Soft magnetic iron alloy plate, method for manufacturing the soft magnetic iron alloy plate, iron core and rotating electric machine using the soft magnetic iron alloy plate

Abstract

To provide a soft-magnetic iron alloy sheet having a saturated magnetic flux density higher than that of an electromagnetic pure iron sheet without excessively increasing iron loses, a method for manufacturing the soft-magnetic iron alloy sheet, an iron core using the soft-magnetic iron alloy sheet, and a rotary electrical machine.SOLUTION: This soft-magnetic iron alloy sheet has a chemical composition containing N by 2-10% atoms, Co by 0-30% atoms, and V by 0-1.2% atoms and having a remaining part of Fe and impurities. In the thickness direction of the soft-magnetic iron alloy sheet, there are provided an outer nitrogen concentration transition region in which an N concentration on a main surface is 1-4% atoms and the N concentration increases from the main surface to the inside, a high nitrogen concentration region in which a maximum N concentration is higher than the N concentration on the main surface and less than 11% atoms, and the fluctuation range of the N concentration is within 1% atom, and an inner nitrogen concentration transition region in which a N concentration is reduced from the high nitrogen concentration region to the inside and a minimum N concentration is lower than the N concentration in the high nitrogen concentration region and 1% atom or more.SELECTED DRAWING: Figure 1

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 manufacturing the soft magnetic iron alloy plate, and an iron core and a rotating electric machine using the soft magnetic iron alloy plate. [Background technology]

[0002] Electromagnetic iron sheets (e.g., 0.01 to 1 mm thick), such as electromagnetic steel sheets and electromagnetic pure iron sheets, are materials used as iron cores for rotating electrical machines and transformers by laminating multiple sheets together. For iron cores, high conversion efficiency between electrical energy and magnetic energy is important, making high magnetic flux density crucial. To increase magnetic flux density, it is desirable for the material to have a high saturation magnetic flux density Bs. Fe-Co alloy materials and iron nitride materials are known as iron-based materials with high Bs.

[0003] Naturally, reducing the cost of the iron core is one of the most important issues, and active research has been carried out into the development of technologies for stably and inexpensively producing materials with high Bs.

[0004] For example, Patent Document 1 (JP 2007-046074 A) discloses magnetic metal microparticles that are primarily composed of Fe and coated with graphite, contain 0.1 to 5% by weight of nitrogen, and contain at least one of Fe4N and Fe3N. The method for producing the magnetic metal microparticles also includes mixing an iron oxide powder with a powder containing carbon, heat-treating the mixed powder in a non-oxidizing atmosphere to obtain metal microparticles that are primarily composed of Fe and coated with graphite, and then nitriding the microparticles to obtain the magnetic metal microparticles.

[0005] According to Patent Document 1, it is possible to provide magnetic metal fine particles having excellent corrosion resistance and a method for producing the same.

[0006] In addition, Patent Document 2 (JP 2020-132894 A) discloses a soft magnetic material in the form of a plate or foil having a high saturation magnetic flux density, which contains iron, carbon, and nitrogen, and includes martensite containing carbon and nitrogen and γ-Fe, in which a nitrogen-containing phase is formed 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, and by using this material, it is possible to improve the characteristics of magnetic circuits of electric motors and the like, thereby realizing miniaturization of electric motors and the like, high torque, etc. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-046074 [Patent Document 2] Japanese Patent Publication No. 2020-132894 Summary of the Invention [Problem to be solved by the invention]

[0009] Powder magnetic cores are suitable for relatively small electrical components such as noise filters and reactors, but for relatively large electrical machines such as rotating electrical machines and transformers, iron cores made by laminating and molding electromagnetic iron sheets are advantageous from the standpoint of mechanical strength. Patent Document 1 is considered to be a suitable technology for powder magnetic cores, but it cannot be said to be suitable for the manufacture and use of thin sheet materials such as electromagnetic iron sheets.

[0010] Furthermore, in order to increase the electric / magnetic energy conversion efficiency in an iron core, low iron loss Pi is important in addition to high saturation magnetic flux density Bs. Pi is the sum of hysteresis loss and eddy current loss, and a small coercive force Hc is desirable to reduce hysteresis loss. The magnetic properties of commercially available electromagnetic pure iron sheets are said to be Bs ≒ 2.1 T and Hc ≒ 80 A / m. The soft magnetic material in Patent Document 2 has the advantage of having a higher Bs than electromagnetic pure iron sheets, but is thought to have a weakness in Hc.

[0011] From the perspective of high-output design in rotating electrical machines and transformers, improving the Bs of the iron core is given priority, and if the degree of improvement in Bs is large, a certain degree of increase in Pi is acceptable.

[0012] Among currently commercially available soft magnetic bulk materials, permendur (49Fe-49Co-2V mass% = 50Fe-48Co-2V atomic%, Bs = 2.4 T) is well known as the material with the highest Bs. However, the material cost of Co, although it fluctuates depending on market conditions, is about 100 times higher than that of Fe, making permendur a very expensive material. In other words, in Fe-Co alloy materials, reducing the Co content can reduce material costs accordingly.

[0013] On the other hand, in recent years, there has been a strong demand for small, high-power rotating electrical machines (e.g., motors and generators), and improving the properties of the iron core is an urgent issue. Furthermore, as mentioned above, reducing the cost of the iron core is, of course, one of the most important issues. For these reasons, there is a demand for soft magnetic materials that have a higher Bs than electromagnetic pure iron sheets, an increase in Pi within an acceptable range, and are less expensive than permendur.

