Soft magnetic iron alloy plate, method for producing the same, iron core using the same, and rotating electrical machine

Abstract

Provided are a soft magnetic iron alloy plate having a higher saturation magnetic flux density than an electromagnetic pure iron plate without excessively increasing iron loss, a method for producing the soft magnetic iron alloy plate, an iron core, and a rotating electrical machine using the soft magnetic iron alloy plate. The soft magnetic iron alloy plate of the present invention is characterized by having a chemical composition comprising 2 to 10 atomic % of N, 0 to 30 atomic % of Co, and 0 to 1.2 atomic % of V, with the balance being Fe and impurities. The soft magnetic iron alloy plate comprises, along the thickness direction of the soft magnetic iron alloy plate, an outer nitrogen concentration transition region having a nitrogen concentration of 1 to 4 atomic % on the main surface and increasing inward from the main surface, a high nitrogen concentration region having a maximum nitrogen concentration higher than the main surface and less than 11 atomic %, and a nitrogen concentration variation range of 1 atomic % or less, and an inner nitrogen concentration transition region having a nitrogen concentration decreasing inward from the high nitrogen concentration region and a minimum nitrogen concentration lower than that of the high nitrogen concentration region and not less than 1 atomic %.

Description

Technical Field

[0001] The present invention relates to magnetic material technology, and in particular to a soft magnetic iron alloy plate having a higher saturation magnetic flux density than an electromagnetic pure iron plate, a method for producing the soft magnetic iron alloy plate, and an iron core and a rotating electric machine using the soft magnetic iron alloy plate. Background Art

[0002] Electromagnetic iron sheets (e.g., with a thickness of 0.01 to 1 mm), such as electromagnetic steel sheets and pure electromagnetic iron sheets, are laminated and used as the core materials for rotating electrical machines and transformers. High conversion efficiency between electrical and magnetic energy is crucial in iron cores, and high magnetic flux density is therefore crucial. To increase magnetic flux density, a material with a high saturation magnetic flux density (Bs) is desirable. Known iron-based materials with high Bs include Fe-Co alloys and iron nitride.

[0003] Furthermore, reducing the cost of the iron core is naturally one of the most important issues, and conventionally, active efforts have been made to develop technologies for stably and inexpensively producing materials having a high Bs.

[0004] For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-046074) discloses magnetic metal fine particles composed primarily of Fe, coated with graphite, and having a nitrogen content of 0.1 to 5% by weight, including at least one of Fe4N and Fe3N. Furthermore, as a method for producing these magnetic metal fine particles, the following method is disclosed: iron oxide powder is mixed with a powder containing carbon, and the mixed powder is heat-treated in a non-oxidizing atmosphere to produce metal fine particles composed primarily of Fe and coated with graphite. These fine particles are then further nitrided to produce the magnetic metal fine particles.

[0005] According to Patent Document 1, magnetic metal fine particles having excellent corrosion resistance and a method for producing the same can be provided.

[0006] In addition, Patent Document 2 (Japanese Patent Application No. 2020-132894) discloses a soft magnetic material, which is a plate-shaped or foil-shaped soft magnetic material with a high saturation magnetic flux density, comprising iron, carbon and nitrogen, and comprising martensite and γ-Fe containing carbon and nitrogen, forming a phase containing nitrogen in the γ-Fe.

[0007] According to Patent Document 2, a soft magnetic material having a saturation magnetic flux density exceeding that of pure iron and thermal stability can be manufactured at low cost. This soft magnetic material can be used to improve the characteristics of the magnetic circuit of an electric motor, etc., thereby achieving miniaturization and higher torque of the electric motor, etc.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-046074

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2020-132894 Summary of the Invention

[0012] Problems to be solved by the invention

[0013] While dust cores are suitable for smaller electrical components such as noise filters and reactors, larger electrical machines such as rotating motors and transformers benefit from a core made of laminated electromagnet plates from a mechanical strength perspective. While Patent Document 1 is a technology suitable for dust cores, it is not suitable for the manufacture and use of thin sheet materials such as electromagnet plates.

[0014] Furthermore, in an iron core, to improve the efficiency of electrical / magnetic energy conversion, not only a high saturation magnetic flux density (Bs) but also low iron loss (Pi) is important. Pi is the sum of hysteresis loss and eddy current loss. To reduce hysteresis loss, a low coercive force (Hc) is desirable. The magnetic properties of commercially available electromagnetic pure iron plates are believed to be Bs ≈ 2.1 T and Hc ≈ 80 A / m. The soft magnetic material of Patent Document 2 is believed to have an advantage in having a higher Bs than electromagnetic pure iron plates, but a disadvantage in Hc.

[0015] Note that, from the perspective of high-output design of rotating electrical machines and transformers, priority is given to improving the Bs of the core. If the degree of improvement in Bs is large, a certain degree of increase in Pi is acceptable.

[0016] Among currently commercialized soft magnetic bulk materials, Perminder alloy (49Fe-49Co-2V mass% = 50Fe-48Co-2V atomic%, Bs = 2.4T) is widely known as the material with the highest Bs. However, the material cost of Co is approximately 100 times that of Fe, though this varies depending on market conditions. Therefore, Perminder alloy has the disadvantage of being a very expensive material. In other words, if the Co content in Fe-Co alloys can be reduced, the material cost can be reduced accordingly.

[0017] On the other hand, in recent years, there has been a strong demand for small, high-output rotating electrical machines (such as motors and generators), and improving the properties of iron cores has become an urgent issue. Furthermore, as mentioned above, reducing the cost of iron cores is undoubtedly one of the most important issues. Therefore, there is a need for a soft magnetic material that has a higher Bs than electromagnetic pure iron plates, an increase in Pi within an allowable range, and is less expensive than Perminder alloys.

[0018] However, technology for stably producing soft magnetic materials exhibiting such magnetic properties at low cost has not yet been fully established.

