Bearing component and rolling bearing
A bearing component composed of steel which contains carbon not less than 0.95 mass % and not more than 1.1 mass %, silicon less than 0.3 mass %, manganese less than 0.5 mass %, sulfur less than 0.008 mass %, and chromium not less than 1.4 mass % and less than 1.6 mass % and is composed of remainder iron and an impurity and having a carbonitrided layer formed at a surface portion including a contact surface which is a surface in contact with other components is provided. An average concentration of nitrogen in the surface portion is not lower than 0.3 mass % and not higher than 0.6 mass % and variation in nitrogen concentration in the surface portion is not higher than 0.1 mass %.
1. A bearing component, composed of steel which contains carbon not less than 0.95 mass % and not more than 1.1 mass %, silicon less than 0.3 mass %, manganese less than 0.5 mass %, sulfur less than 0.008 mass %, and chromium not less than 1.4 mass % and less than 1.6 mass % and is composed of remainder iron and an impurity and having a carbonitrided layer formed at a surface portion including a contact surface which is a surface in contact with other components,
an average concentration of nitrogen in said surface portion being not lower than 0.3 mass % and not higher than 0.6 mass and variation in nitrogen concentration in said surface portion being not higher than 0.1 mass %, and
the surface portion being a region extending from the contact surface to a depth of not more than 20 μm in a direction of thickness of the bearing component.
2. The bearing component according to claim 1 , wherein
an inclination of nitrogen concentration in a direction of thickness of said bearing component is not less than −15 (l/m).
3. The bearing component according to claim 1 , wherein
an average amount of retained austenite at a position at a depth of 0.05 mm from said contact surface is not lower than 25 volume % and not higher than 35 volume %, and variation in amount of retained austenite at the position at the depth of 0.05 mm from said contact surface is not higher than 3 volume %.
4. The bearing component according to claim 1 , wherein an average amount of retained austenite as a whole is not higher than 18 volume %.
5. The bearing component according to claim 1 , wherein said surface portion includes five or more carbonitrides per 100 μm 2 , the carbonitrides each having a diameter not greater than 0.5 μm.
6. The bearing component according to claim 1 , wherein
the nitrogen concentration in a non-ground portion including a non-ground surface which is a surface other than said contact surface is lower than 0.7 mass %.
7. The bearing component according to claim 6 , wherein
a hardness at a position at a depth of 0.1 mm from said non-ground surface is not lower than 700 HV.
8. The bearing component according to claim 1 , wherein
after heat treatment in which a heating temperature is set to 500° C. and a retention time period is set to 1 hour, a Vickers hardness at a position at a depth of 0.4 (mm) from said contact surface is higher by at least 80 HV than a Vickers hardness in a region where no said carbonitrided layer is formed in a direction of thickness of said bearing component.
9. The bearing component according to claim 1 , wherein
said carbonitrided layer is formed by performing carbonitriding treatment such that a c * defined in an expression (1) below is not smaller than 0.88 and not greater than 1.27 and α defined in an expression (2) is not smaller than 0.012 and not greater than 0.020
a
c
*
=
(
Pco
)
2
K
×
Pco
2
(
1
)
Pco: partial pressure (atm) of carbon monoxide, Pco 2 : partial pressure (atm) of carbon dioxide
K: equilibrium constant in <C>+CO 2 2CO
α
=
P
N
0.006
×
(
P
H
)
1
2
×
(
1.877
-
1.055
×
a
c
*
)
100
(
2
)
where P N represents a partial pressure of undecomposed ammonia and P H represents a partial pressure of hydrogen.
10. A rolling bearing, comprising the bearing component according to claim 1 .