PRODUCTION OF API STANDARD CLASS X80 STEEL PIPE OF SUPERIOR LOW TEMPERATURE TOUGHNESS

摘要

PURPOSE:To obtain a steel pipe of superior low temp. toughness by forming a steel pipe from steel plate which contains specific ratios of C, Si, Mn, P, etc. and is hot rolled under prescribed conditions and subjecting the pipe to an aging treatment at prescribed temps. CONSTITUTION:The steel contg., by weight, =0.15% C, =0.7% Si, 0.5-2.5% Mn, =0.025% P, =0.005% S, 0.01-0.15% Nb, =0.07% Al, and furhter if necessary, contg. 0.01-0.15% V, 0.005-0.15% Ti, 0.005-0.15% Zr, etc. is produced by melting, and a slab having the thickness from 300mm. up to three times the thickness of the final product is cast continuously from said steel. At the point of the time when the surface temp. of the slab attains 1,000-750 deg.C, rough rolling is begun. Finish rolling is completed at Ar3 transformation point -650 deg.C temps. with =60sec sum total of the air cooling time when no rolling is executed in the rolling stage of 700 deg.C or above. Such hot rolled steel plate is formed to a steel pipe. The steel pipe is subjected to an aging treatment at 100-400 deg.C.