[0019] Therefore, an object of the present invention is to provide a soft magnetic iron alloy plate having a higher saturation magnetic flux density than an electromagnetic pure iron plate without excessively increasing iron loss, a method for producing the soft magnetic iron alloy plate, and an iron core and a rotating electric machine using the soft magnetic iron alloy plate.

[0020] Means for solving problems

[0021] (I) One embodiment of the present invention provides a soft magnetic iron alloy plate characterized in that:

[0022] It has a chemical composition comprising 2 atomic % to 10 atomic % of nitrogen (N), 0 atomic % to 30 atomic % of cobalt (Co), and 0 atomic % to 1.2 atomic % of vanadium (V), with the balance being iron (Fe) and impurities.

[0023] In the thickness direction of the soft magnetic iron alloy plate, there are:

[0024] an outer nitrogen concentration transition region in which the nitrogen concentration of the main surface is not less than 1 atomic % and not more than 4 atomic %, and the nitrogen concentration increases from the main surface toward the inside;

[0025] a high nitrogen concentration region having a maximum N concentration higher than the N concentration of the main surface and lower than 11 atomic %, and a variation range of the N concentration being within 1 atomic % (within ±0.5 atomic %); and

[0026] An inner nitrogen concentration transition region in which the N concentration decreases from the high nitrogen concentration region toward the inside and a minimum N concentration is lower than the N concentration of the high nitrogen concentration region and is 1 atomic % or more.

[0027] The present invention can implement the following improvements and modifications in the soft magnetic iron alloy plate (I) of the present invention.

[0028] (i) The maximum N concentration in the high nitrogen concentration region is not less than 6 atomic % and not more than 10 atomic %, and the minimum N concentration in the inner nitrogen concentration transition region is not less than 1 atomic % and not more than 4 atomic %.

[0029] (ii) The average N concentration gradient of the outer nitrogen concentration transition region is greater than or equal to 0.1 atomic % / μm and less than or equal to 0.6 atomic % / μm, and the average N concentration gradient of the inner nitrogen concentration transition region is greater than or equal to 0.1 atomic % / μm and less than or equal to 0.3 atomic % / μm.

[0030] (iii) When the value of the Co concentration (unit: atomic %) is set to x, the value of the saturation magnetic flux density y (unit: T) of the soft magnetic iron alloy plate satisfies the empirical formula (1) "y ≥ 1.02 × (0.01 × x + 2.14)", and when the value of the iron loss (unit: W / kg) is set to z, the iron loss under the conditions of magnetic flux density of 1.0 T and 400 Hz satisfies the empirical formula (2) "z < 150 × y - 295".

[0031] (vi) The thickness of the soft magnetic iron alloy plate is 0.03 mm or more and 0.3 mm or less.

[0032] (II) Another aspect of the present invention provides a method for producing a soft magnetic iron alloy plate, which is the method for producing the soft magnetic iron alloy plate described above, and is characterized by comprising the following steps:

[0033] a starting material preparation step of preparing a starting material formed of a soft magnetic material having Fe as a main component and having a thickness of 0.03 mm to 0.3 mm;

[0034] a nitrogen concentration distribution controlled heat treatment step of performing a predetermined nitrogen concentration distribution controlled heat treatment on the starting material to form a predetermined nitrogen concentration distribution along the thickness direction of the starting material; and

[0035] Phase transformation / iron nitride phase generation step, wherein the starting material having the predetermined N concentration distribution is subjected to martensitic transformation, and the iron nitride phase is dispersed and generated,

[0036] The prescribed nitrogen concentration distribution control heat treatment is a heat treatment carried out within the austenite phase formation temperature range, and is a combination of a nitriding process and a nitrogen diffusion / denitrification process. The nitriding process is carried out in a prescribed ammonia atmosphere to allow N atoms to intrude and diffuse from both main surfaces of the starting material. The nitrogen diffusion / denitrification process is carried out in a prescribed nitrogen atmosphere to allow the N atoms to diffuse further inwardly of the starting material and release nitrogen from both main surfaces of the starting material to form the outer nitrogen concentration transition region.

[0037] The present invention can implement the following improvements and modifications in the above-mentioned method (II) for producing a soft magnetic iron alloy plate of the present invention.

[0038] (v) The predetermined nitrogen concentration distribution control heat treatment is a heat treatment in which the nitriding process and the nitrogen diffusion / denitrification process are alternately performed for a plurality of cycles.

[0039] (vi) The phase transformation / iron nitride phase formation step includes quenching to a temperature below 100°C and cryogenic treatment to a temperature below 0°C.

[0040] (III) Another aspect of the present invention provides an iron core formed of a laminate of soft magnetic iron alloy plates, wherein the soft magnetic iron alloy plates are the soft magnetic iron alloy plates of the present invention.

[0041] (IV) Another aspect of the present invention provides a rotating electrical machine including an iron core, wherein the iron core is the iron core of the present invention described above.

[0042] Effects of the Invention

[0043] According to the present invention, a soft magnetic iron alloy plate having a higher saturation magnetic flux density than an electromagnetic pure iron plate without excessively increasing iron loss and a method for manufacturing the soft magnetic iron alloy plate can be provided. Furthermore, an iron core and a rotating electric machine can be provided that, by using the soft magnetic iron alloy plate, contribute to higher output of a rotating electric machine compared to an iron core using pure iron. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] [ Figure 1 ] is a graph showing an example of the relationship between the nitrogen concentration in the soft magnetic iron alloy plate of the present invention and the length in the plate thickness direction.

[0045] [ Figure 2 ] is a process diagram showing an example of a method for manufacturing the soft magnetic iron alloy plate of the present invention.

[0046] [ Figure 3A ] is a perspective schematic diagram showing an example of a stator of a rotating electrical machine.

[0047] [ Figure 3B ] is an enlarged cross-sectional schematic diagram of the slot area of ​​the stator.

