WO2017170749A1 - 電磁鋼板およびその製造方法 - Google Patents
電磁鋼板およびその製造方法 Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
- C23C10/06—Solid state diffusion of only metal elements or silicon into metallic material surfaces using gases
- C23C10/08—Solid state diffusion of only metal elements or silicon into metallic material surfaces using gases only one element being diffused
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
- C21D8/1244—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest
- C21D8/1255—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties the heat treatment(s) being of interest with diffusion of elements, e.g. decarburising, nitriding
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C10/00—Solid state diffusion of only metal elements or silicon into metallic material surfaces
- C23C10/60—After-treatment
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/147—Alloys characterised by their composition
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/12—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials
- H01F1/14—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of soft-magnetic materials metals or alloys
- H01F1/147—Alloys characterised by their composition
- H01F1/14766—Fe-Si based alloys
- H01F1/14775—Fe-Si based alloys in the form of sheets
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/001—Austenite
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D2211/00—Microstructure comprising significant phases
- C21D2211/005—Ferrite
Definitions
- the present invention relates to an electromagnetic steel sheet used for iron core materials such as a high frequency transformer, a reactor, and a motor for power electronics, and a method for manufacturing the same.
- the iron loss of magnetic steel sheets consists of hysteresis loss that strongly depends on precipitates, crystal grain size, texture, etc. in steel, and eddy current loss that strongly depends on plate thickness, specific resistance, magnetic domain structure, and the like.
- General magnetic steel sheet increases crystal grain growth and reduces history loss by reducing impurities in the steel as much as possible.
- the ratio of hysteresis loss is large in the iron loss of electrical steel sheets.
- the hysteresis loss increases in proportion to the frequency
- the eddy current loss increases in proportion to the square of the frequency. Therefore, when the frequency is higher than several kHz, the ratio of the eddy current loss is increased.
- elements such as Si and Al, which are thinner than the conventional general electrical steel sheet thickness of 0.3 to 0.5 mm, that is, to reduce the sheet thickness to 0.2 mm or less, or to increase the specific resistance of the steel, are added. Attempts have been made to reduce eddy current losses by increasing the amount. Recently, not only automobiles and air conditioners but also new energy fields such as solar power generation, switching elements of several kHz to 50 kHz have been used in relatively large-capacity power supplies, and iron cores with lower high-frequency iron loss. There is a need for materials.
- ultra-thin electromagnetic steel sheets with a thickness of 0.1 mm or less, high-Si electromagnetic steel sheets, or powder magnetic cores obtained by solidifying iron powder are applied to such power supply fields.
- Mn-Zn ferrite having a specific resistance several orders of magnitude higher than that of metallic soft magnetic materials is used.
- the ultra-thin electrical steel sheet cannot be said to have a sufficiently low eddy current loss even if the plate thickness is 0.1 mm.
- high-Si electrical steel sheets having a Si concentration exceeding 4% by mass are hard and brittle and are not easy to manufacture.
- the dust core has a remarkably large hysteresis loss as compared with the magnetic steel sheet, so that the iron loss is greatly deteriorated at a frequency of several kHz.
- Mn-Zn ferrite has extremely small eddy current loss, but the saturation magnetic flux density is 0.5T at most, which is very low compared with 2.0T of a general electromagnetic steel sheet.
- Patent Document 1 discloses a method for producing a 6.5 mass% Si steel sheet by a siliconization method.
- This technology is a process for increasing the Si concentration in steel by reacting a 3% by mass Si steel sheet having a thickness of 0.05 to 0.3 mm with silicon tetrachloride gas at a high temperature.
- the 6.5 mass% Si steel sheet has a specific resistance approximately twice that of the 3 mass% Si steel sheet, and can effectively reduce eddy current loss. This is because the effect is excellent in reducing the noise of the iron core.
- Patent Document 2 discloses a so-called “Si” which is a steel plate having a Si concentration gradient in the plate thickness direction by interrupting Si homogenization diffusion when the surface Si concentration becomes 6.5 mass% in the siliconization process. It is disclosed that an “inclined steel plate” can be obtained, and that when this material is used, iron loss in a high frequency region is reduced as compared with the case where Si is made uniform.
- Patent Document 3 specifies the Si concentration difference (maximum-minimum), the surface Si concentration, and the Si concentration difference between the front and back surfaces of the steel sheet in order to reduce the high-frequency iron loss of the Si-gradient steel sheet.
- the lowest iron loss can be obtained when the surface Si concentration is 6.5 mass%.
- an electrical steel sheet containing 3 mass% or more of Si does not become an austenite phase ( ⁇ phase) even when heated to a high temperature, and remains in a ferrite phase ( ⁇ phase) until a liquid phase is generated. Accordingly, the above-described siliconization treatment is all performed in the ⁇ phase.
- Patent Document 4 by applying a siliconization treatment only to the surface layer in a temperature range of 900 to 1000 ° C. for a steel plate having less than 3% by mass of Si, the average Si concentration of the entire plate thickness is as low as 0.5 to 4% by mass, A magnetic steel sheet for motors with excellent workability and high frequency characteristics is disclosed.
- Patent Documents 5 and 6 there is a technique for obtaining excellent magnetic properties by diffusing a ferrite-forming element from a steel sheet surface to an internal austenite phase, transforming it into a ferrite phase, and forming a structure strongly accumulated on a specific crystal plane. It is disclosed.
- Patent Document 7 a partial region in the plate thickness direction has an ⁇ - ⁇ transformation composition and a portion where elements other than Fe are concentrated is imparted to reduce residual stress on the surface of the steel plate, thereby obtaining excellent magnetic properties.
- Technology is disclosed.
- Patent Document 8 eddy current loss can be greatly reduced by subjecting a low-carbon steel sheet to silicon agitation at 1050 to 1250 ° C in the austenite phase region and cooling the surface layer with a high Si concentration to obtain a Si-gradient steel sheet. Is disclosed.
- Patent Document 9 discloses a technique for obtaining a clad electromagnetic steel sheet having excellent magnetic properties by subjecting a steel sheet containing 0.003 to 0.02 mass% of C to an austenite phase at a high temperature to siliconization.
- iron loss is represented by the sum of hysteresis loss and eddy current loss. It is known that the higher the excitation frequency, the higher the proportion of eddy current loss in the total iron loss. Since the eddy current becomes difficult to flow as the specific resistance of the material increases, a material having a large specific resistance is used for the magnetic core for high frequency.
- Si, Al, Cr, and Mn are known as elements that increase the specific resistance of the steel sheet, and a general electromagnetic steel sheet increases the specific resistance mainly by adding Si.
- Si concentration exceeds 4% by mass, the material becomes extremely brittle and cold rolling becomes difficult. Therefore, the upper limit of Si addition is usually around 4% by mass, and in order to further increase the specific resistance, 1 to 4% by mass of Al and Cr are added and added.
- the saturation magnetic flux density of 3% by mass Si steel is 2.03T, but if 1% by mass of Al and 3% by mass of Cr are added thereto, the saturation magnetic flux density is reduced to about 1.80T.
- high-frequency core materials must be designed with the assumption that the excitation current contains a DC component of a certain magnitude and that the material is magnetically saturated by the high current that flows instantaneously.
- the core is increased in size.
- Patent Document 1 after rolling a 3% by mass Si steel plate to the final plate thickness, it has been difficult to produce by the rolling method until now by the siliconization process in which silicon tetrachloride is sprayed at a high temperature during the final annealing.
