| 摘要 |
PURPOSE: To produce a steel tube excellent in high temp. oxidation resistance, strength, and workability at a low cost by rolling a high Cr steel of specific composition into a steel strip under specific temp. conditions, applying annealing to the steel strip, forming it into cylindrical shape, and then welding both edges. CONSTITUTION: A high Cr steel, having a composition which contains, by weight, 10-30% Cr, 0.02-2.0% Mn, 0.01-1.0% Al, <0.03% C, <2.0% Si, <0.03% P, <0.03% S, <0.02% N, 0.01-1.0%, in total, of one or >=2 elements among V, Ti, Nb, Zr, Ta, and Hf, and further 0.03-3.0%, in total, of Mo and/or W and in which the MD value represented by equation I is regulated to <0, is used. A slab of this high Cr steel is heated to 1100-1300 deg.C and formed into a steel strip by means of hot rolling finishing at 700-1000 deg.C. This steel strip is annealed at 700-1000 deg.C for a time where the λ-value given by equation II becomes >20 and formed into cylindrical shape, and then, both edges are welded by means of electric welding, etc., by which the steel tube can be produced. At this time, the steel tube is produced while requlating the total strain amount (ε)(mm) from steel strip to tube making to <=t/D+0.03 [where (t) and D represent the plate thickness and outside diameter of the steel tube, respectively]. |
