Gear having excellent seizing resistance

Patent metadata

Field	Value
Publication number	US-9587288-B2
Application number	US-201314383726-A
Country	US
Kind code	B2
Filing date	Mar 29, 2013
Priority date	Mar 30, 2012
Publication date	Mar 7, 2017
Grant date	Mar 7, 2017

Abstract

This gear has a predetermined chemical composition and has, in a surface-layer part, a texture of tempered martensite and/or tempered bainite and a steel material texture in which retained austenite exists in 1-10% by area percentage and in which a carbide is deposited in at least 5% by area percentage, and the nitrogen content at a depth of 20 μm below the surface is 2.0-6.0%. Thus, a gear that achieves even better seizing resistance in a power transmission part subjected to high rotation and high slippage and using a low-kinematic-viscosity lubricating oil is provided.

First claim

The invention claimed is:

1. A gear prepared by subjecting a gear precursor comprising iron and, in mass percent:
C: 0.15 to 0.45%,
Si: 0.05 to 1.0%,
Mn: 1.0 to 2.0%,
P: 0.05% or less,
S: 0.05% or less,
Cr: 0.9 to 2%,
Al: 0.01 to 0.1%, and
N: 0.02% or less,

to super-carburizing, quenching, optional tempering, and nitriding, in that order,
wherein said gear has a surface-layer part ranging from the surface of the gear to a depth of 20 μm below the surface of the gear that has a steel microstructure comprising a phase of tempered martensite, a phase of tempered bainite, or a composite phase of tempered martensite and tempered bainite, 1 to 10% retained austenite by area percentage, and 5% or more carbide being precipitated by area percentage, the gear also having a nitrogen content of 2.0 to 6.0% in said surface-layer part.

2. The gear according to claim 1 , the gear precursor further comprising: Mo: 0.5% or less (not including 0%).

3. The gear according to claim 1 the gear precursor further comprising at least one element selected from the group consisting of V: 0.2% or less (not including 0%), Ti: 0.1% or less (not including 0%), and Nb: 0.2% or less (not including 0%).

4. The gear according to claim 1 , the gear precursor further comprising: B: 0.01% or less (not including 0%).

5. The gear according to claim 1 , the gear precursor further comprising at least one element selected from the group consisting of Cu: 5% or less (not including 0%) and Ni: 5% or less (not including 0%).

6. The gear according to claim 1 , wherein a nitrided layer having a content of iron nitride of 80 mass % or more exists in the surface-layer part ranging from the surface to the depth of 20 μm, and the nitrided layer has a proportion of Fe 4 N of 20 mass % or more in the iron nitride.

7. The gear according to claim 1 , further comprising a lubrication film on a surface thereof.

8. An electric car motor comprising the gear according to claim 1 .

9. The gear according to claim 1 , prepared by subjecting said gear precursor to super-carburizing, quenching, tempering, and nitriding, in that order.

10. The gear according to claim 1 , prepared by subjecting said gear precursor to super-carburizing, quenching, and nitriding, in that order.

11. The gear according to claim 1 , wherein said surface-layer part has 2 to 9% retained austenite by area percentage, 6% or more carbide precipitated by area percentage, and a nitrogen content of 3.2 to 5.8%.

12. The gear according to claim 1 , wherein said surface-layer part has 3 to 8% retained austenite by area percentage, 7% or more carbide precipitated by area percentage, and a nitrogen content of 3.5 to 5.5%.

13. The gear according to claim 1 , wherein the gear precursor comprises iron and, in mass percent:
C: 0.20 to 0.35%,
Si: 0.15 to 0.5%,
Mn: 1.2 to 1.7%,
P: 0.040% or less,
S: 0.040% or less,
Cr: 01.2 to 1.8%,
Al: 0.020 to 0.06%, and
N: 0.016% or less.

14. The gear according to claim 1 , wherein a nitrided layer having a content of iron nitride of 90 mass % or more exists in the surface-layer part ranging from the surface to the depth of 20 μm, and the nitrided layer has a proportion of Fe 4 N of 30 mass % or more in the iron nitride.

15. The gear according to claim 13 , wherein a nitrided layer having a content of iron nitride of 90 mass % or more exists in the surface-layer part ranging from the surface to the depth of 20 μm, and the nitrided layer has a proportion of Fe 4 N of 30 mass % or more in the iron nitride.

16. The gear according to claim 15 , wherein said surface-layer part has 3 to 8% retained austenite by area percentage, 7% or more carbide precipitated by area percentage, and a nitrogen content of 3.5 to 5.5%.

17. The gear according to claim 1 , wherein the surface-layer part has a steel microstructure comprising a phase of tempered martensite.

18. The gear according to claim 1 , wherein the surface-layer part has a steel microstructure comprising a phase of tempered bainite.

19. The gear according to claim 1 , wherein the content of Si in the gear precursor is 0.10 to 1.0%.

20. The gear according to claim 1 , wherein the surface-layer part has a steel microstructure comprising a composite phase of tempered martensite and tempered bainite.

Assignees

• Kobe Steel Ltd

Inventors

• Nagamatsu Sayaka
• Shindo Yosuke

Classifications

• C23C8/34

  more than one element being applied in more than one step · CPC title

• C10M103/06

  Metal compounds · CPC title

• F16H57/041

  Coatings or solid lubricants, e.g. anti-seize layers or pastes · CPC title

• C21D2211/001

  Austenite · CPC title

• C21D9/32 Primary

  for gear wheels, worm wheels, or the like · CPC title