[0014] However, the technology for producing soft magnetic materials exhibiting such magnetic properties stably at low cost has not yet been fully established.

[0015] Therefore, an object of the present invention is to provide a soft magnetic iron alloy plate having a saturation magnetic flux density higher than that of an electromagnetic pure iron plate without excessively increasing iron loss, a method for manufacturing the soft magnetic iron alloy plate, and an iron core and a rotating electric machine using the soft magnetic iron alloy plate. [Means for solving the problem]

[0016] (I) One aspect of the present invention is a soft magnetic iron alloy plate, A chemical composition containing 2 atomic % or more and 10 atomic % or less of nitrogen (N), 0 atomic % or more and 30 atomic % or less of cobalt (Co), 0 atomic % or more and 1.2 atomic % or less of vanadium (V), with the balance being iron (Fe) and impurities; In the thickness direction of the soft magnetic iron alloy plate Along the range from the main surface to the center of the plate thickness Leave, When quantitative analysis of nitrogen concentration was performed using an electron probe microanalyzer with a spot diameter of 1 μm, The aforementioned The N concentration at the main surface is 1 atomic % or more and 4 atomic % or less, and the N concentration gradually increases from the main surface toward the inside. With an average nitrogen concentration gradient of 0.1 atomic % / μm or more and 0.6 atomic % / μm or less Increasing outer nitrogen concentration transition region and 、 N concentration Inside Towards the side With an average nitrogen concentration gradient of 0.1 atomic % / μm or more and 0.3 atomic % / μm or less Declining and minimum N concentration is 1 an inner nitrogen concentration transition region of at.% or more; 、 a high nitrogen concentration region having a thickness of 3 μm or more and 20 μm or less, which is formed between the outer nitrogen concentration transition region and the inner nitrogen concentration transition region and includes a location of the maximum nitrogen concentration, the maximum nitrogen concentration being higher than the nitrogen concentration of the main surface and less than 11 atomic %, and the average nitrogen concentration gradient within this region being smaller than those of the outer nitrogen concentration transition region and the inner nitrogen concentration transition region, with the nitrogen concentration fluctuating within a range of ±0.5 atomic %; When the value of the cobalt concentration (unit: atomic %) is x, the value y (unit: T) of the saturation magnetic flux density of the soft magnetic iron alloy plate satisfies the empirical formula (1) "y ≧ 1.02 × (0.01 × x + 2.14)", When the iron loss (unit: W / kg) is z, the iron loss under the condition of a magnetic flux density of 1.0 T and 400 Hz satisfies the empirical formula (2) "z < 150 × y - 295". The present invention provides a soft magnetic iron alloy plate characterized by the above-mentioned.

[0017] The present invention allows the following improvements and modifications to be made to the soft magnetic iron alloy plate (I) according to the present invention. (i) the maximum N concentration in the high nitrogen concentration region is 6 atomic % or more and 10 atomic % or less, and the minimum N concentration in the inner nitrogen concentration transition region is 1 atomic % or more and 4 atomic % or less; 。 (ii ) The thickness of the soft magnetic iron alloy plate is 0.03 mm or more and 0.3 mm or less.

[0018] (II) Another aspect of the present invention is a method for producing the soft magnetic iron alloy plate described above, a starting material preparation step of preparing a starting material made of a soft magnetic material containing Fe as a main component and having a thickness of 0.03 mm or more and 0.3 mm or less; a nitrogen concentration distribution control heat treatment step of subjecting the starting material to a predetermined nitrogen concentration distribution control heat treatment to form a predetermined N concentration distribution along the thickness direction of the starting material; a phase transformation and iron nitride phase generation step of transforming the starting material having the predetermined N concentration distribution into martensitic and dispersing and generating iron nitride phases, The specified nitrogen concentration distribution control heat treatment is a heat treatment carried out in an austenite phase formation temperature range, and is a combination of a nitriding process carried out in a specified ammonia gas atmosphere to cause N atoms to penetrate and diffuse from both main surfaces of the starting material, and a nitrogen diffusion / denitriding process carried out in a specified nitrogen gas atmosphere to diffuse the N atoms further inward of the starting material and release nitrogen from both main surfaces of the starting material, thereby forming the outer nitrogen concentration transition region.

[0019] The present invention allows the following improvements and modifications to be made to the above-described method (II) for producing a soft magnetic iron alloy plate according to the present invention. ( iii The predetermined nitrogen concentration distribution control heat treatment is a heat treatment in which the nitriding process and the nitrogen diffusion / denitriding process are alternately performed in multiple cycles. ( iv The phase transformation and iron nitride phase generation process includes quenching, which involves rapid cooling to less than 100°C, and sub-zero treatment, which involves cooling to 0°C or below.

[0020] (III) Yet another aspect of the present invention is an iron core made of a laminate of soft magnetic iron alloy plates, The present invention provides an iron core, wherein the soft magnetic iron alloy plate is the soft magnetic iron alloy plate according to the present invention.

