Bearing steel and method for producing same

Patent metadata

Field	Value
Publication number	US-9732407-B2
Application number	US-201214352290-A
Country	US
Kind code	B2
Filing date	Oct 5, 2012
Priority date	Oct 20, 2011
Publication date	Aug 15, 2017
Grant date	Aug 15, 2017

Abstract

A bearing steel includes, as a metallographic structure, inclusions which contain complex oxysulfides including Rare Earth Metal, Ca, O, S, and Al, TiN, MnS, Al 2 O 3 , and complex oxides including Al and Ca, wherein, a number fraction of the complex oxysulfides in a total number of the inclusions is 50% to less than 100% and a number of complex oxysulfides having a major axis of 5 μm or more is 0.001 pieces to 2 pieces in an observed section of 1 mm 2 , and a number of TiN existing independently from the complex oxysulfides and having a major axis of 5 μm or more is 0.001 pieces to less than 1.0 piece in an observed section of 1 mm 2 .

First claim

The invention claimed is:

1. A bearing steel comprising, as a chemical composition, by mass %,
C: 0.9% to 1.5%,
Si: 0.1% to 0.8%,
Mn: 0.1% to 1.5%,
Cr: 0.5% to 2.0%,
Al: 0.01% to 0.05%,
Ca: 0.00001% to 0.0050%,
Rare Earth Metal: 0.0001% to 0.050%,
O: 0.0001% to 0.0030%,
Ti: limited to less than 0.005%,
N: limited to 0.015% or less,
P: limited to 0.03% or less,
S: limited to 0.05% or less, and
a balance consisting of iron and unavoidable impurities, and
comprising, as a metallographic structure, inclusions which contain complex oxysulfides including Rare Earth Metal, Ca, O, S, and Al, TiN, MnS, Al 2 O 3 , and complex oxides including Al and Ca,
wherein, a number fraction of the complex oxysulfides in a total number of the inclusions is 50% to less than 100% and a number of complex oxysulfides having a major axis of 5 μm or more is 0.001 pieces to 2 pieces in an observed section of 1 mm 2 , and
a number of TiN existing independently from the complex oxysulfides and having a major axis of 5 μm or more is 0.001 pieces to less than 1.0 piece in the observed section of 1 mm 2 .

2. The bearing steel according to claim 1 ,
wherein, when the S content in the chemical composition is more than 0.01% to 0.05%, the Ca content is 0.00050% to 0.0050%.

3. The bearing steel according to claim 1 , further comprising, as the chemical composition, by mass %, at least one of
V: 0.05% to 0.70%,
Mo: 0.05% to 1.00%,
W: 0.05% to 1.00%,
Ni: 0.10% to 3.50%,
Cu: 0.10% to 0.50%,
Nb: 0.005% to less than 0.050%, and
B: 0.0005% to 0.0050%.

4. The bearing steel according to claim 2 , further comprising, as the chemical composition, by mass %, at least one of
V: 0.05% to 0.70%,
Mo: 0.05% to 1.00%,
W: 0.05% to 1.00%,
Ni: 0.10% to 3.50%,
Cu: 0.10% to 0.50%,
Nb: 0.005% to less than 0.050%, and
B: 0.0005% to 0.0050%.

5. The bearing steel according to any one of claims 1 to 4 ,
wherein an Al content in the complex oxysulfides is 20 mass % or less in Al 2 O 3 equivalent.

6. The bearing steel according to any one of claims 1 to 4 ,
wherein a total number of MnS having a major axis of 10 μm or more and the TiN existing independently from the complex oxysulfides and having the major axis of 5 μm or more is 5 pieces or less in the observed section of 1 mm 2 .

7. The bearing steel according to claim 3 ,
wherein the Cu content and the Ni content expressed in mass % satisfy Cu≦Ni.

8. The bearing steel according to claim 4 ,
wherein the Cu content and the Ni content expressed in mass % satisfy Cu≦Ni.

9. A method for producing a bearing steel, the method comprising:
Al-deoxidizing a molten steel utilizing Al;
REM-deoxidizing the molten steel utilizing Rare Earth Metal after the Al-deoxidizing for 5 minutes to 10 minutes;
casting the molten steel after the REM-deoxidizing so as to obtain a cast piece which includes, as a chemical composition, by mass %,
C: 0.9% to 1.5%,
Si: 0.1% to 0.8%,
Mn: 0.1% to 1.5%,
Cr: 0.5% to 2.0%,
Al: 0.01% to 0.05%,
Ca: 0.00001% to 0.0050%,
Rare Earth Metal: 0.0001% to 0.050%,
O: 0.0001% to 0.0030%,
Ti: limited to less than 0.005%,
N: limited to 0.015% or less,
P: limited to 0.03% or less,
S: limited to 0.05% or less, and
a balance consisting of iron and unavoidable impurities;

heating the cast piece in a temperature range of 1270° C. to 1300° C. and holding the cast piece after the heating in a temperature range of 1200° C. to 1250° C. for 60 seconds or more; and
hot-plastic-working the cast piece after the heating and the holding so as to obtain a hot-worked steel.

