Ferritic stainless steel excellent in corrosion resistance in environment of condensed water from hydrocarbon combustion gas

Abstract

The present invention provides a ferritic stainless steel exhibiting excellent corrosion resistance in a condensed water environment arising from a hydrocarbon combustion exhaust gas typified by the use environment of a structural member of a secondary heat exchanger, which stainless steel is a ferritic stainless steel comprising, in mass %, C: 0.030% or less, N: 0.030% or less, Si: 0.4% or less, Mn: 0.01 to 0.5%, P: 0.05% or less, S: 0.01% or less, Cr: 16 to 24%, Mo: 0.30 to 3%, Ti: 0.05 to 0.25%, Nb: 0.05 to 0.50%, Al: 0.01 to 0.2%, and Cu: 0.4% or less, the balance being Fe and unavoidable impurities, and satisfying Expression (A): Cr+Mo+10Ti≧18 and Expression (B): Si+Cu≦0.5.

1 - 3 . (canceled) 
     
     
         4 . A highly corrosion resistant ferritic stainless steel excellent in corrosion resistance in a condensed water environment arising from a hydrocarbon combustion exhaust gas characterized in comprising, in mass %, C: 0.030% or less, N: 0.030% or less, Si: 0.4% or less, Mn: 0.01 to 0.5%, P: 0.05% or less, S: 0.01% or less, Cr: 16 to 24%, Mo: 0.30 to 3%, Ti: 0.05 to 0.25%, Nb: 0.05 to 0.50%, Al: 0.01 to 0.20%, and Cu: 0.4% or less, the balance being Fe and unavoidable impurities, and satisfying Expression (A): Cr+Mo+10Ti≧22 and Expression (B): Si+Cu<0.2,
 where Cr, Mo, Ti, Si and Cu in the Expressions represent the contents (mass %) of the respective elements. 
 
     
     
         5 . A highly corrosion resistant ferritic stainless steel excellent in corrosion resistance in a condensed water environment arising from a hydrocarbon combustion exhaust gas as set out in  claim 4 , characterized by further comprising, in mass %, one or two or more among Ni: 0.3 to 3%, B: 0.0001 to 0.003%, V: 0.03 to 1.0%, Sn: 0.005 to 1.0%, and Sb: 0.005 to 1.0%. 
     
     
         6 . A highly corrosion resistant ferritic stainless steel excellent in corrosion resistance in a condensed water environment arising from a hydrocarbon combustion exhaust gas as set out in  claim 4 , characterized in that after conducting 14 cycles of a wet and dry cyclic test of half-immersing a test specimen of the steel in an aqueous solution of pH 2.5 and containing 100 ppm nitrate ions, 10 ppm sulfate ions and 10 ppm chloride ions and holding it at 80° C. for 24 hours, maximum corrosion depth is 20 μM or less. 
     
     
         7 . A highly corrosion resistant ferritic stainless steel excellent in corrosion resistance in a condensed water environment arising from a hydrocarbon combustion exhaust gas as set out in  claim 5 , characterized in that after conducting 14 cycles of a wet and dry cyclic test of half-immersing a test specimen of the steel in an aqueous solution of pH 2.5 and containing 100 ppm nitrate ions, 10 ppm sulfate ions and 10 ppm chloride ions and holding it at 80° C. for 24 hours, maximum corrosion depth is 20 μM or less.