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  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
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  • C21D1/26—Methods of annealing
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  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
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  • C21D6/00—Heat treatment of ferrous alloys
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  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/007—Heat treatment of ferrous alloys containing Co
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  • 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
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  • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1216—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties characterised by the working steps
  • C21D8/1222—Hot rolling
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  • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1216—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties characterised by the working steps
  • C21D8/1233—Cold rolling
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  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1244—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties characterised by the heat treatment
  • C21D8/1261—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties characterised by the heat treatment following hot rolling
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  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
  • C21D8/12—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
  • C21D8/1244—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties characterised by the heat treatment
  • C21D8/1272—Final recrystallisation annealing
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  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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  • 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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  • 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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  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
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  • C22C38/007—Ferrous alloys, e.g. steel alloys containing silver
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  • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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• • C—CHEMISTRY; METALLURGY
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  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
• • C—CHEMISTRY; METALLURGY
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  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • 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
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
  • C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
  • C23G1/08—Iron or steel
• • 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
• • 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
  • H01F1/16—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 in the form of sheets
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
  • H01F3/00—Cores, Yokes, or armatures
  • H01F3/02—Cores, Yokes, or armatures made from sheets
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K1/00—Details of the magnetic circuit
  • H02K1/02—Details of the magnetic circuit characterised by the magnetic material
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K15/00—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines
  • H02K15/02—Processes or apparatus specially adapted for manufacturing, assembling, maintaining or repairing of dynamo-electric machines of stator or rotor bodies
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C2202/00—Physical properties
  • C22C2202/02—Magnetic
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/60—Other road transportation technologies with climate change mitigation effect
  • Y02T10/64—Electric machine technologies in electromobility

Definitions

• the present invention relates to a non-oriented electrical steel sheet, a manufacturing method thereof, and a motor core using the non-oriented electrical steel sheet.
• Motor cores are divided into stator cores and rotor cores, and the rotor core of an HEV drive motor has a large outer diameter, so it is subjected to large centrifugal forces.
• the rotor core has a very narrow portion (width: 1 to 2 mm) called the rotor core bridge, which is particularly subject to high stress when the motor is running.
• the electromagnetic steel sheets used in the rotor core must have excellent fatigue properties.
• it is desirable for the electromagnetic steel sheets used in the stator core to have high magnetic flux density and low iron loss in order to achieve a smaller motor with higher output.
• the properties required for the electromagnetic steel sheets used in the motor core are that the electromagnetic steel sheets for the rotor core have excellent fatigue properties, and that the electromagnetic steel sheets for the stator core have high magnetic flux density and low iron loss.
• Patent Document 1 discloses a technology for manufacturing a high-strength rotor core and a low-iron-loss stator core from the same material, in which a high-strength non-oriented electromagnetic steel sheet is manufactured, a rotor core material and a stator core material are extracted from the steel sheet by punching, which are then laminated, and after assembling the rotor core and the stator core, only the stator core is subjected to stress relief annealing.
• Patent Document 1 has the concern that although the use of high-strength non-oriented electrical steel sheet improves yield stress, it does not necessarily improve fatigue strength, which is the most important characteristic. Furthermore, there is a problem with the technology disclosed in Patent Document 1 in that the iron loss value after stress relief annealing cannot necessarily stably achieve the level required in industry.
• the present invention was made in consideration of the problems with the above-mentioned conventional technology, and its purpose is to provide a high-strength non-oriented electromagnetic steel sheet with good fatigue properties suitable for rotor cores, and a non-oriented electromagnetic steel sheet with excellent magnetic properties suitable for stator cores, and to propose a method for inexpensively manufacturing the non-oriented electromagnetic steel sheet.
• the inventors have discovered that by controlling the grain size distribution, a non-oriented electrical steel sheet with high fatigue strength can be obtained, and that when the non-oriented electrical steel sheet is subjected to stress relief annealing (heat treatment) for grain growth, excellent low iron loss can be stably achieved. Furthermore, they have also found that the grain size distribution can be controlled by optimizing the rolling conditions in the final pass of cold rolling.
• the present invention was made based on such findings and has the following configuration.
• a non-oriented electrical steel sheet In mass percent, C: 0.01% or less, Si: 2.0% or more and less than 4.5% Mn: 0.05% or more and 5.00% or less, P: 0.1% or less, S: 0.01% or less, Al: 3.0% or less and N: 0.0050% or less, Si + Al is less than 4.5%, and the balance is Fe and unavoidable impurities, Regarding the crystal grains in the steel sheet, the average crystal grain size X1 is 50 ⁇ m or less, and the standard deviation S1 of the crystal grain size distribution is expressed by the following formula (1): S1 / X1 ⁇ 0.75... (1) and the kurtosis K1 of the grain size distribution is 20.0 or less.
• composition further comprises, in mass%, The non-oriented electrical steel sheet according to the above [1], containing Co: 0.0005% or more and 0.0050% or less.
• composition further comprises, in mass%, The non-oriented electrical steel sheet according to the above [1] or [2], wherein Cr is 0.05% or more and 5.00% or less.
