Corrosion behaviour of various duplex stainless steels in welded condition

Abstract

A number of duplex stainless steels, whoseferrite content ranged from 25 to 70%, were studied for evidence of corrosion in the aged and welded conditions. Microstructural reasons for differences in corrosion properties have been investigated, together with the influence of base alloy con1position. The corrosion performance of duplex stainless steels was tested in highly aggressive media: sulphuric acid andferric chloride solutions. It was found that 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 been observed to have a beneficial effect. Selective corrosion was observed in weldments and the heat affected zones of samples with adverse microstructural features. The average corrosion rates calculated from weight loss on as-received, aged, and welded samples after immersion in the abovementioned solutions and the critical pitting temperature measured in FeCl₃ solution were in agreement with the above assertions.