| 摘要 |
PURPOSE:To make possible the production of large-diameter thick-walled steel pipes provided with high tensile strength and high toughness by a stable mass production system by applying the specific rolling and pipe making heat treatment to the steel contg. the specific amount of N. CONSTITUTION:The steel consisting essentially of 0.05-0.20% C, 0.05-0.50% Si, 0.3-2.0% Mn, 0.003-0.010% Ni, 0.05-0.10% sol. Al, 0.0005-0.008% B, and if necessary, contg. one or two or more kinds of 0.05-1.0% Cu, 0.05-2.0% Ni, 0.05-2.0% Cr, 0.05-1.0 Mo, 0.005-0.08% V is heated to >=1,100 deg.C and is then subjected to rolling in which the cumulative draft within 900 deg.C-Ar3 temperature range is regulated to >=20%. Next, it is cooled down to <=Ar1 and if necessary it is reheated to a temperature below the AC3 point after the cooling and is made into a plate thicker than 25mm., whereby the steel plate of 25mm. thickness and <=50kg/mm.<2> yield strength is obtained. From this steel plate, pipes are made and the pipes are seam-welded, which are heated to above the AC3 point by induction heating, thereafter they are cooled at a higher cooling rate the cooling rate with air. |