[0021] (IV) Yet another aspect of the present invention is a rotating electric machine having an iron core, The present invention provides a rotating electric machine, wherein the iron core is the iron core according to the present invention. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a soft magnetic iron alloy plate having a saturation magnetic flux density higher than that of an electromagnetic pure iron plate without excessively increasing iron loss, and a method for manufacturing the soft magnetic iron alloy plate. Furthermore, by using the soft magnetic iron alloy plate, it is possible to provide an iron core and a rotating electric machine that are more advantageous for increasing the output of a rotating electric machine than iron cores using pure iron. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a graph showing an example of the relationship between the nitrogen concentration and the plate thickness length in a soft magnetic iron alloy plate according to the present invention. [Figure 2] 1 is a process diagram showing an example of a method for manufacturing a soft magnetic iron alloy plate according to the present invention. [Figure 3A] FIG. 1 is a schematic perspective view showing an example of a stator of a rotating electric machine. [Figure 3B] FIG. 2 is an enlarged cross-sectional schematic view of a slot region of the stator. [Figure 4] 1 shows X-ray diffraction patterns of A-8, a reference sample, and A-1, a sample of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] [Basic concept of the present invention] Pure iron has the advantages of being inexpensive and having a high saturation magnetic flux density Bs (2.1 T). Fe-Si alloys, which contain 1 to 3 mass% silicon (Si), can significantly reduce iron loss Pi compared to pure iron, but have the disadvantage of slightly lowering Bs (2.0 T). Permendur, which contains approximately 50 mass% Co, exhibits a Bs (2.4 T) that is significantly higher than pure iron and a low Pi, but has the disadvantage that the material cost of Co is significantly higher than that of Fe.

[0025] On the other hand, soft magnetic materials that exhibit a higher Bs than pure iron include the aforementioned iron nitride phases (e.g., Fe8N phase (α' phase), Fe 16The present inventors have focused on a technology (for example, Patent Document 2) that shows that Bs can be improved by causing N to penetrate and diffuse into a soft magnetic material whose main component is Fe, thereby generating iron nitride phases of α' phase or α" phase. However, although the soft magnetic material of Patent Document 2 has the advantage of having a higher Bs than electromagnetic pure iron sheet, it was thought to have a weakness in Hc.

[0026] Therefore, the inventors of the present invention have conducted extensive research into a method for consistently producing N-containing soft magnetic iron alloy sheets that exhibit a Bs superior to that of pure iron sheets for electromagnetic applications, without excessively increasing Pi (where the increase in Pi is within the acceptable range for designing a rotating electrical machine). As a result, they have found that by subjecting the starting material to a prescribed nitrogen concentration distribution control heat treatment that combines a nitriding process with a nitrogen diffusion / denitriding process to achieve a prescribed N concentration distribution along the sheet thickness direction, followed by a prescribed phase transformation / iron nitride phase generation treatment, it is possible to consistently 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.

[0027] Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. However, the present invention is not limited to the embodiments described herein, and can be appropriately combined with or improved on known techniques without departing from the technical spirit of the invention.

[0028] [Soft magnetic iron alloy plate of the present invention] Fig. 1 is a graph showing an example of the relationship between nitrogen concentration and thickness length in a soft magnetic iron alloy plate according to the present invention. The soft magnetic iron alloy plate shown in Fig. 1 is a sample with a thickness of 0.1 mm (100 µm), and in the figure, "thickness length 0 µm" refers to one main surface of the iron alloy plate, and "thickness length 50 µm" refers to the center of the iron alloy plate in the thickness direction. The N concentration was measured by quantitative analysis using an electron probe microanalyzer (EPMA, manufactured by JEOL Ltd., JXA-8800RL) with a spot diameter of 1 µm.

[0029] 1, the soft magnetic iron alloy sheet of the present invention has, in its thickness direction, roughly an outer nitrogen concentration transition region 10 where the N concentration increases from the main surface toward the inside, a high nitrogen concentration region 20 where the maximum N concentration is higher than the N concentration at the main surface and less than 11 atomic %, and an inner nitrogen concentration transition region 30 where the N concentration decreases toward the inside from the high nitrogen concentration region 20. In the soft magnetic iron alloy sheet of the present invention, N atoms penetrate and diffuse from both main surfaces, so the N concentration distribution in the thickness direction is, in principle, symmetrical about the center of the sheet thickness.

[0030] A more specific explanation will be given.

[0031] The high nitrogen concentration region 20 is a region in which the maximum N concentration is higher than the N concentration at least on the main surface, and the fluctuation 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 10.5 atomic % or less, and even more preferably 6 atomic % or more and 10 atomic % or less. By making the maximum N concentration 2 atomic % or more, it is possible to form an iron nitride phase (FeN phase (α' phase)) with a tetragonal structure and / or Fe 16 It is believed that an effective amount (e.g., 10 volume % or more) of N phase (α″ phase) is formed, which contributes to improving the Bs of the soft magnetic iron alloy sheet. On the other hand, by controlling the maximum N concentration to less than 11 atomic %, it is possible to suppress the formation of undesired iron nitride phases (e.g., FeN phase (γ' phase) and FeN phase (ε phase)) that do not contribute to improving the Bs.

[0032] Although there is no particular limitation on the thickness (length in the sheet thickness direction) of the high nitrogen concentration region 20, from the viewpoint of improving Bs, it is preferably 3 μm or more, more preferably 5 μm or more. Also, from the viewpoint of ease of N concentration control, it is preferably 20 μm or less, more preferably 15 μm or more.

[0033] In the iron nitride phase with a tetragonal structure (α' phase and / or α" phase), the distortion of the crystal lattice caused by the intrusion of N atoms contributes to an improvement in Bs. On the other hand, the α' phase and α" phase have the disadvantage that Hc and Pi tend to increase due to an increase in magnetocrystalline anisotropy.

[0034] 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, which have a relatively low N concentration, are intentionally formed adjacent to the high nitrogen concentration region 20, and magnetic coupling is generated between the high nitrogen concentration region 20 and the outer nitrogen concentration transition region 10, and between the high nitrogen concentration region 20 and the inner nitrogen concentration transition region 30, thereby suppressing excessive increases in Pi throughout the soft magnetic iron alloy plate.

