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Abstract

Disclosed is a ferritic heat-resistant steel which has the following chemical composition (by weight): C: 0.01-0.10%; Si: 0.30-1.0%; P: 0.02 or less; S: 0.010% or less; Mn: 0.2-1.2%; Ni: 0.3% or less; Cr: 8.0-11.0%; Mo: 0.1-1.2%; W: 1.0-2.5%; V: 0.10-0.30%; Nb: 0.02-0.12%; Co: 0.01-4.0%; N: 0.01-0.08%; B: not less than 0.001% and less than 0.010%; Cu: 0.3% or less; and Al: 0.010% or less, provided that the chemical composition satisfies the following equations: Mo(%)+0.5×W(%)=1.0-1.6, and C(%)+N(%)=0.02-0.15%, and which comprises a tempered martensite single-phase tissue produced by thermal refining. The steel shows an excellent long-term creep rupture strength even when used at a steam temperature around 650˚C and also has excellent steam oxidizability. When the value represented by the equation: Al(%)+0.1×Ni(%) is adjusted to 0.02 or less, the creep strength can be more stabilized.

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