# UNS S31254 Open-Die Forgings (254 SMO / ASTM A182 F44 / EN 1.4547)

**UNS S31254, better known as 254 SMO, is a super austenitic stainless steel with nominally 20% chromium, 18% nickel and 6% molybdenum, alloyed with nitrogen and copper. Molybdenum and nitrogen together lift its pitting resistance equivalent number above 43, comparable to a super duplex grade while keeping a fully austenitic structure. Strength is roughly twice that of the 300 series, with impact toughness and resistance to chloride stress corrosion cracking, pitting and crevice attack.**

Two limits shape how it is made. The grade does not respond to heat treatment, so strength comes only from cold reduction. Hot work must stay inside 982-1149 C, because above that the surface scales and workability drops away.

Jiangyin Jiangnan Metal Co., Ltd. melts, forges, heat treats, machines and tests this grade on one site in Jiangyin, Jiangsu Province, China. Rings roll to 6,000 mm outside diameter, single pieces reach 30 tonnes, and minimum order is 10 kg with no minimum piece count.

| Field | Detail |
|---|---|
| UNS | S31254 |
| Trade name | 254 SMO |
| ASTM forging grade | A182 F44 |
| EN number | 1.4547 |
| Structure | Austenitic, not hardenable by heat treatment |
| PREN | Above 43 |
| Density | 8 g/cm3 |
| Solution anneal | 1149-1204 C, water quench |
| Hot working range | 982-1149 C |
| Minimum order | 10 kg, no minimum piece count |
| Lead time | 20 to 60 days |
| Telephone | +86 189 2135 9659 |
| Email | sales@steelforgepieces.com |
| Page | https://www.steelforgepieces.com/Stainless-Steel/UNS-S31254.html |

## Designation and equivalents

| System | Designation |
|---|---|
| UNS | S31254 |
| Trade name | 254 SMO |
| EN number | 1.4547 |
| ASTM forgings | A182 Grade F44 |
| ASTM plate and sheet | A240 |
| ASTM seamless pipe | A312 |
| ASTM welded tube | A249 |
| ASTM seamless tube | A269 |
| ASTM welded pipe | A813, A814 |

Check which specification governs before ordering. ASTM A182 F44 is a pressure-part forging specification with its own composition limits and mechanical minimums. A general forging to ASTM A473 is a different acceptance basis, certified differently and with a different heat treatment record.

## Chemical composition

| Element | A182 F44 limits | Typical analysis |
|---|---|---|
| Chromium, Cr | 19.5 - 20.5 | 20 |
| Nickel, Ni | 17.5 - 18.5 | 18 |
| Molybdenum, Mo | 6.00 - 6.50 | 6.1 |
| Nitrogen, N | 0.18 - 0.25 | 0.20 |
| Copper, Cu | 0.50 - 1.00 | - |
| Carbon, C | 0.020 max | 0.010 |
| Manganese, Mn | 1.00 max | - |
| Silicon, Si | 0.80 max | - |
| Phosphorus, P | 0.030 max | - |
| Iron, Fe | Balance | 55.69 |

Sulfur and other residual limits apply as stated in the governing edition of ASTM A182 and are reported on the certificate for each melt. Composition is verified on the liquid steel during refining and again on the solid product.

### Pitting resistance

PREN for this grade is above 43, reached by raising molybdenum to 6%. The calculation is %Cr + 3.3 x %Mo + 16 x %N; one mill datasheet for seamless tube quotes at least 42.5 on that formula. PREN is a screening index for comparing grades from chemistry, not a prediction of service life. Chloride concentration, temperature, crevice geometry and surface finish all move the real outcome, so corrosion testing in the actual medium is the only sound basis for a critical selection.