[0035] 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 at the main surface is preferably 1 atomic % or more and 4 atomic % or less, and more preferably 2 atomic % or more and less than 4 atomic %. If the N concentration at the main surface is less than 1 atomic %, the region near the main surface cannot sufficiently contribute to the objective of improving Bs. If the N concentration at the main surface exceeds 4 atomic %, the influence of magnetocrystalline anisotropy (increase in Pi) due to the α' phase and α" phase cannot be ignored.

[0036] The average N concentration gradient in the outer nitrogen concentration transition region 10 is preferably 0.1 atomic % / μm or more and 0.6 atomic % / μm or less, and more preferably 0.2 atomic % / μm or more and less than 0.6 atomic % / μm. If the average N concentration gradient is less than 0.1 atomic % / μm, it is difficult to overcome the potential for magnetization pinning due to magnetocrystalline anisotropy. If the average N concentration gradient is more than 0.6 atomic % / μm, the gradient becomes too steep, making it difficult to generate magnetic coupling.

[0037] There is no particular limitation on the thickness of the outer nitrogen concentration transition region 10, but from the viewpoint of ease of N concentration control, it is preferably 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 25 μm or less.

[0038] 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 sheet thickness. The minimum N concentration is at least lower than the N concentration of the high nitrogen concentration region 20, and is preferably 1 atomic % or more and 4 atomic % or less, and more preferably 2 atomic % or more and less than 4 atomic %. If the minimum N concentration is less than 1 atomic %, the region near the center of the sheet thickness cannot sufficiently contribute to the purpose of improving Bs. If the minimum N concentration exceeds 4 atomic %, the effect of magnetocrystalline anisotropy (increase in Pi) due to the α' phase and α" phase cannot be ignored.

[0039] The average N concentration gradient in the inner nitrogen concentration transition region 30 is preferably 0.1 atomic % / μm or more and 0.3 atomic % / μm or less, and more preferably greater than 0.1 atomic % / μm and 0.2 atomic % / μm or less. If the average N concentration gradient is less than 0.1 atomic % / μm, the difference between adjacent magnetic domains is small, weakening the propagation of the magnetization state. If the average N concentration gradient is more than 0.3 atomic % / μm, the minimum N concentration in the region near the center of the sheet thickness is likely to be less than 1 atomic %.

[0040] Although specific examples will be described later, the results of wide-angle X-ray diffraction (WAXD) measurements indicate that the entire soft magnetic iron alloy sheet does not become the α' phase and / or α" phase due to the penetration and diffusion of N atoms, but rather that the α phase (ferrite phase, body-centered cubic crystal) is the main phase (the phase with the largest volume fraction), with the α' phase and / or α" phase dispersed and generated. Furthermore, since the γ phase (austenite phase, face-centered cubic crystal) is nearly non-magnetic, if the volume fraction of the γ phase exceeds 5%, it becomes difficult to improve Bs, coupled with the reduction in the volume fraction of the α phase. The volume fraction of the γ phase is more preferably 3% or less, and more preferably 1% or less.

[0041] Regarding the composition of the soft magnetic iron alloy sheet, there are no particular limitations other than that Fe is the main component (the component with the highest content rate) and N is contained, and soft magnetic materials that are easily available industrially or commercially as thin plate materials (e.g., electromagnetic pure iron sheet, Fe-Co alloy material, Fe-Si alloy material) can be used as appropriate.

[0042] Electromagnetic pure iron is one of the cheapest starting materials.

[0043] As an Fe-Co alloy material, an alloy containing Fe as the main component and Co at more than 0 atomic % and 30 atomic % or less can be suitably used. By setting the Co content to 30 atomic % or less, material costs can be significantly reduced compared to permendur. The Co content is more preferably 3 atomic % or more and 25 atomic % or less, and even more 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 %).

[0044] Furthermore, as the Fe-Si alloy material, an alloy containing Fe as the main component and Si in an amount of more than 0 atomic % and 3 atomic % or less can also be suitably used.

[0045] 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), and copper (Cu)) are permitted within a range that does not have a significant adverse effect on the Bs of the soft magnetic iron alloy plate (for example, a total concentration of 2 atomic % or less).

[0046] By forming the nitrogen concentration profile defined in the present invention based on these soft magnetic materials, it is possible to achieve a higher Bs than the base soft magnetic material. For example, when using pure iron sheet as the starting material, it is possible to achieve a Bs of more than 2.14 T.

[0047] There is no particular limitation on the thickness of the soft magnetic iron alloy plate, and it can be appropriately selected within the range of 0.01 mm or more and 1 mm or less. From the viewpoint of controllability of the N concentration distribution, however, it is preferably 0.03 mm or more and 0.3 mm or less, and more preferably 0.05 mm or more and 0.2 mm or less.

[0048] Here, we will briefly explain the allowable range of Pi when designing a rotating electrical machine. As mentioned above, from the perspective of designing high-output rotating electrical machines and transformers, improving the Bs of the iron core is given priority, and if the improvement in Bs is large, a certain degree of increase in Pi is acceptable.

[0049] Numerous experiments by the inventors and others have shown that a 2% or more improvement in Bs over the base soft magnetic material can be considered a clear improvement / significant difference in characteristics. Furthermore, it has been empirically shown that if the empirical formula "z < 150 × y - 295" is satisfied, where "y" is the numerical value of Bs (unit: T) of a soft magnetic material and "z" is the numerical value of Pi (unit: W / kg) under conditions of a magnetic flux density of 1.0 T and 400 Hz, it is possible to design a rotating electrical machine with high output.

