Data completeness: partial. Last verified 19 August 2026.
Designations
| Common name | 654 SMO |
| UNS | S32654 |
| EN number | 1.4652 |
| Class | Super-austenitic stainless steel |
| Specified by | ASTM A240/A240M, EN 10088-2 |
654 SMO is the highest pitting ranking in the datasheet consulted — 56, against 43 for both 254 SMO and 2507 — and it gets there on 7.3% molybdenum and half a percent of nitrogen. The nitrogen also gives it a proof strength minimum on plate that exceeds every duplex row in the sister datasheet. It is a nickel alloy in everything but name and price bracket, and it is bought when the alternative is titanium.
Properties, with what each one rests on
| Property | Value | Unit | Condition | Evidence | Source | Retrieved |
|---|---|---|---|---|---|---|
| Proof strength Rp0.2, minimum (EN) | 430 | MPa | Quarto plate, 20 °C | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Tensile strength Rm, minimum | 750 | MPa | Quarto plate; datasheet gives a 750–1000 range | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Elongation A, minimum | 40 | % | Quarto plate; A and A80 both 40 | E3 | EN 10088-2 via Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| PREN | 56 | — | 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 | 190 | GPa | 20 °C | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Thermal conductivity | 11 | W/(m·K) | 20 °C | E3 | Outokumpu Ultra range datasheet — high-alloy austenitic stainless steels | 2026-08-20 |
| Cold rolled and hot rolled minima | not established | — | — | — | the datasheet consulted lists only Quarto plate for this grade | — |
| Critical pitting and crevice temperatures | not established | — | — | — | not in the datasheet consulted; at this alloy level they are the only meaningful selection criteria | — |
| Composition limits | not established | — | — | — | ASTM A240 is paywalled; the datasheet gives typical values, which are not limits | — |
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). Plate. The datasheet consulted lists no cold rolled row for this grade, so there is nothing here to compare with a cold rolled figure from another page without changing product form as well as material.
Elongation A, minimum. 40% elongation at 430 MPa proof strength is the combination that distinguishes a nitrogen-strengthened austenitic from a duplex of similar strength, which gives 20 to 25%.
PREN. 24% Cr, 7.3% Mo and 0.50% N give 56.1 in the datasheet’s own formula. The highest number in the source, and far enough above the seawater convention of 40 that the ranking has stopped being the interesting question — corrosion rates and crevice behaviour are.
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 654 SMO is usually chosen for
Hot, aerated seawater and the harshest bleaching and scrubbing duties, where 254 SMO and super duplex both have a service record of crevice attack. The usual comparison at this level is not against another stainless but against a nickel alloy or titanium, and 654 SMO wins on fabricability and on the fact that it is still a steel.
And what it is usually rejected for
Price and everything that follows from it. Seven percent molybdenum and 22% nickel make it one of the most expensive alloys in any stainless catalogue, welding needs an overmatching nickel-base filler, and lead times are long because almost nobody stocks it. Every project that can be solved one grade down is solved one grade down.
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.
Compare
654 SMO vs 2507 · 654 SMO vs 254smo
What this page does not cover
- Only plate minima are established here.
- Critical pitting and crevice temperatures, which are the whole basis for choosing this alloy.
- Corrosion rate data in the services it is bought for.
- Welding practice, filler selection and the properties of the resulting weld metal.
- Composition limits, not established.
Generated from data/materials/654smo.yaml. Regenerate rather than editing this file by hand — edits here are lost on the next build.