• composition further comprises, in mass%, Ca: 0.001% to 0.100%
• composition further comprises, in mass%, The non-oriented electrical steel sheet according to any one of [1] to [4], comprising one or two of Sn: 0.001% or more and 0.200% or less; and Sb: 0.001% or more and 0.200% or less.
• the composition further comprises, in mass%, Cu: 0% or more and 0.5% or less, Ni: 0% or more and 0.5% or less, Ti: 0% or more and 0.005% or less, Nb: 0% or more and 0.005% or less, V: 0% or more and 0.010% or less, Ta: 0% or more and 0.002% or less, B: 0% or more and 0.002% or less, Ga: 0% or more and 0.005% or less, Pb: 0% or more and 0.002% or less Zn: 0% or more and 0.005% or less, Mo: 0% or more and 0.05% or less, W: 0% or more and 0.05% or less,
• the non-oriented electrical steel sheet according to any one of [1] to [5], comprising one or more of Ge: 0% or more and 0.05% or less, and As: 0% or more and 0.05% or less.
• a non-oriented electrical steel sheet The component composition according to any one of [1] to [6] above, Regarding the crystal grains in the steel sheet, the average crystal grain size X2 is 80 ⁇ m or more, and the standard deviation S2 of the crystal grain size distribution is expressed by the following formula (2): S2 / X2 ⁇ 0.75 ... (2) and the kurtosis K2 of the grain size distribution is 3.00 or less.
• a method for producing a non-oriented electrical steel sheet according to any one of [1] to [6], A hot rolling process in which a steel material having a component composition according to any one of [1] to [6] is hot rolled to obtain a hot rolled sheet;
• a pickling process for pickling the hot-rolled sheet; a cold rolling step of cold rolling the hot-rolled sheet after the pickling under conditions of a final pass work roll diameter D of 150 mm ⁇ or more, a final pass rolling reduction r of 15% or more, and a final pass strain rate ⁇ m of 100 s -1 or more and 1300 s -1 or less to obtain a cold-rolled sheet;
• An annealing process in which the cold-rolled sheet is heated to an annealing temperature T2 of 700°C or higher and 850°C or lower under conditions of an average heating rate V1 of 10°C/s or higher from 500°C to 700°C, and then cooled to obtain a cold-rolled annealed sheet which is a non-oriented electrical
• a method for producing the non-oriented electrical steel sheet according to the above [7], comprising a heat treatment step of heating the non-oriented electrical steel sheet according to any one of the above [1] to [6] at a heat treatment temperature T3 of 750°C or higher and 900°C or lower.
• a motor core consisting of a rotor core that is a laminate of non-oriented electromagnetic steel sheets described in any one of [1] to [6] above, and a stator core that is a laminate of non-oriented electromagnetic steel sheets described in [7] above.
• non-oriented electrical steel sheet with good fatigue strength suitable for rotor cores and a non-oriented electrical steel sheet with excellent magnetic properties (low iron loss) suitable for stator cores.
• these non-oriented electrical steel sheets can be provided from the same steel sheet. Therefore, by using the non-oriented electrical steel sheet of the present invention, high-performance motor cores can be provided at low cost with good material yield.
• the non-oriented electrical steel sheet of the present invention can also be suitably used in small, high-output motors.
• composition of non-oriented electrical steel sheet The preferred composition of the non-oriented electrical steel sheet and motor core of the present invention will be described below.
• the unit of the content of elements in the composition is always “mass %", but hereinafter, it will be simply represented as “%” unless otherwise specified.
• the non-oriented electromagnetic steel sheet of the present invention includes a first non-oriented electromagnetic steel sheet that is mainly suitable for rotor cores, and a second non-oriented electromagnetic steel sheet that is mainly suitable for stator cores.
• the suitable composition of the components is the same for the first non-oriented electromagnetic steel sheet and the second non-oriented electromagnetic steel sheet.
• C 0.01% or less C is a harmful element that forms carbides during use of the motor, causing magnetic aging and degrading the iron loss characteristics.
• the C content in the steel sheet is 0.01% or less.
• the C content is 0.004% or less.
• the C content be 0.0001% or more.
• Si 2.0% or more and less than 4.5%
• Si has the effect of increasing the resistivity of steel and reducing iron loss, and also has the effect of increasing the strength of steel by solid solution strengthening.
• the Si content is set to 2.0% or more.
• the Si content is 4.5% or more, the magnetic flux density drops significantly with the drop in saturation magnetic flux density, so the Si content is set to less than 4.5%. Therefore, the Si content is set to a range of 2.0% or more and less than 4.5%.
• the Si content is preferably 2.5% or more and less than 4.5%, and more preferably 3.0% or more and less than 4.5%.
• Mn 0.05% to 5.00% Mn, like Si, is a useful element for increasing the resistivity and strength of steel. To obtain such an effect, the Mn content must be 0.05% or more. On the other hand, if the Mn content exceeds 5.00%, it may promote the precipitation of MnC and deteriorate the magnetic properties, so the upper limit of the Mn content is set to 5.00%. Therefore, the Mn content is set to 0.05% to 5.00%.
• the Mn content is preferably 0.10% or more and 3.00% or less.