[0048] [ Figure 4 ] are X-ray diffraction patterns of reference sample A-8 and sample A-1 of the present invention. DETAILED DESCRIPTION

[0049] [Basic concept of the present invention]

[0050] Pure iron has the advantages of being inexpensive and having a high saturation magnetic flux density (Bs) (2.1 T). Fe-Si alloys containing approximately 1-3% silicon (Si) by mass can significantly reduce iron loss (Pi) compared to pure iron, but suffer from a slightly lower Bs (2.0 T). Furthermore, Permind alloys containing approximately 50% Co by mass exhibit a sufficiently high Bs (2.4 T) and low Pi compared to pure iron, but suffer from the disadvantage that the material cost of Co is significantly higher than that of Fe.

[0051] On the other hand, as soft magnetic materials showing higher Bs than pure iron, there are the aforementioned iron nitride phases (e.g., Fe8N phase (α' phase), Fe 16N2 phase (α" phase). The inventors of this application have focused on a technology that improves Bs by allowing nitrogen to intrude and diffuse into a soft magnetic material mainly composed of Fe to form α' phase and α" phase iron nitride phases (for example, Patent Document 2). However, the soft magnetic material of Patent Document 2 is considered to have an advantage of having a higher Bs than electromagnetic pure iron plates, but is weak in terms of Hc.

[0052] Therefore, the inventors of the present application conducted intensive research on methods for stably producing nitrogen-containing soft magnetic iron alloy sheets that exhibit a Bs superior to that of electromagnetic pure iron sheets, without excessively increasing Pi (the increase in Pi is within the permissible range in the design of rotating electrical machines). As a result, they discovered that by subjecting the starting material to a predetermined nitrogen concentration distribution-controlled heat treatment, which combines a nitriding process with a nitrogen diffusion / denitrification process to achieve a predetermined nitrogen concentration distribution along the sheet thickness, and then performing a predetermined phase transformation / iron nitride phase formation process, it is possible to stably produce soft magnetic iron alloy sheets that exhibit a Bs higher than that of pure iron, without excessively increasing Pi. The present invention was completed based on this finding.

[0053] The embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. However, the present invention is not limited to the embodiments set forth herein, and can be appropriately combined with or improved upon known technologies within the scope of the technical concept of the invention.

[0054] [Soft Magnetic Iron Alloy Sheet of the Present Invention]

[0055] Figure 1 This is a graph showing an example of the relationship between the nitrogen concentration and the length in the thickness direction of the soft magnetic iron alloy plate of the present invention. Figure 1 The soft magnetic iron alloy plate shown in the figure is a 0.1 mm (100 μm) thick sample. "Thickness length 0 μm" in the figure indicates one main surface of the iron alloy plate, and "Thickness length 50 μm" indicates the thickness center of the iron alloy plate. Nitrogen concentration was quantitatively analyzed using an electron probe microanalyzer (EPMA, JEOL Ltd., JXA-8800RL) with a spot diameter of 1 μm.

[0056] like Figure 1 As shown, the soft magnetic iron alloy plate of the present invention generally comprises, in the thickness direction, an outer nitrogen concentration transition region 10 in which the nitrogen concentration increases inward from the main surface, a high nitrogen concentration region 20 in which the maximum nitrogen concentration is higher than the nitrogen concentration at the main surface and less than 11 atomic %, and an inner nitrogen concentration transition region 30 in which the nitrogen concentration decreases inward from the high nitrogen concentration region 20. Since nitrogen atoms intrude and diffuse from both main surfaces in the soft magnetic iron alloy plate of the present invention, the nitrogen concentration distribution in the thickness direction is, in principle, line-symmetrical about the center of the plate thickness.

[0057] This will be described in more detail.

[0058] The high nitrogen concentration region 20 is a region where the maximum N concentration is at least higher than the N concentration of the main surface and the variation range of the N concentration is within 1 atomic % (within ±0.5 atomic %). The maximum N concentration is preferably 2 atomic % or more and less than 11 atomic %, more preferably more than 4 atomic % and less than 10.5 atomic %, and further preferably 6 atomic % or more and less than 10 atomic %. It is believed that by setting the maximum N concentration to 2 atomic % or more, a tetragonal iron nitride phase (Fe8N phase (α' phase) and / or Fe 16 The N2 phase (α" phase) contributes to the improvement of the Bs of the soft magnetic iron alloy plate. On the other hand, by controlling the maximum N concentration to less than 11 atomic %, the formation of undesirable iron nitride phases (for example, Fe4N phase (γ' phase) and Fe3N phase (ε phase)) that do not contribute to the improvement of Bs can be suppressed.

[0059] The thickness (length in the plate thickness direction) of the high nitrogen concentration region 20 is not particularly limited, but is preferably 3 μm or greater, more preferably 5 μm or greater, from the perspective of improving Bs. Furthermore, from the perspective of ease of nitrogen concentration control, it is preferably 20 μm or less, more preferably 15 μm or less.

[0060] For the tetragonal iron nitride phase (α' phase and / or α" phase), the lattice deformation caused by the invasion of N atoms helps to improve Bs. On the other hand, the α' phase and α" phase have the weakness that Hc becomes larger due to the increase in magnetocrystalline anisotropy, and Pi is also easily increased.

[0061] Therefore, in the soft magnetic iron alloy plate of the present invention, an outer nitrogen concentration transition region 10 and an inner nitrogen concentration transition region 30 having a lower N concentration are intentionally formed adjacent to the high nitrogen concentration region 20, thereby generating magnetic coupling between the high nitrogen concentration region 20 and the outer nitrogen concentration transition region 10, and magnetic coupling between the high nitrogen concentration region 20 and the inner nitrogen concentration transition region 30, thereby suppressing an excessive increase in Pi as a whole in the soft magnetic iron alloy plate.

[0062] The outer nitrogen concentration transition region 10 is a region having a concentration distribution in which the N concentration gradually increases from the main surface toward the high nitrogen concentration region 20. The N concentration of the main surface is preferably greater than 1 atomic % and less than 4 atomic %, and more preferably greater than 2 atomic % and less than 4 atomic %. If the N concentration of the main surface is less than 1 atomic %, the vicinity of the main surface cannot fully contribute to the purpose of increasing Bs. If the N concentration of the main surface exceeds 4 atomic %, the influence of the magnetocrystalline anisotropy caused by the α' phase and the α" phase can no longer be ignored (increase in Pi).

