Steel material treatment method and electromagnetic steel sheet

Abstract

An electromagnetic steel sheet in which Al is appropriately diffused is manufactured at a relatively low cost. Disclosed is a steel material treatment method for performing diffusion treatment in an oxidizing atmosphere on a steel material for an electromagnetic steel sheet having an aluminum-containing layer formed on the surface thereof. It is preferable that the steel material contains Si in an amount of more than 0.00 mass% but 7.00 mass% or less and Al in an amount of more than 0.00 mass% but 2.00 mass% or less. The aluminum-containing layer is preferably in the form of a plating layer having a thickness of 2 [mu] m or more and 30 [mu] m or less, and the composition of the plating layer contains Al, and may further contain Fe or the like. The diffusion treatment is preferably performed under treatment conditions such that a gradient in which the Al concentration gradually decreases from the surface of the steel material toward the inside can be obtained.

Description

Technical Field

[0001] The invention relates to a steel material processing method and an electromagnetic steel plate. Background Art

[0002] There is a known technology for reducing the loss of an electromagnetic steel sheet by forming a coating on the surface of the electromagnetic steel sheet through an aluminizing treatment (hot dip aluminizing treatment) and then forming a state in which the Al concentration is inclined from the surface through a subsequent diffusion treatment in a non-oxidizing atmosphere (see, for example, Patent Documents 1 and 2).

[0003] In addition, there is also known a technology for reducing the loss of the electromagnetic steel sheet by coating the surface of the electromagnetic steel sheet with a slurry containing Al and then performing a diffusion treatment in a non-oxidizing atmosphere to form a state where the Al concentration is inclined from the surface (see, for example, Patent Document 3).

[0004] In addition, there is also known a technology that forms a plating layer on the surface of an electromagnetic steel sheet by an aluminizing treatment, and then infiltrates Al by a subsequent high-temperature and long-term diffusion treatment in an oxidizing atmosphere to achieve a directional electromagnetic steel sheet with an increased Al concentration, thereby seeking to reduce the loss of the electromagnetic steel sheet (see, for example, Patent Document 4). Patent Literature

[0005] Patent Document 1: German Patent Invention No. 102005004037 Patent Document 2: European Patent Application Publication No. 1260598 Patent Document 3: International Publication No. 2021 / 155280 Patent Document 4: Japanese Patent Application No. 2018-509522 Summary of the invention

[0006] However, in the conventional technology as described above, it is difficult to manufacture an electromagnetic steel sheet in which Al is appropriately diffused at a relatively low cost.

[0007] Therefore, in one aspect, an object of the present invention is to manufacture an electromagnetic steel sheet in which Al is appropriately diffused at a relatively low cost.

[0008] In one embodiment, a method for treating a steel material is provided for subjecting a steel material for an electromagnetic steel sheet having an aluminum-containing layer formed on its surface to diffusion treatment in an oxidizing atmosphere.

[0009] In one aspect, according to the present invention, an electromagnetic steel sheet in which Al is appropriately diffused can be manufactured at a relatively low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a flow chart schematically showing the flow of each step included in the steel material processing method according to the present embodiment. Figure 2 This is a diagram schematically showing the cross-sectional structure of a steel material obtained by an aluminizing treatment. Figure 3 This is a diagram schematically showing the cross-sectional structure of a steel material obtained by diffusion treatment. Figure 4 This is an explanatory diagram of a desired diffusion form of aluminum, and is also a diagram showing an example of the diffusion form of aluminum in a steel material obtained by the steel material processing method according to the present embodiment. Figure 5 This is a flow chart schematically showing the flow of each step included in the steel material processing method of Comparative Example 1. Figure 6 This is a flow chart schematically showing the flow of each step included in a steel material processing method according to another comparative example. Figure 7 This is a diagram schematically showing the Al concentration curve of the steel material obtained in Comparative Example 2. Figure 8 This is a diagram for explaining the calculation method of the Al infiltration amount (Part 1). Fig. 9 This is an explanatory diagram of the calculation method of the Al infiltration amount (Part 2). Fig.10 A graph showing the relationship between Al gradient thickness ratio × (Al penetration thickness ratio) ^ 0.5 and the magnetic flux density reduction rate. Fig.11 A graph showing the relationship between the Al penetration amount and the plate thickness ratio and the magnetic flux density reduction rate. DETAILED DESCRIPTION

[0011] Hereinafter, each embodiment will be described in detail with reference to the accompanying drawings. It should be noted that the dimensional ratios in the accompanying drawings are only examples and have no limiting effect. In addition, for the convenience of description, the shapes in the accompanying drawings may be partially exaggerated. In addition, in the following description, various substances are sometimes specifically referred to using commonly known abbreviations or chemical symbols, such as aluminum being referred to as aluminum (or Al).

