Patent ID: 8778260

Claim:
Duplex stainless steel characterized by containing, by mass %, C: 0.06% or less, Si: 0.05 to 3.0%, Mn: 0.1 to 6.0%, P: 0.05% or less, S: 0.010% or less, Ni: 1.0 to 10.0%, Cr: 18 to 30%, Mo: 3.0% or less, Cu: 3.0% or less, N: 0.10 to 0.40%, Al: 0.001 to 0.08%, Ti: 0.003 to 0.042%, Mg: 0.0001 to 0.0030%, and O: 0.010% or less, having a product of f N , Ti content, and N content as f N ×Ti×N of 0.00004% 2 or more, having a product of Ti content and N content as Ti×N of 0.008% 2 or less, having a balance of Fe and unavoidable impurities; where f N is a numerical value satisfying the following formula (1): log 10 f N =−0.046×Cr−0.02×Mn−0.011×Mo+0.048×Si+0.007×Ni+0.009×Cu (1) each element is shown by content (%), and having an equiaxial crystal structure and a ferrite phase ratio in the range of 30 to 70%.