Manufacturing method, rotary electric machine, and electromagnetic steel sheet

Abstract

The present invention applies an appropriate stress state to an aluminum diffusion layer into which Al is diffused in an electromagnetic steel sheet. Disclosed is a rotary electric machine including an iron core formed by laminating electromagnetic steel sheets and a support member for supporting the iron core, wherein: the electromagnetic steel sheet includes an aluminum diffusion layer; and the support member is arranged so that in-plane tensile stress is introduced into the aluminum diffusion layer.

Description

Manufacturing method, rotating electric machine and electromagnetic steel sheet

[0001] The present disclosure relates to a manufacturing method, a rotating electric machine, and an electromagnetic steel sheet.

[0002] A known technique involves forming a plating layer on the surface of an electrical steel sheet by an aluminizing treatment (hot-dip aluminum plating treatment), followed by a diffusion treatment in a non-oxidizing atmosphere to create a state in which the Al concentration is gradient from the surface, thereby reducing loss in the electrical steel sheet (see, for example, Patent Documents 1 and 2).

[0003] Also, a technique is known in which an Al-containing slurry is applied to the surface of an electrical steel sheet, followed by a diffusion treatment in a non-oxidizing atmosphere to create a gradient in the Al concentration from the surface, thereby reducing loss in the electrical steel sheet (see, for example, Patent Document 3).

[0004] Also, a technology is known in which a plating layer is formed on the surface of an electrical steel sheet by an aluminizing treatment, and then Al is penetrated by a long-term high-temperature diffusion treatment in an oxidizing atmosphere to realize a grain-oriented electrical steel sheet with an increased Al concentration, thereby reducing loss in the electrical steel sheet (see, for example, Patent Document 4).

[0005] German Patent Invention No. 102005004037 European Patent Application Publication No. 1260598 International Publication No. 2021 / 155280 Pamphlet Special Publication No. 2018-509522

[0006] None of the above documents suggests that the stress state of an aluminum diffusion layer in which Al is diffused in an electrical steel sheet can affect characteristics such as core loss.

[0007] Therefore, in one aspect, an object of the present disclosure is to impart an appropriate stress state to an aluminum diffusion layer in which Al is diffused in an electrical steel sheet.

[0008] In one aspect, a rotating electric machine is provided, which includes an iron core formed by stacking electromagnetic steel sheets, and a support member that supports the iron core, wherein the electromagnetic steel sheets include an aluminum diffusion layer, and the support member is positioned so that in-plane tensile stress is introduced into the aluminum diffusion layer.

[0009] According to one aspect, the present disclosure makes it possible to impart an appropriate stress state to an aluminum diffusion layer in which Al is diffused in an electrical steel sheet.

[0010] Fig. 1 is a flowchart showing the flow of each step included in the manufacturing method according to the present embodiment; Fig. 2 is a diagram showing a cross-sectional structure of a steel material obtained by an aluminizing treatment; Fig. 3 is a diagram showing a cross-sectional structure of a steel material obtained by a diffusion treatment; Fig. 4 is a plan view showing a steel material punched into a shape for a rotor core; Fig. 5 is a diagram showing an example of a stress state of a part of a steel material; Fig. 6 is an explanatory diagram of a method for calculating the amount of Al penetration (part 1); Fig. 7 is an explanatory diagram of a method for calculating the amount of Al penetration (part 2);

[0011] Each embodiment will be described in detail below with reference to the accompanying drawings. Note that the dimensional ratios in the drawings are merely examples and are not limiting. Shapes and the like in the drawings may be partially exaggerated for the sake of explanation. In the following description, various substances may be identified by commonly known abbreviations or chemical symbols, such as aluminum being referred to as aluminum (or Al). Hereinafter, when an interatomic distance widens, it is expressed as tensile stress occurring in the direction of the widening.

[0012] Fig. 1 is a flowchart showing the flow of each step included in the manufacturing method according to the present embodiment. Fig. 2 is a diagram showing a cross-sectional structure of a steel material obtained by aluminizing treatment (a steel material after aluminizing treatment).

