Method for manufacturing a rolling element bearing

1. A method for manufacturing a rolling-element bearing, which includes an inner ring having an inner-ring raceway, an outer ring having an outer-ring raceway and a plurality of rolling elements that are rollable on the inner-ring raceway and on the outer-ring raceway, the method comprising:

forming the inner ring from a steel having a sulfur content of 0.002 to 0.015 mass % and an oxygen content of less than 15 ppm,

subjecting the inner ring to a heat treatment to harden it, which heat treatment ends by performing a final hardening heat treatment step at a predetermined temperature,

cold working the inner-ring raceway to generate compressive residual stresses at least in a surface layer of the inner-ring raceway,

subjecting the cold-worked inner ring to a bluing treatment to form a blued layer on an outer surface of the inner ring, and

subjecting the blued inner ring to a thermal post-treatment process at a temperature below the predetermined temperature of the final hardening heat treatment step.

2. The method according to claim 1 , wherein the temperature of the thermal post-treatment process is at least 10 K below the predetermined temperature of the final hardening heat treatment step.

3. The method according to claim 2 , wherein the temperature of the thermal post-treatment process is at least 100° C.

4. The method according to claim 3 , wherein the temperature of the thermal post-treatment process is no more than 100 K below the predetermined temperature of the final hardening heat treatment step.

5. The method according to claim 1 , wherein the hardening heat treatment step comprises subjecting the inner ring to martensitic, case and/or induction hardening and

wherein the predetermined temperature of the final hardening heat treatment step is a tempering temperature of the inner ring.

6. The method according to claim 5 , wherein a retained austenite content of 8 to 18 volume % is formed in the inner ring by the martensitic, case, and/or induction hardening.

7. The method according to claim 1 , wherein the cold working step is performed such that compressive residual stresses are formed in the inner ring up to a minimum depth beneath the outer surface of the inner-ring raceway with an absolute value of a minimum value or greater, the minimum depth being 0.1 mm and the minimum value being at least 200 MPa.

8. The method according to claim 7 , wherein the minimum depth is 0.2 mm and the minimum value is 400 MPa or more.

9. The method according to claim 1 , wherein the cold working step is performed such that compressive residual stresses formed in the inner ring have a maximum absolute value of 1500 MPa or less.

10. The method according to claim 9 , wherein the maximum absolute value is 800 MPa or less.

11. The method according to claim 1 , wherein the hardening heat treatment step comprises subjecting the inner ring to bainitic hardening, and

wherein the predetermined temperature of the final heat treatment step is a bainitic transformation temperature of the inner ring.

12. The method according to claim 1 , wherein the temperature of the final hardening heat treatment step is higher than temperatures of the cold working, the bluing treatment and the thermal post-treatment process.

13. The method according to claim 1 , wherein the inner ring is formed from a steel having a sulfur content of 0.006 to 0.015 mass % and an oxygen content of less than 10 ppm.

14. The method according to claim 1 , wherein the inner ring is formed from a steel that comprises 0.65-1.20 wt % C, 0.05-1.70 wt % Si, 1.1-2.2 wt % Cr, 0.10-1.0 wt % Mn, 0.02-1.0 wt % Ni, 0.02-0.70 wt % Mo.

15. A method for manufacturing a rolling-element bearing, which includes an inner ring having an inner-ring raceway, an outer ring having an outer-ring raceway and a plurality of rolling elements that are rollable on the inner-ring raceway and on the outer-ring raceway, the method comprising:

forming the inner ring from a steel having a sulfur content of 0.006 to 0.015 mass % and an oxygen content of less than 10 ppm, the inner ring having an inner diameter of at least 50 centimeters,

subjecting the inner ring to a hardening heat treatment that ends by performing a final hardening heat treatment step at a predetermined temperature,

cold working the inner-ring raceway to generate compressive residual stresses at least in a surface layer of the inner-ring raceway, the compressive residual stresses having an absolute value of at least 500 MPa at 0.2 mm beneath an outer surface of the inner-ring raceway and a maximum value of 800 MPa or less throughout the inner ring,

subjecting the cold-worked inner ring to a bluing treatment to form a blued layer on an outer surface of the inner-ring raceway, and

subjecting the blued inner ring to a thermal post-treatment process at a temperature of at least 100° C. and between 10-100° C. below the predetermined temperature of the final hardening heat treatment step.

16. The method according to claim 15 , wherein:

the inner ring is formed from a steel that comprises 0.8-1.20 wt % C, 0.05-1.70 wt % Si, 1.1-2.2 wt % Cr, 0.10-1.0 wt % Mn, 0.02-1.0 wt % Ni, 0.02-0.70 wt % Mo;

the hardening heat treatment is a bainite transformation performed at a temperature between 210-240° C.; and

the thermal post-treatment process is performed at a temperature between 190-230° C.