[0050] [Method of manufacturing the soft magnetic iron plate of the present invention] Fig. 2 is a process diagram showing an example of a method for producing a soft magnetic iron alloy sheet according to the present invention. As shown in Fig. 2, the method for producing a soft magnetic iron alloy sheet 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 carried out between steps S2 and S3. Each step will be described in more detail below.

[0051] (Starting material preparation process) In this step S1, a thin sheet of soft magnetic material (e.g., 0.03 to 0.3 mm thick) is prepared as the starting material. There are no particular limitations on the soft magnetic material as long as it is primarily composed of iron; for example, electromagnetic pure iron material, Fe-Co alloy material, or Fe-Si alloy material can be suitably used. As mentioned above, in the case of Fe-Co alloy material, an Fe-Co alloy material containing more than 0 atomic % and not more than 30 atomic % of Co is preferred. In the case of Fe-Si alloy material, an Fe-Si alloy material containing more than 0 atomic % and not more than 3 atomic % of Si is preferred. Because these soft magnetic materials have a low carbon content, it is relatively easy to control the nitrogen concentration distribution in the starting material in subsequent processes, which also contributes to reducing process costs.

[0052] (Nitrogen concentration distribution control heat treatment process) In step S2, the starting material is subjected to a predetermined nitrogen concentration distribution control heat treatment (a heat treatment that combines a nitrogen immersion process S2a and a nitrogen diffusion / denitrification process S2b) to form a predetermined nitrogen concentration distribution along the thickness direction of the starting material. The manufacturing method of the present invention is characterized by step S2.

[0053] In the nitriding process S2a, N atoms penetrate and diffuse from both main surfaces of the starting material at a temperature of 500°C or higher (e.g., in the austenite (γ) phase) formation temperature range) in a predetermined ammonia (NH3) gas atmosphere so that the N concentration in the surface region of the starting material (substantially the region corresponding to the outer nitrogen concentration transition region 10) reaches a predetermined concentration. Suitable NH3 gas atmospheres include a mixture of NH3 gas and N2 gas, a mixture of NH3 gas and Ar gas, and a mixture of NH3 gas and H2 gas. The N concentration in the surface region of the starting material can be controlled mainly by controlling the partial pressure of the NH3 gas. The thickness (length in the sheet thickness direction) of the surface region can be controlled mainly by controlling the temperature and time.

[0054] It is preferable to introduce NH3 gas after the temperature reaches 500°C or higher. This is because if NH3 gas is actively introduced in the stable temperature range of the ferrite phase (α phase), the desired iron nitride phase (Fe8N phase (α' phase) and / or Fe 16 This is because undesired iron nitride phases (for example, Fe4N phase (γ' phase) and Fe3N phase (ε phase)) are more likely to form than undesired iron nitride phases (for example, Fe4N phase (γ' phase) and Fe3N phase (ε phase)).

[0055] The nitrogen immersion process S2a is followed by the nitrogen diffusion / denitrification process S2b. In process S2b, the NH3 gas partial pressure is reduced to zero while maintaining the temperature of process S2a. This process diffuses some of the N atoms introduced in process S2a further into the starting material, while simultaneously releasing some of the introduced N atoms from the main surface of the starting material, thereby reducing the N concentration at 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.) during process S2a to compensate for the NH3 gas partial pressure.

[0056] By combining the nitrogen immersion process S2a and the nitrogen diffusion and 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.

[0057] Furthermore, by repeating the combination of process S2a and process S2b multiple times (by intermittently controlling the time when NH3 gas is supplied and the time when it is not), the N concentration distribution inside the iron alloy plate (the outer nitrogen concentration transition region 10, the high nitrogen concentration region 20, and the inner nitrogen concentration transition region 30) can be more easily controlled.

[0058] (Carburizing heat treatment process) 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 an essential step, but by infiltrating C atoms into the outer nitrogen concentration transition region 10, it is possible to suppress an increase in Pi without decreasing the Bs of the soft magnetic iron alloy plate.

[0059] There are no particular limitations on the method of carburizing heat treatment, and conventional methods (e.g., heat treatment under an acetylene (C2H2) gas atmosphere) can be suitably used. As an example, it can be performed by changing the atmospheric gas to C2H2 gas following the nitrogen diffusion and denitrification process S2b.

[0060] (Phase transformation and iron nitride phase formation process) In step S3, the iron alloy plate having the predetermined N concentration distribution formed in step S2 is quenched by rapidly cooling to below 100°C, causing a phase transformation from the γ phase to a martensite structure and dispersing iron nitride phases (α' phase and / or α" phase) with a tetragonal crystal structure. There are no particular limitations on the quenching method, and conventional methods (for example, water quenching and oil quenching) can be suitably used.

[0061] In order to transform the residual γ phase in the iron alloy plate into a martensite structure, it is preferable to perform sub-zero treatment (e.g., ordinary sub-zero treatment using dry ice or ultra-sub-zero treatment using liquid nitrogen) in which the plate is cooled to below 0°C.

[0062] Although not an essential step, tempering at 100° C. or higher and 210° C. or lower may be carried out as necessary to impart toughness to the final soft magnetic iron alloy plate (not shown in FIG. 2).