## Mechanical properties

ASTM A182 Grade F44 minimums:

| Property | Minimum |
|---|---|
| Tensile strength | 650 MPa / 94 ksi |
| Yield strength, 0.2% offset | 300 MPa / 44 ksi |
| Elongation in 50 mm or 4D | 35% |
| Reduction of area | 50% |

Typical properties, solution annealed:

| Property | Metric | Imperial |
|---|---|---|
| Tensile strength | 680 MPa | 98,600 psi |
| Yield strength | 300 MPa | 43,500 psi |
| Elongation at break | 50% | 50% |
| Modulus of elasticity | 195 GPa | 28,300 ksi |
| Shear modulus | 75 GPa | 10,900 ksi |
| Poisson's ratio | 0.30 | 0.30 |
| Hardness, Brinell | 210 | 210 |
| Density | 8 g/cm3 | 0.289 lb/in3 |
| Thermal conductivity | 14 W/m.K | 97.2 BTU in/hr.ft2.F |
| Thermal expansion, 20-100 C | 16.5 um/m.C | 9.17 uin/in.F |

## Melting, forging, heat treatment, machining

**Melting.** S31254 runs the electric arc furnace route with ladle refining and vacuum oxygen decarburisation. VOD earns its place on this grade: carbon has to come down to 0.020% max while 6% molybdenum and 0.18-0.25% nitrogen stay in the bath. Maximum heat size is 60 tonnes. Electroslag remelting is available where cleanliness or segregation control justifies it.

**Forging.** Hot work runs 982-1149 C. That is a narrow window by forging standards, and the upper bound is not a soft limit: above it the surface scales and workability falls off. The lower bound matters as much, because a cooling piece worked too cold in a grade with this work hardening rate will tear. Heavy sections return to the furnace more often than a carbon steel equivalent would. Presses are 6,300 t, 4,000 t and 2,000 t, with radial-axial ring mills at 6 m, 3 m and 1 m, plus hammers from 750 kg to 5 t.

**Heat treatment.** Solution annealing at 1149-1204 C followed by water quench. The purpose is to return molybdenum and nitrogen to solution and clear intermetallic precipitation picked up during hot work, restoring corrosion resistance; it does not raise strength. Post-forging annealing is advisable for that reason on any part entering chloride-bearing service. The top of that range needs real high-temperature furnace capacity, provided by three RTX-12-350KW car-bottom furnaces alongside eleven other car-bottom and pit furnaces, including two 15 m deep well furnaces for vertical quenching of long shafts. The grade does not respond to hardening heat treatment; strength is raised only by cold reduction.

**Machining.** Difficult, from a very high work hardening rate combined with the absence of sulfur that would help chip breaking. Workable practice is sharp tools, machine tools with power in reserve, positive feeds, generous lubrication and slow speeds. Avoid light rubbing passes, which glaze the surface and leave the next cut fighting a harder skin. Vertical lathes run to 5,000 mm swing, horizontal lathes to 14,000 mm between centres, deep-hole drilling to 1,600 mm diameter by 10,000 mm.

**Welding.** All common processes are usable, but filler metal is required; welding without it produces poor strength properties. Recommended fillers are AWS A5.14 ERNiCrMo-3 and alloy 625, with covered electrodes matching AWS A5.11 ENiCrMo-12. The nickel-base filler is deliberate, since a matching-composition filler would leave weld metal short of the molybdenum needed to match parent-metal pitting resistance.

## Product forms and size limits

| Form | Limit | Set by |
|---|---|---|
| Seamless rolled rings | OD 50 to 6,000 mm | 6 m radial-axial ring mill; upset and punch below 500 mm |
| Forged rings and sleeves | To 6,000 mm OD | Press route outside the mill envelope |
| Forged flanges | To drawing, ASME B16.5 and B16.47 | Press and vertical lathe |
| Shafts and spindles | To 14,000 mm turned length | Horizontal lathe; 15 m well furnace for vertical quench |
| Discs, tube sheets, blocks | To 5,000 mm machined diameter | 5,000 mm vertical turning lathe |
| Bored cylinders, hollow bar | To 1,600 mm dia x 10,000 mm | CNC deep-hole drilling machine |
| Round, flat and square bar | To drawing | Press and hammer route |
| Valve bodies, nozzles, pump parts | To drawing | Press and machine shop |
| Single piece weight | To 30,000 kg | 60 t heat size, 6,300 t press |
| Minimum order | 10 kg | No minimum piece count, prototypes accepted |

## Applications

S31254 earns its cost where chlorides and halides attack conventional austenitic stainless. For some duties it has been reported as a cost-effective substitute for high nickel and titanium alloys.

