Bearing component

Abstract

A bearing component formed from a steel composition and providing carbon, silicon, manganese, chromium, cobalt, vanadium, and at least one of the following elements sulphur, phosphorous, molybdenum, aluminum, arsenic, tin, antimony, and the balance iron, together with impurities.

Claims

1. A bearing component formed from a steel composition comprising: 1.8-2.8 wt. % carbon, 1.0-2.0 wt. % silicon, 1.0-2.5 wt. % manganese, 1.0-2.5 wt. % chromium, 1.0-2.0 wt. % cobalt, 5.0-11.0 wt. % vanadium, 0-0.1 wt. % sulphur, 0-0.1 wt. % phosphorous, 0-1.35 wt. % molybdenum, 0-0.5 wt. % aluminium, 0-0.075 wt. % arsenic, 0-0.075 wt. % tin, and 0-0.075 wt. % antimony, the balance being iron and unavoidable impurities.

2. The bearing component as claimed in claim 1, comprising 1.2-2.0 wt. % silicon.

3. The bearing component as claimed in claim 1, comprising 1.2-2.5 wt. % manganese.

4. The bearing component as claimed in claim 1, comprising 1.0-1.8 wt. % chromium.

5. The bearing component as claimed in claim 1, comprising 6.5-11.0 wt. % vanadium.

6. The bearing component as claimed in claim 1, comprising 2.2 to 2.5 wt. % carbon.

7. The bearing component as claimed in claim 1, comprising 1.4-1.6 wt. % silicon.

8. The bearing component as claimed in claim 1, comprising 1.6-1.8 wt. % manganese.

9. The bearing component as claimed in claim 1, comprising 1.6-1.8 wt. % chromium.

10. The bearing component as claimed in claim 1, comprising 11.3-1.5 wt. % cobalt.

11. The bearing component as claimed in claim 1, comprising 7.0-8.0 wt. % vanadium.

12. The bearing component as claimed in claim 1, wherein the microstructure of the steel composition comprises bainite and/or martensite.

13. The bearing component as claimed in claim 1, wherein the microstructure of the steel composition comprises vanadium carbide precipitates.

14. The bearing component as claimed in claim 1, wherein the microstructure of the steel composition comprises plates of bainite of less than 100 nm thickness.

15. The bearing component as claimed in claim 1, wherein the microstructure of the steel composition comprises plates of bainite interspersed with austenite films.

16. The bearing component as claimed in claim 1, wherein the bearing component is formed as one of a rolling element, an inner ring, or an outer ring.

17. The bearing component as claimed in claim 1, comprising: 1.2-1.8 wt. % silicon, 1.2-2.3 wt. % manganese, and 6.5-9.0 wt. % vanadium.

18. The bearing component as claimed in claim 1, wherein the steel composition has a microstructure composed of at least 60 vol. % bainite.

19. A bearing component formed from a steel composition consisting of: 1.8-2.8 wt. % carbon, 1.0-2.0 wt. % silicon, 1.0-2.5 wt. % manganese, 1.0-2.5 wt. % chromium, 1.0-2.0 wt. % cobalt, 5.0-11.0 wt. % vanadium, and 0-0.1 wt. % sulphur, 0-0.1 wt. % phosphorous, 0-1.35 wt. % molybdenum, 0-0.5 wt. % aluminium, 0-0.075 wt. % arsenic, 0-0.075 wt. % tin, 0-0.075 wt. % antimony, the balance being iron and unavoidable impurities.

20. The bearing component as claimed in claim 19, wherein the steel composition has a microstructure composed of at least 60 vol. % bainite and the bainite is composed of plates having a thickness of less 100 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention will now be further described with reference to the following non-limiting Figures in which:

(2) FIG. 1 shows a scanning electron microscope image of a steel alloy for use in the present invention after hot isostatic pressing (HIP).

(3) FIG. 2 shows a scanning electron microscope image of a steel alloy for use in the present invention after spheroidise-annealing heat treatment.

(4) FIG. 3 shows a scanning electron microscope image of a steel alloy for use in the present invention after martensitic tempering heat treatment.

(5) FIG. 4 shows a scanning electron microscope image of a steel alloy for use in the present invention after bainitic heat treatment.

EXAMPLES

(6) The present invention will now be further described with reference to the following non-limiting Examples.