[0012] Figure 1 This is a flow chart schematically showing the flow of each step included in the steel material processing method according to the present embodiment. Figure 2 This is a diagram schematically showing the cross-sectional structure of a steel material obtained by an aluminizing treatment (aluminizing steel material).

[0013] The steel material processing method of the present embodiment first includes a process of preparing a steel material (parent material) of a desired plate thickness (step S100). The steel material of the desired plate thickness can be obtained, for example, by rolling a material obtained by casting or the like (for example, a steel slab or even a steel billet). The desired plate thickness is any thickness, but preferably, it can also be substantially the same as the thickness of the final product (for example, an electromagnetic steel sheet) manufactured by this method. In this case, the rolling process after the subsequent aluminizing process is not required, which can reduce the manufacturing cost.

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

[0015] In the present embodiment, the steel material is used for the electromagnetic steel sheet, preferably containing Si and Al. This is because if Si and Al are added to the steel material, the crystal magnetic anisotropy is reduced and the hysteresis loss is reduced. In addition, it is also because the addition of Si and Al increases the electrical resistance of the steel material, which helps to reduce the eddy current loss. Therefore, the addition of Si and Al is related to the reduction of the iron loss (hysteresis loss and eddy current loss) of the steel material. On the other hand, if Si and Al are added excessively, not only the magnetic flux density will be reduced, but also the processability in the manufacturing process (rolling, stamping, etc.) of the steel material will be reduced. It should be noted that in order to form the rotor core, stator core, etc. of the rotating electric machine, as a final product, for example, the electromagnetic steel sheet can be formed into a desired shape by stamping, etc. In view of the above-mentioned contradictory matters, the steel material (parent material) preferably contains Si in a range of greater than 0.00 mass% and less than 7.00 mass%, and Al in a range of greater than 0.00 mass% and less than 2.00 mass%.

[0016] Next, the steel material processing method of this embodiment includes forming an aluminum-containing layer on the steel material (see Figure 2 The aluminum-containing layer may be formed by, for example, aluminizing. For example, the aluminum-containing layer is in the form of a plating layer having a thickness in the range of 2 μm to 30 μm. For example, a plating layer having a thickness in the range of 2 μm to 30 μm may be formed by gas wiping or the like.

[0017] It should be noted that in a modified example, an aluminum-containing layer may be formed by applying an aluminum-containing slurry instead of aluminizing. However, applying an aluminum-containing slurry is disadvantageous in that it is difficult for Al to penetrate into the steel sheet in the subsequent diffusion treatment.

[0018] In the case of an aluminum-containing layer formed by, for example, sputtering, the composition of the aluminum-containing layer (plating) may be aluminum alone. Alternatively, the composition of the aluminum-containing layer (plating) is to contain one or more of iron (Fe), silicon (Si), and manganese (Mn) on the basis of aluminum. Preferably, Al, Fe, and Si are contained. For example, in the plating, Al in the range of 20 mass % or more and 100 mass % or less, Fe in the range of 0.00 mass % or more and 80 mass % or less, and Si in the range of 0.00 mass % or more and 15 mass % or less may be contained. It should be noted that the plating may be a single layer or a multilayer.

[0019] It should be noted that in the steel material processing method of the present embodiment, by preparing a steel material of a desired plate thickness in the above-mentioned manner, the necessity of performing a treatment to reduce the plate thickness of the steel material having an aluminum-containing layer by rolling or the like as a pretreatment before the subsequent diffusion treatment process can be eliminated or reduced. However, in a modified example, the steel material having an aluminum-containing layer may be subjected to a treatment to reduce the plate thickness by rolling or the like.

