Soft magnetic iron alloy plate and manufacturing method thereof

Abstract

Provided are soft magnetic iron alloy sheets having a saturation magnetic flux density comparable to that of Perminder alloys and iron losses equivalent to those of electromagnetic pure iron, while being less expensive than Perminder alloys, and a method for producing the same. The soft magnetic iron alloy sheet according to the present invention is characterized in that it has a chemical composition comprising 0 atomic % to 30 atomic % of Co, 0.1 atomic % to 11 atomic % of N, and 0 atomic % to 1.2 atomic % of vanadium, with the balance consisting of Fe and impurities. The sheet also includes a surface region having an average nitrogen concentration of 1 atomic % to 15 atomic % and an inner region having an average nitrogen concentration lower than the average nitrogen concentration of the surface region, the surface region having a thickness of 1% to 30% of the thickness of the soft magnetic iron alloy sheet from both main surfaces, and in which tetragonal iron nitride martensite is formed.

Description

Technical Field

[0001] The present invention relates to the technology of magnetic materials, and more particularly to a soft magnetic iron alloy plate having a higher saturation magnetic flux density than an electromagnetic pure iron plate and a method for manufacturing the same. Background Art

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

[0003] Furthermore, reducing the cost of the iron core is naturally one of the most important issues, and technical development for stably and inexpensively producing materials having a high Bs has been actively pursued.

[0004] For example, Patent Document 1 (Japanese Patent Publication 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. The soft magnetic material contains iron, carbon and nitrogen, and contains martensite containing carbon and nitrogen and γ-Fe, in which a nitrogen-containing phase is formed.

[0005] According to Patent Document 1, 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 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.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2020-132894 Summary of the Invention

[0009] Problems to be solved by the invention

[0010] Among currently commercialized soft magnetic materials, Permendur alloy (49Fe-49Co-2V mass % = 50Fe-48Co-2V atomic %) is well-known as the material with the highest Bs. However, the material cost of Co, while fluctuating depending on market conditions, is 100 to 200 times that of Fe. Therefore, Permendur alloy suffers from its high cost. In other words, reducing the Co content in Fe-Co alloys can reduce material costs accordingly.

[0011] However, Fe-Co alloys have a weakness in that reducing the Co content also reduces Bs. While it is conceivable that the reduction in Bs caused by the reduction in the Co content can be compensated by forming ferrous nitride martensite, nitrogen atoms have difficulty penetrating and diffusing into Fe-Co alloys, making the formation of ferrous nitride martensite difficult. Consequently, a method for forming ferrous nitride martensite in Fe-Co alloys has not yet been established.

[0012] Furthermore, if elements that promote the intrusion and diffusion of nitrogen atoms (such as Al, Cr, Mo, and Nb) are added to the Fe—Co alloy material in order to form nitride iron martensite, another problem arises in that Bs is further reduced and the iron loss Pi is increased.

[0013] On the other hand, in iron cores for rotating electrical machines (eg, motors and generators), mechanical strength (eg, tensile strength) that can withstand the centrifugal force of rotation is also an important requirement in addition to high Bs and low Pi.

[0014] In recent years, there has been a strong demand for compact, high-output rotating electrical machines, making improving core properties an urgent task. Furthermore, as mentioned above, reducing core costs is naturally one of the most important issues.

[0015] Therefore, an object of the present invention is to provide a soft magnetic iron alloy plate having a saturation magnetic flux density comparable to that of Perminder alloy and an iron loss equivalent to that of electromagnetic pure iron, and at a lower cost than that of Perminder alloy, and a method for producing the same.

[0016] Means for solving problems

[0017] (I) One embodiment of the present invention provides a soft magnetic iron alloy plate characterized by having a chemical composition comprising 0 atomic % to 30 atomic % of cobalt (Co), 0.1 atomic % to 11 atomic % of nitrogen (N), 0 atomic % to 1.2 atomic % of vanadium (V), and the balance consisting of iron (Fe) and impurities.

