| 摘要 |
PURPOSE:To obtain an electric-welded steel pipe having superior toughness at low temp. at the weld zone as well as the base metal part by specifying the composition of a steel plate as a material and conditions during the heating and cooling of a weld zone formed by electric welding. CONSTITUTION:A steel plate consisting of 0.01-0.08% C, <=1.5% Mn, <=0.5% Si, <=0.03% P, <=0.008% S, <=0.04% Ti, 0.001-0.050% Nb, 0.001-0.050% V, <=0.010% N and the balance Fe is electric-welded. The weld zone is heated at 790-1,050 deg.C for >=5sec and rapidly cooled from 750-950 deg.C at 30-150 deg.C/sec cooling rate. By this method, a fine acicular ferrite structure can be provided to the weld zone, and an electric-welded steel pipe having high toughness at low temp. is obtd. |
