BEARING COMPONENT FORMED FROM A STEEL ALLOY

Abstract

A bearing component formed from a steel alloy having from 0.7 to 0.9 wt. % carbon, from 0.05 to 0.16 wt. % silicon, from 0.7 to 0.9 wt. % manganese, from 1.4 to 2.0 wt. % chromium, from 0.7 to 1.0 wt. % molybdenum, from 0.03 to 0.15 wt. % vanadium, from 0 to 0.25 wt. % nickel, from 0 to 0.3 wt. % copper, from 0 to 0.2 wt. % cobalt, from 0 to 0.1 wt. % aluminum, from 0 to 0.1 wt. % niobium, from 0 to 0.2 wt. % tantalum, from 0 to 0.025 wt. % phosphorous, from 0 to 0.015 wt. % sulphur, from 0 to 0.075 wt. % tin, from 0 to 0.075 wt. % antimony, from 0 to 0.04 wt. % arsenic, from 0 to 0.002 wt. % lead, up to 350 ppm nitrogen, up to 20 ppm oxygen, up to 50 ppm calcium, up to 30 ppm boron, up to 50 ppm titanium, the balance iron, together with any unavoidable impurities.

Claims

1. A bearing component formed from a steel alloy comprising: from 0.7 to 0.9 wt. % carbon, from 0.05 to 0.16 wt. % silicon, from 0.7 to 0.9 wt. % manganese, from 1.4 to 2.0 wt. % chromium, from 0.7 to 1.0 wt. % molybdenum, from 0.03 to 0.15 wt. % vanadium, from 0 to 0.25 wt. % nickel, from 0 to 0.3 wt. % copper, from 0 to 0.2 wt. % cobalt, from 0 to 0.1 wt. % aluminium, from 0 to 0.1 wt. % niobium, from 0 to 0.2 wt. % tantalum, from 0 to 0.025 wt. % phosphorous, from 0 to 0.015 wt. % sulphur, from 0 to 0.075 wt. % tin, from 0 to 0.075 wt. % antimony, from 0 to 0.04 wt. % arsenic, from 0 to 0.002 wt. % lead, up to 350 ppm nitrogen, up to 20 ppm oxygen, up to 50 ppm calcium, up to 30 ppm boron, up to 50 ppm titanium, the balance iron, together with any unavoidable impurities.

2. The bearing component of claim 1, wherein the steel alloy comprises from 0.7 to 0.8 wt. % carbon.

3. The bearing component of claim 1, wherein the steel alloy comprises from 0.06 to 0.16 wt. % silicon.

4. The bearing component of claim 1, wherein the steel alloy comprises from 0.7 to 0.9 wt. % molybdenum.

5. The bearing component of claim 1, wherein the steel alloy comprises molybdenum and silicon in a weight ratio of 3.5≦Mo/Si≦33.3.

6. The bearing component of claim 1, wherein the steel alloy comprises molybdenum and chromium in a weight ratio of 0.35≦Mo/Cr≦0.71.

7. The bearing component of claim 1, wherein the steel alloy comprises chromium and carbon in a weight ratio of Cr/C ratio≦2.

8. The bearing component of claim 1, wherein the steel alloy comprises from 0.03 to 0.12 wt. % vanadium.

9. The bearing component of claim 1, wherein the steel alloy comprises from 50 to 350 ppm nitrogen.

10. The bearing component of claim 1, wherein the steel alloy comprises at least 100 ppm nitrogen.

11. The bearing component of claim 1, wherein the steel alloy has a bainitic and/or martensitic microstructure, optionally including carbides, nitrides and/or carbonitrides.

12. The bearing component of claim 1, wherein the bearing component is a rolling element or an inner ring or an outer ring for a bearing.

