Heat resistant high chromium ferritic steel

Abstract

A heat resistant high Cr ferritic steel comprising, in mass %, C : 0.02 to 0.15%, Mn: 0.05 to 1.5%, P : 0.03% or less, S : 0.015% or less, Cr: 8 to 13%, W : 1.5 to 4%, Co: 2 to 6%, V : 0.1 to 0.5%, Ta: 0.01 to 0.15%, Nb: 0.01 to 0.15%, Nd: 0.001 to 0.2%, N : 0.02% or less, B : 0.0005 to 0.02%, Al: 0.001 to 0.05%, Mo: 0 to 1%, Si: 0 to 1%, Ca: 0 to 0.02%, La: 0 to 0.2%, Ce: 0 to 0.2%, Y : 0 to 0.2%, Hf: 0 to 0.2%, the contents of Nd and N satisfying the formula: Nd(%) ≦5×N(%)+0.1(%), and the balance being Fe and incidental impurities. The steel is excellent in high temperature long term creep strength and toughness and can be used under the ultra super critical steam condition such as a temperature of 625° C. and a pressure of 300 atm.

What is claimed is:  
     
         1 . A heat resistant high Cr ferritic steel excellent in high temperature long term creep strength and toughness, which comprises, in mass %,  
       
         
           
                 
                 
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C 
                   0.02 to 0.15% 
                   Mn 
                   0.05 to 1.5% 
                 
                     
                   P 
                   0.03% or less 
                   S 
                   0.015% or less 
                 
                     
                   Cr 
                   8 to 13% 
                   W 
                   1.5 to 4% 
                 
                     
                   Co 
                   2 to 6% 
                   V 
                   0.1 to 0.5% 
                 
                     
                   Ta 
                   0.01 to 0.15% 
                   Nb 
                   0.01 to 0.15% 
                 
                     
                   Nd 
                   0.001 to 0.2% 
                   N 
                   less than 0.02% 
                 
                     
                   B 
                   0.0005 to 0.02% 
                   Al 
                   0.001 to 0.05% 
                 
                     
                   Mo 
                   0 to 1% 
                   Si 
                   0 to 1% 
                 
                     
                   Ca 
                   0 to 0.02% 
                   La 
                   0 to 0.2% 
                 
                     
                   Ce 
                   0 to 0.2% 
                   Y 
                   0 to 0.2% 
                 
                     
                   Hf 
                   0 to 0.2%, 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
       
       the contents of Nd and N satisfying the following formula, and the balance being Fe and incidental impurities.  
       Nd(%)≦5×N(%)+0.1(%) 
     
     
         2 . A ferritic steel according to  claim 1 , wherein the W content is 2 to 3.5%.  
     
     
         3 . A ferritic steel according to  claim 1 , wherein the V content is 0.15 to 0.35% and the Nd content is 0.005 to 0.15%.  
     
     
         4 . A ferritic steel according to  claim 2 , wherein the V content is 0.15 to 0.35% and the Nd content is 0.005 to 0.15%.