Austenitic Stainless Steel

Abstract

An austenitic stainless steel includes base metal and a coating film formed on at least part of a surface of the base metal, a chemical composition of the base metal containing, in mass percent: C: 0.05% or less; Si: 1.0% or less; Mn: 2.0% or less; P: 0.040% or less; S: 0.010% or less; O: 0.020% or less; N: less than 0.050%; Ni: 12.0 to 27.0%; Cr: 15.0% or more to less than 20.0%; Cu: more than 3.5% to 8.0% or less; Mo: more than 2.0% to 5.0% or less; Co: 0.05% or less; Sn: 0.05% or less, V: 0 to 0.5%, Nb: 0 to 1.0%, Ti: 0 to 0.5%, W: 0 to 5.0%, Zr: 0 to 1.0%, Al: 0 to 0.5%, Ca: 0 to 0.01%, B: 0 to 0.01%, REM: 0 to 0.01%, and the balance: Fe and impurities, wherein a chemical composition at a maximum-Cr depth where a concentration of Cr in the coating film reaches a maximum satisfies, in at %, [(Cr+Ni+Cu+Mo)/Fe≥1.0].

1 . An austenitic stainless steel comprising base metal and a coating film formed on at least part of a surface of the base metal,
 a chemical composition of the base metal consisting of, in mass percent:   C: 0.05% or less;   Si: 1.0% or less;   Mn: 2.0% or less;   P: 0.040% or less;   S: 0.010% or less;   O: 0.020% or less;   N: less than 0.050%;   Ni: 12.0 to 27.0%;   Cr: 15.0% or more to less than 20.0%;   Cu: more than 3.5% to 8.0% or less;   Mo: more than 2.0% to 5.0% or less;   Co: 0.05% or less;   Sn: 0.05% or less;   V: 0 to 0.5%;   Nb: 0 to 1.0%;   Ti: 0 to 0.5%;   W: 0 to 5.0%;   Zr: 0 to 1.0%;   Al: 0 to 0.5%;   Ca: 0 to 0.01%;   B: 0 to 0.01%;   REM: 0 to 0.01%, and   the balance: Fe and impurities, wherein   a chemical composition at a maximum-Cr depth where a concentration of Cr in the coating film reaches a maximum satisfies a following formula (i):
   (Cr+Ni+Cu+Mo)/Fe≥1.0  (i)
 
   where each symbol of element in the formula denotes a content (at %) of a corresponding element.   
     
     
         2 . The austenitic stainless steel according to  claim 1 , wherein
 the chemical composition of the base metal containing one or more elements selected from, in mass percent:   V: 0.01 to 0.5%;   Nb: 0.02 to 1.0%;   Ti: 0.01 to 0.5%;   W: 0.1 to 5.0%;   Zr: 0.02 to 1.0%;   Al: 0.01 to 0.5%;   Ca: 0.0005 to 0.01%;   B: 0.0005 to 0.01%; and   REM: 0.0005 to 0.01%.   
     
     
         3 . The austenitic stainless steel according to  claim 1 , wherein
 a minimum-Cr depth where the concentration of Cr in the coating film falls to a minimum lies closer to the base metal than the maximum-Cr depth, and   a chemical composition at the maximum-Cr depth satisfies a following formula (ii), and a chemical composition at the minimum-Cr depth satisfies a following formula (iii):
   Cr/(Ni+Cu+Mo)≥1.0  (ii)
 
   Cr/(Ni+Cu+Mo)<1.0  (iii)
 
   where each symbol of element in the formulas denotes a content (at %) of a corresponding element.   
     
     
         4 . The austenitic stainless steel according to  claim 2 , wherein
 a minimum-Cr depth where the concentration of Cr in the coating film falls to a minimum lies closer to the base metal than the maximum-Cr depth, and   a chemical composition at the maximum-Cr depth satisfies a following formula (ii), and a chemical composition at the minimum-Cr depth satisfies a following formula (iii):
   Cr/(Ni+Cu+Mo)≥1.0  (ii)
 
   Cr/(Ni+Cu+Mo)<1.0  (iii)
 
   where each symbol of element in the formulas denotes a content (at %) of a corresponding element.