[0063] The average nitrogen concentration gradient in the outer nitrogen concentration transition region 10 is preferably 0.1 atomic % / μm to 0.6 atomic % / μm, more preferably 0.2 atomic % / μm to less than 0.6 atomic % / μm. If the average nitrogen concentration gradient is less than 0.1 atomic % / μm, it is difficult to overcome the potential for magnetization pinning caused by magnetocrystalline anisotropy. If the average nitrogen concentration gradient exceeds 0.6 atomic % / μm, the gradient becomes steep, making it difficult to achieve magnetic coupling.

[0064] The thickness of the outer nitrogen concentration transition region 10 is not particularly limited, but is preferably 5 μm to 30 μm, and more preferably 10 μm to 25 μm, from the viewpoint of ease of N concentration control.

[0065] The inner nitrogen concentration transition region 30 is a region where the N concentration gradually decreases from the high nitrogen concentration region 20 toward the center of the plate thickness. The minimum N concentration is at least lower than the N concentration of the high nitrogen concentration region 20, preferably not less than 1 atomic % and not more than 4 atomic %, and more preferably not less than 2 atomic % and not more than 4 atomic %. If the minimum N concentration is less than 1 atomic %, the region near the center of the plate thickness cannot fully contribute to the purpose of improving Bs. If the minimum N concentration exceeds 4 atomic %, the effects of the α' phase and α" phase on the magnetocrystalline anisotropy can no longer be ignored (increase in Pi).

[0066] The average nitrogen concentration gradient in the inner nitrogen concentration transition region 30 is preferably between 0.1 atomic % / μm and 0.3 atomic % / μm, more preferably between 0.1 atomic % / μm and 0.2 atomic % / μm. If this average nitrogen concentration gradient is less than 0.1 atomic % / μm, the difference between adjacent magnetic domains decreases, weakening the transfer of magnetization states. If this average nitrogen concentration gradient exceeds 0.3 atomic % / μm, the minimum nitrogen concentration in the region near the center of the plate thickness tends to fall below 1 atomic %.

[0067] It should be noted that, as will be described later with specific examples, according to the results of wide-angle X-ray diffraction (WAXD) measurements, the soft magnetic iron alloy plate does not transform into the α' phase and / or α" phase as a whole due to the intrusion and diffusion of N atoms, but rather becomes a state in which the α phase (ferrite phase, body-centered cubic crystal) is the main phase (the phase with the largest volume fraction) and the α' phase and / or α" phase are dispersed and generated. In addition, since the γ phase (austenite phase, face-centered cubic crystal) is close to non-magnetic, if the volume fraction of the γ phase exceeds 5%, it becomes difficult to increase Bs in combination with reducing the volume fraction of the α phase. It is more preferred that the volume fraction of the γ phase is 3% or less, and even more preferred that it is 1% or less.

[0068] There is no particular limitation on the composition of the soft magnetic iron alloy plate except that it is mainly composed of Fe (the component with the highest content) and contains N. As the thin plate material, soft magnetic materials that are easily purchased industrially / commercially (such as electromagnetic pure iron plates, Fe-Co alloy materials, Fe-Si alloy materials) can be appropriately used.

[0069] Electromagnetic pure iron sheet is one of the cheapest starting materials.

[0070] As the Fe-Co alloy material, an alloy having Fe as the main component and containing Co in an amount exceeding 0 atomic % and not exceeding 30 atomic % can be preferably used. By setting the Co content to 30 atomic % or less, the material cost can be significantly reduced compared to the Perminder alloy. More preferably, the Co content is 3 atomic % or more and 25 atomic % or less, and further preferably 5 atomic % or more and 20 atomic % or less. Although not an essential component, V may be further contained within 4% of the Co content (for example, when Co = 30 atomic %, V ≤ 1.2 atomic %).

[0071] Furthermore, as the Fe—Si alloy material, an alloy containing Fe as a main component and containing more than 0 atomic % and 3 atomic % or less of Si can also be appropriately used.

[0072] Regarding impurities (impurities that may be contained in the starting material, such as hydrogen (H), boron (B), carbon (C), phosphorus (P), sulfur (S), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), etc.), they are allowed within a range that does not particularly affect the Bs of the soft magnetic iron alloy plate (for example, the total concentration is within 2 atomic %).

[0073] By forming the nitrogen concentration distribution specified in the present invention using these soft magnetic materials as a base, a higher Bs than the base soft magnetic material can be achieved. For example, when using electromagnetic pure iron plate as the starting material, a Bs exceeding 2.14T can be achieved.

[0074] The thickness of the soft magnetic iron alloy plate is not particularly limited and can be appropriately selected within the range of 0.01 mm to 1 mm. From the viewpoint of controllability of the N concentration distribution, it is preferably 0.03 mm to 0.3 mm, more preferably 0.05 mm to 0.2 mm.

[0075] Here, we briefly explain the permissible range of Pi in rotating electrical machine design. As mentioned above, from the perspective of high-output design in rotating electrical machines and transformers, improving the Bs of the core is prioritized. If the degree of Bs improvement is large, a certain degree of Pi increase is permissible.

[0076] Extensive experiments by the inventors of this application have shown that an improvement of 2% or more compared to the Bs of the underlying soft magnetic material indicates a clear improvement in properties and a significant difference. Furthermore, assuming the Bs value (unit: T) of the soft magnetic material is denoted by "y" and the Pi value (unit: W / kg) at a magnetic flux density of 1.0 T and 400 Hz is denoted by "z," empirically, if the empirical formula "z < 150 × y - 295" is satisfied, a high-output design for the rotating electrical machine can be achieved.

[0077] [Method for producing soft magnetic iron plate of the present invention]

[0078] Figure 2 1 is a process diagram showing an example of a method for manufacturing a soft magnetic iron alloy plate of the present invention. Figure 2 As shown, the method for producing a soft magnetic iron alloy plate according to the present invention generally comprises a starting material preparation step S1, a nitrogen concentration distribution control heat treatment step S2, and a phase transformation / iron nitride phase formation step S3. A carburizing heat treatment step S4 may be further performed between steps S2 and S3. Each step will be described in more detail below.

