STEEL
A steel according to an aspect of the present invention includes, as a chemical composition, by unit mass %, C: 0.15% to 0.40%, Mn: 0.10% to 1.50%, S: 0.002% to 0.020%, Ti: 0.005% to 0.050%, B: 0.0005% to 0.0050%, Bi: 0.0010% to 0.0100%, P: 0.020% or less, N: 0.0100% or less, Si: 0% or more and less than 0.30%, Cr: 0% to 1.50%, Al: 0% to 0.050%, Mo: 0% to 0.20%, Cu: 0% to 0.20%, Ni: 0% to 0.20%, Nb: 0% to 0.030%, and a remainder including Fe and impurities.
1 . A steel comprising, as a chemical composition, by unit mass %,
C: 0.15% to 0.40%,
Mn: 0.10% to 1.50%,
S: 0.002% to 0.020%,
Ti: 0.005% to 0.050%,
B: 0.0005% to 0.0050%,
Bi: 0.0010% to 0.0100%,
P: 0.020% or less,
N: 0.0100% or less,
Si: 0% or more and less than 0.30%,
Cr: 0% to 1.50%,
Al: 0% to 0.050%,
Mo: 0% to 0.20%,
Cu: 0% to 0.20%,
Ni: 0% to 0.20%,
Nb: 0% to 0.030%, and
a remainder including Fe and impurities.
2 . The steel according to claim 1 , comprising, as the chemical composition, by unit mass %, one or more selected from the group consisting of
Si: 0.01% or more and less than 0.30%,
Cr: 0.01% to 1.50%, and
Al: 0.001% to 0.050%.
3 . The steel according to claim 1 , comprising, as the chemical composition, by unit mass %, one or more selected from the group consisting of
Mo: 0.02% to 0.20%,
Cu: 0.02% to 0.20%,
Ni: 0.02% to 0.20%, and
Nb: 0.002% to 0.030%.
4 . The steel according to claim 1 ,
wherein a N fixation index I FN defined by the following Expression 1 is 0 or more,
I FN =[Ti]−3.5×[N] (Expression 1)
where, [Ti] indicates a Ti content by unit mass % and [N] indicates a N content by unit mass %.
5 . The steel according to claim 1 ,
wherein a Ti—Nb-based precipitate generation index I P defined by the following Expression 2 is 0.0100 or less,
I P =0.3×[Ti]+0.15×[Nb]−[N] (Expression 2)
where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.
6 . The steel according to claim 2 , comprising, as the chemical composition, by unit mass %, one or more selected from the group consisting of
Mo: 0.02% to 0.20%,
Cu: 0.02% to 0.20%,
Ni: 0.02% to 0.20%, and
Nb: 0.002% to 0.030%.
7 . The steel according to claim 2 ,
wherein a N fixation index I FN defined by the following Expression 1 is 0 or more,
I FN =[Ti]−3.5×[N] (Expression 1)
where, [Ti] indicates a Ti content by unit mass % and [N] indicates a N content by unit mass %.
8 . The steel according to claim 3 ,
wherein a N fixation index I FN defined by the following Expression 1 is 0 or more,
I FN =[Ti]−3.5×[N] (Expression 1)
where, [Ti] indicates a Ti content by unit mass % and [N] indicates a N content by unit mass %.
9 . The steel according to claim 6 ,
wherein a N fixation index I FN defined by the following Expression 1 is 0 or more,
I FN =[Ti]−3.5×[N] (Expression 1)
where, [Ti] indicates a Ti content by unit mass % and [N] indicates a N content by unit mass %.
10 . The steel according to claim 2 ,
wherein a Ti—Nb-based precipitate generation index I P defined by the following Expression 2 is 0.0100 or less,
I P =0.3×[Ti]+0.15×[Nb]−[N] (Expression 2)
where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.
11 . The steel according to claim 3 ,
wherein a Ti—Nb-based precipitate generation index I P defined by the following Expression 2 is 0.0100 or less,
I P =0.3×[Ti]+0.15×[Nb]−[N] (Expression 2)
where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.
12 . The steel according to claim 4 ,
wherein a Ti—Nb-based precipitate generation index I P defined by the following Expression 2 is 0.0100 or less,
I P =0.3×[Ti]+0.15×[Nb]−[N] (Expression 2)
where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.
13 . The steel according to claim 6 ,
wherein a Ti—Nb-based precipitate generation index I P defined by the following Expression 2 is 0.0100 or less,
I P =0.3×[Ti]+0.15×[Nb]−[N] (Expression 2)
where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.
14 . The steel according to claim 7 ,
wherein a Ti—Nb-based precipitate generation index I P defined by the following Expression 2 is 0.0100 or less,
I P =0.3×[Ti]+0.15×[Nb]−[N] (Expression 2)
where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.
15 . The steel according to claim 8 ,
wherein a Ti—Nb-based precipitate generation index I P defined by the following Expression 2 is 0.0100 or less,
I P =0.3×[Ti]+0.15×[Nb]−[N] (Expression 2)
where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.
16 . The steel according to claim 9 ,
wherein a Ti—Nb-based precipitate generation index I P defined by the following Expression 2 is 0.0100 or less,
I P =0.3×[Ti]+0.15×[Nb]−[N] (Expression 2)
where, [Ti] indicates a Ti content by unit mass %, [Nb] indicates a Nb content by unit mass %, and [N] indicates a N content by unit mass %.