[0020] Next, the steel material processing method of the present embodiment includes a diffusion treatment step of performing a diffusion treatment in an oxidizing atmosphere on the steel material having the aluminum-containing layer formed thereon (step S104 ).

[0021] The diffusion treatment is a treatment for forming a state in which the Al concentration is inclined from the surface of the steel material based on the Al contained in the aluminum-containing layer. That is, the diffusion treatment is to form an Al diffusion layer by diffusing the Al contained in the aluminum-containing layer from the surface of the steel material in the thickness direction (see Figure 3 The Al diffusion layer has an Al concentration inclination (variation gradient) in such a way that the Al concentration increases as it approaches the surface side in the thickness direction, which will be referred to later. Figure 4 Provide explanation.

[0022] In addition, in this embodiment, the diffusion treatment in an oxidizing atmosphere can also form an insulating film on the surface of the steel material (see Figure 3 Symbol 30). That is, the diffusion treatment in an oxidizing atmosphere is to oxidize the aluminum-containing layer on the surface of the steel material to form an oxide layer as an insulating coating on the surface of the steel material. At this time, an oxide layer based on aluminum and iron contained in the aluminum-containing layer and oxygen contained in the oxidizing atmosphere is formed simultaneously with the Al diffusion layer. The oxide layer is a single oxide or a composite oxide of Al, Fe, Si, and Mn, but it may also contain other elements depending on the components contained in the aluminum-containing layer. For example, the oxide layer may contain 20 to 80% by mass of Al or Fe. As a result, the formation of the desired oxide layer described later will become easy.

[0023] The "oxidizing atmosphere" described in this specification is a general term, and in essence, it is a concept that excludes an atmosphere that does not substantially contain oxygen, and is also a concept that includes reactions that are carried out in air. Therefore, in this embodiment, a vacuum device is not required. That is, the manufacturing cost can be reduced. In addition, continuous processing can be performed, and the manufacturing efficiency can be improved.

[0024] The diffusion treatment may be performed under predetermined temperature conditions and for a predetermined treatment time (hereinafter also referred to as “diffusion time”).

[0025] Here, if the diffusion temperature is too low, not only does it take time to form the oxide layer, infiltrate and diffuse Al, but the desired oxide layer cannot be obtained. In this case, sufficient insulation cannot be obtained. In addition, on the contrary, even if the diffusion temperature is too high, the desired oxide layer cannot be obtained. In addition, if the diffusion time is too short or too long, the desired diffusion form of aluminum described later cannot be obtained.

[0026] Therefore, considering the above-mentioned conflicting matters, the diffusion treatment can be preferably performed at a temperature in the range of 900° C. to 1200° C. (hereinafter also referred to as “diffusion temperature”) and a diffusion time in the range of 0.1 minute to 1920 minutes. Thus, as described later, it is possible to easily form a desired oxide layer and realize a desired diffusion form of aluminum.

[0027] It should be noted that the details of the manufacturing conditions (temperature conditions, processing time) involved in the diffusion treatment can be adapted according to the thickness of the aluminum-containing layer obtained in step S102 (i.e., the plating thickness), etc., so that the desired oxide layer and the desired aluminum diffusion form (penetration amount, tilt state) can be obtained at the same time. It should be noted that the temperature condition is a concept that includes not only the diffusion temperature, but also the heating rate of heating to the diffusion temperature, the cooling rate of cooling from the diffusion temperature, etc.

[0028] The thickness of the desired oxide layer can be basically any thickness as long as it functions as an insulating coating, but it is desirable that the thickness be as thin as possible. On the other hand, if the thickness of the oxide layer is too thick, the total magnetic flux of the steel material will decrease. In view of this, the thickness of the desired oxide layer is within the range of 1 μm or more and 25 μm or less.

[0029] The desired aluminum diffusion form can be basically any form as long as the Al diffusion layer has an inclination (gradient) of Al concentration, but the preferred ranges of various parameters will be referred to. Figure 4 This will be explained later.

