# US 11,078,559 B2 · Rolling element bearing having bainite microstructure

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- Number: US 11,078,559 B2
- Document ID: US11078559B2
- Status: Granted
- Kind: B2
- Application number: 15/944,921
- Filed: 2018-04-04
- Published: 2018-08-09
- Granted: 2021-08-03
- Earliest claimed: 2012-09-26
- Assignees: Aktiebolaget Skf
- Applicants: Aktiebolaget Skf
- Inventors: Mohamed Sherif; Urszula Alicja Sachadel-Solarek
- Web page: https://patentgrep.com/patent/US11078559B2

## CPC

- C22C 38/54: with boron
- C21D 1/20: Isothermal quenching, e.g. bainitic hardening
- C21D 1/32: Soft annealing, e.g. spheroidising
- C22C 38/001: {containing N}
- C22C 38/002: {containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60}
- C22C 38/008: {containing tin}
- C22C 38/02: containing silicon
- C22C 38/04: containing manganese
- C22C 38/06: containing aluminium
- C22C 38/22: with molybdenum or tungsten
- C22C 38/24: with vanadium
- C22C 38/26: with niobium or tantalum
- C22C 38/42: with copper
- C22C 38/44: with molybdenum or tungsten
- C22C 38/46: with vanadium
- C22C 38/50: with titanium or zirconium
- F16C 33/121: {Use of special materials}
- C21D 2211/002: Bainite
- F16C 2204/64: Medium carbon steel, i.e. carbon content from 0.4 to 0,8 wt%
- F16C 2204/70: with chromium as the next major constituent
- C22C: ALLOYS (treatment of alloys C21D, C22F)
- C21D: MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING (surface treatment of metallic material involving at least one process provided for in class C23 and at least one process covered by this subclass C23F17/00; unidirectional solidification of eutectic materials or unidirectional demixing of eutectoid materials C30B)
- F16C: SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS

## Abstract

A steel alloy for bearings contains: 0.6 to 0.9 wt. % carbon, 0.1 to 0.5 wt. % silicon, 0.1 to 1.5 wt. % manganese, 1.5 to 2.0 wt. % chromium, 0.2 to 0.6 wt. % molybdenum, 0 to 0.25 wt. % nickel, 0 to 0.3 wt. % copper, 0 to 0.2 wt. % vanadium, 0 to 0.2 wt. % cobalt, 0 to 0.2 wt. % aluminium, 0 to 0.1 wt. % niobium, 0 to 0.2 wt. % tantalum, 0 to 0.05 wt. % phosphorous, 0 to 0.03 wt. % sulphur, 0 to 0.075 wt. % tin, 0 to 0.075 wt. % antimony, 0 to 0.075 wt. % arsenic, 0 to 0.01 wt. % lead, up to 350 ppm nitrogen, up to 100 ppm oxygen, up to 50 ppm calcium, up to 50 ppm boron, up to 50 ppm titanium, the balance being iron, together with any other unavoidable impurities. Furthermore, the steel alloy contains (i) molybdenum and silicon in a weight ratio of 0.4<Mo/Si<6.0 and (ii) molybdenum and chromium in a weight ratio of 0.1<Mo/Cr<0.4.

## Claims

### Claim 1

A rolling element bearing prepared according to a process comprising:
forming an inner raceway and an outer raceway, wherein at least one of the inner raceway and the outer raceway is composed of a steel alloy consisting of:
0.7 to 0.9 wt. % carbon,
0.1 to 0.4 wt. % silicon,
0.7 to 0.9 wt. % manganese,
1.5 to 1.8 wt. % chromium,
0.2 to 0.4 wt. % molybdenum,
0 to 0.25 wt. % nickel,
0 to 0.3 wt. % copper,
0.05 to 0.2 wt. % vanadium,
0 to 0.2 wt. % cobalt,
0 to 0.2 wt. % aluminium,
0 to 0.1 wt. % niobium,
0 to 0.2 wt. % tantalum,
0 to 0.05 wt. % phosphorous,
0 to 0.03 wt. % sulphur,
0 to 0.075 wt. % tin,
0 to 0.075 wt. % antimony,
0 to 0.075 wt. % arsenic,
0 to 0.01 wt. % lead,
50 to 350 ppm nitrogen,
up to 15 ppm oxygen,
less than 10 ppm calcium,
up to 50 ppm boron, and
up to 50 ppm titanium, the balance being iron and unavoidable impurities,
austenitizing the at least one of the inner raceway and the outer raceway composed of said steel alloy at 800° C.-890° C. for 10 to 120 minutes;
through-hardening the austenitized inner raceway and/or outer raceway by quenching;
heating the through-hardened inner raceway and/or outer raceway to form bainite until bainite transformation has ceased and the inner raceway and/or outer raceway has a uniform bainite microstructure; and
assembling the rolling element bearing by disposing a plurality of rolling elements between the inner raceway and the outer raceway.

