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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