[0063] [Iron core and rotating electrical machine using the soft magnetic iron alloy plate of the present invention] Fig. 3A is a schematic perspective view showing an example of a stator of a rotating electric machine, and Fig. 3B is an enlarged schematic cross-sectional view of a slot region of the stator. Note that the cross-sectional view refers to a cross section perpendicular to the rotation axis direction (a cross section whose normal is parallel to the axial direction). In the rotating electric machine, a rotor (not shown) is disposed radially inside the stator of Figs. 3A and 3B.

[0064] 3A and 3B, stator 50 has stator coils 60 wound in a plurality of stator slots 52 formed on the inner circumferential side of iron core 51. Stator slots 52 are spaces that are arranged at a predetermined circumferential pitch around the circumferential direction of iron core 51 and penetrate the axial direction, with slits 53 opening in the innermost circumferential portion and extending in the axial direction. The areas separating adjacent stator slots 52 are called teeth 54 of iron core 51, and the parts of the inner circumferential tip areas of teeth 54 that define slits 53 are called tooth claw portions 55.

[0065] The stator coil 60 is usually made up of a plurality of segment conductors 61. For example, in Figures 3A and 3B, the stator coil 60 is made up of three segment conductors 61 corresponding to the U-phase, V-phase, and W-phase of a three-phase AC. In order to prevent partial discharge between the segment conductors 61 and the iron core 51 and between the phases (U-phase, V-phase, and W-phase), the outer periphery of each segment conductor 61 is usually covered with an electrical insulating material 62 (for example, insulating paper or enamel coating).

[0066] The iron core and rotating electric machine using the soft magnetic iron alloy plate of the present invention are an iron core 51 formed by axially stacking multiple soft magnetic iron alloy plates of the present invention that have been formed into a predetermined shape, and a rotating electric machine that uses the iron core 51. As described above, the soft magnetic iron alloy plate of the present invention has a higher Bs than electromagnetic pure iron plates, and therefore can provide an iron core with higher electrical energy to magnetic energy conversion efficiency than iron cores using conventional electromagnetic pure iron plates or electromagnetic steel plates. A highly efficient iron core leads to higher torque and smaller size of the rotating electric machine. [Example]

[0067] The present invention will be explained in more detail below with reference to various experiments, however, the present invention is not limited to the configurations and structures described in these experiments.

[0068] [Experiment 1] (Production of soft magnetic iron alloy plates A-1 to A-8) A commercially available electromagnetic pure iron plate (thickness = 0.1 mm) was prepared as a starting material (step S1). The starting material was heated to 1000 ° C at a temperature increase rate of 15 ° C / min and then subjected to nitrogen concentration distribution control heat treatment by holding at 1000 ° C for 2.5 hours while controlling the atmosphere (step S2).

[0069] More specifically, when the temperature reached 500°C during the heating process, NH3 gas (partial pressure = 1 × 10 5 When the temperature reached 1000°C, NH3 gas (partial pressure = 5 × 10 4 Pa) and N2 gas (partial pressure = 4 × 10 4 The mixture was switched to a gas mixture of N2 gas (pressure = 9 × 10 Pa) and held for 20 minutes (process S2a), and then N2 gas only (pressure = 9 × 10 4 The pressure was switched to N2 gas (Pa) and held for 5 minutes (Process S2b). After that, a total of six cycles of combinations of Process S2a and Process S2b were performed: 20 minutes with mixed gas, 5 minutes with N2 gas only, 15 minutes with mixed gas, 10 minutes with N2 gas only, 10 minutes with mixed gas, 15 minutes with N2 gas only, 10 minutes with mixed gas, 15 minutes with N2 gas only, 10 minutes with mixed gas, 15 minutes with N2 gas only, 10 minutes with mixed gas, 15 minutes with N2 gas only.

[0070] Following the nitrogen concentration distribution control heat treatment, the starting material was oil quenched (60°C) to transform into martensitic, and then subjected to ultra-subzero treatment to transform the residual γ phase into martensitic (step S3), thereby producing sample A-1, a soft magnetic iron alloy plate.

[0071] Next, using the same magnetic pure iron plate as above as the starting material, samples A-2 to A-7 of soft magnetic iron alloy plates were produced by varying the time allocation of process S2a and process S2b. In addition, the starting sample without steps S2 to S3 was prepared as sample A-8 (reference sample).

[0072] [Experiment 2] (Production of soft magnetic iron alloy plates B-1 to B-8) Commercially available pure metal raw materials (Fe, Co, each 99.9% pure) were mixed and an alloy ingot was produced by arc melting on a water-cooled copper hearth (Dai-A Vacuum Co., Ltd., automatic arc melting furnace, reduced pressure Ar atmosphere). To homogenize the alloy ingot, the sample was remelted six times while being inverted. The resulting alloy ingot was pressed and rolled to prepare a 95 atomic % Fe-5 atomic % Co alloy plate (thickness = 0.1 mm) as the starting material (step S1).

[0073] Next, steps S2 and S3 were carried out in the same manner as in Experiment 1 to prepare soft magnetic iron alloy plate samples B-1 to B-7. In addition, the starting sample without steps S2 and S3 was prepared as sample B-8 (reference sample).

[0074] [Experiment 3] (Production of soft magnetic iron alloy plates C-1 to C-8) Using commercially available pure metal raw materials (Fe, Co, each with a purity of 99.9%), a 90 atomic % Fe-10 atomic % Co alloy plate (thickness = 0.1 mm) was prepared as the starting material in the same manner as in Experiment 2 (Step S1).