• P 0.1% or less
• P is a useful element used to adjust the strength (hardness) of steel.
• the P content is set to 0.1% or less.
• the P content is 0.001% or more.
• the P content is preferably 0.003% or more and 0.08% or less.
• S 0.01% or less
• S is an element that forms fine precipitates and adversely affects iron loss characteristics.
• the S content is set to 0.01% or less.
• the S content is 0.0001% or more.
• the S content is preferably 0.0003% or more, and is preferably 0.0080% or less, and more preferably 0.0050% or less.
• Al 3.0% or less
• Al is a useful element that has the effect of increasing the resistivity of steel and reducing iron loss.
• the Al content is 0.005% or more.
• the Al content is more preferably 0.010% or more, and even more preferably 0.015% or more.
• the Al content exceeds 3.0%, it may promote nitriding of the steel sheet surface and deteriorate the magnetic properties, so the upper limit of the Al content is set to 3.0%.
• the Al content is preferably 2.0% or less.
• N is an element that forms fine precipitates and adversely affects iron loss characteristics. In particular, if the N content exceeds 0.0050%, the adverse effects become significant, so the N content is set to 0.0050% or less.
• the N content is preferably 0.0030% or less. Although there is no particular lower limit for the N content, since steel sheets with excessively reduced N content are very expensive, the N content is preferably 0.0005% or more.
• the N content is preferably 0.0008% or more, and preferably 0.0030% or less.
• Si+Al Less than 4.5%
• the remainder other than the above components is Fe and unavoidable impurities.
• one or more elements selected from those described below can be contained in a specified amount depending on the required characteristics.
• Co 0.0005% or more and 0.0050% or less
• Co has the effect of reinforcing the effect of reducing the kurtosis of the grain size distribution of the annealed sheet by appropriate control of Si + Al and cold rolling conditions. That is, the addition of a small amount of Co can stably reduce the kurtosis of the grain size distribution. To obtain such an effect, the Co content should be 0.0005% or more.
• the content of Co exceeds 0.0050%, the effect is saturated and the cost increases unnecessarily, so when Co is added, the upper limit of the Co content is set to 0.0050%. Therefore, it is preferable that the above composition further contains Co: 0.0005% or more and 0.0050% or less.
• Cr 0.05% to 5.00% Cr has the effect of increasing the resistivity of steel and reducing iron loss. To obtain such an effect, the Cr content should be 0.05% or more. On the other hand, if the Cr content exceeds 5.00%, the magnetic flux density drops significantly with the drop in saturation magnetic flux density, so when Cr is added, the upper limit of the Cr content is set to 5.00%. Therefore, it is preferable that the above composition further includes Cr: 0.05% to 5.00%.
• Ca 0.001% or more and 0.100% or less
• Ca is an element that fixes S as sulfides and contributes to reducing iron loss.
• the Ca content should be 0.001% or more.
• the upper limit of the Ca content is set to 0.100%.
• Mg 0.001% or more and 0.100% or less
• Mg is an element that fixes S as sulfides and contributes to reducing iron loss. To obtain such an effect, the Mg content should be 0.001% or more. On the other hand, if the Mg content exceeds 0.100%, the effect saturates and the cost increases unnecessarily, so when Mg is added, the upper limit of the Mg content is set to 0.100%.
• REM 0.001% to 0.100% REM is a group of elements that fix S as sulfides and contribute to reducing iron loss. To obtain this effect, the REM content should be 0.001% or more. However, if the REM content exceeds 0.100%, the effect saturates and costs increase unnecessarily, so when REM is added, the upper limit of the REM content is set to 0.100%.
• the above composition further contains one or more of the following: Ca: 0.001% to 0.100%, Mg: 0.001% to 0.100%, and REM: 0.001% to 0.100%.
• Sn 0.001% to 0.200%
• Sn is an element that is effective in improving the magnetic flux density and reducing iron loss by improving the texture. To obtain this effect, the Sn content should be 0.001% or more. However, if the Sn content exceeds 0.200%, the effect saturates and the cost increases unnecessarily, so when Sn is added, the upper limit of the Sn content is set to 0.200%.
• Sb 0.001% to 0.200%
• Sb is an element that is effective in improving magnetic flux density and reducing iron loss by improving the texture. To obtain this effect, the Sb content should be 0.001% or more. However, if the Sb content exceeds 0.200%, the effect saturates and the cost increases unnecessarily, so when Sb is added, the upper limit of the Sb content is set to 0.200%.
• the above composition further contains one or two of Sn: 0.001% to 0.200% and Sb: 0.001% to 0.200%.
• Cu 0% or more and 0.5% or less Cu is an element that improves the toughness of steel and can be added as appropriate. However, the effect of Cu is saturated when the content exceeds 0.5%, so when Cu is added, the upper limit of the Cu content is set to 0.5%. When Cu is added, the Cu content is more preferably 0.01% or more, and more preferably 0.1% or less. The Cu content may be 0%.
• Ni 0% or more and 0.5% or less
• Ni is an element that improves the toughness of steel, and can be added as appropriate. However, the effect of Ni is saturated when the content exceeds 0.5%, so when Ni is added, the upper limit of the Ni content is set to 0.5%.
