FIRST LAYER OR UPPER LAYER WELDING SECTION OF HIGH Cr STEEL TURBINE ROTOR, OVERLAY WELDING MATERIAL FOR WELDING SECTION, AND METHOD FOR MANUFACTURING OVERLAY WELDING SECTION

1 . A first layer welding section of a high Cr steel turbine rotor, which is a first layer welding section among a multilayer overlay welding section formed on a bearing contact surface of the high Cr steel turbine rotor, the first layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.5%,

Cr: 4.0 to 7.7%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weight based on the first layer welding section.

2 . The first layer welding section of the high Cr steel turbine rotor according to claim 1 , which satisfies an expression (1):

Pcr (1)=(a Cr amount in the first layer welding section)×0.65−(a Cr amount of the high Cr steel turbine rotor−the Cr amount in the first layer welding section)×0.35>0.7  (1).

3 . An overlay welding material for a first layer welding section of a high Cr steel turbine rotor, which is a welding material for obtaining the first layer welding section according to claim 1 among the multilayer overlay welding section formed on the bearing contact surface of the high Cr steel turbine rotor, the welding material comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.2%,

Cr: 2.0 to 5.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the welding material.

4 . An upper layer welding section of a high Cr steel turbine rotor, which is an upper layer welding section formed on the first layer welding section according to claim 1 , among the multilayer overlay welding section formed on the bearing contact surface of the high Cr steel turbine rotor, the upper layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 2.5%,

Cr: 1.0 to 4.0%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.15% or less, Ni: 0.3% or less, and Nb: 0.07% or less in terms of % by weight based on the upper layer welding section.

5 . The upper layer welding section of the high Cr steel turbine rotor according to claim 4 , wherein an amount of V contained in the upper layer welding section is smaller than an amount of V contained in the first layer welding section.

6 . The upper layer welding section of the high Cr steel turbine rotor according to claim 4 , which satisfies an expression (2):

Pcr ( n )=(a Cr amount in the upper layer welding section at n -th layer)×0.65−{a Cr amount in the upper layer welding section at ( n− 1)-th layer−the Cr amount in the upper layer welding section at the n -th layer}×0.35>0.7  (2),

in which when N represents the number of layers constituting the multilayer overlay welding section, 2≦n≦N.

7 . An overlay welding material for an upper layer welding section of a high Cr steel turbine rotor, which is a welding material for obtaining the upper layer welding section according to claim 4 formed on the first layer welding section of the multilayer overlay welding section formed on the bearing contact surface of the high Cr steel turbine rotor, the welding material comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the welding material.

8 . A process for producing a multilayer overlay welding section of a high Cr steel turbine rotor, the process comprising:

forming a first layer welding section of a high Cr steel turbine rotor, which is a first layer welding section among a multilayer overlay welding section formed on a bearing contact surface of the high Cr steel turbine rotor, the first layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.5%,

Cr: 4.0 to 7.7%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weight based on the first layer welding section, on the bearing contact surface of the high Cr steel turbine rotor by welding using an overlay welding material for the first layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.2%,

Cr: 2.0 to 5.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the first layer welding section, and

forming the upper layer welding section according to claim 4 on an upper layer of the thus-formed first layer welding section by welding using an overlay welding material for the upper layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the upper layer welding section.

9 . The upper layer welding section of the high Cr steel turbine rotor according to claim 5 , which satisfies an expression (2):

Pcr ( n )=(a Cr amount in the upper layer welding section at n -th layer)×0.65−{a Cr amount in the upper layer welding section at ( n− 1)-th layer−the Cr amount in the upper layer welding section at the n -th layer}×0.35>0.7  (2),

in which when N represents the number of layers constituting the multilayer overlay welding section, 2≦n≦N.

10 . An overlay welding material for an upper layer welding section of a high Cr steel turbine rotor, which is a welding material for obtaining the upper layer welding section according to claim 5 formed on the first layer welding section of the multilayer overlay welding section formed on the bearing contact surface of the high Cr steel turbine rotor, the welding material comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the welding material.

11 . An overlay welding material for an upper layer welding section of a high Cr steel turbine rotor, which is a welding material for obtaining the upper layer welding section according to claim 6 formed on the first layer welding section of the multilayer overlay welding section formed on the bearing contact surface of the high Cr steel turbine rotor, the welding material comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the welding material.

12 . An overlay welding material for an upper layer welding section of a high Cr steel turbine rotor, which is a welding material for obtaining the upper layer welding section according to claim 9 formed on the first layer welding section of the multilayer overlay welding section formed on the bearing contact surface of the high Cr steel turbine rotor, the welding material comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the welding material.

13 . A process for producing a multilayer overlay welding section of a high Cr steel turbine rotor, the process comprising:

forming a first layer welding section of a high Cr steel turbine rotor, which is a first layer welding section among a multilayer overlay welding section formed on a bearing contact surface of the high Cr steel turbine rotor, the first layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.5%,

Cr: 4.0 to 7.7%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weight based on the first layer welding section,

on the bearing contact surface of the high Cr steel turbine rotor by welding using an overlay welding material for the first layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.2%,

Cr: 2.0 to 5.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the first layer welding section, and

forming the upper layer welding section according to claim 5 on an upper layer of the thus-formed first layer welding section by welding using an overlay welding material for the upper layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the upper layer welding section.

