Non-directional electromagnetic steel sheet

Abstract

To provide a non-oriented electrical steel sheet having all of low iron loss, high magnetic flux density, and high strength.SOLUTION: A non-oriented electrical steel sheet contains, in mass%, 1.5%≤Ni≤5.0% and 1.0%≤Al≤3.8%, with the balance being Fe and inevitable impurities. When the contents of Ni and Al in mass% are expressed as [Ni] and [Al], [Ni]≤[Al]+2.5 holds, and at least one of [Ni]≥2.2 and [Al]≥2.7 holds.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-oriented electrical steel sheet, and more particularly to a non-oriented electrical steel sheet that can be used for motor cores and the like. [Background technology]

[0002] The widespread use of hybrid vehicles and electric vehicles is accelerating, and the demand for non-oriented electrical steel sheets that form the iron cores of the motors installed in these vehicles is also increasing. For example, Patent Documents 1 and 2 listed below disclose such non-oriented electrical steel sheets. Non-oriented electrical steel sheets that form the iron cores of motors are desired to have properties such as low iron loss to improve motor efficiency, high magnetic flux density to obtain high torque, and high strength to withstand the centrifugal force of high rotation. Non-oriented electrical steel sheets that form the iron cores are selected depending on the properties required for the specific motor specifications, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-219692 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-199999 Summary of the Invention [Problem to be solved by the invention]

[0004] As mentioned above, it is desirable for the non-oriented electrical steel sheets that make up the iron core of a motor to have low iron loss, high magnetic flux density, and high strength. However, it is difficult for a single steel type to satisfy all of these characteristics. For example, there are non-oriented electrical steel sheets on the market that have a high strength of 650 to 800 MPa, but they are only available in thicknesses of 0.35 mm and have a low W 10 / 400 It is difficult to find one that also has low core loss such as ≦30W / kg.

[0005] The problem to be solved by the present invention is to provide a non-oriented electrical steel sheet that combines low core loss, high magnetic flux density, and high strength. [Means for solving the problem]

[0006] In order to solve the above problems, the non-oriented electrical steel sheet according to the present invention contains, by mass%, 1.5%≦Ni≦5.0%, 1.0%≦Al≦3.8%, with the remainder being Fe and unavoidable impurities, and the contents of Ni and Al in mass%, [Ni] and [Al], respectively, satisfy [Ni]≦[Al]+2.5 and at least one of [Ni]≧2.2 and [Al]≧2.7.

[0007] The non-oriented electrical steel sheet may further contain, by mass%, 0.1%≦V≦1.0%.

[0008] The non-oriented electrical steel sheet has a tensile strength of 700 MPa or more and a thickness of 0.35 mm. 10 / 400 It is preferable that the core loss is ≦30 W / kg and the saturation magnetization is 1.90 T or more. [Effects of the Invention]

[0009] The non-oriented electrical steel sheet according to the present invention contains the above-mentioned predetermined amounts of Ni and Al, and is highly effective in precipitation strengthening of NiAl and suppressing the formation of austenite phase, and thus exhibits low iron loss, high magnetic flux density, and high strength. [Brief explanation of the drawings]

[0010] [Figure 1] 3 is a graph showing the relationship between the Ni content and the Al content for a non-oriented electrical steel sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] A non-oriented electrical steel sheet (hereinafter sometimes simply referred to as electrical steel sheet) according to an embodiment of the present invention will be described in detail below. The non-oriented electrical steel sheet according to this embodiment contains Ni and Al in the amounts (1) and (2) below, with the remainder being Fe and unavoidable impurities. The Ni and Al contents satisfy the relationships (3) and (4) below. In this specification, the content of each element is expressed in mass%. In addition, in formulas showing the relationship between the content of each element, the element symbol is enclosed in square brackets [ ] to indicate the concentration value in mass%. In this specification, unless otherwise specified, each characteristic value is a value evaluated at room temperature (approximately 25°C) for a material that has undergone magnetic annealing.

[0012] [Composition of non-oriented electrical steel sheets] (1) 1.5%≦Ni≦5.0% When Ni is contained in an electrical steel sheet together with Al, NiAl precipitates. NiAl improves the strength of the electrical steel sheet through precipitation strengthening. From the viewpoint of sufficiently precipitating NiAl, the Ni content is set to 1.5%≦Ni. Preferably, it is set to 2.0%≦Ni, and more preferably, it is set to 2.5%≦Ni.

