What is the PREN of S31254?

S31254 is the Unified Numbering System (UNS) designation for an austenitic stainless steel alloy most commonly known as 254SMO or 6Mo. The UNS system was created by a number of trade groups working together in the 1970’s, to reduce confusion from the same alloy being called different things or vice-versa. Each metal is indicated by a letter followed by five numbers, where the letter indicates the family of metals i.e. S for stainless steels.

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 the equivalent of a super duplex stainless steel. However, the higher alloy content does mean that it is a more expensive choice, and therefore is used mainly where the operating temperature is outside that of a super duplex.

254SMO is a registered trademark of Outokumpu OYJ.

This material contains approximately 20% chromium, 18% nickel, 6% molybdenum, and 1% copper. UNS S31254 possesses a lower yield strength than that of duplex stainless steel and much lower than that of super duplex steel.

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