[0018] The soft magnetic iron alloy plate has, in the thickness direction, a surface region having an average nitrogen concentration of 1 atomic % or more and 15 atomic % or less, and an inner region having an average nitrogen concentration lower than the average nitrogen concentration of the surface region.

[0019] The surface layer region has a thickness of not less than 1% and not more than 30% of the thickness of the soft magnetic iron alloy plate from both main surfaces, and has formed therein iron nitride martensite with a tetragonal structure.

[0020] In the present invention, the surface region is defined as the outermost region including the main surface along the thickness direction of the iron plate, and the inner region is defined as the region sandwiched by the surface region.

[0021] In the soft magnetic iron alloy plate (I) of the present invention, the present invention can implement the following improvements and modifications.

[0022] (i) The average nitrogen concentration of the surface region is higher than the average nitrogen concentration of the inner region by 0.5 atomic % or more.

[0023] (ii) In the inner region, a ferrite phase with a cubic crystal structure is a main phase.

[0024] (iii) The average nitrogen concentration of the inner region is less than 1 atomic %.

[0025] (iv) The saturation magnetic flux density is 2.2 T or higher, and the iron loss under the conditions of a magnetic flux density of 1.0 T and 400 Hz is less than 50 W / kg.

[0026] (II) Another aspect of the present invention provides a method for producing the soft magnetic iron alloy plate, characterized by comprising:

[0027] a starting material preparation step of preparing a starting material, wherein the starting material comprises a soft magnetic material having Fe as a main component and containing 0 atomic % to 30 atomic % of Co, and having a thickness of 0.01 mm to 1 mm;

[0028] a nitriding heat treatment step, wherein the starting material is heated and quenched in a predetermined ammonia (NH 3 ) gas atmosphere to allow nitrogen to intrude and diffuse into a surface region of the starting material in an amount of not less than 1 atomic % and not more than 15 atomic %; and

[0029] A subzero treatment step, wherein the starting material after the nitriding heat treatment step is cooled to below 0°C.

[0030] The nitriding heat treatment process includes: a nitriding process of heating the starting material while controlling the nitriding potential in the atmosphere within a predetermined range; and a cooling process of rapidly cooling the starting material to below 100° C. at a cooling rate of 100° C. / s or more while controlling the nitriding potential in the atmosphere within a predetermined range.

[0031] In the method (II) for producing a soft magnetic iron alloy plate according to the present invention, the present invention can implement the following improvements and modifications.

[0032] (v) The nitriding potential K N The NH3 gas partial pressure P in the NH3 gas atmosphere NH3 and hydrogen (H2) gas partial pressure P H2 Defined as “K N =P NH3 / P H2 3 / 2 ”, to become “0.001atm-1 / 2 ≤K N ≤10atm -1 / 2 " to control.

[0033] Effects of the Invention

[0034] According to the present invention, a soft magnetic iron alloy plate having a saturation magnetic flux density comparable to that of Perominder alloy and iron loss equivalent to that of electromagnetic pure iron and at a lower cost than that of Perominder alloy and a method for producing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] [ Figure 1 ] is a process diagram showing an example of a method for manufacturing a soft magnetic iron alloy plate according to the present invention.

[0036] [ Figure 2A ] are the results of quantitative analysis of the N concentration in the thickness direction of the cross section of Example 1, and the X-ray diffraction pattern of the surface of Example 1.

[0037] [ Figure 2B ] are the results of quantitative analysis of the N concentration in the thickness direction of the cross section of Comparative Example 1, and the X-ray diffraction pattern of the surface of Comparative Example 1.

[0038] [ Figure 2C ] are the results of quantitative analysis of the N concentration in the thickness direction of the cross section of Comparative Example 2, and the X-ray diffraction pattern of the surface of Comparative Example 2.

[0039] [ Figure 3 ] are the results of quantitative analysis of the N concentration in the thickness direction of the cross section of Example 2, and the X-ray diffraction pattern of the surface of Example 2.