• the Ni content is more preferably 0.01% or more, and more preferably 0.1% or less.
• the Ni content may be 0%.
• Ti 0% to 0.005% Ti can be added as appropriate because it forms fine carbonitrides and increases the strength of the steel sheet through precipitation strengthening, thereby improving fatigue strength. On the other hand, if the Ti content exceeds 0.005%, it deteriorates grain growth in the heat treatment process, leading to an increase in iron loss. Therefore, when Ti is added, the upper limit of the Ti content is set to 0.005%. The Ti content is more preferably 0.002% or less. The Ti content may be 0%.
• Nb 0% or more and 0.005% or less Nb can be added appropriately because it forms fine carbonitrides and increases the strength of the steel sheet through precipitation strengthening, thereby improving fatigue strength.
• the content of Nb exceeds 0.005%, it deteriorates grain growth in the heat treatment process and leads to an increase in iron loss. Therefore, when Nb is added, the upper limit of the Nb content is set to 0.005%.
• the Nb content is more preferably 0.002% or less.
• the Nb content may be 0%.
• V 0% or more and 0.010% or less V can be added appropriately because it forms fine carbonitrides and increases the strength of the steel sheet through precipitation strengthening, thereby improving fatigue strength.
• the V content exceeds 0.010%, it deteriorates grain growth in the heat treatment process, leading to an increase in iron loss. Therefore, when V is added, the upper limit of the V content is set to 0.010%.
• the V content is more preferably 0.005% or less.
• the V content may be 0%.
• Ta 0% or more and 0.002% or less Ta can be added appropriately because it forms fine carbonitrides and increases the strength of the steel sheet through precipitation strengthening, thereby improving fatigue strength.
• the Ta content exceeds 0.002%, it deteriorates grain growth in the heat treatment process and leads to an increase in iron loss. Therefore, when Ta is added, the upper limit of the Ta content is set to 0.0020%.
• the Ta content is more preferably 0.001% or less.
• the Ta content may be 0%.
• B 0% or more and 0.002% or less B can be added as appropriate because it forms fine nitrides and increases the strength of the steel sheet through precipitation strengthening, thereby improving fatigue strength.
• the B content exceeds 0.002%, it deteriorates grain growth in the heat treatment process, leading to an increase in iron loss. Therefore, when B is added, the upper limit of the B content is set to 0.002%.
• the B content is more preferably 0.001% or less.
• the B content may be 0%.
• Ga 0% or more and 0.005% or less Ga can be added appropriately because it forms fine nitrides and increases the strength of the steel sheet through precipitation strengthening, thereby improving fatigue strength.
• the Ga content exceeds 0.005%, it deteriorates grain growth in the heat treatment process and leads to an increase in iron loss. Therefore, when Ga is added, the upper limit of the Ga content is set to 0.005%.
• the Ga content is more preferably 0.002% or less.
• the Ga content may be 0%.
• Pb 0% or more and 0.002% or less Pb can be added as appropriate to form fine Pb particles and increase the steel sheet strength through precipitation strengthening, thereby improving fatigue strength.
• the Pb content exceeds 0.002%, it deteriorates grain growth in the heat treatment process and leads to an increase in iron loss. Therefore, when Pb is added, the upper limit of the Pb content is set to 0.002%.
• the Pb content is more preferably 0.001% or less.
• the Pb content may be 0%.
• Zn 0% or more and 0.005% or less
• Zn is an element that increases fine inclusions and increases iron loss, and the adverse effects become particularly noticeable when the content exceeds 0.005%. Therefore, when Zn is added, the upper limit of the Zn content is set to 0.005%.
• the Zn content is more preferably 0.003% or less.
• the Zn content may be 0%.
• Mo 0% or more and 0.05% or less Mo can be added appropriately because it forms fine carbides and increases the strength of the steel sheet through precipitation strengthening, thereby improving fatigue strength.
• the content of Mo exceeds 0.05%, it deteriorates grain growth in the heat treatment process, leading to an increase in iron loss. Therefore, when Mo is added, the upper limit of the Mo content is set to 0.05%.
• the Mo content is more preferably 0.02% or less.
• the Mo content may be 0%.
• W 0% or more and 0.05% or less W can be added as appropriate because it forms fine carbides and increases the strength of the steel sheet through precipitation strengthening, thereby improving fatigue strength.
• the W content exceeds 0.05%, it deteriorates grain growth in the heat treatment process, leading to an increase in iron loss. Therefore, when W is added, the upper limit of the W content is set to 0.05%.
• the W content is more preferably 0.02% or less.
• the W content may be 0%.
• Ge 0% or more and 0.05% or less Ge is an element that is effective in improving the magnetic flux density and reducing iron loss by improving the texture, so it can be added appropriately.
• the effect of Ge is saturated when the content exceeds 0.05%, so when Ge is added, the upper limit of the Ge content is set to 0.05%.
• the Ge content is more preferably 0.002% or more, and more preferably 0.01% or less.
• the Ge content may be 0%.
