| 摘要 |
PURPOSE:To obtain a titled thick walled steel pipe for pipelines by reducing down steel of a specific compsn. at the total draft in a temp. region below specific temp. higher than specific values and rolling the same in a specific reducing down and finishing temp. range thereby forming the same to a steel pipe consisting of the two layers wherein the thickness of the single layer is smaller than specific values. CONSTITUTION:The steel consisting, 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 the balance Fe is reduced down with plate mills or hot strip mills at >=60% the total draft in a temp. region below 950 deg.C. The steel is rolled at the rolling finish temp. in an Ar3 transformation point -650 deg.C range, and such rolled steel plate is formed to a steel pipe in such a way as to have 2 layers wherein the thickness of the single layer is <=18mm.. If necessary, 1 or >=2 kinds among 0.01-0.15 V, 0.005-0.15 Ti, 0.005-0.15 Zr, 0.05-0.5 Mo, 0.1-1 Cu, 0.1-4 Ni, 0.1-1 Cr, <0.02 rare earth elements, <0.01 Ca are added other than the above-described compsn. |