- 6.5 mass% Si steel sheet can be manufactured. Since 6.5 mass% Si steel sheet has a specific resistance approximately twice that of 3 mass% Si steel sheet, it is a suitable material for high frequency iron cores. However, in order to actually use it as an iron core, it is necessary to further slit, press or bend the 6.5 mass% Si steel sheet of the material, and in that case, cracks and chipping often occur, yield. In order to produce a core well, a high processing technique is required. Further, since the Si content is large, there is a problem that the saturation magnetic flux density is lowered to about 1.80 T.
- Patent Documents 2 and 3 describe a Si-gradient steel plate having a Si concentration gradient in the thickness direction as a material having higher frequency characteristics than a 6.5 mass% Si steel plate. Even if the surface Si concentration is as high as 6.5%, this Si grade steel plate has a low Si concentration of 3-4% by mass in the center of the plate thickness, and the average Si concentration of the entire steel sheet can be kept low, so 6.5% by mass Compared to Si steel plate, it is easier to work with, and the saturation magnetic flux density is also high at 1.85 to 1.90T.
- Patent Document 4 when manufacturing a steel sheet having a Si concentration gradient in the sheet thickness direction, a material having a Si concentration of less than 3% is used as a material to lower the average Si concentration of the entire steel sheet, and high frequency low iron with good workability. I am trying to get a lossy material.
- a material having a low Si concentration can become an austenite ( ⁇ ) phase at a high temperature.
- ⁇ austenite
- Patent Document 4 if silicon is silicified with a ⁇ phase at a high temperature exceeding 1000 ° C., it cracks at the interface of the surface ⁇ / ⁇ transformation. Will occur. Therefore, the siliconizing treatment is performed in the temperature range of 900 to 1000 ° C. where almost no austenite phase is generated.
- Patent Documents 5 and 6 attempt to improve soft magnetic properties by diffusing ferrite-forming elements from the steel sheet surface to the internal austenite phase and forming a specific texture using the ⁇ ⁇ ⁇ transformation.
- changes in texture strongly affect hysteresis loss, which is part of iron loss, but have little effect on eddy current loss, and can be said to be effective in reducing eddy current loss, which accounts for most of iron loss at high frequencies. Absent. Rather, developing a texture that is effective in reducing hysteresis loss leads to an increase in magnetic domain width and increases abnormal eddy current loss.
- Patent Document 7 in a steel sheet having a concentration difference of elements other than Fe in the sheet thickness direction, soft magnetic characteristics are improved by keeping the residual stress on the surface low.
- the technique for reducing the residual stress in order to suppress the increase in the hysteresis loss of the soft magnetic material has been performed for a long time, and the relation with the reduction in eddy current loss is not clear.
- Patent Document 8 low carbon steel with C exceeding 0.02% by mass is used as a raw material, and it is silicon-treated by high-temperature treatment exceeding 1050 ° C. to form a Si-gradient steel plate, with in-plane tensile stress on the surface layer and in-plane compressive stress on the inner layer.
- the eddy current loss is drastically reduced by forming a stress distribution.
- the central portion of the plate thickness of this material has a complex transformation structure, and there is a problem that the DC magnetic characteristics as an electromagnetic steel plate are extremely poor.
- the magnetic flux density B8 corresponding to a magnetization force of 800 A / m in the magnetization curve is only about 0.75 T.
- the actual size of the core material is determined by the magnetic flux density at which the differential permeability of the magnetization curve starts to decrease rapidly, the so-called BH curve shoulder height, and the value of B8 is often used as the index. Therefore, even if the saturation magnetic flux density is high, a material having poor DC magnetic characteristics and low B8 is substantially unsuitable for downsizing the core.
- Patent Document 9 when an impact force such as shearing is applied, the crystal of the surface layer part is cracked in the plate thickness direction along the grain boundary, or cracks occur at the boundary between the surface layer part and the inner layer part. A phenomenon of variation was also observed. In fact, even in the same production conditions, there were cases in which the variation in soft magnetic characteristics increased depending on the sample, and this tendency was particularly remarkable when the C content was 0.005% by weight or less. High-frequency switching elements of 10k to 50kHz have recently begun to be used in relatively large-capacity power sources such as hybrid vehicles, electric vehicles, and solar power generation, and have high saturation magnetic flux density and low high-frequency iron loss. There is a demand for practical materials with little variation. From this point, variation in magnetic characteristics becomes a problem.
- An object of the present invention is to solve such problems and to provide an electrical steel sheet having a high saturation magnetic flux density and a low high-frequency iron loss and a method for producing the same.
- the present inventors diligently studied means for obtaining an electrical steel sheet having a high saturation magnetic flux density and a low high-frequency iron loss.
- a Si-gradient steel plate as shown in FIG. 1 as an electromagnetic steel plate.
- the Si-gradient steel plate in FIG. 1 has a surface layer part that continuously changes from a high Si concentration to a low Si concentration in the plate thickness depth direction from the steel plate surface, with the center of the plate thickness as the symmetry plane, and the Si concentration is low. It has a continuously changing boundary portion and an inner layer portion including a thickness center where the Si concentration does not substantially change in the thickness direction, and the surface layer portion has an in-plane tensile stress, and the inner layer portion has an in-plane compressive stress.
- This is an electrical steel sheet that reduces high-frequency iron loss by utilizing the stress distribution.
- test piece having a width of 50 mm and a length of 200 mm was cut out from a cold-rolled sheet having a thickness of 0.2 mm made of impurities and subjected to siliconization treatment and diffusion treatment using this as a raw material.
- the amount of silicon immersion that is, the amount of Si added to the steel sheet by the siliconization treatment is within 2.4 ⁇ 0.2%
- the ratio of the thickness ds of the surface layer portion that is, the Si concentrated layer to the plate thickness d0 is 30%.
- the siliconizing treatment conditions and the diffusion treatment conditions were adjusted to be within ⁇ 3%.
- both the widths of the siliconized and diffused samples were sheared to a width of 30 mm, and a magnetic measurement was performed by a method (Epstein test method) based on JIS C2550 using a small single-plate test frame. After completion of the magnetic measurement, the sample was further sheared, and the microstructure of the cross section was confirmed with an optical microscope, and the Si distribution in the thickness direction was confirmed with EPMA.
- the form of the crystal grains in the surface layer can be adjusted according to the siliconization treatment conditions. For example, when performing the siliconizing treatment within the austenite temperature range of the material (steel plate), the higher the temperature or the lower the silicon tetrachloride gas concentration, the larger the crystal grains in the surface layer grow in the direction parallel to the plate surface. A trend is observed. On the other hand, when performing the siliconizing treatment within the austenite temperature range of (steel plate), the lower the temperature, or the higher the silicon tetrachloride concentration, the larger the crystal grains in the surface layer portion tend to grow in the thickness direction. It is done.
- FIG. 3 is a cross-sectional view in the L direction (rolling direction) schematically showing the aspect ratio b / a of the crystal grains in the surface layer portion.
- a and b are the maximum value in the plate thickness direction and the maximum value in the direction parallel to the surface of each crystal grain.
- the aspect ratio does not cause a difference between the L direction (rolling direction) and the C direction (sheet width direction), but in the present invention, the aspect ratio is evaluated by the aspect ratio in the L direction.
- FIG. 2 shows the relationship between the average aspect ratio b / a of the crystal grains in the surface layer part (abbreviated as the average aspect ratio b / a in the surface part in the figure) and the iron loss.
- b / a values ranging from 0.5 to 4.5 were obtained.
- the iron loss showed a value above a certain level and reduced iron loss. No effect was found.