[0030] Figure 41 is an explanatory diagram of a desired aluminum diffusion form, and is a schematic diagram of an example of the aluminum diffusion form in the steel obtained by the steel processing method of this embodiment. Figure 4 In the figure, a cross-sectional view of the steel is schematically shown on the upper side, and the diffusion form of aluminum in the thickness direction of the steel is shown on the lower side. It should be noted that the Al concentration curve of the steel in the thickness direction is used to show the diffusion form of aluminum in the steel, with the horizontal axis being the distance from the center of the steel plate thickness and the vertical axis being the Al concentration. It should be noted that the Al concentration curve of the steel in the thickness direction can be symmetrical about the center of the plate thickness. Figure 4 In the figure, d1 represents the thickness of the insulating film, and d2 represents the diffusion depth of Al. Figure 4 In FIG. 1 , α1 represents the Al concentration in the insulating film, and α2 represents the Al concentration at the surface of the Al diffusion layer.

[0031] like Figure 4 As shown, in this embodiment, the Al diffusion layer has an inclination (variation gradient) of Al concentration in a form where the Al concentration increases as it approaches the surface side in the thickness direction. Specifically, in the Al diffusion layer, the Al concentration is the largest at the surface of the Al diffusion layer (i.e., the boundary surface with the oxide layer) and gradually decreases toward the center of the plate thickness.

[0032] Here, if the Al concentration at the surface of the Al diffusion layer (hereinafter, also referred to as "surface Al concentration of the Al diffusion layer") is low, the above-mentioned iron loss reduction effect cannot be obtained, and if it is too high, as described above, there is a possibility of causing a decrease in magnetic flux density and a decrease in workability in the manufacturing process (rolling, stamping, etc.) of the steel material. In addition, as described above, if the Al diffusion depth is too shallow, the above-mentioned iron loss reduction effect cannot be obtained, and if it is too deep, there is a possibility of causing a decrease in magnetic flux density, etc., as described above.

[0033] Taking the above-mentioned conflicting matters into consideration, the surface Al concentration of the Al diffusion layer is preferably within a range of 1.50 mass % to 10.00 mass %. Next, refer to Figure 5 The effect of this embodiment is further explained by comparing it with the steel processing method of the comparative example.

[0034] Figure 5 This is a flow chart schematically showing the flow of each step included in the steel material processing method of Comparative Example 1.

[0035] The steel material processing method of Comparative Example 1 is the same as the steel material processing method of the present embodiment in terms of the preparation step (step S100 ) and the aluminum-containing layer forming step (step S102 ), but is different in terms of the subsequent steps.

[0036] Specifically, the steel material processing method of Comparative Example 1 includes a diffusion treatment step (step S104') of performing a diffusion treatment in a non-oxidizing atmosphere on the steel material on which the aluminum-containing layer is formed. The diffusion treatment conditions other than the atmosphere may be the same as those of the above-mentioned diffusion treatment step (step S104). Such a diffusion treatment in a non-oxidizing atmosphere is different from the diffusion treatment in an oxidizing atmosphere performed in the steel material processing method of the present embodiment, and since it is a non-oxidizing atmosphere, no oxide layer is formed.

[0037] Next, the steel material processing method of Comparative Example 1 includes a step of forming an insulating film on the steel material subjected to the diffusion treatment in the non-oxidizing atmosphere (step S106 ′). In this case, the insulating film may be a film different from the oxide layer.

[0038] In the above-mentioned Comparative Example 1, since the diffusion process is performed in a non-oxidizing atmosphere, a vacuum equipment is required.

[0039] In contrast, in this embodiment, as described above, by utilizing the diffusion process in an oxidizing atmosphere, vacuum equipment etc. is not required, and the manufacturing cost can be reduced. In addition, continuous processing can be performed, and the manufacturing efficiency can be improved.

[0040] Furthermore, in the above-mentioned Comparative Example 1, it is necessary to separately add a step for forming an insulating film after the diffusion process in the non-oxidizing atmosphere.

[0041] In contrast, in this embodiment, as described above, an oxide layer can be formed as an insulating film by diffusion processing in an oxidizing atmosphere. That is, diffusion processing in an oxidizing atmosphere is a process that can simultaneously obtain a desired oxide layer and a desired diffusion form of aluminum.

