The pitting resistance equivalent number (PREN) of UNS S31254 is greater than 43 - equivalent to a super duplex stainless steel. UNS S31254 (ASTM F44, 1.4547, also known as 254SMO or 6Mo) is a super austenitic stainless steel that reaches this PREN by raising its molybdenum content to 6%.
S31254 is the Unified Numbering System (UNS) designation for an austenitic stainless steel best known as 254SMO or 6Mo. In the UNS system a letter followed by five numbers identifies each metal, with S indicating stainless steels. The system was created by several trade groups in the 1970s to reduce confusion caused by one alloy being known by different names.
The higher alloy content makes UNS S31254 a more expensive choice, so it is used mainly where the operating temperature falls outside the range of a super duplex.
| Element | Approx. content |
|---|---|
| Chromium | 20% |
| Nickel | 18% |
| Molybdenum | 6% |
| Copper | 1% |
Its yield strength is lower than that of duplex stainless steel and much lower than that of super duplex steel.