- the material component, the plate thickness, the amount of silicon immersion, the thickness of the surface layer are aligned, and for each of the plurality of samples prepared by changing the average aspect ratio of the crystal grains of the surface layer, the average value of iron loss is m, When the standard deviation is ⁇ and the variation coefficient ⁇ / m is less than 10%, it is considered that the variation is small. As a result, it was found that when the average aspect ratio of the crystal grains in the surface layer portion is 0.7 or more and 4.0 or less, the variation in iron loss can be suppressed small.
- the direct relationship between the iron loss and the average aspect ratio of the crystal grains in the surface layer is not clear, when the sample shear plane is observed with a magnifying glass, in the sample with a large iron loss, the crystal grains in the surface layer are cracked or missing. Many were recognized. In the sample showing the average iron loss, almost no cracks or missing parts were observed. It is considered that the average aspect ratio of the crystal grains in the surface layer has an influence on the variation in the iron loss because the susceptibility to cracking and missing varies depending on the average aspect ratio of the crystal grains in the surface layer. Also in the cross-sectional structure observation, it was confirmed that a crack occurred at the boundary between the surface layer portion and the inner layer portion.
- Such defects are conspicuous in a sample having a very small average aspect ratio of crystal grains in the surface layer portion or a sample having a very large average aspect ratio. Conversely, in a sample in which the average aspect ratio of crystal grains in the surface layer portion is within a certain range, It is presumed that defects are less likely to occur and variations in iron loss are kept small.
- An electrical steel sheet characterized in that the steel sheet has an average aspect ratio of crystal grains in the surface layer portion: a dimension ratio in the plate surface parallel direction to the plate surface vertical direction (depth direction) is 0.7 or more and 4.0 or less.
- the average aspect ratio is an average value of the aspect ratios of 50 or more crystal grains.
- the plate surface vertical direction (depth direction) Dimensions shall be measured including the inner layer.
- a non-oxidizing atmosphere containing silicon at a temperature of 1100 to 1250 ° C, Si is infiltrated from the steel sheet surface to make the steel sheet surface layer a ferrite phase, and then the austenite phase is left in the inner layer, and a non-oxidizing atmosphere containing no Si Inside, hold at a temperature of 1100 to 1250 ° C for a certain period of time until the surface layer part, which is a ferrite phase, becomes 10 to 40% of the plate thickness,
- a method for producing an electrical steel sheet characterized by cooling to 400 ° C. at an average cooling rate of 5 to 30 ° C./s.
- “%” indicating the component of steel is “% by mass” unless otherwise specified.
- an electrical steel sheet having a high saturation magnetic flux density and a low high-frequency iron loss can be obtained.
- an electromagnetic steel sheet having a high saturation magnetic flux density and a low high-frequency iron loss can be obtained with stable characteristics with little variation, and an iron core material that is advantageous for downsizing a high-frequency transformer or the like can be provided. it can. Therefore, the steel plate of this invention can be used suitably for the high frequency transformer for power electronics, a reactor, and the iron core material of a motor.
- the electrical steel sheet of the present invention heats a steel sheet having a low Si concentration to a high temperature austenite phase, changes the surface layer to a high Si concentration by a siliconizing treatment / diffusion treatment, further transforms the surface layer into a ferrite phase, and forms a low Si concentration austenite in the inner layer.
- Si gradient steel sheet obtained by cooling while leaving the phase, and the surface layer continuously changes from high Si concentration to low Si concentration in the plate thickness depth direction from the steel sheet surface, with the plate thickness center as the symmetry plane A boundary portion where the Si concentration changes discontinuously, and an inner layer portion including a plate thickness center where the Si concentration does not change substantially in the plate thickness direction.
- the inner layer part including the center of the plate thickness in which the Si concentration does not substantially change in the plate thickness direction is located in the center part in the plate thickness direction from the boundary part, and is between one boundary part and the other boundary part.
- the boundary where the Si concentration changes discontinuously is that the difference in Si concentration is 0.2% or more within the range of plate thickness ⁇ 1 ⁇ m, and the minimum Si concentration in the surface layer and the maximum Si concentration in the inner layer are discontinuous. This is the distribution area that appears.
- the electrical steel sheet of the present invention has a stress distribution that is in-plane tensile stress in the surface layer part and in-plane compressive stress in the inner layer part. By using this stress distribution, eddy current loss is reduced and high-frequency iron is reduced. Loss can be reduced.
- the Si steel sheet of the present invention has a Si concentration distribution with the center of the steel plate thickness as the plane of symmetry.
- the Si concentration distribution on the front and back sides of the steel sheet becomes asymmetrical, not only does the steel sheet warp significantly, it becomes defective in shape, but it also has a characteristic of Si-gradient steel sheet that has in-plane tensile stress at the surface layer and in-plane compressive stress at the inner layer.
- the stress distribution becomes asymmetric with respect to the center plane of the plate thickness, and the effect of reducing eddy current loss is reduced.
- the smaller the Si concentration difference between the front and back surfaces of the steel plate the better, and 0.2% or less is preferable.
- the magnetic steel sheet of the present invention that is, the Si inclined steel sheet obtained by the siliconization treatment in the austenite phase, has a discontinuous Si concentration distribution region resulting from the ⁇ / ⁇ transformation, that is, Si.
- a boundary (Si concentration gap) where the concentration changes discontinuously.
- This boundary part is a Si concentration difference of 0.1% or more per ⁇ m in the plate thickness direction (concentration gradient of 0.1% / ⁇ m or more), that is, a portion where the Si concentration difference is 0.2% or more within the range of plate thickness ⁇ 1 ⁇ m. is there.
- This Si concentration gap existing at the boundary between the surface layer portion and the inner layer portion can be said to be suitable for reducing the eddy current loss by concentrating the magnetic flux on the surface layer portion.
- the stress distribution changes abruptly at this boundary portion, there is a risk that it is easy to break at the interface when subjected to an impact force such as shearing. Such cracks do not propagate to the entire plate and remain in a small range, so the material itself does not break down, but appears as variations in magnetic properties, particularly iron loss.
- the stabilization of the characteristics of the Si gradient steel sheet having a discontinuous Si distribution at the interface between the surface layer portion and the inner layer portion and an abrupt stress distribution is an issue.
- the present invention solves the problem by defining the average aspect ratio of the crystal grains in the surface layer portion: the dimensional ratio in the plate surface parallel direction to the plate surface vertical direction (depth direction).
- the average aspect ratio of the crystal grains of the surface layer portion 0.7 or more and 4.0 or less, variation in iron loss is suppressed and specific stabilization is achieved.
- Average aspect ratio of crystal grains in the surface layer part dimensional ratio in the plate surface parallel direction to the plate surface vertical direction (depth direction) is 0.7 or more and 4.0 or less
- the average aspect ratio b / a of crystal grains in the surface layer was found to be a very important factor.
- b / a is less than 0.7, the shearing process causes cracks or omissions at the grain boundaries of the crystal grains in the surface layer portion, and the variation in iron loss becomes obvious.
- b / a exceeds 4.0, cracks are likely to occur at the boundary between the surface layer portion and the inner layer portion during the shearing process, and variations in iron loss become apparent.
- b / a is 0.7 or more and 4.0 or less, such cracks are almost eliminated, and the variation in iron loss can be suppressed to an extremely small level.
- the average aspect ratio is an average value of the aspect ratios of 50 or more crystal grains.
- the plate surface vertical direction (depth direction) Dimensions are measured including the inner layer.
- the texture of the surface layer portion and the inner layer portion is not particularly limited, and may be a structure in which crystal orientation is random or highly integrated in a specific plane and a specific orientation.
