Classifications

• • 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%
• • 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
• • 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 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
• • 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 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
• • 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 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
• • 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 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
• • 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 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
• • 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
• • 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
• • 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
  • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
• • 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
  • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
• • 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
• • 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
• • 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
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
• • 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
• • 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
  • H01F1/147—Alloys characterised by their composition
  • H01F1/14766—Fe-Si based alloys
  • H01F1/14791—Fe-Si-Al based alloys, e.g. Sendust
• • 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

Definitions

• This invention relates to a non-oriented electrical steel sheet having low iron loss and also having high strength at an operating temperature, and a method for producing the same.
• Non-oriented electrical steel sheets used in an iron core of a motor have also been demanded to have excellent iron loss properties and higher strength from the viewpoint of durability.
• the steel sheet has variation of strength, the risk of breakage is increased in a low-strength portion of the sheet during use as an iron core, so that the strength in the steel sheet is required to be uniform.
• driving motors for automobiles are required to be small in size and large in power, which increases the temperature during use of the motor, and hence the high strength is required even at about 150°C.
• it is essential for the non-oriented electrical steel sheet used as an iron core to have not only excellent magnetic properties but also high yield strength in a high temperature range with minimal variability.
• Patent Literature 1 proposes a non-oriented electrical steel sheet having a chemical composition comprising Si: 1.5 mass% or more but 3.5 mass% or less, Mn: 1.5 mass% or less, Al: 0.2 mass% or more but 3.0 mass% or less, Mg: 0.0003 mass% or more but 0.0050 mass% or less, and the balance being Fe and inevitable impurities and having a high yield strength, wherein a crystal grain size d is 5 ⁇ m or more but 40 ⁇ m or less and the relationship of d ⁇ 50 ⁇ (Si + 0.5Al - 2) is satisfied.
• Patent Literature 2 proposes a method for producing a non-oriented electrical steel sheet having low iron loss, characterized in that a silicon steel slab containing C: 0.005 mass% or less, Si: 2.5 to 4.0 mass%, S: 0.005mass% or less, Al: 0.3 to 1.5 mass%, and N: 0.004 mass% or less is subjected to hot rolling, hot-band annealing, and one cold rolling step or two or more cold rolling steps with intermediate annealing between each step to obtain a final sheet thickness, soaked at temperatures of 900 to 1200°C for 5 seconds to 15 minutes, subjected to finishing annealing involving cooling the steel sheet until the temperature at the sheet width central portion reaches 600°C while the temperature across the sheet width direction is maintained within ⁇ 20°C of the temperature at the central portion, followed by insulation treatment.
• Patent Literature 1 the yield strength at room temperature is sufficiently high while that at 150°C is not sufficient, and good iron loss cannot be obtained.
• the technique disclosed in Patent Literature 2 although the variation of the iron loss in the sheet width direction can be reduced, the yield strength at 150°C tends to vary.
• the technique disclosed in Patent Literature 3 can achieve good magnetic properties, but the yield strength at 150°C decreases.
• the invention has been contrived in view of the above problems of the prior arts, and an object thereof is to provide a non-oriented electrical steel sheet having not only good magnetic properties but also high yield strength at the operating temperature of a motor with minimal variation, and a production method advantageous thereto.
• the inventors have made intensive studies on the chemical composition of the steel sheet and the production method thereof, with particular emphasis on carbon C, which deteriorates iron loss and is usually reduced.
• the inventors found the following insight. That is, by properly controlling the cooling rate in a given temperature range, together with the composition and dew point of the atmosphere gas in a furnace during the cooling step of finishing annealing, the steel sheet can be cooled uniformly across its entire width. This ensures that the dissolution carbon remains uniform across the width of the steel sheet. Consequently, good iron loss is achieved and high yield strength at 150°C, which is the operating temperature of the motor, is imparted with minimal variation in the sheet width direction.
• the present invention has thus been achieved.
• the invention is a non-oriented electrical steel sheet with a chemical composition comprising C: 0.0005 to 0.0100 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.1 to 2.0 mass%, P: 0.050 mass% or less, S: 0.0050 mass% or less, Al: 0.20 to 2.50 mass%, N: 0.0050 mass% or less, O: 0.0050 mass% or less, at least one of Sn and Sb: 0.01 to 0.20 mass% in total, and the balance being Fe and inevitable impurities, having a minimum value of yield strength at 150°C in the sheet width direction of 300 MPa or more and a variation of the yield strength in the sheet width direction of 30 MPa or less.
