Austenitic Alloy Material and Austenitic Alloy Pipe

Abstract

An austenitic alloy material is provided that includes a base metal having a surface, and a film containing chromium oxide having a thickness of 0.1 to 50 μm on at least one portion of the surface. A chemical composition at a depth position in the film at which the Cr concentration is highest contains, by atom %, 50% or more of Cr as a proportion occupied among components excluding O, C and N. The chemical composition of the base metal consists of, by mass %, C: 0.001 to 0.6%, Si: 0.01 to 5.0%, Mn: 0.1 to 10.0%, P: 0.08% or less, S: 0.05% or less, Cr: 15.0 to 55.0%, Ni: 30.0 to 80.0%, N: 0.001 to 0.25%, O: 0.02% or less, Mo: 0 to 20.0%, Cu: 0 to 5.0%, Co: 0 to 5.0%, W: 0 to 10.0%, Ta: 0 to 6.0%, Nb: 0 to 5.0%, Ti: 0 to 1.0%, B: 0 to 0.1%, Zr: 0 to 0.1%, Hf: 0 to 0.1%, Al: 0 to 1.0%, Mg: 0 to 0.1%, and Ca: 0 to 0.1%, the balance being Fe and impurities.

1 . An austenitic alloy material comprising a base metal having a surface, and a film containing chromium oxide having a thickness of 0.1 to 50 μm on at least one portion of the surface, wherein:
 a chemical composition at a depth position in the film at which a Cr concentration is highest contains, by atom %, 50% or more of Cr as a proportion occupied among components excluding O, C and N; and 
 a chemical composition of the base metal consists of, by mass %: 
 C: 0.001 to 0.6%, 
 Si: 0.01 to 5.0%, 
 Mn: 0.1 to 10.0%, 
 P: 0.08% or less, 
 S: 0.05% or less, 
 Cr: 15.0 to 55.0%, 
 Ni: 30.0 to 80.0%, 
 N: 0.001 to 0.25%, 
 O: 0.02% or less, 
 Mo: 0 to 20.0%, 
 Cu: 0 to 5.0%, 
 Co: 0 to 5.0%, 
 W: 0 to 10.0%, 
 Ta: 0 to 6.0%, 
 Nb: 0 to 5.0%, 
 Ti: 0 to 1.0%, 
 B: 0 to 0.1%, 
 Zr: 0 to 0.1%, 
 Hf: 0 to 0.1%, 
 Al: 0 to 1.0%, 
 Mg: 0 to 0.1%, 
 Ca: 0 to 0.1%, and 
 the balance: Fe and impurities. 
 
     
     
         2 . The austenitic alloy material according to  claim 1 , wherein the chemical composition of the base metal contains, by mass %, one or more elements selected from:
 Mo: 0.01 to 20.0%,   Cu: 0.01 to 5.0%,   Co: 0.01 to 5.0%,   W: 0.01 to 10.0%,   Ta: 0.01 to 6.0%,   Nb: 0.01 to 5.0%,   Ti: 0.01 to 1.0%,   B: 0.001 to 0.1%,   Zr: 0.001 to 0.1%,   Hf: 0.001 to 0.1%,   Al: 0.01 to 1.0%,   Mg: 0.0005 to 0.1%, and   Ca: 0.0005 to 0.1%.   
     
     
         3 . The austenitic alloy material according to  claim 1 , wherein:
 one or more elements selected from Cu, V, W, Mo and precious metal elements is contained in the film.   
     
     
         4 . The austenitic alloy material according to  claim 3 , wherein:
 a chemical composition in an outer layer of the film satisfies formulas (i) and (ii) below:
   [Cu] S +[V] S +[W] S +[Mo] S +[PM] S ≥30  (i)
 
   [Cr] S ≤70  (ii)
 
   where, with respect to each symbol in the formulas above, each element in the outer layer of the film represents a proportion (atom %) occupied by the corresponding element among components excluding O, C and N, and PM means precious metal elements.   
     
     
         5 . The austenitic alloy material according to  claim 3 , wherein:
 the chemical composition at a depth position at which the Cr concentration is highest satisfies formula (iii) below:
   0.5≤[Cu] P +[V] P +[W] P +[Mo] P +[PM] P ≤50  (iii)
 
   where, with respect to each symbol in the above formula, each element at a depth position at which the Cr concentration is highest represents a proportion (atom %) occupied by the corresponding element among components excluding O, C and N, and PM means precious metal elements.   
     
     
         6 . The austenitic alloy material according to  claim 3 , wherein:
 the film contains a complex oxide containing one or more elements selected from Cu, V, W and Mo, and Cr.   
     
     
         7 . The austenitic alloy material according to  claim 1 , wherein:
 the film has an action that decomposes SO 3 .   
     
     
         8 . The austenitic alloy material according to  claim 7 , wherein:
 an SO 3  decomposition rate is 8.0×10 −5  g/cm 2 /min or more under conditions of an SO 3  supply rate per unit area of 0.0071 g/cm 2 /min, and a reaction temperature of 850° C.   
     
     
         9 . The austenitic alloy material according to  claim 8 , wherein:
 an SO 3  decomposition rate is 1.0×10 −3  g/cm 2 /min or more under conditions of an SO 3  supply rate per unit area of 0.0071 g/cm 2 /min, and a reaction temperature of 850° C.   
     
     
         10 . An austenitic alloy pipe comprising an austenitic alloy material according to  claim 1 . 
     
     
         11 . An austenitic alloy pipe comprising an austenitic alloy material according to  claim 2 . 
     
     
         12 . An austenitic alloy pipe comprising an austenitic alloy material according to  claim 3 . 
     
     
         13 . An austenitic alloy pipe comprising an austenitic alloy material according to  claim 4 . 
     
     
         14 . An austenitic alloy pipe comprising an austenitic alloy material according to  claim 5 . 
     
     
         15 . An austenitic alloy pipe comprising an austenitic alloy material according to  claim 6 . 
     
     
         16 . An austenitic alloy pipe comprising an austenitic alloy material according to  claim 7 . 
     
     
         17 . An austenitic alloy pipe comprising an austenitic alloy material according to  claim 8 . 
     
     
         18 . An austenitic alloy pipe comprising an austenitic alloy material according to  claim 9 .