- the crystal orientation is random, the dislocation movement for each crystal is the average Therefore, cracks are less likely to occur at high Si-concentration surface layer grains and at boundaries where there are discontinuous Si concentration differences. Therefore, the crystal orientation is preferably random.
- the thickness of the surface layer is 10 to 40% of the plate thickness (preferred conditions)
- the thickness of the surface layer portion becomes magnetically saturated at the stage where the excitation magnetic flux density is low, and the magnetic permeability decreases.
- the inner layer portion also begins to be magnetized, and the effect of reducing eddy current loss is diminished.
- the thickness of the surface layer exceeds 40% of the plate thickness, a wide range from the surface to the depth near the center of the plate thickness is magnetized, resulting in a magnetic flux distribution close to Si uniform material, and the eddy current reduction effect diminishes. End up.
- the thickness of the surface layer portion is preferably 10% or more and 40% or less of the plate thickness. More preferably, it is 20% or more and 35% or less.
- Average Si concentration in the surface layer is 2.5 to 6.5% (preferred conditions) When the average Si concentration in the surface layer is less than 2.5%, the eddy current reduction effect is small. On the other hand, when it exceeds 6.5%, the frequency of surface cracks may increase rapidly. Therefore, the average Si concentration in the surface layer is preferably 2.5 to 6.5%.
- the average Si concentration in the inner layer is 2.0% or less (preferred conditions) When the average Si concentration exceeds 2.0%, it is difficult to form a discontinuous Si concentration distribution (boundary portion) at the boundary between the surface layer portion and the inner layer portion, and a sufficient eddy current loss reduction effect cannot be obtained. Therefore, the average Si concentration in the inner layer portion is preferably 2.0% or less. On the other hand, if the average Si concentration in the inner layer is less than 0.15%, even if the siliconization treatment conditions and diffusion treatment conditions are adjusted, the crystal grains in the surface layer grow elongated in the plate thickness direction, and the average of the crystal grains in the surface layer part The aspect ratio b / a tends to be less than 0.7, and cracks are likely to occur on the surface layer. Therefore, the average Si concentration in the inner layer portion is preferably 0.15% or more.
- Si concentration difference at the boundary is 0.4% or more (preferred condition)
- the Si concentration difference at the boundary portion is less than 0.4%, the inner layer portion is also easily magnetized and the effect of concentrating the magnetic flux on the surface layer portion is diminished, so that a sufficient eddy current loss reduction effect may not be obtained. Therefore, the Si concentration difference at the boundary is preferably 0.4% or more.
- the minimum concentration of Si in the boundary portion is equivalent to the concentration in the inner layer portion, and the maximum concentration is the lowest Si concentration that the surface layer portion ( ⁇ phase) can take in the temperature range where the siliconization treatment and diffusion treatment are performed. Equivalent to.
- the eddy current loss is reduced by making the stress distribution of the tensile stress in the surface layer portion and the compressive stress in the inner layer portion.
- the tensile stress of the surface layer is 50 MPa or more and the compressive stress of the inner layer is 50 MPa. The above is preferable.
- the tensile stress of the surface layer portion exceeds 200 MPa and the compressive stress of the inner layer portion exceeds 200 MPa, even when the aspect ratio of the crystal grains of the surface layer portion is within the range of the present invention, the crack at the time of shearing is significant and the iron loss varies. May become large. Accordingly, it is preferable that the tensile stress of the surface layer portion is 50 to 200 MPa and the compressive stress of the inner layer portion is 50 to 200 MPa.
- these internal stress values are values obtained from the curvature radius of the plate warpage that is observed when the surface is removed by chemical polishing from the surface to the center of the plate thickness only on one side of the Si-gradient steel plate that has substantially no plate warpage. It is.
- Thickness 0.03-0.5mm (preferred conditions) The eddy current loss can be reduced as the plate thickness is reduced. However, if it is less than 0.03 mm, not only will the manufacturing cost of rolling increase, but it is expected that a large load will be imposed on the processing and assembly of the core material. On the other hand, when the thickness exceeds 0.5 mm, it takes time for the siliconizing treatment from the steel plate surface and the diffusion treatment for optimizing the Si distribution. Even when the core is processed, if the plate thickness exceeds 0.5 mm, cracks are likely to occur on the sheared surface, which may increase the variation in characteristics. Therefore, the plate thickness is preferably 0.03 to 0.5 mm.
- the electrical steel sheets of the present invention described above are in mass%, C: 0.020% or less, Si: 0.15-2.0%, Mn: 0.05-2.00%, P: 0.1% or less, S: 0.01% or less, Al: 0.1% or less , N: 0.01% or less, steel sheet having a composition composed of Fe and inevitable impurities in the balance, heated to 1100-1250 ° C in a non-oxidizing atmosphere to form an austenite phase, and then 10 mol% or more In a non-oxidizing atmosphere containing less than 45 mol% silicon tetrachloride, at a temperature of 1100 to 1250 ° C., Si is infiltrated from the steel sheet surface to make the steel sheet surface layer a ferrite phase, and then the austenite phase is left in the inner layer part, In a non-oxidizing atmosphere that does not contain copper, hold at a temperature of 1100 to 1250 ° C for a certain period of time until the surface layer portion, which is a ferrite phase, has
- the C concentration of the material is preferably low for improving soft magnetic properties.
- the material C concentration should be 0.020% or less.
- the lower limit of the C concentration is not particularly limited, but as in the case of the ultra-low carbon steel, when the solid solution C concentration in the steel becomes extremely low, intergranular fracture tends to occur. Therefore, it is preferably 0.0005 to 0.020%.
- Si 0.15-2.0% If the Si concentration of the material is less than 0.15%, surface grains with an aspect ratio of less than 0.7 that are elongated in the thickness direction during the siliconization treatment and diffusion treatment are likely to occur. This leads to frequent cracking and increased iron loss variation during shearing. On the other hand, when the material Si concentration exceeds 2.0%, a discontinuous Si concentration distribution (boundary portion) is hardly formed at the boundary between the surface layer portion and the inner layer portion, and a sufficient eddy current loss reduction effect cannot be obtained. Therefore, the material Si concentration is 0.15 to 2.0%.
- Mn 0.05-2.00%
- Mn is an element effective for improving the toughness of steel. In steel, it combines with S and precipitates as MnS. When the Mn concentration of the material is less than 0.05%, S is segregated at the grain boundary, and the grain boundary fracture is likely to occur in the crystal grains of the surface layer portion having a high Si concentration. Mn is also an element that stabilizes the austenite phase. When the material Mn concentration exceeds 2.00%, large transformation strain tends to remain in the inner layer portion when the inner layer portion transforms from austenite to ferrite in the cooling process after the siliconization treatment and the diffusion treatment. Since this transformation distortion disturbs the stress distribution of the Si-gradient steel sheet, the eddy current reduction effect is suppressed. Therefore, the material Mn concentration is set to 0.05 to 2.00%.
- P 0.1% or less
- P is an element effective for improving the strength of steel, but also an element that promotes embrittlement. There is also a tendency to segregate at the phase transformation interface. If it is 0.1% or less, the grain boundary cracks in the surface layer part and the cracks at the boundary part are not substantially realized. Therefore, the material P concentration is 0.1% or less.
- S 0.01% or less S is an element that easily segregates at grain boundaries, and the concentration is preferably low in order to prevent embrittlement. If it is 0.01% or less, cracks are not substantially realized. Therefore, the material S concentration should be 0.01% or less.
- Al 0.1% or less Al, like Si, is an element that increases the specific resistance of steel, and is often combined with Si in electrical steel sheets.