13. (canceled)

14. A process for the manufacture of a bearing component, comprising: (i) continuously casting a steel alloy composition comprising: from 0.7 to 0.9 wt. % carbon, from 0.05 to 0.16 wt. % silicon, from 0.7 to 0.9 wt. % manganese, from 1.4 to 2.0 wt. % chromium, from 0.7 to 1.0 wt. % molybdenum, from 0.03 to 0.15 wt. % vanadium, from 0 to 0.25 wt. % nickel, from 0 to 0.3 wt. % copper, from 0 to 0.2 wt. % cobalt, from 0 to 0.1 wt. % aluminium, from 0 to 0.1 wt. % niobium, from 0 to 0.2 wt. % tantalum, from 0 to 0.025 wt. % phosphorous, from 0 to 0.015 wt. % sulphur, from 0 to 0.075 wt. % tin, from 0 to 0.075 wt. % antimony, from 0 to 0.04 wt. % arsenic, from 0 to 0.002 wt. % lead, up to 350 ppm nitrogen, up to 20 ppm oxygen, up to 50 ppm calcium, up to 30 ppm boron, up to 50 ppm titanium, the balance iron, together with any unavoidable impurities; and (ii) forming a bearing component from the continuously cast steel alloy.

Description

EXAMPLES

[0059] The invention will now be described further with reference to the following non-limiting examples.

[0060] Steel 1, comprising in wt. %

[0061] C: 0.75

[0062] Si: 0.1

[0063] Mn: 0.8

[0064] Mo: 0.7

[0065] Cr: 1.6

[0066] Ni: 0.1

[0067] Cu: 0.2

[0068] V: 0.1

[0069] P: max 0.01

[0070] S: max 0.015

[0071] As+Sn+Sb: max 0.075

[0072] Pb: max 0.002

[0073] Al: max 0.050

[0074] Fe: Balance

[0075] Oxygen level should be less than 10 ppm, Ti level less than 30 ppm and Ca level less than 10 ppm. Nitrogen is present as a trace element (at least 50 ppm). The maximum limit for As is 0.04 wt. %.

[0076] Steel 2, comprising in wt. %

[0077] C: 0.75

[0078] Si: 0.05

[0079] Mn: 0.8

[0080] Mo: 0.7

[0081] Cr: 1.6

[0082] Ni: 0.1

[0083] Cu: 0.2

[0084] V: 0.1

[0085] P: max 0.01

[0086] S: max 0.015

[0087] As+Sn+Sb: max 0.075

[0088] Pb: max 0.002

[0089] Al: max 0.050

[0090] Fe: Balance

[0091] Oxygen level should be less than 10 ppm, Ti level less than 30 ppm and Ca level less than 10 ppm. Nitrogen is present as a trace element (at least 50 ppm). The maximum limit for As is 0.04 wt. %.

[0092] Fully bainitic hardened components manufactured from the reference Steel compositions 1 and 2 above exhibited a hardness of about 60 HRC or higher.

[0093] Comparative Steel 1, comprising in wt. %

[0094] C: 0.75

[0095] Si: 0.2

[0096] Mn: 0.8

[0097] Mo: 0.36

[0098] Cr: 1.6

[0099] Ni: 0.1

[0100] Cu: 0.2

[0101] V: 0.1

[0102] P: max 0.01

[0103] S: max 0.015

[0104] As+Sn+Sb: max 0.075

[0105] Pb: max 0.002

[0106] Al: max 0.050

[0107] Fe: Balance

[0108] Oxygen level should be less than 10 ppm, Ti level less than 30 ppm and Ca level less than 10 ppm. Nitrogen is present as a trace element (at least 50 ppm). The maximum limit for As is 0.04 wt. %.

[0109] Comparative Steel 2, comprising in wt. %

[0110] C: 0.75

[0111] Si: 0.35

[0112] Mn: 0.8

[0113] Mo: 0.36

[0114] Cr: 1.6

[0115] Ni: 0.1

[0116] Cu: 0.2

[0117] V: 0.1

[0118] P: max 0.01

[0119] S: max 0.015

[0120] As+Sn+Sb: max 0.075

[0121] Pb: max 0.002

[0122] Al: max 0.050

[0123] Fe: Balance

[0124] Oxygen level should be less than 10 ppm, Ti level less than 30 ppm and Ca level less than 10 ppm. Nitrogen is present as a trace element (at least 50 ppm). The maximum limit for As is 0.04 wt. %.

