BEARING COMPONENT

Abstract

Bearing component (10) containing steel that comprises, by weight, 10-30 ppm Ca, max 20 ppm S and max 15 ppm O and in that said steel includes sulphide inclusions and less than 5% of the sulphide inclusions contain encapsulated or embedded oxide inclusions.

Claims

1-6. (canceled)

7. A method for manufacturing a bearing, comprising: reducing a sulphur content of a bearing steel to a level substantially of a same order as an oxygen content in the bearing steel; after reducing the sulphur content of the bearing steel, adding calcium to the bearing steel, wherein the bearing steel comprises sulphide inclusions, and wherein adding the calcium to the bearing steel after reducing the sulphur content causes less than 5% of the sulphide inclusions to contain encapsulated or embedded oxide inclusions; and forming at least a part of the bearing using the bearing steel after reducing the sulphur content and after adding the calcium.

8. The method of claim 7, wherein the bearing steel that forms the at least a part of the bearing comprises by weight: 10-30 ppm CA; at most 20 ppm S; and at most 15 ppm O.

9. The method of claim 7, wherein the bearing steel that forms the at least a part of the bearing comprises by weight: 10-30 ppm CA; at most 20 ppm S; and at most 10 ppm O.

10. The method of claim 7, wherein the bearing steel that forms the at least a part of the bearing comprises by weight: 10-30 ppm CA; at most 20 ppm S; and at most 8 ppm O.

11. The method of claim 7, wherein the sulphide inclusions each have an aspect ratio of less than 3:1, wherein the aspect ratio is a ratio of a largest diameter to a smallest diameter for any one of the sulphide inclusions.

12. The method of claim 7, wherein a maximum length of a sulphide inclusion of the sulphide inclusions of the bearing steel is 125 m at a Reduced Variate equal to 3.

13. The method of claim 7, wherein forming the at least a part of the bearing comprises forming at least one of: an inner race; an outer race; or one or more rolling elements configured to roll between an inner race and an outer race.

14. The method of claim 7, wherein the bearing steel comprises 0.70-1.20 wt % carbon.

15. The method of claim 7, further comprising through-hardening the bearing steel.

16. The method of claim 7, wherein the bearing steel comprises: 0.70-0.95 wt % carbon; 0.05-1.5 wt % silicon; 0.15-0.50 wt % manganese; 0.5-2.5 wt % chromium; 0.10-1.5 wt % molybdenum; at most 0.25 wt % vanadium; 10-30 ppm calcium; at most 20 ppm sulphur; at most 15 ppm oxygen; and a balance substantially being iron.

17. The method of claim 7, wherein at most 1% of the sulphide inclusions contain encapsulated or embedded oxide inclusions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will hereinafter be further explained by means of non-limiting examples with reference to the appended figures in which;

[0012] FIG. 1 schematically shows a bearing component according to an embodiment of the invention,

[0013] FIG. 2 shows the percentage of sulphide inclusions containing encapsulated or embedded oxide inclusions in standard steel, and

[0014] FIG. 3 shows the percentage of sulphide inclusions containing encapsulated or embedded oxide inclusions in the steel of a bearing component according to the present invention.

[0015] It should be noted that the drawing has not been drawn to scale and that the dimensions of certain features have been exaggerated for the sake of clarity.

DETAILED DESCRIPTION OF EMBODIMENTS

[0016] FIG. 1 schematically shows an example of a bearing component 10, namely a ball bearing that may range in size from 10 mm diameter to a few metres diameter and have a load-carrying capacity from a few tens of grams to many thousands of tonnes. The bearing component according to the present invention may namely be of any size and have any load-carrying capacity. The bearing component 10 has an inner race 12 and an outer race 14 and a set of balls 16. The inner race 12, the outer race 14 and/or the balls 16 of the ball bearing 10, and preferably all of the rolling contact parts of the ball bearing 10 are manufactured from steel that comprises, by weight, 10-30 ppm Ca, max 20 ppm S and max 15 ppm O, preferably 10-30 ppm Ca, max 20 ppm S and max 8 ppm O. Less than 5% of the sulphide inclusions contained in the steel contain encapsulated or embedded oxide inclusions. All of the sulphide inclusions have an aspect ratio less than 3:1 and the maximum length of the suphide inclusions is 125 m at a Reduced Variate equal to 3 (determined using ASTM E2283-03 Extreme Value Analysis).

[0017] The steel from which at least part of the ball bearing 10 is manufactured may for example contain between 0.70 to 1.20% carbon. For example the steel may have the following 20 composition:

TABLE-US-00001 0.70-0.95 weight-% carbon 0.05-1.5 weight-% silicon 0.15-0.50 weight-% manganese 0.5-2.5 weight-% chromium 0.10-1.5 weight-% molybdenum max. 0.25 weight-% vanadium
the remainder being Fe, and normally occurring impurities comprising 10-30 ppm Ca, max 20 ppm S and max 15 ppm O, preferably max 10 ppm O or most preferably max 8 ppm O.

[0018] FIGS. 2 and 3 show the percentage of sulphide inclusions containing encapsulated or embedded oxide inclusions in standard steel, and in the steel of a bearing component according to the present invention respectively. It can be seen that only about 1% of the sulphide inclusions of the steel of a bearing component according to the present invention contain encapsulated or embedded oxide inclusions. On the contrary, in standard steel, about 80% of the steel's sulphide inclusions contain encapsulated or embedded oxide inclusions. It has been found that the fatigue strength (measured in rotating beam tests at 950 MPa) of the steel of a bearing component according to the present invention is substantially higher than the fatigue strength of standard steel.