[0013] The manufacturing method of this embodiment first includes a step of preparing a steel material (base material) having a desired plate thickness (step S100). The steel material having the desired plate thickness can be obtained, for example, by rolling a material obtained by casting or the like (for example, in the form of a steel slab or steel billet).

[0014] The desired thickness of the steel material is arbitrary, but may be, for example, 0.20 mm to 0.35 mm, and more preferably 0.25 mm to 0.30 mm.

[0015] In this embodiment, the steel material is for use in an electrical steel sheet and preferably contains Si and Al. Adding Si and Al to a steel material reduces magnetocrystalline anisotropy and hysteresis loss. Furthermore, adding Si and Al increases the electrical resistance of the steel material, thereby contributing to a reduction in eddy current loss. Therefore, adding Si and Al reduces iron loss (hysteresis loss and eddy current loss) in the steel material. On the other hand, adding excessive Si and Al not only reduces the magnetic flux density but also reduces workability in the steel material's manufacturing process (rolling, pressing, etc.). Note that the final product, for example, an electrical steel sheet, can be pressed into a desired shape to form a rotor core, stator core, or the like of a rotating electrical machine. Taking these tradeoffs into consideration, the steel material (base metal) preferably contains Si in a range of more than 0.00% by mass but not more than 7.00% by mass and Al in a range of more than 0.00% by mass but not more than 2.00% by mass.

[0016] Next, the manufacturing method of this embodiment includes an aluminum-containing layer forming step (step S102) in which an aluminum-containing layer (see reference numeral 20 in FIG. 2) is formed on the steel material. The aluminum-containing layer 20 can be formed, for example, by an aluminizing process. For example, the aluminum-containing layer is in the form of a plating layer having a thickness in the range of 2 μm to 30 μm. For example, a plating layer having a thickness in the range of 2 μm to 30 μm may be formed by gas wiping or the like.

[0017] In a modified example, the aluminum-containing layer may be formed by applying an aluminum-containing slurry instead of the aluminizing treatment, although the application of an aluminum-containing slurry has the disadvantage that it is difficult to penetrate Al into the steel sheet in the subsequent diffusion treatment.

[0018] The aluminum-containing layer (plating layer) may be composed of only aluminum, for example, when the aluminum-containing layer is formed by sputtering or the like. Alternatively, the aluminum-containing layer (plating layer) may contain, in addition to aluminum, one or more of iron (Fe), silicon (Si), and manganese (Mn). Preferably, it contains Al, Fe, and Si. For example, the plating layer may contain Al in a range of 20% by mass or more and 100% by mass or less, Fe in a range of 0.00% by mass or more and 80% by mass or less, and Si in a range of 0.00% by mass or more and 15% by mass or less. The plating layer may be a single layer or a multi-layer.

[0019] Next, the manufacturing method of this embodiment includes a diffusion treatment step (step S104) in which a diffusion treatment is performed on the steel material on which the aluminum-containing layer has been formed.

[0020] The diffusion treatment is a treatment for forming a state in which the Al concentration is gradient from the surface of the steel material based on the Al contained in the aluminum-containing layer. That is, the diffusion treatment forms an Al diffusion layer (see reference numeral 32 in FIG. 3 ) by diffusing the Al contained in the aluminum-containing layer from the surface of the steel material in the thickness direction. The Al diffusion layer may have a gradient (change gradient) of the Al concentration in such a manner that the Al concentration becomes higher toward the surface in the thickness direction.

[0021] The diffusion process may be carried out under predetermined temperature conditions for a predetermined processing time (hereinafter also referred to as "diffusion time").

[0022] The desired aluminum diffusion pattern is basically arbitrary as long as the Al diffusion layer has a gradient (gradient of change) of the Al concentration.

[0023] The Al diffusion layer has a gradient (change gradient) of Al concentration such that the Al concentration increases toward the surface in the thickness direction. Specifically, the Al concentration is highest at the surface of the Al diffusion layer and gradually decreases toward the center of the plate thickness. In a modified example, the Al concentration may be approximately constant in the Al diffusion layer.

