High-strength welded steel pipe and method for producing the same
View Patent ↗A high-strength welded steel pipe is obtained by welding a seam weld portion of a steel plate that are formed in a pipe shape. In the high-strength welded steel pipe, a base metal of the steel plate includes, by mass %, C: 0.010% to 0.080%, Si: 0.01% to 0.50%, Mn: 0.50% to 2.00%, S: 0.0001% to 0.0050%, Ti: 0.003% to 0.030%, Mo: 0.05% to 1.00%, B: 0.0003% to 0.0100%, O: 0.0001% to 0.0080%, N: 0.006% to 0.0118%, P: limited to 0.050% or less, Al: limited to 0.008% or less, and the balance of Fe and inevitable impurities, Ceq is 0.30 to 0.53, Pcm is 0.10 to 0.20, [N]−[Ti]/3.4 is less than 0.003, the average grain size of the prior γ grains in heat affected zones in the steel plate is 250 μm or less, and the prior γ grains include bainite and intragranular bainite.
1. A high-strength welded steel pipe obtained by welding a seam weld portion of a steel plate into forming a pipe shape,
wherein a base metal of the steel plate includes, by mass %,
C: 0.010% to 0.080%,
Si: 0.01% to 0.50%,
Mn: 0.50% to 2.00%,
S: 0.0001% to 0.0050%,
Ti: 0.003% to 0.030%,
Mo: 0.05% to 1.00%,
B: 0.0003% to 0.0100%,
O: 0.0001% to 0.0080%,
N: 0.006% to 0.0118%,
P: limited to 0.050% or less,
Al: limited to 0.008% or less, and
a balance of iron and inevitable impurities,
wherein a Ceq that is obtained from a following equation <7> is 0.30 to 0.53, a Pcm that is obtained from a following equation <8> is 0.10 to 0.20, the [N] and the [Ti] satisfy a following equation <9>, wherein an average grain size of prior γ grains in a heat affected zone in the steel plate is 250 μm or less, and the prior γ grains include bainite and intragranular bainite,
Ceq=[C]+[Mn]/6+([Ni]+[Cu])/15+([Cr]+[Mo]+[V])/5 <7>
Pcm=[C]+[Si]/30+([Mn]+[Cu]+[Cr])/20+[Ni]/60+[Mo]/15+[V]/10+5[B] <8>
[N]−[Ti]/3.4<0.003% <9>
wherein [C], [Si], [Mn], [Ni], [Cu], [Cr], [Mo], [V], [B], [N], and [Ti] are defined as the amounts of C, Si, Mn, Ni, Cu, Cr, Mo, V, B, N, and Ti in mass %, respectively.
2. The high-strength welded steel pipe according to claim 1 ,
wherein the base metal further includes, by mass %, one or more selected from
Cu: 0.05% to 1.5%,
Ni: 0.05% to 5.00%,
Cr: 0.02% to 1.50%,
W: 0.01% to 0.50%,
V: 0.010% to 0.100%,
Nb: 0.001% to 0.200%,
Zr: 0.0001% to 0.0500%,
Ta: 0.0001% to 0.0500%,
Mg: 0.0001% to 0.0100%,
Ca: 0.0001% to 0.0050%,
REM: 0.0001% to 0.0050%,
Y: 0.0001% to 0.0050%,
Hf: 0.0001% to 0.0050%, and
Re: 0.0001% to 0.0050%.
3. The high-strength welded steel pipe according to claim 1 ,
wherein a plate thickness of the base metal is 20 mm to 40 mm.
4. The high-strength welded steel pipe according to claim 1 ,
wherein, in a case in which a circumferential direction is a tensile direction, a tensile strength of the base metal is 500 MPa to 800 MPa.
5. A method of manufacturing a high-strength welded steel pipe, the method comprising:
forming a steel plate having the chemical composition according to claim 1 into a pipe shape; and
seam-welding a seam weld portion through an arc welding so as to form a seam-welded portion.
6. The method of manufacturing the high-strength welded steel pipe according to claim 5 ,
wherein the arc welding is a submerged arc welding.
7. The method of manufacturing the high-strength welded steel pipe according to claim 6 ,
wherein a heat input of the submerged arc welding is 3.5 kJ/mm to 10.0 kJ/mm.
8. The method of manufacturing the high-strength welded steel pipe according to claim 5 , the method further comprising,
performing a heat treatment of the seam-welded portion.
9. The method of manufacturing the high-strength welded steel pipe according to claim 8 ,
wherein a heating temperature is 300° C. to 600° C. during the heat treatment.