10. The method for producing the bearing steel according to claim 9 , the method further comprising
vacuum-degassing the molten steel utilizing Ca after the REM-deoxidizing and before the casting, when the molten steel includes, as a chemical composition, by mass %,
S: more than 0.01% to 0.05%.

11. The method for producing the bearing steel according to claim 9 ,
wherein the cast piece further includes, as the chemical composition, by mass %, at least one of
V: 0.05% to 0.70%,
Mo: 0.05% to 1.00%,
W: 0.05% to 1.00%,
Ni: 0.10% to 3.50%,
Cu: 0.10% to 0.50%,
Nb: 0.005% to less than 0.050%, and
B: 0.0005% to 0.0050%.

12. The method for producing the bearing steel according to claim 10 ,
wherein the cast piece further includes, as the chemical composition, by mass %, at least one of
V: 0.05% to 0.70%,
Mo: 0.05% to 1.00%,
W: 0.05% to 1.00%,
Ni: 0.10% to 3.50%,
Cu: 0.10% to 0.50%,
Nb: 0.005% to less than 0.050%, and
B: 0.0005% to 0.0050%.

13. The method for producing the bearing steel according to any one of claims 9 to 12 ,
wherein, in the casting, the molten steel is cast while being rotated horizontally in a mold under a condition of 0.1 m/minute to 0.5 m/minute.

14. The method for producing the bearing steel according to any one of claims 9 to 12 , the method further comprising
soft-annealing the hot-worked steel after the hot-plastic-working by being heated in a temperature range of 700° C. to 750° C. and by being held for 30 hours to 50 hours so as to obtain a softened steel.

15. The method for producing the bearing steel according to claim 10 or 12 , the method further comprising
fluxing the molten steel utilizing CaO—CaF 2 for a desulfurization after the REM-deoxidizing and before the vacuum-degassing.

16. A bearing steel comprising, as a chemical composition, by mass %,
C: 0.9% to 1.5%,
Si: 0.1% to 0.8%,
Mn: 0.1% to 1.5%,
Cr: 0.5% to 2.0%,
Al: 0.01% to 0.05%,
Ca: 0.00001% to 0.0050%,
Rare Earth Metal: 0.0001% to 0.050%,
O: 0.0001% to 0.0030%,
Ti: limited to less than 0.005%,
N: limited to 0.015% or less,
P: limited to 0.03% or less,
S: limited to 0.05% or less, and
a balance comprising iron and unavoidable impurities, and
comprising, as a metallographic structure, inclusions which contain complex oxysulfides including Rare Earth Metal, Ca, O, S, and Al, TiN, MnS, Al 2 O 3 , and complex oxides including Al and Ca,
wherein, a number fraction of the complex oxysulfides in a total number of the inclusions is 50% to less than 100% and a number of complex oxysulfides having a major axis of 5 μm or more is 0.001 pieces to 2 pieces in an observed section of 1 mm 2 , and
a number of TiN existing independently from the complex oxysulfides and having a major axis of 5 μm or more is 0.001 pieces to less than 1.0 piece in the observed section of 1 mm 2 .

17. A method for producing a bearing steel, the method comprising:
Al-deoxidizing a molten steel utilizing Al;
REM-deoxidizing the molten steel utilizing Rare Earth Metal after the Al-deoxidizing for 5 minutes to 10 minutes;
casting the molten steel after the REM-deoxidizing so as to obtain a cast piece which includes, as a chemical composition, by mass %,
C: 0.9% to 1.5%,
Si: 0.1% to 0.8%,
Mn: 0.1% to 1.5%,
Cr: 0.5% to 2.0%,
Al: 0.01% to 0.05%,
Ca: 0.00001% to 0.0050%,
Rare Earth Metal: 0.0001% to 0.050%,
O: 0.0001% to 0.0030%,
Ti: limited to less than 0.005%,
N: limited to 0.015% or less,
P: limited to 0.03% or less,
S: limited to 0.05% or less, and
a balance comprising iron and unavoidable impurities;

heating the cast piece in a temperature range of 1270° C. to 1300° C. and holding the cast piece after the heating in a temperature range of 1200° C. to 1250° C. for 60 seconds or more; and
hot-plastic-working the cast piece after the heating and the holding so as to obtain a hot-worked steel.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Hashimura Masayuki
• Miyazaki Masafumi
• Yamamura Hideaki
• Suzuki Takahisa
• Fujita Takashi

Classifications

• C21D8/00

  Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment (hardening articles or materials formed by forging or rolling with no further heating beyond that required for the formation C21D1/02) · CPC title

• C22C38/22

  with molybdenum or tungsten · CPC title

• C22C38/20

  with copper · CPC title

• C22C38/46

  with vanadium · CPC title

• C21D8/005

  Chemistry & Metallurgy · mapped topic