[0042] As described above, according to the steel material processing method of the present embodiment, it is possible to manufacture, at a relatively low cost, an electromagnetic steel sheet in which Al is appropriately diffused in a form having an inclination (variation gradient) in Al concentration.

[0043] Figure 6 This is a flow chart schematically showing the flow of each step included in a steel material processing method of another comparative example (hereinafter also referred to as “Comparative Example 2”).

[0044] The steel material processing method of Comparative Example 2 is the same as the steel material processing method of the present embodiment in terms of the preparation step (step S100 ) and the aluminum-containing layer forming step (step S102 ), but is different in terms of the subsequent steps.

[0045] Specifically, the steel material processing method of Comparative Example 2 includes a processing step (step S10") of performing a grain growth promotion treatment in an oxidizing atmosphere on the steel material having the aluminum-containing layer formed thereon. The grain growth promotion treatment differs from the diffusion treatment in an oxidizing atmosphere performed in the steel material processing method of the present embodiment in that the treatment is performed under such conditions that the Al concentration is diffused in a manner that becomes uniform inside the steel material. Specifically, the grain growth promotion treatment tends to have a significantly higher diffusion temperature and a significantly longer diffusion time than the diffusion treatment in an oxidizing atmosphere performed in the steel material processing method of the present embodiment.

[0046] Figure 7 This is a diagram schematically showing the Al concentration curve of the steel material obtained in Comparative Example 2 and the Al concentration curve of the steel material obtained in the present embodiment. Figure 4 Contrast with the figure on the lower side.

[0047] like Figure 7 As shown in FIG. 1 , the Al diffusion layer has approximately the same Al concentration at the surface of the Al diffusion layer and at the center of the steel plate thickness. That is, the Al concentration is approximately constant from the surface of the Al diffusion layer to the center of the steel plate thickness (see concentration α3). In such a steel, a sufficient iron loss reduction effect based on Al infiltration cannot be obtained.

[0048] In contrast, in the present embodiment, as described above, a steel material having a desired oxide layer and a desired aluminum diffusion form can be obtained without making the diffusion temperature too high or the diffusion time too long. That is, from the viewpoint of energy efficiency and manufacturing efficiency, an electromagnetic steel sheet having excellent characteristics that is less likely to cause problems such as a decrease in magnetic flux density can be efficiently manufactured.

[0049] As described above, according to the steel material processing method of the present embodiment, it is possible to manufacture, at a relatively low cost, an electromagnetic steel sheet in which Al is appropriately diffused in a form having an inclination (variation gradient) in Al concentration. Example

[0050] Next, several examples of steel materials actually processed by the inventors of the present application using the steel material processing method according to the present embodiment will be described.

[0051] The inventors of the present application prepared three types of steel materials (recorded as steel material types A, B, and C) having the component characteristics shown in Table 1 below, and after performing treatments based on the steel material treatment method of the present embodiment, the results shown in Table 2 were obtained. Specifically, in Example 1, a ring-shaped test piece having an outer diameter of 64 mm and an inner diameter of 50 mm was cut out from a steel plate having the chemical composition shown in Table 1 by laser, and the test piece was subjected to aluminizing treatment to obtain the coating thickness shown in Table 2. Then, after the aluminizing treatment, a diffusion treatment was performed under the conditions shown in Table 2. In Example 5, a single plate test piece was cut out from a steel plate having the chemical composition shown in Table 1 by laser, and the test piece was also subjected to aluminizing treatment to obtain the coating thickness shown in Table 2. Then, after the aluminizing treatment, a diffusion treatment was performed under the conditions shown in Table 2. It should be noted that although there are differences in the form of the test piece, such as a ring shape or a single plate (rectangular shape with a size of 20×50 mm), it has no substantial effect on the test results (for example, the iron loss reduction rate, the magnetic flux density reduction rate, etc.).

[0052] In addition, the conditions shown in Table 2 show whether annealing is performed or not. As the annealing condition, after holding at 750°C for 60 minutes, furnace cooling is performed, but any conditions may be used. Annealing affects the test results in terms of reducing the influence of cutting by laser (for example, increase in iron loss). It should be noted that when the steel plate is a steel plate for a rotor, annealing may not be performed.