[0040] [ Figure 4 ] is the result of quantitative analysis of the N concentration in the thickness direction of the cross section of Comparative Example 3. DETAILED DESCRIPTION

[0041] The inventors of this application conducted extensive research into methods for generating ferrous nitride martensite by invading and diffusing nitrogen atoms into Fe-Co alloy plates. They discovered that by setting the Co content to 30 atomic percent or less, controlling the nitriding potential during nitriding heat treatment within a specified range, and controlling the cooling rate during cooling, ferrous nitride martensite can be efficiently generated in the surface region of the Fe-Co alloy plate. The resulting Fe-Co alloy plate was found to possess a saturation magnetic flux density comparable to that of Perminder alloy and iron loss equivalent to that of electromagnetic pure iron, despite a reduced Co content. The present invention was completed based on this discovery.

[0042] Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail along the manufacturing steps. It should be noted that the present invention is not limited to the embodiments listed here, and can be appropriately combined with known technologies or improved based on known technologies within the scope of the technical concept of the invention. In addition, in this specification, the case of using Fe-Co alloy plates as starting materials is described in detail. However, even when using foils that do not contain Co as starting materials, by giving a difference in the average nitrogen concentration between the surface area and the internal area, it is possible to achieve both high saturation magnetic flux density and low iron loss.

[0043] Figure 1 FIG. 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 1 As shown, the method for producing a soft magnetic iron alloy plate of the present invention generally comprises a starting material preparation step S1, a nitriding heat treatment step S2, and a low-temperature treatment step S3. The nitriding heat treatment step S2 includes a nitriding process S2a and a cooling process S2b. Each step will be described in more detail below.

[0044] In the starting material preparation step S1, a plate (thickness 0.01 to 1 mm) containing Fe as the main component (the component with the highest content) and Co at 0 atomic % to 30 atomic % is prepared as the starting material. Setting the Co content to 30 atomic % or less allows for the intrusion and diffusion of N, and significantly reduces material costs compared to Perminder alloy. The content is preferably 3 atomic % to 30 atomic %, more preferably 5 atomic % to 25 atomic %, and even more preferably 8 atomic % to 20 atomic %.

[0045] Although not an essential component, V may be contained within 4% of the Co content (for example, when Co = 30 atomic %, V ≤ 1.2 atomic %). The means of the starting material preparation step S1 is not particularly limited, and a known method can be used as appropriate. Commercially available products may also be used.

[0046] It should be noted that impurities (impurities that may be contained in the starting material, such as H (hydrogen), B (boron), C (carbon), Si (silicon), phosphorus (P), sulfur (S), chromium (Cr), manganese (Mn), nickel (Ni), copper (Cu), etc.) are allowed within a range that does not cause particularly adverse effects on the Bs of the soft magnetic iron alloy plate (for example, the total concentration is within 2 atomic %).

[0047] Next, in the nitriding heat treatment step S2, a nitriding heat treatment is performed to allow nitrogen to penetrate into the surface region of the prepared starting material plate. The nitriding heat treatment in the present invention comprises a nitriding step S2a, in which heating is performed while controlling the nitriding potential within a predetermined range, and a cooling step S2b, in which the cooling rate is controlled while controlling the nitriding potential within a predetermined range. The most significant feature of the manufacturing method according to the present invention lies in the nitriding heat treatment step S2.

[0048] In the nitriding step S2a, nitrogen is allowed to intrude and diffuse until a desired N concentration is reached in a predetermined ammonia atmosphere at a temperature of 500°C or higher (e.g., in the austenite phase (γ phase) formation temperature range). As the ammonia atmosphere, a mixed gas of NH3 gas and N2 gas, a mixed gas of NH3 gas and Ar gas, or a mixed gas of NH3 gas and H2 gas can be preferably used.

[0049] In addition, the nitriding potential in the nitriding heat treatment step S2 is controlled within a predetermined range. NH3 and hydrogen partial pressure P H2 The nitriding potential K N Defined as “K N =P NH3 / P H2 3 / 2 ”, to become “0.001atm -1 / 2 ≤K N ≤10atm -1 / 2 "The NH3 gas flow rate, carrier gas (N2 gas, Ar gas, H2 gas) flow rate, and total pressure in the heat treatment furnace are controlled in a manner. Preferably, the total pressure in the heat treatment furnace is above 0.4 atm.

