| 摘要 |
PROBLEM TO BE SOLVED: To produce a steel tube excellent in high temp. creep fracture characteristics and toughness by subjecting a steel stock having a specified compsn. to blooming, executing cooling, holding the same under soaking to an austenite single phase region and subsequently executing seamless steel tube rolling. SOLUTION: The compsn. of a steel is composed of, by weight, 0.01 to 0.15% C, 0.01 to 0.80% Si, 0.05 to 1.50% Mn, 8.00 to 13.00% Cr, 0.05 to 1.50% Mo, 0.05 to 4.00% W, 0.05 to 0.50% V, 0.02 to 0.15% Nb, 0.010 to 0.110% N, 0.002 to 0.050% Al, <=0.030% P, <=0.010% S, <=0.015% O, and the balance Fe. Furthermore, the conditions in the inequality I are allowed to satisfy. This ingot or east billet is rolled at >=1.5% draft and is cooled to the Mf point or below. Next, it is held under soaking to a temp. in an austenite single phase region for diffusing time estimated from the relation in the formula II and is cooled to the Ms point or below. The obtd. square billet is reheated and is thereafter subjected to seamless steel tube rolling. In this way, the martensitic seamless heat resistant steel tube in which the formation ofδferrite is suppressed can be obtd.
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