Data completeness: partial. Last verified 19 August 2026.
Designations
| Common name | 254 SMO |
| UNS | S31254 |
| EN number | 1.4547 |
| Class | Super-austenitic stainless steel |
| Specified by | ASTM A240/A240M, EN 10088-2 |
254 SMO is the six-molybdenum super-austenitic, and the nitrogen in it does two jobs: it lifts the pitting ranking by more than three points and it raises the proof strength minimum by a third over ordinary austenitics. At PREN 43 it sits level with 2507 and above 2205, which makes the choice between it and a super duplex a question about temperature, fabrication and price rather than about corrosion.
Properties, with what each one rests on
| Property | Value | Unit | Condition | Evidence | Source | Retrieved |
|---|---|---|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 320 | MPa | cold rolled coil and sheet, 20 °C | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Tensile strength Rm, minimum | 650 | MPa | cold rolled; datasheet gives a 650–850 range | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Elongation A, minimum | 35 | % | cold rolled; A and A80 both 35 | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| PREN | 43 | — | from typical composition, not from a heat | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Density | 8.0 | g/cm³ | 20 °C | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Modulus of elasticity | 195 | GPa | 20 °C | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Thermal conductivity | 14 | W/(m·K) | 20 °C | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Critical pitting and crevice temperatures | not established | — | — | — | not in the datasheet consulted; for a seawater alloy these are the selection criteria and the pitting ranking is not | — |
| Composition limits | not established | — | — | — | ASTM A240 is paywalled; the datasheet gives typical values, which are not limits | — |
| Weld metal properties | not established | — | — | — | super-austenitics are normally welded with an overmatching nickel-base filler and the datasheet consulted does not cover it | — |
7 sourced values, 3 gaps named. Publishing the gaps is more useful than filling them from an aggregator that does not say where its numbers came from. The routes to filling them are the standard itself, a mill datasheet, or a mill certificate for your actual heat — which supersedes both at E5.
Where the numbers come from
Proof strength Rp0.2, minimum (EN). A third above 316L on the same product form, and the reason is nitrogen in solid solution rather than any change of structure — this is still a single-phase austenitic. Quarto plate drops to 300 MPa.
PREN. 20% Cr, 6.1% Mo and 0.20% N give 43.3 in the datasheet’s own formula. Level with 2507 and eight points above 2205. Above 40 the number is usually read as seawater capable, which is a convention rather than a qualification and says nothing about crevices.
Why we do not just copy an aggregator. Because then this page would be a worse copy of MatWeb with no way for you to tell which rows to trust, and the one thing we have that MatWeb does not is the evidence column. Our coverage and its limits.
What 254 SMO is usually chosen for
Seawater and strong chloride service where a single-phase austenitic is wanted rather than a duplex — because the part runs hot, because it must stay non-magnetic, or because the shop is set up for austenitic fabrication and not for phase-balance control. Desalination, seawater cooling, bleaching plant and offshore piping are the recurring uses.
And what it is usually rejected for
Price and strength per unit cost. At six percent molybdenum the alloy content is expensive, and 2507 reaches the same pitting ranking with far more proof strength, so a strength-driven seawater part is usually cheaper in super duplex. Segregation on solidification also makes weld metal the weak point unless an overmatching filler is used.
The number to be more careful with than any of the above is the difference between a specified minimum and a typical value — a floor the standard guarantees, versus what a supplier’s production usually does. The full version, and the most expensive routine mistake in material data.
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What this page does not cover
- Critical pitting and crevice temperatures are not established here, and they are what the alloy is selected on.
- Weld metal corrosion behaviour, which is where this alloy family usually fails first.
- Elevated temperature strength, fatigue and fracture toughness.
- Composition limits, not established.
- Whether a super duplex is the better answer for your part. This page gives you the numbers, not the decision.
Generated from data/materials/254smo.yaml. Regenerate rather than editing this file by hand — edits here are lost on the next build.