[0079] (Starting material preparation process)

[0080] In this step S1, a thin plate material of a soft magnetic material (for example, with a thickness of 0.03 to 0.3 mm) is prepared as a starting material. If it is a soft magnetic material with iron as the main component, there is no particular limitation, and for example, electromagnetic pure iron material, Fe-Co alloy material, Fe-Si alloy material can be appropriately used. As mentioned above, in the case of Fe-Co alloy material, it is preferred that the Fe-Co alloy material contains Co at a content of more than 0 atomic % and less than 30 atomic %. In the case of Fe-Si alloy material, it is preferred that the Fe-Si alloy material contains Si at a content of more than 0 atomic % and less than 3 atomic %. Since these soft magnetic materials have a low C content, it becomes easier to control the N concentration distribution in the starting material in the subsequent steps, which also helps to reduce process costs.

[0081] (Nitrogen Concentration Distribution Control Heat Treatment Process)

[0082] This step S2 is a step in which the starting material is subjected to a predetermined nitrogen concentration distribution control heat treatment (a heat treatment combining the nitriding step S2a with the nitrogen diffusion / denitrification step S2b) to form a predetermined nitrogen concentration distribution along the thickness direction of the starting material. The manufacturing method of the present invention has a significant feature in step S2.

[0083] In the nitriding process S2a, N atoms are allowed to intrude and diffuse from both main surfaces of the starting material in a temperature of 500°C or higher (e.g., in the austenite phase (γ phase) formation temperature range) and in a predetermined ammonia (NH3) gas atmosphere, so that the N concentration in the surface region of the starting material (substantially corresponding to the outer nitrogen concentration transition region 10) reaches a predetermined concentration. As the NH3 gas atmosphere, a mixture of NH3 gas and N2 gas, a mixture of NH3 gas and Ar gas, or a mixture of NH3 gas and H2 gas can be appropriately used. The N concentration in the surface region of the starting material can be controlled primarily by controlling the NH3 gas partial pressure. The thickness (length in the thickness direction) of this surface region can be controlled primarily by controlling the temperature and time.

[0084] It is preferable to introduce NH3 gas after the temperature reaches 500°C or higher. The reason is that if NH3 gas is actively introduced in the stable temperature range of the ferrite phase (α phase), the desired tetragonal iron nitride phase (Fe8N phase (α' phase) and / or Fe 16 Compared with the N2 phase (α” phase), it is easy to generate undesirable iron nitride phases (such as Fe4N phase (γ’ phase) and Fe3N phase (ε phase)).

[0085] Following the nitriding process S2a, the nitrogen diffusion / denitrification process S2b is performed. Process S2b is a process in which the NH3 gas partial pressure is set to zero while maintaining the temperature of process S2a. This allows a portion of the N atoms that infiltrated during process S2a to diffuse further into the starting material. Simultaneously, a portion of the infiltrated N atoms is released from the main surface of the starting material, thereby reducing the N concentration on the main surface. The NH3 gas partial pressure can be controlled, for example, by increasing the partial pressure of the carrier gas (N2 gas, Ar gas, H2 gas, etc.) used during process S2a to supplement the NH3 gas partial pressure.

[0086] By combining the nitriding process S2a with the nitrogen diffusion / denitrification process S2b, an outer nitrogen concentration transition region 10, a high nitrogen concentration region 20, and an inner nitrogen concentration transition region 30 are formed along the thickness direction of the iron alloy plate.

[0087] In addition, the combination of process S2a and process S2b is repeated for multiple cycles (intermittent control of the supply time and non-supply time of NH3 gas is performed), so that the N concentration distribution inside the iron alloy plate (the outer nitrogen concentration transition zone 10, the high nitrogen concentration zone 20 and the inner nitrogen concentration transition zone 30) can be more easily controlled.

[0088] (Carburizing heat treatment process)

[0089] Step S4 is a heat treatment for infiltrating carbon into the outer nitrogen concentration transition region 10 formed in step S2. Step S4 is not essential, but infiltrating C atoms into the outer nitrogen concentration transition region 10 can suppress an increase in Pi without reducing Bs of the soft magnetic iron alloy plate.

[0090] The carburizing heat treatment method is not particularly limited, and existing methods (such as heat treatment in an acetylene (C2H2) gas atmosphere) can be appropriately used. As an example, the carburizing heat treatment can be performed by changing the atmosphere gas to C2H2 gas following the nitrogen diffusion / denitrification step S2b.

[0091] (Phase transformation / iron nitride phase formation process)

[0092] This step S3 is a step of rapidly cooling the iron alloy plate having a predetermined nitrogen concentration distribution in step S2 to a temperature below 100°C to cause a phase transformation from the γ phase to the martensite structure, thereby dispersing and generating a tetragonal iron nitride phase (α' phase and / or α" phase). The quenching method is not particularly limited, and existing methods (e.g., water quenching, oil quenching) can be appropriately used.

[0093] In order to transform the retained γ phase in the iron alloy plate into a martensite structure, it is preferable to perform a cryogenic treatment (for example, ordinary cryogenic treatment using dry ice or ultra-cryogenic treatment using liquid nitrogen) to 0°C or lower.

[0094] In addition, although it is not an essential step, in order to give toughness to the final soft magnetic iron alloy plate, tempering at 100°C or higher and 210°C or lower may be further performed as needed ( Figure 2 (not shown in the figure).

[0095] [Iron Core and Rotating Electric Machine Using the Soft Magnetic Iron Alloy Plate of the Present Invention]

[0096] Figure 3A is a perspective schematic diagram showing an example of a stator of a rotating electrical machine, Figure 3B It is an enlarged cross-sectional view of the stator slot area. It should be noted that the cross section represents a section perpendicular to the axis of rotation (a section whose normal is parallel to the axis). Figure 3A-3B A rotor (not shown) is arranged radially inside the stator.

