| 摘要 |
<p><P>PROBLEM TO BE SOLVED: To provide a method for producing an ultrahigh strength welded steel pipe having excellent deformability which has a tensile strength of >800 MPa and is suitable as the one for transporting natural gas and crude oil. <P>SOLUTION: A steel sheet having a composition comprising, by mass, 0.03 to 0.12% C,≤0.5% Si, 1.8 to 3.0% Mn,≤0.010% P,≤0.002% S, 0.01 to 0.08% Al,≤0.7% Cu, 0.01 to 3.0% Ni,≤1.0% Cr,≤1.0% Mo, 0.01 to 0.08% Nb,≤0.10% V, 0.005 to 0.025% Ti,≤0.005% B,≤0.01% Ca,≤0.02% REM,≤0.03% Zr,≤0.01% Mg, 0.001 to 0.006% N and≤0.22 PcmB, and the balance Fe with inevitable impurities, and having a yield ratio of≤80% and a tensile strength of≥800 MPa is subjected to cold working, so as to be formed into a pipe shape. Thereafter, the butted parts are welded by a hybrid welding process in which laser welding using CO<SB>2</SB>gas shield and gas shielded arc welding using Ar-CO<SB>2</SB>gas shield are combined. <P>COPYRIGHT: (C)2008,JPO&INPIT</p> |