[0053] It should be noted that the three types of steel (recorded as steel types A, B, and C) all contain 0 to 7.00 mass% Si, 0 to 1.00 mass% Mn, and 0 to 2.00 mass% Al. Although such a composition of the base material is preferred, it is not limited thereto. It should be noted that in Table 2, mass% represents mass%.

[0054] [Table 1]

[0055] [Table 2]

[0056] [Table 3]

[0057] [Table 4]

[0058] [Table 5] As a result, the results of Tables 3, 4 and 5 were obtained. Evaluation 1 involved in Tables 3 and 4 is an evaluation based on FE (Field Emission)-EPMA (Electron Probe Micro Analyzer) analysis. The Al concentration and Fe concentration involved in the oxide layer in Evaluation 1 may be the concentrations in the center or vicinity of the oxide layer. It should be noted that the Fe concentration tends to be higher on the surface side of the oxide layer. The iron loss of Evaluation 2 involved in Table 5 is the result of AC magnetic measurement, and the magnetic flux density of Evaluation 2 is the result of DC magnetic measurement. It should be noted that the diffusion depth to thickness ratio refers to the value of the diffusion depth divided by the thickness. In Table 5, the magnetic flux density represents the magnetic flux density (B50) at a magnetizing force of 5000 A / m, and the iron loss represents the iron loss (W10 / 400) at a frequency of 400 Hz and a magnetic flux density of 1.0 T. In addition, in Table 5, the iron loss reduction rate is the ratio obtained by dividing the reduction in iron loss compared to the untreated product by the iron loss of the untreated product.

[0059] From Evaluation 1 of Tables 3 and 4 and Evaluation 2 of Table 5, it can be seen that the iron loss reduction rate of each embodiment at a frequency of 400 Hz and a magnetic flux density of 1 T is greater than 0%, and the magnetic flux density reduction rate at 5 kA / m is less than 25%, obtaining good characteristics.

[0060] From the evaluation 1 of Tables 3 and 4 and the evaluation 2 of Table 5, it can be seen that in Example 3, since the diffusion depth to thickness ratio is too large, although the magnetic flux density reduction rate (relative to the reduction rate of the untreated product) becomes relatively large, it converges to less than 25%. On the other hand, in Comparative Example 1, since the surface Al concentration of the diffusion layer is too large, the magnetic flux density reduction rate becomes relatively large, exceeding 25%. According to the above evaluation results, in the steel material processing method of this embodiment, in order to suppress the amount of Al penetration, the coating thickness is preferably less than 50μm, more preferably less than 30μm (less than 20% of the plate thickness). In addition, it can be seen that the surface Al concentration of the diffusion layer is preferably less than 14.0 mass%, and more preferably less than 10.0 mass%.

[0061] As shown in Table 2, the atmosphere of Examples 6, 7 and Comparative Examples 2 and 3 is set to a low oxygen potential atmosphere instead of air. A low oxygen potential atmosphere is an atmosphere containing oxygen, hydrogen, and argon, and the oxygen concentration is significantly lower than that of air. Therefore, as shown in Evaluation 1 of Tables 3 and 4, the thickness of the oxide layer becomes relatively small. In order to ensure the necessary electrical insulation as an insulating coating, as described above, the thickness of the oxide layer is expected to be 1 μm or more. It should be noted that the oxide layer is a single layer or a multilayer, but in the case of a multilayer, it is expected to be 1 μm or more as a whole. The thicker the oxide layer, the smaller the iron loss can be expected to become (for example, referring to the significant difference between Comparative Examples 2 and 3 and Examples 8 and 9). As shown in Tables 3 and 4, the inventors of the present application used two evaluation parameters: Al infiltration thickness ratio (unit: mass %) and Al gradient thickness ratio × (Al infiltration thickness ratio) ^ 0.5 (unit: mass % ^ 1.5 / [μm] ^ 2). It should be noted that the symbol "^" in ^ 0.5 and ^ 2 represents exponentiation, for example, ^ 0.5 represents 0.5 power. It should be noted that the symbol "*" in Table 4 represents multiplication.

