Method for manufacturing steel sheet for rotor core for IPM motor

{
  "publication_number": "US9847168B2",
  "country": "US",
  "kind": "B2",
  "title": "Method for manufacturing steel sheet for rotor core for IPM motor",
  "abstract": "The present invention manufactures a steel sheet for a rotor core for an IPM motor, wherein the steel sheet has a magnetic flux density B 8000 of 1.65 T or more as measured when magnetic field strength is 8000 A/m, and a residual magnetic flux density Br of 0.5 T or more as measured at that time, and optionally, a coercivity Hc of 100 A/m or more as measured after magnetization reaches 8000 A/m. By using the steel sheet manufactured according to the present invention for a rotor core of an IPM motor, it is possible to increase further an output torque in a high-speed rotational range and raise further the maximum rotational speed.",
  "claims": [
    "1. A method for manufacturing a steel sheet for a rotor core for an IPM motor, which has a magnetic flux density B 8000 of 1.65 T or more as measured when magnetic field strength is 8000 A/m and a residual magnetic flux density Br of 0.5 T or more as measured at that time, wherein a hot-rolled steel sheet having a composition comprising: C: more than 0.0005% by mass to 0.90% by mass, Si: 0% by mass to 3.0% by mass, Mn: 0% by mass to 0.05% by mass, P: 0.05% by mass or less, S: 0.02% by mass or less, acid-soluble Al: 0.005% by mass to 3.0% by mass, and Si+Al: 5.0% by mass or less, with a balance of Fe and inevitable impurities, is cold rolled, heated to 800° C. or more in a continuous annealing line or continuous quenching line, then cooled down to 450° C. or less at a cooling speed of 10° C./sec or more and held at a temperature range of 200° C. to 450° C. for at least 20 seconds and less than 120 seconds, and then a step of adjusting a flatness defined by a steepness per sheet width to 0.1% or less by performing inline or offline press tempering treatment in a state of being held at said temperature range of 200° C. to 450° C.",
    "2. The method for manufacturing a steel sheet for a rotor core for an IPM motor according to claim 1, wherein the steel sheet for a rotor core for an IPM motor has a coercivity Hc of 100 A/m or more as measured after magnetization reaches 8000 A/m.",
    "3. The method for manufacturing a steel sheet for a rotor core for an IPM motor according to claim 1, wherein the metallographic structure of the steel sheet for a rotor core for an IPM motor is composed of a single phase of martensite, a single phase of bainite, or a composite structure including less than 10% by volume of ferrite in addition to martensite.",
    "4. The method for manufacturing a steel sheet for a rotor core for an IPM motor according to claim 1, wherein the hot-rolled steel sheet further comprises one or more components selected from the group consisting of Ti, Nb, and V at 0.01% by mass to 0.20% by mass in total.",
    "5. The method for manufacturing a steel sheet for a rotor core for an IPM motor according to claim 1, wherein the hot-rolled steel sheet further comprises one or more components selected from the group consisting of Mo: 0.1% by mass to 0.6% by mass, Cr: 0.1% by mass to 1.0% by mass and B: 0.0005% by mass to 0.005% by mass.",
    "6. The method for manufacturing a steel sheet for a rotor core for an IPM motor according to claim 1, wherein the hot-rolled steel sheet further comprises one or more components selected from the group consisting of Cu: 0.05% by mass to 1.5% by mass and Ni: 0.05% by mass to 1.0% by mass.",
    "7. The method for manufacturing a steel sheet for a rotor core for an IPM motor according to claim 1, wherein the content of C in the hot-rolled steel sheet is more than 0.0005% by mass to 0.058% by mass.",
    "8. The method for manufacturing a steel sheet for a rotor core for an IPM motor according to claim 1, further comprising a step of forming an insulating coating consisting of an organic material, an insulating coating consisting of an inorganic material or an insulating coating consisting of an organic-inorganic composite material on at least one surface of the steel sheet in an inline or offline process.",
    "9. The method for manufacturing a steel sheet for a rotor core for an IPM motor according to claim 1, wherein a pressure in the inline or offline press tempering treatment is less than 1 kg/cm 2."