Example 1

(7) An example of a suitable bainitic steel composition for use in the present invention includes (the balance being Fe and any unavoidable impurities):

(8) 2.45 wt. % carbon,

(9) 1.5 wt. % silicon,

(10) 1.7 wt. % manganese,

(11) 1.7 wt. % chromium,

(12) 1.4 wt. % cobalt, and

(13) 7.6 wt. % vanadium.

(14) Shown below is a thermodynamic calculation, at equilibrium, demonstrating the composition of the austenitic matrix phase at 1080 C.:

(15) TABLE-US-00001 Conditions: T = 1353.15, N = 1, P = 1E5, W(C) = 2.45E2, W(MN) = 1.7E2, W(SI) = 1.5E2, W(CR) = 1.7E2, W(CO) = 1.4E2, W(V) = 7.6E2 DEGREES OF FREEDOM 0 Temperature 1353.15 K (1080.00 C), Pressure 1.000000E+05 Number of moles of components 1.00000E+00, Mass in grams 5.02055E+01 Total Gibbs energy 7.74529E+04, Enthalpy 2.81541E+04, Volume 5.77499E06 Component Moles W-Fraction Activity Potential Ref. stat C 1.0241E01 2.4500E02 4.8940E02 3.3945E+04 SER CO 1.1927E02 1.4000E02 2.2682E05 1.2031E+05 SER CR 1.6415E02 1.7000E02 8.3701E05 1.0563E+05 SER FE 7.5200E01 8.3650E01 1.9376E03 7.0276E+04 SER MN 1.5536E02 1.7000E02 1.2104E05 1.2738E+05 SER SI 2.6814E02 1.5000E02 1.2400E07 1.7892E+05 SER V 7.4902E02 7.6000E02 1.7230E06 1.4931E+05 SER FCC_A1#1 Status ENTERED Driving force 0.0000E+00 Moles 8.4565E01, Mass 4.5150E+01, Volume fraction 9.9545E01 Mass fractions: FE 9.28077E01 SI 1.66797E02 CR 1.06944E02 V 2.23794E03 MN 1.88144E02 CO 1.55443E02 C 7.95206E03 FCC_A1#2 Status ENTERED Driving force 0.0000E+00 Moles 1.5435E01, Mass 5.0559E+00, Volume fraction 4.5531E03 Mass fractions: V 7.34703E01 CR 7.33096E02 MN 7.97272E04 SI 1.07181E07 C 1.72275E01 FE 1.87062E02 CO 2.08912E04

Example 2

(16) A steel alloy powder was prepared having the following chemical composition:

(17) 2.4 wt. % carbon,

(18) 1.42 wt. % silicon,

(19) 1.74 wt. % manganese,

(20) 1.9 wt. % chromium,

(21) 1.31 wt. % cobalt, and

(22) 7.53 wt. % vanadium,

(23) the balance being iron and any unavoidable impurities (including trace amounts of phosphorus and sulphur).

(24) Hot isostatic pressing (HIP) was carried out on the steel alloy powder. FIG. 1 shows a scanning electron microscope image of the steel alloy after HIP (EHT=10.00 kV, Signal A=SE2, Pixel Size=11.2 nm, WD=11 mm, Mag=10.00 k X). The microstructure can be seen to comprise a pearlitic matrix with vanadium carbides.

(25) A spheroidise-annealing heat treatment was then carried out on the steel alloy, which involved heating the alloy to approximately 800 C., holding at that temperature for approximately 60 minutes, and then slowly cooling to room temperature. This heat treatment may enhance the machinability of the material as well as provide a structure that has a better response to hardening. FIG. 2 shows a scanning electron microscope image of the steel alloy after spheroidise-annealing (EHT=10.00 kV, Signal A=SE2, Pixel Size=37.2 nm, WD=6 mm, Mag=3.00 k X). The microstructure can be seen to comprise numerous fine, small iron carbides and vanadium carbides embedded in a soft ferritic matrix.