[0097] like Figure 3A-3BAs shown, the stator 50 is constructed by winding a stator coil 60 around a plurality of stator slots 52 formed on the inner circumference of an iron core 51. Stator slots 52 are arranged at predetermined circumferential intervals around the circumference of the iron core 51 and extend axially through the circumference. Axially extending slits 53 are formed in the innermost circumference. The region separating adjacent stator slots 52 is referred to as a tooth 54 of the iron core 51, and the portion defining the slits 53 at the inner circumferential tip of each tooth 54 is referred to as a claw portion 55.

[0098] The stator coil 60 is generally composed of a plurality of segment conductors 61. For example, Figure 3A-3B In the embodiment, the stator coil 60 is composed of three segment conductors 61 corresponding to the U phase, V phase, and W phase of the three-phase AC. Furthermore, to prevent partial discharge between the segment conductor 61 and the iron core 51 and partial discharge between the phases (U phase, V phase, and W phase), each segment conductor 61 is typically covered with an electrically insulating material 62 (e.g., insulating paper or enamel).

[0099] The iron core and rotating electric machine using the soft magnetic iron alloy plates of the present invention are an iron core 51 formed by axially stacking multiple sheets of the soft magnetic iron alloy plates of the present invention, each formed into a predetermined shape. As previously mentioned, the soft magnetic iron alloy plates of the present invention have a higher Bs than electromagnetic pure iron plates, thus providing an iron core with improved electrical and magnetic energy conversion efficiency compared to conventional iron cores using electromagnetic pure iron plates or electromagnetic steel plates. This high-efficiency iron core contributes to higher torque and smaller size in rotating electric machines.

[0100] Example

[0101] The present invention will be described in more detail below using various experiments, but the present invention is not limited to the configurations and structures described in these experiments.

[0102] [Experiment 1]

[0103] (Production of Soft Magnetic Iron Alloy Plates A-1 to A-8)

[0104] A commercially available electromagnetic pure iron plate (thickness = 0.1 mm) was prepared as a starting material (step S1). This starting material was then subjected to a nitrogen concentration distribution controlled heat treatment (step S2) by heating to 1000°C at a temperature increase rate of 15°C / min and holding at 1000°C for 2.5 hours while maintaining atmosphere control.

[0105] More specifically, NH3 gas (partial pressure = 1×10 5 Pa), and switched to NH3 gas (partial pressure = 5×10 4 Pa) and N2 gas (partial pressure = 4×10 4Pa) and maintained for 20 minutes (process S2a), and then switched to only N2 gas (pressure = 9×10 4 Then, a combination of process S2a and process S2b is performed for a total of 6 cycles: maintaining in the mixed gas for 20 minutes - maintaining in the N2 gas only for 5 minutes, maintaining in the mixed gas for 15 minutes - maintaining in the N2 gas only for 10 minutes, maintaining in the mixed gas for 10 minutes - maintaining in the N2 gas only for 15 minutes, maintaining in the mixed gas for 10 minutes - maintaining in the N2 gas only for 15 minutes, maintaining in the mixed gas for 10 minutes - maintaining in the N2 gas only for 15 minutes, and maintaining in the mixed gas for 10 minutes - maintaining in the N2 gas only for 15 minutes.

[0106] Following the nitrogen concentration distribution controlled heat treatment, the starting material was oil quenched (60°C) to undergo martensitic transformation, and then cryogenically treated to transform the retained γ phase into martensitic transformation (step S3). Thus, soft magnetic iron alloy plate sample A-1 was produced.

[0107] Next, using the same electromagnetic pure iron plate as described above as the starting material, various changes were made to the timing of steps S2a and S2b to produce soft magnetic iron alloy plate samples A-2 to A-7. In addition, a starting sample without steps S2 and S3 was prepared as sample A-8 (reference sample).

[0108] [Experiment 2]

[0109] (Production of Soft Magnetic Iron Alloy Plates B-1 to B-8)

[0110] Commercially available pure metal raw materials (Fe and Co, each with a purity of 99.9%) were mixed and then melted on a water-cooled copper hearth using an arc melting method (manufactured by Taia Vacuum Co., Ltd., in an automatic arc melting furnace under a reduced pressure Ar atmosphere) to produce an alloy ingot. To homogenize the alloy ingot, the sample was turned over and remelted six times. The resulting alloy ingot was then stamped and rolled to prepare a 95 atomic % Fe-5 atomic % Co alloy plate (thickness = 0.1 mm) as the starting material (Step S1).

[0111] Next, steps S2 and S3 were performed in the same manner as in Experiment 1 to produce soft magnetic iron alloy plate samples B-1 to B-7. In addition, a starting sample without performing steps S2 and S3 was prepared as sample B-8 (reference sample).

[0112] [Experiment 3]

[0113] (Production of Soft Magnetic Iron Alloy Plates C-1 to C-8)

[0114] Using commercially available pure metal raw materials (purity of each of Fe and Co = 99.9%), a 90 atomic % Fe-10 atomic % Co alloy plate (thickness = 0.1 mm) as a starting material was prepared in the same manner as in Experiment 2 (Step S1).

[0115] Next, steps S2 and S3 were performed in the same manner as in Experiment 1 to produce soft magnetic iron alloy plate samples C-1 to C-7. In addition, a starting sample without performing steps S2 and S3 was prepared as sample C-8 (reference sample).

[0116] [Experiment 4]

[0117] (Production of Soft Magnetic Iron Alloy Plates D-1 to D-8)

[0118] Using commercially available pure metal raw materials (purity of each of Fe and Co = 99.9%), an 80 atomic % Fe-20 atomic % Co alloy plate (thickness = 0.1 mm) was prepared as a starting material in the same manner as in Experiment 2 (Step S1).

[0119] Next, steps S2 and S3 were performed in the same manner as in Experiment 1 to produce soft magnetic iron alloy plate samples D-1 to D-7. In addition, a starting sample without performing steps S2 and S3 was prepared as sample D-8 (reference sample).

