Corrosion behaviour of various duplex stainless steels in welded conditions

A number of duplex stainless steels whose ferritic content ranged from 25 to 70% were studied in the aged and welded conditions. Microstructural reasons for differences in corrosion properties have been investigated, together with the influence of composition. The corrosion performance was tested in sulfuric acid and ferric chloride solutions. The best corrosion resistance is obtained from alloys whose microstructures change little with increasing aging temperatures and whose composition is such as to give austenite/ferrite ratios close to 50:50. High chromium contents which stabilize the passive film and the addition of nickel and molybdenum have a beneficial effect. Selective corrosion was observed in weldments and the heat affected zones of samples with adverse microstructural features.