, unless otherwise specified, each characteristic value is a value evaluated at room temperature (approximately 25° C.).

[Composition of soft magnetic steel sheet]
The soft magnetic steel sheet according to the embodiment of the present invention contains Al in the amount shown in (1) below, and the remainder consists of Fe and inevitable impurities. Alternatively, it optionally further contains at least one of Co in the amount of (2) below and Ni in the amount of (3) below.

(1) 1.6%≦Al≦3.8%
Al contributes to the formation of an oxide film on the surface of the soft magnetic steel sheet. If the Al content is too low, the formation of an oxide film will be difficult to proceed, but if 1.6%≦Al, an oxide film with sufficient thickness and insulation properties will be easily formed on the surface. . Preferably, 2.0%≦Al, more preferably 2.5%≦Al.

On the other hand, when Al is added excessively, an excessively thick oxide film is likely to be formed on the surface of the soft magnetic steel sheet. Moreover, in soft magnetic steel sheets, it causes a decrease in saturation magnetization and a decrease in workability. From the viewpoint of suppressing these phenomena, the Al content is set to Al≦3.8%. Preferably, Al≦3.5%, more preferably Al≦3.0%.

(2) 0%<Co≦25%
When Co is contained in the soft magnetic steel sheet, the saturation magnetic flux density of the soft magnetic steel sheet can be improved. Even if a small amount of Co is added, such an effect can be obtained, so there is no particular lower limit to the Co content, and it is set to 0%<Co. Preferably, 15%≦Co. Note that since Co hardly contributes to the formation of an oxide film on the surface of a soft magnetic steel sheet, by containing the predetermined amount of Al, regardless of the presence or absence of Co, it is possible to form a thin, highly insulating oxide film. A coating is formed on the surface.

On the other hand, when Co is excessively contained in a soft magnetic steel sheet, an Fe--Co-based ordered phase is generated, which makes the soft magnetic steel sheet brittle. Further, Co is an expensive element, and adding a large amount leads to an increase in cost. From the viewpoint of suppressing these phenomena, Co≦25%. Preferably, Co≦20%.

(3) 0%<Ni≦2.5%
When Ni is contained in the soft magnetic steel sheet, the electrical resistance of the soft magnetic steel sheet can be increased and eddy current loss can be reduced. Since such an effect can be obtained even if a small amount of Ni is added, there is no particular lower limit to the Ni content, and it is set to 0%<Ni. Preferably, 0.5%≦Ni. Note that Ni also hardly contributes to the formation of an oxide film on the surface of a soft magnetic steel sheet, so regardless of the presence or absence of Ni, by containing the predetermined amount of Al, a thin and highly insulating oxide film can be formed. A film forms on the surface.

On the other hand, when Ni is excessively contained in a soft magnetic steel sheet, an austenite phase is generated and grain growth is promoted. Then, the magnetic properties may deteriorate. From the viewpoint of suppressing these phenomena, Ni is set to 2.5%. Preferably, Ni≦2.0%.

(4) Unavoidable impurities Unavoidable impurities are allowed to be included within a range that does not significantly impair the properties of the soft magnetic steel sheet. Specific examples of unavoidable impurities include, in mass %, C≦0.04%, N≦0.06%, O≦0.06%, Mn≦0.3%, P≦0.06. %, S≦0.06%, Si≦0.2%, Cu≦0.3%, and Cr≦0.2%. As mentioned above, this specification shows the component composition excluding oxygen contained in the oxide film on the surface, and the oxygen atoms listed here as unavoidable impurities also constitute the oxide film. Does not include those who are present.

[Condition and properties of soft magnetic steel sheet]
As shown in FIG. 1, the soft magnetic steel plate 1 according to this embodiment has an oxide film 2 on its surface. Preferably, the soft magnetic steel plate 1 has an oxide film 2 on both front and back surfaces.

The thickness of the oxide film on the surface of the soft magnetic steel plate is 0.15 μm or more and 0.50 μm or less. The oxide film is formed as an oxide film containing Al as a main component (Al has the highest content among metal elements). Then, mainly corresponding to the fact that the soft magnetic steel sheet has the above-mentioned composition containing a predetermined amount of Al, an oxide film having a thickness in the range of 0.15 μm or more and 0.50 μm or less is obtained. In addition, when oxide films are formed on both the front and back surfaces of the soft magnetic steel sheet, each of these oxide films shall have a thickness within the above range.

When the thickness of the oxide film is 0.15 μm or more, the insulation properties of the surface of the soft magnetic steel plate can be sufficiently improved. Instability of the film quality of the oxide film, such as the formation of cracks, is also less likely to occur. Then, when the soft magnetic steel plates are laminated to form the iron core of the motor, eddy current loss can be effectively suppressed. Preferably, the thickness of the oxide film is 0.20 μm or more, more preferably 0.25 μm or more.