### Claim 2 (depends on 1)

The rolling element bearing according to claim 1, wherein the process further comprises, prior to austenitizing, spheroidize-annealing the at least one of the inner raceway and the outer raceway composed of said steel alloy.

### Claim 3 (depends on 1)

The rolling element bearing according to claim 1, wherein the process further comprises, after quenching and before through-hardening, deep-freezing the austenitized inner raceway and/or outer raceway.

### Claim 4 (depends on 1)

The rolling element bearing according to claim 1, wherein the at least one of the inner raceway and the outer raceway composed of said steel alloy is austenitized at 885° C.-890° C.

### Claim 5 (depends on 1)

The rolling element bearing according to claim 1, wherein the bainite transformation is performed at 200-250° C.

### Claim 6 (depends on 1)

The rolling element bearing according to claim 1, wherein nickel is 0.02 to 0.2 wt. % and copper is 0.02 to 0.2 wt. %.

### Claim 7 (depends on 6)

The rolling element bearing according to claim 6, wherein molybdenum is 0.3 to 0.4 wt. %.

### Claim 8 (depends on 7)

The rolling element bearing according to claim 7, wherein chromium is 1.5 to 1.7 wt. %.

### Claim 9 (depends on 8)

The rolling element bearing according to claim 8, wherein:
carbon is 0.7 to 0.8 wt. %,
silicon is 0.2 to 0.4 wt. %,
aluminium is 0 to 0.1 wt. %,
phosphorous is 0 to 0.025 wt. %,
sulphur is 0 to 0.015 wt. %, and
oxygen is up to 10 ppm.

### Claim 10 (depends on 9)

The rolling element bearing according to claim 9, wherein calcium is 3 ppm or less.

### Claim 11 (depends on 10)

The rolling element bearing according to claim 10, wherein the process further comprises:
prior to austenitizing, spheroidize-annealing the at least one of the inner raceway and the outer raceway composed of said steel alloy, and
after quenching and before through-hardening, deep-freezing the austenitized inner raceway and/or outer raceway,
wherein the at least one of the inner raceway and the outer raceway composed of said steel alloy is austenitized at 885° C.-890° C., and
the bainite transformation is performed at 200-250° C.

### Claim 12

A rolling element bearing, comprising:
an inner raceway and an outer raceway, and
a plurality of rolling elements disposed between the inner raceway and the outer raceway,
wherein at least one of the inner raceway and the outer raceway is composed of a steel alloy consisting of:
0.7 to 0.9 wt. % carbon,
0.1 to 0.4 wt. % silicon,
0.7 to 0.9 wt. % manganese,
1.5 to 1.8 wt. % chromium,
0.2 to 0.4 wt. % molybdenum,
0 to 0.25 wt. % nickel,
0 to 0.3 wt. % copper,
0.05 to 0.2 wt. % vanadium,
0 to 0.2 wt. % cobalt,
0 to 0.2 wt. % aluminium,
0 to 0.1 wt. % niobium,
0 to 0.2 wt. % tantalum,
0 to 0.05 wt. % phosphorous,
0 to 0.03 wt. % sulphur,
0 to 0.075 wt. % tin,
0 to 0.075 wt. % antimony,
0 to 0.075 wt. % arsenic,
0 to 0.01 wt. % lead,
50 to 350 ppm nitrogen,
up to 15 ppm oxygen,
less than 10 ppm calcium,
up to 50 ppm boron, and
up to 50 ppm titanium, the balance being iron and unavoidable impurities, and
wherein the at least one of the inner raceway and the outer raceway composed of said steel alloy has a uniform bainite microstructure throughout the entire at least one of the inner raceway or the outer raceway.

### Claim 13 (depends on 12)

The rolling element bearing according to claim 12, wherein nickel is 0.02 to 0.2 wt. % and copper is 0.02 to 0.2 wt. %.

### Claim 14 (depends on 12)

The rolling element bearing according to claim 12, wherein molybdenum is 0.3 to 0.4 wt. %.

### Claim 15 (depends on 12)

The rolling element bearing according to claim 12, wherein chromium is 1.5 to 1.7 wt. %.

### Claim 16 (depends on 12)

The rolling element bearing according to claim 12, wherein:
carbon is 0.7 to 0.8 wt. %,
silicon is 0.2 to 0.4 wt. %,
aluminium is 0 to 0.1 wt. %,
phosphorous is 0 to 0.025 wt. %,
sulphur is 0 to 0.015 wt. %, and
oxygen is up to 10 ppm.

### Claim 17 (depends on 12)

The rolling element bearing according to claim 12, wherein calcium is 3 ppm or less.

### Claim 18 (depends on 16)

The rolling element bearing according to claim 16, wherein:
nickel is 0.02 to 0.2 wt. %,
copper is 0.02 to 0.2 wt,
molybdenum is 0.3 to 0.4 wt,
chromium is 1.5 to 1.7 wt. %, and
calcium is 3 ppm or less.