[0013] On the other hand, excessive Ni content in electrical steel sheet promotes the formation of austenite phase. When austenite phase is formed during magnetic annealing, crystal grains become finer, and magnetic properties deteriorate, such as increased iron loss. Therefore, from the viewpoint of suppressing the formation of austenite phase, Ni≦5.0% is set. Preferably, Ni≦4.5%, and even more preferably, Ni≦4.0%.

[0014] (2) 1.0%≦Al≦3.8% As described above, Al forms NiAl together with Ni, which is effective in improving the strength of electrical steel sheets. Furthermore, the addition of Al increases the resistivity of electrical steel sheets and reduces iron loss. To fully obtain these effects, the Al content is set to 1.0%≦Al. Preferably, it is set to 1.5%≦Al, and more preferably, it is set to 2.0%≦Al.

[0015] On the other hand, adding excessive Al leads to a decrease in the magnetic flux density (decrease in saturation magnetization) of the electrical steel sheet. It also reduces the workability of the electrical steel sheet. To suppress these phenomena, the Al content is set to Al≦3.8%, preferably Al≦3.5%, and even more preferably Al≦3.0%.

[0016] (3) [Ni]≦[Al]+2.5 As mentioned above, Ni and Al form NiAl, which contributes to improving the strength of electrical steel sheets. Ni is an element that stabilizes the austenite phase. On the other hand, Al is an element that stabilizes the ferrite phase. When the Al content is low relative to Ni, the austenite phase is more likely to be stabilized. To prevent the formation of the austenite phase from causing an increase in iron loss and other deterioration in magnetic properties, a sufficient amount of Al is contained relative to Ni. In order to prevent this, the relationship [Ni]≦[Al]+A is set to A=2.5. Preferably, A=1.5, or even A=1.0. According to thermodynamic calculations, the region [Ni]≦[Al]+2.5 is a component system that has a ferrite single-phase region.

[0017] (4) At least one of [Ni] ≥ 2.2 and [Al] ≥ 2.7 As described above, Ni and Al are effective in improving the strength of electrical steel sheets by forming NiAl. To achieve this strength-improving effect, their respective contents must be equal to or greater than the lower limits of (1) and (2). However, if both Ni and Al are present in small amounts within the respective ranges of (1) and (2), it is difficult to obtain a sufficient strength-improving effect. Therefore, by setting the Ni and Al contents to satisfy at least one of [Ni] ≥ 2.2 and [Al] ≥ 2.7, a situation in which only small amounts of both Ni and Al are contained can be avoided, ensuring a high strength-improving effect. Preferably, both [Ni] ≥ 2.2 and [Al] ≥ 2.7 should be satisfied.

[0018] As described above, in the electrical steel sheet according to this embodiment, the contents of Ni and Al are defined by the above conditions (1) to (4). Figure 1 shows the relationship between the Ni and Al contents, with the composition range that satisfies all of the above conditions (1) to (4) indicated by diagonal lines. By containing Ni and Al in such amounts, the electrical steel sheet of this embodiment achieves the effect of increasing strength through the formation of NiAl, while at the same time achieving high magnetic properties such as low iron loss by suppressing austenite formation. Furthermore, by limiting the content of non-magnetic metal elements, excluding unavoidable impurities, to only the above-mentioned Al (and V as an optional element, described below), a high magnetic flux density (high saturation magnetization) can be achieved.

[0019] (5) Any element: 0.1%≦V≦1.0% The electrical steel sheet according to this embodiment may contain a predetermined amount of V in addition to the amounts of Ni and Al that satisfy the above conditions (1) to (4). V is effective in improving the resistivity and strength of the electrical steel sheet. From the viewpoint of fully obtaining these effects, the V content is set to 0.1%≦V. More preferably, it is set to 0.2%≦V.

[0020] On the other hand, if an excessive amount of V is contained, the saturation magnetization of the electrical steel sheet will decrease. From the viewpoint of maintaining a high saturation magnetization, the V content is set to V≦1.0%, and more preferably V≦0.7%.

[0021] (6) Inevitable impurities The inclusion of unavoidable impurities is permitted to the extent that they do not significantly impair the properties of the electrical steel sheet. Specific examples of unavoidable impurities, in mass%, include C≦0.04%, N≦0.06%, O≦1.0%, Mn≦0.3%, P≦0.06%, S≦0.06%, Si≦0.2%, Cu≦0.3%, and Cr≦0.2%.

