Method for producing steel

1. A method for producing steel, comprising:

adding a first group of alloys to molten steel, wherein the molten steel has an amount of dissolved oxygen of 0.0050 mass % or more;

after the adding the first group of alloys, adding deoxidizer to the molten steel for deoxidation;

after the adding the deoxidizer, adding a second group of alloys, which includes certain amounts of oxygen, to the deoxidized molten steel; and

after the adding the second group of alloys, adding REM to the molten steel, wherein

amounts of oxygen introduced from the first group of alloys and amounts of oxygen introduced from the second group of alloys satisfy formulas (i) to (iii), and

after the adding REM, the ratio between REM and T.O satisfies formula (iv):

O a ≤0.00100  (i)

O b +O a ≥0.00150  (ii)

O b /O a ≥2.0  (iii)

0.05≤ REM/T.O≤ 0.5  (iv)

where symbols in the formulas are defined as follows:

O b : the amounts of oxygen introduced from the first group of alloys, in mass %;

O a : the amounts of oxygen introduced from the second group of alloys, in mass %;

REM: content of REM, in mass %;

T.O: total content of oxygen, in mass %.

2. The method for producing steel according to claim 1 , wherein the first group of alloys and the second group of alloys are selected from the group consisting of manganese metal, titanium metal, copper metal, nickel metal, FeMn, FeP, FeTi, FeS, FeSi, FeCr, FeMo, FeB, and FeNb.

3. The method for producing steel according to claim 1 , wherein a chemical composition of the steel consists of, in mass %:

C: 0.0005 to 1.5%;

Si: 0.005 to 1.2%;

Mn: 0.05 to 3.0%;

P: 0.001 to 0.2%;

S: 0.0001 to 0.05%;

T.Al: 0.005 to 1.5%;

Cu: 0 to 1.5%;

Ni: 0 to 10.0%;

Cr: 0 to 10.0%;

Mo: 0 to 1.5%;

Nb: 0 to 0.1%;

V: 0 to 0.3%;

Ti: 0 to 0.25%;

B: 0 to 0.005%;

REM: 0.00001 to 0.0020%; and

T.O: 0.0005 to 0.0050%,

with the balance being Fe and impurities

where T.Al in the defined as total content of Al.

4. The method for producing steel according to claim 3 , wherein the chemical composition of the steel contains one or more elements selected from, in mass %:

Cu: 0.1 to 1.5%;

Ni: 0.1 to 10.0%;

Cr: 0.1 to 10.0%;

Mo: 0.05 to 1.5%;

Nb: 0.005 to 0.1%;

V: 0.005 to 0.3%;

Ti: 0.001 to 0.25%; and

B: 0.0005 to 0.005%.

5. The method for producing steel according to claim 1 , wherein in the steel, a maximum diameter of alumina clusters is 100 μm or less.

6. The method for producing steel according to claim 5 , wherein in the steel, numbers of alumina clusters having diameters of 20 μm or more are 2.0 clusters/kg or less.

7. The method for producing steel according to claim 2 , wherein a chemical composition of the steel consists of, in mass %:

C: 0.0005 to 1.5%;

Si: 0.005 to 1.2%;

Mn: 0.05 to 3.0%;

P: 0.001 to 0.2%;

S: 0.0001 to 0.05%;

T.Al: 0.005 to 1.5%;

Cu: 0 to 1.5%;

Ni: 0 to 10.0%;

Cr: 0 to 10.0%;

Mo: 0 to 1.5%;

Nb: 0 to 0.1%;

V: 0 to 0.3%;

Ti: 0 to 0.25%;

B: 0 to 0.005%;

REM: 0.00001 to 0.0020%; and

T.O: 0.0005 to 0.0050%,

with the balance being Fe and impurities

where T.Al in the above is defined as total content of Al.

8. The method for producing steel according to claim 7 , wherein the chemical composition of the steel contains one or more elements selected from, in mass %:

Cu: 0.1 to 1.5%;

Ni: 0.1 to 10.0%;

Cr: 0.1 to 10.0%;

Mo: 0.05 to 1.5%;

Nb: 0.005 to 0.1%;

V: 0.005 to 0.3%;

Ti: 0.001 to 0.25%; and

B: 0.0005 to 0.005%.

9. The method for producing steel according to claim 2 , wherein in the steel, a maximum diameter of alumina clusters is 100 μm or less.

10. The method for producing steel according to claim 3 , wherein in the steel, a maximum diameter of alumina clusters is 100 μm or less.

11. The method for producing steel according to claim 4 , wherein in the steel, a maximum diameter of alumina clusters is 100 μm or less.

12. The method for producing steel according to claim 9 , wherein in the steel, numbers of alumina clusters having diameters of 20 μm or more are 2.0 clusters/kg or less.

13. The method for producing steel according to claim 10 , wherein in the steel, numbers of alumina clusters having diameters of 20 μm or more are 2.0 clusters/kg or less.

14. The method for producing steel according to claim 11 , wherein in the steel, numbers of alumina clusters having diameters of 20 μm or more are 2.0 clusters/kg or less.