Welding material for ferritic heat-resistant steel, welded joint for ferritic heat-resistant steel, and method for producing welded joint for ferritic heat-resistant steel

1. A welding material for ferritic heat-resistant steel having a chemical composition containing, in mass percent:

C: 0.06 to 0.10%;

Si: 0.1 to 0.4%;

Mn: 0.3 to 0.7%;

P: 0.01% or less;

S: 0.003% or less;

Co: 2.6 to 3.4%;

Ni: 0.01 to 1.10%;

Cr: 8.5 to 9.5%;

W: 2.5 to 3.5%;

Mo: less than 0.01%;

Nb: 0.02 to 0.08%;

V: 0.1 to 0.3%;

Ta: 0.02 to 0.08%;

B: 0.007 to 0.015%;

N: 0.005 to 0.020%;

Al: 0.03% or less;

O: 0.02% or less;

Cu: 0 to 1%;

Ti: 0 to 0.3%;

Ca: 0 to 0.05%;

Mg: 0 to 0.05%, and

rare earth metals: 0 to 0.1%, with a balance being Fe and impurities, and satisfying Formula (1):

0.5≤Cr+6Si+1.5W+11V+5Nb+10B−40C−30N−4Ni−2Co−2Mn≤10.0   (1)

where symbols of elements in Formula (1) are to be substituted by contents of corresponding elements (in mass percent).

2. The welding material for ferritic heat-resistant steel according to claim 1 , further containing, in mass percent,

an element one or more types selected from following first group to third group:

first group: Cu: 0.05 to 1.00%;

second group: Ti: 0.02 to 0.30%; and

third group: Ca: 0.001 to 0.050%, Mg: 0.001 to 0.050%, and rare earth metals: 0.001 to 0.10% or less.

3. The welding material for ferritic heat-resistant steel according to claim 2 , wherein an area fraction of δ ferrite is 0.5% or less.

4. The welded joint for ferritic heat-resistant steel comprising:

a weld metal having the chemical composition according to claim 3 ; and

a base material made of a ferritic heat-resistant steel, wherein

the base material has a chemical composition containing, in mass percent:

Cr: 8 to 10%;

Co: 2 to 4%;

W: 2 to 4%; and

B: 0.005 to 0.020%.

5. The welded joint for ferritic heat-resistant steel according to claim 4 , wherein

the chemical composition of the base material contains, in mass percent:

C: 0.04 to 0.12%;

Si: 0.05 to 0.60%;

Mn: 0.1 to 0.8%;

P: 0.02% or less;

S: 0.01% or less;

Co: 2 to 4%;

Ni: 0 to 0.4%;

Cr: 8 to 10%;

W: 2 to 4%;

Nb and/or Ta: 0.02 to 0.18% in total;

V: 0.05 to 0.40%;

B: 0.005 to 0.020%;

Nd: 0.01 to 0.06%;

N: 0.002 to 0.025%;

Al: 0.03% or less, and

O: 0.02% or less, with the balance being Fe and impurities.

6. The welded joint for ferritic heat-resistant steel according to claim 5 , wherein the base material contains Ni: 0.05 to 0.4%.

7. The welded joint for ferritic heat-resistant steel comprising:

a weld metal having the chemical composition according to claim 2 ; and

a base material made of a ferritic heat-resistant steel, wherein

the base material has a chemical composition containing, in mass percent:

Cr: 8 to 10%;

Co: 2 to 4%;

W: 2 to 4%; and

B: 0.005 to 0.020%.

8. The welded joint for ferritic heat-resistant steel according to claim 7 , wherein

the chemical composition of the base material contains, in mass percent:

C: 0.04 to 0.12%;

Si: 0.05 to 0.60%;

Mn: 0.1 to 0.8%;

P: 0.02% or less;

S: 0.01% or less;

Co: 2 to 4%;

Ni: 0 to 0.4%;

Cr: 8 to 10%;

W: 2 to 4%;

Nb and/or Ta: 0.02 to 0.18% in total;

V: 0.05 to 0.40%;

B: 0.005 to 0.020%;

Nd: 0.01 to 0.06%;

N: 0.002 to 0.025%;

Al: 0.03% or less, and

O: 0.02% or less, with the balance being Fe and impurities.

