Duplex stainless steel material and duplex stainless steel tube

Abstract

Disclosed herein is a duplex stainless steel material including a ferrite phase and an austenite phase, wherein the steel material contains, as metal component composition, at least one X-group element selected from 0.01 to 0.50 mass % of V, 0.0001 to 0.0500 mass % of Ti, 0.0005 to 0.0500 mass % of Nb, and 0.01 to 0.50 mass % of Ta. The steel material has composite inclusions or has composite inclusions and inclusions, in which each of the inclusions includes at least one of an oxide, a sulfide, and an oxysulfide; each of the composite inclusions includes one of the inclusions as a nucleus and includes an outer shell existing around the nucleus and having a carbide or a nitride containing Cr and the at least one X-group element, and the proportion of the number of the composite inclusions with respect to the total number of the inclusions is 30% or more.

1 : A duplex stainless steel material, comprising a ferrite phase and an austenite phase,
 wherein:   the duplex stainless steel material comprises, as metal component composition, at least one X-group element selected from the group consisting of 0.01 to 0.50 mass % of V, 0.0001 to 0.0500 mass % of Ti, 0.0005 to 0.0500 mass % of Nb, and 0.01 to 0.50 mass % of Ta;   the duplex stainless steel material has composite inclusions or has composite inclusions and inclusions;   each of the inclusions comprises at least one of an oxide, a sulfide, and an oxysulfide;   each of the composite inclusions comprises one of the inclusions as a nucleus and an outer shell existing around the nucleus and having a carbide or a nitride containing Cr and the at least one X-group element; and   a proportion of a number of the composite inclusions with respect to a total number of the inclusions is 30% or more.   
     
     
         2 : The duplex stainless steel material according to  claim 1 , wherein the duplex stainless steel material comprises 0.01 to 0.50 mass % of Ta as the metal component composition, and the outer shell comprises Ta in an amount satisfying formula (1) below:
   ([Ta]/[M]total)×100≥5  formula (1)
   
       where [Ta] represents a number of Ta atoms contained in the outer shell, and [M]total represents a total number of atoms of metal elements contained in the outer shell. 
     
     
         3 : The duplex stainless steel material according to  claim 1 , wherein the duplex stainless steel material comprises 0.01 to 0.50 mass % of Ta and 0.0001 to 0.0500 mass % of Ti as the metal component composition, and a (Ta mass %/Ti mass %) ratio satisfies formula (2) below:
   Ta mass %/Ti mass %≥25  formula (2).
   
     
     
         4 : The duplex stainless steel material according to  claim 1 , wherein the duplex stainless steel material comprises 0.0001 to 0.0200 mass % of Mg and 0.001 to 0.050 mass % of Al as the metal component composition, and the nucleus in each of the composite inclusions comprises an oxide of Mg and Al. 
     
     
         5 : The duplex stainless steel material according to  claim 1 , wherein the metal component composition of the duplex stainless steel material is:
 0.100 mass % or less of C,   0.10 to 2.00 mass % of Si,   0.10 to 3.00 mass % of Mn,   0.0100 mass % or less of S,   1.0 to 10.0 mass % of Ni,   0.05 to 6.00 mass % of Mo,   0.10 to 0.50 mass % of N,   20.0 to 28.0 mass % of Cr,   0.030 mass % or less of O, and   Fe and unavoidable impurities.   
     
     
         6 : The duplex stainless steel material according to  claim 1 , wherein the metal component composition of the duplex stainless steel material is:
 0.100 mass % or less of C,   0.10 to 2.00 mass % of Si,   0.10 to 3.00 mass % of Mn,   0.0100 mass % or less of S,   3.0 to 7.0 mass % of Ni,   0.05 to 1.00 mass % of Mo,   0.05 to 0.20 mass % of N,   20.0 to 25.0 mass % of Cr,   0.030 mass % or less of O, and   Fe and unavoidable impurities.   
     
     
         7 : The duplex stainless steel material according to  claim 5 , wherein the metal component composition further comprises:
 0.0001 to 0.0200 mass % of Ca.   
     
     
         8 : The duplex stainless steel material according to  claim 5 , wherein the metal component composition further comprises:
 at least one selected from the group consisting of 0.1 to 2.0 mass % of Co and 0.1 to 2.0 mass % of Cu.   
     
     
         9 : The duplex stainless steel material according to  claim 5 , wherein the metal component composition further comprises:
 0.0005 to 0.0100 mass % of B.   
     
     
         10 : A duplex stainless steel tube, comprising the duplex stainless steel material according to  claim 1 . 
     
     
         11 : The duplex stainless steel material according to  claim 6 , wherein the metal component composition further comprises:
 0.0001 to 0.0200 mass % of Ca.   
     
     
         12 : The duplex stainless steel material according to  claim 6 , wherein the metal component composition further comprises:
 at least one selected from the group consisting of 0.1 to 2.0 mass % of Co and 0.1 to 2.0 mass % of Cu.   
     
     
         13 : The duplex stainless steel material according to  claim 6 , wherein the metal component composition further comprises:
 0.0005 to 0.0100 mass % of B.