On the other hand, since the thickness of the oxide film is 0.50 μm or less, the volume fraction (hereinafter sometimes simply referred to as volume fraction) of the alloy portion that does not constitute the oxide film can be kept large. As a result, in the soft magnetic steel sheet, the properties originally possessed by the soft magnetic alloy, such as magnetic properties, are effectively exhibited. Furthermore, by keeping the thickness of the oxide film small, the oxide film is less likely to peel off from the surface of the soft magnetic steel sheet. From the viewpoint of further enhancing these effects, the thickness of the oxide film is preferably 0.40 μm or less, more preferably 0.30 μm or less.

The thickness of the soft magnetic steel plate is not particularly limited. However, from the viewpoint of fully utilizing the effects of ensuring insulation and improving volume fraction by forming an oxide film having a thickness in the above range on the surface, the preferred thickness of the soft magnetic steel sheet is 0. An example of the range is .1 mm or more and 0.5 mm or less.

In the soft magnetic steel sheet according to this embodiment, the volume fraction of the unoxidized alloy is preferably 99.5% or more. This is a sufficiently high volume fraction of soft magnetic steel sheets laminated and used for applications such as iron cores. Although the upper limit of the volume fraction is not particularly specified, the volume fraction is preferably less than 99.9% from the viewpoint of ensuring the amount of oxide film that contributes to the insulation of the soft magnetic steel sheet. As shown in FIG. 1, in a soft magnetic steel sheet, when the thickness of the unoxidized alloy portion is t0 and the thickness of the oxide film is t1, the volume fraction F is expressed by the following equation (1).
F=t0/(t0+2・t1)×100% (1)

Furthermore, in the soft magnetic steel sheet according to this embodiment, the insulation resistance between the oxide films on both the front and back surfaces is preferably 3×10 ⁸ Ω·cm ² or more. Then, when the electromagnetic steel plates are used in a stacked manner, the insulation between the layers becomes high, and the effect of reducing eddy current loss can be greatly obtained. The upper limit of the insulation resistance is not particularly limited, and it is preferable that the insulation resistance be as large as possible within the range obtained by an oxide film having a thickness of 0.50 μm or less.

[Method for forming oxide film]
The soft magnetic steel sheet according to the present embodiment can be manufactured by using a soft magnetic steel sheet having a predetermined alloy composition as a raw material and through a process of forming an oxide film with a predetermined thickness on the raw material steel sheet. The raw material steel plate can be obtained through processes such as melting, casting, and forging of alloy materials, and further processes such as hot rolling, cold rolling, and annealing.

Formation of an oxide film having a predetermined thickness can be suitably performed by heat treatment in a reducing atmosphere, particularly in an atmosphere containing hydrogen. It is preferable that the oxygen partial pressure in the atmosphere during the heat treatment is suppressed to 10 ⁻¹⁷ Pa or less. If the oxygen partial pressure becomes too large, in addition to oxides containing Al as a main component, oxides containing Fe as a main component are likely to be generated on the surface of the electrical steel sheet. When an oxide of Fe is formed, the thickness of the oxide film tends to increase, and the oxide film tends to peel off. However, if the oxygen partial pressure during heat treatment is kept below 10 ⁻¹⁷ Pa, the thickness of the oxide film on the surface of the soft magnetic steel sheet can be kept small, and the volume fraction of the unoxidized alloy can be easily increased. More preferably, the oxygen partial pressure is 10 ⁻²⁰ Pa or less. Although the lower limit of the oxygen partial pressure is not particularly specified, if it is 10 ⁻³⁰ Pa or more, an oxide film sufficient for surface insulation can be suitably formed. The oxygen partial pressure in the atmosphere can be estimated from the dew point of the atmosphere. From the viewpoint of achieving an oxygen partial pressure of 10 ⁻¹⁷ Pa or less, the dew point of the atmosphere is preferably 0° C. or less.

The heat treatment temperature is preferably 800°C or higher. This makes it easy to sufficiently form an oxide film containing Al as a main component. More preferably, the heat treatment temperature is 850°C or higher. On the other hand, the heat treatment temperature is preferably kept below 950°C. Then, excessive grain growth during heat treatment can be prevented, and iron loss can be suppressed when the obtained soft magnetic steel sheet is used in a high frequency region. More preferably, the heat treatment temperature is 900°C or lower.

Hereinafter, the present invention will be explained more specifically using Examples.

<Preparation of sample>
Soft magnetic steel plates having oxide films were prepared as samples for Examples 1 to 5 and Comparative Examples 1 to 4, respectively. First, soft magnetic steel plates having the compositions shown in Table 1 were produced as raw steel plates. The manufacturing method involved melting metal materials having various composition ratios in a vacuum induction furnace, and performing casting, hot forging, hot rolling, hot-rolled plate annealing, and cold rolling to produce plates with a thickness of 0.2 mm. Created. Magnetic annealing was performed on the obtained plate material. In this way, a raw steel sheet was obtained.