9. The welded joint for ferritic heat-resistant steel according to claim 8 , wherein the base material contains Ni: 0.05 to 0.4%.

10. The welded joint for ferritic heat-resistant steel according to claim 7 , wherein an area fraction of δ ferrite in the weld metal is 0.5% or less.

11. The welding material for ferritic heat-resistant steel according to claim 1 , wherein an area fraction of δ ferrite is 0.5% or less.

12. The welded joint for ferritic heat-resistant steel comprising:

a weld metal having the chemical composition according to claim 11 ; and

a base material made of a ferritic heat-resistant steel, wherein

the base material has a chemical composition containing, in mass percent:

Cr: 8 to 10%;

Co: 2 to 4%;

W: 2 to 4%; and

B: 0.005 to 0.020%.

13. The welded joint for ferritic heat-resistant steel according to claim 12 , wherein

the chemical composition of the base material contains, in mass percent:

C: 0.04 to 0.12%;

Si: 0.05 to 0.60%;

Mn: 0.1 to 0.8%;

P: 0.02% or less;

S: 0.01% or less;

Co: 2 to 4%;

Ni: 0 to 0.4%;

Cr: 8 to 10%;

W: 2 to 4%;

Nb and/or Ta: 0.02 to 0.18% in total;

V: 0.05 to 0.40%;

B: 0.005 to 0.020%;

Nd: 0.01 to 0.06%;

N: 0.002 to 0.025%;

Al: 0.03% or less, and

O: 0.02% or less, with the balance being Fe and impurities.

14. The welded joint for ferritic heat-resistant steel according to claim 13 , wherein the base material contains Ni: 0.05 to 0.4%.

15. The welded joint for ferritic heat-resistant steel according to claim 12 , wherein an area fraction of δ ferrite in the weld metal is 0.5% or less.

16. A welded joint for ferritic heat-resistant steel comprising:

a weld metal having the chemical composition according to claim 1 ; and

a base material made of a ferritic heat-resistant steel, wherein

the base material has a chemical composition containing, in mass percent:

Cr: 8 to 10%;

Co: 2 to 4%;

W: 2 to 4%; and

B: 0.005 to 0.020%.

17. The welded joint for ferritic heat-resistant steel according to claim 16 , wherein

the chemical composition of the base material contains, in mass percent:

C: 0.04 to 0.12%;

Si: 0.05 to 0.60%;

Mn: 0.1 to 0.8%;

P: 0.02% or less;

S: 0.01% or less;

Co: 2 to 4%;

Ni: 0 to 0.4%;

Cr: 8 to 10%;

W: 2 to 4%;

Nb and/or Ta: 0.02 to 0.18% in total;

V: 0.05 to 0.40%;

B. 0.005 to 0.020%;

Nd: 0.01 to 0.06%;

N: 0.002 to 0.025%;

Al: 0.03% or less, and

O: 0.02% or less, with the balance being Fe and impurities.

18. The welded joint for ferritic heat-resistant steel according to claim 17 , wherein the base material contains Ni: 0.05 to 0.4%.

19. The welded joint for Ferritic heat-resistant steel according to claim 16 , wherein an area fraction of δ ferrite in the weld metal is 0.5% or less.

20. A method for producing a welded joint for ferritic heat-resistant steel, the method comprising:

a step of forming a weld metal by performing gas tungsten arc welding on a base material made of a ferritic heat-resistant steel, with a welding heat input of 6 to 20 kJ/cm using the welding material for ferritic heat-resistant steel according to claim 1 , the ferritic heat-resistant steel having a chemical composition containing, in mass percent, Cr: 8 to 10%, Co: 2 to 4%, W: 2 to 4%, and B: 0.005 to 0.020%; and

a step of performing heat treatment on the weld metal formed on the base material at a heat treatment temperature of 740 to 780° C. for 0.5 to 4.0 hours per 25.4 mm thickness of the base material.