Austenitic Heat Resistant Alloy and Method for Producing the Same

Abstract

Provided is an austenitic heat resistant alloy having high creep strength and high toughness even in a high temperature environment. This austenitic heat resistant alloy has a chemical composition consisting of: in mass %, C: 0.03 to less than 0.25%, Si: 0.01 to 2.0%, Mn: not more than 2.0%, Cr: 10 to less than 30%, Ni: more than 25 to 45%, Al: more than 2.5 to less than 4.5%, Nb: 0.2 to 3.5%, N: not more than 0.025%, with the balance being Fe and impurities, wherein P and S in the impurities are respectively, P: not more than 0.04% and S: not more than 0.01%. In the structure, a total volume ratio of precipitates having a circle equivalent diameter of not less than 6 μm is not more than 5%.

1 . An austenitic heat resistant alloy comprising a chemical composition, consisting of: in mass %,
 C: 0.03 to less than 0.25%,   Si: 0.01 to 2.0%,   Mn: not more than 2.0%,   Cr: 10 to less than 30%,   Ni: more than 25 to 45%,   Al: more than 2.5 to less than 4.5%,   Nb: 0.2 to 3.5%,   N: not more than 0.025%,   Ti: 0 to less than 0.2%,   W: 0 to 6%,   Mo: 0 to 4%,   Zr: 0 to 0.1%,   B: 0 to 0.01%,   Cu: 0 to 5%,   rare earth metals: 0 to 0.1%,   Ca: 0 to 0.05%, and   Mg: 0 to 0.05%, with the balance being Fe and impurities, wherein P and S in the impurities are respectively, P: not more than 0.04% and S: not more than 0.01%, and wherein   in a structure, a total volume ratio of precipitates having a circle equivalent diameter of not less than 6 μm is not more than 5%.   
     
     
         2 . The austenitic heat resistant alloy according to  claim 1 , wherein
 the chemical composition contains one or more kinds selected from the group consisting of, in mass %,   Ti: 0.005 to less than 0.2%,   W: 0.005 to 6%,   Mo: 0.005 to 4%,   Zr: 0.0005 to 0.1%, and   B: 0.0005 to 0.01%.   
     
     
         3 . The austenitic heat resistant alloy according to  claim 1 , wherein
 the chemical composition contains one or more kinds selected from the group consisting of, in mass %,   Cu: 0.05 to 5%, and   rare earth metals: 0.0005 to 0.1%.   
     
     
         4 .- 5 . (canceled) 
     
     
         6 . The austenitic heat resistant alloy according to  claim 2 , wherein
 the chemical composition contains one or more kinds selected from the group consisting of, in mass %,   Cu: 0.05 to 5%, and   rare earth metals: 0.0005 to 0.1%.   
     
     
         7 . The austenitic heat resistant alloy according to  claim 1 , wherein
 the chemical composition contains one or more kinds selected from the group consisting of, in mass %,   Ca: 0.0005 to 0.05%, and   Mg: 0.0005 to 0.05%.   
     
     
         8 . The austenitic heat resistant alloy according to  claim 2 , wherein
 the chemical composition contains one or more kinds selected from the group consisting of, in mass %,   Ca: 0.0005 to 0.05%, and   Mg: 0.0005 to 0.05%.   
     
     
         9 . The austenitic heat resistant alloy according to  claim 3 , wherein
 the chemical composition contains one or more kinds selected from the group consisting of, in mass %,   Ca: 0.0005 to 0.05%, and   Mg: 0.0005 to 0.05%.   
     
     
         10 . The austenitic heat resistant alloy according to  claim 6 , wherein
 the chemical composition contains one or more kinds selected from the group consisting of, in mass %,   Ca: 0.0005 to 0.05%, and   Mg: 0.0005 to 0.05%.   
     
     
         11 . A method for producing an austenitic heat resistant alloy comprising steps of:
 performing hot forging at a reduction of area of not less than 30% on a starting material having the chemical composition according to  claim 1 ;   producing an intermediate material by performing hot working on the starting material after hot forging; and   performing solution treatment at 1100 to 1250° C. on the intermediate material.