- Si is an element that reduces the interstitial distance of the Fe crystal
- Al is an element that conversely increases the interstitial distance of the Fe crystal.
- Al addition is not preferable because it works in the direction of relaxing the stress distribution suitable for eddy current reduction obtained by Si addition. However, if it is 0.1% or less, no adverse effect occurs. Therefore, the material Al concentration is set to 0.1% or less.
- the lower limit of the Al concentration is not particularly limited, but when it is limited to less than 0.002%, a structure in which various particle diameters are mixed tends to be formed, and iron loss may be deteriorated.
- the upper limit is not particularly limited, but is preferably 0.01% or less from the viewpoint of processing. Therefore, it is preferably 0.002 to 0.01%.
- N 0.01% or less When N exceeds 0.01%, iron loss increases. Therefore, 0.01% or less.
- the balance is Fe and inevitable impurities.
- the slab having the above component composition is heated, hot-rolled, and cold-rolled or cold-rolled with one or more intermediate annealings is repeated to obtain a steel plate having a predetermined thickness. You may perform finish annealing as needed. Thereafter, the steel sheet is heated to 1100 to 1250 ° C. in a non-oxidizing atmosphere to form an austenite phase, and then at a temperature of 1100 to 1250 ° C. in a non-oxidizing atmosphere containing 10 mol% or more and less than 45 mol% of silicon tetrachloride.
- Si is infiltrated from the steel sheet surface to make the steel sheet surface layer (up to a depth of 5 to 40% of the plate thickness) a ferrite phase, and then the austenite phase is left in the inner layer portion, in a non-oxidizing atmosphere containing no Si.
- the ferrite layer is maintained for a certain period of time until the surface layer of the ferrite phase becomes 10 to 40% of the plate thickness, and then cooled to 400 ° C. at an average cooling rate of 5 to 30 ° C./s.
- the steel sheet in a state of high-temperature austenite phase is subjected to siliconization treatment / diffusion treatment, and only the surface layer portion is set to a high Si ferrite phase, and the inner layer portion is left in a state in which the austenite phase remains.
- the inner layer is also transformed into a ferrite phase in the course of cooling to room temperature.
- the siliconization treatment condition is one of the important factors for obtaining the electrical steel sheet of the present invention.
- a method of infiltrating (siliciding) Si a conventionally known method may be used, and examples thereof include a vapor phase siliconization method, a liquid phase siliconization method, and a solid phase siliconization method.
- the Si-based gas used at that time is not particularly limited.
- one or more gases selected from silicon tetrachloride, trichlorosilane, dichlorosilane, monosilane, and disilane are preferable.
- a description will be given by a vapor phase siliconization method in which a steel plate is heated in a non-oxidizing atmosphere and silicon tetrachloride gas is used.
- the silicon tetrachloride gas concentration, reaction temperature, and reaction time are adjusted in a non-oxidizing atmosphere such as nitrogen and argon, and the subsequent non-oxidizing atmosphere does not contain silicon tetrachloride gas.
- a non-oxidizing atmosphere such as nitrogen and argon
- the subsequent non-oxidizing atmosphere does not contain silicon tetrachloride gas.
- the siliconization treatment in the high temperature region of the austenite phase, it is possible to change the crystal grain morphology of the surface layer by adjusting the siliconization treatment conditions and the diffusion treatment conditions.
- the concentration of silicon tetrachloride in the non-oxidizing atmosphere is about 50 to 75 mol% from the viewpoint of the efficiency of the siliconization treatment.
- the concentration of silicon tetrachloride is increased in this way, the siliconization rate increases, and the surface layer grains transformed into the ferrite phase grow in the thickness direction and tend to have a small aspect ratio b / a.
- the aspect ratio b / a of the surface grain of Si-gradient steel sheet is set to 0.7 or more and 4.0 or less to suppress the occurrence of defects during shearing and to reduce the iron loss variation, so that the silicon tetrachloride concentration is 10 mol% or more and less than 45 mol%.
- the temperature of the siliconization treatment is set to a range of 1100 to 1250 ° C.
- diffusion treatment is performed at 1100 to 1250 ° C. in a non-oxidizing atmosphere containing no Si until the surface layer portion, which is a ferrite phase, has a predetermined thickness. That is, the diffusion treatment is performed until the thickness of the surface layer portion that is a ferrite phase becomes 10 to 40% of the plate thickness.
- Cooling after the siliconization / diffusion treatment is performed at an average cooling rate of 5-30 ° C / s up to 400 ° C. If it is less than 5 ° C./s, the internal stress is relaxed and a sufficient effect of reducing eddy current loss cannot be obtained. On the other hand, when rapidly cooled at a rate exceeding 30 ° C./s, the inner layer portion of the steel sheet has a structure distorted in various directions, and the soft magnetic properties are greatly deteriorated. Therefore, in order to obtain good DC magnetic characteristics, it is necessary to set the average cooling rate up to 400 ° C. in the range of 5 to 30 ° C./s.
- a steel ingot containing the components shown in Table 1 and the balance consisting of Fe and inevitable impurities is heated to 1100 ° C and hot-rolled to a thickness of 2.3 mm, and then cold-rolled to a thickness of 0.2 mm did.
- a test piece for siliconizing treatment having a width of 50 mm and a length of 150 mm was cut out from the cold-rolled sheet.
- the test piece was heated while being transported from a room temperature range to a temperature range of 1100 to 1225 ° C. where an austenite phase was generated in an argon atmosphere, and then argon gas containing 8 to 66% silicon tetrachloride by volume was placed in the furnace.
- the siliconizing treatment was performed for 1 to 6 minutes at the same temperature as described above.
- a non-oxidizing atmosphere containing only silicon tetrachloride was switched to a non-oxidizing atmosphere containing only argon, and diffusion treatment was performed for 2 to 30 minutes in a temperature range of 1100 to 1250 ° C.
- the amount of silicon immersion that is, the amount of Si added to the steel sheet was adjusted by the concentration of silicon tetrachloride in the atmosphere and the treatment time.
- the thickness of the surface layer that transforms from the austenite phase to the ferrite phase by Si diffusion from the surface is adjusted by the time of the siliconization treatment and diffusion treatment.
- the Si concentration distribution in the steel sheet cross section is changed to EPMA (electron beam microanalyzer). ).
- EPMA electron beam microanalyzer
- the sample After completion of the siliconization treatment and diffusion treatment, the sample was cooled to an average cooling rate of 15 ° C./s to 400 ° C. or less by being transported to a room temperature region in a nitrogen atmosphere, and taken out when the temperature reached 100 ° C. or less. . It was confirmed that the samples prepared under the same conditions have the same silicon immersion amount due to mass change before and after the treatment.
- one sheet is covered with a seal on one side of the plate surface and removed by chemical polishing using hydrofluoric acid from the surface on the opposite side to the center of the plate thickness. It was confirmed that a stress distribution occurred.
- the remaining 10 samples were sheared by 10 mm from both ends of the plate width with a precision shearing machine dedicated to thin plates, and cut out a single plate sample for magnetic property evaluation having a width of 30 mm.
- Magnetic measurement was performed by measuring the iron loss (W1 / 10k) by a method (Epstein test method) based on JIS C2550 using a single-plate test frame that can magnetize and evaluate a sample 30 mm wide ⁇ 100 mm long.
- the sample after measurement was cut with a high-speed rotating cutter for microstructural examination, and the microstructure was observed with an optical microscope and the Si concentration distribution was investigated with EPMA in the plate thickness direction.
- the ratio of the iron loss average value of the other samples to the iron loss value of the sample with the uniform Si concentration is 0.9 or less.