[0120] [Experiment 5]

[0121] (Investigation of properties of samples A-1 to A-8, B-1 to B-8, C-1 to C-8, and D-1 to D-8)

[0122] The cross-sections of 100 samples obtained by stacking them were subjected to WAXD measurement using Cu-Kα radiation to identify the detected phases. The X-ray diffraction apparatus used was Rint-Ultima III manufactured by Rigaku Corporation.

[0123] Figure 4 These are the X-ray diffraction patterns of A-8, which is a reference sample, and A-1, which is a sample of the present invention.

[0124] like Figure 4 As shown in FIG, only α phase (ferrite phase) was confirmed in reference sample A-8. In contrast, in sample A-1 of the present invention, α phase was confirmed as the main phase and α" phase (iron nitride phase with tetragonal structure) was generated. γ phase (austenite phase) and γ' phase (Fe4N phase) were not detected. In addition, it was confirmed that the same phase as Figure 4 Same result.

[0125] Based on these results, it is believed that the soft magnetic iron alloy plate of the present invention does not transform the entire iron alloy plate into a tetragonal iron nitride phase (α' phase and / or α" phase) due to the intrusion and diffusion of N atoms, but rather becomes a state in which the ferrite phase (α phase) is the main phase and the α' phase and / or α" phase are dispersed.

[0126] Next, the N concentration distribution in the plate thickness direction was investigated using EPMA on the cross section of each sample obtained. Figure 1 This is the result of sample A-1 of the present invention. As described above, in the plate thickness direction, there is a nitrogen concentration distribution that can be classified into the outer nitrogen concentration transition region 10, the high nitrogen concentration region 20, and the inner nitrogen concentration transition region 30.

[0127] The measurement results of the N concentration (Ns) of the main surface of each sample, the maximum N concentration (Nmax) of the high nitrogen concentration region 20, the minimum N concentration (Nmin) of the inner nitrogen concentration transition region 30, the average N concentration gradient (AGout) of the outer nitrogen concentration transition region 10, and the average N concentration gradient (AGin) of the inner nitrogen concentration transition region 30 are summarized in Table 1 described below.

[0128] As the magnetic properties of each sample, Bs and Pi were measured. The magnetization (unit: emu) of the sample was measured using a vibrating sample magnetometer (VSM, Riken Electronics Co., Ltd. BHV-525H) under the conditions of a magnetic field of 1.6 MA / m and a temperature of 20°C, and Bs (unit: T) was calculated based on the sample volume and sample mass. In addition, the Pi of the sample was measured under the conditions of a magnetic flux density of 1.0 T, 400 Hz, and a temperature of 20°C using a BH loop analyzer (IFG Co., Ltd., IF-BH550) and the H coil method using a vertical yoke single-plate tester. -1.0 / 400 (Unit: W / kg) The results of the magnetic properties are shown in Table 1.

[0129] [Table 1]

[0130] Table 1 Results of property investigation of samples A-1 to A-8, B-1 to B-8, C-1 to C-8, and D-1 to D-8

[0131]

[0132] Ns: N concentration on the main surface

[0133] Nmax: Maximum nitrogen concentration in high nitrogen concentration areas

[0134] Nmin: Minimum nitrogen concentration in the inner nitrogen concentration transition zone

[0135] AGout: Average nitrogen concentration gradient in the outer nitrogen concentration transition region

[0136] AGin: Average nitrogen concentration gradient in the inner nitrogen concentration transition zone

[0137] Samples A-8, B-8, C-8, and D-8 are reference samples made from the original starting materials. Comparison of the Bs values ​​of samples A-8, B-8, C-8, and D-8 reveals a linear increase in Bs with increasing Co content.

[0138] As previously mentioned, the inventors of this application have found through extensive experiments that an improvement of 2% or more compared to the Bs of the soft magnetic material serving as the base material indicates a clear improvement in properties and a significant difference. Therefore, in the present invention, when the value of the Co concentration (unit: atomic %) in the starting material is x, the Bs value y (unit: T) of the soft magnetic iron alloy plate satisfies the empirical formula (1) "y ≥ 1.02 × (0.01 × x + 2.14)" to determine that "Bs has been improved."

[0139] Furthermore, assuming the value of the soft magnetic material's Bs (unit: T) is "y" and the value of Pi (unit: W / kg) at a magnetic flux density of 1.0 T and 400 Hz is "z," it has been empirically shown that if the empirical formula (2) "z < 150 × y - 295" is satisfied, a high-output design of the rotating electrical machine can be achieved. Therefore, in the present invention, if the empirical formula (2) "z < 150 × y - 295" is satisfied, it is determined that "Pi has not increased excessively / the increase in Pi is within the allowable range."

[0140] Furthermore, when both empirical formula (1) and empirical formula (2) are satisfied, the result is judged as "qualified", and otherwise, the result is judged as "unqualified".

[0141] From this perspective, the results of Table 1 show that the Bs of samples A-1 to A-3, which have the outer nitrogen concentration transition region, high nitrogen concentration region, and inner nitrogen concentration transition region specified in the present invention, are improved by more than 2% compared to the Bs of reference sample A-8, and Pi satisfies empirical formula (2). Similarly, the Bs of samples B-1 to B-3 are improved by more than 2% compared to the Bs of reference sample B-8, and Pi satisfies empirical formula (2). The Bs of samples C-1 to C-3 are improved by more than 2% compared to the Bs of reference sample C-8, and Pi satisfies empirical formula (2). The Bs of samples D-1 to D-3 are improved by more than 2% compared to the Bs of reference sample D-8, and Pi satisfies empirical formula (2).