• the non-oriented electrical steel sheet according to the invention contains at least one group selected from the following groups A to F:
• the invention also proposes a method for producing a non-oriented electrical steel sheet including: hot rolling a steel slab having a chemical composition comprising C: 0.0005 to 0.0100 mass%, Si: 2.0 to 4.5 mass%, Mn: 0.1 to 2.0 mass%, P: 0.050 mass% or less, S: 0.0050 mass% or less, Al: 0.20 to 2.50 mass%, N: 0.0050 mass% or less, O: 0.0050 mass% or less, at least one of Sn and Sb: 0.01 to 0.20 mass% in total, and the balance being Fe and inevitable impurities, followed by hot-band annealing, cold rolling, and finishing annealing, in which
• the cooling is conducted such that the difference between the maximum and minimum values of an average cooling rate every 100°C in a temperature range from 700°C to 200°C during the finishing annealing is 20°C/s or less.
• the steel slab used in the method for producing a non-oriented electrical steel sheet according to the invention contains, in addition to the above chemical composition, at least one group selected from the following groups A to F:
• the present invention can stably provide a non-oriented electrical steel sheet not only having good magnetic properties but also having high yield strength over the entire width of the steel sheet at an operating temperature of a motor. Therefore, the present invention can provide a material suitable for use in a motor required to have high efficiency and high durability.
• C is an element necessary to obtain high yield strength at 150°C, which is the operating temperature of a motor.
• Dissolution C in a steel sheet product contributes to increasing yield strength as it causes dislocations in the steel sheet or be segregated in grain boundaries when heated to 150°C.
• C is necessary to be contained at 0.0005 mass% or more.
• an excessive C content causes such disadvantages that yield strength largely varies and iron loss deteriorates. Therefore, the C content is limited to 0.0100 mass% or less. It is preferably in the range of 0.0008 to 0.0060 mass%.
• Si has an effect of increasing the specific resistance of steel and thus reducing iron loss, so that it is contained at 2.0 mass% or more in the present invention.
• Si also has an effect of increasing the yield strength.
• Si is preferably added at 2.7 mass% or more, particularly at more than 3.0 mass% for a high-quality material where low iron loss is highly required.
• the upper limit of Si content should be 4.5 mass%, preferably 4.0 mass%.
• the P content should be 0.050 mass% or less, preferably 0.030 mass% or less, more preferably 0.015 mass% or less.
• the lower limit of P is not specified, but it is preferably about 0.004 mass%, from the viewpoint of suppressing the cost increase for removing P in the steelmaking process.
• the S content is limited to 0.0050 mass% or less, preferably 0.0020 mass% or less.
• Al similar to Si, has an effect of increasing the specific resistance of steel to thus reduce iron loss and also has an effect of increasing the yield strength. Therefore, in the invention, Al is contained at 0.20 mass% or more, preferably 0.50 mass% or more. Meanwhile, when Al is excessively contained, the variation of yield strength increases or alumina is formed in a large amount to induce surface defects. Therefore, the upper limit of Al is 2.50 mass%, preferably at 2.20 mass% or less.
• N is a harmful element which forms fine nitride such as AlN, thus increasing yield strength variation and deteriorating iron loss. Therefore, the N content is limited to 0.0050 mass% or less, preferably 0.0030 mass% or less. In addition, the lower limit of N is not particularly specified but is preferably about 0.0005 mass% from the viewpoint of suppressing the cost increase in steelmaking.
• O is a harmful element which forms fine oxide, hindering crystal grain growth and deteriorating iron loss. Also, the fine oxide refines crystal grains, causing yield strength to vary. Therefore, the O content is limited to 0.0050 mass% or less, preferably 0.0025 mass% or less.
• At least one of Sn and Sb 0.01 to 0.20 mass% in total
• Sn and Sb are elements effective in improving the texture of the steel sheet after finishing annealing to thus improve magnetic properties. Therefore, at least one of Sn and Sb is added at 0.01 mass% or more in total. Meanwhile, the above effect is saturated when Sn and Sb are added excessively, so that the total content of at least one of Sn and Sb should be 0.20 mass% or less.