- a steel ingot containing the components shown in Table 3 and the balance consisting of Fe and inevitable impurities is heated to 1100 ° C and hot-rolled to a thickness of 2.3 mm, and then cold-rolled to a thickness of 0.5 to 0.08 mm Rolled.
- a test piece for siliconizing treatment having a width of 50 mm and a length of 150 mm was cut out from the cold-rolled sheet. Next, the test piece is heated while being transported from a room temperature range to a temperature range of 1200 ° C. where an austenite phase is generated in an argon atmosphere, and then argon gas containing 8 to 57% silicon tetrachloride by volume is flowed into the furnace.
- the siliconizing treatment was performed at the same temperature as above for 1 to 10 minutes.
- the atmosphere was switched to a non-oxidizing atmosphere containing only silicon tetrachloride and containing only argon, and diffusion treatment was carried out at a temperature of 1200 ° C. for 2 to 40 minutes.
- the amount of silicon immersion that is, the amount of Si added to the steel sheet was adjusted by the concentration of silicon tetrachloride in the atmosphere and the treatment time.
- the thickness of the surface layer that transforms from the austenite phase to the ferrite phase by Si diffusion from the surface is adjusted by the time of the siliconization treatment and diffusion treatment.
- the Si concentration distribution in the steel sheet cross section is changed to EPMA (electron beam microanalyzer). ). Eleven samples of the same form were prepared.
- the sample after the above treatment was transported to room temperature in a nitrogen atmosphere, cooled to 400 ° C. or lower at a cooling rate of 15 ° C./s, and taken out when cooled to 100 ° C. or lower. It was confirmed that the samples prepared under each condition had the same silicon immersion amount due to the weight change before and after the treatment.
- the remaining 10 samples were sheared by 10 mm from both ends of the plate width with a precision shearing machine dedicated to thin plates, and cut out a single plate sample for magnetic property evaluation having a width of 30 mm.
- Magnetic measurement was performed by measuring the iron loss (W1 / 10k) by a method (Epstein test method) based on JIS C2550 using a single-plate test frame that can magnetize and evaluate a sample 30 mm wide ⁇ 100 mm long.
- the sample after measurement was cut with a high-speed rotating cutter for microstructural examination, and the microstructure was observed with an optical microscope and the Si concentration distribution was investigated with EPMA in the plate thickness direction.
- the Si concentration on the steel sheet surface As described above, the Si concentration on the steel sheet surface, the average Si concentration in the surface layer, the thickness ratio of the surface layer to the plate thickness, the average aspect ratio of the crystal grains in the surface layer, the Si concentration difference at the boundary, and the magnetic flux density of 0.1 T; excitation at 10 kHz
- the average value m of the high-frequency iron loss W 1 / 10k , its standard deviation ⁇ , and the coefficient of variation ⁇ / m were measured. Table 4 shows the obtained results.
- a steel ingot containing the components shown in Table 5 and the balance consisting of Fe and inevitable impurities was heated to 1100 ° C. and hot rolled to a thickness of 2.3 mm, and then rolled to a thickness of 0.2 mm by cold rolling. .
- a test piece for siliconizing treatment having a width of 50 mm and a length of 150 mm was cut out from the cold-rolled sheet. Next, the test piece is heated while being conveyed from a room temperature range to an temperature range of 1100 to 1250 ° C. where an austenite phase is generated in an argon atmosphere, and then argon gas containing 10 to 30% by volume of silicon tetrachloride is introduced into the furnace.
- the siliconizing treatment was performed for 1 to 6 minutes at the same temperature as described above.
- a non-oxidizing atmosphere containing only silicon tetrachloride was switched to a non-oxidizing atmosphere containing only argon, and diffusion treatment was performed for 2 to 30 minutes in a temperature range of 1100 to 1250 ° C.
- the amount of silicon immersion that is, the amount of Si added to the steel sheet was adjusted by the concentration of silicon tetrachloride in the atmosphere and the treatment time.
- the thickness of the surface layer that transforms from the austenite phase to the ferrite phase by Si diffusion from the surface is adjusted by the time of the siliconization treatment and diffusion treatment.
- the Si concentration distribution in the steel sheet cross section is changed to EPMA (electron beam microanalyzer). ). Twelve samples each having the same form were prepared.
- the sample after the above treatment was transported to a room temperature in a nitrogen atmosphere, cooled to 400 ° C. or lower at a cooling rate of 15 ° C./s, and then taken out when cooled to 100 ° C. or lower. It was confirmed that the samples prepared under each condition had the same silicon immersion amount due to the weight change before and after the treatment.
- one sheet is covered with a seal on one side of the plate surface and removed by chemical polishing using hydrofluoric acid from the surface on the opposite side to the center of the plate thickness. It was confirmed that a stress distribution occurred.
- the remaining 10 samples were sheared by 10 mm from both ends of the plate width with a precision shearing machine dedicated to thin plates, and cut out a single plate sample for magnetic property evaluation having a width of 30 mm.
- Magnetic measurement was performed by measuring the iron loss (W1 / 10k) by a method (Epstein test method) based on JIS C2550 using a single-plate test frame that can magnetize and evaluate a sample 30 mm wide ⁇ 100 mm long.
- the sample after the measurement was cut with a high-speed rotating cutter for microstructural examination, and the microstructure was observed with an optical microscope, and the Si concentration distribution was investigated in the plate thickness direction with EPMA.
- the sample was cut with a high-speed rotating cutter for microstructural examination, and the structure was observed with an optical microscope, and the Si concentration distribution was investigated in the thickness direction with EPMA.
- the average value m of the high-frequency iron loss W1 / 10k, its standard deviation ⁇ , and the coefficient of variation ⁇ / m were measured.
- the iron loss W1 / 10k of the sample with uniform Si concentration (Si uniform material) was measured, and the ratio of the iron loss average value of the Si gradient material measured above to the iron loss of the Si uniform material for each experiment number. was calculated. The results obtained are shown in Table 6.
- ds / d0 is less than 10% or more than 40%, the iron loss is reduced, but compared to the sample with ds / d0 of 10-40% Is small.
- the iron loss with respect to the Si uniform sample is close to 1, and the iron loss is hardly reduced by providing the Si concentration distribution.
