Corrosion performance of welds in duplex, superduplex and lean duplex stainless steels

To achieve good corrosion resistance in a weld is much more challenging than for plate or sheet material, which has undergone controlled rolling, heat treatment and pickling processes in the steel mill. The choice of weld procedure and parameters, filler metal and shielding gas all play important roles. For duplex and lean duplex grades it is essential to ensure that an adequate amount of austenite is formed in the weld metal and heat affected zone, in order to fulfil requirements in terms of austenite-ferrite phase balance, but also to avoid the precipitation of detrimental phases such as intermetallics and nitrides. In addition, the importance of good post-weld cleaning to ensure good corrosion properties cannot be over-emphasised. This paper focuses on a number of different examples of pitting corrosion of welds in the duplex grades UNS S32101, S32304, S32205, S82441 and S32750. These illustrate the role of microstructure control to attain good corrosion performance. The effect of residual weld oxides or heat tint in degrading the corrosion performance is also explored, together with evaluation of the degree to which the corrosion resistance can be restored by the use of appropriate pickling processes.