14 . A process for producing a multilayer overlay welding section of a high Cr steel turbine rotor, the process comprising:

forming a first layer welding section of a high Cr steel turbine rotor, which is a first layer welding section among a multilayer overlay welding section formed on a bearing contact surface of the high Cr steel turbine rotor, the first layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.5%,

Cr: 4.0 to 7.7%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weight based on the first layer welding section,

on the bearing contact surface of the high Cr steel turbine rotor by welding using an overlay welding material for the first layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.2%,

Cr: 2.0 to 5.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the first layer welding section, and

forming the upper layer welding section according to claim 6 on an upper layer of the thus-formed first layer welding section by welding using an overlay welding material for the upper layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the upper layer welding section.

15 . A process for producing a multilayer overlay welding section of a high Cr steel turbine rotor, the process comprising:

forming a first layer welding section of a high Cr steel turbine rotor, which is a first layer welding section among a multilayer overlay welding section formed on a bearing contact surface of the high Cr steel turbine rotor, the first layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.5%,

Cr: 4.0 to 7.7%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weight based on the first layer welding section,

on the bearing contact surface of the high Cr steel turbine rotor by welding using an overlay welding material for the first layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.2%,

Cr: 2.0 to 5.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the first layer welding section, and

forming the upper layer welding section according to claim 9 on an upper layer of the thus-formed first layer welding section by welding using an overlay welding material for the upper layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the upper layer welding section.

16 . A process for producing a multilayer overlay welding section of a high Cr steel turbine rotor, the process comprising:

forming a first layer welding section of a high Cr steel turbine rotor, which is a first layer welding section among a multilayer overlay welding section formed on a bearing contact surface of the high Cr steel turbine rotor, the first layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.5%,

Cr: 4.0 to 7.7%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weight based on the first layer welding section,

on the bearing contact surface of the high Cr steel turbine rotor by welding using an overlay welding material for the first layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.2%,

Cr: 2.0 to 5.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the first layer welding section, and

forming the upper layer welding section according to claim 7 on an upper layer of the thus-formed first layer welding section by welding using an overlay welding material for the upper layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the upper layer welding section.

17 . A process for producing a multilayer overlay welding section of a high Cr steel turbine rotor, the process comprising:

forming a first layer welding section of a high Cr steel turbine rotor, which is a first layer welding section among a multilayer overlay welding section formed on a bearing contact surface of the high Cr steel turbine rotor, the first layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.5%,

Cr: 4.0 to 7.7%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weight based on the first layer welding section,

on the bearing contact surface of the high Cr steel turbine rotor by welding using an overlay welding material for the first layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.2%,

Cr: 2.0 to 5.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the first layer welding section, and

forming the upper layer welding section according to claim 10 on an upper layer of the thus-formed first layer welding section by welding using an overlay welding material for the upper layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the upper layer welding section.

18 . A process for producing a multilayer overlay welding section of a high Cr steel turbine rotor, the process comprising:

forming a first layer welding section of a high Cr steel turbine rotor, which is a first layer welding section among a multilayer overlay welding section formed on a bearing contact surface of the high Cr steel turbine rotor, the first layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.5%,

Cr: 4.0 to 7.7%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weight based on the first layer welding section,

on the bearing contact surface of the high Cr steel turbine rotor by welding using an overlay welding material for the first layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.2%,

Cr: 2.0 to 5.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the first layer welding section, and

forming the upper layer welding section according to claim 11 on an upper layer of the thus-formed first layer welding section by welding using an overlay welding material for the upper layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the upper layer welding section.

19 . A process for producing a multilayer overlay welding section of a high Cr steel turbine rotor, the process comprising:

forming a first layer welding section of a high Cr steel turbine rotor, which is a first layer welding section among a multilayer overlay welding section formed on a bearing contact surface of the high Cr steel turbine rotor, the first layer welding section comprising, in terms of % by weight:

C: 0.05 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.5%,

Cr: 4.0 to 7.7%, and

Mo: 0.5 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, V: 0.2% or less, Ni: 0.3% or less, Co: 1.5% or less, B: 0.005% or less, W: 1.5% or less, and Nb: 0.07% or less in terms of % by weight based on the first layer welding section,

on the bearing contact surface of the high Cr steel turbine rotor by welding using an overlay welding material for the first layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 1.2%,

Cr: 2.0 to 5.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the first layer welding section, and

forming the upper layer welding section according to claim 12 on an upper layer of the thus-formed first layer welding section by welding using an overlay welding material for the upper layer welding section comprising, in terms of % by weight:

C: 0.03 to 0.2%,

Si: 0.1 to 1.0%,

Mn: 0.3 to 3.0%,

Cr: 1.0 to 2.5%, and

Mo: 0.1 to 1.5%,

with a remainder including Fe and unavoidable impurities, in which the unavoidable impurities contain P: 0.015% or less, S: 0.015% or less, Cu: 0.2% or less, and V: 0.1% or less, and a sum of one or more kinds selected from the group consisting of Ni, Nb and Ti is 0.2% or less in terms of % by weight based on the overlay welding material for the upper layer welding section.