The obtained raw steel sheet was subjected to heat treatment in a hydrogen atmosphere. For the heat treatment, hydrogen gas at 1 atm was used, and heating was performed for 2 hours at the heat treatment temperatures shown in Table 1. Table 1 shows the dew point and oxygen partial pressure calculated from the dew point for each atmospheric gas. Note that in Comparative Example 2, water vapor was intentionally added to the hydrogen gas.

<Evaluation method>
The thickness, volume fraction, and insulation resistance of the oxide film were evaluated for each sample of soft magnetic steel sheet obtained above as follows.

(Thickness of oxide film and volume fraction of unoxidized alloy)
A cross section of the soft magnetic steel plate was observed using a scanning electron microscope (SEM), and the thickness of the oxide film on the surface was measured. When the thicknesses of the oxide films on the front and back sides were different, the average value thereof was taken as the film thickness. Furthermore, using the obtained film thickness value, the volume fraction of the unoxidized alloy was estimated using the above equation (1). If the volume fraction is 99.5% or more, it can be considered to be sufficiently high.

(insulation resistance)
Using a resistivity meter, the resistance value between the oxide films on the front and back sides of the soft magnetic steel plate was measured by the two-terminal method, and was taken as the insulation resistance. If the insulation resistance is 3×10 ⁸ Ω·cm ² or more, it can be considered that the insulation is sufficiently high.

<Results>
Table 1 shows the component compositions, heat treatment conditions, and results of the above evaluation tests for the soft magnetic steel sheets of Examples 1 to 5 and Comparative Examples 1 to 4.

According to Table 1, the component compositions of Examples 1 to 5 all contain (1) 1.6%≦Al≦3.8%, and optionally (2) 0%<Co≦25% and ( 3) Contains at least one of 0%<Ni≦2.5%, with the remainder being Fe and inevitable impurities. Then, by undergoing heat treatment in a hydrogen atmosphere with a low oxygen partial pressure, it has an oxide film with a thickness of 0.15 μm or more and 0.50 μm or less. Corresponding to having such a thin oxide film, a volume fraction of 99.5% or more was obtained in all of these samples. In addition, the insulation resistance is 3×10 ⁸ Ω·cm ² or more, corresponding to the sufficient thickness of the oxide film. Note that elemental analysis using SEM (SEM-EDX) was performed on the oxide film of each example, and it was confirmed that the oxide film was mainly composed of Al.

On the other hand, in Comparative Example 1, although the soft magnetic steel sheet has a composition within the above range, the heat treatment is performed at a low temperature of 750°C. Correspondingly, the formation of the oxide film did not progress sufficiently, and the thickness of the oxide film did not reach 0.15 μm. The insulation resistance is also much lower than 3×10 ⁸ Ω·cm ² .

In Comparative Example 2, although the soft magnetic steel sheet has a component composition within the above range, the heat treatment is performed in an atmosphere containing a large amount of oxygen. In Comparative Example 2, the oxide film peeled off, making it impossible to perform each evaluation. This is considered to be due to the formation of a thick oxide film containing a large amount of Fe.

In Comparative Example 3, the Al content in the alloy is less than 1.6%. Correspondingly, even though the same heat treatment conditions as in Example 4 were adopted, the thickness of the oxide film did not reach 0.15 μm. The insulation resistance is also much lower than 3×10 ⁸ Ω·cm ² . In Comparative Example 4, the Al content in the alloy exceeds 3.8%. Corresponding to this, the thickness of the oxide film exceeds 0.50 μm, and the volume fraction does not reach 99.5%.

From the above, if an alloy having a predetermined composition is used as a raw material as in Examples 1 to 5, an oxide film with a thickness of 0.15 μm or more and 0.50 μm or less can be formed after heat treatment in an atmosphere with a low oxygen concentration. It can be seen that a soft magnetic steel sheet having the following properties can be obtained. In the obtained soft magnetic steel sheet, a high volume fraction and insulation resistance can be obtained.

1 Soft magnetic steel plate 2 Oxide film

Claims (4)

Contains 1.6%≦Al≦3.8% in mass%,
The remainder consists of Fe and unavoidable impurities,
A soft magnetic steel sheet having an oxide film on the surface mainly composed of Al and having a thickness of 0.15 μm or more and 0.50 μm or less. Furthermore, in mass%,
0%<Co≦25%, and 0%<Ni≦2.5%
The soft magnetic steel sheet according to claim 1, containing at least one of the following. The soft magnetic steel sheet according to claim 1 or 2, wherein the volume fraction of the unoxidized alloy is 99.5% or more. The soft magnetic steel plate has the oxide film on both the front and back surfaces,
The soft magnetic steel sheet according to claim 1 or 2, wherein the insulation resistance between the oxide films on both the front and back surfaces is 3×10 ⁸ Ω·cm ² or more.

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