• As 0% or more and 0.05% or less As is an element that is effective in improving the magnetic flux density and reducing iron loss by improving the texture, so it can be added appropriately.
• the effect of As is saturated when the content exceeds 0.05%, so when As is added, the upper limit of the As content is set to 0.05%.
• the As content is more preferably 0.002% or more, and more preferably 0.01% or less.
• the As content may be 0%.
• the remainder other than the above-mentioned components is Fe and unavoidable impurities.
• the first non-oriented electrical steel sheet is a material particularly suitable for rotor cores.
• the fatigue strength is improved by fine grains in the steel sheet. That is, if the average grain size X1 is 50 ⁇ m or less, the fatigue strength can satisfy the value required for rotor materials of motors applied to HEVs or EVs (hereinafter referred to as HEV/EV motors), so in the first non-oriented electrical steel sheet, the average grain size X1 is set to 50 ⁇ m or less.
• HEV/EV motors the value required for rotor materials is 500 MPa or more.
• the lower limit of the average grain size X1 is not particularly specified, if the grain size is too fine, the ductility of the steel sheet decreases and processing becomes difficult, so that the average grain size X1 is preferably 1 ⁇ m or more.
• the standard deviation S1 of the grain size distribution is set to be greater than or equal to the following formula (1): S1 / X1 ⁇ 0.75... (1)
• the first non-oriented electrical steel sheet has a standard deviation S1 of the grain size distribution that satisfies the following formula (1'): S1 / X1 ⁇ 0.70...(1') It is preferable that the following is satisfied.
• kurtosis K1 of crystal grain size distribution 20.0 or less
• the inventors have found that by controlling the kurtosis of the grain size distribution, a non-oriented electrical steel sheet having excellent fatigue strength can be obtained, and excellent low iron loss can be achieved when grains are grown by stress relief annealing (heat treatment). Such effects can be obtained by simultaneously controlling the kurtosis of the grain size distribution and the standard deviation S1 of the grain size distribution described above.
• kurtosis corresponds to the (sample) peak in JIS Z8101-1:2015 and is related to the weight of the tail of the distribution.
• JIS Z8101-1:2015 corresponds to ISO 3534-1:2006.
• kurtosis is an index of the frequency of the existence of extremely coarse crystal grains and/or extremely fine crystal grains with respect to the variation in the crystal grain size distribution.
• kurtosis is high, the frequency of the existence of extremely coarse crystal grains and/or extremely fine crystal grains is high.
• extremely coarse crystal grains and extremely fine crystal grains are mixed, excessive stress concentration and local repeated strain caused by it are likely to occur during repeated stress loading, which deteriorates fatigue properties.
• the kurtosis K1 of the grain size distribution is set to 20.0 or less.
• the kurtosis K1 of the grain size distribution of the first non-oriented electrical steel sheet is preferably 15.0 or less.
• the lower limit of the kurtosis K1 does not need to be particularly limited, but is usually 0 or more even when the steel sheet is manufactured by making full use of the method of the present invention.
• the kurtosis K1 can be determined according to the procedure described in the Examples below, and is a value calculated using a formula in which the normal distribution value is adjusted to 0.
• the first non-oriented electrical steel sheet having the above-mentioned microstructure can become the second non-oriented electrical steel sheet when subjected to a heat treatment to grow grains, as described below.
• the microstructure (crystal grain configuration) in the second non-oriented electrical steel sheet of the present invention will be described.
• Such a second non-oriented electrical steel sheet is particularly suitable for a stator core.
• the iron loss of non-oriented electrical steel sheet varies depending on the average grain size.
• the average grain size X2 is set to 80 ⁇ m or more. This makes it possible to achieve the target iron loss characteristic (W10 /400 ⁇ 13.0 (W/kg)).
• the standard deviation S2 of the grain size distribution is set to satisfy the following formula (2): S2 / X2 ⁇ 0.75...(2)
• the second non-oriented electrical steel sheet has a standard deviation S2 of the grain size distribution that satisfies the following formula (2'): S2 / X2 ⁇ 0.70...(2') It is preferable that the following is satisfied.
• the kurtosis K2 of the grain size distribution is set to 3.00 or less.
• the kurtosis K2 of the grain size distribution in the second non-oriented electrical steel sheet is preferably 2.50 or less, more preferably 2.00 or less.
• the lower limit of the kurtosis K2 does not need to be particularly specified, but is usually 0 or more even in the case of manufacturing by making full use of the technique of the present invention.
• the kurtosis K2 can be determined according to the procedure described in the Examples below, and is a value calculated using a formula in which the normal distribution value is adjusted to 0.
• the motor core of the present invention comprises a rotor core which is a laminate of the first non-oriented electrical steel sheet, i.e., a non-oriented electrical steel sheet having an average grain size X1 of 50 ⁇ m or less, a standard deviation S1 which satisfies [ S1 / X1 ⁇ 0.75], and a kurtosis K1 of 20.0 or less, and a stator core which is a laminate of the second non-oriented electrical steel sheet, i.e., a non-oriented electrical steel sheet having an average grain size X2 of 80 ⁇ m or more, a standard deviation S2 which satisfies [ S2 / X2 ⁇ 0.75], and a kurtosis K2 of 3.00 or less.