[0024] Next, the manufacturing method of this embodiment includes a tensile stress generating step (step S106) of introducing an in-plane tensile stress into the Al diffusion layer.

[0025] FIG. 4 is a plan view schematically showing a steel material punched into a shape for a rotor core. Here, as an example, a steel material 70 punched into a shape for a rotor core will be described. Note that the steel material 70 has magnet holes 72, but the shape and arrangement of the magnet holes 72 are optional, and the magnet holes 72 themselves may be omitted. FIG. 5 is a schematic diagram showing an example of the stress state of a portion Q4 of the steel material 70. FIG. 5 schematically shows an example of the stress state occurring in a region within the range of radius r + dr and angle dθ. Note that σθ indicates circumferential stress, and σr indicates radial capacity.

[0026] The tensile stress is preferably generated along the direction in which the magnetic flux is formed, and may be generated in substantially all directions, for example, in any part Q4 (see Figure 4) of the steel material 70, as shown in Figure 5.

[0027] The tensile stress may be generated by any method, such as by an insulating film formed on the Al diffusion layer, or by a support member (e.g., a nut or an end plate) in an assembled state as a rotating electric machine. In this case, the manufacturing method for the rotating electric machine includes a step of supporting the laminated core with the support member in a manner that generates tensile stress. In this case, the laminated core is formed by laminating steel materials having the above-mentioned Al diffusion layer. The laminated core forms a rotor core, a stator core, or the like.

[0028] In this way, according to the manufacturing method of this embodiment, tensile stress can be generated in an electrical steel sheet having an Al-diffused layer in which Al is diffused with a gradient (change gradient) of Al concentration. The effects of generating tensile stress will be described in detail with reference to the following examples.

[0029] Next, several examples of steel materials that the inventors of the present invention actually processed using the manufacturing method according to this embodiment will be described.

[0030] The inventors of the present application prepared one type of steel (referred to as steel type C) having the component properties shown in Table 1 below, and performed a process based on the manufacturing method of this embodiment, resulting in the results shown in Table 2. Specifically, in Example 1 and the like, a single test piece (rectangular, 20 × 50 mm in size) was cut out by laser from a steel sheet having the chemical components shown in Table 1, and the test piece was subjected to an aluminizing process, resulting in the plating thickness shown in Table 2. Next, after the aluminizing process, a diffusion process was performed under the conditions shown in Table 2. Note that in Comparative Examples 6 to 8, the aluminizing process and the diffusion process were not performed.

[0031] All steels of steel type C contain 0 to 7.00 mass% Si, 0 to 1.00 mass% Mn, and 0 to 2.00 mass% Al. A base material with such a composition is preferred, but is not limited to this. In Table 2, mass% represents mass%.

[0032]

[0033]

[0034]

[0035]

[0036]

[0037] As a result, the results in Tables 3, 4, and 5 were obtained. Evaluation 1 in Tables 3 and 4 was evaluated by FE (Field Emission)-EPMA (Electron Probe Micro Analyzer) analysis. In Table 3, the symbol "" indicates "same as above." In this test, the type of coating and the coating formation temperature (of the coating) were the same in each example and each comparative example in that they were oxides mainly composed of aluminum and were equal to the temperature during the diffusion treatment. The iron loss in Evaluation 2 in Table 5 was the result of AC magnetic measurement, and the magnetic flux density in Evaluation 2 was the result of measurement using the initial magnetization curve of AC (50 Hz). The diffusion depth to plate thickness ratio is the value obtained by dividing the diffusion depth by the plate thickness. In Table 5, the magnetic flux density represents the magnetic flux density (B50) at a magnetizing force of 5000 A / m, and the iron loss represents the iron loss (W10 / 400) at a frequency of 400 Hz and a magnetic flux density of 1.0 T. In addition, in Table 5, the iron loss reduction rate is the rate obtained by dividing the amount of reduction from the iron loss of an untreated product by the iron loss of the untreated product.