(26) Martensitic Hardening

(27) From the as-annealed condition, a martensitic tempering heat treatment was then carried out on the steel alloy. During the heat treatment the steel alloy was quenched from approximately 880 C. to approximately 60 C. and then held at that temperature for approximately 15 minutes. A first specimen of the steel alloy was then further quenched into cold water kept at approximately 15 C. The first specimen was held in the water for approximately 10 minutes and then immediately tempered at approximately 160 C. for approximately 90 minutes. Following tempering, the steel alloy was air-cooled to room temperature. FIG. 3 shows a scanning electron microscope image of the steel alloy after the heat treatment (EHT=10.00 kV, Signal A=SE2, Pixel Size=11.2 nm, WD=6 mm, Mag=10.00 k X). The microstructure can be seen to comprise numerous, relatively small iron carbides and vanadium carbides in a tempered martensite matrix.

(28) Hardness measurements were carried out on the heat-treated steel alloy and indicated a hardness of 870 HV10, which corresponds to about 65.3 HRC. It was found that if sub-zero treatment is combined with the above heat treatment, the hardness could be increased by 1 to 2 HRC more.

(29) Instead of further quenching the steel alloy in cold water for 10 minutes, as occurred with the first specimen, it is also possible to further quench the steel alloy in liquid nitrogen. A second specimen of the steel alloy was further quenched in liquid nitrogen and kept in that medium for 10 minutes, then tempered as described above. After tempering, the second speciment exhibited a hardness of approximately 911 HV10, which corresponds to about 66.6 HRC. This improvement of hardness, and accordingly strength, is possibly attributable to the reduction of the austenite content in the final hardened and tempered structure. It is anticipated that by increasing the temperature at which the steel is austenitised, but not exceeding the limits stated herein, the resulting hardness can be increased further.

(30) A third specimen of the steel alloy was also quenched from approximately 880 C. to approximately 60 C. and then held at that temperature for approximately 15 minutes followed by further quenching into cold water kept at approximately 15 C. The third specimen was held in the water for approximately 10 minutes and then immediately tempered at approximately 500 C. for approximately 60 minutes. Following tempering, the steel alloy was air-cooled to room temperature. The measured hardness was 647 HV10, which corresponds to approximately 56.6 HRC.

(31) A fourth specimen of the steel alloy was quenched from approximately 920 C. to approximately 60 C. and then held at that temperature for approximately 15 minutes, followed by further quenching into liquid nitrogen. The fourth specimen was held in liquid nitrogen for approximately 10 minutes and then immediately tempered at approximately 550 C. for approximately 60 minutes. Following tempering, the steel alloy was air-cooled to room temperature. The measured hardness was 611 HV10, which corresponds to approximately 54.7 HRC.

(32) It can therefore be concluded that the alloy structure holds its hardness well when tempered at relatively high temperatures, allowing the inventive steel alloy to be used to be used in high temperature bearing applications.

(33) Bainitic Hardening

(34) From the as-annealed condition, a bainitic austempering heat treatment was carried out on a fifth specimen of the steel alloy. During this heat treatment the steel alloy was quenched from approximately 880 C. to approximately 250 C. and then held at that temperature for 18 hours. Afterwards, the steel alloy was air-cooled to room temperature. FIG. 4 shows a scanning electron microscope image of the steel alloy after the bainitic heat treatment (EHT=10.00 kV, Signal A=SE2, Pixel Size=37.2 nm, WD=4 mm, Mag=3.00 k X). The microstructure can be seen to comprise numerous, relatively small iron carbides and vanadium carbides in a very fine bainitic matrix that is comprising bainitic ferrite with thin austenite films. Some quite small austenite blocks could also be observed.

(35) For comparison, a reference steel alloy (Alloy 3 in: C. Garcia-Mateo et al., ISIJ International, Vol. 43 (2003), No. 11, pp. 1821-1825) was also bainitically hardened in exactly the same way as the fifth specimen of the inventive steel alloy presented herein. Hardness measurements were carried out on both steels. The reference steel had a hardness of 585 HV10 (approximately 53.4 HRC) compared with 662 HV10 (approximately 57.3 HRC) for the fifth specimen.

(36) This represents a significant improvement of the hardness of such bainitic steels, and the shown examples demonstrate the versatility of the inventive steel presented herein.

(37) Moreover, it is expected that the hardness will improve further by transforming into bainite at lower temperatures, albeit with longer holding times.

(38) The foregoing detailed description has been provided by way of explanation and illustration, and is not intended to limit the scope of the appended claims. Many variations in the presently preferred embodiments illustrated herein will be apparent to one of ordinary skill in the art, and remain within the scope of the appended claims and their equivalents.