| 摘要 |
PURPOSE:To obtain a high-tensile large-diameter steel pipe for pipelines suited for cold climatic areas by heating and machining steel contg. prescribed contents of C, Si, Mn, P, S, Nb, etc. under prescribed conditions. 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, etc. is melted. A slab of thickness from 300mm. up to 3 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 started, and at Ar3 transformation point -650 deg.C, the rough rolling is stopped and the slab is formed into a steel pipe. The steel pipe is heated to an Ac3 transformation point -50 deg.C-1,100 deg.C range, and is cooled between 800-500 deg.C at the average cooling rate CR ( deg.C/sec) satisfying the equation. Finally, the steel plate is cooled down to ordinary temp. |