[0142] In contrast, the Bs of samples A-4 to A-5, B-4, B-6 to B-7, C-4 to C-5, C-7, D-4 to D-5, and D-7, which do not meet the requirements of the outer nitrogen concentration transition region of the present invention, do not satisfy empirical formula (1) (a 2% improvement in Bs of the reference sample is not achieved). The Pi of samples A-6 to A-7, B-5 ​​to B-7, C-5 to C-7, and D-5 to D-7, which do not meet the requirements of the high nitrogen concentration region of the present invention, do not satisfy empirical formula (2). Furthermore, the Bs of samples A-7, B-7, C-7, and D-7, which do not meet the requirements of the inner nitrogen concentration transition region of the present invention, do not satisfy empirical formula (1) (a 2% improvement in Bs of the reference sample is not achieved).

[0143] In other words, the soft magnetic iron alloy plate having the outer nitrogen concentration transition region, high nitrogen concentration region, and inner nitrogen concentration transition region specified in the present invention showed higher Bs than the electromagnetic pure iron plate without excessive increase in Pi.

[0144] The above descriptions of the embodiments and experiments facilitate understanding of the present invention, and the present invention is not limited to the specific configurations described. For example, portions of the configurations of the embodiments may be replaced with configurations that are within the technical knowledge of those skilled in the art, and further, configurations that are within the technical knowledge of those skilled in the art may be added to the configurations of the embodiments. In other words, the present invention allows for deletion of portions of the configurations of the embodiments and experiments described herein, substitution with other configurations, or addition of other configurations, without departing from the technical concept of the invention.

[0145] Description of Reference Numerals

[0146] 10…outer nitrogen concentration transition region, 20…high nitrogen concentration region, 30…inner nitrogen concentration transition region, 50…stator, 51…iron core, 52…stator slot, 53…slit, 54…teeth, 55…tooth claw portion, 60…stator coil, 61…segment conductor, 62…electrical insulating material.

Claims

1. Soft magnetic iron alloy plate, characterized in that having a chemical composition containing 2 atomic % to 10 atomic % of nitrogen, 0 atomic % to 30 atomic % of cobalt, 0 atomic % to 1.2 atomic % of vanadium, with the balance being iron and impurities, In the thickness direction of the soft magnetic iron alloy plate, there are: an outer nitrogen concentration transition region in which the nitrogen concentration of the main surface is not less than 1 atomic % and not more than 4 atomic %, and the nitrogen concentration increases from the main surface toward the inside; a high nitrogen concentration region having a maximum nitrogen concentration higher than the nitrogen concentration of the main surface and lower than 11 atomic %, and a nitrogen concentration variation range within 1 atomic %; and An inner nitrogen concentration transition region in which the nitrogen concentration decreases from the high nitrogen concentration region toward the inside and the minimum nitrogen concentration is lower than the N concentration of the high nitrogen concentration region and is 1 atomic % or more.

2. The soft magnetic iron alloy plate according to claim 1, characterized in that The maximum nitrogen concentration of the high nitrogen concentration region is not less than 6 atomic % and not more than 10 atomic %, The minimum nitrogen concentration in the inner nitrogen concentration transition region is not less than 1 atomic % and not more than 4 atomic %.

3. The soft magnetic iron alloy plate according to claim 1 or 2, characterized in that: The average nitrogen concentration gradient of the outer nitrogen concentration transition region is not less than 0.1 atomic % / μm and not more than 0.6 atomic % / μm, The average nitrogen concentration gradient of the inner nitrogen concentration transition region is not less than 0.1 atomic % / μm and not more than 0.3 atomic % / μm.

4. The soft magnetic iron alloy plate according to claim 1 or 2, characterized in that: When the value of the cobalt concentration (unit: atomic %) is x, the value of the saturation magnetic flux density y (unit: T) of the soft magnetic iron alloy plate satisfies the empirical formula (1) "y ≥ 1.02 × (0.01 × x + 2.14)", When the value of the iron loss (unit: W / kg) is z, the iron loss under the conditions of a magnetic flux density of 1.0 T and 400 Hz satisfies the empirical formula (2) "z < 150 × y - 295".

5. The soft magnetic iron alloy plate according to claim 1 or 2, characterized in that: The soft magnetic iron alloy plate has a thickness of 0.03 mm to 0.3 mm.

6. A method for producing a soft magnetic iron alloy plate, the method for producing a soft magnetic iron alloy plate according to any one of claims 1 to 5, characterized in that: The process includes the following steps: a starting material preparation step of preparing a starting material formed of a soft magnetic material having iron as a main component and having a thickness of not less than 0.03 mm and not more than 0.3 mm; a nitrogen concentration distribution controlled heat treatment step of subjecting the starting material to a predetermined nitrogen concentration distribution controlled heat treatment to form a predetermined nitrogen concentration distribution along the thickness direction of the starting material; and Phase transformation / iron nitride phase generation step, wherein the starting material after forming the predetermined nitrogen concentration distribution is transformed into a martensitic structure and the iron nitride phase is dispersed and generated, The prescribed nitrogen concentration distribution control heat treatment is a heat treatment carried out in the austenite phase formation temperature range, and is a combination of a nitriding process and a nitrogen diffusion / denitrification process, wherein the nitriding process is carried out in a prescribed ammonia atmosphere to allow nitrogen atoms to intrude and diffuse from the two main surfaces of the starting material, and the nitrogen diffusion / denitrification process is carried out in a prescribed nitrogen atmosphere to allow the nitrogen atoms to diffuse further inwardly of the starting material and release nitrogen from the two main surfaces of the starting material to form the outer nitrogen concentration transition region.

7. The method for producing a soft magnetic iron alloy plate according to claim 6, wherein: The predetermined nitrogen concentration distribution control heat treatment is a heat treatment in which the nitriding process and the nitrogen diffusion / denitrification process are alternately performed for a plurality of cycles.

8. The method for producing a soft magnetic iron alloy plate according to claim 6 or 7, wherein: The phase transformation / iron nitride phase formation step includes quenching to below 100° C. and cryogenic treatment to below 0° C.

9. An iron core formed of a laminate of soft magnetic iron alloy plates, characterized in that: The soft magnetic iron alloy plate is the soft magnetic iron alloy plate according to any one of claims 1 to 5.

10. A rotating electrical machine comprising an iron core, characterized in that: The iron core is the iron core according to claim 9.

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