• the total content is preferably in the range of 0.02 to 0.05 mass%.
• the non-oriented electrical steel sheet according to the invention contains Fe and inevitable impurities as the balance other than the above elements.
• the steel sheet may contain at least one group selected from the following groups A to F to further improve the magnetic and strength properties.
• Group A at least one element selected from the group consisting of Ca, Mg, and REM: 0.0010 to 0.0080 mass% in total
• Group B at least one element selected from the group consisting of Cr, Mo, Cu, and Ni: 0.01 to 0.60 mass% in total
• Cr, Mo, Cu, and Ni have an effect of increasing the specific resistance of steel to improve iron loss. Therefore, it is preferable to contain at least one of Cr, Mo, Cu, and Ni in a total content of 0.01 mass% or more. However, excessive contents of Cr, Mo, Cu, and Ni deteriorate the surface properties. Therefore, at least one element selected from the group consisting of Cr, Mo, Cu, and Ni is preferably contained in a total content of 0.60 mass% or less, and more preferably in a range of 0.03 to 0.50 mass% in total. It should be noted that Cu is preferably contained at 0.50 mass% or less as it largely affects the surface properties. Cu is more preferably contained at 0.10 mass% or less where severe surface properties are required.
• Group C at least one element selected from the group consisting of Ti, Nb, and V: 0.0005 to 0.0050 mass% in total
• Ti, Nb, and V have an effect of forming precipitates to increase the yield strength. Therefore, at least one element selected from the group consisting of Ti, Nb, and V is preferably contained at 0.0005 mass% or more in total. Meanwhile, the excessive additions of Ti, Nb, and V hinders the crystal grain growth significantly and deteriorate iron loss. Therefore, at least one element selected from the group consisting of Ti, Nb, and V is preferably contained at 0.0050 mass% or less in total, more preferably in a range of 0.0010 to 0.0025 mass% in total.
• Group D at least one element selected from the group consisting of B: 0.0001 to 0.0020 mass%, Pb: 0.0001 to 0.0010 mass%, and W: 0.0005 to 0.0050 mass%
• B, Pb, and W all have an effect of refining the texture of the steel sheet after finishing annealing, thereby increasing its yield strength.
• B and Pb at 0.0001 mass% or more each and W at 0.0005 mass% or more.
• B, Pb, and W are preferably contained at 0.0020 mass% or less, 0.0010 mass% or less, and 0.0050 mass% or less, respectively. More preferably, B, Pb, and W are contained in the ranges of 0.0003 to 0.0010 mass%, 0.0002 to 0.0006 mass%, and 0.0020 to 0.0035 mass%, respectively.
• Group E Zn: 0.001 to 0.010 mass%
• Zn has an effect of forming an oxide or a sulfide and refining the texture of the steel sheet, thereby increasing the yield strength.
• Zn is preferably added at 0.001 mass% or more. Meanwhile, excessive addition of Zn can deteriorate iron loss. Therefore, Zn is preferably contained at 0.010 mass% or less when added. It is more preferably contained in the range of 0.003 to 0.006 mass%.
• Group F Co: 0.0010 to 0.0500 mass%
• Co has effects such as increasing the specific resistance of steel to reduce its iron loss and increasing its yield strength.
• Co is preferably contained at 0.0010 mass% or more. Meanwhile, excessive addition of Co only saturates the effect, so that Co is preferably contained at 0.0500 mass% or less, more preferably in the range of 0.0040 to 0.0200 mass%.
• the yield strength at 150°C is defined as 300 MPa or more, preferably 340 MPa or more in the present invention.
• the yield strength at 150°C is the minimum value of the yield strength values (upper yield point or 0.2% proof stress if there is no upper yield point) measured in accordance with JIS Z2241 for test specimens taken from 10 or more positions in the sheet width direction of the steel sheet.
• the variation of yield strength at 150°C in the sheet width direction is limited to 30 MPa or less.
• the variation of yield strength in the sheet width direction means a difference between the maximum value and the minimum value when the yield strength is measured at 10 or more positions in the width direction of the steel sheet.
• the raw steel material (slab) used in the production of a non-oriented electrical steel sheet according to the invention needs to be adjusted to have the above-described chemical composition.
