Carburized part, method for manufacturing thereof, and steel for carburized part

Patent metadata

Field	Value
Publication number	US-9771643-B2
Application number	US-201414245229-A
Country	US
Kind code	B2
Filing date	Apr 4, 2014
Priority date	Apr 8, 2013
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

The invention provides a carburized part which has excellent medium-cycle fatigue strength in particular subjected to surface-hardening treatment by carburization. The invention provides a carburized part including a carburized layer formed by performing carburizing treatment to a steel, the steel including, in terms of % by mass: 0.15% to 0.25% of C, 0.15% or less of Si, 0.4% to 1.1% of Mn, 0.8% to 1.4% of Cr, 0.25% to 0.55% of Mo, 0.015% or less of P, and 0.035% or less of S, with the remainder being Fe and unavoidable impurities, and the steel satisfying the following relation; 0.10≦[Mo]/(10[Si]+[Mn]+[Cr])≦0.40, in which [M] represents a content of element M in terms of % by mass.

First claim

What is claimed is:

1. A carburized part comprising a carburized layer formed by performing a carburizing treatment to an outer surface of steel, the steel consisting of, in terms of % by mass:
0.15% to 0.25% of C,
0.15% or less of Si,
0.4% to 1.1% of Mn,
0.8% to 1.4% of Cr,
0.25% to 0.55% of Mo,
0.015% or less of P,
0.035% or less of S, and
a remainder of Fe and unavoidable impurities,

and the steel satisfying the following relation:
0.10≦[Mo]/(10[Si]+[Mn]+[Cr])≦0.40

wherein [M] represents a content of element M in terms of % by mass,
wherein, in the carburized part, a maximum C content of the carburized layer in terms of % by mass is within a range of 0.61% to 0.75%, and
wherein
a hardness HV d=25 μm at a depth of 25 μm below the outer surface of the steel is 650 Hv or higher,
a hardness HV d=50 μm at a depth of 50 μm below the outer surface of the steel is 750 Hv or lower,
a difference between the hardness HV d=25 μm and the hardness Hv d=50 μm is 50 Hv or smaller, and
the hardness HV d=25 μm is less than the hardness Hv d=50 μm .

2. The carburized part according to claim 1 , wherein any depth where a hardness is 700 Hv is 0.35 mm or less from the outer surface.

3. A method for manufacturing a carburized part, at least comprising:
performing a predetermined machining to an outer surface of a steel consisting of, in terms of % by mass:
0.15% to 0.25% of C,
0.15% or less of Si,
0.4% to 1.1% of Mn,
0.8% to 1.4% of Cr,
0.25% to 0.55% of Mo,
0.015% or less of P, and
0.035% or less of S,
a remainder of Fe and unavoidable impurities, and the steel satisfying the following relation:
0.10≦[Mo]/(10[Si]+[Mn]+[Cr])≦0.40

wherein [M] represents a content of element M in terms of % by mass; and
performing a carburizing treatment wherein the machined steel is heated at a predetermined temperature and subjected to a carburizing and diffusing treatment in a carburizing atmosphere having a predetermined carbon potential, and then hardened in a low-temperature oil bath kept at a temperature 80° C. or lower at the highest, thereby providing a carburized layer,
wherein, in the carburizing treatment, a maximum C content of the carburized layer in terms of % by mass is controlled to be within a range of 0.61% to 0.75%, and
wherein
a hardness HV d=25 μm at a depth of 25 μm below the outer surface of the steel is controlled to be 650 Hv or higher,
a hardness HV d=50 μm at a depth of 50 μm below the outer surface of the steel is controlled to be 750 Hv or lower,
a difference between the hardness HV d=25 μm and the hardness Hv d=50 μm is controlled to be 50 Hv or smaller, and the hardness HV d=25 μm is less than the hardness Hv d=50 μm .

4. The method for manufacturing a carburized part according to claim 3 , wherein the carburizing treatment provides a region having a hardness of 700 Hv or higher at a depth within 350 μm or less below the outer surface of the steel.

Assignees

• Ninomiya Akihito
• Okada Yoshinari
• Miyazaki Takahiro
• Matsumura Yasushi
• Kato Shinichiro
• Shimomura Tetsuya
• Honda Motor Co Ltd
• Daido Steel Co Ltd

Inventors

• Ninomiya Akihito
• Okada Yoshinari
• Miyazaki Takahiro
• Matsumura Yasushi
• Kato Shinichiro
• Shimomura Tetsuya
• Yamaguchi Katsuya

Classifications

• C23C8/22 Primary

  of ferrous surfaces · CPC title

• C23C8/80

  After-treatment · CPC title

• C23C8/02

  Pretreatment of the material to be coated (C23C8/04 takes precedence) · CPC title