[0038] In Table 4, the Al penetration amount / thickness ratio is the value obtained by dividing the amount of aluminum penetration in the Al diffusion layer (hereinafter also referred to as "Al penetration amount") based on the aluminum diffusion depth and the aluminum concentration at the center of the base material thickness (hereinafter also referred to as "median Al concentration") by the base material thickness. Specifically, in this test, the Al penetration amount was calculated as follows based on the aluminum diffusion depth, the surface Al concentration, and the median Al concentration: If the aluminum diffusion depth is less than the base material thickness / 2, then the Al penetration amount = (surface Al concentration - median Al concentration) × aluminum diffusion depth × 1 / 2. In this case, the Al penetration amount corresponds to the area S11 of the triangle indicated by the dashed-dotted line in FIG. 6. In this case, the three vertices of the triangle correspond to a position on the base material surface corresponding to the surface Al concentration, a position on the base material surface corresponding to the median Al concentration, and a position inward from the base material surface by the aluminum diffusion depth corresponding to the median Al concentration, as shown in FIG. 6. When the aluminum diffusion depth is greater than or equal to the base metal thickness / 2, the amount of Al penetration is equal to (surface Al concentration + central Al concentration - base metal Al concentration × 2) × aluminum diffusion depth × 1 / 2. In this case, the amount of Al penetration corresponds to the area S12 of the trapezoid shown by the dashed line in FIG. 7. In this case, the four vertices of the trapezoid correspond to the base metal surface and the surface Al concentration, the base metal surface and the base metal Al concentration, the position inward from the base metal surface by the aluminum diffusion depth and corresponding to the central Al concentration, and the position inward from the base metal surface by the aluminum diffusion depth and corresponding to the base metal Al concentration, as shown in FIG. 7. The case where the aluminum diffusion depth is greater than or equal to the base metal thickness / 2 corresponds to the case where the diffusion depth to thickness ratio is 0.50 or more in Table 3. The base metal Al concentration corresponds to the base metal components in Table 2 (D in FIG. 7). ０ (See also Table 2.) The thickness of the base material corresponds to the thickness in Table 2, and is the thickness obtained by subtracting the thickness of the coating from the total thickness.

[0039] 6 and 7 show Al concentration profiles when an oxide layer is formed on the Al diffusion layer, where α1 represents the Al concentration in the insulating coating (oxide layer) and α2 represents the Al concentration on the surface of the Al diffusion layer.

[0040] The Al gradient thickness ratio is the gradient of change in aluminum concentration with respect to the change in the thickness direction in the Al diffusion layer. The Al gradient thickness ratio is the value obtained by dividing the Al gradient by the base material thickness. Specifically, in this test, the Al gradient was calculated as follows: Al gradient = (surface Al concentration - center Al concentration) / aluminum diffusion depth. Note that the base material thickness corresponds to the thickness in Table 2 and is the total thickness excluding the coating thickness.

[0041] Here, with continued reference to Tables 2, 3, 4, and 5, the case where a load is applied using the magnetic measurement method will be described.

[0042] In Tables 2 to 5, Examples 3 and onward and Comparative Examples 6 and onward correspond to cases where load application is performed using the magnetic measurement method. Comparative Examples 6 and onward correspond to cases where aluminizing treatment and diffusion treatment are not performed. In other words, Comparative Examples 6 and onward show the characteristics of the base material itself.

[0043] In this test, a load was applied in the tensile direction to confirm the effect of the tensile stress described above. The parameter values ​​corresponding to the magnitude of the applied load when the load was applied are shown as "Introduced Stress" in Table 5. In other words, in this test, magnetic measurements were performed with the tensile stress applied.

[0044] Comparing Example 3 and subsequent Examples with Comparative Example 4 and subsequent Examples, it can be seen that the iron loss reduction rate is significantly greater when tensile stress is applied. It can also be seen that when aluminizing and diffusion treatments are performed, the iron loss reduction rate is significantly greater when tensile stress is applied, compared to when they are not (Comparative Example 6 and subsequent Examples). Furthermore, in Example 3 and subsequent Examples, the magnetic flux density reduction rate is within 25%, and the magnetic flux density reduction rate when tensile stress is applied is also good.