  ],
  "description_excerpt": "The present invention relates to a method for manufacturing a steel sheet for a rotor core for an interior permanent magnet motor (hereafter “IPM motor”) that is used mainly for electric vehicles, hybrid vehicles and machine tools.\n\nGenerally, IPM motors, which use expensive permanent magnets, are expensive, but are more efficient than induction motors. For this reason, IPM motors are widely used, for example, for driving motors and power generating motors for hybrid vehicles and electric vehicles, and also motors for home electric appliances, various machine tools and industrial machines.\n\nAn iron core of an IPM motor is composed of a stator and a rotor. Since an AC magnetic field is directly applied to the iron core on the stator side through windings, the iron core on the stator side must have high magnetic permeability and also high volume resistivity so as to reduce iron loss. Therefore, electromagnetic steel sheets with soft magnetic characteristics improved by the addition of Si to ultra-low-carbon steel are used for the iron core on the stator side (see, for example, Patent Documents 1 and 2).\n\nOn the other hand, since a permanent magnet is embedded in the iron core on the rotor side, this iron core mainly acts as a yoke to increase magnetic flux density. The iron core on the rotor side is slightly affected by the AC magnetic field generated from the stator side, but this influence is limited. Therefore from the standpoint of characteristics, it is not necessary to use electromagnetic steel sheets, which are advantageous for the iron loss characteristic, for the iron core on the rotor side.",
  "cpc": [
    "H01F 41/024",
    "C21D 2211/002",
    "C21D 2211/008",
    "C21D 6/001",
    "C21D 6/002",
    "C21D 6/005",
    "C21D 6/008",
    "C21D 8/02",
    "C21D 8/12",
    "C21D 8/1233",
    "C21D 8/1244",
    "C21D 8/125",
    "C21D 8/1283",
    "C21D 9/46",
    "C21D 9/573",
    "C22C 38/00",
    "C22C 38/002",
    "C22C 38/004",
    "C22C 38/02",
    "C22C 38/04",
    "C22C 38/06",
    "C22C 38/08",
    "C22C 38/12",
    "C22C 38/14",
    "C22C 38/16",
    "C22C 38/18",
    "C22C 38/20",
    "C22C 38/26",
    "C22C 38/28",
    "C22C 38/32",
    "H01F 1/16",
    "H02K 15/00"
  ],
  "ipc": [
    "C21D 9/46",
    "C21D 6/00",
    "C21D 8/12",
    "C22C 38/00",
    "C22C 38/02",
    "C22C 38/04",
    "C22C 38/06",
    "C22C 38/12",
    "C22C 38/14",
    "C22C 38/16",
    "C22C 38/20",
    "C22C 38/26",
    "C22C 38/28",
    "C22C 38/32",
    "H01F 41/02",
    "H02K 15/00",
    "C21D 8/02",
    "C21D 9/573",
    "C22C 38/08",
    "C22C 38/18",
    "H01F 1/16"
  ],
  "assignees": [
    "Nisshin Steel Co Ltd"
  ],
  "inventors": [
    "Tomonaga Iwatsu",
    "Yukio Katagiri",
    "Susumu Fujiwara",
    "Akito Kawamoto"
  ],
  "filing_date": "2013-03-27",
  "publication_date": "2017-12-19",
  "grant_date": "2017-12-19",
  "priority_date": "2012-03-30",
  "application_number": "US-201314389595-A",
  "family_id": "49260135",
  "cited_by_count": 1,
  "citations": [
    "JP2000278900A",
    "JP2005060811A",
    "JP2005113184A",
    "JP2005133175A",
    "CN101454465A",
    "JP2009046738A",
    "EP2693602A1"
  ]
}