Duplex stainless steel, duplex stainless steel sheet and duplex stainless steel material

摘要

A duplex stainless steel consisting of, in mass%: C: 0.03% or less; Si: 0.05% to 1.0%; Mn: 0.1% to 7.0%; P: 0.05% or less; S: 0.0001% to 0.0010%; Ni: 0.5% to 5.0%; Cr: 18.0% to 25.0%; N: 0.10% to 0.30%; Al: 0.05% or less; Ca: 0.0010% to 0.0040%; Sn: 0.01% to 0.2%; optionally one or more selected from Mo: 1.5% or less, Cu: 0.3% to 2.0%, W: 0.05% to 1.0%, Co: 2.0% or less, V: 0.05% to 0.5%, Nb: 0.01% to 0.20%, Ti: 0.003% to 0.05%, B: 0.0005% to 0.0050%, Mg: 0.0001% at 0.0030%, and REM: 0.005 to 0.10%; and the remainder being Fe and unavoidable impurities, where a Ca / O ratio of the amounts of Ca and O is in a range of 0.3 to 1.0, and a pitting index PI shown by formula (1) is in a range less than 30, PI = Cr + 3.3Mo + 16N (1), where the chemical symbols in formula (1) indicate the amounts of the elements.