Gear and method for manufacturing the same

Patent metadata

Field	Value
Publication number	US-2016108490-A1
Application number	US-201414894239-A
Country	US
Kind code	A1
Filing date	Apr 21, 2014
Priority date	Jun 20, 2013
Publication date	Apr 21, 2016
Grant date	—

Abstract

A gear that is formed of material steel molded to include a disc portion and a plurality of tooth portions circumferentially discretely formed on the disc portion and have a shape in which tooth root portions are formed between the tooth portions, and is subjected to vacuum carburizing treatment and subsequent quenching treatment with high-density energy heating after being molded.

First claim

1 - 8 . (canceled)

9 . A gear that is formed of material steel molded to include a disc portion and a plurality of tooth portions circumferentially discretely formed on the disc portion and have a shape in which tooth root portions are formed between the tooth portions, and is subjected to vacuum carburizing treatment and subsequent quenching treatment with high-density energy heating after being molded, wherein
the material steel has a chemical composition of:
C: 0.10% by mass to 0.30% by mass;
Si: 0.50% by mass to 3.00% by mass;
Mn: 0.30% by mass to 3.00% by mass;
P: 0.030% by mass or less;
S: 0.030% by mass or less;
Cu: 0.01% by mass to 1.00% by mass;
Ni: 0.01% by mass to 3.00% by mass;
Cr: 0.20% by mass to 1.00% by mass;
Mo: 0.10% by mass or less;
N: 0.05% by mass or less; and
Fe and unavoidable impurities: a residual portion, where
Si(% by mass)+Ni(% by mass)+Cu(% by mass)−Cr(% by mass)>0.5 is satisfied,
a partially tempered region is provided in a surface layer of at least a part of a portion including an edge part at an end in an axial direction in the tooth portions and the tooth root portions, the partially tempered region has hardness lower than hardness of a martensitic structure generated in the surface layer of the part of the portion by the quenching treatment, and a surface layer of a portion other than the partially tempered region in the tooth portions and the tooth root portions is formed by the martensitic structure generated by the quenching treatment.

10 . The gear according to claim 9 , wherein
the chemical composition of the material steel further includes:
B: 0.005% by mass or less; and
Ti: 0.10% by mass or less.

11 . The gear according to claim 9 , wherein
a meshing region on each of tooth flanks meshing with another gear is not included in the partially tempered region, and is formed by the martensitic structure generated by the quenching treatment.

12 . The gear according to claim 10 , wherein
a meshing region on each of tooth flanks meshing with another gear is not included in the partially tempered region, and is formed by the martensitic structure generated by the quenching treatment.

13 . The gear according to claim 9 , wherein
the gear has a beveled shape in which an end thereof in the axial direction has a diameter larger than that of the other end, and the partially tempered region is provided to at least a part of the surface layer including the edge part at the end on the larger diameter side in the tooth portions and the tooth root portions.

14 . The gear according to claim 10 , wherein
the gear has a beveled shape in which an end thereof in the axial direction has a diameter larger than that of the other end, and the partially tempered region is provided to at least a part of the surface layer including the edge part at the end on the larger diameter side in the tooth portions and the tooth root portions.

15 . A side gear and a pinion gear in a differential device configured such that a plurality of gears according to claim 13 are meshed with each other, wherein
a meshing region on each of tooth flanks of the gears meshing with the other of the meshing gears is not included in the partially tempered region, and is formed by the martensitic structure generated by the quenching treatment.

16 . A side gear and a pinion gear in a differential device configured such that a plurality of gears according to claim 14 are meshed with each other, wherein
a meshing region on each of tooth flanks of the gears meshing with the other of the meshing gears is not included in the partially tempered region, and is formed by the martensitic structure generated by the quenching treatment.

17 . A method for manufacturing a gear that is formed of material steel molded to include a disc portion and a plurality of tooth portions circumferentially discretely formed on the disc portion and have a shape in which tooth root portions are formed between the tooth portions, wherein
the material steel has a chemical composition of:
C: 0.10% by mass to 0.30% by mass,
Si: 0.50% by mass to 3.00% by mass,
Mn: 0.30% by mass to 3.00% by mass,
P: 0.030% by mass or less,
S: 0.030% by mass or less,
Cu: 0.01% by mass to 1.00% by mass,
Ni: 0.01% by mass to 3.00% by mass,
Cr: 0.20% by mass to 1.00% by mass,
Mo: 0.10% by mass or less,
N: 0.05% by mass or less, and
Fe and unavoidable impurities: a residual portion, where
Si(% by mass)+Ni(% by mass)+Cu(% by mass)−Cr(% by mass)>0.5 is satisfied is used,
the method for manufacturing a gear comprising: a vacuum carburizing step of heating the gear formed of the molded material steel to a temperature at or higher than an austenitizing temperature of the material steel in a carburizing atmosphere at a pressure lower than the atmospheric pressure to form a carburized layer on a surface of the gear; a cooling step of cooling the gear, after the vacuum carburizing step, to a temperature lower than a temperature at which structure transformation due to the cooling is completed, at a cooling rate lower than a cooling rate at which the material steel is transformed into martensite; a quenching step of heating the gear after the cooing step with high-density energy heating to increase the temperature of the gear to a temperature at or higher than the austenitizing temperature of the material steel and, from that state, cooling the gear at a cooling rate at or higher than the cooling rate at which the material steel is transformed into martensite to form a martensitic structure at least in a portion of the carburized layer; and a partial tempering step of heating at least a part of a portion including an edge part at an end in an axial direction in the tooth portions and the tooth root portions of the gear with the high-density energy heating after the quenching step to increase the temperature of at least the part of the portion including the edge part to a temperature of 180° C. or higher at which austenitization of the material steel does not occur and, from that state, cooling the gear to reduce a concentration of carbon dissolved in a solid state in the martensitic structure in the portion of the carburized layer in at least the part of the portion including the edge part.

18 . The method for manufacturing a gear according to claim 17 , wherein the chemical composition of the material steel used includes:
B: 0.005% by mass or less; and Ti: 0.10% by mass or less.

19 . The method for manufacturing a gear according to claim 17 , wherein
the gear to be manufactured is a gear having a beveled shape in which an end thereof in the axial direction has a diameter larger than that of the other end and including the edge part at an end on the larger diameter side, and in the partial tempering step, the heating is performed in the state in which the end on the larger diameter side of the bevel-shaped gear lies in the space inside an exciting coil, and the end on the smaller diameter side of the bevel-shaped gear lies outside the exciting coil.

20 . The method for manufacturing a gear according to claim 18 , wherein
the gear to be manufactured is a gear having a beveled shape in which an end thereof in the axial direction has a diameter larger than that of the other end and including the edge part at an end on the larger diameter side, and in the partial tempering step, the heating is performed in the state in which the end on the larger diameter side of the bevel-shaped gear lies in the space inside an exciting coil, and the end on the smaller diameter side of the bevel-shaped gear lies outside the exciting coil.

Assignees

• Daido Steel Co Ltd
• Aisin Aw Co

Inventors

• Eto Yutaka
• Mizuno Koki
• Matsumura Yasushi
• Yamaguchi Kohei

Classifications

• C23C8/22

  of ferrous surfaces · CPC title

• C23C8/80

  After-treatment · CPC title

• C22C38/54

  with boron · CPC title

• C21D6/004

  containing Cr and Ni · CPC title

• C21D6/005

  containing Mn · CPC title