[0050] The introduction of NH3 gas is preferably carried out after the temperature reaches 500°C or above. This is because if NH3 gas is actively introduced in the stable temperature range of the ferrite phase (α phase) (increasing K N ), then the desired tetragonal structure of iron nitride phase (Fe8N phase (α' phase) and / or Fe 16 Compared with the N2 phase (α” phase), it is easier to generate undesirable iron nitride phases (such as Fe4N phase (γ’ phase) and Fe3N phase (ε phase)).

[0051] By adjusting the temperature, time and K in the nitriding process S2a N By controlling the thickness and nitrogen concentration of the surface region (high nitrogen concentration layer) where nitrogen invades and diffuses, the soft magnetic iron alloy plate as a whole contains nitrogen at a level of 0.1 atomic % to 11 atomic %. The average nitrogen concentration in the surface region, which serves as the high nitrogen concentration layer, is preferably 1 atomic % to 15 atomic %, and more preferably 2 atomic % to 11 atomic %.

[0052] The thickness of the surface region (high N concentration layer) is preferably controlled to be 1% to 30% of the thickness of the plate from both main surfaces. In other words, the inner region of the plate is preferably a low N concentration layer (average N concentration <1 atomic %) where nitrogen does not penetrate or diffuse, and more preferably, the average N concentration is 0.5 atomic % or less.

[0053] As for the tetragonal iron nitride martensite (α' phase and / or α" phase) generated in the subsequent cooling process S2b, the lattice strain caused by the invasion of nitrogen atoms helps to improve Bs. On the other hand, the α' phase and α" phase also have the weakness that Pi is easily increased due to the increase in magnetocrystalline anisotropy. In this regard, the iron alloy plate of the present invention is able to suppress the increase in Pi of the entire iron alloy plate by setting the internal region to a ferrite phase (α phase) with a low N concentration.

[0054] Furthermore, it is preferred that a portion of the surface region (high N concentration layer) forms a nitrogen concentration transition region (average concentration gradient of 0.1 atomic % / μm to 10 atomic % / μm) in which the N concentration decreases as it approaches the inner region (low N concentration layer). Forming the N concentration gradient facilitates the propagation of the magnetization state (magnetic domain, magnetization) in the high N concentration α' phase and / or α" phase to the low N concentration α phase. As a result, the overall coercive force decreases, contributing to a reduction in Pi.

[0055] In the nitriding process S2a, nitrogen is allowed to penetrate and diffuse until the desired N concentration is reached. N In the cooling process S2b, the steel is rapidly cooled to below 100°C while in a state of being cooled. The cooling rate at this time is preferably 100°C / s or higher, more preferably 200°C / s or higher, and even more preferably 400°C / s or higher. This generates the desired tetragonal iron nitride martensite. If the cooling rate is lower than 100°C / s, the undesirable iron nitride phase is likely to form.

[0056] In addition, when K is not maintained N When the cooling process S2b is carried out in the state of , a denitrification phenomenon occurs in which nitrogen that has invaded the surface area is separated, and the formation of the iron nitride phase itself becomes difficult.

[0057] The cooling process S2b can transform most of the austenite phase (γ phase) into martensite, but some γ phase (retained γ phase) may remain. The γ phase is non-magnetic, so from the perspective of magnetic properties, the volume fraction of the retained γ phase is preferably 5% or less.

[0058] Therefore, in order to transform the retained γ phase into martensite, it is preferable to perform a low-temperature treatment step S3 of cooling to 0°C or below (for example, ordinary low-temperature treatment using dry ice or ultra-low-temperature treatment using liquid nitrogen) after the cooling process S2b.

[0059] Although not an essential step, in order to impart toughness to the soft magnetic iron alloy plate, a tempering step S4 at 100°C or higher and 210°C or lower may be further performed after the low temperature treatment step S3 (in the Figure 1 (not shown in the figure).

