| 摘要 |
PURPOSE:To obtain the titled steel pipe having effectively improved toughness after aging, by specifying a composition consisting of C, Si, Mn, Cr, Mo, V, Nb, P, S, N, W, Al, Ni, B, and Fe and the relations among them. CONSTITUTION:The steel pipe consists of, by weight, 0.04-0.12% C, <=0.5% Si, <=1.5% Mn, 8-12% Cr, 0.7-1.5% Mo, 0.05-0.35% V, <=0.15% Nb, <=0.02% P, <=0.03% S, <=0.1% N, <=1.5% W, 0.01-0.1% Al, <=1% Ni, <=0.01% B, and the balance Fe with inevitable impurities and satisfies the relations in Si+V+ Nb+(10XP)+1/3X(Mo+W)<=1%. This pipe is, preferably, a heat-resisting steel pipe of martensite type or of <=20% ferrite-contg. high-chromium martensite type, which has such superior toughness as to maintain sufficient toughness even after exposed to high temp. for a long period.
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