# US 9,435,012 B2 · Method for producing powder for magnet

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- Number: US 9,435,012 B2
- Document ID: US9435012B2
- Status: Granted
- Kind: B2
- Application number: 14/979,111
- Filed: 2015-12-22
- Published: 2016-04-21
- Granted: 2016-09-06
- Earliest claimed: 2009-12-04
- Assignees: Sumitomo Electric Industries, Ltd.
- Applicants: Sumitomo Electric Industries, Ltd.
- Inventors: Toru Maeda
- Web page: https://patentgrep.com/patent/US9435012B2

## CPC

- C21D 1/74: Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
- B22F 1/00: Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
- B22F 1/102: Metallic powder coated with organic material
- B22F 3/02: Compacting only
- B22F 9/00: Making metallic powder or suspensions thereof
- C21D 6/00: Heat treatment of ferrous alloys
- C22C 33/02: by powder metallurgy
- C22C 33/0228: {comprising other non-metallic compounds or more than 5% of graphite}
- C22C 38/001: {containing N}
- C22C 38/005: {containing rare earths, i.e. Sc, Y, Lanthanides}
- H01F 1/0552: {with a protective layer}
- H01F 1/0553: {obtained by reduction or by hydrogen decrepitation or embrittlement}
- H01F 1/0556: {pressed}
- H01F 1/059: and Va elements, e.g. Sm2Fe17N2
- H01F 1/08: pressed, sintered, or bound together
- H01F 1/22: pressed, sintered, or bound together
- H01F 41/0246: {Manufacturing of magnetic circuits by moulding or by pressing powder (magnetic cores made by moulding or by pressing powder H01F27/255; soft magnetic particles H01F1/20, H01F1/36)}
- H01F 41/0266: {Moulding; Pressing (H01F41/0273 takes precedence; hard magnetic particles H01F1/06, H01F1/11)}
- B22F 2998/10: Processes characterised by the sequence of their steps
- B22F 2999/00: Aspects linked to processes or compositions used in powder metallurgy
- C22C 2202/02: Magnetic
- 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 (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- B22F: WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER (making alloys by powder metallurgy C22C); APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES

## Abstract

Provided are a method for producing powder for a magnet, and methods for producing a powder compact, a rare-earth-iron-based alloy material, and a rare-earth-iron-nitrogen-based alloy material. Magnetic particles constituting the powder each have a texture in which grains of a phase of a hydride of a rare-earth element are dispersed in a phase of an iron-containing material. The uniform presence of the phase of the iron-containing material in each magnetic particle results in powder having excellent formability, thereby providing a powder compact having high relative density. The powder is produced by heat-treating rare-earth-iron-based alloy powder in a hydrogen atmosphere to separate the rare-earth element and the iron-containing material and then forming a hydride of the rare-earth element. The powder is compacted. The powder compact is heat-treated in vacuum to form a rare-earth-iron-based alloy material. The rare-earth-iron-based alloy material is heat-treated in a nitrogen atmosphere to form a rare-earth-iron-nitrogen-based alloy material.

## Claims

### Claim 1

A method for producing a rare-earth-iron-nitrogen-based alloy material used for a rare-earth magnet, the method comprising:
a preparation step of preparing an alloy powder composed of a rare-earth-iron-based alloy that contains a rare-earth element serving as an additional element;
a hydrogenation step of heat-treating the rare-earth-iron-based alloy powder in a hydrogen element-containing atmosphere at a temperature equal to or higher than a disproportionation temperature of the rare-earth-iron-based alloy to form a powder for a magnet, wherein the powder is constituted by magnetic particles, each of the magnetic particles contains a hydride of a rare-earth element in an amount of less than 40% by volume and the balance being an iron-containing material that contains Fe, wherein a phase of the hydride of the rare-earth element is adjacent to a phase of the iron-containing material, and an interval between adjacent phases of the hydride of the rare-earth element with the phase of the iron-containing material provided therebetween is 3 μm or less;
a coating step of coating an antioxidation layer on a surface of each of the magnetic particles, the antioxidation layer including a low-oxygen-permeability layer composed of a material having an oxygen permeability coefficient at 30° C. of less than 1.0×10−11 m3·m/(s·m2·Pa) and a low-moisture-permeability layer composed of a material having a moisture permeability coefficient at 30° C. of less than 1000×10−13 kg/(m·s·MPa), the low-oxygen-permeability layer is polyester or polyvinyl chloride;
a compacting step of compacting the powder for the magnet to provide a powder compact having a relative density of 85% or more; and
a dehydrogenation step of heat-treating the powder compact in an inert atmosphere or a reduced atmosphere at a temperature equal to or higher than a recombination temperature of the powder compact to form the rare-earth-iron-based alloy material.

### Claim 2

A method for producing a rare-earth-iron-nitrogen-based alloy material used for a rare-earth magnet, the method comprising:
a preparation step of preparing an alloy powder composed of a rare-earth-iron-based alloy that contains a rare-earth element serving as an additional element;
a hydrogenation step of heat-treating the rare-earth-iron-based alloy powder in a hydrogen element-containing atmosphere at a temperature equal to or higher than a disproportionation temperature of the rare-earth-iron-based alloy to form a powder for a magnet, wherein the powder is constituted by magnetic particles, each of the magnetic particles contains a hydride of a rare-earth element in an amount of less than 40% by volume and the balance being an iron-containing material that contains Fe, wherein a phase of the hydride of the rare-earth element is adjacent to a phase of the iron-containing material, and an interval between adjacent phases of the hydride of the rare-earth element with the phase of the iron-containing material provided therebetween is 3 μm or less;
a coating step of coating an antioxidation layer on a surface of each of the magnetic particles, the antioxidation layer including a low-oxygen-permeability layer composed of a material having an oxygen permeability coefficient at 30° C. of less than 1.0×10−11 m3·m/(s·m2·Pa) and a low-moisture-permeability layer composed of a material having a moisture permeability coefficient at 30° C. of less than 1000×10−13 kg/(m·s·MPa), the low-oxygen-permeability layer is polyester or polyvinyl chloride;
a compacting step of compacting the powder for the magnet to provide a powder compact having a relative density of 85% or more; and
a dehydrogenation step of heat-treating the powder compact in an inert atmosphere or a reduced atmosphere at a temperature equal to or higher than a recombination temperature of the powder compact to form the rare-earth-iron-based alloy material,
wherein the rare-earth-iron-based-alloy is a Sm—Fe—Ti alloy.