[0125] Comparative Steel 3, comprising in wt. %

[0126] C: 0.75

[0127] Si: 0.05

[0128] Mn: 0.8

[0129] Mo: 0.5

[0130] Cr: 1.6

[0131] Ni: 0.1

[0132] Cu: 0.2

[0133] V: 0.1

[0134] P: max 0.01

[0135] S: max 0.015

[0136] As+Sn+Sb: max 0.075

[0137] Pb: max 0.002

[0138] Al: max 0.050

[0139] Fe: Balance

[0140] Oxygen level should be less than 10 ppm, Ti level less than 30 ppm and Ca level less than 10 ppm. Nitrogen is present as a trace element (at least 50 ppm). The maximum limit for As is 0.04 wt. %.

[0141] The effect on hardness retention upon tempering at 260° C. for 1 hour was investigated. For the reference steel compositions according to the above examples, the change in hardness (Vickers hardness, ΔHv) was approximately +7.5 (Steel 1), +4.5 (Steel 2), 0 (Comparative Steel 1), +7 (Comparative Steel 2), and −3 (Comparative Steel 3). Thus, the best results were obtained for Steels 1 and 2. Steels 1 and 2 also lend themselves to continuous casting because they exhibit reduced macro-segregation effects. While Comparative Steel 2 also exhibited a good result in terms of hardness, the high silicon content in this example (which is expected to improve tempering resistance) does not lend itself to continuous casting in view of relatively significant macro-segregation effects. The same is true of Comparative Steel 1, although to a lesser degree.

[0142] The following two further examples (V91 and V92) were also compared in terms of macrosegregation.

[0143] Comparative Steel V91, comprising in wt. %

[0144] C: 0.953

[0145] Si: 0.308

[0146] Mn: 0.671

[0147] Mo: 0.245

[0148] Cr: 1.721

[0149] Ni: 0.175

[0150] Cu: 0.155

[0151] V: 0.01

[0152] N: 0.0093

[0153] Al: 0.007

[0154] Nb: 0.002

[0155] Sn: 0.012

[0156] P: 0.017

[0157] S: 0.009

[0158] B: 0.0002

[0159] As+Sn+Sb: max 0.075

[0160] Fe: Balance

[0161] Oxygen level should be less than 10 ppm, Ti level less than 30 ppm and Ca level less than 10 ppm. The maximum limit for As is 0.04 wt. %.

[0162] Steel V92, comprising in wt. %

[0163] C: 0.749

[0164] Si: 0.134

[0165] Mn: 0.808

[0166] Mo: 0.705

[0167] Cr: 1.593

[0168] Ni: 0.114

[0169] Cu: 0.202

[0170] V: 0.112

[0171] N: 0.0049

[0172] Al: 0.007

[0173] Nb: 0.002

[0174] Sn: 0.002

[0175] P: 0.006

[0176] S: 0.005

[0177] B: 0.0003

[0178] As+Sn+Sb: max 0.075

[0179] Fe: Balance

[0180] Oxygen level should be less than 10 ppm, Ti level less than 30 ppm and Ca level less than 10 ppm. The maximum limit for As is 0.04 wt. %.

[0181] The two steel alloys V91 and V92 were melted in vacuum (Vacuum Induction Melted) and then cast in sand moulds. Their chemical compositions are recited above.

[0182] After casting, the head and the bottom of each steel ingot were sectioned and discarded.

[0183] Afterwards, the ingots were homogenised for a minimum of 6 hours at 1200° C., and then furnace cooled.

[0184] The ingots were cold-charged and heated to the said temperature at a rate of 100° C./hour. Once the desired temperature was reached, the total holding time was 8 hours to ensure that the central regions in each ingot are soaked for at least 6 hours, at temperature.

[0185] The furnace atmosphere was controlled by using a continuous nitrogen gas flow, initially with the rate 28 litre/min. During the cooling to room temperature, the nitrogen gas flow rate was increased to 100 litre/min. Nevertheless, the cooling rate of the ingots was sufficiently low.

[0186] Two slices were sectioned from each ingot and were then ground and finish-polished prior to macroetching in accordance with the ASTM E 381 standard to reveal the as-solidified structure of each alloy.

[0187] The macroetched sections for both alloys were then compared. The steel alloy V92 showed a structure that was finer than that of the comparative, reference steel alloy V91.

[0188] The bearing component according to the present invention is formed from a steel alloy having high hardness, relative weldability, hardenability and toughness, and resistance to rolling contact fatigue, wear and creep, as well as micro-defect tolerance. Moreover, it also exhibits reduced segregation during continuous casting.

[0189] 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.