[0075] Next, steps S2 and S3 were carried out in the same manner as in Experiment 1 to prepare soft magnetic iron alloy plate samples C-1 to C-7. In addition, the starting sample without steps S2 and S3 was prepared as sample C-8 (reference sample).

[0076] [Experiment 4] (Soft magnetic iron alloy plate D-1~ D-4, D-6~ Preparation of D-8) Using commercially available pure metal raw materials (Fe, Co, each with a purity of 99.9%), an 80 atomic % Fe-20 atomic % Co alloy plate (thickness = 0.1 mm) was prepared as the starting material in the same manner as in Experiment 2 (Step S1).

[0077] Next, steps S2 to S3 were carried out in the same manner as in Experiment 1, and samples D-1 to D-3 of the soft magnetic iron alloy plate were obtained. D-4, D-6~ In addition, the starting sample without undergoing steps S2 and S3 was prepared as sample D-8 (reference sample).

[0078] [Experiment 5] (Samples A-1 to A-8, B-1 to B-8, C-1 to C-8, D-1 to D-4, D-6~ D-8 property survey) The cross sections of 100 stacked samples were subjected to WAXD measurement using Cu-Kα radiation to identify the detected phases. The X-ray diffractometer used was Rigaku Corporation's Rint-Ultima III.

[0079] FIG. 4 shows the X-ray diffraction patterns of the reference sample A-8 and the inventive sample A-1. As shown in FIG. 4, only the α phase (ferrite phase) is observed in the reference sample A-8. In contrast, in the inventive sample A-1, the α phase is the main phase, and the formation of the α″ phase (iron nitride phase with a tetragonal crystal structure) is confirmed. The γ phase (austenite phase) and the γ′ phase (FeN phase) are not detected. It was also confirmed separately that the same results as those in FIG. 4 were obtained in the other samples.

[0080] From these results, it is considered that the soft magnetic iron alloy sheet according to the present invention does not become an iron nitride phase (α' phase and / or α" phase) with a tetragonal crystal structure as a whole due to the penetration and diffusion of N atoms, but is in a state in which the ferrite phase (α phase) is the main phase and the α' phase and / or α" phase are dispersed and generated.

[0081] Next, the cross section of each sample was examined for the N concentration distribution in the thickness direction using an EPMA. Figure 1 shows the results for sample A-1, which is the sample of the present invention. As mentioned above, the N concentration distribution in the thickness direction can be classified into an outer nitrogen concentration transition region 10, a high nitrogen concentration region 20, and an inner nitrogen concentration transition region 30.

[0082] The measurement results of the N concentration (Ns) on the main surface, the maximum N concentration (Nmax) in the high nitrogen concentration region 20, the minimum N concentration (Nmin) in the inner nitrogen concentration transition region 30, the average N concentration gradient (AGout) in the outer nitrogen concentration transition region 10, and the average N concentration gradient (AGin) in the inner nitrogen concentration transition region 30 for each sample are summarized in Table 1 below.

[0083] 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 conditions of a magnetic field of 1.6 MA / m and a temperature of 20°C, and Bs (unit: T) was calculated from the sample volume and mass. In addition, Pi of the sample was measured under conditions of a magnetic flux density of 1.0 T, 400 Hz, and a temperature of 20°C using the H coil method using a BH loop analyzer (IFG Co., Ltd., IF-BH550) and a vertical yoke single sheet tester. -1.0 / 400 The magnetic properties were measured (unit: W / kg). The results are also shown in Table 1.

[0084] [Table 1]

[0085] Samples A-8, B-8, C-8, and D-8 are reference samples that are the starting materials. Comparing the Bs of samples A-8, B-8, C-8, and D-8, it can be seen that the Bs increases linearly with increasing Co content.

[0086] As mentioned above, numerous experiments by the inventors and others have revealed that an improvement of 2% or more in Bs from the base soft magnetic material can be said to be a clear improvement / significant difference in characteristics. Therefore, in the present invention, when the Co concentration (unit: atomic %) in the starting material is x, and 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)", it is determined that there is an "improvement in Bs."

[0087] Furthermore, it has been empirically proven that if the empirical formula (2) "z < 150×y - 295" is satisfied, where "y" is the value of Bs (unit: T) of a soft magnetic material and "z" is the value of Pi (unit: W / kg) under conditions of a magnetic flux density of 1.0 T and 400 Hz, a rotating electric machine can be designed with high output. 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 an acceptable range."

[0088] If both the empirical formula (1) and the empirical formula (2) are satisfied, the product is judged as "passed," otherwise it is judged as "failed."

[0089] Looking at the results in Table 1 from this perspective, samples A-1 to A-3, which have the outer nitrogen concentration transition region, high nitrogen concentration region, and inner nitrogen concentration transition region defined by the present invention, each have a Bs that is 2% or more higher than that of reference sample A-8, and their Pi satisfies empirical formula (2). Similarly, samples B-1 to B-3 each have a Bs that is 2% or more higher than that of reference sample B-8, and their Pi satisfies empirical formula (2). samples C-1 to C-3 each have a Bs that is 2% or more higher than that of reference sample C-8, and their Pi satisfies empirical formula (2). samples D-1 to D-3 each have a Bs that is 2% or more higher than that of reference sample D-8, and their Pi satisfies empirical formula (2).

[0090] In contrast to these, samples A-4 to A-5, B-4, B-6 to B-7, C-4 to C-5, C-7, D- 4、The Bs of samples A-6 to A-7, B-5 ​​to B-7, C-5 to C-7, and D-7 do not satisfy the empirical formula (1) (they do not achieve a 2% improvement in Bs of the reference sample). 6 For samples A-7 to D-7, Pi does not satisfy empirical formula (2). Also, for samples A-7, B-7, C-7, and D-7, which fall outside the definition of the inner nitrogen concentration transition region of the present invention, Bs does not satisfy empirical formula (1) (they do not achieve a 2% improvement in Bs of the reference sample).

