Nitrocarburized crankshaft and method of manufacturing the same

Patent metadata

Field	Value
Publication number	US-9593404-B2
Application number	US-201414263254-A
Country	US
Kind code	B2
Filing date	Apr 28, 2014
Priority date	May 1, 2013
Publication date	Mar 14, 2017
Grant date	Mar 14, 2017

Abstract

Provided is a method of manufacturing a nitrocarburized crankshaft which is obtained by subjecting a bainitic microalloyed steel to a forging and a machining, and further subjecting the bainitic microalloyed steel to at least a strain releasing heat treatment and a subsequent nitrocarburizing treatment, the bainitic microalloyed steel containing, as essentially added elements, in terms of mass %: 0.10% to 0.40% of C; 0.10% to 1.0% of Si; 1.0% to 2.0% of Mn; 0.05% to 0.40% of Mo; and 0.05% to 0.40% of V, and the bainitic microalloyed steel optionally further containing, as arbitrarily added elements, in terms of mass %: 0.01% to 0.1% of S; 0.005% to 0.2% of Ti; 0.001% to 0.03% of Al; 0.50% or less of Cr; 0.5% or less of Cu; and 0.5% or less of Ni, with the balance being Fe and unavoidable impurities.

First claim

What is claimed is:

1. A nitrocarburized crankshaft obtained by
subjecting a bainitic microalloyed steel to a forging and a machining and
further subjecting the bainitic microalloyed steel to at least a strain releasing heat treatment and
a subsequent nitrocarburizing treatment,
the bainitic microalloyed steel containing, as essentially added elements, in terms of mass %:
0.16% to 0.40% of C;
0.13% to 1.0% of Si;
1.0% to 2.0% of Mn;
0.05% to 0.40% of Mo; and
0.05% to 0.30% of V, and the bainitic microalloyed steel optionally further containing, as arbitrarily added elements, in terms of mass %:
0.01% to 0.1% of S;
0.005% to 0.2% of Ti;
0.001% to 0.03% of Al;
0.50% or less of Cr;
0.5% or less of Cu; and
0.5% or less of Ni,
with the balance being Fe and unavoidable impurities,
wherein at least a content of P as one of the unavoidable impurities is suppressed to be 0.025% or less,
wherein the microalloyed steel satisfies the following expressions:
[C]+0.27[Mn]+0.32[Cr]+0.27[Mo]+0.38[V]≧0.72,

[C]+0.01[Si]+0.09[Mn]+0.13[Cr]+0.12[Mo]+0.28[V]<0.65, and
[C]+0.11[Si]+0.11[Mn]+0.09[Cr]+0.21[Mo]+0.60[V]≧0.54,

in which [M] represents a content of element M in terms of % by mass, and
wherein an amount of residual γ is controlled to be less than 5.0%, and a core part has a hardness of 270 HV or greater.

2. A method of manufacturing a nitrocarburized crankshaft which is obtained by
subjecting a bainitic microalloyed steel to a forging and a machining, and
further subjecting the bainitic microalloyed steel to at least a strain releasing heat treatment and
a subsequent nitrocarburizing treatment,
the bainitic microalloyed steel containing, as essentially added elements, in terms of mass %:
0.16% to 0.40% of C;
0.13% to 1.0% of Si;
1.0% to 2.0% of Mn;
0.05% to 0.40% of Mo; and
0.05% to 0.30% of V, and the bainitic microalloyed steel optionally further containing, as arbitrarily added elements, in terms of mass %:
0.01% to 0.1% of S;
0.005% to 0.2% of Ti;
0.001% to 0.03% of Al;
0.50% or less of Cr;
0.5% or less of Cu; and
0.5% or less of Ni,
with the balance being Fe and unavoidable impurities,
wherein at least a content of P as one of the unavoidable impurities is suppressed to be 0.025% or less,
wherein the microalloyed steel is selected so as to satisfy:
[C]+0.27[Mn]+0.32[Cr]+0.27[Mo]+0.38[V]≧0.72,

[C]+0.01[Si]+0.09[Mn]+0.13[Cr]+0.12[Mo]+0.28[V]<0.65, and
[C]+0.11[Si]+0.11[Mn]+0.09[Cr]+0.21[Mo]+0.60[V]≧0.54,

in which [M] represents a content of element M in terms of % by mass, and
wherein the strain releasing heat treatment is performed to satisfy the following expressions regarding a holding temperature T (° C.) and a holding time t (hr):
21.6+14.2[C]+1.5[Si]+2.6[Mn]+6.5[Cr]+2.7[Mo]+1.6[V]+10 −7 ×γ h1 2 −3.7×10 −3 ×γ h1 <0.70,

and
γ h1 =( T+ 273)×(20+Log( t ).

3. The method of manufacturing a nitrocarburized crankshaft according to claim 2 , wherein the nitrocarburizing treatment is performed for 0.5 hours or longer under a gas atmosphere at a temperature in a range of from 550° C. to 650° C., and a core part has a hardness of 270 HV or greater.

4. The method of manufacturing a nitrocarburized crankshaft according to claim 2 , wherein the bainitic microalloyed steel is subjected to the forging after heating the bainitic microalloyed steel to a temperature in a range of 1150° C. or more and lower than 1350° C., and then the forged steel is at least cooled at a cooling rate controlled to be within a range of from 0.25° C./sec to 1.50° C./sec in a carbon diffusion temperature range, thereby obtaining a hardness of less than 33.0 HRC.

5. The method of manufacturing a nitrocarburized crankshaft according to claim 4 , wherein in the strain releasing heat treatment, the holding temperature T is set in a range of from 400° C. to 600° C. and the holding time t is set in a range of from 0.5 hours to 5.0 hours so as to control an amount of residual γ to less than 5.0%.

6. The method of manufacturing a nitrocarburized crankshaft according to claim 4 , wherein the nitrocarburizing treatment is performed for 0.5 hours or longer under a gas atmosphere at a temperature in a range of from 550° C. to 650° C., and a core part has a hardness of 270 HV or greater.

7. The method of manufacturing a nitrocarburized crankshaft according to claim 5 , wherein the nitrocarburizing treatment is performed for 0.5 hours or longer under a gas atmosphere at a temperature in a range of from 550° C. to 650° C., and a core part has a hardness of 270 HV or greater.

8. The method of manufacturing a nitrocarburized crankshaft according to claim 2 , wherein in the strain releasing heat treatment, the holding temperature T is set in a range of from 400° C. to 600° C. and the holding time t is set in a range of from 0.5 hours to 5.0 hours so as to control an amount of residual γ to less than 5.0%.

9. The method of manufacturing a nitrocarburized crankshaft according to claim 8 , wherein the nitrocarburizing treatment is performed for 0.5 hours or longer under a gas atmosphere at a temperature in a range of from 550° C. to 650° C., and a core part has a hardness of 270 HV or greater.

Assignees

• Masuda Hiroki
• Matsuda Hideki
• Yamazaki Ayumi
• Kato Shinichiro
• Miyazaki Takahiro
• Daido Steel Co Ltd
• Honda Motor Co Ltd

Inventors

• Masuda Hiroki
• Matsuda Hideki
• Yamazaki Ayumi
• Kato Shinichiro
• Miyazaki Takahiro

Classifications

• C21D9/30

  for crankshafts; for camshafts · CPC title

• C23C8/02

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

• F16C3/08

  made in one piece (features relating to lubrication F16C3/14, to cooling F16C3/16) · CPC title

• C23C8/32 Primary

  of ferrous surfaces · CPC title

• F16C3/06

  Crankshafts · CPC title