Bearing device and method of manufacturing the bearing device

1. A bearing device comprising:

a bearing ring;

a shaft body having a cylindrical portion that is made of carbon steel including pearlite having a cementite layer structure, and the cylindrical portion having an end portion caulked onto the bearing ring; and

said shaft body being processed to provide, at least in the end portion of the cylindrical portion of the shaft body, a lamella layer gap of the cementite in the pearlite made greater in thickness than a layer gap outside of the end portion, wherein the shaft body is processed such that a set of characteristics is provided in the end portion, wherein:

the characteristics include:

the end portion of the shaft body having an average value of the lamella layer gaps of the cementite in a range from 0.2 μm to not more than 0.35 μm,

the carbon steel having a carbon content in a range from not less than 0.37% to not more than 0.65%, and

the end portion of the shaft body having a hardness of in the range of 20 HRC down to but not less than 15 HRC.

2. The bearing device according to claim 1 , wherein the carbon steel has a carbon range of 0.52% to 0.58%, is in the range of 0.15% to 0.25%, Mn in the range of 0.60% to 0.90%, P in the range of 0.30% or less and S in the range of 0.035% or less.

3. The bearing device according to claim 1 , wherein the average value of the lamella layer gaps of the cementite is set in a range from not less than 0.15 μm to not more than 0.23 μm.

4. The bearing device according to claim 3 , wherein the carbon steel has a carbon range of 0.52% to 0.58%, is in the range of 0.15% to 0.25%, Mn in the range of 0.60% to 0.90%, P in the range of 0.030% or less and S in the range of 0.035% or less.

5. The bearing device according to claim 1 wherein:

the end portion of the shaft body cylinder shaped as part of the cylindrical portion prior to caulking and which is deformed when caulked to the bearing ring;

said shaft body processed to provide a set of characteristics in only the end portion of the shaft body and not in a remainder of the shaft body such that the end portion has a lower hardness than the remainder of the shaft body and has a gap spacing in the range of 0.15 to 0.35 μm only in the end portion, the range of spacing being greater than that in a remainder of the shaft body; and

the end portion is increased in diameter by said caulking so as to engage an outer end face of the bearing ring.

6. A manufacturing method of a bearing device comprising the steps of:

forming a shaft body of carbon steel, having pearlite, such that the shaft body has a cylindrical portion having an end portion to be caulked onto a bearing ring, said forming of the shaft body being done by a hot forging process; and

cooling the end portion of the shaft body, wherein in a cooling process, by adjusting a cooling rate in at least the end portion, lamella layer gaps of cementite contained in pearlite as layers forming a cementite layer structure are set to be greater in thickness than layer gaps outside of the end portion such that a set of characteristics is provided in the end portion, wherein:

said characteristics include:

the end portion of the shaft body having an average value of the lamella layer gaps of the cementite in a range from 0.2 μm to not more than 0.35 μm,

the carbon steel having a carbon content in a range from not less than 0.37% to not more than 0.65%, and

the end portion of the shaft body having a hardness of in the range of 20 HRC down to but not less than 15 HRC; and

installing the bearing ring on said end portion and caulking said end portion to secure the bearing ring.

7. The manufacturing method of a bearing device according to claim 6 , wherein in the cooling process, at least the end portion is high-frequency heated to adjust the cooling rate so that the lamella layer gaps of cementite contained in the pearlite as layers are set to be greater in thickness than the layer gaps outside of the end portion.

8. The manufacturing method of a bearing device according to claim 6 , wherein in the cooling process, at least the end portion is high-frequency heated to be temporarily maintained at not less than 750° C. so that the cooling rate is adjusted.

9. The method according to claim 6 , wherein the carbon steel has a carbon range of 0.52% to 0.58%, is in the range of 0.15% to 0.25%, Mn in the range of 0.60% to 0.90%, P in the range of 0.030% or less and S in the range of 0.35% or less.

10. A manufacturing method of a bearing device comprising the steps of:

forming a shaft body of carbon steel, having pearlite, such that the shaft body has a cylindrical portion having an end portion to be caulked onto a bearing ring, said forming of the shaft body being done by a hot forging process; and

cooling the shaft body,

wherein in a cooling process, by adjusting a cooling rate in at least the end portion, lamella layer gaps of cementite contained in the pearlite as lamella layers forming a cementite layer structure in the shaft body are set in thickness relative to layer gaps outside the end portion so as to prevent cracks from occurring in the end portion when the end portion is caulked onto the bearing ring such that a set of characteristics is provided in the end portion, wherein:

said set of characteristics includes:

the end portion of the shaft body having an average value of the lamella layer gaps of the cementite in a range from 0.2 μm to not more than 0.35 μm,

the carbon steel having a carbon content in a range from not less than 0.37% to not more than 0.65%, and

the end portion of the shaft body having a hardness of in the range of 20 HRC down to but not less than 15 HRC; and

installing the bearing ring on said end portion and caulking said end portion to secure the bearing ring.

11. The method according to claim 10 , wherein the carbon steel has a carbon range of 0.52% to 0.58%, is in the range of 0.15% to 0.25%, Mn in the range of 0.60% to 0.90%, P in the range of 0.30% or less and S in the range S of 0.35% or less.