Duplex stainless steel, duplex stainless steel slab, and duplex stainless steel material

Abstract

One aspect of this duplex stainless steel contains, in mass %, C: 0.03% or less, Si: 0.05% to 1.0%, Mn: 0.1% to 7.0%, P: 0.05% or less, S: 0.0001% to 0.0010%, Ni: 0.5% to 5.0%, Cr: 18.0% to 25.0%, N: 0.10% to 0.30%, Al: 0.05% or less, Ca: 0.0010% to 0.0040%, and Sn: 0.01% to 0.2%, with the remainder being Fe and inevitable impurities, wherein a ratio Ca/O of the amounts of Ca and O is in a range of 0.3 to 1.0, and a pitting index PI shown by formula (1) is in a range of less than 30, PI=Cr+3.3Mo+16N  (1).

1 . A duplex stainless steel comprising, in mass %:
 C: 0.03% or less;   Si: 0.05% to 1.0%;   Mn: 0.1% to 7.0%;   P: 0.05% or less;   S: 0.0001% to 0.0010%;   Ni: 0.5% to 5.0%;   Cr: 18.0% to 25.0%;   N: 0.10% to 0.30%;   Al: 0.05% or less;   Ca: 0.0010% to 0.0040%; and   Sn: 0.01% to 0.2%,   with the remainder being Fe and inevitable impurities,   wherein a ratio Ca/O of the amounts of Ca and O is in a range of 0.3 to 1.0, and a pitting index PI shown by formula (1) is in a range of less than 30,
   PI=Cr+3.3Mo+16N  (1),
 
   (the chemical symbols in the formula (1) indicate the amounts of the elements).   
     
     
         2 . The duplex stainless steel according to  claim 1  further comprising:
 one or more selected from 
 Mo: 1.5% or less, 
 Cu: 2.0% or less, 
 W: 1.0% or less, and 
 Co: 2.0% or less. 
 
     
     
         3 . The duplex stainless steel according to  claim 1  or  2 , further comprising:
 one or more selected from 
 V: 0.05% to 0.5%, 
 Nb: 0.01% to 0.20%, and 
 Ti: 0.003% to 0.05%. 
 
     
     
         4 . The duplex stainless steel according to any one of  claims 1  to  3 , further comprising:
 one or more selected from 
 B: 0.0050% or less, 
 Mg: 0.0030% or less, and 
 REM: 0.10% or less. 
 
     
     
         5 . A duplex stainless steel comprising, in mass %:
 C: 0.03% or less;   Si: 0.05% to 1.0%;   Mn: 0.1% to 4.0%;   P: 0.05% or less;   S: 0.0001% to 0.0010%;   Cr: 23.0% to 28.0%;   Ni: 2.0% to 6.0%;   Co: 0% to 1.0%;   Cu: 0.2% to 3.0%;   Sn: 0.01% to 0.2%;   N: 0.20% to 0.30%;   Al: 0.05% or less; and   Ca: 0.0010% to 0.0040%,   with the remainder being Fe and inevitable impurities,   wherein Ni+Co is in a range of 2.5% or more and a ratio Ca/O of the amounts of Ca and O is in a range of 0.3 to 1.0, and   PI shown by formula (1) is in a range of 30 or more to less than 40,
   PI=Cr+3.3Mo+16N  (1),
 
   (the chemical symbols in the formula (1) indicate the amounts of the elements).   
     
     
         6 . The duplex stainless steel according to  claim 5 , further comprising:
 either one or both of   Mo: 2.0% or less, and   W: 1.0% or less.   
     
     
         7 . The duplex stainless steel according to  claim 5  or  6 , further comprising:
 one or more selected from 
 V: 0.05% to 0.5%, 
 Nb: 0.01% to 0.15%, and 
 Ti: 0.003% to 0.05%. 
 
     
     
         8 . The duplex stainless steel according to any one of  claims 5  to  7 , further comprising:
 one or more selected from 
 B: 0.0050% or less, 
 Mg: 0.0030% or less, and 
 REM: 0.10% or less. 
 
     
     
         9 . A cast steel of a duplex stainless steel which has a composition according to any one of  claims 1  to  8 ,
 wherein a fracture reduction of area at 1000° C. is in a range of 70% or more. 
 
     
     
         10 . A duplex stainless steel material which is manufactured by hot working the cast steel of the duplex stainless steel according to  claim 9 .