[0045] Therefore, it is preferable that the steel sheet having the above-described Al diffusion layer is formed into a laminated core (stator core or rotor core) of a rotating electrical machine in a state in which tensile stress is applied. In this regard, any method may be used to form the laminated core in a state in which tensile stress is applied, but the state in which tensile stress is applied may be achieved, for example, by a supporting step in which a supporting member such as a nut presses the laminated core in the axial direction.

[0046] Alternatively, when a coating is applied to a steel sheet having an Al diffusion layer in addition to or instead of an oxide layer, the coating may be formed in a manner that generates tensile stress.

[0047] Here, it is predicted that tensile stress occurs due to the difference in thermal expansion coefficient between the coating and the Al diffusion layer in Examples 1 and 2. In Comparative Examples 1 and 2, the coating is thin, as shown in Table 3, and no such tensile stress occurs. Due to this difference, there is a significant difference in the iron loss reduction rate between Examples 1 and 2 and Comparative Examples 1 and 2, as shown in Table 5.

[0048] It should be noted that even in the steel sheets according to Comparative Examples 1 and 2, a new insulating film may be separately provided to generate tensile stress in the Al diffusion layer. Alternatively, as described above, tensile stress may be generated in the laminated core state by a support member such as a nut.

[0049] Although each embodiment has been described in detail above, it is not limited to a specific embodiment, and various modifications and changes are possible within the scope of the claims. It is also possible to combine all or a plurality of components of the above-described embodiments.

[0050] For example, in the above-described embodiment, the diffusion treatment may be performed immediately after the formation of the Al-containing layer, or may be performed after the Al-containing layer is formed and then processed, such as by pressing. Furthermore, the Al-containing layer may be formed by methods other than aluminizing or slurry, such as vapor deposition, sputtering, calorizing, shot peening, or foil bonding.

[0051] 20: Aluminum-containing layer (aluminum-containing layer), 32: Al diffusion layer (aluminum diffusion layer)

Claims

1. A rotating electric machine comprising: an iron core formed by laminating electromagnetic steel sheets; and a support member supporting the iron core, wherein the electromagnetic steel sheets include an aluminum diffusion layer, and the support member is positioned so that in-plane tensile stress is introduced into the aluminum diffusion layer.

2. A rotating electric machine comprising an iron core formed by laminating electromagnetic steel sheets, the electromagnetic steel sheets including a coating on a base material surface and an aluminum diffusion layer, the coating being formed so as to introduce in-plane tensile stress into the aluminum diffusion layer.

3. A rotating electric machine according to claim 1 or 2, wherein the aluminum concentration in the aluminum diffusion layer gradually decreases from the surface of the base material toward the center of the base material thickness.

4. An electrical steel sheet comprising: a coating on a surface of a base material; and an aluminum diffusion layer in which the aluminum concentration gradually decreases from the surface of the base material toward the center of the thickness of the base material, the coating being formed so as to introduce in-plane tensile stress into the aluminum diffusion layer.

5. Electrical steel sheet having an aluminum diffusion layer with tensile stress introduced in-plane.

6. The electrical steel sheet according to claim 4 or 5, wherein the aluminum concentration in the aluminum diffusion layer gradually decreases from the surface of the base material toward the center of the base material thickness.

7. A method for manufacturing a rotating electric machine, comprising the steps of: forming an aluminum diffusion layer on a steel material for an electromagnetic steel plate having an aluminum-containing layer formed on its surface; and forming an insulating coating on the surface of the base material so as to introduce tensile stress into the aluminum diffusion layer.

8. A method for manufacturing a rotating electric machine, comprising: a step of forming an aluminum diffusion layer on a steel material for an electromagnetic steel plate having an aluminum-containing layer formed on its surface; a step of laminating the steel material to form an iron core; and a step of supporting the iron core on a support member so that tensile stress is introduced into the aluminum diffusion layer.

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