• Methods of melting steel having the chemical composition include well-known refining processes using a converter, an electric furnace, or a secondary refining apparatus such as a vacuum degassing apparatus or the like, and are not particularly specified.
• a continuous casting method is preferably used to produce the slab, but an ingot making-blooming method and a thin slab casting method are acceptable.
• the raw material may be an iron scrap and a direct reduced iron.
• the steel slab is heated to a given temperature and hot rolled to form a hot-rolled sheet of a given thickness.
• the hot rolling conditions are not specified, but the heating temperature of the slab is preferably in the range of 1000°C to 1160°C, inclusive.
• the slab may be subjected to direct rolling in which the slab is hot-rolled immediately after continuous casting without heating.
• the winding temperature of a coil after hot rolling is preferably in the range of 500°C to 650°C, inclusive.
• the steel sheet (hot-rolled sheet) after the hot rolling is then subjected to hot-band annealing.
• the conditions of the hot-band annealing are not specified, but the annealing temperature is preferably in the range of 800 to 1000°C, inclusive. It is also preferable to remove scales formed on the surface of steel sheet by pickling in a pre-stage or post-stage of the hot-band annealing.
• the pickling may be conducted in a usual manner and is not specified.
• the cold rolled sheet with the final sheet thickness then undergoes finishing annealing to impart the desired magnetic and strength properties. Finishing annealing is the most important step in the invention and needs to be conducted under the following conditions.
• the steel sheet is cooled at a given cooling rate uniformly in the sheet width direction, so that dissolution C remains uniform in the sheet width direction, thereby increasing the yield strength at 150°C and reducing the variation thereof in the sheet width direction.
• the cooling rate from 700°C to 200°C falls below 10°C/s, C is precipitated as Fe carbide during cooling to reduce amount of dissolution C, and thus the high yield strength at 150°C is not obtained. Therefore, the cooling rate from 700°C to 200°C is required to 10°C/s or more. In order to further increase the yield strength at 150°C, it is preferably 15°C/s or more.
• the upper limit is preferably about 50°C/s.
• the dew point of the atmosphere gas in the furnace is high in the range where the steel sheet temperature is between the soaking temperature and 300°C, the surface layer of the steel sheet is oxidized non-uniformly to form an oxide film, which causes a difference in heat exchange with the cooling gas and promotes the temperature variation in the sheet width direction. Therefore, the dew point of the atmosphere gas in the furnace in the temperature range from the soaking temperature to 300°C should be -30°C or less, preferably -40°C or less. Considering that the effect saturates if the dew point of the furnace atmosphere gas is too low, and taking into account the dew point of industrially usable atmosphere gases, the lower limit is preferably about -70°C.
• the variation of the steel sheet temperature in the sheet width direction in the temperature range of 500 to 200°C is large, the amount of dissolution C in the sheet width direction is varied, which may increase the variation of yield strength at 150°C in the sheet width direction. Therefore, the variation of the steel sheet temperature between 500 and 200°C in the sheet width direction should be limited to 40°C or less. Preferably, it should be 30°C or less.
• the variation of the steel sheet temperature in the sheet width direction is the difference between the maximum and minimum temperatures in the sheet width direction at positions excluding 10 mm from the widthwise edges.
• the steel sheet subjected to the finishing annealing as described above is coated with an insulating film, if required, to form a product sheet.
• the insulating film may be an inorganic film, organic film or mixture of inorganic and organic films and is not specified.
• a steel having a chemical composition comprising various elements shown in Table 1 and the balance being Fe and inevitable impurities is melted by a usual refining process and produced into a raw steel material (slab) by a continuous casting method.
• the slab is then heated to 1130°C in a heating furnace for 60 minutes and subjected to hot rolling involving rough rolling and finish rolling to form a hot-rolled sheet of a sheet thickness of 1.8 mm, which was wound into a coil at 550°C.
• the hot-rolled sheet is subjected to hot-band annealing at a soaking temperature of 960°C and cold rolled to form a cold-rolled sheet of a final sheet thickness of 0.30 mm.
• the evaluation test results are also shown in Table 2. It shows that the steel sheets of the invention examples produced under the conditions adapted to the present invention have a yield strength at 150°C of 300 MPa or more, a variation of the yield strength in the sheet width direction of 30 MPa or less, and good magnetic properties such that iron loss W 10/400 is 15.0 W/kg or less.

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• 2023
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