Duplex stainless steel material

Abstract

A duplex stainless steel material according to the present disclosure consists of, in mass %, C: 0.030% or less, Si: 0.20 to 1.00%, Mn: 0.5 to 7.0%, P: 0.040% or less, S: 0.0200% or less, Al: 0.100% or less, Ni: 4.0 to 9.0%, Cr: 20.0 to 30.0%, Mo: 0.5 to 2.0%, Cu: 1.5 to 3.0%, N: 0.15 to 0.30%, V: 0.01 to 0.50%, Co: 0.05 to 1.00%, and Sn: 0.001 to 0.050%, with the balance being Fe and impurities. The yield strength is 758 MPa or more. The microstructure is composed of, in volume ratio, ferrite in an amount of 35 to 65%, with the balance being austenite. A dislocation density ρ(α) in the ferrite and a dislocation density ρ(γ) in the austenite satisfy the following Formula (1): 0.3 < ρ ⁡ ( γ ) / ρ ⁡ ( α ) < 4. ( 1 )

1 . A duplex stainless steel material consisting of, in mass %,
 C: 0.030% or less,   Si: 0.20 to 1.00%,   Mn: 0.5 to 7.0%,   P: 0.040% or less,   S: 0.0200% or less,   Al: 0.100% or less,   Ni: 4.0 to 9.0%,   Cr: 20.0 to 30.0%,   Mo: 0.5 to 2.0%,   Cu: 1.5 to 3.0%,   N: 0.15 to 0.30%,   V: 0.01 to 0.50%,   Co: 0.05 to 1.00%,   Sn: 0.001 to 0.050%,   Nb: 0 to 0.300%,   Ta: 0 to 0.100%,   Ti: 0 to 0.100%,   Zr: 0 to 0.100%,   Hf: 0 to 0.100%,   W: 0 to 0.200%,   Sb: 0 to 0.100%,   Ca: 0 to 0.020%,   Mg: 0 to 0.020%,   B: 0 to 0.020%, and   rare earth metal: 0 to 0.200%,   with the balance being Fe and impurities,   wherein:   a yield strength is 758 MPa or more;   the microstructure is composed of, in volume ratio, ferrite in an amount of 35 to 65%, with the balance being austenite; and   a dislocation density ρ(α) in the ferrite and a dislocation density ρ(γ) in the austenite satisfy Formula (1):   
       
         
           
             
               
                 
                   
                     0.3 
                     < 
                     
                       
                         ρ 
                         ⁡ 
                         ( 
                         γ 
                         ) 
                       
                       / 
                       
                         ρ 
                         ⁡ 
                         ( 
                         α 
                         ) 
                       
                     
                     < 
                     4. 
                   
                 
                 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
         where, in Formula (1), a dislocation density in the austenite in m −2  is substituted for ρ(γ), and a dislocation density in the ferrite in m −2  is substituted for ρ(α). 
       
     
     
         2 . The duplex stainless steel material according to  claim 1 , comprising one or more elements selected from a group consisting of:
 Nb: 0.001 to 0.300%,   Ta: 0.001 to 0.100%,   Ti: 0.001 to 0.100%,   Zr: 0.001 to 0.100%,   Hf: 0.001 to 0.100%,   W: 0.001 to 0.200%,   Sb: 0.001 to 0.100%,   Ca: 0.001 to 0.020%,   Mg: 0.001 to 0.020%,   B: 0.001 to 0.020%, and   rare earth metal: 0.001 to 0.200%.