| 摘要 |
PURPOSE:To obtain a high tension electric welded steel pipe having excellent low temp. toughness by subjecting a steel plate contg. a specific amt. of C, Mn, Si, P, S, Ti, Nb, V, N and sol.Al to electric welding, limiting the heating condition in the electric weld zone and the succeeding cooling condition and subjecting the pipe to a stress relief treatment. CONSTITUTION:A steel plate is composed, by wt%, of 0.01-0.08 C, <=1.5 Mn, <=0.5 Si, <=0.03 P, <=0.008 S, <=0.04 Ti, 0.001-0.05 Nb, 0.001-0.05 V, <=0.01N, and the balance sol. Al that remains when the degree of deoxidation is adjusted, Fe and inevitable impurities. Such steel plate is subjected to electric seam welding and the electric weld zone is heated for >=5 seconds at 790-1050 deg.C and is quickly cooled at a cooling rate of 30-150 deg.C/sec from 750-950 deg.C to form fine acicular ferrite structure. The weld zone is then heated within one minute at 400-700 deg.C to relieve stress therefrom. |