[0022] [Characteristics of non-oriented electrical steel sheets] The electrical steel sheet according to this embodiment has the above-mentioned composition, and thus has high strength, low iron loss, and high magnetic flux density. Specifically, it has a tensile strength of 700 MPa or more, and a W 10 / 400 It is possible to achieve an iron loss of 30 W / kg or less, or even 25 W / kg or less, and a saturation magnetization of 1.90 T or more, or even 2.00 T or more. Here, the tensile strength is measured in accordance with JIS Z 2241:2011. 10 / 400 is measured as the loss of electrical energy when a sheet having a thickness of 0.35 mm is magnetized with a 400 Hz alternating current at a maximum magnetic flux density of 1.0 T. The electrical steel sheet according to this embodiment preferably also has a resistivity of 30 μΩ·cm or more, and even 35 μΩ·cm or more, as a factor in imparting low iron loss. The electrical steel sheet according to this embodiment combines the above-mentioned high strength, low iron loss, and high magnetic flux density, making it suitable for use as a constituent material for the iron cores of motors used in hybrid vehicles, electric vehicles, etc.

[0023] In the electrical steel sheet according to this embodiment, the above-described composition suppresses the formation of austenite phase, which leads to coarsening of the grain size. The coarsening of the grain size is one of the factors that contributes to the low iron loss described above. For example, it is preferable that the average grain size after magnetic annealing is 120 μm or more, and even 180 μm or more.

[0024] The size of the crystal grains in the electrical steel sheet can be adjusted by the temperature during magnetic annealing. From the viewpoint of suppressing the formation of austenite phase, it is preferable to perform magnetic annealing at a temperature below the austenite formation temperature, or even in the ferrite single-phase region. This generates a fine austenite phase from the ferrite grain boundaries, resulting in finer crystal grains, which can suppress deterioration of the magnetic properties of the resulting electrical steel sheet, such as an increase in iron loss due to hysteresis loss. Furthermore, the magnetic annealing temperature can be selected so that the desired average crystal grain size is obtained in the region below the austenite formation temperature. The thickness of the electrical steel sheet is not particularly limited, but can be in the range of 0.1 mm to 0.5 mm. [Example]

[0025] The present invention will be described in more detail below using examples.

[0026] <Sample preparation> For Examples 1 to 11 and Comparative Examples 1 to 6, electrical steel sheets having the component compositions shown in Table 1 were produced. The production method involved melting metal materials having the respective composition ratios in a vacuum induction furnace, followed by casting, hot forging, hot rolling, hot-rolled sheet annealing, and cold rolling to produce sheets with a thickness of 0.35 mm. The resulting sheets were subjected to magnetic annealing for 120 minutes at the temperatures shown in Table 1, and then to heat treatment at 500°C for 24 hours to precipitate NiAl. Measurement specimens for the following tests were taken from these samples.

[0027] <Evaluation method> Using the test specimens of each sample obtained above, evaluations were carried out for tensile strength, core loss, resistivity, saturation magnetization, average grain size, and austenite formation temperature. Unless otherwise specified, each evaluation was carried out at room temperature in air. Furthermore, the relationship between the magnetic annealing temperature and grain size was evaluated for representative samples.

[0028] (tensile strength) JIS No. 13B test pieces were prepared and subjected to a tensile test according to JIS Z 2241:2011 at room temperature in the air to measure the tensile strength.

[0029] (iron loss) Each magnetic steel sheet was processed into a ring shape with an outer diameter of 45 mm, an inner diameter of 33 mm, and a thickness of 0.35 mm to form a magnetic ring (iron core). A primary coil (250 turns) and a secondary coil (70 turns) were formed using this magnetic ring to form a measurement sample. Then, using a BH analyzer, iron loss (W) was measured under the conditions of 400 Hz and a maximum magnetic flux density of 1.0 T. 10 / 400 ) was measured.

[0030] (specific resistivity) The volume resistivity of the electrical steel sheets was measured by the four-terminal method using a resistivity meter.

[0031] (Saturation magnetization) The saturation magnetization was determined by measuring the full loop with a vibrating sample magnetometer (VSM).

[0032] (Average grain size) The surfaces of the electrical steel sheets were polished and corroded, and observed with an optical microscope, and the average crystal grain size was measured using a method in accordance with JIS G 0551:2020.

[0033] (Austenite formation temperature) After annealing the electrical steel sheets at a predetermined temperature, the structures were observed using an optical microscope. Observations were made while changing the heat treatment temperature in increments of 5°C, and the heat treatment temperature at which the formation of austenite phase was confirmed was taken as the austenite formation temperature. Note that if the formation of austenite phase was not confirmed at any temperature, the austenite phase formation temperature was not specified.

[0034] (Relationship between magnetic annealing temperature and grain size) The relationship between the magnetic annealing temperature and the crystal grain size was investigated using Example 4 as a representative example. Specifically, magnetic annealing was performed at temperatures varying from 750°C to 950°C in 50°C increments to produce five types of samples. The average crystal grain size of these samples was then evaluated in the same manner as above.

