Bearing steel and method for producing same

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.

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, Al2O3, 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 mm2, 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 mm2.

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.