254 SMO Stainless Steel
A super-austenitic stainless steel with 6% molybdenum (6Mo)
Typical values for the temper in the title
254 SMO is a super-austenitic stainless: about 20% chromium, 18% nickel, 6% molybdenum and nitrogen. Its PREN is about 43, almost double 316L, and it resists seawater, including crevice corrosion, in conditions where 316L fails quickly.
The name is a trade name (developed by Avesta, now Outokumpu), and the material is defined in the standard as UNS S31254. It is used in desalination plants, seawater heat exchangers, the paper industry and marine piping.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 650 MPa | |
| Yield strength Rp0.2 | 295 MPa | |
| Elongation A | 40% | |
| Hardness | 200 HB | |
| Modulus of elasticity E | 195 GPa | |
| Density ρ | 7.97 g/cm³ | |
| Machinability | 30% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| Cr chromium | 19.5–20.5 | the protective layer |
| Ni nickel | 17.5–18.5 | austenitic structure |
| Mo molybdenum | 6.0–6.5 | very high pitting and crevice resistance |
| N nitrogen | 0.18–0.22 | strengthens and improves resistance |
| Cu copper | 0.50–1.00 | resistance in acids |
| C carbon | max 0.020 | |
| Mn manganese | max 1.00 | |
| Si silicon | max 0.80 | |
| Fe iron | balance |
Ranges per ASTM A240 (plate and sheet). Other product standards, and different editions of the standard, vary slightly. For purchasing, rely on the standard in the order.
Conditions and heat treatment
Like all austenitic stainless, it is not hardened by heat treatment. The normal delivery condition is annealed.
| Condition | Properties | When to choose it |
|---|---|---|
| Annealed | the normal condition: soft, ductile, most corrosion resistant | most applications |
| Cold worked (¼H to full hard) | much higher strength, slightly magnetic | strong springs, sheet and strip |
| Not hardenable by heat treatment | — | austenitic stainless strengthens only by cold work |
Applications
- Desalination plants
- Seawater heat exchangers
- Marine piping and offshore fire systems
- Paper industry (bleach plants)
- Chemical equipment in chlorides
Fabrication
Welding
Weldable, but in the weld molybdenum tends to segregate and weaken. So an "overalloyed" nickel filler (for example ERNiCrMo-3) is used, which is more resistant than the base metal.
Machining
Difficult: the material is strong and work hardens. Sharp tools, low speeds and a steady feed.
Cost
Much more expensive than 316L. It is chosen when the cost of failure is high.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| 904L | 490–690 / 220–350 MPa | Good | cheaper, for acids rather than seawater · material page |
| 2507 Super Duplex | 795–900 / 550–680 MPa | Good — ER2594 | super duplex: stronger, with similar resistance · material page |
| 316 / 316L | 485–620 / 170–310 MPa | Excellent — ER316L | for much milder conditions · material page |
Common mistakes
Welding 254 SMO with ordinary stainless filler
The weld will be weak in corrosion and fail first. Use an overalloyed nickel filler.
Choosing 904L for seawater
904L is good in acids, but in seawater 6Mo or super duplex are better.
Skipping inspections
With such a material failure is expensive. Check composition, ferrite and weld quality.
Equivalents, standards and supply
| EN | 1.4547 |
|---|---|
| DIN | X1CrNiMoCuN20-18-7 |
| JIS | SUS312L |
| Standards | ASTM A240 / EN 10088-2 |
| Forms | plate · rod · pipe |
| Producers | Outokumpu 254 SMO · Valbruna |
Learn more
Values are typical and for comparison only. For design, rely on the standard and on the mill certificate. Sources: ASTM A240, ASTM A276 and EN 10088 (composition), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026