[0062] When the amount of aluminum infiltration in the Al diffusion layer (hereinafter also referred to as "Al infiltration amount") is calculated based on the aluminum diffusion depth and the aluminum concentration at the center of the base material plate thickness (hereinafter also referred to as "central Al concentration"), the Al infiltration amount plate thickness ratio is the value of the Al infiltration amount divided by the base material plate thickness. Specifically, in this test, the Al infiltration amount is calculated as follows based on the aluminum diffusion depth, the surface Al concentration, and the central Al concentration. When the aluminum diffusion depth is less than the base material thickness / 2, the amount of Al penetration = (surface Al concentration - center Al concentration) × aluminum diffusion depth × 1 / 2 In this case, the Al infiltration amount corresponds to Figure 8 The area of ​​the triangle shown by the dotted line is S11. Figure 8 As shown, the three vertices of the triangle correspond to the position of the surface Al concentration corresponding to the base material surface, the position of the central Al concentration corresponding to the base material surface, and the position of the central Al concentration corresponding to the inner side of the aluminum diffusion depth from the base material surface. When the aluminum diffusion depth is greater than or equal to the base material thickness / 2, the amount of Al penetration = (surface Al concentration + center Al concentration - base material Al concentration × 2) × aluminum diffusion depth × 1 / 2 In this case, the Al infiltration amount corresponds to Fig. 9 The area of ​​the trapezoid shown by the dotted line is S12. Fig. 9 As shown, the four vertices of the trapezoid correspond to the position corresponding to the surface of the base material and the surface Al concentration, the position corresponding to the surface of the base material and the base material Al concentration, the position corresponding to the inner side of the diffusion depth of aluminum from the base material surface and the central Al concentration, and the position corresponding to the inner side of the diffusion depth of aluminum from the base material surface and the base material Al concentration. The case where the aluminum diffusion depth ≥ the base material thickness / 2 corresponds to the case where the diffusion depth to thickness ratio in Table 3 is 0.50 or more. It should be noted that the base material Al concentration corresponds to the base material composition in Table 2 (see also Fig. 9 In addition, the base material thickness corresponds to the plate thickness in Table 2, which is the plate thickness after removing the thickness of the oxide layer from the whole.

[0063] The Al gradient thickness ratio is the change gradient of the aluminum concentration in the Al diffusion layer relative to the change in the thickness direction. The Al gradient thickness ratio is the value obtained by dividing the Al gradient by the base material thickness. Specifically, in this test, the Al gradient is calculated as follows. Al gradient = (surface Al concentration - central Al concentration) / aluminum diffusion depth It should be noted that the base plate thickness corresponds to the plate thickness in Table 2, which is the plate thickness after removing the thickness of the oxide layer from the entire plate. It should be noted that, similar to the above-mentioned Al infiltration amount to thickness ratio, when the aluminum diffusion depth ≥ base plate thickness / 2, the aluminum diffusion depth can be set to be the base plate thickness / 2.

[0064] Fig.10 The results of each embodiment and comparative example are plotted by taking Al gradient thickness ratio × (Al penetration thickness ratio)^0.5 as the horizontal axis and the magnetic flux density reduction rate as the vertical axis. Fig.10 The curves obtained by interpolating the above plotted points are also shown in FIG.

[0065] from Fig.10 It can be seen that if the Al gradient thickness ratio × (Al penetration thickness ratio) ^ 0.5 is less than 0.000400, the magnetic flux density reduction rate can be suppressed to less than about 25%. Fig.10 In the figure, two plotted points with a magnetic flux density reduction rate exceeding 25% correspond to Comparative Examples 1 and 4. Each plotted point with a magnetic flux density reduction rate within 25% corresponds to each Example.

[0066] Fig.11 The graph is obtained by plotting the results of each embodiment and comparative example with Al penetration amount to thickness ratio as the horizontal axis and magnetic flux density reduction rate as the vertical axis. Fig.11 The straight line obtained by interpolating the above plotted points is also shown in FIG.