[0035] <Result> Table 1 shows the composition and the results of the above-mentioned evaluation tests for the electrical steel sheets according to Examples 1 to 11 and Comparative Examples 1 to 6.

[0036] [Table 1]

[0037] According to Table 1, the composition of each of Examples 1 to 11 satisfies all of the following conditions: (1) 1.5%≦Ni≦5.0%, (2) 1.0%≦Al≦3.8%, (3) [Ni]≦[Al]+2.5, and (4) at least one of [Ni]≧2.2 and [Al]≧2.7. Furthermore, magnetic annealing was performed at a temperature below the austenite formation temperature. Correspondingly, each of Examples 1 to 11 achieved a high tensile strength of 700 MPa or more, a low core loss of 30 W / kg or less, and a high saturation magnetization of 1.90 T or more. Furthermore, a resistivity of 30 μΩ·cm or more and an average grain size of 120 μm or more were achieved.

[0038] Regarding condition (4), Examples 1 to 8 and 11 only satisfy either [Ni] ≥ 2.2 or [Al] ≥ 2.7, but still achieve the high tensile strength, low iron loss, and high saturation magnetization described above. This confirms that satisfying at least one of the relationships in condition (4) is sufficient. However, Example 10, which satisfies both, achieves the highest tensile strength among all Examples, and Example 9 also achieves a relatively high tensile strength.

[0039] Example 2 and Example 3 differ only in the presence or absence of V. Comparing these properties reveals that the inclusion of V slightly reduces saturation magnetization, but is effective in improving tensile strength, increasing resistivity, and reducing iron loss.

[0040] Comparative Examples 1 to 6 do not satisfy at least one of the above conditions (1) to (4). Therefore, the electrical steel sheets do not have a tensile strength of 700 MPa or more, an iron loss of 30 W / kg or less, and a saturation magnetization of 1.90 T or more. In Comparative Example 3, the Ni content is lower than the range defined by condition (1), and therefore the tensile strength is low. In Comparative Example 4, the Al content is lower than the range defined by condition (2), and therefore the tensile strength is low. On the other hand, in Comparative Example 6, the Al content is higher than the range defined by condition (2), and therefore the saturation magnetization is low.

[0041] In Comparative Example 5, the individual contents of Ni and Al satisfy conditions (1) and (2), respectively, but "Ni" = [Al] + 3.0, which does not satisfy condition (3). Correspondingly, the iron loss is large. In Comparative Examples 1 and 2, the individual contents of Ni and Al also satisfy conditions (1) and (2), respectively, but [Ni] < 2.2 and [Al] < 2.7, which does not satisfy condition (4). Correspondingly, sufficient tensile strength is not obtained.

[0042] Finally, we will consider the relationship between the crystalline structure and iron loss. Table 1 shows that, in general, the larger the average crystal grain size, the smaller the iron loss. Furthermore, Table 2 below shows the relationship between the magnetic annealing temperature and the average crystal grain size for Example 4.

[0043] [Table 2]

[0044] As shown in Table 1, the austenite formation temperature in Example 4 is 845°C. According to Table 2, the crystal grains are refined in the region higher than the austenite formation temperature, but large crystal grains of 120 μm or more are formed in the region lower than the austenite formation temperature. In particular, when magnetic annealing is performed at a high temperature of 800°C, which is below the austenite formation temperature, a large average crystal grain size of 130 μm is obtained. From these results, it can be said that by selecting a magnetic annealing temperature in the region lower than the austenite formation temperature, the crystal grain size can be controlled, and the larger the crystal grain size, the easier it is to reduce iron loss.

[0045] The embodiments and examples of the present invention have been described above. The present invention is not particularly limited to these embodiments and examples, and various modifications can be made.

Claims

1. In mass%, 1.5%≦Ni≦5.0%, Contains 1.0%≦Al≦3.8%; the balance being Fe and unavoidable impurities; The contents of Ni and Al in mass% are [Ni] and [Al], respectively. [Ni]≦[Al]+2.5 is satisfied, and At least one of [Ni] ≧ 2.2 and [Al] ≧ 2.7 is satisfied; A tensile strength of 700 MPa or more; With a plate thickness of 0.35 mm, the iron loss is W 10 / 400 ≦30 W / kg. Saturation magnetization of 1.90 T or more, A non-oriented electrical steel sheet having the above structure.

2. Furthermore, in mass%, The non-oriented electrical steel sheet according to claim 1, containing 0.1%≦V≦1.0%.

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