• the rotor core has high fatigue strength, and the stator core has excellent magnetic properties, so that the motor core can be easily downsized and has high output.
• the method is a method in which a steel material having the above-mentioned composition is used as a starting material and a hot rolling process, an optional hot-rolled sheet annealing process, a pickling process, a cold rolling process, and an annealing process are sequentially performed, thereby obtaining the first non-oriented electrical steel sheet of the present invention described above.
• the first non-oriented electrical steel sheet of the present invention described above can be obtained by subjecting the first non-oriented electrical steel sheet to a heat treatment.
• the composition of the steel material, the conditions of the cold rolling process and the annealing process, and the conditions of the heat treatment process are within predetermined ranges, other conditions are not particularly limited.
• the method for manufacturing the motor core is not particularly limited, and a commonly known method can be used.
• the steel material is not particularly limited as long as it has the composition described above for the non-oriented electrical steel sheet.
• the method for producing the steel material is not particularly limited, and may be a known method using a converter, an electric furnace, etc. From the viewpoint of productivity, it is preferable to produce a slab (steel material) by a continuous casting method after the production, but the slab may be produced by a known casting method such as an ingot making-blooming rolling method or a thin slab continuous casting method.
• the hot rolling process is a process of obtaining a hot-rolled sheet by hot rolling a steel material having the above-mentioned composition.
• the hot rolling process is not particularly limited as long as it is a process in which a steel material having the above-mentioned composition is heated and hot-rolled to obtain a hot-rolled sheet of a predetermined size, and a conventional hot rolling process can be applied.
• a typical hot rolling process is, for example, to heat a steel material to a temperature of 1000°C or higher and 1200°C or lower, hot roll the heated steel material at a finish rolling outlet temperature of 800°C or higher and 950°C or lower, and after hot rolling is completed, to perform appropriate post-rolling cooling (for example, cooling in the temperature range of 450°C or higher and 950°C or lower at an average cooling rate of 20°C/s or higher and 100°C/s or lower), and coiling at a coiling temperature of 400°C or higher and 700°C or lower to produce a hot-rolled sheet of the specified dimensions and shape.
• appropriate post-rolling cooling for example, cooling in the temperature range of 450°C or higher and 950°C or lower at an average cooling rate of 20°C/s or higher and 100°C/s or lower
• coiling at a coiling temperature of 400°C or higher and 700°C or lower to produce a hot-rolled sheet of the specified dimensions and shape.
• the hot-rolled sheet annealing process is a process of annealing the hot-rolled sheet by heating the hot-rolled sheet and holding it at a high temperature.
• the hot-rolled sheet annealing process is not particularly limited, and a conventional hot-rolled sheet annealing process can be applied. Note that this hot-rolled sheet annealing process is not essential and can be omitted.
• the pickling process is a process of pickling the hot-rolled sheet after the hot rolling process or any of the above-mentioned hot-rolled sheet annealing processes.
• the pickling process is not particularly limited as long as it is a process that can pickle the steel sheet after pickling to an extent that cold rolling can be performed, and for example, a conventional pickling process using hydrochloric acid or sulfuric acid can be applied.
• this pickling process may be performed continuously in the same line as the hot-rolled sheet annealing process, or may be performed in a separate line.
• the cold rolling process is a process of cold rolling the hot-rolled sheet (pickled sheet) that has been subjected to the above pickling. More specifically, in the cold rolling process, the hot-rolled sheet that has been subjected to the above pickling is cold-rolled under the conditions that the work roll diameter D of the final pass is 150 mm ⁇ or more, the rolling reduction r of the final pass is 15% or more, and the strain rate ⁇ m of the final pass is 100 s -1 or more and 1300 s -1 or less to obtain a cold-rolled sheet.
• a cold-rolled sheet of a predetermined size may be obtained by performing two or more cold rollings with intermediate annealing in between as necessary.
• the conditions of the intermediate annealing in this case are not particularly limited, and conventional intermediate annealing can be applied.
• the work roll diameter D in the final pass is set to 150 mm ⁇ or more.
• the reason for setting the work roll diameter D in the final pass to 150 mm ⁇ or more is to make the kurtosis K1 of the grain size distribution in the obtained first non-oriented electrical steel sheet to 20.0 or less, thereby forming a desired steel sheet structure.
• the work roll diameter D in the final pass is smaller than 150 mm ⁇ , the state is far removed from the flat compression state, and the non-uniformity of shear strain at the grain level is enhanced compared to when the work roll diameter is larger.
• the work roll diameter D of the final pass is preferably 170 mm ⁇ or more, and more preferably 200 mm ⁇ or more. There is no particular upper limit to the work roll diameter D of the final pass, but if the roll diameter is excessively large, the rolling load increases, so it is preferably 700 mm ⁇ or less.
• the reduction ratio r of the final pass is set to 15% or more.