[0067] from Fig.11 It is known that when the Al penetration amount to thickness ratio is 5.50 or less, the magnetic flux density reduction rate can be expected to be suppressed to about 25% or less. Fig.11 In the figure, the two plotted points with a magnetic flux density reduction rate exceeding 25% correspond to Comparative Examples 1 and 4. The plotted points with a magnetic flux density reduction rate of less than 25% correspond to the respective embodiments. The Al penetration amount to thickness ratio of the plotted points corresponding to Comparative Examples 1 and 4 is also less than 5.50, but referring to the example Fig.10 As mentioned above, since the condition of Al inclination gradient thickness ratio × (Al infiltration amount thickness ratio) ^ 0.5 being less than 0.000400 is not satisfied, it can be excluded by the above conditions.

[0068] Although each embodiment has been described in detail above, the present invention is not limited to a specific embodiment, and various modifications and changes can be made within the scope of the claims. In addition, all or a plurality of constituent elements of the above-described embodiments may be combined.

[0069] For example, in the above-mentioned embodiment, the diffusion treatment may be performed immediately after the Al-containing layer is formed, or after the Al-containing layer is formed and then subjected to processing such as stamping. In addition, the Al-containing layer may be formed by evaporation, sputtering, calorizing, shot peening, foil bonding, etc., in addition to aluminizing and slurry. Explanation of symbols

[0070] 20 ... aluminum-containing layer (aluminum-containing layer), 30 ... insulating film (oxide layer), 32 ... Al diffusion layer (aluminum diffusion layer).

Claims

1. A method for processing steel, wherein: A steel material for an electromagnetic steel sheet having an aluminum-containing layer formed on its surface is subjected to diffusion treatment in an oxidizing atmosphere.

2. The steel material processing method according to claim 1, wherein: The steel material before forming the aluminum-containing layer contains silicon (Si) in a range of greater than 0.00 mass % and less than 7.00 mass %, aluminum (Al) in a range of greater than 0.00 mass % and less than 2.00 mass %, and manganese (Mn) in a range of greater than 0.00 mass % and less than 1.00 mass %.

3. The steel material processing method according to claim 2, wherein: The aluminum-containing layer is in the form of a plated layer having a thickness in the range of 2 μm to 30 μm. The plating layer is composed of aluminum (Al), or in addition to aluminum (Al), contains at least one of iron (Fe), silicon (Si) and manganese (Mn).

4. The steel material processing method according to claim 2, wherein: The diffusion treatment is performed under treatment conditions that provide a gradient in which the aluminum concentration gradually decreases from the surface of the steel material toward the center of the plate thickness.

5. The steel material processing method according to claim 2, wherein: The diffusion treatment is performed at a temperature in a range of 900° C. to 1200° C. and for a time in a range of 0.1 minute to 1920 minutes.

6. The steel material processing method according to any one of claims 1 to 5, wherein: The diffusion process simultaneously forms an aluminum diffusion layer based on aluminum contained in the aluminum containing layer and an oxide layer based on aluminum contained in the aluminum containing layer and oxygen contained in the oxidizing atmosphere.

7. An electromagnetic steel sheet, comprising: an oxide layer, the oxide layer being an oxide layer forming an insulating coating on the surface of a base material and containing any one or more of aluminum, iron, silicon, and manganese; and An aluminum diffusion layer in which the aluminum concentration gradually decreases from the surface of the base material toward the center of the base material thickness.

8. The electromagnetic steel sheet according to claim 7, wherein: The oxide layer has a thickness in a range of 1 μm to 25 μm, and contains aluminum or iron in a range of 20 mass % to 80 mass %.

9. The electromagnetic steel sheet according to claim 7 or 8, wherein: When the change gradient of the aluminum concentration relative to the change in the thickness direction of the aluminum diffusion layer is taken as the Al gradient, and the value obtained by dividing the Al gradient by the base material thickness is taken as the Al gradient thickness ratio, Furthermore, when the amount of aluminum in the aluminum diffusion layer is calculated based on the aluminum diffusion depth in the aluminum diffusion layer and the aluminum concentrations at the base material surface and the base material plate thickness center, and the value obtained by dividing the amount of aluminum infiltration by the base material plate thickness is taken as the Al infiltration amount plate thickness ratio, Al gradient thickness ratio × (Al penetration thickness ratio) 1 / 2 In the range of greater than 0 and less than 0.000400.

10. The electromagnetic steel sheet according to claim 9, wherein: The Al infiltration amount to thickness ratio is within a range of greater than 0 and not more than 5.50.

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