[0060] As described above, by allowing nitrogen to penetrate and diffuse only into the surface region of a sheet material containing Fe as the main component and 30 atomic percent or less of Co, followed by quenching, a composite material is obtained in which the surface region is a phase with high Bs and high mechanical strength, while the interior region is a phase with low magnetocrystalline anisotropy. As a result, the soft magnetic iron alloy sheet of the present invention exhibits high Bs, low Pi, and high mechanical strength.

[0061] Example

[0062] The present invention is further described in detail below through various experiments, but the present invention is not limited to the configurations and structures described in these experiments.

[0063] [Experiment 1]

[0064] (Preparation of Starting Material 1)

[0065] Commercially available pure metal raw materials (Fe and Co, each with a purity of 99.9%) were mixed and prepared using an arc melting method on a water-cooled copper hearth (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, remelting was repeated six times while the sample was turned over. The resulting alloy ingot was then stamped and rolled to prepare an 80 atomic % Fe-20 atomic % Co alloy plate (thickness = 0.07-0.09 mm), which served as starting material 1.

[0066] [Experiment 2]

[0067] (Preparation of Soft Magnetic Iron Alloy Sheets of Example 1 and Comparative Examples 1 and 2)

[0068] Three nitriding heat treatments with different cooling processes were performed on the starting material 1 prepared in Experiment 1. During the nitriding process, NH3 gas was introduced at a temperature of 500°C and the total pressure was 0.8 atm and the nitriding potential was ≈ 4 atm. -1 / 2 The reaction was carried out in an NH3 gas atmosphere at 500°C for 2 hours and then at 900°C for 1 hour.

[0069] Cooling process 1: After the nitriding process, the NH3 gas atmosphere (total pressure = 0.8atm, nitriding potential ≈ 4atm) is maintained. -1 / 2) state, the specimen was placed in room temperature (20°C) water for water quenching / water quenching (average cooling rate ≈ 400°C / s). The NH3 gas atmosphere was then replaced with an N2 gas atmosphere, and within 5 minutes of the start of the quenching (the beginning of the cooling process), the specimen was immersed in liquid nitrogen for cryogenic treatment to transform the retained γ phase into martensite. This specimen was designated as Example 1.

[0070] Cooling process 2: At 900°C, the NH3 gas atmosphere is replaced with an N2 gas atmosphere, and then the test piece is plunged into room temperature (20°C) water for water rapid cooling / water quenching (average cooling rate ≈ 400°C / s). Then, while maintaining the N2 gas atmosphere, the test piece is immersed in liquid nitrogen for ultra-low temperature treatment within 5 minutes from the start of rapid cooling (start of the cooling process) to transform the retained γ phase into a martensite structure. Cooling process 2 is a process in which the atmosphere during cooling is different from that in cooling process 1. This sample is referred to as Comparative Example 1.

[0071] Cooling process 3: After holding at 900°C for 1 hour during the nitriding process, the specimen was subjected to gas quenching / gas quenching (average cooling rate ≈ 80°C / s) by blowing N2 gas at room temperature (20°C) into the specimen. Then, while maintaining the N2 gas atmosphere, the specimen was immersed in liquid nitrogen for a cryogenic treatment within 5 minutes from the start of the quenching (the start of the cooling process) to transform the retained γ phase into martensite. The cooling rate of Cooling process 3 was different from that of Cooling process 1. This specimen was designated as Comparative Example 2.

[0072] [Experiment 3]

[0073] (Structure Investigation of Soft Magnetic Iron Alloy Sheets of Example 1 and Comparative Examples 1 and 2)

[0074] The cross sections of the soft magnetic iron alloy plate samples prepared in Experiment 2 (Example 1 and Comparative Examples 1 and 2) were subjected to quantitative analysis of N concentration in the plate thickness direction using an electron probe analyzer (JXA-8800RL, manufactured by JEOL Ltd., spot diameter 2 μm).

[0075] In addition, wide-angle X-ray diffraction (WAXD) using Cu-Kα radiation was performed on the surface of the soft magnetic iron alloy plate samples (Example 1 and Comparative Examples 1-2) to identify the detected phase. The X-ray diffraction apparatus used was Rint-Ultima III manufactured by Rigaku Corporation. The results are shown in FIG. Figures 2A to 2C .