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Abstract
Description
また、最近は、自動車やエアコンのみならず太陽光発電等の新エネルギー分野においても、比較的大容量の電源において数kHz~50kHzのスイッチング素子が使われるようになり、さらに高周波鉄損の低い鉄心材料が求められてきている。
しかしながら、実際に鉄心として使用するには、材料の6.5質量%Si鋼板に対して、さらにスリット、プレスまたは曲げ加工などを施す必要があり、その際に、割れや欠けが生じることが多く、歩留まり良くコアを作製するためには高い加工技術が要求される。またSi含有量が多いため、飽和磁束密度が1.80T程度と低くなる問題も有していた。
[1]鋼板の板厚中心を対称面として、鋼板表面より板厚深さ方向に高Si濃度から低Si濃度に連続的に変化する表層部と、Si濃度が不連続的に変化する境界部と、Si濃度が実質的に板厚方向に変化しない板厚中心を含む内層部とを有し、前記表層部で面内引張応力、前記内層部で面内圧縮応力となる応力分布を有する電磁鋼板であり、前記表層部の結晶粒の平均アスペクト比:板面垂直方向(深さ方向)に対する板面平行方向の寸法比が0.7以上4.0以下であることを特徴とする電磁鋼板。
なお、前記平均アスペクト比とは、50個以上の結晶粒のアスペクト比の平均値であり、表層部の結晶粒が境界部を超えて内層部に及ぶ場合、板面垂直方向(深さ方向)寸法は内層部も含めて計測することとする。
[2]前記表層部の厚さは板厚の10~40%の範囲であることを特徴とする上記[1]に記載の電磁鋼板。
[3]質量%で、前記表層部の平均Si濃度が2.5~6.5%、前記内層部の平均Si濃度が2.0%以下であることを特徴とする上記[1]または[2]に記載の電磁鋼板。
[4]前記表層部では、板面と平行方向に50~200MPaの引張応力を、前記内層部では、板面と平行方向に50~200MPaの圧縮応力を、有することを特徴とする上記[1]~[3]のいずれかに記載の電磁鋼板。
[5]板厚が0.03~0.5mmであることを特徴とする上記[1]~[4]のいずれかに記載の電磁鋼板。
[6]質量%で、C:0.020%以下、Si:0.15~2.0%、Mn:0.05~2.00%、P:0.1%以下、S:0.01%以下、Al: 0.1%以下、N:0.01%以下を含有し、残部がFe及び不可避的不純物からなる成分組成を有する鋼板に対して、非酸化雰囲気中で、1100~1250℃に加熱しオーステナイト相とし、次いで、10mol%以上45mol%未満の四塩化珪素を含む非酸化雰囲気中、1100~1250℃の温度で、鋼板表面からSiを浸透させて鋼板表層をフェライト相とし、次いで、内層部にオーステナイト相を残したまま、Siを含まない非酸化雰囲気中、1100~1250℃の温度で、フェライト相である表層部が板厚に対し10~40%の厚さとなるまで一定時間保持し、
次いで、400℃まで、5~30℃/sの平均冷却速度で冷却することを特徴とする電磁鋼板の製造方法。
なお、本明細書において、鋼の成分を示す%は特に断りのない限り質量%である。
したがって、本発明の鋼板は、パワーエレクトロニクス用の高周波トランス、リアクトル、モーターの鉄心材料に好適に用いることができる。
まず、鋼板の基本構造の限定理由について述べる。
前述したように、発明者らが鋭意調査を進めた結果、Si傾斜鋼板では、表層部の結晶粒の平均アスペクト比b/aが極めて重要な因子であることを見出した。b/aが0.7未満の場合、剪断加工により表層部の結晶粒の粒界で割れが生じたり欠落が生じて鉄損のバラツキが顕在化してしまう。一方、b/aが4.0を超える場合、剪断加工の際に、表層部と内層部の境界部で割れが生じやすくなり、やはり鉄損のバラツキが顕在化してしまう。b/aが0.7以上4.0以下の場合、このような割れは殆どなくなり、鉄損のバラツキも極めて小さく抑えることができる。
表層部の厚さが板厚の10%未満の場合、励磁磁束密度の低い段階で、表層部が磁気的に飽和近くなり透磁率が低下する。その結果、内層部も磁化し始めるため、渦電流損の低減効果が薄れてしまう。一方、表層部の厚さが板厚の40%を超える場合、表面から板厚中心付近の深さまでの広範囲が磁化されるため、Si均一材に近い磁束分布となり、渦電流低減効果は薄れてしまう。Si傾斜鋼板において、渦電流損を効果的に低減するためには、表層の一定領域に磁束を集中させることが重要である。以上より、表層部の厚さは板厚の10%以上40%以下が好ましい。より好まくは、20%以上35%以下である。
表層部の平均Si濃度が2.5%未満の場合、渦電流低減効果が少ない。一方、6.5%を超える場合は、表層割れの頻度が急激に増加する場合がある。よって、表層部の平均Si濃度は、2.5~6.5%が好ましい。
平均Si濃度が2.0%を超える場合、表層部と内層部の境界で不連続なSi濃度分布(境界部)が形成されにくく、十分な渦電流損低減効果が得られない。よって、内層部の平均Si濃度は2.0%以下が好ましい。一方、内層部の平均Si濃度が、0.15%未満の場合、浸珪処理条件や拡散処理条件を調整しても表層部の結晶粒が板厚方向に細長く成長して表層部の結晶粒の平均アスペクト比b/aが0.7未満となりやすく、表層で割れが生じやすい。よって、内層部の平均Si濃度は0.15%以上が好ましい。
表層部と内層部を分ける境界部の板厚±1μm以内の範囲のSi濃度差が0.4%以上の場合、Si濃度分布を完全に均一化した場合より、10%以上の渦電流損低減効果が得られる。一方、境界部のSi濃度差が0.4%未満の場合、内層部も磁化されやすくなり、表層部への磁束集中効果が薄れるため、十分な渦電流損低減効果が得られない場合がある。よって境界部のSi濃度差は0.4%以上が好ましい。ここで、境界部におけるSiの最小濃度は内層部の濃度に相当とし、最大の濃度は浸珪処理・拡散処理を行った温度域において、表層部(α相)がとりうる最低のSi濃度に相当する。
本発明では、表層部に引張応力、内層部に圧縮応力の応力分布とすることで渦電流損の低減をはかる。同板厚かつ平均Si濃度の同じSi均一鋼板と比較して、明確な渦電流損低減(10%以上)を図るためには、表層部の引張応力が50MPa以上、内層部の圧縮応力が50MPa以上とすることが好ましい。一方、表層部の引張応力が200MPa、内層部の圧縮応力が200MPaを超える場合、表層部の結晶粒のアスペクト比を本発明範囲内にしたとしても、剪断時の割れが著しく、鉄損のバラツキが大きくなってしまう恐れがある。したがって、表層部の引張応力は50~200MPa、内層部の圧縮応力は50~200MPaの範囲が好ましい。なお、これらの内部応力値は、実質的に板反りのないSi傾斜鋼板に対し、片面のみ表面から板厚中心部まで化学研磨で除去したときに観察される板反りの曲率半径から求めた値である。
板厚を薄くするほど渦電流損を低減できる。しかし、0.03mm未満は圧延の製造コストが増加するのみならず、コア材の加工・組立作業にも大きな負荷がかかると予想される。一方、板厚0.5mmを超える場合、鋼板表面からの浸珪処理、およびSi分布適正化のための拡散処理に時間がかかる。またコア加工時においても、板厚0.5mmを超える場合、剪断面で割れが発生し易く特性のバラツキを増大させるおそれがある。よって、板厚は0.03~0.5mmが好ましい。
素材のC濃度は、軟磁気特性向上のため低い方が好ましい。0.020%を超える場合、浸珪処理・拡散処理後の冷却時において、Si濃度の低い内層部でパーライト組織やベイナイト組織、マルテンサイト組織が形成されやすく、これらは鋼板の保磁力を増し、ヒステリシス損を増大させる。したがって、素材C濃度は0.020 %以下とする。なお、C濃度の下限はとくに限定されるものではないが、極低炭素鋼の場合と同様に、鋼中の固溶C濃度が極めて低くなると粒界破壊が生じやすくなる。よって、好ましくは、0.0005~0.020%である。
素材のSi濃度は、0.15 %未満の場合、浸珪処理・拡散処理時に板厚方向に細長く伸びたアスペクト比0.7未満の表層粒が生じやすい。これは、剪断加工時の割れ多発、鉄損バラツキ増大を招く。一方、素材Si濃度が2.0%を超える場合、表層部と内層部の境界で不連続なSi濃度分布(境界部)が形成されにくく、十分な渦電流損低減効果が得られない。
