Bearing steel and method for producing same
View Patent ↗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 .
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.