Method for producing R-T-B sintered magnet

• US 9,478,332 B2
• Filed: 01/17/2013
• Issued: 10/25/2016
• Est. Priority Date: 01/19/2012
• Status: Active Grant

• Current Assignee: Proterial Ltd.
• Original Assignee: Hitachi Metals (Thailand) Ltd.
• Inventors: Kuniyoshi, Futoshi, Ishii, Rintaro, Yamagata, Ryouichi
• Primary Examiner(s): Yang, Jie
• Assistant Examiner(s): Su, Xiaowei
• Application Number:
  US14/372,543
• Publication Number:
  US 20140375404A1
• Time in Patent Office: 1,377 Days
• US Class Current: 1/1
• CPC Class Codes: B22F 2003/248 Thermal after-treatment
• CPC Class Codes: B22F 2207/01 Composition gradients
• CPC Class Codes: B22F 2207/20 Cooperating components
• CPC Class Codes: B22F 3/003 Apparatus, e.g. furnaces in general F27B
• CPC Class Codes: B22F 3/24 After-treatment of workpieces or articles B22F3/1146 takes precedence
• CPC Class Codes: B22F 3/26 Impregnating making ferrous alloys by impregnation C22C33/0242
• CPC Class Codes: B22F 9/023 Hydrogen absorption
• CPC Class Codes: C22C 2202/02 Magnetic
• CPC Class Codes: C22C 28/00 Alloys based on a metal not provided for in groups C22C5/00 - C22C27/00
• CPC Class Codes: C22C 30/00 Alloys containing less than 50% by weight of each constituent
• CPC Class Codes: C22C 38/00 Ferrous alloys, e.g. steel alloys cast-iron alloys C22C37/00
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/005 containing rare earths, i.e. Sc, Y, Lanthanides
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/10 containing cobalt
• CPC Class Codes: C22C 38/16 containing copper
• CPC Class Codes: H01F 1/0536 sintered
• CPC Class Codes: H01F 1/0577 sintered
• CPC Class Codes: H01F 41/0293 diffusion of rare earth elements, e.g. Tb, Dy or Ho, into permanent magnets
• CPC Class Codes: H01F 7/02 : Permanent magnets [PM]

Abstract

A method for producing a sintered R-T-B based magnet includes providing a sintered R-T-B based magnet body, of which the rare-earth-element mole fraction falls within the range of 31 mass % to 37 mass %; providing an RH diffusion source including a heavy rare-earth element RH (which is at least one of Dy and Tb) and 30 mass % to 80 mass % of Fe; loading the sintered magnet body and the RH diffusion source into a processing chamber so that the magnet body and the diffusion source are movable relative to each other and readily brought close to, or in contact with, each other; and performing an RH diffusion process by conducting a heat treatment on the sintered magnet body and the RH diffusion source at a process temperature of 700° C. to 1000° C. while moving the sintered magnet body and the RH diffusion source either continuously or discontinuously.

Claims

1. A method for producing a sintered magnet, the method comprising the steps of:

providing a sintered R-T-B based magnet body, of which the R mole fraction that is defined by the content of a rare-earth element falls within the range of 31 mass % to 37 mass %;

providing an RH diffusion source including a heavy rare-earth element RH, which is at least one of Dy and Tb, and including a volume percentage of an RHFe₂ compound and/or an RHFe₃ compound of 90% or more;

loading the sintered magnet body and the RH diffusion source into a processing chamber so that the magnet body and the diffusion source are movable relative to each other and readily brought close to, or in contact with, each other; and

performing an RH diffusion process by conducting a heat treatment on the sintered magnet body and the RH diffusion source at a process temperature of 870°

C. to 970°

C. and at an internal processing pressure of 10<sup>−

2</sup> Pa to atmospheric pressure while rotating the processing chamber at a peripheral velocity of 0.01 m/s or more to continuously or discontinuously move the sintered magnet body and the RH diffusion source in the processing chamber;

wherein

the sintered magnet body has an effective rare-earth content of 28 mass % to 35 mass %, in which the effective rare-earth content is defined by the following equation;

the effective rare-earth content=the R mole fraction−

(6×

O mole fraction+8×

C mole fraction+10×

N mole fraction),

where the O mole fraction is an oxygen content of the sintered magnet body, the C mole fraction is a carbon content of the sintered magnet body, and the N mole fraction is a nitrogen content of the sintered magnet body.