[0076] Figure 2A These are the results of quantitative analysis of the N concentration in the thickness direction of the cross section of Example 1 and the X-ray diffraction pattern of the surface of Example 1.

[0077] like Figure 2AAs shown, in Example 1, quantitative analysis of N concentration through the thickness direction confirmed the formation of a high N concentration layer in the surface region, a low N concentration layer in the interior region, and a N concentration transition region in part of the surface region. Furthermore, the surface XRD pattern confirmed that the α phase (ferrite phase) was the main phase, with the α' phase (tetragonal iron nitride martensite) also forming.

[0078] The γ phase (austenite phase) and γ' phase (Fe4N phase) were hardly detected.

[0079] This suggests that the nitriding process forms a high-N concentration layer in the surface region, and the cooling process generates the α' phase, while the low-temperature treatment virtually eliminates any residual γ phase. Furthermore, since the XRD pattern shows the α phase as the primary phase, it is believed that the high-N concentration layer in the surface region is not entirely converted to the α' phase, but rather a mixed phase of α and α' phases.

[0080] Figure 2B The figures show the results of quantitative analysis of the N concentration in the thickness direction of the cross section of Comparative Example 1 and the X-ray diffraction pattern of the surface of Comparative Example 1.

[0081] like Figure 2B As shown, in Comparative Example 1, quantitative analysis of the N concentration in the plate thickness direction confirmed that no high N concentration layer was formed in the surface region, and a low N concentration layer was formed throughout the plate thickness direction. In addition, only the α phase was confirmed from the surface XRD pattern.

[0082] This confirmed that if the atmosphere during the cooling process deviates from the conditions of the present invention, denitrification occurs and the high N concentration layer in the surface region cannot be maintained.

[0083] Figure 2C The figures show the results of quantitative analysis of the N concentration in the thickness direction of the cross section of Comparative Example 2 and the X-ray diffraction pattern of the surface of Comparative Example 2.

[0084] like Figure 2C As shown, in Comparative Example 2, quantitative analysis of N concentration in the thickness direction confirmed that, similar to Example 1, a high N concentration layer was formed in the surface region, a low N concentration layer was present in the interior region, and a N concentration transition region was formed in part of the surface region. However, the XRD pattern of the surface confirmed peaks of the α phase and the γ' phase (Fe4N phase), but no peak of the α' phase was detected.

[0085] From the above, it is believed that if the cooling rate during the cooling process deviates from the conditions of the present invention, the α' phase due to martensitic transformation is not produced, but the γ' phase closer to the thermal equilibrium state is produced.

[0086] [Experiment 4]

[0087] (Preparation of Soft Magnetic Iron Alloy Plate of Example 2)

[0088] The test material of the starting material 1 prepared in Experiment 1 was subjected to a nitriding heat treatment different from that of Experiment 2. In the nitriding process, NH3 gas was introduced at a stage of reaching 1000°C, and the total pressure was 0.8 atm and the nitriding potential was ≈ 4.3 atm. -1 / 2 The NH3 gas atmosphere was maintained at 1000 ° C for 2 hours. In addition, the NH3 gas atmosphere was set to a total pressure of 0.8 atm and a nitriding potential of 4.3 atm. -1 / 2 The cooling process was otherwise carried out in the same manner as in the cooling process 1 of Experiment 2. This sample was designated as Example 2.

[0089] (Structure Investigation of Soft Magnetic Iron Alloy Plate of Example 2)

[0090] Similar to Experiment 3, quantitative analysis of N concentration in the thickness direction of Example 2 was performed using EPMA on the cross section, and identification of the detected phases on the surface of Example 2 was performed using XRD. Figure 3 .

[0091] Figure 3 These are the results of quantitative analysis of the N concentration in the thickness direction of the cross section of Example 2 and the X-ray diffraction pattern of the surface of Example 2.

