254 SMO Stainless Steel (UNS S31254)
Super-austenitic (6Mo) · ASTM A240/A240M · Density 8 g/cm³
254 SMO (UNS S31254) is a 6% molybdenum super-austenitic stainless steel developed for chloride environments that defeat 316L and standard duplex grades. With a PREN above 42 it approaches titanium in seawater pitting resistance at far lower cost, which makes it a standard choice for seawater handling, desalination and flue-gas cleaning equipment.
Chemical Composition (wt%)
| C | Mn | Si | Cr | Ni | Mo | N | Cu | P | S |
|---|---|---|---|---|---|---|---|---|---|
| ≤0.020 | ≤1.00 | ≤0.80 | 19.5–20.5 | 17.5–18.5 | 6.0–6.5 | 0.18–0.25 | 0.50–1.00 | ≤0.030 | ≤0.010 |
Single values are maximums unless a range is shown. Balance: Fe. Per ASTM A240/A240M.
Mechanical Properties
| Tensile strength | ≥650 MPa (94 ksi) |
|---|---|
| Yield strength (0.2%) | ≥300 MPa (44 ksi) |
| Elongation (50 mm) | ≥35% |
| Hardness | ≤223 HBW |
Room-temperature minimum values are summarized for annealed flat product under ASTM A240/A240M unless a condition is named in the property label; product form and thickness can change the requirement.
Physical Properties & Structure
| Density | 8 g/cm³ |
|---|---|
| Magnetic response | Essentially non-magnetic after solution annealing; cold work can introduce a measurable magnetic response. |
| Microstructure | Super-austenitic (6Mo) |
Corrosion Resistance & Limits
- General corrosion resistance comes from the chromium-rich passive film; nickel, molybdenum, nitrogen and copper change performance by grade.
- Check chlorides, temperature, crevices, deposits, process chemistry and cleaning conditions. A grade designation alone is not a service-life guarantee.
Fabrication & Heat Treatment
| Welding | Generally weldable with a qualified procedure and matching or over-alloyed filler where required; remove heat tint when corrosion service demands it. |
|---|---|
| Forming | Good ductility is typical, but rapid work hardening increases forming load and springback; bend radius and intermediate annealing depend on grade and reduction. |
| Machining | Use rigid tooling, positive feeds and controlled heat because the material work-hardens; free-machining grades require separate corrosion and welding review. |
| Heat treatment | Solution annealing and rapid cooling restore the intended condition where applicable. Austenitic grades are not hardened by conventional quench-and-temper treatment. |
Equivalent Grades
The closest international equivalents of 254 SMO Stainless Steel are 1.4547 (X1CrNiMoCuN20-18-7) in the EN system, 015Cr20Ni18Mo6CuN in the GB system.
These are common corresponding designations, not unconditional substitutes. Verify chemistry, mechanical properties, product standard, delivery condition, dimensions and project approval before changing designation.
| System | Designation |
|---|---|
| UNS | S31254 |
| EN | 1.4547 (X1CrNiMoCuN20-18-7) |
| GB | 015Cr20Ni18Mo6CuN |
Reference Product Forms & Dimensional Ranges
Common reference product forms for 254 smo stainless steel: Sheet / Plate, Coil / Strip, Pipe / Tube, Bar.
| Finishes | No.1, 2B |
|---|---|
| Sheet / coil thickness | 0.5–6.0 mm |
| Plate thickness | 6–50 mm |
Common surface and delivery options: No.1, 2B, BA or mechanically polished finish when supported by the product route; Annealed and pickled, descaled or polished tube finish as specified; Hot rolled, peeled, bright drawn, ground or polished bar condition according to tolerance.
These published ranges are engineering references, not a live-stock or production-capability promise. Confirm the required product form, dimensions, condition, finish and supply route in the quotation.
Typical Applications
- Seawater piping, pumps and valves
- Desalination plant components
- Flue-gas desulfurization equipment
- Pulp bleach plant washers and towers
- Offshore oil and gas hardware
Frequently Asked Questions
Is 254 SMO a standard grade or a trade name?
254 SMO is a trade name associated with UNS S31254 and EN 1.4547. Referencing the UNS number can broaden sourcing, but substitution still requires review of chemistry, product standard, condition, dimensions, mechanical properties and project approval.
How does 254 SMO compare with 2507 super duplex?
Their PREN values are similar (both above 40), so pitting resistance is comparable. 2507 is stronger and usually cheaper; 254 SMO is easier to form and weld, tougher at low temperatures, and free of the sigma-phase and 475 °C embrittlement limits that restrict duplex service temperatures.
Can 254 SMO replace titanium in seawater service?
In many piping, pump and plate heat-exchanger duties, yes — at a fraction of titanium's cost. Titanium keeps the advantage in hot seawater above roughly 30–40 °C crevice conditions and in the most aggressive brine loops, so the split is usually decided by design temperature.
254 SMO Compared With Other Grades
Organizational author: Tsingshan (Shandong) Iron & Steel Co., Ltd..Review method, status and limitations.
Other stainless steel grades:
304304L316316L201321310S4104302205202301309S316Ti347904L409L4204394414442507303317L440C17-4 PH2304
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