• the reason for setting the reduction ratio r of the final pass to 15% or more is to obtain the effect of a series of cold rolling controls and form a desired steel sheet structure. If the reduction ratio r of the final pass is less than 15%, the reduction ratio is too low, making it difficult to control the structure after annealing. On the other hand, if the reduction ratio r of the final pass is 15% or more, the effect of the series of cold rolling control is exerted. As a result, the desired steel sheet structure is obtained.
• the reduction ratio r of the final pass is preferably 20% or more. There is no particular upper limit to the reduction ratio r of the final pass, but since a reduction ratio that is too high requires a large amount of equipment capacity and also makes it difficult to control the shape of the cold-rolled sheet, the reduction ratio r of the final pass is usually 50% or less.
• strain rate ⁇ m in the final pass 100 s ⁇ 1 or more and 1300 s ⁇ 1 or less
• the strain rate ⁇ m in the final pass is set to 100 s -1 or more and 1300 s -1 or less.
• the reason for setting the strain rate ⁇ m in the final pass to 100 s-1 or more and 1300 s -1 or less is to suppress fracture during rolling while setting the kurtosis K1 of the grain size distribution in the obtained first non-oriented electrical steel sheet to 20.0 or less, and form a desired steel sheet structure.
• the strain rate ⁇ m of the final pass is less than 100 s -1 , the non-uniformity of shear strain in the grain units of the cold-rolled sheet is enhanced, and the location dependency of nucleation and grain growth in the subsequent annealing process is emphasized, so that the kurtosis K 1 of the grain size distribution of the annealed sheet becomes large.
• the inventors speculate that the low strain rate ⁇ m reduces the flow stress, making it easier for strain to concentrate on grains with easily deformed crystal orientations, and making the strain distribution non-uniform.
• the strain rate ⁇ m of the final pass is more than 1300 s -1 , the flow stress increases excessively, making it easier for brittle fracture to occur during rolling.
• the strain rate ⁇ m in the final pass is 100 s -1 or more and 1300 s -1 or less, the kurtosis K1 of the grain size distribution becomes 20.0 or less after the annealing process described later while suppressing breakage during rolling. As a result, a desired steel sheet structure is obtained.
• the strain rate ⁇ m in the final pass is preferably 150 s ⁇ 1 or more and preferably 1000 s ⁇ 1 or less.
• vR is the roll peripheral speed (mm/s)
• R' is the roll radius (mm)
• h1 is the roll entry side plate thickness (mm)
• r is the reduction rate (%).
• the annealing process is a process of annealing the cold-rolled sheet that has been through the cold rolling process. More specifically, in the annealing process, the cold-rolled sheet that has been through the cold rolling process is heated to an annealing temperature T2 of 700°C or more and 850°C or less under the condition that the average heating rate V1 from 500°C to 700°C is 10°C/s or more, and then cooled to obtain a cold-rolled annealed sheet (first non-oriented electrical steel sheet). After the annealing process, an insulating coating can be applied to the surface. The coating method and type of coating are not particularly limited, and a commonly used insulating coating process can be applied.
• the average heating rate V1 from 500°C to 700°C is set to 10°C/s or more.
• the reason for setting the average heating rate V1 to 10°C/s or more is to make the standard deviation S1 of the grain size distribution in the obtained non-oriented electrical steel sheet satisfy the above formula (1) and form a desired steel sheet structure.
• the average heating rate V1 is less than 10°C/s, the frequency of recrystallization nuclei generation decreases due to excessive recovery, and the number of recrystallization nuclei becomes more location-dependent.
• the standard deviation S1 of the crystal grain size distribution becomes large, and the above formula (1) is not satisfied.
• the average heating rate V1 is 10°C/s or more, the frequency of recrystallization nuclei is high and the location dependency of the number of recrystallization nuclei is small. As a result, the standard deviation S1 of the crystal grain size distribution becomes small, and the above formula (1) is satisfied.
• the average heating rate V1 from 500° C. to 700° C. is preferably 20° C./s or more, more preferably 50° C./s or more. There is no particular upper limit to the average heating rate V1 , but an excessively high heating rate is likely to cause temperature unevenness, so the average heating rate V1 is preferably 500° C./s or less.
• the annealing temperature T2 is set to 700° C. or more and 850° C. or less.
• the reason for setting the annealing temperature T2 to 700° C. or more and 850° C. or less is as follows.
• the annealing temperature T2 is less than 700°C, grain growth is suppressed, emphasizing the location dependency of the number of recrystallized nuclei, resulting in a structure that retains the initial non-uniformity. As a result, the standard deviation S1 of the grain size distribution becomes large.
• the annealing temperature T2 is 700°C or higher, sufficient grain growth occurs, and the standard deviation S1 of the grain size distribution can be made to satisfy the above formula (1), and a desired steel sheet structure can be obtained.
• the annealing temperature T2 is preferably 750°C or higher.
• the annealing temperature T2 exceeds 850°C, the recrystallized grains grow excessively, and the average grain size X1 cannot be set to 50 ⁇ m or less. Therefore, the annealing temperature T2 is set to 850°C or less.
• the annealing temperature T2 is preferably 825°C or less.
• the steel sheet is heated to the annealing temperature T2 and then cooled.
• This cooling is preferably performed at a cooling rate of 50° C./s or less in order to prevent uneven cooling.