[0091] In other words, it has been confirmed that a soft magnetic iron alloy plate having an outer nitrogen concentration transition region, a high nitrogen concentration region, and an inner nitrogen concentration transition region as defined by the present invention exhibits a higher Bs than an electromagnetic pure iron plate without an excessive increase in Pi.

[0092] The above-described embodiments and experiments have been described to aid in understanding the present invention, and the present invention is not limited to the specific configurations described. For example, it is possible to replace part of the configuration of the embodiments with configurations within the technical common sense of those skilled in the art, and it is also possible to add configurations within the technical common sense of those skilled in the art to the configuration of the embodiments. In other words, it is possible to delete, replace, or add part of the configurations of the embodiments and experiments in this specification without departing from the technical spirit of the invention. [Explanation of symbols]

[0093] 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... teeth claw portion, 60...stator coil, 61...segment conductor, 62...electrical insulating material.

Claims

1. A soft magnetic iron alloy plate, It has a chemical composition containing 7.4 atomic percent or less of nitrogen, with the balance being iron and impurities, In the thickness direction of the soft magnetic iron alloy plate, in the range from the main surface to the plate thickness center, When quantitative analysis of nitrogen concentration was performed using an electron probe microanalyzer with a spot diameter of 1 μm, an outer nitrogen concentration transition region in which the nitrogen concentration at the main surface is 3.5 atomic % and the nitrogen concentration increases inward from the main surface at an average nitrogen concentration gradient of 0.24 atomic % / μm; an inner nitrogen concentration transition region in which the nitrogen concentration decreases inward at an average nitrogen concentration gradient of 0.15 atomic % / μm and has a minimum nitrogen concentration of 3.7 atomic %; a high nitrogen concentration region having a thickness of 3 μm to 20 μm, which is formed between the outer nitrogen concentration transition region and the inner nitrogen concentration transition region and includes a location of the maximum nitrogen concentration, the maximum nitrogen concentration being 7.4 atomic %, and the average nitrogen concentration gradient within the region being smaller than those of the outer nitrogen concentration transition region and the inner nitrogen concentration transition region, with the nitrogen concentration varying within a range of ±0.5 atomic %; When the saturation magnetic flux density (unit: T) of the soft magnetic iron alloy plate is y and the iron loss (unit: W / kg) is z, the iron loss under the condition of a magnetic flux density of 1.0 T and 400 Hz satisfies the empirical formula (2) "z < 150 × y - 295", A soft magnetic iron alloy plate characterized by:

2. The soft magnetic iron alloy plate according to claim 1, The thickness of the soft magnetic iron alloy plate is 0.1 mm. A soft magnetic iron alloy plate characterized by:

3. A method for manufacturing a soft magnetic iron alloy plate according to claim 1 or claim 2, a starting material preparation step of preparing a starting material made of a soft magnetic material containing iron as a main component and having a thickness of 0.1 mm; a nitrogen concentration distribution control heat treatment step of subjecting the starting material to a predetermined nitrogen concentration distribution control heat treatment to form a predetermined nitrogen concentration distribution along the thickness direction of the starting material; a phase transformation / iron nitride phase generation step of transforming the starting material having the predetermined nitrogen concentration distribution into a martensite structure and dispersing and generating iron nitride phases, The heat treatment for controlling the nitrogen concentration distribution was carried out by introducing ammonia gas (partial pressure = 1 x 105 Pa) when the temperature reached 500°C during the temperature rise process, and then switching to a mixed gas of ammonia gas (partial pressure = 5 x 104 Pa) and nitrogen gas (partial pressure = 4 x 104 Pa) while maintaining the temperature when the temperature reached 1000°C. This was followed by a nitrogen immersion process for 20 minutes in which nitrogen atoms penetrated and diffused from both main surfaces of the starting material, and then nitrogen gas alone (pressure = 9 x 104 and performing a nitrogen diffusion and denitrification process for 5 minutes, switching the pressure (MPa) to diffuse the nitrogen atoms further inwardly of the starting material and release nitrogen from both major surfaces of the starting material to form the outer nitrogen concentration transition region, followed by performing the nitrogen immersion process for 20 minutes, the nitrogen diffusion and denitrification process for 5 minutes, the nitrogen immersion process for 15 minutes, the nitrogen immersion process for 10 minutes, the nitrogen diffusion and denitrification process for 10 minutes, the nitrogen immersion process for 15 minutes, the nitrogen immersion process for 10 minutes, the nitrogen diffusion and denitrification ... and the nitrogen diffusion and denitrification process for 15 minutes. A method for manufacturing a soft magnetic iron alloy plate.

4. 4. The method for producing a soft magnetic iron alloy plate according to claim 3, The method for producing a soft magnetic iron alloy sheet is characterized in that the phase transformation / iron nitride phase generation process includes quenching, which involves rapidly cooling to less than 100°C, and sub-zero treatment, which involves cooling to 0°C or below.

5. An iron core made of a laminate of soft magnetic iron alloy plates, An iron core, wherein the soft magnetic iron alloy plate is the soft magnetic iron alloy plate according to claim 1 or 2.

6. A rotating electric machine having an iron core, A rotating electric machine, wherein the iron core is the iron core according to claim 5.

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