Duplex stainless steel

Abstract

A duplex stainless steel excellent in the weldability during large heat input welding and in the stress corrosion cracking resistance in a chloride environment containing corrosive associated gases has a chemical composition consisting, by mass %, of C: 0.03% or less, Si: 0.2 to 1%, Mn: 5.0% or less, P: 0.040% or less, S: 0.010% or less, sol. Al: 0.040% or less, Ni: 4 to 8%, Cr: 20 to 28%, Mo: 0.5 to 2.0%, Cu: more than 2.0% and 4.0% or less and N: 0.1 to 0.35%, and optionally contains one or more selected from among V, Ca, Mg, B and a rare earth metal(s), with the balance being Fe and impurities; wherein the duplex stainless steel satisfies the following formulas: 2.2Cr+7Mo+3Cu>66   (1) Cr+11Mo+10Ni<12(Cu+30N)   (2), wherein the symbols represent mass % of the elements in the steel.

1 . A duplex stainless steel that has a chemical composition consisting, by mass %, of C: 0.03% or less, Si: 0.2 to 1%, Mn: 5.0% or less, P: 0.040% or less, S: 
     
     
         0 . 010% or less, sol. Al: 0.040% or less, Ni: 4 to 8%, Cr: 20 to 28%, Mo: 0.5 to 2.0%, Cu: more than 2.0% and 4.0% or less and N: 0.1 to 0.35%, with the balance being Fe and impurities; wherein the duplex stainless steel satisfies the relations of the following formulas (1) and (2):
   2Cr+7Mo+3Cu>66   (1)
     Cr+11 Mo+10Ni<12(Cu+30N)   (2)
   
       wherein the symbols of elements in formulas (1) and (2) respectively represent the contents (unit: mass %) of the elements in the steel. 
     
     
         2 . The duplex stainless steel according to  claim 1 , which further contains, by mass %, V: 1.5% or less, in place of part of Fe. 
     
     
         3 . The duplex stainless steel according to  claim 1 , which further contains, by mass %, one or more selected from among Ca: 0.02% or less, Mg: 0.02% or less and B: 0.02% or less, in place of part of Fe. 
     
     
         4 . The duplex stainless steel according to  claim 1 , which further contains, by mass %, rare earth metal(s): 0.2% or less, in place of part of Fe.