How does 254SMO compare with super duplex stainless steels? Stainless Steels

254SMO (UNS S31254, ASTM F44, 1.4547) is a so-called super austenitic stainless steel. By increasing the molybdenum content to 6%, it achieves a pitting resistance equivalent number (PREN) > 43, which is similar to that of a super duplex stainless steel (SDSS).

When comparing 254SMO vs super duplex stainless steels, it is non-magnetic, potentially more straightforward to weld and has a wider operating temperature range. However, it is considerably more expensive due to its greater nickel and molybdenum content and has a significantly lower strength. Therefore, it will mostly be used in applications where the use of super duplex stainless steels is limited. This could include applications at lower temperatures (<-50degC) where the impact strength of SDSS drops, or at higher temperatures (>250degC) where there is a risk of forming deleterious phases if exposed for extended periods.

254SMO and other super austenitics have been specified for marine scrubbers, as their intermittent use can result in operating temperatures >250degC. However, super duplex stainless steels have been successfully used in flue gas desulphurization systems for power stations, as continuous operation results in lower temperatures. Super austenitics such as 254SMO have been substituted by super duplex stainless steels in water treatment systems, such as RO/desalination.

254SMO is a registered trademark of Outokumpu OYJ.

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