High-chromium containing ferrite based heat resistant steel

Abstract

A high-Cr containing ferrite heat resistant steel having not only an excellent long-term creep strength at a high temperature exceeding 650° C., but also an improved oxidation resistance, which is based on ferritic phase and contains 13% by weight or more of chromium, and containing precipitates of intermetallic compounds.

What is claimed is:  
     
         1 . A heat resistant high-chromium containing ferrite steel based on ferritic phase and containing 13% by weight or more of chromium, and containing precipitates of intermetallic compounds.  
     
     
         2 . The heat resistant high-chromium containing ferrite steel as claimed in  claim 1 , wherein the intermetallic compound is at least one type of precipitates selected from the group consisting of a Laves phase, a μ phase, a σ phase, or a compound represented by Ni 3 X, where X is Al or Ti.  
     
     
         3 . The heat resistant high-chromium containing ferrite steel as claimed in  claim 1  or  2 , wherein the ferritic phase is contained 70% by volume or more.  
     
     
         4 . The heat resistant high-chromium containing ferrite steel as claimed in anyone of  claims 1  to  3 , wherein Mo is contained 0.5% by weight or more and W is contained 1.0% by weight or more.  
     
     
         5 . The heat resistant high-chromium containing ferite steel as claimed in anyone of  claims 1  to  4 , wherein Co is contained 1.0% by weight or more.  
     
     
         6 . The heat resistant high-chromium containing ferrite steel as claimed in anyone of  claims 1  to  5 , wherein the ferrite steel has a following chemical composition (weight %). 
 Cr 13˜30  
 Mo 0.5˜8.0  
 W 1.0˜8.0  
 Co 1.0˜10.0  
 C 0.50 or less  
 N 0.20 or less  
 B 0.01 or less  
 Nb 0.01˜2.0  
 Fe residue  
 and may contain unevitable impurities.  
 
     
     
         7 . A method for producing a heat resistant high-chromium containing ferrite steel as claimed in anyone of  claims 1  to  6 , comprising steps of a hot working bulky steel derived from a melt raw materials and a annealing hot worked steel.  
     
     
         8 . The method for producing a heat resistant high-chromium containing ferrite steel as claimed in  claim 7 , wherein the step of annealing is comprised with processes of a heating at the temperature of 1000° or more and a cooling in a furnace.