Ferritic Heat-Resistant Steel

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.

1 . A ferritic heat-resistant steel which has the following chemical composition (by weight): carbon (C): 0.01-0.10%; silicon (Si): 0.30-1.0%; phosphorus (P): 0.020% or less; sulfur (S): 0.010% or less, manganese (Mn): 0.2-1.2%; nickel (Ni): 0.3% or less; chromium (Cr): 8.0-11.0%, molybdenum (Mo): 0.1-1.2%; tungsten (W): 1.0-2.5%; vanadium (V): 0.10-0.30%; niobium (Nb): 0.02-0.12%; cobalt (Co): 0.01-4.0%; nitrogen (N): 0.01-0.08%; boron (B): not less than 0.001% and not more than 0.010%; copper (Cu): 0.3% or less; aluminum (Al): 0.010% or less, provided that the amount of (Mo %+0.5W %) is limited to 1.0-1.6, and the amount of (C %+N %) is limited to 0.02-0.15%, and which comprises a tempered martensite single-phase tissue produced by thermal refining. 
     
     
         2 . The ferritic heat-resistant steel according to  claim 1 , having the chemical composition in which the amount of (Al %+0.1Ni %) is limited to 0.02% by weight or less. 
     
     
         3 . The ferritic heat-resistant steel according to  claim 1 , containing 30% by weight or less of δ ferrite. 
     
     
         4 . The ferritic heat-resistant steel according to  claim 2 , containing 30% by weight or less of δ ferrite.