- **Seawater and desalination.** Saltwater handling systems, desalination plant, heat exchangers, with forged flanges, tube sheets and shafts.
- **Flue gas cleaning.** Flue gas desulfurisation scrubbers and flue-gas cleaning equipment, where chloride condensate attacks lesser grades.
- **Pulp and paper.** Bleaching equipment exposed to chloride and chlorine dioxide bleach liquors.
- **Chemical process plant.** Process equipment including forged valve bodies, nozzles and pump components.
- **Oil and gas.** Components used in petroleum production, and tall oil distillation columns.
- **Food processing.** Equipment where brine and acidic media rule out standard 316.

## Testing and certification

Every forging leaves with chemical analysis and mechanical test results traceable to the melt number. Non-destructive examination is to EN 10228-3, SEP 1921 or ASTM A388 as the order specifies, with class and acceptance level set by the purchase order. Certification is issued to EN 10204 3.1, or 3.2 with third-party witness. The works holds CCS, BV, DNV, LR and NK approvals, and inspection can be arranged through one of those societies or your own nominated inspector. Positive material identification, corrosion testing to ASTM A262 or ASTM G48, ferrite measurement and impact testing are available as supplementary requirements.

## Common questions

**What is UNS S31254?**
A super austenitic stainless steel with nominally 20% chromium, 18% nickel and 6% molybdenum, alloyed with nitrogen and copper. Known as 254 SMO, listed in ASTM A182 as forging grade F44, European number 1.4547. PREN above 43, comparable to a super duplex stainless steel.

**What is the PREN of UNS S31254?**
Above 43, reached by raising molybdenum to 6%. Calculated as %Cr + 3.3 x %Mo + 16 x %N; one mill datasheet quotes at least 42.5 for seamless tube. PREN compares grades from chemistry and does not predict service life in a given medium.

**Can the grade be hardened by heat treatment?**
No. It does not respond to heat treatment, and hardening is possible only through cold reduction. Solution annealing at 1149-1204 C with a water quench restores corrosion resistance rather than raising strength.

**What is the forging temperature range?**
982-1149 C for forging, upsetting and related operations. Exceeding that range causes scaling and reduces workability. Annealing after hot work is advisable to recover maximum corrosion resistance.

**Which filler metal should be used for welding?**
Filler is required, since welding without it gives poor strength properties. Use AWS A5.14 ERNiCrMo-3 or alloy 625, with covered electrodes matching AWS A5.11 ENiCrMo-12.

**Is it difficult to machine?**
Yes, from a very high work hardening rate and the absence of sulfur. Sharp tools, machine tools with power in reserve, positive feeds, plenty of lubrication and slow speeds give good results.

**What is the minimum order, and can you work from a drawing?**
Minimum order is 10 kg with no minimum piece count, so single prototypes are accepted alongside production lots. Send a drawing, 3D model or sample with the specification, ultrasonic class and certificate type. Lead time runs 20 to 60 days depending on section size and heat treatment route.

## Contact

Jiangyin Jiangnan Metal Co., Ltd.
Melting works and open-die forge, established 1997.
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China.
Telephone +86 189 2135 9659. Email sales@steelforgepieces.com.

## Sources

1. AZoM, Stainless Steel Grade 254 SMO (UNS S31254): https://www.azom.com/article.aspx?ArticleID=9157
2. Ferrobend, ASTM A182 / A182M F44: https://ferrobend.com/specifications/astm/forgings/a182-a182m-f44/
3. Langley Alloys, What is the PREN of S31254: https://www.langleyalloys.com/technical-resources/what-is-the-pren-s31254/
4. Alleima, 254 SMO seamless tube and pipe datasheet: https://www.alleima.com/en/technical-center/material-datasheets/tube-and-pipe-seamless/alleima-254-smo/
5. ASTM A182 / A182M, Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service.
6. ASTM A473, Standard Specification for Stainless Steel Forgings.

Typical property values are published figures for grade identification and do not replace the governing standard. Contractual properties are those stated on the purchase order and the material certificate. Reviewed 5 October 2026.