Steel for welding

1. A steel for welding comprising, as steel components, by mass %,

C: a content [C] of 0.015% to 0.045%,

Si: a content [Si] of 0.05% to 0.20%,

Mn: a content [Mn] of 1.7% to 2.02%,

Ni: a content [Ni] of 0.1% to 0.52%,

Ti: a content [Ti] of 0.005% to 0.015%,

B: a content [B] of 0.0003% to 0.0015%,

N: a content [N] of 0.002% to 0.006%,

O: a content [O] of 0.0015% to 0.0035%,

P: a content [P] limited to 0.008% or less,

S: a content [S] limited to 0.005% or less,

Al: a content [Al] limited to 0.004% or less,

Nb: a content [Nb] limited to 0.004% or less,

Cu: a content [Cu] limited to 0.03% or less,

V: a content [V] limited to 0.02% or less, and

a balance consisting of Fe and unavoidable impurities,

wherein:

P CTOD in a following equation 1 is less than or equal to 0.065%,

CeqH in a following equation 2 is less than or equal to 0.225%,

FB in a following equation 3 is greater than or equal to 0.0003%, and

Bp in a following equation 4 is 0.09% to 0.30%,

wherein in a thickness center portion of a cross-section in a thickness direction, the number of oxide particles having an equivalent circle diameter of 2 μm or greater is less than or equal to 20 particles/mm 2 ,

wherein the number of Ti oxides having an equivalent circle diameter of 0.05 μm to 0.5 μm is 1.0×10 3 particles/mm 2 to 1.0×10 5 particles/mm 2 , and

wherein:

P CTOD =[C]+[Cu]/22+[Ni]/67+[V]/3  Equation 1

CeqH =[C]+[Si]/4.16+[Mn]/14.9+[Cu]/12.9+[Ni]/105+[V]/1.82  Equation 2

FB =[B]−0.77×([N]−0.29×([Ti]−2×([O]−0.89×[Al])))  Equation 3; and

Bp =(884×[C]×(1−0.3×[C] 2 )+294)× FB   Equation 4;

wherein:

0 is substituted for ([O]−0.89×[Al]) in the Equation 3 when ([O]−0.89×[Al]) is 0 or less;

0 is substituted for ([Ti]−2×([O]−0.89×[Al])) in the Equation 3 when ([Ti]−2×([O]−0.89×[Al])) is 0 or less;

0 is substituted for ([N]−0.29×([Ti]−2×([O]−0.89×[Al]))) in the Equation 3 when ([N]−0.29×([Ti]−2×([O]−0.89×[Al]))) is 0 or less; and

0 is substituted for FB in the Equation 4 when FB is 0 or less.

2. The steel for welding according to claim 1 ,

wherein the B content [B] is 0.0006% to 0.0015%.

3. The steel for welding according to claim 1 ,

wherein the Mn content [Mn] is 1.8% to 2.02%.

4. The steel for welding according to claim 1 ,

wherein the Mn content [Mn] is 1.9% to 2.02%.

5. The steel for welding according to claim 1 ,

wherein the C content [C] is 0.015% to 0.039%.

6. The steel for welding according to claim 1 ,

wherein the C content [C] is 0.015% to 0.035%.

7. The steel for welding according to claim 1 ,

wherein the O content [O] is 0.0020% to 0.0035%.

8. The steel for welding according to claim 2 ,

wherein the O content [O] is 0.0020% to 0.0035%.