Steel for welded structure and producing method thereof
View Patent ↗A steel for a welded structure includes the following composition: by mass %, C at a C content [C] of 0.015 to 0.045%; Si at a Si content [Si] of 0.05 to 0.20%; Mn at a Mn content [Mn] of 1.5 to 2.0%; Ni at a Ni content [Ni] of 0.10 to 1.50%; Ti at a Ti content [Ti] of 0.005 to 0.015%; O at an O content [O] of 0.0015 to 0.0035%; and N at a N content [N] of 0.002 to 0.006%, and a balance composed of Fe and unavoidable impurities. In the steel for a welded structure, the P content [P] is limited to 0.008% or less, the S content [S] is limited to 0.005% or less, the Al content [Al] is limited to 0.004% or less, the Nb content [Nb] is limited to 0.005% or less, the Cu content [Cu] is limited to 0.24% or less, the V content [V] is limited to 0.020% or less, and a steel composition parameter P CTOD is 0.065% or less, and a steel composition hardness parameter CeqH is 0.235% or less.
1. A steel for a welded structure, comprising the following composition:
by mass %,
C at a C content [C] of 0.015 to 0.045%;
Si at a Si content [Si] of 0.05 to 0.20%;
Mn at a Mn content [Mn] of 1.5 to 2.0%;
Ni at a Ni content [Ni] of 0.73% to 1.50%;
Ti at a Ti content [Ti] of 0.005 to 0.015%;
O at an O content [O] of 0.0015 to 0.0032%; and
N at a N content [N] of 0.002 to 0.006%,
and a balance composed of Fe and unavoidable impurities,
wherein, a P content [P] is limited to 0.008% or less,
a S content [S] is limited to 0.005% or less,
an Al content [Al] is limited to 0.004% or less,
a Nb content [Nb] is limited to 0.005% or less,
a Cu content [Cu] is limited to 0.24% or less,
a V content [V] is limited to 0.020% or less, and
a steel composition parameter P CTOD of a following equation (3) is 0.065% or less, and a steel composition hardness parameter CeqH of a following equation (4) is 0.200% or less, where
P CTOD =[C]+[V]/3+[Cu]/22+[Ni]/67 (3)
CeqH=[C]+[Si]/4.16+[Mn]/14.9+[Cu]/12.9+[Ni]/105+1.12[Nb]+[V]/1.82 (4),
and the steel for welded structure wherein a CTOD (dc min) value in an IC zone at −60° C., which is obtained by a CTOD test of BS 5762 method, is 0.59 mm or more.
2. The steel for welded structure according to claim 1 , wherein Cu is included, by mass %, at the Cu content [Cu] of 0.03% or less.
3. A producing method of a steel for welded structure, comprising:
continuously casting steel satisfying the steel composition according to claim 1 or 2 to manufacture a slab; and
heating the slab to a temperature of 950 to 1100° C. and then subjecting the slab to a thermo-mechanical control process.
4. The steel for welded structure according to claim 1 , wherein the composition contains: by mass %, O at an O content [O] of 0.0015 to 0.0028%.
5. The steel for welded structure according to claim 1 , wherein the steel composition hardness parameter CeqH is 0.191% or less.