[0092] like Figure 3 As shown, in Example 2, similar to Example 1, a high N concentration layer was observed in the surface region, a low N concentration layer was observed in the interior region, and an N concentration transition region was observed in a portion of the surface region. Furthermore, the XRD pattern of the surface confirmed that the α phase was the main phase, with the α' phase also forming.

[0093] Based on the results of Experiments 2 to 4, it was confirmed that for the manufacturing method of the soft magnetic iron alloy plate involved in the present invention, the nitriding process S2a (the process of controlling the nitriding potential within a specified range and heating) and the cooling process S2b (the process of controlling the nitriding potential within a specified range and controlling the cooling rate) in the nitriding heat treatment step S2 are key points.

[0094] [Experiment 5]

[0095] (Preparation of Soft Magnetic Iron Alloy Plate of Comparative Example 3)

[0096] Prepare a commercially available electromagnetic pure iron plate (thickness = 0.1 mm). In the nitriding heat treatment, NH3 gas is introduced at the stage of reaching 750°C during the nitriding process, and the total pressure = 1 atm and the NH3 partial pressure P NH3 =1×10 4 Pa and N2 partial pressure P N2=2×10 4 The reaction was carried out in a NH3 gas atmosphere at 750°C for 5 hours.

[0097] During the cooling process, the specimen was oil-quenched by immersing it in 60°C oil while maintaining the same NH3 gas atmosphere. The NH3 gas atmosphere was then replaced with an N2 gas atmosphere, and the specimen was immersed in liquid nitrogen for a period of 5 minutes from the start of rapid cooling (the beginning of the cooling process) to undergo cryogenic treatment, transforming the retained γ phase into martensite. This specimen is designated Comparative Example 3.

[0098] (Structure Investigation of Soft Magnetic Iron Alloy Plate of Comparative Example 3)

[0099] Similar to Experiment 3, quantitative analysis of N concentration in the thickness direction of the cross section of Comparative Example 3 was performed using EPMA. The results are shown in Figure 4 .

[0100] Figure 4 These are the results of a quantitative analysis of the N concentration in the thickness direction of a cross section of Comparative Example 3. In Comparative Example 3, a high N concentration layer was uniformly formed along the thickness direction, with no low N concentration layer or N concentration transition layer. This is believed to be due to the absence of Co, a component that inhibits N intrusion and diffusion, in Comparative Example 3.

[0101] [Experiment 6]

[0102] (Investigation of Properties of Soft Magnetic Iron Alloy Sheets of Examples 1 and 2 and Comparative Examples 1 to 4)

[0103] The properties of the various soft magnetic iron alloy plates thus produced were investigated. As a benchmark for the properties, starting material 1 (a sample not subjected to nitriding heat treatment) was used as Comparative Example 4.

[0104] As magnetic properties, the saturation magnetic flux density Bs and iron loss Pi were measured. Using a vibrating sample magnetometer (RIKEN DONGXING CO., LTD. BHV-525H), the magnetization (unit: emu) of the sample was measured 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, using a BH loop analyzer (IFG Co., Ltd., IF-BH550) and the H coil method of a longitudinal yoke single plate tester, 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. -1.0 / 400 (Unit: W / kg).

[0105] As mechanical properties, the tensile strength of some samples was measured using a universal material testing machine.

[0106] Furthermore, the Vickers hardness (Hv) of the sample surface was measured using a micro Vickers hardness tester (AMT-X7AFS, manufactured by Matsuzawa Co., Ltd.) (load: 25 gf, holding time: 20 seconds, average of 5-point measurements).

[0107] In the Vickers hardness test, commercially available non-oriented electrical steel sheets and Permanent alloy sheets were separately prepared as comparative samples.

[0108] Table 1 shows the results of magnetic properties and tensile strength.

[0109] [Table 1]

[0110] Table 1 Magnetic and mechanical properties of Examples 1 to 2 and Comparative Example 14

[0111]

[0112] As shown in Table 1, Examples 1 to 2 according to the present invention showed higher Bs than Comparative Examples 1 to 4. Although the Co content was less than half of that of the Perminder alloy, it was confirmed that the Bs was still as high as that of the Perminder alloy. -1.0 / 400 Examples 1 and 2 also had almost no adverse effects caused by the high N concentration layer and showed iron losses that were approximately equivalent to those of the electromagnetic pure iron plate.