したがって、素材Si濃度は0.15~2.0%とする。
Mnは鋼の靱性改善に有効な元素である。鋼中ではSと結合しMnSとして析出する。素材のMn濃度が0.05%未満の場合、Sが粒界偏析して高Si濃度の表層部の結晶粒で粒界破壊が生じやすくなる。またMnはオーステナイト相を安定化させる元素でもある。素材Mn濃度が2.00%を超える場合、浸珪処理・拡散処理した後の冷却過程で内層部がオーステナイトからフェライトに変態する際、内層部に大きな変態歪みが残留し易い。この変態歪みは、Si傾斜鋼板の応力分布を乱すため、渦電流低減効果が抑制されてしまう。したがって、素材Mn濃度は0.05~2.00%とする。
Pは、鋼の強度向上に有効な元素である反面、脆化を促進させる元素でもある。また相変態の界面で偏析する傾向もある。0.1%以下であれば、実質的に表層部の粒界割れや境界部の割れが顕在化することはない。そこで、素材P濃度は0.1%以下とする。
Sは、粒界に偏析しやすい元素であり、脆化防止のためには濃度は低い方が好ましい。0.01%以下であれば、実質的に割れが顕在化することはない。そこで、素材S濃度は0.01 %以下とする。
AlはSiと同様に鋼の固有抵抗を増加させる元素であり、電磁鋼板においてはSiと複合添加されることも多い。一方、SiはFe結晶の格子間距離を縮める元素であるのに対し、Alは逆にFe結晶の格子間距離を拡げる元素である。Si傾斜鋼板においては、Al添加はSi添加によって得られる渦電流低減に適した応力分布を緩和する方向に働くため、好ましくない。しかし、0.1%以下であれば、悪影響は生じない。よって、素材Al濃度は0.1%以下とする。Al濃度の下限はとくに限定するものではないが、0.002%未満に制限した場合、種々の粒径が混在した組織となりやすく、鉄損を劣化させる場合がある。また、上限についてもとくに限定するものではないが、加工の観点から0.01%以下とすることが有利である。よって、好ましくは0.002~0.01%である。
Nは、0.01%を超えて含有した場合、鉄損の増大を招いてしまう。よって、0.01%以下とする。
表1に示す成分を含有し、残部がFe及び不可避的不純物からなる鋼塊を、1100℃に加熱し板厚2.3mmまで熱間圧延を施した後、冷間圧延により板厚0.2mmまで圧延した。この冷延板から幅50mm×長さ150mmの浸珪処理用の試験片を切り出した。次いで、試験片を、アルゴン雰囲気中で室温域からオーステナイト相が生じる1100~1225℃の温度域まで搬送しながら加熱し、次いで体積比で8~66%の四塩化珪素を含むアルゴンガスを炉内に流し、上記と同じ温度で1~6分間の浸珪処理を行った。その後、四塩化珪素を含まないアルゴンのみの非酸化雰囲気に切り替え1100~1250℃の温度域で2~30分間の拡散処理を行った。ここで、浸珪量すなわち鋼板へのSi添加量は、雰囲気中の四塩化珪素濃度と処理時間により調整した。また、表面からのSi拡散によりオーステナイト相からフェライト相に変態させる表層部の厚さは、浸珪処理および拡散処理の時間により調整し、後で鋼板断面のSi濃度分布をEPMA(電子線マイクロアナライザ)で確認した。実験番号ごと、同じ処理条件で同じ形態の試料を各12枚ずつ作製した。
以上により、内層部の平均Si濃度、鋼板表面のSi濃度、表層部の平均Si濃度、板厚に対する表層部厚さ比、表層部の結晶粒の平均アスペクト比、境界部のSi濃度差、飽和磁束密度Bs、磁束密度0.1T;10kHzで励磁したときの高周波鉄損W1/10kの平均値m、その標準偏差σ、および変動係数σ/mを計測した。また、Si濃度を均一化した試料(Si均一材)の鉄損W1/10kを測定し、実験番号毎にSi均一材の鉄損に対する上記で測定したSi傾斜材の鉄損平均値との比を算出した。得られた結果を表6に示す。
ds/d0が10%以上40%以下で境界部のSi濃度差が0.2%以上、かつ表層部の結晶粒の平均アスペクト比が0.7以上4.0以下の本発明例は、Si濃度を均一化した場合より10%以上の低鉄損化が成されており、鉄損のバラツキも変動係数10%未満と小さく抑えられていることがわかる。
Claims (6)
- 鋼板の板厚中心を対称面として、鋼板表面より板厚深さ方向に高Si濃度から低Si濃度に連続的に変化する表層部と、Si濃度が不連続的に変化する境界部と、Si濃度が実質的に板厚方向に変化しない板厚中心を含む内層部とを有し、
前記表層部で面内引張応力、前記内層部で面内圧縮応力となる応力分布を有する電磁鋼板であり、
前記表層部の結晶粒の平均アスペクト比:板面垂直方向(深さ方向)に対する板面平行方向の寸法比が0.7以上4.0以下であることを特徴とする電磁鋼板。
なお、前記平均アスペクト比とは、50個以上の結晶粒のアスペクト比の平均値であり、表層部の結晶粒が境界部を超えて内層部に及ぶ場合、板面垂直方向(深さ方向)寸法は内層部も含めて計測することとする。 - 前記表層部の厚さは板厚の10~40%の範囲であることを特徴とする請求項1に記載の電磁鋼板。
- 質量%で、前記表層部の平均Si濃度が2.5~6.5%、前記内層部の平均Si濃度が2.0%以下であることを特徴とする請求項1または2に記載の電磁鋼板。
- 前記表層部では、板面と平行方向に50~200MPaの引張応力を、前記内層部では、板面と平行方向に50~200MPaの圧縮応力を、有することを特徴とする請求項1~3のいずれか一項に記載の電磁鋼板。
- 板厚が0.03~0.5mmであることを特徴とする請求項1~4のいずれか一項に記載の電磁鋼板。
- 質量%で、C:0.020%以下、Si:0.15~2.0%、Mn:0.05~2.00%、P:0.1%以下、S:0.01%以下、Al: 0.1%以下、N:0.01%以下を含有し、残部がFe及び不可避的不純物からなる成分組成を有する鋼板に対して、
非酸化雰囲気中で、1100~1250℃に加熱しオーステナイト相とし、
次いで、10mol%以上45mol%未満の四塩化珪素を含む非酸化雰囲気中、1100~1250℃の温度で、鋼板表面からSiを浸透させて鋼板表層をフェライト相とし、
次いで、内層部にオーステナイト相を残したまま、Siを含まない非酸化雰囲気中、1100~1250℃の温度で、フェライト相である表層部が板厚に対し10~40%の厚さとなるまで一定時間保持し、
次いで、400℃まで、5~30℃/sの平均冷却速度で冷却する
ことを特徴とする電磁鋼板の製造方法。
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- 2017-03-29 EP EP17775283.9A patent/EP3438314B1/en active Active
- 2017-03-29 US US16/089,734 patent/US20190112697A1/en not_active Abandoned
- 2017-03-29 JP JP2017541118A patent/JP6319522B2/ja active Active
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Also Published As
Publication number | Publication date |
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US20190112697A1 (en) | 2019-04-18 |
EP3438314B1 (en) | 2020-12-30 |
EP3438314A4 (en) | 2019-02-20 |
EP3438314A1 (en) | 2019-02-06 |
KR102129846B1 (ko) | 2020-07-03 |
CN108884535A (zh) | 2018-11-23 |
JP6319522B2 (ja) | 2018-05-09 |
KR20180120717A (ko) | 2018-11-06 |
JPWO2017170749A1 (ja) | 2018-04-05 |
CN108884535B (zh) | 2020-08-18 |
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