Dual-phase stainless steel

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Problem to be Solved : To provide a duplex stainless steel excellent in the weldability during large heat input welding and excellent in the stress corrosion cracking resistance in a chloride environment containing corrosive associated gases. Solution : 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%, 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 relations of the following formulas (1) and (2) : 2.2 ¢ Cr + 7 ¢ Mo + 3 ¢ Cu > 66 Cr + 11 ¢ Mo + 10 ¢ Ni < 12 ¢ Cu + 30 ¢ N wherein the symbols of elements in formulas (1) and (2) respectively represent the contents (unit : mass%) of the elements in the steel.