[0113] The tensile strength of Example 2, which has nitrided iron martensite in the surface region, was significantly improved compared to Comparative Example 4, which did not undergo nitriding heat treatment. Furthermore, the Vickers hardness of Example 2 was 218 Hv. This confirms that the soft magnetic iron alloy sheet of the present invention has a hardness comparable to that of commercially available non-oriented electrical steel sheets and permanganate alloy sheets, and is therefore believed to exhibit workability comparable to that of existing materials.

[0114] The above-described embodiments and experiments are provided to facilitate understanding of the present invention, and the present invention is not limited to the specific configurations described. For example, a portion of the configurations of the embodiments may be replaced with configurations common to those skilled in the art, or a configuration common to those skilled in the art may be added to the configurations of the embodiments. In other words, the present invention may delete, replace, or add other configurations to the configurations of the embodiments and experiments described herein without departing from the technical concept of the invention.

Claims

1. A soft magnetic iron alloy plate, characterized in that: having a chemical composition comprising 3 atomic % to 30 atomic % of cobalt, 0.1 atomic % to 11 atomic % of nitrogen, 0 atomic % to 1.2 atomic % of vanadium, with the balance being iron and impurities, The soft magnetic iron alloy plate has, in the thickness direction, a surface region having an average nitrogen concentration of 1 atomic % or more and 15 atomic % or less, and an inner region having an average nitrogen concentration lower than that of the surface region. The surface layer region has a thickness of 1% to 30% of the soft magnetic iron alloy plate from both main surfaces, and contains a ferrite phase and a tetragonal iron nitride martensite, with an austenite phase of 5% by volume or less.

2. The soft magnetic iron alloy plate according to claim 1, characterized in that The average nitrogen concentration of the surface region is higher than the average nitrogen concentration of the inner region by 0.5 atomic % or more.

3. The soft magnetic iron alloy plate according to claim 2, characterized in that In the inner region, a ferrite phase with a cubic crystal structure is a main phase.

4. The soft magnetic iron alloy plate according to claim 2, characterized in that The average nitrogen concentration of the inner region is less than 1 atomic %.

5. The soft magnetic iron alloy plate according to claim 3, characterized in that The average nitrogen concentration of the inner region is less than 1 atomic %.

6. The soft magnetic iron alloy plate according to any one of claims 1 to 5, characterized in that The saturation magnetic flux density of the soft magnetic iron alloy plate is 2.3T or more, The iron loss at a magnetic flux density of 1.0 T and 400 Hz is less than 50 W / kg.

7. A method for producing a soft magnetic iron alloy plate, which is the method for producing a soft magnetic iron alloy plate according to any one of claims 1 to 5, characterized in that: have: a starting material preparation step of preparing a starting material, wherein the starting material comprises a soft magnetic material having iron as a main component and containing 30 atomic % or less of cobalt, and having a thickness of 0.01 mm or more and 1 mm or less; a nitriding heat treatment step, wherein the starting material is heated and quenched in a predetermined ammonia atmosphere to allow nitrogen to infiltrate and diffuse into a surface region of the starting material at a concentration of 1 atomic % to 15 atomic %; and A low temperature treatment step, wherein the starting material after the nitriding heat treatment step is cooled to below 0°C, The nitriding heat treatment process includes: a nitriding process of heating the starting material while controlling the nitriding potential in the atmosphere within a predetermined range; and a cooling process of rapidly cooling the starting material to below 100° C. at a cooling rate of 100° C. / s or more while controlling the nitriding potential in the atmosphere within a predetermined range.

8. The method for producing a soft magnetic iron alloy plate according to claim 7, wherein: The nitriding potential K N The ammonia partial pressure P in the ammonia atmosphere NH3 and hydrogen partial pressure P H2 Defined as "K N =P NH3 / P H2 3 / 2 ”, to become "0.001atm -1 / 2 ≤K N ≤10atm -1 / 2 " to control.

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