Duplex stainless steel material

Abstract

A duplex stainless steel material that has high strength and excellent low-temperature toughness is provided. A duplex stainless steel material according to the present disclosure consists of, by mass %, C: 0.030% or less, Si: 0.20 to 1.00%, Mn: 0.50 to 7.00%, P: 0.040% or less, S: 0.0200% or less, Al: 0.100% or less, Ni: 4.20 to 9.00%, Cr: 20.00 to 30.00%, Mo: 0.50 to 2.00%, Cu: 0.50 to 3.00%, N: 0.150 to 0.350%, and V: 0.01 to 1.50%, with the balance being Fe and impurities. The duplex stainless steel material has a yield strength of 552 MPa or more, and when an austenite grain with a minor axis of 20 μm or more is defined as primary austenite and the balance of austenite is defined as secondary austenite, the microstructure is composed of, in volume ratio, ferrite in an amount of 35 to 55%, primary austenite in an amount of 40 to 55%, and secondary austenite in an amount of 5 to 20%.

1 . A duplex stainless steel material consisting of, by mass %,
 C: 0.030% or less,   Si: 0.20 to 1.00%,   Mn: 0.50 to 7.00%,   P: 0.040% or less,   S: 0.0200% or less,   Al: 0.100% or less,   Ni: 4.20 to 9.00%,   Cr: 20.00 to 30.00%,   Mo: 0.50 to 2.00%,   Cu: 0.50 to 3.00%,   N: 0.150 to 0.350%,   V: 0.01 to 1.50%,   Nb: 0 to 0.100%,   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%,   Co: 0 to 0.500%,   Sn: 0 to 0.100%,   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 552 MPa or more; and   when, in a microstructure, an austenite grain with a minor axis of 20 μm or more is defined as primary austenite, and the balance of austenite is defined as secondary austenite,   the microstructure is composed of, in volume ratio, ferrite in an amount of 35 to 55%, the primary austenite in an amount of 40 to 55%, and the secondary austenite in an amount of 5 to 20%.   
     
     
         2 . The duplex stainless steel material according to  claim 1 , containing one or more elements selected from a group consisting of:
 Nb: 0.001 to 0.100%,   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%,   Co: 0.001 to 0.500%,   Sn: 0.001 to 0.100%,   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%.