How do super austenitic and super duplex stainless steels compare?
Super austenitic and super duplex stainless steels have comparable corrosion resistance, but super duplex offers greater strength at a lower cost, making it the more effective choice for most applications. Choose super austenitic instead where low-temperature impact toughness is needed below -50°C, or where long-term service above 250°C rules out super duplex.
Super austenitic vs Alloy 32750: the numbers
| Property | Super austenitic | Alloy 32750 |
|---|---|---|
| PREN | >=43 | >40 |
| Chromium | - | 24.5-26.0% |
| Molybdenum | >6% | 3.00-5.00% |
| Nickel | - | 6.00-8.00% |
| Nitrogen | - | 0.24-0.32% |
| 0.2% proof strength | - | 550 N/mm² (79.8 ksi) |
| Tensile strength | - | 800 N/mm² (116 ksi) |
| General corrosion resistance | Comparable to super duplex overall | Outstanding resistance to pitting, crevice corrosion and stress corrosion cracking |
| Pitting / CPT resistance | PREN 43 or greater | PREN >40; comparable to super austenitic |
| Typical applications | - | - |
Calculate PREN for your own composition with our PREN calculator.
What sets super austenitic grades apart
Super austenitic grades such as Alloy 254 are a significant step up from regular austenitic stainless steels such as Alloy 304 and Alloy 316. Their chromium and nickel contents are raised and more than 6% molybdenum is added, giving a pitting resistance equivalent number (PREN) of 43 or greater. As austenitic steels they retain excellent impact toughness at low temperatures and good fabricability.
Where super duplex takes over
Super duplex stainless steels are usually preferred on strength and cost. The exceptions are where low-temperature impact toughness is needed (below -50°C) or where long-term service occurs at higher temperatures (above 250°C), which can preclude grades like Alloy 32750.
Which should you choose?
Super duplex is usually preferred on strength and cost, and its corrosion resistance matches super austenitic grades for most applications. The exceptions are temperature-driven: choose super austenitic where low-temperature impact toughness is needed below -50°C, or where long-term service occurs above 250°C, both of which can preclude super duplex.