Duplex stainless steel material and duplex stainless steel pipe

Abstract

This duplex stainless steel material is composed of a ferrite phase and an austenite phase, and has a component composition that contains 0.100% by mass or less of C, 0.10-2.00% by mass of Si, 0.10-2.00% by mass of Mn, 0.050% by mass or less of P, 0.0100% by mass or less of S, 0.001-0.050% by mass of Al, 1.0-10.0% by mass of Ni, 22.0-28.0% by mass of Cr, 2.0-6.0% by mass of Mo and 0.20-0.50% by mass of N, while containing 0.01-0.50% by mass of Ta and/or 0.1-1.0% by mass of Ge, with the balance made up of Fe and unavoidable impurities.

1 . A duplex stainless steel material consisting of a ferrite phase and an austenite phase, wherein the duplex stainless steel material comprises:
 Fe   C: 0.100 mass % or less,   Si: 0.10 to 2.00 mass %,   Mn: 0.10 to 2.00 mass %,   P: 0.050 mass % or less,   S: 0.0100 mass % or less,   Al: 0.001 to 0.050 mass %,   Ni: 1.0 to 10.0 mass %,   Cr: 22.0 to 28.0 mass %,   Mo: 2.0 to 6.0 mass %,   N: 0.20 to 0.50 mass % and [[,]]   one or more elements selected from the group consisting of Ta: 0.01 to 0.50 mass % and Ge: 0.1 to 1.0 mass %   
     
     
         2 . The duplex stainless steel material according to  claim 1 , wherein a PRE value represented by the following formula is 40 or more
   PRE=[Cr]+3.3 [Mo]+16 [N]   wherein [Cr] is a content of Cr in mass %, [Mo] is a content of Mo in mass %, and [N] is a content of N in mass %.   
     
     
         3 . The duplex stainless steel material according to  claim 1 , comprising Ta, and comprising 0.01 mass % or less of oxygen, and
 wherein Ta-containing sulfide-oxide-based composite inclusions having a major diameter of 1 μm or more are present in a number of 500 or less per 1 mm 2  of a cross section perpendicular to a working direction in the inclusions of the duplex stainless steel material, and a Ta content of the sulfide-oxide-based composite inclusions is 5 at % or more.   
     
     
         4 . The duplex stainless steel material according to  claim 1 , further contains further comprising one or more elements selected from the group consisting of Co: 0.10 to 2.00 mass %, Cu: 0.10 to 2.00 mass %, V: 0.01 to 0.50 mass %, Ti: 0.01 to 0.50 mass %, Nb: 0.01 to 0.50 mass %, Mg: 0.0005 to 0.020 mass %, and Ca: 0.0005 to 0.020 mass %. 
     
     
         5 . A duplex stainless steel pipe comprising the duplex stainless steel material according to  claim 1 . 
     
     
         6 . The duplex stainless steel material according to  claim 1 , comprising Ta. 
     
     
         7 . The duplex stainless steel material according to  claim 1 , comprising Ge. 
     
     
         8 . The duplex stainless steel material according to  claim 1 , comprising Ta and Ge.