• the heat treatment step is a step of subjecting the cold-rolled annealed sheet (first non-oriented electrical steel sheet) that has been subjected to the annealing step to a heat treatment temperature T3 of 750°C to 900°C. After heating, the sheet is cooled to obtain a heat-treated sheet (second non-oriented electrical steel sheet).
• the heat treatment step is usually performed on a stator core formed by laminating the non-oriented electrical steel sheets, but the same effect can be obtained even when the heat treatment step is performed on the non-oriented electrical steel sheets before lamination.
• Heat treatment temperature T3 750°C or higher and 900°C or lower
• the heat treatment temperature T3 is set to 750° C. or more and 900° C. or less.
• the reason for setting the heat treatment temperature T3 to 750° C. or more and 900° C. or less is as follows. If the heat treatment temperature T3 is less than 750°C, the crystal grain growth becomes insufficient, and the average crystal grain size X2 in the obtained second non-oriented electrical steel sheet cannot be made 80 ⁇ m or more. Therefore, the heat treatment temperature T3 is set to 750°C or more.
• the heat treatment temperature T3 is preferably 775°C or more.
• the heat treatment temperature T3 is set to 900°C or less.
• the heat treatment temperature T3 is preferably 875°C or less.
• the microstructure of the second non-oriented electrical steel sheet described above is obtained, that is, the microstructure of the steel sheet having an average crystal grain size X2 of 80 ⁇ m or more, a standard deviation S2 satisfying [ S2 / X2 ⁇ 0.75], and a kurtosis K2 of 3.00 or less.
• This structural change is influenced by the microstructure of the steel sheet before the heat treatment process.
• the steel sheet before the heat treatment process needs to have a standard deviation S1 satisfying [ S1 / X1 ⁇ 0.75] and a kurtosis K1 of 20.0 or less.
• the obtained slab was hot-rolled to obtain a hot-rolled sheet having a thickness of 2.0 mm.
• the obtained hot-rolled sheet was annealed and pickled by a known method, and then cold-rolled to the thickness shown in Table 2 to obtain a cold-rolled sheet.
• the obtained cold-rolled sheet was annealed under the conditions shown in Table 2, and then coated by a known method to obtain a cold-rolled annealed sheet (first non-oriented electrical steel sheet).
• a rotor core made by laminating cold-rolled annealed sheets (first non-oriented electromagnetic steel sheets) and a stator core made by laminating heat-treated sheets (second non-oriented electromagnetic steel sheets) were combined using a known method to obtain a motor core.
• ⁇ Evaluation> (Observation of Microstructure) Test pieces for microstructural observation were taken from the obtained cold-rolled annealed sheet and heat-treated sheet. Next, the taken test pieces were reduced in thickness by chemical polishing so that the position corresponding to 1/4 of the sheet thickness on the rolled surface (ND surface) was the observation surface, and were mirror-finished. Electron backscatter diffraction (EBSD) measurement was performed on the mirror-finished observation surface to obtain local orientation data. At this time, for the cold-rolled annealed sheet, the step size was 2 ⁇ m and the measurement area was 4 mm2 or more, and for the heat-treated sheet, the step size was 10 ⁇ m and the measurement area was 100 mm2 or more.
• EBSD Electron backscatter diffraction
• the size of the measurement area was appropriately adjusted so that the number of crystal grains in the subsequent analysis was 5000 or more.
• the measurement may be performed in one scan of the entire area, or the results of multiple scans may be combined using the Combo Scan function.
• the obtained local orientation data was analyzed using analysis software: OIM Analysis 8.
• grain average data points were selected using the Partition Properties of the analysis software under the condition Formula: GCI[&;5.000,2,0.000,0,0,8.0,1,1,1.0,0;]>0.1, and data points unsuitable for analysis were excluded. At this time, more than 97% of the data points were valid.
• Grain Tolerance Angle 5°
• Minimum Grain Size 2
• Minimum Anti Grain Size 2
• Multiple Rows Requirement 2
• Anti-Grain Multiple Rows Requirement OFF.
• the grain information was output using the Export Grain File function for the pre-processed data.
• the Grain Size (Diameter in microns) of Grain File Type 2 was used as the grain size (x i ).
• the average grain size, standard deviation, and kurtosis were calculated for all the obtained grain information using the following formulas.
• the obtained average grain size, standard deviation, and kurtosis are X 1 , S 1 , and K 1 for the cold-rolled annealed sheet, and X 2 , S 2 , and K 2 for the heat-treated sheet.
• n is the number of crystal grains
• x i is each crystal grain size data (i: 1, 2, . . . , n).
• Tensile fatigue test pieces (same shape as No. 1 test piece conforming to JIS Z2275:1978, b: 15 mm, R: 100 mm) were taken from the obtained cold-rolled annealed sheet with the rolling direction as the longitudinal direction, and subjected to fatigue testing. Here, the end faces of the test pieces were machined to be smooth.

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• 2022
  • 2022-10-26 CN CN202280101266.8A patent/CN120077155A/zh active Pending
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  • 2022-10-28 TW TW111141197A patent/TWI837908B/zh active
• 2025
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